To see the other types of publications on this topic, follow the link: A-type Stars.
Dissertations / Theses on the topic 'A-type Stars'
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the top 47 dissertations / theses for your research on the topic 'A-type Stars.'
Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.
You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.
Browse dissertations / theses on a wide variety of disciplines and organise your bibliography correctly.
1
Önehag, Anna. "Solar Type Stars as Calibrators : A Photometric and Spectroscopic Study on the Atmospheric Properties of Late-type Stars." Doctoral thesis, Uppsala universitet, Institutionen för fysik och astronomi, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-158709.
Full textAbstract:
Detailed knowledge of solar-type stars is essential in the understanding of the evolutionary past, presence and future of the Sun as well as the formation of its planetary system. Moreover, solar-type stars are of key significance for the study of the evolution of the Galaxy. The ages of solar-type stars map the full galactic evolution. Their surface layers are well mixed and just little affected by the interior nuclear processes. They may therefore be used as samples of the gas from which the stars were once formed. Models of stellar atmospheres are used to derive fundamental stellar quantities such as chemical composition, effective temperature, surface gravity, age and rotation. It is therefore also important to investigate the progress and shortcomings of the atmospheric models and the reliability of calibrations based upon these. In this thesis we explore the potential of synthetic uvbyHβ colours for deriving atmospheric parameters. The theoretical colours are derived using high-resolution synthetic spectra based on 1D atmosphere models of late-type stars. Furthermore, possible applications of the established synthetic colours on globular stellar clusters are tested. Observations of solar-type stars have demonstrated the existence of stars very similar to the Sun, so-called solar twins. A detailed chemical analysis of these stars, however, shows that most solar-twins are systematically richer, as compared with the Sun, in refractory elements such as Fe, Ni and Al, relative to volatile elements like C, N and O. This chemical abundance pattern has been suggested to be related to the formation of planets or the birth environment of the respective star. In this thesis we present a high-accuracy study on a solar-twin star in the old open cluster M67. We find that the star is very similar to the Sun when comparing their atmospheric parameters, effective temperature, surface gravity and metallicity. Remarkably enough, unlike most solar twins observed in the solar vicinity, the cluster twin shows the same refractory to volatile pattern as the Sun.The reason for this similarity is still unknown but further observations of the cluster will help to clarify the matter. M dwarfs constitute a large fraction of the detectable baryonic matter. In spite of this, detailed knowledge on the numerous neighbouring low-mass stars is still not available. The presence of strong molecular features in the spectra, and incomplete line lists for the corresponding molecules have made metallicity determinations of M dwarfs difficult. Furthermore, the faint M dwarfs require long exposure times for a signal-to-noise ratio sufficient for detailed spectroscopic abundance analysis. In this thesis we present a high resolution spectroscopic study of early-type M dwarfs in the infrared. The lack of prominent molecular bands in parts of the infrared J-band (1100--1400 nm) allows a precise continuum placement. Furthermore, we verify the adequacy of using the model atmospheres for abundance determination by observing a set of binary systems with a solar-type primary and an M dwarf companion. We present a reliable zero-point for the metallicity scale of early-type M dwarfs and verify the reliability of spectroscopic abundance analyses in the infrared.
2
Murphy, Simon James. "Investigating the A-type stars using Kepler data." Thesis, University of Central Lancashire, 2013. http://clok.uclan.ac.uk/9635/.
Full textAbstract:
Rotation is a key physical process operating in the A stars. We present a method by which rotation periods might be measured with Fourier transforms of Kepler data, potentially removing the requirement of spectroscopic observations to acquire similar information. Angular rotational velocities reach their maximum at about A5, but slowly rotating A stars are also seen and these tend to be chemically peculiar. For Ap stars, rotational braking is understood, but too few progenitors are observed. A review of a rare class of stars, the ‘sn’ stars, leads us to suggest these may contribute to the ‘missing’ Ap progenitors. For Am stars, we find the tidal braking mechanisms proposed in the literature induce mixing that is incompatible with observed abundance anomalies. At the other end of the scale are the λ Boo stars, whose rotation velocities are above average. The two main theories for the origin of their metal underabundances are discussed and it is suggested that both of them imply the λ Boo stars contain a high fraction of pulsators – a suggestion that is backed up by observations in the literature. Many λ Boo stars also have circumstellar material, suggesting they are potential planet hosts. This, and the use of asteroseismology to study their interiors, are two excellent reasons to adopt them as prime targets for detailed investigation with Kepler. Pulsation is a common phenomenon in A stars. The δ Sct stars receive wide attention but the fraction of stars that pulsate at the 50 μmag level is shown to be only 56 per cent. The non-δ Sct stars in the δ Sct instability strip receive far less attention. Some of these stars, without appreciable granulation or stellar winds, are probably the least variable objects on the HR diagram. It is shown that they have the potential to be among the most peculiar Am stars. Their investigation has led to two important conclusions: (1) the presence of γ Dor pulsation in non-δ Sct stars in the δ Sct instability strip may inhibit the development of the expected Am peculiarities; and (2) chemically normal, non-δ Sct stars in the δ Sct instability strip do exist at the μmag level. Fourier transforms are invaluable tools in the field of stellar pulsation. The Kepler Space Telescope is providing data of exquisite precision, and thus more detail is seen in the Fourier transform than ever before. Truly understanding the properties of the data is fundamental to their successful utilisation. Through statistical analysis of noise levels in over 20 000 stars, granulation is concluded to be visible in Fourier transforms of stars cooler than 7500 K. Another property investigated is the Nyquist frequency. We found that periodically modulated sampling on board Kepler allows distinction between real pulsation frequencies and Nyquist aliases, even when those real frequencies exceed the Nyquist frequency of the data. This discovery opens up study of many hundreds of stars previously thought to have insurmountable Nyquist ambiguities in their data.
3
Holdsworth, Daniel L. "A survey for pulsations in A-type stars using SuperWASP." Thesis, Keele University, 2015. http://eprints.keele.ac.uk/1557/.
Full textAbstract:
A survey of A-type stars is conducted with the SuperWASP archive in the search for pulsationally variable stars. Over 1.5 million stars are selected based on their (J − H) colour. Periodograms are calculated for light curves which have been extracted from the archive and cleaned of spurious points. Peaks which have amplitudes greater than 0.5 millimagnitude are identified in the periodograms. In total, 202 656 stars are identified to show variability in the range 5 − 300 d−1. Spectroscopic follow-up was obtained for 38 stars which showed high-frequency pulsations between 60 and 235 d−1, and a further object with variability at 636 d−1. In this sample, 13 were identified to be normal A-type δ Sct stars, 14 to be pulsating metallic-lined Am stars, 11 to be rapidly oscillating Ap (roAp) stars, and one to be a subdwarf B variable star. The spectra were used not only to classify the stars, but to determine an effective temperature through Balmer line fitting. Hybrid stars have been identified in this study, which show pulsations in both the high- and low-overtone domains; an observation not predicted by theory. These stars are prime targets to perform follow-up observations, as a confirmed detection of this phenomenon will have significant impact on the theory of pulsations in A-type stars. The detected number of roAp stars has expanded the known number of this pulsator class by 22 per cent. Within these results both the hottest and coolest roAp star have been identified. Further to this, one object, KIC 7582608, was observed by the Kepler telescope for 4 yr, enabling a detailed frequency analysis. This analysis has identified significant frequency variations in this star, leading to the hypothesis that this is the first close binary star of its type. The observational results presented in this thesis are able to present new challenges to the theory of pulsations in A-type stars, with potentially having the effect of further delaying the full understanding of ‘so simple a thing as a star’.
4
Wade, Gregg Allan. "Investigations of the magnetic A and B type stars." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/tape15/PQDD_0023/NQ31167.pdf.
Full text
5
Raghavan, Deepak. "A Survey of Stellar Families: Multiplicity of Solar-type Stars." unrestricted, 2009. http://etd.gsu.edu/theses/available/etd-04212009-165714/.
Full textAbstract:
Thesis (Ph. D.)--Georgia State University, 2009.<br>Title from file title page. Harold A. McAlister, committee chair; Russel J. White, Brian D. Mason, Douglas R. Gies, David W. Latham, A.G. Unil Perera, Todd J. Henry, committee members. Description based on contents viewed Aug. 24, 2009. Includes bibliographical references (p. 391-410).
6
Jarad, Majeed M. "A spectroscopic study of some early-type emission-line stars." Thesis, University of St Andrews, 1986. http://hdl.handle.net/10023/14418.
Full textAbstract:
Spectroscopic observations of 18 of the brighter Be and 0e stars in the Northern Hemisphere have been presented in this project. About 900 spectrograms were secured and measured using the more objective numerical technique (REDUCE and VCROSS) to obtain as many accurate radial velocities as possible for these stars. The analysis of these measurements has demonstrated clearly, that most of these early-type stars are indeed variable in radial velocity, while a real periodicity in the radial velocities of some of the programme stars is found. The long-term periodicities were attributed to the binary nature, while the short ones could be ascribed to the pulsation phenomenon. Orbital elements are determined for four newly discovered binary systems, and improved orbits are determined for four known binaries. Five other stars display short time-scale periodicity (less than 1.5 days) attributable to radial or non-radial pulsation, whilst three variables show little evidence for periodicity. Only two stars are found to have constant radial velocities. A brief summary of the properties of Be stars and all the available models to explain the Be phenomenon is presented in chapter one. Chapter two contains a brief description of the observing equipment and the techniques used. The reasons for selecting the programme stars are given in the same chapter. A complete explanation of the measuring technique used in this investigation is given in chapter three. In chapter four, all the analyses and the results for each star are given individually, while a discussion of previous work on these stars appears in the relevant sections. The final chapter contains a discussion of the results from this study together with an analysis of the energy distributions of the programme stars, compiled by the author from published fluxes and photometry from the ultraviolet to the infra-red parts of the electromagnetic spectrum. Some consideration of future work to be done on these types of stars is also given.
7
Heuser, Christian [Verfasser], and Ulrich [Gutachter] Heber. "Spectroscopy of A-type-stars / Christian Heuser ; Gutachter: Ulrich Heber." Erlangen : Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), 2018. http://d-nb.info/1155006151/34.
Full text
8
Kirkpatrick, Joseph Davy. "Spectroscopic and photometric studies of main sequence M stars and a search for late-type dwarfs in the solar vicinity." Diss., The University of Arizona, 1992. http://hdl.handle.net/10150/185978.
Full textAbstract:
As any introductory astronomy student knows, M dwarfs are the most common stars in the Galaxy and are the faintest of the core hydrogen burners. A comprehensive study of these faint objects is crucial to our understanding of the stellar composition of the Galaxy and necessary for a more complete knowledge of the transition between main sequence M stars and their slightly less massive counterparts, the brown dwarfs, which never achieve hydrogen burning in their cores. In this thesis, a spectroscopic catalog of 125 K and M dwarfs is first presented. This catalog covers the wavelength range from 6300 to 9000 Å, near where these objects emit most of their light. Eight of these spectra, covering classes M2 through M9, are combined with infrared spectra from 0.9 to 1.5 μm to create a second catalog. The two sets of spectra are used to search for temperature-sensitive atomic lines and molecular bands, which are then used in fitting the observed spectra to a sequence of theoretical models. As a result, a new temperature scale for M dwarfs is determined, and this scale is more accurate than previous determinations which have depended on blackbody energy distributions. The sequence of spectra is also used to compare the spectrum of the brown dwarf candidate GD 165 B to known M dwarfs. Furthermore, the spectral catalog is used in an attempt to separate the spectra of faint companions from their M dwarf primaries in systems where the two objects are too close for conventional spectroscopy to resolve the individual components. A survey for faint M dwarfs is also launched using the data acquired through the CCD/Transit Instrument (CTI) on Kitt Peak, Arizona. Follow-up spectroscopy is presented for 133 of these objects, and several more very late M dwarfs are identified. This spectroscopy combined with photometric data from the CTI are used to construct a luminosity function for M dwarfs which is in excellent agreement with determinations from previous surveys. Finally, possible avenues for future work are discussed. These include spectroscopic follow-up of the reddest of Luyten's proper motion objects--the first results from which have uncovered, in just twelve observations, two objects of type M7 and one of type M8, among the coolest objects yet recognized. Future searches, such as an all-sky survey for objects of extremely high proper motion, are also outlined.
9
Leto, P., Courtney Trigilio, Lidia M. Oskinova, et al. "A Combined Multiwavelength VLA/ALMA/Chandra Study Unveils the Complex Magnetosphere of the B-Type Star HR5907." Digital Commons @ East Tennessee State University, 2018. https://dc.etsu.edu/etsu-works/2682.
Full textAbstract:
We present new radio/millimeter measurements of the hot magnetic star HR 5907 obtained with the VLA and ALMA interferometers. We find that HR 5907 is the most radio luminous early type star in the cm–mm band among those presently known. Its multi-wavelength radio light curves are strongly variable with an amplitude that increases with radio frequency. The radio emission can be explained by the populations of the non-thermal electrons accelerated in the current sheets on the outer border of the magnetosphere of this fast-rotating magnetic star. We classify HR 5907 as another member of the growing class of strongly magnetic fast-rotating hot stars where the gyro-synchrotron emission mechanism efficiently operates in their magnetospheres. The new radio observations of HR 5907 are combined with archival X-ray data to study the physical condition of its magnetosphere. The X-ray spectra of HR 5907 show tentative evidence for the presence of non-thermal spectral component. We suggest that non-thermal X-rays originate a stellar X-ray aurora due to streams of non-thermal electrons impacting on the stellar surface. Taking advantage of the relation between the spectral indices of the X-ray power-law spectrum and the non-thermal electron energy distributions, we perform 3-D modelling of the radio emission for HR 5907. The wavelength-dependent radio light curves probe magnetospheric layers at different heights above the stellar surface. A detailed comparison between simulated and observed radio light curves leads us to conclude that the stellar magnetic field of HR 5907 is likely non-dipolar, providing further indirect evidence of the complex magnetic field topology of HR 5907.
10
Briggs, Kevin. "Coronal emission from late-type stars : a ROSAT and XMM view." Thesis, University of Leicester, 2002. http://hdl.handle.net/2381/30656.
Full textAbstract:
In Chapter I, I introduce the framework of observational and theoretical evidence that has been constructed to understand the vast range of X-ray characteristics exhibited by late-type stars on the basis of the magnetic dynamo that is thought to power the Sun's own modest X-ray activity, and describe the spectral analysis techniques and X-ray instruments used in this work. In Chapter 2 I present a catalogue-based classification of X-ray sources detected in the ROSAT PSPC Galactic Plane Survey in the Third Quadrant (3QGPS) and use the results to infer a denser spatial distribution of young, X-ray active stars in the local Galaxy than has been traditionally assumed. In Chapter 3 I exploit the high coronal activity of young stars to search for unrecognised members of the Hyades-age open clusters NGC 6633 and IC 4756 in deep ROSAT HRI images, and make a novel comparison of the X-ray activity levels of these clusters with that of the Hyades. In Chapter 4 I explore the X-ray emission from very low mass stars in an XMM-Newton EPIC pointing in the Pleides, finding marginal support for a decline in X-ray activity for stars with spectral types later than " M4 that may be a signature of the changeover to a non-solar-like dynamo in fully-convective stars. I also undertake spectral and variability studies of the X-ray-bright members in the field, and present evidence that the detection of early-type stars in the cluster are fully consistent with emission from late-type companions. In Chapter 5 I perform a time-resolved spectroscopic study of the nearby active K0 star AB Dor using the XMM-Newton EPIC pn, with comparison to a study using the higher-resolution XMM-Newton RGS, investigating the temperature structure and elemental adundance changes during the course of a moderate flare.
11
Husseini, Majid. "Magnetic field strength of chemically peculiar A and B-type stars." Thesis, Uppsala universitet, Institutet för rymdfysik, Uppsalaavdelningen, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-454565.
Full textAbstract:
The goal of this work is to detect Zeeman split lines and measure magnetic field strength in a sample of Ap stars. This work aims to analyse spectra of 454 stars and find stars that show spectral lines resolved into their magnetically split components. The work included writing and applying a computer code to visualize astronomical spectra and estimate the mean surface magnetic field strength by fitting resolved Zeeman split lines. The data represent spectroscopic measurements obtained from November 2018 to March 2020 with the HERMES spectrograph. This study investigated high-resolution spectra of 454 Ap stars and identified 31 stars showing resolved Zeeman split lines. The majority of these stars were already known to have resolved magnetically split lines, but this paper reports the discovery of 12 new stars having this property. This paper presents 67 measurements of the mean magnetic field modulus of 31 Ap stars with resolved magnetically split lines.
12
Lew, Ben W. P., Daniel Apai, Yifan Zhou, et al. "CLOUD ATLAS: DISCOVERY OF PATCHY CLOUDS AND HIGH-AMPLITUDE ROTATIONAL MODULATIONS IN A YOUNG, EXTREMELY RED L-TYPE BROWN DWARF." IOP PUBLISHING LTD, 2016. http://hdl.handle.net/10150/622769.
Full textAbstract:
Condensate clouds fundamentally impact the atmospheric structure and spectra of exoplanets and brown dwarfs, but the connections between surface gravity, cloud structure, dust in the upper atmosphere, and the red colors of some brown dwarfs remain poorly understood. Rotational modulations enable the study of different clouds in the same atmosphere, thereby providing a method to isolate the effects of clouds. Here, we present the discovery of high peak-to-peak amplitude (8%) rotational modulations in a low-gravity, extremely red (J-K-s = 2.55) L6 dwarf WISEP J004701.06+680352.1 (W0047). Using the Hubble Space Telescope (HST) time-resolved grism spectroscopy, we find a best-fit rotational period (13.20 +/- 0.14 hr) with a larger amplitude at 1.1 mu m than at 1.7 mu m. This is the third-largest near-infrared variability amplitude measured in a brown dwarf, demonstrating that large-amplitude variations are not limited to the L/T transition but are present in some extremely red L-type dwarfs. We report a tentative trend between the wavelength dependence of relative amplitude, possibly proxy for small dust grains lofted in the upper atmosphere, and the likelihood of large-amplitude variability. By assuming forsterite as a haze particle, we successfully explain the wavelength-dependent amplitude with submicron-sized haze particle sizes of around 0.4 mu m. W0047 links the earlier spectral and later spectral type brown dwarfs in which rotational modulations have been observed; the large amplitude variations in this object make this a benchmark brown dwarf for the study of cloud properties close to the L/T transition.
13
McFadzean, A. D. "A study of early and intermediate type stars at the Galactic Poles." Thesis, University of St Andrews, 1985. http://hdl.handle.net/10023/14331.
Full textAbstract:
A catalogue of faint blue stars at the North Galactic Pole, compiled from the literature, is presented. Spectral classifications for catalogue stars within 3° of the pole have been obtained from U.K.S.T. objective prism and St. Andrews grism plates. Photometric data on the uvbyβ system is presented for 572 U-F8 stars at the South Galactic Pole, with radial velocities being given for 161 of these stars. From this South Galactic Pole data the interstellar reddening towards the Pole is shown to be negligible, in agreement with the findings of other authors. A number of photometrically odd stars are isolated, including several intermediate Population II, Population II and Am stars. From available data at both Poles the relative proportions of various population groups as a function of height are discussed. There is an apparent excess of PI A over iPII stars out to Ikpc., relative to the numbers expected on the basis of the 'thick disk' of iPII stars reported by Gilmore and Reid (1983). The w-velocity distributions of Pop.I A and F stars within 200pc. of both Poles are shown to be well fitted by gaussians and these gaussians are shown to be the same for both Poles. The Pop.I A stars are shown to have a mean w-velocity of 0,6 kms⁻¹ (rms 11.1 kms.⁻¹) and the corresponding F stars to have a mean w-velocity of -2.9 kms⁻¹ (rms 10.9 kms⁻¹), implying negligible net streaming through the galactic plane.
14
Mentz, Jacobus Johannes. "A search for pulsating B-type variable stars in the southern open clusters NGC 6204 and Hogg 22 / Jacobus Johannes (Jaco) Mentz." Thesis, North-West University, 2013. http://hdl.handle.net/10394/9520.
Full textAbstract:
The theory of stellar evolution and stellar structure relies on the observation of stars
in di erent phases of their evolutionary cycle. The relation between observations and
theory can be strengthened by obtaining observational data of a large sample of stars in a particular evolutionary phase. The search for Cephei stars, as conducted in this study,
can contribute to the sample of known Cephei stars, where these interesting stars are
massive non-supergiant early B-type stars, displaying pulsating behaviour which is not
well understood.
Stars tend to form in clusters where it can therefore be expected that young massive
stars can be found in open clusters. For this reason two young southern open clusters
were observed in order to search for B-type pulsating stars. The region of NGC 6204
and Hogg 22 was observed over a period of thirteen nights in Johnson B, V and I bands.
NGC 6204 is believed to be the oldest cluster of the two at a distance of 0.8 kpc while the
much younger Hogg 22 is more distant at 2.8 kpc. These two open clusters are located
6 arcminutes apart which made it possible to observe them simultaneously with a 12.8
12.8 arcminute eld of view. The observations were done with the newly installed 1600
telescope of the North-West University, South Africa.
In order to do a variability search, periodic stars need to be identi ed from the cluster
data, where a typical data set may contain thousands of scienti c images. In addition
to the main motivation for this study, a pipeline was created in order to automate the
photometry and data reduction processes. A Lomb-Scargle transform was applied to the
stellar light curves in order to identify periodic sources. 354 signi cantly periodic stars
were identi ed from the 3182 observed stars. Amongst them, two new possible Cephei
stars were found together with a possible slowly pulsating B star (SPB), and numerous
eclipsing binary systems.
By using photometry of this region obtained by Forbes & Short (1996), instrumental
magnitudes were transformed to a standard system in order to compare photometry
results. From the constructed colour magnitude diagram of the two clusters, it could be
seen that some stars, indicated by Forbes & Short (1996) to be cluster members, were
in fact eld stars belonging to neither cluster. The reduction and photometry pipeline was implemented successfully on the data set,
which also highlighted the importance of instrumentation and correct data analysis
procedures. Possible improvements were identi ed in order to overcome di culties experienced
during this study.<br>Thesis (MSc (Space Physics))--North-West University, Potchefstroom Campus, 2013
15
Manjavacas, Elena, Dániel Apai, Yifan Zhou, et al. "Cloud Atlas: Discovery of Rotational Spectral Modulations in a Low-mass, L-type Brown Dwarf Companion to a Star." IOP PUBLISHING LTD, 2017. http://hdl.handle.net/10150/626404.
Full textAbstract:
Observations of rotational modulations of brown dwarfs and giant exoplanets allow the characterization of condensate cloud properties. As of now, rotational spectral modulations have only been seen in three L-type brown dwarfs. We report here the discovery of rotational spectral modulations in LP261-75B, an L6-type intermediate surface gravity companion to an M4.5 star. As a part of the Cloud Atlas Treasury program, we acquired time-resolved Wide Field Camera 3 grism spectroscopy (1.1-1.69 mu m) of LP261-75B. We find gray spectral variations with the relative amplitude displaying only a weak wavelength dependence and no evidence for lower-amplitude modulations in the 1.4. mu m water band than in the adjacent continuum. The likely rotational modulation period is 4.78 +/- 0.95. hr, although the rotational phase is not well sampled. The minimum relative amplitude in the white light curve measured over the whole wavelength range is 2.41% +/- 0.14%. We report an unusual light curve, which seems to have three peaks approximately evenly distributed in rotational phase. The spectral modulations suggests that the upper atmosphere cloud properties in LP261-75B are similar to two other mid-L dwarfs of typical infrared colors, but differ from that of the extremely red L-dwarf WISE0047.
16
Sahai, Raghvendra Scoville Nicholas Zabriskie Scoville Nicholas Zabriskie. "Circumstellar shells of late-type stars--a study at millimeter and infrared wavelengths /." Diss., Pasadena, Calif. : California Institute of Technology, 1985. http://resolver.caltech.edu/CaltechETD:etd-09042008-105047.
Full text
17
Murdoch, Kaylene A. "A high-precision radial-velocity search for substellar companions to southern solar-type stars." Thesis, University of Canterbury. Astronomy, 1992. http://hdl.handle.net/10092/8073.
Full textAbstract:
A system has been developed at the Mt John University Observatory to enable relative radial velocities of solar-type stars to be obtained with a characteristic random error of 55 m/s. The high radial-velocity precision has been achieved by interfacing a single optical fibre feed between the telescope and spectrograph, which has enabled the spectrograph to be mounted in a thermally and mechanically stable configuration and has virtually eliminated guiding errors.
Using this system, a programme of observation of 29 solar-type stars and 10 giant International Astronomical Union radial-velocity standard stars was carried out over 2.5 years with a view to the detection of low-mass companions to the dwarf stars. One star, HR3220, turned out to have a previously-undiscovered stellar companion but no dwarfs showed obvious radial-velocity variability suggesting the presence of sub-stellar companions, although β Hyi showed a possible variation. This is despite the programme's sensitivity to the discovery of companions of mass 20 M₄ or greater in orbits of periods less than about 8 years (and larger masses in longer period orbits). In contrast, at least half the giant 'standard' stars were variable in radial velocity. Four and possibly five of the giant standards are probably intrinsic (pulsating) red or yellow (Walker et al. 1989) variables. Two further standards, β Aqr and δ Sgr, showed long-period variability suggestive of companions of indeterminable but low mass.
The lack of brown dwarfs observed in this programme is consistent with the results of other recent surveys. High-mass brown dwarfs appear to be rare as companions to stars and are probably rare in the field as well. They are unlikely to contribute significantly to the local mass density. Low-mass brown dwarfs (or high-mass planets) seem to be rare in orbits closer than 10 AU but could yet be found to abound in wider orbits or in the field.
18
Andrews, Jennifer E., Nathan Smith, Curtis McCully, Ori D. Fox, S. Valenti, and D. A. Howell. "Optical and IR observations of SN 2013L, a Type IIn Supernova surrounded by asymmetric CSM." OXFORD UNIV PRESS, 2017. http://hdl.handle.net/10150/625795.
Full textAbstract:
We present optical and near-IR photometry and spectroscopy of SN 2013L for the first 4 yr post-explosion. SN 2013L was a moderately luminous (M-r = -19.0) Type IIn supernova (SN) that showed signs of strong shock interaction with the circumstellar medium (CSM). The CSM interaction was equal to or stronger to SN 1988Z for the first 200 d and is observed at all epochs after explosion. Optical spectra revealed multicomponent hydrogen lines appearing by day 33 and persisting and slowly evolving over the next few years. By day 1509, the Ha emission was still strong and exhibiting multiple peaks, hinting that the CSM was in a disc or torus around the SN. SN 2013L is part of a growing subset of SNe IIn that shows both strong CSM interaction signatures and the underlying broad lines from the SN ejecta photosphere. The presence of a blue Ha emission bump and a lack of a red peak does not appear to be due to dust obscuration since an identical profile is seen in Pa beta. Instead this suggests a high concentration of material on the near-side of the SN or a disc inclination of roughly edge-on and hints that SN 2013L was part of a massive interactive binary system. Narrow Ha P-Cygni lines that persist through the entirety of the observations measure a progenitor outflow speed of 80-130 km s(-1), speeds normally associated with extreme red supergiants, yellow hypergiants, or luminous blue variable winds. This progenitor scenario is also consistent with an inferred progenitor mass-loss rate of 0.3-8.0 x 10(-3) M-circle dot yr(-1).
19
Larson, Ana Marie. "A study of high quality, near-infrared spectra of eight spectral type of K stars: precise radial velocities, chromospheric emission, and fundamental stellar parameters." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1996. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/nq21938.pdf.
Full text
20
Hardegree-Ullman, Kevin Karlyle. "Kepler Planet Occurrence Rates for Mid-Type M Dwarfs as a Function of Spectral Type." University of Toledo / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1533214839813619.
Full text
21
Sabotta, Silvia [Verfasser], Artie [Gutachter] Hatzes, Konstanze [Gutachter] Zwintz, and Magali [Gutachter] Deleuil. "The frequency of planets around A- and M-type stars / Silvia Sabotta ; Gutachter: Artie Hatzes, Konstanze Zwintz, Magali Deleuil." Jena : Friedrich-Schiller-Universität Jena, 2021. http://nbn-resolving.de/urn:nbn:de:gbv:27-dbt-20210818-100712-001.
Full text
22
Williamson, Jacob. "SN2005da: A Spectroscopic and Photometric Analysis of a Peculiar Type Ic Supernova." Ohio University Art and Sciences Honors Theses / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=ouashonors1493239779235968.
Full text
23
Grunhut, J., G. Wade, M. Leutenegger, et al. "Discovery of a Magnetic Field in the Rapidly-Rotating O-Type Secondary of the Colliding-Wind Binary HD 47129 (Plaskett’s Star)." Digital Commons @ East Tennessee State University, 2013. https://dc.etsu.edu/etsu-works/6247.
Full textAbstract:
We report the detection of a strong, organized magnetic field in the secondary component of the massive O8III/I+O7.5V/III double-lined spectroscopic binary system HD 47129 (Plaskett's star) in the context of the Magnetism in Massive Stars survey. Eight independent Stokes V observations were acquired using the Echelle SpectroPolarimetric Device for the Observations of Stars (ESPaDOnS) spectropolarimeter at the Canada–France–Hawaii Telescope and the Narval spectropolarimeter at the Télescope Bernard Lyot. Using least-squares deconvolution we obtain definite detections of signal in Stokes V in three observations. No significant signal is detected in the diagnostic null (N) spectra. The Zeeman signatures are broad and track the radial velocity of the secondary component; we therefore conclude that the rapidly rotating secondary component is the magnetized star. Correcting the polarized spectra for the line and continuum of the (sharp-lined) primary, we measured the longitudinal magnetic field from each observation. The longitudinal field of the secondary is variable and exhibits extreme values of −810 ± 150 and +680 ± 190 G, implying a minimum surface dipole polar strength of 2850 ± 500 G. In contrast, we derive an upper limit (3σ) to the primary's surface magnetic field of 230 G. The combination of a strong magnetic field and rapid rotation leads us to conclude that the secondary hosts a centrifugal magnetosphere fed through a magnetically confined wind. We revisit the properties of the optical line profiles and X-ray emission – previously interpreted as a consequence of colliding stellar winds – in this context. We conclude that HD 47129 represents a heretofore unique stellar system – a close, massive binary with a rapidly rotating, magnetized component – that will be a rich target for further study.
24
Pablo, Herbert, Noel Richardson, Anthony Moffat та ін. "A Coordinated X-ray and Optical Campaign of the Nearest Massive Eclipsing Binary, δ Orionis Aa. III. Analysis of Optical Photometric (MOST) and Spectroscopic (Ground Based) Variations". Digital Commons @ East Tennessee State University, 2015. https://dc.etsu.edu/etsu-works/6234.
Full textAbstract:
We report on both high-precision photometry from the Microvariability and Oscillations of Stars (MOST) space telescope and ground-based spectroscopy of the triple system δ Ori A, consisting of a binary O9.5II+early-B(Aa1 and Aa2) with P=5.7 days, and a more distant tertiary(O9 IV P 400 years). This data was collected in concert with X-ray spectroscopy from the Chandra X-ray Observatory. Thanks to continuous coverage for three weeks, the MOST light curve reveals clear eclipses between Aa1 and Aa2 for the first time in non-phased data. From the spectroscopy, we have a well-constrained radial velocity (RV)curve of Aa1. While we are unable to recover RV variations of the secondary star, we are able to constrain several fundamental parameters of this system and determine an approximate mass of the primary using apsidal motion. We also detected second order modulations at 12 separate frequencies with spacings indicative of tidally influenced oscillations. These spacings have never been seen in a massive binary, making this system one of only a handful of such binaries that show evidence for tidally induced pulsations.
25
Eidam, Jéssica Mayara. "Estrelas do tipo A da Campanha 8 da Missão Kepler K2." Universidade Estadual de Ponta Grossa, 2018. http://tede2.uepg.br/jspui/handle/prefix/2646.
Full textAbstract:
Submitted by Angela Maria de Oliveira (amolivei@uepg.br) on 2018-10-09T12:41:56Z
No. of bitstreams: 2
license_rdf: 811 bytes, checksum: e39d27027a6cc9cb039ad269a5db8e34 (MD5)
Jessica Mayara Eidam.pdf: 7618711 bytes, checksum: 8899a404c0b09be99db22ac7f334ae5b (MD5)<br>Made available in DSpace on 2018-10-09T12:41:56Z (GMT). No. of bitstreams: 2
license_rdf: 811 bytes, checksum: e39d27027a6cc9cb039ad269a5db8e34 (MD5)
Jessica Mayara Eidam.pdf: 7618711 bytes, checksum: 8899a404c0b09be99db22ac7f334ae5b (MD5)
Previous issue date: 2018-07-30<br>Coordenação de Aperfeiçoamento de Pessoal de Nível Superior<br>Buscando melhorar a estatística de parâmetros sismológicos de estrelas do tipoA,apresentamosnestetrabalhoaanálisededadosespectroscópicosefotométricos de oito estrelas observadas na direção do Pólo Galáctico durante a Campanha 8 da missão Kepler K2, proposto pelo nosso grupo de pesquisa. A observação fotométrica pelo satélite espacial Kepler ocorreu entre janeiro e março de 2016. A análise das frequências das oito curvas de luz foi feita usando o algoritmo CLEANEST e Period04. A espectroscopia de solo foi feita no OPD/LNA em outubro de 2015 com o telescópio Zeiss (0,6m) e em agosto de 2016 com o telescópio Perkin-Elmer (1,6m).Informaçõesespectroscópicascompletamosdadosdascurvasdeluzdosatélite, permitindo a caracterização da estrutura interna das estrelas. A determinação dos parâmetros estelares foi realizada por meio do Spectroscopy Made Easy (SME). Parâmetros como massa, raio e luminosidade foram obtidos usando as grades Code dÉvolution Stellaire Adaptatif et Modulaire (CESAM) e Porto Oscillations Code (POSC). Permitindo assim, gerar o modelo evolutivo para as oito estrelas. Estrelas dotipoespectralBmuitasvezessãoerroneamenteclassificadascomoestrelasdotipo espectralA,quandosomentedadosdefotometriasãoutilizadosparaaclassificação. Como exemplo, temos as estrelas: Epic220679442 e Epic220607132. Classificadas fotométricamente como tipo espectral A0, revelaram através da análise espectral, tratar-se do tipo espectral B9V. Epic220532854 é uma binária, Epic220466722 é uma δ e Epic220679442 possue variações fotométrica e, dados de espectroscopia revelam linha de Silício pronunciada (SiII λ4128), característica apresentada pela classe peculiar de estrelas Bp magnética.<br>Searching to improve the statistics of seismological parameters of stars of type A, we this work we present the analysis of spectroscopic and photometric data of eight stars observed in the direction of the Galactic Pole during the Kepler mission Campaign 8, proposed by our research group. The photometric observation occurred between January and March 2016. Frequency analysis of the eight light curves was made using the CLEANEST and Period04 algorithm. In addition to the photometric data, ground-based spectroscopy was done at the OPD/LNA in October 2015 with the Zeiss Telescope (0.6m) and in August 2016 with the Perkin-Elmer Telescope (1.6m). Spectroscopic information enhances the data from thesatellite’slightcurves,allowingthecharacterizationoftheinternalstellarstructure. Spectral characterization was done using Spectroscopy Made Easy (SME). Parameters such as mass, radius and luminosity were obtained using the Code d Évolution Stellaire Adaptatif et Modulaire (CESAM) and Porto Oscillations Code (POSC) grids, allowing to generate evolutionary models for the eight stars. Stars of spectral type B are often erroneously classified as stars of spectral type A, when only photometry data is used for classification. As an example, we have the stars: Epic220679442 and Epic220607132. Photometrically classified as spectral type A0, revealed through spectral analysis, to be spectral type B9V. Epic220532854 is a binary, Epic220466722 is a δ Scuti and Epic220679442 has photometric variations and spectroscopy data reveals pronounced silicon line (SiII λ4128), characteristic presented by the class peculiar stars Ap magnetic.
26
Bell, Steven A. "A study of early-type close binaries." Thesis, University of St Andrews, 1987. http://hdl.handle.net/10023/3702.
Full textAbstract:
It has become increasingly clear that many binary systems will pass through a common envelope stage at some point during their evolution. For short period systems composed of main-sequence 0 and early B stars this stage will probably occur for the first time towards the end of hydrogen-core burning in the primary component (case A evolution) rather than during the transition to the giant stage (case B evolution). If masses, radii, luminosities, temperatures and orbital parameters were well determined for a good sample of those systems, it could be established whether the individual components were so close that case A evolution was inevitable or whether the primary component had enough room to complete its main-sequence phase before reaching its Roche. limit and hence case B evolution. The latter mode has been studied extensively (both conservatively and non-conservatively) whereas the reception of matter by the secondary component in the rapid mass-transfer phase of case A evolution has only very recently been investigated. It is still one of the principal problems impeding further progress on this scenario. To resolve this situation and provide observational material with which to compare these theoretical models, an observing program was established to study systems of spectral type earlier than B5 and of orbital period of less than 1.8 in both the Northern and Southern Hemispheres. Light curves were obtained at St Andrews using the newly-refurbished Twin Photometric Telescope and analysed using software developed specifically for this instrument. Further spectroscopic and photometric data were obtained at La Palma SAAO, Sierra Nevada and Boyden. Analyses of these spectroscopic and photometric observations have provided the necessary physical parameters to determine the evolutionary status of these systems. The systems observed were AH Cephei and V1182 Aquilae which are shown to be detached systems, TT Aurigae, SX Aurigae and AI Crucis which are all semi-detached systems and V701 Scorpii and HZ Pyxidis which are contact systems. Accurately-determined parameters of 14 stars have been found, including four 0 stars in detached systems. Therefore-the number of stars with well-determined masses of greater than 30M has been increased by 25%. It is clear from this study that case A mass transfer will play and has played an important role in the evolution of five out of the seven systems. It is debatable whether or not the contact systems have passed through a mass transfer phase, particularly RZ Pyx. The evolutionary history of this system is of particular interest, especially if this binary was in a marginal contact configuration when it arrived on the main sequence. Attempts have been made to look for intrinsic variability in these systems but no periodic variation has been found in any of them. If such a phenomenon exists in one of the components of the binaries in the sample then it must have an amplitude of less than 0.01. The comparison of the physical parameters of 67 stars compiled by the author from this work and from published data with theoretical zero-age and terminal-age main sequences shows that traditional modelling of semi-convection without mass loss is not adequate. Convective overshooting and mass loss play a very important role in the evolution of massive close binary systems of short period.
27
Currie, Thayne, Olivier Guyon, Motohide Tamura, et al. "Subaru/SCExAO First-light Direct Imaging of a Young Debris Disk around HD 36546." IOP PUBLISHING LTD, 2017. http://hdl.handle.net/10150/624379.
Full textAbstract:
We present H-band scattered light imaging of a bright debris disk around the A0 star HD 36546 obtained from the Subaru Coronagraphic Extreme Adaptive Optics (SCExAO) system with data recorded by the HiCIAO camera using the vector vortex coronagraph. SCExAO traces the disk from r similar to 0."3 to r similar to 1" (34-114 au). The disk is oriented in a near east-west direction (PA similar to 75 degrees), is inclined by i similar to 70 degrees-75 degrees, and is strongly forward-scattering (g > 0.5). It is an extended disk rather than a sharp ring; a second, diffuse dust population extends from the disk's eastern side. While HD 36546 intrinsic properties are consistent with a wide age range (t similar to 1-250 Myr), its kinematics and analysis of coeval stars suggest a young age (3-10 Myr) and a possible connection to Taurus-Auriga's star formation history. SCExAO's planet-to-star contrast ratios are comparable to the first-light Gemini Planet Imager contrasts; for an age of 10 Myr, we rule out planets with masses comparable to HR 8799 b beyond a projected separation of 23 au. A massive icy planetesimal disk or an unseen super-Jovian planet at r > 20 au may explain the disk's visibility. The HD 36546 debris disk may be the youngest debris disk yet imaged, is the first newly identified object from the now-operational SCExAO extreme AO system, is ideally suited for spectroscopic follow-up with SCExAO/CHARIS in 2017, and may be a key probe of icy planet formation and planet-disk interactions.
28
Kellogg, Kendra, Stanimir Metchev, Paulo A. Miles-Páez, and Megan E. Tannock. "A Statistical Survey of Peculiar L and T Dwarfs in SDSS, 2MASS, and WISE." IOP PUBLISHING LTD, 2017. http://hdl.handle.net/10150/625747.
Full textAbstract:
We present the final results from a targeted search for brown dwarfs with unusual near-infrared colors. From a positional cross-match of the Sloan Digital Sky Survey (SDSS), 2-Micron All-Sky Survey (2MASS), and Wide-Field Infrared Survey Explorer (WISE) catalogs, we have identified 144 candidate peculiar L and T dwarfs. Spectroscopy confirms that 20 of the objects are peculiar or are candidate binaries. Of the 420 objects in our full sample 9 are young (less than or similar to 200 Myr; 2.1%) and another 8 (1.9%) are unusually red, with no signatures of youth. With a spectroscopic J-K-s color of 2.58 +/- 0.11 mag, one of the new objects, the L6 dwarf 2MASS J03530419 +0418193, is among the reddest field dwarfs currently known and is one of the reddest objects with no signatures of youth known to date. We have also discovered another potentially very-low-gravity object, the L1 dwarf 2MASS J00133470+1109403, and independently identified the young L7 dwarf 2MASS J00440332+0228112, which was first reported by Schneider and collaborators. Our results confirm that signatures of low gravity are no longer discernible in low to moderate resolution spectra of objects older than similar to 200 Myr. The 1.9% of unusually red L dwarfs that do not show other signatures of youth could be slightly older, up to similar to 400 Myr. In this case a red J - K-s color may be more diagnostic of moderate youth than individual spectral features. However, its is also possible that these objects are relatively metal-rich, and thus have enhanced atmospheric dust content.
29
Horrobin, Matthew. "A study of T Tauri stars with multiple spectral types and their surface temperatures." Thesis, University of Edinburgh, 2000. http://hdl.handle.net/1842/28248.
Full textAbstract:
This thesis describes the results of two spectral studies of T Tauri stars. T Tauri stars are young, low mass, stars which have yet to evolve to the point where Hydrogen fusion occurs in their cores. They are normally found in groups associated with gas clouds in locations called star forming regions. Much work has been done to explain the bizarre spectral features of T Tauri stars, and this has led to the development of a standard model for their structures. Classical T Tauri stars are thought to be surrounded by large discs of accreting material, which slowly adds to the mass of the star. This accretion process results in large U.V. and I.R. fluxes for the stars when compared to their main sequence counterparts. Weak-line T Tauri stars do not display any accretion features and are thought to be more evolved than Classical T Tauri stars. Observations show that both types of T Tauri star have active chromospheres and large cool spots, which are both thought to be a result of strong magnetic fields. This thesis is motivated by two studies, one spectroscopic, one photometric, both of which suggest that some T Tauri stars display photospheric features from regions of different temperatures, or multiple spectral types (MST). The first spectral study discussed is of near-I.R. data taken with UKIRT. The spectra are of high resolution data from the region around 1.63 <i>m</i>m, and are of T Tauri, giant and dwarf stars of known spectral type. It is shown that a ratio of selected OH to Fe lines gives a good trend with the optically measured <i>T<sub>eff</sub></i>, derived from spectral types, for both dwarfs and giants. Whilst some of the T Tauri stars fit this trend, it is found that 4 stars clearly lie above it. This is taken as an induction of cooler regions in the spectra than had previously been detected, an MST effect. The second spectral study discussed is of optical data taken with the FLAIR system on the UKST. The spectra span the entire optical region observable with this instrument, and are intended to show variation in temperature sensitive features between the blue and red optical regions. Spectra are presented from 2 consecutive nights of observations and previously discovered MST stars are found to show deeper G bands than would be predicted from the TiO bands in the red spectra. It is found that the G band of one object has varied both on a night to night basis and since the previous observations from the mid-1980's. It is also shown that no variation has occurred in the red spectra.
30
Wakamatsu, Yasuyuki. "ASASSN-18aan: An Eclipsing SU UMa-type Cataclysmic Variable with a 3.6-hour Orbital Period and a Late G-type Secondary Star." Doctoral thesis, Kyoto University, 2021. http://hdl.handle.net/2433/263475.
Full text
31
Washüttl, Albert. "EI Eridani and the art of doppler imaging : a long-term study." Phd thesis, Universität Potsdam, 2004. http://opus.kobv.de/ubp/volltexte/2005/180/.
Full textAbstract:
Das Verständnis magnetisch verursachter Aktivität auf Sternen sowie der zugrundeliegenden Dynamoprozesse ist von fundamentaler Bedeutung für das Verständnis von Entstehung und Entwicklung von Sternen sowie des Lebens im Universum. Sichtbare Erscheinungen dieser stellaren Aktivität sind u.a. Sternflecken, welche als Indikatoren des zugrundeliegenden Magnetfeldes dienen. Solche Flecken können auf anderen Sternen als der Sonne nicht direkt beobachtet werden, zumal mit den heutigen technischen Mitteln eine Auflösung der Oberfläche selbst der benachbarten Sterne unmöglich ist. Eine indirekte Rekonstruktionsmethode namens 'Doppler Imaging' erlaubt es jedoch, auf die Temperaturverteilung auf der Sternoberfläche zu schließen.
Für diese Arbeit wurden elf Jahre kontinuierlicher spektroskopischer Beobachtungen des aktiven Doppelsterns EI Eridani herangezogen, um insgesamt 34 Dopplerkarten zu erstellen. In der Folge wird versucht, eine Grundlage zu schaffen für die Analyse des zweidimensionalen Informationsgehalts dieser Karten. Drei Oberflächenkartenparameter werden vorgeschlagen: gemittelte Temperatur, getrennt für verschiedenen stellare Breitenbänder; relative Fleckenhäufigkeit; und, zum Zwecke der Auswertung der strukturellen Temperaturverteilung, Längen- und Breiten-Ortsfunktion der Sternfleckenhäufung. Die resultierenden Werte zeigen deutlich, daß kein zeitlicher Zusammenhang mit dem photometrischen Aktivitätszyklus besteht. Die Morphologie der Fleckenverteilung bleibt während des kompletten Beobachtungszeitraums im wesentlichen konstant. Im Gegensatz zur Sonne gibt es also, im beobachteten Zeitraum und innerhalb der bestehenden Genauigkeit, keinen Fleckenzyklus auf dem aktiven Stern EI Eri.
Darüberhinaus wurde eine ausführliche Studie der stellaren Parameter von EI Eri und eine vorläufige Abschätzung der differentiellen Rotation auf EI Eri durchgeführt, die eine anti-solare Ausrichtung aufzuweisen scheint, d.h. der Pol rotiert schneller als der Äquator.<br>Understanding stars, their magnetic activity phenomena and the underlying dynamo action is the foundation for understanding 'life, the universe and everything' - as stellar magnetic fields play a fundamental role for star and planet formation and for the terrestrial atmosphere and climate. Starspots are the fingerprints of magnetic field lines and thereby the most important sign of activity in a star's photosphere. However, they cannot be observed directly, as it is not (yet) possible to spacially resolve the surfaces of even the nearest neighbouring stars. Therefore, an indirect approach called 'Doppler imaging' is applied, which allows to reconstruct the surface spot distribution on rapidly rotating, active stars.
In this work, data from 11 years of continuous spectroscopic observations of the active binary star EI Eridani are reduced and analysed. 34 Doppler maps are obtained and the problem of how to parameterise the information content of Doppler maps is discussed. Three approaches for parameter extraction are introduced and applied to all maps: average temperature, separated for several latitude bands; fractional spottedness; and, for the analysis of structural temperature distribution, longitudinal and latitudinal spot-occurrence functions. The resulting values do not show a distinct correlation with the proposed activity cycle as seen from photometric long-term observations, thereby suggesting that the photometric activity cycle is not accompanied by a spot cycle as seen on the Sun. The general morphology of the spot pattern on EI Eri remains persistent for the whole period of 11 years.
In addition, a detailed parameter study is performed. Improved orbital parameters suggest that EI Eri might be complemented by a third star in a wide orbit of about 19 years. Preliminary differential rotation measurements are carried out, indicating an anti-solar orientation.
32
Corcoran, Michael, Joy Nichols, H. Pablo та ін. "A Coordinated X-ray and Optical Campaign of the Nearest Massive Eclipsing Binary, δ Ori Aa: I. Overview of the X-ray Spectrum". Digital Commons @ East Tennessee State University, 2015. https://dc.etsu.edu/etsu-works/6238.
Full textAbstract:
We present an overview of four deep phase-constrained Chandra HETGS X-ray observations of δ Ori A. Delta Ori A is actually a triple system that includes the nearest massive eclipsing spectroscopic binary, δ Ori Aa, the only such object that can be observed with little phase-smearing with the Chandra gratings. Since the fainter star, δ Ori Aa2, has a much lower X-ray luminosity than the brighter primary (δ Ori Aa1), δ Ori Aa provides a unique system with which to test the spatial distribution of the X-ray emitting gas around δ Ori Aa1 via occultation by the photosphere of, and wind cavity around, the X-ray dark secondary. Here we discuss the X-ray spectrum and X-ray line profiles for the combined observation, having an exposure time of nearly 500 ks and covering nearly the entire binary orbit. The companion papers discuss the X-ray variability seen in the Chandra spectra, present new space-based photometry and ground-based radial velocities obtained simultaneously with the X-ray data to better constrain the system parameters, and model the effects of X-rays on the optical and UV spectra. We find that the X-ray emission is dominated by embedded wind shock emission from star Aa1, with little contribution from the tertiary star Ab or the shocked gas produced by the collision of the wind of Aa1 against the surface of Aa2. We find a similar temperature distribution to previous X-ray spectrum analyses. We also show that the line half-widths are about 0.3−0.5 times the terminal velocity of the wind of star Aa1. We find a strong anti-correlation between line widths and the line excitation energy, which suggests that longer-wavelength, lower-temperature lines form farther out in the wind. Our analysis also indicates that the ratio of the intensities of the strong and weak lines of Fe XVII and Ne X are inconsistent with model predictions, which may be an effect of resonance scattering.
33
May, Leah R. "Southside Simple Suppers Scale-Up (S4): Results of a Type Two Hybrid Effectiveness-Implementation Trial of an Evidence-Based Family Meals Program." The Ohio State University, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=osu1593176589768861.
Full text
34
Wenell, Lydia. "The effect on HbA1c in patients with type 2diabetes who start with FreeStyle Libre– a retrospective study of medical records in Region Örebro County, 2019." Thesis, Örebro universitet, Institutionen för medicinska vetenskaper, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:oru:diva-81558.
Full textAbstract:
IntroductionFreeStyle Libre (FSL) has mostly been used by patients with type 1 diabetes. In 2019, newrecommendations were announced regarding prescriptions to patients with type 2 diabetes(T2D) who have insulin treatment (basal/bolus), HbA1c > 70 mmol/mol and/or repeatedhypoglycemic events despite great effort to adjust insulin doses.AimTo evaluate if HbA1c improves with FSL compared with self-monitoring of blood glucose. Thesecondary aim was to investigate if patients with recurrent hypoglycemic events experiencedless hypoglycemic events.MethodsThis study was designed as a retrospective systematic review of medical records of patientswith T2D in Region Örebro County (RÖC) who have received an FSL 1st of January to 13th ofSeptember 2019. A control group (n = 142) was created from the National Diabetes Register tothe indication group HbA1c > 70 mmol/mol. A paired sample t-test was used to assess theprimary endpoint.ResultsHbA1c decreased significantly from 73 mmol/mol to 65 mmol/mol (p <0.001) in the wholestudy population (n = 58). Indication group HbA1c > 70 mmol/mol (n = 38) had the greatestchange, 80 mmol/mol to 68 mmol/mol (p <0.001). The mean HbA1c in the control group was82 mol/mol. There were 15 patients in the indication group with hypoglycemic events (n = 20)who experienced less hypoglycemic events.ConclusionFSL has a positive effect on the metabolic control in patients with T2D who have HbA1c > 70mmol/mol when starting with FSL in RÖC.
35
Schumacher, Hana Josephine. "Analysis of three close eclipsing binary systems : BP Velorum, V392 Carinae and V752 Centauri : a thesis submitted in partial fulfilment of the requirements for the degree of Master of Science, University of Canterbury /." Thesis, University of Canterbury. Physics and Astronomy, 2008. http://hdl.handle.net/10092/1511.
Full textAbstract:
This thesis reports photometric and spectroscopic studies of three close binary systems; BP Velorum, V392 Carinae and V752 Centauri. BP Velorum, a W UMa-type binary, was observed photometrically in February 2007. The light curves in four filters were fitted simultaneously with a model generated in the eclipsing binary modeling software package PHOEBE. The best model was one with a cool star spot on the secondary larger component. The light curves showed additional cycle-to-cycle variations near the times of maximum light which may indicate the presence of star spots that vary in strength and/or location on a time scale comparable with the orbital period, (P = 0.265 d). The system was confirmed to belong to the W-type subgroup of W UMa binaries for which the deeper primary minimum is due to an occultation. V392 Carinae, a detached binary with an orbital period of 3.147 d, was observed photometrically by Michael Snowden in 1997. These observations were reduced and combined with the published light curve from Debernardi and North (2001). High resolution spectroscopic images were taken using the University of Canterbury's HERCULES spectrograph. The radial velocities measured from these observations were combined with velocities from Debernardi and North (2001). The radial velocity and light curves were fit simultaneously, confirming that V392 Car is a detached system of two main sequence A stars with a mass-ratio of 0.95. The derived systematic velocity is consistent with V392 Car being a member of the open cluster NGC 2516. The W UMa-type binary V752 Centauri was observed photometrically and spectroscopically during 2007. The high resolution spectra displayed weak sharp lined features superimposed over the strong broad lined spectrum expected from the 0.370 d contact binary. Fourier methods were used to separate the broad and sharp spectral features and radial velocities for each were measured by cross-correlation. A fit to the photometry and radial velocities for the contact binary implied a system of two late F stars with a mass-ratio of 3.38 in an over-contact configuration. The derived systematic velocity (−13.8km/s), has changed significantly from the 1972 value (29.2km/s). The third (sharp lined) component's radial velocities were measured and found to have a period of 5.147 d, semi-amplitude of 43.4km/s and systematic velocity of −7.3km/s. The likely configuration of the entire system is that of a contact binary in a long period orbit about a lower mass detached binary. V752 Cen is thus a triple lined spectroscopic quadruple.
36
Fenollosa, Artés Felip. "Contribució a l'estudi de la impressió 3D per a la fabricació de models per facilitar l'assaig d'operacions quirúrgiques de tumors." Doctoral thesis, Universitat Politècnica de Catalunya, 2019. http://hdl.handle.net/10803/667421.
Full textAbstract:
La present tesi doctoral s’ha centrat en el repte d’aconseguir, mitjançant Fabricació Additiva (FA), models per a assaig quirúrgic, sota la premissa que els equips per fer-los haurien de ser accessibles a l’àmbit hospitalari. L’objectiu és facilitar l’extensió de l’ús dels prototips com a eina de preparació d’operacions quirúrgiques, transformant la pràctica mèdica actual de la mateixa manera que en el seu moment ho van fer tecnologies com les que van facilitar l’ús de radiografies. El motiu d’utilitzar FA, en lloc de tecnologies més tradicionals, és la seva capacitat de materialitzar de forma directa les dades digitals obtingudes de l’anatomia del pacient mitjançant sistemes d’escanejat tridimensional, fent possible l’obtenció de models personalitzats. Els resultats es centren en la generació de nou coneixement sobre com aconseguir equipaments d’impressió 3D multimaterials accessibles que permetin l’obtenció de models mimètics respecte als teixits vius. Per facilitar aquesta buscada extensió de la tecnologia, s’ha focalitzat en les tecnologies de codi obert com la Fabricació per Filament Fos (FFF) i similars basades en líquids catalitzables. La recerca s’alinea dins l’activitat de desenvolupament de la FA al CIM UPC, i en aquest àmbit concret amb la col·laboració amb l’Hospital Sant Joan de Déu de Barcelona (HSJD). El primer bloc de la tesi inclou la descripció de l’estat de l’art, detallant les tecnologies existents i la seva aplicació a l’entorn mèdic. S’han establert per primer cop unes bases de caracterització dels teixits vius -sobretot tous- per donar suport a la selecció de materials que els puguin mimetitzar en un procés de FA, a efectes de millorar l’experiència d’assaig dels cirurgians. El caràcter rígid dels materials majoritàriament usats en impressió 3D els fa poc útils per simular tumors i altres referències anatòmiques. De forma successiva, es tracten paràmetres com la densitat, la viscoelasticitat, la caracterització dels materials tous a la indústria, l’estudi del mòdul elàstic de teixits tous i vasos, la duresa d’aquests, i requeriments com l’esterilització dels models. El segon bloc comença explorant la impressió 3D mitjançant FFF. Es classifiquen les variants del procés des del punt de vista de la multimaterialitat, essencial per fer models d’assaig quirúrgic, diferenciant entre solucions multibroquet i de barreja al capçal. S’ha inclòs l’estudi de materials (filaments i líquids) que serien més útils per mimetitzar teixits tous. Es constata com en els líquids, en comparació amb els filaments, la complexitat del treball en processos de FA és més elevada, i es determinen formes d’imprimir materials molt tous. Per acabar, s’exposen sis casos reals de col·laboració amb l’HJSD, una selecció d’aquells en els que el doctorand ha intervingut en els darrers anys. L’origen es troba en la dificultat de l’abordatge d’operacions de resecció de tumors infantils com el neuroblastoma, i a la iniciativa del Dr. Lucas Krauel. Finalment, el Bloc 3 té per objecte explorar nombrosos conceptes (fins a 8), activitat completada al llarg dels darrers cinc anys amb el suport dels mitjans del CIM UPC i de l’activitat associada a treballs finals d’estudis d’estudiants de la UPC, arribant-se a materialitzar equipaments experimentals per validar-los. La recerca ampla i sistemàtica al respecte fa que s’estigui més a prop de disposar d’una solució d’impressió 3D multimaterial de sobretaula. Es determina que la millor via de progrés és la de disposar d’una pluralitat de capçals independents a fi de capacitar la impressora 3D per integrar diversos conceptes estudiats, materialitzant-se una possible solució. Cloent la tesi, es planteja com seria un equipament d’impressió 3D per a models d’assaig quirúrgic, a fi de servir de base per a futurs desenvolupaments.<br>La presente tesis doctoral se ha centrado en el reto de conseguir, mediante Fabricación
Aditiva (FA), modelos para ensayo quirúrgico, bajo la premisa que los equipos para
obtenerlos tendrían que ser accesibles al ámbito hospitalario. El objetivo es facilitar la
extensión del uso de modelos como herramienta de preparación de operaciones
quirúrgicas, transformando la práctica médica actual de la misma manera que, en su
momento, lo hicieron tecnologías como las que facilitaron el uso de radiografías. El
motivo de utilizar FA, en lugar de tecnologías más tradicionales, es su capacidad de
materializar de forma directa los datos digitales obtenidos de la anatomía del paciente
mediante sistemas de escaneado tridimensional, haciendo posible la obtención de
modelos personalizados.
Los resultados se centran en la generación de nuevo conocimiento para conseguir
equipamientos de impresión 3D multimateriales accesibles que permitan la obtención de
modelos miméticos respecto a los tejidos vivos. Para facilitar la buscada extensión de la
tecnología, se ha focalizado en las tecnologías de código abierto como la Fabricación
por Hilo Fundido (FFF) y similares basadas en líquidos catalizables. Esta investigación
se alinea dentro de la actividad de desarrollo de la FA en el CIM UPC, y en este ámbito
concreto con la colaboración con el Hospital Sant Joan de Déu de Barcelona (HSJD).
El primer bloque de la tesis incluye la descripción del estado del arte, detallando las
tecnologías existentes y su aplicación al entorno médico. Se han establecido por primera
vez unas bases de caracterización de los tejidos vivos – principalmente blandos – para
dar apoyo a la selección de materiales que los puedan mimetizar en un proceso de FA, a
efectos de mejorar la experiencia de ensayo de los cirujanos. El carácter rígido de los
materiales mayoritariamente usados en impresión 3D los hace poco útiles para simular
tumores y otras referencias anatómicas. De forma sucesiva, se tratan parámetros como
la densidad, la viscoelasticidad, la caracterización de materiales blandos en la industria,
el estudio del módulo elástico de tejidos blandos y vasos, la dureza de los mismos, y
requerimientos como la esterilización de los modelos.
El segundo bloque empieza explorando la impresión 3D mediante FFF. Se clasifican las
variantes del proceso desde el punto de vista de la multimaterialidad, esencial para hacer
modelos de ensayo quirúrgico, diferenciando entre soluciones multiboquilla y de mezcla
en el cabezal. Se ha incluido el estudio de materiales (filamentos y líquidos) que serían
más útiles para mimetizar tejidos blandos. Se constata como en los líquidos, en
comparación con los filamentos, la complejidad del trabajo en procesos de FA es más
elevada, y se determinan formas de imprimir materiales muy blandos. Para acabar, se
exponen seis casos reales de colaboración con el HJSD, una selección de aquellos en los
que el doctorando ha intervenido en los últimos años. El origen se encuentra en la
dificultad del abordaje de operaciones de resección de tumores infantiles como el
neuroblastoma, y en la iniciativa del Dr. Lucas Krauel.
Finalmente, el Bloque 3 desarrolla numerosos conceptos (hasta 8), actividad completada a lo largo de los últimos cinco años con el apoyo de los medios del CIM UPC y de la actividad asociada a trabajos finales de estudios de estudiantes de la UPC, llegándose a materializar equipamientos experimentales para validarlos. La investigación amplia y sistemática al respecto hace que se esté más cerca de disponer de una solución de impresión 3D multimaterial de sobremesa. Se determina que la mejor vía de progreso es la de disponer de una pluralidad de cabezales independientes, a fin de capacitar la impresora 3D para integrar diversos conceptos estudiados, materializándose una posible solución.
Para cerrar la tesis, se plantea cómo sería un equipamiento de impresión 3D para
modelos de ensayo quirúrgico, a fin de servir de base para futuros desarrollos.
37
Carter, Barbara J. "Galaxy spectral type and star formation as a function of density /." 1999. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&res_dat=xri:pqdiss&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&rft_dat=xri:pqdiss:9951771.
Full text
38
Lin, Chia-Lung, and 林家龍. "A comparative study of the magnetic activities of low-mass stars from G-type to M-type." Thesis, 2018. http://ndltd.ncl.edu.tw/handle/jb54mn.
Full textAbstract:
碩士<br>國立中央大學<br>天文研究所<br>106<br>The habitability of exoplanets is a hot topic in both astronomy and astrobiology. Among many factors, the atmospheric and surface environments of the habitable super-Earths could be significantly influenced by the physical conditions of the central stars. For example, robust stellar winds and magnetic storms could lead to stripping away of the planetary atmospheres thus limiting the sustainability of any biospheres. The pioneering work of Maehara et al. (2012) demonstrated that the high-precision measurements of the Kepler space telescope are ideal for the investigations of superflares with energy far beyond the maximal level of solar flare events (i.e., the Carrington event in 1859); they have found 365 flares on 148 G dwarfs. Shibayama et al. (2013) explored more flaring solar-type stars; they have detected 1547 superflares on 279 G dwarfs. At NCU, Wu et al. (2015) and Chang et al. (2017) carried out the statistical studies of the "Kepler" flare activities of the G-type and M-type dwarf stars, respectively. They found that the flare occurrence frequencies and strengths regarding the flare energy have the strong dependencies on the rotation periods and hence the ages of the stars. Those younger and faster-rotating (with rotation periods < 10 days) tend to have stronger magnetic activities. In this work, we report on the results of a comprehensive study of the flare effects covering the temperature range from M dwarfs to the solar-type stars thus bridging the gap of the K-type stars. We have detected 3589 flares on 584 M dwarfs, 1647 flares on 343 K dwarfs by analyzing the K2 long cadence data. We compared the M, K dwarfs’ flares we found with G dwarfs’ flares from Shibayama et al. (2013).
39
Sahai, Raghvendra. "Circumstellar Shells of Late-Type Stars -- A Study at Millimeter and Infrared Wavelenghts." Thesis, 1985. https://thesis.library.caltech.edu/3328/1/Sahai_r_1985.pdf.
Full textAbstract:
<p>This thesis describes an investigation of the physical conditions and molecular abundances in mass-loss envelopes around late-type stars based on millimeter and near infrared spectroscopy, concentrating on the high mass loss, carbon-rich star IRC +10216.</p>
<p>The first part of this thesis is a multi-transition study of the rotational spectrum of SiS from the IRC +10216 envelope. The observational results are described in Chapter 2. A general numerical model to calculate the excitation and radiative transfer for rotation and vibration-rotation lines in circumstellar envelopes is developed in Chapter 3.</p>
<p>Applying this model to fit the observed SiS lines from IRC +10216 (Chapter 4), we find that the undissociated abundance [SiS]/[H<sub>2</sub>] in the shielded inner regions of the circumstellar shell is ~2.4 x 10<sup>-7</sup>, roughly a factor of 100 smaller than that predicted previously by chemical models. The SiS density falls steeply with radius, reaching one-half the undissociated abundance at r = 9 x 10<sup>16</sup> cms. We show that a) Si, not S depletion is responsible for the low SiS abundance, and b) most of the available Si has probably been used up in forming SiC grains in the cool IRC +10216 atmosphere.</p>
<p>Variations in the 13 µm infrared flux over the 644 day light-cycle of IRC +10216 produce observable changes in some of the SiS lines. Sharp cusps in the J = 5-4 line wings, observed with the Onsala 20 m antenna, are explained in terms of weak maser emission at maximum light. The model predicts a different shape for this line at minimum light, in excellent agreement with a recent Onsala observation. Line coincidences, involving 13 µm transitions of HCN and C<sub>2</sub>H<sub>2</sub> (not considered in the model), may be responsible for poor fits to some of the SiS rotational spectrum.</p>
<p>A sensitive search for SiS J = 7-6 and J = 6-5 lines in other carbon-rich, oxygen-rich, and S-type circumstellar shells was also conducted (Chapter 2). Three new SiS sources, CIT 6, CRL 2688 and IRC +20370, all of which are carbon-rich were detected, in agreement with the chemical equilibrium models predicting SiS to be significantly more abundant in a carbon-rich environment than in an oxygen-rich environment.</p>
<p>The second part of the thesis (Chapters 5 and 6) deals with the investigation of physical conditions in the inner (r ~ 2") envelope of IRC +10216 -- a scale size that has never been observed previously. We have devised a new observational technique, employing an annular aperture (size 2 - 3.45") to measure extended emission from resonant-scattered photons in the 4.6 µm CO vibration-rotation band from IRC +10216. In addition to the expected emission up to the expansion velocity of the envelope, both CO and <sup>13</sup>CO show evidence of high velocity features in the blue wing of the line, beyond the 15 km s<sup>-1</sup> expansion velocity (Chapter 5).</p>
<p>In order to derive physical quantities from the many P and R branch lines present in the infrared spectra, we develop an analytical model to calculate the excitation of these lines due to radiative pumping by thermal emission from circumstellar dust (Chapter 6). The lines are optically thick, and trapping of line radiation has been included. The model emission intensity is found to vary in a simple manner with radius, velocity, J value of the lower state, and the kinetic temperature (which we expect characterises the populations of the V = 0 rotational levels). Our model shows the V = 1 rotational level populations to be in equilibrium with the kinetic temperature despite being excited by infrared radiation.</p>
<p>We derive the following results for the IRC +10216 inner envelope:</p>
<p>i) The kinetic temperature at radius r = 2" is ~ 244 K, roughly twice the extrapolation of the Kwan and Hill (1977) thermodynamic model. This measurement forces revision of analyses of infrared absorption lines in which the radial information was derived assuming a temperature profile (known a priori).</p>
<p>ii) The gas density in the inner regions of the envelope is characterised by a minimum mass loss rate of</p>
<p>[Equation; see abstract in scanned thesis for details].</p>
40
McArthur, Ian Albert. "Minimum entropy techniques for determining the period of W UMA stars." Diss., 2014. http://hdl.handle.net/10500/19898.
Full textAbstract:
This MSc report discusses the attributes of W Ursae Majoris (W UMa) stars and an investigation into the Minimum Entropy (ME) method, a digital technique applied to the determination of their periods of variability. A Python code programme was written to apply the ME method to photometric data collected on W UMa stars by the All Sky
Automated Survey (ASAS). Starting with the orbital period of the binaries estimated by ASAS, this programme systematically searches around this period for the period which corresponds to the lowest value of entropy. Low entropy here means low scatter (or spread) of data across the phase-magnitude plane. The ME method divides the light curve plot area into a number of elements of the investigators choosing. When a particular orbital period is applied to this photometric data, the resulting distribution of this data in the light curve plane corresponds to a speci c number of data points in each element into which this plane has been divided. This data spread is measured and calculated in terms of entropy and the lowest value of entropy corresponds to the lowest spread of data across the light curve plane. This should correspond to the best light curve shape available from the data and therefore the most accurate orbital period available. Subsequent to the testing of this Python code on perfect sine waves, it was applied, and its results compared, to the 62 ASAS eclipsing binary stars which were investigated by Deb and Singh (2011). The method was then applied to selected stars from the ASAS data base.<br>School of Environmental Sciences<br>M. Sc. (Astronomy)
41
Jones, Jeremy W. "The Ages of A-Stars." 2016. http://scholarworks.gsu.edu/phy_astr_diss/86.
Full textAbstract:
Stars with spectral type `A' (also called A-type stars or just A-stars) are bright intermediate mass stars (∼1.5-2.5 M⊙) that make up ∼1% of stars within 25 parsecs, and ∼20% of the brightest stars in the night sky (V < 3 mag). Most A-stars rotate rapidly with rotational velocities that range from ∼100 to ∼200 km/s in most cases, but can exceed 300 km/s. Such rapid rotation not only causes a star's observed properties (flux, temperature, and radius) to be inclination dependent, but also changes how the star evolves both chemically and structurally.
Herein we conduct an interferometric survey of nearby A-stars using the CHARA Array. The long baselines of this optical/infrared interferometer enable us to measure the angular sizes of stars as small as ∼0.2 mas, and directly map the oblate shapes of rotationally distorted stars. This in turn allows us to more accurately determine their photospheric properties and estimate their ages and masses by comparing to evolution models that account for rotation. To facilitate this survey, we construct a census of all 232 A-stars within 50 parsecs (the 50PASS) and from that construct a sample of A-stars (the OSESNA) that lend themselves to interferometric observations with the CHARA Array (i.e., are in the northern hemisphere and have no known, bright, and nearby companions - 108 stars in total). The observations are interpreted by constructing a physical model of a rapidly rotating star from which we generate both photometric and interferometric model observations for comparison with actual observations. The stellar properties of the best fitting model are then compared to the MESA evolution models to estimate an age and a mass.
To validate this physical model and the adopted MESA code, we first determine the ages of seven members of the Ursa Major moving group, which are expected to be coeval. With the exception of one star with questionable membership, these stars show a 1-σ spread in age of 56 Myr. This agreement validates our technique and provides a new estimate of the age for the group of 414 ± 23 Myr. We apply this validated technique to the directly-imaged `planet' host star κ Andromedae and determine its age to be 47+27-40 Myr. This implies the companion has a mass of 22+8-9 MJup and is thus more likely a brown dwarf than a giant planet. In total, we present new age and mass estimates for 55 nearby A-stars including six members of the Hyades open cluster, five stars with the λ Boötis chemical peculiarity, nine stars which have an infrared excess, possibly from a debris disk, and nine pulsating stars.
42
鄭善韋, Shan-Wei Zheng, and 鄭善韋. "Analysis of Stairs-Climbing Ability for a Tracked Chain-Type Robot." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/3z9v6h.
Full textAbstract:
碩士<br>國立臺北科技大學<br>機電整合研究所<br>99<br>By comparing the rescue robot nowadays, so far most of the rescue robots are manipulated by single unit, which limits the robot’s ability deep into disaster area. Furthermore, lack of analytic results from changing position of robots and also short of standardized definition of terrain overcome, only by showing photos and videos for display is not as supportive as experimental data.Consequently, the aim of this study is to design a simple-and-compact tracked chain-type robot to overcome complex terrains in living. The developed tracked chain-type robot comprises of stood tracked robots ; through the use of chain-typed structure and 2-DOF (degree of freedom) joint design, the tracked chain-typed robot can overcome rough terrain easily by pushing, pulling elevating and twisty of tracked robot.In the stair climbing ability experiment, the analytic results from one, two and three units robots shows that maximal stairs height for respective robot are 24.6 mm, 94mm, and 217mm. Thus, through adjustments of joint angle of positioned robots, the subsequent experimental results display that climbing ability actually benefits from increasing the chained units and the results reassure the robot position settings and correct stair height during climbing.In the end, the experimental data proved that chain-type robot can climb stair in consistent with construction regulation that stair is 18 cm in height and 26cm in depth successfully.
43
Chen, Kuan-Ju, and 陳冠儒. "A Low Transmission Latency Method of Star Type Architecture Based on 2D Mesh NOC." Thesis, 2009. http://ndltd.ncl.edu.tw/handle/48641168568972686158.
Full textAbstract:
碩士<br>國立臺灣大學<br>電機工程學研究所<br>98<br>The size of semiconductor technology is reducing to 32 nm and is getting smaller. At the same time the intellectual properties (IP) cores is increasing. With the progressing of deep submicron chip technology, we can put billions of transistors on a single chip nowadays. Therefore System on Chip (SoC) designs will be able to put large numbers of IP cores on one chip. On chip communication architectures becomes an important issue in System on Chip (SoC) design in order to get a better performance. Lately Network on Chip (NoC) has been brought up to solve complex SoC communication problems and is now widely accepted by academe and industry due to its better scalability and reliability. The 2D mesh NoC has simple routing algorithm and good network scalability therefore becomes a well-liked topology of earlier NoC designs. While some packet with large distance traffic may have higher transmission latency due to the comparatively long average distance between any different two nodes in a 2D mesh. We propose a simple design method for 2D mesh NoC called Star Type architecture in this thesis. The basic concept is to let the packets with large distance traffic travel on an extra second level mesh. The experiment environment is using a 12 × 12 Star Type NoC, which is divided by 3 × 3 sub-mesh. We use the ORION 2.0 power and area model to simulate. Simulation results demonstrate that it can reduce the hops traversed for long distance traffic. And the product of area, power and hop counts of Star Type 12 × 12 mesh can be decreased by 17.2%, and 10.3% compared to normal mesh architectures and 2-Level mesh, respectively.
44
陳雅萍. "A Robust Switch-mode Li-Ion Battery Charger with Bootstrap Detector and Soft-start Embedded in Type Ⅲ compensation Technique." Thesis, 2012. http://ndltd.ncl.edu.tw/handle/32955274556394674647.
Full textAbstract:
碩士<br>國立交通大學<br>電控工程研究所<br>100<br>Bootstrap detector and soft-start embedded in Type Ⅲ compensation are implemented in the switch-mode lithium-ion charger to achieve robustness and high efficiency. Based on the physical properties of the battery cell, the charger charges the cell with three stages, which are trickle current (TC), constant current (CC), and constant voltage (CV) stages [1], [2]. How to deliver power to charge battery in an optimal and safe way is important for fast charging.
Switch-mode charger is able to guarantee high efficiency regardless of the applications and provides higher current capability to accelerate charging process. To ensure the stability of both CC stage and CV stage, the switch-mode charger employ one Type Ⅲ compensation circuit to two parallel loop CC loop and CV loop. For applications with removable battery packs, a soft-start mechanism is necessary to ensure the operation of charger system and prevent inrush current whether battery is connected or not.
Considering area and cost, two N-type power MOSFETs is adopted in the switch-mode charger. For appropriate turn-on resistance to maintain high efficiency and prevent the power MOSFET to burn out, the gate-source voltage of the N-type power MOSFET should be large enough. The proposed BSD monitors the voltage across the bootstrap capacitor, which is the source applies the high side power MOSFET driving voltage to avoid low efficiency and serous burning problem in both synchronous and non-synchronous charging mode.
Furthermore, soft-start embedded in type Ⅲ compensation technique employs the compensation elements and the error amplifier of the type Ⅲ compensation circuit to achieve soft-start function without any external components and auxiliary circuits to greatly minimize the chip and footprint areas.
45
Mbonambi, Martin Sipho. "An exploration of grade 11 mathematical literacy learner's engagement with start-unknown and result-unknown type problems set in a variety of real life contexts." Thesis, 2013. http://hdl.handle.net/10413/11432.
Full textAbstract:
With the introduction in 2006 of the school subject Mathematical Literacy (ML) in the further Education and Training band, there have been expectations that such a subject might develop responsible citizens, contributing workers and self-managing people. The extent to which the subject can meet these aims is dependent on the ways in which the subject is taught and assessed, which influences the focus of ML in the classrooms. One of the differences between the respective subjects of Mathematics and Mathematical Literacy is that when it comes to the latter, there has been less emphasis on carrying out algebraic procedures, and a greater focus on working with contexts. However, algebraic skills can be advantageous even when solving problems set within contexts. One area, which surfaces the distinction between arithmetic and algebraic skills, is in the substitution and computation of a formula, as compared to the solution of equations. In this study, I focus on this distinction by examining Grade 11 ML learner skills in solving both result-unknown problems and start-unknown problems, where the former involves substituting and computing the result of a formula or equation for which the input is given. The latter involves re-arranging the equation or formula in order to solve for the input when the output is given. With this in mind, this study sets out to explore the strategies used by Grade 11 learners to solve result-unknown and start-unknown problems set in real life contexts.
This is a qualitative study, carried out with three hundred and forty Grade 11 Mathematical Literacy learners from rural and urban school in North Durban. Data was gathered from a document analysis of 340 learners’ written responses to the research instrument, along with interviews with ten of these learners. There were four tasks in the research instrument, each of which had a result-unknown, a start-unknown and a reflection question. In the four tasks with the exception of Question 1.2.1 and 1.2.2 in tasks one, were set around a linear equation, while Question 1.2.1 and 1.2.2 involved a hyperbolic equation. Semi-structured interviews were conducted individually with ten learners and the audio recorded. The purpose of the interviews was to explore some of the factors that influenced their written responses. The findings revealed the solving of start-unknown questions to be a serious problem for learners. On average, the success rate at result-unknown questions was 75%, while it was 26% for start-unknown questions. For start-unknown questions based on linear equations only, the success rate was a mere 19 percent.
Some strategies used by learners in responding to start-unknown questions included number grabbing, systematic guess and test, conjoining, symbol manipulation and working backwards. On average, over the four tasks based on linear equations, only nine percent of learners successfully used strategies based on algebraic skill. Most learners who obtained correct answers in the start-unknown questions used the guess and test strategy. Strategies identified in result-unknown questions included direct arithmetic strategy.
The study recommends that for ML learners, teachers need to impress upon learners that the location of the formula in the question is not an indication that certain questions would be answered using the formula, because the formula is placed next to them. It also recommends that teachers create opportunities for learners to continue to practice the algebraic skills they learned in the GET band, particularly in the area of transforming and solving simple linear equations.<br>M. Ed. University of KwaZulu-Natal, Durban 2013.
46
Wu, Jian-Zhang, and 吳建璋. "Development of a Swiss-Type Mill-Turn Machine Tool Soild Cutting Simulation System with Case Study on Cutting Parameter Optimization for STAR SR-20RII." Thesis, 2018. http://ndltd.ncl.edu.tw/handle/wm936v.
Full textAbstract:
碩士<br>國立中正大學<br>機械工程系研究所<br>106<br>Mill-turn machine plays an important role in the machine tool industry, which has complex actuation characteristics and is often used to process complex components. In response to the complex diversification of processing products in the automotive, aerospace and medical industries, and the demand for customization.
Swiss-Type mill-turn machines, which are capable of multi-axis machining and controlling two independent system, are widely used in machining lots of small precision parts in turn-mill machines. However, due to the complex operations and high risk of tool-workpiece collisions, learning curve of Swiss-Type mill-turn operations is comparatively very long. Indirectly, the experience of senior engineers is very difficult to pass down, resulting in the phenomenon of technical inheritance.
How can we test the appropriate cutting parameters after purchasing the tool? In general, it depends on the experience of senior engineers, combined with the suggestions of the tool manufacturer manual. It takes a lot of time and cost of materials through trial-and-error one by one. And eventually on only can get a set of cutting parameter. If one want to enhance performance of the manufacture, it will be limited. In order to produce the NC program, the engineering type mostly relies on the CAD/CAM software for process design. In the process of setting the processing conditions, it is also necessary to rely on the experience of CAD/CAM engineer to complete the setting of the processing parameters, which might also become a technical inheritance gap.
In order to solve these problems, this research adopted CUTPRO® software, combined with the experience of experienced engineers, and a series of experiments to establish a cutting parameter optimization suggestion process with chatter avoidance. Real cutting experiment was conduct for the verification to provide users with a set of scientific processing parameters setting basis. At the same time, the research use Visual Studio 2013 C# and OpenGL-based API to construct virtual 3D machine tool, cutting simulation, and integrate interactive virtual human-machine interface. An interactive virtual human-machine interface has been developed to interact with the virtual 3D machine tool to help users quickly understand the working conditions of the machine tool. The experience of senior engineers can the be visualized scientifically, and a Swiss-Type mill-turn machine education training and cutting parameter optimization suggestion system has been successfully established.
47
Tan, Yi-Wei, and 譚貽維. "A study of the relationship among Types of New Enterprises、start-up entrepreneurs’ characteristics、resources provided by the incubation centers and performance of the start-up enterprises- A case study of the Lung-Yuan incubator center." Thesis, 2005. http://ndltd.ncl.edu.tw/handle/59pj98.
Full textAbstract:
碩士<br>中原大學<br>企業管理研究所<br>93<br>Abstract
The successful economic development of Taiwan in past decades was largely ascribed to experiences accumulated by the many small and medium enterprises (SMEs). But after joining the WTO, in order to survive from global competition and overcome pressures from large enterprises’ scale-superiority, SMEs have to adopt strategic transformation and operate with processes of integrating all the available resources.
Peter Drucker noted that the high risks of innovation come from the lack of management over the innovation methods. In other words, the risks of innovation can be reduced by effective management. So, to help the SMEs become more innovative and adaptive by focusing on the management of innovation is at emergent priority for Taiwan to elevate its economic development.
Most of previous research relating incubator center focuses on its functions and resources it provided, but not investigates its performance from the needs of start-up enterprises. This study investigates the supportive services the innovative incubator center provides, and analyzes the incubation effectiveness by studying how the start-up enterprises stationed in the industrial park through using offerings of the incubator center. In addition, this study also analyzes the relationships between types of new enterprises and start-up entrepreneurs’ characteristics. The results reveal the followings:
1. Most of high-tech industrial start-up entrepreneurs tend to begin their businesses between ages 30-45. The age apparently affects the performance of the start-up enterprises.
2. Most of High-tech industrial entrepreneurs have a Bachelor degree.
3. Start-up entrepreneurs’ business characteristics directly relate to their academic background.
4. Start-up entrepreneurs’ previous working experiences have a positive effect on the performance of their new businesses.
5. Family’s support affects one’s will to start a new business and has a positive effect on the performance of new business as well.
6. An entrepreneur’s characteristics have a strong influence on the business performance.
7. The fund is the key factor of influencing the performance of a start-up business.
8. The resources, such as equipment, space, administrative and management skills, provided by an incubator center have a significant influence on the performance of a start-up business.
9. The technical resources that provided by an incubator center have a significant impact on overall performance of a business’s production and marketing.
10. The resources provided by an incubator center have a directly impact on satisfaction of the business’s performance.