To see the other types of publications on this topic, follow the link: Ring currents.
Dissertations / Theses on the topic 'Ring currents'
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the top 50 dissertations / theses for your research on the topic 'Ring currents.'
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
Clarke, Joseph. "A graph-theoretical analysis of ring currents." Thesis, University of Sheffield, 2018. http://etheses.whiterose.ac.uk/19700/.
Full text
2
Bean, David Edward. "Aromaticity in molecular systems with multiple ring currents." Thesis, University of Sheffield, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.531195.
Full text
3
Medforth, C. J. "Cobalt (III) porphyrin N.M.R. shift reagents." Thesis, University of Liverpool, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.384368.
Full text
4
Pecci, Giovanni. "Persistent currents in a Fermi gas confined on a ring shaped potential." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2019. http://amslaurea.unibo.it/18803/.
Full textAbstract:
This thesis aims to study an ultracold atoms Fermi gas confined on a ring-shaped potential and subjected to attractive contact interactions. In particular, we focus on the analysis of the continuous crossover between the weakly interacting regime, in which the ground state of the system is composed of weakly bound paired fermions and the strongly interacting regime, in which the tight bounds among the atoms allow to neglect the fermionic nature of the pairs. In this limit, the particles can be effectively considered as point-like bosons. In order to determine some observables that keep track of the different regimes of this crossover, we consider an artificial gauge field acting on the gas: the latter induces a persistent current in the ring that presents a periodic behaviour with respect to the artificial gauge flux. The exact solution to this model is provided using Bethe Ansatz and the periodicity can be determined at any interaction strength. Afterwards, we study in detail the number parity effect, that is measurable at low interactions and vanishes in the high interacting bosonic limit of the model, as we expect from the general theory. Such parity effect, that can be detected studying the behaviour of the persistent current, results to be a useful tool to probe the different regimes of the crossover, providing a well-defined distinction between the fermionic and the bosonic limit of the gas.
5
Howell, Gareth David. "Measurement of the e+p charged current cross-section with the Zeus detector at HERA." Thesis, Imperial College London, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.299898.
Full text
6
Edmonds, Joanna Kate. "Measurement of the neutral current deep inelastic scattering cross section at HERA using positron data from the ZEUS detector." Thesis, University of Oxford, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.298310.
Full text
7
Barth, Ingo [Verfasser]. "Quantum control of electron and nuclear circulations, ring currents, and induced magnetic fields in atoms, ions, and molecules by circularly polarized laser pulses / Ingo Barth." Berlin : Freie Universität Berlin, 2009. http://d-nb.info/1023663929/34.
Full text
8
Burrage, Anna Lucy. "A study of radiative charged current interactions in ep collisions." Thesis, University of Liverpool, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.343862.
Full text
9
McCance, Gavin John. "Event shapes and power corrections at HERA." Thesis, University of Glasgow, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.342040.
Full text
10
Himmerich, Markus. "Persistent currents in quantum rings." [S.l. : s.n.], 2004. http://deposit.ddb.de/cgi-bin/dokserv?idn=971950164.
Full text
11
Forster, David Robert. "Ring current ion populations during geomagnetically disturbed periods." Thesis, Aberystwyth University, 2011. http://hdl.handle.net/2160/5864b468-d9e7-462f-be82-a9b130b1004f.
Full textAbstract:
Charge exchange is investigated as a source of magnetospheric He+ . Ionic data from the Magnetospheric Ion Composition Spectrometer (MICS) on the Combined Release and Radiation Effects Satellite (CRRES) are investigated during storm and quiet periods. A He+ /He++ maximum is observed at Ring Current altitudes, where particle trapping is relatively stable. A study of ionic number density across the main and recovery phases of geomagnetic storms provides evidence of a recovery phase source of He+ that does not include the other species. It is suggested that charge exchange of trapped He++ ions with exospheric neutral hydrogen is the source of this He + . Cross sections are obtained for the He++ He+ charge exchange reaction. A new population of He+ ions is observed within the drift echo of an injection which occurred during orbit 497 of CRRES, at E/q values not present in the injection. The possibility of this new He+ population having arisen due to charge exchange is discussed, and charge exchange cross sections are calculated for the reaction. The cross sections calculated for these data are larger than those found by previous work, and it is concluded that the observed effect cannot be explained entirely by charge exchange. Solar wind precursors to pseudobreakups are compared to those of substorms. [Tsurutani et al., 2003] gave examples of stormtime periods which did not contain substorm expansion phases. These are investigated for evidence of electron injections at geosynchronous altitude. It is shown that injections did occur during these periods, though generally at lower energy than those with expansions. The injections are attributed to pseudobreakup activity rather than full substorms. Solar wind parameters are compared to injection energy for storms with expansions and without. It is shown that the occurrence of expansions is associated with spikes in solar wind density, though a time lag of up to 20 minutes is required. This is explained in relation to the pressure catastrophe ([Erickson and Wolf, 1980]), whereby some time is required for magnetospheric convection.
12
Silva, Neto José Amaro da. "Anéis quânticos em grafeno na presença de defeitos topológicos." Universidade Federal da Paraíba, 2013. http://tede.biblioteca.ufpb.br:8080/handle/tede/9571.
Full textAbstract:
Submitted by Vasti Diniz (vastijpa@hotmail.com) on 2017-09-19T14:26:49Z
No. of bitstreams: 1
arquivototal.pdf: 24337857 bytes, checksum: 4dcf09dcc5c804cc2b7b0de0feb30331 (MD5)Made available in DSpace on 2017-09-19T14:26:49Z (GMT). No. of bitstreams: 1 arquivototal.pdf: 24337857 bytes, checksum: 4dcf09dcc5c804cc2b7b0de0feb30331 (MD5) Previous issue date: 2013-03-25
Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES
The Graphene is a two-dimensional(2-D) semiconductor crystal with null gap, where charge carriers behave as massless particles. In this speci c dynamics in the limit of low energies, the energy dispersion relation is linear, and this material can be described by massless Dirac equation contrasts with the semiconductors, for which the charge carriers are massive. In this framework, there is the problem of the electronic con nement in graphene because of tunneling. For overcome this di culty, is proposed a new model of quantum ring, based on Dirac oscillator and models of rings Tan-Inkson and Bakke- Furtado. From this new coupling, are obtainable the energy spectrum, persistent currents and positive spinors to a graphene sheet with / without topological defect type disclination by massless Dirac equation (2+1).
O grafeno e um cristal bidimensional(2-D) semicondutor com gap nulo, onde os portadores de cargas se comportam como part culas sem massa. Nesta din^amica espec ca, no limite de baixas energias, a rela c~ao de dispers~ao de energia e linear, sendo que este material pode ser descrito pela equa c~ao de Dirac sem massa contrastando com os semicondutores, cujos portadores de cargas t^em massa. Neste quadro, h a o problema do con namento eletr^onico no grafeno devido ao tunelamento. Para contornar esta di culdade, e proposto um novo modelo de anel qu^antico, baseado no oscilador de Dirac e nos modelos de an eis de Tan-Inkson e Bakke-Furtado. A partir desse novo acoplamento, s~ao obtidos o espectro de energia, as correntes persistentes e os espinores positivos para uma folha de grafeno com/sem defeito topol ogico do tipo desclina c~ao, via equa c~ao de Dirac (2+1) sem massa
13
Kellett, Stephanie. "Cassini observations of the ring current in Saturn’s magnetosphere." Thesis, University of Leicester, 2011. http://hdl.handle.net/2381/9633.
Full textAbstract:
In this thesis we have employed plasma and magnetic field data from the Cassini spacecraft in order to better understand Saturn’s ring current region. Three data studies are presented along with a derivation of the general expression for the field-perpendicular current density in terms of the plasma bulk parameters. In the first data study an essentially direct determination of the equatorial current sheet thickness was made using data from six north-south Cassini orbits. The dayside data indicated the presence of an equatorial current disk with a near constant half-thickness of ~1.5 RS. More variable conditions were found on the nightside. The data examined also provided evidence of a northward displacement of the current layer from the equatorial plane. Next, the nature of the ring current in Saturn’s dayside magnetosphere was investigated. The total azimuthal current density was found to rise from small values near ~6 RS, peak at ~100 pA m-2 near ~8 RS, and then reduce to values below ~25 pA m-2 at distances beyond ~15 RS, up to the 20 RS limit of our study. The overall total current density profile was found to be similar to that produced by the pressure gradient current, but augmented in strength by factors of ~1.5-2.0 by the difference between the inertia and pressure anisotropy currents. Comparison of the current density profiles deduced from plasma data with those obtained from current disk modelling of the magnetic field perturbations showed good agreement with the gross features. Finally, both the local time dependency and temporal variability of Saturn’s ring current was explored using data obtained from eleven near-equatorial Cassini orbits. In general, the plasma parameters, azimuthal current, and related magnetic perturbation fields were found to exhibit only modest variations with local time and from pass-to-pass over the interval of this study.
14
蔡福陽 and Fuk-yeung Tsoi. "Persistent currents in Anderson-Hubbard mesoscopic rings." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1999. http://hub.hku.hk/bib/B31223539.
Full text
15
Tsoi, Fuk-yeung. "Persistent currents in Anderson-Hubbard mesoscopic rings /." Hong Kong : University of Hong Kong, 1999. http://sunzi.lib.hku.hk/hkuto/record.jsp?B21490120.
Full text
16
Kazi, Ibrahim. "Low Power Current Mode Delta-SigmaADC using Ring Oscillator basedQuantizer." Thesis, KTH, Skolan för informations- och kommunikationsteknik (ICT), 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-119803.
Full textAbstract:
Low power ADCs have wide range of applications, from battery operated systems like biomedical devices to on chip power measurement systems. A more digital implementation is also desirable to take advantage of the technology scaling in digital CMOS technologies. This thesis explores the idea of a low power continuous time Delta-Sigma ADC using current mode signaling. It achieves a second order noise shaping by using a first order current filter, a digital dierence block and a current controlled ring oscillator. This type of ADC has a mostly digital implementation, as the main analog blocks are the current-mode filter and two op-amps which are used for biasing.The behavioral level ADC is implemented in VerilogA and the transistor level ADC is deisgned in CADENCE using UMC 180nm process. MonteCarlo simulations are also performed to ensure the proper operation of the current-mode filter in presence of mismatches, as log-domain filters are very sensitive to transistors mismatches. The ADC performance obtained from transistor level simulation is 7:3 Effective Number of Bits (ENOB) over 30KHz bandwidth and 5.3W power consumption.
17
Xu, Zhonghua. "Study of Geomagnetic Disturbances and Ring Current Variability During Storm and Quiet Times Using Wavelet Analysis and Ground-based Magnetic Data from Multiple Stations." DigitalCommons@USU, 2011. https://digitalcommons.usu.edu/etd/984.
Full textAbstract:
The magnetosphere-ionosphere contains a number of current systems. These currents vary on a wide range of spatial and temporal scales and physically couple with each other. To study the complicated behaviors of these coupled current systems, the ground-based magnetometer has been a useful tool, but the recorded magnetometer data are always multi-scaled and intermittent due to the nature of these current systems. To distinguish these geomagnetic effects with multiple temporal and frequency scales, the wavelet analysis technique is especially suitable because of its special abilities of presenting information in both temporal and frequency domains. In this dissertation, the geomagnetic disturbances and the ring current variability during storm and quiet times are studied by using wavelet analysis and ground-based magnetic data from multiple stations. The first part of this dis- sertation investigates the strengths of applying the wavelet procedure to geomagnetic data for ring current study during storm and quiet periods. The second part of this dissertation characterizes the geomagnetic effects caused by symmetric and asymmetric components of ring currents during storm and quiet times by applying wavelet analysis to geomagnetic data from multiple stations. The third part of this dissertation studies the spatial variabil- ity of the symmetric ring current by applying the wavelet analysis technique to multiple components of magnetic data from multiple stations. The results show the unique strengths of the wavelet method allow us to quantitatively distinguish the geomagnetic effects on ring current variations from other M-I current systems. The unique strengths of wavelet method also allow us to separate the magnetic effects of the symmetric ring current from those caused by the asymmetric ring current. Quantitative information of the spatial variability of the ring currents is essential for understanding the dynamics of the ring currents, as well as the magnetic storm processes. The techniques developed in this dissertation have potential values as space weather monitoring tools for satellite controls, power grids, com- munication systems, oil pipelines, and other high-tech systems that are vulnerable to the negative impacts of disruptive geomagnetic events.
18
Kumar, Pavan M. R. "Analysis, design and control of a hybrid multilevel switching converter for synchrotron ring-magnet power." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1996. https://dspace.library.uvic.ca//handle/1828/9708.
Full textAbstract:
This thesis presents the development of a Hybrid Multilevel Switching Converter (HMSC) for Ring-Magnet Power Supplies (RMPS). The thesis includes the analysis, design and control of the proposed converter. It introduces multilevel switching converters to the field of ring-magnet power supplies.
RMPS feed the electromagnets that produce the magnetic field required to energize and guide subatomic particles in a synchrotron. The accuracy and extreme precision of this magnetic field imposes stringent restrictions on the design and performance of the RMPS used. Study of conventional power supplies highlights the need for modern power supply solutions which can meet the specifications of RMPS.
The complete frequency-domain analysis of the conventional resonant-type RMPS along with the Energy Make-up Unit (EMU) is presented. The resonant frequency drift is identified as the main factor in the design of the EMU. The analysis of the input filter network is presented for development of design criteria for input filter components. The principle advantages and disadvantages of the resonant-type RMPS are summarized before identifying multilevel converters as a viable option among switching converters for a non-resonant type of RMPS.
The Hybrid Multilevel Switching Converter (HMSC) is proposed as a non-resonant type RMPS to overcome the disadvantages of the resonant-type RMPS. The operational features of the HMSC are explained and the simplification of the general HMSC configuration for positive output currents is identified. The steady-state analysis of the HMSC develops comprehensive design criteria for the device ratings and component stresses, including the methods for reducing the switching losses in the HMSC. Multilevel converters encounter voltage balancing problem among the DC-link capacitors. It is shown that the HMSC configuration is versatile in minimizing this problem. Harmonic spectrum of the output voltage of the HMSC is derived and the effect of number of output voltage levels in reducing the harmonic contents is established.
A detailed survey of different current control techniques is presented to form the background for developing an effective current control algorithm for multilevel converters. A dead-beat current control strategy is chosen as an appropriate control technique to suit the needs of RMPS. The control scheme is extended to the control of multilevel converters in general. The control algorithm is developed to track a given arbitrary current reference signal for both single-variable and multi-variable systems. It is also shown that the output dead-beat control is a special case of the pole placement technique. The transient behaviour of the system has been studied and stability considerations of the system are examined.
Extensive computer simulation studies have been performed using SABER to study the reference tracking nature of the proposed control scheme. The output current of the HMSC using the modified dead-beat control scheme is shown to follow a given arbitrary-reference with very small tracking error. The reference tracking nature has been simulated for a simple RL magnet load and a magnet load with LCR filter. Experimental results obtained from a laboratory prototype of the HMSC with an RL load, have been presented to substantiate the analytical results. Criteria for improvement in the reference tracking properties of the proposed system have been identified.Graduate
19
Castelao, Guilherme. "The Internal Structure, Seasonality, and Generation Mechanisms of Surface North Brazil Current Rings." Scholarly Repository, 2011. http://scholarlyrepository.miami.edu/oa_dissertations/703.
Full textAbstract:
In the western tropical Atlantic, the North Brazil Current retroflection periodically sheds large anticyclonic rings, which then propagate northwestward. Between 1998 and 2000, the North Brazil Current Rings Experiment sampled a large number of these rings by shipboard and moored acoustic Doppler current profiler. Ten of the sampled rings are analyzed in this study, focusing on their sea surface dynamic properties. The rings exhibit a radial structure consisting of two regimes, an ``inner'' core region in near solid body rotation and an ``outer'' ring regime with an approximately exponentially decaying structure. The observations show a sharp change in vorticity at the regime transition and the presence of a strong opposite vorticity shield bounding the inner solid body core. We show that Gaussian models, commonly used to represent the surface expression of these and other rings, are adequate for determining the sea surface height anomaly but tend to poorly estimate other properties such as the maximum swirl velocity. Therefore, we propose a new two--part model as a better approximation of the rings' radial structure. According to the cyclogeostrophic balance approximation, the sea surface height distribution across the inner ring has a parabolic shape, while the outer ring has an exponential structure similar to the velocity field. Interestingly, many of the observed rings have an intensity very close to the theoretical limit for anticyclones at these latitudes, which is believed to be due to inertial instability. A climatology of the NBCR is developed from 17 years of satellite altimetry. Usually 5 to 7 NBCR are observed per year, leading to an average of 6.1 rings per year, higher than the previously accepted 5.5 rings per year. A new methodology, more robust and consistent, is developed to track the rings, showing an impressive skill. The methodology can be applied to any velocity field, including irregular data grids. In contrast to what was previously believed, the NBCR do have a seasonal cycle. While so clear in the number of generated rings the seasonal cycle is explicit in the rhythm of formation. The rings are usually formed every 30--70 days, being more frequent during the Spring, when they are generated in a regular pace of near 40 days. In the Fall, the rings are less frequent, with a longer and variable time interval between them. The generation of North Brazil Current Rings (NBCR) has been proposed from numerical simulations to result from westward propagation Rossby waves originating from the instability of the North Equatorial Countercurrent (NECC). Other mechanisms, such as instability of he North Brazil Current where it crosses the equator, are also possible, and the precise mechanisms controlling NBCR formation are still undetermined. Here the ``NECC wave mechanism'' for generation of the near surface NBCR is evaluated for the first time from observations -- 18 years of satellite altimetry. Using a Complex Principal Component analysis on maps of absolute dynamic topography, it is shown that the NECC is the origin of the coherent propagating rings along the NBCR corridor. In agreement with the results proposed from previous simulations, the modal solution has a longer wavelength before the retroflection and shorter wavelength along the ring corridor. The seasonal signal of the wave energy in the NECC is also found to be coherent with the seasonal production cycle of the rings, after taking into account phase lags due to wave propagation. It is therefore confirmed that the of NBCR shedding is defined by wave processes arising in the NECC. Further, in contrast with prior understanding, the NBCR are shown to have a seasonal signal that follows the seasonal cycle of the NECC intensity.
20
Yu, Yixin. "Negative bias temperature instability and charge trapping effects on analog and digital circuit reliability." Master's thesis, University of Central Florida, 2007. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/4056.
Full textAbstract:
Nanoscale p-channel transistors under negative gate bias at an elevated temperature show threshold voltage degradation after a short period of stress time. In addition, nanoscale (45 nm) n-channel transistors using high-k (HfO2) dielectrics to reduce gate leakage power for advanced microprocessors exhibit fast transient charge trapping effect leading to threshold voltage instability and mobility reduction. A simulation methodology to quantify the circuit level degradation subjected to negative bias temperature instability (NBTI) and fast transient charge trapping effect has been developed in this thesis work. Different current mirror and two-stage operation amplifier structures are studied to evaluate the impact of NBTI on CMOS analog circuit performances for nanoscale applications. Fundamental digital circuit such as an eleven-stage ring oscillator has also been evaluated to examine the fast transient charge transient effect of HfO2 high-k transistors on the propagation delay of ring oscillator performance. The preliminary results show that the negative bias temperature instability reduces the bandwidth of CMOS operating amplifiers, but increases the amplifier's voltage gain at mid-frequency range. The transient charge trapping effect increases the propagation delay of ring oscillator. The evaluation methodology developed in this thesis could be extended to study other CMOS device and circuit reliability issues subjected to electrical and temperature stresses.M.S.E.E.
School of Electrical Engineering and Computer Science
Engineering and Computer Science
Electrical Engineering MSEE
21
Stackhouse, Jeffery Wilson. "Ring-Necked Pheasant: Evaluation of Winter Survival, Habitat Use, and Current Research Methods of Nest Searching." Thesis, North Dakota State University, 2013. https://hdl.handle.net/10365/26643.
Full textAbstract:
Radio telemetry was used to monitor a population of male and female ring-necked pheasant (Phasianus colchicus; hereafter pheasant) in southwestern North Dakota to examine pheasant habitat selection. Study objectives were to: 1) determine preferred pheasant winter cover habitat; 2) develop management recommendations to increase pheasant abundance; 3) identify habitat use, survival, and dispersion differences between male and female pheasants; and 4) compare nest-searching techniques to determine most efficient research technique for finding pheasant nests. We captured 191 pheasants, assessed weekly survival using known-fate models in Program MARK and determined home ranges and habitat selection and preference using ArcGIS. We assessed three common methods of nest searching: intense ground searching, chain dragging, and telemetry. Averaging >2000 hectares, our home ranges estimates. Pheasant showed selection toward farmsteads with livestock, large wetlands, and CRP-type grasslands. Pheasant survival estimates for the winters of 2011 and 2012 were 91 and 84 percent, respectively.
22
Yamamoto, Kazuhiro. "Excitation of High-m Poloidal ULF Waves in the Inner Magnetosphere during Geomagnetic Storms and Substorms: Importance of Radial Gradient of Proton Distributions in Drift-Bounce Resonance." Kyoto University, 2020. http://hdl.handle.net/2433/253099.
Full text
23
Nakayama, Yohei. "Simulation Study on Enhancements of Energetic Heavy Ions in the Magnetosphere." Kyoto University, 2017. http://hdl.handle.net/2433/218015.
Full text
24
Jariwala, Enrique Manher Quinto. "On the typical and average contributions to the persistent current in mesoscopic rings." College Park, Md. : University of Maryland, 2004. http://hdl.handle.net/1903/1748.
Full textAbstract:
Thesis (Ph. D.) -- University of Maryland, College Park, 2004.Thesis research directed by: Physics. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.
25
Saiga, Y., D. S. Hirashima, and J. Usukura. "Ground-state properties of quantum rings with a few electrons: Magnetization, persistent current, and spin chirality." American Physical Society, 2007. http://hdl.handle.net/2237/8835.
Full text
26
Keika, Kunihiro. "Outflow and charge-exchange losses of the ring-current ions during magnetic storms : estimate based on measurement of energetic ions and neutral atoms." 京都大学 (Kyoto University), 2006. http://hdl.handle.net/2433/144192.
Full textAbstract:
Kyoto University (京都大学)0048
新制・課程博士
博士(理学)
甲第12109号
理博第3003号
新制||理||1448(附属図書館)
23945
UT51-2006-J104
京都大学大学院理学研究科地球惑星科学専攻
(主査)教授 町田 忍, 教授 家森 俊彦, 教授 淡路 敏之
学位規則第4条第1項該当
27
Kernel, Philippe. "High current single bunch transverse instabilities in storage ring light sources : a new approach highlighting a post-head-tail mechanism : application to the ESRF." Université Joseph Fourier (Grenoble), 2000. http://www.theses.fr/2000GRE10160.
Full textAbstract:
Les instabilites transverses sont le principal obstacle a l'augmentation du seuil de courant, en mode mono-paquet, dans les sources de rayonnement synchrotron. A partir de mesures, de simulations et de la base theorique preexistante, une interpretation de ces mecanismes d'instabilites est presentee. Au-dela de l'instabilite habituelle de couplage de modes et des modes "tete-queue" decouples, qui ont ete observes a l'esrf, une nouvelle forme d'instabilite, l'instabilite "post-synchrotronique", est caracterisee. Une theorie expliquant cette instabilite post-synchrotronique est developpee. Cette theorie est consistente avec les mesures effectuees a l'esrf.
28
Ouimet-Storrs, Alexandre. "Development of a cavity ring-down spectroscopy setup and validation with carbon-hydrogen radical measurements in an argon and acetylene direct currentb low-pressure glow discharge plasma." Thesis, McGill University, 2006. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=99004.
Full textAbstract:
Cavity ring-down spectroscopy (CRDS) is a novel, accurate, sensitive and non-intrusive laser-based technique using multiple-paths molecular absorption to measure weak absolute concentrations of atoms or molecules (ppm range or better). In CRDS, a laser pulse is coupled into an optical cavity equipped of highly reflective mirrors mounted at both ends and containing the absorbing medium. The laser pulse experiences numerous round trips inside the cavity thus considerably increasing the absorption path. The decay of the laser pulse intensity leaking out of one of the cavity mirrors is monitored in real-time and the concentration of the species is obtained by fitting a Beer-Lambert's decay to the measured signal. The resulting signal is an exponentially decaying function with a 1/e cavity ring-down (tau), proportional to the absolute concentration of the absorbing species.The main objective of this Master's project was to develop a CRDS system to be used for the study of plasma-surface interactions. The CRDS cavity measures 92 cm in length and has a spatial resolution of 1 mm2, and is flexible enough in its design to accommodate a low-pressure glow discharge or a miniature atmospheric pressure plasma torch at the centre of the cavity. In this study, the low-pressure glow discharge plasma is used to produce CH radicals from a 95% Ar - 5% C2H2 gas mixture. Preliminary optical emission spectroscopy- (OES) measurements near 431 rim indicated the presence of CH radicals in the plasma. For the CRDS experiments, the electronic transition A2Delta ← X2pi of the CH radical was probed using a tunable dye laser (10Hz, 5 ns pulse, 0.8 cm -1 linewidth) tuned to 431.131 nm, and at a pulse energy of approximately 30-40 muJ. The CRDS system was able to measure CH radical concentrations ranging from 1.78x1012cm-3 to 2.18 x10 12 cm-3.
29
Peeks, Martin. "Electronic delocalisation in linear and cyclic porphyrin oligomers." Thesis, University of Oxford, 2016. https://ora.ox.ac.uk/objects/uuid:58a35932-320c-47dc-828e-0d121d693fd8.
Full textAbstract:
This thesis presents a combined experimental and computational evaluation of the physical-organic properties of butadiyne-linked porphyrin oligomers. The principal result from the thesis is the synthesis and characterisation of the largest aromatic and antiaromatic systems to date, in the form of an oxidised [6]-porphyrin nanoring, with diameter 2.4 nm. This large electronically coherent system provides insight into the connection between aromatic ring currents and persistent currents in metal and semiconductor mesoscopic rings. Chapter 1 briefly reviews the concepts used in the remainder of the thesis, with a particular focus on aromaticity. In Chapter 2, the barrier to inter-porphyrin torsional rotation in a butadiyne-linked porphyrin dimer is determined computationally and experimentally to be 3 kJ mol-1. The barrier height is closely related to the resonance delocalisation energy between the porphyrin subunits. In Chapter 3 we show that by oxidising a butadiyne-linked [6]-porphyrin nanoring to its 4+ and 6+ oxidation states, the nanoring becomes antiaromatic and aromatic respectively. In contrast, the neutral oxidation state exhibits only local aromaticity for the six porphyrin units. The 12+ cation can also be generated, and exhibits local antiaromaticity for each porphyrin unit. The characterisation of (anti)aromaticity employs NMR and computational techniques. In Chapter 4, the properties of cation radicals of linear and cyclic porphyrin oligomers are explored. Cations generated by spectroelectrochemistry are measured by optical spectroscopies, and chemically generated radical monocations are examined by cw/pulsed EPR spectroscopies. EPR and optical spectroscopies agree that the dimer monocation radical is fully delocalised, in Robin-Day Class III, whereas the monocations of longer oligomers are localised over 2-3 porphyrin units (Class II). In Chapter 5, photophysical and computational investigations into excited state aromaticity in porphyrin nanorings are presented. The computational results suggest the presence of aromaticity in the triplet excited states, but experiment fails to convincingly demonstrate the effect. Computational results in Chapter 6 show that a butadiyne linked [6]-porphyrin nanoring in which one butadiyne (C≡C-C≡C) is truncated to an alkyne (C≡C) exhibits a reversal of aromaticity and antiaromaticity in its oxidised states, compared to the all-butadiyne linked nanoring, consistent with Hückel's law.
30
Brinkfeldt, Klas. "Instrumentation for energetic Neutral atom measurements at Mars, Venus and The Earth." Doctoral thesis, Kiruna : Swedish Institute of Space Physics, 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-657.
Full text
31
Lang, Radek. "Vysokofrekvenční oscilátor v technologii CMOS." Master's thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2015. http://www.nusl.cz/ntk/nusl-221110.
Full textAbstract:
This project focus to desing an on-chip oscillator in function as a clock generator. Frequency stability of the oscillator is affected by supply voltage, temperature and process variations. The aim is to propose a clock generator with sufficient frequency stability, low power consumption and a small chip area. This work deals with the types of oscillators and their basic building blocks suitable for our application. It also deals with the study and design options of temperature and process compensation circuit generating the current control, which provides the frequency stabilization of the output signal.
32
Dantas, Lincoanderson Oliveira. "Efeitos não-inerciais em Anéis Quânticos." Universidade Federal da Paraíba, 2015. http://tede.biblioteca.ufpb.br:8080/handle/tede/8014.
Full textAbstract:
Submitted by Maike Costa (maiksebas@gmail.com) on 2016-03-18T13:56:29Z
No. of bitstreams: 1
arquivo total.pdf: 1539512 bytes, checksum: 4aa510877c1a4800c42aaf9dfdae33d3 (MD5)Made available in DSpace on 2016-03-18T13:56:29Z (GMT). No. of bitstreams: 1 arquivo total.pdf: 1539512 bytes, checksum: 4aa510877c1a4800c42aaf9dfdae33d3 (MD5) Previous issue date: 2015-03-26
In this thesis, we investigate by the first time the impact of non-inertial effects associated with the rotation of the reference system on charged and neutral particles confined by a quantum ring, which is described by the potential of Tan-Inkson. The contribution of the rotation is introduced by its coupling with angular momentum of the system. We show that the rotation is introduced via a non-minimum coupling to the kinetic part of the Hamiltonian describing the quantum dynamics of systems studied here. Thus, we show that non-inertial effects of the rotation induce on the quantum properties of the particles similar effects generated by a magnetic field. We also investigated the contribution of a screw dislocation on the physical properties of the particles. The topological defect contributes as a torsion source, presenting a contribution similar to the Aharonov-Bohm flux. Besides charged particles (electrons and holes), we also study the effects of rotation on neutral particles in three different scenarios: a neutral particle with a permanent magnetic dipole moment coupled by the Aharanov-Casher interaction; a neutral particle with a permanent electric dipole moment coupled by the interaction proposed by He-McKellar-Wilkens and a neutral particle with an electric dipole moment induced by the field configuration proposed by Wei-Han-Wei. In all three cases it is shown the similarity between the neutral and charged particles. We analyze the non-relativistic quantum dynamics of these particles by solving the Schrödinger equation. In addition to the energy spectrum and wave functions, we calculate the persistent current and the magnetization for the four systems studied here, and we also analyzed, from the expression for the persistent current for quantum rings, the limit case for quantum dots.
Neste trabalho, investigamos pela primeira vez na literatura o impacto de efeitos nãoinerciais associados com a rotação do sistema de referência de partículas carregadas e neutras confinadas por um anel quântico, descrito pelo potencial de Tan-Inkson. A contribuição da rotação é introduzida através de seu acoplamento com o momento angular do sistema. Mostramos que a rotação entra como uma espécie de acoplamento mínimo na parte cinética do Hamiltoniano que descreve a dinâmica quântica dos sitemas em questão. Com isso, mostramos que a rotação induz efeitos típicos de campos magnéticos sobre as propriedades quânticas das partículas. Também investigamos os efeitos da contribuição de uma deslocação tipo-hélice sobre as propriedades físicas das partículas. O defeito topológico contribui como uma fonte de fluxo de torção, tendo um comportamento similar ao do fluxo Aharonov-Bohm. Além de partículas carregadas (elétrons e buracos), estudamos os efeitos da rotação sobre partículas neutras em três cenários diferentes: uma partícula neutra com momento de dipolo magnético permanente acoplado pela interação proposta por Aharanov- Casher; uma partícula neutra com momento de dipolo elétrico permanente acoplada pela interação proposta por He-McKellar-Wilkens e uma partícula neutra como momento de dipolo elétrico induzido pela interação proposta por Wei-Han-Wei. Em todos os três casos mostramos que existe uma estreita analogia entre partículas neutras e carregadas. A metodologia utilizada consiste em analizar a dinâmica quântica não-relativistica dessas partículas via resolução da equação de Schrödinger. Além do espectro de energia e das funções de onda, calculamos as correntes persistentes e a magnetização para os quatro sistemas aqui estudados, e também analizamos, a partir da expressão para a corrente persistes para anéis quânticos, o caso limte para pontos quânticos.
33
Souza, José Fernando Oliveira de. "Anéis quânticos em superfícies não-orientáveis." Universidade Federal da Paraíba, 2011. http://tede.biblioteca.ufpb.br:8080/handle/tede/5693.
Full textAbstract:
Made available in DSpace on 2015-05-14T12:13:59Z (GMT). No. of bitstreams: 1
arquivototal.pdf: 798447 bytes, checksum: d94f874d062caea280c4ce462ab3837a (MD5)
Previous issue date: 2011-12-22Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES
In this work, we explore the link between geometry and physical properties in 2D quantum rings. With focus on the non-orientable mesoscopic structures, we solve the quantum Möbius strip problem, a quantum ring whose lockdown surface is a Möbius strip, and investigate how the physical properties of those structures answer to the geometric variation of this particular configuration. More precisely, we investigate how the adoption of boundary conditions associated to this specific geometric configuration, in particular, can change the general properties of the 2D quantum rings. In addition, we still study the generalized version of the problem, where the Möbius strip has a finite number n of torsions.
Neste trabalho, exploramos o elo entre geometria e propriedades físicas no caso de anéis quânticos bidimensionais. Com o foco nas estruturas mesoscópicas não-orientáveis, resolvemos o problema da faixa de Möbius quântica, um anel quântico cuja superfície de confinamento é uma faixa de Möbius, e investigamos de que maneira as propriedades físicas de tais estruturas respondem à variação geométrica característica dessa particular configuração de confinamento. Mais precisamente, investigamos o modo pelo qual a adoção de condições de contorno associadas a essa configuração geométrica específica, em particular, pode interferir nas propriedades gerais dos anéis quânticos bidimensionais. Além disso, ainda estudamos a versão generalizada do problema, em que a faixa de Möbius apresenta um número finito n de torções.
34
Arias, Olivares David. "Relation Among Localization, Delocalization and Physicochemical Properties. From Electron Density Databases to Magnetic Properties Effects of the acceptor unit in dyes with acceptor–bridge–donor architecture on the electron photo-injection mechanism and aggregation in DSSCs The role of Cr, Mo and W in the electronic delocalization and the metal–ring interaction in metallocene complexes." Thesis, Sorbonne université, 2019. http://www.theses.fr/2019SORUS015.
Full textAbstract:
Tout d'abord, nous évoquerons un aperçu général de l'analyse topologique basée sur la densité d'électronique, le trou d'échange-corrélation et la densité de paires. Une fois la densité électronique rappelée, l'analyse topologique de la densité électronique est expliquée, ainsi que la procédure de calcul des points critiques de la densité électronique, le calcul de la matrice hessienne de la densité électronique et la définition des points critiques à la surface. Tous ces outils topologiques permettent de caractériser la nature des liaisons chimiques parallèlement à l'indice basé sur la délocalisation. Afin de comprendre la nature des énergies et des interactions dans les systèmes, l'analyse d'interaction non covalente est expliquée et combinée à l'analyse de décomposition d?énergie. De plus, les états de transition seront étudiés en appliquant les orbitales naturelles pour la valence chimique (ETS-NOCV). Les concepts clés du magnétisme moléculaire sont abordés. Nous nous concentrons sur l'aimantation et la susceptibilité magnétique, les composants diamagnétiques et paramagnétiques provenant de toute réponse magnétique dans les systèmes. Les propriétés de champs magnétiques induits sont étudiés dans le but de comprendre l'aromaticité à travers de deux descripteurs, les déplacements chimiques indépendants du noyau et les densités de courant induit. En annexe à la théorie, l'interaction isotrope dans les composés dinucléaires est introduite pour expliquer et mesurer certaines erreurs trouvées dans la théorie de la fonctionnelle de densité (TFD). [...]The first property here analysed and related with electronic localization/delocalization is the aromaticity. Aromaticity is an important concept introduced by Kekulé; since then, theoreticians and experimentalist have tried to understand it in different groups of molecules analogues to benzene. The importance of this concept and how the aromaticity is affected by the chemical environment is important to understand and link some physicochemical properties. i.e., reactivity, stability, magnetic response. The physicochemical properties of interest are the electronic structure, the nature of bonds and organometallic interactions(differentiation between metallocenes and metallabencenes). Furthermore, the magnetic response and the study of building blocks as possible candidates to make nano-wires or new low-dimension magnetic materials. Finally, we try to understand the interaction and the errors involved in some properties theoretically computed like, the isotropic coupling between metals through aromatic (or organic) units that have become important benchmark molecules to study magnetic properties in inorganic as well as metal-organic systems [...]
35
Kozák, Petr. "Napojení JV obchvatu města Jihlavy-křižovatka silnic I/38 a II/523." Master's thesis, Vysoké učení technické v Brně. Fakulta stavební, 2013. http://www.nusl.cz/ntk/nusl-225923.
Full textAbstract:
This diploma work deals with researching study of transport junction of main road I/38 and major road II/523 and than link-up of the proposed Outer ring road (VMO) and Southeastern by-pass (JVO) routes of region capital Jihlava, district of Jihlava, Vysočina region. Road structure will solve designed staged link-up of aboved mentioned roads according to their construction schedule. The design takes into account current roads and completed stages, with respect to minimum costs. Road structure is situated on Czech-Moravian Highlands. Its terrain is hilly, pondy and composed of agricultural parcels. The main purpose of this design is steady link-up of all considered traffic flows in the given locality.
36
Prado, Fabiano Oliveira. "Peso de Drude em anéis unidimensionais com potenciais de substituição e atravessados por fluxo magnético." Universidade Federal de São Carlos, 2002. https://repositorio.ufscar.br/handle/ufscar/5005.
Full textAbstract:
Made available in DSpace on 2016-06-02T20:16:43Z (GMT). No. of bitstreams: 1
1994.pdf: 1761798 bytes, checksum: 183ce1c471cf1079a1302b309c923a68 (MD5)
Previous issue date: 2002-04-11Financiadora de Estudos e Projetos
In the present work the Drude weight is calculated to study the capacity of conduction at finite temperatures in one-dimensional rings with the potencial given by the sequences of different degrees of randomness and threaded by a time independent magnetic flux. In this context, the tight-binding approximation is used to solve the Schrödinger equation,also permitting the potencials, given by substitution sequences, to be implemented in a simple way. We study four situations in which the potencial is given by periodic and random sequence. The transport properties exhibited by the system in each case are to reflect the degree of randomness presented by these potencials, although in a nontrivial manner if one considers a hierarchy of disorder based on the Fourier transform of the sequences. The role played by temperature in the capacity of conduction, as compared with the role played by the potencials, is also described.
No presente trabalho, através do cálculo do peso de Drude estudamos a capacidade de condução a temperaturas finitas, em anéis unidimensionais com potenciais dados por seqüências de diferentes graus de desordem e atravessados por fluxo magnético independente do tempo. Neste contexto, utilizamos o modelo tight-binding na resolução da equação de Schrödinger, o que permite inserir os potenciais, dados por seqüências de substituição, de maneira simples. Estudamos quatro casos em que esse potencial seja dado por seqüências não periódicas. Os resultados são comparados com os dois casos limites de organização, a saber, as seqüências periódica e desordenada. Observa-se que o grau de desordem apresentado por estes potenciais reflete-se nas propriedades de transporte exibidas pelo sistema em cada caso, embora de maneira não trivial se considerada uma hierarquia de desordem baseada na transformada de Fourier das seqüências. Descreve-se também a influência da temperatura, frente à influência dos potenciais, na capacidade de condução.
37
ANOSHKIN, KONSTANTIN. "Persistent currents in bosonic mixtures in the ring geometry." Thesis, 2012. http://hdl.handle.net/1974/7037.
Full textAbstract:
The present thesis is devoted to an analysis of the possibility of Bose condensates
supporting persistent currents in the ring geometry. Our analysis is based on an
approach developed by F. Bloch which focuses on the ground state energy of the
condensate as a function of its angular momentum L. According to this approach,
persistent currents are stable if the energy exhibits a local minimum at some nonzero
angular momentum. We have used this approach for a single-species gas within
a mean- eld approximation to show that persistent currents are stable at integral
multiples of N*hbar, where N is the number of atoms in the system, provided a certain
interaction parameter exceeds some critical value. These results are extended to a
binary mixture of bosonic atoms and we show that the system is still capable of
supporting persistent currents under certain conditions. Some of our conclusions
contradict those appearing in the earlier literature.Thesis (Master, Physics, Engineering Physics and Astronomy) -- Queen's University, 2012-03-27 10:05:21.831
38
"Studies of persistent current and critical current of Y123 superconducting ring." Chinese University of Hong Kong, 1989. http://library.cuhk.edu.hk/record=b5886175.
Full text
39
YU, LU-ZHENG, and 呂正瑜. "A Study on Calculations of Short-Circuit Currents in Shipboard Ring-Type Power Systems." Thesis, 2018. http://ndltd.ncl.edu.tw/handle/g9h3mw.
Full textAbstract:
碩士國立高雄海洋科技大學
輪機工程研究所
106
Short circuit current analysis is used to calculate fault currents at different fault locations in ship electric power systems for determining proper protection devices. In the past, ship building corporations and design centers have a well-done computation program for the radial power system based on the existing standard for ship short-circuit current calculation. However, in the recent years a new generation of loop power systems has increasingly been paid an attention and discussed by ship building corporations and design centers in the world. Therefore, the effectiveness of existing methods for short circuit current calculation is necessary to be verified against the changes. This project aims at developing a set of analysis model for calculation of short-circuit currents in naval ship closed-loop power systems through comparative analysis of international regulations by developed calculation tools and commercial power system analysis software.
40
Pembroke, Asher. "A Dynamic Coupled Magnetosphere-Ionosphere-Ring Current Model." Thesis, 2013. http://hdl.handle.net/1911/72018.
Full textAbstract:
In this thesis we describe a coupled model of Earth's magnetosphere that consists of the Lyon-Fedder-Mobarry (LFM) global magnetohydrodynamics (MHD) simulation, the MIX ionosphere solver and the Rice Convection Model (RCM). We report some results of the coupled model using idealized inputs and model parameters. The algorithmic and physical components of the model are described, including the transfer of magnetic field information and plasma boundary conditions to the RCM and the return of ring current plasma properties to the LFM. Crucial aspects of the coupling include the restriction of RCM to regions where field-line averaged plasma-beta <=1, the use of a plasmasphere model, and the MIX ionosphere model. Compared to stand-alone MHD, the coupled model produces a substantial increase in ring current pressure and reduction of the magnetic field near the Earth. In the ionosphere, stronger region-1 and region-2 Birkeland currents are seen in the coupled model but with no significant change in the cross polar cap potential drop, while the region-2 currents shielded the low-latitude convection potential. In addition, oscillations in the magnetic field are produced at geosynchronous orbit with the coupled code. The diagnostics of entropy and mass content indicate that these oscillations are associated with low-entropy flow channels moving in from the tail and may be related to bursty bulk flows and bubbles seen in observations. As with most complex numerical models, there is the ongoing challenge of untangling numerical artifacts and physics, and we find that while there is still much room for improvement, the results presented here are encouraging. Finally, we introduce several new methods for magnetospheric visualization and analysis, including a fluid-spatial volume for RCM and a field-aligned analysis mesh for the LFM. The latter allows us to construct novel visualizations of flux tubes, drift surfaces, topological boundaries, and bursty-bulk flows.
41
Jing-Nuo, Wu. "Persistent Currents in One-Dimensional Mesoscopic Rings." 2005. http://www.cetd.com.tw/ec/thesisdetail.aspx?etdun=U0021-2004200716092947.
Full text
42
Wu, Jing-Nuo, and 吳靜娜. "Persistent Currents in One-Dimensional Mesoscopic Rings." Thesis, 2006. http://ndltd.ncl.edu.tw/handle/62488035995551517581.
Full textAbstract:
博士國立臺灣師範大學
物理學系
94
In this dissertation, we address the topics of persistent charge current and spin current in one-dimensional mesoscopic rings. In Chap. 1, we review the persistent charge current in a normal metal ring without spin degree of freedom. The existence of the persistent charge current is related to the Aharonov-Bohm phase acquired by the electrons while circling the ring. In Chap. 2, we concentrate on the spin-orbit coupling in two-dimensional system with both charge and spin degrees of freedom. We investigate a mesoscopic and isolated conducting annulus with Rashba spin-orbit coupling. The effect of the Rashba spin-orbit coupling on energy levels, and the behaviors of the persistent charge and spin currents are reported. In Chap. 3, we study the persistent spin current (the current of magnons) in an insulating ferrimagnetic ring subjects to a nonuniform magnetic field. The existence of the persistent spin current is related to the Berry phase acquired by the magnons while circling the ring.
43
ZHAN, SHU-HUA, and 詹淑華. "The study of the potential and current distribution of the disk, ring and ring-disk electrodes." Thesis, 1991. http://ndltd.ncl.edu.tw/handle/36452506394528078650.
Full text
44
Himmerich, Markus [Verfasser]. "Persistent currents in quantum rings / von Markus Himmerich." 2004. http://d-nb.info/971950164/34.
Full text
45
Chao, Chun-chieh, and 趙俊傑. "Ring-Oscillator-Based Wide Locking Range and Current Reused Frequency Dividers." Thesis, 2006. http://ndltd.ncl.edu.tw/handle/h95cgj.
Full textAbstract:
碩士國立臺灣科技大學
電子工程系
94
Chapter 4 in this thesis proposes a wide locking range injection locked frequency divider (ILFD) and describes the operation principle of the ILFD. The circuit is made of a dual band 2-stage differential CMOS ring oscillator and is based on MOS switches directly coupled to the differential outputs of the ring oscillator. The divide-by-2 and 4 ILFD can provide wide locking range and the measurement results show that at the supply voltage of 1.8-V, the divider free-running frequencies are 1.36 GHz and 2.3 GHz, and at the incident power of 0 dBm, the locking range are 64% from the incident frequency 1.9 GHz to 3.65 GHz at low band and 55% from 2.95 GHz to 5.5 GHz at high band. The ILFD can provide a locking range of 6.3% from 5.39 GHz to 6.12 GHz at low band and a locking range of 5.9% from 8.84 GHz to 9.38 GHz at high band when Vinj changes from 0.7V to 1.1V. Chapter 5 presents new LC-tank injection locked frequency divider with current reuse topology, the current reused frequency divider is implemented using a standard TSMC 0.18-um CMOS process. The wide locking range is performed by adding an injection nMOS between the differential outputs of the divider with the structure of the cross-coupled n-core VCO that stacks two nMOS transistors in series like a cascode. The measurement results show that at the supply voltage of 1.5-V, the divider free-running frequency is tunable from 2.25-GHz to 2.4-GHz, and at the incident power of 0-dBm the locking range in the divide-by-2 mode is about 0.9-GHz, from the incident frequency 4.1-GHz to 5.0-GHz. The core power consumption is 0.975mW. Chapter 6 proposes 5GHz low power differential Armstrong voltage controlled oscillators (VCOs) based on balanced topology. We designed a VCO using current-reused VCO with two single-ended Armstrong VCOs stacked in series. The VCO operates from 4.98GHz to 5.45GHz and dissipates 2.59mW at 1.8V supply voltage. The measured phase noise is -110.02 dBc/Hz at 1MHz offset frequency. This differential VCOs have an advantage of low power consumption and provide good figure of merit about -180 dBc/Hz.
46
Wu, Chih-Wei, and 吳智偉. "Persistent current and spin density in a mesoscopic Dresselhaus-type quantum ring." Thesis, 2009. http://ndltd.ncl.edu.tw/handle/98756262511386838318.
Full textAbstract:
碩士國立交通大學
電子物理系所
97
The work of this thesis is to explore and to understand physical insights on the effects of Dresselhaus spin-orbit interaction (DSOI) in a ‾nite width mesoscopic ring, both with and without a magnetic flux. The physical quantifies of interest are the spin density and persistent current. Specifcally, our insight is obtained from a detail analysis of the eigenstates and the energy spectrum as the DSOI is turned on and, independently, when the magnetic flux is turned on. For the case of turning on of the DSOI strength, we demonstrate that all energy levels are doubly degenerate, of the Kramer's type, and the trend of the energy spectrum is understood by level repulsions and the relative weighting between the constituent bases state ket. The energy spectrum depends on the DSOI quadratically in the weak SOI field regime, and this is consistent with our perturbation result. For the case of increasing the magnetic flux, we show that the Kramer degenerate states split and the physical reason for the subsequent order in the energy splitting is identified. For the eigenstate in the presence of the DSOI and the magnetic flux, we have developed a systematic way to produce its general form. We have calculated the spin density and the net spin Sz of an eigenstate. Summing these gives us the total when there are N electrons in the system.
47
Lin, Jong-chin, and 林榮欽. "Current-spin-density-functional studies of quantum dots and rings." Thesis, 2001. http://ndltd.ncl.edu.tw/handle/11284417370360221879.
Full text
48
Jyh-Ming, Lin, and 林志明. "Study of the Fault Current Limiter with single-grained Y-Ba-Cu-O High temperature Superconductor Ring." Thesis, 2000. http://ndltd.ncl.edu.tw/handle/90481212711843503703.
Full textAbstract:
碩士國立成功大學
材料科學及工程學系
88
Abstract The single-grained Y-Ba-Cu-O high Tc superconductors(HTS) offer applications in the field of Fault Current Limiter (FCL) in electric power networks. Current limitation can be accomplished by means of the non-linear impedance of a transformer with a primary winding carrying the power circuit current and a short-circuited secondary winding consisting of a hollow cylinder or ring of single grained YBCO material. The latter remains superconductive at normal load current level which act as a magnetic flux shielding device to provide a low impedance. If the defined current level is exceeded a certain level, which generates a sufficient high magnetic flux penetrating into the superconducting ring, the secondary winding turns resistive providing a high impedance which limits the prospective fault current. A laboratory screening fault current limiter has been built and its performance has been tested. The relationship between the superconducting properties of single grained YBCO materials and the performance will be reported.
49
Yao, Hai-Ying, and Le-Wei Li. "Performance Analysis of Metamaterials With Two-dimensional Isotropy." 2003. http://hdl.handle.net/1721.1/3889.
Full textAbstract:
A two-dimensional isotropic metamaterials formed by crossed split-ring resonators (CSRRs) are studied in this paper. The effective characteristic parameters of this media are determined by quasi-static Lorentz theory. The induced current distributions of a single CSRR at the resonant frequency are presented. Moreover, the dependence of the resonant frequency on the dimensions of single CSRR and the spaces of the array are also discussed.Singapore-MIT Alliance (SMA)
50
Sundholm, Eric Steven. "Amorphous oxide semiconductor thin-film transistor ring oscillators and material assessment." Thesis, 2010. http://hdl.handle.net/1957/16365.
Full textAbstract:
Amorphous oxide semiconductor (AOS) thin-film transistors (TFTs) constitute the central theme of this thesis. Within this theme, three primary areas of focus are pursued.
The first focus is the realization of a transparent three-stage ring oscillator with buffered output and an output frequency in the megahertz range. This leads to the possibility of transparent radio frequency applications, such as transparent RFID tags. At the time of its fabrication, this ring oscillator was the fastest oxide electronics ring oscillator reported, with an output frequency of 2.16 MHz, and a time delay per stage of 77 ns.
The second focus is to ascertain whether a three-terminal device (i.e., a TFT) is an appropriate structure for conducting space-charge-limited-current (SCLC) measurements. It is found that it is not appropriate to use a diode-tied or gate-biased TFT configuration for conducting a SCLC assessment since square-law theory shows that transistor action alone gives rise to I proportional to V² characteristics, which can easily be mistakenly attributed to a SCLC mechanism. Instead, a floating gate TFT configuration is recommended for accomplishing SCLC assessment of AOS channel layers.
The final focus of this work is to describe an assessment procedure appropriate for determining if a dielectric is suitable for use as a TFT gate insulator. This is accomplished by examining the shape of a MIM capacitor's log(J)-ξ curve, where J is the measured current density and ξ is the applied electric field. An appropriate dielectric for use as a TFT gate insulator will have a log(J)-ξ curve that expresses a clear breakover knee, indicating a high-field conduction mechanism dominated by Fowler-Nordheim tunneling. Such a dielectric produces a TFT with a minimal gate
leakage which does not track with the drain current in a log(I[subscript D])-V[subscript GS] transfer curve. An inappropriate dielectric for use as a TFT gate insulator will have a log(J)-ξ curve that does not express a clear breakover knee, indicating that the dominate conduction mechanism is defect driven (i.e., pin-hole like shunt paths) and, therefore, the dielectric is leaky. It is shown that experimental log(J)-ξ leakage curves can be accurately simulated using Ohmic, space-charge-limited current (SCLC), and Fowler-Nordheim tunneling conduction mechanisms.Graduation date: 2010