To see the other types of publications on this topic, follow the link: Plate radiation.
Dissertations / Theses on the topic 'Plate radiation'
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 'Plate radiation.'
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
Chu, Pearl. "Nonaxisymmetric radiation patterns of a vibrating elastic plate." Thesis, Georgia Institute of Technology, 1990. http://hdl.handle.net/1853/17902.
Full text
2
Sors, Thomas Christopher. "Active structural acoustic control of sound transmission through a plate." Thesis, University of Southampton, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.326822.
Full text
3
Wachsmuth, Matthew George. "Measurement and Characterization of Terahertz Radiation Propagating Through a Parallel Plate Waveguide." PDXScholar, 2011. https://pdxscholar.library.pdx.edu/open_access_etds/317.
Full textAbstract:
As the amount of study into the terahertz (THz) region of the electromagnetic spectrum steadily increases, the parallel plate waveguide has emerged as a simple and effective fixture to perform many experiments. The ability to concentrate THz radiation into a small area or volume enables us to analyze smaller samples and perform more repeatable measurements, which is essential for future research. While the fundamental physics of PPW transmission are understood mathematically, the practical knowledge of building such a fixture for the THz domain and taking measurements on it with a real system needs to be built up through experience. In this thesis, multiple PPW configurations are built and tested. These include waveguides of different lengths and opening heights, using lenses and antennas to focus and collect radiation from the input and output, and different amounts of polish on the waveguide surface. A basic resonator structure is also built and measured as a proof of concept for future research. The two most useful propagation modes through the waveguide, the lowest order transverse magnetic (TEM) and transverse electric (TE) modes, were characterized on all of the setups. Additionally, a flexible fixture was designed and measured which will allow future work in the THz field to be much more reliable and repeatable.
4
Rew, Gayle Astrid Adele. "Studies in zone plate encoded holography with high energy gamma rays." Thesis, University of Birmingham, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.366166.
Full text
5
Abrahamson, Stuart M. "In-situ measurement of total dose radiation effects on parallel plate MOS capacitors using the NPS linear accelerator." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 1995. http://handle.dtic.mil/100.2/ADA306694.
Full textAbstract:
Thesis (M.S. in Electrical Engineering and M. S. in Astronautical Engineering) Naval Postgraduate School, December 1995."December 1995." Thesis advisor(s): Sherif Michael, Oscar Biblarz. Includes bibliographical references. Also available online. Mode of access: World Wide Web.
6
Salem, Said Abdel-Halim Saber. "Large Eddy Simulation of Shear-Free Interaction of Homogeneous Turbulence with a Flat-Plate Cascade." Diss., Virginia Tech, 2007. http://hdl.handle.net/10919/28520.
Full textAbstract:
Studying the effects of free stream turbulence on noise, vibration, and heat transfer on structures is very important in engineering applications. The problem of the interaction of large scale turbulence with a flat-plate cascade is a model of important problems in propulsion systems. Addressing the problem of large scale turbulence interacting with a flat plate cascade requires flow simulation over a large number of plates (6-12 plates) in order to be able to represent numerically integral length scales on the order of blade-to-blade spacing. Having such a large number of solid surfaces in the simulation requires very large computational grid points to resolve the boundary layers on the plates, and that is not possible with the current computing resources.
In this thesis we develop a computational technique to predict the distortion of homogeneous isotropic turbulence as it passes through a cascade of thin flat plates. We use Large-Eddy Simulation (LES) to capture the spatial development of the incident turbulence and its interaction with the plates which are assumed to be inviscid walls.
The LES is conducted for a linear cascade composed of six plates. Because suppression of the normal component of velocity is the main mechanism of distortion, we neglect the presence of mean shear in the boundary layers and wakes, and allow slip velocity on the plate surfaces. We enforce the zero normal velocity condition on the plates. This boundary condition treatment is motivated by rapid distortion theory (RDT) in which viscous effects are neglected, however, the present LES approach accounts for nonlinear and turbulence diffusion effects by a sub-grid scale model. We refer to this type of turbulence-blade interaction as shear-free interaction.
To validate our calculations, we computed the unsteady loading and radiated acoustic pressure field from flat plates interacting with vortical structures. We consider two fundamental problems: (1) A linear cascade of flat plates excited by a vortical wave (gust) given by a 2D Fourier mode, and (2) The parallel interaction of a finite-core vortex with a single plate. We solve the nonlinear Euler equations by a high-order finite-differece method. We use nonreflecting boundary conditions at the inflow and outflow boundaries. For the gust problem, we found that the cascade response depends sensitively on the frequency of the convicted gust. The unsteady surface pressure distribution and radiated pressure field agree very well with predictions of the linear theory for the tested range of reduced frequency. We have also investigated the effects of the incident gust frequency on the undesirable wave reflection at the inflow and outflow boundaries. For the vortex-plate interaction problem, we investigate the effects of the internal structure of the vortex on the strength and directivity of radiated sound.
Then we solved the turbulence cascade interaction problem. The normal Reynolds stresses and velocity spectra are analyzed ahead, within, and downstream of the cascade. Good agreement with predictions of rapid distortion theory in the region of its validity is obtained. Also, the normal Reynolds stress profiles are found to be in qualitative agreement with available experimental data. As such, this dissertation presents a viable computational alternative to rapid distortion theory (RDT) for the prediction of noise radiation due to the interaction of free stream turbulence with structures.Ph. D.
7
Jones, Cameron Bennion. "Development and Validation of a Vibration-Based Sound Power Measurement Method." BYU ScholarsArchive, 2019. https://scholarsarchive.byu.edu/etd/9260.
Full textAbstract:
The International Organization for Standardization (ISO) provides no vibration-based sound power measurement standard that provides Precision (Grade 1) results. Current standards that provide Precision (Grade 1) results require known acoustic environments or complex setups. This thesis details the Vibration Based Radiation Mode (VBRM) method as one approach that could potentially be used to develop a Precision (Grade 1) standard. The VBRM method uses measured surface velocities of a structure and combines them with the radiation resistance matrix to calculate sound power. In this thesis the VBRM method is used to measure the sound power of a single-plate and multiple plate system. The results are compared to sound power measurements using ISO 3741 and good alignment between the 200 Hz and 4 kHz one-third octave band is shown. It also shows that in the case of two plates separated by a distance and driven with uncorrelated sources, the contribution to sound power of each individual plate can be calculated while they are simultaneously excited. The VBRM method is then extended to account for acoustically radiating cylindrical geometries. The mathematical formulations of the radiation resistance matrix and the accompanying acoustic radiation modes of a baffled cylinder are developed. Numberical sound power calculations using the VBRM method and a boundary element method (BEM) are compared and show good alignment. Experimental surface velocity measurements of a cylinder are taken using a scanning laser Doppler vibrometer (SLDV) and the VBRM method is used to calculate the sound power of a cylinder experimentally. The results are compared to sound power measurements taken using ISO 3741.
8
Johansson, Helena. "Nocturnal cooling : Study of heat transfer from a flat-plate solar collector." Thesis, Karlstad University, Faculty of Technology and Science, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:kau:diva-1523.
Full textAbstract:
This thesis investigates the possibility of using an unglazed flat-plate solar collector as a cooling radiator. The solar collector will be connected to the condenser of a heat pump and used as cooler during nighttime. Daytime the solar collector will be connected to the evaporator of the heat pump and used as heat source. The two widely differing fields of application make special demands on the solar collector. The task is given by the heat pump manufacturer Thermia and the main objective is to find out whether a solar collector should be used as a cooler or not. The performance of the solar collector under varying environmental conditions is investigated using COMSOL Multiphysics 3.3. Only the cooling properties are investigated here. The performance of the solar collector as a heat exchanger is estimated using the effectiveness-NTU method, and the solar collector is found to be a good heat exchanger at low wind speeds. The heat transfer coefficients of the convection and radiation are determined for varying temperature and wind speeds. The convective heat transfer coefficient is lowered by tubes above the absorber plate and for a high convective heat transfer rate the solar collector surface should be smooth. For a high radiative heat transfer rate the surface needs to have a high emissivity. The cooling rate is higher from a warm surface than from a cold and since no temperature change of the heat carrier is necessary the solar collector should be kept at a high temperature. To increase the cooling rate alterations need to be made to the solar collector that makes its heating performance deteriorate. A solar collector that can be used for cooling is not an efficient solar collector.
9
Hendricks, Daniel R. "An Experimental Analysis of the Weighted Sum of Spatial Gradients Minimization Quantity in Active Structural Acoustic Control of Vibrating Plates." BYU ScholarsArchive, 2013. https://scholarsarchive.byu.edu/etd/3827.
Full textAbstract:
Active Structural Acoustic Control (ASAC) is a subcategory of the more widely known field of Active Noise control (ANC). ASAC is different from traditional ANC methods because it seeks to attenuate noise by altering the noise producing structure instead of altering the acoustic waves traveling through the air. The greatest challenge currently facing ASAC researchers is that a suitable parameter has not yet been discovered which can be easily implemented as the minimization quantity in the control algorithms. Many parameters have been tried but none effectively attenuate the sound radiation in a way that can be easily implemented. A new parameter was recently developed which showed great potential for use as a minimization quantity. This parameter has been termed the "weighted sum of spatial gradients" (WSSG) and was shown by previous researchers to significantly reduce noise emissions from a vibrating simply supported plate in computer simulations. The computer simulations indicate that WSSG-based control provides as good or better control than volume velocity and does so with a single point measurement which is relatively insensitive to placement location. This thesis presents the experimental validation of the WSSG computer simulations. This validation consists of four major components. First, additional research was needed in to extend the use of WSSG from computer simulations to experimental setups. Second, the WSSG-based control method was performed on simply supported plates to validate the computer simulations. Third, the WSSG-based control method on was used on clamped plates to validate the computer simulations, and fourth, the WSSG-based control method was validated on plates with ribs. The important results are discussed and conclusions summarized for each of these sections. Recommendations are made for future work on the WSSG parameter.
10
Rousset, Philippe. "Etude expérimentale et théorique du fonctionnement du détecteur gazeux à lame en mode proportionnel." Grenoble 1, 1986. http://www.theses.fr/1986GRE10076.
Full textAbstract:
Detecteur gazeux courbe a lame anode. Fonctionnement en mode proportionnel resultant de phenomenes de compensation electrostatique dus a l'extension des lames a condition d'utiliser des melanges gazeux adequats
11
Putra, Azma. "Sound radiation from perforated plates." Thesis, University of Southampton, 2008. https://eprints.soton.ac.uk/63161/.
Full textAbstract:
Perforated plates are quite often used as a means of engineering noise control to reduce the sound radiated by structures. However, there appears to be a lack of representative models to determine the sound radiation from a perforated plate. The aim of this thesis is to develop such a model that can be used to give quantitative guidance corresponding to the design and effectiveness of this noise control measure. Following an assessment of various models for the radiation efficiency of an unbaffled plate, Laulagnet’s model is implemented. Results are calculated and compared with those for baffled plates. From this, simple empirical formulae are developed and give a very good agreement with the analytical result. Laulagnet’s model is then modified to include the effect of perforation in terms of a continuously distributed surface impedance to represent the holes. This produces a model for the sound radiation from a perforated unbaffled plate. It is found that the radiation efficiency reduces as the perforation ratio increases or as the hole size reduces. An approximate formula for the effect of perforation is proposed which shows a good agreement with the analytical calculation up to half the critical frequency. This could be used for an engineering application to predict the noise reduction due to perforation. The calculation for guided-guided boundary conditions shows that the radiation efficiency of an unbaffled plate is not sensitive to the edge conditions. It is also shown that perforation changes the plate bending stiffness and mass and hence increases the plate vibration. The situation is also considered in which a perforated unbaffled plate is located close to a reflecting rigid surface. This is established by modifying the Green’s function in the perforated unbaffled model to include an imaginary source to represent the reflected sound. The result shows that the presence of the rigid surface reduces the radiation efficiency at low frequencies. The limitation of the assumption of a continuous acoustic impedance is investigated using a model of discrete sources. The perforated plate is discretised into elementary sources representing the plate and also the holes. It is found that the uniform surface impedance is only valid if the hole distance is less than an acoustic wavelength for a vibrating rectangular piston and less than half an acoustic wavelength for a rectangular plate in bending vibration. Otherwise, the array of holes is no longer effective to reduce the sound radiation. Experimental validation is conducted using a reciprocity technique. A good agreement is achieved between the measured results and the theoretical calculation for both the unbaffled perforated plate and the perforated plate near a rigid surface.
12
Solomon, Brad K. "Methods for Identifying Acoustic Emissions From the Front Face of a Small Piezoelectric Blower." BYU ScholarsArchive, 2012. https://scholarsarchive.byu.edu/etd/3542.
Full textAbstract:
This thesis focuses on identifying acoustic noise generating components in piezoelectric blowers through transverse velocity measurements and the development of a numerical fluid model. Piezoelectric ceramics have proven useful for many industries and areas of research involving: high precision actuators, noise control, ultrasonic devices, and many other areas. As of late, a unique adaptation of piezoelectric ceramics is surfacing in the area of pumping and cooling. Air pumps that use these ceramics replace the traditional electric motor, resulting in lower power consumption, less moving parts, constant pressure gradients, lower overall weight, and a low profile. The current drawback of this application is the acoustic radiation produced by the blowers. Since these blowers are new to market, little research or development has been done to characterize the noise emissions. This thesis studies the acoustic emissions from the front face of a Murata piezoelectric blower. Jet noise and structural vibrations are two acoustic sources of interest that are studied in this research. A Direct Numerical Simulation (DNS) of the fluid flow through a Murata blower is developed to better identify noise generating mechanisms. The model solutions predict trends in sound pressure levels (SPL) of the jet noise and volumetric flow rates. Both the SPL and flow rate are shown to be functions of critical geometrical dimensions within the flow path of a Murata blower. Important dimensional components are identified as well as non-influential ones. Design guidelines are given to reduce noise emission from the front side of a blower and increase the volumetric flow rate. The results of this research have a direct impact on the piezoelectric blower industry and future blower designs.
13
Wang, Duo. "Analyse et conception de répéteurs passifs plans à rayonnement quasi-latéral pour communications «indoor» à 60GHz." Thesis, Rennes, INSA, 2015. http://www.theses.fr/2015ISAR0011/document.
Full textAbstract:
Le développement rapide de l’industrie des systèmes sans fil suscite une demande urgente pour des communications à haut débit, notamment en environnement « indoor ». Toutefois, les protocoles traditionnels de communications sont incapables de supporter de très hauts débits et, surtout, il n'y a pas de ressources spectrales disponibles à basse fréquence. Comme une alternative, la bande des 60GHz est préconisée parce qu’elle permet un débit de plus de 5Gbit/s, grâce à son large spectre (57GHz à 64 GHz). Toutefois, en pratique, l’environnement « indoor » est complexe et, dans les situations d’absence de visibilité directe, la couverture radio est difficile à assurer à cause des fortes atténuations. Afin de remédier à ce problème, l’utilisation de répéteurs est possible. Dans cette thèse, l’intérêt est porté sur les répéteurs passifs, plus simples à installer et compatibles avec une réalisation faible coût. Le cas critique de la couverture radio d’un couloir en T est choisi comme fil conducteur, tout au long de cette étude. Les solutions préconisées visent aussi la compacité, ce qui justifie l’utilisation de réflecteurs plans. A partir de la théorie des réseaux d’antennes, une structure périodique générique pour le répéteur est proposée. Elle implique deux cellules réfléchissantes élémentaires (espacées de /2), produisant des ondes en opposition de phase. Plusieurs topologies et technologies sont ensuite envisagées et étudiées pour la mise en oeuvre. La première utilise des antennes à résonateur diélectrique (DRA). Deux topologies différentes sont étudiées et comparées, le DRA à encoche et le DRA couplé à une ligne déphaseuse en circuit ouvert. Différentes stratégies de modélisation sont également étudiées en utilisant une cellule unique, un couple de 2 cellules avec phases opposées ou un petit réseau. Pour chaque topologie, un réseau canonique de 6×6 éléments est simulé. La deuxième technologie étudiée utilise des guides d’ondes rectangulaires chargés par un matériau diélectrique et courtcircuités. Des analyses paramétriques sont effectuées et un 6 ×6 réseau est conçu et optimisé pour valider la faisabilité de la solution. Finalement, une structure en guide à plaques métalliques parallèles est analysée. Dérivant de la solution précédente, elle permet une fabrication plus simple. Pour cette dernière solution, une analyse plus complète est menée incluant des considérations sur la bande passante, les performances en incidence oblique et la direction de rayonnement maximal. Enfin, un réseau à base de cet élément rainuré est fabriquée présentant une taille de 200 mm×200 mm. Des mesures expérimentales à 60GHz sont réalisées pour tester les performances du réseau. La preuve de concept est ainsi donnée et les résultats expérimentaux sont analysésThe fast development of information and consumer electronics industries creates a pressing demand for high-speed indoor communications. Traditional communication protocols are unable to support such high transmission rate, and there are no radio bands available at lower frequency. As an alternative, 60GHz communications have sparked great attention, since it enables a maximum data transmission rate more than 5Gbit/s based on its wide unlicensed bandwidth. However, practical indoor environment is usually complicated (e.g. walls, corridors, stairs, etc.), thus the non-line-of-sight (NLOS) areas cannot be covered due to the significant attenuation. Considering the requirements for signal recovery in the NLOS environment, a planar passive repeater with endfire radiation and high directivity, low profile and low cost is investigated and designed in this thesis. Based on array theory, a periodic structure for the foreseen printed repeater is derived out. It involves two reflector elements (in the spacing of 2) to provide 0° and 180°reflection phases respectively. In order to construct a proper reflector element, four topologies are proposed and analyzed. In the first part of the study, DRA (Dielectric Resonator Antenna) technology is the main focus. Two different topologies are investigated and compared, including notched DRA and DRA coupled to phase-shift stub. Different modeling strategies are also studied using either a single cell, a couple of cells with opposite phases or a small array. For each topology, a preliminary 6×6 array is simulated. Optimization at the array level is emphasized through the whole thesis. In the second part, investigations are taken on a rectangular dielectric filled waveguide element. Parametric analyses are carried out and possible fabrication technologies are discussed. Once again, a preliminary 6×6 array is designed and optimized to validate the feasibility of such a structure. In the third part, a parallel-plate groove structure is analyzed. It evolves from the rectangular waveguide, and enjoys more simplification. Further work is taken to explore the arrays’ bandwidth, oblique incidence performance and maximum radiation direction. Detailed theoretical analysis based on the simulation results are demonstrated in the end. Finally, an array based on the groove elements is fabricated in the size of 200mm×200mm. Practical measurements for 60GHz communications in NLOS environment are designed to test the array’s performance. Analyses on the experiment results are given
14
Gu, Yi. "Active control of sound radiation from fluid loaded plates." Diss., Virginia Tech, 1992. http://hdl.handle.net/10919/39888.
Full textAbstract:
Active control of sound radiation due to subsonic wave scattering from an infinite or a finite fluid-loaded plate excited below the critical frequency is analytically studied. The disturbance is caused by a flexural wave in an infinite plate, or by a point force on a finite plate at subsonic frequencies. The wave scattering is caused by discontinuities on the plate or by the boundary conditions.
A feed-forward control approach is applied by implementing either point/line forces or piezoelectric actuators on the plate. The amplitude and phase of control forces are determined by the optimal solution of a cost function which minimizes the far-field radiated acoustic power over a prescribed surface in the half space of the fluid field.
The results show that for subsonic excitations, high global reduction in radiated pressure is possible with properly located active control forces. The number and location of control forces employed in order to obtain high control performance are related to the excitation frequency. The far-field sound radiation directivity pattern, the modal amplitudes of the plate vibration, the plate vibration autospectrum in the wave number domain, and the near-field intensity distribution are extensively studied in order to uncover the mechanisms of control.Ph. D.
15
Llewellyn, Smith Stefan Gregory. "Vortices and Rossby-wave radiation on the beta-plane." Thesis, University of Cambridge, 1996. https://www.repository.cam.ac.uk/handle/1810/244817.
Full textAbstract:
The Earth’s atmosphere and oceans contain strongly swirling coherent structures. The sphericity of the Earth’s surface, which may be modelled by the beta-effect, is responsible for the motion of these vortices, and also for the existence of Rossby waves. This dissertation examines the evolution of distributed vortices on the beta-plane when the vortices are much stronger than the background beta-effect. There is a small nondimensional parameter ε , and a solution to the problem may be sought as an asymptotic expansion in ε. The near-field equation is then, to first order, a forced radial Rayleigh equation. For the nondivergent case, with no vortex stretching, a different dynamical balance holds in the far field. Chapter 2 derives an exact mode-one solution for the radial Rayleigh operator and completely solves the classical inviscid instability initial-value problem for mode-one disturbances to a circular basic state. Disturbances tend to a steady-state solution if the basic state circulation is nonzero, and grow algebraically without bound otherwise. Chapter 3 examines properties of the causal Green’s function for the far-field Rossby wave equation. Chapter 4 calculates the first-order solution to the global problem in the nondivergent case by the method of Matched Asymptotic Expansions. For zero circulation, there is no far field. The resulting trajectory of vortices is computed; several ways of identifying the centre of the vortices are presented. Trajectories are calculated for the Rankine and Gaussian vortices. Chapter 5 calculates the asymptotic behaviour of the second-order solution, and examines the nonuniformity of the asymptotic expansion. In the case of nonzero circulation, the expansion loses validity for times t = 0( ε -2/3 ) and spatial scales r = 0( ε -1/3 ), rather than t = 0( ε -1) and r = 0(1) respectively. Chapter 6 solves the divergent problem numerically to first order, and also analytically for asymptotically large Rossby radii of deformation. The order of breakdown is then t = 0( ε -1). Chapter 7 presents conclusions and suggestions for further research.
16
Meulle, Aline. "Place des adipocytes dans la réponse tissulaire aux radiations ionisantes." Toulouse 3, 2008. http://thesesups.ups-tlse.fr/333/.
Full textAbstract:
La radiothérapie est un traitement majeur des cancers car les radiations ionisantes (RI) vont induire différents dommages à l'ADN dont les cassures doubles brins (CDB). Lors de l'irradiation d'une tumeur, les cellules du microenvironnements vont être aussi irradiées et cela pourraient modifier la réponse des cellules cibles. Parmi les cellules du stroma mammaire, les adipocytes pourraient jouer un rôle important car ce sont les cellules les plus abondantes du stroma mammaires et elles sécrètent de nombreux facteurs susceptibles de modifier le comportement de la tumeur. Je me suis intéressé dans un premier temps à la réponse des adipocytes à l'exposition aux RI, et dans un deuxième temps à l'influence des adipocytes sur la radiosensibilité de cellules tumorales mammaires. Nous avons pu montrer qu'au cours de l'adipogenèse, l'activité de réparation des CDBs est augmentée et cela est du à l'augmentation de l'expression et de l'activité d'une protéine clé de ce mécanisme de réparation, la DNA-PKcs. Ces résultats sont retrouvés pour une adipogenèse murine et humaine. Par ailleurs, nous avons pu montrer que les adipocytes étaient des cellules radiorésistantes, ce qui favorise l'hypothèse de leur participation à la réponse tissulaire aux RI. Effectivement, les premiers résultats obtenus montrent que dans un système de coculture en 2D, les adipocytes protègent les cellules tumorales mammaires de la mort clonogène, cet effet étant dépendant de facteurs solubles sécrétés par les adipocytes. Il serait intéressant d'étudiant l'influence des adipocytes dans un contexte d'obésité, car l'obésité est associée à un mauvais pronostic des cancersRadiotherapy is a major therapeutic strategy in the treatment of many human tumors becase the exposure to ionizing radiation (IR) induces DNA damage and among them DNA double strand breaks (DSBs). However, cancer is a tissue-based disease in which malignant cells interact dynamically with multiple normal cell or stroma, and to the response to IR, emerging studies suggest that the irradiated stroma can influence the sensibility of cancer cell. Stroma was composed by differents types of cell, and adipocytes cells are excellent candidat because they are highly represented in breast tumor stroma and are able to secrete many factors. So the goal of our project was to investigate if adipocyte can influence the tissue response to IR. As a first step, we have demonstrated that the ability to repair DSBs is increased during adipocyte differentiation, that can explain by the increase of expression and activity of a key protei of DSB repair, DNA-PKcs. This result are observed during human and mrin adipogenesis. Moreover, we are observed that adipocyte are radioresistan cell and this ability to resist to genotoxic stress supports the idea that adipocytes might participate to radioresistance at a tissue level. In fact we demonstrated, in a 2D co-culture model that adipocytes protect breast cancer cell from clonogenic cell death in a manner that is dependent of secreted soluble factors. Accordingly, it would be of interest to evaluate the paracrine role of adipocytes within the context of obesity that has been recently established a negative prognostic factor even for localized breast tumors
17
Stewart, Kristin J. "Accurate radiation dosimetry using liquid- or air-filled plane-parallel ionization chambers." Thesis, McGill University, 2001. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=29576.
Full textAbstract:
To optimize delivery of radiation therapy treatments, accurate knowledge of absorbed dose in the clinical beam is essential. In this work we investigated issues related to the use of different types of ionization chambers for accurate radiation dosimetry. We determined values of Pwall at 60Co for plane-parallel chambers and used them to derive the conversion factors kecal k'R 50 or kQ for a 20 MeV electron beam. Our results agreed within 0.4% with kQ values given in the IAEA TRS-398 protocol, but differences of up to 1.8% were found between our kecalk' R50 values and those in the AAPM TG-51 protocol. We also investigated the behavior of two liquid-filled ionization chambers in megavoltage photon beams, examining stability, ion recombination and beam quality dependence. Methods for determining and correcting for recombination were investigated. Preliminary results show that the energy dependence of a liquid-filled chamber can typically be limited to less than 1% for megavoltage photon beams.
18
Ali, Syed Mahmood. "Plane wave scattering from circular and hollow circular slit cylinders using the On Surface Radiation Condition (OSRC) approach." Thesis, Monterey, California : Naval Postgraduate School, 1990. http://handle.dtic.mil/100.2/ADA243793.
Full textAbstract:
Thesis (M.S. in Electrical and Computer Engineering)--Naval Postgraduate School, December 1990.Thesis Advisor(s): Janaswamy, R. Second Reader: Adler, Richard W. "December 1990." Description based on title screen as viewed on March 30, 2010. DTIC Descriptor(s): Linear systems, thickness, scattering, polarization, distribution, formulations, integrals, shape, structures, theses, electromagnetic wave propagation, reflection, surfaces, surface properties, wave propagation, cylindrical bodies, width, integral equations, frequency domain, plane waves, circular, truncation, concave bodies, convex bodies, radiation DTIC Identifier(s): Radar reflections, hollow cylinders, slit cylinders, OSRC (on surface radiation condition). Author(s) subject terms: Surface radiation conditions; transverse electric; circular cylinders; hollow cylinder slit cylinders Includes bibliographical references (p. 68-69 ). Also available in print.
19
Hoppe, Stefan. "Emitters of VHE gamma-radiation as revealed by the H.E.S.S. galactic plane survey." [S.l. : s.n.], 2008. http://nbn-resolving.de/urn:nbn:de:bsz:16-opus-88939.
Full text
20
Wang, Bor-Tsuen. "Active control of sound transmission/radiation from elastic plates using multiple piezoelectric actuators." Diss., Virginia Tech, 1991. http://hdl.handle.net/10919/39956.
Full text
21
Chin, Erika. "Calculation of water and graphite perturbation correction factors for the NACP-02 plane-parallel ionization chamber in high-energy electron beams." Thesis, McGill University, 2008. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=18699.
Full textAbstract:
For megavoltage electron beams, current dosimetry protocols assume well-guarded plane-parallel ionization chambers have electron perturbation correction factors of unity. Papers by other researchers have shown the contrary. The National Physical Laboratory (NPL), Teddington UK, has an electron calibration service that requires knowledge of the ratio of perturbation factors in water to graphite for their NACP-02 chamber. Using the Monte Carlo code EGSnrcMP, perturbation correction factors at depth zref in graphite for the NPL's Radiation Dynamics linac 4 – 19 MeV were calculated. These results combined with those in water calculated by Zakikhani (2006) showed that only the ratio of perturbation factors in water to graphite for the 4 MeV and 12 MeV beams, at 1.0080 ± 0.27 % and 1.0071 ± 0.28 %, were significantly different from unity. Perturbation correction factors in water and graphite for the Varian clinical linacs 4 – 18 MeV were also investigated. Important issues that arose requiring further study included the discrepancy in results caused by 1 keV vs. 10 keV transport cutoffs and whether the depth of the effective point of measurement should account for the phantom equivalent thickness of the chamber window.Pour les faisceaux d'électrons de haute énergie (MV), les protocoles de dosimétrie actuels supposent que les chambres d'ionisation à plaques parallèles ont des facteurs de correction de perturbation électronique égaux à l'unité. Plusieurs articles d'autres auteurs ont démontré le contraire. Le National Physical Laboratory (NPL), Teddington Royaume-Uni, possède un service d'étalonnage qui requiert de savoir les facteurs de perturbation de l'eau par rapport au graphite pour leur chambre NACP-02. A l'aide du code Monte Carlo EGSnrcMP, les facteurs de correction de perturbation à profondeur zref dans le graphite ont été calculés pour le linac Radiation Dynamics du NPL à des énergies de 4-19 MeV. Ces résultats, combinés à ceux dans l'eau calculés par Zakikhani (2006), ont montré que seulement les facteurs de perturbation de l'eau par rapport au graphite des faisceaux de 4 MeV et 12 MeV, à 1,0080 ± 0,27 % et 1,0071 ± 0,28 % respectivement, étaient significativement différents de l'unité. Les facteurs de correction de perturbation dans l'eau et dans le graphite ont aussi été étudiés pour les linacs cliniques de Varian à 4-18 MeV. D'importants problèmes ont alors été soulevés, notamment des différences dans les résultats causés par des énergies de coupure de 1 keV par rapport à 10 keV ainsi que la question de savoir si la profondeur du point de mesure devrait prendre en compte l'épaisseur effective de la fenêtre d'entrée. Ces problèmes requièrent davantage d'études.
22
Morris, Russell A. "Optimal state estimation for the optimal control of far-field acoustic radiation pressure from submerged plates." Thesis, This resource online, 1992. http://scholar.lib.vt.edu/theses/available/etd-06232009-063036/.
Full text
23
Lee, Hyeongill. "Modal acoustic radiation characteristics of a thick annular disk." Connect to this title online, 2003. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1053709926.
Full textAbstract:
Thesis (Ph. D.)--Ohio State University, 2003.Title from first page of PDF file. Document formatted into pages; contains xxix, 163 p. : ill. (some col.). Advisor: Rajendra Singh, Department of Mechanical Engineering. Includes bibliographical references (p. 160-163).
24
Bernier, Marie-Odile. "Mise en place d'une cohorte d'enfants exposés au scanner et analyse du risque de cancer radio-induit." Thesis, Paris 6, 2016. http://www.theses.fr/2016PA066744/document.
Full textAbstract:
L'exposition médicale diagnostique aux rayonnements ionisants représente environ 40% de l'exposition totale aux radiations en France. L'utilisation du scanner, beaucoup plus irradiant que l'imagerie conventionnelle, ne cesse de progresser, y compris chez les enfants, dont la radiosensibilité est supérieure à celle des adultes. Plusieurs études récentes sont en faveur d'une augmentation du risque de leucémie et de tumeur cérébrale après exposition au scanner dans l'enfance. Une cohorte nationale multicentrique a été mise en place à l'IRSN depuis 2009 incluant plus de 108 137 enfants soumis à un ou plusieurs scanners avant l'âge de 10 ans sur la période 2000-2010 dans 23 services de radiologie pédiatriques de CHU, répartis sur l'ensemble du territoire. L'estimation des doses reçues au niveau des principaux organes a été faite en fonction des protocoles utilisés. La grande variabilité des doses selon les services témoigne de la nécessité d'optimisation des protocoles. Près de 3% des enfants de la cohorte présentaient un facteur de prédisposition aux cancers étudiés. Le croisement de la cohorte avec le registre national des cancers pédiatriques a identifié 106 cas incidents de cancer, dont 22 tumeurs cérébrales et 17 leucémies. Chez les enfants sans facteur de prédisposition, un excès de risque positif mais non significatif était observé pour la leucémie et les tumeurs cérébrales en fonction de la dose, similaire à celui observé pour la population d'étude dans son ensemble. Chez les enfants avec un facteur de prédisposition au cancer, le risque diminuait, possiblement en lien avec une mortalité précoce augmentée entrainant un déficit de risque de cancer radio-induit à plus long terme. Le projet européen EPI-CT inclut 9 cohortes nationales, dont la cohorte française et regroupera plus d’un million d’enfants exposés au scanner. L’analyse conjointe de ces données permettra d’apporter prochainement des résultats complémentaires sur ce sujetMedical diagnostic exposure to ionizing radiation represents about 40% of the total annual radiation exposure in France. The CT scans, which represent only 5% of the total number of X-rays examinations, account for half of the total collective dose associated with medical diagnostic exposure. However, its use continues to grow, including in children, for whom the radio sensitivity is known to be greater than in adults. Several recent studies support an increased risk of leukemia and brain tumors after exposure to CT scan in childhood. A national multicenter cohort was set up at the IRSN since 2009 including 108 137 children subjected to at least one CT scans before the age of 10 during the 2000 to 2013 period in 23 French University hospital’s pediatric radiology departments. Children's exposure was assessed based on radiological protocols. It was observed high variability of doses according to the participant departments, reflecting the need for protocol optimization. Moreover, children with predisposing factor for studied cancers represented 3% of the study population, a percentage well above that observed in the general population. The linkage of the cohort with the National Register of pediatric cancers identified 106 incident cases of cancer in the cohort, 22 brain tumors and 17 leukemias. For children without predisposing factor, it was observed a non-significant excess risk of cancer according to the received dose, similar to that observed for the whole study population. For children with predisposing factor to cancer, the risk decreased without reaching significance, possibly linked to earlier non-cancer mortality in this group and then to a lower risk to develop later radiation induced cancer. The European project EPI-CT, which includes 9 national cohorts (including the French cohort), will include more than one million children and then will bring further results on this topic
25
Matsuda, Yoshinobu. "Polar-Plane-Free Faceted InGaN-LEDs toward Highly Radiative Polychromatic Emitters." Doctoral thesis, Kyoto University, 2020. http://hdl.handle.net/2433/253285.
Full textAbstract:
京都大学0048
新制・課程博士
博士(工学)
甲第22449号
工博第4710号
新制||工||1736(附属図書館)
京都大学大学院工学研究科電子工学専攻
(主査)教授 川上 養一, 教授 野田 進, 教授 山田 啓文
学位規則第4条第1項該当
Doctor of Philosophy (Engineering)
Kyoto University
DFAM
26
Kitts, Zachary Todd. "An Analytical Study of the Weak Radiating Cell as a Passive Low Frequency Noise Control Device." Thesis, Virginia Tech, 2000. http://hdl.handle.net/10919/35507.
Full textAbstract:
At low frequency where the acoustic wavelength is greater than the size of the vibrating structure, the radiated acoustic power is directly related to the volume velocity of the structure. Thus, minimizing the volume velocity is an effective noise reduction approach for low frequency structurally radiated noise. This thesis analytically investigates a passive volume velocity noise control device for acoustic surface treatment of planar structures. The device is referred to as a weak radiating cell. This device consists of two mechanically coupled surfaces such that, when placed on a vibrating structure, the response of the two surfaces are nearly out-of-phase and of equal strength over a wide frequency range. The response of the two surfaces forms a local acoustic dipole, with minimum volume velocity, that results in noise reduction. Thus, the control of low frequency structurally radiated noise is achieved by covering the structure with an array of these weak radiating cells. Several numerical models are developed to investigate the weak radiating cell noise control mechanisms. The first model consists of a simply supported beam treated with an array of weak radiating cell. In this model, the dynamic interaction effects between the beam and the cells are included. Results from this model predict an overall sound power level reduction of 9.8 dB between 0-1600 Hz and 20 dB between 0-251 Hz. In addition, this model is used to investigate techniques to improve the noise reduction capabilities of the device. A model of weak radiating cells applied to a simply supported plate is next developed as an extension of the beam model. The results from this model are compared to previous experimental data. Good agreement is observed between results, which validates the modeling technique. Lastly, a model of an infinite 2D plate treated with weak radiating cells is developed. The model does not consider any dynamic interaction effect between the structure and the cells. Only the acoustic behavior of the weak radiating cell is included in this model. In addition, both the structural and acoustic responses are obtained in closed form through a wavenumber transform approach. Each of these models and their results offer valuable information that results in a better understanding the weak radiating cell and it potential as a low frequency passive noise control device.Master of Science
27
Alves, Marta Isabel Rocha. "Diffuse radio recombination line emission on the galactic plane." Thesis, University of Manchester, 2011. https://www.research.manchester.ac.uk/portal/en/theses/diffuse-radio-recombination-line-emission-on-the-galactic-plane(54655adf-a0da-4f27-86fb-0d8ae43e1e80).html.
Full textAbstract:
A full-sky free-free template is increasingly important for the high-sensitivity Cosmic Microwave Background (CMB) experiments, such as Planck. On the Galactic plane, where free-free estimations from Halpha measurements become unreliable, Radio Recombination Lines (RRLs) can be used to determine the thermal brightness temperature unambiguously with no dust contamination. RRLs are a powerful tool for the diagnostic of the interstellar medium, tracing the ionised component, its electron temperature, velocity and radial distributions.This thesis describes the investigation of the ionised emission from HII regions and diffuse gas along the Galactic plane using RRLs, with the aim of providing a map of the free-free emission to complement the high latitude Halpha observations. Measuring the free-free emission on the Galactic plane is of great importance to understand and characterise other Galactic emission components: synchrotron, anomalous dust and thermal dust emission. The fully-sampled HI Parkes All-Sky Survey and associated deep Zone of Avoidance Survey are re-analysed to recover extended RRL emission. They include three RRLs (H166alpha, H167alpha and H168alpha) at frequencies near 1.4 GHz. A data cube covering l=20 degree to 44 degree and |b| < 4 degree is constructed of RRL spectra with velocity and spatial resolution of 20 km/s and 14.8 arcmin, respectively. Well-known HII regions are identified as well as the diffuse RRL emission on the Galactic plane.In order to convert the integrated RRL emission into a free-free brightness temperature a value of the electron temperature (Te) of the ionised gas is needed. Using the continuum and line data from the present survey, the variation of Te with Galactocentric radius was derived for the longitude range l=20 degree to 44 degree, with a mean Te on the Galactic plane of 6000 K. The derived Te variation was used to obtain the first direct measure of the free-free brightness in this region of the Galactic plane. Subtraction of this thermal emission from the total continuum at 1.4 GHz leaves the first direct measurement of the synchrotron emission. A narrow component of width 2 degree is identified in the synchrotron latitude distribution.Determining the free-free and synchrotron emission in this region of the Galactic plane identifies the anomalous microwave component, when combined with WMAP and IRIS data. The results are in agreement with models of small spinning dust grains.
28
NONATO, FERNANDA B. C. "Projeto, construção e caracterização de sistemas de referência para feixes de elétrons de aceleradores clínicos." reponame:Repositório Institucional do IPEN, 2014. http://repositorio.ipen.br:8080/xmlui/handle/123456789/23232.
Full textAbstract:
Submitted by Claudinei Pracidelli (cpracide@ipen.br) on 2015-01-07T16:00:13Z
No. of bitstreams: 0Made available in DSpace on 2015-01-07T16:00:14Z (GMT). No. of bitstreams: 0
Tese (Doutorado em Tecnologia Nuclear)
IPEN/T
Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP
29
Zakikhani, Ramtin. "Calculated perturbation factors for the NACP-02 plane-parallel ionization chamber irradiated in water by megavoltage electron beams." Thesis, McGill University, 2006. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=99213.
Full textAbstract:
Measurements of absorbed dose to water in megavoltage electron beams are carried out with cylindrical or plane-parallel ionization chambers. The perturbation factor associated with plane-parallel ionization chambers that have sufficiently large guard rings is assumed to be unity. The NACP-02 chamber is one such chamber that we have investigated in order to determine if this assumption is valid. By performing Monte Carlo simulations with the EGSnrc code, water-to-air Spencer-Attix stopping powers and perturbation factors were calculated in water with a detailed model of the NACP chamber that was validated through results obtained from measurements and simulations. These were determined for electron beam energies between 4 MeV and 19 MeV for a clinical and PSDL linear accelerator. The overall perturbation factor was found to decrease with energy at dref from 1.015 at 4 MeV to 1.004 at 19 MeV and increase with depth for a fixed beam quality.
30
Mehrtash, Mehdi. "Numerical Investigation Of Natural Convection From Plate Finned Heat Sinks." Master's thesis, METU, 2011. http://etd.lib.metu.edu.tr/upload/12613530/index.pdf.
Full textAbstract:
Finned heat sink use for electronics cooling via natural convection is numerically investigated. An experimental study from the literature that is for vertical surfaces is taken as the base case and the experimental setup is numerically modeled using commercial CFD software. The flow and temperature fields are resolved. A scale analysis is applied to produce an order-of-magnitude estimate for maximum convection heat transfer corresponding to the optimum fin spacing. By showing a good agreement of the results with the experimental data, the model is verified. Then the model is used for heat transfer from inclined surfaces. After a large number of simulations for various forward and backward angles between 0-90 degrees, the dependence of heat transfer to the angle and Rayleigh number is investigated. It is observed that the contributions of radiation and natural convection changes with the angle considerably. Results are also verified by comparing them with experimental results available in literature.
31
Field, Parker Lawrence. "Comparison of RANS and Potential Flow Force Computations for the ONR Tumblehome Hullfrom in Vertical Plane Radiation and Diffraction Problems." Thesis, Virginia Tech, 2013. http://hdl.handle.net/10919/23123.
Full textAbstract:
The commercial CFD software STAR-CCM+ is applied as a RANS solver for comparison with potential flow methods in the calculation of vertical plane radiation and diffraction problems. A two-dimensional rectangular cylinder oscillating in an unbounded fluid is first considered, and the added mass result shown to agree well with the analytical potential flow solution. Hydrodynamic coefficients are then determined for the cylinder oscillating in heave and sway about a calm free surface. Predicted values are observed to coincide with available experimental and linear potential flow results for most amplitudes and frequencies of oscillation examined. A three-dimensional radiation problem is then studied in which 1-DoF heave and pitch motions are prescribed to the ONR Tumblehome hullform in calm water at zero forward speed and Fn 0.3. Combinations of amplitude and frequency of oscillation ranging from small to large are considered. Results are compared with several potential flow codes which utilize varying degrees of linearization. Differences in the force and moment results are attributed to particular code characteristics, and overall good agreement is demonstrated between RANS and potential flow codes which employ a nonlinear formulation. The ONR Tumblehome is next held static in incident head waves of small and large steepness and zero forward speed or Fn 0.3. Force and moment time histories of the periodic response are compared with the same set of potential flow codes used in the radiation problem. Agreement between potential flow and RANS is reasonable in the small wave steepness case. For large wave steepness, the nonlinear wave response is seen to be important and the RANS solution does not generally agree well with potential flow results.Master of Science
32
Pelteku, Altin E. "Development of an electromagnetic glottal waveform sensor for applications in high acoustic noise environments." Link to electronic thesis, 2004. http://www.wpi.edu/Pubs/ETD/Available/etd-0114104-142855/.
Full textAbstract:
Thesis (M.S.)--Worcester Polytechnic Institute.Keywords: basis functions; perfectly matched layers; PML; neck model; parallel plate resonator; finite element; circulator; glottal waveform; multi-transmission line; dielectric properties of human tissues; radiation currents; weighted residuals; non-acoustic sensor. Includes bibliographical references (p. 104-107).
33
Scheibe, Oskar. "Modelling of Heat Transfer for Convection-boosted Flat Vertical Radiator Surfaces : An investigation of how heat transfer is influenced by radiator height and freestream air velocity." Thesis, KTH, Strömnings- och klimatteknik, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-220138.
Full textAbstract:
In this thesis, a calculation model is created to study a theoretical radiator-like configuration, consisting of a flat vertical plate heated with a constant capacity rate. This lumped capacitance model is partly created to more theoretically look at radiators with add-on-fans, but also to in such a setting look at fundamental heat transfer relationships. System heat transfer is studied for various heights, H (m), and freestream velocities, u (m/s). These results are then subject to validation, where comparison is made with values derived from two relevant reference studies. It is found that polynomial fits well describe the results obtained from calculation. The relationships for heat transfer Q (W), heat flux q (W/m2) thus become: 𝑄(𝐻,𝑢) = 𝑎00 + 𝑎01𝑢 + 𝑎10𝐻 + 𝑎11𝐻𝑢 + 𝑎02𝑢2 (W) 𝑞(𝐻,𝑢) =𝑄/𝐻= 𝑎00𝐻-1 + 𝑎01𝐻-1𝑢 + 𝑎10 + 𝑎11𝑢 + 𝑎02𝐻-1𝑢2 (W/m2) For these relationships, polynomial coefficients 𝑎00, 𝑎01, 𝑎10, 𝑎11 and 𝑎02 are found for three temperature set-ups of system supply and return temperature at zero freestream velocity: 55/45, 45/35 and 35/25 (°C). These values are chosen as they correspond to standard temperatures for low-temperature heating set-ups. Model validation is successful for the case of natural convection (u = 0), whereas difficulties are encountered for the cases of mixed and forced convection. Reasons for these difficulties are discussed and it is concluded that there is a need for more experimental studies of flat vertical plates with non-isothermal wall temperature profiles.
34
Emonet, Piccardi Nathalie. "Place des thiols dans la photoprotection." Université Joseph Fourier (Grenoble), 1998. http://www.theses.fr/1998GRE10246.
Full textAbstract:
L'irradiation ultraviolette a (uva : 320-400 nm) exerce un role potentiel dans la carcinogenese cutanee, ainsi que dans l'heliodermie, par des mecanismes impliquant les especes reactives de l'oxygene. La mise au point d'une protection efficace contre ce type de radiations devient donc une necessite en termes de sante publique. L'utilisation des topiques solaires actuels ne permet pas de garantir une protection optimale contre les uva. En dernier ressort, la protection des cellules cutanees, exposees aux uva, repose sur les systemes de la defense antiradicalaires, dont les thiols. Par une approche originale, nous avons montre les limites des photoprotecteurs externes en termes de prevention des degats genomiques et d'epargne des systemes antioxydants intracellulaires, definissant ainsi l'adn et le glutathion comme des biomarqueurs potentiels de l'efficacite reelle apportee par les topiques solaires. Par ailleurs, ce travail montre l'interet d'un apport exogene de thiols et/ou d'oligo-elements (selenium et zinc) en termes de photoprotection. La modulation redox de la synthese des proteines de stress sous uva a egalement ete apprehendee. Cette etude conduit a associer photoprotection externe et interne, dans un nouvel axe de recherche permettant la mise au point d'une photoprotection parfaite, s'opposant aux effets immediats et a longs termes de l'exposition solaire.
35
Nontakaew, Udomkiat. "Etude théorique et expérimentale du problème de radiation d'ondes par une plaque plane en oscillations forcées avec vitesse d'avance." Poitiers, 1996. http://www.theses.fr/1996POIT2313.
Full textAbstract:
Le developpement des calculs de tenue a la mer des navires demande la mise au point de codes de calculs d'ecoulements instationnaires autour de navires ou d'elements de ceux-ci. La presente etude porte essentiellement sur le developpement d'une methode de calcul de radiation d'ondes par une plaque plane oscillante avec vitesse d'avance, en derapage, percant la surface libre. Par utilisation de la troisieme formule de green, ce probleme est ramene a la resolution d'une equation integrale de fredholm de premiere espece par la methode des singularites avec fonction de green. On utilise ici la fonction de green de diffraction-radiation avec vitesse d'avance. Nous avons pour cette etude developpe une procedure d'integration adaptative afin d'avoir des temps de calcul moderes de la fonction de green. Le schema simplifie de surface portante permet de determiner les sauts de pression a travers la plaque et par consequent les efforts globaux sur celle-ci, avec des temps de calcul reduits. Les resultats obtenus sont compares a ceux d'autres methodes numeriques, en hydrodynamique et en aerodynamique, et a des resultats experimentaux obtenus en bassin des carenes. Afin de completer notre etude theorique, une approche experimentale a ete menee au ceat en tunnel hydrodynamique a grand nombre de froude. Trois types de mouvements ont ete etudies: mouvement d'embardee, de lacet et mixte
36
Whelan, Jedidiah J. "Diverse Polarization Extension to MUSIC Applied to a Circular Array of H-Plane Horns." University of Dayton / OhioLINK, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1291326302.
Full text
37
Gonneau, Vincent. "Modélisation du transfert thermique par marcheurs browniens dans des milieux hétérogènes." Thesis, université Paris-Saclay, 2020. http://www.theses.fr/2020UPAST022.
Full textAbstract:
Ce travail porte sur la modélisation par marcheurs browniens du transfert conductif instationnaire au sein d’un milieu hétérogène. Le milieu est représenté par une structure voxélisée 3D. Chaque marcheur transporte une enthalpie élémentaire au cours de son déplacement. Ce mouvement d’enthalpie représente le flux conductif et permet de simuler la conduction en régime transitoire de façon quantitative. Une étude a montré l’importance du choix du pas de temps du calcul. Une valeur empirique de ce paramètre, dépendant du pas spatial et de la diffusivité des constituants, a été établie, permettant de modéliser correctement la conduction dans chacun des régimes de transfert. Plusieurs problèmes liés au comportement des marcheurs ont dû être résolus pour pouvoir modéliser deux techniques expérimentales de caractérisation thermique bien connues : la technique dite de la plaque chaude gardée et la méthode flash. Une condition de température imposée est modélisée par un réservoir dont le nombre de marcheurs est régulé. Une condition de paroi adiabatique impose une réflexion spéculaire aux marcheurs. Un critère stochastique de transmission basé sur les effusivités a été établi pour traiter la rencontre d’un marcheur avec une interface entre deux constituants d’un milieu hétérogène. La gestion des pertes convectives aux frontières du domaine de calcul se base également sur un critère de transmission faisant intervenir l’effusivité du constituant, le pas de temps et le coefficient d’échange convectif. Une condition de flux imposé, de profil temporel quelconque, se traduit par une injection de marcheurs à travers la frontière concernée. L’association complexe de ces briques a permis de modéliser le transfert thermique instationnaire dans des structures hétérogènes voxélisées. La comparaison de nos résultats à ceux issus d’approches plus classiques a permis de valider la capacité de notre modèle à caractériser les propriétés thermiques phoniques de structures virtuelles ou réelles. On conclut ce travail en posant les bases d’une stratégie de simulation du couplage conducto-radiatif à l’échelle locale de la structure voxélisée : l’apport énergétique du rayonnement est modélisé par un terme source de puissance volumique dans les voxelsThis work deals with the modeling of transient conduction heat transfer by brownian walkers within a heterogenous medium. The medium is described by a 3D voxelised structure. Each walker carries an elementary enthalpy during its movement. This enthalpy motion represents the thermal flux and allows to solve quantitatively the transient thermal conduction. A study demonstrates the importance of the time step chosen in the simulations. An empirical value of this parameter, based on the spatial resolution and the thermal diffusivities of the constituents, has been established to model accurately the conduction at each step of the heat transfer. Several problems related to the behavior of the walkers had to be solved to model two well-known experimental thermal characterization techniques: the hot guarded plate technique and the flash method. An imposed temperature condition is modeled by a reservoir where the number of walkers is regulated. An adiabatic wall condition imposes a specular reflection to the walkers. A stochastic transmission criterion, based on the thermal effusivities, was established to treat the behavior of a walker at voxel-voxel interface between two different constituents. Convective losses at a boundary of the numerical structure are represented by an analogous stochastic transmission criterion involving the effusivity, the convective exchange coefficient and the time step. An imposed thermal flux condition, of any temporal profile, is modeled by an injection of walkers through the boundary. The complex combination of these computing blocks allowed to model transient heat transfer within voxelised heterogeneous structures. The comparison between our results and those issued from more classical approaches allowed to validate the ability of our model to characterize the phonic thermal properties of virtual and real structures. We conclude this PhD work with preliminary activities aiming at the simulation of conduction-radiation coupling at the voxel scale of the structure: the radiative contribution is modeled by an internal power source term within the voxels
38
FONSECA, GABRIEL P. "Projeto e construcao de placas espalhadoras e degradadoras de energia para uso em radioterapia com feixe de eletrons para doencas de pele." reponame:Repositório Institucional do IPEN, 2010. http://repositorio.ipen.br:8080/xmlui/handle/123456789/9550.
Full textAbstract:
Made available in DSpace on 2014-10-09T12:27:55Z (GMT). No. of bitstreams: 0Made available in DSpace on 2014-10-09T13:59:32Z (GMT). No. of bitstreams: 0
Dissertacao (Mestrado)
IPEN/D
Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP
39
Moukarzel, Camille. "Modélisation mathématique des transferts de masse et de chaleur dans des fours de verre plat." Paris, ENMP, 2003. http://www.theses.fr/2003ENMP1208.
Full text
40
Suleiman, Ahed. "Evaluation par méthode inverse de la distribution de flux de chaleur pariétaux d'une plaque plane verticale en présence d'une perturbation radiative." Toulouse, INSA, 2002. http://www.theses.fr/2002ISAT0017.
Full textAbstract:
Le but de cette recherche est d’identifier, à l'aide d'une méthode inverse, la valeur des échanges convectifs générés par une plaque plane verticale, uniformément chauffée et perturbée par une source d'éclairement locale sur sa face avant. La réalisation de ce travail a nécessité une approche à la fois expérimentale et numérique. L'expérimentation est constituée d'une enceinte de dimensions réduites, de la plaque plane et d'une source de rayonnement modulable en puissance qui a nécessité un étalonnage préalable. Une méthode de simulation inverse, basée sur un algorithme adapté, détermine le flux global libéré par la plaque active ainsi que ses températures de surface. Un calcul des flux radiatifs de l'enceinte permet, par bilan thermique, d'obtenir les différents flux convectifs sur la face avant de la plaque et on déduit ainsi la valeur des coefficients d'échanges convectifs. Deux types de résultats sont proposés. Ceux correspondant aux études menées en régime permanent qui ont permis de valider, de manière satisfaisante, la méthode inverse utilisée par rapport à des corrélations de la littérature. D'autres, menées en régime transitoire, conduisent à l'évaluation en fonction du temps des coefficients d'échanges convectifs. Un calcul d'erreurs complète cette étude et confirme la fiabilité de la méthode. La conclusion finale de ce travail est que les algorithmes de simulation développés sont robustes, ce qui rend la méthode utilisable pour d'autres applicationsThe aim of this research is to identify, with the help of an inverse method, the value of convective heat exchanges generated by a uniformly heated vertical plane plate on which a radiative local perturbation is imposed. Experimental and numerical approaches were necessary to develop this work. The experimental system was composed of an enclosure with reduced dimensions, of the plane plate and of the radiative source of which the power was first determined by calibration. The use of the inverse method leads to the knowledge of the global flux leaving the plate and of the surface temperatures. Flux radiative calculations lead, by application of a thermal balance, to the determination of the convective heat exchanges. Finally, we can determine the values of the convective heat exchange coefficients. Two types of results are proposed. Those, corresponding to the steady state lead to the correct validation of the inverse method by comparison with a relation provided by the literature. The other ones lead in unsteady state give the evaluation of the heat exchange coefficients depending from the time. Uncertainty calculations confirm the viability of the inverse method. Finally, the main results given by this work correspond to the algorithm's robustness, which can lead to the use of the method for other applications
41
Josset, Damien. "Etude du couplage radar-lidar sur plates-formes spatiales et aéroportées : application à l'étude des nuages, des aérosols et de leurs interactions." Paris 6, 2009. http://www.theses.fr/2009PA066061.
Full textAbstract:
L'effet des aérosols et des nuages sur le climat, qu'il s'agisse de leur forçage radiatif propre ou de leur interactions constitue actuellement la plus grande incertitude du système climatique. L'utilisation couplée d'un lidar et d'un radar fait partie des pistes de recherches retenues par la communauté scientifique pour résoudre ces incertitudes, et c'est un des buts justifiant le développement des nouveaux instruments embarqués sur les plates-formes de l'A-Train et le développement des algorithmes opérationnels associés. Ces algorithmes possèdent certaines limitations intrinsèques, ce qui nous a amené à la révision des méthodes d'analyse standard des plates-formes spatiales de l'A-Train (CALIPSO, CLOUDSAT) et au développement de nos propres algorithmes à travers l'étude de l'écho de surface océanique, et à l'identification un modèle théorique de répartition des ondes de gravité et de capillarité compatible avec les observations multispectrales de ces instruments actifs. L'utilisation de ce modèle avec les observations actives et celles du radiomètre micro-onde AMSR-E a permis d'améliorer les procédures d'étalonnage absolu du lidar et du radar en offrant une référence systématique possédant un important rapport signal sur bruit. L'amélioration de l'étalonnage de ces instruments permet ensuite d'améliorer la précision de la restitution des paramètres microphysiques dans les produits opérationnels de recherche, et doit donner accès à un plus grand nombre de produits dérivés. La référence de surface issue des mesures des instruments micro-ondes actifs (radar) et passifs (radiomètre) permet ainsi de déterminer l'épaisseur optique des aérosols aux longueurs d'onde du lidar. Cette méthode de restitution ne fait aucune hypothèse sur la microphysique des particules diffusantes, est utilisable de jour et de nuit, possède un rapport signal sur bruit important à grande résolution spatiale et offre la possibilité de discriminer les aérosols et les nuages grâce aux mesures multispectrales sur la verticale. Les comparaisons avec les mesures du radiomètre MODIS montrent un bon accord statistique. Ces mesures d'épaisseur optique au-dessus de l'océan et des nuages d'eau liquide ouvrent une nouvelle voie pour quantifier le forçage radiatif direct des aérosols en présence de nuage, hors de portée des mesures radiométriques actuelles. Les premières études que nous avons menées ont confirmé que lors des épisodes de feux observés pendant la campagne AMMA, le forçage est fortement positif sur le Golfe de Guinée. Le forçage négatif en air non-nuageux au-dessus de l'océan est inférieur d'un ordre de grandeur à celui positif au-dessus des nuages. Le forçage radiatif positif observé sur le Golfe de Guinée est fortement dépendant de la couverture nuageuse que les mesures à petite échelle de l'A-Train permettent de mieux caractériser, et le réchauffement induit par l'effet direct des aérosols doit être mieux pris en compte dans les modèles climatiques. L'émission d'aérosols absorbants (feux, pollution. . . ) et leur transport à grande échelle représente une contrainte croissante du système climatique et des interactions environnement-climat. L'hypothèse usuellement admise d'un forçage direct négatif de-0,5 W. M-2 pour caractériser l'effet radiatif des aérosols demande à être examinée avec attention.
42
Demarez, Valérie. "Modélisation du transfert radiatif et télédétection hyperspectrale pour le suivi temporel de la teneur en chlorophylle d'une forêt temùpérée." Toulouse 3, 1997. http://www.theses.fr/1997TOU30284.
Full textAbstract:
Mon travail de these se situe dans le contexte de l'etude du fonctionnement d'une foret temperee a partir de donnees de teledetection. Deux activites complementaires ont ete poursuivies : developpement d'un modele de transfert radiatif 3d et determination de la chlorophylle de couverts forestiers avec des mesures spectrometriques aeroportees. Durant la premiere partie de ma these, j'ai participe au developpement d'un modele de transfert radiatif a la fois performant et original : le modele dart. Ce dernier simule les reflectances et images directionnelles des couverts, ainsi que la distribution 3d du rayonnement absorbe. Sa principale originalite est de permettre des etudes a la fois simples et precises de l'environnement radiatif de paysages heterogenes, tels que les forets. Le modele dart pallie a plusieurs limitations classiques des modeles actuels, car il prend en compte l'anisotropie du rayonnement atmospherique et de la reflectance du sol, l'effet de la retrodiffusion, le relief, la structure des couverts, etc. De plus, il permet de distinguer le rayonnement diffuse par le mesophylle foliaire, ce qui est tres utile pour les etudes spectrometriques. Finalement, le modele dart est tres souple, notamment en ce qui concerne la gestion des parametres d'entree. Ces derniers peuvent etre tres complets ou simplement identiques a ceux du modele sail. La validite du modele dart a ete testee avec des donnees de terrain (parabola) et aeroportees (polder) sur des forets boreales. Aucune reponse definitive n'a pu etre apportee en raison de difficultes classiques liees a l'incertitude des mesures experimentales. Toutefois, les resultats obtenus montrent que la simulation de reflectances precises de couverts forestiers necessite l'utilisation d'un modele 3d capable de prendre en compte leur architecture. Les travaux presentes dans la deuxieme partie portent sur l'etude du potentiel de la haute resolution spectrale (visible et proche infrarouge) pour determiner le contenu en chlorophylle de la foret de fontainebleau (chenes, hetres, pins. . . ). Ils ont ete realises dans le cadre du projet europeen emac (european multisensors airborne campaign), avec les donnees du spectrometre aeroporte rosis. Une approche empirique et une approche theorique ont ete utilisees. L'approche empirique m'a permis de relier la concentration en chlorophylle mesuree sur le terrain au point d'inflexion (#i) des reflectances rosis situees dans la zone rouge-proche infrarouge. La relation obtenue s'est averee peu sensible aux directions d'observations et d'eclairement ainsi qu'a l'atmosphere. L'approche theorique a consiste a analyser des spectres de couverts simules par couplage du modele dart et du modele foliaire prospect. Elle a permis de confirmer l'existence d'une relation entre (#i) et la chlorophylle du couvert, ainsi que sa robustesse aux conditions d'acquisition des mesures.
43
Franceschelli, Luca. "Cooling Performance Analysis and Design of an Instrumented Radiator in a MotoGP Wind Tunnel Model." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2021.
Find full textAbstract:
The present thesis work was developed in collaboration with the Ducati Corse Aerodynamic Department. It is focused on the measurement system employed on the MotoGP Wind Tunnel model in order to evaluate the cooling performances at the radiators.
As first, an analysis of the current methodology is conducted. Based on the arrangement of hybrid-Kiel probes behind the radiators, it was observed that an improvement in the calibration procedure is required in order to account for inter-probe and support frame interference. Furthermore, a correlation process with the CFD simulation was carried out. A good agreement in trend with CFD results was displayed, despite a low accuracy. The need for higher spatial resolution was stated.
In order to update the CFD implementation of the actual water radiator, the latter has been characterized in terms of pressure drop on a dedicate radiator test bench, provided by Dallara Automobili. A suitable convergent frame has been designed for the purpose.
Finally, a new methodology for cooling performance evaluation was developed and calibrated. The method exploits a set of static and Kiel probes in a dummy radiator core. An honeycomb structure and a perforated plate are implemented to reproduce the real radiator behaviour.
Experiments have been performed with half-radiator equipped with the new set up and the other half instrumented with Pitot tubes, showing good agreement between the two probe-types.
A set of plates have been characterized. It allowed also to highlight the relevance of the solid part distribution - and related holes' diameter - on the pressure drop and the effect on the measured pressures from the probes.
44
Niezgoda, Mathieu. "Modélisation du transfert thermique au sein de matériaux poreux multiconstituants." Phd thesis, Université d'Orléans, 2012. http://tel.archives-ouvertes.fr/tel-00829217.
Full textAbstract:
Le CEA travaille sur des matériaux poreux - alvéolaires, composites, céramiques, etc. - et cherche à optimiser leurs propriétés pour des utilisations spécifiques. Ces matériaux, souvent composés de plusieurs constituants, ont en général une structure complexe avec une taille de pores de quelques dizaines de microns. Ils sont mis en oeuvre dans des systèmes de grande échelle, supérieure à leurs propres échelles caractéristiques, dans lesquels on les considère comme équivalents à des milieux homogènes, sans prendre en compte sa microstructure locale, pour simuler leur comportement dans leur environnement d'utilisation.Nous nous intéressons donc à la caractérisation des propriétés thermiques effectives de matériaux à microstructure hétérogène en cherchant à déterminer par méthode inverse en fonction de la température la diffusivité thermique qu'ils auraient s'ils étaient homogènes.L'identification de la diffusivité de matériaux poreux et/ou semi-transparents est rendue difficile par le couplage conducto-radiatif fort qui peut se développer rapidement dans ces milieux avec une augmentation de la température. Nous avons donc modélisé le transfert de chaleur couplé conducto-radiatif en fonction de la température au sein de matériaux poreux multiconstituants à partir de leur microstructure numérisée en voxels. Notre démarche consiste à nous appuyer sur la microstructure 3D obtenue par tomographie. Ces microstructures servent de support numérique à cette modélisation qui permet d'une part de simuler tout type d'expériences thermiques numériques - en particulier la méthode flash dont les résultats nous permettent de déduire la diffusivité thermique -, et d'autre part de reproduire le comportement thermique de ces échantillons dans leur condition d'utilisation.
45
Leray, Cedric. "Etude du comportement thermique et thermomécanique des récepteurs solaires sous haut flux radiatif." Thesis, Perpignan, 2017. http://www.theses.fr/2017PERP0003/document.
Full textAbstract:
Dans le contexte énergétique qui se profile, la production d’électricité par voie solaire thermodynamique s’avère une solution prometteuse, que ce soit pour des considérations économiques, d’échelle de production ou environnementales. Une voie d’amélioration du rendement des centrales solaires à tour consiste à utiliser des cycles thermodynamiques à haut rendement type cycles combinés. Cela nécessite de pouvoir fournir un fluide de travail pressurisé à très haute température (10bar et 1000°C minimum). Ce manuscrit présente les travaux menés afin de développer et de viabiliser un concept d’absorbeur solaire surfacique modulaire en céramique (carbure de silicium) capable de répondre à ces exigences. Le choix du carbure de silicium s’est imposé pour sa résistance aux hautes températures et aux problèmes d’oxydation. Cependant, l’utilisation d’une céramique comme matériau implique un risque de casse des modules. Les céramiques sont en effet fragiles lorsqu’elles sont soumises à des contraintes de traction. C’est la connaissance et la maitrise de ce risque qui fait l’objet de cette étude. L’approche adoptée combine le développement d’outils numériques et d’études expérimentales réalisées sur le site de la centrale solaire Thémis (Targassonne, 66, France). La méthodologie desimulation développée permet de prédire le comportement thermique et le comportement mécanique de l’absorbeur. Ceci permet de réduire les risques encourus par l’absorbeur et d’en connaitre les performances. Cette méthodologie a été éprouvée à l’aide des résultats expérimentauxFor the future, using thermodynamical solar power plant seems to be a good solution to ensure electrical production. Solar tower plants are able to produce electricity in significant amount, are environmentally friendly and economically competitive. One way to increase the yield of these plants is using high efficiency thermodynamical cycles, like combined cycle. That requires to providing a working fluid at high temperature and high pressure (10bar and 1000°C at least). This PHD thesis presents the works performed to develop and enhance a concept of modular plate solar ceramic absorber that can ensure the required air production. We chose the silicon carbide as material due to its resistance to high temperatures and oxidation problems. The drawback is ceramic modules are weak to traction stresses. The study focuses on the knowledge and the control of this phenomenon. This work combines the developments of numerical tools and experimental studies performed at Thémis power plant (Targassonne, 66, FRANCE). The numerical method permits simulations to predict the thermal behavior and the mechanical behavior of a solar module absorber. It allows the reduction of the mechanical stresses undergone by solar receiver and the prediction of its performances. This methodology was tested using experimental results
46
Alvarez, Nadir. "Plantes-hôtes et organisation de la diversité des insectes phytophages, des radiations évolutives aux processus populationnels : Le cas des bruches du genre Acanthoscelides Schilsky (Coleoptera : Bruchidae)." Montpellier 2, 2004. http://www.theses.fr/2004MON20127.
Full text
47
Romero, Eric. "Modèles C. F. D. Et éléments finis pour la trempe thermique du verre plat : estimation des échanges radiatifs et convectifs, prédiction et contrôle des contraintes résiduelles." Valenciennes, 2005. http://ged.univ-valenciennes.fr/nuxeo/site/esupversions/90ecadca-bb2b-4b0c-adbf-b68adc35d34c.
Full textAbstract:
La thèse porte sur la trempe thermique du verre plat sur une plate-forme de laboratoire en configuration simple-jet et sur une plate-forme industrielle en configuration multi-jets. La première partie concerne l'influence de la prise en compte du rayonnement sur l'estimation des contraintes résiduelles et transitoires. Des modèles CFD sont ensuite développés pour analyser l'écoulement d'air et déterminer le transfert convectif à la surface du verre. Par couplage des modèles EF 3D, les contraintes résiduelles sont calculées. Des mesures de contraintes par photoélasticité permettent une première validation de l'approche numérique. Finalement, une nouvelle méthode de contrôle par ultrasons est proposéeThe framework of the thesis is the thermal tempering of flat glass on a laboratory installation and an industrial unit with single-jet and multi-jets coolings. The first part deals with the influence of radiation in the thermal modeling for the estimation of the transient and residual stresses along the thickness. CFD 3D models are then developed to analyze the air flow and determine the convective heat transfer on the glass surface during the tempering. By coupling these with 3D finite elements models, the tempering residual stresses are computed. Photoelasticity measurements of the stresses on the surface and the thickness of the tempered glass specimens validate the numerical approach. Finally, a new ultrasonic method to control the stresses is proposed
48
Valdenaire, Simon. "Mise en place et utilisation des faisceaux FFF en radiothérapie : radiobiologie, caractérisation physique, contrôles qualité, modélisation et planification de traitement." Thesis, Aix-Marseille, 2017. http://www.theses.fr/2017AIXM0037/document.
Full textAbstract:
Les faisceaux de photons produits par les accélérateurs d'électrons linéaires médicaux sont plats, grâce à un cône égalisateur. Les technologies ont évolué et la présence d'un cône n'est plus indispensable. On parle alors de faisceaux FFF (flattening filter free). Les faisceaux FFF présentent des débits de dose plus élevés, des profils de dose hétérogènes, des spectres énergétiques différents et une diminution de la dose hors-champ. Cette thèse a eu pour but d'étudier les caractéristiques des faisceaux FFF, ainsi que l'impact de leur utilisation thérapeutique. Plusieurs thématiques ont été. Des expériences d'irradiation in vitro ont tout d'abord permis de s'assurer que les débits de dose FFF n'ont pas d'impact radiobiologique sur la réponse des cellules irradiées. Une large revue de la littérature a permis de corroborer ces résultats. Afin de maitriser les caractéristiques physiques des faisceaux FFF, des mesures ont été faites avec différents détecteurs. Les effets du spectre et du débit de dose sur la calibration en dose ont aussi été étudiés. Les faisceaux FFF ont été modélisés dans deux TPS. Les modèles ont été comparés entre les deux types de faisceaux et entre les deux TPS. La mise en place des traitements stéréotaxiques a aussi été l'occasion d'appréhender la dosimétrie des petits faisceaux. Nous avons étudié des cas VMAT de cancer de la prostate et des cas de stéréotaxies 3D de tumeurs pulmonaires. La comparaison donne un avantage aux faisceaux FFF. La maitrise de la physique et de la biologie des haut débits a permis de débuter les traitements FFF à l'IPC. Des études comparatives nous permettent aujourd'hui d'adapter leur utilisation au cas par casIn medical linear electron accelerators, photon beams profiles are homogenised using flattening filters. Technologies have evolved and the presence of this filter is no longer necessary. Flattening filter free (FFF) beams exhibit higher dose rates, heterogeneous dose profiles, modified energy spectra and lower out-of-field dose. This PhD aimed at studying the characteristics of unflattened beams, as well as their impact in clinical utilization. Several subjects were thoroughly investigated: radiobiology, dosimetry, quality controls, modelling and treatment planning. In vitro experiments ensured that the high dose-rate of FFF beams had not a radiobiological impact. A wide review of the literature was conducted to corroborate these results. In order to understand thoroughly the characteristics of FFF beams, measurements were conducted using several detectors. The effect of the spectra and dose rates of unflattened beams on dose calibration were also studied. FFF beams were modeled in two TPSs. The methods, results and model parameters have been compared between the available beam qualities as well as between both TPSs. Furthermore, the implementation of stereotactic treatments technique was the occasion to investigate small beam dosimetry. Prostate cancer cases treated with VMAT and pulmonary tumors treated with stereotactic 3D beams were also studied. The comparison of dose distributions and treatment metrics give advantage to FFF beams. Mastering physical and biological aspects of flattening filter free beams allowed the IPC to start FFF treatments. Comparative studies have since resulted in a deeper understanding on the pertinent use of these beams
49
Josset, Damien. "Etude du couplage radar-lidar sur plates-formes spatiales et aeroportees. Application a l'etude des nuages, des aerosols et de leurs interactions." Phd thesis, Université Pierre et Marie Curie - Paris VI, 2009. http://tel.archives-ouvertes.fr/tel-00559472.
Full textAbstract:
L'effet des aerosols et des nuages sur le climat, qu'il s'agisse de leur forcage radiatif propre ou de leur interactions constitue actuellement la plus grande incertitude du systeme climatique. L'utilisation couplee de nouveaux moyens d'observations comme le lidar ou le radar avec la radiometrie fait partie des pistes de recherches retenues par la communaute scientique pour reduire ces incertitudes justifiant le developpement et la mise en oeuvre de ces nouveaux instruments sur les plates-formes de l'A-Train et le developpement des algorithmes operationnels associes. Ces algorithmes possedent certaines limitations intrinseques, ce qui nous a amene a la revision des methodes d'analyse standard des donnees issues des plates-formes spatiales de l'A-Train (CALIPSO, CLOUDSAT), au developpement de nos propres algorithmes a travers l'etude de l'echo de surface oceanique, et a l'identication d'un modele theorique de diffusion par la surface compatible avec les observations multispectrales de ces instruments actifs. L'utilisation de ce modele avec les observations actives et celles du radiometre micro-onde AMSR-E a permis d'ameliorer les procedures d'etalonnage absolu du lidar et du radar en offrant une reference systematique possedant un important rapport signal sur bruit. L'amelioration de l'etalonnage de ces instruments permet ensuite d'affiner la precision de la restitution des parametres microphysiques dans les produits operationnels de recherche, et doit donner acces a un plus grand nombre de produits derives. La reference de surface issue des mesures des instruments micro-ondes actifs (radar) et passifs (radiometre) permet ainsi de determiner l'epaisseur optique des aerosols aux longueurs d'onde du lidar. Cette methode de restitution ne fait aucune hypothese sur la microphysique des particules diffusantes, est utilisable de jour et de nuit, possede un rapport signal sur bruit important a grande resolution spatiale et offre la possibilite de discriminer les aerosols et les nuages grace aux mesures multispectrales sur la verticale. Les comparaisons avec les mesures du radiometre MODIS montrent un bon accord statistique. Ces mesures d'epaisseur optique au-dessus de l'ocean et des nuages d'eau liquide ouvrent une nouvelle voie pour quantier le forcage radiatif direct des aerosols en presence de nuage, hors de portee des mesures radiometriques actuelles. Les premieres etudes que nous avons effectuees ont confirme que lors des episodes de feux observes pendant la campagne AMMA, le forcage est fortement positif sur le Golfe de Guinee (entre +5 et +10 W/m2 en moyenne diurne). Le forcage negatif en air non-nuageux au-dessus de l'ocean est inferieur d'un ordre de grandeur au forcage positif du aux aerosols transportes au-dessus des nuages. Le forcage radiatif positif observe sur le Golfe de Guinee est ainsi fortement dependant de la couverture nuageuse et les mesures a petite echelle de l'A-Train permettent de mieux le caracteriser a plus grande echelle. Ainsi, le rechauffement induit par l'effet direct des aerosols sera mieux pris en compte dans les modeles climatiques. L'emission d'aerosols absorbants (feux, pollution...) et leur transport a moyenne et grande echelle en altitude representent un point critique de l'evolution du systeme climatique et des interactions environnement-climat. L'hypothese usuellement admise d'un forcage direct negatif de -0, 5 W/m2 pour caracteriser l'effet radiatif des aerosols demande a etre examinee avec attention en etablissant une meilleure quantication de la contribution des aerosols absorbants (d'origine naturelle ou anthropique) au-dessus des nuages a l'echelle globale.
50
Mourcin, Frédéric. "Etude de la réponse cellulaire et moléculaire des cellules souches et progéniteurs hématopoïetiques aux radiations ionisantes : implication pour la mise en place d'une thérapie cellulaire de l'aplasie médullaire radio-induite." Université Joseph Fourier (Grenoble), 2004. http://www.theses.fr/2004GRE10234.
Full textAbstract:
De nouveaux traitements de l'aplasie médullaire radio-induite (RI) fondés sur la lutte in vitro, voire in vivo, contre l'apoptose des cellules souches et progéniteurs hématopoïétiques (CSPH) sont actuellement à l'étude. Ces approches sont en grande partie fondées sur le caractère hétérogène des irradiations accidentelles qui se traduit par une épargne relative des CSPH. Ainsi la thérapie cellulaire autologue (TCA) consisterait en la collecte puis la mise en culture (6-7 jours) des CSPH résiduels dans un but de greffe. Dans ce cadre notre travail a porté d'abord sur l'étude des mécanismes fondamentaux de l'apoptose RI des CSPH avant d'aborder l'optimisation de la TCA. Pour cette étude nous avons utilisé un modèle d'irradiation in vitro des cellules CD34+ de primate non humain. Concernant les mécanismes fondamentaux de l'apoptose RI, nos résultats confirment pour les CSPH la complexité des mécanismes de la réponse moléculaire et cellulaire à l'irradiation, notamment en terme de cycle cellulaire et d'apoptose. Les caspases 1 et 6 semblent jouer un rôle fondamental comme effecteurs terminaux. Concernant la culture de cellules CD34+ irradiées nos résultats montrent que 1) la sélection négative des CSPH résiduels apoptotiques avant mise en culture n'apporte pas de bénéfice en terme de rendement d'expansion 2) l'expansion de cellules CD34+ irradiées à la dose 4Gy peut être envisagée uniquement en présence d'un soutien stromal de type Dexter ou de cellules souches mésenchymateuses 3) l'addition séquentielle d'un inhibiteur de l'hématopoïèse, le TNF-a, à une combinaison activatrice réduit l'apoptose et favorise l'expansion ultérieure des cellules CD34+ irradiéesNew treatments of radio-induced bone marrow aplasia were based on the apoptosis reduction (in vivo or in vitro) of the hematopoietic stem and progenitor cells (HSPC). These approaches were founded on the heterogeneity of irradiation injury, which preserves some HSPC. The autologous cell therapy (ACT) is based on: the collect of residual HSPC and then on a phase of in vitro culture (6 to 7 days) ir the final goal to graft these expanded cells. Our work has consisted to study the fundamental mechanism of radio-induced apoptosis of HSPC before to optimise the ACT. We have used an in vitro model of irradiation of CD34+ cells come from non-human primate. Our results show a complexity of mechanisms that has been implicated in the molecular and cellular response, in case of cell cycle and apoptosis. But Caspases 1 and 6 was seen to play an important role in terms of final effectors. The cultures of irradiated cells show that 1 the negative selection of apoptotic residual HSPC before cell culture did not improve the expansion rate 2) the expansion of 4Gy irradiate CD34+ cells can only be considered with a support stromal has weil has Dexter or Mesenchymal Stem Cells 3) the sequential addition of an inhibitory of haematopoiesis (TNF-a) with a cocktail activation reduce apoptosis and increased expansion of CD34+ irradiated cells. Finally this study 1) suggest different molecular targets for new anti-apoptotic treatments and 2) show the difficulty to used the ACT in the case of an accidental irradiation