Дисертації: "Low surface"

1

McLaughlin, Keith. "Toward understanding low surface friction on quasiperiodic surfaces." [Tampa, Fla] : University of South Florida, 2009. http://purl.fcla.edu/usf/dc/et/SFE0003161.

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2

Mouncey, Simon Patrick. "Low energy ion-surface interactions." Thesis, Queen's University Belfast, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.333823.

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3

Kälberer, Felix [Verfasser]. "Low Distortion Surface Parameterization / Felix Kälberer." Berlin : Freie Universität Berlin, 2013. http://d-nb.info/1045859273/34.

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4

Zhao, Yajing S. M. Massachusetts Institute of Technology. "Dropwise condensation of water and low surface tension fluids on structured surfaces." Thesis, Massachusetts Institute of Technology, 2018. http://hdl.handle.net/1721.1/118679.

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Thesis: S.M., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2018.
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 55-57).
Condensation is a ubiquitous process often observed in nature and our daily lives. The large amount of latent heat released during the condensation process has been harnessed in many industrial processes such as power generation, building heating and cooling, desalination, dew harvesting, thermal management, and refrigeration. Condensation has two modes: dropwise mode and filmwise mode. Although it has been known for decades that dropwise condensation outperforms filmwise condensation in heat transfer owing to the droplet shedding effects which can efficiently reduce thermal resistance, filmwise condensation still dominates industrial applications currently due to the high costs, low robustness and technical challenges of manufacturing dropwise coatings. During water condensation, dropwise mode can be readily promoted with thin hydrophobic coatings. Superhydrophobic surfaces made out of hydrophobic coatings on micro-or-nano-engineered surfaces have shown further heat transfer enhancement in dropwise condensation of water; however, the applications of these micro- or nanoscale structured surface designs have been restricted by the high manufacturing expenses and short range of subcooling limit. Recent studies have shown that the combination of millimeter sized geometric features and plain hydrophobic coatings can effectively manipulate droplet distribution of water condensate, which provides opportunities to locally facilitate dropwise condensation at relatively low manufacturing expenses as compared to those delicate micro- and nano-structured hydrophobic surfaces. Low surface tension fluids such as hydrocarbons pose a unique challenge to achieving dropwise condensation, because common hydrophobic coatings are not capable of repelling low surface tension fluids. Recent development in lubricant infused surfaces (LIS) offers promising solutions to achieving dropwise condensation of low surface tension fluids by replacing the solid-condensate interface in conventional hydrophobic coatings with a smooth lubricant-condensate interface. However, only a few experimental studies have applied LIS to promoting dropwise condensation of low surface tension fluids (y as low as 15 mN/m). In this work, we investigated dropwise condensation of both water (y ~ 72 mN/m) and a low surface tension fluid, namely butane (y - 13 mN/m) on structured surfaces. For water condensation, we studied the effects of millimeter sized geometric structures on dropwise condensation heat transfer under two different environments: pure vapor and an air-vapor mixture. Our experimental results show that, although convex structures enable faster droplet growth in an air-vapor mixture, the same structures impose the opposite effect during pure vapor condensation, hindering droplet growth. We developed a numerical model for each case to predict the heat flux distribution along the structured surface, and the model shows good agreement with experimental results. This work demonstrates that the effects of geometric features on dropwise condensation are not invariable but rather dependent on the scenario of resistances to heat and mass transfer in the system. For butane condensation, based on a design guideline we recently developed for lubricant infused surfaces, we successfully designed an energy-favorable combination of lubricant and structured solid substrate, which was further demonstrated to promote dropwise condensation of butane. The fundamental understanding of dropwise condensation of water and low surface tension fluids on structured surfaces developed in this study provides useful guidelines for condensation applications including power generation, desalination, dew harvesting, and thermal management.
by Yajing Zhao.
S.M.

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5

Rosenbaum, Dominik. "Low surface brightness galaxies and their environments." [S.l.] : [s.n.], 2006. http://deposit.ddb.de/cgi-bin/dokserv?idn=979834880.

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6

Brear, Michael John. "Pressure surface separations in low pressure turbines." Thesis, University of Cambridge, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.620981.

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7

Sprayberry, David. "Cosmological implications of low surface brightness galaxies." Diss., The University of Arizona, 1994. http://hdl.handle.net/10150/187022.

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This dissertation briefly presents the results of a survey for galaxies that have been overlooked by previous surveys because their surface brightness, or brightness per unit area on the night sky, is too low. This dissertation then makes use of the survey results to estimate the density of these galaxies and to delineate some of their properties. Chapter 1 describes the selection bias against finding galaxies of low surface brightness and outlines the importance of these galaxies for a more complete knowledge of the true local galaxy population. Chapter 2 discusses the techniques employed for identifying low surface brightness (LSB) galaxies for the survey, calibrating the photometry, and estimating the survey incompleteness as a function of galaxy parameters. Chapter 3 presents luminosity functions for the low surface brightness galaxies identified in the present survey, and for a combined sample of low surface brightness and high surface brightness galaxies. The overall space density of low surface brightness galaxies is about one-fourth to one-third as great as the density determined from standard field galaxy luminosity functions, and that the total luminosity density due to these low surface brightness galaxies is about one-third to one-half the level derived from other surveys. Chapter 4 presents 21 cm profiles and CCD surface photometry for a subset of the low surface brightness spiral galaxies found by the survey. The general trend of the LSB galaxies in the Tully-Fisher relation, relative to the trend of higher surface brightness galaxies, forms the basis of the conclusion that LSB spiral generally have mass-to-light ratios comparable to that of higher surface brightness spirals but with a much larger scatter. Various possible reasons for the higher scatter are explored. Chapter 5 presents CCD surface photometry and optical spectroscopy for a sample of eight low surface brightness spiral galaxies that are extraordinary because of their large physical sizes and high total luminosities. The properties of these galaxies are analyzed and compared to those of more normal spirals. Chapter 6 summarizes the findings of the preceding chapters and presents some ideas for future investigations.

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8

Porter, Stephen Christopher. "Synthesis, surface characterization, and biointeraction studies of low-surface energy side-chain polyetherurethanes /." Thesis, Connect to this title online; UW restricted, 1999. http://hdl.handle.net/1773/9845.

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9

Tang, Kah Beng-Kirel. "Excitation of surface systems by low energy electrons." Thesis, University of Cambridge, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.627598.

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10

Heideman, Kyle C., and John E. Greivenkamp. "Low-coherence interferometer for contact lens surface metrology." SPIE-SOC PHOTO-OPTICAL INSTRUMENTATION ENGINEERS, 2016. http://hdl.handle.net/10150/621479.

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Contact lens performance depends on a number of lens properties. Many metrology systems have been developed to measure different aspects of a contact lens, but none test the surface figure in reflection to subwavelength accuracy. Interferometric surface metrology of immersed contact lenses is complicated by the close proximity of the surfaces, low surface reflectivity, and instability of the lens. An interferometer to address these issues was developed and is described here. The accuracy of the system is verified by comparison of glass reference sample measurements against a calibrated commercial interferometer. The described interferometer can accurately reconstruct large surface departures from spherical with reverse raytracing. The system is shown to have residual errors better than 0.05% of the measured surface departure for high slope regions. Measurements made near null are accurate to lambda/20. Spherical, toric, and bifocal soft contact lenses have been measured by this system and show characteristics of contact lenses not seen in transmission testing. The measurements were used to simulate a transmission map that matches an actual transmission test of the contact lens to lambda/18. (C) 2016 Society of Photo-Optical Instrumentation Engineers (SPIE)

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11

Mapledoram, Leigh David. "Quantitative surface structural determination by low energy electron diffraction." Thesis, University of Cambridge, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.338267.

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12

Jensen, Erik Troels. "Low energy electron scattering studies of molecules at surfaces." Thesis, University of Cambridge, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.334137.

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13

Motta, Marcelo Jorge de Assis. "Equivalent impedance of rough surface at low grazing angles." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 1999. http://handle.dtic.mil/100.2/ADA369420.

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Thesis (M.S. in Electrical Engineering) Naval Postgraduate School, September 1999.
"September 1999". Thesis advisor(s): R. Janaswamy. Includes bibliographical references (p. 77). Also avaliable online.

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14

Marshall, James J. "A large survey for very low surface brightness galaxies." College Park, Md. : University of Maryland, 2004. http://hdl.handle.net/1903/2049.

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Thesis (Ph. D.) -- University of Maryland, College Park, 2004.
Thesis research directed by: Astronomy. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.

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15

Bray, Kevin R. "Surface Mechanisms in Low-Temperature Plasma Deposition of Silicon." NCSU, 2002. http://www.lib.ncsu.edu/theses/available/etd-08122002-155312/.

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Dynamic scaling of surface roughness evolution during plasma deposition of amorphous silicon is utilized to characterize surface transport mechanisms. Different surface transport mechanisms leave distinct imprints in the surface that can be distinguished through fractal analysis. Surface roughness is characterized using atomic force microscopy (AFM) and the static and dynamic scaling coefficients a and b and the lateral correlation length Lc are extracted from the evolution of surface roughness and are used to identify surface mechanisms. Values of a = 1.0 and b = 0.3 have been obtained, which reveal that surfaces are smoothed through surface diffusion during film growth. Temperature dependence of the Lc is used to calculate diffusion barriers with values around 0.2 eV, consistent with the diffusion of a weakly bound physisorbed species. The effects of process conditions such as substrate temperature, diluent gases composition, process pressure, RF power density, and reactor configuration on the scaling parameters have been investigated. An amorphous silicon kinetic growth model has been developed that incorporates surface coverage dependent diffusion barriers. The model reproduces most experimentally observed results, although some deposition conditions are identified where the model is not valid.

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16

Midgley, B. "Evaluation of adhesion energetics involving low surface energy films." Thesis, University of Bradford, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.373227.

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17

Howard, Lowell Paine. "Advances in ultra-low contact force nanometric surface metrology." Thesis, University of Warwick, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.357233.

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18

Schwartzenberg, Jean Marc. "Field and cluster surveys for low surface brightness galaxies." Thesis, University of Bristol, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.336873.

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19

Farnham, Taylor A. "Hydrate formation and adhesion on low surface energy materials." Thesis, Massachusetts Institute of Technology, 2016. http://hdl.handle.net/1721.1/104142.

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Thesis: S.M., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2016.
This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (pages 43-44).
Clathrate hydrates are ice-like solid substances that often form inside oil and gas pipelines and are responsible for flow blockages, sometimes leading to catastrophic disasters. Minimizing hydrate adhesion and accumulation of solids on pipelines can effectively address this problem. In this thesis, we reduce the adhesion of cyclopentane hydrates by promoting the formation of a cyclopentane barrier film between the hydrate and the solid surface. The presence of this liquid film depends on the spreading coefficient of cyclopentane on the solid in the presence of water. Through a systematic modification of the surface chemistry of the solid surface using two different silanes, we correlate the wettability of water and cyclopentane to the adhesion of cyclopentane hydrates. We demonstrate negligible hydrate formation and adhesion on octadecyltrichlorosilane-coated surfaces via macroscopic visualization, surface tilt and adhesion measurements. The use of the spreading coefficient as a design parameter could further advance the development of effective, passive, hydrate-repelling surfaces.
by Taylor A. Farnham.
S.M.

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20

Chen, Tianjiao. "Low Temperature Surface Reconstruction Study on Wurtzite Gallium Nitride." Ohio University Honors Tutorial College / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=ouhonors1392904494.

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21

Yu, Liyang. "Expected modeling errors and low cost response surface methods /." The Ohio State University, 2000. http://rave.ohiolink.edu/etdc/view?acc_num=osu1488194825668827.

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22

Kim, Ji Hoon. "The star formation history of low surface brightness galaxies." College Park, Md.: University of Maryland, 2007. http://hdl.handle.net/1903/7646.

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Thesis (Ph. D.) -- University of Maryland, College Park, 2007.
Thesis research directed by: Dept. of Astronomy. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.

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23

Nash, Geoffrey Richard. "Surface acoustic wave investigations of low dimensional electron systems." Thesis, University of Bath, 1996. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.320474.

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24

Sauerhammer, Björn. "New frontiers in surface structure determination using low energy electron diffraction : surface reconstructions, complex adsorbates and a chiral surface." Thesis, University of Cambridge, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.620335.

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25

Ion, Richard Henry. "An evaluation of ultra-low-load indentation." Thesis, Lancaster University, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.255354.

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26

Pena, Vivar Jose Miguel. "Interactions of carbon black with stabilisers in low density polyethylene stabilisation." Thesis, Manchester Metropolitan University, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.324004.

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27

Holmes, Daniel John. "Surface structure determination by surface extended X-ray absorption fine structure and low energy electron diffraction." Thesis, University of Liverpool, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.235773.

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28

Suerich-Gulick, Irmgard Frances. "Axial stretching, viscosity, surface tension and turbulence in free surface vortices at low-head hydropower intakes." Thesis, McGill University, 2013. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=119367.

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Free surface vortices at low-head hydropower intakes can harm plant performance or cause premature failure of mechanical components by inducing unsteady or non-uniform flow or by entraining air, ice or floating debris down towards the turbines. Laboratory-scale physical modelling to assess vortex activity in proposed intakes is effective and remains the standard practice in industry, but it is costly and uncertainty remains as to how viscosity, turbulence and surface tension influence the translation of observed vortex characteristics from the laboratory model to the full-scale intake. Computational fluid dynamics (CFD) has been proposed as a potentially cheaper alternative without scale effects, but it requires further validation. This work sheds additional light on scale effects in laboratory-scale models and assesses the ability of a widely used commercial CFD package to predict vortex characteristics within the constraints of the hydraulic engineering context. A physical laboratory-scale model of a simplified intake is constructed with piers that produce vortices in their wake and that roughly resemble those that support trash racks at hydropower intakes. Instantaneous measurements of the three-dimensional velocity field inside the vortex are taken over a range of vortex intensities produced by eight operating conditions, with simultaneous recording of the free surface depression. The collected data are used to adapt Burgers's vortex model to link vortex characteristics (the characteristic radius, the bulk circulation, the depth and shape of the free surface depression, and the size of the largest floating particles entrained) to the operating conditions and intake geometry. The resulting model is then used to examine how viscosity, turbulence and surface tension influence vortex characteristics and their scaling behaviour. Finally, three operating conditions documented experimentally are numerically modelled using CFD with asimplified custom turbulence modelling strategy. The experimental results indicate that the axial profile of axial velocity in the vortex core, in combination with effective radial diffusivity due to viscosity and/or turbulence, plays a key role in determining the vortex characteristic radius. The magnitude of surface tension effects is shown to be relatively easily predicted and possibly far less important than scale effects associated with viscosity and turbulence. The CFD results further support the conclusion that modelling turbulence in interaction with the vortices remains one of the principal hurdles to overcome in predicting vortex characteristics at intakes in an industrial context.
La présence de tourbillons à l'amont de prises d'eau de centrales hydroélectriques à basse chute peut nuire à la performance de la centrale ou causer le bris prématuré de composants mécaniques, en provoquant des conditions d'écoulement non uniformes ou en entraînant de l'air, de la glace ou des débris flottants vers les turbines. Les modèles physiques à échelle réduite sont efficaces pour évaluer la présence de tourbillons à l'amont de prises d'eau proposées et ce mode d'évaluation demeure la pratique courante en industrie. C'est par contre une technique coûteuse et des incertitudes demeurent quant à l'influence de la viscosité, la turbulence et la tension superficielle sur le transfert des caractéristiques de tourbillons observés en modèle de laboratoire vers l'échelle de la centrale à grandeur nature. L'analyse numérique de dynamique des fluides (CFD) est souvent proposée comme alternative moins coûteuse et sans les effets d'échelle, mais le besoin d'une évaluation plus détaillée demeure. Le travail présenté ici apporte des nouvelles idées sur les effets d'échelle dans les modèles physiques à échelle réduite et évalue la capacité d'un logiciel commercial de CFD couramment utilisé pour prédire les caractéristiques de tourbillons dans les limites du contexte de génie hydraulique. Un modèle physique simplifié d'une prise d'eau à échelle réduite est construit avec des piliers provoquant un décollement qui génère des tourbillons. Ces piliers reproduisent approximativement ceux qui retiennent les grilles qui filtrent les gros débris dans les centrales hydroélectriques. Des mesures tridimensionnelles du champ de vitesse instantané sont collectées à l'intérieur des tourbillons de diverses intensités produits par huit conditions d'exploitation étudiées, avec enregistrement simultané de la dépression de la surface libre produite par le tourbillon. Les données ainsi collectées sont utilisées pour adapter le modèle de vortex de Burgers afin de lier les caractéristiques des tourbillons (le rayon caractéristique, la circulation totale, la profondeur et la forme de la dépression de la surface libre, et la dimension des plus grandes particules flottantes entraînées par le tourbillon) à la géométrie de la prise d'eau et aux conditions d'exploitation. Ce modèle adapté est ensuite utilisé pour examiner l'influence de la viscosité, de la turbulence et de la tension superficielle sur les caractéristiques des tourbillons et les lois de changement d'échelle. Enfin, trois conditions d'exploitation documentées expérimentalement sont simulées par CFD en utilisant une stratégie simplifiée de modélisation de turbulence adaptée pour cette étude. Les résultats expérimentaux indiquent que le profil de vitesse axiale le long de l'axe du du tourbillon en son centre, en combinaison avec la diffusivité radiale réelle due à la viscosité et/ou à la turbulence, a une influence déterminante sur la dimension du rayon caractéristique du tourbillon. L'amplitude des effets de tension superficielle peut être prédite relativement facilement et serait possiblement beaucoup moins importante que l'amplitude des effets d'échelle liés à la viscosité et à la turbulence. Les résultats des simulations par CFD renforcent la conclusion que la modélisation de la turbulence en interaction avec les tourbillons demeure un des obstacles principaux à surmonter afin de pouvoir prédire les caractéristiques de tourbillons aux prises d'eau dans un contexte industriel.

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29

Mak, Nin-fung Joseph. "Dynamic surface electromyography in functional assessment of low back musculature." Click to view the E-thesis via HKUTO, 2004. http://sunzi.lib.hku.hk/hkuto/record/B31972020.

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30

Balog, Richard. "Low energy electrons as a soft tool for surface modification." [S.l. : s.n.], 2004. http://www.diss.fu-berlin.de/2004/263/index.html.

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31

Hill, Steven. "Measurements of low frequency acoustic backscatter from the sea surface." Thesis, University of British Columbia, 1991. http://hdl.handle.net/2429/31022.

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The overall objective of this thesis was to predict, model and measure low frequency acoustic backscatter from the sea surface zone (SSZ). In particular, the objectives were fourfold: to relate the acoustic backscatter Doppler spectrum to the directional waveheight spectrum (DWS) through a perturbation analysis; to develop instrumentation suitable for measuring the properties of acoustic backscatter from the SSZ; to design and implement signal processing hardware and software to process raw data from the instrument; and to deploy the instrument and make measurements to test the validity of the predictions of the theoretical development. A theoretical framework was developed to enable a test of the acoustic analogue of the Coastal Ocean Dynamics Applications Radar (CODAR) technique, using beamforming techniques to simulate the CODAR antennas. Expressions relating the CODAR antenna outputs to the output of an array of omnidirectional acoustic point sensors were developed, and mathematical algorithms and techniques were derived to extract information about the DWS of surface gravity waves from acoustic Doppler backscatter measurements with the array. Models were developed and implemented, showing the expected form of the power spectral density of the acoustic Doppler backscatter seen by single omnidirectional receivers, and the expected form of data products of the beamformed array. An acoustic instrument — the Upward-Looking Sonar Array System (ULSAS) — was developed for stand-alone, remotely controlled operation in both bottom-situated and deep-water, surface-tethered configurations. This device can collect and store large quantities of acoustic data from a multi-element array, under the control of a distant operator over a radio link. The bottom-situated version was deployed in the coastal waters of British Columbia, and the deep water version was deployed in the recent Surface Wave Processes (SWAPP) experiment. A preliminary test of the acoustic CODAR technique was made, yielding information consistent with the known wind and wave field. The form of the non-directional part of the extracted DWS followed approximately the expected k⁻⁴ shape for k values above saturation. Beamforming results using frequency-domain data show that the Doppler-shifted acoustic backscatter is directional in nature. These are the first results of this kind to be reported. The deep-water version of ULSAS was tested for the first time during the SWAPP cruise. In spite of a problem limiting the power output of the projector, estimates of the surface scattering strength parameter over angles of incidence less than 45° were made, showing some surprising departures from the Chapman-Harris empirical formula for S₅ , and interesting angular structure. Measurements of the ambient noise field were also made under calm conditions and during 14 kt winds.
Science, Faculty of
Earth, Ocean and Atmospheric Sciences, Department of
Graduate

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32

O'Neill, Daniel Scott Materials Science &amp Engineering Faculty of Science UNSW. "An investigation of surface hot shortness in low carbon steel." Awarded by:University of New South Wales. Materials Science and Engineering, 2002. http://handle.unsw.edu.au/1959.4/18274.

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A series of model steels containing copper levels up to 0.48wt%, nickel up to 0.22wt% and silicon levels of 0.52wt% were oxidised in air at 1050 and 1150??C, and in a CO2-N2 mixture at 1250??C for times of up to 3 hours. The scaling kinetics were measured and the behaviour of copper-rich phase formation at the scale/metal interface was investigated. When oxidised at 1050/1150??C, significant quantities of copper-rich phase were observed for most model steels. The relatively high oxidation rate under these conditions led to the rapid development of a copper-rich layer with little copper diffusing into the metal. However, when oxidised at 1250??C, the copper-rich phase did not form for a significant amount of time; and for some model steels, not at all. This was attributed to the considerably lower oxidation rate and the fact that more copper was found to have diffused into the metal. Alloying additions of nickel and silicon were found to be beneficial in reducing the amount of copper-rich phase measured at the scale/metal interface under the conditions investigated at 1150??C and 1250??C. This occurred because nickel and silicon addition promoted the occlusion of copper-rich phase into the scale. Copper enrichment during oxidation was modelled using a numerical description of the diffusion processes involved. Predictions of the time for commencement of copper-rich phase formation at 1250??C were in close agreement with observation. Agreement between predicted and observed copper-rich layer thickness was less successful under conditions where occlusion was significant, and the measured thickness varied non-uniformly with time. The cracking susceptibility of the model steels was examined using a hot compression test. Oxidation was performed in air at 1050, 1150 and 1250??C and most specimens were compressed at 1050??C. The amount of cracking was found to increase with the amount of copper-rich phase precipitated at the scale/metal interface during oxidation. In general, nickel addition reduced the amount of cracking at all temperatures; and under some conditions prevented cracking altogether. Silicon reduced or completely suppressed cracking when the subscale formed was liquid. The beneficial effects of nickel and silicon addition were attributed to their effect of promoting copper occlusion.

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33

Holmes, Darran Mark. "STM studies of GaAs homoepitaxy on low index surface orientations." Thesis, Imperial College London, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.300577.

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34

Roberts, Sarah. "Search for low surface brightness dwarf galaxies in different environments." Thesis, Cardiff University, 2005. http://orca.cf.ac.uk/56002/.

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Current theories of large scale structure and galaxy formation predict the existence of numerous low mass dark matter haloes in the Universe today. If these haloes contain sufficient stars they should be detectable as low luminosity stellar systems or dwarf galaxies. We have searched for these objects in four regions of increasing density - the general field, the area around a giant spiral galaxy, the low density Ursa Major cluster, and the high density Virgo cluster. Using identical deep optical data covering a total of 602 and probing fainter magnitudes than has been done previously, we used identical selection and detection methods to compare the dwarf galaxy populations in these different environments. We found substantially more dwarfs per giant galaxy in the Virgo cluster (20:1) compared to the field environment (6:1 max). A comparison of the HI properties and (B-I) colours for the objects for which we had additional data also showed that in general, the cluster objects are redder and gas poor compared to the objects in the field. We discuss the possible mechanisms which may have resulted in creating a population of cluster dwarf galaxies, which would explain the high number density which we found in our data. It is likely that a combination of tidal interactions and transformation of infalling dlrrs into dEs will result in the large population of cluster dwarfs. Conclusive evidence regarding their formation must now be obtained by a more detailed investigation of their stellar populations. The lack of dwarf galaxies in the field region is likely to be due to the effect of inefficient star formation in the field environment compared to the cluster. Thus the low mass dark matter haloes predicted by CDM models must still be 'dark' and can only be identified by further deep HI studies of the field environment, and future gravitational lensing studies of substructure.

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35

Mak, Nin-fung Joseph, and 麥年豐. "Dynamic surface electromyography in functional assessment of low back musculature." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2004. http://hub.hku.hk/bib/B31972020.

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36

Tse, Yuk-hang Jessica, and 謝毓衡. "Application of surface electromyography topography in low back pain rehabilitation." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2014. http://hdl.handle.net/10722/208612.

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The management of low back pain (LBP) has long been a challenge as it is a highly prevalent disease worldwide due to the lack of an apparent etiology and a conclusive therapeutic treatment. Heterogeneous groups of LBP patients with diverse medical backgrounds also complicate the problem. A clinical threshold is demanded to match the patients and treatments appropriately in order to maximize the treatment success rate. Besides, the assessments of disability and pain perception due to LBP made by self-evaluated questionnaires in current clinical setting are highly susceptible to subjective feeling and the memory of patients. LBP and spasm are closely related but little is known for the underlying physiology, especially the musculature of LBP patients with spasm. These problems exacerbate the difficulty in LBP rehabilitation further. Surface electromyography (sEMG) topography is a cutting- edge technology to assess the lumbar muscle in vivo non-invasively by illustrating the distribution of global muscle activity visually. sEMG topography has the potential application as an objective assessment tool for LBP rehabilitation. In present study, sEMG topography was used to address 1) the prognostic value of sEMG topography on LBP rehabilitation, 2) the establishment and validation of a clinical classification threshold for identification of LBP patients who are responsive to exercise therapy and 3) the investigation of sEMG topography in accordance with the physiological outcomes (functional disability, pain perception and spasm). Forty-five healthy subjects and fifty patients with chronic non-specific LBP were enrolled to the study. sEMG test was conducted to every subject under the motions of lumbar flexion and extension in order to gather the myoelectric signals by a 16-channel sEMG. Various sEMG topographic parameters (sEMG parameters) were developed for quantitative analysis of sEMG topography. They were Root-Mean-Square-Difference of Relative Area (RMSD RA), Relative Width (RMSD RW) and Relative Height (RMSD RH) at flexion and extension. Results showed that sEMG parameters were of significant prognostic value for LBP patients towards exercise therapy. A clinical threshold of 0.21 was proposed and validated based on the geometric calculation of RMSD RA and RMSD RW at flexion and extension. The threshold was substantiated to increase the success rate of exercise therapy from 46% to 86% when the value measured by sEMG topography was below 0.21. sEMG parameters were found significantly associated with disability and pain perception in a positive manner. Severer disability and pain perception were represented by larger values of sEMG parameters. sEMG topography demonstrated symmetric patterns for patients with or without spasms on bilateral sides of lumbar muscles. The symmetry in sEMG topography evinced the consistency of the musculature of bilateral lumbar muscles while the lost of symmetry might indicate malfunction of lumbar muscles unilaterally. To conclude, this study corroborated versatile roles of sEMG topography in LBP rehabilitation as a prognosis, clinical threshold, and objective measurement. The findings of this study have paved the way of sEMG topography for future application in clinical setting. A study of larger scale would be recommended to complement the present findings.
published_or_final_version
Orthopaedics and Traumatology
Master
Master of Philosophy

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37

Pickering, Timothy Edward 1970. "Kinematics and star formation properties of low surface brightness galaxies." Diss., The University of Arizona, 1998. http://hdl.handle.net/10150/282756.

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We present detailed studies of the kinematics and star formation properties of low surface brightness (LSB) galaxies. A total of five giant LSB galaxies including the prototype, Malin 1, were imaged in the 21-cm line of H sc I to provide the first glimpse into the kinematics of these systems. We find that these are some of the first examples to be uncovered of galaxies that are both massive and dark matter dominated. We also find that most of the galaxies have gas surface densities that lie below the critical density for star formation at all radii, consistent with their lack of star formation. In a couple of cases, though, the gas exceeds the critical density where there is no star formation implying a higher gas velocity dispersion or strong flaring of the gas disk. Long-slit optical spectroscopy and broadband CCD imaging are presented for a total of 71 LSB galaxies. We find that these galaxies follow a Fisher-Tully relation with a slope that is in good agreement with the slopes found for other samples of LSB and HSB galaxies. We interpret both the optical and H sc I rotation curves in terms of mass models consisting of a halo only or a stellar component plus a halo of either an isothermal form or an NFW halo of the form described by Navarro et al. (1996) and find that the rotation curves are generally best modeled by low mass-to-light ratio stellar components. By modeling the rotation curves with only an NFW halo and comparing the results with the predictions of cosmological simulations we find that these data are marginally consistent at best with Standard Cold Dark Matter and generally favor lower density models. However, we also find that when including the stellar component, the NFW halo gives a significantly worse fit than an isothermal halo in many cases. This suggests that the inner parts of galactic halos may not be well described by the NFW halo profile.

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38

Williams, R. P. "Low surface brightness galaxies and the galaxy stellar mass function." Thesis, Liverpool John Moores University, 2017. http://researchonline.ljmu.ac.uk/6652/.

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The galaxy stellar mass function (GSMF) has been well measured by the Galaxy And Mass Assembly (GAMA) survey down to a mass of $\mstar = 10^{8}\,\msun$. Below this mass the values produced so far can only be taken as lower limits on the distribution. One source of this incompleteness is failing to account for undetected low-surface-brightness galaxies (LSBGs) within the fields observed. These galaxies have been known about for some time, however, taking a true census of their population is difficult because of the biases associated with their detection in large surveys. The focus of this thesis is to improve the census of these objects and to try and apply those results to the low-mass end of the GSMF. First the SDSS data used to create the original GAMA catalogues is re-examined for low-surface brightness galaxies (LSBGs). To accomplish this SDSS DR7 imaging was used and a specialised detection algorithm created. This was based on masking sources detected with SDSS \textsc{photo}, combining the {\it gri} images with a weighting that maximises the signal-to-noise (SNR), and smoothing the images. These were then run through a detection algorithm which finds all pixels above a set threshold and groups them based on their proximity to one another. The list of detections is cleaned of contaminants such as diffraction spikes and the faint wings of masked objects. This produces a final list of 343 newly discovered LSBGs. Measuring their $g-i$ and $J-K$ colours shows that most are likely to be at redshifts less than 0.15. The photometry is carried out using a flexible auto aperture for each detection giving surface brightness measurements of $\mu_{r} > 23.7$\,mag arcsec$^{-2}$ and $r$-band magnitudes of $r_{AUTO} \gtrsim 20$\, mag. Through this method we show there are at least 343 new LSBGs within the GAMA fields, however none of these galaxies are bright enough to be within the GAMA main survey limit. It was noticed during the previous work that the detected LSBGs were all visible in VIKING $Z$-band data, and so it was decided to run a more traditional detection algorithm over these data to increase the number of LSBGs detected. This could then be used to create a new GSMF based on the deeper $Z$-band imaging. By using this imaging it will be possible to detect many more faint galaxies than previously and also increase the depth to which surface brightness can be effectively probed. The three GAMA equatorial regions have had mosaics created from the $Z$-band imaging which are searched using \textsc{Source Extractor} (\textsc{SExtractor}) and catalogues of detections are made. These are then compared to the original GAMA catalogues to remove duplicate detections and identify any possible new ones. Criteria are then applied to the source lists to remove any stars or objects which are either not galaxies or artefacts. This then leaves only likely galaxies in the catalogue to be used. The next stage is to create the GSMF based on the data collected, through applying corrections for the volume searched, and the spectroscopic completeness of the objects after they have been binned in $g-i$, $J-K$, and apparent magnitude. The GSMF created is compared to previous versions, namely that from \cite{Baldry+2012}, and a rise in the number density at masses of $\mstar \le 10^{8}\,\msun$ is shown. These can still only be thought of as lower limits however as improvement to the imaging can still be made in future surveys. With a full catalogue obtained using the VIKING Z-band it was decided to revisit the detection algorithm developed in Chapter 2. A pilot study was undertaken to both test the validity of the method, and the suitability of the VIKING images for further study. Whilst applying the detection algorithm to the data improved the ability to detect low surface brightness features within the images, no new galaxies were discovered over the pilot study area of $0.75$ deg$^{2}$. This method applied to the Z-band data, even over the full area, is unlikely to lead to large numbers of new LSBGs. This work has shown that there are still LSBGs in the field to be discovered. The result of finding new LSBGs has been to raise the measurement of the GSMF at low masses, further constraining the number of low mass galaxies in the Universe.

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39

Lawes, Simon Donald A. J. "The application of surface coatings for low wear and low friction performance between valve train components." Thesis, University of Leicester, 2009. http://hdl.handle.net/2381/7554.

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40

Cameron, Thomas P. "Low-voltage SAW amplifiers on multilayer GaAs/ZnO substrates." Diss., Georgia Institute of Technology, 1996. http://hdl.handle.net/1853/15463.

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41

Barnard, John Cameron. "Low energy electron scattering by ordered adsorbed molecules." Thesis, University of Cambridge, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.321430.

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42

Pettersson, Ulrika. "Surfaces Designed for High and Low Friction." Doctoral thesis, Uppsala : Acta Universitatis Upsaliensis : Univ.-bibl. [distributör], 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-5835.

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43

Zackrisson, Erik. "Quasars and Low Surface Brightness Galaxies as Probes of Dark Matter." Doctoral thesis, Uppsala University, Department of Astronomy and Space Physics, 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-5826.

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Most of the matter in the Universe appears to be in some form which does not emit or absorb light. While evidence for the existence of this dark matter has accumulated over the last seventy years, its nature remains elusive. In this thesis, quasars and low surface brightness galaxies (LSBGs) are used to investigate the properties of the dark matter.

Quasars are extremely bright light sources which can be seen over vast distances. These cosmic beacons may be used to constrain dark matter in the form of low-mass, compact objects along the line of sight, as such objects are expected to induce brightness fluctuations in quasars through gravitational microlensing effects. Using a numerical microlensing model, we demonstrate that the uncertainty in the typical size of the optical continuum-emitting region in quasars represents the main obstacle in this procedure. We also show that, contrary to claims in the literature, microlensing fails to explain the observed long-term optical variability of quasars. Here, quasar distances are inferred from their redshifts, which are assumed to stem from the expansion of the Universe. Some astronomers do however defend the view that quasar redshifts could have a different origin. A number of potential methods for falsifying claims of such non-cosmological redshifts are proposed.

As the ratio of dark to luminous matter is known to be unusually high in LSBGs, these objects have become the prime targets for probing dark matter halos around galaxies. Here, we use spectral evolutionary models to constrain the properties of the stellar populations in a class of unusually blue LSBGs. Using rotation curve data obtained at the ESO Very Large Telescope, we also investigate the density profiles of their dark halos. We find our measurements to be inconsistent with the predictions of the currently favoured cold dark matter scenario.

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44

Blake, Robert. "The effects of realistic surface properties on low temperature space observatories." Thesis, Open University, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.262697.

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45

Preston, Daniel J. (Daniel John). "Enhanced condensation heat transfer for water and low surface tension fluids." Thesis, Massachusetts Institute of Technology, 2017. http://hdl.handle.net/1721.1/113167.

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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2017.
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 68-79).
Vapor condensation is routinely used as an effective means of transferring heat or separating fluids for applications ranging from personal electronic device thermal management to natural gas processing and electric power generation. Filmwise condensation, where the condensed fluid forms a liquid film, is prevalent in typical industrial-scale systems. Conversely, dropwise condensation, where the condensate forms discrete liquid droplets, results in an improvement in heat transfer performance of up to an order of magnitude compared to filmwise condensation. We explored rare earth oxides (REOs) as a potential coating to induce dropwise condensation of water; specifically, we experimentally demonstrated that the mechanism for REO hydrophobicity results from adsorption of contaminants from the atmosphere. We also used graphene, which is hydrophobic in nature, as a coating to achieve robust dropwise water condensation. With a graphene coating, we demonstrated a 4x improvement in water condensation heat transfer compared to filmwise condensation with robustness superior to state-of-the-art hydrophobic monolayer coatings. Meanwhile, low surface tension condensates pose a unique challenge since they often form a film, even on hydrophobic coatings. Lubricant infused surfaces (LIS) represent a potential solution, where a lubricant immiscible with the low surface tension condensate is infused into a rough structure on the condenser surface to repel the condensate. We developed a detailed surface-energy-based model to provide design guidelines for any arbitrary LIS system. We then characterized heat transfer coefficients during condensation of low surface tension fluids on LIS in a controlled environmental chamber for the first time, where a 5x improvement was demonstrated compared to filmwise condensation. The improved condensation heat transfer coefficients realized by LIS for low surface tension fluids and by REOs and graphene for water present opportunities for significant energy savings in device thermal management, heating and cooling, and power generation.
by Daniel John Preston.
Ph. D.

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46

Puisto, Sakari Rainer. "Surface crystallography of complex structures studied by low energy electron diffraction." Thesis, University of Cambridge, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.616126.

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47

Marks, Christopher R. "Surface Stress Sensors for Closed Loop Low Reynolds Number Separation Control." Wright State University / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=wright1309998636.

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48

Mancillas, Vaquera Brisa. "Extending the realm of galaxies to the low surface brightness universe." Thesis, Paris Sciences et Lettres (ComUE), 2019. http://www.theses.fr/2019PSLEO013.

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L'exploration de l'émission de lumière diffuse et de la périphérie des galaxies dans le régime de faible luminosité de surface (LSB pour ses sigles en anglais) est essentielle afin de comprendre le mécanisme de formation de l'évolution des galaxies, et élémentaire pour pouvoir contraindre les modèles théoriques et simulations numériques dans un contexte cosmologique. Les donnés observationnelles, aussi bien dans le domaine optique que radio, complémentées par des simulations numériques nous fournissent des informations cruciales sur les propriétés morphologiques des sous-structures autour des galaxies massives, ainsi que sur leur distribution de masse, le contenu du gaz moléculaire et la formation des étoiles des galaxies LSB telles que galaxies ultra diffuses (UDGs) récemment recouvertes.Dans cette thèse, nous présentons plusieurs analyses destinés à l'étude de ces sujets. Dans un premier temps, motivés par les récents travaux sur les observations du télescope CFHT des sondant de profondes images, qui ont révélé d'importantes structures fines dans les galaxies LSB, comme des queues de marée, des courants stellaires et des coquilles, nous avons calculé des statistiques d'une simulation numérique hydrodynamique afin d’interpréter les observations et faire des prédictions sur la distribution en masse des galaxies dans le passé. Nous avons fait un recensement de ces sous-structures et nous avons calculé leur temps de survie. Nous avons aussi étudié leur dépendance vis à vis de plusieurs propriétés comme, par exemple, leur luminosité de surface et projection. Nous avons trouvé que les coquilles et les courants restent visibles environ 4 Gyr et qu'ils sont principalement associés à des fusions mineures et a une accumulation continue de gaz diffus, alors que les queues de marée ont une durabilité d'environ 1 Gyr et sont corrélées avec des événements de fusion majeurs. En parallèle, dans ces travaux, nous avons employé d'une approche semi-empirique pour construire un catalogue factice afin de faire des prédictions sur des relations d'échelle et contraindre des paramètres physiques des galaxies UDGs et LSB. D'un autre côté, nous avons réalisé de la spectroscopie CO des galaxies UDGs observées à IRAM-30m pour quantifier leur contenu en gaz moléculaire. Les galaxies sélectionnées étaient constituées de sources provenant de plusieurs environnements et avec des propriétés différentes, notamment des objets comme les galaxies très rouges Dragonfly 44 et DGSAT I. Nous avons obtenu des limites supérieures sans précédent de leur masse de CO (quelques 10^6-10^7 masses solaires). Aussi, nous avons fait des observations à IRAM-30m pour détecter le contenu de gaz moléculaire dans un échantillon de 4 galaxies jeunes qui présentent des galaxies avec coquilles proéminents, comme c'est le cas, par exemple, du NGC 0474 et Arp 230. Notre but est de tester le modèle de formation enroulement de phase proposé dans des simulations numériques. Nous avons détecté une masse moléculaire d'environ 10^8 masses solaires dans plusieurs coquilles d'une des galaxies de notre échantillon et nous rapportons les limites supérieures de masse dans les autres cas
The exploration of diffuse light emission and the outskirts of galaxies in the regime of the Low Surface Brightness (LSB) is of utmost importance to understand the formation mechanism of galaxy evolution, and is essential to constrain the current theoretical models and numerical simulations in the cosmological context. Observational data, both in optical and radio emission, complemented with hydrodynamical cosmological numerical simulations provide us a crucial information about the morphological properties of substructures surrounding massive galaxies, as well as the mass distribution, molecular gas content and star formation of LSB galaxies such as the recently discovered Ultra Diffuse Galaxies (UDGs).This thesis presents several analysis addressed to the study of these schemes. In first instance, motivated in the most recent works about optimized deep imaging surveys observed with the CFHT telescope, which have revealed prominent LSB fine structures classified like tidal tails, stellar streams and shells, we have computed statistics of an hydrodynamical numerical simulation in order to interpret observations and make inferences about the past mass assembly of galaxies. We made a census of these substructures and computed their survival time. We also studied their dependence with several properties like the projection and the surface brightness. We found that shells and streams remains visible around 4 Gyr and they are mainly associated to minor mergers and a continuous diffuse gas accretion, while tidal tails have a durability time of around 1 Gyr and are correlated with major merger events. In parallel, in this work we made use of a semi-empirical approach to build-up a mock catalog with the aim to make predictions about scaling relations and constrain physical parameters of UDGs and LSB galaxies.On the other hand, we have performed CO spectroscopy surveys of UDGs observed at IRAM-30m to quantify the molecular gas content. The selected galaxies were conformed by sources from several environments and different properties, including objects like the very red galaxies Dragonfly 44 and DGSAT I. We have obtained unprecedented upper limits of their CO mass (few 10^6 - 10^7 solar masses). We also made CO observations at IRAM-30m to detect molecular gas content in a sample of four early-type galaxies that exhibit prominent shell galaxies like the case of NGC 0474 and Arp 230. Our goal is to test the phase wrapping formation model proposed in numerical simulations. We detected a molecular mass of around 10^8 solar masses in several shells of one galaxy of our sample and we report the mass upper limits for the other cases

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49

Oliver, Trevor N. "Surface acoustic wave devices with low loss and high frequency operation." Thesis, Aston University, 1989. http://publications.aston.ac.uk/8083/.

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This thesis describes an industrial research project carried out in collaboration with STC Components, Harlow, Essex. Technical and market trends in the use of surface acoustic wave (SAW) devices are reviewed. As a result, three areas not previously addressed by STC were identified: lower insertion loss designs, higher operating frequencies and improved temperature dependent stability. A review of the temperature performance of alternative lower insertion loss designs,shows that greater use could be made of the on-site quartz growing plant. Data is presented for quartz cuts in the ST-AT range. This data is used to modify the temperature performance of a SAW filter. Several recently identified quartz orientations have been tested. These are SST, LST and X33. Problems associated with each cut are described and devices demonstrated. LST quartz, although sensitive to accuracy of cut, is shown to have an improved temperature coefficient over the normal ST orientation. Results show that its use is restricted due to insertion loss variations with temperature. Effects associated with split-finger transducers on LST-quartz are described. Two low-loss options are studied, coupled resonator filters for very narrow bandwidth applications and single phase unidirectional transducers (SPUDT) for fractional bandwidths up to about 1%. Both designs can be implemented with one quarter wavelength transducer geometries at operating frequencies up to 1GHz. The SPUDT design utilised an existing impulse response model to provide analysis of ladder or rung transducers. A coupled resonator filter at 400MHz is demonstrated with a matched insertion loss of less than 3.5dB and bandwidth of 0.05%. A SPUDT device is designed as a re-timing filter for timing extraction in a long haul PCM transmission system. Filters operating at 565MHz are demonstrated with insertion losses of less than 6dB. This basic SPUDT design is extended to a maximally distributed version and demonstrated at 450MHz with 9.8dB insertion loss.

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50

Busayaporn, Wutthikrai. "TiO2(110) surface structure." Thesis, University of Manchester, 2010. https://www.research.manchester.ac.uk/portal/en/theses/tio2110-surface-structure(9641eaab-818a-4928-a0b2-78312de050d5).html.

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In this thesis three studies of the geometric structure of the (110) surface of single crystal rutile TiO2 are presented. Firstly, quantitative low energy electron diffraction (LEED-IV) data acquired from TiO2(110)(1x1) are reanalysed to confirm the integrity of the previously reported optimized geometries by performing structural optimisation as a function of depth into the selvedge. The second study addresses the geometry of the x-linked (1x2) reconstruction of the same surface. Again, LEED-IV data are analysed to quantitatively determine the surface structure. Part of this effort involved substantial development of the code (SATLEED) employed for simulating the experimental data, to allow simultaneous optimisation of more than one surface termination. In contrast to recent scanning probe work, the analysis indicates that the surface consists of two differently relaxed Ti2O3 added rows. The last study concerns ab initio calculations of the structure of benzoate on TiO2(110)(1x1). Of particular interest is the impact of surface coverage on the orientation of the benzene ring. It is predicted that the benzene ring twists and tilts away from high symmetry with increasing coverage due to adsorbate-adsorbate interactions. No evidence is found to support the formation of benzoate dimers or trimers, as was concluded in earlier experimental work.

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