Dissertations / Theses on the topic 'Helium'
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Yu, Nan. "The infrared spectrum of the helium molecular ion helium-3 positive helium-4." Diss., The University of Arizona, 1988. http://hdl.handle.net/10150/184419.
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This dissertation is concerned with the first experimental observation of the vibration-rotation spectrum of the helium molecular ion, ³He⁴He⁺. The Doppler-tuned fast-beam laser-resonance technique has been used. The ions produced in an electron-impact ion source form an ion beam of a few KeV and then intersect nearly colinearly with a CO IR laser beam of fixed frequency. The velocity of the ions is scanned to tune the ions into resonance with the laser frequency. Subsequent resonance detection is realized by using charge exchange processes of the ion with a target gas. Twelve spectral lines have been measured which correspond to nine different vibration-rotation transitions of the R branch in the fundamental band of the ground state of ³He⁴He⁺. The combination of the kinematic compression of the fast-beam method and the special frequency stabilization of the CO laser render an experimental accuracy of 0.0006 cm⁻¹ or 0.4 ppm. The accuracy exceeds that of the available theory by three orders of magnitude. The narrow spectral linewidth also allows partial resolution of the magnetic hyperfine structure due to helium-3. A hyperfine structure calculation has been carried out using a numerical multi-configuration self-consistent-field method. The agreement between the calculation and the observation is very satisfying.
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Hjort, Hans H. "Helium-Helium scattering in vacuum and in liquid ³HE /." The Ohio State University, 1999. http://rave.ohiolink.edu/etdc/view?acc_num=osu1488187049539918.
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Jörder, Felix [Verfasser], and Andreas [Akademischer Betreuer] Buchleitner. "Dynamical localization in driven helium = Dynamische Lokalisierung in getriebenem Helium." Freiburg : Universität, 2015. http://d-nb.info/1119805643/34.
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Todd, Allan. "Helium-Antihydrogen Interactions." Thesis, University of Nottingham, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.485533.
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Blancafort, Jorquera Miquel. "Theoretical reaction and relaxation dynamics in superfluid helium nanodroplets." Doctoral thesis, Universitat de Barcelona, 2019. http://hdl.handle.net/10803/668116.
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The study of superfluid helium has been carried out mainly by physicists. In recent years, taking advantage of the potentialities presented by superfluid helium nanodroplets (HeNDs) as inert matrices at very low temperatures (0.37 K), the chemical community became involved in its application to high-resolution spectroscopy. More recently (early 2000s), this community began to be involved in research using HeNDs to investigate chemical reactivity in this quantum solvent. As for the theoretical studies on the dynamics of physicochemical processes in HeNDs, they have been possible about five years ago and the number of theoretical dynamics studies, despite their interest, is very scarce. The main objective of this thesis is to contribute to the development of the research in this area.
To introduce the reader into the topic, Chapter 1 is divided into four sections: the first one describes the properties of helium, the second one considers the history of the discovery and research carried out on the superfluidity phenomenon, the third one outlines the properties of superfluid helium nanodroplets, and the last one gives an overview of the applications and fields of study implying HeNDs.
The theoretical and numerical methods used to describe superfluid liquid helium are detailed in Chapter 2. In the first section attention has been paid on the density functional theory (DFT) and its time dependent extension for real-time simulations (TDDFT). The second section describes the main density functionals used and the third section is aimed to present the numerical methods employed to perform the TDDFT calculations.
The following four chapters contain the original studies carried out in this thesis. The investigation of the capture process of a Ne atom by a HeND can be found in Chapter 3. Here, the atom is treated using classical mechanics and the influence of energy and angular momentum is examined for a wide set of initial conditions. The microscopic mechanism, energy and angular momentum exchanges and vortex formation have been extensively analysed. The present contribution corresponds to the first systematic analysis of the influence of angular momentum in the capture process and vortex formation.
Chapter 4 represents a natural evolution from Chapter 3 and describes the formation of a neon dimer or neon adduct inside a superfluid helium nanodroplet, treating both atoms classically. Analogously as in the previous chapter, angular momentum has also been taken into consideration and the mechanism, energy an angular momentum exchanges and vortex formation are analysed. These two chapters complement and extend two previous investigations of our group where the Ne atoms were treated using standard quantum mechanics at zero angular momentum. The contents of Chapter 4 correspond to the second theoretical investigation on bimolecular reaction dynamics in HeNDs.
The following two chapters use a full quantum hybrid approach to explore rotational and vibrational energy relaxation dynamics. Chapter 5 corresponds to the first theoretical study reported so far on the rotational energy relaxation dynamics of molecules in HeNDs. This process has been studied using several isotopes of the H2 molecule (fast rotors) and considering a set of initial excitations and nanodroplet sizes.
The last investigation (Chapter 6) is centred on the study of the vibrational energy relaxation in HeNDs. Thus, the influence of the energy gap between the vibrational levels, molecule-helium interaction energy and nanodroplet size on the vibrational relaxation dynamics has been analysed, taking as a reference the I2@(4He)100 doped nanodroplet which was recently studied in our group. To the best of our knowledge it is the first time that the influence of these key factors has been examined.
Finally, in Chapters 7 and 8 the main conclusions and a summary in Catalan are presented.Les nanogotes d’heli superfluid (HeNDs) són matrius inerts i nanoreactors ideals a baixa temperatura (0.37 K). Això ha atret l’atenció de químics doncs permeten realitzar espectroscopia d’altra resolució, estudiar la reactivitat i sintetitzar en condicions especials. L’estudi teòric de la dinàmica de processos en HeND ha estat possible tan sols fa cinc anys i, tot i el seu interès, n’hi ha molt pocs estudis. L’objectiu d’aquesta tesi és contribuir a la recerca en aquesta àrea. El Capítol 1 descriu les propietats de l’heli, la història de la superfluïdesa i les propietats i aplicacions de les HeNDs. La teoria del funcional de la densitat (DFT) i l’extensió de la mateixa depenent del temps (TDDFT), els principals funcionals per HeNDs i els mètodes numèrics es presenten al Capítol 2. Els següents capítols contenen els estudis originals d’aquesta tesi. En el Capítol 3 s’investiga la captura de Ne en una HeND on l’àtom es tracta clàssicament. El mecanisme, els intercanvis d’energia i moment angular i la formació de vòrtexs s’han analitzat àmpliament. Aquest és el primer anàlisi rigorós de la influència del moment angular en la captura i formació de vòrtexs. El Capítol 4 descriu la formació de Ne2/Ne-Ne en HeND tractant ambdós àtoms clàssicament. El mecanisme, bescanvis d’energia i moment angular i formació de vòrtexs també s’han estudiat. És el segon estudi sobre reaccions bimoleculars en HeNDs. Els Capítols 3 i 4 complementen i amplien dues investigacions del nostre grup on els àtoms es van tractar quànticament amb moment angular zero. En els propers dos capítols es consideren les relaxacions rotacional i vibracional utilitzant enfocs quàntics híbrids. El Capítol 5 correspon al primer estudi teòric de la relaxació rotacional de molècules en HeNDs, i s’han considerat varis isòtops de H2 i excitacions inicials i mides de nanogota. El Capítol 6 detalla la influència de la separació energètica vibracional, interacció molècula-heli i mida de nanogota en la relaxació vibracional en HeNDs, agafant com a referència el sistema I2@(4He)100. És el primer cop que s’examina l’efecte d’aquestes propietats clau. Els Capítols 7 i 8 presenten les principals conclusions i un resum en català, respectivament.
Las nanogotas de helio superfluido (HeNDs) son matrices inertes y nanoreactores ideales a baja temperatura (0.37 K). Esto ha atraído a los químicos pues posibilitan realizar espectroscopia de alta resolución, así como estudiar de la reactividad y síntesis en condiciones especiales. La dinámica teórica de procesos en HeND ha sido posible tan sólo hace cinco años y, a pesar de su interés, todavía hay muy pocos estudios. Esta tesis pretende contribuir a la investigación en esta área. El Capítulo 1 describe las propiedades del helio, la superfluidez y las propiedades y aplicaciones de las HeNDs. La teoría del funcional de la densidad (DFT) y su extensión dependiente del tiempo (TDDFT), los principales funcionales para HeNDs y los métodos numéricos se presentan en el Capítulo 2. Los siguientes capítulos contienen los estudios originales de esta tesis. En el Capítulo 3 se investiga la captura de Ne en una HeND donde el átomo se trata clásicamente. El mecanismo microscópico, intercambios de energía y momento angular y formación de vórtices se han analizado ampliamente. Este es el primer análisis detallado de la influencia del momento angular en la captura y la formación de vórtices. El Capítulo 4 describe la formación de Ne2/Ne-Ne en HeND tratando ambos átomos clásicamente. El mecanismo, intercambios de energía y momento angular y formación de vórtices también se han estudiado. Los Capítulos 3 y 4 complementan y amplían dos investigaciones de nuestro grupo donde los átomos se trataron cuánticamente con momento angular cero. En los dos capítulos siguientes se estudian las relajaciones rotacional y vibracional utilizando enfoques cuánticos híbridos. El Capítulo 5 corresponde al primer estudio teórico de la relajación rotacional de moléculas en HeNDs, y se han considerando varios isótopos de H2, excitaciones iniciales y tamaños de nanogota. El Capítulo 6 detalla la influencia de la separación energética, interacción molécula-helio y tamaño de nanogota en la relajación vibracional en HeND, habiéndose tomando como referencia el sistema I2@(4He)100. Es la primera vez que se examina el efecto de estas propiedades clave en la dinámica. Los Capítulos 7 y 8 presentan las principales conclusiones y un resumen en catalán, respectivamente.
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Sawkey, Daren Lewis. "Thermomechanical effect in normal liquid helium-3 with helium-4 pre-plating." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp04/mq22392.pdf.
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Porter, Ryan Lucian. "THEORY AND APPLICATION OF HELIUM AND HELIUM-LIKE IONS IN ASTROPHYSICAL ENVIRONMENTS." UKnowledge, 2006. http://uknowledge.uky.edu/gradschool_diss/430.
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A complete model of helium-like line and continuum emission in astrophysical plasmas has been incorporated into the plasma simulation code CLOUDY. All elements between He and Zn are treated, any number of levels can be considered, and a full treatment of radiative and collisional processes is included. This includes photoionization from all levels, line transfer including continuum pumping and destruction by background opacities, scattering, and collisional processes. The model is calculated self-consistently with the ionization and thermal structure of the surrounding nebula. The result is a complete line and continuum spectrum of the nebula. The model helium atom is described and compared to a second standalone helium atom in the low-density case. The effects of the mixing of singlet and triplet terms, the truncation of the physical system, and the convergence of the predicted line intensities as a function of the number of quantum levels explicitly included are considered. New Case-B emissivities are calculated for the helium atom at a range of electron temperatures and densities common in planetary nebulae. Observations of the Orion Nebula are analyzed and compared with predictions of the model helium atom. Observations of low-metallicity extragalactic objects by other authors are analyzed. The methods and details of the model helium-like ions are described. The standard X-ray diagnostics of these ions are revisited and augmented with semi-analytical and numerical calculations of ultraviolet line diagnostics. Finally, a new interface between CLOUDY and the X-ray spectral analysis tool XSPEC is discussed.
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Batey, G. J. "Thermal measurements in helium." Thesis, University of Nottingham, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.376489.
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Steer, A. P. "Liquid helium acoustic microscope." Thesis, University of Exeter, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.381340.
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Turner, Robert Paul. "Pumping helium 3 in a helium mixture with a magnetic field : thermal boundary resistance between liquid helium mixtures and silver sinters." Thesis, Lancaster University, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.242945.
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Petluri, Raghuram. "Angular dependent interaction of metastable helium molecules on the surfaces of helium nanodroplets /." View online ; access limited to URI, 2005. http://0-wwwlib.umi.com.helin.uri.edu/dissertations/dlnow/3186917.
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Gspann, J. [Verfasser], and R. [Verfasser] Ries. "Wechselwirkung eines Caesiumatomstrahls mit Helium-3- und Helium-4-Clusterstrahlen / J. Gspann, R. Ries." Karlsruhe : KIT-Bibliothek, 2014. http://d-nb.info/1196577234/34.
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Mendoza, Luna Luis Guillermo. "Free and hindered-rotation of helium excimers in liquid helium via a bulk experiment." Thesis, University of Leicester, 2015. http://hdl.handle.net/2381/35982.
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Superfluidity is a many-body quantum effect observed for the first time in liquid helium. In the context of modern nanoscience, a natural question is whether superfluidity exists at the nanoscale and if so, under what conditions it occurs. Superfluidity can be probed by means of a torsional pendulum immersed in liquid helium: a decrease in the moment of inertia of the pendulum was observed during the superfluid transition. By replacing the torsional pendulum with a carbonyl sulfide molecule embedded in helium droplets, Grebenev and coworkers explored superfluidity at the nanoscale. They established that 60 4He atoms is the threshold to observe superfluidity. The thermodynamic conditions necessary for this transition could not be ascertained in Grebenev's work since in the helium droplet technique the transition into the superfluid state is impossible to control. One possible way around this experimental limitation is to perform a bulk experiment and embed short-lived helium excimers because all other molecules would freeze. The excimers are in Rydberg states and emit fluorescence sensitive to their environment. In this work, helium excimers have been produced in bulk liquid helium using corona discharges. A wide range of the phase diagram of helium has been probed via fluorescence spectroscopy of Rydberg excimers for the first time: molecular transitions in gaseous, supercritical, vapor and normal liquid phases have been studied systematically. Depending on the thermodynamic conditions, sharp as well as broadened spectra have been observed. The linewidths and lineshifts of a transition of interest have been interpreted on the basis of a model that considers emission from two kinds of excimer: on the one hand, excimers embedded in voids and fully solvated in liquid helium exhibiting hindered rotation, and on the other hand, excimers residing in larger gas pockets within the liquid helium, exhibiting free rotation. The relative contributions of each species of excimer have been estimated in a ratio of approximately 1:5. Hindered transitions were identified for pressures and temperatures in the vapor phase, before helium liquefies. These points in the phase diagram show the formation of clusters between excimers and ground-state helium atoms, indicating that the He_2 -He interaction is stronger than that of He-He.
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Zhu, Jinzhen [Verfasser], and Armin [Akademischer Betreuer] Scrinzi. "Photoionization of the helium hydride ions and helium atoms / Jinzhen Zhu ; Betreuer: Armin Scrinzi." München : Universitätsbibliothek der Ludwig-Maximilians-Universität, 2020. http://d-nb.info/1223849813/34.
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Claas, Patrick. "Femtosekundenspektroskopie an alkalidotierten Helium-Nanotröpfchen." [S.l.] : [s.n.], 2006. http://deposit.ddb.de/cgi-bin/dokserv?idn=978886488.
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Wendler, Martin. "Helium- und Sauerstoffdiffusion in Glasschmelzen /." Clausthal-Zellerfeld : Papierflieger, 1996. http://bvbr.bib-bvb.de:8991/F?func=service&doc_library=BVB01&doc_number=007293193&line_number=0001&func_code=DB_RECORDS&service_type=MEDIA.
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Matthias, John Robert. "Quantum evaporation from superfluid helium." Thesis, University of Exeter, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.390167.
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Klingner, Nico. "Ionenstrahlanalytik im Helium-Ionen-Mikroskop." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2017. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-220036.
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Die vorliegende Arbeit beschreibt die Implementierung ionenstrahlanalytischer Methoden zur Charakterisierung der Probenzusammensetzung in einem Helium-Ionen-Mikroskop mit einem auf unter einen Nanometer fokussierten Ionenstrahl. Zur Bildgebung wird dieser im Mikroskop über Probenoberflächen gerastert und die lokale Ausbeute an Sekundärelektronen gemessen. Obwohl sich damit ein hoher topografischer Kontrast erzeugen lässt, lassen sich weder aus der Ausbeute noch aus der Energieverteilung der Sekundärelektronen verlässliche Aussagen zur chemischen Zusammensetzung der Probe treffen. Daher wurden in dieser Arbeit verschiedene ionenstrahlinduzierte Sekundärteilchen hinsichtlich ihrer Eignung für die Elementanalytik im Helium-Ionen-Mikroskop verglichen. Zur Evaluation standen der Informationsgehalt der Teilchen, deren Analysierbarkeit sowie deren verwertbare Ausbeute. Die Spektrometrie rückgestreuter Teilchen sowie die Sekundärionen-Massenspektrometrie wurden dabei als die geeignetsten Methoden identifiziert und im Detail untersucht. Gegenstand der Untersuchung waren physikalische Limitierungen und Nachweisgrenzen der Methoden sowie deren Eignung zum Einbau in ein Helium-Ionen-Mikroskop. Dazu wurden verschiedene Konzepte von Spektrometern evaluiert, erprobt und hinsichtlich ihrer Effizienz, Energieauflösung und Umsetzbarkeit im Mikroskop bewertet. Die Flugzeitspektrometrie durch Pulsen des primären Ionenstrahls konnte als die geeignetste Technik identifiziert werden und wurde erfolgreich in einem Helium-Ionen-Mikroskop implementiert. Der Messaufbau, die Signal- und Datenverarbeitung sowie vergleichende Simulationen werden detailliert beschrieben. Das Spektrometer wurde weiterhin ausführlich hinsichtlich Zeit-, Energie- und Massenauflösung charakterisiert. Es werden ortsaufgelöste Rückstreuspektren vorgestellt und damit erstmalig die Möglichkeit zur Ionenstrahlanalytik im Helium-Ionen-Mikroskop auf einer Größenskala von ≤ 60 nm aufgezeigt. Das Pulsen des primären Ionenstrahls erlaubt es zudem, die Technik der Sekundärionen-Massenspektrometrie anzuwenden. Diese Methode bietet Informationen zur molekularen Probenzusammensetzung und erreicht für einige Elemente niedrigere Nachweisgrenzen als die Rückstreuspektrometrie. Damit konnten erstmalig im Helium-Ionen-Mikroskop gemessene Sekundärionen-Massenspektren sowie die ortsaufgelöste Elementanalyse durch spektrometrierte Sekundärionen demonstriert werden. Die Ergebnisse dieser Arbeit sind in der Fachzeitschrift Ultramicroscopy Band 162 (2016) S. 91–97 veröffentlicht. Ab Oktober 2016 werden diese auch in Form eines Buchkapitels in dem Buch „Helium Ion Microscopy“, Springer Verlag Heidelberg zur Verfügung stehenThe present work describes the implementation of ion beam analysis methods in a helium-ion-microscope for the determination of sample compositions with a focused ion beam of < 1 nm size. Imaging in the microscope is realized by scanning the focused ion beam over the sample surface while measuring the local secondary electron yield. Although this procedure leads to a high topographical contrast, neither the yield nor the energy distribution of the secondary electrons deliver reliable information on the chemical composition of the sample. For this purpose, in this work different ion beam induced secondary particles were compared with respect to their suitability for the analysis of the chemical composition in the helium-ion-microscope. In particular the information content of the particles, their analysability and their yield were evaluated. As a result, the spectrometry of backscattered particles and the mass spectrometry of sputtered secondary ions were identified as the most promising methods and regarded in detail. The investigation focused on physical limitations and detection limits of the methods as well as their implementability into a helium-ion-microscope. Therefor various concepts of spectrometers were evaluated, tested and validated in terms of their efficiency, energy resolution and practicability in the microscope. Time-of-flight spectrometry by pulsing the primary ion beam could be identified as the most suitable technique and has been successfully implemented in a helium-ion-microscope. The measurement setup, signal processing and data handling as well as comparative simulations are described in detail. Further the spectrometer was characterized explicitly in terms of time, energy and mass resolution. Spatially resolved backscattering spectra will be shown demonstrating the feasibility of performing ion beam analysis in a helium-ion-microscope for the first time on a size scale of ≤ 60 nm. By pulsing the primary ion beam the technique of secondary ion mass spectrometry becomes automatically accessible. This method provides information on the molecular composition of samples and can reach higher detection limits than those from backscattering spectrometry. For the first time, in a helium-ion-microscope measured secondary ion mass spectra and spatially resolved elemental analysis by spectrometry of secondary ions, could be demonstrated. The results of this work are published 2016 in the scientific journal Ultramicroscopy, volume 162 on pages 91 to 971. In October 2016 there will be another publication as a book chapter in „Helium Ion Microscopy“ (publisher: Springer Verlag Heidelberg)
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Haynes, S. R. "Condensed phases of confined helium." Thesis, University of Sussex, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.372719.
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Rorai, Cecilia. "Vortex reconnection in superfluid helium." Doctoral thesis, Università degli studi di Trieste, 2012. http://hdl.handle.net/10077/7868.
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2010/2011La presente tesi concerne la modellizzazione e simulazione numerica, attraverso l'equazione di Gross-Pitaevskii (chiamata anche equazione di Schroedinger non lineare), della dinamica dei vortici quantistici nell'elio superfluido e in particolare del fenomeno della riconnessione. La riconnessione si verifica qualora due vortici approssimativamente antiparalleli, si intersecano e si scambiano le estremità. Questo fenomeno è stato osservato sperimentalmente e risulta essere una caratteristica essenziale della turbolenza quantistica.
XXIII Ciclo
1983
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Gaiser, Christof. "Properties of helium and gas thermometry." Aachen Shaker, 2008. http://d-nb.info/990735125/04.
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Gerlach, Stefan. "Dipol-Dipol-Wechselwirkungen ultrakalter Helium-Rydbergatome." [S.l.] : [s.n.], 2006. http://deposit.ddb.de/cgi-bin/dokserv?idn=981536980.
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Bussiahn, René. "Laserabsorptionsspektroskopische Untersuchungen in Helium-Xenon-Glimmentladungen." [S.l.] : [s.n.], 2006. http://deposit.ddb.de/cgi-bin/dokserv?idn=98444811X.
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Guilleumas, Montserrat. "Nucleation and cavitation in liquid helium." Doctoral thesis, Universitat de Barcelona, 1995. http://hdl.handle.net/10803/667593.
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Las transiciones de fase no siempre ocurren bajo condiciones de equilibrio. Un fluido puede ser conducido a un estado metastable. A pesar de ser internamente estable, existe otra configuración con un potencial termodinámico menor, por tanto energéticamente más favorable y a la cual tenderá el sistema. Esta transición está bloqueada por una barrera termodinámica que puede ser superada con resultado de la formación y crecimiento de pequeños nucleos de la nueva fase estable en la fase metastable. Este proceso se llama nucleación (formación de gotas en un vapor sub-enfriado) o cavitacion (burbujas en un líquido sobre-calentado).
En esta tesis hemos estudiado los fenómenos de cavitación y nucleación en helio dentro del marco de la teoria del funcional de la densidad. Primero hemos estudiado la activación térmica en 3He y 4He puros y en las mezclas 3He-4He, estimando la presión a partir de la cual tiene lugar la transición de fase. Para los sistemas puros hemos estudiado también la activación cuántica a muy bajas temperaturas, estimando la temperatura de transición entre ambos regímenes.
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Cai, Zhiming. "A study of global helium resources." Thesis, University of Cambridge, 2010. https://www.repository.cam.ac.uk/handle/1810/252193.
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Helium investment is fundamentally driven by the expectations of future helium demand of both oil & gas companies and the major industrial gas companies. When they conduct helium business, the relationship between the two groups of companies is governed by long-term contracts with take-or-pay clauses. System dynamics has been applied as a main research methodology, complemented by critical review, time series data analysis, interviews and private communications with helium industry experts and data collection. A system dynamics model of helium resources and the market has been created on the basis of the fundamental principles of economic theory, to examine the likely dynamic behaviour of the future helium market (i.e. the path of prices and resources extraction rate). The following issues have been thoroughly investigated: the nature of helium resources, supply chain and production technologies; helium market structure and production policies of competing firms; and the dynamics of the interaction among demand, supply, Government policy and technology. Monte Carlo simulation was conducted to examine the main uncertainties in connection with the dynamics of the future helium market: future supply from natural gas and the length of time that supply will be available; costs of obtaining helium from lean sources, including the atmosphere; future demand and how sensitive the demand will be to unprecedented prices. Key findings: (1) helium depletion is not imminent, and there is at least 30-50 years to allow users to develop new technologies to avoid or lessen their dependency on helium molecules; panic about helium depletion is unwarranted; (2) the periodical occurrences of helium shortages is fundamentally dependent on the investment policies of producers and their expectations of future helium demand, the lead time of investment, and realisation of demand; any helium supply shortage is not necessarily an indication of the imminence of helium depletion; (3) helium production as a by-product of the cryogenic separation of oxygen and nitrogen from air could be a potential solution for particular types of helium user when the cost of extraction from natural gas resources rises to a point at which backstop resources (e.g. helium from the atmosphere) comes into play; (4) increase in inventory in trans-fill facilities could be another way to smooth out the irregularities of supply and demand balance, especially after the BLM reserve, which has served as a crude helium inventory, is depleted; (5) potential big users of helium, such as fusion technology, need to take sustained action to reduce the potential demand for helium.
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Paetkau, Mark Jeffrey. "Helium mixtures in 87% porous aerogel." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/nq29088.pdf.
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Huang, Jiachang. "A helium high-temperature drift chamber." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape9/PQDD_0013/NQ38900.pdf.
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Miller, Jonathan I. "The design of robust helium aerostats /." Thesis, McGill University, 2005. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=99000.
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Tethered helium aerostats are receiving renewed attention in the scientific and surveillance communities. However, conventional aerostats cannot consistently survive high winds. The goal of this research was to design an aerostat that could be deployed for very long periods, thus reducing operating costs and interruptions in data acquisition. Existing designs and fabrication techniques were first reviewed and replicated in the construction of a 2.5 m diameter spherical aerostat. The constructed balloon was then flown outdoors to observe its operational qualities. A low-cost data acquisition system was assembled to characterize the balloon's dynamics. The results were used to inform a Finite Element Analysis model evaluating the critical stresses in a 10.15 m diameter balloon's envelope and its tendency to "dimple" when subjected to high wind speeds. A second model was created to appraise the performance of an aerostat with a partially hard shell, made of carbon fiber, in highly loaded areas.
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Lee, Richard Albert Marlor. "A cosmological experiment in liquid helium." Thesis, Lancaster University, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.239061.
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Buckland, J. R. "New methods in helium atom scattering." Thesis, University of Cambridge, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.597056.
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This thesis presents developments in both the experimental techniques and in the theoretical understanding of the helium atom scattering. These contributions open the way for more effective experimental investigations and more quantitative analysis of helium - surface scattering data. The introduction starts with an outline of the contents of the thesis, followed by a description of the diffraction geometry of the Cambridge helium scattering apparatus and a method of measuring diffraction intensities at constant incident condition. The next two chapters describe two experimental improvements in the field of helium scattering. In chapter 2 the characterisation of a molecular beam source shows that high performance (velocity spread < 1%) can be achieved with a simple and inexpensive design. Chapter 3 describes the development, testing and characterisation of a 2-dimensional multichannel scalar data acquisition device for use with two experimental methods under development, namely an imaging helium detector and time-of-flight measurements using a double chopper gate helium beam. Chapter 4 describes the investigation of helium scattering from a lattice gas of Pb adsorbed on the Cu(001) surface. Experimental helium diffraction intensities for the Pb/Cu(001) system were previously accounted for by invoking an adsorbate - induced corrugation in the Cu(001) substrate. In this work, a more detailed analysis shows that a substrate corrugation is not necessary to reproduce the experimental results. The investigation includes a review of a range of approximations and methods available for calculating scattered intensities within the hard wall approximation of the helium-surface potential. The remainder of the thesis presents a detailed experimental and theoretical investigation of elastic helium scattering from the Si(111)-(1x1)H surface.
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Lusher, C. P. "Nuclear magnetic relaxation in gaseous helium." Thesis, University of Sussex, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.356513.
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Longitudinal relaxation times T1 have been measured in 'He gas, using pulsed NMR, for number densities between 3x 1023 and 6x 102' spins/m' and temperatures between 0.6 and 15K. Relaxation takes place on or near the walls of the pyrex sample cells and measurements of Tl give information about the surface phases. A low temperature amplifier containing GaAs FET devices was developed to improve the spectrometer sensitivity. An amplifier noise temperature of 0.9 ± 0.5K was obtained at 1.16 MHz and an NMR signal was observed at 4.2K with the sensitivity being mainly limited by Johnson noise in the receiver coil. Baking the pyrex cells under vacuum and discharge cleaning the walls before sealing in the sample gas were found to increase the bulk gas Tl's by two or three orders of magnitude. A cryogenic wall coating of solid molecular hydrogen was found to delay the formation of a 'He monolayer on cooling and T, measurements were consistent with a binding energy of %, 13K for a 3He atom to a hydrogen surface. Once a 3He monolayer has formed the dipolar interaction between adsorbed spins is thought to be the dominant source of relaxation in the sealed cells. The presence of "He generally causes T, to rise on cooling below 2K due to preferential adsorption of "He at the surface. However, 'He atoms which dissolve in quasiparticle states in the superfluid helium film can be an extra source of relaxation. In the dirty cells relaxation probably takes place in quasiparticle states at the free surface of the saturated helium film, which are bound with an energy of 5.1 t 0.3K. In a cleaned, sealed cell a T, of ti 8 hours was measured at 7.7 MHz and 0.8K. In this case relaxation is probably occurring 2 or 3 helium layers away from the helium-hydrogen interface
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Marchalant, Pascale J. "(e, 2e) excitation-ionization of helium." Thesis, Queen's University Belfast, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.337019.
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Boatwright, Adrian Lional. "Molecular behaviour in superfluid helium clusters." Thesis, University of Nottingham, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.478961.
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Klier, Jurgen. "Liquid helium on weak binding substrates." Thesis, University of Exeter, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.337745.
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Christie, S. "Contrast in the helium acoustic microscope." Thesis, University of Exeter, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.381299.
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Tanner, Marc D. (Marc David) 1974. "Helium breath : an updated 6.111 curriculum." Thesis, Massachusetts Institute of Technology, 1998. http://hdl.handle.net/1721.1/47585.
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Thesis (S.B. and M.Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1998.Includes bibliographical references (p. 85).
by Marc D. Tanner.
S.B.and M.Eng.
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Hofmans, Marlous. "Experimental characterization of helium plasma jets." Thesis, Institut polytechnique de Paris, 2020. http://www.theses.fr/2020IPPAX062.
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Cette thèse porte sur l’étude d’un jet de plasma d'hélium à pression atmosphérique alimenté par des impulsions positives unipolaires à une fréquence de l’ordre du kHz. Des expériences sont effectuées pour caractériser la dynamique de propagation, la structure de l'écoulement et la température dans un jet en expansion libre, ainsi que l'influence d'une cible métallique sur le plasma.La spectroscopie à polarisation Stark indique un champ électrique axial d'environ 10 kV/cm dans le capillaire du jet et une augmentation jusqu'à 20 kV/cm dans le panache, qui est constante pour différentes amplitudes et durées de l'impulsion de tension appliquée. La diffusion Thomson et la diffusion Raman rotationnelle sont utilisées pour déterminer la densité électronique et la température électronique, à différentes positions axiales et radiales, ainsi que la température du gaz et la densité de N2 et O2 de l'air environnant qui sont mélangés dans le flux d’hélium.La comparaison quantitative de ces résultats expérimentaux avec les résultats d'un modèle fluide 2D montre une bonne concordance et permet une meilleure compréhension des résultats obtenus, à savoir que le champ électrique dans le front d'ionisation augmente avec la quantité d’air intégré au flux d’hélium au lond de la propagation. L'imagerie Schlieren révèle l'apparition de structures turbulentes à des débits élevés et lors de l'application des impulsions de tension. On constate que la température du gaz, mesurée par une sonde de température, augmente d'environ 12 C quand le plasma est allumé et d'environ 25 C lorsqu'une cible métallique est placée devant le jetThis thesis studies an atmospheric pressure helium plasma jet that is powered by positive, unipolar pulses at a kHz frequency. Experiments are performed that focus on the propagation dynamics, flow structure and temperature in a freely expanding jet, as well as the influence of a metallic target on the plasma.Stark polarization spectroscopy yields an axial electric field of around 10 kV/cm in the capillary of the jet and an increase up to 20 kV/cm in the plume, which is constant for different amplitudes and durations of the applied voltage pulse. Thomson and rotational Raman scattering are used to determine the electron density and electron temperature, at different axial and radial positions, as well as the gas temperature and the density of N2 and O2 that are mixed into the helium from the surrounding air.Quantitative comparison of these experimental results with results from a 2D fluid model show a good agreement and allow for a better understanding of the obtained results, namely that the electric field in the ionization front depends linearly on the flow composition at that location. Schlieren imaging shows the onset of turbulent structures at high applied flow rates and at the application of the voltage pulses. The gas temperature, as measured by a temperature probe, is found to increase by around 12 C when the plasma is ignited and by around 25 C when a metallic target is placed in front of the jet
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Masuhara, Naoto. "Spin waves in liquid helium-3 /." The Ohio State University, 1985. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487259580261871.
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Agarwal, Shradha. "Helium mobility in advanced nuclear ceramics." Thesis, Paris 11, 2014. http://www.theses.fr/2014PA112197/document.
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Cette thèse a pour objectif d’apporter des informations quantitatives sur la mobilité de l’hélium dans des céramiques nucléaires avancées comme TiC, TiN et ZrC, soumises à des traitements thermiques ou bien en présence de dommages d’irradiation. L’approche expérimentale développée au cours de ce travail est basée sur l’implantation ionique d’ions d’hélium-3 de 3 MeV en profondeur dans les trois matériaux précédemment cités et sur la mesure du profil de concentration en profondeur de l’isotope 3He au moyen d’une réaction nucléaire spécifique induite par des deutérons, 3He(d, p0)4He. La microscopie électronique à transmission et la spectrométrie Raman sont couplées à l’analyse par réaction nucléaire.Parmi les principaux résultats obtenus :- aucun relâchement d’hélium n’est observé à température ambiante pour les trois composés. Les valeurs d’énergie d’activation associée au relâchement d’hélium après un recuit thermique dans l’intervalle 1100 – 1600°C sont comprises entre 0,77 et 1,2 eV et semblent étroitement liées à la microstructure initiale du composé (stoéchiométrie et taille de grains). La capacité de rétention de l’hélium-3 dans des carbures ou nitrures de métaux de transition soumis à des traitements thermiques en conditions contrôlées croît dans l’ordre ZrC < TiC < TiN.- la formation de blisters n’et observée qu’à la surface de ZrC.- les profils d’implantation d’hélium présentent deux composantes pour les trois matériaux, l’une située au voisinage de la fin de parcours des ions et la seconde plus proche de la surface. Cette dernière résulte probablement du piégeage d’atomes d’hélium par les lacunes natives présentes.- les valeurs obtenues pour le coefficient apparent de diffusion de l’hélium varient dans l’intervalle 3,58E-19 – 5,296E-18 m^2s^-1 pour TiN et 4,20E-18 – 2,59E-17 m^2s^-1 pour TiC.Les valeurs correspondantes obtenues pour l’énergie d’activation sont respectivement de 2,50 eV pour TiC et de 1,05 eV pour TiN. Le mécanisme impliqué repose sur une dissociation des amas atomes d’hélium – lacunes au voisinage de la fin de parcours des ions. Plus en surface, la diffusion est plutôt du type substitutionnel.- l’observation au MET de sections transverses de TiN préparées par la technique FIB révèlent la présence de bulles d’hélium dès recuit à 1100°C et montrent la croissance des bulles avec la température. L’énergie d’activation de croissance des bulles a été estimée à 0,38 eV. A partir de 1400°C, cette croissance résulte vraisemblablement de l’absorption de lacunes par les amas.- la pression interne des bulles a été calculée à l’aide du modèle de Trinkaus, et nous avons montré qu’à partir de 1500°C, cette pression tendait à s’approcher de la valeur du module de cisaillement de TiN (240 GPa) et qu’elle atteignait la pression d’équilibre de 2 GPa à 1600°C.- à 1100°C, il semble que la densité des bulles présentes dans TiN varie linéairement avec la fluence d’implantation. A 1500°C, la taille des bulles est d’autant plus grande que la fluence est faible.- pour ZrC, l’effet de la fluence sur la mobilité de l’hélium est comparable à celui observé pour TiN. A la plus basse fluence, le relâchement d’hélium est très faible. Il croît avec la température de recuit et avec la fluence d’implantation.- la pré-Irradiation des trois composés par des auto-Ions avant implantation d’hélium provoque une augmentation de la dureté au moins =jusqu’à une dose de 27 dpa. Une très faible augmentation du paramètre de maille est alors détectée (≤ 0.5%).- dans le cas de ces matériaux non amorphisables sous irradiation aux ions, le recuit par perte d’énergie électronique ou bien le pré-Endommagement balistique ne jouent a priori aucun rôle sur la mobilité de l’hélium, étudiée sous l’angle d’une activation thermiqueWhile the current second and third generation nuclear plant designs provides an economically, technically, and publicly acceptable electricity supply in many markets, further advances in nuclear energy system design can broaden the opportunities for the use of nuclear energy. The fourth generation of nuclear reactors is under development. These new reactors are designed with the following objective in mind: sustainability, safety and reliability, economics, proliferation resistance. Out of six Generation IV systems namely, Gas-Cooled Fast Reactor (GFR), Lead-Cooled fast reactor (LFR), Molten Salt Reactor (MSR), Sodium-Cooled Fast Reactor (SFR), Supercritical-Water-Cooled Reactor (SCWR), Very-High-Temperature Reactor (VHTR), this work is dedicated to identify specific fuel type that is compatible with gas-Cooled fast reactor (GFR) in-Core service conditions and could be extended to diagnose potential cladding material for SFR. The French strategy is mainly oriented towards the development of sodium-Cooled fast reactors (SFR) and very slightly focused on GFR. This dissertation is focused on the study of transition metal ceramics which are candidates for fuel coatings in GFR and have been considered as potential cladding materials for SFR. The specific fuel type in GFR should consists of spherical fuel particle made up of UC or UN, surrounded by a ceramic coating which provides structural integrity and containment of fission products. The most promising candidates for ceramic coatings are ZrN, ZrC, TiN, TiC & SiC due to a combination of neutronic performance, thermal properties, chemical behavior, crystal structure, and physical properties. It is obvious that these ceramics would be exposed to energetic fission products from fuel such as heavy ions and neutrons. These high-Energy neutron will knock the atoms in the surrounding materials and can induce (n, α) reactions, thus producing high concentration of helium atoms during and after reactor operation. The helium atoms produced are energetic and can easily penetrate into the surrounding material. Helium atoms are considered to be highly insoluble in previously studied structural nuclear materials. The accumulation of helium into solid matrix, can lead to the formation of bubbles, cavity, swelling, embrittlement etc. Helium can strongly induce grain boundary cavitation that can produce formation of inter-Granular channels, which may serve as pathways for release of radioactive elements to the environment or lead to grain-Boundary weakening and de-Cohesion. Particularly in ceramics, large quantities of helium can also lead to dimensional changes and cracks due to over-Pressurized helium bubbles. Therefore, study of helium behavior in advanced nuclear ceramics under high operating temperatures and extreme radiation conditions predicted for GFRs is viewed as crucial. In this thesis, ion-Implantation technique and material characterization techniques are used to study diffusion of helium in transition metal ceramics under thermal and extreme irradiation environments. Our main aim during this thesis is: 1) To calculate diffusion and migration energies of helium under different experimental conditions by applying theoretical models on experimental data.2) To investigate the role of microstructure such as grain boundaries, native vacancies and porosity on helium accumulation and its evolution after helium accumulation.3) To know the role of helium introduction conditions on helium diffusion. 4) To establish and validate an approach to calculate pressure built by helium gas inside the bubbles and to verify if the pressure approaches mechanical stability limit
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Liu, Shikang. "Spin noise spectroscopy in metatable helium." Electronic Thesis or Diss., université Paris-Saclay, 2023. http://www.theses.fr/2023UPASP051.
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Cette thèse porte principalement sur la spectroscopie de bruit de spin de l'hélium métastable.Nous rapportons pour la première fois dans cette thèse la mesure du bruit de spin spontané d'un ensemble d'atomes d'hélium métastable en utilisant la spectroscopie de bruit de spin non invasive.Nous utilisons un laser hors résonance pour étudier les fluctuations aléatoires des sous-niveaux Zeeman du niveau métastable de l'hélium sous un champ magnétique relativement faible d'environ 1 Gauss. De plus, nous examinons les changements dans le spectre lorsque la sonde s'approche de la résonance.Nous étudions les deux principaux types de bruit de polarisation de la sonde, à savoir le bruit de rotation de Faraday et le bruit d'ellipticité. Pour reproduire qualitativement et quantitativement le signal de bruit de spin expérimental, nous construisons un modèle de simulation qui fonctionne bien même près de la résonance.Après l'étude de la transition la plus simple de l'hélium métastable, nous étudions la spectroscopie de bruit de spin aux transitions de l'hélium métastable avec des structures plus compliquées.Nos résultats de simulation sont cohérents avec les résultats expérimentaux, qui sont distincts de ceux obtenus en utilisant la structure de niveau la plus simple. Pour expliquer les caractéristiques du SNS près des différentes transitions, nous avons développé un modèle théorique complet basé sur le modèle d'états de superposition.Nous avons ensuite étudié la corrélation entre le bruit de rotation de Faraday et le bruit d'ellipticité. En utilisant les huit modes de bruit du spin-1, nous sommes capables d'expliquer les corrélations dans différentes conditions. De plus, nous avons étudié l'effet du bruit du champ magnétique sur le modèle SNS. On a constaté que le bruit du champ magnétique altérait le spectre de bruit, et la théorie des huit modes de bruit est capable d'expliquer correctement ce phénomène.Ce travail de thèse sert principalement de preuve de principe. La structure de niveaux simple de l'hélium métastable a fourni un modèle idéal pour étudier le phénomène de spectroscopie de bruit de spin dans les systèmes de spin-1. Ces résultats offrent une nouvelle perspective pour comprendre le SNS et la caractérisation des systèmes de spin-1, ce qui peut aider à poursuivre les recherches dans ce domaineThis PhD thesis mainly addresses the spin noise spectroscopy of metastable helium.We report for the first time the measurement of spontaneous spin noise of metastable helium atom ensemble using non-invasive spin noise spectroscopy.We utilize an off-resonant laser to investigate the random fluctuations of the Zeeman states of the ground level of metastable helium with a mild magnetic field of approximately 1 Gauss. Moreover, we examine the changes in the spectral pattern when the probe approaches the resonance.We investigate the two main types of polarization noise of the probe, namely Faraday rotation noise and ellipticity noise. To replicate the experimental spin noise signal qualitatively and quantitatively, we construct a simulation model that performs well even near resonance.After the investigation of simpler level structure of metastable helium transition line, we extend spin noise spectroscopy to the transition lines with more complicated structures.Our simulation results are consistent with the experimental findings, which are distinct from those obtained using the simpler level structure. To explain the SNS pattern's characteristics near different transition lines, we have developed a comprehensive theoretical model based on the superposition states theory.We then investigate the correlation between Faraday rotation noise and ellipticity noise. Using the eight noise modes of spin-1, we are able to explain the correlation under different conditions. Additionally, we study the effect of magnetic field noise on the SNS pattern. The magnetic field noise is found to alter the noise spectra pattern, and the eight noise modes theory is able to well explain this phenomenon well.This PhD work mainly serves as proof of principle. The simple level structure of metastable helium provids an ideal model to study the phenomenon of spin noise spectroscopy in spin-1 systems. These findings provide a new perspective to understand SNS and the characterization of spin-1 systems, which can aid further research in this area
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Hoendervanger, Lynn. "A New Metastable Helium Machine : An Investigation into the Attributes of Trapping, Cooling and Detecting Metastable Helium." Thesis, Palaiseau, Institut d'optique théorique et appliquée, 2014. http://www.theses.fr/2014IOTA0006/document.
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Cette thèse décrit le travail accompli au cours des trois dernières années sur la nouvelle expérience d’Hélium métastable de l'Institut d'Optique à Palaiseau.Le premier chapitre décrit une étude visant à améliorer à la fois l'efficacité et la précision du système de détection par galettes à micro-canaux (MCP). Nous avons fait des mesures avec des galettes recouvertes d'une couche d'or sur la face avant, obtenant un accroissement de l'efficacité de détection mais également une réduction de la précision. L'ajout d'une tension intermédiaires entre les deux galettes empilées a au contraire améliorer à la fois l'efficacité et la précision des MCP, en l’absence d’une couche d’or.Le deuxième chapitre est consacré à la construction de l'appareil expérimental pour le refroidissement et le piégeage d’atomes. L’excitation de l'état fondamental de l’Hélium à l'état métastable est décrite, ainsi que la collimation et le refroidissement ultérieur par Zeeman lent du faisceau atomique chaud résultant. Le faisceau ralenti est alors capturé dans un piège magnéto-optique (PMO), dans lequel nous avons capturé 8x108 atomes.Dans le troisième chapitre une étude originale du refroidissement Doppler tridimensionnel dans un PMO et une mélasse désaccordée vers le rouge de la transition atomique est discutée. L’atome d’Hélium métastable est unique et ses propriétés ont permis une telle étude. En effet, les faibles densités atomiques impliquent qu’il n'y a pas de diffusion multiple de photons d’une part, et la faible masse et la faible largeur de la transition 23S1 -> 23P2 rend inefficace les processus de refroidissement sous la limite Doppler. Ces conditions nous ont permis d’observer pour la première fois à trois dimensions un gaz refroidit dans le régime Doppler.Le quatrième chapitre présente une étude sur les collisions dans un piège magnéto-optique d’Hélium métastable. Les collisions Penning induites par la lumière, en particulier à des intensités élevées et à des fréquences proches de la fréquence de transition, sont responsables de pertes élevées d’atomes piégés. Nous mesurons le coefficient de taux associé à ces pertes, Ksp = 2,8 ± 0,4 x 10-7cm3/ sThis thesis describes the work done over the past three and a half years on the new metastable helium experiment at the Institut d'Optique in Palaiseau. In the first chapter it describes a study to improve both the efficiency and the accuracy of the Microchannel Plate (MCP) detection system. We have experimented with adding a gold layer on the top of the input plate, something that we have found increases the efficiency but also decreases the accuracy. The addition of a voltage between the two stacked plates has been shown to both raise the efficiency and improve the accuracy in non-coated MCPs.The second chapter is devoted to the construction of the experimental apparatus. Here the excitation of ground state helium to its metastable state is described, as well as the subsequent collimation and cooling by Zeeman slower of the resulting hot atomic beam. The slowed beam is then captured in a Magneto-Optical Trap, in which we have captured 8x108 atoms.In the third chapter an original study on three-dimensional Doppler cooling in a red-detuned molasses and in the Magneto-Optical trap is presented. The metastable helium system is unique as there is no multiple scattering of photons and there are no sub-Doppler effects. This allows for a never before seen experimental realisation of pure Doppler cooling theory. The fourth chapter describes a study on collisions in a magneto-optical trap of metastable helium. Light-induced Penning collisions are responsible for high trap losses at high intensities and at frequencies close to the transition frequency. We measure the constant rate coefficient to Ksp = 2.8 ± 0.4 x 10-7cm3/s
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Alahmade, Walaa. "EXPERIMENTAL INVESTIGATION AND MONTE CARLO SIMULATION OF QUASIELASTIC ELECTRON SCATTERING FROM HELIUM-3 CLUSTERS IN HELIUM-4." Kent State University / OhioLINK, 2021. http://rave.ohiolink.edu/etdc/view?acc_num=kent1619697731858548.
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Ludwig, Thorsten. "Anticrossing-Spektroskopie schnell bewegter Heliumatome nach Elektroneneinfang in 10 bis 50 keV HE+-He-Stössen." [S.l.] : [s.n.], 2005. http://deposit.ddb.de/cgi-bin/dokserv?idn=974015822.
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Schmidt, Lothar. "Effekte molekularer Symmetrien in der Elektronenemission bei langsamen He2+-He-Stössen eine kinematisch vollständige experimentelle Untersuchung /." [S.l. : s.n.], 2000. http://deposit.ddb.de/cgi-bin/dokserv?idn=961247037.
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Walter, Michael. "Photo(doppel)ionisation von Helium und einfachen Molekülen." [S.l. : s.n.], 2000. http://deposit.ddb.de/cgi-bin/dokserv?idn=961295074.
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Czasch, Achim. "Doppelt hoch angeregte Zustände von Helium partielle Wirkungsquerschnitte und Winkelverteilungen der Elektronenemission /." [S.l. : s.n.], 2004. http://deposit.ddb.de/cgi-bin/dokserv?idn=972184260.
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Christie, Megan Allison. "KERATINOCYTE AND HEPATOCYTE GROWTH PROLIFERATION AND ADHESION TO HELIUM AND HELIUM/OXYGEN ATMOSPHERIC PRESSURE PLASMA TREATED POLYETHYLENE TEREPHTHALATE." NCSU, 2005. http://www.lib.ncsu.edu/theses/available/etd-11022005-223628/.
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To improve the surface properties of biomaterials, the effects of changes in surface chemistry and morphology of polyethylene terephthalate (PET) films treated with atmospheric pressure plasma were investigated as a function of cellular growth, proliferation, and adhesion. PET films were subjected to helium and helium/oxygen gas plasmas. The contact angle of the treated films decreased due to plasma etching and possible scission indicating that the surfaces become more hydrophilic. Atomic force microscopy results had a large standard error, however the surface visually showed changes in surface micro and nanoscale roughness corresponding to treatment duration. Keratinocytes were plated on the day of plasma treatment and two and five days after plasma treatment and tested half a day, one, two, three, and six days after plating. The same methodology of plating and testing was also applied to hepatocytes. Cell growth, proliferation, and adhesion were characterized via a fluorescent probe based assay and were correlated with surface chemical and nanostructural features. Both the helium and helium/oxygen plasma-treated PET had little or no effect on cell behavior for both keratinocytes and hepatocytes. The nanoscale surface changes due to the plasma surface treatment are believed to be masked by the protein adherence in the media on the surface of the PET.
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LARAT, CHRISTIAN. "Laser lna de puissance; application au pompage optique de l'helium-3 et des melanges helium-3/helium-4." Paris 6, 1991. http://www.theses.fr/1991PA066191.
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Nous avons cherche a augmenter les taux de polarisation nucleaire de l'helium-3 obtenus par pompage optique. Dans ce but, nous avons travaille suivant deux directions: developpement d'une source laser puissante a 1083 nm et etude des conditions de pompage optique. Nous avons ainsi realise une source laser a solide (lna) excitee par lampes qui delivre une puissance de sortie elevee (5w), accordable sur toute la structure de la raie 2#3s-2#3p de l'helium avec une largeur spectrale bien adaptee au pompage optique. L'accord en frequence est obtenu par l'intermediaire de deux etalons solides thermostates. Nous avons de meme teste un nouveau materiau laser prometteur, le lma: cr, nd. Nous avons egalement etudie les caracteristiques du pompage a forte et faible puissance laser dans l'helium-3 pur et dans les melanges helium-3/helium-4. Les resultats experimentaux ont ete confrontes aux resultats numeriques d'un modele que nous avons developpe. Nous avons ainsi obtenu des polarisations nucleaires de l'helium-3 jamais encore enregistrees: superieures a 85% en pompage optique dans l'helium-3 pur et 80% dans les melanges. A faible puissance laser (1 mw), les taux de polarisation nucleaire sont plus eleves dans les melanges que dans l'helium-3 pur a pression totale donnee
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Ghosh, Ambarish. "Experiments with electron bubbles in liquid helium /." View online version; access limited to Brown University users, 2005. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&res_dat=xri:pqdiss&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&rft_dat=xri:pqdiss:3174609.
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Nissen, Joel Alan. "The Tensile Strength of Liquid Helium Four." PDXScholar, 1988. https://pdxscholar.library.pdx.edu/open_access_etds/1357.
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It is well known that most liquids exhibit a tensile strength which is much smaller in magnitude than the tensile strength predicted by homogeneous nucleation theory. This lack of agreement is usually attributed to the difficulty of preparing liquid samples free from foreign gases which act as heterogeneous nucleation sites. Liquid helium occupies a unique place among liquids for tensile strength measurements because all foreign gases are frozen out at liquid helium temperatures. Furthermore, superfluid 4He should fill all crevices on solid surfaces, eliminating the chance of heterogeneous nucleation on helium vapor pockets. Despite the quantum mechanical nature of liquid helium, Becker-Doring theory of nucleation of the vapor phase from the liquid phase should be valid down to 0.3 K in 4 He, yet previous results have been in stark disagreement with the theory. In this study, a piezoelectric transducer in the form of a hemispherical shell was used to focus high-intensity ultrasound into a small volume of 4He . The transducer was gated at its resonant frequency of 566 kHz with gate widths of less than 1 msec in order to minimize the effects of transducer heating and acoustic streaming. The onset of nucleation was detected from the absorption of acoustic energy and the scattering of laser light from microscopic bubbles. A new theory for the diffraction of light from the focal zone of a spherical converging sound wave was developed to confirm calculations of the acoustic pressure amplitude at the focus of the piezoelectric transducer, calculations which were based on the acoustic power radiated into the liquid and the nonlinear absorption of sound. The experimental results were in agreement with homogeneous nucleation theory for a nucleation rate of approximately 1015 critical size bubbles/sec-cm3. This is only the third liquid for which the theoretical tensile strength has been reached and it confirms homogeneous nucleation theory over a range three times greater than any other experiment. A noticeable decrease in the magnitude of the tensile strength was noted at temperatures near the lambda transition and a hypothesis that bubbles are being nucleated heterogeneously quantized vortices is presented.