To see the other types of publications on this topic, follow the link: Density wave.
Dissertations / Theses on the topic 'Density wave'
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the top 50 dissertations / theses for your research on the topic 'Density wave.'
Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.
You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.
Browse dissertations / theses on a wide variety of disciplines and organise your bibliography correctly.
1
Gaspar, Luis Alejandro Ladino. "CHARGE DENSITY WAVE POLARIZATION DYNAMICS." UKnowledge, 2008. http://uknowledge.uky.edu/gradschool_diss/643.
Full textAbstract:
We have studied the charge density wave (CDW) repolarization dynamics in blue bronze (K0.3MoO3) by applying symmetric bipolar square-wave voltages of different frequencies to the sample and measuring the changes in infrared transmittance, proportional to CDW strain. The frequency dependence of the electro-transmittance was fit to a modified harmonic oscillator response and the evolution of the parameters as functions of voltage, position, and temperature are discussed. We found that resonance frequencies decrease with distance from the current contacts, indicating that the resulting delays are intrinsic to the CDW with the strain effectively flowing from the contact. For a fixed position, the average relaxation time for most samples has a voltage dependence given by τ0 ∼ V −p, with 1 < p < 2. The temperature dependence of the fitting parameters shows that the dynamics are governed by both the force on the CDW and the CDW current: for a given force and position, both the relaxation and delay times are inversely proportional to the CDW current as temperature is varied. The long delay times (∼ 100 μs) for large CDW currents suggest that the strain response involves the motion of macroscopic objects, presumably CDW phase dislocation lines.
We have done frequency domain simulations to study charge-density-wave (CDW) polarization dynamics when symmetric bipolar square current pulses of different frequencies and amplitudes are applied to the sample, using parameters appropriate for NbSe3 at T = 90 K. The frequency dependence of the strain at one fixed position was fit to the same modified harmonic oscillator response and the behavior of the parameters as functions of current and position are discussed. Delay times increase nonlinearly with distance from the current contacts again, indicating that these are intrinsic to the CDWwith the strain effectively flowing from the contact. For a fixed position and high currents the relaxation time increases with decreasing current, but for low currents its behavior is strongly dependent on the distance between the current contact and the sample ends. This fact clearly shows the effect of the phase-slip process needed in the current conversion process at the contacts. The relaxation and delay times computed (∼ 1 μs) are much shorter than observed in blue bronze (> 100 μs), as expected because NbSe3 is metallic whereas K0.3MoO3 is semiconducting. While our simulated results bear a qualitative resemblance with those obtained in blue bronze, we can not make a quantitative comparison with the K0.3MoO3 results since the CDW in our simulations is current driven, whereas the electro-optic experiment was voltage driven.
Different theoretical models predict that for voltages near the threshold Von, quantities such as the dynamic phase velocity correlation length and CDW velocity vary as ξ ∼ |V/Von − 1| −ν and v ∼ |V/Von − 1|ξ with ν ∼ 1/2 and ζ = 5/6. Additionally, a weakly divergent behavior for the diffusion constant D ∼ |V/Von − 1|−2ν+ζ is expected. Motivated by these premises and the fact that no convincing experimental evidence is known, we carried out measurements of the parameters that govern the CDW repolarization dynamic for voltages near threshold. We found that for most temperatures considered the relaxation time still increases for voltages as small as 1.06Von indicating that the CDW is still in the plastic and presumably in the noncritical limit. However, at one temperature we found that the relaxation time saturates with no indication of critical behavior, giving a new upper limit to the critical regime, of |V/Von − 1| < 0.06.
2
Zheng, Liqiu. "Spin density wave phases in semiconductor superlattices." Connect to this title online, 2007. http://etd.lib.clemson.edu/documents/1202500635/.
Full text
3
Aldridge, Christopher John. "Density-wave oscillations in two-phase flows." Thesis, University of Oxford, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.260741.
Full text
4
Rai, Ram C. "ELECTRO-OPTICAL STUDIES OF CHARGE-DENSITY-WAVE MATERIALS." UKnowledge, 2004. http://uknowledge.uky.edu/gradschool_diss/427.
Full textAbstract:
A searched for narrow-band-noise (NBN) modulations of the infrared transmission in blue bronze has been performed. No modulations were observed, giving an upper limits for NBN changes in the absorption coefficient of )2000/(/3.0.andlt;.cmNBN. The implication of these results on proposed CDW properties and NBN mechanisms are discussed. An infrared microscope with a capability of doing both reflectance and transmission measurements has been integrated into the previous electro-transmission system with tunable diode lasers. Electro-optic experiments were done using the microscope for the studies of the CDW states of K0.3MoO3 (blue bronze) and orthorhombic TaS3. The electro-reflectance signal for blue bronze has been evidenced for the first time. The infrared reflectance of K0.3MoO3 varied with position when a voltage greater than the CDW depinning threshold is applied. The spatial dependence of .R/R was slightly different than for ./, in that the magnitude of .R/R decreased and, for low voltages and frequencies, the signal became inverted near the contacts. Perhaps the differences might be associated with changes in the CDW properties on the surface. For blue bronze, the electro-reflectance signal was measured to be smaller than electro-transmittance signal by one order of magnitude for light polarized transverse to the chain direction, while the electro-reflectance signal for parallel polarized light was found to be a few times smaller than for transverse polarized light. The fits of the electro-reflectance spectrum showed that the changes in background dielectric constant were ~ 0.05 % and/or oscillator strength and/or frequency shifts of the phonons were ~ 0.05 % and ~ 0.005 cm-1 in the applied electric field. We also found that parallel polarized phonons are affected by CDW strain, and these changes dominate the electro-reflectance spectrum. We have examined the electro-reflectance spectra associated with CDW current investigation for light polarized parallel to the conducting chains for signs of expected current-induced intragap states, and conclude that the density of any such states is at most a few times less than expected. We have observed a large (~1%) change in infrared reflectance of orthorhombic TaS3, when its CDW is depinned. The change is concentrated near one current contact. Assuming that the change in reflectance is proportional to the degree of CDW polarization, we have studied the dynamics of CDW repolarization through position dependent measurements of the variation of the electro-reflectance with the frequency of square wave voltages applied to the sample, and have found that the response could be characterized as a damped harmonic oscillator with a distribution of relaxation (i.e. damping) times. The average relaxation time, which increases away from the contacts, varies with applied voltage as with p ~ 3/2, but the distribution of times broadens as the voltage approaches the depinning threshold. Very low resonant frequencies (~ 1 kHz) indicate a surprisingly large amount of inertia, which is observable in the time dependence of the change in reflectance as a polarity dependent delay of ~ 100 s.
5
Dent, Zoë Claire. "ULF wave remote sensing of magnetospheric plasma density." Thesis, University of York, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.403796.
Full text
6
Ru, Nancy. "Charge density wave formation in rare-earth tritellurides /." May be available electronically:, 2008. http://proquest.umi.com/login?COPT=REJTPTU1MTUmSU5UPTAmVkVSPTI=&clientId=12498.
Full text
7
Hite, Omar. "Controlling the Charge Density Wave in VSE2 Containing Heterostructures." Thesis, University of Oregon, 2018. http://hdl.handle.net/1794/23179.
Full textAbstract:
Exploring the properties of layered materials as a function of thickness has largely
been limited to semiconducting materials as thin layers of metallic materials tend to
oxidize readily in atmosphere. This makes it challenging to further understand properties
such as superconductivity and charge density waves as a function of layer thickness that
are unique to metallic compounds. This dissertation discusses a set of materials that use
the modulated elemental reactants technique to isolate 1 to 3 layers of VSe2 in a
superlattice in order to understand the role of adjacent layers and VSe2 thickness on the
charge density wave in VSe2.
The modulated elemental reactants technique was performed on a custom built
physical vapor deposition to prepare designed precursors that upon annealing will self
assemble into the desired heterostructure. First, a series of (PbSe)1+δ(VSe2)n for n = 1 – 3
were synthesized to explore if the charge density wave enhancement in the isovalent
(SnSe)1.15VSe2 was unique to this particular heterostructure. Electrical resistivity
measurements show a large change in resistivity compared to room temperature
resistivity for the n = 1 heterostructure. The overall change in resistivity was larger than
what was observed in the analogous SnSe heterostructure.
v
A second study was conducted on (BiSe)1+δVSe2 to further understand the effect
of charge transfer on the charge density wave of VSe2. It was reported that BiSe forms a
distorted rocksalt layer with antiphase boundaries. The resulting electrical resistivity
showed a severely dampened charge density wave when compared to both analogous
SnSe and PbSe containing heterostructures but was similar to bulk.
Finally, (SnSe2)1+δVSe2 was prepared to further isolate the VSe2 layers and
explore interfacial effects on the charge density wave by switching from a distorted
rocksalt structure to 1T-SnSe2. SnSe2 is semiconductor that is used to prevent adjacent
VSe2 layers from coupling and thereby enhancing the quasi two-dimensionality of the
VSe2 layer. Electrical characterization shows behavior similar to that of SnSe and PbSe
containing heterostructures. However, structural characterization shows the presence of a
SnSe impurity that is likely influencing the overall temperature dependent resistivity.
This dissertation includes previously published and unpublished co-authored
materials.
8
Goddard, Paul. "Magnetotransport studies of layered metallic systems." Thesis, University of Oxford, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.275491.
Full text
9
Franck, Odile. "A closer look at wave-function/density-functional hybrid methods." Thesis, Paris 6, 2016. http://www.theses.fr/2016PA066303/document.
Full textAbstract:
La théorie de la fonctionnelle de la densité (DFT) est une reformulation du problème quantique à N corps où l'énergie de l'état fondamental est exprimée sous la forme d'une fonction de la densité électronique. Dans l'approche de Kohn-Sham de la DFT, seule l'énergie dite d'échange-corrélation décrivant la partie non classique de l'interaction électron-électron nécessite d'être approchée comme une fonctionnelle de la densité. Dans le cadre de la thèse nous nous intéressons à une approximation visant à améliorer la précision et qui consiste à combiner de façon rigoureuse une approximation de type " fonctionnelle de la densité " avec un calcul explicite de type " fonction d'onde " à l'aide d'une décomposition de l'interaction électron-électron coulombienne. L'objectif est de disposer de méthodes améliorant la précision de la DFT actuelle avec un effort de calcul restant compétitif. Ce travail de thèse se décompose en trois études distinctes. Une première étude a consisté a étendre l'analyse de la convergence en base à la séparation de portée qui a permit de mettre en évidence une convergence exponentielle pour l'énergie de corrélation MP2 de longue portée. Dans un second temps nous nous sommes intéressés à une approximation auto-cohérente des fonctionnelles double-hybride utilisant la méthode des potentiels-effectifs-optimisés. Finalement la troisième étude propose une analyse de l'approximation adiabatique semi-locale du noyau d'échange et de corrélation de courte portée dans le cadre de la TDDFT avec séparation de portée dans son formalisme de réponse linéaireThe theory of the functional of the density ( DFT) is a reformulation of the quantum problem in N body where the energy of the fundamental state is expressed under the shape of a function(office) of the electronic density. In the approach of Kohn-Sham of the DFT, only the said energy of exchange-correlation describing the not classic part(party) of the interaction electron-electron requires to be approached as a functional of the density. Within the framework of the thesis(theory) we are interested in an approximation to improve the precision and which consists in combining(organizing) in a rigorous way an approximation of type(chap) " functional of the density " with an explicit calculation of type(chap) " function(office) of wave " by means of a decomposition of the interaction electron-electron coulombienne. The objective is to have methods
10
Reynolds, Eric W. "Laboratory observation of evolution of IEDD-wave-modified equilibrium and density-gradient effects on SMIA wave propagation." Morgantown, W. Va. : [West Virginia University Libraries], 2009. http://hdl.handle.net/10450/10471.
Full textAbstract:
Thesis (Ph. D.)--West Virginia University, 2009.Title from document title page. Document formatted into pages; contains xxviii, 307 p. : ill. Includes abstract. Includes bibliographical references (p. 118-131).
11
Bellec, Ewen. "Study of charge density wave materials under current by X-ray diffraction." Thesis, Université Paris-Saclay (ComUE), 2019. http://www.theses.fr/2019SACLS437/document.
Full textAbstract:
Ce manuscrit a pour sujet principal la diffraction par rayons X des matériaux ondes de densité de charges (ODC). Nous avons étudié le cristal quasi-1D NbSe3 ainsi que le quasi-2D TbTe3. Plusieurs grands instruments ont été utilisés pour cette étude, le synchrotron ESRF de Grenoble sur la ligne ID01 ainsi que le laser à électron libre LCLS à Stanford. Premièrement, grâce à la cohérence du faisceau X à LCLS, nous avons pu observer une perte de cohérence transverse dans NbSe3 lors de l’application d’un courant électrique au-dessus d’un certain seuil ainsi qu’une compression longitudinale de l’ODC. Ensuite, à l’ESRF, nous avons utilisé un faisceau X focalisé au micromètre par une Fresnel zone plate pour scanner l’ODC localement par diffraction sur NbSe3 puis ensuite sur TbTe3. Lorsqu’un courant est appliqué sur l’échantillon, nous avons observé une déformation transverse indiquant que l’ODC est bloquée au niveau de la surface de l’échantillon dans NbSe3. Dans le cas de TbTe3, l’ODC tourne sous courant présentant un cycle d’hystérésis lorsque le courant passe continument de positif à négatif. Nous avons aussi pu constater dans plusieurs régions, toujours pour TbTe3, la création de défauts d’irradiation localisés induisant une compression-dilatation de l’ODC. Dans une dernière partie théorique, nous montrons comment la théorie du transport électrique de l’ODC par un train de solitons portants chacun une charge ainsi que la prise en compte du blocage de l’ODC sur la surface de l’échantillon que nous avons vu expérimentalement permet de comprendre plusieurs mesures de résistivité en fonction des dimensions de l’échantillon trouvées dans la littérature. Nous présentons ensuite plusieurs idées pour expliquer du blocage de l’ODC sur les surfaces au niveau microscopique et proposons l’hypothèse d’une ODC commensurable en surface (et incommensurable dans le volume)The main subject of this manuscript is the X-ray diffraction of charge density wave (CDW) materials. We studied the quasi-1D NbSe3 crystal and the quasi-2D TbTe3. Several large instruments facilities were used for this study, the ESRF synchrotron in Grenoble on the ID01 line and the LCLS free electron laser in Stanford. First, thanks to the coherence of the X-beam at LCLS, we were able to observe a loss of transverse coherence in NbSe3 when applying an electrical current above a certain threshold as well as a longitudinal compression of the CDW. Then, at the ESRF, we used an X-ray beam focused on the micrometer scale by a Fresnel zone plate to scan the CDW locally by diffraction on NbSe3 and on TbTe3. When a current is applied to the sample, we observed a transverse deformation indicating that the CDW is pinned on the sample surface in NbSe3. In the case of TbTe3, the CDW rotates under current showing a hysteresis cycle when one is continuously changing from positive to negative current. We have also observed in several regions, in TbTe3, the creation of localized irradiation defects inducing a compression-dilation of the CDW. In a last theoretical part, we show how the theory of electric transport in the CDW state by a train of charged solitons, as well as taking into account the CDW pinning on the surface of the sample that we have seen experimentally, allows us to understand several resistivity measurements, found in the literature, made on samples with different dimensions. Finally, we present several ideas for an explanation of the CDW pinning at the surfaces on a microscopic level and propose the hypothesis of a commensurate CDW on the surface (and incommensurate in volume)
12
Strømsvåg, Dag. "Fundamental mechanisms of density wave oscillations and the effect of subcooling." Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for energi- og prosessteknikk, 2011. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-12583.
Full textAbstract:
Boiling two-phase flow is found in many industrial applications such as boiling water reactors, two-phase flow heat exchangers and refrigeration systems. The physics of two-phase gas-liquid flow may lead to undesirable system instabilities, and in the literature density wave oscillations (DWO) is reported to be the most commonly observed instability phenomenon. However, the literature alsoprovides two opposing views on what the fundamental mechanism of DWO is. The so-called classical description of DWO focuses on the variation in mixture density as the governing mechanism, and the oscillation period will consequently be about one to two times the channel residence time. The findings presented in citet{Rizwan-Uddin1994} show that it is the variation in mixture velocity that hasthe dominating effect, and the oscillation period was reported to be closer to four times the channel residence time. citet{Ambrosini2000} united the two opposing views by stating that the governing mechanismdepends on the level of system subcooling. The classical description of DWO is based on a lower level of subcooling, while citet{Rizwan-Uddin1994} considered higher subcooling. Here, the fundamental mechanisms of DWO and the effect of system subcooling is investigated further by performing a numerical analysis using a one dimensional homogenous equilibrium flow model. The modeled system consists of a horizontal uniformlyheated boiling channel with an inlet- and exit restriction. The system is exposed to constant externally imposed pressure drop. The effect of system subcooling is investigated by comparing the self-sustained periodicoscillations which make out the modeled stability threshold. The flow model is validated by observing the above mentioned effects of subcooling on DWO. Further, it is found that the change from a density dominated exit restriction towards a velocity dominated exit restriction is a smooth transition for increased subcooling. The amplitude of the variations in exit mixture velocity increases continuously with subcooling, anddue to the squared relationship between the exit restriction pressure drop and the exit mixture velocity, velocity becomes the governing mechanism at high subcooling.The modeled stability threshold approaches a straight line at high subcooling. This line represents operating conditions which have the same mean boiling boundary location. However, the amplitude of the variations about this mean limit grows exponentially at high subcooling. The oscillation period of the observed DWO grows continuously with higher subcooling, and the period increases exponentially at high subcooling. In contrast, the mean boiling channel residence time approaches an upper mean limit at high subcooling. It is postulated that it is the transition towards a more mixture velocity dominated system that causes the oscillation period to evolve as it does with respect to the level of subcooling.
13
Cottet, Didier. "Characterisation of high density substrates for use at millimetre-wave frequencies /." [S.l.] : [s.n.], 2003. http://e-collection.ethbib.ethz.ch/show?type=diss&nr=15205.
Full text
14
Boshoff, Ilana. "Ultrafast electron diffraction on the charge density wave compound 4Hb-TaSe2." Thesis, Stellenbosch : Stellenbosch University, 2012. http://hdl.handle.net/10019.1/20062.
Full textAbstract:
Thesis (MSc)--Stellenbosch University, 2012.ENGLISH ABSTRACT: Ultrafast electron diffraction is a powerful method to study atomic movement in crystals on sub-picosecond timescales. This thesis consists of three parts. In part one the ultrafast electron diffraction machine is described, followed by improvements that were made and techniques that were developed in order to bring the system to state of the art level and enable the acquisition of suffcient data to obtain information on the structural dynamics in crystals. The second part contains a description of the sample which was studied in our fi rst time-resolved measurements, the transition-metal dichalcogenide 4Hb-TaSe2. This particular crystal is an example of a strongly coupled electronic system which develops a charge density wave (CDW) accompanied by a periodic lattice distortion (PLD). An overview of the formation of electron diffraction patterns and what can be learned from them are also given, followed by the results of the ultrafast electron diffraction experiments done with 4Hb-TaSe2. Part three describes an alternative source to study dynamics in crystalline samples, namely laser plasma-based ultrafast X-ray diffraction. The ultrafast electron diffraction group functions as a unit, but my tasks ranged from sample preparation and characterisation of the electron beam to the setting up and execution of experiments. I was involved in analysing the data and contributed small parts to the data analysis software.
AFRIKAANSE OPSOMMING: Ultravinnige elektron diffraksie is a metode om die beweging van atome in kristalle op sub-pikosekonde tydskale te bestudeer. Hierdie tesis bestaan uit drie dele. In deel een van die tesis word die ultravinnige elektron diffraksie masjien beskryf, gevolg deur verbeteringe wat aangebring is en tegnieke wat ontwikkel is om die sisteem tot op 'n wêreldklas vlak te bring waar die insameling van genoegsame data om inligting oor die strukturele dinamika in kristalle te bekom, moontlik is. Die tweede deel bevat 'n beskrywing van die monster wat in ons eerste tydopgeloste eksperimente gebruik is, naamlik die oorgangsmetaaldichalkogenied 4Hb-TaSe2. Hierdie kristal is 'n voorbeeld van 'n sterk gekoppelde elektroniese sisteem wat 'n ladingsdigtheid-golf en 'n gepaardgaande periodiese versteuring van die kristalrooster ontwikkel. 'n Oorsig van die formasie van elektron diffraksiepatrone en wat ons daaruit kan leer word ook gegee. Daarna word die resultate van die ultravinnige elektron diffraksie eksperimente wat op 4Hb-TaSe2uitgevoer is beskryf en bespreek. In deel drie word 'n alternatiewe metode om die dinamika in kristalmonsters te bestudeer, naamlik laser plasma-gebaseerde ultravinnige X-straal diffraksie, beskryf. Die ultravinnige elektron diffraksie groep funksioneer as 'n eenheid, maar my verantwoordelikhede het gestrek van die voorbereiding van monsters en die karakterisering van die elektron bundel tot die opstel en uitvoer van eksperimente. Ek was ook betrokke by die analisering van data en het dele van die data analise sagteware geskryf.
15
Thomas, Matthew. "3D full-wave modelling of microwave interactions with plasma density fluctuations." Thesis, University of York, 2018. http://etheses.whiterose.ac.uk/20481/.
Full textAbstract:
The scattering of microwaves by density fluctuations in magnetised plasmas where the inhomogeneity scale length is comparable to the wavelength is not fully understood. Yet microwaves are used extensively in magnetically confined fusion plasmas not only to provide a wealth of information through diagnostics but for heating and current drive. To this end a 3D full-wave finite difference time domain code (EMIT-3D) has been designed to model the quasi-3D Doppler reflectometry data from a novel synthetic aperture microwave imaging diagnostic (SAMI) and to understand the scattering ef- fects of turbulence on heating and current drive beams. SAMI captures a 2D view of the plasma in a ±40 ◦ illumination from the mid-plane. A vast spatial grid is required to capture the inhomogeneous, curved plasma and magnetic geometry whilst considerable acquisition time is required for Doppler resolution. For this reason EMIT-3D has been parallelised in 3D which is shown to scale well to large machines. EMIT-3D is shown to agree with the extensive benchmarking tests and demonstrates stability to large time iterations. EMIT-3D has been applied to electron cyclotron resonance heating (ECRH) deposition broadening in the DIII-D tokamak. Significant ECRH deposition broadening was measured in three different operating scenarios: L-mode, H-mode and negative triangularity. Each scenario corresponds to distinct turbulence characteristics in the edge region through which the beam must propagate. The turbulence is gen- erated through the Hermes model in the BOUT++ framework which takes as input the measured time averaged electron density, temperature and magnetic field profiles for the specific shot in question. The simulated turbulence is constrained to match the experimentally measured correlation length and normalised fluctuation levels. The predictions of the beam broadening from the simulations are found to agree very well with the experimentally-observed broadening in all cases.
16
Harris, Victoria Siân. "Creation of nonlinear density gradients for use in internal wave research." Thesis, Massachusetts Institute of Technology, 2007. http://hdl.handle.net/1721.1/40437.
Full textAbstract:
Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2007."June 2007."
Includes bibliographical references.
A method was developed to create a nonlinear density gradient in a tank of water. Such gradients are useful for studying internal waves, an ocean phenomenon that plays an important role in climate and ocean circulation. The method was developed by expanding on the two-tank system currently used to create linear density gradients. A mathematical model of the two-tank system was used and a Matlab script was written to solve the model for the required flow rates in the system given a desired density gradient. The method was tested by creating three different density gradients: a linear gradient, a hyperbolic gradient, and a two-layer gradient. It was discovered that for a two-layer gradient the flow rates for each layer must be calculated independently of each other, because of problems integrating over a density gradient with a non-continuous slope. It was also discovered that the system failed at very low flow rates; insufficient mixing in the two-tank system led to gradients weaker than expected. Overall, the measured gradients matched up well with the expected gradients, and it was concluded that the system can successfully produce nonlinear density gradients.
by Victoria Siân Harris.
S.B.
17
Yetman, Paul John. "Experimental studies on the size dependence of sliding charge-density wave phenomena." Thesis, University of Bristol, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.279769.
Full text
18
Rubenstein, Richard Alan 1971. "Longitudinal atom optics : measuring the density matrix of a matter wave beam." Thesis, Massachusetts Institute of Technology, 1999. http://hdl.handle.net/1721.1/85255.
Full text
19
Ren, Yuhang. "Time-resolved optical studies of colossal magnetoresistance and charge -density wave materials." W&M ScholarWorks, 2003. https://scholarworks.wm.edu/etd/1539623421.
Full textAbstract:
This thesis presents measurements of collective modes and ultrafast carrier relaxation dynamics in charge-density-wave (CDW) conductors and colossal magnetoresistance (CMR) manganites. A femtosecond laser pump pulse excites a broad frequency spectrum of low-energy collective modes and electron-hole pairs thereby changing its optical properties. The low-energy collective excitations and quasiparticle relaxation and recombination processes are monitored by measuring the resulting photoinduced absorption as a function of probe pulse wavelength and time delay.;A general model was developed for the photogeneration and detection mechanism of collective modes based on light absorption in two-color pump-probe experiments. A broad spectrum of collective modes (phasons and amplitudons) with frequencies down to a few GHz is excited and propagates normal to the surface into the material. The dispersion of the long-wavelength phason and amplitudon can be measured by changing the probe wavelength.;The first pump-probe spectroscopy was performed from the ultraviolet to mid-infrared wavelength range to study low-frequency collective excitations, including temperature evolution, dispersion, damping, and anisotropy of amplitude mode and transverse phason in quasi-one dimensional CDW conductors, K 0.3MoO3 and K0.33MoO3 on ultrafast time scale. The transverse phason exhibits an acoustic-like dispersion relation in the frequency range from 5--40 GHz. The phason velocity is strongly anisotropic with a very weak temperature dependence. In contrast, the amplitude mode exhibits a weak (optic-like) dispersion relation with a frequency of 1.66 THz at 30 K.;The studies were extended to doped perovskite manganite thin films and single crystals. A low-energy collective mode is observed and discussed in terms of the opening of a pseudogap resulting from charge/orbital ordering phases. The softening of the collective mode is necessary to explain by combining a cooperative Jahn-Teller type distortion of the MnO6 octahedra with the collective mode. The quasiparticle dynamics in the vicinity of the metal-insulator transition is strongly affected by the presence of a pseudogap, phase separation and percolation, which are strongly dependent on temperature. A very long-lived relaxation process is observed due to a slow spin relaxation process. The dynamics of the spin system is further investigated in strained and unstrained thin films, which show a strong strain effect.
20
Heinemann, Tobias. "The dynamics of spiral density waves in turbulent accretion discs." Thesis, University of Cambridge, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.608944.
Full text
21
Edkins, Stephen David. "Visualising the charge and Cooper pair density waves in cuprates." Thesis, University of St Andrews, 2016. http://hdl.handle.net/10023/9888.
Full textAbstract:
The study of cuprate high-temperature superconductors has undergone a recent resurgence due to the discovery of charge order in several families of cuprate materials. While its existence is now well established, little is known about its microscopic origins or its relationship to high-temperature superconductivity and the pseudogap. The aim of the research presented in this thesis is to address these questions. In this thesis I will report on the use of spectroscopic-imaging scanning tunnelling microscopy (SI-STM) to visualise the short-ranged charge density wave (CDW) in Bi₂Sr₂CaCu₂O₈₊ₓ and NaxCa₂₋ₓCuO₂Cl₂. Building on previous measurements of the intra unit-cell electronic structure of cuprates, I introduce sub-lattice segregated SISTM to individually address the atomic sub-lattices in the CuO₂ plane with spatial phase sensitivity. Using this technique I establish that the CDW in Bi₂Sr₂CaCu₂O₈+x and NaxCa₂₋ₓCuO₂Cl₂ has a previously unobserved d-symmetry form factor, where a breaking of rotational symmetry within the unit cell is modulated periodically in space. Towards identifying a mechanism of CDW formation, I establish that the amplitude of CDW modulations in the electronic structure are maximal at the pseudogap energy-scale and that these modulations exhibit a spatial phase difference of π between filled and empty states. Together with the doping evolution of the CDW wave-vector this highlights the role of the low-energy electronic structure of the pseudogap regime in CDW formation. To elucidate the relationship between the CDW and the superconducting condensate I will introduce nanometer resolution scanned Josephson tunnelling microscopy (SJTM). In this approach the Cooper pair (Josephson) tunnelling current between a Bi₂Sr₂CaCu₂O₈₊ₓ sample and a scan-able Bi₂Sr₂CaCu₂O₈₊ₓ nano-flake STM tip is used to directly visualise the superconducting condensate. I will report the observation of a periodic modulation in the Cooper pair condensate at the same wave-vector as the CDW, the first direct detection of a periodically modulating condensate in any superconductor.
22
Rand, Richard J. Kulkarni S. R. "The relationship between the density wave, molecular gas and star formation in M51 /." Diss., Pasadena, Calif. : California Institute of Technology, 1991. http://resolver.caltech.edu/CaltechETD:etd-09162008-105121.
Full text
23
Toh, Justin Sieu-Sung. "Iterative diagonalisation algorithms in plane wave density functional theory with applications to surfaces." Thesis, University of Cambridge, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.615143.
Full text
24
Reilly, David James. "Experimental study of shock-driven, variable-density turbulence using a complex interface." Thesis, Georgia Institute of Technology, 2015. http://hdl.handle.net/1853/54456.
Full textAbstract:
The overarching goal of this work is to advance the current knowledge of hydrodynamic instabilities (namely, Richtmyer-Meshkov and Kelvin-Helmholtz instabilities) and associated turbulent mixing phenomena which is important for several emerging technologies and verification/validation of numerical models being developed to study these phenomena. Three experimental campaigns were designed to focus on understanding the evolution of the instability under different impulsive acceleration histories and highlight the impact of initial conditions on the developing turbulent flow environment. The first campaign highlights the importance of initial baroclinic torque distribution along the developing shocked interface in a twice-shocked variable-density flow environment. The second campaign is a parametric study which aims at providing a large dataset for validating models in literature as well as simulations. In the last study, a new type of initial condition was designed to study the effect of initial conditions on late time turbulent flows. A description of the optical diagnostic techniques developed in our laboratory in order to complete these studies will be given. Now each campaign will be introduced.
In the first campaign, an inclined interface perturbation is used as the initial condition. The Mach number (1.55), angle of inclination (60 degrees), and gas pair (N2/CO2) were held constant. The parameter which changed was the distance that the initial condition was placed relative to the end of the shock tube (i.e., the end of the test section). Three distances were used. The vorticity distribution was found to be very different for the most developed case after reshock. Furthermore, the most developed case started to develop an inertial range before reshock.
The second campaign is parametric and seeks to test a proposed inclined interface scaling technique. The data is also useful for comparing to Ares simulation results. The parameter space covered Mach number (1.55 and 2.01), inclination angle (60 degrees and 80 degrees), and Atwood number (0.23 and 0.67). PLIF was developed and used to collect data for four cases before and after reshock. Linear and nonlinear cases developed very differently before reshock, but their mixing widths converged after reshock.
The last campaign involves a new perturbation technique which generates what will be referred to as a complex interface. Counter-flowing jets were placed near the interface exit ports to create shear. The perturbation was made more complex by also injecting light (heavy) gas into the heavy (light) one. Density and velocity statistics were collected simultaneously. The complex case retained a signature of the inclined interface perturbation at late time before reshock and developed a larger inertial range than its inclined interface counterpart. Important parameters for a variable-density turbulence model are also presented.
25
Lee, Allison Marie. "An Experimental and Theoretical Investigation of Internal Wave Kinetic Energy Density in Variable Stratifications." BYU ScholarsArchive, 2019. https://scholarsarchive.byu.edu/etd/7737.
Full textAbstract:
Internal waves are generated in a fluid if the density increases continuously with depth. The variation in density with depth, or stratification, defines the natural frequency of the fluid N. Two common examples of stratified fluids are the ocean and atmosphere; internal waves are generated continuously in both mediums. Although there are many internal wave generation mechanisms, one common and frequently studied method is tidal flow over oceanic bathymetry. If the local natural frequency of the water near the topography is greater than the tidal frequencyω, internal waves will be generated by the tidal flow over the topography. If N=ω, only evanescent waves will be formed. Unlike internal waves, evanescent waves decay rapidly as they move vertically away from their generation site. As evanescent waves pass from an evanescent region (N=ω),through a turning depth (N=ω) and into a propagating region (N=ω), they become propagating internal waves. Because internal waves can propagate energy across large distances, they play an important role in oceanic mixing and the overall energy budget of the ocean. Knowing where these waves are formed from evanescent waves and their corresponding energy improves understanding of the impact on their surrounding area.Kinetic energy density of evanescent and internal waves formed from oscillatory flow over topography in evanescent regions is first estimated using synthetic schlieren experiments and a novel linear theory model. Experiments were performed with two Gaussian topographies in an exponential density profile. The linear theory model, which uses a set of equations that links the evanescent and propagating regions with the Airy function to overcome the discontinuity inherent with a turning depth, was compared to the experiments. Both methods showed that increasing Fr1,the strength of the evanescent region relative to the excitation frequency, causes the propagating kinetic energy to decrease. In addition, kinetic energy decreased with increasing distance between the topography and the turning depth. Because the model does not account for non-linearities such as turbulence generation, it regularly overestimates propagating kinetic energy relative to the experiments. After comparing the model with synthetic schlieren experiments, it was used to estimate that 25% of the evanescent wave energy generated by an oceanic topography located at 15◦N, 130◦E can become propagating wave energy.The influence of topography shape and fluid density profile on kinetic energy density was also explored through a combination of experiments, a linear theory model, and numerical simulations. From numerical simulations, kinetic energy can be directly calculated with the velocity pro-file and indirectly with the density perturbation field, in the same manner as the synthetic schlieren experiments. Average propagating internal wave kinetic energy (KE∗ 2) as a function of Fr1D/H,which combines Fr1 with the relative distance between the topography and the turning depth D/H,was compared for all methods. KE∗ 2 decreases with increasing Fr1D/H for all methods. Also, far from the turning depth, the direct and indirect simulations indicate similar kinetic energy when in the propagating region, where a distance from the turning depth can be quantified based on N and ω. This work was expanded to include a medium Gaussian, steep Gaussian, sinusoidal, and complex topography with two layer linear, parabolic, cubic, and exponential density profiles to investigate the validity of assuming an average natural frequency in the evanescent region and the impact of the topographic slope on KE∗ 2. A comparison of the density profiles indicated that using a two layer linear density profile has similar results compared to the other density profiles for estimating KE∗ 2 as a function of Fr1D/H. Also, KE∗ 2 is non-negligible for Fr1D/H<4. Increasing the maximum slope of a topography shape decreases the kinetic energy of the generated internal waves, though it was found that the energy is dependent upon the actual shape of the topography as well.Particle image velocimetry (PIV) experiments were performed and compared to synthetic schlieren (SS). While SS experiments generally resulted in an overestimate of kinetic energy relative to the PIV results, the trends from each experimental method matched well. It is recommended that SS be used in regions away from turning depths, but that either are valid in the evanescent and propagating regions. PIV methods should be used when results near the turning depth or the topography are desired.
26
Ramakrishnan, Sitaram [Verfasser], and Smaalen Sander [Akademischer Betreuer] van. "Charge-density-wave ordering in three-dimensional metallic compounds / Sitaram Ramakrishnan ; Betreuer: Sander van Smaalen." Bayreuth : Universität Bayreuth, 2020. http://d-nb.info/1213348951/34.
Full text
27
Flanagan, Timothy McGuire. "Observations of thermal creep gas flow and dust-density waves in dusty plasma experiments." Diss., University of Iowa, 2010. https://ir.uiowa.edu/etd/802.
Full textAbstract:
In laboratory experiments, I study strongly-coupled dusty plasma levitated in a glow-discharge plasma. Dusty plasma is an arrangement of small dust particles in a plasma background of electrons, ions, and neutral gas. The dust particles are negatively charged because they collect electrons and ions from the background plasma. Depending on the experimental setup, the plasma's electric field can help to balance the dust particles against gravity. The high dust charge causes dust particles to repel each other, while confinement forces prevent their escape. The dust particles cannot easily move past one another, and instead organize themselves into highly-ordered structures. The neutral gas also plays a key role in these experiments. Depending on the relative motion between gas and dust particles, the neutral gas can either impede dust motion or it can drive the dust into motion.
In this thesis, I report the findings of three separate experiments. In the first experiment, I use a spherically-shaped dusty plasma (Yukawa ball) as an indicator of a flow of neutral gas, called thermal creep flow. In the second and third experiments, I study naturally occurring dust-density waves, which propagate within the volume of a dusty plasma that has many horizontal layers.
In Ch.2 of this thesis, I study thermal creep flow (TCF), which is a flow of gas driven by a temperature gradient along a solid boundary. Stripes on a glass box are heated by laser beam absorption, leading to both TCF and a thermophoretic force. A stirring motion of the dust particle suspension is observed. By eliminating all other explanations for this motion, I conclude that TCF at the boundary couples by drag to the bulk gas, causing the bulk gas to flow, thereby stirring the suspension of dust particles. This result provides an experimental verification that TCF in the slip-flow regime causes steady-state gas flow in a confined volume.
In Ch.3, I observe the growth of a naturally occurring dust-density wave (DDW) using high-speed imaging. This low-frequency wave (∼ 25 Hz) grows in amplitude as it propagates downward through a dusty plasma. I measure the wave's linear growth rate using a phase-sensitive analysis method. For the conditions studied here, the growth rate increases as gas pressure decreases. At a critical gas pressure that I observe, a balance between an ion-flow instability and dissipation by neutral gas drag determines a threshold for wave propagation. A linear dispersion relation is derived, taking into account effects of strong coupling, to compare to the experiment.
In Ch.4, I observe the development of nonlinearity in the naturally occurring dust-density wave by measuring harmonics of the fundamental. Using high-speed imaging, I measure amplitudes, wave numbers and growth rates for the fundamental and its harmonics. The amplitudes of the harmonics exhibit a strong exponential increase with diminishing gas pressure, and they saturate at lower gas pressures. My measurements show that the wave numbers and growth rates of harmonics are near integer multiples of the fundamental.
28
Yi, Tianyou. "Modeling of dynamical vortex states in charge density waves." Phd thesis, Université Paris Sud - Paris XI, 2012. http://tel.archives-ouvertes.fr/tel-00768237.
Full textAbstract:
Formation of charge density waves (CDW) is a symmetry breaking phenomenon found in electronic systems, which is particularly common in quasi-one-dimensional conductors. It is widely observed from highly anisotropic materials to isotropic ones like the superconducting pnictides. The CDW is seen as a sinusoidal deformation of coupled electronic density and lattice modulation; it can be also viewed as a crystal of singlet electronic pairs. In the CDW state, the elementary units can be readjusted by absorbing or rejecting pairs of electrons. Such a process should go via topologically nontrivial configurations: solitons and dislocations - the CDW vortices. An experimental access to these inhomogeneous CDW states came from studies of nano-fabricated mesa-junctions, from the STM and from the X-ray micro-diffraction. Following these requests, we have performed a program of modeling stationary states and of their transient dynamic for the CDW in restricted geometries under applied voltage or at passing normal currents. The model takes into account multiple fields in mutual nonlinear interactions: the two components of the CDW complex order parameter, and distributions of the electric field, the density and the current of normal carriers. We were using the Ginzburg-Landau type approach and also we have derived its extension based on the property of the chiral invariance. We observed the incremental creation of static dislocations within the junctions. The transient dynamics is very rich showing creation, annihilation and sweeping of multiple vortices. The dislocations cores concentrate the voltage drops thus providing self-tuned microscopic junctions where the tunneling creation of electron-hole pairs can take place. The results obtained from this model agree with experiment observations. The methods can be extended to other types of charge organization known under the general name of the Electronic Crystal. It takes forms of Wigner crystals at hetero-junctions and in nano-wires, CDWs in chain compounds, spin density waves in organic conductors, and stripes in doped oxides. The studied reconstruction in junctions of the CDW may be relevant also to modern efforts of the field-effect transformations in strongly correlated materials with a spontaneous symmetry breaking.
29
Fumis, Cristiana. "Mechanical Wave Propagation in Civil Engineering Materials." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2017.
Find full textAbstract:
Mechanical wave propagation in civil engineering materials is important for different application fields, such as thermal conductivity, damage detection and sound transmission (including filters and sound barriers). A current open challenge is to understand how the chemistry and microstructures of cementitious materials impact the propagation of mechanical waves in them.
The challenge is heightened by the fact that cementitious materials are very heterogeneous at the microscale. In this project, molecular and nanoparticle based simulations will be used in order to construct microstructures of cement hydrates with a range of chemistries and morphologies. I will simulate the dynamic behaviour of these model structures and quantify it in terms of vibrational band structure and density of states. This will open
the way to a new and fundamental understanding of how the chemistry and microstructure of cementitious materials can be tailored in order to engineer their vibrational behaviour, for controlled thermal conductivity, soundroof applications, and more efficient damage detection.
30
Feng, Ning-Ning Huang Wei-Ping. "Modeling, simulation and design techniques for high-density complex photonic integrated devices and circuits." *McMaster only, 2005.
Find full text
31
Latt, Kyaw Zin. "Manipulation of Molecular Charge Density Waves and Molecular Transport Systems." Ohio University / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1557418915977344.
Full text
32
Boulet, Antoine. "Density functional theory for Fermi systems with large s-wave scattering length : application to atomic and nuclear physics." Thesis, Université Paris-Saclay (ComUE), 2019. http://www.theses.fr/2019SACLS212/document.
Full textAbstract:
Dans ce travail de thèse, des théories de type fonctionnelle de la densité sont développées pour des systèmes en interaction forte possédant une longueur de diffusion en onde s, notée as, anormalement grande. Les gaz atomiques ou la matière neutronique sont des exemples physiques de tels systèmes. La théorie des perturbations à N-corps est tout d'abord utilisée pour décrire les systèmes de fermions dilués. Cette approche conduit par exemple à la fonctionnelle de Lee-Yang qui est valide dans une plage de densité très restreinte lorsque la longueur de diffusion en onde s devient grande. Pour étendre le domaine de validité de l’approche perturbative, des techniques de resommation associées à l’approximation dite en échelle sont utilisée. Cette approche conduit à des expressions compactes pour l'énergie et/ou la self-énergie on-shell dans des systèmes infinis pouvant être appliquées à des systèmes plus ou moins denses. Cela conduit également à une énergie finie du gaz atomique à la limite unitaire, i.e. lorsque |askF|→+∞. Les fonctionnelles ainsi déduites restent assez complexes et manquent en général de pouvoir prédictif. Pour simplifier ces fonctionnelles, des approximations appelées respectivement approximations de “l’espace des phases” ou de “l'espace des phases partiel” sont proposées pour l'énergie ou la self-énergie. Ces approximations simplifient non seulement la forme des fonctionnelles, mais améliorent également leur pouvoir prédictif tout en reproduisant correctement la limite de basse densité. Guidé par les techniques de resommation non-perturbatives développées dans cette thèse, plusieurs nouvelles fonctionnelles sont proposées ainsi que leurs extensions permettant d’inclure des effets de portée effective. Ces fonctionnelles non empiriques, qui ne contiennent aucun paramètre libre, sont testées par rapport aux propriétés des systèmes d'atomes froids et/ou de la matière neutronique. Ces fonctionnelles reproduisent très bien les propriétés obtenues dans les calculs ab-initio ou observées expérimentalement dans les systèmes d'atomes froids. L'équation d'état de la matière neutronique est également reproduite jusqu'à ρ = 0.01 fm⁻³. La réponse statique de la matière neutronique, récemment calculée dans des théories ab-initio, est également mieux reproduite par rapport aux fonctionnelles empiriques utilisées généralement en physique nucléaire. Cette étude a aussi mis en évidence la nécessité de mieux comprendre les propriétés des quasi-particules telle que la masse effective. Pour progresser sur ce point, en partant des expressions resommées de la self-énergie et de l’approximation de l’espace des phases partiel, des expressions compactes du potentiel chimique et de la masse effective ont été obtenues ; ces expressions étant compatibles avec les fonctionnelles proposées dans la première partie de cette thèse. Ces expressions devraient élargir considérablement le domaine de validité des fonctionnelles non-empiriques par rapport aux théories perturbatives. Enfin, il est montré que les développements de ce travail sont également utiles pour réconcilier les paramètres généralement utilisés dans les fonctionnelles empiriques de la physique nucléaire avec les propriétés de l’interaction nucléaire forteIn the present work, a density functional theory (DFT) is developed for systems interacting through an anomalously large s-wave scattering length as. Examples of such systems are atomic gas or neutron matter. The Many-Body Perturbation Theory (MBPT) is first discussed to describe dilute Fermi systems. This approach leads to the well-known Lee-Yang functional valid in a very narrow range of density when the s-wave scattering length is large. To extend the domain of validity of the perturbative approach, resummation techniques with the ladder approximation is used. This leads to compact expressions for both the energy and/or the on-shell self-energy in infinite spin-degenerated systems that can be applied from diluted to dense systems. It also leads to finite energy in atomic gas at the unitary limit, i.e. when |askF|→+∞. The deduced functionals remain rather complex and lacks of predictive power in general. To simplify the functional, approximations called phase-space or partial phase-space approximations respectively for the energy or for the self-energy, are proposed. These approximations not only simplify the form of the functionals, but also improve their predictive power at various density while properly reproducing the low density limit. Guided by the non-perturbative resummation technique developed in this thesis, several novel functionals are proposed as well as extensions of them to include effective range effects. These non-empirical functionals, that essentially contain no free parameters, are tested against cold atom and/or neutron matter properties. A very good reproduction of ab initio and experimental observations in cold atom is obtained. The equation of state obtained for neutron matter is also reproduced up to ρ = 0.01 fm⁻³. The static response of neutron matter, recently obtained from ab initio theory, is also better reproduced compared to standardly used empirical nuclear DFT. This study has also pointed out the necessity to better understand quasi-particle properties like the effective mass. To further progress, starting from resummed expressions of the self-energy together with partial phase-space approximation, compact expressions of the chemical potential and effective masses are obtained that are eventually compatible with the DFTs proposed in the first part of this thesis. These expressions are anticipated to significantly extend the domain of validity compared to the perturbative approach. We finally show that the developments made in this work are also useful to reconcile the parameters generally used in the empirical nuclear DFT with the properties of the strong nuclear interaction
33
Niesert, Manfred [Verfasser]. "Ab initio calculations of spin-wave excitation spectra from time-dependent density-functional theory / Manfred Niesert." Aachen : Hochschulbibliothek der Rheinisch-Westfälischen Technischen Hochschule Aachen, 2012. http://d-nb.info/102156754X/34.
Full text
34
Mares, Aimee Gail. "Remotely sensed density measurements of volcanic sulfur dioxide plumes using a spectral long wave infrared imager." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2002. http://library.nps.navy.mil/uhtbin/hyperion-image/02Sep%5FMares.pdf.
Full textAbstract:
Thesis (M.S. in Space Systems Operations)--Naval Postgraduate School, September 2002.Thesis advisor(s): Richard C. Olsen, Paul G. Lucey. Includes bibliographical references (p. 123-125). Also available online.
35
AL, Ismail Marwah I. "On the relationship between compressional wave velocity of saturated porous rocks and density : theory and application." Thesis, Massachusetts Institute of Technology, 2017. http://hdl.handle.net/1721.1/108912.
Full textAbstract:
Thesis: S.M., Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 2017.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 97-98).
Understanding the velocity of the compressional waves travelling through rocks is essential for the purposes of applied geophysics in such areas as groundwater and hydrocarbon exploration. The wave velocity is defined theoretically by the Newton-Laplace equation, which relates the wave velocity, V, to the square root of the ratio of the rock's elastic modulus, M, and its density, [rho] (Bourvie et al., 1987). Therefore, the equation indicates that the velocity is inversely proportional to density. However, the in-situ field measurements and laboratory experiments of compressional wave velocity through different rocks show otherwise. In other words, the velocity is directly proportional to approximately the 4th power of density as stated by Gardner (Gardner et al., 1974). This thesis investigates the inconsistency between theory and observations regarding the relationship between velocity and density of saturated porous rocks. The inconsistency is clarified by deriving a new expression for the elastic modulus, M, using Wyllie's time average equation and the Newton-Laplace equation. The new derived expression of the elastic modulus, M, provides dependence of M on density to approximately the 9th power. In addition, Gardner's equation is modified to accurately obtain the velocity over the entire range of densities (from 1.00 g/cm³ to around 3.00 g/cm³) and porosity (from 0% to 100%). The end of this thesis is an application of the previous outcomes with real data sets, where the results validate the derived expression of the elastic modulus as well as the generalized form of Gardner's equation.
by Marwah I. AL Ismail.
S.M.
36
Stoyanova, Alexandrina. "Delocalized and correlated wave functions for excited states in extended systems." [S.l. : [Groningen : s.n.] ; University Library Groningen] [Host], 2006. http://irs.ub.rug.nl/ppn/297656074.
Full text
37
Shao, Yongmei. "X-ray scattering study of the critical behavior of the second harmonic in the density wave system 7APCBB." Thesis, Massachusetts Institute of Technology, 1994. http://hdl.handle.net/1721.1/32146.
Full text
38
Calderín, L., V. V. Karasiev, and S. B. Trickey. "Kubo–Greenwood electrical conductivity formulation and implementation for projector augmented wave datasets." ELSEVIER SCIENCE BV, 2017. http://hdl.handle.net/10150/626127.
Full textAbstract:
As the foundation for a new computational implementation, we survey the calculation of the complex electrical conductivity tensor based on the Kubo-Greenwood (KG) formalism (Kubo, 1957; Greenwood, 1958), with emphasis on derivations and technical aspects pertinent to use of projector augmented wave datasets with plane wave basis sets (BIlichl, 1994). New analytical results and a full implementation of the KG approach in an open-source Fortran 90 post-processing code for use with Quantum Espresso (Giannozzi et al., 2009) are presented. Named KGEC ([K]ubo [G]reenwood [E]lectronic [C]onductivity), the code calculates the full complex conductivity tensor (not just the average trace). It supports use of either the original KG formula or the popular one approximated in terms of a Dirac delta function. It provides both Gaussian and Lorentzian representations of the Dirac delta function (though the Lorentzian is preferable on basic grounds). KGEC provides decomposition of the conductivity into intra- and inter band contributions as well as degenerate state contributions. It calculates the dc conductivity tensor directly. It is MPI parallelized over k-points, bands, and plane waves, with an option to recover the plane wave processes for their use in band parallelization as well. It is designed to provide rapid convergence with respect to k-point density. Examples of its use are given.
39
Rocha, Matthew Paul. "A high-resolution study of the electronic structure of NbSe3 in normal and charge density wave states with angle resolved photoemission spectroscopy /." view abstract or download file of text, 2003. http://wwwlib.umi.com/cr/uoregon/fullcit?p3113025//.
Full textAbstract:
Thesis (Ph. D.)--University of Oregon, 2003.Typescript. Includes vita and abstract. Includes bibliographical references (leaves 166-167). Also available for download via the World Wide Web; free to University of Oregon users.
40
Gerlach, Max Henner [Verfasser], Simon [Gutachter] Trebst, and Achim [Gutachter] Rosch. "Quantum Monte Carlo studies of a metallic spin-density wave transition / Max Henner Gerlach ; Gutachter: Simon Trebst, Achim Rosch." Köln : Universitäts- und Stadtbibliothek Köln, 2017. http://d-nb.info/112720002X/34.
Full text
41
Southern, Rodney George. "Comparison of the obturation density of resilon[TM] using cold lateral condensation and varying continuous wave of condensation techniques." Morgantown, W. Va. : [West Virginia University Libraries], 2006. https://eidr.wvu.edu/etd/documentdata.eTD?documentid=4683.
Full textAbstract:
Thesis (M.S.)--West Virginia University, 2006.Title from document title page. Document formatted into pages; contains vii, 47 p. : ill. (some col.). Vita. Includes abstract. Includes bibliographical references (p. 35-38).
42
LePage, Jeffrey Guy. "Projector-augmented wave method calculation of Ga adatom diffusion and local density of states for GaAs and Si surfaces /." The Ohio State University, 1997. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487943341528438.
Full text
43
Mahler, Andrew. "The One Electron Basis Set: Challenges in Wavefunction and Electron Density Calculations." Thesis, University of North Texas, 2016. https://digital.library.unt.edu/ark:/67531/metadc849642/.
Full textAbstract:
In the exploration of chemical systems through quantum mechanics, accurate treatment of the electron wavefunction, and the related electron density, is fundamental to extracting information concerning properties of a system. This work examines challenges in achieving accurate chemical information through manipulation of the one-electron basis set.
44
Zhang, Ye. "High cell density perfusion process development for antibody producing Chinese Hamster Ovary cells." Doctoral thesis, KTH, Industriell bioteknologi, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-207600.
Full textAbstract:
Perfusion operation mode is currently under fast expansion in mammalian cell based manufacturing of biopharmaceuticals, not only for labile drug protein but also for stable proteins such as monoclonal antibodies (mAbs). Perfusion mode can advantageously offer a stable cell environment, long-term production with high productivity and consistent product quality. Intensified high cell density culture (HCDC) is certainly one of the most attractive features of a perfusion process due to the high volumetric productivity in a small footprint that it can provide. Advancements in single-use technology have alleviated the intrinsic complexity of perfusion processes while the maturing in cell retention devices has improved process robustness. The knowledge for perfusion process has been gradually built and the “continuous” concept is getting more and more acceptance in the field. This thesis presents the development of robust perfusion process at very high cell densities in various culture systems. Four HCDC perfusion systems were developed with industrial collaborators with three different mAb producing Chinese Hamster Ovary (CHO) cell lines: 1-2) WAVE Bioreactor™ Cellbag prototype equipped with cell separation by hollow fiber filter utilizing Alternating Tangential Flow (ATF) and Tangential Flow Filtration (TFF) techniques; 3) Fiber matrix based CellTank™ prototype; 4) Glass stirred tank bioreactor equipped with ATF. In all the systems, extremely high viable cell densities above 130 million viable cells per milliliter (MVC/mL) up to 214 MVC/mL were achieved. Steady states were maintained and studied at 20-30 MVC/mL and 100-130 MVC/mL for process development. Perfusion rate selection based on cell specific perfusion rate (CSPR) was systematically investigated and exometabolome study was performed to explore the metabolic footprint of HCDC perfusion process.QC 20170523
45
Puikkonen, Panu Tapani. "Development of an Adaptive Equalization Algorithm Using Acoustic Energy Density." BYU ScholarsArchive, 2009. https://scholarsarchive.byu.edu/etd/1686.
Full textAbstract:
Sound pressure equalization of audio signals using digital signal processors has been a subject of ongoing study for many years. The traditional approach is to equalize sound at a point in a listening environment, but because of its specific dependence on the room frequency response between a source and receiver position, this equalization generally causes the spectral response to worsen significantly at other locations in the room. This work presents both a time-invariant and a time-varying implementation of an adaptive acoustic energy density equalization filter for a one-dimensional sound field. Energy density equalization addresses the aforementioned challenge and others that relate to sound equalization. The theory and real-time implementation of time-invariant sound pressure and energy density equalizers designed using the least-squares method are presented, and their performances are compared. An implementation of a time-varying energy density equalizer is also presented. Time-invariant equalization results based on real-time measurements in a plane-wave tube are presented. A sound pressure equalizer results in a nearly flat spectral magnitude at the point of equalization. However, it causes the frequencies corresponding to spatial nulls at that point to be undesirably boosted elsewhere in the sound field, where those nulls do not exist at the same frequencies. An energy density equalization filter identifies and compensates for all resonances and other global spectral effects of the tube and loudspeaker. It does not attempt to equalize the spatially varying frequency nulls caused by local pressure nodes at the point of equalization. An implementation of a time-varying energy density equalizer is also presented. This method uses the filtered-x filter update to adjust the filter coefficients in real-time to adapt to changes in the sound field. Convergence of the filter over time is demonstrated as the closed end of the tube is opened, then closed once again. Thus, the research results demonstrate that an acoustic energy density filter can be used to time-adaptively equalize global spectral anomalies of a loudspeaker and a one-dimensional sound field.
46
Sellam, Mohamed Amine. "Competition between charge density wave and metallic/superconducting states in metastable 1T-TaS2 and 1T-VS2 synthesised under high pressure." Paris 6, 2011. http://www.theses.fr/2011PA066585.
Full textAbstract:
L’objectif de cette Thèse est une étude de la stabilité des phases d’onde de densité de charge (CDW) et supraconductrice en compétition dans les dichalcogénures lamellaires de métaux de transition. Dans ce but, nous avons employé une technique de synthèse sous haute pression pour induire des modifications de la structure cristalline dans deux composés 1T-TaS2 et 1T-VS2 ayant la même structure 1T (ou de type CdI2) et la même configuration électronique d1. Dans le cas de 1T-TaS2, notre étude de diffraction de rayons X synchrotron et de neutrons sur poudre montre que des conditions de synthèse de 2-6 GPa et 400 °C induisent un désordre dans les plans S et une contraction (expansion) notable de l’axe a dans les plans (c hors plan). Ceci suggère un modèle de désordre d’orientation de ces plans correspondant à l’empilement aléatoire de couches TaS2 de type 1T ou 2H qui correspondent à une coordinance octaédrique ou trigonal prismatique des ions Ta. Ce modèle est en accord avec nos mesures magnétiques et de transport. Cette phase désordonnée est caractérisée par deux phases CDW, une non commensurée, l’autre quasi-commensurée (NCCDW, ICCDW), observées à température ambiante et à basse température respectivement. Ces phases diffèrent de celles observées dans les composés 1T ou 2H synthétisés sous conditions standard. Cette différence met en évidence la métastabilité du composé synthétisé sous haute pression et explique son comportement paramagnétique et métallique/supraconducteur avec Tc ~ 2. 5 K. Afin d’étudier les propriétés supraconductrices, nous avons intercalé le carbone entre les plans à des concentrations x = 0. 05-0. 3 sous les mêmes conditions de pression et de température. Une augmentation notable de Tc a été observée. Notamment, la dépendance de Tc avec x montre un maximum de 4 K pour x=0. 2. Considérant que l’électronégativité du carbone est identique à celle du souffre, ce résultat démontre que la stabilisation de la phase supraconductrice est uniquement due à la séparation des plans et l’effet du dopage sujet à controverse dans la littérature peut être exclu. Dans le cas de 1T-VS2, nous avons réussi la synthèse de la phase stoichiométrique de haute pureté sous forme de poudre à des conditions de haute pression (P = 4 GPa) et à T = 700 °C. Des travaux précédents concernent uniquement la synthèse par dé-intercalation de Li à partir de LiVS2, donc ce résultat montre que 1T-VS2 est une phase métastable à haute pression. Dans ce cas la synthèse à haute pression produit un composé bien cristallisé et sans désordre, ce qui a permis un affinement structural de haute qualité entre 5 et 300 K par diffraction de rayons X synchrotron. Les données montrent que la structure reste de type CdI2 dans toute cette gamme de température. Cependant, une expansion thermique négative de l’axe c est observée dans la gamme 50-150 K, ce qui reflète une augmentation anormale de la distance V-S. Cette anomalie est accompagnée d’un crossover marqué du comportement Curie-Weiss; à haute température la constante de Weiss = – 43 K révèle un échange antiférromagnétique qui devient négligeable à basse température, alors que le moment localisé et le terme paramagnétique de Pauli restent inchangés. Cela reflète un changement dans les propriétés de cohésion de l’orbitale hybride 3d(V)-3p(S). Le crossover de régime magnétique est corrélé à un crossover de régime de transport; la résistivité électrique dc montre un comportement métallique à haute température et faiblement isolante au dessous de 200 K. Ce résultat contredit la prédiction d’une phase métallique très stable selon des calculs ab initio dans le cadre de la théorie de la fonctionelle densité. Ce désaccord conduit à formuler l’hypothèse que l’interaction d’échange joue un rôle déterminant sur l’état fondamental et que un état métallique peut être stabilisé sous haute pression
47
Ren, Zhensong. "Combined neutron, transport and material based investigation in Ca₃Ir₄Sn₁₃." Thesis, Boston College, 2015. http://hdl.handle.net/2345/bc-ir:104538.
Full textAbstract:
Thesis advisor: Stephen D. WilsonThis dissertation investigates the cubic type II superconductor, Ca₃Ir₄Sn₁₃, discovered by Remeika and the coauthors more than 30 years ago. It was originally discovered be to a superconductor and later suggested to host ferromagnetic spin fluctuations, which lead to a peak-like anomaly in thermodynamic and transport measurements. Later detailed x-ray single crystal structural refinement associated the peak-like anomaly in transport and magnetization measurements with a charge density wave phase transition at the same temperature. The potential charge density wave phase transition T* can be suppressed either by pressure or chemical potential through substitution on the Ca and Ir site such that a temperature-pressure/composition phase diagram can be constructed. Upon investigating magnetism in this compound, polarized neutron scattering and μSR data from our group and other researchers did not reveal any magnetic order or magnetic spin fluctuations at the time scale of μSR . However, through the partial substitution of Ir by Rh, we realized a structural quantum critical point at ambient pressure with 30% of Ir substituted by Rh--providing the research community a valuable material's platform for studying the interplay between 3D charge density wave order and superconductivity. On the other hand, our surprising discovery of the weak HHL (L=odd) type of super-lattice peaks from neutron scattering led us to a tentative model of a distorted Ca sublattice in this material. The similarity of the lattice instabilites of the Remeika compound and A15 superconductors are discussed, which may give us more insight into its role in the formation of the superconducting phase
Thesis (PhD) — Boston College, 2015
Submitted to: Boston College. Graduate School of Arts and Sciences
Discipline: Physics
48
Souza, Valdeci Pereira Mariano de [UNESP]. "Estudo das propriedades elétricas não lineares de polímeros conjugados." Universidade Estadual Paulista (UNESP), 2003. http://hdl.handle.net/11449/91942.
Full textAbstract:
Made available in DSpace on 2014-06-11T19:25:32Z (GMT). No. of bitstreams: 0
Previous issue date: 2003-02-18Bitstream added on 2014-06-13T20:27:50Z : No. of bitstreams: 1
souza_vpm_me_rcla.pdf: 535132 bytes, checksum: d3bce6e40a2c0ef0a0bc8cc227fe99dd (MD5)Neste trabalho, apresentamos um estudo experimental das propriedades elétricas não lineares de polímeros conjugados, como por exemplo, curvas I(V) não lineares para baixos valores de campo elétrico aplicado e existência de um campo elétrico de threshold. Investigamos o comportamento elétrico não linear em pastilhas prensadas de poli(3-metiltiofeno) (P3MT) oxidadas, obtidas através do processo de síntese eletroquímica. Das medidas elétricas realizadas, na faixa de temperatura (~9 K - ~297 K), os resultados experimentais obtidos: curvas I(V), condutividade versus freqüência e constante dielétrica versus freqüência, foram comparados com os diversos modelos teóricos existentes na literatura. Os dados obtidos em toda a faixa de temperatura mencionada mostraram boa concordância com a teoria de tunelamento para CDW (charge density wave deppining) proposta por J. Bardeen.
In this work, we present an experimental study of the non-linear electrical properties in conjugated polymers, as for example, non-linear I(V) curves at low electric fields and existence of a threshold electric field. We investigated the non linear electrical behavior of pressed pellets of poly(3-methilthiopene) (P3MT), which were obtained through electrochemical synthesis oxidized. From the electrical measurements, in the temperature range (~9K - ~297K), the experimental results: I(V) curves, conductivity versus frequency and dielectric constant versus frequency, were compared with the several theoretical models discussed in the literature. The data obtained in the whole temperature range have shown good agreement on the tunneling theory for CDW systems (charge density wave depinning) proposed by J. Bardeen.
49
Cai, Xuguang. "The Investigation of Gravity Waves in the Mesosphere / Lower Thermosphere and Their Effect on Sporadic Sodium Layer." DigitalCommons@USU, 2017. https://digitalcommons.usu.edu/etd/6891.
Full textAbstract:
Gravity waves in the atmosphere are the waves with gravity and buoyancy force as the restoring forces. Gravity waves will significantly impact the Mesosphere Lower / Thermosphere (MLT), and the breaking of gravity waves is the key factor to cause the cool summer and warm winter in the Mesopause region. Therefore, it is important for us to investigate gravity waves. In this dissertation, we mainly use USU Na lidar data to explore gravity waves in the MLT. The exploration is made up of two projects. One is the investigation of gravity wave breaking and the associated dynamic instability by USU Na Lidar and Advanced Mesosphere Temperature Mapper (AMTM). Another is the calculation of gravity wave temperature perturbations and potential energy density by least-squares fitting based on the data from the full-diurnal cycle observation of Na lidar. The sporadic sodium layer is the sharp increase of Na density in a small vertical range (several kilometers) above the Na main layer in the MLT. The formation of the sporadic sodium layer above 100 km remains unknown until now. Here we will investigate the mechanism of the generation of sporadic sodium layer using numeric modeling, including the effect of tide and gravity wave on the variation of Na density.
50
Tuma, Christian. "A QM/QM hybrid method for MP2/Plane-Wave-DFT studies of extended systems." Doctoral thesis, [S.l.] : [s.n.], 2006. http://deposit.ddb.de/cgi-bin/dokserv?idn=983810583.
Full text