No description available.

Thesis (Ph.D.)--Australian National University, 2005.

Active fluids are an interesting new class of non-equilibrium systems in physics. In such fluids, the system is forced out of equilibrium by the individual active particles - in contrast to driven systems where the system is forced out of equilibrium by some external forces. Some biological examples of active fluids are bacterial suspensions and actomyosin solutions inside eukaryotic cells. In the case of bacterial suspensions, the fluid is stirred internally by the swimming bacteria and as a consequence of this, active fluids can have some interesting physics of their own such as hydrodynamic instabilities and spontaneous symmetry breaking. Here, in particular, we study how such instabilities may arise and how they may lead to a non-equilibrium steady state. We also study numerically a droplet of active matter as a simple representation of cell extract comprising actomyosin solution bounded by a cell membrane. It is widely believed that cell motility is driven only by actin polymerization pushing against the cell membrane. However, we show that even in the absence of actin polymerization, actin-myosin contraction alone can also generate a unidirectional motion. This happens due to the spontaneous breakdown of a discrete symmetry at large enough activity (i.e. actomyosin contraction). This non-equilibrium phase transition from stationary to motile state is somewhat similar to the second order phase transition in equilibrium thermodynamics. Finally, we studied the behaviour of an active droplet on a two-dimensional surface to mimic cell crawling. Whereas cell migration in 3D environment maybe driven mainly by actin-myosin contraction (described above), cell crawling on a 2D surface is driven mainly by actin polymerisation. Here we find that localised actin polymerisation can cause protrusion in the cell membrane which is qualitatively similar to lamellipodium formation in cell crawling.

在近期的研究結果中, 相分離被發現發生在具非晶結構的Pd₄₁.₂₅Ni₄₁.₂₅P₁₇.₅合金，而該合金的構成元素之間的有負值的混合焓。通過高分辨率透射電子顯微鏡的直接成像的方法，他們為Pd-Ni-P非晶系統相分離的發生提供了證據。 / 在這篇論文所論述的研究工作中，我們運用類似的技術來研究Pḍ₄₀₊₀₅{U+2093}Nị₄₀₊₀₅{U+2093}P₂₀₋{U+2093}的合金系統從 x = 0到3.5的非晶相分離。 / 實驗結果顯示，任何在空氣中冷卻到578 K再在613K退火一小時的樣品 (乙類樣本)，非晶相分離都沒有發生。然而，在613K退火一小時而沒有經過578K和613K溫度範圍的Pḍ₄₀₊₀₅{U+2093}Nị₄₀₊₀₅{U+2093}P₂₀₋{U+2093}大塊非晶金屬(丙類樣本)，卻在部分成分範圍中發生相分離。在丙類樣本中，當x>1，相分離發生；而當x≤1，相分離沒有發生。通過量度高角環形暗場影像中顯示的兩個相的平均波長，我們可得出其統計結果，而該統計結果與槓桿規則吻合。從此可見，在過冷的Pd-Ni-P熔合合金中存在著亞穩液態混溶間隙。並且這種出現在有負值混合焓的系統的亞穩液態混溶間隙，可以以短程有序的模型來解釋。 / Recently, the phase separation was found in the system of amorphous Pd₄₁.₂₅Ni₄₁.₂₅P₁₇.₅ alloys which has negative heat of mixing among the constituent elements. In their work, the directly imaging method by technique of high resolution TEM provided the evidence of phase separation in amorphous Pd-Ni-P system. / In this work, by applying the similar technique of that previous studies, the alloy systems of Pḍ₄₀₊₀₅{U+2093}Nị₄₀₊₀₅{U+2093}P₂₀₋{U+2093} for x = 0 to 3.5were studied for amorphous phase separation. / The experimental result showed that for any sample which was allowed to cool down in air to 578 K before thermal annealing (B-type), there was no amorphous phase separation. But for the Pḍ₄₀₊₀₅{U+2093}Nị₄₀₊₀₅{U+2093}P₂₀₋{U+2093} BMG that was annealed at 613K for one hour without bypassing the temperature range between 578K and 613K (C-type), phase separation occurred with x>1 but absented when x≤1. The result of average wavelength measurement of the two phases in the HAADF images of the sample with phase separation obeyed the lever rule. This result suggested that in undercooled molten Pd-Ni-P alloys, there is a metastable liquid state miscibility gap. The formation of such miscibility gap in a system with negative heat of mixing can be explained by the model of unique short range orders. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Lau, Man Tat = 過冷鈀、鎳、磷熔化物中的亞穩液態互溶間隙 / 劉文達. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2012. / Includes bibliographical references. / Abstracts also in Chinese. / Lau, Man Tat = Guo leng ba, nie, lin rong hua wu zhong de ya wen ye tai hu rong jian xi / Liu Wenda. / Abstract --- p.i / Acknowledgement --- p.iv / List of Tables --- p.vii / List of Figures --- p.viii / Chapter Chapter 1 --- : Introduction --- p.1 / Chapter 1.1 --- Amorphous metal --- p.1 / Chapter 1.2 --- Phase Separation --- p.3 / Chapter 1.3 --- Nucleation --- p.6 / Chapter 1.4 --- Spinodal Decomposition --- p.10 / Chapter 1.5 --- Objective of the project --- p.16 / Figures --- p.18 / References --- p.26 / Chapter Chapter 2 --- : Experiment --- p.27 / Chapter 2.1 --- Preparation of sample --- p.27 / Chapter 2.2 --- Differential scanning calorimetry --- p.30 / Chapter 2.3 --- Preparation of TEM sample --- p.31 / Chapter 2.4 --- Microstructural analysis --- p.33 / Figures --- p.36 / References --- p.39 / Chapter Chapter 3 --- : A metastable liquid state miscibility gap in undercooled Pd-Ni-P melts --- p.40 / Chapter 3.1 --- Introduction --- p.40 / Chapter 3.2 --- Materials and experimental --- p.41 / Chapter 3.3 --- Results --- p.44 / Chapter 3.4 --- Discussions --- p.49 / Chapter 3.5 --- Conclusions --- p.52 / Table --- p.53 / Figures --- p.54 / References --- p.75

No description available.

Thesis (Ph. D.)--Drexel University, 2005. / Includes abstract and vita. Includes bibliographical references (leaf 130).

Thesis (Ph. D.)--Drexel University, 2006. / Includes abstract and vita. Includes bibliographical references (leaves 157-163).

Thesis (Ph. D.)--Drexel University, 2007. / Includes abstract and vita. Includes bibliographical references (leaves 140-145).

In this thesis the nonlinear and nonequilibrium properties of graphene are experimentally investigated using degenerate four--wave mixing and time--resolved pump--probe spectroscopy. High quality exfoliated natural graphite and large area epitaxial graphene on silicon carbide are investigated with femtosecond and picosecond ultrafast pulses in the near--infrared. A bespoke technique for suspending exfoliated graphene is also presented. In Chapter 3, the third--order nonlinear susceptibility of graphene is measured for the first time and shows a remarkably large response. Degenerate four--wave mixing at near--infrared wavelengths demonstrates an almost dispersionless emission over a broad spectral range. Quantum kinetic theory is employed to estimate the magnitude of the response and is in good agreement with the experimental data. The large susceptibility enables high contrast imaging, with a monolayer flake contrast of the order 10^{7} times higher than for standard reflection imaging. The degenerate four--wave mixing technique is utilised in Chapter 4 to measure the interface carbon signal of epitaxially grown graphene on silicon carbide. Comparable third--order signal from the silicon carbide bulk prevents true interface imaging. Excluding the third--order emission from detection by elongating the emission to outside a band--pass filter range allows for pure interfacial luminescence imaging. Features within the two growth faces are investigated with Raman spectroscopy. Nonlinear measurements are an increasingly popular tool for investigating fundamental properties of graphene. Chapter 5 investigates the influence of ultrafast pulses on the nonlinear response of graphene. High instantaneous intensities at the sample are shown to reduce the nonlinear emission by a factor or two. Comparing the Raman peak positions, widths and intensities before and after irradiation points to a huge doping of the samples, of the order 500 meV. In Chapter 6 the relaxation of photoexcited carriers is measured via time--resolved pump--probe spectroscopy, where a layer dependence of hot phonon decay is observed. Single layer flakes are observed to relax faster than bilayers and trilayers, with an asymptote reached at approximately four layers. Removing the substrate and measuring fully suspended samples reveals the same trend, suggesting that substrate interactions are not the cause of the enhanced decay. The decay mechanism is therefore intrinsic to graphene, perhaps due to coupling to out--of--plane, flexural phonons. The thickness dependence of epitaxial graphene on silicon carbide is compared to that of exfoliated flakes where the layer dependence is not observed. Phonon relaxation times, however, are in good agreement. Predictions for future investigations into this novel material based on the works here are suggested in Chapter 7. Preliminary pump--probe measurements at high carrier concentrations are an example of such progress, which will offer an insight into further decay mechanisms in graphene.

Thesis (Ph.D)--Mathematics, Georgia Institute of Technology, 2009. / Committee Chair: Yi, Yingfei; Committee Member: Chow, Shui-Nee; Committee Member: Dieci, Luca; Committee Member: Verriest, Erik; Committee Member: Weiss, Howie. Part of the SMARTech Electronic Thesis and Dissertation Collection.