Self consistent kinetic simulations of SPT and HEMP thrusters including the near-field plume region

The Particle-in-Cell (PIC) method was used to study two different ion thruster concepts - Stationary Plasma Thrusters (SPT) and High Efficiency Multistage Plasma Thrusters (HEMP-T), in particular the plasma properties in the discharge chamber due to the different magnetic field configurations. Special attention was paid to the simulation of plasma particle fluxes on the thrusters channel surfaces. In both cases, PIC proved itself as a powerful tool, delivering important insight into the basic physics of the different thruster concepts. The simulations demonstrated that the new HEMP thruster concept allows for a high thermal efficiency due to both minimal energy dissipation and high acceleration efficiency. In the HEMP thruster the plasma contact to the wall is limited only to very small areas of the magnetic field cusps, which results in much smaller ion energy flux to the thruster channel surface as compared to SPT. The erosion yields for dielectric discharge channel walls of SPT and HEMP thrusters were calculated with the binary collision code SDTrimSP. For SPT, an erosion rate on the level of 1 mm of sputtered material per hour was observed. For HEMP, thruster simulations have shown that there is no erosion inside the dielectric discharge channel.Comment: 14 pages, 11 figures This work was presented at 21st International Conference on Numerical Simulation of Plasmas (ICNSP'09

Radio-frequency discharges in Oxygen. Part 1: Modeling

In this series of three papers we present results from a combined experimental and theoretical effort to quantitatively describe capacitively coupled radio-frequency discharges in oxygen. The particle-in-cell Monte-Carlo model on which the theoretical description is based will be described in the present paper. It treats space charge fields and transport processes on an equal footing with the most important plasma-chemical reactions. For given external voltage and pressure, the model determines the electric potential within the discharge and the distribution functions for electrons, negatively charged atomic oxygen, and positively charged molecular oxygen. Previously used scattering and reaction cross section data are critically assessed and in some cases modified. To validate our model, we compare the densities in the bulk of the discharge with experimental data and find good agreement, indicating that essential aspects of an oxygen discharge are captured.Comment: 11 pages, 10 figure

Comparative study of semiclassical approaches to quantum dynamics

Quantum states can be described equivalently by density matrices, Wigner functions or quantum tomograms. We analyze the accuracy and performance of three related semiclassical approaches to quantum dynamics, in particular with respect to their numerical implementation. As test cases, we consider the time evolution of Gaussian wave packets in different one-dimensional geometries, whereby tunneling, resonance and anharmonicity effects are taken into account. The results and methods are benchmarked against an exact quantum mechanical treatment of the system, which is based on a highly efficient Chebyshev expansion technique of the time evolution operator.Comment: 32 pages, 8 figures, corrected typos and added references; version as publishe

On the Wake Structure in Streaming Complex Plasmas

The theoretical description of complex (dusty) plasmas requires multiscale concepts that adequately incorporate the correlated interplay of streaming electrons and ions, neutrals, and dust grains. Knowing the effective dust-dust interaction, the multiscale problem can be effectively reduced to a one-component plasma model of the dust subsystem. The goal of the present publication is a systematic evaluation of the electrostatic potential distribution around a dust grain in the presence of a streaming plasma environment by means of two complementary approaches: (i) a high precision computation of the dynamically screened Coulomb potential from the dynamic dielectric function, and (ii) full 3D particle-in-cell simulations, which self-consistently include dynamical grain charging and non-linear effects. The applicability of these two approaches is addressed

Детектирование индуцированных тепловым потоком напряжений в твердом теле с помощью фотоупругого микроскопа

Мета цієї статті полягає в представленні переваг практичного та ефективного методу модуляційної поляриметрії (МПМ), застосованого до зразка кварцового скла у вигляді пластини для виявлення його найменших внутрішніх термонапружень, викликаних поширення теплової хвилі. Описаний МПМ дозволив провести точні вимірювання двопроменезаломлення, яке супроводжує динаміку термопружності, що зробило можливим обчислення значення розподілу напружень вздовж і поперек напрямку теплового потоку в певні моменти часу, а також їх залежність від часу в певних координатах теплового потоку. Основна мета даної роботи є не тільки вирішення обернених задач нестаціонарної термопружності, що дозволяє отримати просторово-часові температурні функції графічним інтегруванням експериментальних характеристик, але й дослідження динаміки точки максимуму кривизни температурної функції T(t), що є характеристикою теплового фронту в процесі встановлення теплового потоку. Окрім того, було показано, що завдяки високій виявній здатності МПМ застосованої у фотопружному мікроскопі, стало можливим спостерігати радіаційну складову теплопереносу.The aim of this paper is to present adventures of practical and effective modulation polarimetry method (MPM) applied to the plate sample of quartz glass for detection of its minute internal thermoelastic stresses induced by heat wave propagation. Described MPM allowed to make accurate measuring of birefringence that accompany the dynamics of thermoelasticity and made possible to calculate the value of stress distribution along and crosswise to the direction of heat flow at certain moments of time, as well as its dependence on time in defined heat flux coordinates. The main goal of this paper is not only the solution of inverse problems of nonstationary thermoelasticity that allowed obtaining spatio-temporal temperature functions by graphical integration of the experimental characteristics but researching the dynamics of the maximum curvature point of the temperature function T(t) that is a characteristic of the thermal front in the process of heat flow establishment. In addition, it is shown that due to the high detectability of MPM applied in photoelastic microscope became possible to observe the radiation component of the heat transfer process.Цель этой статьи заключается в представлении преимуществ практического и эффективного метода модуляционной поляриметрии (МПМ), примененного к образцу кварцевого стекла в виде пластины для выявления его самых малых внутренних термонапряжений, вызванных распространением тепловой волны. Описанный МПМ позволил провести точные измерения двулучепреломления, которое сопровождает динамику термоупругости, что сделало возможным вычисление значения распределения напряжений вдоль и поперек направления теплового потока в определенные моменты времени, а также их зависимость от времени в определенных координатах теплового потока. Основная цель данной работы является не только решение обратной задачи нестационарной термоупругости, что позволяет получить пространственно-временные температурные функции графическим интегрированием экспериментальных характеристик, но и исследование динамики точки максимума кривизны температурной функции T(t), что является характеристикой теплового фронта в процессе установления теплового потока. Кроме того, было показано, что благодаря применению высокой обнаружительной способности МПМ в фотоупругом микроскопе сделало возможным наблюдать радиационную составляющую теплопереноса

Employing an open-source tool to assess astrocyte tridimensional structure

Astrocytes display important features that allow them to maintain a close dialog with neurons, ultimately impacting brain function. The complex morphological structure of astrocytes is crucial to the role of astrocytes in brain networks. Therefore, assessing morphologic features of astrocytes will help provide insights into their physiological relevance in healthy and pathological conditions. Currently available tools that allow the tridimensional reconstruction of astrocytes present a number of disadvantages, including the need for advanced computational skills and powerful hardware, and are either time-consuming or costly. In this study, we optimized and validated the FIJI-ImageJ, Simple Neurite Tracer (SNT) plugin, an open-source software that aids in the reconstruction of GFAP-stained structure of astrocytes. We describe (1) the loading of confocal microscopy Z-stacks, (2) the selection criteria, (3) the reconstruction process, and (4) the post-reconstruction analysis of morphological features (process length, number, thickness, and arbor complexity). SNT allows the quantification of astrocyte morphometric parameters in a simple, efficient, and semi-automated manner. While SNT is simple to learn, and does not require advanced computational skills, it provides reproducible results, in different brain regions or pathophysiological states.The authors acknowledge funding from national funds through the FCT—Foundation for Science and Technology—project (PTDC/SAU-NSC/118194/2010) to G.T., V.M.S., S.G.G. and J.F.O., and fellowships (SFRH/BD/89714/2012 to V.M.S., SFRH/BPD/97281/2013 to J.F.O., SFRH/BD/101298/2014 to S.G.G., PD/BD/114120/2015 to S.P.N, and PD/BD/127822/2016 to G.T.); Marie Curie Fellowship FP7-PEOPLE-2010-IEF 273936 and BIAL Foundation Grants and 207/14 to J.F.O.; QREN and FEDER funds through Operational program for competitiveness factors—COMPETE, “ON.2 SR&TD Integrated Program—NORTE-07-0124-FEDER-000021”; National and European funds through FCT, and FEDER through COMPETE (PEst-C/SAU/LA0026/2011 and FCOMP-01-0124-FEDER-022724; PEst-C/SAU/LA0026/2013 and FCOMP-01-0124-FEDER-037298, respectively)info:eu-repo/semantics/publishedVersio

The role of thermal energy accommodation and atomic recombination probabilities in low pressure oxygen plasmas

International audienceSurface interaction probabilities are critical parameters that determine the behaviour of low pressure plasmas and so are crucial input parameters for plasma simulations that play a key role in determining their accuracy. However, these parameters are difficult to estimate without in situ measurements. In this work, the role of two prominent surface interaction probabilities, the atomic oxygen recombination coefficient ? O and the thermal energy accommodation coefficient ? E in determining the plasma properties of low pressure inductively coupled oxygen plasmas are investigated using two-dimensional fluid-kinetic simulations. These plasmas are the type used for semiconductor processing. It was found that ? E plays a crucial role in determining the neutral gas temperature and neutral gas density. Through this dependency, the value of ? E also determines a range of other plasma properties such as the atomic oxygen density, the plasma potential, the electron temperature, and ion bombardment energy and neutral-to-ion flux ratio at the wafer holder. The main role of ? O is in determining the atomic oxygen density and flux to the wafer holder along with the neutral-to-ion flux ratio. It was found that the plasma properties are most sensitive to each coefficient when the value of the coefficient is small causing the losses of atomic oxygen and thermal energy to be surface interaction limited rather than transport limited

Investigating mechanisms underpinning the detrimental impact of a high-fat diet in the developing and adult hypermuscular myostatin null mouse

Background: Obese adults are prone to develop metabolic and cardiovascular diseases. Furthermore, over-weight expectant mothers give birth to large babies who also have increased likelihood of developing metabolic and cardiovascular diseases. Fundamental advancements to better understand the pathophysiology of obesity are critical in the development of anti-obesity therapies not only for this but also future generations. Skeletal muscle plays a major role in fat metabolism and much work has focused in promoting this activity in order to control the development of obesity. Research has evaluated myostatin inhibition as a strategy to prevent the development of obesity and concluded in some cases that it offers a protective mechanism against a high-fat diet. Results: We hypothesised that myostatin inhibition should protect not only the mother but also its developing foetus from the detrimental effects of a high-fat diet. Unexpectedly, we found muscle development was attenuated in the foetus of myostatin null mice raised on a high-fat diet. We therefore re-examined the effect of the high-fat diet on adults and found myostatin null mice were more susceptible to diet-induced obesity through a mechanism involving impairment of inter-organ fat utilization. Conclusions: Loss of myostatin alters fatty acid uptake and oxidation in skeletal muscle and liver. We show that abnormally high metabolic activity of fat in myostatin null mice is decreased by a high-fat diet resulting in excessive adipose deposition and lipotoxicity. Collectively, our genetic loss-of-function studies offer an explanation of the lean phenotype displayed by a host of animals lacking myostatin signalling. Keywords: Muscle, Obesity, High-fat diet, Metabolism, Myostati