Time Tn Research Articles

Spent Time of Orbiting Eletron Generating the Quantized Energy En in the Hydrogen Like Atom

Despite the large literature on hydrogen-like atoms, one cannot find any mention as to how long an electron spends in the orbit to generate the quanized radiation energy En. Here, the Heisenberg representation of operators is exteded so as to be able to deal also with imverse oprators. This is necessary when dealing with Coulomb potentials. This then allows to write down the general hydrogen-like atom in a compact form. With the help of operator algebra that includes also the inverse operators, one arrives at the differential equation of the electron trajectory with respect to time.The time solution is achieved through established coupled integral equations. While already established quantized radiation electron energy En is proportional to 1/n2, the newely derived quantized electron circular time tn(e) is proportional to n3 with n=1,2,3,..,and tn(e) being of the order of 10−16 sec in magnitude.

A NUMERICAL STUDY OF JOULE HEATING EFFECT IN ELECTRODEPOSITION PROCESS-CASE OF COPPER ELECTRODEPOSITION

The electrochemical process in the presence of heat dissipation effect (Joule heating effect) is highly detected in practical electroplating solutions such as 0.6 M CuSO4+0.5 M H2SO4 electrolyte, where currents passing through the cathode-anode-electrolyte increase temperature in the electrolyte and electrodes. Due to the complex nature of such systems and the diversity of physics describing it, a theoretical approach of appearance for natural convection on vertical and horizontal sides of a cathode in the presence and absence of Joule effect under unsteady state condition was observed using Comsol Multiphysics. It was found that the onset of natural convection on a vertical side depends on the Joule effect, and the time (tn) for appearance is longer on the edges than in other areas. The horizontal side of a cathode assists the appearance of natural convection in the presence and absence of the Joule effect. The Rayleigh (Ra) number has larger values on the vertical side than the horizontal side due to the effect of surface concentration distribution Cs. A Sherwood, Sh-Ra mathematical relation such that Sh=0.03Ra0.86 was proposed where natural convection had no pronounced effect on the deposition process. It was found that the Joule heating effect negatively affects the electrodeposition process by reducing the local current values.

Neural Network for Solving Nonlinear Parabolic Differential Equations

We develop a cell-average-based neural network (CANN) method to compute nonlinear differential equations. Using feedforward networks, we can train average solutions from t0 + Δt with initial values. In order to find the optimal parameters for the network, in combination with supervised training, we use a BP algorithm. By the trained network, we may compute the approximate solutions at the time t n+1 with the ones at time tn . Numerical results show CANN method permits a very large time step size for solution evolution.

Prediction of Newtonian Droplet Breaking Time from a Capillary at Low Weber Numbers.

Droplet formation and growth processes have numerous scientific and industrial applications. Experimental and numerical studies on the formation, growth, and breaking of droplet are carried out in present work. The numerical results are in good agreement with the experiment. This work focused on the effect of different Weber numbers (We) on the droplet breaking time. The results show when We < 0.05, the length and volume of the droplet increase, and the breaking time decreases rapidly. The resultant force acting on the main droplet suddenly drops around the critical breaking time. The difference rate between the time tn (when the resultant force is zero) and the breaking time tb is less than 8.49%. For the dimensional analysis of the numerical results, a prediction formula of breaking time on the Weber number is modeled as aWeb + c for We < 0.5.

Systemic analysis of a manufacturing process based on a small scale bakery.

The main aim of the article is to present two new innovative concepts of reliability of a functioning manufacturing system in the process of making bread in small-scale bakeries. Reliability is understood as one of the representations of an operator acting on specific streams in time to to t. One of these represents the global reliability of a system as a function of parallel action of all the streams of the system in time to to t and is denoted as Pg(t). The second representation of reliability is a scalar value, Pss It shows a new function of global reliability of a manufacturing process as a product of system stream reliability. In order to plot the flow of the manufacturing process’s global reliability function, we need to perform detailed calculations, computations, and analysis of the differences of individual values in real time, as well as plan an algorithm of the flow of system streams. This needs a lot of effort, translating however, to a detailed picture of the process. In the analysed example, measurements and research revealed an important increase of the value of reliability in a transition from a traditional to a robotised bakery. The article also presents a new concept of the reliability of a technological process, based on the analysis of relations of elements of the following streams: energy, matter, information, time, and finances. It shows the method of specifying streams and the method for defining the reliability of important and supportive relations. Important relations between stream elements are defined as having the reliability value of one in time. Supportive relations bear the reliability within a continuum between zero and one. Important relations are designated based on research, experience, and knowledge. Stream systemic reliability Pss is a scalar value, i.e. a number from the continuum between zero and one. The Pss value characterises failure-free operation of the whole system. Its average value in the normative time tn expresses the efficiency of the manufacturing system. The value Pss is a quotient of the number of important relation and the sum of important and supportive relations. The formula for Pss shows the method of optimising the process through the increasing of the number of important relations between the input stream components. The concept has been applied to study the efficiency of operation of a small-scale bakery. Systemic analysis of a bakery allows for important increase in the reliability of baking bread if robotisation has been implemented. The concept of systemic-stream reliability Pss may be applied to analyse the efficiency of any technological process and optimisation of any manufacturing process.

An a posteriori strategy for adaptive schemes in time for one-dimensional advection-diffusion transport equations

Stability condition is a more restrictive constraint that leads to unnecessary small-time steps with respect to the accuracy and results in computational time wastage. We propose a node by node adaptive time scheme to relax the stability constraint enabling a larger global time step for all the nodes. A nonlinear procedure for optimising both the schemes in time and space is proposed in view of increasing the numerical efficiency and reducing the computational time. The method is based on a four-parameter family of schemes we shall tune in function of the physical data (velocity, diffusion), the characteristic size in time and space, and the local regularity of the function leading to a nonlinear procedure. The a posteriori strategy we adopt consists in, given the solution at time tn, computing a candidate solution with the highest accurate schemes in time and space for all the nodes. Then, for the nodes that present some instabilities, both the schemes in time and space are modified and adapted in order to preserve the stability with a large time step. The updated solution is computed with node-dependent schemes both in time and space. For the sake of simplicity, only convection-diffusion problems are addressed as a prototype with a two-parameters five-points finite difference method for the spatial discretisation together with an explicit time two-parameters four-stages Runge–Kutta method. We prove that we manage to obtain an optimal time-step algorithm that produces accurate numerical approximations exempt of non-physical oscillations.

Simulation study of local thermal runaway of 18650 lithium battery module under multi-point thermal trigger

The thermal runaway of lithium power battery is the key problem of battery safety, according to the standard SAE J2464–2009 single point heating key position, the proposed multi-point trigger based thermal runaway of lithium power battery module simulation method and battery module thermal runaway battery monomer ratio PN, thermal runaway trigger time tn two indicators, the thermal runaway rule of 18650 lithium power battery module under different trigger position, trigger points. The results show that considering the external thermal insulation conditions of the power lithium battery module, the geometric angular position in the module is the most dangerous position, and the number of thermal trigger points is positively correlated with PN.

Double gloving of disposable nitrile gloves exposed to diethylene glycol mono-n-butyl ether

Double gloving of disposable gloves is now commonplace in healthcare settings when extra protection is needed against aqueous solutions and especially for antineoplastic drugs in isotonic aqueous media. In the present study, an ASTM F739 2.54 cm cell with closed-loop water collection without recirculation at 35 °C in a moving tray water bath was used to test the permeation of diethylene glycol mono-n-butyl ether (DGBE) through four types of disposable nitrile gloves that were singly and doubly layered in the permeation cell. Samples were taken over 8 hr for capillary gas chromatograph-mass spectrometer quantitation. The breakthrough time (tn) at a permeation of 250 ng/cm2 increased as thickness increased for single layers, but the steady-state permeation rates Ps in µg/cm2/min did not always decrease with increasing thickness. The double-layer tn, Ps and thickness were also more variable relative to a single layer. The thinnest glove with 80 m thickness showed a tn = 0–5 min whereas its double layer was 15–20 min. The thickest glove of 132 µm exhibited a tn = 10–15 min but its double layer was tn = 45–55 min. The adjusted double-layer average tn divided by the adjusted single-layer average tn was 4.0 ± 0.8. The adjusted average single-layer Ps divided by the adjusted average double-layer Ps was 3.5 ± 0.8. Other results showed that the average glove swelling was <10%; microscopic and leak testing indicated no penetration and reflectance infrared analysis also showed no chemical changes on the inside glove surfaces. Thus, the permeations were adjudged to obey Fick’s First Law of Diffusion to allow calculation of diffusion coefficients D in cm2/min. The average single-layer D divided by the average double-layer D was 1.3 ± 0.2. Double gloving in the field is therefore also probably more protective than single gloving against DGBE for the four types of disposable nitrile gloves tested.

High order direct Arbitrary-Lagrangian-Eulerian schemes on moving Voronoi meshes with topology changes

We present a new family of very high order accurate direct Arbitrary-Lagrangian-Eulerian (ALE) Finite Volume (FV) and Discontinuous Galerkin (DG) schemes for the solution of nonlinear hyperbolic PDE systems on moving two-dimensional Voronoi meshes that are regenerated at each time step and which explicitly allow topology changes in time. The Voronoi tessellations are obtained from a set of generator points that move with the local fluid velocity. We employ an AREPO-type approach [173], which rapidly rebuilds a new high quality mesh exploiting the previous one, but rearranging the element shapes and neighbors in order to guarantee that the mesh evolution is robust even for vortex flows and for very long simulation times. The old and new Voronoi elements associated to the same generator point are connected in space–time to construct closed space–time control volumes, whose bottom and top faces may be polygons with a different number of sides. We also have to incorporate some degenerate space–time sliver elements, which are needed in order to fill the space–time holes that arise because of the topology changes in the mesh between time tn and time tn+1. The final ALE FV-DG scheme is obtained by a novel redesign of the high order accurate fully discrete direct ALE schemes of Boscheri and Dumbser [21,23], which have been extended here to general moving Voronoi meshes and space–time sliver elements. Our new numerical scheme is based on the integration over arbitrary shaped closed space–time control volumes combined with a fully-discrete space–time conservation formulation of the governing hyperbolic PDE system. In this way the discrete solution is conservative and satisfies the geometric conservation law (GCL) by construction. Numerical convergence studies as well as a large set of benchmark problems for hydrodynamics and magnetohydrodynamics (MHD) demonstrate the accuracy and robustness of the proposed method. Our numerical results clearly show that the new combination of very high order schemes with regenerated meshes that allow topology changes in each time step lead to substantial improvements compared to direct ALE methods on moving conforming meshes without topology change.

High order direct Arbitrary-Lagrangian-Eulerian (ALE) PNPM schemes with WENO Adaptive-Order reconstruction on unstructured meshes

In this work we present a conservative WENO Adaptive Order (AO) reconstruction operator applied to an explicit one-step Arbitrary-Lagrangian-Eulerian (ALE) discontinuous Galerkin (DG) method. The spatial order of accuracy is improved by reconstructing higher order piecewise polynomials of degree M>N, starting from the underlying polynomial solution of degree N provided by the DG scheme. High order of accuracy in time is achieved by the ADER approach, making use of an element-local space-time Galerkin finite element predictor that arises from a one-step time integration procedure. As a result, space-time polynomials of order M+1 are obtained and used to perform the time evolution of the numerical solution adopting a fully explicit DG scheme.To maintain algorithm simplicity, the mesh motion is restricted to be carried out using straight lines, hence the old mesh configuration at time tn is connected with the new one at time tn+1 via space-time segments, which result in space-time control volumes on which the governing equations have to be integrated in order to obtain the time evolution of the discrete solution. Our algorithm falls into the category of direct Arbitrary-Lagrangian-Eulerian (ALE) schemes, where the governing PDE system is directly discretized relying on a space-time conservation formulation and which already takes into account the new grid geometry directly during the computation of the numerical fluxes. A local rezoning strategy might be used in order to locally optimize the mesh quality and avoiding the generation of invalid elements with negative determinant. The proposed approach reduces to direct ALE finite volume schemes if N=0, while explicit direct ALE DG schemes are recovered in the case of N=M.In order to stabilize the DG solution, an a priori WENO based limiting technique is employed, that makes use of the numerical solution inside the element under consideration and its neighbor cells to find a less oscillatory polynomial approximation. By using a modal basis in a reference element, the evaluation of the oscillation indicators is very easily and efficiently carried out, hence allowing higher order modes to be properly limited, while leaving the zero-th order mode untouched for ensuring conservation.Numerical convergence rates for 2≤N,M≤4 are presented as well as a wide set of benchmark test problems for hydrodynamics on moving and fixed unstructured meshes.

Slower variation of the generation sizes induced by heavy-tailed environment for geometric branching

Motivated by seminal paper of Kozlov et al. Kesten et al. (1975) we consider in this paper a branching process with a geometric offspring distribution parametrized by random success probability A and immigration equals 1 in each generation. In contrast to above mentioned article, we assume that environment is heavy-tailed, that is logA−1(1−A) is regularly varying with a parameter α>1, that is that P(logA−1(1−A)>x)=x−αL(x) for a slowly varying function L. We will prove that although the offspring distribution is light-tailed, the environment itself can produce extremely heavy tails of distribution of the population at nth generation which gets even heavier with n increasing. Precisely, in this work, we prove that asymptotic tail P(Zl≥m) of lth population Zl is of order (log(l)m)−αL(log(l)m) for large m, where log(l)m=log…logm. The proof is mainly based on Tauberian theorem. Using this result we also analyze the asymptotic behavior of the first passage time Tn of the state n∈Z by the walker in a neighborhood random walk in random environment created by independent copies (Ai:i∈Z) of (0,1)-valued random variable A.

Quantitative Comparison of Photoplethysmographic Waveform Characteristics: Effect of Measurement Site.

Introduction: Photoplethysmography (PPG) has been widely used to assess cardiovascular function. However, few studies have comprehensively investigated the effect of measurement site on PPG waveform characteristics. This study aimed to provide a quantitative comparison on this.Methods: Thirty six healthy subjects participated in this study. For each subject, PPG signals were sequentially recorded for 1 min from six different body sites (finger, wrist under (anatomically volar), wrist upper (dorsal), arm, earlobe, and forehead) under both normal and deep breathing patterns. For each body site under a certain breathing pattern, the mean amplitude was firstly derived from recorded PPG waveform which was then normalized to derive several waveform characteristics including the pulse peak time (Tp), dicrotic notch time (Tn), and the reflection index (RI). The effects of breathing pattern and measurement site on the waveform characteristics were finally investigated by the analysis of variance (ANOVA) with post hoc multiple comparisons.Results: Under both breathing patterns, the PPG measurements from the finger achieved the highest percentage of analyzable waveforms for extracting waveform characteristics. There were significant effects of breathing pattern on Tn and RI (larger Tn and smaller RI with deep breathing on average, both p < 0.03). The effects of measurement site on mean amplitude, Tp, Tn, and RI were significant (all p < 0.001). The key results were that, under both breathing patterns, the mean amplitude from finger PPG was significantly larger and its Tp and RI were significantly smaller than those from the other five sites (all p < 0.001, except p = 0.04 for the Tp of “wrist under”), and Tn was only significantly larger than that from the earlobe (both p < 0.05).Conclusion: This study has quantitatively confirmed the effect of PPG measurement site on PPG waveform characteristics (including mean amplitude, Tp, Tn, and RI), providing scientific evidence for a better understanding of the PPG waveform variations between different body sites.

Fast real-time time-dependent hybrid functional calculations with the parallel transport gauge and the adaptively compressed exchange formulation

We present a new method to accelerate real-time time-dependent density functional theory (rt-TDDFT) calculations with hybrid exchange–correlation functionals. In the context of a large basis set such as planewaves and real space grids, the main computational bottleneck for large scale calculations is the application of the Fock exchange operator to the time-dependent orbitals. Our main goal is to reduce the frequency of applying the Fock exchange operator, without loss of accuracy. We achieve this by combining the recently developed parallel transport (PT) gauge formalism (Jia et al. J. Chem. Theory Comput. 2018) and the adaptively compressed exchange operator (ACE) formalism (Lin, J. Chem. Theory Comput. 2016). The PT gauge yields the slowest possible dynamics among all choices of gauge. When coupled with implicit time integrators such as the Crank–Nicolson (CN) scheme, the resulting PT–CN scheme can significantly increase the time step from sub-attoseconds to 10−100 attoseconds. At each time step tn, PT–CN requires the self-consistent solution of the orbitals at time tn+1. We use ACE to delay the update of the Fock exchange operator in this nonlinear system, while maintaining the same self-consistent solution. We verify the performance of the resulting PT–CN–ACE method by computing the absorption spectrum of a benzene molecule and the response of bulk silicon systems to an ultrafast laser pulse, using the planewave basis set and the HSE exchange–correlation functional. We report the strong and weak scaling of the PT–CN–ACE method for silicon systems ranging from 32 to 1024 atoms, on a parallel computer with up to 2048 computational cores. Compared to standard explicit time integrators such as the 4th order Runge–Kutta method (RK4), we find that the PT–CN–ACE can reduce the frequency of the Fock exchange operator application by nearly 70 times, and the thus reduce the overall wall clock time by 46 times for the system with 1024 atoms. Hence our work enables hybrid functional rt-TDDFT calculations to be routinely performed with a large basis set for the first time.

Analysis of evolving capillary transition, gravitational fingering, and dissolution trapping of CO2 in deep saline aquifers during continuous injection of supercritical CO2

Dissolution trapping of supercritical CO2 (ScCO2) in deep saline aquifers undergoes different stages such as ScCO2 mixing with brine, buoyant convection and slumping of CO2 rich brine. The effects of permeability and capillarity on these stages were previously studied for (i) uniformly injected ScCO2 at the top of the aquifer and (ii) spreading from a finite initial patch of CO2 or after short injection duration of CO2. In this paper we discuss the results of continuous injection of CO2 from a well that is screened inside the aquifer between caprock at the top and bedrock at the bottom. For this case, the injection pressure significantly influences the spreading of CO2 plumes. The injection pressure decreases with time for constant mass injection flux of ScCO2 (m˙). Injected ScCO2 flows upward and spreads laterally below the caprock. An evolving capillary transition zone is one of the main features of this study. Below the capillary transition zone, the diffusive boundary layer of dissolved CO2 becomes unstable depending on the injection pressure (PScCO2), permeability (k) and capillary entry pressure (Pc0). The evolution of ScCO2 and dissolved CO2 plume and injection pressure history are directly proportional to m˙/k. The evolution rate and the onset time of gravitational instability are inversely proportional to k. For very small and large m˙/k ratio, gravitational instability may not occur. Higher permeability yields more effective CO2 dissolution trapping and dissolution flux increases after onset of convection. For continuous injection case, the plume tip position varies as the power law of time tn where 0.6 < n < 0.85 where t is in years and plume tip position is in meter.

A posteriori sub-cell finite volume limiting of staggered semi-implicit discontinuous Galerkin schemes for the shallow water equations

We propose a novel family of a posteriori sub-cell finite volume limiters for spatially high order accurate semi-implicit discontinuous Galerkin (DG) schemes on staggered Cartesian grids for the solution of the shallow water equations expressed in conservative form in one and two space dimensions.We start from the unlimited arbitrary high order accurate staggered semi-implicit DG scheme proposed by Dumbser and Casulli (2013). In this method, the continuity equation and the momentum equations are integrated using a discontinuous finite element strategy on staggered control volumes, where the discrete free surface elevation is defined on the main grid and the discrete momentum is defined on edge-based staggered dual control volumes. In the semi-implicit approach, pressure terms are discretized implicitly, while the nonlinear convective terms are discretized explicitly. Inserting the momentum equations into the discrete continuity equation leads to a well conditioned block penta-diagonal linear system for the free surface elevation which can be efficiently solved with modern iterative methods. However, according to Godunov's theorem, any unlimited high order scheme inevitably produces spurious oscillations in the vicinity of discontinuities and strong gradients.In the present paper, we therefore propose to extend the successful family of a posteriori subcell finite volume limiters recently introduced by Dumbser et al. (2014) for explicit DG schemes also to semi-implicit time discretizations. At time tn the unlimited DG scheme is run in order to produce a so-called candidate solution for time tn+1. Then, the cells characterized by a non-admissible candidate solution are found by using physical and numerical detection criteria based on the positivity of the solution, the absence of floating point errors and the use of a relaxed discrete maximum principle (DMP) according to the MOOD strategy of Clain, Loubère and Diot (2013). In all the cells that are flagged as troubled control volumes a more robust semi-implicit finite volume (FV) method is then applied on a sub-grid composed of 2P+1 cells, where P denotes the polynomial degree used for approximating the discrete solution within the DG scheme. Then, after having identified the troubled cells, the linear system for the new free surface elevation is assembled and solved again, where unlimited cells use the high order semi-implicit DG scheme and limited cells are evolved via the more robust finite volume method. Finally, from the subcell finite volume averages a higher order DG polynomial is reconstructed and the scheme proceeds with the next time step.We apply the new semi-implicit staggered DG method with a posteriori subcell FV limiter to classical benchmarks such as Riemann problems in 1D and circular dam-break problems in 2D with shock waves, showing that the new subcell finite volume limiter is able to resolve shocks accurately without producing spurious oscillations. Moreover, if the solution is smooth, the detector does not find any troubled cells, as expected; consequently, the limiter is not activated and the method corresponds to the unlimited staggered semi-implicit DG scheme. In addition, we carry out numerical tests which show that the new scheme is well-balanced and able to deal with wet and dry fronts.

A novel finite difference discrete scheme for the time fractional diffusion-wave equation

In this article, we consider initial and boundary value problems for the diffusion-wave equation involving a Caputo fractional derivative (of order α, with 1<α<2) in time. A novel finite difference discrete scheme is developed for using discrete fractional derivative at time tn in which some new coefficients (k+12)2−α−(k−12)2−α instead of (k+1)2−α−k2−α are derived. Stability and convergence of the method are rigorously established. We prove that the novel discretization is unconditionally stable, and the optimal convergence orders O(τ3−α+h2) both in L2 and L∞ are derived, where τ is the time step and h is space mesh size. Moreover, the applicability and accuracy of the scheme are demonstrated by numerical experiments to support our theoretical analysis.

Arbitrary-Lagrangian–Eulerian Discontinuous Galerkin schemes with a posteriori subcell finite volume limiting on moving unstructured meshes

We present a new family of high order accurate fully discrete one-step Discontinuous Galerkin (DG) finite element schemes on moving unstructured meshes for the solution of nonlinear hyperbolic PDE in multiple space dimensions, which may also include parabolic terms in order to model dissipative transport processes, like molecular viscosity or heat conduction. High order piecewise polynomials of degree N are adopted to represent the discrete solution at each time level and within each spatial control volume of the computational grid, while high order of accuracy in time is achieved by the ADER approach, making use of an element-local space–time Galerkin finite element predictor. A novel nodal solver algorithm based on the HLL flux is derived to compute the velocity for each nodal degree of freedom that describes the current mesh geometry. In our algorithm the spatial mesh configuration can be defined in two different ways: either by an isoparametric approach that generates curved control volumes, or by a piecewise linear decomposition of each spatial control volume into simplex sub-elements. Each technique generates a corresponding number of geometrical degrees of freedom needed to describe the current mesh configuration and which must be considered by the nodal solver for determining the grid velocity.The connection of the old mesh configuration at time tn with the new one at time tn+1 provides the space–time control volumes on which the governing equations have to be integrated in order to obtain the time evolution of the discrete solution. Our numerical method belongs to the category of so-called direct Arbitrary-Lagrangian–Eulerian (ALE) schemes, where a space–time conservation formulation of the governing PDE system is considered and which already takes into account the new grid geometry (including a possible rezoning step) directly during the computation of the numerical fluxes. We emphasize that our method is a moving mesh method, as opposed to total Lagrangian formulations that are based on a fixed computational grid and which instead evolve the mapping of the reference configuration to the current one.Our new Lagrangian-type DG scheme adopts the novel a posteriori sub-cell finite volume limiter method recently developed in [62] for fixed unstructured grids. In this approach, the validity of the candidate solution produced in each cell by an unlimited ADER-DG scheme is verified against a set of physical and numerical detection criteria, such as the positivity of pressure and density, the absence of floating point errors (NaN) and the satisfaction of a relaxed discrete maximum principle (DMP) in the sense of polynomials. Those cells which do not satisfy all of the above criteria are flagged as troubled cells and are recomputed at the aid of a more robust second order TVD finite volume scheme. To preserve the subcell resolution capability of the original DG scheme, the FV limiter is run on a sub-grid that is 2N+1 times finer compared to the mesh of the original unlimited DG scheme. The new subcell averages are then gathered back into a high order DG polynomial by a usual conservative finite volume reconstruction operator.The numerical convergence rates of the new ALE ADER-DG schemes are studied up to fourth order in space and time and several test problems are simulated in order to check the accuracy and the robustness of the proposed numerical method in the context of the Euler and Navier–Stokes equations for compressible gas dynamics, considering both inviscid and viscous fluids. Finally, an application inspired by Inertial Confinement Fusion (ICF) type flows is considered by solving the Euler equations and the PDE of viscous and resistive magnetohydrodynamics (VRMHD).

Growth of silicon nitride by nitridation of amorphous silicon at low temperature in hot-wire CVD

Silicon nitride (SiNx) layers of varying thickness were fabricated in a a-Si/SiNx/a-Si heterostructure via nitridation of the bottom a-Si layer, using ammonia (NH3) gas, in the hot-wire chemical vapor deposition (HWCVD) chamber at 250°C. The thickness of the SiNx in the film was varied by changing the nitridation time (tN) in range of 1–30min. Raman analysis showed that the a-Si and SiNx layers formed in the films were amorphous. Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS) results indicated Si3N4 was formed in the nitrided a-Si. Presence of strong SiH2 (2086cm−1) peaks in the FTIR spectrum suggested the hydrogen in a-Si effused at 250°C. XPS Si2p spectra and high resolution transmission electron microscopy images showed thin SiNx layer of thickness 1.8–7.6nm was formed. Formation of SiNx thicker than 7.6nm even at a low temperature (250°C) is suggestive of the H effusion promoting both the reaction and the diffusion of the nitridants in a-Si. The kinetics of the growth of SiNx during nitridation of the a-Si layer closely matches the growth process described by diffusion model, wherein the reaction of nitridants and a-Si is controlled by diffusion in the SiNx layer formed.

How humans use visual optic flow to regulate stepping during walking

Humans use visual optic flow to regulate average walking speed. Among many possible strategies available, healthy humans walking on motorized treadmills allow fluctuations in stride length (Ln) and stride time (Tn) to persist across multiple consecutive strides, but rapidly correct deviations in stride speed (Sn=Ln/Tn) at each successive stride, n. Several experiments verified this stepping strategy when participants walked with no optic flow. This study determined how removing or systematically altering optic flow influenced peoples’ stride-to-stride stepping control strategies. Participants walked on a treadmill with a virtual reality (VR) scene projected onto a 3m tall, 180° semi-cylindrical screen in front of the treadmill. Five conditions were tested: blank screen (“BLANK”), static scene (“STATIC”), or moving scene with optic flow speed slower than (“SLOW”), matched to (“MATCH”), or faster than (“FAST”) walking speed. Participants took shorter and faster strides and demonstrated increased stepping variability during the BLANK condition compared to the other conditions. Thus, when visual information was removed, individuals appeared to walk more cautiously. Optic flow influenced both how quickly humans corrected stride speed deviations and how successful they were at enacting this strategy to try to maintain approximately constant speed at each stride. These results were consistent with Weber’s law: healthy adults more-rapidly corrected stride speed deviations in a no optic flow condition (the lower intensity stimuli) compared to contexts with non-zero optic flow. These results demonstrate how the temporal characteristics of optic flow influence ability to correct speed fluctuations during walking.

Long-term photometric behavior of the eclipsing cataclysmic variable V729 Sagittarii

Abstract We present the analysis results of an eclipsing cataclysmic variable (CV) V729 Sgr, based on our observations and American Association of Variable Star Observers data. Some outburst parameters are determined, such as outburst amplitude (An) and recurrence time (Tn), and then the relationship between An and Tn is discussed. A cursory examination of the long-term light curves reveals that there are small-amplitude outbursts and dips present, which is similar to the behavior seen in some novalike CVs (NLs). More detailed inspection suggests that the outbursts in V729 Sgr may be Type A (outside-in) with a rise time ∼1.76 d. Further analysis also shows that V729 Sgr is an intermediate between dwarf nova and NLs, and we constrain its mass transfer rate to $1.59\times 10^{-9}&amp;lt;\skew5\dot{M}_{2}&amp;lt;5.8\times 10^{-9}\,M_{\odot }\:$yr−1 by combining the theory for Z Cam type stars with observations. Moreover, the rapid oscillations in V729 Sgr were detected and analyzed for the first time. Our results indicate that the oscillation at ∼25.5 s is a true dwarf nova oscillation (DNO), being associated with the accretion events. The classification of the oscillations at ∼136 and 154 s as longer-period DNOs (lpDNOs) is based on the relation between PlpDNOs and PDNOs. Meanwhile, quasi-periodic oscillations with periods of hundreds of seconds are also detected.