Static Configuration Research Articles

Mixed convection in a PCM filled cavity under the influence of a rotating cylinder

In this study, mixed convection in a phase change material filled square cavity under the effect of a rotating cylinder was numerically investigated. The vertical walls are kept at constant temperatures while the horizontal walls are adiabatic. The effects of angular rotational speed of the cylinder (between −7.5 and 7.5), vertical location of the cylinder (between 0.25 and 0.75) and two different cylinder sizes (0.05 and 0.1) on the fluid flow and heat transfer were numerically investigated in detail. It was observed that rotating cylinder parameters can be used to control the heat transfer and melting process in the cavity. For angular rotational speed of cylinder at (ω=7.5) compared to motionless cylinder (ω=0), average heat transfer enhances by about 22.50%. The highest value of the average heat transfer for different vertical locations of the cylinder depends on the angular rotational speed of the cylinder. The average Nusselt number increases 10% when a large cylinder is used compared to smaller one for clockwise rotation of the cylinder and it is 19.8% for the stationary cylinder configuration.

A Novel Feature Incremental Learning Method for Sensor-Based Activity Recognition

Recognizing activities of daily living is an important research topic for health monitoring and elderly care. However, most existing activity recognition models only work with static and pre-defined sensor configurations. Enabling an existing activity recognition model to adapt to the emergence of new sensors in a dynamic environment is a significant challenge. In this paper, we propose a novel feature incremental learning method, namely the Feature Incremental Random Forest (FIRF), to improve the performance of an existing model with a small amount of data on newly appeared features. It consists of two important components – 1) a mutual information based diversity generation strategy (MIDGS) and 2) a feature incremental tree growing mechanism (FITGM). MIDGS enhances the internal diversity of random forests, while FITGM improves the accuracy of individual decision trees. To evaluate the performance of FIRF, we conduct extensive experiments on three well-known public datasets for activity recognition. Experimental results demonstrate that FIRF is significantly more accurate and efficient compared with other state-of-the-art methods. It has the potential to allow the dynamic exploitation of new sensors in changing environments.

27Al NMR Chemical Shifts and Relative Stabilities of Aqueous Monomeric Al3+ Hydrolytic Species with Different Coordination Structures

In this study, the 27Al NMR chemical shifts and relative stabilities of monomeric Al3+ hydrolytic species with different coordination structures in aqueous solution are systematically investigated by using the density functional theory quantum chemical cluster model (DFT-CM) at the B3LYP/6-311+G(d,p) level. The main work includes: the static configurations of 20 possible existing monomeric Al3+ hydrolytic species from Al3+ to Al(OH)4– are optimized, and their 27Al NMR shieldings are calculated; the dehydration reaction pathways for typical monomeric Al3+ hydrolytic species are modeled, and the dominant forms of the intermediate hydrolytic species of Al(OH)2+, Al(OH)2+, and Al(OH)30 are analyzed based on the Gibbs free energy changes of the dehydration reactions. The important role of the tetracoordinated Al(H2O)(OH)30 in the formation mechanism of the polynuclear Keggin-Al13 is discussed. This work provides valuable references for further studying the formation and transformation mechanisms of the aqueous...

On complex structure of local free volume in bond fluctuation model of polymer matrix

Complex dynamics in model polymer-based host-guest systems is ascribed to jamming effects resulting from inhomogeneous dynamics of local free volume in polymer matrix. As a first step towards quantification of this assumption we study the local free volume in static configurations in Monte Carlo Bond Fluctuation Model (BFM), using specially devised local free volume parameter V. Statistical analysis, including various correlation functions and probabilistic distributions, yields a quantitative characterization of a typical equilibrium local volume configuration V(r→) on large, intermediate and local scales. Two types of spatial organizations of local free volume are found and characterized: a liquid-like, constrained by steric interactions, and local voids nearly free of monomers. Those voids form large scale-free clusters with power-law distribution of sizes and complex fractal structure with fractal dimension dependent on cluster's size. The emerging physical picture offers a promising starting point for the characterization of inhomogeneous dynamics of local free volume in BFM and of guest molecules embedded in local volume mosaic states of BFM.

LECTOR incorporated differential cascode voltage swing logic (L-DCVSL)

This contribution aims at incorporating leakage control transistors (LCTs) in differential cascode voltage swing logic (DCVSL) to reduce leakage and is named as L-DCVSL. The concept multi threshold is also introduced in LCTs and resulting static, dynamic and enhanced DCVSL variants are referred as MTL-DCVSL, MTL-dyDCVSL and MTL-EDCVSL. The performance at 90 nm, 65 nm, and 45 nm technology nodes is investigated using SymicaDE tool. Two input exclusive OR/NOR (XOR2/XNOR2) gate is used to illustrate the proposed technique due to its extensive use in arithmetic cores. The leakage current is examined in all the examples and it is found that leakage current decreases with scaling down of geometry. Maximum saving in leakage current is observed to be 81.27% while minimum is 44.18% for MTL-DCVSL. Similar observations for MTL-dyDCVSL and MTL-EDCVSL are (12.24%, 9.52%)/(33%, 66.04%) and (16.06%, 61.67%)/(37.11%, 78.45%) respectively for precharge/evaluate state. Effect of temperature is also investigated and it is found that leakage current in both static and dynamic configurations of DCVSL follows a directly proportional behaviour with respect to temperature.

Type II critical behavior of gravitating magnetic monopoles

I study type II critical collapse in the spherically symmetric gravitating magnetic monopole system. This is an Einstein-Yang-Mills-Higgs system with two matter fields: a field parametrizing the scalar field gauged under $SU(2)$ and a field parametrizing the gauge field. This system offers interesting differences compared to what is commonly found for type II collapse in other systems. For example, instead of the critical solution sitting between collapse and complete dispersal of the matter fields, on the nonblack hole side of the critical solution, the matter fields settle down to a static and stable configuration. More interesting, however, is that I find strong evidence for the existence of two critical solutions, each with their own set of scaling and echoing exponents, which I determine numerically.

Black and gray solitons in holographic superfluids at zero temperature

We construct gray soliton configurations, which move at constant speeds, in holographic superfluids for the first time. Since there should be no dissipation for a moving soliton to exist, we use the simplest holographic superfluid model at zero temperature, considering both the standard and alternative quantizations. For comparison purpose, we first investigate black solitons in the zero temperature holographic superfluids, which are static configurations. Then we focus on the numerical construction of gray solitons under both quantizations, which interpolate between the (static) black solitons and sound waves (moving at the speed of sound). Interestingly, under the standard quantization, a peculiar oscillation of the soliton configurations is observed, very much resembling the Friedel oscillation in fermionic superfluids at the BCS regime. Some implications and other aspects of the soliton configurations are also discussed.

Generating elastic solutions of the Einstein field equations from the Schwarzschild vacuum solution

The problem of generating solutions of the Einstein field equations with an elastic energy–momentum tensor from the Schwarzschild vacuum solution by means of conformal transformations is analyzed. Applying the formulation of relativistic elasticity, suitable conformal factors are obtained for static and non-static elastic spacetime configurations and particular solutions are presented. This work shows that the technique used here permits generating new elastic matter solutions from a vacuum spacetime.

Contact angle hysteresis in a microchannel: Statics

We study contact angle hysteresis in a chemically heterogeneous microchannel by tracking static meniscus configurations in the microchannel upon varying the volume of liquid. We first construct a graphical force balance similar to a previous approach by Joanny and de Gennes for this system, though here with a straight contact line. It is shown that hysteresis is induced by wettability gradients above a finite threshold value. This is also visualized in a phase-plane plot enabling to easily predict stick-slip events of the contact line and the occurrence of hysteresis. Above the threshold and for nonoverlapping Gaussian defects, we find good agreement with the expressions by Joanny and de Gennes for the hysteresis amplitude induced by a dilute system of defects. In particular, the hysteresis amplitude is found to be proportional to the square of the defect force and to the defect concentration. For a model sinusoidal heterogeneity, decreasing the ratio between the heterogeneity wavelength and the microchannel gap size brings the system from a subthreshold regime, to a stick-slip dominated regime, and finally to a regime with a quasiconstant advancing and receding angle. In the latter case, the hysteresis amplitude is found to be proportional to the defect force. We also consider an unusual heterogeneity for which the gradients of increasing and decreasing wettability are different. In such a situation breaking the left/right symmetry, whether or not hysteresis is observed will depend on the side the liquid enters the microchannel.

Dynamics and stationary configurations of heterogeneous foams.

We consider the variational foam model, where the goal is to minimize the total surface area of a collection of bubbles subject to the constraint that the volume of each bubble is prescribed. We apply sharp interface methods to develop an efficient computational method for this problem. In addition to simulating time dynamics, we also report on stationary states of this flow for ≤ 21 bubbles in two dimensions and ≤ 17 bubbles in three dimensions. For small numbers of bubbles, we recover known analytical results, which we briefly discuss. In two dimensions, we also recover previous numerical results, computed using other methods. Particular attention is given to locally optimal foam configurations and heterogeneous foams, where the volumes of the bubbles are not equal. Configurational transitions are reported for the quasi-stationary flow where the volume of one of the bubbles is varied and, for each volume, the stationary state is computed. The results from these numerical experiments are described and accompanied by many figures and videos.

Decentralized MPC for UAVs Formation Deployment and Reconfiguration with Multiple Outgoing Agents

This paper presents a new decentralized algorithm for the deployment and reconfiguration of a multi-agent formation in a convex bounded polygonal area when considering several outgoing agents. The system is deployed over a two-dimensional convex bounded area, each agent being driven by its own linear model predictive controller. At each time instant, the area is partitioned into Voronoi cells associated with each agent. Due to the movement of the agents, this partition is time-varying. The objective of the proposed algorithm is to drive the agents into a static configuration based on the Chebyshev center of each Voronoi cell. When some agents present a non-cooperating behavior (e.g. agents required for a different mission, faulty agents, etc.), they have to leave the formation by tracking a reference outside the system’s workspace. The outgoing agents and their objective positions partition the convex bounded polygonal area into working regions. Each remaining agent will track a new objective point allowing it to avoid the trajectory of the outgoing agents. The computation of this objective position is based on the agent’s safety region (i.e. the intersection of the contracted Voronoi cell and the contracted working region). When the outgoing agents have left the workspace, the remaining agents resume their deployment objective. Simulation results on a formation of a team of unmanned aerial vehicles are finally presented to validate the algorithm proposed in this paper when several agents leave the formation.

The Enigma of the Muon and Tau Solved by Emergent Quantum Mechanics?

This paper addresses the long-standing question of how it may be explained that the three charged leptons (the electron, muon and tau particle) have different masses, despite their conformity in other respects. In the field of Emergent Quantum Mechanics non-singular electron models are being revisited, and from this exploration has come a possible answer. In this paper a deformable droplet model is considered. It is shown how the model can be made self-consistent, whilst obeying the laws of momentum and energy conservation as well as Larmor’s radiation law. The droplet appears to have three different static equilibrium configurations, each with a different mass. Tentatively, these three equilibrium masses were assumed to correspond with the measured masses of the charged leptons. The droplet model was tuned accordingly, and was thereby completely quantified. The dynamics of the droplet then showed a “De Broglie-like” relation p = K / λ . Beat patterns in the vibrations of the droplet play the role of the matter waves of usual quantum mechanics. The value of K , calculated by the droplet theory, practically equals Planck’s constant: K ≅ h . This fact seems to confirm the correctness of identifying the three types of charged leptons with the equilibria of a droplet of charge.

Post-Buckling Analysis of a Uniform Self-Weight Beam with Application to Catenary Riser

This paper focused on a simply supported beam under uniform self-weight, subjected to an axial force at the roller end. The principle of virtual work-energy was used to formulate the equation for the nonlinear deformation of the beam, which involves the bending strain energy, the virtual work due to self-weight, and the virtual work of the axial force applied at the free-sliding roller end. The work–energy functional was expressed in terms of the arc-length coordinate. The functional vanished, yielding the static equilibrium configuration of the beam — a highly nonlinear problem. Finite element and Newton–Raphson iterative methods were used to solve the problem. The beam theory was extended to large sag analysis of a catenary riser. With this, some interesting features of the various configurations of the catenary riser under various end forces were evaluated.

Mechanisms of Oxygen Vacancy Aggregation in SiO2 and HfO2

Dielectric oxide films in electronic devices undergo significant structural changes during device operation under bias. These changes are usually attributed to aggregation of oxygen vacancies resulting in formation of oxygen depleted regions and conductive filaments. However, neutral oxygen vacancies have high diffusion barriers in ionic oxides and their interaction and propensity for aggregation are still poorly understood. In this paper we briefly review the existing data on static configurations of neutral dimers and trimers of oxygen vacancies in technologically relevant SiO$_2$ and HfO$_2$ and then provide new results on the structure and properties of these defects in amorphous SiO$_2$ and HfO$_2$. These results demonstrate weak interaction between neutral O vacancies, which does not explain their quick aggregation. We propose that trapping of electrons, injected from an electrode, by the vacancies may result in creation of new neutral vacancies in the vicinity of pre-existing vacancies. We describe this mechanism in a-SiO$_2$ and demonstrate that this process becomes more efficient as the vacancy clusters grow larger.

Pattern formation for a two-dimensional reaction-diffusion model with chemotaxis

This paper is devoted to study the formation of stationary patterns for a chemotaxis model with nonlinear diffusion and volume-filling effect over a bounded rectangular domain. By using linear stability analysis around the homogeneous steady states we establish conditions for the existence of unstable mode bands that lead to the formation of spatial patterns. We derive the Stuart-Landau equations for the pattern amplitudes by means of weakly nonlinear multiple scales analysis and Fredholm theory. In particular, we find asymptotic expressions for a wide range of patterns sustained by the system. These patterns include mixed-mode, square, hexagonal, and roll stationary configurations. Our analytical results are corroborated by direct simulations of the underlying chemotaxis system.

Experiences of Civil Certification of Multi-Core Processing Systems in Commercial and Military Avionics, Integration Activities, and Analysis

<div class="section abstract"><div class="htmlview paragraph">Avionics systems are currently undergoing a transition from single core processor architectures to multi-core processor architectures. This transition enables significant advantages in reduction in size, weight, power (SWaP) and cost. However, avionics hardware and software certification policies and guidance are evolving as research and experience is gained with multi-core processor architectures. The unique challenges of using multi-core processors in certified avionics will be discussed. The requirements for a virtualization platform supporting multiple real-time operating system (RTOS) partitions on a multi-core processor used in safety-critical avionics systems are defined, including the ability to support multiple design assurance levels (DAL) on multiple cores, fault isolation and containment, static configuration as per ARINC 653, role-based development as per DO-297, and robust partitioning to reduce cost of incremental certification. The paper will present a collaborative approach undertaken by a leading avionics system supplier and a leading safety-critical commercial-off-the-shelf (COTS) RTOS supplier in the development of a multi-core real-time system with DO-178C DAL A software and DO-254 DAL A hardware safety certification on an FAA Program of Record (PoR). The approach taken to comply with FAA CAST-32A objectives will be presented. Particular focus is provided for integration activities and program specific analysis performed by the IMA application developer and integrator to guarantee determinism in the deployed system. Using the approach defined under the PoR, the application developer performs activities including foot-printing under worst-case execution time (WCET) loads and application of numerical methods to predict interference effects. The IMA integrator uses this data to define a performance restricted environment (PRE) and uses WCET verification in the PRE. Tools, analysis methods, and sample results will be presented. The method to capture results is discussed. Finally the paper includes lessons learned during the program.</div></div>

Chemical bonding and nonadiabatic electron wavepacket dynamics in densely quasi-degenerate excited electronic state manifold of boron clusters.

Formation of chemical bonds is theoretically discerned by the presence of static nuclear configuration on a potential energy surface given within the Born-Oppenheimer framework. We here study dynamical chemical bonding for molecules residing in the electronic excited states that are in a densely quasi-degenerate electronic state manifold and thereby keep undergoing extremely frequent nonadiabatic transitions. For this type of the states, the notion of global potential energy surfaces based on the adiabatic representation loses the usual sense. Nonetheless, chemical bonding exists and associated chemical reactions certainly proceed, for which we call chemistry without potential surfaces. As such, we investigate the highly excited states of boron clusters, which have extraordinarily long lifetimes with neither ionization nor dissociation. The dynamical chemical bonds keep rearranging themselves without converging to a static structure, the vivid electron dynamics of which is tracked by means of the nonadiabatic electron wavepacket dynamics theory. To characterize the dynamical bonding theoretically, we propose the notion of hyper-resonance.

Lattice-Boltzmann Simulations of Electrowetting Phenomena.

When a voltage difference is applied between a conducting liquid and a conducting (solid) electrode, the liquid is observed to spread on the solid. This phenomenon, generally referred to as electrowetting, underpins a number of interfacial phenomena of interest in applications that range from droplet microfluidics to optics. Here, we present a lattice-Boltzmann method that can simulate the coupled hydrodynamics and electrostatics equations of motion of a two-phase fluid as a means to model the electrowetting phenomena. Our method has the advantage of modeling the electrostatic fields within the lattice-Boltzmann algorithm itself, eliminating the need for a hybrid method. We validate our method by reproducing the static equilibrium configuration of a droplet subject to an applied voltage and show that the apparent contact angle of the drop depends on the voltage following the Young-Lippmann equation up to contact angles of ≈50°. At higher voltages, we observe a saturation of the contact angle caused by the competition between electric and capillary stresses, similar to previous experimental observations. We also study the stability of a dielectric film trapped between a conducting fluid and a solid electrode and find a good agreement with analytical predictions based on lubrication theory. Finally, we investigate the film dynamics at long times and report observations of film breakup and entrapment similar to previously reported experimental results.

Suppression of Rayleigh-Taylor turbulence by time-periodic acceleration.

The dynamics of Rayleigh-Taylor turbulence convection in the presence of an alternating, time-periodic acceleration is studied by means of extensive direct numerical simulations of the Boussinesq equations. Within this framework, we discover a mechanism of relaminarization of turbulence: the alternating acceleration, which initially produces a growing turbulent mixing layer, at longer times suppresses turbulent fluctuation and drives the system toward an asymptotic stationary configuration. Dimensional arguments and linear stability theory are used to predict the width of the mixing layer in the asymptotic state as a function of the period of the acceleration.

Calibration and External Force Sensing for Soft Robots Using an RGB-D Camera

Benefiting from the deformability of soft robots, calibration, and force sensing for soft robots are possible using an external vision-based system, instead of embedded mechatronic force sensors. In this letter, we first propose a calibration method to calibrate both the sensor-robot coordinate system and the actuator inputs. This task is addressed through a sequential optimization problem for both variables. We also introduce an external force sensing system based on a real-time finite element (FE) model with the assumption of static configurations, and which consists of two steps: force location detection and force intensity computation. The algorithm that estimates force location relies on the segmentation of the point cloud acquired by an RGB-D camera. Then, the force intensities can be computed by solving an inverse quasi-static problem based on matching the FE model with the point cloud of the soft robot. As for validation, the proposed strategies for calibration and force sensing have been tested using a parallel soft robot driven by four cables.