Non-uniform System Research Articles

Hall voltages without a magnetic field in a non-uniform two-dimensional electron system

We report on a measurement of giant second-harmonic Hall voltages which occur without a magnetic field and do not change their sign on current reversal in a two-dimensional electron system with a transverse density gradient. A quadratic dependence on the electric field, a strong temperature dependence, and both magnitude and directional dependence on the magnetic field are also observed. Such behavior points towards a plausible explanation based on a novel spin Hall effect with in-plane spin polarization.

Modeling and Control of a Nonuniform Vibrating String Under Spatiotemporally Varying Tension and Disturbance

In this paper, robust adaptive boundary control is developed for a class of flexible string systems under unknown spatiotemporally varying distributed disturbance and time-varying boundary disturbance. The vibrating string is nonuniform since the spatiotemporally varying tension applied to the system. The nonuniform vibrating string system is represented by a nonlinear nonhomogeneous partial differential equation (PDE) and two ordinary differential equations (ODEs). Model-based control is first proposed at the right boundary of the string to suppress the vibration of the flexible nonuniform string system. To compensate for the system parametric uncertainties, robust adaptive boundary control is developed. With the proposed control, the uniformly ultimate boundness of the closed-loop system is demonstrated via Lyapunov's direct method. The state of the nonuniform string system is proven to converge to a small neighborhood of zero by appropriately choosing the design parameters. Simulations are provided to illustrate the effectiveness of the proposed control.

RST controller design for a non-uniform multi-rate control system

In this work, a non-uniform multi-rate controller which includes an RST control stage is introduced. Due to several issues, in some systems the use of non-uniform (irregular) multi-rate sampling becomes inevitable. When using a uniform (regular) multi-rate controller in this kind of situations, control performance is usually degraded (if it is compared to that obtained in the nominal, uniform sampling context). Thus, the design of a non-uniform controller proper for this sampling scheme is needed to keep the performance. A sequence of different non-uniform sampling frames can be considered, and different controllers must be designed for each frame using appropriate methods. When switching among these controllers, stability problems can appear. So, the control system stability will be assured in terms of Linear Matrix Inequalities (LMIs). To achieve some advantages at the design step, the discrete-time input–output representation will be used. But, since the classical, uniform z−i delay operator could not be able to represent non-uniform sampling situations, the so-called non-uniform operator will be required. Simulation results illustrate that this control proposal is able to keep control system performance and preserve stability.

A 2uFunction representation for non-uniform type-2 fuzzy sets: Theory and design

The theoretical and computational complexities involved in non-uniform type-2 fuzzy sets (T2 FSs) are main obstacles to apply these sets to modeling high-order uncertainties. To reduce the complexities, this paper introduces a 2uFunction representation for T2 FSs. This representation captures the ideas from probability theory. By using this representation, any non-uniform T2 FS can be represented by a function of two uniform T2 FSs. In addition, any non-uniform T2 fuzzy logic system (FLS) can be indirectly designed by two uniform T2 FLSs. In particular, a 2uFunction-based trapezoid T2 FLS is designed. Then, it is applied to the problem of forecasting Mackey–Glass time series corrupted by two kinds of noise sources: (1) stationary and (2) non-stationary additive noises. Finally, the performance of the proposed FLS is compared by (1) other types of FLS: T1 FLS and uniform T2 FLS, and (2) other studies: ANFIS [54], IT2FNN-1 [54], T2SFLS [3] and Q-T2FLS [35]. Comparative results show that the proposed design has a low prediction error as well as is suitable for online applications.

The nondissipative spin Hall current in a nonuniform Rashba effect system

The spin Hall current in a two-dimensional electron system with nonuniform Rashba spin–orbit interaction (SOI) is investigated by means of the lattice Green's function method. Large electric and spin Hall currents are produced by this nonuniform Rashba SOI, while the electric Hall current vanishes in the uniform Rashba SOI system. A nondissipative spin Hall current is also produced, without any longitudinal voltage bias, any external magnetic field and any special class of band insulators.

Aware conflict detection of non-uniform memory access system and prevention for transactional memory

Most transactional memory (TM) research focused on multi-core processors, and others investigated at the clusters, leaving the area of non-uniform memory access (NUMA) system unexplored. The existing TM implementations made significant performance degradation on NUMA system because they ignored the slower remote memory access. To solve this problem, a latency-based conflict detection and a forecasting-based conflict prevention method were proposed. Using these techniques, the NUMA aware TM system was presented. By reducing the remote memory access and the abort rate of transaction, the experiment results show that the NUMA aware strategies present good practical TM performance on NUMA system.

Impacts of the mixed wettability on liquid water and reactant gas transport through the gas diffusion layer of proton exchange membrane fuel cells

In this paper, we develop a pore network model for liquid water and reactant gas transport through the porous gas diffusion layer (GDL) of mixed wettability. We first consider the case of uniform distribution of hydrophilic fraction along the GDL thickness. It is revealed that the addition of hydrophilic pores has a negligible impact on liquid saturation profile when the hydrophilic fraction is low (⩽0.2), whereas in the case of higher hydrophilic fraction (⩾0.4), a flat shape of liquid saturation profile is observed along the GDL thickness. The total liquid saturation in the GDL is found to first decrease and then increase with the increase of hydrophilic pores; and an optimum hydrophilic fraction exists leading to the maximum limiting current density. Also, we investigate the transport process in the GDL of non-uniform wettability (i.e., the hydrophilic fraction is 0.4 near the network inlet, while at the downstream region it is 0.3). As compared to the uniform case, the liquid saturation level at the downstream region is drastically decreased in the non-uniform system, thereby leading to a higher limiting current density. These findings suggest that the fuel cell performance can be improved by designing the GDL with appropriate wettability distribution.

THE NEAR FIELD IN THE MIXING OF A THREE-DIMENSIONAL INCLINED POLLUTANT JET WITH A CROSSFLOW

An experimental investigation was carried out to study the structure of the flow field resulting from the interaction of an inclined pollutant jet with a crossflow. The study of the flow field was conducted in a wind tunnel test by means of particle image velocimetry (PIV) system. As the jet was discharged with a variable angle, the resulting flow has been found to be quite complex owing to its three-dimensional nature and the interaction between several flow regions. Results showed the dependence of the emerging jet flow structure on its ratio velocity and the Reynolds number. Extensive wind tunnel experimental results are presented; they concern the Kelvin-Helmholtz vortical structures and the effect of the velocity ratio v0=u1 on the interacting zone. A three-dimensional numerical model with a second-order turbulent model (RSM) and a nonuniform grid system is used to examine the behavior of the emerging jet. The comparison of the numerical and experimental results gives satisfactory agreement.

Limiting kinetic equation for describing a first-order chemical reaction with spatially nonuniform diffusion and kinetic coefficients

A spatially nonuniform system in which a first-order chemical reaction occurs is considered. Both the diffusion coefficient and the kinetic coefficient of the reaction are assumed to be dependent on spatial coordinates. An asymptotically valid method is proposed for reducing a diffusion equation (under the described conditions) in the presence of a source (a reaction) to a simple kinetic equation containing a constant kinetic coefficient. A functional is derived that makes it possible to use variational methods for determining the kinetic coefficient.

A potential distribution induced mapping of free energies for simple fluids

The potential distribution theorem (PDT) is utilized to construct an effective density, the pseudo-densityρpseudo(z), that enables mapping of the free energies of the uniform fluid exactly onto the nonuniform system values. In addition, a similar quantity, the pseudo-chemical potentialμpseudo(z), is given as the chemical potential produced by the uniform equation of state upon using the nonuniform density ρw(1)(z) as input. The PDT connects three quantities: the work Wins(z) for inserting a test particle into the fluid, the chemical potential μ0 of the bulk fluid, and the nonuniform singlet density ρw(1)(z). We perform Metropolis NVT ensemble Monte Carlo (MC) simulations to obtain the insertion work Wins(z) (via Widom’s particle insertion) and the densities ρw(1)(z). We illustrate the mapping on two simple fluids adsorbed on a hard wall: the Lennard-Jones and the attractive Yukawa fluids. The pseudo-density is determined via an accurate uniform-fluid equation of state for the Lennard-Jones system, and for the Yukawa fluid via direct MC simulations. We characterize the behavior of the effective density and the pseudo-chemical potential vis-à-vis the cases of enhancement and depletion of the fluid density near the wall. These quantities (ρpseudo&μpseudo) are found to exhibit for enhanced adsorption out-of-phase oscillations compared to ρw(1)(z) and βWins(z). For depleted adsorption, we do not observe oscillations and the trends of ρpseudo and μpseudo are in good agreement with those of ρw(1)(z) and βWins. We analyze the differences in behavior in terms of the concavity of the chemical-potential function. We also show the equivalence of the potential distribution theorem to the Euler–Lagrange equation of the density functional theory.

Large-Scale Institutional Changes: Land Demarcation in the British Empire

Abstract We examine adoption of land demarcation in the British Empire during the seventeenth through nineteenth centuries. We develop a model and test its implications against data from temperate British colonies in North America, Australia, and New Zealand. Three arrangements were implemented: individualized, idiosyncratic metes and bounds; a centralized, uniform rectangular system; and a centralized, nonuniform demarcation system. The choice of arrangement is determined using demarcation, topographical, and soil quality data sets with qualitative, historical information. We find that centralized systems provide coordination benefits, but adoption is less likely when implementation is slow and controlling settlement is costly. In centralized systems, we find that uniform rectangular demarcation lowers transaction costs, but its rigid structure is costly in rugged terrain, and alternatives are adopted.

Transient Radiative Heat Transfer Analysis of Turbid Tissues Subjected to Short-Pulsed Irradiations

Transient radiative heat transfer of turbid tissues with a focused short-pulsed laser is studied. To investigate radiation transfer phenomenon during ultra short time regime, transient radiative transfer equation is adopted and it is solved by TDOM (Transient Discrete Ordinate Method). The nonuniform grid system is considered to capture abrupt change of radiation energy absorption. The hyperbolic conduction model is considered to predict temperature increment of turbid tissues.

Thermodynamic functions of fluctuating electromagnetic fields within a heterogeneous system

Thermodynamic functions of the equilibrium fluctuating electromagnetic fields within a nonuniform dispersive and absorptive system are calculated and discussed. The near-interface subsystem of the fields deserves special attention. Density of states and spectral characteristics of thermal surface waves in equilibrium at the interface between two media, one of them being lossy, are calculated for the first time. Thermodynamic characteristics of thermal fields are calculated both in vacuum and inside bulk lossy material described by spatially local and nonlocal optical responses. It was shown that the higher the temperature of the system, the smaller the relative contribution of the evanescent part of thermodynamic functions of thermal fields in vacuum compared with those of the black-body radiation. It is suggested that the evanescent part of the thermally excited fields can be treated as the physical transition layer localized near the interface between two subsystems of photons in vacuum and photons in bulk matter. In fact, such a layer forms a physical boundary between those subsystems of thermal photons in equilibrium.

Welfare effects of VAT reforms: a general equilibrium analysis

Indirect taxes such as value added taxes (VAT) generate a substantial part of tax revenue in many countries. In practice, VAT systems are often characterized by exemptions, reduced rates, and zero ratings. A nonuniform VAT system may generate an efficiency loss and encourage rent-seeking and tax fraud activities. It also has high administrative costs. We use an empirically based computable general equilibrium model for the small, open economy of Norway with a detailed description of direct and indirect taxes, to compare three VAT systems; two different nongeneral and nonuniform VAT systems exemplified by the former and current Norwegian VAT systems and a general and uniform VAT system. Our analysis shows that an imperfect extension of the VAT system to cover more but not all services is welfare inferior to the baseline nonuniform VAT system only covering goods. However, a general and uniform VAT system covering all goods and services is welfare superior to both the imperfect VAT systems.

Suppression of the vibrations of wind turbine towers

We investigate the suppression of the vibrations of a wind turbine tower using colocated feedback to achieve strong stability. We decompose the system into one model describing the vibrations in the plane of the turbine axis and another model in the plane of the turbine blades. In the plane of the turbine axis, we obtain a non-uniform Spacecraft Control Laboratory Experiment (SCOLE) model with either force control or torque control. We show that this system is strongly stabilizable by static output feedback from either the velocity or the angular velocity of the nacelle. In the plane of the turbine blades, we model the wind turbine tower as a non-uniform SCOLE system coupled with a two-mass drive-train model, the control being the torque created by the electrical generator. We prove that generically, this system can be strongly stabilized by feedback from the angular velocity of the nacelle and the angular velocity of the generator rotor.

A structured but non‐uniform Cartesian grid‐based model for the shallow water equations

AbstractIn large‐scale shallow flow simulations, local high‐resolution predictions are often required in order to reduce the computational cost without losing the accuracy of the solution. This is normally achieved by solving the governing equations on grids refined only to those areas of interest. Grids with varying resolution can be generated by different approaches, e.g. nesting methods, patching algorithms and adaptive unstructured or quadtree gridding techniques. This work presents a new structured but non‐uniform Cartesian grid system as an alternative to the existing approaches to provide local high‐resolution mesh. On generating a structured but non‐uniform Cartesian grid, the whole computational domain is first discretized using a coarse background grid. Local refinement is then achieved by directly allocating a specific subdivision level to each background grid cell. The neighbour information is specified by simple mathematical relationships and no explicit storage is needed. Hence, the structured property of the uniform grid is maintained. After employing some simple interpolation formulae, the governing shallow water equations are solved using a second‐order finite volume Godunov‐type scheme in a similar way as that on a uniform grid. Copyright © 2010 John Wiley & Sons, Ltd.

Images of a Spin-Torque-Driven Magnetic Nano-Oscillator

We present the first space- and time-resolved images of the spin-torque-induced steady-state oscillation of a magnetic vortex in a spin-valve nanostructure. We find that the vortex structure in a nanopillar is considerably more complicated than the 2D idealized structure often-assumed, which has important implications for the driving efficiency. The sense of the vortex gyration is uniquely determined by the vortex core polarity, confirming that the spin-torque acts as a source of negative damping even in such a strongly nonuniform magnetic system. The orbit radius is ∼10 nm, in agreement with micromagnetic simulations.

Dynamical behavior of networks of non-uniform Timoshenko beams system with boundary time-delay inputs

The dynamical stability of planar networks of non-uniform Timoshenkobeams system is considered. Suppose that the displacement and rotational angle iscontinuous at the common vertex of this network and the bendingmoment and shear force satisfies Kirchhoff's laws, respectively.Time-delay terms exist in control inputs at exterior vertices. Thefeedback control laws are designed to stabilize this kind ofnetworks system. Then it is proved that the corresponding closedloop system is well-posed. Under certain conditions, the asymptoticstability of this system is shown. By a complete spectral analysis,the spectrum-determined-growth condition is proved to be satisfiedfor this system. Finally, the exponentialstability of this system is discussed for a special case and somesimulations are given to support these results.

Study of the Performance of Smoke Control under Non-uniform Smoke Exhaust Velocity

Measurements of vents wind velocity of smoke control system in metro station prove it is a universal problem that the long air duct can’t distribute air equally. Therefore, mathematical simulation of fire smoke flow in tunnel has been done under three smoke extract system modes. Results show the temperature in non-uniform smoke exhaust system is the biggest near the fire source; the uniform smoke exhaust system can control smoke movement well. Therefore, it is crucial to make every vent equalvelocity in the long smoke removal pipe.

Non-uniform stress distribution and deformation bifurcation of thin film/substrate system subjected to gradient temperature

Stresses in thin films or coatings control the reliability of the thin film/substrate structure. By considering a circular thin film/substrate system subjected to gradient temperature, we derive relations between the non-uniform stresses in film and temperature, and between the non-uniform system curvatures and temperature. These relations featured a “local” part that involves a direct dependence of the stress or curvature components on the temperature at the same point, and a “non-local” part which reflects the effect of temperature of other points on the location of scrutiny. Furthermore, the deformation bifurcation behavior of the thin film/substrate system is analyzed. As the thermo-mismatch strain in the thin film increases, the system may transit to a biaxial curvature state (non-spherical deformation), in other words, the bifurcation of curvature will occur.