Multi Field Research Articles

Mixed variational principles for the evolution problem of gradient–extended dissipative solids

AbstractThis work develops minimization and saddle point principles for a class of gradient–extended dissipative solids, incorporating micro–structural fields (micro–displacements, order parameters or generalized internal variables), whose gradients enter the energy storage and dissipation potential functions. In contrast to classical local continuum approaches to inelastic solids based on locally evolving internal variables, these global micro–structural fields are governed by additional balance–type partial differential equations including micro–structural boundary conditions. Typical examples are theories of phase field evolution, gradient damage or strain gradient plasticity. Such models incorporate non–local effects based on length scales, which reflect properties of the material micro–structure. We outline a unified variational framework for the evolution problem of first–order gradient–extended standard dissipative solids. Particular emphasis is put on mixed multi–field representations, where both the microstructural variable itself as well as the local driving forces are present (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Phenomenology of a pseudo-scalar inflaton: naturally large nongaussianity

Many controlled realizations of chaotic inflation employ pseudo-scalar axions. Pseudo-scalars ϕ are naturally coupled to gauge fields through cϕFF̃. In the presence of this coupling, gauge field quanta are copiously produced by the rolling inflaton. The produced gauge quanta, in turn, source inflaton fluctuations via inverse decay. These new cosmological perturbations add incoherently with the ``vacuum'' perturbations, and are highly nongaussian. This provides a natural mechanism to generate large nongaussianity in single or multi field slow-roll inflation. The resulting phenomenological signatures are highly distinctive: large nongaussianity of (nearly) equilateral shape, in addition to detectably large values of both the scalar spectral tilt and tensor-to-scalar ratio (both being typical of large field inflation). The WMAP bound on nongaussianity implies that the coupling c of the pseudo-scalar inflaton to any gauge field must be smaller than about 102 Mp−1.

A Power Efficient Linear Equation Solver on A Multi-Fpgaaccelerator

This paper presents an approach to explore a commercial multi field programmable gate array (FPGA) system as high performance accelerator and the problem of solving an LU decomposed linear system of equations using forward and back substitution is addressed. Block-based right-hand-side solver algorithm is described and a novel data flow and memory architectures that can support arbitrary data types, block sizes and matrix sizes is proposed. These architectures have been implemented on a multi-FPGA system. Capabilities of the accelerator system are pushed to its limits by implementing the problem for double precision complex floatingpoint data. Detailed timing data is presented and augmented with data from a performance model proposed in this paper. Performance of the accelerator system is evaluated against that of a state of the art low power Beowulf cluster node running an optimized LAPACK implementation. Both systems are compared using the power efficiency (performance/watt) metric. FPG A system is about eleven times more power efficient than the compute node of a cluster.

Influence on Observation from IR Divergence during Inflation. II: Multi-Field Inflation

We propose one way to regularize the fluctuations generated during inflation, whose infrared (IR) corrections diverge logarithmically. In the case of a single field inflation model, recently, we proposed one solution to the IR divergence problem. There, we introduced new perturbative variables which better mimic actual observable fluctuations, and proved the regularity of correlation functions with respect to these variables. In this paper, we extend our previous discussions to a multi field inflation model. We show that, as long as we consider the case that the non-linear interaction acts for a finite duration, observable fluctuations are free from IR divergences in the multi field model, too. In contrast to the single field model, to discuss observables, we need to take into account the effects of quantum decoherence which pick up a unique history of the universe from various possibilities contained in initial quantum state set naturally in the early stage of the universe.

Energy transfer in multi field inflation and cosmological perturbations

In cascade inflation and some other string inflation models,collisions of mobile branes with other branes or orbifold planesoccur and lead to interesting cosmological signatures. Thefundamental M/string-theory description of these collisions is stilllacking but it is clear that the inflaton looses part of its energyto some form of brane matter, e.g. a component of tensionlessstrings. In the absence of a fundamental description, we assume ageneral barotropic fluid on the brane, which absorbs part of theinflaton's energy. The fluid is modeled by a scalar with a suitableexponential potential to arrive at a full-fledged field theorymodel. We study numerically the impact of the energy transfer from theinflaton to the scalar on curvature and isocurvatureperturbations and demonstrate explicitly that the curvature powerspectrum gets modulated by oscillations which damp away towardsmaller scales. Even though, the contribution of isocurvatureperturbations decays toward the end of inflation, they inducecurvature perturbations on scales that exit the horizon before thecollision. We consider cases where the scalar behaves likeradiation, matter or a web of cosmic strings and discuss thedifferences in the resulting power spectra.

A finite shell element with well balanced approximation functions for piezoelectric coupling

AbstractThis contribution is concerned with a piezoelectric shell formulation. The present shell element has four nodes and bilinear interpolation functions. The nodal degrees of freedom are displacements, rotations and the electric potential on top and bottom of the shell. A 3D–material law is incorporated. In case of bending dominated problems incompatible approximation functions of the electrical and mechanical fields cause incorrect results. This effect occurs in standard element formulations, where the mechanical and electrical degrees of freedom are approximated with lowest order interpolation functions. In order to overcome this problem a mixed multi–field variational approach is introduced. It allows for approximations of the electric field and the strains independent of the bilinear interpolation functions. A quadratic approach for the shear strains and the electric field is proposed through the shell thickness. This leads to well balanced approximation functions regarding coupling of electrical and mechanical fields. A numerical example illustrates the more precise results in contrast to standard elements. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Multisensor for Clinical Analysis with Impact on Public Health Evaluation

The objective of this paper was to study the suitability of multi gate ion sensitive field effect transistors (ISFETs) for clinical work with specific requirements in the public health evaluation. The obtained sensors were used in a flow cell assembly provided by Bellhouse Medical Products. As in our previous work [1], the sensors were intended for use in the analysis of biological fluids, where the concentrations of specific ions as sodium, potassium and calcium are of critical importance. The electrochemical characteristics for use in clinical chemistry were established.

Advanced Smart High Ratio Zoom System with Global Optimization

With an aim to achieve a breakthrough the choke point in research on system design, to achieve the transforming in multiple fields of view, the approaching to system efficacy limit in theory and improving smartness, pure diffractive optical system is chosen. The top idea and main strategy is developed. Some correlative model is established. In optimized design, global optimization algorithm is used to achieve wider spectrum range, multi field view, lower distortion and appropriate MTF. A kind of result works mainly in 3~5%m and 8~12%m with high ratio of more than 20:1 is evaluated. And this integrated multi-sensor electro-optical system satisfies the applied requirements o some criteria, such as Modulation Transfer Function (MTF), Spot Diagram (RMS) and Point Spread Function (PSF) etc., and achieves remarkable advantages in volume, weight, system efficiency and so on.

Towards A Multi-FPGA Infrared Simulator

High speed infrared (IR) scene simulation is used extensively in defense and homeland security to test sensitivity of IR cameras and accuracy of IR threat detection and tracking algorithms used commonly in IR missile approach warning systems (MAWS). A typical MAWS requires an input scene rate of over 100 scenes/second. Infrared scene simulations typically take 32 minutes to simulate a single IR scene that accounts for effects of atmospheric turbulence, refraction, optical blurring and charge-coupled device (CCD) camera electronic noise on a Pentium 4 (2.8GHz) dual core processor [7]. Thus, in IR scene simulation, the processing power of modern computers is a limiting factor. In this paper we report our research to accelerate IR scene simulation using high performance reconfigurable computing. We constructed a multi Field Programmable Gate Array (FPGA) hardware acceleration platform and accelerated a key computationally intensive IR algorithm over the hardware acceleration platform. We were successful in reducing the computation time of IR scene simulation by over 36%. This research acts as a unique case study for accelerating large scale defense simulations using a high performance multi-FPGA reconfigurable computer.

Dual Scale Simulation of Grain Growth Using a Multi Phase Field Model

ABSTRACTThe kinetics of grain growth in multicrystalline materials is determined by the interplay of curvature driven grain boundary motion and interfacial stress balance at the vertices of the grain boundaries. A comprehensive way to treat both effects in one model is given by the time dependent Ginzburg Landau model or phase field model. The paper presents the application of a multi phase field model, recently developed for solidification processes to grain growth of a multicrystalline structure. The specific feature of this multi phase field model is its ability to treat each grain boundary with its individual characteristics dependent on the type of the grain boundary, its orientation or the local pinning at precipitates. The pinning effect is simulated on the nanometer scale resolving the interaction of an individual precipitate with a curved grain boundary. From these simulations an effective pinning force is deduced and a model of driving force dependent grain boundary mobility is formulated accounting for the pinning effect on the mesoscopic scale of the grain growth simulation. 2-D grain growth simulations are presented.

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(4) ムービングビーム全身照射法および電子線全身照射法(2. 全身照射法の技術的諸問題)