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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 865 records · Page 48
All sourcesNASA NTRSDOE OSTI
DOE OSTI2013

Ion extraction system optimization

The extraction of a beam from ion sources is dominated by the strong space charge of the beam, due to the initial low speed of the particles. Several mathematical and computational issues are discussed, with reference to a diode design based on thin anode lens effect, yielding a parallel beam at its exit, which is the first block of many high current electrostatic accelerators. Perturbation to uniform current density are analyzed. Effect of a thick anode lens is also treated.

43 PARTICLE ACCELERATORS↗
DOE OSTI2014

Approximate models for the study of exponential changed quantities: Application on the plasma waves growth rate or damping

Many physical phenomena that concern the research these days are basically complicated because of being multi-parametric. Thus, their study and understanding meets with big if not unsolved obstacles. Such complicated and multi-parametric is the plasmatic state as well, where the plasma and the physical quantities that appear along with it have chaotic behavior. Many of those physical quantities change exponentially and at most times they are stabilized by presenting wavy behavior. Mostly in the transitive state rather than the steady state, the exponentially changing quantities (Growth, Damping etc) depend on each other in most cases. Thus, it is difficult to distinguish the cause from the result. The present paper attempts to help this difficult study and understanding by proposing mathematical exponential models that could relate with the study and understanding of the plasmatic wavy instability behavior. Such instabilities are already detected, understood and presented in previous publications of our laboratory. In other words, our new contribution is the study of the already known plasmatic quantities by using mathematical models (modeling and simulation). These methods are both useful and applicable in the chaotic theory. In addition, our ambition is to also conduct a list of models useful for the study of chaotic problems, such as those that appear into the plasma, starting with this paper's examples.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Static vs stochastic optimization: A case study of FTSE Bursa Malaysia sectorial indices

Traditional portfolio optimization methods in the likes of Markowitz' mean-variance model and semi-variance model utilize static expected return and volatility risk from historical data to generate an optimal portfolio. The optimal portfolio may not truly be optimal in reality due to the fact that maximum and minimum values from the data may largely influence the expected return and volatility risk values. This paper considers distributions of assets' return and volatility risk to determine a more realistic optimized portfolio. For illustration purposes, the sectorial indices data in FTSE Bursa Malaysia is employed. The results show that stochastic optimization provides more stable information ratio.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2014

Topos models for physics and topos theory

What is the role of topos theory in the topos models for quantum theory as used by Isham, Butterfield, Döring, Heunen, Landsman, Spitters, and others? In other words, what is the interplay between physical motivation for the models and the mathematical framework used in these models? Concretely, we show that the presheaf topos model of Butterfield, Isham, and Döring resembles classical physics when viewed from the internal language of the presheaf topos, similar to the copresheaf topos model of Heunen, Landsman, and Spitters. Both the presheaf and copresheaf models provide a “quantum logic” in the form of a complete Heyting algebra. Although these algebras are natural from a topos theoretic stance, we seek a physical interpretation for the logical operations. Finally, we investigate dynamics. In particular, we describe how an automorphism on the operator algebra induces a homeomorphism (or isomorphism of locales) on the associated state spaces of the topos models, and how elementary propositions and truth values transform under the action of this homeomorphism. Also with dynamics the focus is on the internal perspective of the topos.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Geometric quadratic stochastic operator on countable infinite set

In this paper we construct the family of Geometric quadratic stochastic operators defined on the countable sample space of nonnegative integers and investigate their trajectory behavior. Such operators can be reinterpreted in terms of of evolutionary operator of free population. We show that Geometric quadratic stochastic operators are regular transformations.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Computation of entropy and Lyapunov exponent by a shift transform

We present a novel computational method to estimate the topological entropy and Lyapunov exponent of nonlinear maps using a shift transform. Unlike the computation of periodic orbits or the symbolic dynamical approach by the Markov partition, the method presented here does not require any special techniques in computational and mathematical fields to calculate these quantities. In spite of its simplicity, our method can accurately capture not only the chaotic region but also the non-chaotic region (window region) such that it is important physically but the (Lebesgue) measure zero and usually hard to calculate or observe. Furthermore, it is shown that the Kolmogorov-Sinai entropy of the Sinai-Ruelle-Bowen measure (the physical measure) coincides with the topological entropy.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2026

Neural operator transformers capture bifurcating drift-wave turbulence in fusion plasma simulations

Self-consistent modeling of turbulence-driven transport is critical for optimizing confinement in magnetically confined fusion plasmas, such as tokamaks and stellarators. In particular, capturing the long-term co-evolution of turbulence, flow, and background plasma profiles remains computationally challenging. Direct numerical simulation of these multiscale, highly nonlinear processes is often demanding and impractical for real-time control or design optimization. To address this bottleneck, we investigate transformer-based neural operator partial differential equation surrogates for emulating the dynamics of drift-wave turbulence bifurcation mediated by zonal flows, using the modified Hasegawa–Wakatani (MHW) model as a prototypical system. We find that the finetuned neural operator model has excellent performance in capturing the multi-spatiotemporal-scales of MHW turbulence bifurcation and is robust to testing on rare and out-of-distribution dynamics. Specifically, we demonstrate that a single unified model accurately predicts both quasi-steady-state turbulence and a wide range of dynamical transition processes, such as nonlinear saturation, spontaneous suppression of turbulence, and the emergence of macroscopic zonal flows, over time horizons vastly exceeding the local turbulence correlation time. This computationally efficient approach establishes a strong foundation for fast, AI-based modeling of complex, multiscale phenomena in magnetized fusion plasmas.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2010

On the acyclicity of the solution sets of operator equations

A parameter-dependent completely continuous map is considered. The acyclicity of the set of fixed points of this map is proved for some fixed value of the parameter under the assumption that for close values of the parameter the map has a unique fixed point. The results obtained are used to prove the acyclicity of the set of fixed points of a 'nonscattering' map, as well as to study the topological structure of the set of fixed points of an abstract Volterra map. Bibliography: 13 titles.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2011

Spectral decomposition of model operators in de Branges spaces

The paper is devoted to studying a class of completely continuous nonselfadjoint operators in de Branges spaces of entire functions. Among other results, a class of unconditional bases of de Branges spaces consisting of values of their reproducing kernels is constructed. The operators that are studied are model operators in the class of completely continuous non-dissipative operators with two-dimensional imaginary parts. Bibliography: 22 titles.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2011

Triviality of vector bundles on twisted ind-Grassmannians

Twisted ind-Grassmannians are ind-varieties G obtained as direct limits of Grassmannians G(i{sub m},V{sup n}{sub m}) for m element of Z{sub >0} under embeddings of degree greater than 1. It has been conjectured by Donin and Penkov (2003) that any vector bundle of finite rank on a twisted ind-Grassmannian is trivial. We prove this conjecture. Bibliography: 16 titles.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2011

Classification of Ricci-flat metrics on the cotangent bundles of compact rank-one symmetric spaces

All complete Ricci-flat Kaehler G-invariant metrics (g,J,{Omega}) on the cotangent bundle of a compact rank-one symmetric space G/K, dim G/K>=3 (with the fixed Kaehler form, the canonical symplectic structure {Omega}), are classified. It is proved that the set of equivalence classes of such metrics can be parametrized by positive numbers. The representative of each class is constructed by using explicit expressions. An alternative description of these structures based on the Kaehler reduction procedure is proposed. We show also that the complete Ricci-flat Kaehler metrics, constructed by Stenzel, are diffeomorphic to these ones. Bibliography: 26 titles.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2011

On symbolic models for Single-Conclusion Logic of Proofs

In this paper we define symbolic models for Single-Conclusion Logics of Proofs. We prove the soundness and completeness of these logics with respect to the corresponding classes of symbolic models. We apply the semantic methods developed in this paper to justify the use of terms of single-conclusion logic of proofs as notation for derivations in this logic. Bibliography: 17 titles.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2011

On the colouring of spheres embedded in R{sup n}

The work concerns the well-known problem of identifying the chromatic number {chi}(R{sup n}) of the space R{sup n}, that is, finding the minimal number of colours required to colour all points of the space in such a way that any two points at distance one from each other have different colours. A new quantity generalising the chromatic number is introduced in the paper, namely, the speckledness of a subset in a fixed metric space. A series of lower bounds for the speckledness of spheres is derived. These bounds are used to obtain general results lifting lower bounds for the chromatic number of a space to higher dimensions, generalising the well-known 'Moser-Raisky spindle'. As a corollary of these results, the best known lower bound for the chromatic number {chi}(R{sup 12}){>=}27 is obtained, and furthermore, the known bound {chi}(R{sup 4}){>=}7 is reproved in several different ways. Bibliography: 23 titles.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2011

Existence and uniqueness of the measure of maximal entropy for the Teichmueller flow on the moduli space of Abelian differentials

The main result of the paper is the statement that the 'smooth' measure of Masur and Veech is the unique measure of maximal entropy for the Teichmueller flow on the moduli space of Abelian differentials. The proof is based on the symbolic representation of the flow in Veech's space of zippered rectangles. Bibliography: 29 titles.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2011

On the structure of invariant measures for set-valued maps

Properties of measures invariant with respect to set-valued maps are studied. It is shown that an absolutely continuous invariant measure for a set-valued map need not be unique, and the set of all invariant measures need not be a Choquet simplex. The problem concerning the existence of invariant measures with respect to set-valued maps parametrized by single-valued and set-valued maps of the circle having various smoothness classes is studied. Bibliography: 13 titles.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2012

Isometric surfaces with a common mean curvature and the problem of Bonnet pairs

Simple methods are used to give new proofs, and sometimes to make them more precise, of basic theorems on isometric surfaces with a common mean curvature, which are usually called Bonnet pairs. The considerations are conducted under the assumption of minimally admissible smoothness of the objects in question, and certain necessary or sufficient criteria are given for the non-existence of Bonnet pairs with a common non-constant mean curvature among compact surfaces. Bibliography: 26 titles.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2012

Parity and cobordism of free knots

A simple invariant is constructed which obstructs a free knot to be truncated. In particular, this invariant provides an obstruction to the truncatedness of curves immersed in two-dimensional surfaces. A curve on an oriented two-dimensional surface S{sub g} is referred to as truncated (null-cobordant) if there exists a three-dimensional manifold M with boundary S{sub g} and a smooth proper map of a two-disc to M such that the image of the boundary of the disc coincides with the curve. The problem of truncatedness for free knots is solved in this paper using the notion of parity recently introduced by the author. Bibliography: 12 titles.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2012

The multipoint de la Vallee-Poussin problem for a convolution operator

Conditions are discovered which ensure that the space of entire functions can be represented as the sum of an ideal in the space of entire functions and the kernel of a convolution operator. In this way conditions for the multipoint de la Vallee-Poussin problem to have a solution are found. Bibliography: 14 titles.

97 MATHEMATICS AND COMPUTING↗