Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “PHASE SPACE”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 955 records · Page 53
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

PROBABILISTIC MODEL OF BEAM–PLASMA INTERACTION IN RANDOMLY INHOMOGENEOUS PLASMA

We propose a new model that describes beam–plasma interaction in the presence of random density fluctuations with a known probability distribution. We use the property that, for the given frequency, the probability distribution of the density fluctuations uniquely determines the probability distribution of the phase velocity of waves. We present the system as discrete and consisting of small, equal spatial intervals with a linear density profile. This approach allows one to estimate variations in wave energy density and particle velocity, depending on the density gradient on any small spatial interval. Because the characteristic time for the evolution of the electron distribution function and the wave energy is much longer than the time required for a single wave–particle resonant interaction over a small interval, we determine the description for the relaxation process in terms of averaged quantities. We derive a system of equations, similar to the quasi-linear approximation, with the conventional velocity diffusion coefficient D and the wave growth rate γ replaced by the average in phase space, by making use of the probability distribution for phase velocities and by assuming that the interaction in each interval is independent of previous interactions. Functions D and γ are completely determined by the distribution function for the amplitudes of the fluctuations. For the Gaussian distribution of the density fluctuations, we show that the relaxation process is determined by the ratio of beam velocity to plasma thermal velocity, the dispersion of the fluctuations, and the width of the beam in the velocity space.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2016

Fundamental and practical limits of planar tracking solar concentrators

Planar microtracking provides an alternate paradigm for solar concentration that offers the possibility of realizing high-efficiency embedded concentrating photovoltaic systems in the form factor of standard photovoltaic panels. Here, we investigate the thermodynamic limit of planar tracking optical concentrators and establish that they can, in principal, achieve the sine limit of their orientationally-tracked counterparts provided that the receiver translates a minimum distance set by the field of view half-angle. We develop a phase space methodology to optimize practical planar tracking concentrators and apply it to the design of a two surface, catadioptric system that operates with > 90% optical efficiency over a 140° field of view at geometric gains exceeding 1000×. These results provide a reference point for subsequent developments in the field and indicate that planar microtracking can achieve the high optical concentration ratio required in commercial concentrating photovoltaic systems.

47 OTHER INSTRUMENTATION↗
DOE OSTI2018

Global variance reduction method applied to HBR-2 benchmark - 25144

It is a great challenge to obtain reliable results in reasonable time by the Monte Carlo (MC) method in solving deep-penetration shielding problems. Global variance reduction (GVR) method uses biased source and weight window to decrease MC calculation tally error for deep-penetration problems. However, excessive splitting of large weight particles out of the source region is time-consuming for problems with significant fluence rate variation. A new GVR method, which performs space and energy splitting/roulette based on the importance of the phase space, is proposed in this paper to avoid excessive splitting of large weight particles. The improved GVR method is applied to HBR-2 benchmark. Numerical results show that the new GVR method achieves good corresponding results to those of references. (authors)

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS↗
DOE OSTI2018

Effect of minimal length uncertainty on the mass–radius relation of white dwarfs

Generalized uncertainty relation that carries the imprint of quantum gravity introduces a minimal length scale into the description of space–time. It effectively changes the invariant measure of the phase space through a factor (1+βp{sup 2}){sup −3} so that the equation of state for an electron gas undergoes a significant modification from the ideal case. It has been shown in the literature (Rashidi 2016) that the ideal Chandrasekhar limit ceases to exist when the modified equation of state due to the generalized uncertainty is taken into account. To assess the situation in a more complete fashion, we analyze in detail the mass–radius relation of Newtonian white dwarfs whose hydrostatic equilibria are governed by the equation of state of the degenerate relativistic electron gas subjected to the generalized uncertainty principle. As the constraint of minimal length imposes a severe restriction on the availability of high momentum states, it is speculated that the central Fermi momentum cannot have values arbitrarily higher than p{sub max}∼β{sup −1∕2}. When this restriction is imposed, it is found that the system approaches limiting mass values higher than the Chandrasekhar mass upon decreasing the parameter β to a value given by a legitimate upper bound. Instead, when the more realistic restriction due to inverse β-decay is considered, it is found that the mass and radius approach the values 1.4518 M{sub ⊙} and 601.18 km near the legitimate upper bound for the parameter β.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2017

A Test of the Interstellar Boundary EXplorer Ribbon Formation in the Outer Heliosheath

NASA’s Interstellar Boundary EXplorer ( IBEX ) mission is imaging energetic neutral atoms (ENAs) propagating to Earth from the outer heliosphere and local interstellar medium (LISM). A dominant feature in all ENA maps is a ribbon of enhanced fluxes that was not predicted before IBEX . While more than a dozen models of the ribbon formation have been proposed, consensus has gathered around the so-called secondary ENA model. Two classes of secondary ENA models have been proposed; the first class assumes weak scattering of the energetic pickup protons in the LISM, and the second class assumes strong but spatially localized scattering. Here we present a numerical test of the “weak scattering” version of the secondary ENA model using our gyro-averaged kinetic model for the evolution of the phase-space distribution of protons in the outer heliosheath. As input for our test, we use distributions of the primary ENAs from our MHD-plasma/kinetic-neutral model of the heliosphere-LISM interaction. The magnetic field spectrum for the large-scale interstellar turbulence and an upper limit for the amplitude of small-scale local turbulence (SSLT) generated by protons are taken from observations by Voyager 1 in the LISM. The hybrid simulations of energetic protons are also used to set the bounding wavenumbers for the spectrum of SSLT. Our test supports the “weak scattering” version. This makes an additional solid step on the way to understanding the origin and formation of the IBEX ribbon and thus to improving our understanding of the interaction between the heliosphere and the LISM.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1984

Zero-g experiments with a He II active phase separator for space application

An active phase separator (APS) for temperature control of He II space cooling systems was tested in a zero-g environment during a series of parabolic flights on a NASA KC 135 aircraft. The APS provides for liquid-gas separation and features an annular gap, a downstream heat exchanger and an upstream ball closure. The apparatus was operated during acceleration and floating and in two different heat load situations. The tests confirmed that adequate mass flow rates could be maintained using a vacuum pump to simulate space vacuum and that residual liquid could be evaporated from the heat exchanger after closing a ball valve to seal off flows.

Denner, H. D.↗
NASA NTRS1985

Space Shuttle aerothermodynamic data report, phase C

Space shuttle aerothermodynamic data, collected from a continuing series of wind tunnel tests, are permanently stored with the Data Management Services (DMS) system. Information pertaining to current baseline configuration definition is also stored. Documentation of DMS processed data arranged sequentially and by space shuttle configuration are included. An up-to-date record of all applicable aerothermodynamic data collected, processed, or summarized during the space shuttle program is provided. Tables are designed to provide suvery information to the various space shuttle managerial and technical levels.

Source record↗
DOE OSTI2015

Updated constraints on the light-neutrino exchange mechanisms of the 0νββ-decay

The neutrinoless double-beta (0νββ) decay associated with light neutrino exchange mechanisms, which are due to both left-handed V-A and right-handed V+A leptonic and hadronic currents, is discussed by using the recent progress achieved by the GERDA, EXO and KamlandZen experiments. The upper limits for effective neutrino mass m{sub ββ} and the parameters 〈λ〉 and 〈η〉 characterizing the right handed current mechanisms are deduced from the data on the 0νββ-decay of {sup 76}Ge and {sup 136}Xe using nuclear matrix elements calculated within the nuclear shell model and quasiparticle random phase approximation and phase-space factors calculated with exact Dirac wave functions with finite nuclear size and electron screening. The careful analysis of upper constraints on effective lepton number violating parameters assumes a competition of the above mechanisms and arbitrary values of involved CP violating phases.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Projected metastable Markov processes and their estimation with observable operator models

The determination of kinetics of high-dimensional dynamical systems, such as macromolecules, polymers, or spin systems, is a difficult and generally unsolved problem — both in simulation, where the optimal reaction coordinate(s) are generally unknown and are difficult to compute, and in experimental measurements, where only specific coordinates are observable. Markov models, or Markov state models, are widely used but suffer from the fact that the dynamics on a coarsely discretized state spaced are no longer Markovian, even if the dynamics in the full phase space are. The recently proposed projected Markov models (PMMs) are a formulation that provides a description of the kinetics on a low-dimensional projection without making the Markovianity assumption. However, as yet no general way of estimating PMMs from data has been available. Here, we show that the observed dynamics of a PMM can be exactly described by an observable operator model (OOM) and derive a PMM estimator based on the OOM learning.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1989

A control approach for robots with flexible links and rigid end-effectors

Multiarm flexible robots with dexterous end effectors are currently being considered in such tasks as satellite retrieval, servicing and repair where a two phase problem can be identified: Phase 1, robot positioning in space; Phase 2, object retrieval. Some issues in Phase 1 regarding modelling and control strategies for a robotic system comprised of along flexible arm and a rigid three-link end effector are presented. The control objective is to maintain the last (rigid) link stationary in space in the presence of an additive disturbance caused by the flexible energy in the first link after a positioning maneuver has been accomplished. Several configuration strategies can be considered, and optimal decentralized servocompensators can be designed. Preliminary computer simulations are included for a simple proportional controller to illustrate the approach.

Barbieri, Enrique↗
DOE OSTI2018

Three examples of quantum dynamics on the half-line with smooth bouncing

This article is an introductory presentation of the quantization of the half-plane based on affine coherent states (ACS). The half-plane carries a natural affine symmetry, i.e. it is a homogeneous space for the 1d-affine group, and it is viewed as the phase space for the dynamics of a positive physical quantity evolving with time. Its affine symmetry is preserved due to the covariance of this type of quantization. We promote the interest of such a procedure for transforming a classical model into a quantum one, since the singularity at the origin is systematically removed, and the arbitrariness of boundary conditions for the Schrödinger operator can be easily overcome. We explain some important mathematical aspects of the method. Three elementary examples of applications are presented, the quantum breathing of a massive sphere, the quantum smooth bouncing of a charged sphere, and a smooth bouncing of “dust” sphere as a simple model of quantum Newtonian cosmology.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2017

Tunable Mode Coupling in Nanocontact Spin-Torque Oscillators

Recent experiments on spin-torque oscillators have revealed interactions between multiple magneto-dynamic modes, including mode coexistence, mode hopping, and temperature-driven crossover between modes. The initial multimode theory indicates that a linear coupling between several dominant modes, arising from the interaction of the subdynamic system with a magnon bath, plays an essential role in the generation of various multimode behaviors, such as mode hopping and mode coexistence. In this work, we derive a set of rate equations to describe the dynamics of coupled magneto-dynamic modes in a nanocontact spin-torque oscillator. Here, expressions for both linear and nonlinear coupling terms are obtained, which allow us to analyze the dependence of the coupled dynamic behaviors of modes on external experimental conditions as well as intrinsic magnetic properties. For a minimal two-mode system, we further map the energy and phase difference of the two modes onto a two-dimensional phase space and demonstrate in the phase portraits how the manifolds of periodic orbits and fixed points vary with an external magnetic field as well as with the temperature.

36 MATERIALS SCIENCE↗
DOE OSTI2015

β-decay of magic nuclei: Beyond mean-field description

Nuclear β-decay plays an important role not only in nuclear physics but also in astrophysics. The widely used self-consistent Random Phase Approximation (RPA) models tend to overestimate the half-lives of magic nuclei. To overcome this problem, we go beyond the mean-field description and include the effects of particle-vibration coupling (PVC) on top of the RPA model. The β-decay half-lives of {sup 34}Si, {sup 68}Ni, {sup 78}Ni, and {sup 132}Sn are studied within this approach in the case of the Skyrme interaction SkM*. It is found that the low-lying Gamow-Teller (GT) strength is shifted downwards with the inclusion of the PVC effect, and as a consequence, the half-lives are reduced due to the increase of the phase space available for β-decay, which leads to a good agreement between theoretical and experimental lifetimes.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

The time evolution of gaps in tidal streams

We model the time evolution of gaps in tidal streams that are caused by the impact of a dark matter subhalo, while these orbit a spherical gravitational potential. To this end, we make use of the simple behavior of orbits in action-angle space. A gap effectively results from the divergence of two nearby orbits whose initial phase-space separation is, for very cold thin streams, largely given by the impulse induced by the subhalo. We find that in a spherical potential, the size of a gap increases linearly with time for sufficiently long timescales. We have derived an analytic expression that shows how the growth rate depends on the mass of the perturbing subhalo, its scale, and its relative velocity with respect to the stream. We have verified these scalings using N-body simulations and find excellent agreement. For example, a subhalo of mass 10{sup 8} M{sub ⊙} directly impacting a very cold thin stream on an inclined orbit can induce a gap that may reach a size of several tens of kiloparsecs after a few gigayears. The gap size fluctuates importantly with phase on the orbit, and it is largest close to pericenter. This indicates that it may not be fully straightforward to invert the spectrum of gaps present in a stream to recover the mass spectrum of the subhalos.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2019

New M{sub (2 + δ1)}X{sub (2 + δ2)} Superstructure of Ordered Nanocrystalline Titanium Monoxide and the Problem of Transition States

The results of experiments on the vacancy ordering in nanocrystalline nonstoichiometric titanium monoxide TiO{sub y} (space group Fm 3-bar m), which is accompanied by the formation of the orthorhombic Ti{sub 9}O{sub 10} phase (space group Immm), are considered. The vacancy distribution in the ordered phase is described by a two-sublattice-ordering M{sub (2 + δ1)}X{sub (2 + δ2)} superstructure. The disorder–order (TiO{sub y}–Ti{sub (2 + δ1)}O{sub (2 + δ2)}) phase transition is accompanied by symmetry distortions along non-Lifshitz star {k_4}. When ordering, vacancies concentrate in every third (110) plane of the basic B1-type structure. The deviation of stoichiometry is caused by different vacancy concentrations in the defect planes in the metallic and nonmetallic sublattices (parameters δ{sub 1} and δ{sub 2}, respectively). The new class of M{sub (n + δ1)}X{sub (n + δ2)} superstructures is shown to generate numerous order–disorder transition state models, which cannot be described in terms of the mean-field approximation. At δ{sub 1} = δ{sub 2} = 0.5, the orthorhombic M{sub (2 + δ1)}X{sub (2 + δ2)} structure is a particular case of the partly disordered monoclinic M{sub 5}X{sub 5} superstructure (space group C2/m(A2/m)), which is characteristic of a coarse-grained state.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2018

Biparametric investigation of the general standard map: multistability and global bifurcations

We investigate multistability and global bifurcations in the general standard map, a biparametric two-dimensional map. Departing from the conservative case of the map, we describe the evolution of periodic solutions and their basins of attraction as dissipation builds up, paying special attention on how the biparametric variation affects multistability. We examine general and specific phenomena and behavior for three distinct dynamical regimes, namely small, moderate, and large damping and different forcing amplitudes. Also, we report numerically the mechanism of global bifurcations associated to small chaotic attractors in the multistable system. Several global bifurcations are investigated as dissipation increases. Specifically, through the characterization of an interior, a merging and a boundary crisis, we study the crucial role played by fundamental hyperbolic invariant structures, such as unstable periodic orbits and their stable and unstable invariant manifolds, in the mechanisms by which the phase space is globally transformed.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2016

Synchronizing noisy nonidentical oscillators by transient uncoupling

Synchronization is the process of achieving identical dynamics among coupled identical units. If the units are different from each other, their dynamics cannot become identical; yet, after transients, there may emerge a functional relationship between them—a phenomenon termed “generalized synchronization.” Here, we show that the concept of transient uncoupling, recently introduced for synchronizing identical units, also supports generalized synchronization among nonidentical chaotic units. Generalized synchronization can be achieved by transient uncoupling even when it is impossible by regular coupling. We furthermore demonstrate that transient uncoupling stabilizes synchronization in the presence of common noise. Transient uncoupling works best if the units stay uncoupled whenever the driven orbit visits regions that are locally diverging in its phase space. Thus, to select a favorable uncoupling region, we propose an intuitive method that measures the local divergence at the phase points of the driven unit's trajectory by linearizing the flow and subsequently suppresses the divergence by uncoupling.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗