SEARCH · Search NASA

Results for “Analytic linearization”

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.

SourceResearch connectionFrom yearThrough year

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

At least 289 records · Page 16

All sources NASA NTRS DOE OSTI

DOE OSTI2011

Gyrokinetic study of electromagnetic effects on toroidal momentum transport in tokamak plasmas

The effect of a finite {beta}{sub e} = 8{pi}n{sub e}T{sub e}/B{sup 2} on the turbulent transport of toroidal momentum in tokamak plasmas is discussed. From an analytical gyrokinetic model as well as local linear gyrokinetic simulations, it is shown that the modification of the parallel mode structure due to the nonadiabatic response of passing electrons, which changes the parallel wave vector k{sub ||} with increasing {beta}{sub e}, leads to a decrease in size of both the diagonal momentum transport as well as the Coriolis pinch under ion temperature gradient turbulence conditions, while for trapped electron modes, practically no modification is found. The decrease is particularly strong close to the onset of the kinetic ballooning modes. There, the Coriolis pinch even reverses its direction.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2011

Nonlinear behavior of electron acoustic waves in an un-magnetized plasma

The nonlinear electron acoustic wave, which is found in the earth's magnetosphere by satellite observations, is studied analytically by Lagrangian fluid description. The basic linear mode is observed in a two temperature electron species plasma where ions form stationary charge neutral background. We have obtained nonlinear description of this mode, which depends on both time and space. A possible solution shows a soliton like structure, which is localized in space, and the amplitude increases with time in the absence of dispersion. Small dispersive correction, however, shows spread of the solution in space. This method can be generalized to study the nonlinear behavior of a general class of multispecies plasma.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2012

Regions for Brillouin seed pulse growth in relativistic laser-plasma interaction

Parametric plasma processes received renewed interest in the context of generating ultraintense and ultrashort laser pulses up to the exawatt-zetawatt regime. For Brillouin scattering and seed pulse amplification at high intensities, the strong coupling regime is of special interest. The intensity-driven low-frequency modes depend on the amplitudes of the laser fields. It is investigated here how these modes develop in the relativistic regime. Then, a unified treatment of Raman and Brillouin processes becomes necessary. Assuming circular polarization, it is shown that with increasing intensity an overlap of the originally different Raman, Brillouin, and modulational instability branches occurs. Numerical simulations with a linearized Maxwell-fluid code confirm the analytically predicted behavior.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2014

Dual effects of stochastic heating on electron injection in laser wakefield acceleration

Electron injection into the wakefield of an intense short laser pulse by a weaker laser pulse propagating in the opposite direction is reconsidered using two-dimensional (2D) particle-in-cell simulations as well as analytical modeling. It is found that for linearly polarized lasers the injection efficiency and the quality of the wakefield accelerated electrons increase with the intensity of the injection laser only up to a certain level, and then decreases. Theory and simulation tracking test electrons originally in the beat region of the two laser pulses show that the reduction of the injection efficiency at high injection-laser intensities is caused by stochastic overheating of the affected electrons.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2015

An approximation technique for jet impingement flow

The analytical approximate solution of a non-linear jet impingement flow model will be demonstrated. We will show that this is an improvement over the series approximation obtained via the Adomian decomposition method, which is itself, a powerful method for analysing non-linear differential equations. The results of these approximations will be compared to the Runge-Kutta approximation in order to demonstrate their validity.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2016

Analysis of radial and longitudinal field of plasma wakefield generated by a Laguerre-Gauss laser pulse

In the present paper, we study the wakes known as the donut wake which is generated by Laguerre-Gauss (LG) laser pulses. Effects of the special spatial profile of a LG pulse on the radial and longitudinal wakefields are presented via an analytical model in a weakly non-linear regime in two dimensions. Different aspects of the donut-shaped wakefields have been analyzed and compared with Gaussian-driven wakes. There is also some discussion about the accelerating-focusing phase of the donut wake. Variations of longitudinal and radial wakes with laser amplitude, pulse length, and pulse spot size have been presented and discussed. Finally, we present the optimum pulse duration for such wakes.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2020

Nonlinear bubble competition of the multimode ablative Rayleigh–Taylor instability and applications to inertial confinement fusion

The self-similar nonlinear evolution of the multimode ablative Rayleigh–Taylor instability (RTI) and the ablation-generated vorticity effect are studied for a range of initial conditions. We show that, unlike classical RTI, the nonlinear multimode bubble-front evolution remains in the bubble competition regime due to ablation-generated vorticity, which accelerates the bubbles, thereby preventing a transition into the bubble-merger regime. We develop an analytical bubble competition model to describe the linear and nonlinear stages of ablative RTI. Here, we show that vorticity inside the multimode bubbles is most significant at small scales with large initial perturbation. Since these small scales persist in the bubble competition regime, the self-similar growth coefficient ab can be enhanced by up to 30% relative to ablative bubble competition without vorticity effects. We use the ablative bubble competition model to explain the hydrodynamic stability boundary observed in OMEGA low-adiabat implosion experiments.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2021

Multimode two-dimensional vibronic spectroscopy. I. Orientational response and polarization-selectivity

Two-dimensional Electronic–Vibrational (2D EV) spectroscopy and two-dimensional Vibrational–Electronic (2D VE) spectroscopy are among the newest additions to the coherent multidimensional spectroscopy toolbox, and they are directly sensitive to vibronic couplings. In this first of two papers, the complete orientational response functions are developed for a model system consisting of two coupled anharmonic oscillators and two electronic states in order to simulate polarization-selective 2D EV and 2D VE spectra with arbitrary combinations of linearly polarized electric fields. Here, we propose analytical methods to isolate desired signals within complicated spectra and to extract the relative orientation between vibrational and vibronic dipole moments of the model system using combinations of polarization-selective 2D EV and 2D VE spectral features. Time-dependent peak amplitudes of coherence peaks are also discussed as means for isolating desired signals within the time-domain. This paper serves as a field guide for using polarization-selective 2D EV and 2D VE spectroscopies to map coupled vibronic coordinates on the molecular frame.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2011

Plasmon oscillations in a linear cluster of spherical nanoparticles

The eigenfrequencies and eigenfunctions of plasmon oscillations in an infinite linear cluster of spherical nanoparticles are found analytically within the framework of the quasi-static approach and numerically within the framework of the finite element method. It is shown that the spectrum of plasmon oscillations is complex and contains previously unknown, highly localised modes in a high-frequency region of the spectrum. The results obtained can be used in designing plasmon nanowaveguides and nanolasers. (nanostructures)

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2014

Recombination clumping factor during cosmic reionization

We discuss the role of recombinations in the intergalactic medium, and the related concept of the clumping factor, during cosmic reionization. The clumping factor is, in general, a local quantity that depends on both the local overdensity and the scale below which the baryon density field can be assumed smooth. That scale, called the filtering scale, depends on over-density and local thermal history. We present a method for building a self-consistent analytical model of inhomogeneous reionization, assuming the linear growth rate of the density fluctuation, which simultaneously accounts for these effects. We show that taking into account the local clumping factor introduces significant corrections to the total recombination rate, compared to the model with a globally uniform clumping factor.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2025

Current-based metrology with two-terminal mesoscopic conductors

The traditional approach to quantum parameter estimation focuses on the quantum state, deriving fundamental bounds on precision through the quantum Fisher information. In most experimental settings, however, performing arbitrary quantum measurements is highly unfeasible. In open quantum systems, an alternative approach to metrology involves the measurement of stochastic currents flowing from the system to its environment. However, the present understanding of current-based metrology is mostly limited to Markovian master equations. Considering a parameter estimation problem in a two-terminal mesoscopic conductor, we identify the key elements that determine estimation precision within the Landauer-Büttiker formalism. Crucially, this approach allows us to address arbitrary coupling and temperature regimes. Furthermore, we obtain analytical results for the precision in linear-response and zero-temperature regimes. For the specific parameter estimation task that we consider, we demonstrate that the boxcar transmission function is optimal for current-based metrology in all parameter regimes.

Landauer formula↗

DOE OSTI2021

Tracing the Mott-Hubbard transition in one-dimensional Hubbard models without Umklapp scattering

Here we apply the density-matrix renormalization group (DMRG) method to a one-dimensional Hubbard model that lacks Umklapp scattering and thus provides an ideal case to study the Mott-Hubbard transition analytically and numerically. The model has a linear dispersion and displays a metal-to-insulator transition when the Hubbard interaction U equals the bandwidth U c = W, where the single-particle gap opens linearly, Δ(U ≥ W) = U - W. The simple nature of the elementary excitations permits us to determine numerically with high accuracy the critical interaction strength and the gap function in the thermodynamic limit. The jump discontinuity of the momentum distribution $n_k$ at the Fermi wave number $k_F$ = 0 cannot be used to locate accurately U c from finite-size systems. However, the slope of $n_k$ at the band edges $k_B$ = ±π, reveals the formation of a single-particle bound state which can be used to determine U c reliably from $n_k$ using accurate finite-size data.

1-dimensional systems↗

DOE OSTI2024

Radiation by a laser-driven flying-focus electron wave packet

An exact solution of the Dirac equation in the presence of an arbitrary electromagnetic plane wave is found, which corresponds to a focused electron wave packet, with the focus of the wave packet moving at the speed of light in the opposite direction of the average momentum of the electron wave packet (unless the plane wave is so intense to reflect the electron). The photon spectrum emitted by such an electron wave packet in the presence of a linearly polarized plane wave is studied both analytically and numerically. The spectrum is also compared with the one emitted by a single-momentum, plane-wave electron in the case of the electron being initially counterpropagating (on average for the flying-focus case) with the plane wave and within the locally constant field approximation. It is found that if the electron flying-focus wave packet is focused beyond a Compton wavelength, the angular distribution of the emitted radiation along the magnetic field of the electromagnetic plane wave is broader than for an electron with definite momentum. Corresponding the maximum value of the photon yield on the transverse plane is smaller in the flying-focus electron case. This could represent an experimental signature of a laser-driven flying-focus electron wave packet.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2023

Cauchy-type integral method for solving the linearized one-dimensional Vlasov-Poisson equation

Here, we present a method for solving the linearized Vlasov-Poisson equation, based on analyticity properties of the equilibrium and initial condition through Cauchy-type integrals, that produces algebraic expressions for the distribution and field, i.e., the solution is expressed without integrals. Standard extant approaches involve deformations of the Bromwich contour that give erroneous results for certain physically reasonable configurations or eigenfunction expansions that are misleading as to the temporal structure of the solution. Our method is more transparent, lacks these defects, and predicts previously unrecognized behavior.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2022

Alignment Thresholds of Molecules

Molecules have long been known to align in moderately intense, far off-resonance laser fields with a large variety of applications in physics and optics. Here, we illustrate and describe the physical origin of a previously unexplored phenomenon in the adiabatic alignment dynamics of molecules, which is fundamentally interesting and also has an important practical implication. Specifically, the intensity dependence of the degree of adiabatic alignment exhibits a threshold behavior, below which molecules are isotropically distributed rotationally and above which the alignment rapidly reaches a plateau. Furthermore, we show that both the intensity and the temperature dependencies of the alignment of all linear molecules exhibit universal curves and derive analytical forms to describe these dependencies. Finally, we illustrate that the alignment threshold occurs very generally at a lower intensity than the off-resonance ionization threshold, a numerical observation that is readily illustrated analytically. The threshold behavior is attributed to a tunneling mechanism that rapidly switches off at the threshold intensity, where tunneling between the potential wells corresponding to the two orientations of the aligned molecules becomes impossible. The universal threshold behavior of molecular alignment is a simple phenomenon, but one that was not realized before and can be readily tested experimentally.

74 ATOMIC AND MOLECULAR PHYSICS↗

DOE OSTI2024

Optimal function estimation with photonic quantum sensor networks

The problem of optimally measuring an analytic function of unknown local parameters each linearly coupled to a qubit sensor is well understood, with applications ranging from field interpolation to noise characterization. Here we resolve a number of open questions that arise when extending this framework to Mach-Zehnder interferometers and quadrature displacement sensing. In particular, we derive lower bounds on the achievable mean square error in estimating a linear function of either local phase shifts or quadrature displacements. In the case of local phase shifts, these results prove, and somewhat generalize, a conjecture by Proctor []. For quadrature displacements, we extend proofs of lower bounds to the case of arbitrary linear functions. We provide optimal protocols achieving these bounds up to small (multiplicative) constants and describe an algebraic approach to deriving new optimal protocols, possibly subject to additional constraints. Using this approach, we prove necessary conditions for the amount of entanglement needed for any optimal protocol for both local phase and displacement sensing. Published by the American Physical Society 2024

Bringewatt, Jacob↗

DOE OSTI2024

Integrable symplectic maps with a polygon tessellation

Identifying integrable dynamics remains a formidable challenge, and despite centuries of research, only a handful of examples are known to date. In this article, we explore a distinct form of area-preserving (symplectic) mappings derived from the stroboscopic Poincaré cross section of a kicked rotator—an oscillator subjected to an external force periodically switched on in short pulses. The significance of this class of problems extends to various applications in physics and mathematics, including particle accelerators, crystallography, and studies of chaos. Notably, Suris's theorem constrains the integrability within this category of mappings, outlining potential scenarios with analytic invariants of motion. In this paper, we challenge the assumption of the analyticity of the invariant by exploring piecewise linear transformations on a torus ( T 2 ) and associated systems on the plane ( R 2 ), incorporating arithmetic quasiperiodicity and discontinuities. Introducing a new automated technique, we discovered previously unknown scenarios featuring polygonal invariants that form perfect tessellations and, moreover, fibrations of the plane or torus. This work reveals a novel category of planar tilings characterized by discrete symmetries that emerge from the invertibility of transformations and are intrinsically linked to the presence of integrability. Our algorithm relies on the analysis of the Poincaré rotation number and its piecewise monotonic nature for integrable cases, contrasting with the noisy behavior in the case of chaos, thereby allowing for clear separation. Some of the newly discovered systems exhibit the peculiar behavior of “integrable diffusion,” characterized by infinite and quasirandom hopping between tiles while being confined to a set of invariant segments. Finally, through the implementation of a smoothening procedure, all mappings can be generalized to quasi-integrable scenarios with suppressed volume occupied by chaotic trajectories, thereby opening doors to potential practical applications. Published by the American Physical Society 2024

43 PARTICLE ACCELERATORS↗

DOE OSTI2016

Optimization of the thrombin generation test components to measure potency of factor VIII concentrates

Introduction The thrombin generation test (TGT) is used both as a global haemostasis assay, and to compare activities of coagulation factor concentrates that have been spiked into patient plasma. However, TGT has not been systematically optimized to evaluate factor VIII (FVIII) product potency. Aims To improve the sensitivity of TGT to FVIII and allow a comparative analysis of the thrombin generating capacities of FVIII concentrates against reference preparations with known FVIII activity. Methods Concentrations of TGT components (analytical variables) were assessed to maximize the linearity and range of responses to the concentration of FVIII. Results We optimized the range and sensitivity of the TGT assay with respect to FVIII through the addition of FXIa to the assay. Other parameters that were adjusted, i.e. tissue factor (TF), procoagulant lipids and plasma concentrations, did not improve the ability of the assay to measure both high and very low levels of FVIII. In the optimized TF/FXIa‐activated TGT assay, all thrombin generation curve parameters were suitable for FVIII quantification, but thrombin peak height and maximal velocity demonstrated better linearity in the desired FVIII range. We found that the optimized TF/FXIa‐activated TGT has a wider range of sensitivity to FVIII than a commercially available TGT. Additionally, we demonstrated that the TF/FXIa‐activated assay performs adequately by comparing potency measurements of five commercially available FVIII products using TGT and traditional chromogenic and one‐stage clotting assays. Conclusions The optimized TGT assay can be used to quantify and compare the thrombin generating capacities of FVIII concentrates.

Jha, N. K.↗