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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 1,351 records · Page 75
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

Application of cellular automata approach for cloud simulation and rendering

Current techniques for creating clouds in games and other real time applications produce static, homogenous clouds. These clouds, while viable for real time applications, do not exhibit an organic feel that clouds in nature exhibit. These clouds, when viewed over a time period, were able to deform their initial shape and move in a more organic and dynamic way. With cloud shape technology we should be able in the future to extend to create even more cloud shapes in real time with more forces. Clouds are an essential part of any computer model of a landscape or an animation of an outdoor scene. A realistic animation of clouds is also important for creating scenes for flight simulators, movies, games, and other. Our goal was to create a realistic animation of clouds.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

A microsecond time resolved x-ray absorption near edge structure synchrotron study of phase transitions in Fe undergoing ramp heating at high pressure

We report a microsecond time-resolved x-ray absorption near edge structure study using synchrotron radiation to dynamically detect structural phase transitions in Fe undergoing rapid heating along a quasi-isochoric path. Within a few ms, we observed two structural phase transitions, which transform the ambient bcc phase of Fe into the fcc phase, and then into the liquid phase. This example illustrates the opportunities offered by energy dispersive x-ray absorption spectroscopy in the study of matter under extreme dynamic conditions. Advanced simulations are compared to these data.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Efficient self-consistent quantum transport simulator for quantum devices

We present a self-consistent one-dimensional (1D) quantum transport simulator based on the Contact Block Reduction (CBR) method, aiming for very fast and robust transport simulation of 1D quantum devices. Applying the general CBR approach to 1D open systems results in a set of very simple equations that are derived and given in detail for the first time. The charge self-consistency of the coupled CBR-Poisson equations is achieved by using the predictor-corrector iteration scheme with the optional Anderson acceleration. In addition, we introduce a new way to convert an equilibrium electrostatic barrier potential calculated from an external simulator to an effective doping profile, which is then used by the CBR-Poisson code for transport simulation of the barrier under non-zero biases. The code has been applied to simulate the quantum transport in a double barrier structure and across a tunnel barrier in a silicon double quantum dot. Extremely fast self-consistent 1D simulations of the differential conductance across a tunnel barrier in the quantum dot show better qualitative agreement with experiment than non-self-consistent simulations.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

A single-electron tunneling reset-set flip-flop

In this paper, a new Reset-Set flip-flop fully implemented with single-electron devices is proposed. Its topology derived from NAND gates and was validated at room temperature by simulation. Furthermore, a comparison between the proposed single-electron device and MOS devices in terms of power consumption and occupied area is presented.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2014

Intrinsic toroidal rotation in the scrape-off layer of tokamaks

The origin and nature of intrinsic toroidal plasma rotation in the scrape-off-layer (SOL) of tokamaks is investigated both analytically and through numerical simulations. It is shown that the equilibrium poloidal E × B flow, the sheath physics, and the presence of poloidal asymmetries in the pressure profile act as sources of momentum, while turbulence provides the mechanism for the radial momentum transport. An equation for the radial and poloidal dependence of the equilibrium parallel ion flow is derived, and a simple analytical solution is presented. This solution reproduces and explains the main experimental trends for the Mach number found in the SOL of tokamaks. Global, three-dimensional fluid simulations of SOL turbulence in different limiter configurations confirm the validity of the analytical theory.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2014

Adaptive fuzzy dynamic surface control for the chaotic permanent magnet synchronous motor using Nussbaum gain

This paper is concerned with the problem of adaptive fuzzy dynamic surface control (DSC) for the permanent magnet synchronous motor (PMSM) system with chaotic behavior, disturbance and unknown control gain and parameters. Nussbaum gain is adopted to cope with the situation that the control gain is unknown. And the unknown items can be estimated by fuzzy logic system. The proposed controller guarantees that all the signals in the closed-loop system are bounded and the system output eventually converges to a small neighborhood of the desired reference signal. Finally, the numerical simulations indicate that the proposed scheme can suppress the chaos of PMSM and show the effectiveness and robustness of the proposed method.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

Two modes of surface roughening during plasma etching of silicon: Role of ionized etch products

Atomic- or nanometer-scale surface roughening has been investigated during Si etching in inductively coupled Cl{sub 2} plasmas, as a function of rf bias power or ion incident energy E{sub i}, by varying feed gas flow rate, wafer stage temperature, and etching time. The experiments revealed two modes of surface roughening which occur depending on E{sub i}: one is the roughening mode at low E{sub i} < 200–300 eV, where the root-mean-square (rms) roughness of etched surfaces increases with increasing E{sub i}, exhibiting an almost linear increase with time during etching (t < 20 min). The other is the smoothing mode at higher E{sub i}, where the rms surface roughness decreases substantially with E{sub i} down to a low level < 0.4 nm, exhibiting a quasi-steady state after some increase at the initial stage (t < 1 min). Correspondingly, two different behaviors depending on E{sub i} were also observed in the etch rate versus √(E{sub i}) curve, and in the evolution of the power spectral density distribution of surfaces. Such changes from the roughening to smoothing modes with increasing E{sub i} were found to correspond to changes in the predominant ion flux from feed gas ions Cl{sub x}{sup +} to ionized etch products SiCl{sub x}{sup +} caused by the increased etch rates at increased E{sub i}, in view of the results of several plasma diagnostics. Possible mechanisms for the formation and evolution of surface roughness during plasma etching are discussed with the help of Monte Carlo simulations of the surface feature evolution and classical molecular dynamics simulations of etch fundamentals, including stochastic roughening and effects of ion reflection and etch inhibitors.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

The Young's modulus of high-aspect-ratio carbon/carbon nanotube composite microcantilevers by experimental and modeling validation

This paper reports the Young's modulus of a carbon nanotube (CNT)-reinforced carbon/CNT (C/CNT) composite microcantilevers measured by laser Doppler vibrometer and validated by finite element method. Also, the microfabrication process of the high-aspect-ratio C/CNT microcantilever arrays based on silicon micromolding and pyrolysis is presented in detail. With the in-plane natural resonant frequencies of the microcantilevers measured by a laser Doppler vibrometer, a single degree of freedom (SDoF) model based on Euler-Bernoulli (E-B) beam theory is used to calculate the Young's modulus of this composite. To figure out whether this SDoF model can be applied to these composite microcantilevers, the finite element (FE) simulation of these microcantilevers was performed. The Young's modulus of C/CNT composite microcantilevers fabricated by the pyrolysis process at 600 °C is 9391 MPa, and a good agreement between the results from experiments and FE simulation is obtained.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2015

A multi-beamlet analysis of the MITICA accelerator

The thermo-mechanical analysis and the mechanical design of the accelerator of MITICA (i.e. the full size prototype of the ITER neutral beam injector under construction at RFX [1]) are based on the calculation of the power deposition induced by particle impacts. This calculation is performed by EAMCC [2], a relativistic particle tracking code based on the Monte-Carlo method for describing collisions inside the accelerator, under prescribed electric and magnetic fields. The magnetic field maps are produced by 3D codes, while the electric field maps come from the 2D axi-symmetric code SLACCAD [3]. In order to perform a multi-beamlet analysis, which allows to take into account the beamlet-beamlet repulsion, and to consider other effects neglected under the hypothesis of axi-symmetric beam, a fully 3D version of the code is required. In this paper, a modified version of EAMCC, fully 3D, capable of modifying the mesh of the 3D maps and of dealing with uneven meshes is presented. A finer mesh is used just in the regions where a more detailed description of the fields is required, for a more realistic simulation. A comparison between the original code and the modified version is presented at first, as a validation of the modifications introduced in the latter. Subsequently, the main results of a single-beamlet analysis performed with the two versions of the code are shown and the differences between the 2D and the 3D simulations discussed. The last part is dedicated to the multi-beamlet simulation of the accelerator.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2015

Muon background studies for shallow depth Double - Chooz near detector

Muon events are one of the main concerns regarding background in neutrino experiments. The placement of experimental set-ups in deep underground facilities reduce considerably their impact on the research of the expected signals. But in the cases where the detector is installed on surface or at shallow depth, muon flux remains high, being necessary their precise identification for further rejection. Total flux, mean energy or angular distributions are some of the parameters that can help to characterize the muons. Empirically, the muon rate can be measured in an experiment by a number of methods. Nevertheless, the capability to determine the muons angular distribution strongly depends on the detector features, while the measurement of the muon energy is quite difficult. Also considering that on-site measurements can not be extrapolated to other sites due to the difference on the overburden and its profile, it is necessary to find an adequate solution to perform the muon characterization. The method described in this work to obtain the main features of the muons reaching the experimental set-up, is based on the muon transport simulation by the MUSIC software, combined with a dedicated sampling algorithm for shallow depth installations based on a modified Gaisser parametrization. This method provides all the required information about the muons for any shallow depth installation if the corresponding overburden profile is implemented. In this work, the method has been applied for the recently commissioned Double - Chooz near detector, which will allow the cross-check between the simulation and the experimental data, as it has been done for the far detector.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2015

Communication: Modeling of concentration dependent water diffusivity in ionic solutions: Role of intermolecular charge transfer

The translational diffusivity of water in solutions of alkali halide salts depends on the identity of ions, exhibiting dramatically different behavior even in solutions of similar salts of NaCl and KCl. The water diffusion coefficient decreases as the salt concentration increases in NaCl. Yet, in KCl solution, it slightly increases and remains above bulk value as salt concentration increases. Previous classical molecular dynamics simulations have failed to describe this important behavior even when polarizable models were used. Here, we show that inclusion of dynamical charge transfer among water molecules produces results in a quantitative agreement with experiments. Our results indicate that the concentration-dependent diffusivity reflects the importance of many-body effects among the water molecules in aqueous ionic solutions. Comparison with quantum mechanical calculations shows that a heterogeneous and extended distribution of charges on water molecules around the ions due to ion-water and also water-water charge transfer plays a very important role in controlling water diffusivity. Explicit inclusion of the charge transfer allows us to model accurately the difference in the concentration-dependent water diffusivity between Na{sup +} and K{sup +} ions in simulations, and it is likely to impact modeling of a wide range of systems for medical and technological applications.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Frequency dependence of the acoustic field generated from a spherical cavity transducer with open ends

Resolution of high intensity focused ultrasound (HIFU) focusing is limited by the wave diffraction. We have developed a spherical cavity transducer with two open ends to improve the focusing precision without sacrificing the acoustic intensity (App Phys Lett 2013; 102: 204102). This work aims to theoretically and experimentally investigate the frequency dependence of the acoustic field generated from the spherical cavity transducer with two open ends. The device emits high intensity ultrasound at the frequency ranging from 420 to 470 kHz, and the acoustic field is measured by a fiber optic probe hydrophone. The measured results shows that the spherical cavity transducer provides high acoustic intensity for HIFU treatment only in its resonant modes, and a series of resonant frequencies can be choosen. Furthermore, a finite element model is developed to discuss the frequency dependence of the acoustic field. The numerical simulations coincide well with the measured results.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Generating multi-double-scroll attractors via nonautonomous approach

It is a common phenomenon that multi-scroll attractors are realized by introducing the various nonlinear functions with multiple breakpoints in double scroll chaotic systems. Differently, we present a nonautonomous approach for generating multi-double-scroll attractors (MDSA) without changing the original nonlinear functions. By using the multi-level-logic pulse excitation technique in double scroll chaotic systems, MDSA can be generated. A Chua's circuit, a Jerk circuit, and a modified Lorenz system are given as designed example and the Matlab simulation results are presented. Furthermore, the corresponding realization circuits are designed. The Pspice results are in agreement with numerical simulation results, which verify the availability and feasibility of this method.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2013

Dynamics of production of iodine atoms by dissociation of iodides in a pulsed self-sustained discharge

Absorption at the laser transition has been used for the first time to assess the evolution of concentration of iodine atoms in a pulsed self-sustained discharge in mixtures of iodides with a buffer gas such as molecular nitrogen and helium. Dynamics of the iodine atom production is studied by the method of absorption spectroscopy. The dissociation of C{sub n}F{sub 2n+1}I and CnH{sub 2n+1}I (n = 1, 2) iodides is investigated. The energy required to produce atomic iodine is evaluated. The experimental data obtained for CF{sub 3}I are compared with the results of numerical simulations, their reasonable agreement being demonstrated. (active media)

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2017

All-optical XNOR gate based on 2D photonic-crystal ring resonators

A novel all-optical XNOR gate is proposed, which combines the nonlinear Kerr effect with photonic-crystal ring resonators (PCRRs). The total size of the proposed optical XNOR gate based on photonic crystals with a square lattice of silicon rods is equal to 35 × 21 μm. The proposed structure has a bandgap in the range from 0.32 to 0.44. To confirm the operation and feasibility of the overall system use is made of analytical and numerical simulation using the dimensional finite difference time domain (FDTD) and plane wave expansion (PWE) methods. (paper)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Contactless method for studying temperature within the active element of a multidisk cryogenic amplifier

A new original method has been developed and experimentally implemented, allowing temperature fields to be contactlessly measured in the pump region of active elements in high-power-diode-pumped laser amplifiers, including those operating at cryogenic temperatures. The presence of a temperature gradient of ∼57 K mm{sup −1} along the pump beam axis at the centre of the active element of the laser amplification unit operating at cryogenic temperatures with a pulse repetition rate up to 1 kHz is simulated and experimentally confirmed. (paper)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2020

Formula for the ionisation rate of an atom or ion in a strong electromagnetic field for numerical simulation

A formula is proposed for calculating the rate of field ionisation of an atom or ion, taking into account both tunnel ionisation and barrier suppression ionisation. Compared with the previous formula proposed in 2018, it more accurately describes the transition region between both ionisations and is determined mainly by two parameters: the ionisation potential of an atom or ion and the amplitude of an external electric field. This makes the presented formula suitable for use in numerical packages simulating the interaction of high-power laser radiation with matter by the particle-in-cell (PIC) method. (paper)

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2012

LOW-MASS TERTIARY COMPANIONS TO SPECTROSCOPIC BINARIES. I. COMMON PROPER MOTION SURVEY FOR WIDE COMPANIONS USING 2MASS

We report the first results of a multi-epoch search for wide (separations greater than a few tens of AU), low-mass tertiary companions of a volume-limited sample of 118 known spectroscopic binaries within 30 pc of the Sun, using the Two Micron All Sky Survey Point Source Catalog and follow-up observations with the KPNO and CTIO 4 m telescopes. Note that this sample is not volume complete but volume limited, and, thus, there is incompleteness in our reported companion rates. We are sensitive to common proper motion companions with separations from roughly 200 AU to 10,000 AU ({approx}10'' {yields} {approx} 10'). From 77 sources followed-up to date, we recover 11 previously known tertiaries, 3 previously known candidate tertiaries, of which 2 are spectroscopically confirmed and 1 rejected, and 3 new candidates, of which 2 are confirmed and 1 rejected. This yields an estimated wide tertiary fraction of 19.5{sup +5.2}{sub -3.7}%. This observed fraction is consistent with predictions set out in star formation simulations where the fraction of wide, low-mass companions to spectroscopic binaries is >10%.

79 ASTRONOMY AND ASTROPHYSICS↗