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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 1,693 records · Page 94
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

Numerical study of radiation effect on the municipal solid waste combustion characteristics inside an incinerator

Highlights: • A 3-D model for the MSW incinerator with preheated air was developed. • Gas radiative properties were obtained from a statistical narrow-band model. • Non-gray body radiation model can provide more accurate simulation results. - Abstract: Due to its advantages of high degree volume reduction, relatively stable residue, and energy reclamation, incineration becomes one of the best choices for Municipal Solid Waste (MSW) disposal. However, detailed measurements of temperature and gas species inside a furnace are difficulty by conventional experimental techniques. Therefore, numerical simulation of MSW incineration in the packed bed and gas flow field was applied. In this work, a three dimensional (3-D) model of incinerator system, including flow, heat transfer, detailed chemical mechanisms, and non-gray gas models, was developed. Radiation from the furnace wall and the flame formed above the bed is of importance for drying and igniting the waste. The preheated air with high temperature is used for the MSW combustion. Under the conditions of high temperature and high pressure, MSW combustion produces a variety of radiating gases. The wavelength-depend radiative properties of flame adopted in non-gray radiation model were obtained from a statistical narrow-band model. The influence of radiative heat transfer on temperature, flow field is researched by adiabatic model (without considering radiation), gray radiation model, and non-gray radiation model. The simulation results show that taking into account the non-gray radiation is essential.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2011

Calibrated cylindrical Mach probe in a plasma wind tunnel

A simple cylindrical Mach probe is described along with an independent calibration procedure in a magnetized plasma wind tunnel. A particle orbit calculation corroborates our model. The probe operates in the weakly magnetized regime in which probe dimension and ion orbit are of the same scale. Analytical and simulation models are favorably compared with experimental calibration.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2011

{pi} p and {pi}{pi} scattering at LHC

Can we get the information on {pi} p and {pi}{pi} scattering from the LHC data? We present briefly recent results of the IHEP Diffractive Group, which include all the steps: formulation of the problem, an idea how to solve it, experimental tools, Monte-Carlo simulation and preliminary expectations concerning the first data from the LHC.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2013

Sub-250 nm light emission and optical gain in AlGaN materials

We investigate the deep-UV optical emission and gain properties of Al{sub x}Ga{sub 1-x}N/Al{sub y}Ga{sub 1-y}N multiple quantum wells structures. These structures were grown by plasma-assisted molecular-beam epitaxy on 6H-SiC substrates, under a growth mode which promotes various degrees of band-structure potential fluctuations in the form of cluster-like features within the wells. The degree of inhomogeneities in these samples was determined by cathodoluminescence mapping. We measured the TE-polarized amplified spontaneous emission in the sample with cluster-like features and quantified the optical absorption/gain coefficients and gain spectra by the variable stripe length technique under ultrafast optical pumping. A maximum net modal gain of about 120 cm{sup -1} is measured at 4.9 eV. On the other hand, we found that samples with homogeneous quantum wells lead to absorption. Numerical simulations are performed to support our experimental findings.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2013

MD simulations of resistive cooling in HITRAP using GPUs

In the HITRAP facility at GSI it is planned to store 10{sup 5} highly charged ions up to U{sup 92+} in a cryogenic Penning trap and cool them down to 4 K via electron and resistive cooling. During the cooling process the ion density increases and the characteristics of the ion cloud are increasingly determined by Coulomb interactions. We present a parallel algorithm for the simulation of the resistive cooling for ion clouds in cylindrical Penning traps. For the simulation of the resistive cooling we run an Open Cl code on a single GPU device.

43 PARTICLE ACCELERATORS↗
DOE OSTI2014

Equilibrium Cu-Ag nanoalloy structure formation revealed by in situ scanning transmission electron microscopy heating experiments

Using in situ scanning transmission electron microscopy heating experiments, we observed the formation of a 3-dimensional (3D) epitaxial Cu-core and Ag-shell equilibrium structure of a Cu-Ag nanoalloy. The structure was formed during the thermal interaction of Cu(∼12 nm) and Ag NPs(∼6 nm) at elevated temperatures (150–300 °C) by the Ag NPs initially wetting the Cu NP along its (111) surfaces at one or multiple locations forming epitaxial Ag/Cu (111) interfaces, followed by Ag atoms diffusing along the Cu surface. This phenomenon was confirmed through Monte Carlo simulations to be a nanoscale effect related to the large surface-to-volume ratio of the NPs.

36 MATERIALS SCIENCE↗
DOE OSTI2014

An antidot array as an edge for total non-reflection of spin waves in yttrium iron garnet films

An array of antidots has been used as an edge to create the phenomenon of total non-reflection of spin waves in yttrium iron garnet films. At the critical angle between the line of antidots and the magnetic field, we observe a high-intensity beam of spin waves moving along the line of antidots. The properties of these waves are investigated experimentally by Brillouin light scattering spectroscopy. The conditions required for the occurrence of this phenomenon based on an analysis of the properties of the isofrequency dependencies are presented. The numerical simulations are in good agreement with those of the experimental measurements.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2014

Reliable clock estimation using linear weighted fusion based on pairwise broadcast synchronization

Clock synchronization in wireless sensor networks (WSNs) has been studied extensively in recent years and many protocols are put forward based on the point of statistical signal processing, which is an effective way to optimize accuracy. However, the accuracy derived from the statistical data can be improved mainly by sufficient packets exchange, which will consume the limited power resources greatly. In this paper, a reliable clock estimation using linear weighted fusion based on pairwise broadcast synchronization is proposed to optimize sync accuracy without expending additional sync packets. As a contribution, a linear weighted fusion scheme for multiple clock deviations is constructed with the collaborative sensing of clock timestamp. And the fusion weight is defined by the covariance of sync errors for different clock deviations. Extensive simulation results show that the proposed approach can achieve better performance in terms of sync overhead and sync accuracy.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

Dynamic load balance scheme for the DSMC algorithm

The direct simulation Monte Carlo (DSMC) algorithm, devised by Bird, has been used over a wide range of various rarified flow problems in the past 40 years. While the DSMC is suitable for the parallel implementation on powerful multi-processor architecture, it also introduces a large load imbalance across the processor array, even for small examples. The load imposed on a processor by a DSMC calculation is determined to a large extent by the total of simulator particles upon it. Since most flows are impulsively started with initial distribution of particles which is surely quite different from the steady state, the total of simulator particles will change dramatically. The load balance based upon an initial distribution of particles will break down as the steady state of flow is reached. The load imbalance and huge computational cost of DSMC has limited its application to rarefied or simple transitional flows. In this paper, by taking advantage of METIS, a software for partitioning unstructured graphs, and taking the total of simulator particles in each cell as a weight information, the repartitioning based upon the principle that each processor handles approximately the equal total of simulator particles has been achieved. The computation must pause several times to renew the total of simulator particles in each processor and repartition the whole domain again. Thus the load balance across the processors array holds in the duration of computation. The parallel efficiency can be improved effectively. The benchmark solution of a cylinder submerged in hypersonic flow has been simulated numerically. Besides, hypersonic flow past around a complex wing-body configuration has also been simulated. The results have displayed that, for both of cases, the computational time can be reduced by about 50%.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Electron trap level of hydrogen incorporated nitrogen vacancies in silicon nitride

Hydrogen incorporation into nitrogen vacancies in silicon nitride and its effects on electron trap level are analyzed using simulation based on density functional theory with temperature- and pressure-dependent hydrogen chemical potential. If the silicon dangling bonds around a nitrogen vacancy are well separated each other, hydrogen incorporation is energetically stable up to 900 °C, which is in agreement with the experimentally observed desorption temperature. On the other hand, if the dangling bonds strongly interact, the incorporation is energetically unfavorable even at room temperature because of steric hindrance. An electron trap level caused by a nitrogen vacancy becomes shallow by the hydrogen incorporation. An electron is trapped in a deep level created by a silicon dangling bond before hydrogen incorporation, whereas it is trapped in a shallow level created by an anti-bonding state of a silicon-silicon bond after hydrogen incorporation. The simulation results qualitatively explain the experiment, in which reduced hydrogen content in silicon nitride shows superior charge retention characteristics.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Electromagnetically induced transparency with large delay-bandwidth product induced by magnetic resonance near field coupling to electric resonance

In this paper, we numerically and experimentally demonstrate electromagnetically induced transparency (EIT)-like spectral response with magnetic resonance near field coupling to electric resonance. Six split-ring resonators and a cut wire are chosen as the bright and dark resonator, respectively. An EIT-like transmission peak located between two dips can be observed with incident magnetic field excitation. A large delay bandwidth product (0.39) is obtained, which has potential application in quantum optics and communications. The experimental results are in good agreement with simulated results.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Constraint methods that accelerate free-energy simulations of biomolecules

Atomistic molecular dynamics simulations of biomolecules are critical for generating narratives about biological mechanisms. The power of atomistic simulations is that these are physics-based methods that satisfy Boltzmann’s law, so they can be used to compute populations, dynamics, and mechanisms. But physical simulations are computationally intensive and do not scale well to the sizes of many important biomolecules. One way to speed up physical simulations is by coarse-graining the potential function. Another way is to harness structural knowledge, often by imposing spring-like restraints. But harnessing external knowledge in physical simulations is problematic because knowledge, data, or hunches have errors, noise, and combinatoric uncertainties. Here, we review recent principled methods for imposing restraints to speed up physics-based molecular simulations that promise to scale to larger biomolecules and motions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Effect of finite ion mass on relativistic self-induced transparency of plasma layers with a sharp boundary

We consider the effect of ion mobility on the threshold of relativistic self-induced transparency under irradiation of thin plasma layers by circularly polarised laser radiation. An analytical model of the motion of ions during the removal of electrons from the layer surface by the ponderomotive force of laser radiation is constructed. The model is used to analyse the motion of probe electrons in the resulting electromagnetic field. It is shown that the higher the ion mobility and the longer the laser pulse, the more stable the plasma layer to longitudinal perturbations of a finite value and the higher the threshold of self-induced transparency. These conclusions are verified by one-dimensional numerical simulation of a complete system of kinetic equations for plasma and Maxwell’s equations. (paper)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

Alma view of G0.253+0.016: Can cloud-cloud collision form the cloud?

We present the results of the sulfur monoxide, SO, line emission observations of G0.253+0.016 with the Atacama Large Millimeter/Submillimeter Array at an angular resolution of 1.''7. The dense and massive molecular cloud of G0.253+0.016 is highly sub-structured, yet it shows no obvious signs of cluster formation. We found three outstanding features of the cloud from the SO emission, namely, shell structure with a radius of 1.3 pc, large velocity gradients of 20 km s{sup –1} pc{sup –1} with the cloud, and cores with large velocity dispersions (30-40 km s{sup –1}) around the shell structure. We suggest that these large-velocity dispersion cores will form high-mass stars in the future. In an attempt to explore the formation scenario of the dense cloud, we compared our results with numerical simulations; therefore, we propose that G0.253+0.016 may have formed due to a cloud-cloud collision process.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2011

FORMING REALISTIC LATE-TYPE SPIRALS IN A {Lambda}CDM UNIVERSE: THE ERIS SIMULATION

Simulations of the formation of late-type spiral galaxies in a cold dark matter ({Lambda}CDM) universe have traditionally failed to yield realistic candidates. Here we report a new cosmological N-body/smooth particle hydrodynamic simulation of extreme dynamic range in which a close analog of a Milky Way disk galaxy arises naturally. Named 'Eris', the simulation follows the assembly of a galaxy halo of mass M{sub vir} = 7.9 Multiplication-Sign 10{sup 11} M{sub Sun} with a total of N = 18.6 million particles (gas + dark matter + stars) within the final virial radius, and a force resolution of 120 pc. It includes radiative cooling, heating from a cosmic UV field and supernova explosions (blastwave feedback), a star formation recipe based on a high gas density threshold (n{sub SF} = 5 atoms cm{sup -3} rather than the canonical n{sub SF} = 0.1 atoms cm{sup -3}), and neglects any feedback from an active galactic nucleus. Artificial images are generated to correctly compare simulations with observations. At the present epoch, the simulated galaxy has an extended rotationally supported disk with a radial scale length R{sub d} = 2.5 kpc, a gently falling rotation curve with circular velocity at 2.2 disk scale lengths of V{sub 2.2} = 214 km s{sup -1}, an i-band bulge-to-disk ratio B/D = 0.35, and a baryonic mass fraction within the virial radius that is 30% below the cosmic value. The disk is thin, has a typical H I-to-stellar mass ratio, is forming stars in the region of the {Sigma}{sub SFR}-{Sigma}{sub HI} plane occupied by spiral galaxies, and falls on the photometric Tully-Fisher and the stellar-mass-halo-virial-mass relations. Hot (T > 3 Multiplication-Sign 10{sup 5} K) X-ray luminous halo gas makes up only 26% of the universal baryon fraction and follows a 'flattened' density profile {proportional_to}r{sup -1.13} out to r = 100 kpc. Eris appears then to be the first cosmological hydrodynamic simulation in which the galaxy structural properties, the mass budget in the various components, and the scaling relations between mass and luminosity are all consistent with a host of observational constraints. A twin simulation with a low star formation density threshold results in a galaxy with a more massive bulge and a much steeper rotation curve, as in previously published work. A high star formation threshold appears therefore key in obtaining realistic late-type galaxies, as it enables the development of an inhomogeneous interstellar medium where star formation and heating by supernovae occur in a clustered fashion. The resulting outflows at high redshifts reduce the baryonic content of galaxies and preferentially remove low-angular-momentum gas, decreasing the mass of the bulge component. Simulations of even higher resolution that follow the assembly of galaxies with different merger histories shall be used to verify our results.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2012

CATASTROPHIC QUENCHING IN {alpha}{Omega} DYNAMOS REVISITED

At large magnetic Reynolds numbers, magnetic helicity evolution plays an important role in astrophysical large-scale dynamos. The recognition of this fact led to the development of the dynamical {alpha} quenching formalism, which predicts catastrophically low mean fields in open systems. Here, we show that in oscillatory {alpha}{Omega} dynamos this formalism predicts an unphysical magnetic helicity transfer between scales. An alternative technique is proposed where this artifact is removed by using the evolution equation for the magnetic helicity of the total field in the shearing advective gauge. In the traditional dynamical {alpha} quenching formalism, this can be described by an additional magnetic helicity flux of small-scale fields that does not appear in homogeneous {alpha}{sup 2} dynamos. In {alpha}{Omega} dynamos, the alternative formalism is shown to lead to larger saturation fields than what has been obtained in some earlier models with the traditional formalism. We have compared the predictions of the two formalisms to results of direct numerical simulations, finding that the alternative formulation provides a better fit. This suggests that worries about catastrophic dynamo behavior in the limit of large magnetic Reynolds number are unfounded.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

MAGNETIC WREATHS AND CYCLES IN CONVECTIVE DYNAMOS

Solar-type stars exhibit a rich variety of magnetic activity. Seeking to explore the convective origins of this activity, we have carried out a series of global three-dimensional magnetohydrodynamic simulations with the anelastic spherical harmonic code. Here we report on the dynamo mechanisms achieved as the effects of artificial diffusion are systematically decreased. The simulations are carried out at a nominal rotation rate of three times the solar value (3 {Omega}{sub Sun }), but similar dynamics may also apply to the Sun. Our previous simulations demonstrated that convective dynamos can build persistent toroidal flux structures (magnetic wreaths) in the midst of a turbulent convection zone and that high rotation rates promote the cyclic reversal of these wreaths. Here we demonstrate that magnetic cycles can also be achieved by reducing the diffusion, thus increasing the Reynolds and magnetic Reynolds numbers. In these more turbulent models, diffusive processes no longer play a significant role in the key dynamical balances that establish and maintain the differential rotation and magnetic wreaths. Magnetic reversals are attributed to an imbalance in the poloidal magnetic induction by convective motions that is stabilized at higher diffusion levels. Additionally, the enhanced levels of turbulence lead to greater intermittency in the toroidal magnetic wreaths, promoting the generation of buoyant magnetic loops that rise from the deep interior to the upper regions of our simulated domain. The implications of such turbulence-induced magnetic buoyancy for solar and stellar flux emergence are also discussed.

79 ASTRONOMY AND ASTROPHYSICS↗