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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 1,153 records · Page 64
All sourcesNASA NTRSDOE OSTI
DOE OSTI2011

Searches for Rare and Beyond the Standard Model Top Quark Decays at the Tevatron

The Tevatron experiments CDF and D0 investigated the top quark decay in search of deviations from the Standard Model. Rare processes expected in the Standard Model as well as decays including hypothetical particles of models beyond the Standard Model were investigated. This contribution gives an overview of the studies that were performed with datasets of up to 7.5fb^-1 of integrated luminosity.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2019

Modeling Water Uptake and Pt Utilization in High Surface Area Carbon

Local transport losses limit high-current density performance of fuel-cells, especially at low Pt-loadings. Optimizing catalyst-layer structure and material properties to mitigate these losses is critical for wide-scale fuel-cell commercialization. Carbon supports form the primary porous structure of catalyst layers in which Pt particles are deposited and ionomer films are distributed. Unlike non-porous carbon supports, high surface area carbon support is unique in its relative humidity dependent Pt utilization and performance due to presence of Pt particles in the micropores interior of carbon particles. We model water uptake and Pt utilization in catalyst layers with high-surface-area carbon support. Interactions between functional groups on the carbon pore walls and water play a vital role in controlling water uptake from water vapor by catalyst layers. Ionomer is shown to influence proton access in micropores, even though it may not deposit into the micropores.

08 HYDROGEN↗
NASA NTRS1994

Transverse particle acceleration and diffusion in a planetary magnetic field

A general model of particle acceleration by plasma waves coupled with adiabatic radial diffusion in a planetary magnetic field is developed. The model assumes that a spectrum of lower hybird waves is present to resonantly accelerate ions transverse to the magnetic field. The steady state Green's function for the combined radial diffusion and wave acceleration equation is found in terms of a series expansion. The results provide a rigorous demonstration of how a quasi-Maxwellian distribution function is formed in the absence of particle collisons and elucidate the nature of turbulent heating of magnetospheric plasmas. The solution is applied to the magnetosphere of Neptune for which a number of examples are given illustrating how the spectrum of pickup N(+) ions from Triton evolves.

Barbosa, D. D.↗
NASA NTRS2021

An Evaluation of Size-Resolved Cloud Microphysics Scheme Numerics for use with Radar Observations Part II: Condensation and Evaporation

Accurate numerical modeling of clouds and precipitation is essential for weather forecasting and climate change research. While size-resolved (bin) cloud microphysics models predict particle size distributions without imposing shapes, results are subject to artificial size distribution broadening owing to numerical diffusion associated with various processes. Whereas Part 1 addressed collision-coalescence, here we investigate numerical diffusion that occurs in solving condensation and evaporation. In a parcel model framework, all of the numerical schemes examined converge to one solution of condensation and evaporation as the mass grid is refined, and the advection-based schemes are recommended over the reassigning schemes. Including Eulerian vertical advection in a column limits the convergence to some extent, but that limitation occurs at a sufficiently fine mass grid, and the number of iterations in solving vertical advection should be minimized to reduce numerical diffusion. Insubstantial numerical diffusion in solving condensation can be amplified if collision-coalescence is also active, which in turn can be substantially diminished if turbulence effects on collision are incorporated. Large-eddy simulations of a drizzling stratocumulus field reveal that changes in moments of Doppler spectra obtained using different mass grids are consistent with those obtained from the simplified framework, and that spectral moments obtained using a mass grid designed to effectively reduce numerical diffusion are generally closer to observations. Notable differences between the simulations and observations still exist, and our results suggest a need to consider whether factors other than numerical diffusion in the fundamental process schemes employed can cause such differences.

Cloud microphysics↗
DOE OSTI2013

International Linear Collider Technical Design Report - Volume 2: Physics

For more than twenty years, an advanced electron-positron collider has been put forward as a key component of the future program of elementary particle physics. We have a well-established Standard Model of particle physics, but it is known to be incomplete. Among the many questions that this model leaves open, there are two — the origin of the masses of elementary particles and the particle identity of cosmic dark matter – that should be addressed at energy scales below 1 TeV. It has been appreciated for a long time that a next-generation electron-positron collider would give us the ability to make precision measurements that would shed light on these mysteries. Now the technology to build this electron-positron collider has come of age. This report is a volume of the Technical Design Report for the International Linear Collider (ILC). The accompanying volumes of this report lay out the technical design of a high-luminosity e + e - collider at 500 GeV in the center of mass and of detectors that could make use of the collisions to perform high-precision measurements. In this volume, we summarize the physics arguments for building this collider and their appropriate relation to the situation of particle physics as of the fall of 2012. The discussion in this volume supplements the presentation of the physics opportunities for a 500 GeV e + e - collider given in the review articles, the 2001 regional study reports, the 2006 study of ILC/LHC complementarity, and the 2007 ILC Reference Design Report.

43 PARTICLE ACCELERATORS↗
DOE OSTI2025

Particle Size gradients in Modeled Vibrated beds of continuously sized powders

Ensuring powder mixture homogeneity is paramount for modern powder processing techniques. A promising recent development in the field of powder processing, resonant acoustic mixing (RAM), proposes to use low-frequency vertical vibration to deliver well-mixed powders without relying on mechanical agitators. However, an undesirable outcome of vibrations applied to granular materials comprised of non-uniform particle sizes is the tendency towards size segregation. In this work, we experimentally ex

Renfroe, Steven Emad [Sandia National Laboratories↗
NASA NTRS2019

Modeling Heatshield Erosion Due to Dust Particle Impacts for a Martian Entry Vehicle

The modeling assumptions and governing equations required to estimate the heatshield surface recession due to dust particle impacts are presented. The dust particle size distribution can be estimated using a modified gamma distribution. The vertical distribution of dust particles in the atmosphere in terms of the ratio of dust particle to atmospheric density can be related to measured or computed values of the dust opacity. The different approaches to coupling the particle and fluid dynamics are discussed. The equations and modeling assumptions presented in this paper are applied to computing the surface recession due to dust particle impacts on the ExoMars Schiaparelli capsule entering the Martian atmosphere during a representative dust storm. The dust surface recession at the stagnation point of about 1 millimeter is about 40 percent of the recession value due to charring ablation.

Thermal Protection Systems↗
DOE OSTI2024

Utilizing HYSPLIT for Emergency Response Modeling at SRS

At SRS, emergency responders use a variety of tools to detect, track, and mitigate hazardous material releases into the atmosphere. Two models currently used at SRS are Puff-Plume and the Lagrangian Particle Dispersion Model (LPDM), a Gaussian and Lagrangian model, respectively. A decision has been made to replace LPDM with the more widely-supported Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model for evaluating inhalation and ingestion doses following a release. HYSPLIT is designed to compute complex dispersion and deposition simulation To achieve the implementation of HYSPLIT, we have developed a preliminary UI framework that will allow HYSPLIT to be run on ATG computers without the need for active network connections, thus avoiding the loss of capabilities in the event of a network outage during an emergency.

Earley, Ian↗
NASA NTRS1983

A theoretical model study of observed correlations between whistler mode waves and energetic electron precipitation events in the magnetosphere

A recently extended test particle computer model of the gyroresonance wave-particle interaction in the magnetosphere is applied to previously reported cases of observed correlations between whistler mode waves and ionospheric responses to particle precipitation. Three different ionospheric effects, namely, X-ray bursts, photoemissions, and D region perturbations, all correlated with VLF waves and believed to be caused by precipitated particles, are considered. The precipitation flux level, the pulse shape, and the associated time delays are computed for the parameters relevant to each case and are compared with values deduced from the data. The results demonstrate that the existing theoretical model can be useful for interpreting experimental results of this kind. Furthermore, the model results and observations, used together, provide a basis for additional diagnostics of the various parameters of the cold and energetic particle distributions in the magnetosphere. For example, when applied to the observed photoemission case (Helliwell et al., 1980) the model results imply that the trapped energetic particle distribution function at the time could be modeled as proportional to E exp -n/2 with n about 3.5 to 6, where E is the particle energy.

Chang, H. C.↗
DOE OSTI2012

The Standard Model

Fermilab scientist Don Lincoln describes the Standard Model of particle physics, covering both the particles that make up the subatomic realm and the forces that govern them.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2015

Testing model energy spectra of charged particles produced in hadron interactions on the basis of atmospheric muons

An original method for calculating the spectrum of atmospheric muons with the aid of the CORSIKA 7.4 code package and numerical integration is proposed. The first step consists in calculating the energy distribution of muons for various fixed energies of primary-cosmic-ray particles and within several chosen hadron-interaction models included in the CORSIKA 7.4 code package. After that, the spectrum of atmospheric muons is calculated via integrating the resulting distribution densities with the chosen spectrum of primary-cosmic-ray particles. The atmospheric-muon fluxes that were calculated on the basis of the SIBYLL 2.1, QGSJET01, and QGSJET II-04 models exceed the predictions of the wellknown Gaisser approximation of this spectrum by a factor of 1.5 to 1.8 in the range of muon energies between about 10{sup 3} and 10{sup 4} GeV.Under the assumption that, in the region of extremely highmuon energies, a dominant contribution to the muon flux comes from one to two generations of charged π{sup ±} and K{sup ±} mesons, the production rate calculated for these mesons is overestimated by a factor of 1.3 to 1.5. This conclusion is confirmed by the results of the LHCf and TOTEM experiments.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Generalized Bohm Criterion for Electronegative Complex Plasma

In this work, we have generalized the computation of Bohm criterion for electronegative complex plasma. For this, we have established a one-dimensional, unmagnetized and stationary theoretical model where the positive ions and dust particles are modeled by fluid equations. The electrons and negative ions are considered in thermodynamic equilibrium; therefore they obey to Boltzmann's statistic. In this case, the numerical results show that the generalized Bohm velocity is small compared to the classical value. For electronegative dusty plasma, the corrections are less important.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2022

Deep learning for drag force modelling in dilute, poly-dispersed particle-laden flows with irregular-shaped particles

Here, this study applies machine learning-based approaches to develop a drag force model for irregular-shaped particles in incompressible flows. The particle-laden flows are studied through an in-house particle-resolved direct numerical simulation (PR-DNS) at low-intermediate Reynolds numbers (Re). We utilize the PR-DNS to obtain drag force coefficients and flow fields of single particles. A variational auto-encoder model is used to obtain latent vectors to represent the geometrical features of the particles, and artificial neural networks (ANN) are developed to predict drag force coefficients and flow fields of the single particles. This study applies a pairwise interaction extended point-particle (PIEP) model to obtain the coefficients assuming the flow fields of neighboring particles can be linearly superposed. The PIEP method shows significant improvement on prediction for a few neighbored particles. In addition, the results reveal R2 scores of 0.56-0.62 and errors of 9.1-10.0 % for the dilute, polydispersed systems with a volume fraction of 0.5 %.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Monte Carlo simulation of cylinders with short-range attractions

Cylindrical or rod-like particles are promising materials for the applications of fillers in nanocomposite materials and additives to control rheological properties of colloidal suspensions. Recent advances in particle synthesis allows for cylinders to be manufactured with short-ranged attractions to study the gelation as a function of packing fraction, aspect ratio and attraction strength. In order to aid in the analysis of small-angle scattering experiments of rod-like particles, computer simulation methods were used to model these particles with specialized Monte Carlo algorithms and tabular superquadric potentials. The attractive interaction between neighboring rods increases with the amount of locally-accessible surface area, thus leading to patchy-like interactions. We characterize the clustering and percolation of cylinders as the attractive interaction increases from the homogenous fluid at relatively low attraction strength, for a variety of aspect ratios and packing fractions. Comparisons with the experimental scattering results are also presented, which are in agreement.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2013

Particle-scale CO2 adsorption kinetics modeling considering three reaction mechanisms

In the presence of water (H2O), dry and wet adsorptions of carbon dioxide (CO2) and physical adsorption of H2O happen concurrently in a sorbent particle. The three reactions depend on each other and have a complicated, but important, effect on CO2 capturing via a solid sorbent. In this study, transport phenomena in the sorbent were modeled, including the tree reactions, and a numerical solving procedure for the model also was explained. The reaction variable distribution in the sorbent and their average values were calculated, and simulation results were compared with experimental data to validate the proposed model. Some differences, caused by thermodynamic parameters, were observed between them. However, the developed model reasonably simulated the adsorption behaviors of a sorbent. The weight gained by each adsorbed species, CO2 and H2O, is difficult to determine experimentally. It is known that more CO2 can be captured in the presence of water. Still, it is not yet known quantitatively how much more CO2 the sorbent can capture, nor is it known how much dry and wet adsorptions separately account for CO2 capture. This study addresses those questions by modeling CO2 adsorption in a particle and simulating the adsorption process using the model. As adsorption temperature changed into several values, the adsorbed amount of each species was calculated. The captured CO2 in the sorbent particle was compared quantitatively between dry and wet conditions. As the adsorption temperature decreased, wet adsorption increased. However, dry adsorption was reduced.

CO2 capture, Mathematical modeling, Sorbent partic↗
DOE OSTI2022

Breeding Realistic D‐Brane Models

Abstract Intersecting branes provide a useful mechanism to construct particle physics models from string theory with a wide variety of desirable characteristics. The landscape of such models can be enormous, and navigating towards regions which are most phenomenologically interesting is potentially challenging. Machine learning techniques can be used to efficiently construct large numbers of consistent and phenomenologically desirable models. In this work we phrase the problem of finding consistent intersecting D‐brane models in terms of genetic algorithms, which mimic natural selection to evolve a population collectively towards optimal solutions. For a four‐dimensional supersymmetric type IIA orientifold with intersecting D6‐branes, we demonstrate that unique, fully consistent models can be easily constructed, and, by a judicious choice of search environment and hyper‐parameters, of the found models contain the desired Standard Model gauge group factor. Having a sizable sample allows us to draw some preliminary landscape statistics of intersecting brane models both with and without the restriction of having the Standard Model gauge factor.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2023

An introduction to the significance of sample size in particle analyses for nuclear forensics and radiological investigations

Particulate isotopic analysis in nuclear forensics has developed rapidly during the past two decades due to technical advances in determining the isotopic composition of individual particles. This paper introduces basic statistical concepts that can be applied by analysts to understand the importance of statistical adequacy when interpretating particle data. While these basic statistical methods provide a useful point-of-entry to particle data analysis, more sophisticated statistical and modeling approaches are needed to extract maximal information from such datasets in the future.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2018

Asymptotically safe f(R)-gravity coupled to matter I: The polynomial case

We use the functional renormalization group equation for the effective average action to study the non-Gaussian renormalization group fixed points (NGFPs) arising within the framework of f(R)-gravity minimally coupled to an arbitrary number of scalar, Dirac, and vector fields. Based on this setting we provide comprehensible estimates whose gravity–matter systems give rise to NGFPs suitable for rendering the theory asymptotically safe. The analysis employs an exponential split of the metric fluctuations and retains a 7-parameter family of coarse-graining operators allowing the inclusion of non-trivial endomorphisms in the regularization procedure. For vanishing endomorphisms, it is established that gravity coupled to the matter content of the standard model of particle physics and many beyond the standard model extensions exhibit NGFPs whose properties are strikingly similar to the case of pure gravity: there are two UV-relevant directions and the position and critical exponents converge rapidly when higher powers of the scalar curvature are included. Conversely, none of the phenomenologically interesting gravity–matter systems exhibits a stable NGFP when a Type II coarse graining operator is employed. Our analysis resolves this tension by demonstrating that the NGFPs seen in the two settings belong to different universality classes.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗