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At least 271 records · Page 15

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DOE OSTI2014

Effects of the dynamics of droplet-based laser-produced plasma on angular extreme ultraviolet emission profile

The emission distribution of extreme ultraviolet (EUV) radiation from droplet targets is dependent on the dynamics of the laser-produced plasma. The EUV emission is measured on a 2% bandwidth centered at 13.5 nm (in-band). The targets of the laser are small (sub-50 μm) tin droplets, and the in-band emission distribution is measured for different laser irradiances and droplet sizes at various angular positions. Larger droplets lead to a faster decay of EUV emission at larger angles with respect to the laser axis. A decrease in laser irradiance has the opposite effect. The measurements are used together with an analytical model to estimate plume dynamics. Additionally, the model is used to estimate EUV emission distribution for a desired droplet diameter and laser irradiance.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2022

Dynamic force and stability prediction for milling using feed rate scheduling software and time-domain simulation

This paper describes: 1) the use of feed rate scheduling software to predict the radial depth of cut variation for three-axis milling toolpaths and; 2) the use of the radial depth profile in a time-domain simulation to predict dynamic cutting forces. The time-domain simulation, which also includes the tool tip frequency response functions and force model (which relates the cutting force components to the chip geometry) as inputs, enables dynamic force profiles to be predicted and parameter combinations that cause chatter to be identified. A ramp geometry is selected that provides constantly varying radial depth and force predictions are completed at multiple axial depths for comparison to measured forces. Both stable and unstable (chatter) milling conditions were observed with good agreement between time-domain simulation and measurement results. The value of combining the feed rate scheduling software and time-domain simulation is demonstrated.

42 ENGINEERING↗

DOE OSTI2015

A new dynamical mass measurement for the Virgo cluster using the radial velocity profile of the filament galaxies

The radial velocities of the galaxies in the vicinity of a cluster show deviation from the pure Hubble flow due to their gravitational interaction with the cluster. According to a recent study by Falco et al. based on a high-resolution N-body simulation, the radial velocity profile of galaxies located at distances larger than three times the virial radius of a neighboring cluster can be well approximated by a universal formula, and could be reconstructed from direct observables provided that the galaxies are distributed along a one-dimensional filament. They suggested an algorithm designed to estimate the dynamic mass of a cluster M{sub v} by fitting the universal formula from the simulation to the reconstructed radial velocity profile of the filament galaxies around the cluster from observations. We apply the algorithm to two narrow, straight filaments (referred to as Filaments A and B) that were recently identified by Kim et al. in the vicinity of the Virgo cluster from the NASA-Sloan-Atlas catalog. The dynamical mass of the Virgo cluster is estimated to be M{sub v}=(0.84{sub −0.51}{sup +2.75})×10{sup 15} h{sup −1} M{sub ⊙} and M{sub v}=(3.24{sub −1.31}{sup +4.99})×10{sup 15} h{sup −1} M{sub ⊙} for the cases of Filaments A and B, respectively. We discuss the observational and theoretical systematics intrinsic to the method of Falco et al. as well as the physical implication of the final results.

79 ASTRONOMY AND ASTROPHYSICS↗

NASA NTRS2014

In Situ Probe Science at Saturn

A fundamental goal of solar system exploration is to understand the origin of the solar sys-tem, the initial stages, conditions, and processes by which the solar system formed, how the formation pro-cess was initiated, and the nature of the interstellar seed material from which the solar system was born. Key to understanding solar system formation and subsequent dynamical and chemical evolution is the origin and evolution of the giant planets and their atmospheres. Several theories have been put forward to explain the process of solar system formation, and the origin and evolution of the giant planets and their atmospheres. Each theory offers quantifiable predictions of the abundances of noble gases He, Ne, Ar, Kr, and Xe, and abundances of key isotopic ratios 4He3He, DH, 15N14N, 18O16O, and 13C12C. Detection of certain dis-equilibrium species, diagnostic of deeper internal pro-cesses and dynamics of the atmosphere, would also help discriminate between competing theories. Measurements of the critical abundance profiles of these key constituents into the deeper well-mixed at-mosphere must be complemented by measurements of the profiles of atmospheric structure and dynamics at high vertical resolution and also require in situ explora-tion. The atmospheres of the giant planets can also serve as laboratories to better understand the atmospheric chem-istries, dynamics, processes, and climates on all planets including Earth, and offer a context and provide a ground truth for exoplanets and exoplanetary systems. Additionally, Giant planets have long been thought to play a critical role in the development of potentially habitable planetary systems. In the context of giant planet science provided by the Galileo, Juno, and Cassini missions to Jupiter and Sat-urn, a small, relatively shallow Saturn probe capable of measuring abundances and isotopic ratios of key at-mospheric constituents, and atmospheric structure in-cluding pressures, temperatures, dynamics, and cloud locations and properties not accessible by remote sens-ing can serve to test competing theories of solar system and giant planet origin, chemical, and dynamical evolution.

Interstellar↗

DOE OSTI2019

Charge-mediated cation deposition on metallic surfaces

This work reveals the general mechanisms of Li + cation partial reduction and further deposition under specific electrolyte conditions, and in the proximity of an electrified metal surface. The factors affecting the ion complexation and transport and resultant adsorbed structures are identified for various external electric fields and for several applied voltages. Using ab initio methods, we investigate the relation between solvent–salt structures and dynamics, cation reductive stability, and the existing electric field between electrodes, or under the applied potential if the system is designed as an electrochemical cell. In absence of an applied field, it is found that not only cation but also non-solvated salt deposition on a metallic surface is an endothermic process. However, localized surface polarization orbitals created by an external electric field affect both the thermodynamics and kinetics of the adsorption, leading to a drastic change on the energetic profile; ab initio molecular dynamics simulations describe in detail the underlying mechanisms. Externally applied bias to an electrochemical cell also changes the deposition dynamics: by examining various solvent/salt combinations, we unravel the cation deposition mechanisms at both low and moderately high voltages, determining the relative time scale of each separate process. In this work, different polyhedra formed by the metal cation and its surrounding oxygen atoms appear to be the key indicator driving deposition dynamics at different voltages. Our findings disclose the importance of selecting appropriate voltage windows for stable and uniform growth of metal anode layers, showing the mechanisms leading to impurity formation and non-uniform cation deposition, as well as the role of charged interfacial phenomena in designing stable electrode–electrolyte interfaces.

25 ENERGY STORAGE↗

DOE OSTI2023

Disruption event characterization and forecasting in tokamaks

Disruption prediction and avoidance is a critical need for next-step tokamaks, such as ITER. Disruption Event Characterization and Forecasting (DECAF) research fully automates analysis of tokamak data to determine chains of events that lead to disruptions and to forecast their evolution allowing sufficient time for mitigation or complete avoidance of the disruption. Disruption event chains related to local rotating or global magnetohydrodynamic (MHD) modes and vertical instability are examined with warnings issued for many off-normal physics events, including density limits, plasma dynamics, confinement transitions, and profile variations. Along with Greenwald density limit evaluation, a local radiative island power balance theory is evaluated and compared to the observation of island growth. Automated decomposition and analysis of rotating tearing modes produce physical event chains leading to disruptions. A total MHD state warning model comprised of 15 separate criteria produces a disruption forecast about 180 ms before a standard locked mode detector warning. Single DECAF event analyses have begun on KSTAR, MAST, and NSTX/-U databases with thousands of shot seconds of device operation using from 0.5 to 1 × 10 6 tested sample times per device. An initial multi-device database comparison illustrates a highly important result that plasma disruptivity does not need to increase as βN increases. Global MHD instabilities, such as resistive wall modes (RWMs), can give the briefest time period of warning before disruption compared to other physics events. In an NSTX database with unstable RWMs, the mode onset, loss of boundary and current control, and disruption event warnings are found in all cases and vertical displacement events are found in 91% of cases. An initial time-dependent reduced physics model of kinetic RWM stabilization created to forecast the disruption chain predicts instability 84% of the time for experimentally unstable cases with a relatively low false positive rate. Instances of the disruption event chain analysis illustrate dynamics including H–L back transitions for rotating MHD and global RWM triggering events. Furthermore, disruption warnings are issued with sufficient time before the disruption (on transport timescales) to potentially allow active profile control for disruption avoidance, active mode control, or mitigation.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

NASA NTRS1993

Fluctuations at the blue edge of saturated wind lines in IUE spectra of O-type stars

We examine basic issues involved in synthesizing resonance-line profiles from 1-D, dynamical models of highly structured hot-star winds. Although these models exhibit extensive variations in density as well as velocity, the density scale length is still typically much greater than the Sobolev length. The line transfer is thus treated using a Sobolev approach, as generalized by Rybicki & Hummer (1978) to take proper account of the multiple Sobolev resonances arising from the nonmonotonic velocity field. The resulting reduced-Lambda-matrix equation describing nonlocal coupling of the source function is solved by iteration, and line profiles and then derived from formal solution integration using this source function. The more appropriate methods that instead use either a stationary or a structured, local source function yield qualitatively similar line-profiles, but are found to violate photon conservation by 10 percent or more. The full results suggest that such models may indeed be able to reproduce naturally some of the qualitative properties long noted in observed UV line profiles, such as discrete absorption components in unsaturated lines, or the blue-edge variability in saturated lines. However, these particular models do not yet produce the black absorption troughs commonly observed in saturated lines, and it seems that this and other important discrepancies (e.g., in acceleration time scale of absorption components) may require development of more complete models that include rotation and other 2-D and/or 3-D effects.

Owocki, Stanley P.↗

DOE OSTI2015

Spontaneous toroidal flow generation due to negative effective momentum diffusivity

Spontaneous structure formation, and in particular, zonal flows, is observed in a broad range of natural and engineered systems, often arising dynamically as the saturated state of a linear instability. Flows in tokamaks are known to self-organise on small scales, but large scale toroidal flows also arise even when externally applied torques are zero. This has previously been interpreted as the result of small externally imposed breaking of a symmetry. However, we show that for large enough field line pitch, a robust spontaneous symmetry breaking occurs, leading to the generation of strong toroidal flow structures; parameters are typical of Spherical Tokamak discharges with reversed shear profiles. The short wavelength dynamics are qualitatively similar to the growth of poloidal flow structures, and toroidal flow gradients nonlinearly saturate at levels where the shearing rate is comparable to linear growth rate. On long wavelengths, we measure Prandtl numbers of around zero for these systems, in conjunction with the formation of structured toroidal flows, and we show that this is consistent with a model of momentum transport where fluxes act to reinforce small flow gradients: the effective momentum diffusivity is negative. Toroidal flow structures are largely unaffected by collisional damping, so this may allow toroidal bulk flows of order the ion thermal velocity to be maintained with zero momentum input. This phenomenon also provides a mechanism for the generation of localised meso-scale structures like transport barriers.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2018

A Two-Step Load Disaggregation Algorithm for Quasi-static Time-series Analysis on Actual Distribution Feeders

This paper focuses on developing a two-step load disaggregation method for conducting quasi-static time-series analysis using actual distribution feeder data. This can help utilities conduct power flow studies using smart meter measurements to assess the impact of high penetration of distributed energy resources. In the first step, load profiles of residential and commercial buildings obtained from smart meter data are used to match the load profile at the feeder head. This step will determine the number of residential and commercial loads on the feeder. The second step is to allocate the selected load profiles to each load node based on its transformer rating. This allows each load node to have its own load profile and the aggregation of those nodal load profiles matches closely to the metered feeder load shape at the substation. This algorithm is validated using smart meter data and the SCADA data of a real feeder. We compared the performance of the proposed method with the traditional load allocation method (i.e. use the feeder load shape for all subsequent load nodes scaling by the transformer capacities) when conducting quasi-static power flow studies. Results show that the proposed algorithm matches the utility data well and the obtained voltage profiles reveal more voltage dynamics than using the conventional load allocation method. (PDF) A Two-Step Load Disaggregation Algorithm for Quasi-static Time-series Analysis on Actual Distribution Feeders.

load disaggregation, load shape, quasi-static, tim↗

DOE OSTI2014

A molecular dynamics study of polymer/graphene interfacial systems

Graphene based polymer nanocomposites are hybrid materials with a very broad range of technological applications. In this work, we study three hybrid polymer/graphene interfacial systems (polystyrene/graphene, poly(methyl methacrylate)/graphene and polyethylene/graphene) through detailed atomistic molecular dynamics (MD) simulations. Density profiles, structural characteristics and mobility aspects are being examined at the molecular level for all model systems. In addition, we compare the properties of the hybrid systems to the properties of the corresponding bulk ones, as well as to theoretical predictions.

77 NANOSCIENCE AND NANOTECHNOLOGY↗

DOE OSTI2014

Touching the void: A striking drop in stellar halo density beyond 50 kpc

We use A-type stars selected from Sloan Digital Sky Survey data release 9 photometry to measure the outer slope of the Milky Way stellar halo density profile beyond 50 kpc. A likelihood-based analysis is employed that models the ugr photometry distribution of blue horizontal branch and blue straggler stars. In the magnitude range 18.5 < g < 20.5, these stellar populations span a heliocentric distance range of: 10 ≲ D {sub BS}/kpc ≲ 75, 40 ≲ D {sub BHB}/kpc ≲ 100. Contributions from contaminants, such as QSOs, and the effect of photometric uncertainties, are also included in our modeling procedure. We find evidence for a very steep outer halo profile, with power-law index α ∼ 6 beyond Galactocentric radii r = 50 kpc, and even steeper slopes favored (α ∼ 6-10) at larger radii. This result holds true when stars belonging to known overdensities, such as the Sagittarius stream, are included or excluded. We show that, by comparison to numerical simulations, stellar halos with shallower slopes at large distances tend to have more recent accretion activity. Thus, it is likely that the Milky Way has undergone a relatively quiet accretion history over the past several gigayears. Our measurement of the outer stellar halo profile may have important implications for dynamical mass models of the Milky Way, where the tracer density profile is strongly degenerate with total mass estimates.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2023

A 1D Model for Nucleation of Ice From Aerosol Particles: An Application to a Mixed‐Phase Arctic Stratus Cloud Layer

Abstract Mixed‐phase clouds (MPCs) have been identified as significant contributors to uncertainties in climate projections, attributable to model representation of processes controlling the formation and loss of supercooled water droplets and ice particles from the atmosphere. Arctic MPCs are commonly widespread and long‐lived, with sustained ice crystal formation processes that challenge current understanding. This study examines the ice‐nucleating particle (INP) reservoir dynamics governing immersion‐mode heterogeneous freezing in an observed case of Arctic MPCs using a simplified 1D aerosol‐cloud model. The model setup includes prescribed dynamical forcings and thermodynamic profiles, and represents INPs as multicomponent and polydisperse particle size distributions. Diagnostic and prognostic approaches to immersion freezing parameterization are compared, including time‐independent (singular) number‐ and surface area‐based descriptions and a time‐dependent description following classical nucleation theory (CNT). The choice of freezing parameterization defines the size of the INP reservoir. The CNT‐based description yields an orders of magnitude larger INP reservoir than the singular parameterizations, which is the dominant factor for sustained ice crystal formation. The efficiency of the freezing process and cloud cooling are of secondary importance. A diagnostic treatment neglecting INP loss is only accurate when the INP reservoir size is large and INP depletion weak. Since a larger INP reservoir sustains ice crystal formation substantially longer, and ice water path scales with ice crystal concentrations for the conditions considered, resolving the source of differences in INP reservoir dynamics due to model implementation is a high priority for advancing climate model physics.

54 ENVIRONMENTAL SCIENCES↗

NASA NTRS2023

A 1D Model for Nucleation of Ice From Aerosol Particles: An Application to a Mixed-Phase Arctic Stratus Cloud Layer

Mixed-phase clouds (MPCs) have been identified as significant contributors to uncertainties in climate projections, attributable to model representation of processes controlling the formation and loss of supercooled water droplets and ice particles from the atmosphere. Arctic MPCs are commonly widespread and long-lived, with sustained ice crystal formation processes that challenge current understanding. This study examines the ice-nucleating particle (INP) reservoir dynamics governing immersion-mode heterogeneous freezing in an observed case of Arctic MPCs using a simplified 1D aerosol-cloud model. The model setup includes prescribed dynamical forcings and thermodynamic profiles, and represents INPs as multicomponent and polydisperse particle size distributions. Diagnostic and prognostic approaches to immersion freezing parameterization are compared, including time-independent (singular) number- and surface area-based descriptions and a time-dependent description following classical nucleation theory (CNT). The choice of freezing parameterization defines the size of the INP reservoir. The CNT-based description yields an orders of magnitude larger INP reservoir than the singular parameterizations, which is the dominant factor for sustained ice crystal formation. The efficiency of the freezing process and cloud cooling are of secondary importance. A diagnostic treatment neglecting INP loss is only accurate when the INP reservoir size is large and INP depletion weak. Since a larger INP reservoir sustains ice crystal formation substantially longer, and ice water path scales with ice crystal concentrations for the conditions considered, resolving the source of differences in INP reservoir dynamics due to model implementation is a high priority for advancing climate model physics.

aerosol↗

DOE OSTI2015

Study of ablation and implosion stages in wire arrays using coupled ultraviolet and X-ray probing diagnostics

Star and cylindrical wire arrays were studied using laser probing and X-ray radiography at the 1-MA Zebra pulse power generator at the University of Nevada, Reno. The Leopard laser provided backlighting, producing a laser plasma from a Si target which emitted an X-ray probing pulse at the wavelength of 6.65 Å. A spherically bent quartz crystal imaged the backlit wires onto X-ray film. Laser probing diagnostics at the wavelength of 266 nm included a 3-channel polarimeter for Faraday rotation diagnostic and two-frame laser interferometry with two shearing interferometers to study the evolution of the plasma electron density at the ablation and implosion stages. Dynamics of the plasma density profile in Al wire arrays at the ablation stage were directly studied with interferometry, and expansion of wire cores was measured with X-ray radiography. The magnetic field in the imploding plasma was measured with the Faraday rotation diagnostic, and current was reconstructed.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

NASA NTRS1983

TRAGEN: Computer program to simulate an aircraft steered to follow a specified verticle profile. User's guide

The longitudinal dynamics of a medium range twin-jet or tri-jet transport aircraft are simulated. For the climbing trajectory, the thrust is constrained to maximum value, and for descent, the thrust is set at idle. For cruise, the aircraft is held in the trim condition. For climb or descent, the aircraft is steered to follow either (a) a fixed profile which is input to the program or (b) a profile computed at the beginning of that segment of the run. For climb, the aircraft is steered to maintain the given airspeed as a function of altitude. For descent, the aircraft is steered to maintain the given altitude as a function of range-to-go. In both cases, the control variable is angle-of-attack. The given output trajectory is presented and compared with the input trajectory. Step climb is treated just as climb. For cruise, the Breguet equations are used to compute the fuel burned to achieve a given range and to connect given initial and final values of altitude and Mach number.

Source record↗

NASA NTRS1984

Saturn's rings - Structure, dynamics, and particle properties

The current state of knowledge of Saturn's rings is reviewed. A brief historical introduction is given, followed by a discussion of the radial profile of the rings, ring dynamics, features without azimuthal symmetry, ring particle size distribution, and the physical properties of ring particles. The direction for future analysis and observation is considered.

Esposito, L. W.↗

DOE OSTI2012

Simulation of carbon cycling, including dissolved organic carbon transport, in forest soil locally enriched with 14C

The DyDOC model was used to simulate organic matter decomposition and dissolved organic matter (DOM) transport in deciduous forest soils at the Oak Ridge Reservation (ORR) in Tennessee, USA. The model application relied on extensive data from the Enriched Background Isotope study (EBIS), which made use of a local atmospheric enrichment of radiocarbon to establish a large-scale manipulation experiment with different inputs of 14C from both above-ground and below-ground litter. The aim of the modelling was to test if the processes that constitute DyDOC can explain the available observations for C dynamics in the ORR. More specifically we used the model to investigate the origins of DOM, its dynamics within the soil profile, and how it contributes to the formation of stable carbon in the mineral soil. The model was first configured to account for water transport through the soil, then observed pools and fluxes of carbon and 14C data were used to fit the model parameters that describe the rates of the metabolic transformations. The soils were described by a thin O-horizon, a 15 cm thick A-horizon and a 45-cm thick B-horizon. Within the thin O-horizon, litter is either converted to CO2 or to a second organic matter pool, which is converted to CO2 at a different rate, both pools being able to produce DOM. The best model performance was obtained by assuming that adsorption of downwardly transported DOM in horizons A and B, followed by further conversion to stable forms, produces mineral-associated carbon pools, while root litter is the source of non-mineral associated carbon, with relatively short residence times. In the simulated steady-state, most carbon entering the O-horizon leaves quickly as CO2, but 17% (46 gC m-2 a-1) is lost as DOC in percolating water. The DOM comprises mainly hydrophobic material, 40% being derived from litter and 60% from older organic matter pools (residence time ~ 10 years). Most of the DOM is converted to CO2 in the mineral soil, over timescales of 1 to 15 years, but there is a conversion of 11 gC m-2 a-1 into stabilised forms that turnover on a timescale of 100-200 years. The small flux of DOC leaving the B-horizon (1.2 gC m-2 a-1) is mainly hydrophilic material, some of which can penetrate to depth quickly after formation. Considering the soil profile as single entity, the simulated soil carbon pools at ORR have mean residence times in the range 1-200 years, most of the carbon being in the slow pools, most of the turnover associated with the faster ones.

54 ENVIRONMENTAL SCIENCES↗

DOE OSTI2020

Techno-economic analysis of the impact of dynamic electricity prices on solar penetration in a smart grid environment with distributed energy storage

This study investigates the technical and economic feasibility of using high levels of solar energy penetration up to 400 MW into a smart grid system of 60,000 smart houses. A novel non-cooperative Stackelberg game is introduced that incorporates the profitability of the supply-side and helps in solving problems related to overgeneration and photovoltaic curtailment. The non-cooperative game is intended to find the optimal dynamic prices that would leverage distributed storage through the demand-side to stabilize the power grid operation. Ten cases are studied with five photovoltaic plant sizes and two battery designs. Here, a novel quantitative analysis of high levels of solar penetration as a percentage of the total electricity demand is introduced to evaluate the technical feasibility of the studied cases. To evaluate the economic viability of the proposed smart grid system, four metrics were used: the levelized cost of energy, the levelized cost of storage, the payback period, and the net present value. Two out of ten studied cases were concluded to be the most promising cases, one with a solar photovoltaic plant size of 200 MW and the other with 300 MW. The case with 300 MW solar plant is preferred as it paves the way for more solar energy deployment with a solar penetration percentage up to 67.78%. This case had a payback period of 10.72 years and a net present value of $\$51.44$ M for the solar plant and a payback period of 12.06 years and a net present value of $\$40.75$ M for the demand-side.

14 SOLAR ENERGY↗