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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 829 records · Page 46
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

IN-SYNC. II. VIRIAL STARS FROM SUBVIRIAL CORES—THE VELOCITY DISPERSION OF EMBEDDED PRE-MAIN-SEQUENCE STARS IN NGC 1333

The initial velocity dispersion of newborn stars is a major unconstrained aspect of star formation theory. Using near-infrared spectra obtained with the APOGEE spectrograph, we show that the velocity dispersion of young (1-2 Myr) stars in NGC 1333 is 0.92 ± 0.12 km s{sup –1} after correcting for measurement uncertainties and the effect of binaries. This velocity dispersion is consistent with the virial velocity of the region and the diffuse gas velocity dispersion, but significantly larger than the velocity dispersion of the dense, star-forming cores, which have a subvirial velocity dispersion of 0.5 km s{sup –1}. Since the NGC 1333 cluster is dynamically young and deeply embedded, this measurement provides a strong constraint on the initial velocity dispersion of newly formed stars. We propose that the difference in velocity dispersion between stars and dense cores may be due to the influence of a 70 μG magnetic field acting on the dense cores or be the signature of a cluster with initial substructure undergoing global collapse.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

EMBEDDED LENSING TIME DELAYS, THE FERMAT POTENTIAL, AND THE INTEGRATED SACHS–WOLFE EFFECT

We derive the Fermat potential for a spherically symmetric lens embedded in a Friedman–Lemaître–Robertson–Walker cosmology and use it to investigate the late-time integrated Sachs–Wolfe (ISW) effect, i.e., secondary temperature fluctuations in the cosmic microwave background (CMB) caused by individual large-scale clusters and voids. We present a simple analytical expression for the temperature fluctuation in the CMB across such a lens as a derivative of the lens’ Fermat potential. This formalism is applicable to both linear and nonlinear density evolution scenarios, to arbitrarily large density contrasts, and to all open and closed background cosmologies. It is much simpler to use and makes the same predictions as conventional approaches. In this approach the total temperature fluctuation can be split into a time-delay part and an evolutionary part. Both parts must be included for cosmic structures that evolve and both can be equally important. We present very simple ISW models for cosmic voids and galaxy clusters to illustrate the ease of use of our formalism. We use the Fermat potentials of simple cosmic void models to compare predicted ISW effects with those recently extracted from WMAP and Planck data by stacking large cosmic voids using the aperture photometry method. If voids in the local universe with large density contrasts are no longer evolving we find that the time delay contribution alone predicts values consistent with the measurements. However, we find that for voids still evolving linearly, the evolutionary contribution cancels a significant part of the time delay contribution and results in predicted signals that are much smaller than recently observed.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

EVOLUTION OF A DWARF SATELLITE GALAXY EMBEDDED IN A SCALAR FIELD DARK MATTER HALO

The cold dark matter (CDM) model has two unsolved issues: simulations overpredict the satellite abundance around the Milky Way (MW) and it disagrees with observations of the central densities of dwarf galaxies which prefer constant density (core) profiles. One alternative explanation known as the scalar field dark matter (SFDM) model, assumes that dark matter is a scalar field of mass (∼10{sup −22} eV/c{sup 2}); this model can reduce the overabundance issue due to the lack of halo formation below a mass scale of ∼10{sup 8}M{sub ⊙} and successfully fits the density distribution in dwarfs. One of the attractive features of the model is predicting core profiles in halos, although the determination of the core sizes is set by fitting the observational data. We perform N-body simulations to explore the influence of tidal forces over a stellar distribution embedded in an SFDM halo orbiting a MW-like SFDM host halo with a disk. Our simulations intend to test the viability of SFDM as an alternative model by comparing the tidal effects that result in this paradigm with those obtained in the CDM for similar mass halos. We found that galaxies in subhalos with core profiles and high central densities survive for 10 Gyr. The same occurs for galaxies in low density subhalos located far from the host disk influence, whereas satellites in low density DM halos and in tight orbits can eventually be stripped of stars. We conclude that SFDM shows consistency with results from the CDM for dwarf galaxies, but naturally offer a possibility to solve the missing satellite problem.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

The 3D flow field around an embedded planet

3D modifications to the well-studied 2D flow topology around an embedded planet have the potential to resolve long-standing problems in planet formation theory. We present a detailed analysis of the 3D isothermal flow field around a 5 Earth-mass planet on a fixed circular orbit, simulated using our graphics processing unit hydrodynamics code PEnGUIn. We find that, overall, the horseshoe region has a columnar structure extending vertically much beyond the Hill sphere of the planet. This columnar structure is only broken for some of the widest horseshoe streamlines, along which high altitude fluid descends rapidly into the planet’s Bondi sphere, performs one horseshoe turn, and exits the Bondi sphere radially in the midplane. A portion of this flow exits the horseshoe region altogether, which we refer to as the “transient” horseshoe flow. The flow continues as it rolls up into a pair of up–down symmetric horizontal vortex lines shed into the wake of the planet. This flow, unique to 3D, affects both planet accretion and migration. It prevents the planet from sustaining a hydrostatic atmosphere due to its intrusion into the Bondi sphere, and leads to a significant corotation torque on the planet, unanticipated by 2D analysis. In the reported simulation, starting with a Σ∼r{sup −3/2} radial surface density profile, this torque is positive and partially cancels with the negative differential Lindblad torque, resulting in a factor of three slower planet migration rate. Finally, we report 3D effects can be suppressed by a sufficiently large disk viscosity, leading to results similar to 2D.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

The warm CO gas along the uv-heated outflow cavity walls: a possible interpretation for the Herschel/pacs co spectra of embedded YSOs

A fraction of the mid-J (J = 14–13 to J = 24–23) CO emission detected by the Herschel/Photodetector Array Camera and Spectrometer observations of embedded young stellar objects (YSOs) has been attributed to the UV-heated outflow cavity walls. We have applied our newly developed self-consistent models of photon-dominated-region (PDR) and non-local-thermal-equilibrium-line Radiative transfer In general Grid to the Herschel far-infrared observations of 27 low-mass YSOs and one intermediate-mass YSO, NGC 7129-FIRS2. When the contribution of the hot component (traced by transitions of J > 24) is removed, the rotational temperature of the warm component is nearly constant with ∼250 K. This can be reproduced by the outflow cavity wall (n⩾10{sup 6} cm{sup −3}, logG{sub 0}/n⩾−4.5, logG{sub 0}⩾3, T{sub gas} ≥ 300 K, and X(CO) ≥ 10{sup −5}) heated by a UV radiation field with a blackbody temperature of 15,000 or 10,000 K. However, a shock model combined with an internal PDR will be required to determine the quantitative contribution of a PDR relative to a shock to the mid-J CO emission.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

Nonlocal thermal transport across embedded few-layer graphene sheets

Thermal transport across the interfaces between few-layer graphene sheets and soft materials exhibits intriguing anomalies when interpreted using the classical Kapitza model, e.g., the conductance of the same interface differs greatly for different modes of interfacial thermal transport. Using atomistic simulations, we show that such thermal transport follows a nonlocal flux-temperature drop constitutive law and is characterized jointly by a quasi-local conductance and a nonlocal conductance instead of the classical Kapitza conductance. Lastly, the nonlocal model enables rationalization of many anomalies of the thermal transport across embedded few-layer graphene sheets and should be used in studies of interfacial thermal transport involving few-layer graphene sheets or other ultra-thin layered materials.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Three-dimensional Chemical Imaging of Embedded Nanoparticles using Atom Probe Tomography

Analysis of nanoparticles is often challenging especially when they are embedded in a matrix. Hence, we have used laser-assisted atom probe tomography (APT) to analyze the Au-nanoclusters synthesized in situ using ion beam implantation in single crystal MgO matrix. APT analysis along with scanning transmission electron microscopy and energy dispersive spectroscopy (STEM-EDS) indicated that the nanoparticles have an average size ~ 8 - 12 nm. While it is difficult to analyze the composition of individual nanoparticles using STEM, APT analysis can give three dimensional compositions of the same. It was shown that the maximum Au-concentration in the nanoparticles increases with increasing particle size, with a maximum Au-concentration of up to 50%.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2013

Subsurface Synthesis and Characterization of Ag Nanoparticles Embedded in MgO

Metal nanoparticles exhibit localized surface plasmon resonance (LSPR) which is very sensitive to the size and shape of the nanoparticle and the dielectric medium surrounding it. LSPR causes field enhancement near the surface of the nanoparticle making them interesting candidates for plasmonic applications. In particular, partially exposed metallic nanoparticles distributed in a dielectric matrix form hotspots which are prime locations for LSPR spectroscopy and sensing. This study involves synthesizing partially buried Ag nanoparticles in MgO and investigating the characteristics of this material system. Ag nanoparticles of different shapes and size distributions were synthesized below the surface of MgO by implanting 200 keV Ag+ ions followed by annealing at 10000C for 10 and 30 hours. A detailed optical and structural characterization was carried out to understand the evolution of Ag nanoparticle microstructure and size distribution inside the MgO matrix. Micro x-ray diffraction (MicroXRD) was employed to investigate the structural properties and estimate the crystallite size. The nanoparticles evolved from a spherical to faceted morphology with annealing time, assuming an octahedral shape truncated at the (001) planes as seen from aberration corrected transmission electron microscopy (TEM) images. The nanoparticles embedded in MgO were shown to be pure metallic Ag using atom probe tomography (APT). The nanoparticles were partially exposed to the surface employing plasma etch techniques to remove the overlaying MgO. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) were employed to study the surface morphology and obtain a height distribution for the partially exposed nanoparticles.

Environmental Molecular Sciences Laboratory↗
DOE OSTI2023

Atomistic simulation of brittle-to-ductile transition in silicon carbide embedded with nano-sized helium bubbles

In this study, the tensile response of cubic silicon carbide (SiC) bulk containing cavities (voids and He bubbles) has been investigated using molecular dynamic simulations. The formation of cavities in SiC leads to a significant degradation in the mechanical properties of SiC with more influence on material fracture than initial elastic deformation. The brittle-to-ductile transition occurs in cavity-embedded SiC as the pressure in He bubbles increases. This is associated with the deformation mechanism that bond breaking at a low He bubble pressure transfers to extensive dislocation activities at a higher He bubble pressure. The cavities can effectively concentrate stress around them in the direction perpendicular to the tension, which leads to preferred cracking in the region with a higher tensile stress. The failure mechanism as revealed by this study improves understanding of property degradation in SiC that may be useful for applications of SiC in advanced nuclear energy systems.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2019

An embedded-atom method potential parameterized for sulfur-induced embrittlement of nickel

The embrittling or strengthening effect of solute atoms at grain boundaries (GBs), commonly known as the embrittling potency, is a necessary thermodynamic property for characterizing the effects of solute segregation on GB fracture. One of the more technologically relevant material systems related to embrittlement is the Ni–S system where S has a deleterious effect on fracture behavior in polycrystalline Ni. Here, we develop a Ni–S embedded-atom method (EAM) interatomic potential that accounts for the embrittling behavior of S at Ni GBs. Results using this new interatomic potential are then compared to previous density functional theory studies and a reactive force-field potential via a layer-by-layer segregation analysis. Our potential shows strong agreement with existing literature and performs well in predicting properties that are not included in the fitting database. Finally, we calculate embrittling potencies and segregation energies for six [100] symmetric-tilt GBs using the new EAM potential. We observe that embrittling potency is dependent on GB structure, suggesting that specific GBs are more susceptible to sulfur-induced embrittlement.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Reverse-engineering of graphene on metal surfaces: a case study of embedded ruthenium

Using scanning tunneling microscopy, X-ray photoelectron spectroscopy, and X-ray absorption spectroscopy, we show that Ru forms metallic nanoislands on graphite, covered by a graphene monolayer. These islands are air-stable, contain 2-4 layers of Ru, and have diameters on the order of 10 nm. To produce these nanoislands two conditions must be met during synthesis. The graphite surface must be ion-bombarded, and subsequently held at elevated temperature (1000-1180 K) during Ru deposition. A coincidence lattice forms between the graphene overlayer and the Ru island top. Its characteristics – coincidence lattice constant, corrugation amplitude, and variation of carbon lattice appearance within the unit cell – closely resemble the well-established characteristics of single-layer graphene on the (0001) surface of bulk Ru. Quantitative analysis of the graphene lattice in relation to the coincidence lattice on the island tops shows that the twodimensional lattice constant of the underlying metal equals that of bulk Ru(0001), within experimental error. The embedded Ru islands are energetically favored over on-top (adsorbed) islands, based on density-functional-theory calculations for Ru films with 1-3 Ru layers. We propose a formation mechanism in which Ru atoms intercalate via defects that act as entry portals to the carbon galleries, followed by nucleation and growth in the galleries. In this model, high deposition temperature is necessary to prevent blockage of entry portals.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Study of carbon nanotube embedded honey as a resistive switching material

In this paper, natural organic honey embedded with carbon nanotubes (CNTs) was studied as a resistive switching material for biodegradable nonvolatile memory in emerging neuromorphic systems. CNTs were dispersed in a honey-water solution with the concentration of 0.2 wt% CNT and 30 wt% honey. The final honey-CNT-water mixture was spin-coated and dried into a thin film sandwiched in between Cu bottom electrode and Al top electrode to form a honey-CNT based resistive switching memory (RSM). Surface morphology, electrical characteristics and current conduction mechanism were investigated. The results show that although CNTs formed agglomerations in the dried honey-CNT film, both switching speed and the stability in SET and RESET process of honey-CNT RSM were improved. The mechanism of current conduction in CNT is governed by Ohm’s law in low-resistance state and the low-voltage range in high-resistance state, but transits to the space charge limited conduction at high voltages approaching the SET voltage.

36 MATERIALS SCIENCE↗
DOE OSTI2019

An embedding technique to determine $\tau\tau$ backgrounds in proton-proton collision data

An embedding technique is presented to estimate standard model $\tau\tau$ backgrounds from data with minimal simulation input. In the data, the muons are removed from reconstructed $\mu\mu$ events and replaced with simulated tau leptons with the same kinematic properties. In this way a set of hybrid events is obtained that does not rely on simulation except for the decay of the tau leptons. The challenges in describing the underlying event or the production of associated jets in the simulation are avoided. The technique described in this paper was developed for CMS. Its validation and the inherent uncertainties are also discussed. The demonstration of the performance of the technique is based on a sample of proton-proton collisions collected by CMS in 2017 at $\sqrt{s}=$ 13 TeV corresponding to an integrated luminosity of 41.5 fb$^{-1}$.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2021

Design and implementation of the AMIGA embedded system for data acquisition

The Auger Muon Infill Ground Array (AMIGA) is part of the AugerPrime upgrade of the Pierre Auger Observatory. It consists of particle counters buried 2.3 m underground next to the water-Cherenkov stations that form the 23.5 km 2 large infilled array. The reduced distance between detectors in this denser area allows the lowering of the energy threshold for primary cosmic ray reconstruction down to about 1017 eV. At the depth of 2.3 m the electromagnetic component of cosmic ray showers is almost entirely absorbed so that the buried scintillators provide an independent and direct measurement of the air showers muon content. This work describes the design and implementation of the AMIGA embedded system, which provides centralized control, data acquisition and environment monitoring to its detectors. The presented system was firstly tested in the engineering array phase ended in 2017, and lately selected as the final design to be installed in all new detectors of the production phase. The system was proven to be robust and reliable and has worked in a stable manner since its first deployment.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2024

Embedded FPGA developments in 130 nm and 28 nm CMOS for machine learning in particle detector readout

Embedded field programmable gate array (eFPGA) technology allows the implementation of reconfigurable logic within the design of an application-specific integrated circuit (ASIC). This approach offers the low power and efficiency of an ASIC along with the ease of FPGA configuration, particularly beneficial for the use case of machine learning in the data pipeline of next-generation collider experiments. An open-source framework called "FABulous" was used to design eFPGAs using 130 nm and 28 nm CMOS technology nodes, which were subsequently fabricated and verified through testing. The capability of an eFPGA to act as a front-end readout chip was assessed using simulation of high energy particles passing through a silicon pixel sensor. A machine learning-based classifier, designed for reduction of sensor data at the source, was synthesized and configured onto the eFPGA. A successful proof-of-concept was demonstrated through reproduction of the expected algorithm result on the eFPGA with perfect accuracy. Finally, further development of the eFPGA technology and its application to collider detector readout is discussed.

47 OTHER INSTRUMENTATION↗
DOE OSTI2026

Embedded EPICS server for PowerPMAC motion controllers

An embedded server layer of Experimental Physics and Industrial Control System (EPICS) for PowerPMAC motion controllers has been developed and deployed at two undulator beamlines of the National Institute of General Medical Sciences and the National Cancer Institute (GM/CA) Structural Biology Facility at the Advanced Photon Source (APS). This compact, open source solution makes the power and versatility of PowerPMAC motion controls directly accessible to distributed EPICS clients. At GM/CA the system controls about 200 servo and stepper motors — both encoded and unencoded — and multiple digital and analog I/O accessories. The server stack comprises two sublayers: a lower-level driver and database that communicates directly with PowerPMAC, and a facility-specific soft sublayer built on top. The paper describes installing EPICS on PowerPMAC, the implementation of both layers and client examples, including on-the-fly scanning.

EPICS↗
DOE OSTI2012

HIGH-ENERGY EMISSION INDUCED BY ULTRA-HIGH-ENERGY PHOTONS AS A PROBE OF ULTRA-HIGH-ENERGY COSMIC-RAY ACCELERATORS EMBEDDED IN THE COSMIC WEB

The photomeson production in ultra-high-energy cosmic-ray (UHECR) accelerators such as {gamma}-ray bursts and active galaxies may lead to ultra-high-energy (UHE) {gamma}-ray emission. We show that the generation of UHE pairs in magnetized structured regions where the sources are embedded is inevitable, and accompanying {approx}> 0.1 TeV synchrotron emission provides an important probe of UHECR acceleration. It would especially be relevant for powerful transient sources, and synchrotron pair echoes may be detected by future CTA via coordinated search for transients of duration {approx}0.1-1 yr for the structured regions of {approx}Mpc. Detections will be useful for knowing structured extragalactic magnetic fields as well as properties of the sources.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

ALIGNMENT OF PROTOSTARS AND CIRCUMSTELLAR DISKS DURING THE EMBEDDED PHASE

Star formation proceeds via the collapse of a molecular cloud core over multiple dynamical timescales. Turbulence within cores results in a spatially non-uniform angular momentum of the cloud, causing a stochastic variation in the orientation of the disk forming from the collapsing material. In the absence of star-disk angular momentum coupling, such disk-tilting would provide a natural mechanism for the production of primordial spin-orbit misalignments in the resulting planetary systems. However, owing to high accretion rates in the embedded phase of star formation, the inner edge of the circumstellar disk extends down to the stellar surface, resulting in efficient gravitational and accretional angular momentum transfer between the star and the disk. Here, we demonstrate that the resulting gravitational coupling is sufficient to suppress any significant star-disk misalignment, with accretion playing a secondary role. The joint tilting of the star-disk system leads to a stochastic wandering of star-aligned bipolar outflows. Such wandering widens the effective opening angle of stellar outflows, allowing for more efficient clearing of the remainder of the protostar's gaseous envelope. Accordingly, the processes described in this work provide an additional mechanism responsible for sculpting the stellar initial mass function.

79 ASTRONOMY AND ASTROPHYSICS↗