SEARCH · Engineering Papers

Results for “Shell Solar”

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.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 631 records · Page 35

All sources NASA NTRS DOE OSTI

DOE OSTI2015

EVIDENCE OF THE SOLAR EUV HOT CHANNEL AS A MAGNETIC FLUX ROPE FROM REMOTE-SENSING AND IN SITU OBSERVATIONS

Hot channels (HCs), high-temperature erupting structures in the lower corona of the Sun, have been proposed as a proxy of magnetic flux ropes (MFRs) since their initial discovery. However, it is difficult to provide definitive proof given the fact that there is no direct measurement of the magnetic field in the corona. An alternative method is to use the magnetic field measurement in the solar wind from in situ instruments. On 2012 July 12, an HC was observed prior to and during a coronal mass ejection (CME) by the Atmospheric Imaging Assembly high-temperature images. The HC is invisible in the EUVI low-temperature images, which only show the cooler leading front (LF). However, both the LF and an ejecta can be observed in the coronagraphic images. These are consistent with the high temperature and high density of the HC and support that the ejecta is the erupted HC. Meanwhile, the associated CME shock was identified ahead of the ejecta and the sheath through the COR2 images, and the corresponding ICME was detected by the Advanced Composition Explorer, showing the shock, sheath, and magnetic cloud (MC) sequentially, which agrees with the coronagraphic observations. Further, the MC average Fe charge state is elevated, containing a relatively low-ionization-state center and a high-ionization-state shell, consistent with the preexisting HC observation and its growth through magnetic reconnection. All of these observations support that the MC detected near the Earth is the counterpart of the erupted HC in the corona for this event. The study provides strong observational evidence of the HC as an MFR.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2011

Equilibrium compositional distribution in freestanding ternary semiconductor quantum dots: The case of In x Ga 1-x As

Here, we report the findings of a systematic computational study that addresses the effects of surface segregation on the atomic distribution at equilibrium of constituent group-III atoms in freestanding ternary semiconductor In x Ga 1-x As nanocrystals. Our analysis is based on density functional theory calculations in conjunction with Monte Carlo simulations of the freestanding nanocrystals using a DFT-re-parameterized valence force field description of interatomic interactions. We have determined the equilibrium concentration profiles as a function of nanocrystal size (d), composition (x), and temperature (T). The ranges of d, x, and T are explored and demonstrate surface segregation and phase separation that leads to different extents of alloying in the nanocrystal core and in the near-surface regions. We find that formation of core/shell-like quantum dots characterized by an In-deficient core and an In-rich shell with a diffuse interface is favored at equilibrium. The analysis elucidates the relationship between the constituent species distribution in the nanocrystal and the parameters that can be tuned experimentally to design synthesis routes for tailoring the properties of ternary quantum dots.

solar (photovoltaic), charge transport, materials ↗

DOE OSTI2021

Ligand-Controlled Energetics and Charge Transfer in Pure and Doped Nanocrystals

The research in this award period initially focused on the spectroscopy and dynamics of spherical CdSe nanocrystals and CdSe nanoplatelets. In the later part of the grant period we turned our attention to InP-based nanocrystals. It has long been believed that the transient absorption signal from approximately spherical CdSe nanocrystals is dominated by conduction band state filling. However, this long-held belief has recently been challenged, based on femtosecond absorption measurements. However, the recent studies challenging the conventional wisdom do not account of finite rates of spin-lattice relaxation. Our work showed that this is a crucial error and that the recent results are misinterpreted, that is, the previous prevailing wisdom is correct. Another study focused on CdSe nanocrystal photochemistry used transient absorption (TA) spectroscopy to determine the spatial extents of CdSe nanoplatelet (NPL) excitons. Our work shows that the spatial extents of the excitons in the NPLs are far less than the physical dimension of the NPL. Using a model developed to understand the transient absorption spectroscopy, we obtain an average excitonic area of 21.2 ± 2.5 nm 2 , independent of the nanoplatelet size. Our work on InP/ZnSe and InP/ZnS core/shell nanocrystals shows that when there is a small lattice mismatch (InP-ZnSe, 3.5%) a coherent core-shell interface is obtained. In contrast, the InP-ZnS lattice mismatch is much larger, 8.3%. In this case, the experimental results showed best agreement with calculations in which lattice strain is ignored, indicating that the interfaces in InP/ZnS nanocrystals are largely incoherent.

14 SOLAR ENERGY↗

NASA NTRS1964

Stellar evolution. ii. the hydrogen-burning phase of a star of 7.0 solar masses <sternentwicklung. ii. die wasserstoff- brennende phase eines sterns von 7.0 sonnenmassen<

With the computer program by Hofmeister, Kippenhahn, Weigert (1964, from now on referred to as ''I") the evolution of a population I star of 7.0 solar masses has been followed. The results presented here are based on a sequence of 119 models, the first of which represents the homogeneous main sequence state and has a convective core containing 26% of the mass. The following models describe the phase of depletion of hydrogen in the core, which is shrinking in mass until the convection around the centre disappears. After this the gradual development of a hydrogen burning shell source is shown. The models show the evolution into the red giant region, while the helium core is contracting until helium burning starts at the centre and a new convective core is built up. The luminousity is increased about 1 magnitude compared with the main sequence state. At the same time the outer convective region grows in mass and covers at the maximum 71% of the total mass of the star. During the evolution to the red giant state, the evolutionary track crosses the region of the cepheids. Some aspects of the corresponding models are discussed.

STELLAR EVOLUTION↗

NASA NTRS1982

s-process studies in the light of new experimental cross sections - Distribution of neutron fluences and r-process residuals

A best set of neutron-capture cross sections has been evaluated for the most important s-process isotopes. With this data base, s-process studies have been carried out using the traditional model which assumes a steady neutron flux and an exponential distribution of neutron irradiations. The calculated sigma-N curve is in excellent agreement with the empirical sigma-N-values of pure s-process nuclei. Simultaneously, good agreement is found between the difference of solar and s-process abundances and the abundances of pure r-process nuclei. The abundance pattern of the iron group elements where s-process results complement the abundances obtained from explosive nuclear burning is discussed. The results obtained from the traditional s-process model such as seed abundances, mean neutron irradiations, or neutron densities are compared to recent stellar model calculations which assume the He-burning shells of red giant stars as the site for the s-process.

Kaeppeler, F.↗

NASA NTRS1991

The dusty envelopes of FU Orionis variables

The spectral energy distributions of five FU Orionis variables are discussed using new ground-based infrared photometry and IRAS Addscan measurements. V1057 Cyg, V1515 Cyg, and Z CMa have much larger far-infrared fluxes than can be explained by the simple accretion disk models that match their spectral energy distributions less than 10 microns. The 10-20-micron excess emission in V1057 has decreased proportionately with the decline in optical light, which demonstrates that the far-infrared flux arises in a dust shell reprocessing light from the central object. It is suggested that the far-infrared excesses arise in somewhat flattened dusty envelopes with a covering factor in a solid angle of roughly one-half, which is consistent with the fraction of FU Orionis variables that are heavily embedded. It is proposed that the dusty envelope falls onto the outer disk at a rate of about 5 x 10 exp -6 solar mass/yr. The rate is sufficient to replenish disk material accreted during a FU Orionis outburst and allow repetitive eruptions on time scales of several thousand years.

Kenyon, Scott J.↗

DOE OSTI2018

Room-temperature ferromagnetism in Ni( ii )-chromia based core–shell nanoparticles: experiment and first principles calculations

We have synthesized bimagnetic core–shell nanoparticles containing a first-of-its-kind Ni( ii )-chromia nanophase shell and a well-defined, epitaxial core–shell interface.

catalysis (heterogeneous)↗

DOE OSTI2017

Convergence behavior of the random phase approximation renormalized correlation energy

Based on the random phase approximation (RPA), RPA renormalization is a robust many-body perturbation theory that works for molecules and materials because it does not diverge as the Kohn-Sham gap approaches zero. Additionally, RPA renormalization enables the simultaneous calculation of RPA and beyond-RPA correlation energies since the total correlation energy is the sum of a series of independent contributions. The first-order approximation (RPAr1) yields the dominant beyond-RPA contribution to the correlation energy for a given exchange-correlation kernel, but systematically underestimates the total beyond-RPA correction. For both the homogeneous electron gas model and real systems, we demonstrate numerically that RPA renormalization beyond first order converges monotonically to the infinite-order beyond-RPA correlation energy for several model exchange-correlation kernels and that the rate of convergence is principally determined by the choice of the kernel and spin polarization of the ground state. The monotonic convergence is rationalized from an analysis of the RPA renormalized correlation energy corrections, assuming the exchange-correlation kernel and response functions satisfy some reasonable conditions. In this work, for spin-unpolarized atoms, molecules, and bulk solids, we find that RPA renormalization is typically converged to 1 meV error or less by fourth order regardless of the band gap or dimensionality. Most spin-polarized systems converge at a slightly slower rate, with errors on the order of 10 meV at fourth order and typically requiring up to sixth order to reach 1 meV error or less. Slowest to converge, however, open-shell atoms present the most challenging case and require many higher orders to converge.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2026

On the Importance of the Convective Urca Process in 3D Simulations of a Simmering White Dwarf

Type Ia supernovae are bright thermonuclear explosions that are important to numerous areas of astronomy. However, the origins of these events are poorly understood. One proposed setting is that of a near Chandrasekhar mass white dwarf that undergoes runaway carbon burning in the core. During the thousand years leading up to the explosion, the white dwarf undergoes a simmering phase where slow carbon burning heats the core and drives convection. A poorly understood aspect of this phase is the convective Urca process, which links convection with weak nuclear reactions. We use the low Mach number code MAESTROeX to perform full 3D simulations as is required to accurately capture the turbulent convection. We present simulations with and without the A=23 convective Urca process, which have relaxed to a steady state. We characterize the effects of the convective Urca process on the neutrino losses, the nuclear energy generation, and the convective boundary. We find that the size of the convection zone is substantially reduced by the convective Urca process, though convection still extends past the Urca shell. Our findings on the structure of the convective zone and the compositional changes can be used to inform 1D stellar models that track the longer-timescale evolution.

FOS: Physical sciences↗

NASA NTRS1985

An attempt to detect mass loss from Alpha Lyrae with the VLA

The interpretation of the infrared excess from Alpha Lyrae as seen by the Infrared Astronomy Satellite in terms of thermal emission from a circumstellar shell of large particles follows from the recognition that small dust grains would be removed from the vicinity of the star by radiation pressure and Poynting-Robertson drag. However, this explanation is viable only if there is no resupply of small grains via mass loss from Alpha Lyr itself. Radio-continuum observations were used to constrain the stellar mass loss to less than 3.4 x 10 to the -10th solar mass/yr. The observations thus support the conclusion that the infrared excess is due to residual solid matter from the prestellar nebula.

Hollis, J. M.↗

DOE OSTI2017

Ring current Atmosphere interactions Model with Self-Consistent Magnetic field

The Ring current Atmosphere interactions Model with Self-Consistent magnetic field (B) is a unique code that combines a kinetic model of ring current plasma with a three dimensional force-balanced model of the terrestrial magnetic field. The kinetic portion, RAM, solves the kinetic equation to yield the bounce-averaged distribution function as a function of azimuth, radial distance, energy and pitch angle for three ion species (H+, He+, and O+) and, optionally, electrons. The domain is a circle in the Solar-Magnetic (SM) equatorial plane with a radial span of 2 to 6.5 RE. It has an energy range of approximately 100 eV to 500 KeV. The 3-D force balanced magnetic field model, SCB, balances the JxB force with the divergence of the general pressure tensor to calculate the magnetic field configuration within its domain. The domain ranges from near the Earth’s surface, where the field is assumed dipolar, to the shell created by field lines passing through the SM equatorial plane at a radial distance of 6.5 RE. The two codes work in tandem, with RAM providing anisotropic pressure to SCB and SCB returning the self-consistent magnetic field through which RAM plasma is advected.

Jordanova, Vania↗

NASA NTRS1982

Fragmentation, protostellar winds, and star formation

Aspects of the current theory of molecular-cloud (MC) evolution and star formation are reviewed, with consideration of recent star and MC observations. The problem of MC collapse is discussed in terms of fragmentation in spherically symmetric collapse, the role of magnetic fields and density fluctuations, anisotropic collapse, and nonlinear interactions between fragments. Protostellar winds are identified as the source of the energy supporting MC against collapse, sweeping shells of mass into MC to produce low-mass stars continuously, and sustaining the production of massive stars once it is triggered by the collision of MCs, as in the spiral density-wave peaks. The clumping and coagulation processes are considered for the case of the MC in Orion. The protostellar-wind mass input required to inhibit systematic MC-core collapse is estimated at 10 to the -6th solar mass/cu pc year.

Silk, J.↗

NASA NTRS1998

Vacuum Plasma Spray (VPS) Forming of Solar Thermal Propulsion Components Using Refractory Metals

The Thermal Spray Laboratory at NASA's Marshall Space Flight Center has developed and demonstrated a fabrication technique using Vacuum Plasma Spray (VPS) to form structural components from a tungsten/rhenium alloy. The components were assembled into an absorption cavity for a fully-functioning, ground test unit of a solar thermal propulsion engine. The VPS process deposits refractory metal onto a graphite mandrel of the desired shape. The mandrel acts as a male mold, forming the required contour and dimensions of the inside surface of the deposit. Tungsten and tungsten/25% rhenium were used in the development and production of several absorber cavity components. These materials were selected for their high temperature (less than 2500 C) strength. Each absorber cavity comprises 3 coaxial shells with two, double-helical flow passages through which the propellant gas flows. This paper describes the processing techniques, design considerations, and process development associated with forming these engine components.

Zimmerman, Frank↗

DOE OSTI2016

Ring current Atmosphere interactions Model with Self-Consistent Magnetic field

Jordanova, Vania↗

DOE OSTI2020

Binderjet Additive Manufacturing for Complex Heat Exchanger Geometries

Concentrated Solar Power (CSP) systems play a role in the worlds development of renewable energy. Mirrors are used to concentrate sunlight that is converted into electricity or other forms of useful energy. CSP impact depends significantly on its overall economics. The U.S. Department of Energy’s (DOE’s) Solar Energy Technology Office (SETO) cost goals for 2030include $0.05/kWh levelized cost of electricity (LCOE) for a baseload plant [1]. The power cycle cost goal is $900/kWe [1]. The envisioned recompression supercritical carbondioxide (sCO2) power cycle includes four heat exchangers, which together are at least ¾ of the total power cycle cost. Meeting the cost target requires reducing the heat exchanger cost. The 260 bar and 588 °C heat exchanger requirements are challenging. Shell and tube heat exchangers can meet the requirements, but the size and cost are prohibitive. State-of-the-art diffusion bonded printed circuit heat exchanger designs are 3 m3 or larger and expensive to manufacture. Additive manufacturing enables novel heat exchanger geometries that can reduce heat exchanger size and mass [2]. Binderjet technology is an additive manufacturing modality. It selectively deposits binder material onto the powder bed to form a solid part one layer at a time. Once applied, the binder is cured, the remaining powder removed, and the part heat treated in steps to remove the binder, sinter the metal powder, and densify the part. The Binderjet printing process is more than 10x faster than the best-known metal additive modality, direct metal laser melting (DMLM), thus enabling 10x the part through-put rate [3]. The high throughput rate results in a low-cost manufacturing process capable of creating complex heat exchanger geometries. This paper introduces a complex heat exchanger geometry and methods of Binderjet processing to fabricate the geometry.

Barua, Ananda↗

DOE OSTI2021

Ligand Locking on Quantum Dot Surfaces via a Mild Reactive Surface Treatment

At the outermost surface of colloidal QDs are organic surface ligands which dynamically bind and release in solution to control the growth kinetics, control the size/shape of the crystals, passivate surface states, and provide colloidal stability through favorable interactions with the solvent. However, the dynamicity comes at the expense of the stability of the QD suspension. Here, we show that ligands can be permanently locked on the QD surface by a thin layer of an inert metal oxide which forms within the ligand shell, over the headgroup. By interrogating the surface chemistry with different spectroscopic methods, we prove the ligand locking on the QD surface. As a result, an exceptional stability of the coated QD inks is achieved in a wide concentration range, even in the presence of chemically competing surface ligands in solution. We anticipate that this critical breakthrough will benefit different areas related to colloidal QDs, spanning from single-particle studies to displays and solar cells and biological applications. Furthermore, the same chemistry could be easily translated to surface treatments of bulk materials and thin films.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

NASA NTRS1986

The outer atmosphere of the carbon star TX Piscium

A high-resolution LWP IUE spectrum of the bright N-type carbon star TX Psc demonstrates that the Mg II h and k emission profiles are strongly affected by absorption from Mg II, Mn I, probably Fe I, and possibly from molecules. The indication that the absorbing matter has a column density of not less than 10 to the 20th H atoms or molecules per sq cm is consistent with absorption in a slowly expanding envelope. The integrated Mg II line flux is found to be much greater than in 1981, and the radio CO (J = 1 - 0) line from the circumstellar shell is detected. Results for a column density of not larger than 10 to the 22nd H2 molecules/sq cm, and a radial velocity close to that of the star, are in agreement with those obtained from UV data. Some dust emission from carbon grains is suggested by the far infrared flux distribution, and a mass-loss rate estimation for the star of 10 to the -6th to 10 to the -8th solar masses is obtained.

Eriksson, K.↗

NASA NTRS1994

ROSAT HRI observations of Magellanic Cloud supernova remnants

Analysis of deep ROSAT high resolution imager (HRI) observations of two oxygen-rich supernova remnants (SNR's) in the Magellanic Clouds is described. For N132D, I exploit the limited spectral information provided by the HRI to investigate arcsecond scale spectral variations. I find that there is a region of harder X-ray emission near the southern limb and regions of softer emission near the center and northwestern limb. The remnant is believed to be interacting with a molecular cloud and the harder emission to the south is explained as a result of increased absorption along the line-of-sight there. I argue that the softer emission comes from X-ray emitting material with an enhanced abundance of oxygen. For the second SNR, E0102.2 72.2, the spatial structure is investigated in detail using two-dimensional image fitting techniques. Evidence is found for a ring-like and a spherically symmetric shell-like component both of which were modeled as homogeneous regions. In addition, a significant fraction of the observed flux (approximately 11 percent) must come from a resolved clumped component. A comparison with optical and radio imagery is made to provide a physical basis for the components identified in the X-ray analysis. The mass of X-ray emitting gas in the remnant is estimated and a value of approximately 75 M(solar mass) was determined. The dominant uncertainty on this quantity is the extent of unresolved clumping in the X-ray gas. Such clumping would tend to reduce the mass estimate by f(exp 1/2), where f is the mean volume filling factor of the gas.

Hughes, John P.↗