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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 361 records · Page 20
All sourcesNASA NTRSDOE OSTI
NASA NTRS2003

Thermal Iron K and Alpha: Line Emission from the X-Ray Binary GX 339-4

The accretion rate of the black hole candidate X-ray binary GX 339-4 in the 'off' state is low, and an advection dominated accretion flow (ADAF) is present. Hydrogen-like and helium-like iron Kbalpha; emission lines at 6.7 and 6.95 keV from hot plasma of ADAF can be produced by recombination-cascade processes with moderately high intensities, which are markedly distinguished from the fluorescent iron Kα line at approximately 6.4 keV. We show that the observational features of GX 339-4 can be explained by the ADAF model, if the iron abundance is more than 10 times the solar value, though the reason for such a high abundance is still unclear. We suggest that the increase of the accretion rate makes GX 339-4 change from off, low, intermediate, to high and very high states, and the line center of iron Kbalpha; will therefore shift from approximately 6.83 to approximately 6.4 keV, i.e. to the fluorescent disc-line, since the disappearance of the ADAF due to its high accretion rate.

Xu, Y. D.↗
NASA NTRS1998

A role for cyclin-dependent kinase(s) in the modulation of fast anterograde axonal transport: effects defined by olomoucine and the APC tumor suppressor protein

Proteins that interact with both cytoskeletal and membrane components are candidates to modulate membrane trafficking. The tumor suppressor proteins neurofibromin (NF1) and adenomatous polyposis coli (APC) both bind to microtubules and interact with membrane-associated proteins. The effects of recombinant NF1 and APC fragments on vesicle motility were evaluated by measuring fast axonal transport along microtubules in axoplasm from squid giant axons. APC4 (amino acids 1034-2844) reduced only anterograde movements, whereas APC2 (aa 1034-2130) or APC3 (aa 2130-2844) reduced both anterograde and retrograde transport. NF1 had no effect on organelle movement in either direction. Because APC contains multiple cyclin-dependent kinase (CDK) consensus phosphorylation motifs, the kinase inhibitor olomoucine was examined. At concentrations in which olomoucine is specific for cyclin-dependent kinases (5 microM), it reduced only anterograde transport, whereas anterograde and retrograde movement were both affected at concentrations at which other kinases are inhibited as well (50 microM). Both anterograde and retrograde transport also were inhibited by histone H1 and KSPXK peptides, substrates for proline-directed kinases, including CDKs. Our data suggest that CDK-like axonal kinases modulate fast anterograde transport and that other axonal kinases may be involved in modulating retrograde transport. The specific effect of APC4 on anterograde transport suggests a model in which the binding of APC to microtubules may limit the activity of axonal CDK kinase or kinases in restricted domains, thereby affecting organelle transport.

Non-NASA Center↗
DOE OSTI2024

The crystal structure of Acinetobacter baumannii bacterioferritin reveals a heteropolymer of bacterioferritin and ferritin subunits

Iron storage proteins, e.g., vertebrate ferritin, and the ferritin-like bacterioferritin (Bfr) and bacterial ferritin (Ftn), are spherical, hollow proteins that catalyze the oxidation of Fe 2+ at binuclear iron ferroxidase centers (FOC) and store the Fe 3+ in their interior, thus protecting cells from unwanted Fe 3+ /Fe 2+ redox cycling and storing iron at concentrations far above the solubility of Fe 3+ . Vertebrate ferritins are heteropolymers of H and L subunits with only the H subunits having FOC. Bfr and Ftn were thought to coexist in bacteria as homopolymers, but recent evidence indicates these molecules are heteropolymers assembled from Bfr and Ftn subunits. Despite the heteropolymeric nature of vertebrate and bacterial ferritins, structures have been determined only for recombinant proteins constituted by a single subunit type. Herein we report the structure of Acinetobacter baumannii bacterioferritin, the first structural example of a heteropolymeric ferritin or ferritin-like molecule, assembled from completely overlapping Ftn homodimers harboring FOC and Bfr homodimers devoid of FOC but binding heme. The Ftn homodimers function by catalyzing the oxidation of Fe 2+ to Fe 3+ , while the Bfr homodimers bind a cognate ferredoxin (Bfd) which reduces the stored Fe 3+ by transferring electrons via the heme, enabling Fe 2+ mobilization to the cytosol for incorporation in metabolism.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2021

Orbital-resolved calculations of two-center interferences in linear triatomic molecules

In this report we perform ab initio calculations of high-harmonic spectroscopy (HHS) of two-center interference phenomena in oriented carbon-dichalcogen molecules, using time-dependent density functional theory (TDDFT). We show that by resolving the harmonic response into contributions from individual Kohn-Sham orbitals, we can extract target-specific characteristics for both the spectral amplitude and phase. We also discuss that this extraction is predicated on a careful analysis and normalization of the harmonic spectrum. Finally, we present field-free scattering calculations that mimic the recollision step in high-order-harmonic generation and allow the calculation of recombination dipole matrix elements without explicitly calculating the scattering states of a molecule. We show that the orbital-resolved TDDFT HHS results and results based on our field-free scattering calculations are in very good agreement with each other.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2025

Distinctive features of structural evolution and thermodynamic response in wide-bandgap semiconductors driven by intense electronic excitation

Radiation-tolerant material selection requires balancing lattice rigidity, defect dynamics, and electronic stability, as shown by covalent SiC outperforming ionic Ga 2 O 3 and GaN under extreme environments. Responding to intense electronic excitation, irradiation-driven phase segregation (β → δ/κ in Ga 2 O 3 ) and core–shell track (disordered structure in GaN), accompanied by elemental redistribution, contrastingly, exceptional radiation tolerance manifested by comparatively minimal lattice distortion (0.17 % strain variation) was demonstrated in SiC. These differential responses are primarily attributed to two fundamental mechanisms: (i) thermodynamic driving forces governing defect migration and phase separation, and (ii) the synergistic effects of robust covalent bonding composition coupled with efficient defect recombination processes. Here, the stronger electron–phonon (e-ph) coupling in Ga 2 O 3 (4.34 × 1018 W m −3 K −1 ) and GaN (3.55 × 10 18 W m −3 K −1 ) enhances lattice energy deposition, triggering thermal spikes (ΔT ≫ T m ) and structural transition behaviors, whereas weaker e-ph coupling in SiC (3.69 × 10 18 W m −3 K −1 ), relatively high thermodynamic parameters and efficient energy dissipation suppress thermal spikes to maintaining lattice integrity. The photoresponse degradation driven by enhanced radiative recombination is dominant in N-doped SiC, while V-doped systems achieve defect-mediated photoconduction optimization characterized by abrupt current transitions, matching fluorescence yield evolutions, and directly connecting defect engineering to optoelectronic performance.

Intense electronic excitation↗
NASA NTRS1995

Two cis elements collaborate to spatially repress transcription from a sea urchin promoter

The expression pattern of many territory-specific genes in metazoan embryos is maintained by an active process of negative spatial regulation. However, the mechanism of this strategy of gene regulation is not well understood in any system. Here we show that reporter constructs containing regulatory sequence for the SM30-alpha gene of Stronglyocentrotus purpuratus are expressed in a pattern congruent with that of the endogenous SM30 gene(s), largely as a result of active transcriptional repression in cell lineages in which the gene is not normally expressed. Chloramphenicol acetyl transferase assays of deletion constructs from the 2600-bp upstream region showed that repressive elements were present in the region from -1628 to -300. In situ hybridization analysis showed that the spatial fidelity of expression was severely compromised when the region from -1628 to -300 was deleted. Two highly repetitive sequence motifs, (G/A/C)CCCCT and (T/C)(T/A/C)CTTTT(T/A/C), are present in the -1628 to -300 region. Representatives of these elements were analyzed by gel mobility shift experiments and were found to interact specifically with protein in crude nuclear extracts. When oligonucleotides containing either sequence element were co-injected with a correctly regulated reporter as potential competitors, the reporter was expressed in inappropriate cells. When composite oligonucleotides, containing both sequence elements, were fused to a misregulated reporter, the expression of the reporter in inappropriate cells was suppressed. Comparison of composite oligonucleotides with oligonucleotides containing single constituent elements show that both sequence elements are required for effective spatial regulation. Thus, both individual elements are required, but only a composite element containing both elements is sufficient to function as a tissue-specific repressive element.

Non-NASA Center↗
NASA NTRS1993

Characterization of the DNA binding properties of polyomavirus capsid protein

The DNA binding properties of the polyomavirus structural proteins VP1, VP2, and VP3 were studied by Southwestern analysis. The major viral structural protein VP1 and host-contributed histone proteins of polyomavirus virions were shown to exhibit DNA binding activity, but the minor capsid proteins VP2 and VP3 failed to bind DNA. The N-terminal first five amino acids (Ala-1 to Lys-5) were identified as the VP1 DNA binding domain by genetic and biochemical approaches. Wild-type VP1 expressed in Escherichia coli (RK1448) exhibited DNA binding activity, but the N-terminal truncated VP1 mutants (lacking Ala-1 to Lys-5 and Ala-1 to Cys-11) failed to bind DNA. The synthetic peptide (Ala-1 to Cys-11) was also shown to have an affinity for DNA binding. Site-directed mutagenesis of the VP1 gene showed that the point mutations at Pro-2, Lys-3, and Arg-4 on the VP1 molecule did not affect DNA binding properties but that the point mutation at Lys-5 drastically reduced DNA binding affinity. The N-terminal (Ala-1 to Lys-5) region of VP1 was found to be essential and specific for DNA binding, while the DNA appears to be non-sequence specific. The DNA binding domain and the nuclear localization signal are located in the same N-terminal region.

NASA Discipline Cell Biology↗
NASA NTRS1997

Centric rings, acentric rings and excess acentric fragments based on a random-walk interphase chromosome model

Excess acentric fragments, consisting of acentric rings and acentric linear fragments, are among the most frequent kinds of chromosome-type aberrations produced by radiation. The frequency of acentric rings cannot be obtained directly by experiment but is estimated here from the ratio of acentric to centric rings, evaluated using a random-walk model for the organization of chromatin during interphase and an assumption that the probability of an exchange formation is proportional to the rate of collision between two DSB. This ratio is calculated to be 2.5 in low-LET irradiated human fibroblasts, significantly greater than the ratio if proximity effects are not considered. The calculated frequency of acentric rings is insufficient to account for all the observed excess acentric fragments. Assuming that the rest of the excess acentric fragments are due to incomplete exchanges, all possible recombinations between two DSB that result in acentric rings and acentric linear fragments have been identified. From the chromosome aberration data, the incompleteness parameter has been estimated. Intra-arm chromosome exchanges, either complete or incomplete, were estimated to account for more than 50% of the excess acentric fragments in human fibroblasts.

NASA Center JSC↗
NASA NTRS1983

Observations of the 145.5 micron O I forbidden emission line in the Orion Nebula

A first set of observations of the forbidden O I 3P0-3P1 (145.5 micron) transition has been obtained. The line was observed both in a 1 x 1 arcmin beam centered on the Trapezium and in a 7 x 7 arcmin beam encompassing most of the Orion Nebula; a wide-beam (7 x 7 arcmin) map of the region has also been constructed which shows that most of the emission is confined to the central regions of the nebula. These observations are consistent with optically thin emission in the 145.5 micron line and self-absorbed 63.2 micron emission lines. Mechanisms for the excitation of neutral oxygen are considered, and it is concluded that much of the observed emission originates in the thin radio recombination line-emitting C II/H I envelope bordering on the H II region.

Stacey, G. J.↗
NASA NTRS2000

Solid Hydrogen Formed for Atomic Propellants

Several experiments on the formation of solid hydrogen particles in liquid helium were recently conducted at the NASA Glenn Research Center at Lewis Field. The solid hydrogen experiments are the first step toward seeing these particles and determining their shape and size. The particles will ultimately store atoms of boron, carbon, or hydrogen, forming an atomic propellant. Atomic propellants will allow rocket vehicles to carry payloads many times heavier than possible with existing rockets or allow them to be much smaller and lighter. Solid hydrogen particles are preferred for storing atoms. Hydrogen is generally an excellent fuel with a low molecular weight. Very low temperature hydrogen particles (T < 4 K) can prevent the atoms from recombining, making it possible for their lifetime to be controlled. Also, particles that are less than 1 mm in diameter are preferred because they can flow easily into a pipe when suspended in liquid helium. The particles and atoms must remain at this low temperature until the fuel is introduced into the engine combustion (or recombination) chamber. Experiments were, therefore, planned to look at the particles and observe their formation and any changes while in liquid helium.

Palaszewski, Bryan A.↗
NASA NTRS2002

A calmodulin-binding/CGCG box DNA-binding protein family involved in multiple signaling pathways in plants

We reported earlier that the tobacco early ethylene-responsive gene NtER1 encodes a calmodulin-binding protein (Yang, T., and Poovaiah, B. W. (2000) J. Biol. Chem. 275, 38467-38473). Here we demonstrate that there is one NtER1 homolog as well as five related genes in Arabidopsis. These six genes are rapidly and differentially induced by environmental signals such as temperature extremes, UVB, salt, and wounding; hormones such as ethylene and abscisic acid; and signal molecules such as methyl jasmonate, H(2)O(2), and salicylic acid. Hence, they were designated as AtSR1-6 (Arabidopsis thaliana signal-responsive genes). Ca(2+)/calmodulin binds to all AtSRs, and their calmodulin-binding regions are located on a conserved basic amphiphilic alpha-helical motif in the C terminus. AtSR1 targets the nucleus and specifically recognizes a novel 6-bp CGCG box (A/C/G)CGCG(G/T/C). The multiple CGCG cis-elements are found in promoters of genes such as those involved in ethylene signaling, abscisic acid signaling, and light signal perception. The DNA-binding domain in AtSR1 is located on the N-terminal 146 bp where all AtSR1-related proteins share high similarity but have no similarity to other known DNA-binding proteins. The calmodulin-binding nuclear proteins isolated from wounded leaves exhibit specific CGCG box DNA binding activities. These results suggest that the AtSR gene family encodes a family of calmodulin-binding/DNA-binding proteins involved in multiple signal transduction pathways in plants.

Non-NASA Center↗
NASA NTRS1994

Chemical Composition and Flow Velocity as a Function of Operating Conditions for an Arc Jet Heater

We have used laser-induced fluorescence (LIF) to carry out a detailed, systematic survey of the properties of the free stream of the 20 Megawatt Aerodynamic Heating Facility at NASA/Ames Research Center. In both air and nitrogen flows we have measured the atomic nitrogen absolute number density and flow velocity at each operating condition. In air flows we have also measured the atomic oxygen absolute number density and rotational/translational temperature at each operating condition. These results have been used to provide, for the first time, a direct, nonintrusive measurement of the enthalpy on the centerline of the flow. In addition, the observed arc jet properties can be used to test and improve computer simulations of the arc jet flow which include detailed chemical rate processes (especially nitrogen atom recombination) taking place during the supersonic expansion.

Bamford, Douglas J.↗
DOE OSTI2022

Measurement of beauty production via non-prompt D 0 mesons in Pb-Pb collisions at $ \sqrt{{\textrm{s}}_{\textrm{NN}}} $ = 5.02 TeV

The production of non-prompt D 0 mesons from beauty-hadron decays was measured at midrapidity (|y| < 0.5) in Pb-Pb collisions at a nucleon-nucleon center-of-mass energy of $\sqrt{s_{NN}}$= 5.02 TeV with the ALICE experiment at the LHC. Their nuclear modification factor (R AA ), measured for the first time down to p T = 1 GeV/c in the 0–10% and 30–50% centrality classes, indicates a significant suppression, up to a factor of about three, for p T > 5 GeV/c in the 0–10% central Pb-Pb collisions. The data are described by models that include both collisional and radiative processes in the calculation of beauty-quark energy loss in the quark-gluon plasma, and quark recombination in addition to fragmentation as a hadronisation mechanism. The ratio of the non-prompt to prompt D 0 -meson R AA is larger than unity for p T > 4 GeV/c in the 0–10% central Pb-Pb collisions, as predicted by models in which beauty quarks lose less energy than charm quarks in the quark-gluon plasma because of their larger mass.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
NASA NTRS1993

Three distinct cell phenotypes of induced-TNF cytotoxicity and their relationship to apoptosis

We have identified three distinct cell phenotypes with respect to the conditions under which cells became susceptible to TNF-mediated lysis. These conditions include: 1) treatment with the protein synthesis inhibitor, cycloheximide; 2) contact with activated macrophages, and 3) infection with vaccinia virus. Whereas vaccinia virus-infected 3T3 cells became sensitive to soluble TNF, F5b cells required contact with activated macrophages. We showed that the "macrophage-resistant" F5m cells did not become sensitive to TNF or to killing by activated macrophages after infection with vaccinia virus. Therefore, vaccinia infection does not sensitize all cells to TNF. We also determined the pathways of lysis for cells after sensitization. Whereas 3T3, LM929, and F5b cells were killed by the process of necrosis, F5m cells lysis was characterized by the release of low mol wt DNA fragments (apoptosis).

Non-NASA Center↗
NASA NTRS2001

TGF-beta1 release from biodegradable polymer microparticles: its effects on marrow stromal osteoblast function

BACKGROUND: Controlled release of transforming growth factor-beta1 (TGF-beta1) to a bone defect may be beneficial for the induction of a bone regeneration cascade. The objectives of this work were to assess the feasibility of using biodegradable polymer microparticles as carriers for controlled TGF-beta1 delivery and the effects of released TGF-beta1 on the proliferation and differentiation of marrow stromal cells in vitro. METHODS: Recombinant human TGF-beta1 was incorporated into microparticles of blends of poly(DL-lactic-co-glycolic acid) (PLGA) and poly(ethylene glycol) (PEG). Fluorescein isothiocynate-labeled bovine serum albumin (FITC-BSA) was co-encapsulated as a porogen. The effects of PEG content (0, 1, or 5% by weight [wt%]) and buffer pH (3, 5, or 7.4) on the protein release kinetics and the degradation of PLGA were determined in vitro for as long as 28 days. Rat marrow stromal cells were seeded on a biodegradable poly(propylene fumarate) (PPF) substrate. The dose response and biological activity of released TGF-beta1 was determined after 3 days in culture. The effects of TGF-beta1 released from PLGA/PEG microparticles on marrow stromal cell proliferation and osteoblastic differentiation were assessed during a 21-day period. RESULTS: TGF-beta1 was encapsulated along with FITC-BSA into PLGA/PEG blend microparticles and released in a multiphasic fashion including an initial burst for as long as 28 days in vitro. Increasing the initial PEG content resulted in a decreased cumulative mass of released proteins. Aggregation of FITC-BSA occurred at lower buffer pH, which led to decreased release rates of both proteins. The degradation of PLGA was increased at higher PEG content and significantly accelerated at acidic pH conditions. Rat marrow stromal cells cultured on PPF substrates showed a dose response to TGF-beta1 released from the microparticles similar to that of added TGF-beta1, indicating that the activity of TGF-beta1 was retained during microparticle fabrication and after growth factor release. At an optimal TGF-beta1 dosage of 1.0 ng/ml after 3 days, the released TGF-beta1 enhanced the proliferation and osteoblastic differentiation of marrow stromal cells over 21 days of culture, with increased total cell number, alkaline phosphatase activity, and osteocalcin production. CONCLUSIONS: PLGA/PEG blend microparticles can serve as delivery vehicles for controlled release of TGF-beta1, and the released growth factor enhances marrow stromal cell proliferation and osteoblastic differentiation in vitro. CLINICAL RELEVANCE: Controlled release of TGF-beta1 from PLGA/PEG microparticles is representative of emerging tissue engineering technologies that may modulate cellular responses to encourage bone regeneration at a skeletal defect site.

Non-NASA Center↗
NASA NTRS2002

Tissue engineering skeletal muscle for orthopaedic applications

With current technology, tissue-engineered skeletal muscle analogues (bioartificial muscles) generate too little active force to be clinically useful in orthopaedic applications. They have been engineered genetically with numerous transgenes (growth hormone, insulinlike growth factor-1, erythropoietin, vascular endothelial growth factor), and have been shown to deliver these therapeutic proteins either locally or systemically for months in vivo. Bone morphogenetic proteins belonging to the transforming growth factor-beta superfamily are osteoinductive molecules that drive the differentiation pathway of mesenchymal cells toward the chondroblastic or osteoblastic lineage, and stimulate bone formation in vivo. To determine whether skeletal muscle cells endogenously expressing bone morphogenetic proteins might serve as a vehicle for systemic bone morphogenetic protein delivery in vivo, proliferating skeletal myoblasts (C2C12) were transduced with a replication defective retrovirus containing the gene for recombinant human bone morphogenetic protein-6 (C2BMP-6). The C2BMP-6 cells constitutively expressed recombinant human bone morphogenetic protein-6 and synthesized bioactive recombinant human bone morphogenetic protein-6, based on increased alkaline phosphatase activity in coincubated mesenchymal cells. C2BMP-6 cells did not secrete soluble, bioactive recombinant human bone morphogenetic protein-6, but retained the bioactivity in the cell layer. Therefore, genetically-engineered skeletal muscle cells might serve as a platform for long-term delivery of osteoinductive bone morphogenetic proteins locally.

Review↗
DOE OSTI2025

Electrodynamics of photo-carriers in multiferroic Eu 0.75 Y 0.25 MnO 3

Understanding and controlling the antiferromagnetic order in multiferroic materials on an ultrafast time scale is a long standing area of interest, due to their potential applications in spintronics and ultrafast magnetoelectric switching. We present an optical pump-terahertz (THz) probe study on multiferroic Eu 0.75 Y 0.25 MnO 3 . The optical pump predominantly excites the d-d transitions of the Mn 3+ ions, and the temporal evolution of the pump-induced transient conductivity is measured with a subsequent THz pulse. Two distinct, temperature-dependent decay times are revealed. The shorter relaxation time corresponds to spin-lattice thermalization, while the longer one is ascribed to electron-hole recombination. A spin-selection rule in the relaxation process is proposed in the magnetic phase. Slight suppression of the electromagnons was observed after the optical pump pulse within the spin-lattice thermalization time scale. These observed fundamental magnetic processes can shed light on ultrafast control of magnetism and photoinduced phase transitions in multiferroics.

77 NANOSCIENCE AND NANOTECHNOLOGY↗