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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 1,567 records · Page 87
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Preparation and investigation of Dy3+-doped Ca9LiGd2/3(PO4)7 single-phase full-color phosphor

Highlights: • A novel single-phased Ca{sub 9}LiGd{sub 2/3}(PO{sub 4}){sub 7}:xDy{sup 3+} phosphor was firstly synthesized. • Its structure, luminescent properties are well studied and characterized. • It was promising as a single-component white-light-emitting phosphor for w-LEDs. - Abstract: Novel single-phased white-light-emitting Ca{sub 9}LiGd{sub 2/3}(PO{sub 4}){sub 7}:xDy{sup 3+} (x = 0.02, 0.05, 0.10, 0.15, 0.20, 0.25, and 0.30) β-Ca{sub 3}(PO{sub 4}){sub 2}-type phosphate phosphors were synthesized. The phase structure, luminescence, and thermal stability of the phosphors were characterized by X-ray powder diffraction analysis, photoluminescence excitation and emission spectra, thermal quenching, and decay curves. XRD analysis confirmed the phase formation of Ca{sub 9}LiGd{sub 2/3}(PO{sub 4}){sub 7}:Dy{sup 3+} materials. Under the excitation of 352 nm, the emission of the Ca{sub 9}LiGd{sub 2/3}(PO{sub 4}){sub 7}:0.20Dy{sup 3+} sample centered at blue (488 nm) and yellow (580 nm), which corresponded to {sup 4}F{sub 9/2}–{sup 6}H{sub 15/2} transition and {sup 4}F{sub 9/2}–{sup 6}H{sub 13/2} transition. The optimum dopant concentration of Dy{sup 3+} ions was around 20 mol%, and the critical transfer distance of Dy{sup 3+} was calculated as 18 Å. The thermal-quenching temperature was above 500 K for Ca{sub 9}LiGd{sub 2/3}(PO{sub 4}){sub 7}:0.20Dy{sup 3+}. The developed phosphor has a great potential as a single-component white-light-emitting phosphor for UV-light-emitting diodes.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Hysteresis and Allostery in Human UDP-Glucose Dehydrogenase Require a Flexible Protein Core

Human UDP-glucose dehydrogenase (hUGDH) oxidizes UDP-glucose to UDP-glucuronic acid, an essential substrate in the phase II metabolism of drugs. The activity of hUGDH is regulated by the conformation of a buried allosteric switch (T131 loop/α6 helix). Substrate binding induces the allosteric switch to slowly isomerize from an inactive E* conformation to the active E state, which can be observed as enzyme hysteresis. When the feedback inhibitor UDP-xylose binds, the allosteric switch and surrounding residues in the protein core repack, converting the hexamer into an inactive, horseshoe-shaped complex (E Ω ). Here, this allosteric transition is facilitated by large cavities and declivities in the protein core that provide the space required to accommodate the alternate packing arrangements. Here, we have used the A104L substitution to fill a cavity in the E state and sterically prevent repacking of the core into the E Ω state. Steady state analysis shows that hUGDH A104L binds UDP-xylose with lower affinity and that the inhibition is no longer cooperative. This means that the allosteric transition to the high-UDP-xylose affinity E Ω state is blocked by the substitution. The crystal structures of hUGDH A104L show that the allosteric switch still adopts the E and E* states, albeit with a more rigid protein core. However, the progress curves of hUGDH A104L do not show hysteresis, which suggests that the E* and E states are now in rapid equilibrium. Our data suggest that hysteresis in native hUGDH originates from the conformational entropy of the E* state protein core.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Highly resistive epitaxial Mg-doped GdN thin films

We report the growth by molecular beam epitaxy of highly resistive GdN, using intentional doping with magnesium. Mg-doped GdN layers with resistivities of 10{sup 3} Ω cm and carrier concentrations of 10{sup 16 }cm{sup −3} are obtained for films with Mg concentrations up to 5 × 10{sup 19} atoms/cm{sup 3}. X-ray diffraction rocking curves indicate that Mg-doped GdN films have crystalline quality very similar to undoped GdN films, showing that the Mg doping did not affect the structural properties of the films. A decrease of the Curie temperature with decreasing the electron density is observed, supporting a recently suggested magnetic polaron scenario [F. Natali, B. J. Ruck, H. J. Trodahl, D. L. Binh, S. Vézian, B. Damilano, Y. Cordier, F. Semond, and C. Meyer, Phys. Rev. B 87, 035202 (2013)].

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2023

Identifying strengths and weaknesses of methods for computational network inference from single-cell RNA-seq data

Single-cell RNA-sequencing (scRNA-seq) offers unparalleled insight into the transcriptional programs of different cellular states by measuring the transcriptome of thousands of individual cells. An emerging problem in the analysis of scRNA-seq is the inference of transcriptional gene regulatory networks and a number of methods with different learning frameworks have been developed to address this problem. Here, we present an expanded benchmarking study of eleven recent network inference methods on seven published scRNA-seq datasets in human, mouse, and yeast considering different types of gold standard networks and evaluation metrics. We evaluate methods based on their computing requirements as well as on their ability to recover the network structure. We find that, while most methods have a modest recovery of experimentally derived interactions based on global metrics such as Area Under the Precision Recall curve, methods are able to capture targets of regulators that are relevant to the system under study. Among the top performing methods that use only expression were SCENIC, PIDC, MERLIN or Correlation. Addition of prior biological knowledge and the estimation of transcription factor activities resulted in the best overall performance with the Inferelator and MERLIN methods that use prior knowledge outperforming methods that use expression alone. We found that imputation for network inference did not improve network inference accuracy and could be detrimental. Comparisons of inferred networks for comparable bulk conditions showed that the networks inferred from scRNA-seq datasets are often better or at par with the networks inferred from bulk datasets. Our analysis should be beneficial in selecting methods for network inference. At the same time, this highlights the need for improved methods and better gold standards for regulatory network inference from scRNAseq datasets.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2019

Effects of spherical confinement and backbone stiffness on flexible polymer jamming

We use molecular simulations to study jamming of a crumpled bead-spring model polymer in a finite container and compare to jamming of repulsive spheres. After proper constraint counting, the onset of rigidity is seen to occur isostatically as in the case of repulsive spheres. Despite this commonality, the presence of the curved container wall and polymer backbone bonds introduce new mechanical properties. Notably, these include additional bands in the vibrational density of states that reflect the material structure as well as oscillations in local contact number and density near the wall but with lower amplitude for polymers. Polymers have fewer boundary contacts, and this low-density surface layer strongly reduces the global bulk modulus. Here, we further show that bulk-modulus dependence on backbone stiffness can be described by a model of stiffnesses in series and discuss potential experimental and biological applications.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Supertwisted spirals of layered materials enabled by growth on non-Euclidean surfaces

Using curves to make twists The growth of layered materials on flat substrates usually occurs in stacked layers, although defects or a lattice mismatch can induce strains that distort the shape of subsequent layers. However, these effects are usually small and can be uncontrolled. Zhao et al. now demonstrate the possibility of synthesizing multilayers of two-dimensional materials with certain twists between the layers induced by the presence of screw dislocations in combination with curved substrate surfaces. Different twist angles are achieved by varying the amount of nonplanarity and the character (conical or hyperbolic) of the surface. Science , this issue p. 442

Science & Technology - Other Topics↗
DOE OSTI2013

X-ray diffraction study of short-period AlN/GaN superlattices

The structure of short-period hexagonal GaN/AlN superlattices (SLs) has been investigated by X-ray diffraction. The samples have been grown by metalorganic vapor-phase epitaxy (MOVPE) in a horizontal reactor at a temperature of 1050°C on (0001)Al{sub 2}O{sub 3} substrates using GaN and AlN buffer layers. The SL period changes from 2 to 6 nm, and the thickness of the structure varies in a range from 0.3 to 1 μm. The complex of X-ray diffraction techniques includes a measurement of θ-2θ rocking curves of symmetric Bragg reflection, the construction of intensity maps for asymmetric reflections, a measurement and analysis of peak broadenings in different diffraction geometries, a precise measurement of lattice parameters, and the determination of radii of curvature. The thickness and strain of separate SL layers are determined by measuring the θ-2θ rocking curves subsequent simulation. It is shown that most SL samples are completely relaxed as a whole. At the same time, relaxation is absent between sublayers, which is why strains in the AlN and GaN sublayers (on the order of 1.2 × 10{sup −2}) have different signs. An analysis of diffraction peak half-widths allows us to determine the densities of individual sets of dislocations and observe their change from buffer layers to SLs.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Intensity Distribution of the Three-Wave Diffraction from Dislocation Epitaxial Layers in the Reciprocal Space

The three-wave X-ray diffraction in strongly disordered epitaxial layers of GaN and ZnO is experimentally investigated. The charts of the intensity distribution in the reciprocal space are plotted in coordinates q{sub θ} and q{sub ϕ} for the most intensive three-wave combination (1010)/(1011) by means of subsequent θ- and ϕ-scanning. A nontrivial shape of the θ-sections of these contours at a distance from the ϕ center of reflection is revealed; it is different for different samples. For the θ-curves at the center of reflection, we observed a common peak that may be approximated by the Voigt function with a power-low decrease in the intensity at the wings; the decrease law (from–4.5 to–5.0) is found to be considerably greater than that for the similar curves of two-wave diffraction and not depending on the dislocation density and distribution in layers. In some films we observed a coarse-block structure; in addition, it follows from the distribution in the reciprocal space that these blocks are turned with respect to each other around a normal to the surface, which allows us to suggest the existence of low-angle boundaries between them, consisting exclusively of edge dislocations.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Plasma Processing of SRF Cavities for the next Generation Of Particle Accelerators

The cost-effective production of high frequency accelerating fields are the foundation for the next generation of particle accelerators. The Ar/Cl2 plasma etching technology holds the promise to yield a major reduction in cavity preparation costs. Plasma-based dry niobium surface treatment provides an excellent opportunity to remove bulk niobium, eliminate surface imperfections, increase cavity quality factor, and bring accelerating fields to higher levels. At the same time, the developed technology will be more environmentally friendly than the hydrogen fluoride-based wet etching technology. Plasma etching of inner surfaces of standard multi-cell SRF cavities is the main goal of this research in order to eliminate contaminants, including niobium oxides, in the penetration depth region. Successful plasma processing of multi-cell cavities will establish this method as a viable technique in the quest for more efficient components of next generation particle accelerators. In this project the single-cell pill box cavity plasma etching system is developed and etching conditions are determined. An actual single cell SRF cavity (1497 MHz) is plasma etched based on the pill box cavity results. The first RF test of this plasma etched cavity at cryogenic temperature is obtained. The system can also be used for other surface modifications, including tailoring niobium surface properties, surface passivation or nitriding for better performance of SRF cavities. The results of this plasma processing technology may be applied to most of the current SRF cavity fabrication projects. In the course of this project it has been demonstrated that a capacitively coupled radio-frequency discharge can be successfully used for etching curved niobium surfaces, in particular the inner walls of SRF cavities. The results could also be applicable to the inner or concave surfaces of any 3D structure other than an SRF cavity.

43 PARTICLE ACCELERATORS↗
DOE OSTI2023

Demonstrating Load-Shaping Capabilities of Cost Minimizing Heat Pump Water Heater Controls with Varying Price Profiles

Increased penetration of photovoltaics and electrification of traditionally gas appliances are exacerbating existing challenges in cost-effectively balancing electricity grid supply and demand. Decarbonization without incurring expensive transmission and distribution system capacity increases requires shifting building loads from peak demand times to peak renewable production times. Grid operators are evaluating new ways of encouraging load shifting, including using time-varying price structures to provide a financial incentive. If devices incorporate price-responsive controls, a price profile could be designed to yield a wide variety of load curves as needed to optimize grid functionality. Heat pump water heaters (HPWHs) are an ideal device for price-responsive controls because the storage tank enables them to optimize the timing of electricity consumption without impacting hot water delivery service. This paper presents work demonstrating how price-responsive controls for HPWHs can provide different load profiles, as needed to stabilize the grid, in response to different price profiles. HPWH manufacturers now include web API and CTA-2045 communication capabilities which enable sending load shaping control signals. Pilot studies and preliminary programs have utilized these capabilities with uniform control strategies to reduce 4-9 PM electricity consumption. However, no studies have developed flexible controls capable of both a) responding to constantly varying price profiles and b) customizing logic to match the needs of each HPWH. Berkeley Lab's CalFlexHub project is pioneering price-driven load flexibility by developing and deploying cost-minimizing controls utilizing setpoint setting signals for fleets of HPWHs in response to varying price profiles. Control development is based on simulations using the Flexible Heat Pump Water Heater Performance Predictor which captures the control decisions of a residential, integrated HPWH manufacturer’s on-board controller. The proposed cost-reducing controls respond to constantly changing price profiles, providing the ability to change the price profile to generate load curves as needed to maintain grid stability. Preliminary simulations studying the load shaping capabilities of price-responsive controls on a fleet of 60 HPWHs have demonstrated an average of a) 135.4% increases in load during low-price periods, b) >36.8% reductions in electricity peak-price period, and c) 6.2% electricity cost savings.

24 POWER TRANSMISSION AND DISTRIBUTION↗
DOE OSTI2019

Spitzer Microlensing Parallax for OGLE-2016-BLG-1067: A Sub-Jupiter Orbiting an M Dwarf in the Disk

We report the discovery of a sub-Jupiter-mass planet orbiting beyond the snow line of an M dwarf most likely in the Galactic disk as part of the joint Spitzer and ground-based monitoring of planetary microlensing anomalies toward the Galactic bulge. Most of the microlensing parameters are strongly constrained by the light-curve modeling, and in particular there is a Spitzer-based measurement of the microlens parallax, π {sub E}. However, there are no caustic crossings, so the angular Einstein radius has only an upper limit based on the light-curve modeling alone. Additionally, the analysis leads us to identify eight degenerate configurations: the fourfold microlensing parallax degeneracy being doubled by a degeneracy in the caustic structure present at the level of the ground-based solutions. To calculate the physical parameters, and at the same time to break the parallax degeneracy, we make use of a series of arguments: the χ {sup 2} hierarchy, the Rich argument (stating that the small-parallax solution is more likely), and a prior Galactic model. The preferred configuration, favored by a likelihood ratio of at least 4000, is for a host at D{sub L}=3.73{sub −0.67}{sup +0.66} kpc with mass M{sub L}=0.30{sub −0.12}{sup +0.15} M{sub ⊙}, orbited by a Saturn-like planet with M{sub planet} =0.43{sub −0.17}{sup +0.21} M{sub Jup} at projected separation a{sub ⊥}=1.70{sub −0.39}{sup +0.38} au, about 2.1 times beyond the system snow line. Therefore, it adds to the growing population of sub-Jupiter planets orbiting beyond the snow line of M dwarfs discovered by microlensing. Based on the rules of the real-time protocol for the selection of events to be followed up with Spitzer, this planet will not enter the sample for measuring the Galactic distribution of planets.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

Measuring the Growth Rate of Structure with Type IA Supernovae from LSST

We investigate the peculiar motions of galaxies up to z = 0.5 using Type Ia supernovae (SNe Ia) from the Large Synoptic Survey Telescope (LSST) and predict the subsequent constraints on the growth rate of structure. We consider two cases. Our first is based on measurements of the volumetric SNe Ia rate and assumes we can obtain spectroscopic redshifts and light curves for varying fractions of objects that are detected pre-peak luminosity by LSST (some of which may be obtained by LSST itself, and others that would require additional follow-up observations). We find that these measurements could produce growth rate constraints at z<0.5 that significantly outperform those found using Redshift Space Distortions (RSD) with DESI or 4MOST, even though there are ∼4× fewer objects. For our second case, we use semi-analytic simulations and a prescription for the SNe Ia rate as a function of stellar mass and star-formation rate to predict the number of LSST SNe IA whose host redshifts may already have been obtained with the Taipan+WALLABY surveys or with a future multi-object spectroscopic survey. We find ∼18,000 and ∼160,000 SNe Ia with host redshifts for these cases, respectively. While this is only a fraction of the total LSST-detected SNe Ia, they could be used to significantly augment and improve the growth rate constraints compared to only RSD. Ultimately, we find that combining LSST SNe Ia with large numbers of galaxy redshifts will provide the most powerful probe of large-scale gravity in the z<0.5 regime over the coming decades.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1980

Composite structural materials

The use of filamentary composite materials in the design and construction of primary aircraft structures is considered with emphasis on efforts to develop advanced technology in the areas of physical properties, structural concepts and analysis, manufacturing, and reliability and life prediction. The redesign of a main spar/rib region on the Boeing 727 elevator near its actuator attachment point is discussed. A composite fabrication and test facility is described as well as the use of minicomputers for computer aided design. Other topics covered include (1) advanced structural analysis methids for composites; (2) ultrasonic nondestructive testing of composite structures; (3) optimum combination of hardeners in the cure of epoxy; (4) fatigue in composite materials; (5) resin matrix characterization and properties; (6) postbuckling analysis of curved laminate composite panels; and (7) acoustic emission testing of composite tensile specimens.

Ansell, G. S.↗
NASA NTRS1989

Numerical study of turbulent secondary flows in curved ducts

The pressure driven, fully-developed turbulent flow of an incompressible viscous fluid in curved ducts of square cross-section is studied numerically by making use of a finite volume method. A nonlinear Kappa - Iota model is used to represent the turbulence. The results for both straight and curved ducts are presented. For the case of fully-developed turbulent flow in straight ducts, the secondary flow is characterized by an eight-vortex structure for which the computed flowfield is shown to be in good agreement with available experimental data. The introduction of moderate curvature is shown to cause a substantial increase in the strength of the secondary flow and to change the secondary flow pattern to either a double-vortex or a four-vortex configuration.

Hur, N.↗
NASA NTRS1991

Lightweight Composite Core For Curved Composite Mirrors

New type of composite core material for curved composite mirrors proposed. Strips cut from corrugated sheets of graphite/epoxy bonded together at crests and valleys. In comparison with honeycomb and other lightweight core materials, structure less mechanically anisotropic, tailored to have less distortion due to temperature changes, naturally vented, and easily fabricated. Conforms readily to spherical and paraboloidal curvatures and fabricated in large sizes.

Porter, Christopher C.↗
NASA NTRS1991

The physical properties of giant molecular cloud complexes in the outer Galaxy - Implications for the ratio of H2 column density to (C-12)O intensity

The physical properties of 35 giant molecular cloud complexes in the outer Galaxy were derived from the Goddard-Columbia surveys of the Galactic plane region (Dame et al., 1987). The spatial and radial velocity boundaries for the individual cloud complexes were estimated by analyzing the spatial and velocity structure of emission features in the (C-12)O surveys, and the distance to each cmplex was determined kinematically on the assumption of a flat rotation curve. The ratio of the H2 column density to the (C-12)O intensity for the outer Galaxy complexes was found to be about 6.0 x 10 to the 20th molecules/sq cm K per km/sec, which is by a factor of 2-3 greater than the value derived by other auhtors for the inner Galaxy complexes. This increase in the H2 column density/(C-12)O intensity with the distance from with the Galactic center is consistent with predictions of the optically thick cloudlet model of giant molecular cloud complexes.

Sodroski, T. J.↗
NASA NTRS1990

Scaling laws for light-weight optics

Scaling laws for light-weight optical systems are examined. A cubic relationship between mirror diameter and weight has been suggested and used by many designers of optical systems as the best description for all light-weight mirrors. A survey of existing light-weight systems in the open literature has been made to clarify this issue. Fifty existing optical systems were surveyed with all varieties of light-weight mirrors including glass and beryllium structured mirrors, contoured mirrors, and very thin solid mirrors. These mirrors were then categorized and weight to diameter ratio was plotted to find a best fit curve for each case. A best fitting curve program tests nineteen different equations and ranks a 'goodness of fit' for each of these equations. The resulting relationship found for each light-weight mirror category helps to quantify light-weight optical systems and methods of fabrication and provides comparisons between mirror types.

Valente, Tina M.↗
NASA NTRS1993

The evolution of massive stars including mass loss - Presupernova models and explosion

The evolution of massive stars of 35, 40, 60, and 85 solar masses is followed through all stages of nuclear burning to the point of Fe core collapse. Critical nuclear reaction and mass-loss rates are varied. Efficient mass loss during the Wolf-Rayet (WR) stage is likely to lead to final masses as small as 4 solar masses. For a reasonable parameterization of the mass loss, there may be convergence of all WR stars, both single and in binaries, to a narrow band of small final masses. Our representative model, a 4.25 solar-mass WR presupernova derived from a 60 solar mass star, is followed through a simulated explosion, and its explosive nucleosynthesis and light curve are determined. Its properties are similar to those observed in Type Ib supernovae. The effects of the initial mass and mass loss on the presupernova structure of small mass WR models is also explored. Important properties of the presupernova star and its explosion can only be obtained by following the complete evolution starting on the main sequence.

Woosley, S. E.↗