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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 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

Impact of dose size in single fraction spatially fractionated (grid) radiotherapy for melanoma

Purpose: To evaluate the impact of dose size in single fraction, spatially fractionated (grid) radiotherapy for selectively killing infiltrated melanoma cancer cells of different tumor sizes, using different radiobiological models. Methods: A Monte Carlo technique was employed to calculate the 3D dose distribution of a commercially available megavoltage grid collimator in a 6 MV beam. The linear-quadratic (LQ) and modified linear quadratic (MLQ) models were used separately to evaluate the therapeutic outcome of a series of single fraction regimens that employed grid therapy to treat both acute and late responding melanomas of varying sizes. The dose prescription point was at the center of the tumor volume. Dose sizes ranging from 1 to 30 Gy at 100% dose line were modeled. Tumors were either touching the skin surface or having their centers at a depth of 3 cm. The equivalent uniform dose (EUD) to the melanoma cells and the therapeutic ratio (TR) were defined by comparing grid therapy with the traditional open debulking field. The clinical outcomes from recent reports were used to verify the authors’ model. Results: Dose profiles at different depths and 3D dose distributions in a series of 3D melanomas treated with grid therapy were obtained. The EUDs and TRs for all sizes of 3D tumors involved at different doses were derived through the LQ and MLQ models, and a practical equation was derived. The EUD was only one fifth of the prescribed dose. The TR was dependent on the prescribed dose and on the LQ parameters of both the interspersed cancer and normal tissue cells. The results from the LQ model were consistent with those of the MLQ model. At 20 Gy, the EUD and TR by the LQ model were 2.8% higher and 1% lower than by the MLQ, while at 10 Gy, the EUD and TR as defined by the LQ model were only 1.4% higher and 0.8% lower, respectively. The dose volume histograms of grid therapy for a 10 cm tumor showed different dosimetric characteristics from those of conventional radiotherapy. A significant portion of the tumor volume received a very large dose in grid therapy, which ensures significant tumor cell killing in these regions. Conversely, some areas received a relatively small dose, thereby sparing interspersed normal cells and increasing radiation tolerance. The radiobiology modeling results indicated that grid therapy could be useful for treating acutely responding melanomas infiltrating radiosensitive normal tissues. The theoretical model predictions were supported by the clinical outcomes. Conclusions: Grid therapy functions by selectively killing infiltrating tumor cells and concomitantly sparing interspersed normal cells. The TR depends on the radiosensitivity of the cell population, dose, tumor size, and location. Because the volumes of very high dose regions are small, the LQ model can be used safely to predict the clinical outcomes of grid therapy. When treating melanomas with a dose of 15 Gy or higher, single fraction grid therapy is clearly advantageous for sparing interspersed normal cells. The existence of a threshold fraction dose, which was found in the authors’ theoretical simulations, was confirmed by clinical observations.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2022

Five-second coherence of a single spin with single-shot readout in silicon carbide

An outstanding hurdle for defect spin qubits in silicon carbide (SiC) is single-shot readout, a deterministic measurement of the quantum state. Here, we demonstrate single-shot readout of single defects in SiC via spin-to-charge conversion, whereby the defect’s spin state is mapped onto a long-lived charge state. With this technique, we achieve over 80% readout fidelity without pre- or postselection, resulting in a high signal-to-noise ratio that enables us to measure long spin coherence times. Combined with pulsed dynamical decoupling sequences in an isotopically purified host material, we report single-spin T 2 > 5 seconds, over two orders of magnitude greater than previously reported in this system. The mapping of these coherent spin states onto single charges unlocks both single-shot readout for scalable quantum nodes and opportunities for electrical readout via integration with semiconductor devices.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Coherent single-photon emission from colloidal lead halide perovskite quantum dots

Chemically made colloidal semiconductor quantum dots have long been proposed as scalable and color-tunable single emitters in quantum optics, but they have typically suffered from prohibitively incoherent emission. We now demonstrate that individual colloidal lead halide perovskite quantum dots (PQDs) display highly efficient single-photon emission with optical coherence times as long as 80 picoseconds, an appreciable fraction of their 210-picosecond radiative lifetimes. These measurements suggest that PQDs should be explored as building blocks in sources of indistinguishable single photons and entangled photon pairs. Our results present a starting point for the rational design of lead halide perovskite–based quantum emitters that have fast emission, wide spectral tunability, and scalable production and that benefit from the hybrid integration with nanophotonic components that has been demonstrated for colloidal materials.

solar (photovoltaic), solid state lighting, photos↗
DOE OSTI2024

Single-Crystal-to-Single-Crystal Post-Synthetic Modifications

Chalcogenides are the cornerstone of the semiconductor and thermoelectric industries and are up-and-coming materials for superconductors, catalysis, and battery applications. Challenges in synthesizing those materials emerge from the chalcogen's volatility and the tendencies of chalcogenides to react with even trace quantities of oxygen. Many techniques have been applied to the growth of chalcogenide single crystals, which are convenient for structure determinations and intrinsic property measurements. One of the recent advances in chalcogenide chemistry is the intriguing single-crystal-to-single-crystal (SCSC) transformation, leading to new metastable compositions. Post-synthetic transformations are well-known and studied for chalcogenide powders; however, examples of post-synthetic conversions that retain single crystallinity are rare. To date, the scope of SCSC reactions includes (de)intercalation in the layered compositions and ion exchange in open-framework materials, salt-inclusion chalcogenides, and layered structures. This poster will discuss the successful examples of SCSC modifications monitored by single-crystal X-ray diffraction (SC-XRD), emphasizing how post-synthetic transformations affect materials' properties.

chalcogenide↗
DOE OSTI2012

Single-Step Syngas-to-Distillates (S2D) Process Based on Biomass-Derived Syngas – A Techno-Economic Analysis

This study reports the comparison of biomass gasification based syngas-to-distillate (S2D) systems using techno-economic analysis (TEA). Three cases, state of technology (SOT) case, goal case, and conventional case, were compared in terms of performance and cost. The SOT case and goal case represent technology being developed at Pacific Northwest National Laboratory for a process starting with syngas using a single-step dual-catalyst reactor for distillate generation (S2D process). The conventional case mirrors the two-step S2D process previously utilized and reported by Mobil using natural gas feedstock and consisting of separate syngas-to-methanol and methanol-to-gasoline (MTG) processes. Analysis of the three cases revealed that the goal case could indeed reduce fuel production cost over the conventional case, but that the SOT was still more expensive than the conventional. The SOT case suffers from low one-pass yield and high selectivity to light hydrocarbons, both of which drive up production cost. Sensitivity analysis indicated that light hydrocarbon yield, single pass conversion efficiency, and reactor space velocity are the key factors driving the high cost for the SOT case.

Biomass↗
DOE OSTI2018

Single-Doped and Multidoped Transition-Metal (Mn, Fe, Co, and Ni) ZnO and Their Electrocatalytic Activities for Oxygen Reduction Reaction

The electrochemical oxygen reduction reaction (ORR) is the limiting half-reaction of fuel cells, which is mediated by using platinum-based catalysts. Hence, the development of low-cost, active ORR catalysts is highly required to make fuel cell technology commercially available. In this report, transition-metal (TM; Mn, Fe, Co, and Ni) single-doped and multidoped (MD) ZnO nanocrystals (ZNs) were prepared for use as ORR catalysts using a simple precipitation method. The effects of single doping and multidoping on the structure, morphology, and properties of the TM-doped ZNs were analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray fluorescence, X-ray photoelectron microscopy, electron paramagnetic resonance, and Raman and photoluminescence (PL) spectroscopies. The XRD results reveal that synthesized ZnO samples retained a pure hexagonal wurtzite crystal structure, even at high levels of multidoping (nominal 20%). SEM analyses show that the morphology of the prepared ZNs varies with the doping elements, doping mode, and amounts of doping. The observation of peak shifting and peak intensity changes in Raman studies confirms the presence of dopants in ZnO. The PL investigation reveals that the incorporation of dopants into the ZnO structure increases the oxygen vacancies within the materials. The highest oxygen vacancies were present in Mn-doped ZnO and 15% MD ZnO among the single-doped and MD samples, respectively. Linear-sweep voltammetry studies conclude that doped ZnO shows enhanced ORR activity compared to the undoped samples. The Mn-doped ZnO and 15% MD ZnO exhibited the highest ORR activity among the prepared single-doped and MD ZN samples, respectively. In comparison, single doping showed better ORR activity than the multidoping system. The enhanced ORR activity of the synthesized ZN materials correlates with the amount of oxygen vacancies present in the samples. Finally, the enhanced activity of TM-doped ZnO suggests that these materials can be used as potential, low-cost electrocatalysts for ORR in fuel cell technology.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Systematic Comparison of High-throughput Single-Cell and Single-Nucleus Transcriptomes during Cardiomyocyte Differentiation

A comprehensive reference map of all cell types in the human body is necessary for improving our understanding of fundamental biological processes and in diagnosing and treating disease. High-throughput single-cell RNA sequencing techniques have emerged as powerful tools to identify and characterize cell types in complex and heterogeneous tissues. However, extracting intact cells from tissues and organs is often technically challenging or impossible, for example in heart or brain tissue. Single-nucleus RNA sequencing provides an alternative way to obtain transcriptome profiles of such tissues. To systematically assess the differences between high-throughput single-cell and single-nuclei RNA-seq approaches, we compared Drop-seq and DroNc-seq, two microfluidic-based 3' RNA capture technologies that profile total cellular and nuclear RNA, respectively, during a time course experiment of human induced pluripotent stem cells (iPSCs) differentiating into cardiomyocytes. Clustering of timeseries transcriptomes from Drop-seq and DroNc-seq revealed six distinct cell types, five of which were found in both techniques. Furthermore, single-cell trajectories reconstructed from both techniques reproduced expected differentiation dynamics. We then applied DroNc-seq to postmortem heart tissue to test its performance on heterogeneous human tissue samples. Our data confirm that DroNcseq yields similar results to Drop-seq on matched samples and can be successfully used to generate reference maps for the human cell atlas.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2017

Can Kohn–Sham density functional theory predict accurate charge distributions for both single-reference and multi-reference molecules?

Dipole moments are the first moment of electron density and are fundamental quantities that are often available from experiments. An exchange–correlation functional that leads to an accurate representation of the charge distribution of a molecule should accurately predict the dipole moments of the molecule. It is well known that Kohn–Sham density functional theory (DFT) is more accurate for the energetics of single-reference systems than for the energetics of multi-reference ones, but there has been less study of charge distributions. Here, in this work, we benchmark 48 density functionals chosen with various combinations of ingredients, against accurate experimental data for dipole moments of 78 molecules, in particular 55 single-reference molecules and 23 multi-reference ones. We chose both organic and inorganic molecules, and within the category of inorganic molecules there are both main-group and transition-metal-containing molecules, with some of them being multi-reference. As one would expect, the multi-reference molecules are not as well described by single-reference DFT, and the functionals tested in this work do show larger mean unsigned errors (MUEs) for the 23 multi-reference molecules than the single-reference ones. Five of the 78 molecules have relatively large experimental error bars and were therefore not included in calculating the overall MUEs. For the 73 molecules not excluded, we find that three of the hybrid functionals, B97-1, PBE0, and TPSSh (each with less than or equal to 25% Hartree–Fock (HF) exchange), the range-separated hybrid functional, HSE06 (with HF exchange decreasing from 25% to 0 as interelectronic distance increases), and the hybrid functional, PW6B95 (with 28% HF exchange) are the best performing functionals with each yielding an MUE of 0.18 D. Perhaps the most significant finding of this study is that there exists great similarity among the success rate of various functionals in predicting dipole moments. In particular, of 39 functionals designed as general-purpose functionals and that do not have a global value of 100% HF exchange, the average MUE is 0.23 D, with a standard deviation of only 0.04 D. Among gradient approximations, which are especially interesting because of their speed and portability, the best overall performance is by PBE, HCTH/407, OLYP, OreLYP, and GAM, each with MUE of 0.22 D.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

The dilation aided single–line–of–sight x–ray camera for the National Ignition Facility: Characterization and fielding

Crystal x–ray imaging is commonly used in inertial confinement fusion and laser-plasma interaction applications as it has advantages compared to pinhole imaging, such as higher signal throughput, better achievable spatial resolution, and chromatic selection. Yet, currently used x–ray detectors are only able to obtain a single time resolved image per crystal. The dilation aided single–line–of–sight x–ray camera described here was designed for the National Ignition Facility (NIF) and combines two recent diagnostic developments, the pulse dilation principle used in the dilation x-ray imager and a ns–scale multi-frame camera that uses a hold and readout circuit for each pixel. This enables multiple images to be taken from a single–line–of–sight with high spatial and temporal resolution. Presently, the instrument can record two single–line–of–sight images with spatial and temporal resolution of 35 μm and down to 35 ps, respectively, with a planned upgrade doubling the number of images to four. Here we present the dilation aided single–line–of–sight camera for the NIF, including the x–ray characterization measurements obtained at the COMET laser, as well as the results from the initial timing shot on the NIF.

47 OTHER INSTRUMENTATION↗
DOE OSTI2011

Controlling the quantum state of a single photon emitted from a single polariton

We investigate in detail the optimal conditions for a high fidelity transfer from a single-polariton state to a single-photon state and subsequent homodyne detection of the single photon. We assume that, using various possible techniques, the single polariton has initially been stored as a spin-wave grating in a cloud of cold atoms inside a low-finesse cavity. This state is then transferred to a single-photon optical pulse using an auxiliary beam. We optimize the retrieval efficiency and determine the mode of the local oscillator that maximizes the homodyne efficiency of such a photon. We find that both efficiencies can have values close to one in a large region of experimental parameters.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Single pair of Weyl fermions in the half-metallic semimetal EuC d 2 A s 2 [A Single Pair of Weyl Fermions in Half-metallic EuCd 2 As 2 Semimetal]

Materials with the ideal case of a single pair of Weyl points (WPs) are highly desirable for elucidating the unique properties of Weyl fermions. EuCd 2 As 2 is an antiferromagnetic topological insulator or Dirac semimetal depending on the different magnetic configurations. Using first-principles band-structure calculations, we show that inducing ferromagnetism in EuCd 2 As 2 can generate a single pair of WPs from splitting the single pair of antiferromagnetic Dirac points due to its half-metallic nature. Analysis with a low-energy effective Hamiltonian shows that a single pair of WPs is obtained in EuCd 2 As 2 because the Dirac points are very close to the zone center and the ferromagnetic exchange splitting is large enough to push one pair of WPs to merge and annihilate at Γ while the other pair survives. As a result, we predict that alloying with Ba at the Eu site can stabilize the ferromagnetic configuration and generate a single pair of Weyl points without application of a magnetic field.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Nop9 recognizes structured and single-stranded RNA elements of preribosomal RNA

Nop9 is an essential factor in the processing of preribosomal RNA. Its absence in yeast is lethal, and defects in the human ortholog are associated with breast cancer, autoimmunity, and learning/language impairment. PUF family RNA-binding proteins are best known for sequence-specific RNA recognition, and most contain eight α-helical repeats that bind to the RNA bases of single-stranded RNA. Nop9 is an unusual member of this family in that it contains eleven repeats and recognizes both RNA structure and sequence. Here we report a crystal structure of Saccharomyces cerevisiae Nop9 in complex with its target RNA within the 20S preribosomal RNA. This structure reveals that Nop9 brings together a carboxy-terminal module recognizing the 5' single-stranded region of the RNA and a bifunctional amino-terminal module recognizing the central double-stranded stem region. We further show that the 3' single-stranded region of the 20S target RNA adds sequence-independent binding energy to the RNA–Nop9 interaction. Both the amino- and carboxy-terminal modules retain the characteristic sequence-specific recognition of PUF proteins, but the amino-terminal module has also evolved a distinct interface, which allows Nop9 to recognize either single-stranded RNA sequences or RNAs with a combination of single-stranded and structured elements.

59 BASIC BIOLOGICAL SCIENCES↗
NASA NTRS1994

Method for forming single phase, single crystalline 2122 BCSCO superconductor thin films by liquid phase epitaxy

A substantially single phase, single crystalline, highly epitaxial film of Bi.sub.2 CaSr.sub.2 Cu.sub.2 O.sub.8 superconductor which has a T.sub.c (zero resistance) of 83 K is provided on a lattice-matched substrate with no intergrowth. This film is produced by a Liquid Phase Epitaxy method which includes the steps of forming a dilute supercooled molten solution of a single phase superconducting mixture of oxides of Bi, Ca, Sr, and Cu having an atomic ratio of about 2:1:2:2 in a nonreactive flux such as KCl, introducing the substrate, e.g., NdGaO.sub.3, into the molten solution at 850.degree. C., cooling the solution from 850.degree. C. to 830.degree. C. to grow the film and rapidly cooling the substrate to room temperature to maintain the desired single phase, single crystalline film structure.

Pandey, Raghvendra K.↗