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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 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
DOE OSTI2012

Skip the Alignment: Degenerate, Multiplex Primer and Probe Design Using K-mer Matching Instead of Alignments

PriMux is a new software package for selecting multiplex compatible, degenerate primers and probes to detect diverse targets such as viruses. It requires no multiple sequence alignment, instead applying k-mer algorithms, hence it scales well for large target sets and saves user effort from curating sequences into alignable groups. PriMux has the capability to predict degenerate primers as well as probes suitable for TaqMan or other primer/probe triplet assay formats, or simply probes for microarray or other single-oligo assay formats. PriMux employs suffix array methods for efficient calculations on oligos 10-,100 nt in length. TaqManH primers and probes for each segment of Rift Valley fever virus were designed using PriMux, and lab testing comparing signatures designed using PriMux versus those designed using traditional methods demonstrated equivalent or better sensitivity for the PriMux-designed signatures compared to traditional signatures. In addition, we used PriMux to design TaqManH primers and probes for unalignable or poorly alignable groups of targets: that is, all segments of Rift Valley fever virus analyzed as a single target set of 198 sequences, or all 2863 Dengue virus genomes for all four serotypes available at the time of our analysis. The PriMux software is available as open source from http:// sourceforge.net/projects/PriMux.

59 BASIC BIOLOGICAL SCIENCES↗
NASA NTRS2016

Silicon Alignment Pins: An Easy Way to Realize a Wafer-To-Wafer Alignment

A silicon alignment pin is used to align successive layers of components made in semiconductor chips and/or metallic components to make easier the assembly of devices having a layered structure. The pin is made as a compressible structure which can be squeezed to reduce its outer diameter, have one end fit into a corresponding alignment pocket or cavity defined in a layer of material to be assembled into a layered structure, and then allowed to expand to produce an interference fit with the cavity. The other end can then be inserted into a corresponding cavity defined in a surface of a second layer of material that mates with the first layer. The two layers are in registry when the pin is mated to both. Multiple layers can be assembled to create a multilayer structure. Examples of such devices are presented.

Jung-Kubiak, Cecile↗
DOE OSTI2015

Theoretically informed Monte Carlo simulation of liquid crystals by sampling of alignment-tensor fields

A theoretically informed coarse-grained Monte Carlo method is proposed for studying liquid crystals. The free energy functional of the system is described in the framework of the Landau-de Gennes formalism. The alignment field and its gradients are approximated by finite differences, and the free energy is minimized through a stochastic sampling technique. The validity of the proposed method is established by comparing the results of the proposed approach to those of traditional free energy minimization techniques. Its usefulness is illustrated in the context of three systems, namely, a nematic liquid crystal confined in a slit channel, a nematic liquid crystal droplet, and a chiral liquid crystal in the bulk. It is found that for systems that exhibit multiple metastable morphologies, the proposed Monte Carlo method is generally able to identify lower free energy states that are often missed by traditional approaches. Importantly, the Monte Carlo method identifies such states from random initial configurations, thereby obviating the need for educated initial guesses that can be difficult to formulate.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Sub-5 nm, globally aligned graphene nanoribbons on Ge(001)

Graphene nanoribbons (GNRs) hold great promise for future electronics because of their edge and width dependent electronic bandgaps and exceptional transport properties. While significant progress toward GNR devices has been made, the field has been limited by difficulties achieving narrow widths, global alignment, and atomically pristine GNR edges on technologically relevant substrates. A recent advance has challenged these limits by using Ge(001) substrates to direct the bottom-up growth of GNRs with nearly pristine armchair edges and widths near ∼10 nm via atmospheric pressure chemical vapor deposition. In this work, the growth of GNRs on Ge(001) is extended to ultra-high vacuum conditions, resulting in the realization of GNRs with widths narrower than 5 nm. Armchair graphene nanoribbons oriented along Ge 〈110〉 surface directions are achieved with excellent width control and relatively large bandgaps. The bandgap magnitude and electronic uniformity of these sub-5 nm GNRs are well-suited for emerging nanoelectronic applications.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2017

Impact of baryonic physics on intrinsic alignments

We explore the effects of specific assumptions in the subgrid models of star formation and stellar and AGN feedback on intrinsic alignments of galaxies in cosmological simulations of "MassiveBlack-II" family. Using smaller volume simulations, we explored the parameter space of the subgrid star formation and feedback model and found remarkable robustness of the observable statistical measures to the details of subgrid physics. The one observational probe most sensitive to modeling details is the distribution of misalignment angles. We hypothesize that the amount of angular momentum carried away by the galactic wind is the primary physical quantity that controls the orientation of the stellar distribution. Finally, our results are also consistent with a similar study by the EAGLE simulation team.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2018

Electronic Structure and Band Alignment of LaMnO 3 /SrTiO 3 Polar/Nonpolar Heterojunctions

The behavior of polar LaMnO3 (LMO) thin films deposited epitaxially on non-polar SrTiO3(001) (STO) is dictated by both the LMO/STO band alignment and the chemistry of the Mn cation. Using in situ x-ray photoelectron spectros-copy (XPS), we directly measure the valence band offset (VBO) of LMO/STO heterojunctions as a function of thickness, and find that the VBO is 2.5 eV for thicker (= 3 u.c.) films. We find no evidence of a built-in potential in LMO films of any thickness. Measurements of the Mn valence by Mn L-edge x-ray absorption spectroscopy (XAS) and by spatially-resolved electron energy loss spectra in scanning transmission electron microscopy images (STEM-EELS) reveal that Mn2+ is present at the LMO surface, but not at the LMO/STO interface. These results are corroborated by DFT simula-tions that confirm a VBO of approximately 2.5 eV for both ideal and intermixed interfaces. We propose a model for the behavior of polar / non-polar LMO/STO heterojunctions in which the built-in potential is alleviated by the formation of oxygen vacancies at the LMO surface.

Kaspar, Tiffany C.↗
DOE OSTI2015

Microwave conductance properties of aligned multiwall carbon nanotube textile sheets

Understanding the conductance properties of multi-walled carbon nanotube (MWNT) textile sheets in the microwave regime is essential for their potential use in high-speed and high-frequency applications. To expand current knowledge, complex high-frequency conductance measurements from 0.01 to 50 GHz and across temperatures from 4.2 K to 300 K and magnetic fields up to 2 T were made on textile sheets of highly aligned MWNTs with strand alignment oriented both parallel and perpendicular to the microwave electric field polarization. Sheets were drawn from 329 and 520 μm high MWNT forests that resulted in different DC resistance anisotropy. For all samples, the microwave conductance can be modeled approximately by a shunt capacitance in parallel with a frequency-independent conductance, but with no inductive contribution. Finally, this is consistent with diffusive Drude conduction as the primary transport mechanism up to 50 GHz. Further, it is found that the microwave conductance is essentially independent of both temperature and magnetic field.

Brown, Brian L.↗
DOE OSTI2015

Determining the band alignment of TbAs:GaAs and TbAs:In 0.53 Ga 0.47 As

Here, we propose and systematically justify a band structure for TbAs nanoparticles in GaAs and In 0.53 Ga 0.47 As host matrices. Moreover, fluence-dependent optical-pump terahertz-probe measurements suggest the TbAs nanoparticles have a band gap and provide information on the carrier dynamics, which are determined by the band alignment. Spectrophotometry measurements provide the energy of optical transitions in the nanocomposite systems and reveal a large blue shift in the absorption energy when the host matrix is changed from In 0.53 Ga 0.47 As to GaAs. Finally, Hall data provides the approximate Fermi level in each system. From this data, we deduce that the TbAs:GaAs system forms a type I (straddling) heterojunction and the TbAs:In 0.53 Ga 0.47 As system forms a type II (staggered) heterojunction.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Band alignment of epitaxial SrTiO{sub 3} thin films with (LaAlO{sub 3}){sub 0.3}-(Sr{sub 2}AlTaO{sub 6}){sub 0.7} (001)

SrTiO{sub 3} (STO) epitaxial thin films and heterostructures are of considerable interest due to the wide range of functionalities they exhibit. The alloy perovskite (LaAlO{sub 3}){sub 0.3}-(Sr{sub 2}AlTaO{sub 6}){sub 0.7} (LSAT) is commonly used as a substrate for these material structures due to its structural compatibility with STO and the strain-induced ferroelectric response in STO films grown on LSAT. However, surprisingly little is known about the electronic properties of the STO/LSAT interface despite its potentially important role in affecting the overall electronic structure of system. We examine the band alignment of STO/LSAT heterostructures using x-ray photoelectron spectroscopy for epitaxial STO films deposited using two different molecular beam epitaxy approaches. We find that the valence band offset ranges from +0.2(1) eV to −0.2(1) eV depending on the film surface termination. From these results, we extract a conduction band offset from −2.4(1) eV to −2.8(1) eV, indicating that the conduction band edge is more deeply bound in STO and that LSAT will not act as a sink or trap for electrons in the supported film or multilayer.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

Cooperative Behavior in the Evolution of Alignment and Structure in Vertically Aligned Carbon-Nanotube Arrays Grown using Chemical Vapor Deposition

We discuss the origin and the influence of autocatalytic kinetics on the structure-property relationship in the evolution of macromolecular structure during self-organized growth of vertically aligned carbon-nanotube arrays by chemical vapor deposition of acetylene. Real-time thickness measurements consistent with postgrowth structural characterization show that the rate of carbon incorporation governs not just the length of individual nanotubes, but also cooperative properties such as packing density, alignment, and order in the arrays, which profoundly affect the mechanical strength and the thermal and electrical conductivity of the assembly. Our analysis shows that the autocatalytic kinetics points to radical chain polymerization of acetylene as the most likely mechanism capable of producing the large variations in carbon-addition rates revealed by real-time data. Furthermore this fresh insight provides alternative approaches for targeting specific array properties using the polymerization reaction framework for creating novel applications in high-density energy storage, advanced interconnects, and high-efficiency heat dissipation.

36 MATERIALS SCIENCE↗