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Results for “Substrate Specificity”

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 1,189 records · Page 66
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

Black GE based on crystalline/amorphous core/shell nanoneedle arrays

Direct growth of black Ge on low-temperature substrates, including plastics and rubber is reported. The material is based on highly dense, crystalline/amorphous core/shell Ge nanoneedle arrays with ultrasharp tips (.about.4 nm) enabled by the Ni catalyzed vapor-solid-solid growth process. Ge nanoneedle arrays exhibit remarkable optical properties. Specifically, minimal optical reflectance (<1%) is observed, even for high angles of incidence (.about.75.degree.) and for relatively short nanoneedle lengths (.about.1 .mu.m). Furthermore, the material exhibits high optical absorption efficiency with an effective band gap of .about.1 eV. The reported black Ge can have important practical implications for efficient photovoltaic and photodetector applications on nonconventional substrates.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Molecular Beam Epitaxy (MBE) Growth of Model Cathodes to Study Interfacial Ion Diffusion

Lithium-ion batteries (LIBs) have been the focus of research for decades owing to their superior energy storage potential and wide range of applications. However, long-term stability issues still persist in LIB cathodes as the result of the formation of a solid electrolyte interface (SEI), structural transformations, or the loss of active cathode materials. In nanoscale cathodes, it is often impossible to isolate, let alone mitigate the causes of the observed capacity loss. Herein, a novel approach is presented to synthesizing LIB cathode model systems using thin-film molecular beam epitaxy (MBE). Specifically, 100 nm thick LiMn 2 O 4 (LMO) thin-film cathodes are grown on SrRuO 3 /SrTiO 3 (100) single-crystal substrates and characterized in their pristine and cycled states. The pristine thin films exhibit the electro-chemical cycling behavior and structural evolution previously seen in bulk LMO cathodes. The formation of surface-layer rocksalt MnO and spinel Mn 3 O 4 along with the mass-loss associated with the corrosion of active Mn ions is also reported. It is, therefore, demonstrated that these MBE-grown model systems can be used for detailed studies of their surface structures and the electrode/electrolyte interfacial evolution in LIB cathodes, leading to the development of materials for rechargeable batteries with higher capacity and better stability.

25 ENERGY STORAGE↗
DOE OSTI2018

TRPV4 promotes the migration and invasion of glioma cells via AKT/Rac1 signaling

Highlights: • TRPV4 is upregulated in glioma, and high-level of TRPV4 indicates a worse prognosis. • TRPV4 activation enhances the cell migration and invasion of glioma. • TRPV4-induced cell motility via AKT/Rac1 signaling pathway. Experimental evidence indicates a critical role of TRPV4 (Transient Receptor Potential Vanilloid 4) in controlling the cell migratory activity of multiple tumors. However, the oncogenic role of TRPV4 in glioma still remains elusive. In this study, we tried to investigate the oncogenic role of TRPV4 in glioma. We found that the expression levels of TRPV4 were upregulated in glioma and the high levels of TRPV4 indicated a worse prognosis in patients with glioma. TRPV4 was critical for glioma migration and invasion: activating TRPV4 by agonist GSK1016790 A enhanced glioma migration and invasion, while, the specific TRPV4 antagonist HC-067047 suppressed glioma migration and invasion. Mechanically, activated TRPV4 promoted the activation of Rac1 (Ras-related C3 botulinum toxin substrate 1) by targeting the AKT for phosphorylation, then enhanced glioma migration and invasion. All these results suggested that TRPV4 accelerates glioma migration and invasion through the AKT/Rac1 signaling, and TRPV4 might be considered as a potential target for glioma therapy.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2014

Graphene on nanoscale gratings for the generation of terahertz Smith-Purcell radiation

Generation of THz radiation based on the Smith-Purcell effect in graphene is investigated numerically. The specific device geometry considered involves an electrically biased single-layer sheet of graphene deposited on a periodic array of holes in a solid substrate. Rigorous electrodynamic simulations combined with a basic model of charge transport are presented, showing that technologically significant output power levels can be obtained at geometrically tunable THz frequencies. These results suggest that graphene is a uniquely suited materials platform for the demonstration of THz electron-beam radiation mechanisms in compact solid-state systems.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2022

Development of coated heat flux gauges for fast responding measurements

Thermal systems often exhibit transient behaviors that have important implications for the operation of the system and can be difficult to predict. For these reasons, experimental testing is often required to ensure system durability requirements are achieved. One important parameter governing the survivability of components in hot, high-stress environments is the heat flux into the part that dictates the temperature distribution for the component. However, sensors required to experimentally characterize heat fluxes in extreme environments must also be resilient. Here, this study presents the development of coated heat transfer gauges capable of robust, high-frequency measurements in turbine research facilities. The addition of a protective coating increases the durability of the gauge, but inherent of that coating is the attenuation of high-frequency temperature penetrations. As a result, this study first outlines the use of analytical solutions to define a gauge design for a specific frequency range and heat transfer, ensuring that subsurface signals can be rectified to surface conditions through inverse methods. Then, the fabrication of polyimide substrate sensors with a parylene-F coating is described. Micro surface heaters added to the custom sensors were used to determine important geometric and thermal properties necessary to calculate accurate surface heat flux. Ultimately, this work shows increased sensor robustness in a turbine test bed and experimentally validates that the frequency response of the fabricated sensors meet the design intent.

47 OTHER INSTRUMENTATION↗
DOE OSTI2015

High-dose neutron irradiation performance of dielectric mirrors

The study presents the high-dose behavior of dielectric mirrors specifically engineered for radiation-tolerance: alternating layers of Al 2 O 3 /SiO 2 and HfO 2 /SiO 2 were grown on sapphire substrates and exposed to neutron doses of 1 and 4 dpa at 458 10K in the High Flux Isotope Reactor (HFIR). In comparison to previously reported results, these higher doses of 1 and 4 dpa results in a drastic drop in optical reflectance, caused by a failure of the multilayer coating. HfO 2 /SiO 2 mirrors failed completely when exposed to 1 dpa, whereas the reflectance of Al 2 O 3 /SiO 2 mirrors reduced to 44%, eventually failing at 4 dpa. Transmission electron microscopy (TEM) observation of the Al 2 O 3 /SiO 2 specimens showed SiO 2 layer defects which increases size with irradiation dose. The typical size of each defect was 8 nm in 1 dpa and 42 nm in 4 dpa specimens. Buckling type delamination of the interface between the substrate and first layer was typically observed in both 1 and 4 dpa HfO 2 /SiO 2 specimens. Composition changes across the layers were measured in high resolution scanning-TEM mode using energy dispersive spectroscopy. A significant interdiffusion between the film layers was observed in Al 2 O 3 /SiO 2 mirror, though less evident in HfO 2 /SiO 2 system. Lastly, the ultimate goal of this work is the provide insight into the radiation-induced failure mechanisms of these mirrors.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2019

Transcriptomic differences noted in Glaesserella parasuis between growth in broth and on agar

Glaesserella parasuis is the cause of Gla¨sser’s disease in pigs and is a significant contributor to post-weaning mortality in the swine industry. Prevention of G. parasuis disease relies primarily on bacterin vaccines, which have shown good homologous protection and variable heterologous protection. Bacterin production involves large scale growth of the bacteria and proteins produced during the proliferation phase of production become important antigens that stimulate the immune response. In order to evaluate genes activated during G. parasuis growth on different media substrates, the transcriptome of broth and agar grown G. parasuis strain 29755 were sequenced and compared. The transcription of most purported virulence genes were comparable between broth and agar grown G. parasuis; however, four virulence-associated genes, including ompA and vapD, had elevated expression under agar growth, while six virulence-associate genes had elevated expression during broth growth, including several protease genes. Additionally, there were metabolic shifts toward increased protein and lipid production and increased cellular division in broth grown G. parasuis. The results contribute to the understanding of how growth substrate alters gene transcription and protein expression, which may impact vaccine efficacy if immunogens important to the protective immune response are not produced under specific in vitro conditions. While the results of this work are unable to fully elucidate which growth medium presents a transcriptome more representative of in vivo samples or best suited for bacterin production, it forms a foundation that can be used for future comparisons and provides a better understanding of the metabolic differences in broth and agar grown bacteria.

59 BASIC BIOLOGICAL SCIENCES↗
NASA NTRS1990

Osteoclast cytosolic calcium, regulated by voltage-gated calcium channels and extracellular calcium, controls podosome assembly and bone resorption

The mechanisms of Ca2+ entry and their effects on cell function were investigated in cultured chicken osteoclasts and putative osteoclasts produced by fusion of mononuclear cell precursors. Voltage-gated Ca2+ channels (VGCC) were detected by the effects of membrane depolarization with K+, BAY K 8644, and dihydropyridine antagonists. K+ produced dose-dependent increases of cytosolic calcium ([Ca2+]i) in osteoclasts on glass coverslips. Half-maximal effects were achieved at 70 mM K+. The effects of K+ were completely inhibited by dihydropyridine derivative Ca2+ channel blocking agents. BAY K 8644 (5 X 10(-6) M), a VGCC agonist, stimulated Ca2+ entry which was inhibited by nicardipine. VGCCs were inactivated by the attachment of osteoclasts to bone, indicating a rapid phenotypic change in Ca2+ entry mechanisms associated with adhesion of osteoclasts to their resorption substrate. Increasing extracellular Ca2+ ([Ca2+]e) induced Ca2+ release from intracellular stores and Ca2+ influx. The Ca2+ release was blocked by dantrolene (10(-5) M), and the influx by La3+. The effects of [Ca2+]e on [Ca2+]i suggests the presence of a Ca2+ receptor on the osteoclast cell membrane that could be coupled to mechanisms regulating cell function. Expression of the [Ca2+]e effect on [Ca2+]i was similar in the presence or absence of bone matrix substrate. Each of the mechanisms producing increases in [Ca2+]i, (membrane depolarization, BAY K 8644, and [Ca2+]e) reduced expression of the osteoclast-specific adhesion structure, the podosome. The decrease in podosome expression was mirrored by a 50% decrease in bone resorptive activity. Thus, stimulated increases of osteoclast [Ca2+]i lead to cytoskeletal changes affecting cell adhesion and decreasing bone resorptive activity.

NASA Discipline Musculoskeletal↗
NASA NTRS2004

Ordered Nanostructures Made Using Chaperonin Polypeptides

A recently invented method of fabricating periodic or otherwise ordered nanostructures involves the use of chaperonin polypeptides. The method is intended to serve as a potentially superior and less expensive alternative to conventional lithographic methods for use in the patterning steps of the fabrication of diverse objects characterized by features of the order of nanometers. Typical examples of such objects include arrays of quantum dots that would serve as the functional building blocks of future advanced electronic and photonic devices. A chaperonin is a double-ring protein structure having a molecular weight of about 60 plus or minus 5 kilodaltons. In nature, chaperonins are ubiquitous, essential, subcellular structures. Each natural chaperonin molecule comprises 14, 16, or 18 protein subunits, arranged as two stacked rings approximately 16 to 18 nm tall by approximately 15 to 17 nm wide, the exact dimensions depending on the biological species in which it originates. The natural role of chaperonins is unknown, but they are believed to aid in the correct folding of other proteins, by enclosing unfolded proteins and preventing nonspecific aggregation during assembly. What makes chaperonins useful for the purpose of the present method is that under the proper conditions, chaperonin rings assemble themselves into higher-order structures. This method exploits such higher-order structures to define nanoscale devices. The higher-order structures are tailored partly by choice of chemical and physical conditions for assembly and partly by using chaperonins that have been mutated. The mutations are made by established biochemical techniques. The assembly of chaperonin polypeptides into such structures as rings, tubes, filaments, and sheets (two-dimensional crystals) can be regulated chemically. Rings, tubes, and filaments of some chaperonin polypeptides can, for example, function as nano vessels if they are able to absorb, retain, protect, and release gases or chemical reagents, including reagents of medical or pharmaceutical interest. Chemical reagents can be bound in, or released from, such structures under suitable controlled conditions. In an example of a contemplated application, a two-dimensional crystal of chaperonin polypeptides would be formed on a surface of an inorganic substrate and used to form a planar array of nanoparticles or quantum dots. Through genetic engineering of the organisms used to manufacture the chaperonins, specific sites on the chaperonin molecules and, thus, on the two-dimensional crystals can be chemically modified to react in a specific manner so as to favor the deposition of the material of the desired nanoparticles or quantum dots. A mutation that introduces a cysteine residue at the desired sites on a chaperonin of Sulfolobus shibatae was used to form planar arrays of gold nanoparticles (see figure).

Trent, Jonathan↗
DOE OSTI2018

Structural Insight into Allosteric Inhibition of Mycobacterium tuberculosis Tryptophan Synthase

The rise of antibiotic‐resistant pathogens requires redirecting drug discovery effort toward new cellular targets to provide new treatment options. Such alternative, yet unexplored opportunities exist in central metabolism, where many enzymes are only conditionally essential and thus their successful exploitation requires understanding of metabolic fluxes and pathway regulations under certain environmental conditions. In Mycobacterium tuberculosis , tryptophan biosynthesis represents one such promising pathway that could be targeted. In Mtb, the multistep L‐Trp synthesis involves several enzymes: TrpEG, TrpD, TrpC and TrpAB, which is validated as conditionally essential in vivo . The whole‐cell screening of a diversity‐oriented synthetic library identified a novel bactericidal azetidine derivative, BRD4592, that specifically inhibits TrpAB (tryptophan synthase). TrpAB is a heterotetrameric, PLP‐dependent complex catalyzing two last reactions in L‐Trp synthesis: the conversion of indole‐3‐glycerol phosphate to indole and glyceraldehyde 3‐phosphate (TrpA) followed by indole and L‐Ser condensation to yield L‐Trp (TrpB). During the catalytic cycle, indole is transferred from the TrpA to TrpB active site through 25 Å hydrophobic channel to react with the L‐Ser‐PLP adduct. The enzymatic activities and substrate channeling are coordinated by complex allosteric communication between the subunits. This regulation involves cycling between various conformational states, with both subunits adopting either an open (inactive) or closed (active) state. Detailed kinetic, biophysical and structural evidence reveals that BRD4592 is an allosteric, mixed‐type inhibitor, which binds specifically to a novel site within the intersubunit channel, at the TrpA‐TrpB interface. The molecule promotes closed, active state of the TrpB subunit and increases enzyme affinity for the L‐Ser substrate. BRD4592 acts on three levels: it limits flexibility of the interface potentially disrupting mutual activation of the subunits, prevents indole translocation, and increases product inhibition providing means to successfully inhibit both, TrpA and TrpB reactions. Our results indicate that allosteric binders may represent an effective tool to deactivate central metabolism enzymes, which often are allosterically regulated and might be predisposed for this type of inhibition. Support or Funding Information This work was supported by the Broad Institute Tuberculosis donor group, the Pershing Square Foundation, the Bill & Melinda Gates Foundation under grant OPP1032518, the National Institute of Allergy and Infectious Diseases, National Institutes of Health, Department of Health and Human Services, under contracts HHSN272200700058C and HHSN272201200026C and the U. S. Department of Energy, Office of Biological and Environmental Research, under contract DE‐AC02‐06CH11357. For this work, University of Chicago is a subgrantee of Structural Genomics Consortium under a Bill & Melinda Gates Foundation grant for the Structure‐Guided Drug Discovery Coalition.

Michalska, Karolina↗
DOE OSTI2026

Divergent carbon use efficiency-growth rate tradeoff in popular biological growth models

Carbon use efficiency (CUE) is an important trait emerging from processes regulating biological growth. CUE can be computed either based on the growth of structural biomass or total biomass divided by substrate uptake rate. Nonequilibrium thermodynamics and observations suggest that, for an exponentially growing population of cells, structural biomass CUE should first increase, then peak, and finally decrease with specific growth rate; meanwhile, total biomass CUE increases asymptotically with specific growth rate. We compared predictions from six popular models that are often used for plant and microbial growth in existing ecosystem models. We found that, for an exponentially growing population of biological cells, (1) the source-driven Pirt and Compromise models predict that structural biomass CUE increase asymptotically with growth rate; (2) the apparent sink-driven modified Droop model predicts that structural biomass CUE decreases with growth rate; and (3) the sink-driven variable internal storage model and two dynamic energy budget models predict that structural biomass CUE first increases, then peaks, and finally decreases with growth rate. Moreover, the modified Droop model predicts that total biomass CUE is constant with growth rate, while all other five models predict that total biomass CUE increases with growth rate asymptotically. For non-exponential biological growth, we show that there is no static relationship between total biomass CUE or structural biomass CUE with respect to either growth rate or temperature. Therefore, we contend that biological growth models should explicitly represent interactions between substrate acquisition, substate transformation, and maintenance respiration to better capture observed CUE dynamics, and the sink-driven model should be preferred for general ecosystem biogeochemistry modeling.

Tang, Jinyun [Lawrence Berkeley National Laborator↗
DOE OSTI2018

Wucherria bancrofti glutathione S-Transferase: Insights into the 2.3 Å resolution X-ray structure and function, a therapeutic target for human lymphatic filariasis

Highlights: • Crystal structure of W. bancrofti GST with its cofactor GSH at 2.3 Å resolution was determined. • Structural comparison against human GST reveals distinct differences in substrate binding sites. • GST xenobiotic binding site is more substrate accessible and reveals non-catalytic binding sites. • Enzyme kinetic assays reveal that antifilarial drug Diethyl carbamazine binds in an uncompetitive manner. • Structural features provide insights to support future design of parasite specific inhibitors. The notoriety of parasitic nematode survival is directly related to chronic pathogenicity, which is evident in human lymphatic filariasis. It is a disease of poverty which causes severe disability affecting more than 120 million people worldwide. These nematodes down-regulate host immune system through a myriad of strategies that includes secretion of antioxidant and detoxification enzymes like glutathione-S-transferases (GSTs). Earlier studies have shown Wuchereria bancrofti GST to be a potential therapeutic target. Parasite GSTs catalyse the conjugation of glutathione to xenobiotic and other endogenous electrophiles and are essential for their long-term survival in lymph tissues. Hence, the crystal structure of WbGST along with its cofactor GSH at 2.3 Å resolution was determined. Structural comparisons against host GST reveal distinct differences in the substrate binding sites. The parasite xenobiotic binding site is more substrate/solvent accessible. The structure also suggests the presence of putative non-catalytic binding sites that may permit sequestration of endogenous and exogenous ligands. The structure of WbGST also provides a case for the role of the π-cation interaction in stabilizing catalytic Tyr compared to stabilization interactions described for other GSTs. Hence, the obtained information regarding crucial differences in the active sites will support future design of parasite specific inhibitors. Further, the study also evaluates the inhibition of WbGST and its variants by antifilarial diethylcarbamazine through kinetic assays.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2015

A transmission line method for evaluation of vertical InAs nanowire contacts

In this paper, we present a method for metal contact characterization to vertical semiconductor nanowires using the transmission line method (TLM) on a cylindrical geometry. InAs nanowire resistors are fabricated on Si substrates using a hydrogen silsesquioxane (HSQ) spacer between the bottom and top contact. The thickness of the HSQ is defined by the dose of an electron beam lithography step, and by varying the separation thickness for a group of resistors, a TLM series is fabricated. Using this method, the resistivity and specific contact resistance are determined for InAs nanowires with different doping and annealing conditions. The contacts are shown to improve with annealing at temperatures up to 300 °C for 1 min, with specific contact resistance values reaching down to below 1 Ω µm{sup 2}.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Argobots: A Lightweight Low-Level Threading and Tasking Framework

In the past few decades, a number of user-level threading and tasking models have been proposed in the literature to address the shortcomings of OS-level threads, primarily with respect to cost and flexibility. Current state-of-the-art user-level threading and tasking models, however, are either too specific to applications or architectures or are not as powerful or flexible. In this paper, we present Argobots, a lightweight, low-level threading and tasking framework that is designed as a portable and performant substrate for high-level programming models or runtime systems. Argobots offers a carefully designed execution model that balances generality of functionality with providing a rich set of controls to allow specialization by the user or high-level programming model. We describe the design, implementation, and optimization of Argobots and present integrations with three example high-level models: OpenMP, MPI, and co-located I/O service. Evaluations show that (1) Argobots outperforms existing generic threading runtimes; (2) our OpenMP runtime offers more efficient interoperability capabilities than production OpenMP runtimes do; (3) when MPI interoperates with Argobots instead of Pthreads, it enjoys reduced synchronization costs and better latency hiding capabilities; and (4) I/O service with Argobots reduces interference with co-located applications, achieving performance competitive with that of the Pthreads version.

Seo, Sangmin (ORCID:0000000295159836)↗
DOE OSTI2018

A potential substrate binding pocket of BdcA plays a critical role in NADPH recognition and biofilm dispersal

Highlights: • The crystal structure of BdcA in complex with NADPH is determined. • NADPH binding stabilizes a potential substrate binding pocket of BdcA. • The substrate binding pocket is conversely involved in BdcA recognizing NADPH. • Both NADPH and substrate binding are essential for BdcA inducing biofilm dispersal. Biofilm dispersal is characterized by the cell detachment from biofilms and expected to provide novel “anti-biofilm” approaches of prevention and treatment of biofilms in clinical and industrial settings. The E.coli protein BdcA has been identified as a biofilm dispersal factor and designed to be an important component in engineered applications to control biofilm formation. It belongs to short-chain dehydrogenase/reductase (SDR) family with the specific affinity to NADPH. Here, we show the structure of BdcA in complex with NADPH and confirm that NADPH binding is requisite for BdcA facilitating cell motility and increasing biofilm dispersal. Especially, we observe a potential substrate binding pocket surrounded by hydrophobic residues upon NADPH binding and present evidences that this pocket is essential for BdcA binding NADPH and exerting its biological functions. Our study provides the clues for illuminating the molecular mechanism of BdcA regulating biofilm dispersal and better utilizing BdcA to eliminate the biofilms.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2020

Mechanisms of Degradation of Toxic Nerve Agents: Quantum-chemical Insight into Interactions of Sarin and Soman with Molybdenum Dioxide

With the urgent need to provide an efficient and reliable protection for people from fatal chemical and biological weapons, our fundamental understanding of how toxins interact with filters is far from complete. The situation is further complicated by natural difficulties of performing experimental measurements with lethal toxins. Unlike experiments, computational modeling offers an attractive and safe yet reliable way of studying behavior of toxic agents on a variety of substrates at a great level of detail. Here, we report DFT-based quantum-chemical calculations of adsorption and decomposition of DMMP, sarin and soman on MoO 2 (011) surface. Our calculations show that MoO 2 strongly adsorbs toxic nerve agents and quickly decomposes them. Decomposition of DMMP on the MoO 2 (011) surface proceeds via the PO-CH 3 bond breaking and a formation of a surface methoxy group. The calculated activation barrier for this reaction is 131.5 kJ mol -1 . Unlike DMMP, decomposition of sarin and soman proceeds via the dealkylation reaction yielding propene and 3,3-dimethyl-1-butene, respectively. Decomposition of sarin requires a remarkably low energy (53.7 kJ mol- 1 ), whereas the similar reaction in soman requires 50 kJ mol -1 more energy. We also make specific predictions to guide Ambient-Pressure X-ray Photoelectron Spectroscopy (APXPS) experiments on sarin interaction with MoO 2 samples. We conclude that MoO 2 serves as an efficient substrate able of degrading toxins.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗