Intravenous Administration of Stable-Labeled N-Acetylcysteine Demonstrates an Indirect Mechanism for Boosting Glutathione and Improving Redox Status.

PubMed

Zhou, Jie; Coles, Lisa D; Kartha, Reena V; Nash, Nardina; Mishra, Usha; Lund, Troy C; Cloyd, James C

2015-08-01

There is an increasing interest in using N-acetylcysteine (NAC) as a treatment for neurodegenerative disorders to increase glutathione (GSH) levels and its redox status. The purpose of this study was to characterize the biosynthesis of NAC to GSH using a novel stable isotope-labeled technique, and investigate the pharmacodynamics of NAC in vivo. Female wild-type mice were given a single intravenous bolus dose of 150 mg kg(-1) stable-labeled NAC. Plasma, red blood cells (RBC), and brain tissues were collected at predesignated time points. Stable-labeled NAC and its metabolite GSH (both labeled and unlabeled forms) were quantified in blood and brain samples. Molar ratios of the reduced and oxidized forms of GSH (GSH divided by glutathione disulfide, redox ratio) were also determined. The elimination phase half-life of NAC was approximately 34 min. Both labeled and unlabeled GSH in RBC were found to increase; however, the area under the curve above baseline (AUCb0-280 ) of labeled GSH was only 1% of the unlabeled form. These data indicate that NAC is not a direct precursor of GSH. In addition, NAC has prolonged effects in brain even when the drug has been eliminated from systemic circulation. © 2015 Wiley Periodicals, Inc. and the American Pharmacists Association.

Structural characterization of recombinant IAV polymerase reveals a stable complex between viral PA-PB1 heterodimer and host RanBP5.

PubMed

Swale, Christopher; Monod, Alexandre; Tengo, Laura; Labaronne, Alice; Garzoni, Frédéric; Bourhis, Jean-Marie; Cusack, Stephen; Schoehn, Guy; Berger, Imre; Ruigrok, Rob W H; Crépin, Thibaut

2016-04-20

The genome of influenza A virus (IAV) comprises eight RNA segments (vRNA) which are transcribed and replicated by the heterotrimeric IAV RNA-dependent RNA-polymerase (RdRp). RdRp consists of three subunits (PA, PB1 and PB2) and binds both the highly conserved 3'- and 5'-ends of the vRNA segment. The IAV RdRp is an important antiviral target, but its structural mechanism has remained largely elusive to date. By applying a polyprotein strategy, we produced RdRp complexes and define a minimal human IAV RdRp core complex. We show that PA-PB1 forms a stable heterodimeric submodule that can strongly interact with 5'-vRNA. In contrast, 3'-vRNA recognition critically depends on the PB2 N-terminal domain. Moreover, we demonstrate that PA-PB1 forms a stable and stoichiometric complex with host nuclear import factor RanBP5 that can be modelled using SAXS and we show that the PA-PB1-RanPB5 complex is no longer capable of 5'-vRNA binding. Our results provide further evidence for a step-wise assembly of IAV structural components, regulated by nuclear transport mechanisms and host factor binding.

Synoptic Formation of Double Tropopauses

NASA Astrophysics Data System (ADS)

Liu, Chengji; Barnes, Elizabeth

2018-01-01

Double tropopauses are ubiquitous in the midlatitude winter hemisphere and represent the vertical stacking of two stable tropopause layers separated by a less stable layer. By analyzing COSMIC GPS data, reanalysis, and eddy life cycle simulations, we demonstrate that they often occur during Rossby wave breaking and act to increase the stratosphere-to-troposphere exchange of mass. We further investigate the adiabatic formation of double tropopauses and propose two mechanisms by which they can occur. The first mechanism operates at the tropopause break in the subtropics where the higher tropical tropopause sits on one side of the break and the lower extratropical tropopause sits on the other. The double tropopauses are then formed by differential meridional advection of the higher and lower tropopauses on the two sides of the tropopause break. We show that anticyclonic wave breaking can form double tropopauses mainly by providing stronger poleward advection of the higher tropopause in its poleward lobe. Cyclonic wave breaking mainly forms double tropopauses by providing stronger equatorward advection of the lower tropopause in its equatorward lobe. We demonstrate in the COSMIC GPS data and reanalysis that about half of the double tropopauses in the Northern Hemisphere winter can be directly attributed to such differential advection. For the second mechanism, adiabatic destabilization of the air above the tropopause contributes to the formation of a double tropopause. In this case, a tropopause inversion layer is necessary for this destabilization to result in a double tropopause.

Stable carbon and sulfur isotopes as records of the early biosphere

NASA Technical Reports Server (NTRS)

Desmarais, David J.

1989-01-01

The abundance ratios of the stable isotopes of light elements such as carbon and sulfur can differ between various naturally-occurring chemical compounds. If coexisting compounds have achieved mutual chemical and isotopic equilibrium, then the relative isotopic composition can record the conditions at which equilibrium was last maintained. If coexisting chemical compounds indeed formed simultaneously but had not achieved mutual equilibrium, then their relative isotopic compositions often reflect the conditions and mechanisms associated with the kinetically controlled reactions responsible for their production. In the context of Mars, the stable isotopic compositions of various minerals might record not only the earlier environmental conditions of the planet, but also whether or not the chemistry of life ever occurred there. Two major geochemical reservoirs occur in Earth's crust, both for carbon and sulfur. In rocks formed in low temperature sedimentary environments, the oxidized forms of these elements tend to be enriched in the isotope having the larger mass, relative to the reduced forms. In sediments where the organics and sulfides were formed by biological processes, these isotopic contrasts were caused by the processes of biological CO2 fixation and dissimilatory sulfate reduction. Such isotopic contrasts between oxidized and reduced forms of carbon and sulfur are permitted by thermodynamics at ambient temperatures. However, nonbiological chemical reactions associated with the production of organic matter and the reduction of organics and sulfides are extremely slow at ambient temperatures. Thus the synthesis of organics and sulfides under ambient conditions illustrates life's profound role as a chemical catalyst that has altered the chemistry of Earth's crust. Because the stable isotopes of carbon and sulfur can reflect their chemistry, they are useful probes of the Martian surface.

Enzymatic Reaction with Unnatural Substrates: DNA Photolyase (Escherichia coli) Recognizes and Reverses Thymine [2+2] Dimers in the DNA Strand of a DNA/PNA Hybrid Duplex

NASA Astrophysics Data System (ADS)

Ramaiah, Danaboyina; Kan, Yongzhi; Koch, Troels; Orum, Henrik; Schuster, Gary B.

1998-10-01

Peptide nucleic acids (PNA) are mimics with normal bases connected to a pseudopeptide chain that obey Watson--Crick rules to form stable duplexes with itself and natural nucleic acids. This has focused attention on PNA as therapeutic or diagnostic reagents. Duplexes formed with PNA mirror some but not all properties of DNA. One fascinating aspect of PNA biochemistry is their reaction with enzymes. Here we show an enzyme reaction that operates effectively on a PNA/DNA hybrid duplex. A DNA oligonucleotide containing a cis, syn-thymine [2+2] dimer forms a stable duplex with PNA. The hybrid duplex is recognized by photolyase, and irradiation of the complex leads to the repair of the thymine dimer. This finding provides insight into the enzyme mechanism and provides a means for the selective repair of thymine photodimers.

Selenium stable isotope ratios in California agricultural drainage water management systems

USGS Publications Warehouse

Herbel, M.J.; Johnson, T.M.; Tanji, K.K.; Gao, S.; Bullen, T.D.

2002-01-01

Selenium stable isotope ratios are known to shift in predictable ways during various microbial, chemical, and biological processes, and can be used to better understand Se cycling in contaminated environments. In this study we used Se stable isotopes to discern the mechanisms controlling the transformation of oxidized, aqueous forms of Se to reduced, insoluble forms in sediments of Se-affected environments. We measured 80Se/76Se in surface waters, shallow ground waters, evaporites, digested plants and sediments, and sequential extracts from several sites where agricultural drainage water is processed in the San Joaquin Valley of California. Selenium isotope analyses of samples obtained from the Tulare Lake Drainage District flow-through wetland reveal small isotopic contrasts (mean difference 0.7%o) between surface water and reduced Se species in the underlying sediments. Selenium in aquatic macrophytes was very similar isotopically to the NaOH and Na2SO3 sediment extracts designed to recover soluble organic Se and Se(O), respectively. For the integrated on-farm drainage management sites, evaporite salts were slightly (approximately 0.6%o) enriched in the heavier isotope relative to the inferred parent waters, whereas surface soils were slightly (approximately 1.4%o) depleted. Bacterial or chemical reduction of Se(VI) or Se(IV) may be occurring at these sites, but the small isotopic contrasts suggest that other, less isotopically fractionating mechanisms are responsible for accumulation of reduced forms in the sediments. These findings provide evidence that Se assimilation by plants and algae followed by deposition and mineralization is the dominant transformation pathway responsible for accumulation of reduced forms of Se in the wetland sediments.

Implications of Orientation in Sheared Cocoa Butter

NASA Astrophysics Data System (ADS)

Guthrie, Sarah E.; Mazzanti, Gianfranco; Marangoni, Alejandro; Idziak, Stefan H. J.

2004-03-01

We will present x-ray and mechanical studies of oriented phases of cocoa butter. The structural elements of foods play an important role in determining such things as quality and shelf stability. The specific structure and properties of cocoa butter, however, are complicated due to the ability of the cocoa butter to form crystals in six polymorphic forms. Recent work has shown that the application of shear not only accelerates the transitions to more stable polymorphs, but also causes orientation of the crystallites[1]. The implications of orientation on the structures formed under conditions of shear and cooling will be described using x-ray diffraction and mechanical measurements. 1 G. Mazzanti, S. E. Guthrie, E. B. Sirota et al., Crystal Growth & Design 3 (5), 721 (2003).

pH optrode

DOEpatents

Northrup, M. Allen; Langry, Kevin C.

1993-01-01

A process is provided for forming a long-lasting, stable, pH-sensitive dye-acrylamide copolymer useful as a pH-sensitive material for use in an optrode or other device sensitive to pH. An optrode may be made by mechanically attaching the copolymer to a sensing device such as an optical fiber.

Synergistic Effect of Carbon Nanotubes and Graphene on Diopside Scaffolds.

PubMed

Liu, Tingting; Wu, Ping; Gao, Chengde; Feng, Pei; Xiao, Tao; Deng, Youwen; Shuai, Cijun; Peng, Shuping

2016-01-01

A synergetic effect between carbon nanotubes (CNTs) and graphene on diopside (Di) scaffolds was demonstrated. 3D network architecture in the matrix was formed through the 1D CNTs inlaid among the 2D graphene platelets (GNPs). The mechanical properties of the CNTs/GNPs/Di scaffolds were significantly improved compared with the CNTs/Di scaffolds and GNPs/Di scaffolds. In addition, the scaffolds exhibited excellent apatite-forming ability, a modest degradation rate, and stable mechanical properties in simulated body fluid (SBF). Moreover, cell culturing tests indicated that the scaffolds supported the cells attachment and proliferation. Taken together, the CNTs/GNPs/Di scaffolds offered great potential for bone tissue engineering.

Effect of the chiral discrimination on the vibrational properties of (R)-, (S)- and (R, S)-ibuprofen/methyl-β-cyclodextrin inclusion complexes

NASA Astrophysics Data System (ADS)

Crupi, V.; Guella, G.; Majolino, D.; Mancini, I.; Paciaroni, A.; Rossi, B.; Venuti, V.; Verrocchio, P.; Viliani, G.

2011-05-01

The effects of chiral discrimination of ibuprofen (IBP) on the complexation process with methyl-β-cyclodextrin (Me-β-CD) were investigated in the solid phase by FTIR-ATR spectroscopy and numerical simulation. The inclusion mechanism was deduced from the temperature-dependent analysis of the vibrational spectra, in the C=O stretching region, of complexes formed by Me-β-CD with the two enantiomeric and the racemic forms of IBP. The mechanism turned out to be enthalpy-driven, with IBP enantiomers giving rise to more stable inclusion complexes with respect to the racemate.

Molecular mechanisms for protein-encoded inheritance

PubMed Central

Wiltzius, Jed J. W.; Landau, Meytal; Nelson, Rebecca; Sawaya, Michael R.; Apostol, Marcin I.; Goldschmidt, Lukasz; Soriaga, Angela B.; Cascio, Duilio; Rajashankar, Kanagalaghatta; Eisenberg, David

2013-01-01

Strains are phenotypic variants, encoded by nucleic acid sequences in chromosomal inheritance and by protein “conformations” in prion inheritance and transmission. But how is a protein “conformation” stable enough to endure transmission between cells or organisms? Here new polymorphic crystal structures of segments of prion and other amyloid proteins offer structural mechanisms for prion strains. In packing polymorphism, prion strains are encoded by alternative packings (polymorphs) of β-sheets formed by the same segment of a protein; in a second mechanism, segmental polymorphism, prion strains are encoded by distinct β-sheets built from different segments of a protein. Both forms of polymorphism can produce enduring “conformations,” capable of encoding strains. These molecular mechanisms for transfer of information into prion strains share features with the familiar mechanism for transfer of information by nucleic acid inheritance, including sequence specificity and recognition by non-covalent bonds. PMID:19684598

Theoretical and experimental analysis of the reaction mechanism of MrTPS2, a triquinane-forming sesquiterpene synthase from chamomile.

PubMed

Hong, Young J; Irmisch, Sandra; Wang, Selina C; Garms, Stefan; Gershenzon, Jonathan; Zu, Liansuo; Köllner, Tobias G; Tantillo, Dean J

2013-09-27

Terpene synthases, as key enzymes of terpene biosynthesis, have garnered the attention of chemists and biologists for many years. Their carbocationic reaction mechanisms are responsible for the huge variety of terpene structures in nature. These mechanisms are amenable to study by using classical biochemical approaches as well as computational analysis, and in this study we combine quantum-chemical calculations and deuterium-labeling experiments to elucidate the reaction mechanism of a triquinane forming sesquiterpene synthase from chamomile. Our results suggest that the reaction from farnesyl diphosphate to triquinanes proceeds through caryophyllyl and presilphiperfolanyl cations and involves the protonation of a stable (-)-(E)-β-caryophyllene intermediate. A tyrosine residue was identified that appears to be involved in the proton-transfer process. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Formation mechanism of Ruddlesden-Popper-type antiphase boundaries during the kinetically limited growth of Sr rich SrTiO3 thin films

PubMed Central

Xu, Chencheng; Du, Hongchu; van der Torren, Alexander J. H.; Aarts, Jan; Jia, Chun-Lin; Dittmann, Regina

2016-01-01

We elucidated the formation process for Ruddlesden-Popper-type defects during pulsed laser deposition of Sr rich SrTiO3 thin films by a combined analysis of in-situ atomic force microscopy, low energy electron diffraction and high resolution scanning transmission electron microscopy. At the early growth stage of 1.5 unit cells, the excess Sr results in the formation of SrO on the surface, resulting in a local termination change from TiO2 to SrO, thereby forming a Sr rich (2 × 2) surface reconstruction. With progressive SrTiO3 growth, islands with thermodynamically stable SrO rock-salt structure are formed, coexisting with TiO2 terminated islands. During the overgrowth of these thermodynamically stable islands, both lateral as well as vertical Ruddlesden-Popper-type anti-phase boundaries are formed, accommodating the Sr excess of the SrTiO3 film. We suggest the formation of thermodynamically stable SrO rock-salt structures as origin for the formation of Ruddlesden-Popper-type antiphase boundaries, which are as a result of kinetic limitations confined to certain regions on the surface. PMID:27922069

Formation mechanism of Ruddlesden-Popper-type antiphase boundaries during the kinetically limited growth of Sr rich SrTiO3 thin films

NASA Astrophysics Data System (ADS)

Xu, Chencheng; Du, Hongchu; van der Torren, Alexander J. H.; Aarts, Jan; Jia, Chun-Lin; Dittmann, Regina

2016-12-01

We elucidated the formation process for Ruddlesden-Popper-type defects during pulsed laser deposition of Sr rich SrTiO3 thin films by a combined analysis of in-situ atomic force microscopy, low energy electron diffraction and high resolution scanning transmission electron microscopy. At the early growth stage of 1.5 unit cells, the excess Sr results in the formation of SrO on the surface, resulting in a local termination change from TiO2 to SrO, thereby forming a Sr rich (2 × 2) surface reconstruction. With progressive SrTiO3 growth, islands with thermodynamically stable SrO rock-salt structure are formed, coexisting with TiO2 terminated islands. During the overgrowth of these thermodynamically stable islands, both lateral as well as vertical Ruddlesden-Popper-type anti-phase boundaries are formed, accommodating the Sr excess of the SrTiO3 film. We suggest the formation of thermodynamically stable SrO rock-salt structures as origin for the formation of Ruddlesden-Popper-type antiphase boundaries, which are as a result of kinetic limitations confined to certain regions on the surface.

Identification of Complex Carbon Nanotube Structures

NASA Technical Reports Server (NTRS)

Han, Jie; Saini, Subhash (Technical Monitor)

1998-01-01

A variety of complex carbon nanotube (CNT) structures have been observed experimentally. These include sharp bends, branches, tori, and helices. They are believed to be formed by using topological defects such as pentagons and heptagons to connect different CNT. The effects of type, number, and arrangement (separation and orientation) of defects on atomic structures and energetics of complex CNT are investigated using topology, quantum mechanics and molecular mechanics calculations. Energetically stable models are derived for identification of observed complex CNT structures.

Comparative Study of the Mechanical Unfolding Pathways of α- and β-Peptides.

PubMed

Uribe, Lalita; Gauss, Jürgen; Diezemann, Gregor

2015-07-02

Using molecular simulations, we analyze the unfolding pathways of various peptides. We compare the mechanical unfolding of a β-alanine's octamer (β-HAla8) and an α-alanine's decamer (α-Ala10). Using force-probe molecular-dynamics simulations, to induce unfolding, we show that the 3(14)-helix formed by β-HAla8 is mechanically more stable than the α-helix formed by α-Ala10, although both structures are stabilized by six hydrogen bonds. Additionally, computations of the potential of mean force validate this result and show that also the thermal stability of the 3(14)-helix is higher. It is demonstrated that β-HAla8 unfolds in a two-step fashion with a stable intermediate. This is contrasted with the known single-step scenario of the unfolding of α-Ala10. Furthermore, we present a study of the chain-length dependence of the mechanical unfolding pathway of the 3(14)-helix. The calculation of the dynamic strength for oligomers with chain lengths ranging from 6 to 18 monomers shows that the unfolding pathway of helices with an integer and noninteger number of turns has m + 1 and m energy barriers, respectively, with m being the number of complete turns. The additional barrier for helices with an integer number of turns is shown to be related to the breaking of the N-terminus' hydrogen bond.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Stoller, Roger E; Nordlund, Kai; Melerba, L

The processes that give rise to changes in the microstructure and the physical and mechanical properties of materials exposed to energetic particles are initiated by essentially elastic collisions between atoms in what has been called an atomic displacement cascade. The formation and evolution of this primary radiation damage mechanism are described to provide an overview of how stable defects are formed by displacement cascades, as well as the nature and morphology of the defects themselves. The impact of the primary variables cascade energy and irradiation temperature are discussed, along with a range of secondary factors that can influence damage formation.Radiation-inducedmore » changes in microstructure and mechanical properties in structural materials are the result of a complex set of physical processes initiated by the collision between an energetic particle (neutron or ion) and an atom in the lattice. This primary damage event is called an atomic displacement cascade. The simplest description of a displacement cascade is to view it as a series of many billiard-ball-like elastic collisions among the atoms in the material. This chapter describes the formation and evolution of this primary radiation damage mechanism to provide an overview of how stable defects are formed by displacement cascades, as well as the nature and morphology of the defects themselves. The impact of the relevant variables such as cascade energy and irradiation temperature is discussed, and defect formation in different materials is compared.« less

Stable DNA replication: interplay between DNA replication, homologous recombination, and transcription.

PubMed

Kogoma, T

1997-06-01

Chromosome replication in Escherichia coli is normally initiated at oriC, the origin of chromosome replication. E. coli cells possess at least three additional initiation systems for chromosome replication that are normally repressed but can be activated under certain specific conditions. These are termed the stable DNA replication systems. Inducible stable DNA replication (iSDR), which is activated by SOS induction, is proposed to be initiated from a D-loop, an early intermediate in homologous recombination. Thus, iSDR is a form of recombination-dependent DNA replication (RDR). Analysis of iSDR and RDR has led to the proposal that homologous recombination and double-strand break repair involve extensive semiconservative DNA replication. RDR is proposed to play crucial roles in homologous recombination, double-strand break repair, restoration of collapsed replication forks, and adaptive mutation. Constitutive stable DNA replication (cSDR) is activated in mhA mutants deficient in RNase HI or in recG mutants deficient in RecG helicase. cSDR is proposed to be initiated from an R-loop that can be formed by the invasion of duplex DNA by an RNA transcript, which most probably is catalyzed by RecA protein. The third form of SDR is nSDR, which can be transiently activated in wild-type cells when rapidly growing cells enter the stationary phase. This article describes the characteristics of these alternative DNA replication forms and reviews evidence that has led to the formulation of the proposed models for SDR initiation mechanisms. The possible interplay between DNA replication, homologous recombination, DNA repair, and transcription is explored.

Energy landscapes of a mechanical prion and their implications for the molecular mechanism of long-term memory.

PubMed

Chen, Mingchen; Zheng, Weihua; Wolynes, Peter G

2016-05-03

Aplysia cytoplasmic polyadenylation element binding (CPEB) protein, a translational regulator that recruits mRNAs and facilitates translation, has been shown to be a key component in the formation of long-term memory. Experimental data show that CPEB exists in at least a low-molecular weight coiled-coil oligomeric form and an amyloid fiber form involving the Q-rich domain (CPEB-Q). Using a coarse-grained energy landscape model, we predict the structures of the low-molecular weight oligomeric form and the dynamics of their transitions to the β-form. Up to the decamer, the oligomeric structures are predicted to be coiled coils. Free energy profiles confirm that the coiled coil is the most stable form for dimers and trimers. The structural transition from α to β is shown to be concentration dependent, with the transition barrier decreasing with increased concentration. We observe that a mechanical pulling force can facilitate the α-helix to β-sheet (α-to-β) transition by lowering the free energy barrier between the two forms. Interactome analysis of the CPEB protein suggests that its interactions with the cytoskeleton could provide the necessary mechanical force. We propose that, by exerting mechanical forces on CPEB oligomers, an active cytoskeleton can facilitate fiber formation. This mechanical catalysis makes possible a positive feedback loop that would help localize the formation of CPEB fibers to active synapse areas and mark those synapses for forming a long-term memory after the prion form is established. The functional role of the CPEB helical oligomers in this mechanism carries with it implications for targeting such species in neurodegenerative diseases.

Synaptic Scaling in Combination with Many Generic Plasticity Mechanisms Stabilizes Circuit Connectivity

PubMed Central

Tetzlaff, Christian; Kolodziejski, Christoph; Timme, Marc; Wörgötter, Florentin

2011-01-01

Synaptic scaling is a slow process that modifies synapses, keeping the firing rate of neural circuits in specific regimes. Together with other processes, such as conventional synaptic plasticity in the form of long term depression and potentiation, synaptic scaling changes the synaptic patterns in a network, ensuring diverse, functionally relevant, stable, and input-dependent connectivity. How synaptic patterns are generated and stabilized, however, is largely unknown. Here we formally describe and analyze synaptic scaling based on results from experimental studies and demonstrate that the combination of different conventional plasticity mechanisms and synaptic scaling provides a powerful general framework for regulating network connectivity. In addition, we design several simple models that reproduce experimentally observed synaptic distributions as well as the observed synaptic modifications during sustained activity changes. These models predict that the combination of plasticity with scaling generates globally stable, input-controlled synaptic patterns, also in recurrent networks. Thus, in combination with other forms of plasticity, synaptic scaling can robustly yield neuronal circuits with high synaptic diversity, which potentially enables robust dynamic storage of complex activation patterns. This mechanism is even more pronounced when considering networks with a realistic degree of inhibition. Synaptic scaling combined with plasticity could thus be the basis for learning structured behavior even in initially random networks. PMID:22203799

Theoretical and experimental vibrational spectroscopy study on rotational isomer of 4-phenylbutylamine

NASA Astrophysics Data System (ADS)

Ünal, A.; Okur, M.

2017-02-01

The possible four stable rotational isomers of 4-phenylbutylamine (4PBA) molecule were experimentally and theoretically studied by vibrational spectroscopy. The FT-IR (4000-400 cm-1) and Raman (3700-60 cm-1) spectra of 4PBA were recorded at room temperature in liquid phase. The complete vibrational wavenumbers and corresponding vibrational assignments of 4PBA molecule were discussed assisted with B3LYP/6-311++G(d,p) level of theory along with scaled quantum mechanics force field (SQM-FF) method. Results from experimental and theoretical data the most stable form of 4PBA molecule was obtained.

Strengthening of stable Cr-Ni austenitic stainless steel under thermomechanical treatments

NASA Astrophysics Data System (ADS)

Akkuzin, S. A.; Litovchenko, I. Yu.; Tyumentsev, A. N.

2017-12-01

The features of microstructure and mechanical properties of stable austenitic steel after thermomechanical treatment consisted of low-temperature deformation, deformation in the temperature range T = 273-873 K, and subsequent annealing were investigated. It is shown that under such treatment direct (γ → α')- and reverse (α'→γ)-martensitic transformations occur in the steel. As a result of the thermomechanical treatment submicrocrystalline structural states with high density of micro- and nanotwins and localized deformation bands are formed. The strength of the steel in these structural states is several times higher than that in the initial state.

The nucleotide-free state of heterotrimeric G proteins α-subunit adopts a highly stable conformation.

PubMed

Andhirka, Sai Krishna; Vignesh, Ravichandran; Aradhyam, Gopala Krishna

2017-08-01

Deciphering the mechanism of activation of heterotrimeric G proteins by their cognate receptors continues to be an intriguing area of research. The recently solved crystal structure of the ternary complex captured the receptor-bound α-subunit in an open conformation, without bound nucleotide has improved our understanding of the activation process. Despite these advancements, the mechanism by which the receptor causes GDP release from the α-subunit remains elusive. To elucidate the mechanism of activation, we studied guanine nucleotide-induced structural stability of the α-subunit (in response to thermal/chaotrope-mediated stress). Inherent stabilities of the inactive (GDP-bound) and active (GTP-bound) forms contribute antagonistically to the difference in conformational stability whereas the GDP-bound protein is able to switch to a stable intermediate state, GTP-bound protein loses this ability. Partial perturbation of the protein fold reveals the underlying influence of the bound nucleotide providing an insight into the mechanism of activation. An extra stable, pretransition intermediate, 'empty pocket' state (conformationally active-state like) in the unfolding pathway of GDP-bound protein mimics a gating system - the activation process having to overcome this stable intermediate state. We demonstrate that a relatively more complex conformational fold of the GDP-bound protein is at the core of the gating system. We report capturing this threshold, 'metastable empty pocket' conformation (the gate) of α-subunit of G protein and hypothesize that the receptor activates the G protein by enabling it to achieve this structure through mild structural perturbation. © 2017 Federation of European Biochemical Societies.

Synergistic Effect of Carbon Nanotubes and Graphene on Diopside Scaffolds

PubMed Central

Liu, Tingting; Wu, Ping; Gao, Chengde; Feng, Pei; Xiao, Tao; Deng, Youwen; Shuai, Cijun; Peng, Shuping

2016-01-01

A synergetic effect between carbon nanotubes (CNTs) and graphene on diopside (Di) scaffolds was demonstrated. 3D network architecture in the matrix was formed through the 1D CNTs inlaid among the 2D graphene platelets (GNPs). The mechanical properties of the CNTs/GNPs/Di scaffolds were significantly improved compared with the CNTs/Di scaffolds and GNPs/Di scaffolds. In addition, the scaffolds exhibited excellent apatite-forming ability, a modest degradation rate, and stable mechanical properties in simulated body fluid (SBF). Moreover, cell culturing tests indicated that the scaffolds supported the cells attachment and proliferation. Taken together, the CNTs/GNPs/Di scaffolds offered great potential for bone tissue engineering. PMID:27144173

Channelization in porous media driven by erosion and deposition.

PubMed

Jäger, R; Mendoza, M; Herrmann, H J

2017-01-01

We develop and validate a new model to study simultaneous erosion and deposition in three-dimensional porous media. We study the changes of the porous structure induced by the deposition and erosion of matter on the solid surface and find that when both processes are active, channelization in the porous structure always occurs. The channels can be stable or only temporary depending mainly on the driving mechanism. Whereas a fluid driven by a constant pressure drop in general does not form steady channels, imposing a constant flux always produces stable channels within the porous structure. Furthermore we investigate how changes of the local deposition and erosion properties affect the final state of the porous structure, finding that the larger the range of wall shear stress for which there is neither erosion nor deposition, the more steady channels are formed in the structure.

On the asymptotic stability of nonlinear mechanical switched systems

NASA Astrophysics Data System (ADS)

Platonov, A. V.

2018-05-01

Some classes of switched mechanical systems with dissipative and potential forces are considered. The case, where either dissipative or potential forces are essentially nonlinear, is studied. It is assumed that the zero equilibrium position of the system is asymptotically stable at least for one operating mode. We will look for sufficient conditions which guarantee the preservation of asymptotic stability of the equilibrium position under the switching of modes. The Lyapunov direct method is used. A Lyapunov function for considered system is constructed, which satisfies the differential inequality of special form for every operating mode. This inequality is nonlinear for the chosen mode with asymptotically stable equilibrium position, and it is linear for the rest modes. The correlations between the intervals of activity of the pointed mode and the intervals of activity of the rest modes are obtained which guarantee the required properties.

Acoustic relaxation of the hydro-mechanical system under critical expiration of swirl flow

NASA Astrophysics Data System (ADS)

Pozdeeva, I. G.; Mitrofanova, O. V.

2018-03-01

The mechanism of generation of acoustic oscillations associated with the formation of stable vortex structures in the moving fluid was considered for the impact swirl flow. Experimental studies were carried out to determine the relationship between large-scale vortex motion and acoustic effects in hydro-mechanical systems. It was shown that a sharp change of the amplitude-frequency characteristic of the acoustic oscillations of hydro-mechanical system corresponds to the maximal flow rate of the swirl flow. The established connection between the generation of sound waves and geometrical and regime parameters of the hydro-mechanical system formed the basis for the developed method of diagnostics of the processes of vortex formation.

An examination of the mechanisms for stable foam formation in activated sludge systems.

PubMed

Petrovski, Steve; Dyson, Zoe A; Quill, Eben S; McIlroy, Simon J; Tillett, Daniel; Seviour, Robert J

2011-02-01

Screening pure cultures of 65 mycolic acid producing bacteria (Mycolata) isolated mainly from activated sludge with a laboratory based foaming test revealed that not all foamed under the conditions used. However, for most, the data were generally consistent with the flotation theory as an explanation for foaming. Thus a stable foam required three components, air bubbles, surfactants and hydrophobic cells. With non-hydrophobic cells, an unstable foam was generated, and in the absence of surfactants, cells formed a greasy surface scum. Addition of surfactant converted a scumming population into one forming a stable foam. The ability to generate a foam depended on a threshold cell number, which varied between individual isolates and reduced markedly in the presence of surfactant. Consequently, the concept of a universal threshold applicable to all foaming Mycolata is not supported by these data. The role of surfactants in foaming is poorly understood, but evidence is presented for the first time that surfactin synthesised by Bacillus subtilis may be important. Copyright © 2010 Elsevier Ltd. All rights reserved.

Two-level schemes for the advection equation

NASA Astrophysics Data System (ADS)

Vabishchevich, Petr N.

2018-06-01

The advection equation is the basis for mathematical models of continuum mechanics. In the approximate solution of nonstationary problems it is necessary to inherit main properties of the conservatism and monotonicity of the solution. In this paper, the advection equation is written in the symmetric form, where the advection operator is the half-sum of advection operators in conservative (divergent) and non-conservative (characteristic) forms. The advection operator is skew-symmetric. Standard finite element approximations in space are used. The standard explicit two-level scheme for the advection equation is absolutely unstable. New conditionally stable regularized schemes are constructed, on the basis of the general theory of stability (well-posedness) of operator-difference schemes, the stability conditions of the explicit Lax-Wendroff scheme are established. Unconditionally stable and conservative schemes are implicit schemes of the second (Crank-Nicolson scheme) and fourth order. The conditionally stable implicit Lax-Wendroff scheme is constructed. The accuracy of the investigated explicit and implicit two-level schemes for an approximate solution of the advection equation is illustrated by the numerical results of a model two-dimensional problem.

In situ TEM observation of FCC Ti formation at elevated temperatures

DOE PAGES

Yu, Qian; Kacher, Josh; Gammer, Christoph; ...

2017-07-04

Pure Ti traditionally exhibits the hexagonal closed packed (HCP) crystallographic structure under ambient conditions and the body centered cubic (BCC) structure at elevated temperatures. In addition to these typical structures for Ti alloys, the presence of a face centered cubic (FCC) phase associated with thin films, interfaces, or high levels of plastic deformation has occasionally been reported. Here in this paper we show that small FCC precipitates form in freestanding thin foils during in situ transmission electron microscope (TEM) heating and we discuss the potential origins of the FCC phase in light of the in situ observations. This FCC phasemore » was found to be stable upon cooling and under ambient conditions, which allowed us to explore its mechanical properties and stability via nanomechanical in situ TEM testing. It was found that FCC platelets within the HCP matrix phase were stable under mechanical deformation and exhibited similar mechanical deformation behavior as the parent HCP phase.« less

In situ TEM observation of FCC Ti formation at elevated temperatures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yu, Qian; Kacher, Josh; Gammer, Christoph

Pure Ti traditionally exhibits the hexagonal closed packed (HCP) crystallographic structure under ambient conditions and the body centered cubic (BCC) structure at elevated temperatures. In addition to these typical structures for Ti alloys, the presence of a face centered cubic (FCC) phase associated with thin films, interfaces, or high levels of plastic deformation has occasionally been reported. Here in this paper we show that small FCC precipitates form in freestanding thin foils during in situ transmission electron microscope (TEM) heating and we discuss the potential origins of the FCC phase in light of the in situ observations. This FCC phasemore » was found to be stable upon cooling and under ambient conditions, which allowed us to explore its mechanical properties and stability via nanomechanical in situ TEM testing. It was found that FCC platelets within the HCP matrix phase were stable under mechanical deformation and exhibited similar mechanical deformation behavior as the parent HCP phase.« less

Tough Supramolecular Hydrogel Based on Strong Hydrophobic Interactions in a Multiblock Segmented Copolymer

PubMed Central

2017-01-01

We report the preparation and structural and mechanical characterization of a tough supramolecular hydrogel, based exclusively on hydrophobic association. The system consists of a multiblock, segmented copolymer of hydrophilic poly(ethylene glycol) (PEG) and hydrophobic dimer fatty acid (DFA) building blocks. A series of copolymers containing 2K, 4K, and 8K PEG were prepared. Upon swelling in water, a network is formed by self-assembly of hydrophobic DFA units in micellar domains, which act as stable physical cross-link points. The resulting hydrogels are noneroding and contain 75–92 wt % of water at swelling equilibrium. Small-angle neutron scattering (SANS) measurements showed that the aggregation number of micelles ranges from 2 × 102 to 6 × 102 DFA units, increasing with PEG molecular weight. Mechanical characterization indicated that the hydrogel containing PEG 2000 is mechanically very stable and tough, possessing a tensile toughness of 4.12 MJ/m3. The high toughness, processability, and ease of preparation make these hydrogels very attractive for applications where mechanical stability and load bearing features of soft materials are required. PMID:28469284

Pnma-BN: Another Boron Nitride Polymorph with Interesting Physical Properties

PubMed Central

Ma, Zhenyang; Han, Zheng; Liu, Xuhong; Yu, Xinhai; Wang, Dayun; Tian, Yi

2016-01-01

Structural, mechanical, electronic properties, and stability of boron nitride (BN) in Pnma structure were studied using first-principles calculations by Cambridge Serial Total Energy Package (CASTEP) plane-wave code, and the calculations were performed with the local density approximation and generalized gradient approximation in the form of Perdew–Burke–Ernzerhof. This BN, called Pnma-BN, contains four boron atoms and four nitrogen atoms buckled through sp3-hybridized bonds in an orthorhombic symmetry unit cell with Space group of Pnma. Pnma-BN is energetically stable, mechanically stable, and dynamically stable at ambient pressure and high pressure. The calculated Pugh ratio and Poisson’s ratio revealed that Pnma-BN is brittle, and Pnma-BN is found to turn brittle to ductile (~94 GPa) in this pressure range. It shows a higher mechanical anisotropy in Poisson’s ratio, shear modulus, Young’s modulus, and the universal elastic anisotropy index AU. Band structure calculations indicate that Pnma-BN is an insulator with indirect band gap of 7.18 eV. The most extraordinary thing is that the band gap increases first and then decreases with the increase of pressure from 0 to 60 GPa, and from 60 to 100 GPa, the band gap increases first and then decreases again. PMID:28336837

Formation and characterization of mullite fibers produced by inviscid melt-spinning

NASA Astrophysics Data System (ADS)

Xiao, Zhijun

IMS is a technique used to form fibers from low viscosity melts by means of stream stabilization in a reactant gas, in this case propane. Mullite (3Alsb2Osb3*2SiOsb2) was selected as the material to be fiberized. A stable mullite melt was obtained at 2000sp°C. Some short fibers and shot were formed in the fiber forming experiments. Crucible material selection is a prerequisite for proper application of the IMS technique. The effect of two crucible materials-graphite and boron nitride were studied. A carbothermal reaction occurred between the mullite melt and the graphite crucible. Boron nitride was selected as the crucible material because a relatively stable melt could be obtained. Operating environment is another factor that affects IMS mullite fiber formation. The effects of vacuum, nitrogen and argon on mullite melting behavior were studied. Argon gas was selected as the operating environment. A 2sp3 factorial design was developed to study the effect of such variables as temperature, holding time at the temperature, and heating rate on mullite melting behavior. The effects of the variables and interactions were calculated. Temperature has the biggest positive effect, holding time is the second, heating rate just has a very small negative effect. A detailed investigation of the mullite decomposition mechanism and kinetics was conducted in this work. A solid reaction mechanism was proposed. The kinetic results and IR analysis support the proposed mechanism. The carbon source inside the furnace led to the decomposition of mullite. A feasible experimental technique was developed to prevent the decomposition of mullite. The experiments with this design completely controlled the mullite decomposition. The short fibers, shot and some side products formed in the fiber forming experiments were characterized using XRD, XRF and SEM-EDS. The composition of the short fiber and shot was in the range of mullite composition. XRD showed that the diffraction pattern of shot is that of mullite.

Formation mechanism of the protective layer in a blast furnace hearth

NASA Astrophysics Data System (ADS)

Jiao, Ke-xin; Zhang, Jian-liang; Liu, Zheng-jian; Xu, Meng; Liu, Feng

2015-10-01

A variety of techniques, such as chemical analysis, scanning electron microscopy-energy dispersive spectroscopy, and X-ray diffraction, were applied to characterize the adhesion protective layer formed below the blast furnace taphole level when a certain amount of titanium- bearing burden was used. Samples of the protective layer were extracted to identify the chemical composition, phase assemblage, and distribution. Furthermore, the formation mechanism of the protective layer was determined after clarifying the source of each component. Finally, a technical strategy was proposed for achieving a stable protective layer in the hearth. The results show that the protective layer mainly exists in a bilayer form in the sidewall, namely, a titanium-bearing layer and a graphite layer. Both the layers contain the slag phase whose major crystalline phase is magnesium melilite (Ca2MgSi2O7) and the main source of the slag phase is coke ash. It is clearly determined that solid particles such as graphite, Ti(C,N) and MgAl2O4 play an important role in the formation of the protective layer, and the key factor for promoting the formation of a stable protective layer is reasonable control of the evolution behavior of coke.

Preparation and Relaxation of Very Stable Glassy States of a Simulated Liquid

NASA Astrophysics Data System (ADS)

Jack, Robert L.; Hedges, Lester O.; Garrahan, Juan P.; Chandler, David

2011-12-01

We prepare metastable glassy states in a model glass former made of Lennard-Jones particles by sampling biased ensembles of trajectories with low dynamical activity. These trajectories form an inactive dynamical phase whose “fast” vibrational degrees of freedom are maintained at thermal equilibrium by contact with a heat bath, while the “slow” structural degrees of freedom are located in deep valleys of the energy landscape. We examine the relaxation to equilibrium and the vibrational properties of these metastable states. The glassy states we prepare by our trajectory sampling method are very stable to thermal fluctuations and also more mechanically rigid than low-temperature equilibrated configurations.

Effects of volumetric expansion in molecular crystals: A quantum mechanical investigation on aspirin and paracetamol most stable polymorphs

NASA Astrophysics Data System (ADS)

Adhikari, Kapil; Flurchick, Kenneth M.; Valenzano, Loredana

2015-02-01

This work reports a study performed at hybrid semi-empirical density functional level (B3LYP-D2*) of the physico-chemical properties of aspirin (acetylsalicylic acid) and paracetamol (acetaminophen) in their most stable crystalline forms. It is shown how effects arising from volumetric expansions influence the properties of the materials. Structural, energetic, and vibrational properties are in good agreement with experimental values reported at temperatures far from 0 K. Results show that the proposed approach is reliable enough to reproduce effects of volumetric expansion on lattice energies and other measurable physico-chemical observables related to inter-molecular forces.

Reinforcement of single-walled carbon nanotube bundles by intertube bridging

NASA Astrophysics Data System (ADS)

Kis, A.; Csányi, G.; Salvetat, J.-P.; Lee, Thien-Nga; Couteau, E.; Kulik, A. J.; Benoit, W.; Brugger, J.; Forró, L.

2004-03-01

During their production, single-walled carbon nanotubes form bundles. Owing to the weak van der Waals interaction that holds them together in the bundle, the tubes can easily slide on each other, resulting in a shear modulus comparable to that of graphite. This low shear modulus is also a major obstacle in the fabrication of macroscopic fibres composed of carbon nanotubes. Here, we have introduced stable links between neighbouring carbon nanotubes within bundles, using moderate electron-beam irradiation inside a transmission electron microscope. Concurrent measurements of the mechanical properties using an atomic force microscope show a 30-fold increase of the bending modulus, due to the formation of stable crosslinks that effectively eliminate sliding between the nanotubes. Crosslinks were modelled using first-principles calculations, showing that interstitial carbon atoms formed during irradiation in addition to carboxyl groups, can independently lead to bridge formation between neighbouring nanotubes.

Metastability of isoformyl ions in collisions with helium and hydrogen. [in interstellar molecular clouds

NASA Technical Reports Server (NTRS)

Green, S.

1984-01-01

The stability of HOC(+) ions under conditions in interstellar molecular clouds is considered. In particular, the possibility that collisions with helium or hydrogen will induce isomerization to the stable HCO(+) form is examined theoretically. Portions of the electronic potential energy surfaces for interaction with He and H atoms are obtained from standard quantum mechanical calculations. Collisions with He atoms are found to be totally ineffective for inducing isomerization. Collisions with H atoms are found to be ineffective at low interstellar temperatures owing to a small (about 500 K) barrier in the entrance channel; at higher temperatures where this barrier can be overcome, however, collisions with hydrogen atoms do result in conversion to the stable HCO(+) form. Although detailed calculations are not presented, it is argued that low-energy collisions with H2 molecules are also ineffective in destroying the metastable ion.

Analysis of Subsurface Clathrates in the Upper Crust of Titan

NASA Technical Reports Server (NTRS)

Elliott, John

2011-01-01

Titan has an atmosphere rich in methane, which should have long since been depleted unless a mechanism exists for storing this molecule below the surface. One hypothesis is that methane could be stored in the form of a clathrate hydrate, which is a structure with an ice lattice forming molecular cages in which gases are trapped. It is stable at low temperatures and over a wide range of pressures, suggesting that a clathrate hydrate may have stored methane on Titan from the beginning of its history.

Monolithically Integrated, Mechanically Resilient Carbon-Based Probes for Scanning Probe Microscopy

NASA Technical Reports Server (NTRS)

Kaul, Anupama B.; Megerian, Krikor G.; Jennings, Andrew T.; Greer, Julia R.

2010-01-01

Scanning probe microscopy (SPM) is an important tool for performing measurements at the nanoscale in imaging bacteria or proteins in biology, as well as in the electronics industry. An essential element of SPM is a sharp, stable tip that possesses a small radius of curvature to enhance spatial resolution. Existing techniques for forming such tips are not ideal. High-aspect-ratio, monolithically integrated, as-grown carbon nanofibers (CNFs) have been formed that show promise for SPM applications by overcoming the limitations present in wet chemical and separate substrate etching processes.

(YIP-10) Enabling Dynamic Oxidation Mechanisms in Reverse Infiltrated Ultra-High Temperature Ceramic Coated C-C Composites for Application in Hypersonics

DTIC Science & Technology

2013-08-09

of Hf,Zr oxychloride hydrates, triethyl borate , and phenolic resin to form precipitate free sols that turn into stable gels with no catalyst addition...minutes, shows the glass -ceramic coating (that formed a shell upon cooling) was generated from within the UHTC filled C-C composite. Notice, in Figure...generation of the coating during high temperature exposure to oxygen. The formation of a ZrO2-SiO2 glass -ceramic coating on the C-C composite is believed to

Forming Different Planetary Architectures. I. The Formation Efficiency of Hot Jupiters from High-eccentricity Mechanisms

NASA Astrophysics Data System (ADS)

Wang, Ying; Zhou, Ji-lin; hui-gen, Liu; Meng, Zeyang

2017-10-01

Exoplanets discovered over the past decades have provided a new sample of giant exoplanets: hot Jupiters. For lack of enough materials in the current locations of hot Jupiters, they are perceived to form outside the snowline. Then, they migrate to the locations observed through interactions with gas disks or high-eccentricity mechanisms. We examined the efficiencies of different high-eccentricity mechanisms for forming hot Jupiters in near-coplanar multi-planet systems. These mechanisms include planet-planet scattering, the Kozai-Lidov mechanism, coplanar high-eccentricity migration, and secular chaos, as well as other two new mechanisms that we present in this work, which can produce hot Jupiters with high inclinations even in retrograde. We find that the Kozai-Lidov mechanism plays the most important role in producing hot Jupiters among these mechanisms. Secular chaos is not the usual channel for the formation of hot Jupiters due to the lack of an angular momentum deficit within {10}7{T}{in} (periods of the inner orbit). According to comparisons between the observations and simulations, we speculate that there are at least two populations of hot Jupiters. One population migrates into the boundary of tidal effects due to interactions with the gas disk, such as ups And b, WASP-47 b, and HIP 14810 b. These systems usually have at least two planets with lower eccentricities, and remain dynamically stable in compact orbital configurations. Another population forms through high-eccentricity mechanisms after the excitation of eccentricity due to dynamical instability. These kinds of hot Jupiters usually have Jupiter-like companions in distant orbits with moderate or high eccentricities.

Contact Sensor Attachment to Titanium Metal Composites

NASA Technical Reports Server (NTRS)

Vargas-Aburto, Carlos

1997-01-01

A Pd-13wt%Cr solid solution is a promising high-temperature strain gage alloy. In bulk form it has a number of properties that are desirable in a resistance strain gage material, such as a linear electrical-resistance-versus-temperature curve to 1000 C and stable electrical resistance in air at 1000 C. However, unprotected fine wire gages fabricated from this alloy perform well only to 600 C. At higher temperatures severe oxidation degrades their electrical performance. In this work Auger electron spectroscopy has been used to study the oxidation chemistry of the alloy wires and ribbons. Results indicate that the oxidation is caused by a complex mechanism that is not yet fully understood. As expected, during oxidation, a layer of chromium oxide is formed. This layer, however, forms beneath a layer of metallic palladium. The results of this study have increased the understanding of the oxidation mechanism of Pd-13wt%Cr.

Processing and characterization of Al-Al3Nb prepared by mechanical alloying and equal channel angular pressing

NASA Astrophysics Data System (ADS)

Chandran, P.; Zafari, A.; Lui, E. W.; Xia, K.

2017-05-01

Mechanically alloyed Al with immiscible elements such as Nb can lead to a uniform distribution of nanoscaled precipitates which are highly stable compared to conventional alloying and with excellent interface, resulting in significant increase in strength without problems associated with nano ceramic particles in metal matrix composites. Although immiscible, Nb can be alloyed with Al through mechanical milling, forming trialuminide (Al3Nb), either directly or upon subsequent precipitation, which possesses high strength, stiffness and stability at elevated temperatures. In the present study, Al-5 at.% Nb supersaturated solid solution was achieved after prolonged ball milling and nano Al3Nb precipitates were formed during subsequent ageing at 530°C. The Al-Al3Nb powder was consolidated by equal channel angular pressing (ECAP) at 400°C, resulting in a fully dense material with a uniform distribution of nanoscaled Al3Nb precipitates in the Al matrix.

Temporal Interactions between Cortical Rhythms

PubMed Central

Roopun, Anita K.; Kramer, Mark A.; Carracedo, Lucy M.; Kaiser, Marcus; Davies, Ceri H.; Traub, Roger D.; Kopell, Nancy J.; Whittington, Miles A.

2008-01-01

Multiple local neuronal circuits support different, discrete frequencies of network rhythm in neocortex. Relationships between different frequencies correspond to mechanisms designed to minimise interference, couple activity via stable phase interactions, and control the amplitude of one frequency relative to the phase of another. These mechanisms are proposed to form a framework for spectral information processing. Individual local circuits can also transform their frequency through changes in intrinsic neuronal properties and interactions with other oscillating microcircuits. Here we discuss a frequency transformation in which activity in two co-active local circuits may combine sequentially to generate a third frequency whose period is the concatenation sum of the original two. With such an interaction, the intrinsic periodicity in each component local circuit is preserved – alternate, single periods of each original rhythm form one period of a new frequency – suggesting a robust mechanism for combining information processed on multiple concurrent spatiotemporal scales. PMID:19225587

Fabrication of stable electrode/diffusion barrier layers for thermoelectric filled skutterudite devices

DOEpatents

Jie, Qing; Ren, Zhifeng; Chen, Gang

2015-12-08

Disclosed are methods for the manufacture of n-type and p-type filled skutterudite thermoelectric legs of an electrical contact. A first material of CoSi.sub.2 and a dopant are ball-milled to form a first powder which is thermo-mechanically processed with a second powder of n-type skutterudite to form a n-type skutterudite layer disposed between a first layer and a third layer of the doped-CoSi.sub.2. In addition, a plurality of components such as iron, and nickel, and at least one of cobalt or chromium are ball-milled form a first powder that is thermo-mechanically processed with a p-type skutterudite layer to form a p-type skutterudite layer "second layer" disposed between a first and a third layer of the first powder. The specific contact resistance between the first layer and the skutterudite layer for both the n-type and the p-type skutterudites subsequent to hot-pressing is less than about 10.0 .mu..OMEGA.cm.sup.2.

Fabrication of stable electrode/diffusion barrier layers for thermoelectric filled skutterudite devices

DOEpatents

Jie, Qing; Ren, Zhifeng; Chen, Gang

2017-08-01

Disclosed are methods for the manufacture of n-type and p-type filled skutterudite thermoelectric legs of an electrical contact. A first material of CoSi.sub.2 and a dopant are ball-milled to form a first powder which is thermo-mechanically processed with a second powder of n-type skutterudite to form a n-type skutterudite layer disposed between a first layer and a third layer of the doped-CoSi.sub.2. In addition, a plurality of components such as iron, and nickel, and at least one of cobalt or chromium are ball-milled form a first powder that is thermo-mechanically processed with a p-type skutterudite layer to form a p-type skutterudite layer "second layer" disposed between a first and a third layer of the first powder. The specific contact resistance between the first layer and the skutterudite layer for both the n-type and the p-type skutterudites subsequent to hot-pressing is less than about 10.0 .mu..OMEGA.cm.sup.2.

Determination of optimum processing temperature for transformation of glyceryl monostearate.

PubMed

Yajima, Toshio; Itai, Shigeru; Takeuchi, Hirofumi; Kawashima, Yoshiaki

2002-11-01

The purpose of this study was to clarify the mechanism of transformation from alpha-form to beta-form via beta'-form of glyceryl monostearate (GM) and to determine the optimum conditions of heat-treatment for physically stabilizing GM in a pharmaceutical formulation. Thermal analysis repeated twice using a differential scanning calorimeter (DSC) were performed on mixtures of two crystal forms. In the first run (enthalpy of melting: DeltaH1), two endothermic peaks of alpha-form and beta-form were observed. However, in the second run (enthalpy of melting: DeltaH2), only the endothermic peak of the alpha-form was observed. From a strong correlation observed between the beta-form content in the mixture of alpha-form and beta-form and the enthalpy change, (DeltaH1-DeltaH2)/DeltaH2, beta-form content was expressed as a function of the enthalpy change. Using this relation, the stable beta-form content during the heat-treatment could be determined, and the maximum beta-form content was obtained when the heat-treatment was carried out at 50 degrees C. An inflection point existed in the time course of transformation of alpha-form to beta-form. It was assumed that almost all of alpha-form transformed to beta'-form at this point, and that subsequently only transformation from beta'-form to beta-form occurred. Based on this aspect, the transformation rate equations were derived as consecutive reaction. Experimental data coincided well with the theoretical curve. In conclusion, GM was transformed in the consecutive reaction, and 50 degrees C was the optimum heat-treatment temperature for transforming GM from the alpha-form to the stable beta-form.

Methane formation from the hydrogenation of carbon dioxide on Ni(110) surface--a density functional theoretical study.

PubMed

Bothra, Pallavi; Periyasamy, Ganga; Pati, Swapan K

2013-04-21

The complete hydrogenation mechanisms of CO2 are explored on Ni(110) surface catalyst using density functional theory. We have studied the possible hydrogenation mechanism to form product methane from the stable adsorption-co-adsorption intermediates of CO2 and H2 on Ni(110) surface. Our computations clearly elucidate that the mechanism for the formation of methyl, methoxy and methane moieties from carbon dioxide on the nickel catalyst. Moreover, our studies clearly show that the methane formation via hydroxyl carbonyl intermediate requires a lower energy barrier than via carbon monoxide and formate intermediates on the Ni(110) surface.

Computer-Based Methods for Thermodynamic Analysis of Materials Processing.

DTIC Science & Technology

1983-11-30

metallic alloys (12,13), silicides (14),and oxynitride * . systems (15). - . 2. Thermochemical System Employed to Characterize Binary Ill-V Phase Diagrams The...reference to Figure I shows that the stable form of RbF is the sodium chloride S form. Table I shows that OGH -oS -RFRFLS-RFRFLM-12866-.381T J/g.at. (5...KF, BF=(I/3)8aF LF-(I/4)LaF3V PF-(113)PbF 2 S- Sodium Chloride Structures Stable form of NF, KE, RE and (;F L-Liquid, M-Stable form of ZF, KeStable form

SiC Composite for Fuel Structure Applications

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yueh, Ken

Extensive evaluation was performed to determine the suitability of using SiC composite as a boiling water reactor (BWR) fuel channel material. A thin walled SiC composite box, 10 cm in dimension by approximately 1.5 mm wall thickness was fabricated using chemical vapor deposition (CVD) for testing. Mechanical test results and performance evaluations indicate the material could meet BWR channel mechanical design requirement. However, large mass loss of up to 21% was measured in in-pile corrosion test under BWR-like conditions in under 3 months of irradiation. A fresh sister sample irradiated in a follow-up cycle under PWR conditions showed no measureablemore » weight loss and thus supports the hypothesis that the oxidizing condition of the BWR-like coolant chemistry was responsible for the high corrosion rate. A thermodynamic evaluation showed SiC is not stable and the material may oxidize to form SiO 2 and CO 2. Silica has demonstrated stability in high temperature steam environment and form a protective oxide layer under severe accident conditions. However, it does not form a protective layer in water under normal BWR operational conditions due to its high solubility. Corrosion product stabilization by modifying the SiC CVD surface is an approach evaluated in this study to mitigate the high corrosion rate. Titanium and zirconium have been selected as stabilizing elements since both TiSiO 4 and ZrSiO 4 are insoluble in water. Corrosion test results in oxygenated water autoclave indicate TiSiO4 does not form a protective layer. However, zirconium doped test samples appear to form a stable continuous layer of ZrSiO 4 during the corrosion process. Additional process development is needed to produce a good ZrSiC coating to verify functionality of the mitigation concept.« less

Acoustic Cavitation and Bubble Dynamics.

DTIC Science & Technology

1985-06-15

Ultrasound : Chemical, Physical and Biological Effects by Verlag Chemie International, Inc. FORM I47 EDTOO NOV 65 ISOBSOLETE DD , 3 1473 EDITION OF I...SUnclassified S/N 0102- LF-014-6601 SECURITY CLASSIFICATION OF THIS PAGE (When Date Entered) I ULTRASOUND : CHEMICAL, PHYSICAL, AND BIOLOGICAL EFFECTS CHAPTER...stable cavitation. The topic of this chapter, acoustic cavitation, is but one of several possible mechanisms through which ultrasound can interact with a

Tris(trimethylsilyl) Phosphite as an Efficient Electrolyte Additive To Improve the Surface Stability of Graphite Anodes.

PubMed

Yim, Taeeun; Han, Young-Kyu

2017-09-27

Tris(trimethylsilyl) phosphite (TMSP) has received considerable attention as a functional additive for various cathode materials in lithium-ion batteries, but the effect of TMSP on the surface stability of a graphite anode has not been studied. Herein, we demonstrate that TMSP serves as an effective solid electrolyte interphase (SEI)-forming additive for graphite anodes in lithium-ion batteries (LIBs). TMSP forms SEI layers by chemical reactions between TMSP and a reductively decomposed ethylene carbonate (EC) anion, which is strikingly different from the widely known mechanism of the SEI-forming additives. TMSP is stable under cathodic polarization, but it reacts chemically with radical anion intermediates derived from the electrochemical reduction of the carbonate solvents to generate a stable SEI layer. These TMSP-derived SEI layers improve the interfacial stability of the graphite anode, resulting in a retention of 96.8% and a high Coulombic efficiency of 95.2%. We suggest the use of TMSP as a functional additive that effectively stabilizes solid electrolyte interfaces of both the anode and cathode in lithium-ion batteries.

Cell biology of aluminum toxicity and tolerance in higher plants.

PubMed

Matsumoto, H

2000-01-01

Aluminum is the major element in the soil and exists as a stable complex with oxygen and silicate in neutral and weakly acidic soil. When the soil pH is lower than 4.5-5.0, Al is solubilized in the soil water and absorbed by plant roots. Absorbed Al inhibits root elongation severely, and the elongation of roots exposed to Al3+ as low as mumol level is inhibited within an hour(s). Thus much research has been conducted to understand the mechanism of Al toxicity and tolerance. Al is located specifically at the root apex. Al-sensitive plants absorb more Al than do Al-tolerant plants, and thus the exclusion mechanism of Al is the major idea for Al tolerance. The understanding of Al stress in plants is important for stable food production in future. Al is a complicated ion in its chemical form and biological function. In this chapter, mechanisms of Al toxicity and tolerance proposed during the past few decades as well as future topics are described from physiological and molecular points of view.

Acupressure Improves the Weaning Indices of Tidal Volumes and Rapid Shallow Breathing Index in Stable Coma Patients Receiving Mechanical Ventilation: Randomized Controlled Trial

PubMed Central

Maa, Suh-Hwa; Wang, Chiu-Hua; Hsu, Kuang-Hung; Lin, Horng-Chyuan; Yee, Brian; MacDonald, Karen

2013-01-01

Background. Acupressure has been shown to improve respiratory parameters. We investigated the effects of acupressure on weaning indices in stable coma patients receiving mechanical ventilation. Methods. Patients were randomly allocated to one of three treatments: standard care with adjunctive acupressure on one (n = 32) or two days (n = 31) and standard care (n = 31). Acupressure in the form of 10 minutes of bilateral stimulation at five acupoints was administered per treatment session. Weaning indices were collected on two days before, right after, and at 0.5 hrs, 1 hr, 1.5 hrs, 2 hrs, 2.5 hrs, 3 hrs, 3.5 hrs, and 4 hrs after the start of treatment. Results. There were statistically significant improvements in tidal volumes and index of rapid shallow breathing in the one-day and two-day adjunctive acupressure study arms compared to the standard care arm immediately after acupressure and persisting until 0.5, 1 hr, and 2 hrs after adjustment for covariates. Conclusions. In the stable ventilated coma patient, adjunctive acupressure contributes to improvements in tidal volumes and the index of rapid shallow breathing, the two indices most critical for weaning patients from mechanical ventilation. These effects tend to be immediate and likely to be sustained for 1 to 2 hours. PMID:23710234

Bulk Al-Al3Zr composite prepared by mechanical alloying and hot extrusion for high-temperature applications

NASA Astrophysics Data System (ADS)

Pourkhorshid, E.; Enayati, M. H.; Sabooni, S.; Karimzadeh, F.; Paydar, M. H.

2017-08-01

Bulk Al/Al3Zr composite was prepared by a combination of mechanical alloying (MA) and hot extrusion processes. Elemental Al and Zr powders were milled for up to 10 h and heat treated at 600°C for 1 h to form stable Al3Zr. The prepared Al3Zr powder was then mixed with the pure Al powder to produce an Al-Al3Zr composite. The composite powder was finally consolidated by hot extrusion at 550°C. The mechanical properties of consolidated samples were evaluated by hardness and tension tests at room and elevated temperatures. The results show that annealing of the 10-h-milled powder at 600°C for 1 h led to the formation of a stable Al3Zr phase. Differential scanning calorimetry (DSC) results confirmed that the formation of Al3Zr began with the nucleation of a metastable phase, which subsequently transformed to the stable tetragonal Al3Zr structure. The tension yield strength of the Al-10wt%Al3Zr composite was determined to be 103 MPa, which is approximately twice that for pure Al (53 MPa). The yield stress of the Al/Al3Zr composite at 300°C is just 10% lower than that at room temperature, which demonstrates the strong potential for the prepared composite to be used in high-temperature structural applications.

Pathways and intermediates in forced unfolding of spectrin repeats.

PubMed

Altmann, Stephan M; Grünberg, Raik G; Lenne, Pierre-François; Ylänne, Jari; Raae, Arnt; Herbert, Kristina; Saraste, Matti; Nilges, Michael; Hörber, J K Heinrich

2002-08-01

Spectrin repeats are triple-helical coiled-coil domains found in many proteins that are regularly subjected to mechanical stress. We used atomic force microscopy technique and steered molecular dynamics simulations to study the behavior of a wild-type spectrin repeat and two mutants. The experiments indicate that spectrin repeats can form stable unfolding intermediates when subjected to external forces. In the simulations the unfolding proceeded via a variety of pathways. Stable intermediates were associated to kinking of the central helix close to a proline residue. A mutant stabilizing the central helix showed no intermediates in experiments, in agreement with simulation. Spectrin repeats may thus function as elastic elements, extendable to intermediate states at various lengths.

Transport and Transformation of Selenium and Other Constituents of Flue-Gas Desulfurization Wastewater in Water-Saturated Soil Materials.

PubMed

Galkaduwa, Madhubhashini B; Hettiarachchi, Ganga M; Kluitenberg, Gerard J; Hutchinson, Stacy L; Davis, Lawrence; Erickson, Larry E

2017-03-01

Constructed wetland treatment systems are used to remove selenium (Se) from flue-gas desulfurization (FGD) wastewater (WW). However, direct confirmation of the mechanism responsible for FGD WW Se retention in soil is lacking. A laboratory-based soil column study was performed to develop an evidence-based mechanism of Se retention and to study the behavior and the retention capacity of FGD WW constituents in water-saturated soil. A deoxygenated 1:1 mixture of FGD WW and raw water was delivered to the columns bottom-up at a flux of 1.68 cm d for 100 d. Some of the columns were flushed with the raw water at the same rate for an additional 100 d. Column effluent was analyzed for constituents of concern. Results showed a complete retention of FGD WW Se in the soil materials. Boron and fluorine were partially retained; however, sulfur, sodium, and chlorine retention was poor, agreeing with field observations. The FGD WW Se was retained in soil near the inlet end of the columns, indicating its limited mobility under reduced conditions. Sequential extraction procedure revealed that retained Se was mainly sequestered as stable/residual forms. Bulk- and micro-X-ray absorption near-edge structure spectroscopy confirmed that Se was mainly retained as reduced/stable species [Se(IV), organic Se, and Se(0)]. This study provides direct evidence for FGD WW Se retention in water-saturated soil via the transformation of oxidized Se into reduced/stable forms. Copyright © by the American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America, Inc.

Field Theoretic Study of Bilayer Membrane Fusion. I. Hemifusion Mechanism

PubMed Central

Katsov, K.; Müller, M.; Schick, M.

2004-01-01

Self-consistent field theory is used to determine structural and energetic properties of metastable intermediates and unstable transition states involved in the standard stalk mechanism of bilayer membrane fusion. A microscopic model of flexible amphiphilic chains dissolved in hydrophilic solvent is employed to describe these self-assembled structures. We find that the barrier to formation of the initial stalk is much smaller than previously estimated by phenomenological theories. Therefore its creation it is not the rate-limiting process. The relevant barrier is associated with the rather limited radial expansion of the stalk into a hemifusion diaphragm. It is strongly affected by the architecture of the amphiphile, decreasing as the effective spontaneous curvature of the amphiphile is made more negative. It is also reduced when the tension is increased. At high tension the fusion pore, created when a hole forms in the hemifusion diaphragm, expands without bound. At very low membrane tension, small fusion pores can be trapped in a flickering metastable state. Successful fusion is severely limited by the architecture of the lipids. If the effective spontaneous curvature is not sufficiently negative, fusion does not occur because metastable stalks, whose existence is a seemingly necessary prerequisite, do not form at all. However if the spontaneous curvature is too negative, stalks are so stable that fusion does not occur because the system is unstable either to a phase of stable radial stalks, or to an inverted-hexagonal phase induced by stable linear stalks. Our results on the architecture and tension needed for successful fusion are summarized in a phase diagram. PMID:15326031

Adsorption mechanisms of metal ions on the potassium dihydrogen phosphate (1 0 0) surface: A density functional theory-based investigation.

PubMed

Wu, Yulin; Zhang, Lei; Liu, Yao; Qu, Yunpeng

2018-07-15

The adsorption of metal ions (K + , Na + , Ca 2+ , Cu 2+ , Al 3+ , Cr 3+ ) on the (1 0 0) surface of potassium dihydrogen phosphate (KDP) has been studied using density functional theory (DFT). Calculation results show that all the investigated metal ions can be spontaneously adsorbed on the surface with negative adsorption energies. The adsorption stability increases in the order of Na +  < K +  < Cu 2+  < Ca 2+  < Al 3+  < Cr 3+ , and shows a consistent trend as the adsorbed metal ion valence (monovalent < divalent < trivalent). Three types of stable adsorption configurations are observed, corresponding to three different bonding mechanisms. Na + , K + and Ca 2+ ions with a large radius can form two ionic bonds and one weak covalent bond with the O and H atoms respectively. In addition, the medium-sized ion of Cu 2+ forms two covalent bonds with the O and H atoms. Furthermore, Al 3+ and Cr 3+ ions with the smallest radius form two metal-oxygen and one metal-hydrogen covalent bonds with the surface, making one H-O bond broken. Compared with other metal ions, Al 3+ and Cr 3+ have the strongest interactions with the surface, which can be explained by the significant electron transfer and more stable covalent bond formations between these two ions and the surface. Copyright © 2018 Elsevier Inc. All rights reserved.

Development of form stable Poly(methyl methacrylate) (PMMA) coated thermal phase change material for solar water heater applications

NASA Astrophysics Data System (ADS)

Munusamy, Y.; Shanmugam, S.; Shi-Ying, Kee

2018-04-01

Phase change material (PCM) is one of the most popular and widely used thermal energy storage material in solar water heater because it able to absorb and release a large amount of latent heat during a phase change process over a narrow temperature range. However the practical application of PCM is limited by two major issues; 1) leakage which leads to material loss and corrosion of tank and 2) large volume change during phase change process which cause pressure build up in the tank. In this work, form-stable PCM was prepared by coating myristic acid with Poly(methyl methacrylate) (PMMA) to prevent leakage of PCM. PMMA was mixed with different weight percentage (0.1, 0.2, 0.3, 0.4 and 0.5 wt%) of dicumyl peroxide (DCP). The purpose of adding DCP to PMMA is to crosslink the polymer and to increase the mechanical strength of PMMA to hold the myristic acid content inside the coating during the phase change process. Leakage test results showed that PMMA mixed with 0.1% DCP exhibit 0% leakage. This result is further supported by Field Emission Scanning Electron Microscopy (FESEM) images and Fourier transform infrared spectroscopy (FTIR) analysis results, where a compact and uniform coating without cracks were formed for PCM coated with PMMA with 0.1% DCP. Differential scanning calorimetry (DSC) results shows that the melting point of form-stable PCM is 55°C, freezing point is 50°C, the latent heat of melting and freezing is 67.59 J/g.

Microstructural Evolution of Ni-Sn Transient Liquid Phase Sintering Bond during High-Temperature Aging

NASA Astrophysics Data System (ADS)

Feng, Hongliang; Huang, Jihua; Peng, Xianwen; Lv, Zhiwei; Wang, Yue; Yang, Jian; Chen, Shuhai; Zhao, Xingke

2018-05-01

For high-temperature-resistant packaging of new generation power chip, a chip packaging simulation structure of Ni/Ni-Sn/Ni was bonded by a transient liquid-phase sintering process. High-temperature aging experiments were carried out to investigate joint heat stability. The microstructural evolution and mechanism during aging, and mechanical properties after aging were analyzed. The results show that the 30Ni-70Sn bonding layer as-bonded at 340°C for 240 min is mainly composed of Ni3Sn4 and residual Ni particles. When aged at 350°C, because of the difficulty of nucleation for Ni3Sn and quite slow growth of Ni3Sn2, the bonding layer is stable and the strength of that doesn't change obviously with aging time. When aging temperature increased to 500°C, however, the residual Ni particles were gradually dissolved and the bonding layer formed a stable structure with dominated Ni3Sn2 after 36 h. Meanwhile, due to the volume shrinkage (4.43%) from Ni3Sn2 formation, a number of voids were formed. The shear strength shows an increase, resulting from Ni3Sn2 formation, but then it decreases slightly caused by voids. After aging at 500°C for 100 h, shear strength is still maintained at 29.6 MPa. In addition, the mechanism of void formation was analyzed and microstructural evolution model was also established.

Mechanisms of Forming Intergranular Microcracks and Microscopic Surface Discontinuities in Welds

DTIC Science & Technology

1992-06-01

SCC) is defined as slow stable crack extension occurring under static loading in sea water at stress intensity values below KIc (critical stress...preheating on the cold cracking resistance is reflected mainly in a reduction of the degree of localization of microplastic strains, their...deconcentration and an increase of the basis over which microplastic yielding takes place. This increases the amount of energy used for local plastic deformation

Stability branching induced by collective atomic recoil in an optomechanical ring cavity

NASA Astrophysics Data System (ADS)

Ian, Hou

2017-02-01

In a ring cavity filled with an atomic condensate, self-bunching of atoms due to the cavity pump mode produce an inversion that re-emits into the cavity probe mode with an exponential gain, forming atomic recoil lasing. An optomechanical ring cavity is formed when one of the reflective mirrors is mounted on a mechanical vibrating beam. In this paper, we extend studies on the stability of linear optomechanical cavities to such ring cavities with two counter-propagating cavity modes, especially when the forward propagating pump mode is taken to its weak coupling limit. We find that when the atomic recoil is in action, stable states of the mechanical mode of the mirror converge into branch cuts, where the gain produced by the recoiling strikes balance with the multiple decay sources, such as cavity leakage in the optomechanical system. This balance is obtained when the propagation delay in the dispersive atomic medium matches in a periodic pattern to the frequencies and linewidths of the cavity mode and the collective bosonic mode of the atoms. We show an input-output hysteresis cycle between the atomic mode and the cavity mode to verify the multi-valuation of the stable states after branching at the weak coupling limit.

Principles of an enhanced MBR-process with mechanical cleaning.

PubMed

Rosenberger, S; Helmus, F P; Krause, S; Bareth, A; Meyer-Blumenroth, U

2011-01-01

Up to date, different physical and chemical cleaning protocols are necessary to limit membrane fouling in membrane bioreactors. This paper deals with a mechanical cleaning process, which aims at the avoidance of hypochlorite and other critical chemicals in MBR with submerged flat sheet modules. The process basically consists of the addition of plastic particles into the loop circulation within submerged membrane modules. Investigations of two pilot plants are presented: Pilot plant 1 is equipped with a 10 m(2) membrane module and operated with a translucent model suspension; pilot plant 2 is equipped with four 50 m(2) membrane modules and operated with pretreated sewage. Results of pilot plant 1 show that the establishment of a fluidised bed with regular particle distribution is possible for a variety of particles. Particles with maximum densities of 1.05 g/cm(3) and between 3 and 5 mm diameter form a stable fluidised bed almost regardless of activated sludge concentration, viscosity and reactor geometry. Particles with densities between 1.05 g/cm(3) and 1.2 g/cm(3) form a stable fluidised bed, if the velocity at the reactor bottom is sufficiently high. Activities within pilot plant 2 focused on plant optimisation and the development of an adequate particle retention system.

Axial interaction free-electron laser

DOEpatents

Carlsten, Bruce E.

1997-01-01

Electron orbits from a helical axial wiggler in an axial guide field are absolutely unstable as power is extracted from the particles. For off-axis beams an axial FEL mechanism exists when the axial electric field in a TM mode is wiggled to interact with the axial velocity of the electrons that form the beam. The interaction strength is comparable to that for helical FELs and is insensitive to beam orbit errors. The orbits for this mechanism are extremely stable in the absence of space charge and lead to high extraction efficiencies without particle phasing incoherence or interception. This interaction mechanism is suitable for use with intense annular electron beams for high power generation at microwave frequencies.

Axial interaction free-electron laser

DOEpatents

Carlsten, B.E.

1997-09-02

Electron orbits from a helical axial wiggler in an axial guide field are absolutely unstable as power is extracted from the particles. For off-axis beams an axial FEL mechanism exists when the axial electric field in a TM mode is wiggled to interact with the axial velocity of the electrons that form the beam. The interaction strength is comparable to that for helical FELs and is insensitive to beam orbit errors. The orbits for this mechanism are extremely stable in the absence of space charge and lead to high extraction efficiencies without particle phasing incoherence or interception. This interaction mechanism is suitable for use with intense annular electron beams for high power generation at microwave frequencies. 5 figs.

Structure, phase transformations, mechanical characteristics, and cold resistance of low-carbon martensitic steels

NASA Astrophysics Data System (ADS)

Kozvonin, V. A.; Shatsov, A. A.; Ryaposov, I. V.; Zakirova, M. G.; Generalova, K. N.

2016-08-01

Temper-resistant low-carbon Cr-Mn-Ni-Mo-V-Nb steels with concentrations of carbon of 0.15 and 0.27 wt % have been studied. It has been shown that, upon quenching, various morphological types of the α phase can be formed. The structure of the steels is stable in the course of heating below critical temperatures and remains a lath-type structure in the intercritical temperature range. Specific features of structural and phase transformations, as well as the dependence of the mechanical characteristics of the steels, on the tempering temperature have been determined.

A rare case of prosthetic endocarditis and dehiscence in a mechanical valved conduit

PubMed Central

Kannan, Arun; Smith, Cristy; Subramanian, Sreekumar; Janardhanan, Rajesh

2014-01-01

A middle-aged adult patient with a history of aortic root replacement with a mechanical valved conduit and remote chest trauma was referred to our institution with prosthetic endocarditis. Transoesophageal echocardiogram at our institution confirmed a near-complete dehiscence of the prosthetic aortic valve from the conduit, with significant perivalvular flow forming a pseudoaneurysm. The patient underwent a high-risk re-operation, involving redo aortic root replacement with a homograft after extensive debridement of the infected tissue. The patient was discharged to an outside facility after an uncomplicated hospital course, and remains stable. PMID:24510692

A rare case of prosthetic endocarditis and dehiscence in a mechanical valved conduit.

PubMed

Kannan, Arun; Smith, Cristy; Subramanian, Sreekumar; Janardhanan, Rajesh

2014-02-07

A middle-aged adult patient with a history of aortic root replacement with a mechanical valved conduit and remote chest trauma was referred to our institution with prosthetic endocarditis. Transoesophageal echocardiogram at our institution confirmed a near-complete dehiscence of the prosthetic aortic valve from the conduit, with significant perivalvular flow forming a pseudoaneurysm. The patient underwent a high-risk re-operation, involving redo aortic root replacement with a homograft after extensive debridement of the infected tissue. The patient was discharged to an outside facility after an uncomplicated hospital course, and remains stable.

Characteristics and Corrosion Behavior of Pure Titanium Subjected to Surface Mechanical Attrition

NASA Astrophysics Data System (ADS)

Fu, Tianlin; Wang, Xiao; Liu, Jianxiong; Li, Li; Yu, Xiaohua; Zhan, Zhaolin

2017-10-01

A stable passive film exhibiting good corrosion resistance in a 3.5 wt.% NaCl solution was formed on the surface of pure titanium (Ti) subjected to a surface mechanical attrition treatment (SMAT). The corrosion potential (-0.21 V) of the film was significantly higher than that (-0.92 V) of the untreated sample. Moreover, the corrosion current density was an order of magnitude lower than that of the untreated sample. SMAT resulted in a decrease in the vacancy condensation in the TiO2 film, thereby inhibiting the invasion and diffusion of Cl- in the film.

Studies on the kinetics of killing and the proposed mechanism of action of microemulsions against fungi.

PubMed

Al-Adham, Ibrahim S I; Ashour, Hana; Al-Kaissi, Elham; Khalil, Enam; Kierans, Martin; Collier, Phillip J

2013-09-15

Microemulsions are physically stable oil/water clear dispersions, spontaneously formed and thermodynamically stable. They are composed in most cases of water, oil, surfactant and cosurfactant. Microemulsions are stable, self-preserving antimicrobial agents in their own right. The observed levels of antimicrobial activity associated with microemulsions may be due to the direct effect of the microemulsions themselves on the bacterial cytoplasmic membrane. The aim of this work is to study the growth behaviour of different microbes in presence of certain prepared physically stable microemulsion formulae over extended periods of time. An experiment was designed to study the kinetics of killing of a microemulsion preparation (17.3% Tween-80, 8.5% n-pentanol, 5% isopropyl myristate and 69.2% sterile distilled water) against selected test microorganisms (Candida albicans, Aspergillus niger, Schizosaccharomyces pombe and Rhodotorula spp.). Secondly, an experiment was designed to study the effects of the microemulsion preparation on the cytoplasmic membrane structure and function of selected fungal species by observation of 260 nm component leakage. Finally, the effects of the microemulsion on the fungal membrane structure and function using S. pombe were studied using transmission electron microscopy. The results showed that the prepared microemulsions are stable, effective antimicrobial systems with effective killing rates against C. albicans, A. niger, S. pombe and Rhodotorula spp. The results indicate a proposed mechanism of action of significant anti-membrane activity, resulting in the gross disturbance and dysfunction of the cytoplasmic membrane structure which is followed by cell wall modifications, cytoplasmic coagulation, disruption of intracellular metabolism and cell death. Copyright © 2013 Elsevier B.V. All rights reserved.

Kinetics and Mechanism of Bioactivation via S-Oxygenation of Anti-Tubercular Agent Ethionamide by Peracetic Acid.

PubMed

Chipiso, Kudzanai; Logan, Isabelle E; Eskew, Matthew W; Omondi, Benard; Simoyi, Reuben H

2016-10-11

The kinetics and mechanism of the oxidation of the important antitubercular agent, ethionamide, ETA (2-ethylthioisonicotinamide), by peracetic acid (PAA) have been studied. It is effectively a biphasic reaction with an initial rapid first phase of the reaction which is over in about 5 s and a second slower phase of the reaction which can run up to an hour. The first phase involves the addition of a single oxygen atom to ethionamide to form the S-oxide. The second phase involves further oxidation of the S-oxide to desulfurization of ETA to give 2-ethylisonicotinamide. In contrast to the stability of most organosulfur compounds, the S-oxide of ETA is relatively stable and can be isolated. In conditions of excess ETA, the stoichiometry of the reaction was strictly 1:1: CH 3 CO 3 H + Et(C 5 H 4 )C(═S)NH 2 → CH 3 CO 2 H + Et(C 5 H 4 )C(═NH)SOH. In this oxidation, it was apparent that only the sulfur center was the reactive site. Though ETA was ultimately desulfurized, only the S-oxide was stable. Electrospray ionization (ESI) spectral analysis did not detect any substantial formation of the sulfinic and sulfonic acids. This suggests that cleavage of the carbon-sulfur bond occurs at the sulfenic acid stage, resulting in the formation of an unstable sulfur species that can react further to form more stable sulfur species. In this oxidation, no sulfate formation was observed. ESI spectral analysis data showed a final sulfur species in the form of a dimeric sulfur monoxide species, H 3 S 2 O 2 . We derived a bimolecular rate constant for the formation of the S-oxide of (3.08 ± 0.72) × 10 2 M -1 s -1 . Oxidation of the S-oxide further to give 2-ethylisonicotinamide gave zero order kinetics.

Formation and stabilization of nanoemulsion-based vitamin E delivery systems using natural biopolymers: Whey protein isolate and gum arabic.

PubMed

Ozturk, Bengu; Argin, Sanem; Ozilgen, Mustafa; McClements, David Julian

2015-12-01

Natural biopolymers, whey protein isolate (WPI) and gum arabic (GA), were used to fabricate emulsion-based delivery systems for vitamin E-acetate. Stable delivery systems could be formed when vitamin E-acetate was mixed with sufficient orange oil prior to high pressure homogenization. WPI (d32=0.11 μm, 1% emulsifier) was better than GA (d32=0.38 μm, 10% emulsifier) at producing small droplets at low emulsifier concentrations. However, WPI-stabilized nanoemulsions were unstable to flocculation near the protein isoelectric point (pH 5.0), at high ionic strength (>100mM), and at elevated temperatures (>60 °C), whereas GA-stabilized emulsions were stable. This difference was attributed to differences in emulsifier stabilization mechanisms: WPI by electrostatic repulsion; GA by steric repulsion. These results provide useful information about the emulsifying and stabilizing capacities of natural biopolymers for forming food-grade vitamin-enriched delivery systems. Copyright © 2015 Elsevier Ltd. All rights reserved.

Self-organizing layers from complex molecular anions

DOE PAGES

Warneke, Jonas; McBriarty, Martin E.; Riechers, Shawn L.; ...

2018-05-14

The formation of traditional ionic materials occurs principally via joint accumulation of both anions and cations. Here in this paper, we describe a previously unreported phenomenon by which macroscopic liquid-like thin layers with tunable self-organization properties form through accumulation of stable complex ions of one polarity on surfaces. Using a series of highly stable molecular anions we demonstrate a strong influence of the internal charge distribution of the molecular ions, which is usually shielded by counterions, on the properties of the layers. Detailed characterization reveals that the intrinsically unstable layers of anions on surfaces are stabilized by simultaneous accumulation ofmore » neutral molecules from the background environment. Different phases, self-organization mechanisms and optical properties are observed depending on the molecular properties of the deposited anions, the underlying surface and the coadsorbed neutral molecules. This demonstrates rational control of the macroscopic properties (morphology and size of the formed structures) of the newly discovered anion-based layers.« less

Self-organizing layers from complex molecular anions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Warneke, Jonas; McBriarty, Martin E.; Riechers, Shawn L.

The formation of traditional ionic materials occurs principally via joint accumulation of both anions and cations. Here in this paper, we describe a previously unreported phenomenon by which macroscopic liquid-like thin layers with tunable self-organization properties form through accumulation of stable complex ions of one polarity on surfaces. Using a series of highly stable molecular anions we demonstrate a strong influence of the internal charge distribution of the molecular ions, which is usually shielded by counterions, on the properties of the layers. Detailed characterization reveals that the intrinsically unstable layers of anions on surfaces are stabilized by simultaneous accumulation ofmore » neutral molecules from the background environment. Different phases, self-organization mechanisms and optical properties are observed depending on the molecular properties of the deposited anions, the underlying surface and the coadsorbed neutral molecules. This demonstrates rational control of the macroscopic properties (morphology and size of the formed structures) of the newly discovered anion-based layers.« less

Real-time imaging of Huntingtin aggregates diverting target search and gene transcription

PubMed Central

Li, Li; Liu, Hui; Dong, Peng; Li, Dong; Legant, Wesley R; Grimm, Jonathan B; Lavis, Luke D; Betzig, Eric; Tjian, Robert; Liu, Zhe

2016-01-01

The presumptive altered dynamics of transient molecular interactions in vivo contributing to neurodegenerative diseases have remained elusive. Here, using single-molecule localization microscopy, we show that disease-inducing Huntingtin (mHtt) protein fragments display three distinct dynamic states in living cells – 1) fast diffusion, 2) dynamic clustering and 3) stable aggregation. Large, stable aggregates of mHtt exclude chromatin and form 'sticky' decoy traps that impede target search processes of key regulators involved in neurological disorders. Functional domain mapping based on super-resolution imaging reveals an unexpected role of aromatic amino acids in promoting protein-mHtt aggregate interactions. Genome-wide expression analysis and numerical simulation experiments suggest mHtt aggregates reduce transcription factor target site sampling frequency and impair critical gene expression programs in striatal neurons. Together, our results provide insights into how mHtt dynamically forms aggregates and disrupts the finely-balanced gene control mechanisms in neuronal cells. DOI: http://dx.doi.org/10.7554/eLife.17056.001 PMID:27484239

Study of crystallization mechanisms of Fe nanoparticle

NASA Astrophysics Data System (ADS)

Kien, P. H.; Trang, G. T. T.; Hung, P. K.

2017-06-01

In this paper, the nanoparticle (NP) Fe was investigated by means of molecular dynamics simulation. The crystallization mechanism was studied through the time evolution of crystal cluster and potential energies of different atom types. The simulation shows that the NP was crystallized into bcc crystal structure when it was annealed at 900 K for long times. At early stage of the annealing, small nuclei form in different places of NP and dissolve for short times. After long times some nuclei form and gather nearby which create the stable clusters in the core of NP. After that the crystal clusters grow in the direction to cover the core and then to spread into the surface of NP. Analyzing the energies of different type atoms, we found that the crystal growth is originated from specific atomic arrangement in the boundary region of crystal clusters.

Novel stable hard transparent conductors in TiO2-TiC system: Design materials from scratch

PubMed Central

Meng, Xiangying; Liu, Dongyan; Dai, Xuefeng; Pan, Haijun; Wen, Xiaohong; Zuo, Liang; Qin, Gaowu

2014-01-01

Two new ternary compounds in the TiO2-TiC system, Ti5C2O6 and Ti3C2O2, are reported for the first time based on ab initio evolutionary algorithm. Ti5C2O6 has a tube-structure in which sp1 hybridized carbon chains run through the lattice along the b-axis; while in the Ti3C2O2 lattice, double TiO6 polyhedral are separated by the non-coplanar sp2 hybridized hexagon graphite layers along the c-axis, forming a sandwich-like structure. At ambient conditions, the two compounds are found to be mechanically and dynamically stable and intrinsic transparent conductors with high hardness (about twice harder than the conventional transparent conducting oxides). These mechanical, electronic, and optical properties make Ti5C2O6 and Ti3C2O2 ternary compounds be promising robust, hard, transparent, and conductive materials. PMID:25511583

The Subfascial Approach to Primary and Secondary Breast Augmentation with Autologous Fat Grafting and Form-Stable Implants.

PubMed

Sampaio Goes, João Carlos; Munhoz, Alexandre Mendonça; Gemperli, Rolf

2015-10-01

This article presents an overview of the subfascial approach to primary and secondary breast augmentation with form-stable implants associated with autologous fat grafting. Although breast augmentation is a well-studied procedure, there are few previous reports concerning the subfascial technique and, especially, this technique associated with lipofilling. Consequently, the authors present their experience with a form-stable, anatomically shaped silicone gel breast implant, which has recently been approved in the United States following FDA clinical trials. Primary and secondary breast augmentations using form-stable implants resulted in satisfactory outcomes. Copyright © 2015 Elsevier Inc. All rights reserved.

Auger electron spectroscopy study of oxidation of a PdCr alloy used for high-temperature sensors

NASA Technical Reports Server (NTRS)

Boyd, Darwin L.; Zeller, Mary V.; Vargas-Aburto, Carlos

1993-01-01

A Pd-13 wt. percent Cr solid solution is a promising high-temperature strain gage alloy. In bulk form it has a number of properties that are desirable in a resistance strain gage material, such as a linear electrical resistance versus temperature curve to 1000 C and stable electrical resistance in air at 1000 C. However, unprotected fine wire gages fabricated from this alloy perform well only to 600 C. At higher temperatures severe oxidation degrades their electrical performance. In this work Auger electron spectroscopy was used to study the oxidation chemistry of the alloy wires and ribbons. Results indicate that the oxidation is caused by a complex mechanism that is not yet fully understood. As expected, during oxidation, a layer of chromium oxide is formed. This layer, however, forms beneath a layer of metallic palladium. The results of this study have increased the understanding of the oxidation mechanism of Pd-13 wt. percent Cr.

Cyclic trimer of human cystatin C, an amyloidogenic protein - molecular dynamics and experimental studies

NASA Astrophysics Data System (ADS)

Chrabåszczewska, Magdalena; Maszota-Zieleniak, Martyna; Pietralik, Zuzanna; Taube, Michał; Rodziewicz-Motowidło, Sylwia; Szymańska, Aneta; Szutkowski, Kosma; Clemens, Daniel; Grubb, Anders; Kozak, Maciej

2018-05-01

Human cystatin C (HCC) is a cysteine protease inhibitor that takes a series of oligomeric forms in solution (e.g., dimers, trimers, tetramers, decamers, dodecamers, and other higher oligomers). The best-known form of cystatin C is the dimer, which arises as a result of a domain swapping mechanism. The formation of the HCC oligomeric forms, which is most likely due to this domain swapping mechanism, is associated with the aggregation of HCC into amyloid fibrils and deposits. To investigate the structure of a specific HCC oligomer, we developed a covalently stabilized trimer of HCC. An atomic model of this HCC trimer was proposed on the basis of molecular docking and molecular dynamics simulations. The most stable model of the HCC trimer obtained from the molecular dynamics simulations is characterized by a well-preserved secondary structure. The molecular size and structural parameters of the HCC trimer in solution were also confirmed by Small Angle Neutron Scattering and Nuclear Magnetic Resonance Diffusometry.

Effects of F-treatment on degradation of Mg 2Ni electrode fabricated by mechanical alloying

NASA Astrophysics Data System (ADS)

Kim, Jun Sung; Lee, Chang Rae; Choi, Jae Woong; Kang, Sung Goon

The effects of surface fluorination on the electrochemical charge-discharge properties of a Mg 2Ni electrode, prepared by mechanical alloying in Ni-MH batteries are investigated. After 20 h milling, Mg and Ni powder form nanocrystalline Mg 2Ni. The discharge capacity of this alloy increases greatly on the initial cycle but, due to the formation of a Mg(OH) 2 passive layer, displays rapid degradation in alkaline solution within 10 cycles. In a 6 M KOH+ x M KF electrolyte ( x=0.5, 1, and 2), a continuous and stable fluorinated layer is formed and the durability of the Mg 2Ni electrode increases marketly and a high rate discharge capability is obtained (90-100 mAh/g). Addition of 2 M KF leads to the highest durability of all the electrodes tested. The improvement is due to a thin MgF 2—flourinated layer, which reduces the charge-transfer resistance and protects the Mg 2Ni electrode from forming a Mg(OH) 2 layer.

Real-time molecular scale observation of crystal formation.

PubMed

Schreiber, Roy E; Houben, Lothar; Wolf, Sharon G; Leitus, Gregory; Lang, Zhong-Ling; Carbó, Jorge J; Poblet, Josep M; Neumann, Ronny

2017-04-01

How molecules in solution form crystal nuclei, which then grow into large crystals, is a poorly understood phenomenon. The classical mechanism of homogeneous crystal nucleation proceeds via the spontaneous random aggregation of species from liquid or solution. However, a non-classical mechanism suggests the formation of an amorphous dense phase that reorders to form stable crystal nuclei. So far it has remained an experimental challenge to observe the formation of crystal nuclei from five to thirty molecules. Here, using polyoxometallates, we show that the formation of small crystal nuclei is observable by cryogenic transmission electron microscopy. We observe both classical and non-classical nucleation processes, depending on the identity of the cation present. The experiments verify theoretical studies that suggest non-classical nucleation is the lower of the two energy pathways. The arrangement in just a seven-molecule proto-crystal matches the order found by X-ray diffraction of a single bulk crystal, which demonstrates that the same structure was formed in each case.

Reassessing the atmospheric oxidation mechanism of toluene

NASA Astrophysics Data System (ADS)

Ji, Yuemeng; Zhao, Jun; Terazono, Hajime; Misawa, Kentaro; Levitt, Nicholas P.; Li, Yixin; Lin, Yun; Peng, Jianfei; Wang, Yuan; Duan, Lian; Pan, Bowen; Zhang, Fang; Feng, Xidan; An, Taicheng; Marrero-Ortiz, Wilmarie; Secrest, Jeremiah; Zhang, Annie L.; Shibuya, Kazuhiko; Molina, Mario J.; Zhang, Renyi

2017-08-01

Photochemical oxidation of aromatic hydrocarbons leads to tropospheric ozone and secondary organic aerosol (SOA) formation, with profound implications for air quality, human health, and climate. Toluene is the most abundant aromatic compound under urban environments, but its detailed chemical oxidation mechanism remains uncertain. From combined laboratory experiments and quantum chemical calculations, we show a toluene oxidation mechanism that is different from the one adopted in current atmospheric models. Our experimental work indicates a larger-than-expected branching ratio for cresols, but a negligible formation of ring-opening products (e.g., methylglyoxal). Quantum chemical calculations also demonstrate that cresols are much more stable than their corresponding peroxy radicals, and, for the most favorable OH (ortho) addition, the pathway of H extraction by O2 to form the cresol proceeds with a smaller barrier than O2 addition to form the peroxy radical. Our results reveal that phenolic (rather than peroxy radical) formation represents the dominant pathway for toluene oxidation, highlighting the necessity to reassess its role in ozone and SOA formation in the atmosphere.

Formation mechanism of a basin of attraction for passive dynamic walking induced by intrinsic hyperbolicity

PubMed Central

Aoi, Shinya; Tsuchiya, Kazuo; Kokubu, Hiroshi

2016-01-01

Passive dynamic walking is a useful model for investigating the mechanical functions of the body that produce energy-efficient walking. The basin of attraction is very small and thin, and it has a fractal-like shape; this explains the difficulty in producing stable passive dynamic walking. The underlying mechanism that produces these geometric characteristics was not known. In this paper, we consider this from the viewpoint of dynamical systems theory, and we use the simplest walking model to clarify the mechanism that forms the basin of attraction for passive dynamic walking. We show that the intrinsic saddle-type hyperbolicity of the upright equilibrium point in the governing dynamics plays an important role in the geometrical characteristics of the basin of attraction; this contributes to our understanding of the stability mechanism of bipedal walking. PMID:27436971

Toward an understanding of "Legacy P" - phosphorus sorption mechanisms in stream sediments as influenced by organic matter

NASA Astrophysics Data System (ADS)

Audette, Yuki; O'Halloran, Ivan P.; Nowell, Peter M.; Congreves, Katelyn; Voroney, R. Paul

2017-04-01

Water chemistry and phosphorus (P) forms were analyzed to determine the nature of legacy P in sediments of the West Holland River and the adjacent drainage canals of the Holland Marsh drainage system, located in southern Ontario, Canada. The river and canals route water from the intensively cropped muck polders of the Holland Marsh and drain Lake Simcoe. Sediment samples were characterized for mineralogy using X-ray diffraction techniques (XRD); total P (TP); and Ca, Fe, Mn, and Mg contents, as well as cation exchange capacity and organic matter (OM) content. Forms of sediment P in five depth sections (ranging from 0-15 cm depth) were characterized and quantified by sequential P fractionation chemistry. At all study sites, mobile P forms including organic P forms were found to be higher in surface sediments than in deeper sediments. The major P form within the sediments of the two canal sites, where the concentration of TP in the surface water was within the Ontario Provincial Water Quality Objectives (PWQO) of 0.03 mg P L-1, was Ca-bound P, indicating a low risk of soluble reactive P (SRP) release. A trace of apatite (a stable Ca-P mineral) was also detected in these sediments. Conversely, sediments collected from the West Holland River at sites located within the Holland Marsh exhibited a high risk of SRP release, and redox-sensitive P was the dominant P form in the sediment despite the surface water exhibiting higher concentration of Ca and alkaline pH. In addition, the concentrations of TP as measured in surface water samples taken from the site were 8 times greater than PWQO. In the sediments where the risk of SRP release was high, OM contents were also relatively high and traces of brushite (a labile Ca-P mineral) were detected. The formation of OM and cation complexes, such as OM-Fe complexes, may play an important role in regulating the fate of sediment-P forms through the adsorption of SRP. These OM-Fe complexes may inhibit the formation of more stable Ca-P minerals, even under neutral to alkaline conditions. Thus, where OM-Fe-P forms predominate, we predict a high risk of SRP release from sediments when water chemistry changes. In addition, OM may inhibit the transformation of labile Ca-P forms to more stable Ca-P minerals. Loading of OM affects the development of hypoxia in aquatic systems, and the accumulation of OM can promote the release of both SRP and dissolved organic C to downstream environments. This study provides evidence that the presence of OM in stream sediments influences P sorption mechanisms and is critical in understanding P biogeochemistry in freshwater environments.

Protonation States of Homocitrate and Nearby Residues in Nitrogenase Studied by Computational Methods and Quantum Refinement.

PubMed

Cao, Lili; Caldararu, Octav; Ryde, Ulf

2017-09-07

Nitrogenase is the only enzyme that can break the triple bond in N 2 to form two molecules of ammonia. The enzyme has been thoroughly studied with both experimental and computational methods, but there is still no consensus regarding the atomic details of the reaction mechanism. In the most common form, the active site is a MoFe 7 S 9 C(homocitrate) cluster. The homocitrate ligand contains one alcohol and three carboxylate groups. In water solution, the triply deprotonated form dominates, but because the alcohol (and one of the carboxylate groups) coordinate to the Mo ion, this may change in the enzyme. We have performed a series of computational calculations with molecular dynamics (MD), quantum mechanical (QM) cluster, combined QM and molecular mechanics (QM/MM), QM/MM with Poisson-Boltzmann and surface area solvation, QM/MM thermodynamic cycle perturbations, and quantum refinement methods to settle the most probable protonation state of the homocitrate ligand in nitrogenase. The results quite conclusively point out a triply deprotonated form (net charge -3) with a proton shared between the alcohol and one of the carboxylate groups as the most stable at pH 7. Moreover, we have studied eight ionizable protein residues close to the active site with MD simulations and determined the most likely protonation states.

Mechanical characteristics of beta sheet-forming peptide hydrogels are dependent on peptide sequence, concentration and buffer composition

PubMed Central

Müller, Michael; König, Finja; Meyer, Nina; Gattlen, Jasmin; Pieles, Uwe; Peters, Kirsten; Kreikemeyer, Bernd; Mathes, Stephanie; Saxer, Sina

2018-01-01

Self-assembling peptide hydrogels can be modified regarding their biodegradability, their chemical and mechanical properties and their nanofibrillar structure. Thus, self-assembling peptide hydrogels might be suitable scaffolds for regenerative therapies and tissue engineering. Owing to the use of various peptide concentrations and buffer compositions, the self-assembling peptide hydrogels might be influenced regarding their mechanical characteristics. Therefore, the mechanical properties and stability of a set of self-assembling peptide hydrogels, consisting of 11 amino acids, made from four beta sheet self-assembling peptides in various peptide concentrations and buffer compositions were studied. The formed self-assembling peptide hydrogels exhibited stiffnesses ranging from 0.6 to 205 kPa. The hydrogel stiffness was mostly affected by peptide sequence followed by peptide concentration and buffer composition. All self-assembling peptide hydrogels examined provided a nanofibrillar network formation. A maximum self-assembling peptide hydrogel dissolution of 20% was observed for different buffer solutions after 7 days. The stability regarding enzymatic and bacterial digestion showed less degradation in comparison to the self-assembling peptide hydrogel dissolution rate in buffer. The tested set of self-assembling peptide hydrogels were able to form stable scaffolds and provided a broad spectrum of tissue-specific stiffnesses that are suitable for a regenerative therapy. PMID:29657766

β-sheet-like formation during the mechanical unfolding of prion protein

NASA Astrophysics Data System (ADS)

Tao, Weiwei; Yoon, Gwonchan; Cao, Penghui; Eom, Kilho; Park, Harold S.

2015-09-01

Single molecule experiments and simulations have been widely used to characterize the unfolding and folding pathways of different proteins. However, with few exceptions, these tools have not been applied to study prion protein, PrPC, whose misfolded form PrPSc can induce a group of fatal neurodegenerative diseases. Here, we apply novel atomistic modeling based on potential energy surface exploration to study the constant force unfolding of human PrP at time scales inaccessible with standard molecular dynamics. We demonstrate for forces around 100 pN, prion forms a stable, three-stranded β-sheet-like intermediate configuration containing residues 155-214 with a lifetime exceeding hundreds of nanoseconds. A mutant without the disulfide bridge shows lower stability during the unfolding process but still forms the three-stranded structure. The simulations thus not only show the atomistic details of the mechanically induced structural conversion from the native α-helical structure to the β-rich-like form but also lend support to the structural theory that there is a core of the recombinant PrP amyloid, a misfolded form reported to induce transmissible disease, mapping to C-terminal residues ≈160-220.

β-sheet-like formation during the mechanical unfolding of prion protein

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tao, Weiwei; Cao, Penghui; Park, Harold S., E-mail: parkhs@bu.edu

2015-09-28

Single molecule experiments and simulations have been widely used to characterize the unfolding and folding pathways of different proteins. However, with few exceptions, these tools have not been applied to study prion protein, PrP{sup C}, whose misfolded form PrP{sup Sc} can induce a group of fatal neurodegenerative diseases. Here, we apply novel atomistic modeling based on potential energy surface exploration to study the constant force unfolding of human PrP at time scales inaccessible with standard molecular dynamics. We demonstrate for forces around 100 pN, prion forms a stable, three-stranded β-sheet-like intermediate configuration containing residues 155-214 with a lifetime exceeding hundredsmore » of nanoseconds. A mutant without the disulfide bridge shows lower stability during the unfolding process but still forms the three-stranded structure. The simulations thus not only show the atomistic details of the mechanically induced structural conversion from the native α-helical structure to the β-rich-like form but also lend support to the structural theory that there is a core of the recombinant PrP amyloid, a misfolded form reported to induce transmissible disease, mapping to C-terminal residues ≈160-220.« less

Association Mechanisms of Unsaturated C2 Hydrocarbons with Their Cations: Acetylene and Ethylene

NASA Technical Reports Server (NTRS)

Bera, Partha P.; Head-Gordon, Martin; Lee, Timothy J.

2013-01-01

The ion-molecule association mechanism of acetylene and ethylene with their cations is investigated by ab initio quantum chemical methods to understand the structures, association energies, and the vibrational and electronic spectra of the products. Stable puckered cyclic isomers are found as the result of first forming less stable linear and bridge isomers. The puckered cyclic complexes are calculated to be strongly bound, by 87, 35 and 56 kcal/mol for acetylene-acetylene cation, ethylene-ethylene cation and acetylene-ethylene cation, respectively. These stable complexes may be intermediates that participate in further association reactions. There are no association barriers, and no significant inter-conversion barriers, so the initial linear and bridge encounter complexes are unlikely to be observable. However, the energy gap between the bridged and cyclic puckered isomers greatly differs from complex to complex: it is 44 kcal/mol in C4H4 +, but only 6 kcal/mol in C4H8 +. The accurate CCSD(T) calculations summarized above are also compared against less computationally expensive MP2 and density functional theory (DFT) calculations for structures, relative energies, and vibrational spectra. Calculated vibrational spectra are compared against available experiments for cyclobutadiene cation. Electronic spectra are also calculated using time-dependent DFT.

Suppression of Dendritic Lithium Growth by in Situ Formation of a Chemically Stable and Mechanically Strong Solid Electrolyte Interphase.

PubMed

Wan, Guojia; Guo, Feihu; Li, Hui; Cao, Yuliang; Ai, Xinping; Qian, Jiangfeng; Li, Yangxing; Yang, Hanxi

2018-01-10

The growth and proliferation of Li dendrites during repeated Li cycling has long been a crucial issue that hinders the development of secondary Li-metal batteries. Building a stable and robust solid state electrolyte interphase (SEI) on the Li-anode surface is regarded as a promising strategy to overcome the dendrite issues. In this work, we report a simple strategy to engineer the interface chemistry of Li-metal anodes by using tiny amounts of dimethyl sulfate (DMS, C 2 H 6 SO 4 ) as the SEI-forming additive. With the preferential reduction of DMS, an SEI layer composed of Li 2 S/Li 2 O forms on the Li surface. This inorganic SEI layer features high structural modulus and low interfacial resistant, enabling a dense and dendrite-free Li deposition as evidenced by scanning electron microscopy, atomic force microscopy, and in situ optical images. In addition, this SEI layer can prevent the deposited Li from direct contact with corrosive electrolytes, thus rendering an improved cycling stability of Li anodes with an average Coulombic efficiency of 97% for up to 150 cycles. When the DMS additive is introduced into a Li/NCM full cell, the cycle life of Li-metal batteries can be also improved significantly. This work demonstrates a feasible route to suppress Li dendrite growth by designing appropriate film-forming additives to regulate the interfacial properties of the SEI layer, and also the sulfonyl-based derivatives revealed in this work represent a large variety of new film-forming molecules, providing a broad selectivity for constructing high efficiency and cycle-stable Li anodes to address the intrinsic problems of rechargeable Li-metal batteries.

The nanocoherer: an electrically and mechanically resettable resistive switching device based on gold clusters assembled on paper

NASA Astrophysics Data System (ADS)

Minnai, Chloé; Mirigliano, Matteo; Brown, Simon A.; Milani, Paolo

2018-03-01

We report the realization of a resettable resistive switching device based on a nanostructured film fabricated by supersonic cluster beam deposition of gold clusters on plain paper substrates. Through the application of suitable voltage ramps, we obtain, in the same device, either a complex pattern of resistive switchings, or reproducible and stable switchings between low resistance and high resistance states, with an amplitude up to five orders of magnitude. Our device retains a state of internal resistance following the history of the applied voltage similar to that reported for memristors. The two different switching regimes in the same device are both stable, the transition between them is reversible, and it can be controlled by applying voltage ramps or by mechanical deformation of the substrate. The device behavior can be related to the formation, growth and breaking of junctions between the loosely aggregated gold clusters forming the nanostructured films. The fact that our cluster-assembled device is mechanically resettable suggests that it can be considered as the analog of the coherer: a switching device based on metallic powders used for the first radio communication system.

Physicochemical and mechanical properties of carbamazepine cocrystals with saccharin.

PubMed

Rahman, Ziyaur; Samy, Raghu; Sayeed, Vilayat A; Khan, Mansoor A

2012-01-01

The aim of present research was to investigate the physicochemical, mechanical properties, and stability characteristics of cocrystal of carbamazepine (CBZ) using saccharin (SAC) as a coformer. The cocrystals were prepared by solubility method and characterized by pH-solubility profile, intrinsic dissolution by static disk method, and surface morphology by scanning electron microscopy (SEM), crystallinity by differential scanning calorimetry (DSC) and powder X-ray diffraction (PXRD), and mechanical properties by Heckel analysis. Stability of the cocrystals were assessed by storing them at 60 (°)C for two weeks, 25 (°)C/60%RH, 40 (°)C/75%RH and 40 (°)C/94%RH for one month and compared with the stability of CBZ. The solubility profile of cocrystal was similar to CBZ. The cocrystal and CBZ have shown the same stability profile at all the conditions of studies except at 40 (°)C/94%RH. Unlike the CBZ, cocrystal was stable against dihydrate transformation. The compacts of cocrystal have a greater tensile strength and more compressibility. The Heckel analysis suggested that plastic deformation started at low compression pressure in the cocrystal than CBZ. In summary, the cocrystal form of carbamazepine provides another avenue for product development which is more stable than the parent drug.

Isolation of thermally stable cellulose nanocrystals by phosphoric acid hydrolysis.

PubMed

Camarero Espinosa, Sandra; Kuhnt, Tobias; Foster, E Johan; Weder, Christoph

2013-04-08

On account of their intriguing mechanical properties, low cost, and renewable nature, high-aspect-ratio cellulose nanocrystals (CNCs) are an attractive component for many nanomaterials. Due to hydrogen bonding between their surface hydroxyl groups, unmodified CNCs (H-CNCs) aggregate easily and are often difficult to disperse. It is shown here that on account of ionic repulsion between charged surface groups, slightly phosphorylated CNCs (P-CNCs, average dimensions 31 ± 14 × 316 ± 127 nm, surface charge density = 10.8 ± 2.7 mmol/kg cellulose), prepared by controlled hydrolysis of cotton with phosphoric acid, are readily dispersible and form stable dispersions in polar solvents such as water, dimethyl sulfoxide, and dimethylformamide. Thermogravimetric analyses reveal that these P-CNCs exhibit a much higher thermal stability than partially sulfated CNCs (S-CNCs), which are frequently employed, but suffer from limited thermal stability. Nanocomposites of an ethylene oxide-epichlorohydrin copolymer and H-CNCs, S-CNCs, and P-CNCs were prepared, and their mechanical properties were studied by dynamic mechanical thermal analysis. The results show that P-CNCs offer a reinforcing capability that is comparable to that of H-CNCs or S-CNCs.

Tribomaterial factors in space mechanism brake performance

NASA Technical Reports Server (NTRS)

Hawthorne, H. M.

1990-01-01

The asbestos/phenolic pads of Shuttle Remote Manipulator System (SRMS) brakes are unsuitable for use in long life space mechanisms because their friction decreases on extended sliding in high vacuum. Dehydration of the material and accumulation of wear debris in the conforming interface of this tribosystem induces the permanent friction changes. Other polymer and some ceramic based materials exhibit similar frictional torque behavior due to the development of minimal contact patches by the interfacial debris. In contrast, high friction occurs when other ceramics form many small contacts throughout fine debris beds. Generating this latter interfacial structure during run-in ensures that the in-vacuo friction remains stable thereafter. Such materials with low wear rates are potential candidates for friction elements in SSRMS and similar mechanisms.

Computer simulation of ion channel gating: the M(2) channel of influenza A virus in a lipid bilayer

NASA Technical Reports Server (NTRS)

Schweighofer, K. J.; Pohorille, A.

2000-01-01

The transmembrane fragment of the influenza virus M(2) protein forms a homotetrameric channel that transports protons. In this paper, we use molecular dynamics simulations to help elucidate the mechanism of channel gating by four histidines that occlude the channel lumen in the closed state. We test two competing hypotheses. In the "shuttle" mechanism, the delta nitrogen atom on the extracellular side of one histidine is protonated by the incoming proton, and, subsequently, the proton on the epsilon nitrogen atom is released on the opposite side. In the "water-wire" mechanism, the gate opens because of electrostatic repulsion between four simultaneously biprotonated histidines. This allows for proton transport along the water wire that penetrates the gate. For each system, composed of the channel embedded in a hydrated phospholipid bilayer, a 1.3-ns trajectory was obtained. It is found that the states involved in the shuttle mechanism, which contain either single-protonated histidines or a mixture of single-protonated histidines plus one biprotonated residue, are stable during the simulations. Furthermore, the orientations and dynamics of water molecules near the gate are conducive to proton transfer. In contrast, the fully biprotonated state is not stable. Additional simulations show that if only two histidines are biprotonated, the channel deforms but the gate remains closed. These results support the shuttle mechanism but not the gate-opening mechanism of proton gating in M(2).

Biopatterning of Silk Proteins for Soft Micro-optics.

PubMed

Pal, Ramendra K; Kurland, Nicholas E; Wang, Congzhou; Kundu, Subhas C; Yadavalli, Vamsi K

2015-04-29

Silk proteins from spiders and silkworms have been proposed as outstanding candidates for soft micro-optic and photonic applications because of their optical transparency, unique biological properties, and mechanical robustness. Here, we present a method to form microstructures of the two constituent silk proteins, fibroin and sericin for use as an optical biomaterial. Using photolithography, chemically modified silk protein photoresists are patterned in 2D arrays of periodic patterns and Fresnel zone plates. Angle-dependent iridescent colors are produced in these periodic micropatterns because of the Bragg diffraction. Silk protein photolithography can used to form patterns on different substrates including flexible sheets with features of any shape with high fidelity and resolution over large areas. Finally, we show that these mechanically stable and transparent iridescent architectures are also completely biodegradable. This versatile and scalable technique can therefore be used to develop biocompatible, soft micro-optic devices that can be degraded in a controlled manner.

Molecular mechanism of codon recognition by tRNA species with modified uridine in the first position of the anticodon.

PubMed Central

Yokoyama, S; Watanabe, T; Murao, K; Ishikura, H; Yamaizumi, Z; Nishimura, S; Miyazawa, T

1985-01-01

Proton NMR analyses have been made to elucidate the conformational characteristics of modified nucleotides as found in the first position of the anticodon of tRNA [derivatives of 5-methyl-2-thiouridine 5'-monophosphate (pxm5s2U) and derivatives of 5-hydroxyuridine 5'-monophosphate (pxo5U)]. In pxm5s2U, the C3'-endo form is extraordinarily more stable than the C2'-endo form for the ribose ring, because of the combined effects of the 2-thiocarbonyl group and the 5-substituent. By contrast, in pxo5U, the C2'-endo form is much more stable than the C3'-endo form, because of the interaction between the 5-substituent and the 5'-phosphate group. The enthalpy differences between the C2'-endo form and the C3'-endo form have been obtained as 1.1, -0.7, and 0.1 kcal/mol (1 cal = 4.184 J) for pxm5s2U, pxo5U, and unmodified uridine 5'-monophosphate, respectively. These findings lead to the conclusion that xm5s2U in the first position of the anticodon exclusively takes the C3'-endo form to recognize adenosine (but not uridine) as the third letter of the codon, whereas xo5U takes the C2'-endo form as well as the C3'-endo form to recognize adenosine, guanosine, and uridine as the third letter of the codon on ribosome. Accordingly, the biological significance of such modifications of uridine to xm5s2U/xo5U is in the regulation of the conformational rigidity/flexibility in the first position of the anticodon so as to guarantee the correct and efficient translation of codons in protein biosynthesis. PMID:3860833

Ultrafast and ultrasensitive hydrogen sensors based on self-assembly monolayer promoted 2-dimensional palladium nanoclusters

DOEpatents

Xu, Tao; Zach, Michael P.; Xiao, Zhili

2007-02-06

A device and method of making same. The device or hydrogen detector has a non-conducting substrate with a metal film capable of absorbing hydrogen to form a stable metal hydride. The metal film is being on the threshold of percolation and is connected to mechanism for sensing a change in electrical resistance in response to the presence of hydrogen in contact with the metal film which causes an increase in conductivity.

Ultrafast and ultrasensitive hydrogen sensors based on self-assembly monolayer promoted 2-dimensional palladium nanoclusters

DOEpatents

Xu, Tao [Darien, IL; Zach, Michael P [Darien, IL; Xiao, Zhili [Naperville, IL

2008-06-24

A device and method of making same. The device or hydrogen detector has a non-conducting substrate with a metal film capable of absorbing hydrogen to form a stable metal hydride. The metal film is on the threshold of percolation and is connected to mechanism for sensing a change in electrical resistance in response to the presence of hydrogen in contact with the metal film which causes an increase in conductivity.

Different threshold and bipolar resistive switching mechanisms in reactively sputtered amorphous undoped and Cr-doped vanadium oxide thin films

NASA Astrophysics Data System (ADS)

Rupp, Jonathan A. J.; Querré, Madec; Kindsmüller, Andreas; Besland, Marie-Paule; Janod, Etienne; Dittmann, Regina; Waser, Rainer; Wouters, Dirk J.

2018-01-01

This study investigates resistive switching in amorphous undoped and Cr-doped vanadium oxide thin films synthesized by sputtering deposition at low oxygen partial pressure. Two different volatile threshold switching characteristics can occur as well as a non-volatile bipolar switching mechanism, depending on device stack symmetry and Cr-doping. The two threshold switching types are associated with different crystalline phases in the conduction filament created during an initial forming step. The first kind of threshold switching, observed for undoped vanadium oxide films, was, by its temperature dependence, proven to be associated with a thermally triggered insulator-to-metal transition in a crystalline VO2 phase, whereas the threshold switch observed in chromium doped films is stable up to 90 °C and shows characteristics of an electronically induced Mott transition. This different behaviour for undoped versus doped films has been attributed to an increased stability of V3+ due to the Cr3+ doping (as evidenced by X-ray photoelectron spectroscopy analysis), probably favouring the creation of a crystalline Cr-doped V2O3 phase (rather than a Cr-doped VO2 phase) during the energetic forming step. The symmetric Pt/a-(VCr)Ox/Pt device showing high temperature stable threshold switching may find interesting applications as a possible new selector device for resistive switching memory (ReRAM) crossbar arrays.

Design of high-activity single-atom catalysts via n-p codoping

NASA Astrophysics Data System (ADS)

Wang, Xiaonan; Zhou, Haiyan; Zhang, Xiaoyang; Jia, Jianfeng; Wu, Haishun

2018-03-01

The large-scale synthesis of stable single-atom catalysts (SACs) in experiments remains a significant challenge due to high surface free energy of metal atom. Here, we propose a concise n-p codoping approach, and find it can not only disperse the relatively inexpensive metal, copper (Cu), onto boron (B)-doped graphene, but also result in high-activity SACs. We use CO oxidation on B/Cu codoped graphene as a prototype example, and demonstrate that: (1) a stable SAC can be formed by stronger electrostatic attraction between the metal atom (n-type Cu) and support (p-type B-doped graphene). (2) the energy barrier of the prototype CO oxidation on B/Cu codoped graphene is 0.536 eV by the Eley-Rideal mechanism. Further analysis shows that the spin selection rule can provide well theoretical insight into high activity of our suggested SAC. The concept of n-p codoping may lead to new strategy in large-scale synthesis of stable single-atom catalysts.

Silicon algae with carbon topping as thin-film anodes for lithium-ion microbatteries by a two-step facile method

NASA Astrophysics Data System (ADS)

Biserni, E.; Xie, M.; Brescia, R.; Scarpellini, A.; Hashempour, M.; Movahed, P.; George, S. M.; Bestetti, M.; Li Bassi, A.; Bruno, P.

2015-01-01

Silicon-based electrodes for Li-ion batteries (LIB) attract much attention because of their high theoretical capacity. However, their large volume change during lithiation results in poor cycling due to mechanical cracking. Moreover, silicon can hardly form a stable solid electrolyte interphase (SEI) layer with common electrolytes. We present a safe, innovative strategy to prepare nanostructured silicon-carbon anodes in a two-step process. The nanoporosity of Si films accommodates the volume expansion while a disordered graphitic C layer on top promotes the formation of a stable SEI. This approach shows its promises: carbon-coated porous silicon anodes perform in a very stable way, reaching the areal capacity of ∼175 μAh cm-2, and showing no decay for at least 1000 cycles. With requiring only a two-step deposition process at moderate temperatures, this novel very simple cell concept introduces a promising way to possibly viable up-scaled production of next-generation nanostructured Si anodes for lithium-ion microbatteries.

Structural and mechanical properties of glassy water in nanoscale confinement.

PubMed

Lombardo, Thomas G; Giovambattista, Nicolás; Debenedetti, Pablo G

2009-01-01

We investigate the structure and mechanical properties of glassy water confined between silica-based surfaces with continuously tunable hydrophobicity and hydrophilicity by computing and analyzing minimum energy, mechanically stable configurations (inherent structures). The structured silica substrate imposes long-range order on the first layer of water molecules under hydrophobic confinement at high density (p > or = 1.0 g cm(-3)). This proximal layer is also structured in hydrophilic confinement at very low density (p approximately 0.4 g cm(-3)). The ordering of water next to the hydrophobic surface greatly enhances the mechanical strength of thin films (0.8 nm). This leads to a substantial stress anisotropy; the transverse strength of the film exceeds the normal strength by 500 MPa. The large transverse strength results in a minimum in the equation of state of the energy landscape that does not correspond to a mechanical instability, but represents disruption of the ordered layer of water next to the wall. In addition, we find that the mode of mechanical failure is dependent on the type of confinement. Under large lateral strain, water confined by hydrophilic surfaces preferentially forms voids in the middle of the film and fails cohesively. In contrast, water under hydrophobic confinement tends to form voids near the walls and fails by loss of adhesion.

Formation of an optical pulsed discharge in a supersonic air flow by radiation of a repetitively pulsed CO{sub 2} laser

DOE Office of Scientific and Technical Information (OSTI.GOV)

Malov, Aleksei N; Orishich, Anatolii M

Results of optimisation of repetitively pulsed CO{sub 2}-laser generation are presented for finding physical conditions of forming stable burning of an optical pulsed discharge (OPD) in a supersonic air flow and for studying the influence of pulse parameters on the energy absorption efficiency of laser radiation in plasma. The optical discharge in a supersonic air flow was formed by radiation of a repetitively pulsed CO{sub 2} laser with mechanical Q-switching excited by a discharge with a convective cooling of the working gas. For the first time the influence of radiation pulse parameters on the ignition conditions and stable burning ofmore » the OPD in a supersonic air flow was investigated and the efficiency of laser radiation absorption in plasma was studied. The influence of the air flow velocity on stability of plasma production was investigated. It was shown that stable burning of the OPD in a supersonic flow is realised at a high pulse repetition rate where the interval between radiation pulses is shorter than the time of plasma blowing-off. Study of the instantaneous value of the absorption coefficient shows that after a breakdown in a time lapse of 100 - 150 ns, a quasi-stationary 'absorption phase' is formed with the duration of {approx}1.5 ms, which exists independently of air flow and radiation pulse repetition rate. This phase of strong absorption is, seemingly, related to evolution of the ionisation wave. (laser applications and other topics in quantum electronics)« less

Insights into signal transduction by a hybrid FixL: Denaturation study of on and off states of a multi-domain oxygen sensor.

PubMed

Guimarães, Wellinson G; Gondim, Ana C S; Costa, Pedro Mikael da Silva; Gilles-Gonzalez, Marie-Alda; Lopes, Luiz G F; Carepo, Marta S P; Sousa, Eduardo H S

2017-07-01

FixL from Rhizobium etli (ReFixL) is a hybrid oxygen sensor protein. Signal transduction in ReFixL is effected by a switch off of the kinase activity on binding of an oxygen molecule to ferrous heme iron in another domain. Cyanide can also inhibit the kinase activity upon binding to the heme iron in the ferric state. The unfolding by urea of the purified full-length ReFixL in both active pentacoordinate form, met-FixL(Fe III ) and inactive cyanomet-FixL (Fe III -CN - ) form was monitored by UV-visible absorption spectroscopy, circular dichroism (CD) and fluorescence spectroscopy. The CD and UV-visible absorption spectroscopy revealed two states during unfolding, whereas fluorescence spectroscopy identified a three-state unfolding mechanism. The unfolding mechanism was not altered for the active compared to the inactive state; however, differences in the ΔG H2O were observed. According to the CD results, compared to cyanomet-FixL, met-FixL was more stable towards chemical denaturation by urea (7.2 vs 4.8kJmol -1 ). By contrast, electronic spectroscopy monitoring of the Soret band showed cyanomet-FixL to be more stable than met-FixL (18.5 versus 36.2kJmol -1 ). For the three-state mechanism exhibited by fluorescence, the ΔG H2O for both denaturation steps were higher for the active-state met-FixL than for cyanomet-FixL. The overall stability of met-FixL is higher in comparison to cyanomet-FixL suggesting a more compact protein in the active form. Nonetheless, hydrogen bonding by bound cyanide in the inactive state promotes the stability of the heme domain. This work supports a model of signal transduction by FixL that is likely shared by other heme-based sensors. Copyright © 2017 Elsevier Inc. All rights reserved.

Oxidation of selected organophosphate pesticides during chlorination of simulated drinking water.

PubMed

Kamel, Alaa; Byrne, Christian; Vigo, Craig; Ferrario, Joseph; Stafford, Charles; Verdin, Gregory; Siegelman, Frederic; Knizner, Steven; Hetrick, James

2009-02-01

Ten organophosphate (OP) pesticides: phorate, disulfoton, terbufos, methidathion, bensulide, chlorethoxyfos, phosmet, methyl parathion, phostebupirim, and temephos were evaluated for their potential to undergo oxidation to their respective oxons and/or other oxidation analogues in laboratory water. Samples were collected at time intervals up to 72h of chlorination and analyzed by both gas chromatography-mass selective detection (GC-MSD) and liquid chromatography-tandem mass spectrometry (LC-MS/MS). The results show that methidathion and methyl parathion were stable in unchlorinated water, while all other OP pesticides were not stable over the 72h exposure period. In chlorinated water, phorate and disulfoton formed stable sulfone oxons. Temephos formed stable dioxon sulfoxide and dioxon sulfone. Methidathion, bensulide, chlorethyoxyfos, methyl parathion, and phostebupirim formed stable oxons over the 72h exposure period. Terbufos, phorate, disulfoton and temephos oxon sulfoxides; temephos sulfoxide; and phosmet oxon were initially formed but were not detected after 24h. The data illustrate that organothiophosphate pesticides may form oxons and/or other oxidation analogues during chlorination in water treatment plants, which are persistent for at least 72h.

Longevity of Compositionally Stratified Layers in Ice Giants

NASA Astrophysics Data System (ADS)

Friedson, A. J.

2017-12-01

In the hydrogen-rich atmospheres of gas giants, a decrease with radius in the mixing ratio of a heavy species (e.g. He, CH4, H2O) has the potential to produce a density stratification that is convectively stable if the heavy species is sufficiently abundant. Formation of stable layers in the interiors of these planets has important implications for their internal structure, chemical mixing, dynamics, and thermal evolution, since vertical transport of heat and constituents in such layers is greatly reduced in comparison to that in convecting layers. Various processes have been suggested for creating compositionally stratified layers. In the interiors of Jupiter and Saturn, these include phase separation of He from metallic hydrogen and dissolution of dense core material into the surrounding metallic-H envelope. Condensation of methane and water has been proposed as a mechanism for producing stable zones in the atmospheres of Saturn and the ice giants. However, if a stably stratified layer is formed adjacent to an active region of convection, it may be susceptible to progressive erosion as the convection intrudes and entrains fluid into the unstable envelope. We discuss the principal factors that control the rate of entrainment and associated erosion and present a specific example concerning the longevity of stable layers formed by condensation of methane and water in Uranus and Neptune. We also consider whether the temporal variability of such layers may engender episodic behavior in the release of the internal heat of these planets. This research is supported by a grant from the NASA Solar System Workings Program.

Exploring the aggregation free energy landscape of the amyloid-β protein (1–40)

PubMed Central

Zheng, Weihua; Tsai, Min-Yeh; Chen, Mingchen; Wolynes, Peter G.

2016-01-01

A predictive coarse-grained protein force field [associative memory, water-mediated, structure, and energy model for molecular dynamics (AWSEM)-MD] is used to study the energy landscapes and relative stabilities of amyloid-β protein (1–40) in the monomer and all of its oligomeric forms up to an octamer. We find that an isolated monomer is mainly disordered with a short α-helix formed at the central hydrophobic core region (L17-D23). A less stable hairpin structure, however, becomes increasingly more stable in oligomers, where hydrogen bonds can form between neighboring monomers. We explore the structure and stability of both prefibrillar oligomers that consist of mainly antiparallel β-sheets and fibrillar oligomers with only parallel β-sheets. Prefibrillar oligomers are polymorphic but typically take on a cylindrin-like shape composed of mostly antiparallel β-strands. At the concentration of the simulation, the aggregation free energy landscape is nearly downhill. We use umbrella sampling along a structural progress coordinate for interconversion between prefibrillar and fibrillar forms to identify a conversion pathway between these forms. The fibrillar oligomer only becomes favored over its prefibrillar counterpart in the pentamer where an interconversion bottleneck appears. The structural characterization of the pathway along with statistical mechanical perturbation theory allow us to evaluate the effects of concentration on the free energy landscape of aggregation as well as the effects of the Dutch and Arctic mutations associated with early onset of Alzheimer’s disease. PMID:27698130

Mechanical unfolding reveals stable 3-helix intermediates in talin and α-catenin

PubMed Central

2018-01-01

Mechanical stability is a key feature in the regulation of structural scaffolding proteins and their functions. Despite the abundance of α-helical structures among the human proteome and their undisputed importance in health and disease, the fundamental principles of their behavior under mechanical load are poorly understood. Talin and α-catenin are two key molecules in focal adhesions and adherens junctions, respectively. In this study, we used a combination of atomistic steered molecular dynamics (SMD) simulations, polyprotein engineering, and single-molecule atomic force microscopy (smAFM) to investigate unfolding of these proteins. SMD simulations revealed that talin rod α-helix bundles as well as α-catenin α-helix domains unfold through stable 3-helix intermediates. While the 5-helix bundles were found to be mechanically stable, a second stable conformation corresponding to the 3-helix state was revealed. Mechanically weaker 4-helix bundles easily unfolded into a stable 3-helix conformation. The results of smAFM experiments were in agreement with the findings of the computational simulations. The disulfide clamp mutants, designed to protect the stable state, support the 3-helix intermediate model in both experimental and computational setups. As a result, multiple discrete unfolding intermediate states in the talin and α-catenin unfolding pathway were discovered. Better understanding of the mechanical unfolding mechanism of α-helix proteins is a key step towards comprehensive models describing the mechanoregulation of proteins. PMID:29698481

Study on preparation and formation mechanism of n-alkanol/water emulsion using alpha-cyclodextrin.

PubMed

Hashizaki, Kaname; Kageyama, Takashi; Inoue, Motoki; Taguchi, Hiroyuki; Ueda, Haruhisa; Saito, Yoshihiro

2007-11-01

Surfactants are usually used for the preparation of emulsions; however, some have an adverse effect on the human body such as skin irritation, hemolysis, and protein denaturation, etc. In this study, we examined the preparation and formation mechanism of n-alkanol/water emulsions using alpha-cyclodextrin (alpha-CD) as an emulsifier. Emulsions were prepared by mixing oil and water phases for 4 min at 2500 rpm using a vortex mixer. The mechanism of emulsification was investigated with some physico-chemical techniques. From phase diagrams of n-alkanol/alpha-CD/water systems, the emulsion phase extended as the chain length of n-alkanols and the amount of alpha-CD added increased. Furthermore, the emulsion was not formed in the region where the n-alkanol/alpha-CD complex didn't precipitate; however, the emulsion was formed in the region where the complex precipitated. In addition, it was clear that the emulsions have a yield stress value and correspond to the Maxwell model from rheological measurement. Our experiments clearly showed that the stable emulsions are formed because the precipitated complexes form a dense film at the oil-water interface and prevent aggregation among dispersed phases. Furthermore, it is suggested that the creation of a three-dimensional network structure formed by precipitated complexes in the continuous phase contributes to the stabilization of the emulsion. Thus, we concluded that the n-alkanol/water emulsions using alpha-cyclodextrin were a kind of the Pickering emulsion.

Recent development in deciphering the structure of luminescent silver nanodots

NASA Astrophysics Data System (ADS)

Choi, Sungmoon; Yu, Junhua

2017-05-01

Matrix-stabilized silver clusters and stable luminescent few-atom silver clusters, referred to as silver nanodots, show notable difference in their photophysical properties. We present recent research on deciphering the nature of silver clusters and nanodots and understanding the factors that lead to variations in luminescent mechanisms. Due to their relatively simple structure, the matrix-stabilized clusters have been well studied. However, the single-stranded DNA (ssDNA)-stabilized silver nanodots that show the most diverse emission wavelengths and the best photophysical properties remain mysterious species. It is clear that their photophysical properties highly depend on their protection scaffolds. Analyses from combinations of high-performance liquid chromatography, inductively coupled plasma-atomic emission spectroscopy, electrophoresis, and mass spectrometry indicate that about 10 to 20 silver atoms form emissive complexes with ssDNA. However, it is possible that not all of the silver atoms in the complex form effective emission centers. Investigation of the nanodot structure will help us understand why luminescent silver nanodots are stable in aqueous solution and how to further improve their chemical and photophysical properties.

Atomic scale behavior of oxygen-based radicals in water

NASA Astrophysics Data System (ADS)

Verlackt, C. C. W.; Neyts, E. C.; Bogaerts, A.

2017-03-01

Cold atmospheric pressure plasmas in and in contact with liquids represent a growing field of research for various applications. Understanding the interactions between the plasma generated species and the liquid is crucial. In this work we perform molecular dynamics (MD) simulations based on a quantum mechanical method, i.e. density-functional based tight-binding (DFTB), to examine the interactions of OH radicals and O atoms in bulk water. Our calculations reveal that the transport of OH radicals through water is not only governed by diffusion, but also by an equilibrium reaction of H-abstraction with water molecules. Furthermore, when two OH radicals encounter each other, they either form a stable cluster, or react, resulting in the formation of a new water molecule and an O atom. In addition, the O atoms form either oxywater (when in singlet configuration) or they remain stable in solution (when in triplet configuration), stressing the important role that O atoms can play in aqueous solution, and in contact with biomolecules. Our observations are in line with both experimental and ab initio results from the literature.

Dual Effect of (LK)nL Peptides on the Onset of Insulin Amyloid Fiber Formation at Hydrophobic Surfaces.

PubMed

Chouchane, Karim; Vendrely, Charlotte; Amari, Myriam; Moreaux, Katie; Bruckert, Franz; Weidenhaupt, Marianne

2015-08-20

Soluble proteins are constantly in contact with material or cellular surfaces, which can trigger their aggregation and therefore have a serious impact on the development of stable therapeutic proteins. In contact with hydrophobic material surfaces, human insulin aggregates readily into amyloid fibers. The kinetics of this aggregation can be accelerated by small peptides, forming stable beta-sheets on hydrophobic surfaces. Using a series of (LK)nL peptides with varying length, we show that these peptides, at low, substoichiometric concentrations, have a positive, cooperative effect on insulin aggregation. This effect is based on a cooperative adsorption of (LK)nL peptides at hydrophobic surfaces, where they form complexes that help the formation of aggregation nuclei. At higher concentrations, they interfere with the formation of an aggregative nucleus. These effects are strictly dependent on the their adsorption on hydrophobic material surfaces and highlight the importance of the impact of materials on protein stability. (LK)nL peptides prove to be valuable tools to investigate the mechanism of HI aggregation nuclei formation on hydrophobic surfaces.

Organosulfide-plasticized solid-electrolyte interphase layer enables stable lithium metal anodes for long-cycle lithium-sulfur batteries

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Guoxing; Gao, Yue; He, Xin

Lithium metal is a promising anode candidate for the next-generation rechargeable battery due to its highest specific capacity (3860 mA h g -1) and lowest potential, but low Coulombic efficiency and formation of lithium dendrites hinder its practical application. Here, we report a self-formed flexible hybrid solid-electrolyte interphase layer through co-deposition of organosulfides/organopolysulfides and inorganic lithium salts using sulfur-containing polymers as an additive in the electrolyte. The organosulfides/organopolysulfides serve as “plasticizer” in the solid-electrolyte interphase layer to improve its mechanical flexibility and toughness. The as-formed robust solid-electrolyte interphase layers enable dendrite-free lithium deposition and significantly improve Coulombic efficiency (99% overmore » 400 cycles at a current density of 2mAcm -2). A lithium-sulfur battery based on this strategy exhibits long cycling life (1000 cycles) and good capacity retention. This study reveals an avenue to effectively fabricate stable solid-electrolyte interphase layer for solving the issues associated with lithium metal anodes.« less

Organosulfide-plasticized solid-electrolyte interphase layer enables stable lithium metal anodes for long-cycle lithium-sulfur batteries

DOE PAGES

Li, Guoxing; Gao, Yue; He, Xin; ...

2017-10-11

Lithium metal is a promising anode candidate for the next-generation rechargeable battery due to its highest specific capacity (3860 mA h g -1) and lowest potential, but low Coulombic efficiency and formation of lithium dendrites hinder its practical application. Here, we report a self-formed flexible hybrid solid-electrolyte interphase layer through co-deposition of organosulfides/organopolysulfides and inorganic lithium salts using sulfur-containing polymers as an additive in the electrolyte. The organosulfides/organopolysulfides serve as “plasticizer” in the solid-electrolyte interphase layer to improve its mechanical flexibility and toughness. The as-formed robust solid-electrolyte interphase layers enable dendrite-free lithium deposition and significantly improve Coulombic efficiency (99% overmore » 400 cycles at a current density of 2mAcm -2). A lithium-sulfur battery based on this strategy exhibits long cycling life (1000 cycles) and good capacity retention. This study reveals an avenue to effectively fabricate stable solid-electrolyte interphase layer for solving the issues associated with lithium metal anodes.« less

Antihypertensive Effects, Molecular Docking Study, and Isothermal Titration Calorimetry Assay of Angiotensin I-Converting Enzyme Inhibitory Peptides from Chlorella vulgaris.

PubMed

Xie, Jingli; Chen, Xujun; Wu, Junjie; Zhang, Yanyan; Zhou, Yan; Zhang, Lujia; Tang, Ya-Jie; Wei, Dongzhi

2018-02-14

The aim of this work is to explore angiotensin I-converting enzyme (ACE) inhibitory peptides from Chlorella vulgaris (C. vulgaris) and discover the inhibitory mechanism of the peptides. After C. vulgaris proteins were gastrointestinal digested in silico, several ACE inhibitory peptides with C-terminal tryptophan were screened. Among them, two novel noncompetitive ACE inhibitors, Thr-Thr-Trp (TTW) and Val-His-Trp (VHW), exhibited the highest inhibitory activity indicated by IC 50 values 0.61 ± 0.12 and 0.91 ± 0.31 μM, respectively. Both the peptides were demonstrated stable against gastrointestinal digestion and ACE hydrolysis. The peptides were administrated to spontaneously hypertensive rats (SHRs) in the dose 5 mg/kg body weight, and VHW could decrease 50 mmHg systolic blood pressure of SHRs (p < 0.05). Molecular docking displayed that both TTW and VHW formed six hydrogen bonds with active site pockets of ACE. Besides, isothermal titration calorimetry assay discovered that VHW could form more stable complex with ACE than TTW. Therefore, VHW was an excellent ACE inhibitor.

In situ analysis of capacity fade in thin-film anodes for high performance Li-ion all-solid-state batteries

NASA Astrophysics Data System (ADS)

Leite, Marina S.; Gong, Chen; Ruzmetov, Dmitry; Talin, A. Alec

There is still a pressing need to understand how the solid-interfaces in Li-ion all-solid-batteries form, including their chemical composition and electrical characteristics. In order to resolve the origin of the degradation mechanism in Al anodes, we combine in situ scanning electron microscopy in ultra-high vacuum with electrochemical cycling, in addition to ex situ characterization of the morphological, chemical, and electrical changes of the Al anodes upon lithiation. An AlLi alloy capped by a stable Al-Li-O is formed on the top surface of the anode, trapping Li, which results in the capacity fade, from 48.0 to 41.5 μ.Ah/cm2 in two cycles. The addition of a Cu capping layer is insufficient to prevent the device degradation because of the fast Li diffusion within Al. Yet, Si present extremely stable cycling: >92% of capacity retention after 100 cycles, with average Coulombic efficiency of 98%. Our in situ measurements represent a new platform for probing the real-time degradation of electrodes in all-solid-state batteries for energy storage devices.

QR encoded smart oral dosage forms by inkjet printing.

PubMed

Edinger, Magnus; Bar-Shalom, Daniel; Sandler, Niklas; Rantanen, Jukka; Genina, Natalja

2018-01-30

The use of inkjet printing (IJP) technology enables the flexible manufacturing of personalized medicine with the doses tailored for each patient. In this study we demonstrate, for the first time, the applicability of IJP in the production of edible dosage forms in the pattern of a quick response (QR) code. This printed pattern contains the drug itself and encoded information relevant to the patient and/or healthcare professionals. IJP of the active pharmaceutical ingredient (API)-containing ink in the pattern of QR code was performed onto a newly developed porous and flexible, but mechanically stable substrate with a good absorption capacity. The printing did not affect the mechanical properties of the substrate. The actual drug content of the printed dosage forms was in accordance with the encoded drug content. The QR encoded dosage forms had a good print definition without significant edge bleeding. They were readable by a smartphone even after storage in harsh conditions. This approach of efficient data incorporation and data storage combined with the use of smart devices can lead to safer and more patient-friendly drug products in the future. Copyright © 2017 Elsevier B.V. All rights reserved.

Spectroscopic investigations of the charge-transfer interaction between the drug reserpine and different acceptors: Towards understanding of drug-receptor mechanism

NASA Astrophysics Data System (ADS)

Eldaroti, Hala H.; Gadir, Suad A.; Refat, Moamen S.; Adam, Abdel Majid A.

2013-11-01

The study of the charge-transfer interaction of the drugs may be useful in understanding the drug-receptor interactions and the mechanism of drug action. Structural and thermal stability of charge-transfer (CT) complexes formed between the drug reserpine (Res) as a donor and quinol (QL), picric acid (PA), tetracyanoquinodimethane (TCNQ) or dichlorodicyanobenzoquinone (DDQ) as acceptors were reported. Elemental analysis, electronic absorption, spectrophotometric titration, IR, Raman, 1H NMR and X-ray powder diffraction (XRD) were used to characterize the new products. The thermal stability of the synthesized CT complexes was investigated using thermogravimetric (TG) analyses, and the morphology and particle size of these complexes were obtained from scanning electron microscopy (SEM). The stoichiometry of the complexes (donor:acceptor molar ratio) was determined to be 1:1 for all complexes. Accordingly the formed CT complexes could be formulated as [(Res)(QL)], [(Res)(PA)], [(Res)(TCNQ)] and [(Res)(DDQ)]. It was found that the obtained CT complexes are nanoscale, semi-crystalline particles, thermally stable and formed through spontaneous reaction. The results obtained herein are satisfactory for estimation of drug Res in the pharmaceutical form.

Berberine alkaloid: Quantum chemical study of different forms by the DFT and MP2 methods

NASA Astrophysics Data System (ADS)

Danilov, V. I.; Dailidonis, V. V.; Hovorun, D. M.; Kurita, N.; Murayama, Y.; Natsume, T.; Potopalsky, A. I.; Zaika, L. A.

2006-10-01

The stable structures and electronic properties for the berberine cation as well as possible ammonium, carbinol and amino-aldehyde forms of protoberberine salts in the presence of hydroxyl ions were investigated by the B3LYP/6-31G(d,p) and MP2/6-31++G(d,p) methods. The geometry optimizations by both methods lead to the nonplanar propeller-twisted and buckled structure for the all forms. The obtained bond lengths and bond angles agree with the experimental values. The comparison of total energies elucidates that the amino-aldehyde form is the most preferable tautomer in gas phase, while the carbinol form is less stable. The least stable tautomer is the ammonium form.

Technetium incorporation into goethite (α-FeOOH): An atomic-scale investigation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Smith, Frances N.; Taylor, Christopher D.; Um, Wooyong

2015-11-17

During the processing of low-activity radioactive waste to generate solid waste forms (e.g., glass), technetium-99 (Tc) is of concern because of its volatility. A variety of materials are under consideration to capture Tc from waste streams, including the iron oxyhydroxide, goethite (α-FeOOH), which was experimentally shown to sequester Tc(IV). This material could ultimately be incorporated into glass or other low-temperature waste form matrices. However, questions remain regarding the incorporation mechanism for Tc(IV) in goethite, which has implications for predicting the long-term stability of Tc in waste forms under changing conditions. Here, quantum-mechanical calculations were used to evaluate the energy ofmore » five different charge-compensated Tc(IV) incorporation scenarios in goethite. The two most stable incorporation mechanisms involve direct substitution of Tc(IV) onto Fe(III) lattice sites and charge balancing either by removing one nearby H+ (i.e., within 5 Å), or by creating an Fe(III) vacancy when substituting 3 Tc(IV) for 4 Fe(III), with the former being preferred over the latter relative to gas-phase ions. When corrections for hydrated references phases are applied, the Fe(III)-vacancy mechanism becomes more energetically competitive. Calculated incorporation energies and optimized bond-lengths are presented. Proton movement is observed to satisfy under-coordinated bonds surrounding vacancies in the goethite structure.« less

Wine protein haze: mechanisms of formation and advances in prevention.

PubMed

Van Sluyter, Steven C; McRae, Jacqui M; Falconer, Robert J; Smith, Paul A; Bacic, Antony; Waters, Elizabeth J; Marangon, Matteo

2015-04-29

Protein haze is an aesthetic problem in white wines that can be prevented by removing the grape proteins that have survived the winemaking process. The haze-forming proteins are grape pathogenesis-related proteins that are highly stable during winemaking, but some of them precipitate over time and with elevated temperatures. Protein removal is currently achieved by bentonite addition, an inefficient process that can lead to higher costs and quality losses in winemaking. The development of more efficient processes for protein removal and haze prevention requires understanding the mechanisms such as the main drivers of protein instability and the impacts of various wine matrix components on haze formation. This review covers recent developments in wine protein instability and removal and proposes a revised mechanism of protein haze formation.

Supersymmetric oscillator in optics

NASA Technical Reports Server (NTRS)

Chumakov, Sergey M.; Wolf, Kurt Bernardo

1995-01-01

We show that the supersymmetric structure (in the sense of supersymmetric quantum mechanics) appears in Helmholtz optics describing light propagation in waveguides. For the case of elliptical waveguides, with the accuracy of paraxial approximation it admits a simple physical interpretation. The supersymmetry connects light beams of different colors. The difference in light frequencies for the supersymmetric beams is determined by the transverse gradient of the refractive index. These beams have the save wavelength in the propagation direction and can form a stable interference pattern.

XPS and SEM analysis of the surface of gas atomized powder precursor of ODS ferritic steels obtained through the STARS route

NASA Astrophysics Data System (ADS)

Gil, E.; Cortés, J.; Iturriza, I.; Ordás, N.

2018-01-01

An innovative powder metallurgy route to produce ODS FS, named STARS, has succeeded in atomizing steel powders containing the oxide formers (Y and Ti) and, hence, avoids the mechanical alloying (MA) step to dissolve Y in the matrix. A metastable oxide layer forms at the surface of atomized powders and dissociates during HIP consolidation at high temperatures, leading to precipitation of more stable Y-Ti-O nanoparticles.

Crosslinked polyimides prepared from N-(3-ethynylphenyl)maleimide

NASA Technical Reports Server (NTRS)

Gerber, Margaret K. (Inventor); St.clair, Terry L. (Inventor)

1993-01-01

The compound N-(3-ethynylphenyl)maleimide (NEPMI) was used to prepare thermally stable, glassy polyimides which did not exhibit glass transition temperatures below 500 C. NEPMI was blended with the maleimide of methylene dianiline (BMI) and heated to form the polyimide. NEPMI was also mixed with Thermid 600 R, a commercially available bisethynyl oligomeric material, and heated to form a thermally stable, glassy polyimide. Lastly, NEPMI was blended with both BMI and Thermid 600 R to form thermally stable, glassy polyimides.

Mechanism by which DHA inhibits the aggregation of KLVFFA peptides: A molecular dynamics study

NASA Astrophysics Data System (ADS)

Zhou, Hong; Liu, Shengtang; Shao, Qiwen; Ma, Dongfang; Yang, Zaixing; Zhou, Ruhong

2018-03-01

Docosahexaenoic acid (DHA) is one of the omega-3 polyunsaturated fatty acids, which has shown promising applications in lowering Aβ peptide neurotoxicity in vitro by preventing aggregation of Aβ peptides and relieving accumulation of Aβ fibrils. Unfortunately, the underlying molecular mechanisms of how DHA interferes with the aggregation of Aβ peptides remain largely enigmatic. Herein, aggregation behaviors of amyloid-β(Aβ)16-21 peptides (KLVFFA) with or without the presence of a DHA molecule were comparatively studied using extensive all-atom molecular dynamics simulations. We found that DHA could effectively suppress the aggregation of KLVFFA peptides by redirecting peptides to unstructured oligomers. The highly hydrophobic and flexible nature of DHA made it randomly but tightly entangled with Leu-17, Phe-19, and Phe-20 residues to form unstructured but stable complexes. These lower-ordered unstructured oligomers could eventually pass through energy barriers to form ordered β-sheet structures through large conformational fluctuations. This study depicts a microscopic picture for understanding the role and mechanism of DHA in inhibition of aggregation of Aβ peptides, which is generally believed as one of the important pathogenic mechanisms of Alzheimer's disease.

Ericksen number and Deborah number cascade predictions of a model for liquid crystalline polymers for simple shear flow

NASA Astrophysics Data System (ADS)

Klein, D. Harley; Leal, L. Gary; García-Cervera, Carlos J.; Ceniceros, Hector D.

2007-02-01

We consider the behavior of the Doi-Marrucci-Greco (DMG) model for nematic liquid crystalline polymers in planar shear flow. We found the DMG model to exhibit dynamics in both qualitative and quantitative agreement with experimental observations reported by Larson and Mead [Liq. Cryst. 15, 151 (1993)] for the Ericksen number and Deborah number cascades. For increasing shear rates within the Ericksen number cascade, the DMG model displays three distinct regimes: stable simple shear, stable roll cells, and irregular structure accompanied by disclination formation. In accordance with experimental observations, the model predicts both ±1 and ±1/2 disclinations. Although ±1 defects form via the ridge-splitting mechanism first identified by Feng, Tao, and Leal [J. Fluid Mech. 449, 179 (2001)], a new mechanism is identified for the formation of ±1/2 defects. Within the Deborah number cascade, with increasing Deborah number, the DMG model exhibits a streamwise banded texture, in the absence of disclinations and roll cells, followed by a monodomain wherein the mean orientation lies within the shear plane throughout the domain.

A computational investigation on the structure, global parameters and antioxidant capacity of a polyphenol, Gallic acid.

PubMed

Rajan, Vijisha K; Muraleedharan, K

2017-04-01

A computational DFT-B3LYP structural analysis of a poly phenol, Gallic acid (GA) has been performed by using 6-311++ G (df, p) basis set. The GA is a relatively stable molecule with considerable radical scavenging capacity. It is a well known antioxidant. The NBO analysis shows that the aromatic system is delocalized. The results reveal that the most stable radical is formed at O 3 -atom upon scavenging the free radicals. Global descriptive parameters show that GA acts as an acceptor center in charge transfer complex formation which is supported by ESP and contour diagrams and also by Q max value. The GA is a good antioxidant and it can be better understood by HAT and TMC mechanisms as it has low BDE, ΔH acidity and ΔG acidity values. The ΔBDE and ΔAIP values also confirm that the antioxidant capacity of GA can be explained through HAT rather than the SET-PT mechanism. Copyright © 2016 Elsevier Ltd. All rights reserved.

Detection and identification of 2-nitro-morphine and 2-nitro-morphine-6-glucuronide in nitrite adulterated urine specimens containing morphine and its glucuronides.

PubMed

Luong, Susan; Fu, Shanlin

2014-03-01

In vitro urine adulteration is a well-documented practice adopted by individuals aiming to evade detection of drug use, when required to undergo mandatory sports and workplace drug testing. Potassium nitrite is an effective urine adulterant due to its oxidizing potential, and has been shown to mask the presence of many drugs of abuse. However, limited research has been conducted to understand its mechanism of action, and to explore the possibility of the drugs undergoing direct oxidation to form stable reaction products. In this study, opiates including morphine, codeine, morphine-3-glucuronide and morphine-6-glucuronide were exposed to potassium nitrite in water and urine to mimic the process of nitrite adulteration. It was found that two stable reaction products were detected by liquid chromatography-mass spectrometry (LC-MS) when morphine and morphine-6-glucuronide were exposed to nitrite. Isolation and elucidation using spectrometric and spectroscopic techniques revealed that they were 2-nitro-morphine and 2-nitro-morphine-6-glucuronide, respectively. These reaction products were also formed when an authentic morphine-positive urine specimen was fortified with nitrite. 2-Nitro-morphine was found to be stable enough to undergo the enzymatic hydrolysis procedure and also detectable by gas chromatography-mass spectrometry (GC-MS) after forming a trimethylsilyl derivative. On the contrary, morphine-3-glucuronide did not appear to be chemically manipulated when exposed to potassium nitrite in urine. These reaction products are not endogenously produced, are relatively stable and can be monitored with both LC-MS and GC-MS confirmatory techniques. As a result, these findings have revealed the possibility for the use of 2-nitro-morphine and 2-nitro-morphine-6-glucuronide as markers for the indirect monitoring of morphine and morphine-6-glucuronide in urine specimens adulterated with nitrite. Copyright © 2013 John Wiley & Sons, Ltd.

Forming First Impressions of Others in Schizophrenia: Impairments In Fast Processing and In Use of Spatial Frequency Information

PubMed Central

Vakhrusheva, J; Zemon, V; Bar, M; Weiskopf, NG; Tremeau, F; Petkova, E; Su, Z; Abeles, I; Butler, PD

2014-01-01

Individuals form first impressions of others all the time, which affects their social functioning. Typical adults form threat impressions in faces with neutral expressions quickly, requiring less than 40 ms. These impressions appear to be mediated by low spatial frequency (LSF) content in the images. Little is known, however, about mechanisms of first impression formation in schizophrenia. The current study investigated how quickly individuals with schizophrenia can form consistent impressions of threat compared with controls and explored the mechanisms involved. Patients and controls were presented intact, LSF- or high spatial frequency (HSF)-filtered faces with durations that varied from 39 – 1703 ms and were asked to rate how threatening each face was on a scale from 1 to 5. In order to assess the speed of impression formation for intact faces, correlations were calculated for ratings made at each duration compared to a reference duration of 1703 ms for each group. Controls demonstrated a significant relation for intact faces presented for 39 ms, whereas patients required 390 ms to demonstrate a significant relation with the reference duration. For controls, LSFs primarily contributed to the formation of consistent threat impressions at 39 ms, whereas patients showed a trend for utilizing both LSF and HSF information to form consistent threat impressions at 390 ms. Results indicate that individuals with schizophrenia require a greater integration time to form a stable “first impression” of threat, which may be related to the need to utilize compensatory mechanisms such as HSF, as well as LSF, information. PMID:25458862

Forming first impressions of others in schizophrenia: impairments in fast processing and in use of spatial frequency information.

PubMed

Vakhrusheva, J; Zemon, V; Bar, M; Weiskopf, N G; Tremeau, F; Petkova, E; Su, Z; Abeles, I Y; Butler, P D

2014-12-01

Individuals form first impressions of others all the time, which affects their social functioning. Typical adults form threat impressions in faces with neutral expressions quickly, requiring less than 40 ms. These impressions appear to be mediated by low spatial frequency (LSF) content in the images. Little is known, however, about mechanisms of first impression formation in schizophrenia. The current study investigated how quickly individuals with schizophrenia can form consistent impressions of threat compared with controls and explored the mechanisms involved. Patients and controls were presented intact, LSF- or high spatial frequency (HSF)-filtered faces with durations that varied from 39 to 1703 ms and were asked to rate how threatening each face was on a scale from 1 to 5. In order to assess the speed of impression formation for intact faces, correlations were calculated for ratings made at each duration compared to a reference duration of 1703 ms for each group. Controls demonstrated a significant relation for intact faces presented for 39 ms, whereas patients required 390 ms to demonstrate a significant relation with the reference duration. For controls, LSFs primarily contributed to the formation of consistent threat impressions at 39 ms, whereas patients showed a trend for utilizing both LSF and HSF information to form consistent threat impressions at 390 ms. Results indicate that individuals with schizophrenia require a greater integration time to form a stable "first impression" of threat, which may be related to the need to utilize compensatory mechanisms such as HSF, as well as LSF, information. Copyright © 2014 Elsevier B.V. All rights reserved.

Effect of degassing on the aggregation of carbon nanotubes dispersed in water

NASA Astrophysics Data System (ADS)

Chen, C.-J.; Huang, J.-R.; Hwang, I.-S.; Choi, H. J.; Lai, P.-Y.; Chan, C. K.

2017-10-01

Dynamic light scattering (DLS) along with centrifugation and shaking tests reveal that dissolved gases can significantly affect the aggregation behavior of carbon nanotubes (CNTs) dispersed in water. The CNTs in non-degassed samples form loose, stable networks having the DLS result reminiscent of semidilute polymer solutions, whereas the CNTs in degassed samples aggregate to form Brownian colloids that sediment quickly. Interestingly, the CNTs dispersed in acetone, with or without degassing, also behave like semidilute polymers in DLS experiments. We propose a surface nanobubble-assisted mechanism to explain the observed aggregation behaviors. Our work signifies that dissolved gases may play an important role in determining hydrophobicity and biomolecular functions in aqueous environments.

Trimerization and Triple Helix Stabilization of the Collagen XIX NC2 Domain*

PubMed Central

Boudko, Sergei P.; Engel, Jürgen; Bächinger, Hans Peter

2008-01-01

The mechanisms of chain selection and assembly of fibril-associated collagens with interrupted triple helices (FACITs) must differ from that of fibrillar collagens, since they lack the characteristic C-propeptide. We analyzed two carboxyl-terminal noncollagenous domains, NC2 and NC1, of collagen XIX as potential trimerization units and found that NC2 forms a stable trimer and substantially stabilizes a collagen triple helix attached to either end. In contrast, the NC1 domain requires formation of an adjacent collagen triple helix to form interchain disulfide bridges. The NC2 domain of collagen XIX and probably of other FACITs is responsible for chain selection and trimerization. PMID:18845531

Method for producing metal oxide aerogels

DOEpatents

Tillotson, Thomas M.; Poco, John F.; Hrubesh, Lawrence W.; Thomas, Ian M.

1995-01-01

A two-step hydrolysis-condensation method was developed to form metal oxide aerogels of any density, including densities of less than 0.003g/cm.sup.3 and greater than 0.27g/cm.sup.3. High purity metal alkoxide is reacted with water, alcohol solvent, and an additive to form a partially condensed metal intermediate. All solvent and reaction-generated alcohol is removed, and the intermediate is diluted with a nonalcoholic solvent. The intermediate can be stored for future use to make aerogels of any density. The aerogels are formed by reacting the intermediate with water, nonalcoholic solvent, and a catalyst, and extracting the nonalcoholic solvent directly. The resulting monolithic aerogels are hydrophobic and stable under atmospheric conditions, and exhibit good optical transparency, high clarity, and homogeneity. The aerogels have high thermal insulation capacity, high porosity, mechanical strength and stability, and require shorter gelation times than aerogels formed by conventional methods.

Method for producing metal oxide aerogels

DOEpatents

Tillotson, T.M.; Poco, J.F.; Hrubesh, L.W.; Thomas, I.M.

1995-04-25

A two-step hydrolysis-condensation method was developed to form metal oxide aerogels of any density, including densities of less than 0.003g/cm{sup 3} and greater than 0.27g/cm{sup 3}. High purity metal alkoxide is reacted with water, alcohol solvent, and an additive to form a partially condensed metal intermediate. All solvent and reaction-generated alcohol is removed, and the intermediate is diluted with a nonalcoholic solvent. The intermediate can be stored for future use to make aerogels of any density. The aerogels are formed by reacting the intermediate with water, nonalcoholic solvent, and a catalyst, and extracting the nonalcoholic solvent directly. The resulting monolithic aerogels are hydrophobic and stable under atmospheric conditions, and exhibit good optical transparency, high clarity, and homogeneity. The aerogels have high thermal insulation capacity, high porosity, mechanical strength and stability, and require shorter gelation times than aerogels formed by conventional methods. 8 figs.

Structural transformations of heat treated Co-less high entropy alloys

NASA Astrophysics Data System (ADS)

Mitrica, D.; Tudor, A.; Rinaldi, A.; Soare, V.; Predescu, C.; Berbecaru, A.; Stoiciu, F.; Badilita, V.

2018-03-01

Co is considered to be one of the main ingredients in superalloys. Co is considered a critical element and its substitution is difficult due to its unique ability to form high temperature stable structures with high mechanical and corrosion/oxidation resistance. High entropy alloys (HEA) represent a relatively new concept in material design. HEA are characterised by a high number of alloying elements, in unusually high proportion. Due to their specific particularities, high entropy alloys tend to form predominant solid solution structures that develop potentially high chemical, physical and mechanical properties. Present paper is studying Co-less high entropy alloys with high potential in severe environment applications. The high entropy alloys based on Al-Cr-Fe-Mn-Ni system were prepared by induction melting and casting under protective atmosphere. The as-cast specimens were heat treated at various temperatures to determine the structure and property behaviour. Samples taken before and after heat treatment were investigated for chemical, physical, structural and mechanical characteristics. Sigma phase composition and heat treatment parameters had major influence over the resulted alloy structure and properties.

Deformation behavior of a 16-8-2 GTA weld as influenced by its solidification substructure

DOE Office of Scientific and Technical Information (OSTI.GOV)

Foulds, J.R.; Moteff, J.; Sikka, V.K.

1983-07-01

Weldment sections from formed and welded type 316 stainless steel pipe are characterized with respect to some time-independent (tensile) and time-dependent (creep) mechanical properties at temperatures between 25/sup 0/C and 649/sup 0/C. The GTA weldment, welded with 16-8-2 filler metal, is sectioned from pipe in the formed + welded + solution annealed + straightened condition, as well as in the same condition with an additional re-solution treatment. Detailed room temperature microhardness measurements on these sections before and after reannealing enable a determination of the different recovery characteristics of weld and base metal. The observed stable weld metal solidification dislocation substructuremore » in comparison with the base metal random dislocation structure, in fact, adequately explains weld/base metal elevated temperature mechanical behavior differences from this recovery characteristic standpoint. The weld metal substructure is the only parameter common to the variety of austenitic stainless steel welds exhibiting the consistent parent/weld metal deformation behavior differences described. As such, it must be considered the key to understanding weldment mechanical behavior.« less

Equilibrium contact angle or the most-stable contact angle?

PubMed

Montes Ruiz-Cabello, F J; Rodríguez-Valverde, M A; Cabrerizo-Vílchez, M A

2014-04-01

It is well-established that the equilibrium contact angle in a thermodynamic framework is an "unattainable" contact angle. Instead, the most-stable contact angle obtained from mechanical stimuli of the system is indeed experimentally accessible. Monitoring the susceptibility of a sessile drop to a mechanical stimulus enables to identify the most stable drop configuration within the practical range of contact angle hysteresis. Two different stimuli may be used with sessile drops: mechanical vibration and tilting. The most stable drop against vibration should reveal the changeless contact angle but against the gravity force, it should reveal the highest resistance to slide down. After the corresponding mechanical stimulus, once the excited drop configuration is examined, the focus will be on the contact angle of the initial drop configuration. This methodology needs to map significantly the static drop configurations with different stable contact angles. The most-stable contact angle, together with the advancing and receding contact angles, completes the description of physically realizable configurations of a solid-liquid system. Since the most-stable contact angle is energetically significant, it may be used in the Wenzel, Cassie or Cassie-Baxter equations accordingly or for the surface energy evaluation. © 2013 Elsevier B.V. All rights reserved.

Protective V127 prion variant prevents prion disease by interrupting the formation of dimer and fibril from molecular dynamics simulations.

PubMed

Zhou, Shuangyan; Shi, Danfeng; Liu, Xuewei; Liu, Huanxiang; Yao, Xiaojun

2016-02-24

Recent studies uncovered a novel protective prion protein variant: V127 variant, which was reported intrinsically resistant to prion conversion and propagation. However, the structural basis of its protective effect is still unknown. To uncover the origin of the protective role of V127 variant, molecular dynamics simulations were performed to explore the influence of G127V mutation on two key processes of prion propagation: dimerization and fibril formation. The simulation results indicate V127 variant is unfavorable to form dimer by reducing the main-chain H-bond interactions. The simulations of formed fibrils consisting of β1 strand prove V127 variant will make the formed fibril become unstable and disorder. The weaker interaction energies between layers and reduced H-bonds number for V127 variant reveal this mutation is unfavorable to the formation of stable fibril. Consequently, we find V127 variant is not only unfavorable to the formation of dimer but also unfavorable to the formation of stable core and fibril, which can explain the mechanism on the protective role of V127 variant from the molecular level. Our findings can deepen the understanding of prion disease and may guide the design of peptide mimetics or small molecule to mimic the protective effect of V127 variant.

Mechanically flexible organic electroluminescent device with directional light emission

DOEpatents

Duggal, Anil Raj; Shiang, Joseph John; Schaepkens, Marc

2005-05-10

A mechanically flexible and environmentally stable organic electroluminescent ("EL") device with directional light emission comprises an organic EL member disposed on a flexible substrate, a surface of which is coated with a multilayer barrier coating which includes at least one sublayer of a substantially transparent organic polymer and at least one sublayer of a substantially transparent inorganic material. The device includes a reflective metal layer disposed on the organic EL member opposite to the substrate. The reflective metal layer provides an increased external quantum efficiency of the device. The reflective metal layer and the multilayer barrier coating form a seal around the organic EL member to reduce the degradation of the device due to environmental elements.

Effect of Grinding on the Solid-State Stability and Particle Dissolution of Acyclovir Polymorphs.

PubMed

Magnoni, Federico; Gigliobianco, Maria Rosa; Vargas Peregrina, Dolores; Censi, Roberta; Di Martino, Piera

2017-10-01

The present work investigated the solid state change of 4 acyclovir polymorphs when ground at room temperature (Method A) and under cryo-grinding in the presence of liquid nitrogen (Method B). Modifications in particle size and shape (evaluated by scanning electron microscopy) and in the water content (evaluated by thermal analysis) were related to transitions at the solid state, as confirmed by X-ray powder diffractometry. Anhydrous Form I was stable under grinding by both Methods A and B. The anhydrous Form II was stable during grinding under Method A, whereas it was progressively converted to the hydrate Form V during grinding under Method B. The hydrate Form V was stable under Method A, whereas it was converted to the anhydrous Form I after 15 min and then to the hydrate Form VI after 45 min of grinding. The hydrate Form VI proved to be stable under grinding by both Methods A and B. Thus, Form I and VI were the only forms that yielded a sizeable decrease in particle size under grinding, with a consequent increase in particle dissolution rate, while maintaining solid state physicochemical stability. Form I treated under Method B grinding gave the best dissolution rate. Copyright © 2017 American Pharmacists Association®. Published by Elsevier Inc. All rights reserved.

Tutorial on Atomic Oxygen Effects and Contamination

NASA Technical Reports Server (NTRS)

Miller, Sharon K.

2017-01-01

Atomic oxygen is the most predominant specie in low Earth orbit (LEO) and is contained in the upper atmosphere of many other planetary bodies. Formed by photo-dissociation of molecular oxygen, it is highly reactive and energetic enough to break chemical bonds on the surface of many materials and react with them to form either stable or volatile oxides. The extent of the damage for spacecraft depends a lot on how much atomic oxygen arrives at the surface, the energy of the atoms, and the reactivity of the material that is exposed to it. Oxide formation can result in shrinkage, cracking, or erosion which can also result in changes in optical, thermal, or mechanical properties of the materials exposed. The extent of the reaction can be affected by mechanical loading, temperature, and other environmental components such as ultraviolet radiation or charged particles. Atomic oxygen generally causes a surface reaction, but it can scatter under coatings and into crevices causing oxidation much farther into a spacecraft surface or structure than would be expected. Contamination can also affect system performance. Contamination is generally caused by arrival of volatile species that condense on spacecraft surfaces. The volatiles are typically a result of outgassing of materials that are on the spacecraft. Once the volatiles are condensed on a surface, they can then be fixed on the surface by ultraviolet radiation andor atomic oxygen reaction to form stable surface contaminants that can change optical and thermal properties of materials in power systems, thermal systems, and sensors. This tutorial discusses atomic oxygen erosion and contaminate formation, and the effect they have on typical spacecraft materials. Scattering of atomic oxygen, some effects of combined environments and examples of effects of atomic oxygen and contamination on spacecraft systems and components will also be presented.

Molecular mechanisms of the cytotoxicity of human α-lactalbumin made lethal to tumor cells (HAMLET) and other protein-oleic acid complexes.

PubMed

Nakamura, Takashi; Aizawa, Tomoyasu; Kariya, Ryusho; Okada, Seiji; Demura, Makoto; Kawano, Keiichi; Makabe, Koki; Kuwajima, Kunihiro

2013-05-17

Although HAMLET (human α-lactalbumin made lethal to tumor cells), a complex formed by human α-lactalbumin and oleic acid, has a unique apoptotic activity for the selective killing of tumor cells, the molecular mechanisms of expression of the HAMLET activity are not well understood. Therefore, we studied the molecular properties of HAMLET and its goat counterpart, GAMLET (goat α-lactalbumin made lethal to tumor cells), by pulse field gradient NMR and 920-MHz two-dimensional NMR techniques. We also examined the expression of HAMLET-like activities of complexes between oleic acid and other proteins that form a stable molten globule state. We observed that both HAMLET and GAMLET at pH 7.5 were heterogeneous, composed of the native protein, the monomeric molten globule-like state, and the oligomeric species. At pH 2.0 and 50 °C, HAMLET and GAMLET appeared in the monomeric state, and we identified the oleic acid-binding site in the complexes by two-dimensional NMR. Rather surprisingly, the binding site thus identified was markedly different between HAMLET and GAMLET. Furthermore, canine milk lysozyme, apo-myoglobin, and β2-microglobulin all formed the HAMLET-like complex with the anti-tumor activity, when the protein was treated with oleic acid under conditions in which their molten globule states were stable. From these results, we conclude that the protein portion of HAMLET, GAMLET, and the other HAMLET-like protein-oleic acid complexes is not the origin of their cytotoxicity to tumor cells and that the protein portion of these complexes plays a role in the delivery of cytotoxic oleic acid molecules into tumor cells across the cell membrane.

Molecular Mechanisms of the Cytotoxicity of Human α-Lactalbumin Made Lethal to Tumor Cells (HAMLET) and Other Protein-Oleic Acid Complexes*

PubMed Central

Nakamura, Takashi; Aizawa, Tomoyasu; Kariya, Ryusho; Okada, Seiji; Demura, Makoto; Kawano, Keiichi; Makabe, Koki; Kuwajima, Kunihiro

2013-01-01

Although HAMLET (human α-lactalbumin made lethal to tumor cells), a complex formed by human α-lactalbumin and oleic acid, has a unique apoptotic activity for the selective killing of tumor cells, the molecular mechanisms of expression of the HAMLET activity are not well understood. Therefore, we studied the molecular properties of HAMLET and its goat counterpart, GAMLET (goat α-lactalbumin made lethal to tumor cells), by pulse field gradient NMR and 920-MHz two-dimensional NMR techniques. We also examined the expression of HAMLET-like activities of complexes between oleic acid and other proteins that form a stable molten globule state. We observed that both HAMLET and GAMLET at pH 7.5 were heterogeneous, composed of the native protein, the monomeric molten globule-like state, and the oligomeric species. At pH 2.0 and 50 °C, HAMLET and GAMLET appeared in the monomeric state, and we identified the oleic acid-binding site in the complexes by two-dimensional NMR. Rather surprisingly, the binding site thus identified was markedly different between HAMLET and GAMLET. Furthermore, canine milk lysozyme, apo-myoglobin, and β2-microglobulin all formed the HAMLET-like complex with the anti-tumor activity, when the protein was treated with oleic acid under conditions in which their molten globule states were stable. From these results, we conclude that the protein portion of HAMLET, GAMLET, and the other HAMLET-like protein-oleic acid complexes is not the origin of their cytotoxicity to tumor cells and that the protein portion of these complexes plays a role in the delivery of cytotoxic oleic acid molecules into tumor cells across the cell membrane. PMID:23580643

The Absence of a Mature Cell Wall Sacculus in Stable Listeria monocytogenes L-Form Cells Is Independent of Peptidoglycan Synthesis.

PubMed

Studer, Patrick; Borisova, Marina; Schneider, Alexander; Ayala, Juan A; Mayer, Christoph; Schuppler, Markus; Loessner, Martin J; Briers, Yves

2016-01-01

L-forms are cell wall-deficient variants of otherwise walled bacteria that maintain the ability to survive and proliferate in absence of the surrounding peptidoglycan sacculus. While transient or unstable L-forms can revert to the walled state and may still rely on residual peptidoglycan synthesis for multiplication, stable L-forms cannot revert to the walled form and are believed to propagate in the complete absence of peptidoglycan. L-forms are increasingly studied as a fundamental biological model system for cell wall synthesis. Here, we show that a stable L-form of the intracellular pathogen Listeria monocytogenes features a surprisingly intact peptidoglycan synthesis pathway including glycosyl transfer, in spite of the accumulation of multiple mutations during prolonged passage in the cell wall-deficient state. Microscopic and biochemical analysis revealed the presence of peptidoglycan precursors and functional glycosyl transferases, resulting in the formation of peptidoglycan polymers but without the synthesis of a mature cell wall sacculus. In conclusion, we found that stable, non-reverting L-forms, which do not require active PG synthesis for proliferation, may still continue to produce aberrant peptidoglycan.

Engineered elastomeric proteins with dual elasticity can be controlled by a molecular regulator.

PubMed

Cao, Yi; Li, Hongbin

2008-08-01

Elastomeric proteins are molecular springs that confer excellent mechanical properties to many biological tissues and biomaterials. Depending on the role performed by the tissue or biomaterial, elastomeric proteins can behave as molecular springs or shock absorbers. Here we combine single-molecule atomic force microscopy and protein engineering techniques to create elastomeric proteins that can switch between two distinct types of mechanical behaviour in response to the binding of a molecular regulator. The proteins are mechanically labile by design and behave as entropic springs with an elasticity that is governed by their configurational entropy. However, when a molecular regulator binds to the protein, it switches into a mechanically stable state and can act as a shock absorber. These engineered proteins effectively mimic and combine the two extreme forms of elastic behaviour found in natural elastomeric proteins, and thus represent a new type of smart nanomaterial that will find potential applications in nanomechanics and material sciences.

Superradiant instabilities of rotating black branes and strings

NASA Astrophysics Data System (ADS)

Cardoso, Vitor; Yoshida, Shijun

2005-07-01

Black branes and strings are generally unstable against a certain sector of gravitational perturbations. This is known as the Gregory-Laflamme instability. It has been recently argued [1], [2] that there exists another general instability affecting many rotating extended black objects. This instability is in a sense universal, in that it is triggered by any massless field, and not just gravitational perturbations. Here we investigate this novel mechanism in detail. For this instability to work, two ingredients are necessary: (i) an ergo-region, which gives rise to superradiant amplification of waves, and (ii) ``bound'' states in the effective potential governing the evolution of the particular mode under study. We show that the black brane Kerr4×Rp is unstable against this mechanism, and we present numerical results for instability timescales for this case. On the other hand, and quite surprisingly, black branes of the form Kerrd×Rp are all stable against this mechanism for d > 4. This is quite an unexpected result, and it stems from the fact that there are no stable circular orbits in higher dimensional black hole spacetimes, or in a wave picture, that there are no bound states in the effective potential. We also show that it is quite easy to simulate this instability in the laboratory with acoustic black branes.

Probing Toluene and Ethylbenzene Stable Glass Formation using Inert Gas Permeation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Smith, R. Scott; May, Robert A.; Kay, Bruce D.

Inert gas permeation is used to investigate the formation of stable glasses of toluene and ethylbenzene. The effect of deposition temperature (Tdep) on the kinetic stability of the vapor deposited glasses is determined using Kr desorption spectra from within sandwich layers of either toluene or ethylbenzene. The results for toluene show that the most stable glass is formed at Tdep = 0.92 Tg, although glasses with a kinetic stability within 50% of the most stable glass were found with deposition temperatures from 0.85 to 0.95 Tg. Similar results were found for ethylbenzene, which formed its most stable glass at 0.91more » Tg and formed stable glasses from 0.81 to 0.96 Tg. These results are consistent with recent calorimetric studies and demonstrate that the inert gas permeation technique provides a direct method to observe the onset of molecular translation motion that accompanies the glass to supercooled liquid transition.« less

Stabilization of Quinapril by Incorporating Hydrogen Bonding Interactions

PubMed Central

Roy, B. N.; Singh, G. P.; Godbole, H. M.; Nehate, S. P.

2009-01-01

In the present study stability of various known solvates of quinapril hydrochloride has been compared with nitromethane solvate. Nitromethane solvate was found to be more stable compared to other known solvates. Single crystal X-ray diffraction analysis of quinapril nitromethane solvate shows intermolecular hydrogen bonding between quinapril molecule and nitromethane. Stabilization of quinapril by forming strong hydrogen bonding network as in case of co-crystals was further studied by forming co-crystal with tris(hydroxymethyl)amino methane. Quinapril free base forms a stable salt with tris(hydroxymethyl)amino methane not reported earlier. Quinapril tris(hydroxymethyl)amino methane salt found to be stable even at 80° for 72 h i.e. hardly any formation of diketopiperazine and diacid impurity. As expected single crystal X-ray diffraction analysis reveals tris(hydroxymethyl)amino methane salt of quinapril shows complex hydrogen bonding network between the two entities along with ionic bond. The properties of this stable salt - stable in solid as well as solution phase, might lead to an alternate highly stable formulation. PMID:20502545

Exploring monovalent copper compounds with oxygen and hydrogen

PubMed Central

Korzhavyi, Pavel A.; Soroka, Inna L.; Isaev, Eyvaz I.; Lilja, Christina; Johansson, Börje

2012-01-01

New important applications of copper metal, e.g., in the areas of hydrogen production, fuel cell operation, and spent nuclear fuel disposal, require accurate knowledge of the physical and chemical properties of stable and metastable copper compounds. Among the copper(I) compounds with oxygen and hydrogen, cuprous oxide Cu2O is the only one stable and the best studied. Other such compounds are less known (CuH) or totally unknown (CuOH) due to their instability relative to the oxide. Here we combine quantum-mechanical calculations with experimental studies to search for possible compounds of monovalent copper. Cuprous hydride (CuH) and cuprous hydroxide (CuOH) are proved to exist in solid form. We establish the chemical and physical properties of these compounds, thereby filling the existing gaps in our understanding of hydrogen- and oxygen-related phenomena in Cu metal. PMID:22219370

Interactions of aqueous Ag+ with fulvic acids: mechanisms of silver nanoparticle formation and investigation of stability.

PubMed

Adegboyega, Nathaniel F; Sharma, Virender K; Siskova, Karolina; Zbořil, Radek; Sohn, Mary; Schultz, Brian J; Banerjee, Sarbajit

2013-01-15

This study investigated the possible natural formation of silver nanoparticles (AgNPs) in Ag(+)-fulvic acid (FA) solutions under various environmentally relevant conditions (temperature, pH, and UV light). Increase in temperature (24-90 °C) and pH (6.1-9.0) of Ag(+)-Suwannee River fulvic acid (SRFA) solutions accelerated the appearance of the characteristic surface plasmon resonance (SPR) of AgNPs. The rate of AgNP formation via reduction of Ag(+) in the presence of different FAs (SRFA, Pahokee Peat fulvic acid, PPFA, Nordic lake fulvic acid, NLFA) and Suwannee River humic acid (SRHA) followed the order NLFA > SRHA > PPFA > SRFA. This order was found to be related to the free radical content of the acids, which was consistent with the proposed mechanism. The same order of AgNP growth was seen upon UV light illumination of Ag(+)-FA and Ag(+)-HA mixtures in moderately hard reconstituted water (MHRW). Stability studies of AgNPs, formed from the interactions of Ag(+)-SRFA, over a period of several months showed that these AgNPs were highly stable with SPR peak reductions of only ~15%. Transmission electron microscopy (TEM) and dynamic light scattering (DLS) measurements revealed bimodal particle size distributions of aged AgNPs. The stable AgNPs formed through the reduction of Ag(+) by fulvic and humic acid fractions of natural organic matter in the environment may be transported over significant distances and might also influence the overall bioavailability and ecotoxicity of AgNPs.

Stability and free energy calculation of LNA modified quadruplex: a molecular dynamics study

NASA Astrophysics Data System (ADS)

Chaubey, Amit Kumar; Dubey, Kshatresh Dutta; Ojha, Rajendra Prasad

2012-03-01

Telomeric ends of chromosomes, which comprise noncoding repeat sequences of guanine-rich DNA, which are the fundamental in protecting the cell from recombination and degradation. Telomeric DNA sequences can form four stranded quadruplex structures, which are involved in the structure of telomere ends. The formation and stabilization of telomeric quadruplexes has been shown to inhibit the activity of telomerase, thus establishing telomeric DNA quadrulex as an attractive target for cancer therapeutic intervention. Molecular dynamic simulation offers the prospects of detailed description of the dynamical structure with ion and water at molecular level. In this work we have taken a oligomeric part of human telomeric DNA, d(TAGGGT) to form different monomeric quadruplex structures d(TAGGGT)4. Here we report the relative stabilities of these structures under K+ ion conditions and binding interaction between the strands, as determined by molecular dynamic simulations followed by energy calculation. We have taken locked nucleic acid (LNA) in this study. The free energy molecular mechanics Poission Boltzman surface area calculations are performed for the determination of most stable complex structure between all modified structures. We calculated binding free energy for the combination of different strands as the ligand and receptor for all structures. The energetic study shows that, a mixed hybrid type quadruplex conformation in which two parallel strands are bind with other two antiparallel strands, are more stable than other conformations. The possible mechanism for the inhibition of the cancerous growth has been discussed. Such studies may be helpful for the rational drug designing.

A synthetic GFP-like chromophore undergoes base-catalyzed autoxidation into acylimine red form.

PubMed

Ivashkin, Pavel E; Lukyanov, Konstantin A; Lukyanov, Sergey; Yampolsky, Ilia V

2011-04-15

Fluorescent proteins are widely used in modern experimental biology, but much controversy exists regarding details of maturation of different types of their chromophores. Here we studied possible mechanisms of DsRed-type red chromophore formation using synthetic biomimetic GFP-like chromophores, bearing an acylamino substituent, corresponding to an amino acid residue at position 65. We have shown these model compounds to readily react with molecular oxygen to produce a highly unstable DsRed-like acylimine, isolated in the form of stable derivatives. Under the same aerobic conditions an unusual red-shifted imide chromophore--a product of 4-electron oxidation of Gly65 residue--is formed. Our data showed that GFP chromophore is prone to autoxidation at position 65 Cα by its chemical nature with basic conditions being the only key factor required.

Melts of Octaacetyl Sucrose as Oral-Modified Release Dosage Forms for Delivery of Poorly Soluble Compound in Stable Amorphous Form.

PubMed

Haznar-Garbacz, Dorota; Kaminska, Ewa; Zakowiecki, Daniel; Lachmann, Marek; Kaminski, Kamil; Garbacz, Grzegorz; Dorożyński, Przemysław; Kulinowski, Piotr

2018-02-01

The presented work describes the formulation and characterization of modified release glassy solid dosage forms (GSDFs) containing an amorphous nifedipine, as a model BCS (Biopharmaceutical Classification System) class II drug. The GSDFs were prepared by melting nifedipine together with octaacetyl sucrose. Dissolution profiles, measured under standard and biorelevant conditions, were compared to those obtained from commercially available formulations containing nifedipine such as modified release (MR) tablets and osmotic release oral system (OROS). The results indicate that the dissolution profiles of the GSDFs with nifedipine are neither affected by the pH of the dissolution media, type and concentration of surfactants, nor by simulated mechanical stress of biorelevant intensity. Furthermore, it was found that the dissolution profiles of the novel dosage forms were similar to the profiles obtained from the nifedipine OROS. The formulation of GSDFs is relatively simple, and the dosage forms were found to have favorable dissolution characteristics.

Micromotors working in water through artificial aerobic metabolism

NASA Astrophysics Data System (ADS)

Yamamoto, D.; Takada, T.; Tachibana, M.; Iijima, Y.; Shioi, A.; Yoshikawa, K.

2015-07-01

Most catalytic micro/nanomotors that have been developed so far use hydrogen peroxide as fuel, while some use hydrazine. These fuels are difficult to apply because they can cause skin irritation, and often form and store disruptive bubbles. In this paper, we demonstrate a novel catalytic Pt micromotor that does not produce bubbles, and is driven by the oxidation of stable, non-toxic primary alcohols and aldehydes with dissolved oxygen. This use of organic oxidation mirrors living systems, and lends this new motor essentially the same characteristics, including decreased motility in low oxygen environments and the direct isothermal conversion of chemical energy into mechanical energy. Interestingly, the motility direction is reversed by replacing the reducing fuels with hydrogen peroxide. Therefore, these micromotors not only provide a novel system in nanotechnology, but also help in further revealing the underlining mechanisms of motility of living organisms.Most catalytic micro/nanomotors that have been developed so far use hydrogen peroxide as fuel, while some use hydrazine. These fuels are difficult to apply because they can cause skin irritation, and often form and store disruptive bubbles. In this paper, we demonstrate a novel catalytic Pt micromotor that does not produce bubbles, and is driven by the oxidation of stable, non-toxic primary alcohols and aldehydes with dissolved oxygen. This use of organic oxidation mirrors living systems, and lends this new motor essentially the same characteristics, including decreased motility in low oxygen environments and the direct isothermal conversion of chemical energy into mechanical energy. Interestingly, the motility direction is reversed by replacing the reducing fuels with hydrogen peroxide. Therefore, these micromotors not only provide a novel system in nanotechnology, but also help in further revealing the underlining mechanisms of motility of living organisms. Electronic supplementary information (ESI) available: Details of the experimental procedure, supplementary note S1, supplementary Fig. S1 to S5, and supplementary videos S1 to S4. See DOI: 10.1039/c5nr03300d

Metal-oxide-metal point contact junction detectors. [detection mechanism and mechanical stability

NASA Technical Reports Server (NTRS)

Baird, J.; Havemann, R. H.; Fults, R. D.

1973-01-01

The detection mechanism(s) and design of a mechanically stable metal-oxide-metal point contact junction detector are considered. A prototype for a mechanically stable device has been constructed and tested. A technique has been developed which accurately predicts microwave video detector and heterodyne mixer SIM (semiconductor-insulator-metal) diode performance from low dc frequency volt-ampere curves. The difference in contact potential between the two metals and geometrically induced rectification constitute the detection mechanisms.

Upregulation of Ih expressed in IB4-negative Aδ nociceptive DRG neurons contributes to mechanical hypersensitivity associated with cervical radiculopathic pain

PubMed Central

Liu, Da-Lu; Lu, Na; Han, Wen-Juan; Chen, Rong-Gui; Cong, Rui; Xie, Rou-Gang; Zhang, Yu-Fei; Kong, Wei-Wei; Hu, San-Jue; Luo, Ceng

2015-01-01

Cervical radiculopathy represents aberrant mechanical hypersensitivity. Primary sensory neuron’s ability to sense mechanical force forms mechanotransduction. However, whether this property undergoes activity-dependent plastic changes and underlies mechanical hypersensitivity associated with cervical radiculopathic pain (CRP) is not clear. Here we show a new CRP model producing stable mechanical compression of dorsal root ganglion (DRG), which induces dramatic behavioral mechanical hypersensitivity. Amongst nociceptive DRG neurons, a mechanically sensitive neuron, isolectin B4 negative Aδ-type (IB4− Aδ) DRG neuron displays spontaneous activity with hyperexcitability after chronic compression of cervical DRGs. Focal mechanical stimulation on somata of IB4- Aδ neuron induces abnormal hypersensitivity. Upregulated HCN1 and HCN3 channels and increased Ih current on this subset of primary nociceptors underlies the spontaneous activity together with neuronal mechanical hypersensitivity, which further contributes to the behavioral mechanical hypersensitivity associated with CRP. This study sheds new light on the functional plasticity of a specific subset of nociceptive DRG neurons to mechanical stimulation and reveals a novel mechanism that could underlie the mechanical hypersensitivity associated with cervical radiculopathy. PMID:26577374

Structurally Stable Attractive Nanoscale Emulsions with Dipole-Dipole Interaction-Driven Interdrop Percolation.

PubMed

Shin, Kyounghee; Gong, Gyeonghyeon; Cuadrado, Jonas; Jeon, Serim; Seo, Mintae; Choi, Hong Sung; Hwang, Jae Sung; Lee, Youngbok; Fernandez-Nieves, Alberto; Kim, Jin Woong

2017-03-28

This study introduces an extremely stable attractive nanoscale emulsion fluid, in which the amphiphilic block copolymer, poly(ethylene oxide)-block-poly(ϵ-caprolactone) (PEO-b-PCL), is tightly packed with lecithin, thereby forming a mechanically robust thin-film at the oil-water interface. The molecular association of PEO-b-PCL with lecithin is critical for formation of a tighter and denser molecular assembly at the interface, which is systematically confirmed by T 2 relaxation and DSC analyses. Moreover, suspension rheology studies also reflect the interdroplet attractions over a wide volume fraction range of the dispersed oil phase; this results in a percolated network of stable drops that exhibit no signs of coalescence or phase separation. This unique rheological behavior is attributed to the dipolar interaction between the phosphorylcholine groups of lecithin and the methoxy end groups of PEO-b-PCL. Finally, the nanoemulsion system significantly enhances transdermal delivery efficiency due to its favorable attraction to the skin, as well as high diffusivity of the nanoscale emulsion drops. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Sanctions as honest signals--the evolution of pool punishment by public sanctioning institutions.

PubMed

Schoenmakers, Sarah; Hilbe, Christian; Blasius, Bernd; Traulsen, Arne

2014-09-07

In many species, mutual cooperation is stabilized by forms of policing and peer punishment: if cheaters are punished, there is a strong selective pressure to cooperate. Most human societies have complemented, and sometimes even replaced, such peer punishment mechanisms with pool punishment, where punishment is outsourced to central institutions such as the police. Even before free-riding occurs, such institutions require investments, which could serve as costly signals. Here, we show with a game theoretical model that this signaling effect in turn can be crucial for the evolution of punishment institutions: In the absence of such signals, pool punishment is only stable with second-order punishment and can only evolve when individuals have the freedom not to take part in any interaction. With such signals, individuals can opportunistically adjust their behavior, which promotes the evolution of stable pool punishment even in situations where no one can stand aside. Thus, the human propensity to react opportunistically to credible punishment threats is often sufficient to establish stable punishment institutions and to maintain high levels of cooperation. Copyright © 2014 The Authors. Published by Elsevier Ltd.. All rights reserved.

Sanctions as honest signals – The evolution of pool punishment by public sanctioning institutions

PubMed Central

Schoenmakers, Sarah; Hilbe, Christian; Blasius, Bernd; Traulsen, Arne

2014-01-01

In many species, mutual cooperation is stabilized by forms of policing and peer punishment: if cheaters are punished, there is a strong selective pressure to cooperate. Most human societies have complemented, and sometimes even replaced, such peer punishment mechanisms with pool punishment, where punishment is outsourced to central institutions such as the police. Even before free-riding occurs, such institutions require investments, which could serve as costly signals. Here, we show with a game theoretical model that this signaling effect in turn can be crucial for the evolution of punishment institutions: In the absence of such signals, pool punishment is only stable with second-order punishment and can only evolve when individuals have the freedom not to take part in any interaction. With such signals, individuals can opportunistically adjust their behavior, which promotes the evolution of stable pool punishment even in situations where no one can stand aside. Thus, the human propensity to react opportunistically to credible punishment threats is often sufficient to establish stable punishment institutions and to maintain high levels of cooperation. PMID:24768866

Composition, sources, and bioavailability of nitrogen in a longitudinal gradient from freshwater to estuarine waters.

PubMed

Jani, Jariani; Toor, Gurpal S

2018-06-15

Nitrogen (N) transport from land to water is a dominant contributor of N in estuarine waters leading to eutrophication, harmful algal blooms, and hypoxia. Our objectives were to (1) investigate the composition of inorganic and organic N forms, (2) distinguish the sources and biogeochemical mechanisms of nitrate-N (NO 3 -N) transport using stable isotopes of NO 3 - and Bayesian mixing model, and (3) determine the dissolved organic N (DON) bioavailability using bioassays in a longitudinal gradient from freshwater to estuarine ecosystem located in the Tampa Bay, Florida, United States. We found that DON was the most dominant N form (mean: 64%, range: 46-83%) followed by particulate organic N (PON, mean: 22%, range: 14-37%), whereas inorganic N forms (NO x -N: 7%, NH 4 -N: 7%) were 14% of total N in freshwater and estuarine waters. Stable isotope data of NO 3 - revealed that nitrification was the main contributor (36.4%), followed by soil and organic N sources (25.5%), NO 3 - fertilizers (22.4%), and NH 4 + fertilizers (15.7%). Bioassays showed that 14 to 65% of DON concentrations decreased after 5-days of incubation indicating utilization of DON by microbes in freshwater and estuarine waters. These results suggest that despite low proportion of inorganic N forms, the higher concentrations and bioavailability of DON can be a potential source of N for algae and bacteria leading to water quality degradation in the estuarine waters. Copyright © 2018 Elsevier Ltd. All rights reserved.

How can EPR spectroscopy help to unravel molecular mechanisms of flavin-dependent photoreceptors?

PubMed

Nohr, Daniel; Rodriguez, Ryan; Weber, Stefan; Schleicher, Erik

2015-01-01

Electron paramagnetic resonance (EPR) spectroscopy is a well-established spectroscopic method for the examination of paramagnetic molecules. Proteins can contain paramagnetic moieties in form of stable cofactors, transiently formed intermediates, or spin labels artificially introduced to cysteine sites. The focus of this review is to evaluate potential scopes of application of EPR to the emerging field of optogenetics. The main objective for EPR spectroscopy in this context is to unravel the complex mechanisms of light-active proteins, from their primary photoreaction to downstream signal transduction. An overview of recent results from the family of flavin-containing, blue-light dependent photoreceptors is given. In detail, mechanistic similarities and differences are condensed from the three classes of flavoproteins, the cryptochromes, LOV (Light-oxygen-voltage), and BLUF (blue-light using FAD) domains. Additionally, a concept that includes spin-labeled proteins and examination using modern pulsed EPR is introduced, which allows for a precise mapping of light-induced conformational changes.

Computational Calculation Of The Ionization Energies Of The Human Prion Protein By The Coarse-grain Method

NASA Astrophysics Data System (ADS)

Lyu, Justin; Andrianarijaona, V. M.

2016-05-01

The causes of the misfolding of prion protein -i.e. the transformation of PrPC to PrPSc - have not been clearly elucidated. Many studies have focused on identifying possible chemical conditions, such as pH, temperature and chemical denaturation, that may trigger the pathological transformation of prion proteins (Weiwei Tao, Gwonchan Yoon, Penghui Cao, `` β-sheet-like formation during the mechanical unfolding of prion protein'', The Journal of Chemical Physics, 2015, 143, 125101). Here, we attempt to calculate the ionization energies of the prion protein, which will be able to shed light onto the possible causes of the misfolding. We plan on using the coarse-grain method which allows for a more feasible calculation time by means of approximation. We believe that by being able to approximate the ionization potential, particularly that of the regions known to form stable β-strands of the PrPSc form, the possible sources of denaturation, be it chemical or mechanical, may be narrowed down.

Srs2 prevents Rad51 filament formation by repetitive motion on DNA.

PubMed

Qiu, Yupeng; Antony, Edwin; Doganay, Sultan; Koh, Hye Ran; Lohman, Timothy M; Myong, Sua

2013-01-01

Srs2 dismantles presynaptic Rad51 filaments and prevents its re-formation as an anti-recombinase. However, the molecular mechanism by which Srs2 accomplishes these tasks remains unclear. Here we report a single-molecule fluorescence study of the dynamics of Rad51 filament formation and its disruption by Srs2. Rad51 forms filaments on single-stranded DNA by sequential binding of primarily monomers and dimers in a 5'-3' direction. One Rad51 molecule binds to three nucleotides, and six monomers are required to achieve a stable nucleation cluster. Srs2 exhibits ATP-dependent repetitive motion on single-stranded DNA and this activity prevents re-formation of the Rad51 filament. The same activity of Srs2 cannot prevent RecA filament formation, indicating its specificity for Rad51. Srs2's DNA-unwinding activity is greatly suppressed when Rad51 filaments form on duplex DNA. Taken together, our results reveal an exquisite and highly specific mechanism by which Srs2 regulates the Rad51 filament formation.

How can EPR spectroscopy help to unravel molecular mechanisms of flavin-dependent photoreceptors?

PubMed Central

Nohr, Daniel; Rodriguez, Ryan; Weber, Stefan; Schleicher, Erik

2015-01-01

Electron paramagnetic resonance (EPR) spectroscopy is a well-established spectroscopic method for the examination of paramagnetic molecules. Proteins can contain paramagnetic moieties in form of stable cofactors, transiently formed intermediates, or spin labels artificially introduced to cysteine sites. The focus of this review is to evaluate potential scopes of application of EPR to the emerging field of optogenetics. The main objective for EPR spectroscopy in this context is to unravel the complex mechanisms of light-active proteins, from their primary photoreaction to downstream signal transduction. An overview of recent results from the family of flavin-containing, blue-light dependent photoreceptors is given. In detail, mechanistic similarities and differences are condensed from the three classes of flavoproteins, the cryptochromes, LOV (Light-oxygen-voltage), and BLUF (blue-light using FAD) domains. Additionally, a concept that includes spin-labeled proteins and examination using modern pulsed EPR is introduced, which allows for a precise mapping of light-induced conformational changes. PMID:26389123

The Kaye effect revisited: High speed imaging of leaping shampoo

NASA Astrophysics Data System (ADS)

Versluis, Michel; Blom, Cock; van der Meer, Devaraj; van der Weele, Ko; Lohse, Detlef

2003-11-01

When a visco-elastic fluid such as shampoo or shower gel is poured onto a flat surface the fluid piles up forming a heap on which rather irregular combinations of fluid buckling, coiling and folding are observed. Under specific conditions a string of fluid leaps from the heap and forms a steady jet fed by the incoming stream. Momentum transfer of the incoming jet, combined with the shear-thinning properties of the fluid, lead to a spoon-like dimple in the highly viscous fluid pool in which the jet recoils. The jet can be stable for several seconds. This effect is known as the Kaye effect. In order to reveal its mechanism we analyzed leaping shampoo through high-speed imaging. We studied the jet formation, jet stability and jet disruption mechanisms. We measured the velocity of both the incoming and recoiled jet, which was found to be thicker and slower. By inclining the surface on which the fluid was poured we observed jets leaping at upto five times.

Structural study of piracetam polymorphs and cocrystals: crystallography redetermination and quantum mechanics calculations.

PubMed

Tilborg, Anaëlle; Jacquemin, Denis; Norberg, Bernadette; Perpète, Eric; Michaux, Catherine; Wouters, Johan

2011-12-01

Pharmaceutical compounds are mostly developed as solid dosage forms containing a single-crystal form. It means that the selection of a particular crystal state for a given molecule is an important step for further clinical outlooks. In this context, piracetam, a pharmaceutical molecule known since the sixties for its nootropic properties, is considered in the present work. This molecule is analyzed using several experimental and theoretical approaches. First, the conformational space of the molecule has been systematically explored by performing a quantum mechanics scan of the two most relevant dihedral angles of the lateral chain. The predicted stable conformations have been compared to all the reported experimental geometries retrieved from the Cambridge Structural Database (CSD) covering polymorphs and cocrystals structures. In parallel, different batches of powders have been recrystallized. Under specific conditions, single crystals of polymorph (III) of piracetam have been obtained, an outcome confirmed by crystallographic analysis. © 2011 International Union of Crystallography. Printed in Singapore – all rights reserved.

Charge-transfer interaction of drug quinidine with quinol, picric acid and DDQ: Spectroscopic characterization and biological activity studies towards understanding the drug-receptor mechanism.

PubMed

Eldaroti, Hala H; Gadir, Suad A; Refat, Moamen S; Adam, Abdel Majid A

2014-04-01

Investigation of charge-transfer (CT) complexes of drugs has been recognized as an important phenomenon in understanding of the drug-receptor binding mechanism. Structural, thermal, morphological and biological behavior of CT complexes formed between drug quinidine (Qui) as a donor and quinol (QL), picric acid (PA) or dichlorodicyanobenzoquinone (DDQ) as acceptors were reported. The newly synthesized CT complexes have been spectroscopically characterized via elemental analysis; infrared (IR), Raman, 1 H NMR and electronic absorption spectroscopy; powder X-ray diffraction (PXRD); thermogravimetric (TG) analysis and scanning electron microscopy (SEM). It was found that the obtained complexes are nanoscale, semi-crystalline particles, thermally stable and spontaneous. The molecular composition of the obtained complexes was determined using spectrophotometric titration method and was found to be 1:1 ratios (donor:acceptor). Finally, the biological activities of the obtained CT complexes were tested for their antibacterial activities. The results obtained herein are satisfactory for estimation of drug Qui in the pharmaceutical form.

Quantitative evaluation of noncovalent interactions between polyphosphate and dissolved humic acids in aqueous conditions.

PubMed

Fang, Wei; Sheng, Guo-Ping; Wang, Long-Fei; Ye, Xiao-Dong; Yu, Han-Qing

2015-12-01

As one kind of phosphorus species, polyphosphate (poly-P) is ubiquitous in natural environments, and the potential interactions between poly-P and humic substances in the sediments or natural waters would influence the fate of poly-P in the environments. However, the mechanism of the interactions has not yet been understood clearly. In this work, the characteristics and mechanisms of the interactions between humic acids (HA) and two model poly-P compounds with various chain lengths have been investigated. Results show that a stable polyphosphate-HA complex would be formed through the noncovalent interactions, and hydrogen bond might be the main driving force for the binding process, which might be formed between the proton-accepting groups of poly-P (e.g., PO and P-O(-)) and the oxygen containing functional groups in HA. Our findings implied that the presence of humic substances in natural waters, soils and sediments would influence the potential transport and/or mobility of environmental poly-P. Copyright © 2015 Elsevier Ltd. All rights reserved.

Mechanism of acetaldehyde-induced deactivation of microbial lipases

PubMed Central

2011-01-01

Background Microbial lipases represent the most important class of biocatalysts used for a wealth of applications in organic synthesis. An often applied reaction is the lipase-catalyzed transesterification of vinyl esters and alcohols resulting in the formation of acetaldehyde which is known to deactivate microbial lipases, presumably by structural changes caused by initial Schiff-base formation at solvent accessible lysine residues. Previous studies showed that several lipases were sensitive toward acetaldehyde deactivation whereas others were insensitive; however, a general explanation of the acetaldehyde-induced inactivation mechanism is missing. Results Based on five microbial lipases from Candida rugosa, Rhizopus oryzae, Pseudomonas fluorescens and Bacillus subtilis we demonstrate that the protonation state of lysine ε-amino groups is decisive for their sensitivity toward acetaldehyde. Analysis of the diverse modification products of Bacillus subtilis lipases in the presence of acetaldehyde revealed several stable products such as α,β-unsaturated polyenals, which result from base and/or amino acid catalyzed aldol condensation of acetaldehyde. Our studies indicate that these products induce the formation of stable Michael-adducts at solvent-accessible amino acids and thus lead to enzyme deactivation. Further, our results indicate Schiff-base formation with acetaldehyde to be involved in crosslinking of lipase molecules. Conclusions Differences in stability observed with various commercially available microbial lipases most probably result from different purification procedures carried out by the respective manufacturers. We observed that the pH of the buffer used prior to lyophilization of the enzyme sample is of utmost importance. The mechanism of acetaldehyde-induced deactivation of microbial lipases involves the generation of α,β-unsaturated polyenals from acetaldehyde which subsequently form stable Michael-adducts with the enzymes. Lyophilization of the enzymes from buffer at pH 6.0 can provide an easy and effective way to stabilize lipases toward inactivation by acetaldehyde. PMID:21342514

Genetic and Epigenetic Changes in Chromosomally Stable and Unstable Progeny of Irradiated Cells

DOE Office of Scientific and Technical Information (OSTI.GOV)

Baulch, Janet E.; Aypar, Umut; Waters, Katrina M.

2014-09-24

Radiation induced genomic instability is a well-studied phenomenon, the underlying mechanisms of which are poorly understood. Persistent oxidative stress, mitochondrial dysfunction, elevated cytokine levels and epigenetic changes are among the mechanisms invoked in the perpetuation of the phenotype. To determine whether epigenetic aberrations affect genomic instability we measured DNA methylation, mRNA and microRNA (miR) levels in well characterized chromosomally stable and unstable clonally expanded single cell survivors of irradiation. While no changes in DNA methylation were observed for the gene promoters evaluated, increased LINE-1 methylation was observed for two unstable clones (LS12, CS9) and decreased Alu element methylation was observedmore » for the other two unstable clones (115, Fe5.0-8). These relationships also manifested for mRNA and miR expression. mRNA identified for the LS12 and CS9 clones were most similar to each other (261 mRNA), while the 115 and Fe5.0-8 clones were more similar to each other, and surprisingly also similar to the two stable clones, 114 and 118 (286 mRNA among these four clones). Pathway analysis showed enrichment for pathways involved in mitochondrial function and cellular redox, themes routinely invoked in genomic instability. The commonalities between the two subgroups of clones were also observed for miR. The number of miR for which anti-correlated mRNA were identified suggests that these miR exert functional effects in each clone. The results of this study demonstrate significant genetic and epigenetic changes in unstable cells, but similar changes almost equally common in chromosomally stable cells. Possible conclusions might be that the chromosomally stable clones have some other form of instability, or that some of the observed changes represent a sort of radiation signature for and that other changes are related to genomic instability. Irrespective, these findings again suggest that a spectrum of changes both drive genomic instability and permit unstable cells to persist and proliferate.« less

Dynamics of glass-forming liquids. XV. Dynamical features of molecular liquids that form ultra-stable glasses by vapor deposition

NASA Astrophysics Data System (ADS)

Chen, Zhen; Richert, Ranko

2011-09-01

The dielectric relaxation behavior of ethylbenzene (EBZ) in its viscous regime is measured, and the glass transition temperature (Tg = 116 K) as well as fragility (m = 98) are determined. While the Tg of EBZ from this work is consistent with earlier results, the fragility is found much higher than what has been assumed previously. Literature data is supplemented by the present results on EBZ to compile the dynamic behavior of those glass formers that are known to form ultra-stable glasses by vapor deposition. These dynamics are contrasted with those of ethylcyclohexane, a glass former for which a comparable vapor deposition failed to produce an equally stable glassy state. In a graph that linearizes Vogel-Fulcher-Tammann behavior, i.e., the derivative of -logτ with respect to T/Tg raised to the power of -1/2 versus T/Tg, all ultra-stable glass formers fall onto one master curve in a wide temperature range, while ethylcyclohexane deviates for T ≫ Tg. This result suggests that ultra-stable glass formers share common behavior regarding the dynamics of their supercooled liquid state if scaled to their respective Tg values, and that fragility and related features are linked to the ability to form ultra-stable materials.

Hierarchical assembly of Sm2Co7/Co magnetic nanoparticles into highly stable and uniform nanospheres.

PubMed

Saravanan, P; Sreedhar, B; Mishra, D; Perumal, A; Chandrasekaran, V

2011-04-01

Hierarchical assembly of colloidal Sm2Co7/Co clusters in the form of nanospheres has been processed through a polyol process. The SmCo nanospheres are found to be robust, uniform ( 100 nm) and tend to self-assemble in the form of ordered superstructures. Each nanosphere consists of large number of discrete fine particles ( 6.0 nm), having two-phase structure of both Sm2Co7 and Co-phases. Upon annealing, these phases transform into Sm2Co17 phase with very high magnetization (169 emu/g). A possible mechanism on the formation of nanospheres from the individual Sm2Co2o7 and Co nanoparticles is also discussed.

Characterization of Self-Assembled Monolayers on a Ruthenium Surface

PubMed Central

2017-01-01

We have modified and stabilized the ruthenium surface by depositing a self-assembled monolayer (SAM) of 1-hexadecanethiol on a polycrystalline ruthenium thin film. The growth mechanism, dynamics, and stability of these monolayers were studied. SAMs, deposited under ambient conditions, on piranha-cleaned and piranha + H2SO4 cleaned substrates were compared to monolayers formed on H-radical-cleaned Ru surfaces. We found that alkanethiols on H-radical-cleaned Ru formed densely packed monolayers that remained stable when kept in a nitrogen atmosphere. X-ray photoelectron spectroscopy (XPS) shows a distinct sulfur peak (BE = 162.3 eV), corresponding to metal–sulfur bonding. When exposed to ambient conditions, the SAM decayed over a period of hours. PMID:28585831

Formation Mechanisms for Helium White Dwarfs in Binaries

NASA Astrophysics Data System (ADS)

Sandquist, E. L.; Taam, R. E.; Burkert, A.

1999-05-01

We discuss the constraints that can be placed on formation mechanisms for helium degenerate stars in binary systems, as well as the orbital parameters of the progenitor binaries, by using observed systems and numerical simulations of common envelope evolution. For pre-cataclysmic variable stars having a helium white dwarf, common envelope simulations covering the range of observed companion masses indicate that the initial mass of the red giant (parent of the white dwarf) can be constrained by the final period of the system. The formation mechanisms for double helium degenerate systems are also restricted. Using energy arguments, we find that there are almost no parameter combinations for which such a system can be formed using two successive common envelope phases. Observed short-period systems appear to favor an Algol-like phase of stable mass transfer followed by a common envelope phase. However, theory predicts that the brighter component is also the most massive, which is not observed in at least one system. This may require that nuclear burning must have occurred on the white dwarf that formed first, but after its formation. Systems which instead go through a common envelope episode, followed by a phase of nonconservative mass transfer from secondary to primary, would tend to form double degenerates with low mass ratios, which have not been observed to date. Finally, we discuss a new mechanism for producing subdwarf B stars in binaries. This work was supported by NSF grants AST-9415423 and AST-9727875.

Temperature Dependent Characterization of Terahertz Vibrations of Explosives and Related Threat Materials

DTIC Science & Technology

2010-12-10

absorption spectra of 1,3,5,7- tetranitro-1,3,5,7-tetrazocane ( HMX ) polymorphs ,” Chem. Phys. Lett. 489(1-3), 48–53 (2010). 23. P. Main, R. E...The β polymorph is the most stable form of the four polymorphs (α,β,γ,δ) of HMX and the room temperature THz spectrum of β- HMX has been measured by...EXPRESS 27248 polymorph to be formed. The α- HMX and δ- HMX forms are described as stable above room temperature: α- HMX is stable from 377 K to 429 K [24

Gauging the likelihood of stable cavitation from ultrasound contrast agents

NASA Astrophysics Data System (ADS)

Bader, Kenneth B.; Holland, Christy K.

2013-01-01

The mechanical index (MI) was formulated to gauge the likelihood of adverse bioeffects from inertial cavitation. However, the MI formulation did not consider bubble activity from stable cavitation. This type of bubble activity can be readily nucleated from ultrasound contrast agents (UCAs) and has the potential to promote beneficial bioeffects. Here, the presence of stable cavitation is determined numerically by tracking the onset of subharmonic oscillations within a population of bubbles for frequencies up to 7 MHz and peak rarefactional pressures up to 3 MPa. In addition, the acoustic pressure rupture threshold of an UCA population was determined using the Marmottant model. The threshold for subharmonic emissions of optimally sized bubbles was found to be lower than the inertial cavitation threshold for all frequencies studied. The rupture thresholds of optimally sized UCAs were found to be lower than the threshold for subharmonic emissions for either single cycle or steady state acoustic excitations. Because the thresholds of both subharmonic emissions and UCA rupture are linearly dependent on frequency, an index of the form ICAV = Pr/f (where Pr is the peak rarefactional pressure in MPa and f is the frequency in MHz) was derived to gauge the likelihood of subharmonic emissions due to stable cavitation activity nucleated from UCAs.

Including Thermal Fluctuations in Actomyosin Stable States Increases the Predicted Force per Motor and Macroscopic Efficiency in Muscle Modelling

PubMed Central

2016-01-01

Muscle contractions are generated by cyclical interactions of myosin heads with actin filaments to form the actomyosin complex. To simulate actomyosin complex stable states, mathematical models usually define an energy landscape with a corresponding number of wells. The jumps between these wells are defined through rate constants. Almost all previous models assign these wells an infinite sharpness by imposing a relatively simple expression for the detailed balance, i.e., the ratio of the rate constants depends exponentially on the sole myosin elastic energy. Physically, this assumption corresponds to neglecting thermal fluctuations in the actomyosin complex stable states. By comparing three mathematical models, we examine the extent to which this hypothesis affects muscle model predictions at the single cross-bridge, single fiber, and organ levels in a ceteris paribus analysis. We show that including fluctuations in stable states allows the lever arm of the myosin to easily and dynamically explore all possible minima in the energy landscape, generating several backward and forward jumps between states during the lifetime of the actomyosin complex, whereas the infinitely sharp minima case is characterized by fewer jumps between states. Moreover, the analysis predicts that thermal fluctuations enable a more efficient contraction mechanism, in which a higher force is sustained by fewer attached cross-bridges. PMID:27626630

Stabilities of ant nests and their adjacent soils

NASA Astrophysics Data System (ADS)

Echezona, B. C.; Igwe, C. A.

2012-10-01

Nests habour ants and termites and protect them from harsh environmental conditions. The structural stabilities of nests were studied to ascertain their relative vulnerability to environmental stresses. Arboreal-ant nests were pried from different trees, while epigeous-termite nests were excavated from soil surface within the sample area. Soils without any visible sign of ant or termite activity were also sampled 6 m away from the nests as control. Laboratory analysis result showed that irrespective of the tree hosts, the aggregate stabilities of the ant nests were lower than those of the ground termite, with nests formed on Cola nitida significantly showing lower aggregate stability (19.7%) than other antnest structures. Clay dispersion ratio, moisture content, water stable aggregate class <0.25mm and sand mass were each negatively correlated with aggregate stability, while water stable aggregate class1.00-0.50 mm gave a positive correlation. Nest structures were dominated more by water stable aggregate class >2.00 mm but path analysis demonstrated that water stable aggregate class <0.25 mm contributed most to the higher aggregate stability of the termite nest than the other nest. Nest aggregates had greater structural stability compared to the control soil. The higher structural stability of termite nests over other nest and soil was considered a better adaptive mechanism against body desiccation.

Gauging the likelihood of stable cavitation from ultrasound contrast agents.

PubMed

Bader, Kenneth B; Holland, Christy K

2013-01-07

The mechanical index (MI) was formulated to gauge the likelihood of adverse bioeffects from inertial cavitation. However, the MI formulation did not consider bubble activity from stable cavitation. This type of bubble activity can be readily nucleated from ultrasound contrast agents (UCAs) and has the potential to promote beneficial bioeffects. Here, the presence of stable cavitation is determined numerically by tracking the onset of subharmonic oscillations within a population of bubbles for frequencies up to 7 MHz and peak rarefactional pressures up to 3 MPa. In addition, the acoustic pressure rupture threshold of an UCA population was determined using the Marmottant model. The threshold for subharmonic emissions of optimally sized bubbles was found to be lower than the inertial cavitation threshold for all frequencies studied. The rupture thresholds of optimally sized UCAs were found to be lower than the threshold for subharmonic emissions for either single cycle or steady state acoustic excitations. Because the thresholds of both subharmonic emissions and UCA rupture are linearly dependent on frequency, an index of the form I(CAV) = P(r)/f (where P(r) is the peak rarefactional pressure in MPa and f is the frequency in MHz) was derived to gauge the likelihood of subharmonic emissions due to stable cavitation activity nucleated from UCAs.

Gauging the likelihood of stable cavitation from ultrasound contrast agents

PubMed Central

Bader, Kenneth B; Holland, Christy K

2015-01-01

The mechanical index (MI) was formulated to gauge the likelihood of adverse bioeffects from inertial cavitation. However, the MI formulation did not consider bubble activity from stable cavitation. This type of bubble activity can be readily nucleated from ultrasound contrast agents (UCAs) and has the potential to promote beneficial bioeffects. Here, the presence of stable cavitation is determined numerically by tracking the onset of subharmonic oscillations within a population of bubbles for frequencies up to 7 MHz and peak rarefactional pressures up to 3 MPa. In addition, the acoustic pressure rupture threshold of an UCA population was determined using the Marmottant model. The threshold for subharmonic emissions of optimally sized bubbles was found to be lower than the inertial cavitation threshold for all frequencies studied. The rupture thresholds of optimally sized UCAs were found to be lower than the threshold for subharmonic emissions for either single cycle or steady state acoustic excitations. Because the thresholds of both subharmonic emissions and UCA rupture are linearly dependent on frequency, an index of the form ICAV = Pr/f (where Pr is the peak rarefactional pressure in MPa and f is the frequency in MHz) was derived to gauge the likelihood of subharmonic emissions due to stable cavitation activity nucleated from UCAs. PMID:23221109

An examination of age-based stereotype threat about cognitive decline: Implications for stereotype threat research and theory development

PubMed Central

Barber, Sarah J.

2017-01-01

“Stereotype threat” is often thought of as a singular construct, with moderators and mechanisms that are stable across groups and domains. However, this is not always true. To illustrate this, the current review focuses on the stereotype threat that older adults face about their cognitive abilities. Using Shapiro and Neuberg's (2007) Multi-Threat Framework, I first provide evidence that this is a self-concept threat, and not a group-reputation threat. Because this differs from the form(s) of threat experienced by other groups (e.g., the threat that minority students face about their intellectual abilities), the moderators of threat observed in other groups (i.e., group identification) do not always generalize to age-based stereotype threat about cognitive decline. Looking beyond the form(s) of threat elicited, this review also provides evidence that the mechanisms underlying stereotype threat effects may vary across the lifespan. Due to age-related improvements in emotion regulation abilities, stereotype threat does not seem to reduce older adults' executive control resources. Overall, this review highlights the need to approach the concept of stereotype threat with more granularity. This will allow us to design more effective stereotype threat interventions. It will also shed light on why certain effects “fail to replicate” across domains or groups. PMID:28073332

Constitutive equation on basis of electo-thermal uniaxial tension for titanium profile

NASA Astrophysics Data System (ADS)

Baosheng, Liu; Fenggong, Lv; Yuansong, Zeng; Wei, Wu; Yongjun, Wang; Fengchao, Cao

2017-10-01

Titanium alloy profiles are widely applied as airframe parts due to its excellent mechanical properties and high compatibility of electrical potential with resin composite material. The electrical assisted forming is recognized as the effective approach to improve plasticity of titanium alloy profile. In this work, the electo-thermal uniaxial tension was performed to investigate the mechanical properties. The experiment results show that, the stress-strain curves increases sharply to the peak and declines quickly, exhibiting no stable deformation occurring. On basis of the obtained curves, a constitutive equation was established with consideration of the characteristic of self resistance heating, and the microstructure evolution was predicted. A comparison of the calculated stress-strain curves with the experimental ones was conducted, showing a reasonable agreement.

Mechanical Properties of Nb25Mo25Ta25W25 and V20Nb20Mo20Ta20W20 Refractory High Entropy Alloys (Postprint)

DTIC Science & Technology

2011-05-01

Mn, Fe, Co, Ni and Cu. Since metallic alloys for high temperature load bearing structures and thermal protection systems remain in high demand for aer...condition. These results indicate that the BCC crystal structure formed in both alloys during solidification is stable upon heating at least up to 1400 C... solidification (Fig. 5b). Higher magnification images reveal a dendritic structure in both alloys (Fig. 5c and d). Uneven Z contrast inside the grains indicates

Enantioselective direct α-amination of aldehydes via a photoredox mechanism: a strategy for asymmetric amine fragment coupling.

PubMed

Cecere, Giuseppe; König, Christian M; Alleva, Jennifer L; MacMillan, David W C

2013-08-07

The direct, asymmetric α-amination of aldehydes has been accomplished via a combination of photoredox and organocatalysis. Photon-generated N-centered radicals undergo enantioselective α-addition to catalytically formed chiral enamines to directly produce stable α-amino aldehyde adducts bearing synthetically useful amine substitution patterns. Incorporation of a photolabile group on the amine precursor obviates the need to employ a photoredox catalyst in this transformation. Importantly, this photoinduced transformation allows direct and enantioselective access to α-amino aldehyde products that do not require postreaction manipulation.

Dihydropteridine/Pteridine as a 2H+/2e- Redox Mediator for the Reduction of CO2 to Methanol: A Computational Study.

PubMed

Lim, Chern-Hooi; Holder, Aaron M; Hynes, James T; Musgrave, Charles B

2017-04-27

Conflicting experimental results for the electrocatalytic reduction of CO 2 to CH 3 OH on a glassy carbon electrode by the 6,7-dimethyl-4-hydroxy-2-mercaptopteridine have been recently reported [ J. Am. Chem. Soc. 2014 , 136 , 14007 - 14010 , J. Am. Chem. Soc. 2016 , 138 , 1017 - 1021 ]. In this connection, we have used computational chemistry to examine the issue of this molecule's ability to act as a hydride donor to reduce CO 2 . We first determined that the most thermodynamically stable tautomer of this aqueous compound is its oxothione form, termed here PTE. It is argued that this species electrochemically undergoes concerted 2H + /2e - transfers to first form the kinetic product 5,8-dihydropteridine, followed by acid-catalyzed tautomerization to the thermodynamically more stable 7,8-dihydropteridine PTEH 2 . While the overall conversion of CO 2 to CH 3 OH by three successive hydride and proton transfers from this most stable tautomer is computed to be exergonic by 5.1 kcal/mol, we predict high activation free energies (ΔG ‡ HT ) of 29.0 and 29.7 kcal/mol for the homogeneous reductions of CO 2 and its intermediary formic acid product by PTE/PTEH 2 , respectively. These high barriers imply that PTE/PTEH 2 is unable, by this mechanism, to homogeneously reduce CO 2 on a time scale of hours at room temperature.

Structural and phase transformations during ball milling of titanium in medium of liquid hydrocarbons

NASA Astrophysics Data System (ADS)

Dorofeev, G. A.; Lubnin, A. N.; Lad'yanov, V. I.; Mukhgalin, V. V.; Puskkarev, B. E.

2014-02-01

It has been shown using X-ray diffraction, scanning electron microscopy, and chemical analysis that, upon ball milling of α-titanium in liquid organic media (toluene and n-heptane), a nanocrystalline fcc phase is formed that is a metastable carbohydride Ti(C,H) deficient in hydrogen and carbon compared to stable carbohydrides. The dimensions of powder particles after milling in toluene and n-heptane differ substantially (are 5-10 and 20-30 μm, respectively. It has been shown that the kinetics of the formation of Ti(C,H) is independent of the milling medium. The atomic ratios H/C in the products of mechanosynthesis agree well with those corresponding to the employed organic media, i.e., H/C = 1.1 for toluene and 2.3 for n-heptane. A solid-liquid mechanism of mechanosynthesis is suggested, which includes repeated processes of particle fracturing with the formation of fresh surfaces, adsorption of liquid hydrocarbons on these surfaces, and subsequent cold welding of the newly formed particles. It is assumed that the formation of the fcc phase in the process of milling is connected with the generation of stacking faults in α-Ti. Upon annealing at 550°C, the fcc phase decomposes with the formation of stable titanium carbide TiC (annealing in a vacuum) or stable titanium carbohydride and a β-Ti(H) solid solution (annealing in argon) with a partial reverse transformation Ti(C,H) → α-Ti in both cases.

Characterization of a Stable L-Form of Bacillus subtilis 168

PubMed Central

Gilpin, Richard W.; Young, Frank E.; Chatterjee, Anadi N.

1973-01-01

A stable L-form of Bacillus subtilis 168 (sal-1) has been isolated which grows and divides logarithmically in liquid medium with a generation time of 60 min. This mutant does not synthesize cell wall as evidenced by chemical, biochemical, and morphological analyses. Antibiotics which specifically inhibit cell wall biosynthesis do not affect the growth of the L-form. Significant differences exist between the membrane proteins of the bacillary form and the L-form. The relative profile of membrane proteins varies with the salt concentration of the medium in both the L-form and the bacillary form. Images PMID:4631836

Survival and reversion of a stable L form in soil

NASA Technical Reports Server (NTRS)

Horwitz, A. H.; Casida, L. E., Jr.

1978-01-01

The stable L form of Agromyces ramosus reverted to a bacterial form when incubated in sterilized soil. The cellular and colonial morphology of this bacterial form resembled that of the original parent bacterial form. The two forms differed, however, in that the revertant maintained its bacterial form when transferred onto a low-salt (NaCl) medium but was virtually completely induced into the L-form state on a high-salt medium. The original parent bacterial form was not sensitive to salt. The possibility is discussed that an L-form - bacterial-form cycle for this bacterium might occur naturally in soil. This cycle would be mediated by fluctuations in local salt concentrations in the soil.

Self-Functionalization Behind a Solution-Processed NiOx Film Used As Hole Transporting Layer for Efficient Perovskite Solar Cells.

PubMed

Ciro, John; Ramírez, Daniel; Mejía Escobar, Mario Alejandro; Montoya, Juan Felipe; Mesa, Santiago; Betancur, Rafael; Jaramillo, Franklin

2017-04-12

Fabrication of solution-processed perovskite solar cells (PSCs) requires the deposition of high quality films from precursor inks. Frequently, buffer layers of PSCs are formed from dispersions of metal oxide nanoparticles (NPs). Therefore, the development of trustable methods for the preparation of stable colloidal NPs dispersions is crucial. In this work, a novel approach to form very compact semiconducting buffer layers with suitable optoelectronic properties is presented through a self-functionalization process of the nanocrystalline particles by their own amorphous phase and without adding any other inorganic or organic functionalization component or surfactant. Such interconnecting amorphous phase composed by residual nitrate, hydroxide, and sodium ions, proved to be fundamental to reach stable colloidal dispersions and contribute to assemble the separate crystalline nickel oxide NPs in the final film, resulting in a very homogeneous and compact layer. A proposed mechanism behind the great stabilization of the nanoparticles is exposed. At the end, the self-functionalized nickel oxide layer exhibited high optoelectronic properties enabling perovskite p-i-n solar cells as efficient as 16.6% demonstrating the pertinence of the presented strategy to obtain high quality buffer layers processed in solution at room temperature.

The crystal structure of the calcium-bound con-G[Q6A] peptide reveals a novel metal-dependent helical trimer

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cnudde, Sara E.; Prorok, Mary; Jia, Xaofei

2012-02-15

The ability to form and control both secondary structure and oligomerization in short peptides has proven to be challenging owing to the structural instability of such peptides. The conantokin peptides are a family of {gamma}-carboxyglutamic acid containing peptides produced in the venoms of predatory sea snails of the Conus family. They are examples of short peptides that form stable helical structures, especially in the presence of divalent cations. Both monomeric and dimeric conantokin peptides have been identified and represent a new mechanism of helix association, 'the metallozipper motif' that is devoid of a hydrophobic interface between monomers. In the presentmore » study, a parallel/antiparallel three-helix bundle was identified and its crystal structure determined at high resolution. The three helices are almost perfectly parallel and represent a novel helix-helix association. The trimer interface is dominated by metal chelation between the three helices, and contains no interfacial hydrophobic interactions. It is now possible to produce stable monomeric, dimeric, or trimeric metallozippers depending on the peptide sequence and metal ion. Such structures have important applications in protein design.« less

Effect of characteristics of compounds on maintenance of an amorphous state in solid dispersion with crospovidone.

PubMed

Shibata, Yusuke; Fujii, Makiko; Kokudai, Makiko; Noda, Shinobu; Okada, Hideko; Kondoh, Masuo; Watanabe, Yoshiteru

2007-06-01

Solid dispersion (SD) of indomethacin with crospovidone (CrosPVP) shows useful characteristics for preparation of dosage forms. This study aimed to determine the types of drugs that could adopt a stable amorphous form in SD. Twenty compounds with various melting points (70-218 degrees C), molecular weights (135-504) and functional groups (amide, amino, carbonyl, hydroxyl, ketone etc.) were prepared in SD with CrosPVP. The CrosPVP SDs were prepared using a mechanical mixing and heating method. Melting point and molecular weight were found to have no influence on the ability of a compound to maintain an amorphous state in SD. All compounds containing hydrogen-bond-donor functional groups existed in an amorphous state in SD for at least 6 months. Infrared spectra suggested an interaction between the functional groups of these compounds and amide carbonyl group of CrosPVP. Compounds without hydrogen-bond-donor groups could not maintain an amorphous state and underwent recrystallization within 1 month. It was suggested that the presence of a hydrogen-bond-donor functional group in a compound is an important factor affecting the stable formation of SD with CrosPVP, which contains a hydrogen-bond acceptor.

Mechanical Properties and Microstructure of High-Strength Steel Controlled by Hot Stamping Process

NASA Astrophysics Data System (ADS)

Ou, Hang; Zhang, Xu; Xu, Junrui; Li, Guangyao; Cui, Junjia

2018-03-01

A novel design and manufacturing method, dubbed "precast," of the cooling system and tools for a hot forming process was proposed in this paper. The integrated structures of the punch and blank holder were determined by analyzing the bending and reverse-bending deformation of the forming parts. The desired crashworthiness performance of an automotive front bumper constructed with this process was obtained by a tailored phase transformation, which generated martensite-bainite in the middle and full martensite transformation in the corner areas. Varying cooling effects in the formed parts caused the highest temperature to be located in the bottom and the lowest on the end of the formed parts. Moreover, the microstructural distributions demonstrated that the bottom possessed a relatively lower content of martensite, while, conversely, the end possessed a higher content. This was precisely the most desired phase distributions for the hot formed parts. For the six-process cycle stamping, the temperatures reached a stable status after an initial rapid increase in the first three process cycles. The microstructural results verified the feasibility of the hot forming tools under multiprocess cycles.

New insight in the structural features of haloadaptation in α-amylases from halophilic Archaea following homology modeling strategy: folded and stable conformation maintained through low hydrophobicity and highly negative charged surface

NASA Astrophysics Data System (ADS)

Zorgani, Mohamed Amine; Patron, Kevin; Desvaux, Mickaël

2014-07-01

Proteins from halophilic archaea, which live in extreme saline conditions, have evolved to remain folded, active and stable at very high ionic strengths. Understanding the mechanism of haloadaptation is the first step toward engineering of halostable biomolecules. Amylases are one of the main enzymes used in industry. Yet, no three-dimensional structure has been experimentally resolved for α-amylases from halophilic archaea. In this study, homology structure modeling of α-amylases from the halophilic archaea Haloarcula marismortui, Haloarcula hispanica, and Halalkalicoccus jeotgali were performed. The resulting models were subjected to energy minimization, evaluation, and structural analysis. Calculations of the amino acid composition, salt bridges and hydrophobic interactions were also performed and compared to a set of non-halophilic counterparts. It clearly appeared that haloarchaeal α-amylases exhibited lower propensities for helix formation and higher propensities for coil-forming regions. Furthermore, they could maintain a folded and stable conformation in high salt concentration through highly negative charged surface with over representation of acidic residues, especially Asp, and low hydrophobicity with increase of salt bridges and decrease in hydrophobic interactions on the protein surface. This study sheds some light on the stability of α-amylases from halophilic archaea and provides strong basis not only to understand haloadaptation mechanisms of proteins in microorganisms from hypersalines environments but also for biotechnological applications.

New insight in the structural features of haloadaptation in α-amylases from halophilic Archaea following homology modeling strategy: folded and stable conformation maintained through low hydrophobicity and highly negative charged surface.

PubMed

Zorgani, Mohamed Amine; Patron, Kevin; Desvaux, Mickaël

2014-07-01

Proteins from halophilic archaea, which live in extreme saline conditions, have evolved to remain folded, active and stable at very high ionic strengths. Understanding the mechanism of haloadaptation is the first step toward engineering of halostable biomolecules. Amylases are one of the main enzymes used in industry. Yet, no three-dimensional structure has been experimentally resolved for α-amylases from halophilic archaea. In this study, homology structure modeling of α-amylases from the halophilic archaea Haloarcula marismortui, Haloarcula hispanica, and Halalkalicoccus jeotgali were performed. The resulting models were subjected to energy minimization, evaluation, and structural analysis. Calculations of the amino acid composition, salt bridges and hydrophobic interactions were also performed and compared to a set of non-halophilic counterparts. It clearly appeared that haloarchaeal α-amylases exhibited lower propensities for helix formation and higher propensities for coil-forming regions. Furthermore, they could maintain a folded and stable conformation in high salt concentration through highly negative charged surface with over representation of acidic residues, especially Asp, and low hydrophobicity with increase of salt bridges and decrease in hydrophobic interactions on the protein surface. This study sheds some light on the stability of α-amylases from halophilic archaea and provides strong basis not only to understand haloadaptation mechanisms of proteins in microorganisms from hypersalines environments but also for biotechnological applications.

Dynamical systems theory for nonlinear evolution equations.

PubMed

Choudhuri, Amitava; Talukdar, B; Das, Umapada

2010-09-01

We observe that the fully nonlinear evolution equations of Rosenau and Hymann, often abbreviated as K(n,m) equations, can be reduced to Hamiltonian form only on a zero-energy hypersurface belonging to some potential function associated with the equations. We treat the resulting Hamiltonian equations by the dynamical systems theory and present a phase-space analysis of their stable points. The results of our study demonstrate that the equations can, in general, support both compacton and soliton solutions. For the K(2,2) and K(3,3) cases one type of solutions can be obtained from the other by continuously varying a parameter of the equations. This is not true for the K(3,2) equation for which the parameter can take only negative values. The K(2,3) equation does not have any stable point and, in the language of mechanics, represents a particle moving with constant acceleration.

Kinesthetic information disambiguates visual motion signals.

PubMed

Hu, Bo; Knill, David C

2010-05-25

Numerous studies have shown that extra-retinal signals can disambiguate motion information created by movements of the eye or head. We report a new form of cross-modal sensory integration in which the kinesthetic information generated by active hand movements essentially captures ambiguous visual motion information. Several previous studies have shown that active movement can bias observers' percepts of bi-stable stimuli; however, these effects seem to be best explained by attentional mechanisms. We show that kinesthetic information can change an otherwise stable perception of motion, providing evidence of genuine fusion between visual and kinesthetic information. The experiments take advantage of the aperture problem, in which the motion of a one-dimensional grating pattern behind an aperture, while geometrically ambiguous, appears to move stably in the grating normal direction. When actively moving the pattern, however, the observer sees the motion to be in the hand movement direction. Copyright 2010 Elsevier Ltd. All rights reserved.

Comparative proteomics of two life cycle stages of stable isotope-labeled Trypanosoma brucei reveals novel components of the parasite's host adaptation machinery.

PubMed

Butter, Falk; Bucerius, Ferdinand; Michel, Margaux; Cicova, Zdenka; Mann, Matthias; Janzen, Christian J

2013-01-01

Trypanosoma brucei developed a sophisticated life cycle to adapt to different host environments. Although developmental differentiation of T. brucei has been the topic of intensive research for decades, the mechanisms responsible for adaptation to different host environments are not well understood. We developed stable isotope labeling by amino acids in cell culture in trypanosomes to compare the proteomes of two different life cycle stages. Quantitative comparison of 4364 protein groups identified many proteins previously not known to be stage-specifically expressed. The identification of stage-specific proteins helps to understand how parasites adapt to different hosts and provides new insights into differences in metabolism, gene regulation, and cell architecture. A DEAD-box RNA helicase, which is highly up-regulated in the bloodstream form of this parasite and which is essential for viability and proper cell cycle progression in this stage is described as an example.

X2Y2 isomers: tuning structure and relative stability through electronegativity differences (X = H, Li, Na, F, Cl, Br, I; Y = O, S, Se, Te).

PubMed

El-Hamdi, Majid; Poater, Jordi; Bickelhaupt, F Matthias; Solà, Miquel

2013-03-04

We have studied the XYYX and X2YY isomers of the X2Y2 species (X = H, Li, Na, F, Cl, Br, I; Y = O, S, Se, Te) using density functional theory at the ZORA-BP86/QZ4P level. Our computations show that, over the entire range of our model systems, the XYYX isomers are more stable than the X2YY forms except for X = F and Y = S and Te, for which the F2SS and F2TeTe isomers are slightly more stable. Our results also point out that the Y-Y bond length can be tuned quite generally through the X-Y electronegativity difference. The mechanism behind this electronic tuning is the population or depopulation of the π* in the YY fragment.

Controllable growth of aluminum nanorods using physical vapor deposition

PubMed Central

2014-01-01

This letter proposes and experimentally demonstrates that oxygen, through action as a surfactant, enables the growth of aluminum nanorods using physical vapor deposition. Based on the mechanism through which oxygen acts, the authors show that the diameter of aluminum nanorods can be controlled from 50 to 500 nm by varying the amount of oxygen present, through modulating the vacuum level, and by varying the substrate temperature. When grown under medium vacuum, the nanorods are in the form of an aluminum metal - aluminum oxide core-shell. The thickness of the oxide shell is ~2 nm as grown and is stable when maintained in ambient for 30 days or annealed in air at 475 K for 1 day. As annealing temperature is increased, the nanorod morphology remains stable while the ratio of oxide shell to metallic core increases, resulting in a fully aluminum oxide nanorod at 1,475 K. PMID:25170334

Nonaqueous Electrical Storage Device

DOEpatents

McEwen, Alan B.; Evans, David A.; Blakley, Thomas J.; Goldman, Jay L.

1999-10-26

An electrochemical capacitor is disclosed that features two, separated, high surface area carbon cloth electrodes sandwiched between two current collectors fabricated of a conductive polymer having a flow temperature greater than 130.degree. C., the perimeter of the electrochemical capacitor being sealed with a high temperature gasket to form a single cell device. The gasket material is a thermoplastic stable at temperatures greater than 100.degree. C., preferably a polyester or a polyurethane, and having a reflow temperature above 130.degree. C. but below the softening temperature of the current collector material. The capacitor packaging has good mechanical integrity over a wide temperature range, contributes little to the device equivalent series resistance (ESR), and is stable at high potentials. In addition, the packaging is designed to be easily manufacturable by assembly line methods. The individual cells can be stacked in parallel or series configuration to reach the desired device voltage and capacitance.

Mass spectrometric measurements of norepinephrine synthesis in man from infusion of stable isotope-labelled L-threo-3,4-dihydroxyphenylserine

DOE Office of Scientific and Technical Information (OSTI.GOV)

Suzuki, T.; Sakoda, S.; Ueji, M.

The kinetics of stable isotope-labelled L-threo-3,4-dihydroxyphenylserine (L-threo-DOPS), an immediate precursor of (-)-norepinephrine, was studied to investigate the pharmacologic mechanism of its therapeutic effect on orthostatic hypotension in familial amyloid polyneuropathy (FAP) and on akinesia and freezing in parkinsonism. (/sup 13/C,D)-L-threo-DOPS was synthesized, and 100 mg of the compound was infused for 2 h into two normal subjects, two FAP patients and two patients with the degenerative diseases of the central nervous system. Labelled and endogenous norepinephrine in urine and plasma was assayed simultaneously by gas chromatography/mass spectrometry. The results indicate that the increase in norepinephrine in biological fluids after administrationmore » of L-threo-DOPS is attributable mostly to norepinephrine derived from L-threo-DOPS, not to pre-formed endogenous norepinephrine released by L-threo-DOPS.« less

The formation of giant planets in wide orbits by photoevaporation-synchronized migration

NASA Astrophysics Data System (ADS)

Guilera, O. M.; Miller Bertolami, M. M.; Ronco, M. P.

2017-10-01

The discovery of giant planets in wide orbits represents a major challenge for planet formation theory. In the standard core accretion paradigm, planets are expected to form at radial distances ≲20 au in order to form massive cores (with masses ≳10 M⊕) able to trigger the gaseous runaway growth before the dissipation of the disc. This has encouraged authors to find modifications of the standard scenario as well as alternative theories like the formation of planets by gravitational instabilities in the disc to explain the existence of giant planets in wide orbits. However, there is not yet consensus on how these systems are formed. In this Letter, we present a new natural mechanism for the formation of giant planets in wide orbits within the core accretion paradigm. If photoevaporation is considered, after a few Myr of viscous evolution a gap in the gaseous disc is opened. We found that, under particular circumstances planet migration becomes synchronized with the evolution of the gap, which results in an efficient outward planet migration. This mechanism is found to allow the formation of giant planets with masses Mp ≲ 1MJup in wide stable orbits as large as ∼130 au from the central star.

Hydrogen-induced structural transition in single layer ReS2

NASA Astrophysics Data System (ADS)

Yagmurcukardes, M.; Bacaksiz, C.; Senger, R. T.; Sahin, H.

2017-09-01

By performing density functional theory-based calculations, we investigate how structural, electronic and mechanical properties of single layer ReS2 can be tuned upon hydrogenation of its surfaces. It is found that a stable, fully hydrogenated structure can be obtained by formation of strong S-H bonds. The optimized atomic structure of ReS2H2 is considerably different than that of the monolayer ReS2 which has a distorted-1T phase. By performing phonon dispersion calculations, we also predict that the Re2-dimerized 1T structure (called 1T {{}\\text{R{{\\text{e}}2}}} ) of the ReS2H2 is dynamically stable. Unlike the bare ReS2 the 1T {{}\\text{R{{\\text{e}}2}}} -ReS2H2 structure which is formed by breaking the Re4 clusters into separated Re2 dimers, is an indirect-gap semiconductor. Furthermore, mechanical properties of the 1T {{}\\text{R{{\\text{e}}2}}} phase in terms of elastic constants, in-plane stiffness (C) and Poisson ratio (ν) are investigated. It is found that full hydrogenation not only enhances the flexibility of the single layer ReS2 crystal but also increases anisotropy of the elastic constants.

Geometrical families of mechanically stable granular packings

NASA Astrophysics Data System (ADS)

Gao, Guo-Jie; Blawzdziewicz, Jerzy; O'Hern, Corey S.

2009-12-01

We enumerate and classify nearly all of the possible mechanically stable (MS) packings of bidipserse mixtures of frictionless disks in small sheared systems. We find that MS packings form continuous geometrical families, where each family is defined by its particular network of particle contacts. We also monitor the dynamics of MS packings along geometrical families by applying quasistatic simple shear strain at zero pressure. For small numbers of particles (N<16) , we find that the dynamics is deterministic and highly contracting. That is, if the system is initialized in a MS packing at a given shear strain, it will quickly lock into a periodic orbit at subsequent shear strain, and therefore sample only a very small fraction of the possible MS packings in steady state. In studies with N>16 , we observe an increase in the period and random splittings of the trajectories caused by bifurcations in configuration space. We argue that the ratio of the splitting and contraction rates in large systems will determine the distribution of MS-packing geometrical families visited in steady state. This work is part of our long-term research program to develop a master-equation formalism to describe macroscopic slowly driven granular systems in terms of collections of small subsystems.

Influence of Substrate Temperature on the Transformation Front Velocities That Determine Thermal Stability of Vapor-Deposited Glasses

DOE PAGES

Dalal, Shakeel S.; Ediger, M. D.

2015-02-09

Stable organic glasses prepared by physical vapor deposition transform into the supercooled liquid via propagating fronts of molecular mobility, a mechanism different from that exhibited by glasses prepared by cooling the liquid. In this paper, we show that spectroscopic ellipsometry can directly observe this front-based mechanism in real time and explore how the velocity of the front depends upon the substrate temperature during deposition. For the model glass former indomethacin, we detect surface-initiated mobility fronts in glasses formed at substrate temperatures between 0.68T g and 0.94T g. At each of two annealing temperatures, the substrate temperature during deposition can changemore » the transformation front velocity by a factor of 6, and these changes are imperfectly correlated with the density of the glass. We also observe substrate-initiated fronts at some substrate temperatures. By connecting with theoretical work, we are able to infer the relative mobilities of stable glasses prepared at different substrate temperatures. Finally, an understanding of the transformation behavior of vapor-deposited glasses may be relevant for extending the lifetime of organic semiconducting devices.« less

Resistive switching characteristics of manganese oxide thin film and nanoparticle assembly hybrid devices

NASA Astrophysics Data System (ADS)

Abbas, Haider; Park, Mi Ra; Abbas, Yawar; Hu, Quanli; Kang, Tae Su; Yoon, Tae-Sik; Kang, Chi Jung

2018-06-01

Improved resistive switching characteristics are demonstrated in a hybrid device with Pt/Ti/MnO (thin film)/MnO (nanoparticle)/Pt structure. The hybrid devices of MnO thin film and nanoparticle assembly were fabricated. MnO nanoparticles with an average diameter of ∼30 nm were chemically synthesized and assembled as a monolayer on a Pt bottom electrode. A MnO thin film of ∼40 nm thickness was deposited on the nanoparticle assembly to form the hybrid structure. Resistive switching could be induced by the formation and rupture of conducting filaments in the hybrid oxide layers. The hybrid device exhibited very stable unipolar switching with good endurance and retention characteristics. It showed a larger and stable memory window with a uniform distribution of SET and RESET voltages. Moreover, the conduction mechanisms of ohmic conduction, space-charge-limited conduction, Schottky emission, and Poole–Frenkel emission have been investigated as possible conduction mechanisms for the switching of the devices. Using MnO nanoparticles in the thin film and nanoparticle heterostructures enabled the appropriate control of resistive random access memory (RRAM) devices and markedly improved their memory characteristics.

Existence and stability of periodic solutions of quasi-linear Korteweg — de Vries equation

NASA Astrophysics Data System (ADS)

Glyzin, S. D.; Kolesov, A. Yu; Preobrazhenskaia, M. M.

2017-01-01

We consider the scalar nonlinear differential-difference equation with two delays, which models electrical activity of a neuron. Under some additional suppositions for this equation well known method of quasi-normal forms can be applied. Its essence lies in the formal normalization of the Poincare - Dulac obtaining quasi-normal form and the subsequent application of the theorems of conformity. In this case, the result of the application of quasi-normal forms is a countable system of differential-difference equations, which can be turned into a boundary value problem of the Korteweg - de Vries equation. The investigation of this boundary value problem allows us to draw a conclusion about the behaviour of the original equation. Namely, for a suitable choice of parameters in the framework of this equation is implemented buffer phenomenon consisting in the presence of the bifurcation mechanism for the birth of an arbitrarily large number of stable cycles.

Modeling solid-state transformations occurring in dissolution testing.

PubMed

Laaksonen, Timo; Aaltonen, Jaakko

2013-04-15

Changes in the solid-state form can occur during dissolution testing of drugs. This can often complicate interpretation of results. Additionally, there can be several mechanisms through which such a change proceeds, e.g. solvent-mediated transformation or crystal growth within the drug material itself. Here, a mathematical model was constructed to study the dissolution testing of a material, which undergoes such changes. The model consisted of two processes: the recrystallization of the drug from a supersaturated liquid state caused by the dissolution of the more soluble solid form and the crystal growth of the stable solid form at the surface of the drug formulation. Comparison to experimental data on theophylline dissolution showed that the results obtained with the model matched real solid-state changes and that it was able to distinguish between cases where the transformation was controlled either by solvent-mediated crystallization or solid-state crystal growth. Copyright © 2013 Elsevier B.V. All rights reserved.

Spongy Gels by a Top-Down Approach from Polymer Fibrous Sponges.

PubMed

Jiang, Shaohua; Duan, Gaigai; Kuhn, Ute; Mörl, Michaela; Altstädt, Volker; Yarin, Alexander L; Greiner, Andreas

2017-03-13

Ultralight cellular sponges offer a unique set of properties. We show here that solvent uptake by these sponges results in new gel-like materials, which we term spongy gels. The appearance of the spongy gels is very similar to classic organogels. Usually, organogels are formed by a bottom-up process. In contrast, the spongy gels are formed by a top-down approach that offers numerous advantages for the design of their properties, reproducibility, and stability. The sponges themselves represent the scaffold of a gel that could be filled with a solvent, and thereby form a mechanically stable gel-like material. The spongy gels are independent of a time-consuming or otherwise demanding in situ scaffold formation. As solvent evaporation from gels is a concern for various applications, we also studied solvent evaporation of wetting and non-wetting liquids dispersed in the sponge. © 2017 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.

Mechanical characterization of an additively manufactured Inconel 718 theta-shaped specimen

DOE PAGES

Cakmak, Ercan; Watkins, Thomas R.; Bunn, Jeffrey R.; ...

2015-11-20

Two sets of “theta”-shaped specimens were additively manufactured with Inconel 718 powders using an electron beam melting technique with two distinct scan strategies. Light optical microscopy, mechanical testing coupled with a digital image correlation (DIC) technique, finite element modeling, and neutron diffraction with in situ loading characterizations were conducted. The cross-members of the specimens were the focus. Light optical micrographs revealed that different microstructures were formed with different scan strategies. Ex situ mechanical testing revealed each build to be stable under load until ductility was observed on the cross-members before failure. The elastic moduli were determined by forming a correlationmore » between the elastic tensile stresses determined from FEM, and the elastic strains obtained from DIC. The lattice strains were mapped with neutron diffraction during in situ elastic loading; and a good correlation between the average axial lattice strains on the cross-member and those determined from the DIC analysis was found. Lastly, the spatially resolved stresses in the elastic deformation regime are derived from the lattice strains and increased with applied load, showing a consistent distribution along the cross-member.« less

Rigidity of transmembrane proteins determines their cluster shape

NASA Astrophysics Data System (ADS)

Jafarinia, Hamidreza; Khoshnood, Atefeh; Jalali, Mir Abbas

2016-01-01

Protein aggregation in cell membrane is vital for the majority of biological functions. Recent experimental results suggest that transmembrane domains of proteins such as α -helices and β -sheets have different structural rigidities. We use molecular dynamics simulation of a coarse-grained model of protein-embedded lipid membranes to investigate the mechanisms of protein clustering. For a variety of protein concentrations, our simulations under thermal equilibrium conditions reveal that the structural rigidity of transmembrane domains dramatically affects interactions and changes the shape of the cluster. We have observed stable large aggregates even in the absence of hydrophobic mismatch, which has been previously proposed as the mechanism of protein aggregation. According to our results, semiflexible proteins aggregate to form two-dimensional clusters, while rigid proteins, by contrast, form one-dimensional string-like structures. By assuming two probable scenarios for the formation of a two-dimensional triangular structure, we calculate the lipid density around protein clusters and find that the difference in lipid distribution around rigid and semiflexible proteins determines the one- or two-dimensional nature of aggregates. It is found that lipids move faster around semiflexible proteins than rigid ones. The aggregation mechanism suggested in this paper can be tested by current state-of-the-art experimental facilities.

Mechanical characterization of an additively manufactured Inconel 718 theta-shaped specimen

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cakmak, Ercan; Watkins, Thomas R.; Bunn, Jeffrey R.

Two sets of “theta”-shaped specimens were additively manufactured with Inconel 718 powders using an electron beam melting technique with two distinct scan strategies. Light optical microscopy, mechanical testing coupled with a digital image correlation (DIC) technique, finite element modeling, and neutron diffraction with in situ loading characterizations were conducted. The cross-members of the specimens were the focus. Light optical micrographs revealed that different microstructures were formed with different scan strategies. Ex situ mechanical testing revealed each build to be stable under load until ductility was observed on the cross-members before failure. The elastic moduli were determined by forming a correlationmore » between the elastic tensile stresses determined from FEM, and the elastic strains obtained from DIC. The lattice strains were mapped with neutron diffraction during in situ elastic loading; and a good correlation between the average axial lattice strains on the cross-member and those determined from the DIC analysis was found. Lastly, the spatially resolved stresses in the elastic deformation regime are derived from the lattice strains and increased with applied load, showing a consistent distribution along the cross-member.« less

Towards understanding the mechanism of rhenium and osmium precipitation in tungsten and its implication for tungsten-based alloys

NASA Astrophysics Data System (ADS)

Li, Yu-Hao; Zhou, Hong-Bo; Deng, Huiqiu; Lu, Gang; Lu, Guang-Hong

2018-07-01

Using a first-principles method in combination with thermodynamic models, we investigate the interaction between rhenium/osmium (Re/Os) and defects to explore the mechanism of radiation-induced Re/Os precipitation in tungsten (W). We demonstrate that radiation-induced defects play a key role in the solute precipitation in W, especially for self-interstitial atoms (SIAs). The presence of SIAs can significantly reduce the total nucleation free energy change of Re/Os, and thus facilitate the nucleation of Re/Os in W. Further, SIA is shown to be easily trapped by Re/Os once overcoming a low energy barrier, forming a W-Re/Os mixed dumbbell. Such W-Re/Os dumbbell forms a high stable Re/Os-Re/Os dumbbell structure with the substitutional Re/Os atoms, which can serve as a trapping centre for subsequent interstitial-Re/Os, leading to the growth of Re/Os-rich clusters. Consequently, an interstitial-mediated migration and aggregation mechanism for Re/Os precipitation in W has been proposed. Our results reveale that the alloying elements-defects interaction has significantly effect on their behaviors under irradiation, which should be considered in the design of W-based alloys for future fusion devices.

Photophysical and Photochemical Properties of 3-methylpterin as a New and More Stable Pterin-type Photosensitizer.

PubMed

Estébanez, Sandra; Lorente, Carolina; Kaufman, Teodoro S; Larghi, Enrique L; Thomas, Andrés H; Serrano, Mariana P

2018-05-04

Pterin derivatives are heterocyclic compounds which are present in different biological systems. Neutral aqueous solutions of pterins presents acid-base and keto-enol equilibria. These compounds under UV-A radiation fluoresce, undergo photooxidation, generate reactive oxygen species, and photoinduce the oxidation of biological substrates. As photosensitizers, they may act through different mechanisms; mainly through an electron-transfer initiated process (type I mechanism), but they also produce singlet molecular oxygen ( 1 O 2 ) upon irradiation (type II mechanism). In general, upon UV-A excitation two triplet states, corresponding to the lactim and lactam tautomers, are formed, but only the last one is the responsible for the photosensitized reactions of biomolecules. We present a study of the photochemical properties of 3-methylpterin (3-Mep) which, in contrast to most pterin derivatives, exists only in the lactam form. Also an improvement in the synthesis of 3-Mep is reported. The spectroscopic properties 3-Mep in aqueous solution were similar to those of the unsubstituted pterin derivative (Ptr) in its acid form, such as absorption, fluorescent and phosphorescent emission spectra. Experiments using 2'-deoxyguanosine 5'-monophosphate (dGMP) as oxidizable target, demonstrated that methylation at C-3 position of the pterin moiety does not affect significantly the efficiency of photosensitization, but results in a more photostable sensitizer. This article is protected by copyright. All rights reserved. This article is protected by copyright. All rights reserved.

Demineralized bone matrix fibers formable as general and custom 3D printed mold-based implants for promoting bone regeneration.

PubMed

Rodriguez, Rudy U; Kemper, Nathan; Breathwaite, Erick; Dutta, Sucharita M; Hsu, Erin L; Hsu, Wellington K; Francis, Michael P

2016-07-26

Bone repair frequently requires time-consuming implant construction, particularly when using un-formed implants with poor handling properties. We therefore developed osteoinductive, micro-fibrous surface patterned demineralized bone matrix (DBM) fibers for engineering both defect-matched and general three-dimensional implants. Implant molds were filled with demineralized human cortical bone fibers there were compressed and lyophilized, forming mechanically strong shaped DBM scaffolds. Enzyme linked immunosorbent assays and mass spectrometry confirmed that DBM fibers contained abundant osteogenic growth factors (bone morphogenetic proteins, insulin-like growth factor-I) and extracellular matrix proteins. Mercury porosimetry and mechanical testing showed interconnected pores within the mechanically stable, custom DBM fiber scaffolds. Mesenchymal stem cells readily attached to the DBM and showed increasing metabolic activity over time. DBM fibers further increased alkaline phosphatase activity in C2C12 cells. In vivo, DBM implants elicited osteoinductive potential in a mouse muscle pouch, and also promoted spine fusion in a rat arthrodesis model. DBM fibers can be engineered into custom-shaped, osteoinductive and osteoconductive implants with potential for repairing osseous defects with precise fitment, potentially reducing operating time. By providing pre-formed and custom implants, this regenerative allograft may improve patient outcomes following surgical bone repair, while further advancing personalized orthopedic and craniomaxillofacial medicine using three-dimensional-printed tissue molds.

Defeating Leishmania resistance to miltefosine (hexadecylphosphocholine) by peptide-mediated drug smuggling: a proof of mechanism for trypanosomatid chemotherapy.

PubMed

Luque-Ortega, Juan Román; de la Torre, Beatriz G; Hornillos, Valentín; Bart, Jean-Mathieu; Rueda, Cristina; Navarro, Miguel; Amat-Guerri, Francisco; Acuña, A Ulises; Andreu, David; Rivas, Luis

2012-08-10

Miltefosine (hexadecylphosphocholine, HePC), the first orally active drug successful against leishmaniasis, is especially active on the visceral form of the disease. Resistance mechanisms are almost exclusively associated to dysfunction in HePC uptake systems. In order to evade the requirements of its cognate receptor/translocator, HePC-resistant Leishmania donovani parasites (R40 strain) were challenged with constructs consisting of an ω-thiol-functionalized HePC analogue conjugated to the cell-penetrating peptide (CPP) Tat(48-60), either through a disulfide or a thioether bond. The conjugates enter and kill both promastigote and intracellular amastigote forms of the R40 strain. Intracellular release of HePC by reduction of the disulfide-based conjugate was confirmed by means of double tagging at both the CPP (Quasar 670) and HePC (BODIPY) moieties. Scission of the conjugate, however, is not mandatory, as the metabolically more stable thioether conjugate retained substantial activity. The disulfide conjugate is highly active on the bloodstream form of Trypanosoma b. brucei, naturally resistant to HePC. Our results provide proof-of-mechanism for the use of CPP conjugates to avert drug resistance by faulty drug accumulation in parasites, as well as the possibility to extend chemotherapy into other parasites intrinsically devoid of membrane translocation systems. Copyright © 2012 Elsevier B.V. All rights reserved.

Latitudinal Trends in Stable Isotope Signatures of Northeast Atlantic Rhodoliths

NASA Astrophysics Data System (ADS)

Hofmann, Laurie

2017-04-01

Rhodoliths are free-living calcifying red algae that form extensive beds in shallow marine benthic environments (< 200 m) that provide important habitats and nurseries for marine organisms and contribute to carbonate sediment accumulation. There is growing concern that these organisms are sensitive to global climate change, which will have important consequences for coastal productivity and stability. Despite their significance and sensitivity, their basic photosynthetic and calcification mechanisms are not well understood. The goal of this study was to determine the plasticity of dissolved inorganic carbon (DIC) uptake mechanisms of rhodoliths along a latitudinal gradient in the Northeast (NE) Atlantic using natural stable isotope signatures. The delta 13C signature of macroalgae can be used to provide an indication of the preferred inorganic carbon source (CO2 vs. HCO3-). Here we present the total and organic delta 13C signatures of NE Atlantic rhodoliths with respect to changing temperature and light along the latitudinal gradient from the Canary Islands to Spitsbergen. A decreasing trend in delta 13C signatures with increasing latitude suggests that rhodoliths rely solely on CO2 as an inorganic carbon source at mid latitudes, while those at low latitudes may be able to utilize HCO3-. Polar rhodoliths deviate from this trend, suggesting they may have unique physiological mechanisms related to inorganic carbon acquisition and assimilation, which may have important implications for calcification in an environment undergoing rapid changing ocean chemistry.

Public good dynamics drive evolution of iron acquisition strategies in natural bacterioplankton populations.

PubMed

Cordero, Otto X; Ventouras, Laure-Anne; DeLong, Edward F; Polz, Martin F

2012-12-04

A common strategy among microbes living in iron-limited environments is the secretion of siderophores, which can bind poorly soluble iron and make it available to cells via active transport mechanisms. Such siderophore-iron complexes can be thought of as public goods that can be exploited by local communities and drive diversification, for example by the evolution of "cheating." However, it is unclear whether bacterial populations in the environment form stable enough communities such that social interactions significantly impact evolutionary dynamics. Here we show that public good games drive the evolution of iron acquisition strategies in wild populations of marine bacteria. We found that within nonclonal but ecologically cohesive genotypic clusters of closely related Vibrionaceae, only an intermediate percentage of genotypes are able to produce siderophores. Nonproducers within these clusters exhibited selective loss of siderophore biosynthetic pathways, whereas siderophore transport mechanisms were retained, suggesting that these nonproducers can act as cheaters that benefit from siderophore producers in their local environment. In support of this hypothesis, these nonproducers in iron-limited media suffer a significant decrease in growth, which can be alleviated by siderophores, presumably owing to the retention of transport mechanisms. Moreover, using ecological data of resource partitioning, we found that cheating coevolves with the ecological specialization toward association with larger particles in the water column, suggesting that these can harbor stable enough communities for dependencies among organisms to evolve.

A model of EcoRII restriction endonuclease action: the active complex is most likely formed by one protein subunit and one DNA recognition site

NASA Technical Reports Server (NTRS)

Karpova, E. A.; Kubareva, E. A.; Shabarova, Z. A.

1999-01-01

To elucidate the mechanism of interaction of restriction endonuclease EcoRII with DNA, we studied by native gel electrophoresis the binding of this endonuclease to a set of synthetic DNA-duplexes containing the modified or canonical recognition sequence 5'-d(CCA/TGG)-3'. All binding substrate or substrate analogues tested could be divided into two major groups: (i) duplexes that, at the interaction with endonuclease EcoRII, form two types of stable complexes on native gel in the absence of Mg2+ cofactor; (ii) duplexes that form only one type of complex, observed both in the presence and absence of Mg2+. Unlike the latter, duplexes under the first group can be hydrolyzed by endonuclease. Data obtained suggest that the active complex is most likely formed by one protein subunit and one DNA recognition sequence. A model of EcoRII endonuclease action is presented.

Medial prefrontal cortex subserves diverse forms of self-reflection.

PubMed

Jenkins, Adrianna C; Mitchell, Jason P

2011-01-01

The ability to think about oneself--to self--reflect--is one of the defining features of the human mind. Recent research has suggested that this ability may be subserved by a particular brain region: the medial prefrontal cortex (MPFC). However, although humans can contemplate a variety of different aspects of themselves, including their stable personality traits, current feelings, and physical attributes, no research has directly examined the extent to which these different forms of self-reflection are subserved by common mechanisms. To address this question, participants were scanned using functional magnetic resonance imaging (fMRI) while making judgments about their own personality traits, current mental states, and physical attributes as well as those of another person. Whereas some brain regions responded preferentially during only one form of self-reflection, a robust region of MPFC was engaged preferentially during self-reflection across all three types of judgment. These results suggest that--although dissociable--diverse forms of self-referential thought draw on a shared cognitive process subserved by MPFC.

Lyophilized Silk Sponges: A Versatile Biomaterial Platform for Soft Tissue Engineering

PubMed Central

2015-01-01

We present a silk biomaterial platform with highly tunable mechanical and degradation properties for engineering and regeneration of soft tissues such as, skin, adipose, and neural tissue, with elasticity properties in the kilopascal range. Lyophilized silk sponges were prepared under different process conditions and the effect of silk molecular weight, concentration and crystallinity on 3D scaffold formation, structural integrity, morphology, mechanical and degradation properties, and cell interactions in vitro and in vivo were studied. Tuning the molecular weight distribution (via degumming time) of silk allowed the formation of stable, highly porous, 3D scaffolds that held form with silk concentrations as low as 0.5% wt/v. Mechanical properties were a function of silk concentration and scaffold degradation was driven by beta-sheet content. Lyophilized silk sponges supported the adhesion of mesenchymal stem cells throughout 3D scaffolds, cell proliferation in vitro, and cell infiltration and scaffold remodeling when implanted subcutaneously in vivo. PMID:25984573

Merlin negative regulation by miR-146a promotes cell transformation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pérez-García, Erick I.; Meza-Sosa, Karla F.; López-Sevilla, Yaxem

2015-12-25

Inactivation of the tumor suppressor Merlin, by deleterious mutations or by protein degradation via sustained growth factor receptor signaling-mediated mechanisms, results in cell transformation and tumor development. In addition to these mechanisms, here we show that, miRNA-dependent negative regulation of Merlin protein levels also promotes cell transformation. We provide experimental evidences showing that miR-146a negatively regulates Merlin protein levels through its interaction with an evolutionary conserved sequence in the 3´ untranslated region of the NF2 mRNA. Merlin downregulation by miR-146a in A549 lung epithelial cells resulted in enhanced cell proliferation, migration and tissue invasion. Accordingly, stable miR-146a-transfectant cells formed tumorsmore » with metastatic capacity in vivo. Together our results uncover miRNAs as yet another negative mechanism controlling Merlin tumor suppressor functions.« less

Mechanism of Rifampicin Inactivation in Nocardia farcinica

PubMed Central

Abdelwahab, Heba; Martin Del Campo, Julia S.; Dai, Yumin; Adly, Camelia; El-Sohaimy, Sohby; Sobrado, Pablo

2016-01-01

A novel mechanism of rifampicin (Rif) resistance has recently been reported in Nocardia farcinica. This new mechanism involves the activity of rifampicin monooxygenase (RifMO), a flavin-dependent monooxygenase that catalyzes the hydroxylation of Rif, which is the first step in the degradation pathway. Recombinant RifMO was overexpressed and purified for biochemical analysis. Kinetic characterization revealed that Rif binding is necessary for effective FAD reduction. RifMO exhibits only a 3-fold coenzyme preference for NADPH over NADH. RifMO catalyzes the incorporation of a single oxygen atom forming an unstable intermediate that eventually is converted to 2′-N-hydroxy-4-oxo-Rif. Stable C4a-hydroperoxyflavin was not detected by rapid kinetics methods, which is consistent with only 30% of the activated oxygen leading to product formation. These findings represent the first reported detailed biochemical characterization of a flavin-monooxygenase involved in antibiotic resistance. PMID:27706151

Preparation of highly oxidized RBa.sub.2 Cu.sub.4 O.sub.8 superconductors

DOEpatents

Morris, Donald E.

1991-01-01

Novel superconducting materials in the form of compounds, structures or phases are formed by performing otherwise known syntheses in a highly oxidizing atmosphere rather than that created by molecular oxygen at atmospheric pressure or below. This leads to the successful synthesis of novel superconducting compounds which are thermodynamically stable at the conditions under which they are formed. The compounds and structures thus formed are substantially nonsusceptible to variations in their oxygen content when subjected to changing temperatures, thereby forming a temperature-stable substantially single phase crystal.

The topological pressure-temperature phase diagram of fluoxetine nitrate: monotropy unexpectedly turning into enantiotropy

NASA Astrophysics Data System (ADS)

Céolin, René; Rietveld, Ivo B.

2017-04-01

The phase behavior of pharmaceuticals is important for regulatory requirements and dosage form development. Racemic fluoxetine nitrate possesses two crystalline forms for which initial measurements indicated that they have a monotropic relationship with form I the only stable form. By constructing the topological pressure-temperature phase diagram, it has been shown that unexpectedly form II has a stable domain in the phase diagram and can be easily obtained by heating and grinding. The pressure necessary to obtain form II is only 11 MPa, which is much lower than most pressure used for tableting in the pharmaceutical industry.

Form-Stable Phase Change Materials Based on Eutectic Mixture of Tetradecanol and Fatty Acids for Building Energy Storage: Preparation and Performance Analysis

PubMed Central

Huang, Jingyu; Lu, Shilei; Kong, Xiangfei; Liu, Shangbao; li, Yiran

2013-01-01

This paper is focused on preparation and performance analysis of a series of form-stable phase change materials (FSPCMs), based on eutectic mixtures as phase change materials (PCMs) for thermal energy storage and high-density polyethylene (HDPE)-ethylene-vinyl acetate (EVA) polymer as supporting materials. The PCMs were eutectic mixtures of tetradecanol (TD)–capric acid (CA), TD–lauric acid (LA), and TD–myristic acid (MA), which were rarely explored before. Thermal properties of eutectic mixtures and FSPCMs were measured by differential scanning calorimeter (DSC). The onset melting/solidification temperatures of form-stable PCMs were 19.13 °C/13.32 °C (FS TD–CA PCM), 24.53 °C/24.92 °C (FS TD–LA PCM), and 33.15 °C/30.72 °C (FS TD–MA PCM), respectively, and latent heats were almost greater than 90 J/g. The surface morphologies and chemical stability of form-stable PCM were surveyed by scanning electron microscopy (SEM) and Fourier-transform infrared (FT-IR) spectroscopy, respectively. The thermal cycling test revealed that the thermal reliability of these three form-stable PCMs was good. Thermal storage/release experiment indicated melting/solidification time was shortened by introducing 10 wt % aluminum powder (AP). It is concluded that these FSPCMs can act as potential building thermal storage materials in terms of their satisfactory thermal properties. PMID:28788358

Form-Stable Phase Change Materials Based on Eutectic Mixture of Tetradecanol and Fatty Acids for Building Energy Storage: Preparation and Performance Analysis.

PubMed

Huang, Jingyu; Lu, Shilei; Kong, Xiangfei; Liu, Shangbao; Li, Yiran

2013-10-22

This paper is focused on preparation and performance analysis of a series of form-stable phase change materials (FSPCMs), based on eutectic mixtures as phase change materials (PCMs) for thermal energy storage and high-density polyethylene (HDPE)-ethylene-vinyl acetate (EVA) polymer as supporting materials. The PCMs were eutectic mixtures of tetradecanol (TD)-capric acid (CA), TD-lauric acid (LA), and TD-myristic acid (MA), which were rarely explored before. Thermal properties of eutectic mixtures and FSPCMs were measured by differential scanning calorimeter (DSC). The onset melting/solidification temperatures of form-stable PCMs were 19.13 °C/13.32 °C (FS TD-CA PCM), 24.53 °C/24.92 °C (FS TD-LA PCM), and 33.15 °C/30.72 °C (FS TD-MA PCM), respectively, and latent heats were almost greater than 90 J/g. The surface morphologies and chemical stability of form-stable PCM were surveyed by scanning electron microscopy (SEM) and Fourier-transform infrared (FT-IR) spectroscopy, respectively. The thermal cycling test revealed that the thermal reliability of these three form-stable PCMs was good. Thermal storage/release experiment indicated melting/solidification time was shortened by introducing 10 wt % aluminum powder (AP). It is concluded that these FSPCMs can act as potential building thermal storage materials in terms of their satisfactory thermal properties.

Subunit Conformations and Assembly States of a DNA Translocating Motor: The Terminase of Bacteriophage P22

PubMed Central

Němeček, Daniel; Gilcrease, Eddie B.; Kang, Sebyung; Prevelige, Peter E.; Casjens, Sherwood; Thomas, George J.

2007-01-01

Bacteriophage P22, a podovirus infecting strains of Salmonella typhimurium, packages a 42 kbp genome using a headful mechanism. DNA translocation is accomplished by the phage terminase, a powerful molecular motor consisting of large and small subunits. Although many of the structural proteins of the P22 virion have been well characterized, little is known about the terminase subunits and their molecular mechanism of DNA translocation. We report here structural and assembly properties of ectopically expressed and highly purified terminase large and small subunits. The large subunit (gp2), which contains the nuclease and ATPase activities of terminase, exists as a stable monomer with an α/β fold. The small subunit (gp3), which recognizes DNA for packaging and may regulate gp2 activity, exhibits a highly α-helical secondary structure and self-associates to form a stable oligomeric ring in solution. For wildtype gp3, the ring contains nine subunits, as demonstrated by hydrodynamic measurements, electron microscopy and native mass spectrometry. We have also characterized a gp3 mutant (Ala 112 → Thr) that forms a ten subunit ring, despite a subunit fold indistinguishable from wildtype. Both the nonameric and decameric gp3 rings exhibit nonspecific DNA binding activity, and gp2 is able to bind strongly to the DNA/gp3 complex but not to DNA alone. We propose a scheme for the roles of P22 terminase large and small subunits in the recruitment and packaging of viral DNA and discuss the model in relation to proposals for terminase-driven DNA translocation in other phages. PMID:17945256

Brine-in-crude-oil emulsions at the Strategic Petroleum Reserve

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nemer, Martin B.; Lord, David L.; MacDonald, Terry L.

2013-10-01

Metastable water-in-crude-oil emulsion formation could occur in a Strategic Petroleum Reserve (SPR) cavern if water were to flow into the crude-oil layer at a sufficient rate. Such a situation could arise during a drawdown from a cavern with a broken-hanging brine string. A high asphaltene content (> 1.5 wt %) of the crude oil provides the strongest predictor of whether a metastable water-in-crude-oil emulsion will form. However there are many crude oils with an asphaltene content > 1.5 wt % that don't form stable emulsions, but few with a low asphaltene content that do form stable emulsions. Most of themore » oils that form stable emulsions are "sour" by SPR standards indicating they contain total sulfur > 0.50 wt %.« less

Mechanism of Unfolding of Human Prion Protein.

PubMed

Singh, Reman K; Chamachi, Neharika G; Chakrabarty, Suman; Mukherjee, Arnab

2017-01-26

Misfolding and aggregation of prion proteins are associated with several neurodegenerative diseases. Therefore, understanding the mechanism of the misfolding process is of enormous interest in the scientific community. It has been speculated and widely discussed that the native cellular prion protein (PrP C ) form needs to undergo substantial unfolding to a more stable PrP C* state, which may further oligomerize into the toxic scrapie (PrP Sc ) form. Here, we have studied the mechanism of the unfolding of the human prion protein (huPrP) using a set of extensive well-tempered metadynamics simulations. Through multiple microsecond-long metadynamics simulations, we find several possible unfolding pathways. We show that each pathway leads to an unfolded state of lower free energy than the native state. Thus, our study may point to the signature of a PrP C* form that corresponds to a global minimum on the conformational free-energy landscape. Moreover, we find that these global minima states do not involve an increased β-sheet content, as was assumed to be a signature of PrP Sc formation in previous simulation studies. We have further analyzed the origin of metastability of the PrP C form through free-energy surfaces of the chopped helical segments to show that the helices, particularly H2 and H3 of the prion protein, have the tendency to form either a random coil or a β-structure. Therefore, the secondary structural elements of the prion protein are only weakly stabilized by tertiary contacts and solvation forces so that relatively weak perturbations induced by temperature, pressure, pH, and so forth can lead to substantial unfolding with characteristics of intrinsically disordered proteins.

An Improved Method for Generating Consistent Soluble Amyloid-beta Oligomer Preparations for In Vitro Neurotoxicity Studies

PubMed Central

Ryan, Deborah A.; Narrow, Wade C.; Federoff, Howard J.; Bowers, William J.

2010-01-01

Soluble Aβ oligomers are recognized as playing a key role in Alzheimer’s disease (AD) pathophysiology. Despite their significance, many investigators encounter difficulty generating reliable preparations for in vitro and in vivo experiments. Solutions of Aβ are often unstable and soluble conformer profiles inconsistent. In this study we describe detailed methods for preparing Aβ oligomers that are stable for several weeks and are enriched for low and high molecular weight oligomeric forms, including the 56-kDa form, a conformer implicated in AD-related cognitive impairment. We characterize their structural and functional properties using Western blot, dot blot, atomic force microscopy, Thioflavine T fluorescence, and primary neuronal culture toxicity assays. These synthetic preparations should prove valuable to many studying Aβ-mediated mechanisms underlying AD. PMID:20452375

Comparative semiempirical and ab initio study of the structural and chemical properties of uric acid and its anions

NASA Astrophysics Data System (ADS)

Altarsha, Muhannad; Monard, Gérald; Castro, Bertrand

Semiempirical, density functional theory (DFT), and ab initio calculations have been performed to assess the relative stabilities of 15 possible tautomer forms of neutral uric acid, and of the different urate mono- and dianion forms. These methods have also been used to compute ionization potentials (IPs) for uric acid and its derived anions. Overall, we have found that semiempirical calculations, in particular PM3, perform well as compared with B3LYP or MP2 computations toward these different structural and chemical properties of uric acid: the triketo form of uric acid is the most stable tautomer form of neutral uric acid. Three other tautomer forms are relatively close in energy, within the range 2-6 kcal/mol above the triketo form, with a mean energy deviation of only 1.3 kcal/mol between PM3 and DFT or ab initio results; the monoanion form of uric acid obtained by abstracting one proton in position 3 (denoted UAN3-) is the most stable form among all four possible urate monoanions both in gas phase and in solution; the dianion form of uric acid obtained by abstracting two protons, respectively, in positions 3 and 9 of uric acid (denoted UAN3-N9-) is the most stable urate dianion form both in gas phase and in solution. However, these two most stable species do not have the lowest IPs in solution: among monoanions and dianions, respectively, the species with the lowest IPs are UAN7- and UAN7-N9-.

Reaction Mechanisms for the Electrochemical Reduction of CO2 to CO and Formate on the Cu(100) Surface at 298K from Quantum Mechanics Free Energy Calculations with Explicit Water.

PubMed

Cheng, Tao; Xiao, Hai; Goddard, William A

2016-10-11

Copper is the only elemental metal that reduces a significant fraction of CO 2 to hydrocarbons and alcohols, but the atomistic reaction mechanism that controls the product distributions are not known because it has not been possible to detect the reaction intermediates on the electrode surface experimentally, or carry out Quantum Mechanics (QM) calculations with a realistic description of the electrolyte (water). Here, we carry out Quantum Mechanics (QM) calculations with an explicit description of water on the Cu(100) surface (experimentally shown to be stable under CO2RR conditions) to examine the initial reaction pathways to form CO and formate (HCOO - ) from CO 2 through free energy calculations at 298K and pH 7. We find that CO formation proceeds from physisorbed CO 2 to chemisorbed CO 2 (*CO 2 δ- ), with a free energy barrier of ΔG ‡ =0.43 eV, the rate determining step (RDS). The subsequent barriers of protonating *CO 2 δ- to form COOH* and then dissociating COOH* to form *CO are 0.37 eV and 0.30 eV, respectively. HCOO - formation proceeds through a very different pathway in which physisorbed CO 2 reacts directly with a surface H* (along with electron transfer), leading to ΔG ‡ = 0.80 eV. Thus, the competition between CO formation and HCOO - formation occurs in the first electron transfer step. On Cu(100), the RDS for CO formation is lower, making CO the predominant product. Thus, to alter the product distribution we need to control this first step of CO 2 binding, which might involve alloying or changing the structure at the nanoscale.

The Protective Antigen Component of Anthrax Toxin Forms Functional Octameric Complexes

PubMed Central

Kintzer, Alexander F.; Thoren, Katie L.; Sterling, Harry J.; Dong, Ken C.; Feld, Geoffrey K.; Tang, Iok I.; Zhang, Teri T.; Williams, Evan R.; Berger, James M.; Krantz, Bryan A.

2009-01-01

The assembly of bacterial toxins and virulence factors is critical to their function, but the regulation of assembly during infection has not been studied. We begin to address this question using anthrax toxin as a model. The protective antigen (PA) component of the toxin assembles into ring-shaped homooligomers that bind the two other enzyme components of the toxin, lethal factor (LF) and edema factor (EF), to form toxic complexes. To disrupt the host, these toxic complexes are endocytosed, such that the PA oligomer forms a membrane-spanning channel that LF and EF translocate through to enter the cytosol. We show using single-channel electrophysiology that PA channels contain two populations of conductance states, which correspond with two different PA pre-channel oligomers observed by electron microscopy—the well-described heptamer and a novel octamer. Mass spectrometry demonstrates that the PA octamer binds four LFs, and assembly routes leading to the octamer are populated with even-numbered, dimeric and tetrameric, PA intermediates. Both heptameric and octameric PA complexes can translocate LF and EF with similar rates and efficiencies. Here we also report a 3.2-Å crystal structure of the PA octamer. The octamer comprises ∼20−30% of the oligomers on cells, but outside of the cell, the octamer is more stable than the heptamer under physiological pH. Thus the PA octamer is a physiological, stable, and active assembly state capable of forming lethal toxins that may withstand the hostile conditions encountered in the bloodstream. This assembly mechanism may provide a novel means to control cytotoxicity. PMID:19627991

Polymorphs and polymorphic cocrystals of temozolomide.

PubMed

Babu, N Jagadeesh; Reddy, L Sreenivas; Aitipamula, Srinivasulu; Nangia, Ashwini

2008-07-07

Crystal polymorphism in the antitumor drug temozolomide (TMZ), cocrystals of TMZ with 4,4'-bipyridine-N,N'-dioxide (BPNO), and solid-state stability were studied. Apart from a known X-ray crystal structure of TMZ (form 1), two new crystalline modifications, forms 2 and 3, were obtained during attempted cocrystallization with carbamazepine and 3-hydroxypyridine-N-oxide. Conformers A and B of the drug molecule are stabilized by intramolecular amide N--HN(imidazole) and N--HN(tetrazine) interactions. The stable conformer A is present in forms 1 and 2, whereas both conformers crystallized in form 3. Preparation of polymorphic cocrystals I and II (TMZBPNO 1:0.5 and 2:1) were optimized by using solution crystallization and grinding methods. The metastable nature of polymorph 2 and cocrystal II is ascribed to unused hydrogen-bond donors/acceptors in the crystal structure. The intramolecularly bonded amide N-H donor in the less stable structure makes additional intermolecular bonds with the tetrazine C==O group and the imidazole N atom in stable polymorph 1 and cocrystal I, respectively. All available hydrogen-bond donors and acceptors are used to make intermolecular hydrogen bonds in the stable crystalline form. Synthon polymorphism and crystal stability are discussed in terms of hydrogen-bond reorganization.

Noncovalent Polymerization of Mesogens Crystallizes Lysozyme: Correlation between Nonamphiphilic Lyotropic Liquid Crystal Phase and Protein Crystal Formation

PubMed Central

Simon, Karen A.; Shetye, Gauri S.; Englich, Ulrich; Wu, Lei; Luk, Yan-Yeung

2011-01-01

Crystallization of proteins is important for fundamental studies and biopharmaceutical development but remains largely an empirical science. Here, we report the use of organic salts that can form a class of unusual non-amphiphilic lyotropic liquid crystals to crystallize the protein lysozyme. Certain non-amphiphilic organic molecules with fused aromatic rings and two charges can assemble into stable thread-like noncovalent polymers that may further form liquid crystal phases in water, traditionally termed chromonic liquid crystals. Using five of these mesogenic molecules as additives to induce protein crystallization, we discover that molecules that can form liquid crystal phases in water are highly effective at inducing the crystal formation of lysozyme, even at concentrations significantly lower than that required for forming liquid crystal phases. This result reveals an example of inducing protein crystallization by the molecular assembly of the additives, and is consistent with a new mechanism by which the strong hydration of an assembly process provides a gradual means to compete for the water molecules to enable solvated proteins to form crystals. PMID:21786812

Picornaviral Polymerase Structure, Function, and Fidelity Modulation

PubMed Central

Peersen, Olve B.

2017-01-01

Like all positive strand RNA viruses, the picornaviruses replicate their genomes using a virally encoded RNA-dependent RNA polymerase enzyme known as 3Dpol. Over the past decade we have made tremendous advances in our understanding of 3Dpol structure and function, including the discovery of a novel mechanism for closing the active site that allows these viruses to easily fine tune replication fidelity and quasispecies distributions. This review summarizes current knowledge of picornaviral polymerase structure and how the enzyme interacts with RNA and other viral proteins to form stable and processive elongation complexes. The picornaviral RdRPs are among the smallest viral polymerases, but their fundamental molecular mechanism for catalysis appears to be generally applicable as a common feature of all positive strand RNA virus polymerases. PMID:28163093

Effect of post-implantation annealing on Al-N isoelectronic trap formation in silicon: Al-N pair formation and defect recovery mechanisms

NASA Astrophysics Data System (ADS)

Mori, Takahiro; Morita, Yukinori; Matsukawa, Takashi

2018-05-01

The effect of post-implantation annealing (PIA) on Al-N isoelectronic trap (IET) formation in silicon has been experimentally investigated to discuss the Al-N IET formation and implantation-induced defect recovery mechanisms. We performed a photoluminescence study, which indicated that self-interstitial clusters and accompanying vacancies are generated in the ion implantation process. It is supposed that Al and N atoms move to the vacancy sites and form stable Al-N pairs in the PIA process. Furthermore, the PIA process recovers self-interstitial clusters while transforming their atomic configuration. The critical temperature for the formation/dissociation of Al-N pairs was found to be 450 °C, with which we describe the process integration for devices utilizing Al-N IET technology.

Theoretical investigation on the chemoselective N-heterocyclic carbene-catalyzed cross-benzoin reactions.

PubMed

Liu, Tao; Han, Shu-Min; Han, Ling-Li; Wang, Lu; Cui, Xiang-Yang; Du, Chong-Yang; Bi, Siwei

2015-03-28

A density functional theory study was performed to understand the detailed mechanisms of the cross-benzoin reactions catalyzed by N-heterocyclic carbene (NHC) species. Our theoretical study predicted that the first H-transfer operates with water in solution as a mediator, and the second H-transfer undergoes a concerted mechanism rather than a stepwise one. In addition, the chemoselectivity of the reactions studied in this work has been explored. P1 was obtained as a major product mainly due to the more stable intermediate formed by reaction of NHC with reactant R1. Different steric effects resulting from the fused six-membered ring in transition state TS7 and the fused five-membered ring in transition state TS13 are the origin leading to the chemoselectivity.

Routes of Motivation: Stable Psychological Dispositions Are Associated with Dynamic Changes in Cortico-Cortical Functional Connectivity

PubMed Central

Viola, Vanda; Tosoni, Annalisa; Kruglanski, Arie W.; Galati, Gaspare; Mannetti, Lucia

2014-01-01

The present study provides a neurobiological framework to the theory of epistemic motivation that has been extensively studied for the last three decades in the domain of social cognition. Epistemic motivations affect the way people generate and validate hypotheses, and ultimately form and modify knowledge. Strong dispositional measures such as need for cognitive closure (NCC), the desire for a quick firm answer (any answer) to a question, show gross and stable inter-individual differences. The cognitive mechanisms and neural underpinnings of such differences, however, remain largely unexplored. Here we show that high (compared to low) levels of NCC, measured with need for cognitive closure scale, are associated with reduced online adjustment in cognitive control, as indexed by behavioral conflict adaptation. This behavioral effect is mediated by dynamic changes in cortico-cortical functional connectivity between prefrontal regions involved in conflict monitoring and implementation of cognitive control. In particular, these regions show increased functional connectivity after exposure to conflict in low but not high NCC individuals. These results demonstrate that the level of flexibility of functional cortico-cortical connections can mediate stable psychological dispositions. PMID:24892718

The magnetic structure and palaeomagnetic recording fidelity of sub-micron greigite (Fe3S4)

NASA Astrophysics Data System (ADS)

Valdez-Grijalva, Miguel A.; Nagy, Lesleis; Muxworthy, Adrian R.; Williams, Wyn; Fabian, Karl

2018-02-01

We present the results of a finite-element micromagnetic model of 30nm to 300nm greigite (Fe3S4) grains with a variety of equant morphologies. This grain size range covers the magnetic single-domain (SD) to pseudo single-domain (PSD) transition, and possibly also the PSD to multi-domain (MD) transition. The SD-PSD threshold d0 is determined to be 50nm ≤d0 ≤ 56nm depending on grain shape. The nudged elastic-band method was used to determine the room temperature energy barriers between stable states and thus the blocking volumes. It is found that, in the absence of interparticle magnetostatic interactions, the magnetisation of equant SD greigite is not stable on a geological scale and only PSD grains ≥ 70nm can be expected to carry a stable magnetisation over billion-year timescales, i.e., all non-interacting SD particles are essentially superparamagnetic. We further identify a mechanism for the PSD to multi-domain (MD) transition, which is of a continuous nature from PSD nucleation up to 300nm, when structures typical of MD behaviour like closure domains begin to form.

c-di-GMP can form remarkably stable G-quadruplexes at physiological conditions in the presence of some planar intercalators.

PubMed

Nakayama, Shizuka; Kelsey, Ilana; Wang, Jingxin; Sintim, Herman O

2011-04-28

The ubiquitous bacterial biofilm regulator, c-di-GMP can form G-quadruplexes at physiological conditions in the presence of some aromatic compounds, such as acriflavine and proflavine. The fluorescence of these compounds is quenched upon c-di-GMP binding and some of the formed c-di-GMP G-quadruplexes are stable even at 75 °C. © The Royal Society of Chemistry 2011

Effect of Si Content on Oxide Formation on Surface of Molten Fe-Cr-C Alloy Bath During Oxygen Top Blowing

NASA Astrophysics Data System (ADS)

Mihara, Ryosuke; Gao, Xu; Kim, Sun-joong; Ueda, Shigeru; Shibata, Hiroyuki; Seok, Min Oh; Kitamura, Shin-ya

2018-02-01

Using a direct observation experimental method, the oxide formation behavior on the surface of Fe-Cr-5 mass pct C-Si alloy baths during decarburization by a top-blown Ar-O2 mixture was studied. The effects of the initial Si and Cr content of the alloy, temperature, and oxygen feed ratio on oxide formation were investigated. The results showed that, for alloys without Si, oxide particles, unstable oxide films, and stable oxide films formed sequentially. The presence of Si in the alloy changed the formation behavior of stable oxide film, and increased the crucial C content when stable oxide film started to form. Increasing the temperature, decreasing the initial Cr content, and increasing the ratio of the diluting gas decreased the critical C content at which a stable oxide film started to form. In addition, the P CO and a_{{{Cr}2 {O}3 }} values at which oxides started to form were estimated using Hilty's equation and the equilibrium relation to understand the formation conditions and the role of each parameter in oxide formation.

Conformational analysis, tautomerization, IR, Raman, and NMR studies of benzyl acetoacetate

NASA Astrophysics Data System (ADS)

Tayyari, Sayyed Faramarz; Naghavi, Farnaz; Pojhan, Sahar; McClurg, Ryan W.; Sammelson, Robert E.

2011-02-01

A complete conformational analysis of the keto and enol forms of benzyl acetoacetate (BAA), a β-dicarbonyl compound, was carried out by ab initio calculations, at the density functional theory (DFT) level. By inspection of all possible conformers and tautomers, 22 stable cis-enol, 28 stable trans-enol, and five keto conformers were obtained. Among all stable cis-enol forms only six of them are engaged in intramolecular hydrogen bond. The hydrogen bond strength of the most stable conformer of BAA is compared with that of acetylacetone (AA) and dimethyl oxaloacetate (DMOA). Harmonic vibrational frequencies of the most stable enol and keto forms and their deuterated analogues were also calculated and compared with the experimental data. According to the theoretical calculations, the hydrogen bond strength of the most stable enol conformer of BAA is 56.7 kJ/mol (calculated at the B3LYP/6-311++G ∗∗ level), about 10 kJ/mol less than that of AA. This weakening of hydrogen bond is consistent with the spectroscopic results. NMR studies indicate that BAA exists mainly as a keto tautomer in all considered solutions. The Gibbs energies for keto/enol tautomerization were calculated at the B3LYP level, with several basis sets, in both gas phase and CH 3CN solution (using PCM model), for the most stable enol and keto conformers.

Characterization of the fusion core in zebrafish endogenous retroviral envelope protein

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shi, Jian; State Key Laboratory of Virology, Wuhan Institute of Virology, Chinese Academy of Sciences, Wuhan, Hubei 430071; Zhang, Huaidong

2015-05-08

Zebrafish endogenous retrovirus (ZFERV) is the unique endogenous retrovirus in zebrafish, as yet, containing intact open reading frames of its envelope protein gene in zebrafish genome. Similarly, several envelope proteins of endogenous retroviruses in human and other mammalian animal genomes (such as syncytin-1 and 2 in human, syncytin-A and B in mouse) were identified and shown to be functional in induction of cell–cell fusion involved in placental development. ZFERV envelope protein (Env) gene appears to be also functional in vivo because it is expressible. After sequence alignment, we found ZFERV Env shares similar structural profiles with syncytin and other type Imore » viral envelopes, especially in the regions of N- and C-terminal heptad repeats (NHR and CHR) which were crucial for membrane fusion. We expressed the regions of N + C protein in the ZFERV Env (residues 459–567, including predicted NHR and CHR) to characterize the fusion core structure. We found N + C protein could form a stable coiled-coil trimer that consists of three helical NHR regions forming a central trimeric core, and three helical CHR regions packing into the grooves on the surface of the central core. The structural characterization of the fusion core revealed the possible mechanism of fusion mediated by ZFERV Env. These results gave comprehensive explanation of how the ancient virus infects the zebrafish and integrates into the genome million years ago, and showed a rational clue for discovery of physiological significance (e.g., medicate cell–cell fusion). - Highlights: • ZFERV Env shares similar structural profiles with syncytin and other type I viral envelopes. • The fusion core of ZFERV Env forms stable coiled-coil trimer including three NHRs and three CHRs. • The structural mechanism of viral entry mediated by ZFERV Env is disclosed. • The results are helpful for further discovery of physiological function of ZFERV Env in zebrafish.« less

Adaptation of pharmaceutical excipients to FDM 3D printing for the fabrication of patient-tailored immediate release tablets.

PubMed

Sadia, Muzna; Sośnicka, Agata; Arafat, Basel; Isreb, Abdullah; Ahmed, Waqar; Kelarakis, Antonios; Alhnan, Mohamed A

2016-11-20

This work aims to employ fused deposition modelling 3D printing to fabricate immediate release pharmaceutical tablets with several model drugs. It investigates the addition of non-melting filler to methacrylic matrix to facilitate FDM 3D printing and explore the impact of (i) the nature of filler, (ii) compatibility with the gears of the 3D printer and iii) polymer: filler ratio on the 3D printing process. Amongst the investigated fillers in this work, directly compressible lactose, spray-dried lactose and microcrystalline cellulose showed a level of degradation at 135°C whilst talc and TCP allowed consistent flow of the filament and a successful 3D printing of the tablet. A specially developed universal filament based on pharmaceutically approved methacrylic polymer (Eudragit EPO) and thermally stable filler, TCP (tribasic calcium phosphate) was optimised. Four model drugs with different physicochemical properties were included into ready-to-use mechanically stable tablets with immediate release properties. Following the two thermal processes (hot melt extrusion (HME) and fused deposition modelling (FDM) 3D printing), drug contents were 94.22%, 88.53%, 96.51% and 93.04% for 5-ASA, captopril, theophylline and prednisolone respectively. XRPD indicated that a fraction of 5-ASA, theophylline and prednisolone remained crystalline whilst captopril was in amorphous form. By combining the advantages of thermally stable pharmaceutically approved polymers and fillers, this unique approach provides a low cost production method for on demand manufacturing of individualised dosage forms. Copyright © 2016 Elsevier B.V. All rights reserved.

Effects of Different Social and Environmental Conditions on Established Dominance Relationships in Crayfish.

PubMed

Herberholz, Jens; Swierzbinski, Matthew E; Birke, Juliane M

2016-04-01

Like most social animals, crayfish readily form dominance relationships and linear social hierarchies when competing for limited resources. Competition often entails dyadic aggressive interactions, from which one animal emerges as the dominant and one as the subordinate. Once dominance relationships are formed, they typically remain stable for extended periods of time; thus, access to future resources is divided unequally among conspecifics. We previously showed that firmly established dominance relationships in juvenile crayfish can be disrupted by briefly adding a larger conspecific to the original pair. This finding suggested that the stability of social relationships in crayfish was highly context-dependent and more transient than previously assumed. We now report results that further identify the mechanisms underlying the destabilization of crayfish dominance relationships. We found that rank orders remained stable when conspecifics of smaller or equal size were added to the original pair, suggesting that both dominant and subordinate must be defeated by a larger crayfish in order to destabilize dominance relationships. We also found that dominance relationships remained stable when both members of the original pair were defeated by larger conspecifics in the absence of their original opponent. This showed that dominance relationships are not destabilized unless both animals experience defeat together. Lastly, we found that dominance relationships of pairs were successfully disrupted by larger intruders, although with reduced magnitude, after all chemical cues associated with earlier agonistic experiences were eliminated. These findings provide important new insights into the contextual features that regulate the stability of social dominance relationships in crayfish and probably in other species as well. © 2016 Marine Biological Laboratory.

Bionic multisilicon copolymers used as novel cross-linking agents for preparing anion exchange hybrid membranes.

PubMed

Wu, Yonghui; Luo, Jingyi; Wu, Cuiming; Xu, Tongwen; Fu, Yanxun

2011-05-26

Bionic multisilicon copolymers have long-main chains and many branched chains, and contain multifunctional groups of -N(+)(CH(3))(3)Cl(-) and -Si(OCH(3))(3), which are similar to the stem, branch, fruit, and acetabula of a vine from bionic aspect, respectively. They have high flexibility, charge density, and cross-linking ability and thus can be used as novel cross-linking agents for preparing anion-exchange hybrid membranes. High content of -Si(OCH(3))(3) groups (68-78%) is suitable to enhance membrane stabilities. The membranes are stable in 65 °C water up to 120 h and can keep integrity in 2 mol/L NaOH for 192 h. High content of -N(+)(CH(3))(3)Cl(-) groups (42-55%) is suitable to enhance membrane electrical properties. The membranes have low membrane resistance (R(m), 0.59-0.94 Ω cm(2)) and high diffusion dialysis performance. The acid (H(+)) dialysis coefficients (U(H)) are in the range of 0.007-0.075 m h(-1) at room temperature and 0.015-0.115 m h(-1) at 40 °C. The separation factor (S(H/Fe)) can reach up to 43 at room temerature and 49 at 40 °C. All of the membranes are highly homogeneous, mechanically stable (21-31 MPa, 25-147%), and thermally stable (227-275 °C for halide form membranes, and 157-172 °C for OH(-) form membranes). Hence, the investigation of multisilicon copolymers will give rise to a new developing field in material and membrane sciences.

Photochemical isomerizations of thiosemicarbazide, a matrix isolation study.

PubMed

Rostkowska, Hanna; Lapinski, Leszek; Kozankiewicz, Boleslaw; Nowak, Maciej J

2012-10-11

Two thione conformers of monomeric thiosemicarbazide were trapped from the gas phase into a low-temperature Ar matrix. A phototransformation converting the less stable form of the compound into the most stable conformer was induced by irradiation with near-IR (λ = 1462 nm) or UV (λ > 320 nm) light. This photoeffect allowed separation of the IR spectra of the observed thione forms. The structures of both observed isomers were identified by comparison of the separated experimental IR spectra with the spectra theoretically predicted for two most stable forms of the compound. The population ratio of the two conformers in an Ar matrix, prior to any irradiation, was estimated to be equal ≈2:1. Irradiation of matrix-isolated thiosemicarbazide with shorter-wavelength UV (λ > 270 nm) light induced a phototautomeric reaction generating thiol forms of the compound.

Adaptive piezoelectric sensoriactuator

NASA Technical Reports Server (NTRS)

Clark, Jr., Robert L. (Inventor); Vipperman, Jeffrey S. (Inventor); Cole, Daniel G. (Inventor)

1996-01-01

An adaptive algorithm implemented in digital or analog form is used in conjunction with a voltage controlled amplifier to compensate for the feedthrough capacitance of piezoelectric sensoriactuator. The mechanical response of the piezoelectric sensoriactuator is resolved from the electrical response by adaptively altering the gain imposed on the electrical circuit used for compensation. For wideband, stochastic input disturbances, the feedthrough capacitance of the sensoriactuator can be identified on-line, providing a means of implementing direct-rate-feedback control in analog hardware. The device is capable of on-line system health monitoring since a quasi-stable dynamic capacitance is indicative of sustained health of the piezoelectric element.

Propafenone effects on the stable structures of Aβ16-22 system

NASA Astrophysics Data System (ADS)

Tran, Linh; Ngo, Son Tung; Nguyen, Minh Tho

2018-03-01

An extensive replica exchange molecular dynamics (REMD) simulation was performed to investigate the progress patterns of the molecular interactions of propafenone and Aβ16-22 system. Distinct conformational equilibrium of Aβ16-22 system with and without propafenone was analyzed in detail. Propafenone can act to prevent the Alzheimer's disease (AD) by significantly inhibiting Aβ oligomerization. Our calculated results provide insights into the inhibition mechanism of propafenone on the oligomerization process to form Aβ16-22 peptide aggregation. These findings are valuable for the development of therapeutic drugs in the AD early stage.

Stable Boron Nitride Interphases for Ceramic Matrix Composites

NASA Technical Reports Server (NTRS)

Morscher, Gregory N.

1999-01-01

Ceramic matrix composites (CMC's) require strong fibers for good toughness and weak interphases so that cracks which are formed in the matrix debond and deflect around the fibers. If the fibers are strongly bonded to the matrix, CMC's behave like monolithic ceramics (e.g., a ceramic coffee cup), and when subjected to mechanical loads that induce cracking, such CMC's fail catastrophically. Since CMC's are being developed for high temperature corrosive environments such as the combustor liner for advanced High Speed Civil Transport aircraft, the interphases need to be able to withstand the environment when the matrix cracks.

Antimatter as an Energy Source

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jackson, Gerald P.

2009-03-16

Antiprotons and positrons are constantly generated in space, and periodically manufactured by humans here on Earth. Harvesting of these particles in space and forming stable antimatter atoms and molecules would create a significant energy source for power and propulsion. Though dedicated fabrication of these particles on Earth consumes much more energy than could be liberated upon annihilation, manufactured antimatter represents a high-density energy storage mechanism well suited for spacecraft power and propulsion. In this paper the creation, storage, and utilization of antimatter is introduced. Specific examples of electrical energy generation and deep-space propulsion based on antimatter are also reviewed.

Enantioselective Direct α-Amination of Aldehydes via a Photoredox Mechanism: A Strategy for Asymmetric Amine Fragment Coupling

PubMed Central

Cecere, Giuseppe; Koenig, Christian M.; Alleva, Jennifer L.

2013-01-01

The direct, asymmetric α-amination of aldehydes has been accomplished via a combination of photoredox and organocatalysis. Photon-generated, nitrogen-centered radicals undergo enantioselective α-addition to catalytically formed chiral enamines to directly produce stable α-amino aldehyde adducts bearing synthetically useful amine substitution patterns. Incorporation of a photolabile group on the amine precursor obviates the need to employ a photoredox catalyst in this transformation. Importantly, this photoinduced transformation allows direct and enantioselective access to α-amino aldehyde products that do not require post-reaction manipulation. PMID:23869694

Highly Flexible Self-Assembled V2O5 Cathodes Enabled by Conducting Diblock Copolymers

NASA Astrophysics Data System (ADS)

An, Hyosung; Mike, Jared; Smith, Kendall; Swank, Lisa; Lin, Yen-Hao; Pesek, Stacy; Verduzco, Rafael; Lutkenhaus, Jodie

Structural energy storage materials combining load-bearing mechanical properties and high energy storage performance are desired for applications in wearable devices or flexible displays. Vanadium pentoxide (V2O5) is a promising cathode material for possible use in flexible battery electrodes, but it remains limited by low Li+ diffusion coefficient and electronic conductivity, severe volumetric changes upon cycling, and limited mechanical flexibility. Here, we demonstrate a route to address these challenges by blending a diblock copolymer bearing electron- and ion-conducting blocks, poly(3-hexylthiophene)-block-poly(ethyleneoxide) (P3HT- b-PEO), with V2O5 to form a mechanically flexible, electro-mechanically stable hybrid electrode. V2O5 layers were arranged parallel in brick-and-mortar-like fashion held together by the P3HT- b-PEO binder. This unique structure significantly enhances mechanical flexibility, toughness and cyclability without sacrificing capacity. Electrodes comprised of 10 wt% polymer have unusually high toughness (293 kJ/m3) and specific energy (530 Wh/kg), both higher than reduced graphene oxide paper electrodes.

Failure of in vitro-differentiated mesenchymal stem cells from the synovial membrane to form ectopic stable cartilage in vivo.

PubMed

De Bari, Cosimo; Dell'Accio, Francesco; Luyten, Frank P

2004-01-01

We previously reported the identification in a nude mouse assay of molecular markers predictive of the capacity of articular cartilage-derived cells (ACDCs) to form ectopic stable cartilage that is resistant to vascular invasion and endochondral ossification. In the present study, we investigated whether in vitro-differentiated mesenchymal stem cells (MSCs) from the synovial membrane (SM) express the stable-chondrocyte markers and form ectopic stable cartilage in vivo. Chondrogenesis was induced in micromass culture with the addition of transforming growth factor beta1 (TGFbeta1). After acquisition of the cartilage phenotype, micromasses were implanted subcutaneously into nude mice. Alternatively, cells were released enzymatically and either replated in monolayer or injected intramuscularly into nude mice. Marker analysis was performed by quantitative reverse transcription-polymerase chain reaction. Cell death was detected with TUNEL assay. Cartilage-like micromasses and released cells expressed the stable-chondrocyte markers at levels comparable with those expressed by stable ACDCs. The released cells lost chondrocyte marker expression by 24 hours in monolayer and failed to form cartilage when injected intramuscularly into nude mice. Instead, myogenic differentiation was detected. When intact TGFbeta1-treated micromasses were implanted subcutaneously, they partially lost their cartilage phenotype and underwent cell death and neoangiogenesis within 1 week. At later time points (15-40 days), we retrieved neither cartilage nor bone, and human cells were not detectable. The chondrocyte-like phenotype of human SM MSCs, induced in vitro under specific conditions, appears to be unstable and is not sufficient to obtain ectopic formation of stable cartilage in vivo. Studies in animal models of joint surface defect repair are necessary to evaluate the stability of the SM MSC chondrocyte-like phenotype within the joint environment.

Forming-free bipolar resistive switching in nonstoichiometric ceria films

NASA Astrophysics Data System (ADS)

Ismail, Muhammad; Huang, Chun-Yang; Panda, Debashis; Hung, Chung-Jung; Tsai, Tsung-Ling; Jieng, Jheng-Hong; Lin, Chun-An; Chand, Umesh; Rana, Anwar Manzoor; Ahmed, Ejaz; Talib, Ijaz; Nadeem, Muhammad Younus; Tseng, Tseung-Yuen

2014-01-01

The mechanism of forming-free bipolar resistive switching in a Zr/CeO x /Pt device was investigated. High-resolution transmission electron microscopy and energy-dispersive spectroscopy analysis indicated the formation of a ZrO y layer at the Zr/CeO x interface. X-ray diffraction studies of CeO x films revealed that they consist of nano-polycrystals embedded in a disordered lattice. The observed resistive switching was suggested to be linked with the formation and rupture of conductive filaments constituted by oxygen vacancies in the CeO x film and in the nonstoichiometric ZrO y interfacial layer. X-ray photoelectron spectroscopy study confirmed the presence of oxygen vacancies in both of the said regions. In the low-resistance ON state, the electrical conduction was found to be of ohmic nature, while the high-resistance OFF state was governed by trap-controlled space charge-limited mechanism. The stable resistive switching behavior and long retention times with an acceptable resistance ratio enable the device for its application in future nonvolatile resistive random access memory (RRAM).

Inhibition of Voltage-Gated K+ Channel Kv1.5 by Antiarrhythmic Drugs.

PubMed

Chen, Rong; Chung, Shin-Ho

2018-05-08

Molecular dynamics simulations are employed to determine the inhibitory mechanisms of three drugs, 5-(4-phenoxybutoxy)psoralen (PAP-1), vernakalant, and flecainide, on the voltage-gated K + channel Kv1.5, a target for the treatment of cardiac arrhythmia. At neutral pH, PAP-1 is neutral, whereas the other two molecules carry one positive charge. We show that PAP-1 forms stable dimers in water, primarily through hydrophobic interactions between aromatic rings. All three molecules bind to the cavity between the Ile508 and Val512 residues from the four subunits of the channel. Once bound, the drug molecules are flexible, with the average root-mean-square fluctuation being between 2 and 3 Å, which is larger than the radius of gyration of a bulky amino acid. The presence of a monomeric PAP-1 causes the permeating K + ion to dehydrate, thereby creating a significant energy barrier. In contrast, vernakalant blocks the ion permeation primarily via an electrostatic mechanism and, therefore, must be in the protonated and charged form to be effective.

Surface reaction mechanisms during ozone and oxygen plasma assisted atomic layer deposition of aluminum oxide.

PubMed

Rai, Vikrant R; Vandalon, Vincent; Agarwal, Sumit

2010-09-07

We have elucidated the reaction mechanism and the role of the reactive intermediates in the atomic layer deposition (ALD) of aluminum oxide from trimethyl aluminum in conjunction with O(3) and an O(2) plasma. In situ attenuated total reflection Fourier transform infrared spectroscopy data show that both -OH groups and carbonates are formed on the surface during the oxidation cycle. These carbonates, once formed on the surface, are stable to prolonged O(3) exposure in the same cycle. However, in the case of plasma-assisted ALD, the carbonates decompose upon prolonged O(2) plasma exposure via a series reaction kinetics of the type, A (CH(3)) --> B (carbonates) --> C (Al(2)O(3)). The ratio of -OH groups to carbonates on the surface strongly depends on the oxidizing agent, and also the duration of the oxidation cycle in plasma-assisted ALD. However, in both O(3) and O(2) plasma cycles, carbonates are a small fraction of the total number of reactive sites compared to the hydroxyl groups.

Preparation and mechanical properties of modified nanocellulose/PLA composites from cassava residue

NASA Astrophysics Data System (ADS)

Huang, Lijie; Zhang, Xiaoxiao; Xu, Mingzi; Chen, Jie; Shi, Yinghan; Huang, Chongxing; Wang, Shuangfei; An, Shuxiang; Li, Chunying

2018-02-01

Nanocellulose was prepared by a mechanochemical method using cassava residue as a raw material and phosphoric acid as the auxiliary agent. The prepared nanocellulose was hydrophobically modified with stearic acid to improve its dispersibility. This modified nanocellulose was added to polylactic acid (PLA) film-forming liquids at concentrations of 0%, 0.5%, 1.0%, 1.5% and 2.0%, and the effect of modified nanocellulose on the mechanical properties of polylactic acid (PLA) films were investigated. When at least 0.5% modified nanocellulose is added, more active groups of modified nanocellulose are adsorbed onto the PLA molecular chain. Although the tensile strength of the film is only improved by 13.59%, the flexibility of the film decreases, and the elastic modulus decreases by 28.91%. When 1% modified nanocellulose is added, the modified nanocellulose and PLA are tangled together through molecular chains and they co-crystallize to form a stable network structure. The tensile strength of the nanocomposite films is enhanced by 40.03%, the elastic modulus is enhanced by 55.65%, and the flexibility of the film decreases.

Nanocatalytic growth of Si nanowires from Ni silicate coated SiC nanoparticles on Si solar cell.

PubMed

Parida, Bhaskar; Choi, Jaeho; Ji, Hyung Yong; Park, Seungil; Lim, Gyoungho; Kim, Keunjoo

2013-09-01

We investigated the nanocatalytic growth of Si nanowires on the microtextured surface of crystalline Si solar cell. 3C-SiC nanoparticles have been used as the base for formation of Ni silicate layer in a catalytic reaction with the Si melt under H2 atmosphere at an annealing temperature of 1100 degrees C. The 10-nm thick Ni film was deposited after the SiC nanoparticles were coated on the microtextured surface of the Si solar cell by electron-beam evaporation. SiC nanoparticles form a eutectic alloy surface of Ni silicate and provide the base for Si supersaturation as well as the Ni-Si alloy layer on Si substrate surface. This bottom reaction mode for the solid-liquid-solid growth mechanism using a SiC nanoparticle base provides more stable growth of nanowires than the top reaction mode growth mechanism in the absence of SiC nanoparticles. Thermally excited Ni nanoparticle forms the eutectic alloy and provides collectively excited electrons at the alloy surface, which reduces the activation energy of the nanocatalytic reaction for formation of nanowires.

Computer Simulation Studies of Ion Channel Gating: Characteristics of the M2 Channel of Influenza-A Virus in a Phospholipid Bilayer

NASA Technical Reports Server (NTRS)

Schweighofer, Karl J.; Pohorille, Andrew; DeVincenzi, D. (Technical Monitor)

1999-01-01

The 25 amino acids long, transmembrane fragment of the Influenza virus M2 protein forms a homotetrameric channel that transports protons across lipid bilayers. It has been postulated that high efficiency and selectivity of this process is due to gating by four histidine residues that occlude the channel lumen in the closed state. Two mechanisms of gating have been postulated. In one mechanism, the proton is "shuttled" through the gate by attaching to the delta nitrogen atom on the extracellular side of the imidazole ring, followed by the release of the proton attached to the epsilon nitrogen atom on the opposite side. In the second mechanism, the four histidines move away from each other due to electrostatic repulsion upon protonation, thus opening the gate sufficiently that a wire of water molecules can penetrate the gate. Then, protons are transported by "hopping" along the wire. In this paper, both mechanisms are evaluated in a series of molecular dynamics simulations by investigating stability of different protonation states of the channel that are involved in these mechanisms. For the shuttle mechanism, these are states with all epsilon protonated histidines, one biprotonated residue or one histidine protonated in the delta position. For the gate opening mechanism, this is the state in which all four histidines are biprotonated. In addition, a state with two biprotonated histidines is considered. For each system, composed of the protein channel embedded in phospholipid bilayer located between two water lamellae, a molecular dynamics trajectory of approximately 1.3 ns (after equilibration) was obtained. It is found that the states involved in the shuttle mechanism are stable during the simulations. Furthermore, the orientations and dynamics of water molecules near the gate are conducive to proton transfers involved in the shuttle. In contract, the fully biprotonated state, implicated in the gate opening mechanism, is not stable and the channel looses its structural integrity. If only two histidines are biprotonated the channel deforms but remains intact with the gate mostly closed. In summary, the results of this study lend support to the shuttle mechanism but not to the gate opening mechanism of proton gating in M2.

Pattern formation, logistics, and maximum path probability

NASA Astrophysics Data System (ADS)

Kirkaldy, J. S.

1985-05-01

The concept of pattern formation, which to current researchers is a synonym for self-organization, carries the connotation of deductive logic together with the process of spontaneous inference. Defining a pattern as an equivalence relation on a set of thermodynamic objects, we establish that a large class of irreversible pattern-forming systems, evolving along idealized quasisteady paths, approaches the stable steady state as a mapping upon the formal deductive imperatives of a propositional function calculus. In the preamble the classical reversible thermodynamics of composite systems is analyzed as an externally manipulated system of space partitioning and classification based on ideal enclosures and diaphragms. The diaphragms have discrete classification capabilities which are designated in relation to conserved quantities by descriptors such as impervious, diathermal, and adiabatic. Differentiability in the continuum thermodynamic calculus is invoked as equivalent to analyticity and consistency in the underlying class or sentential calculus. The seat of inference, however, rests with the thermodynamicist. In the transition to an irreversible pattern-forming system the defined nature of the composite reservoirs remains, but a given diaphragm is replaced by a pattern-forming system which by its nature is a spontaneously evolving volume partitioner and classifier of invariants. The seat of volition or inference for the classification system is thus transferred from the experimenter or theoretician to the diaphragm, and with it the full deductive facility. The equivalence relations or partitions associated with the emerging patterns may thus be associated with theorems of the natural pattern-forming calculus. The entropy function, together with its derivatives, is the vehicle which relates the logistics of reservoirs and diaphragms to the analog logistics of the continuum. Maximum path probability or second-order differentiability of the entropy in isolation are sufficiently strong interpretations of the second law of thermodynamics to define the approach to and the nature of patterned stable steady states. For many pattern-forming systems these principles define quantifiable stable states as maxima or minima (or both) in the dissipation. An elementary statistical-mechanical proof is offered. To turn the argument full circle, the transformations of the partitions and classes which are predicated upon such minimax entropic paths can through digital modeling be directly identified with the syntactic and inferential elements of deductive logic. It follows therefore that all self-organizing or pattern-forming systems which possess stable steady states approach these states according to the imperatives of formal logic, the optimum pattern with its rich endowment of equivalence relations representing the central theorem of the associated calculus. Logic is thus ``the stuff of the universe,'' and biological evolution with its culmination in the human brain is the most significant example of all the irreversible pattern-forming processes. We thus conclude with a few remarks on the relevance of the contribution to the theory of evolution and to research on artificial intelligence.

Stressed but Stable: Canopy Loss Decreased Species Synchrony and Metabolic Variability in an Intertidal Hard-Bottom Community

PubMed Central

Valdivia, Nelson; Golléty, Claire; Migné, Aline; Davoult, Dominique; Molis, Markus

2012-01-01

The temporal stability of aggregate community properties depends on the dynamics of the component species. Since species growth can compensate for the decline of other species, synchronous species dynamics can maintain stability (i.e. invariability) in aggregate properties such as community abundance and metabolism. In field experiments we tested the separate and interactive effects of two stressors associated with storminess–loss of a canopy-forming species and mechanical disturbances–on species synchrony and community respiration of intertidal hard-bottom communities on Helgoland Island, NE Atlantic. Treatments consisted of regular removal of the canopy-forming seaweed Fucus serratus and a mechanical disturbance applied once at the onset of the experiment in March 2006. The level of synchrony in species abundances was assessed from estimates of species percentage cover every three months until September 2007. Experiments at two sites consistently showed that canopy loss significantly reduced species synchrony. Mechanical disturbance had neither separate nor interactive effects on species synchrony. Accordingly, in situ measurements of CO2-fluxes showed that canopy loss, but not mechanical disturbances, significantly reduced net primary productivity and temporal variation in community respiration during emersion periods. Our results support the idea that compensatory dynamics may stabilise aggregate properties. They further suggest that the ecological consequences of the loss of a single structurally important species may be stronger than those derived from smaller-scale mechanical disturbances in natural ecosystems. PMID:22574181

Performance of Ceramics in Severe Environments

NASA Technical Reports Server (NTRS)

Jacobson, Nathan S.; Fox, Dennis S.; Smialek, James L.; Deliacorte, Christopher; Lee, Kang N.

2005-01-01

Ceramics are generally stable to higher temperatures than most metals and alloys. Thus the development of high temperature structural ceramics has been an area of active research for many years. While the dream of a ceramic heat engine still faces many challenges, niche markets are developing for these materials at high temperatures. In these applications, ceramics are exposed not only to high temperatures but also aggressive gases and deposits. In this chapter we review the response of ceramic materials to these environments. We discuss corrosion mechanisms, the relative importance of a particular corrodent, and, where available, corrosion rates. Most of the available corrosion information is on silicon carbide (SIC) and silicon nitride (Si3N4) monolithic ceramics. These materials form a stable film of silica (SO2) in an oxidizing environment. We begin with a discussion of oxidation of these materials and proceed to the effects of other corrodents such as water vapor and salt deposits. We also discuss oxidation and corrosion of other ceramics: precurser derived ceramics, ceramic matrix composites (CMCs), ceramics which form oxide scales other than silica, and oxide ceramics. Many of the corrosion issues discussed can be mitigated with refractory oxide coatings and we discuss the current status of this active area of research. Ultimately, the concern of corrosion is loss of load bearing capability. We discuss the effects of corrosive environments on the strength of ceramics, both monolithic and composite. We conclude with a discussion of high temperature wear of ceramics, another important form of degradation at high temperatures.

Stability hierarchy between Piracetam forms I, II, and III from experimental pressure-temperature diagrams and topological inferences.

PubMed

Toscani, Siro; Céolin, René; Minassian, Léon Ter; Barrio, Maria; Veglio, Nestor; Tamarit, Josep-Lluis; Louër, Daniel; Rietveld, Ivo B

2016-01-30

The trimorphism of the active pharmaceutical ingredient piracetam is a famous case of polymorphism that has been frequently revisited by many researchers. The phase relationships between forms I, II, and III were ambiguous because they seemed to depend on the heating rate of the DSC and on the history of the samples or they have not been observed at all (equilibrium II-III). In the present paper, piezo-thermal analysis and high-pressure differential thermal analysis have been used to elucidate the positions of the different solid-solid and solid-liquid equilibria. The phase diagram, involving the three solid phases, the liquid phase and the vapor phase, has been constructed. It has been shown that form III is the high-pressure, low-temperature form and the stable form at room temperature. Form II is stable under intermediary conditions and form I is the low pressure, high temperature form, which possesses a stable melting point. The present paper demonstrates the strength of the topological approach based on the Clapeyron equation and the alternation rule when combined with high-pressure measurements. Copyright © 2015 Elsevier B.V. All rights reserved.

DNA CTG triplet repeats involved in dynamic mutations of neurologically related gene sequences form stable duplexes

NASA Technical Reports Server (NTRS)

Smith, G. K.; Jie, J.; Fox, G. E.; Gao, X.

1995-01-01

DNA triplet repeats, 5'-d(CTG)n and 5'-d(CAG)n, are present in genes which have been implicated in several neurodegenerative disorders. To investigate possible stable structures formed by these repeating sequences, we have examined d(CTG)n, d(CAG)n and d(CTG).d(CAG)n (n = 2 and 3) using NMR and UV optical spectroscopy. These studies reveal that single stranded (CTG)n (n > 2) forms stable, antiparallel helical duplexes, while the single stranded (CAG)n requires at least three repeating units to form a duplex. NMR and UV melting experiments show that the Tm increases in the order of [(CAG)3]2 < [(CTG)3]2 << (CAG)3.(CTG)3. The (CTG)3 duplex is stable and exhibits similar NMR spectra in solutions containing 0.1-4 M NaCl and at a pH range from 4.6 to 8.8. The (CTG)3 duplex, which contains multiple-T.T mismatches, displays many NMR spectral characteristics similar to those of B-form DNA. However, unique NOE and 1H-31P coupling patterns associated with the repetitive T.T mismatches in the CTG repeats are discerned. These results, in conjunction with recent in vitro studies suggest that longer CTG repeats may form hairpin structures, which can potentially cause interruption in replication, leading to dynamic expansion or deletion of triplet repeats.

THE STATISTICAL MECHANICS OF PLANET ORBITS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tremaine, Scott, E-mail: tremaine@ias.edu

2015-07-10

The final “giant-impact” phase of terrestrial planet formation is believed to begin with a large number of planetary “embryos” on nearly circular, coplanar orbits. Mutual gravitational interactions gradually excite their eccentricities until their orbits cross and they collide and merge; through this process the number of surviving bodies declines until the system contains a small number of planets on well-separated, stable orbits. In this paper we explore a simple statistical model for the orbit distribution of planets formed by this process, based on the sheared-sheet approximation and the ansatz that the planets explore uniformly all of the stable region ofmore » phase space. The model provides analytic predictions for the distribution of eccentricities and semimajor axis differences, correlations between orbital elements of nearby planets, and the complete N-planet distribution function, in terms of a single parameter, the “dynamical temperature,” that is determined by the planetary masses. The predicted properties are generally consistent with N-body simulations of the giant-impact phase and with the distribution of semimajor axis differences in the Kepler catalog of extrasolar planets. A similar model may apply to the orbits of giant planets if these orbits are determined mainly by dynamical evolution after the planets have formed and the gas disk has disappeared.« less

A heterochromatin domain forms gradually at a new telomere and is dynamic at stable telomeres.

PubMed

Wang, Jinyu; Eisenstatt, Jessica R; Audry, Julien; Cornelius, Kristen; Shaughnessy, Matthew; Berkner, Kathleen L; Runge, Kurt W

2018-05-21

Heterochromatin domains play important roles in chromosome biology, organismal development and aging, including centromere function, mammalian female X-chromosome inactivation and senescence-associated heterochromatin foci. In the fission yeast Schizosaccharomyces pombe and metazoans, heterochromatin contains histone H3 that is dimethylated at lysine 9. While factors required for heterochromatin have been identified, the dynamics of heterochromatin formation are poorly understood. Telomeres convert adjacent chromatin into heterochromatin. To form a new heterochromatic region in S. pombe , an inducible DNA double-strand break (DSB) was engineered next to 48 bp of telomere repeats in euchromatin, which caused formation of a new telomere and the establishment and gradual spreading of a new heterochromatin domain. However, spreading was dynamic even after the telomere had reached its stable length, with reporter genes within the heterochromatin domain showing variegated expression. The system also revealed the presence of repeats located near the boundaries of euchromatin and heterochromatin that are oriented to allow the efficient healing of a euchromatic DSB to cap the chromosome end with a new telomere. Telomere formation in S. pombe therefore reveals novel aspects of heterochromatin dynamics and failsafe mechanisms to repair subtelomeric breaks, with implications for similar processes in metazoan genomes. Copyright © 2018 Wang et al.

High power CO2 laser development with AOM integration for ultra high-speed pulses

NASA Astrophysics Data System (ADS)

Bohrer, Markus; Vaupel, Matthias; Nirnberger, Robert; Weinberger, Bernhard; Jamalieh, Murad

2017-01-01

There is a 500 billion USD world market for packaging expected to grow to a trillion in 2030. Austria plays an important role world wide for high speed laser engraving applications — especially when it comes to high end solutions. Such high end solutions are fundamental for the production of print forms for the packaging and decorating industry (e. g. cans). They are additionally used for security applications (e. g. for printing banknotes), for the textile printing industry and for creating embossing forms (e. g. for the production of dashboards in the automotive industry). High speed, high precision laser engraving needs laser resonators with very stable laser beams (400 - 800W) especially in combination with AOMs. Based upon a unique carbon fiber structure - stable within the sub-micrometer range - a new resonator has been developed, accompanied by most recent thermo-mechanical FEM calculations. The resulting beam is evaluated on an automated optical bench using hexapods, allowing to optimize the complete beam path with collimators and AOM. The major steps related to laser engraving of dry offset printing plates during the full workflow from the artists design to the printed result on an aluminum can is presented in this paper as well as laser characteristics, AOM integration and correlative CLSM and SEM investigation of the results.

The fate of deleted DNA produced during programmed genomic deletion events in Tetrahymena thermophila.

PubMed Central

Saveliev, S V; Cox, M M

1994-01-01

Thousands of DNA deletion events occur during macronuclear development in the ciliate Tetrahymena thermophila. In two deleted genomic regions, designated M and R, the eliminated sequences form circles that can be detected by PCR. However, the circles are not normal products of the reaction pathway. The circular forms occur at very low levels in conjugating cells, but are stable. Sequencing analysis showed that many of the circles (as many as 50% of those examined) reflected a precise deletion in the M and R regions. The remaining circles were either smaller or larger and contained varying lengths of sequences derived from the chromosomal DNA surrounding the eliminated region. The chromosomal junctions left behind after deletion were more precise, although deletions in either the M or R regions can generate any of several alternative junctions (1). Some new chromosomal junctions were detected in the present study. The results suggest that the deleted segment is released as a linear DNA species that is degraded rapidly. The species is only rarely converted to the stable circles we detect. The deletion mechanism is different from those proposed for deletion events in hypotrichous ciliates (2-4), and does not reflect a conservative site-specific recombination process such as that promoted by the bacteriophage lambda integrase (5). Images PMID:7838724

The N-Terminal Residues 43 to 60 Form the Interface for Dopamine Mediated α-Synuclein Dimerisation

PubMed Central

Leong, Su Ling; Hinds, Mark G.; Connor, Andrea R.; Smith, David P.; Illes-Toth, Eva; Pham, Chi L. L.; Barnham, Kevin J.; Cappai, Roberto

2015-01-01

α-synuclein (α-syn) is a major component of the intracellular inclusions called Lewy bodies, which are a key pathological feature in the brains of Parkinson’s disease patients. The neurotransmitter dopamine (DA) inhibits the fibrillisation of α-syn into amyloid, and promotes α-syn aggregation into SDS-stable soluble oligomers. While this inhibition of amyloid formation requires the oxidation of both DA and the methionines in α-syn, the molecular basis for these processes is still unclear. This study sought to define the protein sequences required for the generation of oligomers. We tested N- (α-syn residues 43–140) and C-terminally (1–95) truncated α-syn, and found that similar to full-length protein both truncated species formed soluble DA:α-syn oligomers, albeit 1–95 had a different profile. Using nuclear magnetic resonance (NMR), and the N-terminally truncated α-syn 43–140 protein, we analysed the structural characteristics of the DA:α-syn 43–140 dimer and α-syn 43–140 monomer and found the dimerisation interface encompassed residues 43 to 60. Narrowing the interface to this small region will help define the mechanism by which DA mediates the formation of SDS-stable soluble DA:α-syn oligomers. PMID:25679387

A Multiscale Approach to Characterize the Early Aggregation Steps of the Amyloid-Forming Peptide GNNQQNY from the Yeast Prion Sup-35

PubMed Central

Nasica-Labouze, Jessica; Meli, Massimiliano; Derreumaux, Philippe; Colombo, Giorgio; Mousseau, Normand

2011-01-01

The self-organization of peptides into amyloidogenic oligomers is one of the key events for a wide range of molecular and degenerative diseases. Atomic-resolution characterization of the mechanisms responsible for the aggregation process and the resulting structures is thus a necessary step to improve our understanding of the determinants of these pathologies. To address this issue, we combine the accelerated sampling properties of replica exchange molecular dynamics simulations based on the OPEP coarse-grained potential with the atomic resolution description of interactions provided by all-atom MD simulations, and investigate the oligomerization process of the GNNQQNY for three system sizes: 3-mers, 12-mers and 20-mers. Results for our integrated simulations show a rich variety of structural arrangements for aggregates of all sizes. Elongated fibril-like structures can form transiently in the 20-mer case, but they are not stable and easily interconvert in more globular and disordered forms. Our extensive characterization of the intermediate structures and their physico-chemical determinants points to a high degree of polymorphism for the GNNQQNY sequence that can be reflected at the macroscopic scale. Detailed mechanisms and structures that underlie amyloid aggregation are also provided. PMID:21625573

Shape-transformable liquid metal nanoparticles in aqueous solution† †Electronic supplementary information (ESI) available. See DOI: 10.1039/c7sc00057j Click here for additional data file.

PubMed Central

Lin, Yiliang; Liu, Yang

2017-01-01

Stable suspensions of eutectic gallium indium (EGaIn) liquid metal nanoparticles form by probe-sonicating the metal in an aqueous solution. Positively-charged molecular or macromolecular surfactants in the solution, such as cetrimonium bromide or lysozyme, respectively, stabilize the suspension by interacting with the negative charges of the surface oxide that forms on the metal. The liquid metal breaks up into nanospheres via sonication, yet can transform into rods of gallium oxide monohydroxide (GaOOH) via moderate heating in solution either during or after sonication. Whereas heating typically drives phase transitions from solid to liquid (via melting), here heating drives the transformation of particles from liquid to solid via oxidation. Interestingly, indium nanoparticles form during the process of shape transformation due to the selective removal of gallium. This dealloying provides a mechanism to create indium nanoparticles at temperatures well below the melting point of indium. To demonstrate the versatility, we show that it is possible to shape transform and dealloy other alloys of gallium including ternary liquid metal alloys. Scanning transmission electron microscopy (STEM), energy-dispersive X-ray spectroscopy (EDS) mapping, and X-ray diffraction (XRD) confirm the dealloying and transformation mechanism. PMID:28580116

Formation mechanism of atomic cluster structures in Al-Mg alloy during rapid solidification processes

NASA Astrophysics Data System (ADS)

Liu, Feng-xiang; Liu, Rang-su; Hou, Zhao-yang; Liu, Hai-Rong; Tian, Ze-an; Zhou, Li-li

2009-02-01

The rapid solidification processes of Al 50Mg 50 liquid alloy consisting of 50,000 atoms have been simulated by using molecular dynamics method based on the effective pair potential derived from the pseudopotential theory. The formation mechanisms of atomic clusters during the rapid solidification processes have been investigated adopting a new cluster description method—cluster-type index method (CTIM). The simulated partial structure factors are in good agreement with the experimental results. And Al-Mg amorphous structure characterized with Al-centered icosahedral topological short-range order (SRO) is found to form during the rapid solidification processes. The icosahedral cluster plays a key role in the microstructure transition. Besides, it is also found that the size distribution of various clusters in the system presents a magic number sequence of 13, 19, 23, 25, 29, 31, 33, 37, …. The magic clusters are more stable and mainly correspond to the incompact arrangements of linked icosahedra in the form of rings, chains or dendrites. And each magic number point stands correspondingly for one certain combining form of icosahedra. This magic number sequence is different from that generated in the solidification structure of liquid Al and those obtained by methods of gaseous deposition and ionic spray, etc.

Fullerene (C60) films for solid lubrication

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bhushan, B.; Gupta, B.K.; Van Cleef, G.W.

1993-10-01

The advent of techniques for producing gram quantities of a new form of stable, pure, solid carbon, designated as fullerene, opens a profusion of possibilities to be explored in many disciplines including tribology. Fullerenes take the form of hollow geodesic domes, which are formed from a network of pentagons and hexagons with covalently bonded carbon atoms. The C60 molecule has the highest possible symmetry (icosahedral) and assumes the shape of a soccer ball. At room temperature, fullerene molecules pack in an fcc lattice bonded with weak van der Waals attractions. Fullerenes can be dissolved in solvents such as toluene andmore » benzene and are easily sublimed. The low surface energy, high chemical stability, spherical shape, weak intermolecular bonding, and high load bearing capacity of C60 molecules offer potential for various mechanical and tribological applications. This paper describes the crystal structure and properties of fullerenes and proposes a mechanism for self-lubricating action. Sublimed films of C60 have been produced and friction and wear performance of these films in various operating environments are the subject of this paper. The results of this study indicate that C60, owing to its unique crystal structure and bonding, may be a promising solid lubricant. 31 refs.« less

Relevant role of dissolved humic matter in phosphorus bioavailability in natural and agronomical ecosystems through the formation of Humic-(Metal)-Phosphate complexes

NASA Astrophysics Data System (ADS)

Baigorri, Roberto; Urrutia, Óscar; Erro, Javier; Pazos-Pérez, Nicolás; María García-Mina, José

2016-04-01

Natural Organic Matter (NOM) and the NOM fraction present in soil solution (dissolved organic matter: DOM) are currently considered as fundamental actors in soil fertility and crop mineral nutrition. Indeed, decreases in crop yields as well as soil erosion are closely related to low values of NOM and, in fact, the use of organic amendments as both soil improvers and plant growth enhancers is very usual in countries with soils poor in NOM. This role of NOM (and DOM) seems to be associated with the presence of bio-transformed organic molecules (humic substances) with high cation chelating-complexing ability. In fact, bioavailable micronutrients with metallic character in soil solutions of alkaline and calcareous soils are forming stable complexes with DOM. This beneficial action of DOM also concerns other plant nutrients such as inorganic phosphate (Pi). Among the different mechanisms involved in the beneficial action of DOM on P bioavailability, the possible formation of poly-nuclear complexes including stable chemical bonds between negative binding sites in humic substances and Pi through metal bridges in soil solution might be relevant, especially in acidic soils. In fact, several studies have proven that these complexes can be obtained in the laboratory and are very efficient in prevent Pi soil fixation and improve Pi root uptake. However, clear experimental evidence about their presence in soil solutions of natural and agronomical soil ecosystems has not published yet. We present here experimental results supporting the real presence of stable Pi-metal-Humic (PMH) complexes in the soil solution of several acidic soils. The study is based on the physico-chemical characterization (31P-NMR, FTIR, TEM-EDAX, ICP-OES) of the DOM fraction isolated by ultrafiltration from the soil solution of several representative acidic soils. In average, more than 60 % of Pi was found in the soil solution humic fraction forming stable humic-metal (Fe, Al) complexes.

Homopolymer self-assembly into stable nanoparticles: concerted action of hydrophobic association and hydrogen bonding in thermoresponsive poly(alkylacrylic acid)s.

PubMed

Sedlák, Marián

2012-03-01

A new approach to polymer self-assembly was presented recently [M. Sedlák, Č. Koňák, J. Dybal, Macromolecules 2009, 2, 7430-7438 and 7439-7446.] (1, 2) where stable polymeric nanoparticles were formed from poly(ethylacrylic acid) homopolymers without any assembly triggering additives, simply by heating polymer solution under conditions of thermosensitivity to certain temperature. In the current Article, we present successful results on poly(propylacrylic acid), which is a more hydrophobic polymer. We also present results on a less hydrophobic polymer from this series, poly(methacrylic acid), from which nanoparticles cannot be formed. Comparison of results on all three polymers gives a solid physicochemical insight and supports the molecular mechanism of the self-assembly previously suggested: The solvent quality gradually worsens upon heating of a thermosensitive polymer solution, and polymer-polymer contacts are preferred over polymer-solvent contacts, which leads to the formation of polymer assemblies. The presence of a significant amount of charge on chains prevents macroscopic phase separation. Upon subsequent cooling to laboratory temperature, the assemblies (nanoparticles) should eventually dissolve; however, this is not the case due to the fact that polymer chains brought to a close proximity at elevated temperatures become hydrogen-bonded. In addition, hydrogen bonds strengthen upon cooling. Mainly carboxylic-carboxylate hydrogen bonds (COOH····COO(-)) are responsible for the irreversibility of the process and the stability of nanoparticles. Conclusions are supported by results from static and dynamic light scattering, FTIR spectroscopy, and cryo-TEM microscopy. Size of nanoparticles can be monitored during the growth and custom-tailored by tuning critical parameters, especially the degree of ionization, temperature, and time of heating. Nanoparticles are stable over long periods of time. They are stable in a broad range of salt concentrations, including physiological conditions, and possess a mild acceptable degree of polydispersity.

Stability of aggregates in the environment: role of solid bridging

NASA Astrophysics Data System (ADS)

Seiphoori, A.; Jerolmack, D. J.; Arratia, P. E.

2017-12-01

Colloids in suspension may form larger flocs under favorable conditions, via diffusion- or reaction-limited aggregation. In addition, the process of drying colloidal suspensions drives colloids together via hydrodynamic forces to form aggregates, that may be stable or unstable when subject to re-wetting and transport. Channel banks, shorelines and hillslopes are examples where the periodic wetting and drying results in the aggregation of muds. If aggregates disperse, the mud structure is unstable to subsequent wetting or fluid shear and can easily be detached and transported to rivers and coasts. The effective friction that governs hillslope and channel-bank soil creep rates also depends on the stability of the soil aggregates. Yet, few studies probe the particle-scale assembly or stability of aggregates subject to environmental loads, and the effects of shape or size heterogeneity have not been examined in detail. Here we investigate the formation and stability of aggregates subject to passive re-wetting (by misting) and shearing using a simple Poiseuille flow in a microfluidic device. We study the kinetics of a wide range of silicate colloids of different size and surface charge properties using in situ microscopy and particle tracking. We find that negatively charged silica microspheres are dragged by the retreating edge of an evaporating drop and are resuspended easily on re-wetting, showing that aggregates are unstable. In contrast, a bi-disperse suspension created by the addition of silica nanoparticles forms stable deposits, where nanoparticles bind larger particles by bridging the interparticle space, a mechanism similar to capillary bridging that we refer to as "solid bridging." Although aggregate structure and dynamics of the bi-disperse system changes quantitatively with surface-charge of the nanoparticles, smaller particles always conferred stability on the aggregates. Investigation of other colloids, including asbestos fibers and various clays, reveals that this solid bridging effect is robust across variations in particle shape and material composition. These experiments suggest that natural mud and soil may form more stable aggregates than would naively be expected by considering the charge effects alone, because their inherent size heterogeneity is conducive to solid bridging.

Solid-state properties and crystallization behavior of PHA-739521 polymorphs.

PubMed

Sun, Changquan Calvin

2006-08-17

PHA-739521 is an experimental compound that exhibits polymorphism. The two anhydrous crystal forms, I and II, are characterized using powder X-ray diffractometry, thermal analyses, moisture sorption gravimetry. Both Forms I and II are non-hygroscopic and are stable to compaction pressure. The melting temperature is about 152 degrees C for Form I and 168 degrees C for Form II. Forms I and II are enantiotropically related where Form I is more stable below a transition temperature of approximately 70 degrees C. Crystallization behavior of this compound from solutions and during heating is also studied. Information obtained is used to design an appropriate crystallization process to successfully manufacture desired polymorph at large scale.

Study of the aggregation mechanism of polyglutamine peptides using replica exchange molecular dynamics simulations.

PubMed

Nakano, Miki; Ebina, Kuniyoshi; Tanaka, Shigenori

2013-04-01

Polyglutamine (polyQ, a peptide) with an abnormal repeat length is the causative agent of polyQ diseases, such as Huntington's disease. Although glutamine is a polar residue, polyQ peptides form insoluble aggregates in water, and the mechanism for this aggregation is still unclear. To elucidate the detailed mechanism for the nucleation and aggregation of polyQ peptides, replica exchange molecular dynamics simulations were performed for monomers and dimers of polyQ peptides with several chain lengths. Furthermore, to determine how the aggregation mechanism of polyQ differs from those of other peptides, we compared the results for polyQ with those of polyasparagine and polyleucine. The energy barrier between the monomeric and dimeric states of polyQ was found to be relatively low, and it was observed that polyQ dimers strongly favor the formation of antiparallel β-sheet structures. We also found a characteristic behavior of the monomeric polyQ peptide: a turn at the eighth residue is always present, even when the chain length is varied. We previously showed that a structure including more than two sets of β-turns is stable, so a long monomeric polyQ chain can act as an aggregation nucleus by forming several pairs of antiparallel β-sheet structures within a single chain. Since the aggregation of polyQ peptides has some features in common with an amyloid fibril, our results shed light on the mechanism for the aggregation of polyQ peptides as well as the mechanism for the formation of general amyloid fibrils, which cause the onset of amyloid diseases.

A model for wave control on coral breakage and species distribution in the Hawaiian Islands

USGS Publications Warehouse

Storlazzi, C.D.; Brown, E.K.; Field, M.E.; Rodgers, K.; Jokiel, P.L.

2005-01-01

The fringing reef off southern Molokai, Hawaii, is currently being studied as part of a multi-disciplinary project led by the US Geological Survey. As part of this study, modeling and field observations were utilized to help understand the physical controls on reef morphology and the distribution of different coral species. A model was developed that calculates wave-induced hydrodynamic forces on corals of a specific form and mechanical strength. From these calculations, the wave conditions under which specific species of corals would either be stable or would break due to the imposed wave-induced forces were determined. By combining this hydrodynamic force-balance model with various wave model output for different oceanographic conditions experienced in the study area, we were able to map the locations where specific coral species should be stable (not subject to frequent breakage) in the study area. The combined model output was then compared with data on coral species distribution and coral cover at 12 sites along Molokai's south shore. Observations and modeling suggest that the transition from one coral species to another may occur when the ratio of the coral colony's mechanical strengths to the applied (wave-induced) forces may be as great as 5:1, and not less than 1:1 when corals would break. This implies that coral colony's mechanical strength and wave-induced forces may be important in defining gross coral community structure over large (orders of 10's of meters) spatial scales. ?? Springer-Verlag 2004.

Preformulation stability study of the EGFR inhibitor HKI-272 (Neratinib) and mechanism of degradation.

PubMed

Lu, Qinghong; Ku, Mannching Sherry

2012-03-01

The stability in solution of HKI-272 (Neratinib) was studied as a function of pH. The drug is most stable from pH 3 to 4, and degradation rate increases rapidly around pH 6 and appears to approach a maximum asymptotic limit in the range of pH 812. Pseudo first-order reaction kinetics was observed at all pH values. The structure of the major degradation product indicates that it is formed by a cascade of reactions within the dimethylamino crotonamide group of HKI-272. It is assumed that the rate-determining step is the initial isomerization from allyl amine to enamine functionality, followed by hydrolysis and subsequent cyclization to a stable lactam. The maximum change in degradation rate as a function of pH occurs at about pH 6, which corresponds closely to the theoretical pKa value of the dimethylamino group of HKI-272 when accounting for solvent/temperature effects. The observed relationship between pH and degradation rate is discussed, and a self-catalyzed mechanism for the allylamine-enamine isomerization reaction is proposed. The relevance of these findings to other allylamine drugs is discussed in terms of the relative stability of the allylic anion intermediate through which, the isomerization occurs.

Stable superhydrophilic coating on superhydrophobic porous media by functionalized nanoparticles

NASA Astrophysics Data System (ADS)

Khazaei, Masoud; Taghi Sadeghi, Mohammad; Sadat Hosseini, Marzieh

2018-01-01

In this study, the hydrophilicity property of TiO2 nano-coating was improved by zinc acetate-assisted sol-gel method. The stable superhydrophilic coating was fabricated on a superhydrophobic mineral rock surface. The wettability of surface before and after coating was characterized by contact angle measurements. The n-heptane and water droplet contact angle was 0° and 168° respectively, so the untreated rock was superhydrophobic. After nano-treatment, the n-heptane and water contact angle changed to 172° and 0° respectively, so the superhydrophilic coating was formed on the superhydrophobic surface. The thermal, mechanical and salinity stability of the fabricated coatings was investigated. The coatings had high thermal and salinity stability; they also had moderate mechanical stability that was evaluated by abrasion test. The morphology and composition of synthesized nanoparticles were characterized by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy and x-ray diffraction (XRD) analyses. Characterization of the coated surfaces was conducted by SEM and XRD analyses. Applications of these nano-coatings include surfaces where cleanliness is paramount such as in hospitals as well as the protection of public monuments and building facades from weathering. Novel industrial application includes wettability alteration of oil wet carbonate rock for enhanced oil recovery.

Efficient Removal of Cationic and Anionic Radioactive Pollutants from Water Using Hydrotalcite-Based Getters.

PubMed

Bo, Arixin; Sarina, Sarina; Liu, Hongwei; Zheng, Zhanfeng; Xiao, Qi; Gu, Yuantong; Ayoko, Godwin A; Zhu, Huaiyong

2016-06-29

Hydrotalcite (HT)-based materials are usually applied to capture anionic pollutants in aqueous solutions. Generally considered anion exchangers, their ability to capture radioactive cations is rarely exploited. In the present work, we explored the ability of pristine and calcined HT getters to effectively capture radioactive cations (Sr(2+) and Ba(2+)) which can be securely stabilized at the getter surface. It is found that calcined HT outperforms its pristine counterpart in cation removal ability. Meanwhile, a novel anion removal mechanism targeting radioactive I(-) is demonstrated. This approach involves HT surface modification with silver species, namely, Ag2CO3 nanoparticles, which can attach firmly on HT surface by forming coherent interface. This HT-based anion getter can be further used to capture I(-) in aqueous solution. The observed I(-) uptake mechanism is distinctly different from the widely reported ion exchange mechanism of HT and much more efficient. As a result of the high local concentrations of precipitants on the getters, radioactive ions in water can be readily immobilized onto the getter surface by forming precipitates. The secured ionic pollutants can be subsequently removed from water by filtration or sedimentation for safe disposal. Overall, these stable, inexpensive getters are the materials of choice for removal of trace ionic pollutants from bulk radioactive liquids, especially during episodic environmental crisis.

Stability of direct band gap under mechanical strains for monolayer MoS2, MoSe2, WS2 and WSe2

NASA Astrophysics Data System (ADS)

Deng, Shuo; Li, Lijie; Li, Min

2018-07-01

Single layer transition-metal dichalcogenides materials (MoS2, MoSe2, WS2 and WSe2) are investigated using the first-principles method with the emphasis on their responses to mechanical strains. All these materials display the direct band gap under a certain range of strains from compressive to tensile (stable range). We have found that this stable range is different for these materials. Through studying on their mechanical properties again using the first-principles approach, it is unveiled that this stable strain range is determined by the Young's modulus. More analysis on strains induced electronic band gap properties have also been conducted.

Investigating the principles of recrystallization from glyceride melts.

PubMed

Windbergs, Maike; Strachan, Clare J; Kleinebudde, Peter

2009-01-01

Different lipids were melted and resolidified as model systems to gain deeper insight into the principles of recrystallization processes in lipid-based dosage forms. Solid-state characterization was performed on the samples with differential scanning calorimetry and X-ray powder diffraction. Several recrystallization processes could be identified during storage of the lipid layers. Pure triglycerides that generally crystallize to the metastable alpha-form from the melt followed by a recrystallization process to the stable beta-form with time showed a chain-length-dependent behavior during storage. With increasing chain length, the recrystallization to the stable beta-form was decelerated. Partial glycerides exhibited a more complex recrystallization behavior due to the fact that these substances are less homogenous. Mixtures of a long-chain triglyceride and a partial glyceride showed evidence of some interaction between the two components as the partial glyceride hindered the recrystallization of the triglyceride to the stable beta-form. In addition, the extent of this phenomenon depended on the amount of partial glyceride in the mixture. Based on these results, changes in solid dosage forms based on glycerides during processing and storage can be better understood.

An approximate closed-form solution for lead lag damping of rotor blades in hover

NASA Technical Reports Server (NTRS)

Peters, D. A.

1975-01-01

Simple stability methods are used to derive an approximate, closed-form expression for the lead-lag damping of rotor blades in hover. Destabilizing terms are shown to be a result of two dynamic mechanisms. First, the destabilizing aerodynamic forces that can occur when blade lift is higher than a critical value are maximized when the blade motion is in a straight line equidistant from the blade chord and the average direction of the air flow velocity. This condition occurs when the Coriolis terms vanish and when the elastic coupling terms align the blade motion with this least stable direction. Second, the nonconservative stiffness terms that result from pitch-flap or pitch-lag coupling can add or subtract energy from the system depending upon whether the motion of the blade tip is clockwise or counterclockwise.

ECT imaging with Tc(V)-99m dimercaptosuccinic acid useful to detect lung metastases of osteosarcoma

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ohta, H.; Ishii, M.; Yoshizumi, M.

1985-01-01

ECT imaging, using Tc(V)-99m dimercaptosuccinic acid (Tc(V)-DMS) was performed in two patients with lung metastasis of osteosarcoma, and the results were compared with those of CT scan. Clear accumulation of Tc(V)-DMS was recognized in all cases in the same area that CT scans demonstrated. Tc(V)-DMS was labeled under optimal pH 8, had very low SnCl/sub 2/ concentrations, an equilibrium between a stable form and a dissociated form of anion TcO/sub 4/(3-) structurally similar to PO/sub 4/(3-), and was postulated for tumor uptake. Considering this proposed mechanism for Tc(V)-DMS uptake by tumor cells, ECT imaging using this tracer could be ofmore » use in the early detection of lung metastasis of osteosarcoma.« less

Cured composite materials for reactive metal battery electrolytes

DOEpatents

Harrup, Mason K.; Stewart, Frederick F.; Peterson, Eric S.

2006-03-07

A solid molecular composite polymer-based electrolyte is made for batteries, wherein silicate compositing produces a electrolytic polymer with a semi-rigid silicate condensate framework, and then mechanical-stabilization by radiation of the outer surface of the composited material is done to form a durable and non-tacky texture on the electrolyte. The preferred ultraviolet radiation produces this desirable outer surface by creating a thin, shallow skin of crosslinked polymer on the composite material. Preferably, a short-duration of low-medium range ultraviolet radiation is used to crosslink the polymers only a short distance into the polymer, so that the properties of the bulk of the polymer and the bulk of the molecular composite material remain unchanged, but the tough and stable skin formed on the outer surface lends durability and processability to the entire composite material product.

Understanding the mechanism of DNA deactivation in ion therapy of cancer cells: hydrogen peroxide action*

NASA Astrophysics Data System (ADS)

Piatnytskyi, Dmytro V.; Zdorevskyi, Oleksiy O.; Perepelytsya, Sergiy M.; Volkov, Sergey N.

2015-11-01

Changes in the medium of biological cells under ion beam irradiation has been considered as a possible cause of cell function disruption in the living body. The interaction of hydrogen peroxide, a long-lived molecular product of water radiolysis, with active sites of DNA macromolecule was studied, and the formation of stable DNA-peroxide complexes was considered. The phosphate groups of the macromolecule backbone were picked out among the atomic groups of DNA double helix as a probable target for interaction with hydrogen peroxide molecules. Complexes consisting of combinations including: the DNA phosphate group, H2O2 and H2O molecules, and Na+ counterion, were considered. The counterions have been taken into consideration insofar as under the natural conditions they neutralise DNA sugar-phosphate backbone. The energy of the complexes have been determined by considering the electrostatic and the Van der Waals interactions within the framework of atom-atom potential functions. As a result, the stability of various configurations of molecular complexes was estimated. It was shown that DNA phosphate groups and counterions can form stable complexes with hydrogen peroxide molecules, which are as stable as the complexes with water molecules. It has been demonstrated that the formation of stable complexes of H2O2-Na+-PO4- may be detected experimentally by observing specific vibrations in the low-frequency Raman spectra. The interaction of H2O2 molecule with phosphate group of the double helix backbone can disrupt DNA biological function and induce the deactivation of the cell genetic apparatus. Thus, the production of hydrogen peroxide molecules in the nucleus of living cells can be considered as an additional mechanism by which high-energy ion beams destroy tumour cells during ion beam therapy. Contribution to the Topical Issue "COST Action Nano-IBCT: Nano-scale Processes Behind Ion-Beam Cancer Therapy", edited by Andrey Solov'yov, Nigel Mason, Gustavo García, Eugene Surdutovich.

Interfacial engineering of solution-processed Ni nanochain-SiO x (x< 2) cermets towards thermodynamically stable, anti-oxidation solar selective absorbers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yu, Xiaobai; Wang, Xiaoxin; Zhang, Qinglin

Here, cermet solar thermal selective absorber coatings are an important component of high-efficiency concentrated solar power (CSP) receivers. The oxidation of the metal nanoparticles in cermet solar absorbers is a great challenge for vacuum-free operation. Recently, we have demonstrated that oxidation is kinetically retarded in solution processed, high-optical-performance Ni nanochain-SiO x cermet system compared to conventional Ni-Al 2O 3 system when annealed in air at 450–600 °C for several hours. However, for long-term, high-temperature applications in CSP systems, thermodynamically stable antioxidation behavior is highly desirable, which requires new mechanisms beyond kinetically reducing the oxidation rate. Towards this goal, in thismore » paper, we demonstrate that pre-operation annealing of Ni nanochain-SiO x cermets at 900 °C in N 2 forms the thermodynamically stable orthorhombic phase of NiSi at the Ni/SiO x interfaces, leading to self-terminated oxidation at 550 °C in air due to this interfacial engineering. In contrast, pre-operation annealing at a lower temperature of 750 °C in N 2 (as conducted in our previous work) cannot achieve interfacial NiSi formation directly, and further annealing in air at 450–600 °C for >4 h only leads to the formation of the less stable (metastable) hexagonal phase of NiSi. Therefore, the high-temperature pre-operation annealing is critical to form the desirable orthorhombic phase of NiSi at Ni/SiO x interfaces towards thermodynamically stable antioxidation behavior. Remarkably, with this improved interfacial engineering, the oxidation of 80-nm-diameter Ni nanochain-SiO x saturates after annealing at 550 °C in air for 12 h. Additional annealing at 550 °C in air for as long as 20 h (i.e., 32 h air annealing at >550 °C in total) has almost no further impact on the structural or optical properties of the coatings, the latter being very sensitive to any interfacial changes due to the localized surface plasmon resonances of the metal nanostructures. This phenomenon holds true for Ni nanoparticle diameter down to 40 nm in Ni-SiO x system, where the optical response remains stable for 53 h at 550 °C in air. The oxidation vs. time curve also shows saturation behavior deviating from the kinetic Deal-Grove oxidation model. These results strongly suggest a promising approach to thermodynamically stable, anti-oxidation Ni/SiO x cermet absorbers via interfacial engineering.« less

Interfacial engineering of solution-processed Ni nanochain-SiO x (x< 2) cermets towards thermodynamically stable, anti-oxidation solar selective absorbers

DOE PAGES

Yu, Xiaobai; Wang, Xiaoxin; Zhang, Qinglin; ...

2016-04-01

Here, cermet solar thermal selective absorber coatings are an important component of high-efficiency concentrated solar power (CSP) receivers. The oxidation of the metal nanoparticles in cermet solar absorbers is a great challenge for vacuum-free operation. Recently, we have demonstrated that oxidation is kinetically retarded in solution processed, high-optical-performance Ni nanochain-SiO x cermet system compared to conventional Ni-Al 2O 3 system when annealed in air at 450–600 °C for several hours. However, for long-term, high-temperature applications in CSP systems, thermodynamically stable antioxidation behavior is highly desirable, which requires new mechanisms beyond kinetically reducing the oxidation rate. Towards this goal, in thismore » paper, we demonstrate that pre-operation annealing of Ni nanochain-SiO x cermets at 900 °C in N 2 forms the thermodynamically stable orthorhombic phase of NiSi at the Ni/SiO x interfaces, leading to self-terminated oxidation at 550 °C in air due to this interfacial engineering. In contrast, pre-operation annealing at a lower temperature of 750 °C in N 2 (as conducted in our previous work) cannot achieve interfacial NiSi formation directly, and further annealing in air at 450–600 °C for >4 h only leads to the formation of the less stable (metastable) hexagonal phase of NiSi. Therefore, the high-temperature pre-operation annealing is critical to form the desirable orthorhombic phase of NiSi at Ni/SiO x interfaces towards thermodynamically stable antioxidation behavior. Remarkably, with this improved interfacial engineering, the oxidation of 80-nm-diameter Ni nanochain-SiO x saturates after annealing at 550 °C in air for 12 h. Additional annealing at 550 °C in air for as long as 20 h (i.e., 32 h air annealing at >550 °C in total) has almost no further impact on the structural or optical properties of the coatings, the latter being very sensitive to any interfacial changes due to the localized surface plasmon resonances of the metal nanostructures. This phenomenon holds true for Ni nanoparticle diameter down to 40 nm in Ni-SiO x system, where the optical response remains stable for 53 h at 550 °C in air. The oxidation vs. time curve also shows saturation behavior deviating from the kinetic Deal-Grove oxidation model. These results strongly suggest a promising approach to thermodynamically stable, anti-oxidation Ni/SiO x cermet absorbers via interfacial engineering.« less

Stable powders made from photosensitive polycrystalline complexes of heterocyclic monomers and their polymers

NASA Technical Reports Server (NTRS)

Murphy, Oliver J. (Inventor); Hitchens, G. Duncan (Inventor); Hodko, Dalibor (Inventor)

1999-01-01

The present invention relates to a low electronic conductivity polymer composition having well dispersed metal granules, a stable powder made from photosensitive polycrystalline complexes of pyrrole, or its substituted derivatives and silver cations for making the polymer composition, and methods of forming the stable powder and polymer composition, respectively. A polycrystalline complex of silver and a monomer, such as pyrrole, its substituted derivatives or combinations thereof, is precipitated in the form of a stable photosensitive powder upon addition of the monomer to a solvent solution, such as toluene containing an electron acceptor. The photosensitive powder can be stored in the dark until needed. The powder may be dissolved in a solvent, cast onto a substrate and photopolymerized.

Cooperative DNA binding and protein/DNA fiber formation increases the activity of the Dnmt3a DNA methyltransferase.

PubMed

Emperle, Max; Rajavelu, Arumugam; Reinhardt, Richard; Jurkowska, Renata Z; Jeltsch, Albert

2014-10-24

The Dnmt3a DNA methyltransferase has been shown to bind cooperatively to DNA and to form large multimeric protein/DNA fibers. However, it has also been reported to methylate DNA in a processive manner, a property that is incompatible with protein/DNA fiber formation. We show here that the DNA methylation rate of Dnmt3a increases more than linearly with increasing enzyme concentration on a long DNA substrate, but not on a short 30-mer oligonucleotide substrate. We also show that addition of a catalytically inactive Dnmt3a mutant, which carries an amino acid exchange in the catalytic center, increases the DNA methylation rate by wild type Dnmt3a on the long substrate but not on the short one. In agreement with this finding, preincubation experiments indicate that stable protein/DNA fibers are formed on the long, but not on the short substrate. In addition, methylation experiments with substrates containing one or two CpG sites did not provide evidence for a processive mechanism over a wide range of enzyme concentrations. These data clearly indicate that Dnmt3a binds to DNA in a cooperative reaction and that the formation of stable protein/DNA fibers increases the DNA methylation rate. Fiber formation occurs at low μm concentrations of Dnmt3a, which are in the range of Dnmt3a concentrations in the nucleus of embryonic stem cells. Understanding the mechanism of Dnmt3a is of vital importance because Dnmt3a is a hotspot of somatic cancer mutations one of which has been implicated in changing Dnmt3a processivity. © 2014 by The American Society for Biochemistry and Molecular Biology, Inc.

Ex-vivo absorption study of lysine R-lipoate salt, a new pharmaceutical form of R-ALA.

PubMed

Amenta, Francesco; Buccioni, Michela; Ben, Diego Dal; Lambertucci, Catia; Navia, Aleix Martí; Ngouadjeu Ngnintedem, Michael A; Ricciutelli, Massimo; Spinaci, Andrea; Volpini, Rosaria; Marucci, Gabriella

2018-06-15

Alpha-lipoic acid (ALA) oral supplements were used in many pathologies associated with increased oxidative stress. Although only R-ALA is considered the biologically active form, R,S-ALA is used in therapeutic applications even showing poor water solubility. The aim of this work was to study the absorption and transport mechanism across the intestinal barrier of new R-ALA stable and water soluble form, consisting in the lysine R-ALA salt, in presence and absence of specific inhibitors of Na + /multivitamin (SMVT) and monocarboxylic acids (MCT). The absorption of a new ALA form was investigated at rat everted sacs in comparison with R-ALA, S-ALA, and R,S-ALA. Results showed that duodenum is the best portion of intestine for ALA forms absorption. The absorption percentage of R-ALA, S-ALA, R,S-ALA, and lysine R-ALA salt was 66%, 43%, 55%, and 70%, respectively. The modest effect of the SMVT inhibitor biotin demonstrated that this transporter system is not principally involved in the absorption of lysine R-lipoate salt across the rat intestinal barrier. On the contrary, the MCT inhibitor octanoic acid significantly reduced the transport of this salt, whit an absorption decrease of R-ALA and lysine R-lipoate salt of 28% and 24%, respectively. Since the highest concentration of these inhibitors did not completely inhibit the absorption of lysine R-lipoate salt, other transport mechanisms probably operate for its intracellular delivery. The new form of ALA, lysine R-lipoate salt, was the most absorbed respect to the other ALA forms demonstrating that this compound is more suitable for oral administration. This new salt could represent a promising candidate for ALA oral supplementation. Copyright © 2018 Elsevier B.V. All rights reserved.

A stable compound of helium and sodium at high pressure

DOE PAGES

Dong, Xiao; Oganov, Artem R.; Goncharov, Alexander F.; ...

2017-02-06

Helium is generally understood to be chemically inert and this is due to its extremely stable closed-shell electronic configuration, zero electron affinity and an unsurpassed ionization potential. It is not known to form thermodynamically stable compounds, except a few inclusion compounds. Here, using the ab initio evolutionary algorithm USPEX and subsequent high-pressure synthesis in a diamond anvil cell, we report the discovery of a thermodynamically stable compound of helium and sodium, Na 2He, which has a fluorite-type structure and is stable at pressures >113 GPa. We show that the presence of He atoms causes strong electron localization and makes thismore » material insulating. This phase is an electride, with electron pairs localized in interstices, forming eight-centre two-electron bonds within empty Na 8 cubes. As a result, we also predict the existence of Na 2HeO with a similar structure at pressures above 15 GPa.« less

A stable compound of helium and sodium at high pressure

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dong, Xiao; Oganov, Artem R.; Goncharov, Alexander F.

Helium is generally understood to be chemically inert and this is due to its extremely stable closed-shell electronic configuration, zero electron affinity and an unsurpassed ionization potential. It is not known to form thermodynamically stable compounds, except a few inclusion compounds. Here, using the ab initio evolutionary algorithm USPEX and subsequent high-pressure synthesis in a diamond anvil cell, we report the discovery of a thermodynamically stable compound of helium and sodium, Na 2He, which has a fluorite-type structure and is stable at pressures >113 GPa. We show that the presence of He atoms causes strong electron localization and makes thismore » material insulating. This phase is an electride, with electron pairs localized in interstices, forming eight-centre two-electron bonds within empty Na 8 cubes. We also predict the existence of Na 2HeO with a similar structure at pressures above 15 GPa.« less

A stable compound of helium and sodium at high pressure

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dong, Xiao; Oganov, Artem R.; Goncharov, Alexander F.

Helium is generally understood to be chemically inert and this is due to its extremely stable closed-shell electronic configuration, zero electron affinity and an unsurpassed ionization potential. It is not known to form thermodynamically stable compounds, except a few inclusion compounds. Here, using the ab initio evolutionary algorithm USPEX and subsequent high-pressure synthesis in a diamond anvil cell, we report the discovery of a thermodynamically stable compound of helium and sodium, Na 2He, which has a fluorite-type structure and is stable at pressures >113 GPa. We show that the presence of He atoms causes strong electron localization and makes thismore » material insulating. This phase is an electride, with electron pairs localized in interstices, forming eight-centre two-electron bonds within empty Na 8 cubes. As a result, we also predict the existence of Na 2HeO with a similar structure at pressures above 15 GPa.« less

Correlating Polymer Crystals via Self-Induced Nucleation

NASA Astrophysics Data System (ADS)

Reiter, Günter

Crystallizable polymers often form multiple stacks of uniquely oriented lamellae, which have good registry despite being separated by amorphous fold surfaces. These correlations require multiple synchronized, yet unidentified, nucleation events. Here, we demonstrate that in thin films of isotactic polystyrene, the probability of generating correlated lamellae is controlled by the branched morphology of a single primary lamella. The nucleation density ns of secondary lamellae is found to be dependent on the width of the branches of the primary lamella. This relation is independent of molecular weight, crystallization temperature, and film thickness. We propose a nucleation mechanism based on the insertion of polymers into a branched primary lamellar crystal. Even in single crystals, characterized by faceted structures with a well-defined envelope reflecting the underlying crystal unit cell, polymers are folded and thus in a meta-stable state. Annealing such meta-stable single crystals allowed to unveil the initial morphological framework of a dendritic single crystal, i.e. the initial stages of growth.

Formation of Stoichiometric CsFn Compounds

PubMed Central

Zhu, Qiang; Oganov, Artem R.; Zeng, Qingfeng

2015-01-01

Alkali halides MX, have been viewed as typical ionic compounds, characterized by 1:1 ratio necessary for charge balance between M+ and X−. It was proposed that group I elements like Cs can be oxidized further under high pressure. Here we perform a comprehensive study for the CsF-F system at pressures up to 100 GPa, and find extremely versatile chemistry. A series of CsFn (n ≥ 1) compounds are predicted to be stable already at ambient pressure. Under pressure, 5p electrons of Cs atoms become active, with growing tendency to form Cs (III) and (V) valence states at fluorine-rich conditions. Although Cs (II) and (IV) are not energetically favoured, the interplay between two mechanisms (polyfluoride anions and polyvalent Cs cations) allows CsF2 and CsF4 compounds to be stable under pressure. The estimated defluorination temperatures of CsFn (n = 2,3,5) compounds at atmospheric pressure (218°C, 150°C, -15°C, respectively), are attractive for fluorine storage applications. PMID:25608669

Accretion disc origin of the Earth's water.

PubMed

Vattuone, Luca; Smerieri, Marco; Savio, Letizia; Asaduzzaman, Abu Md; Muralidharan, Krishna; Drake, Michael J; Rocca, Mario

2013-07-13

Earth's water is conventionally believed to be delivered by comets or wet asteroids after the Earth formed. However, their elemental and isotopic properties are inconsistent with those of the Earth. It was thus proposed that water was introduced by adsorption onto grains in the accretion disc prior to planetary growth, with bonding energies so high as to be stable under high-temperature conditions. Here, we show both by laboratory experiments and numerical simulations that water adsorbs dissociatively on the olivine {100} surface at the temperature (approx. 500-1500 K) and water pressure (approx. 10⁻⁸ bar) expected for the accretion disc, leaving an OH adlayer that is stable at least up to 900 K. This may result in the formation of many Earth oceans, provided that a viable mechanism to produce water from hydroxyl exists. This adsorption process must occur in all disc environments around young stars. The inevitable conclusion is that water should be prevalent on terrestrial planets in the habitable zone around other stars.

Interdependency and phosphorylation of KIF4 and condensin I are essential for organization of chromosome scaffold.

PubMed

Poonperm, Rawin; Takata, Hideaki; Uchiyama, Susumu; Fukui, Kiichi

2017-01-01

Kinesin family member 4 (KIF4) and condensins I and II are essential chromosomal proteins for chromosome organization by locating primarily to the chromosome scaffold. However, the mechanism of how KIF4 and condensins localize to the chromosome scaffold is poorly understood. Here, we demonstrate a close relationship between the chromosome localization of KIF4 and condensin I, but not condensin II, and show that KIF4 and condensin I assist each other for stable scaffold formation by forming a stable complex. Moreover, phosphorylation of KIF4 and condensin I by Aurora B and polo-like kinase 1 (Plk1) is important for KIF4 and condensin I localization to the chromosome. Aurora B activity facilitates the targeting of KIF4 and condensin I to the chromosome, whereas Plk1 activity promotes the dissociation of these proteins from the chromosome. Thus, the interdependency between KIF4 and condensin I, and their phosphorylation states play important roles in chromosome scaffold organization during mitosis.

Interdependency and phosphorylation of KIF4 and condensin I are essential for organization of chromosome scaffold

PubMed Central

Uchiyama, Susumu; Fukui, Kiichi

2017-01-01

Kinesin family member 4 (KIF4) and condensins I and II are essential chromosomal proteins for chromosome organization by locating primarily to the chromosome scaffold. However, the mechanism of how KIF4 and condensins localize to the chromosome scaffold is poorly understood. Here, we demonstrate a close relationship between the chromosome localization of KIF4 and condensin I, but not condensin II, and show that KIF4 and condensin I assist each other for stable scaffold formation by forming a stable complex. Moreover, phosphorylation of KIF4 and condensin I by Aurora B and polo-like kinase 1 (Plk1) is important for KIF4 and condensin I localization to the chromosome. Aurora B activity facilitates the targeting of KIF4 and condensin I to the chromosome, whereas Plk1 activity promotes the dissociation of these proteins from the chromosome. Thus, the interdependency between KIF4 and condensin I, and their phosphorylation states play important roles in chromosome scaffold organization during mitosis. PMID:28817632

Understanding carbon nanotube channel formation in the lipid membrane

NASA Astrophysics Data System (ADS)

Choi, Moon-ki; Kim, Hyunki; Lee, Byung Ho; Kim, Teayeop; Rho, Junsuk; Kim, Moon Ki; Kim, Kyunghoon

2018-03-01

Carbon nanotubes (CNTs) have been considered a prominent nano-channel in cell membranes because of their prominent ion-conductance and ion-selectivity, offering agents for a biomimetic channel platform. Using a coarse-grained molecular dynamics simulation, we clarify a construction mechanism of vertical CNT nano-channels in a lipid membrane for a long period, which has been difficult to observe in previous CNT-lipid interaction simulations. The result shows that both the lipid coating density and length of CNT affect the suitable fabrication condition for a vertical and stable CNT channel. Also, simulation elucidated that a lipid coating on the surface of the CNT prevents the CNT from burrowing into the lipid membrane and the vertical channel is stabilized by the repulsion force between the lipids in the coating and membrane. Our study provides an essential understanding of how CNTs can form stable and vertical channels in the membrane, which is important for designing new types of artificial channels as biosensors for bio-fluidic studies.

Complementary p- and n-type polymer doping for ambient stable graphene inverter.

PubMed

Yun, Je Moon; Park, Seokhan; Hwang, Young Hwan; Lee, Eui-Sup; Maiti, Uday; Moon, Hanul; Kim, Bo-Hyun; Bae, Byeong-Soo; Kim, Yong-Hyun; Kim, Sang Ouk

2014-01-28

Graphene offers great promise to complement the inherent limitations of silicon electronics. To date, considerable research efforts have been devoted to complementary p- and n-type doping of graphene as a fundamental requirement for graphene-based electronics. Unfortunately, previous efforts suffer from undesired defect formation, poor controllability of doping level, and subtle environmental sensitivity. Here we present that graphene can be complementary p- and n-doped by simple polymer coating with different dipolar characteristics. Significantly, spontaneous vertical ordering of dipolar pyridine side groups of poly(4-vinylpyridine) at graphene surface can stabilize n-type doping at room-temperature ambient condition. The dipole field also enhances and balances the charge mobility by screening the impurity charge effect from the bottom substrate. We successfully demonstrate ambient stable inverters by integrating p- and n-type graphene transistors, which demonstrated clear voltage inversion with a gain of 0.17 at a 3.3 V input voltage. This straightforward polymer doping offers diverse opportunities for graphene-based electronics, including logic circuits, particularly in mechanically flexible form.

Formation of a quinoneimine intermediate of 4-fluoro-N-methylaniline by FMO1: carbon oxidation plus defluorination.

PubMed

Driscoll, James P; Aliagas, Ignacio; Harris, Jennifer J; Halladay, Jason S; Khatib-Shahidi, Sheerin; Deese, Alan; Segraves, Nathaniel; Khojasteh-Bakht, S Cyrus

2010-05-17

Here, we report on the mechanism by which flavin-containing monooxygenase 1 (FMO1) mediates the formation of a reactive intermediate of 4-fluoro-N-methylaniline. FMO1 catalyzed a carbon oxidation reaction coupled with defluorination that led to the formation of 4-N-methylaminophenol, which was a reaction first reported by Boersma et al. (Boersma et al. (1993) Drug Metab. Dispos. 21 , 218 - 230). We propose that a labile 1-fluoro-4-(methylimino)cyclohexa-2,5-dienol intermediate was formed leading to an electrophilic quinoneimine intermediate. The identification of N-acetylcysteine adducts by LC-MS/MS and NMR further supports the formation of a quinoneimine intermediate. Incubations containing stable labeled oxygen (H(2)(18)O or (18)O(2)) and ab initio calculations were performed to support the proposed reaction mechanism.

Affinity resins as new tools for identifying target proteins of ascorbic acid.

PubMed

Iwaoka, Yuji; Nishino, Kohei; Ishikawa, Takahiro; Ito, Hideyuki; Sawa, Yoshihiro; Tai, Akihiro

2018-02-12

l-Ascorbic acid (AA) has diverse physiological functions, but little is known about the functional mechanisms of AA. In this study, we synthesized two types of affinity resin on which AA is immobilized in a stable form to identify new AA-targeted proteins, which can provide important clues for elucidating unknown functional mechanisms of AA. To our knowledge, an affinity resin on which AA as a ligand is immobilized has not been prepared, because AA is very unstable and rapidly degraded in an aqueous solution. By using the affinity resins, cytochrome c (cyt c) was identified as an AA-targeted protein, and we showed that oxidized cyt c exhibits specific affinity for AA. These results suggest that two kinds of AA-affinity resin can be powerful tools to identify new target proteins of AA.

Fabrication of a stretchable solid-state micro-supercapacitor array.

PubMed

Kim, Daeil; Shin, Gunchul; Kang, Yu Jin; Kim, Woong; Ha, Jeong Sook

2013-09-24

We fabricated a stretchable micro-supercapacitor array with planar SWCNT electrodes and an ionic liquid-based triblock copolymer electrolyte. The mechanical stability of the entire supercapacitor array upon stretching was obtained by adopting strategic design concepts. First, the narrow and long serpentine metallic interconnections were encapsulated with polyimide thin film to ensure that they were within the mechanical neutral plane. Second, an array of two-dimensional planar micro-supercapacitor with SWCNT electrodes and an ion-gel-type electrolyte was made to achieve all-solid-state energy storage devices. The formed micro-supercapacitor array showed excellent performances which were stable over stretching up to 30% without any noticeable degradation. This work shows the strong potential of a stretchable micro-supercapacitor array in applications such as wearable computers, power dressing, electronic newspapers, paper-like mobile phones, and other easily collapsible gadgets.

Displacement Cascade Damage Production in Metals

DOE Office of Scientific and Technical Information (OSTI.GOV)

Stoller, Roger E; Malerba, Lorenzo; Nordlund, Kai

Radiation-induced changes in microstructure and mechanical properties in structural materials are the result of a complex set of physical processes initiated by the collision between an energetic particle (neutron or ion) and an atom in the lattice. This primary damage event is called an atomic displacement cascade. The simplest description of a displacement cascade is to view it as a series of many billiard-ball-like elastic collisions among the atoms in the material. This chapter describes the formation and evolution of this primary radiation damage mechanism to provide an overview of how stable defects are formed by displacement cascades, as wellmore » as the nature and morphology of the defects themselves. The impact of the relevant variables such as cascade energy and irradiation temperature is discussed, and defect formation in different materials is compared.« less

Modeling and simulation of combustion chamber and propellant dynamics and issues in active control of combustion instabilities

NASA Astrophysics Data System (ADS)

Isella, Giorgio Carlo

A method for a comprehensive approach to analysis of the dynamics of an actively controlled combustion chamber, with detailed analysis of the combustion models for the case of a solid rocket propellant, is presented here. The objective is to model the system as interconnected blocks describing the dynamics of the chamber, combustion and control. The analytical framework for the analysis of the dynamics of a combustion chamber is based on spatial averaging, as introduced by Culick. Combustion dynamics are analyzed for the case of a solid propellant. Quasi-steady theory is extended to include the dynamics of the gas-phase and also of a surface layer. The models are constructed so that they produce a combustion response function for the solid propellant that can be immediately introduced in the our analytical framework. The principal objective mechanisms responsible for the large sensitivity, observed experimentally, of propellant response to small variations. We show that velocity coupling, and not pressure coupling, has the potential to be the mechanism responsible for that high sensitivity. We also discuss the effect of particulate modeling on the global dynamics of the chamber and revisit the interpretation of the intrinsic stability limit for burning of solid propellants. Active control is also considered. Particular attention is devoted to the effect of time delay (between sensing and actuation); several methods to compensate for it are discussed, with numerical examples based on the approximate analysis produced by our framework. Experimental results are presented for the case of a Dump Combustor. The combustor exhibits an unstable burning mode, defined through the measurement of the pressure trace and shadowgraph imaging. The transition between stable and unstable modes of operation is characterized by the presence of hysteresis, also observed in other experimental works, and hence not a special characteristic of this combustor. Control is introduced in the form of pulsed secondary fuel. We show the capability of forcing the transition from unstable to stable burning, hence extending the stable operating regime of the combustor. The transition, characterized by the use of a shadowgraph movie sequence, is attributed to a combined fluid-mechanic and combustion mechanism.

Dilute condition corrosion behavior of glass-ceramic waste form

DOE PAGES

Crum, Jarrod V.; Neeway, James J.; Riley, Brian J.; ...

2016-08-11

Borosilicate glass-ceramics are being developed to immobilize high-level waste generated by aqueous reprocessing into a stable waste form. The corrosion behavior of this multiphase waste form is expected to be complicated by multiple phases and crystal-glass interfaces. A modified single-pass flow-through test was performed on polished monolithic coupons at a neutral pH (25 °C) and 90 °C for 33 d. The measured glass corrosion rates by micro analysis in the samples ranged from 0.019 to 0.29 g m -2 d -1 at a flow rate per surface area = 1.73 × 10 -6 m s -1. The crystal phases (oxyapatitemore » and Ca-rich powellite) corroded below quantifiable rates, by micro analysis. While, Ba-rich powellite corroded considerably in O10 sample. The corrosion rates of C1 and its replicate C20 were elevated an order of magnitude by mechanical stresses at crystal-glass interface caused by thermal expansion mismatch during cooling and unique morphology (oxyapatite clustering).« less

Structural Study of the RIPoptosome Core Reveals a Helical Assembly for Kinase Recruitment

PubMed Central

2015-01-01

Receptor interaction protein kinase 1 (RIP1) is a molecular cell-fate switch. RIP1, together with Fas-associated protein with death domain (FADD) and caspase-8, forms the RIPoptosome that activates apoptosis. RIP1 also associates with RIP3 to form the necrosome that triggers necroptosis. The RIPoptosome assembles through interactions between the death domains (DDs) of RIP1 and FADD and between death effector domains (DEDs) of FADD and caspase-8. In this study, we analyzed the overall structure of the RIP1 DD/FADD DD complex, the core of the RIPoptosome, by negative-stain electron microscopy and modeling. The results show that RIP1 DD and FADD DD form a stable complex in vitro similar to the previously described Fas DD/FADD DD complex, suggesting that the RIPoptosome and the Fas death-inducing signaling complex share a common assembly mechanism. Both complexes adopt a helical conformation that requires type I, II, and III interactions between the death domains. PMID:25119434

Dilute condition corrosion behavior of glass-ceramic waste form

DOE Office of Scientific and Technical Information (OSTI.GOV)

Crum, Jarrod V.; Neeway, James J.; Riley, Brian J.

Borosilicate glass-ceramics are being developed to immobilize high-level waste generated by aqueous reprocessing into a stable waste form. The corrosion behavior of this multiphase waste form is expected to be complicated by multiple phases and crystal-glass interfaces. A modified single-pass flow-through test was performed on polished monolithic coupons at a neutral pH (25 °C) and 90 °C for 33 d. The measured glass corrosion rates by micro analysis in the samples ranged from 0.019 to 0.29 g m -2 d -1 at a flow rate per surface area = 1.73 × 10 -6 m s -1. The crystal phases (oxyapatitemore » and Ca-rich powellite) corroded below quantifiable rates, by micro analysis. While, Ba-rich powellite corroded considerably in O10 sample. The corrosion rates of C1 and its replicate C20 were elevated an order of magnitude by mechanical stresses at crystal-glass interface caused by thermal expansion mismatch during cooling and unique morphology (oxyapatite clustering).« less

Laboratory Alluvial Rivers

NASA Astrophysics Data System (ADS)

Devauchelle, O.; Abramian, A.; Seizilles, G.; Lajeunesse, E.

2015-12-01

By which physical mechanisms does a river select its shape and size? We investigate this question using small laboratory rivers formed by laminar flows.In its simplest form, this experiment consists in a flow of glycerol over a uniform layer of plastic sediments. After a few hours, a channel forms spontaneously, and eventually reaches a stable geometry. This equilibrium state corresponds accurately to the force balance proposed by Henderson (1961).If we impose a sediment discharge at the inlet of the experiment, the river adjusts to this boundary condition by widening its channel. Observation suggests that this new equilibrium results from the balance between gravity, which pulls the entrained grains towards the center of the channel, and bedload diffusion, which returns them towards the banks. This balance explains why experimental rivers get wider and shallower as their sediment load increases.However, to test quantitatively this theory against observation, we need to evaluate independently the effect of transverse slope on bedload transport. We propose to use an instability generated by bedload diffusion to do so.

A cyclobutane thymine–N4-methylcytosine dimer is resistant to hydrolysis but strongly blocks DNA synthesis

PubMed Central

Yamamoto, Junpei; Oyama, Tomoko; Kunishi, Tomohiro; Masutani, Chikahide; Hanaoka, Fumio; Iwai, Shigenori

2014-01-01

Exposure of DNA to ultraviolet light produces harmful crosslinks between adjacent pyrimidine bases, to form cyclobutane pyrimidine dimers (CPDs) and pyrimidine(6–4)pyrimidone photoproducts. The CPD is frequently formed, and its repair mechanisms have been exclusively studied by using a CPD formed at a TT site. On the other hand, biochemical analyses using CPDs formed within cytosine-containing sequence contexts are practically difficult, because saturated cytosine easily undergoes hydrolytic deamination. Here, we found that N-alkylation of the exocyclic amino group of 2′-deoxycytidine prevents hydrolysis in CPD formation, and an N-methylated cytosine-containing CPD was stable enough to be derivatized into its phosphoramidite building block and incorporated into oligonucleotides. Kinetic studies of the CPD-containing oligonucleotide indicated that its lifetime under physiological conditions is relatively long (∼7 days). In biochemical analyses using human DNA polymerase η, incorporation of TMP opposite the N-methylcytosine moiety of the CPD was clearly detected, in addition to dGMP incorporation, and the incorrect TMP incorporation blocked DNA synthesis. The thermodynamic parameters confirmed the formation of this unusual base pair. PMID:24185703

Structure of solvates of o-hydroxybenzoic acid in supercritical CO2-cosolvent media, according to molecular dynamics data

NASA Astrophysics Data System (ADS)

Petrenko, V. E.; Antipova, M. L.; Gurina, D. L.

2015-03-01

Three-component supercritical carbon dioxide-cosolvent (methanol, ethanol, water)- o-hydroxybenzoic acid ( o-HBA) mixtures at a density of 0.7 g/cm3 and temperatures of 318 and 348 K are simulated by means of molecular dynamics. The solvate structures are investigated. It is shown that the solvation mechanism of o-HBA (particularly the o-HBA molecule forming a stable solvate complex with one molecule of a cosolvent via a hydrogen bond through the carboxyl group) does not depend on the temperature or the cosolvent. It is noted that the form of the cosolvent in a supercritical fluid varies: alcohols are distributed in the bulk in the form of monomers and hydrogen-bonded dimers, and water molecules tend to form microclusters along with chained and spatially branched structures by means of hydrogen bonds. It is established that the local molar fraction of cosolvent around the solvate complexes grows. It is concluded that the solvation of o-HBA is determined by the behavior of cosolvent in media of supercritical CO2.

Crystallization and transformation of polymorphic forms of trioleoyl glycerol and 1,2-dioleoyl-3-rac-linoleoyl glycerol.

PubMed

Bayés-García, Laura; Calvet, Teresa; Cuevas-Diarte, Miquel Àngel; Ueno, Satoru; Sato, Kiyotaka

2013-08-08

This study examined the influence of different thermal treatments on the crystallization and transformation of trioleoyl glycerol (OOO) and 1,2-dioleoyl-3-rac-linoleoyl glycerol (OOL). Two triacylglycerol (TAG) samples were cooled at 0.5-15 °C·min(-1) and heated at 2 and 15 °C·min(-1). The polymorphic characteristics of the two TAGs were analyzed in situ using differential scanning calorimetry, Raman spectroscopy, and synchrotron radiation X-ray diffraction. Multiple polymorphic forms were identified in OOO (α, β'2, β'1, β2, and β1) and OOL (α, β'2, and β'1). Larger quantities of more stable forms (e.g., β2 and β1 of OOO and β'1 of OOL) were obtained when the samples were slowly cooled and heated. In contrast, less stable polymorphs were obtained with increased cooling and heating rates. Polymorphic transformations occurred in either solid-state or melt-mediation and were influenced by heating rates. The results were analyzed by considering the activation energies for crystallization and transformation of stable and less stable polymorphic forms in comparison with previous studies on 1,3-dipalmitoyl-2-oleoyl-glycerol and 1, 3-dioleoyl-2-palmitoyl-glycerol.

Experimental Constraints on the Stability of Clinopyroxene (+) Magnesite in Iron Bearing Planetary Mantles: Implications for Nakhlite Formation

NASA Technical Reports Server (NTRS)

Martin, Audrey M.; Righter, Kevin

2010-01-01

Carbon is present in various forms in the Earth s upper mantle (carbonate- or diamond-bearing mantle xenoliths, carbonatite magmas, CO2 emissions from volcanoes...). Moreover, there is enough carbon in chondritic material to stabilize carbonates into the mantles of Mars or Venus as well as in the Earth. However, the interactions with iron have to be constrained, because Fe is commonly thought to buffer oxygen fugacity into planetary mantles. [1] and [2] show evidences of the stability of clinopyroxene Ca(Mg,Fe)Si2O6 + magnesite (Mg,Fe)CO3 in the Earth s mantle around 6GPa (about 180km). The stability of oxidized forms of carbon (like magnesite) depends on the oxygen fugacity of the system. In the Earth s mantle, the maximum carbon content is 10000 ppm [3]. The fO2 parameter varies vertically as a function of pressure, but also laterally because of geodynamic processes like subduction. Thus, carbonates, graphite, diamond, C-rich gases and melts are all stable forms of carbon in the Earth s mantle. [4] show that the fO2 variations observed in SNC meteorites can be explained by polybaric graphite-CO-CO2 equilibria in the Martian mantle. [5] inferred from thermodynamic calculations that the stable form of carbon in the source regions of the Martian basalts should be graphite (and/or diamond). After [6], a metasomatizing agent like a CO2-rich melt may infiltrate the mantle source of nakhlites. However, according to [7] and [8], the FeO wt% value in the Martian bulk mantle is more than twice that of the Earth s mantle (KLB-1 composition by [9]). As iron and carbon are two elements with various oxidation states, Fe/C interaction mechanisms must be considered.

Conditional bistability, a generic cellular mnemonic mechanism for robust and flexible working memory computations.

PubMed

Rodriguez, Guillaume; Sarazin, Matthieu; Clemente, Alexandra; Holden, Stephanie; Paz, Jeanne T; Delord, Bruno

2018-04-30

Persistent neural activity, the substrate of working memory, is thought to emerge from synaptic reverberation within recurrent networks. However, reverberation models do not robustly explain fundamental dynamics of persistent activity, including high-spiking irregularity, large intertrial variability, and state transitions. While cellular bistability may contribute to persistent activity, its rigidity appears incompatible with persistent activity labile characteristics. Here, we unravel in a cellular model a form of spike-mediated conditional bistability that is robust, generic and provides a rich repertoire of mnemonic computations. Under asynchronous synaptic inputs of the awakened state, conditional bistability generates spiking/bursting episodes, accounting for the irregularity, variability and state transitions characterizing persistent activity. This mechanism has likely been overlooked because of the sub-threshold input it requires and we predict how to assess it experimentally. Our results suggest a reexamination of the role of intrinsic properties in the collective network dynamics responsible for flexible working memory. SIGNIFICANCE STATEMENT This study unravels a novel form of intrinsic neuronal property, i.e. conditional bistability. We show that, thanks of its conditional character, conditional bistability favors the emergence of flexible and robust forms of persistent activity in PFC neural networks, in opposition to previously studied classical forms of absolute bistability. Specifically, we demonstrate for the first time that conditional bistability 1) is a generic biophysical spike-dependent mechanism of layer V pyramidal neurons in the PFC and that 2) it accounts for essential neurodynamical features for the organisation and flexibility of PFC persistent activity (the large irregularity and intertrial variability of the discharge and its organization under discrete stable states), which remain unexplained in a robust fashion by current models. Copyright © 2018 the authors.

Atomistic modeling of alternating access of a mitochondrial ADP/ATP membrane transporter with molecular simulations

PubMed Central

Hayashi, Shigehiko

2017-01-01

The mitochondrial ADP/ATP carrier (AAC) is a membrane transporter that exchanges a cytosolic ADP for a matrix ATP. Atomic structures in an outward-facing (OF) form which binds an ADP from the intermembrane space have been solved by X-ray crystallography, and revealed their unique pseudo three-fold symmetry fold which is qualitatively different from pseudo two-fold symmetry of most transporters of which atomic structures have been solved. However, any atomic-level information on an inward-facing (IF) form, which binds an ATP from the matrix side and is fixed by binding of an inhibitor, bongkrekic acid (BA), is not available, and thus its alternating access mechanism for the transport process is unknown. Here, we report an atomic structure of the IF form predicted by atomic-level molecular dynamics (MD) simulations of the alternating access transition with a recently developed accelerating technique. We successfully obtained a significantly stable IF structure characterized by newly formed well-packed and -organized inter-domain interactions through the accelerated simulations of unprecedentedly large conformational changes of the alternating access without a prior knowledge of the target protein structure. The simulation also shed light on an atomistic mechanism of the strict transport selectivity of adenosine nucleotides over guanosine and inosine ones. Furthermore, the IF structure was shown to bind ATP and BA, and thus revealed their binding mechanisms. The present study proposes a qualitatively novel view of the alternating access of transporters having the unique three-fold symmetry in atomic details and opens the way for rational drug design targeting the transporter in the dynamic functional cycle. PMID:28727843

Quantum Mechanics/Molecular Mechanics Simulations Identify the Ring-Opening Mechanism of Creatininase.

PubMed

Jitonnom, Jitrayut; Mujika, Jon I; van der Kamp, Marc W; Mulholland, Adrian J

2017-12-05

Creatininase catalyzes the conversion of creatinine (a biosensor for kidney function) to creatine via a two-step mechanism: water addition followed by ring opening. Water addition is common to other known cyclic amidohydrolases, but the precise mechanism for ring opening is still under debate. The proton donor in this step is either His178 or a water molecule bound to one of the metal ions, and the roles of His178 and Glu122 are unclear. Here, the two possible reaction pathways have been fully examined by means of combined quantum mechanics/molecular mechanics simulations at the SCC-DFTB/CHARMM22 level of theory. The results indicate that His178 is the main catalytic residue for the whole reaction and explain its role as proton shuttle during the ring-opening step. In the first step, His178 provides electrostatic stabilization to the gem-diolate tetrahedral intermediate. In the second step, His178 abstracts the hydroxyl proton of the intermediate and delivers it to the cyclic amide nitrogen, leading to ring opening. The latter is the rate-limiting step with a free energy barrier of 18.5 kcal/mol, in agreement with the experiment. We find that Glu122 must be protonated during the enzyme reaction, so that it can form a stable hydrogen bond with its neighboring water molecule. Simulations of the E122Q mutant showed that this replacement disrupts the H-bond network formed by three conserved residues (Glu34, Ser78, and Glu122) and water, increasing the energy barrier. Our computational studies provide a comprehensive explanation for previous structural and kinetic observations, including why the H178A mutation causes a complete loss of activity but the E122Q mutation does not.

Reaction Mechanisms for the Electrochemical Reduction of CO 2 to CO and Formate on the Cu(100) Surface at 298 K from Quantum Mechanics Free Energy Calculations with Explicit Water

DOE PAGES

Cheng, Tao; Xiao, Hai; Goddard, William A.

2016-10-11

Copper is the only elemental metal that reduces a significant fraction of CO 2 to hydrocarbons and alcohols, but the atomistic reaction mechanism that controls the product distributions is not known because it has not been possible to detect the reaction intermediates on the electrode surface experimentally, or to carry out Quantum Mechanics (QM) calculations with a realistic description of the electrolyte (water). We carry out QM calculations with an explicit description of water on the Cu(100) surface (experimentally shown to be stable under CO 2 reduction reaction conditions) to examine the initial reaction pathways to form CO and formatemore » (HCOO –) from CO 2 through free energy calculations at 298 K and pH 7. We find that CO formation proceeds from physisorbed CO 2 to chemisorbed CO 2 (*CO 2 δ-), with a free energy barrier of ΔG ‡ = 0.43 eV, the rate-determining step (RDS). The subsequent barriers of protonating *CO 2 δ- to form COOH* and then dissociating COOH* to form *CO are 0.37 and 0.30 eV, respectively. HCOO– formation proceeds through a very different pathway in which physisorbed CO 2 reacts directly with a surface H* (along with electron transfer), leading to ΔG ‡ = 0.80 eV. Thus, the competition between CO formation and HCOO – formation occurs in the first electron-transfer step. On Cu(100), the RDS for CO formation is lower, making CO the predominant product. Therefore, to alter the product distribution, we need to control this first step of CO 2 binding, which might involve controlling pH, alloying, or changing the structure at the nanoscale.« less

Stability of Electrodeposition at Solid-Solid Interfaces and Implications for Metal Anodes

NASA Astrophysics Data System (ADS)

Ahmad, Zeeshan; Viswanathan, Venkatasubramanian

2017-08-01

We generalize the conditions for stable electrodeposition at isotropic solid-solid interfaces using a kinetic model which incorporates the effects of stresses and surface tension at the interface. We develop a stability diagram that shows two regimes of stability: a previously known pressure-driven mechanism and a new density-driven stability mechanism that is governed by the relative density of metal in the two phases. We show that inorganic solids and solid polymers generally do not lead to stable electrodeposition, and provide design guidelines for achieving stable electrodeposition.

[Alternative stable states in coastal intertidal wetland ecosystems of Yangtze estuary, China].

PubMed

Li, Hui; Yuan, Lin; Zhang, Li Quan; Li, Wei; Li, Shi Hua; Zhao, Zhi Yuan

2017-01-01

Alternative stable states phenomenon widely exists in a variety of ecosystems and is closely related to ecosystem health and sustainable development. Although alternative stable states research has become the focus and hotspot of the ecology researches, only a few empirical evidences supported its behavior and mechanisms in coastal wetland ecosystems up to now. In our study, ta-king the intertidal wetland ecosystem in Chongming Dongtan Nature Reserve as study area, we aimed to: 1) test the existence of alternative stable states based on judgment conditions (bimodal characteristic and threshold effect) and determine the relative stable state types; 2) explore the formation mechanisms of alternative stable states by monitoring hydrological conditions, sediment accretion dynamics as well as vegetation growth parameters and analyzing the positive feedbacks between saltmarsh vegetation and sedimentary geomorphology. Our results showed that: 1) Normalized difference vegetation index (NDVI) frequentness distribution revealed obvious bimodality at saltmarsh pioneer zone. Propagule biomass threshold limited the establishment of plant patches representing the "saltmarsh" state. The presence of bimodality and biomass threshold demonstrated there are "mudflat" stable state and "saltmarsh" stable state with distinct structure and function in intertidal wetland ecosystem. 2) Current velocities, turbidities and direction perpendicular to the vegetation zone were the most important factors responsible for the sediments rapid accretion at saltmarsh pioneer zone in spring and summer. Sediments accretion significantly promoted the growth of saltmarsh plant. The positive feedbacks between plant growth and sediments accretion resulted in the formation of alternative stable states. 3) The expansion pattern of saltmarshes in the Chongming Dongtan intertidal wetland ecosystem also suggested that increases of sediments accretion could trigger the formation of "mudflat" stable state and "saltmarsh" stable state on landscape scale. The results from this study could enrich regime shift mechanisms researches and provide the scientific supports for coastal zone protection, restoration and comprehensive management, which could have important theoretical and practical meaning.

Electrospun polylactic acid and polyvinyl alcohol fibers as efficient and stable nanomaterials for immobilization of lipases.

PubMed

Sóti, Péter Lajos; Weiser, Diana; Vigh, Tamás; Nagy, Zsombor Kristóf; Poppe, László; Marosi, György

2016-03-01

Electrospinning was applied to create easy-to-handle and high-surface-area membranes from continuous nanofibers of polyvinyl alcohol (PVA) or polylactic acid (PLA). Lipase PS from Burkholderia cepacia and Lipase B from Candida antarctica (CaLB) could be immobilized effectively by adsorption onto the fibrous material as well as by entrapment within the electrospun nanofibers. The biocatalytic performance of the resulting membrane biocatalysts was evaluated in the kinetic resolution of racemic 1-phenylethanol (rac-1) and 1-phenylethyl acetate (rac-2). Fine dispersion of the enzymes in the polymer matrix and large surface area of the nanofibers resulted in an enormous increase in the activity of the membrane biocatalyst compared to the non-immobilized crude powder forms of the lipases. PLA as fiber-forming polymer for lipase immobilization performed better than PVA in all aspects. Recycling studies with the various forms of electrospun membrane biocatalysts in ten cycles of the acylation and hydrolysis reactions indicated excellent stability of this forms of immobilized lipases. PLA-entrapped lipases could preserve lipase activity and enantiomer selectivity much better than the PVA-entrapped forms. The electrospun membrane forms of CaLB showed high mechanical stability in the repeated acylations and hydrolyses than commercial forms of CaLB immobilized on polyacrylamide beads (Novozyme 435 and IMMCALB-T2-150).

Carbonization of a stable β-sheet-rich silk protein into a pseudographitic pyroprotein

PubMed Central

Cho, Se Youn; Yun, Young Soo; Lee, Sungho; Jang, Dawon; Park, Kyu-Young; Kim, Jae Kyung; Kim, Byung Hoon; Kang, Kisuk; Kaplan, David L.; Jin, Hyoung-Joon

2015-01-01

Silk proteins are of great interest to the scientific community owing to their unique mechanical properties and interesting biological functionality. In addition, the silk proteins are not burned out following heating, rather they are transformed into a carbonaceous solid, pyroprotein; several studies have identified potential carbon precursors for state-of-the-art technologies. However, no mechanism for the carbonization of proteins has yet been reported. Here we examine the structural and chemical changes of silk proteins systematically at temperatures above the onset of thermal degradation. We find that the β-sheet structure is transformed into an sp2-hybridized carbon hexagonal structure by simple heating to 350 °C. The pseudographitic crystalline layers grew to form highly ordered graphitic structures following further heating to 2,800 °C. Our results provide a mechanism for the thermal transition of the protein and demonstrate a potential strategy for designing pyroproteins using a clean system with a catalyst-free aqueous wet process for in vivo applications. PMID:25990218

Preparation of plutonium-bearing ceramics via mechanically activated precursor

NASA Astrophysics Data System (ADS)

Chizhevskaya, S. V.; Stefanovsky, S. V.

2000-07-01

The problem of excess weapons plutonium disposition is suggested to be solved by means of its incorporation in stable ceramics with high chemical durability and radiation resistivity. The most promising host phases for plutonium as well as uranium and neutron poisons (gadolinium, hafnium) are zirconolite, pyrochlore, zircon, zirconia [1,2], and murataite [3]. Their production requires high temperatures and a fine-grained homogeneous precursor to reach final waste form with high quality and low leachability. Currently various routes to homogeneous products preparation such as sol-gel technology, wet-milling, and grinding in a ball or planetary mill are used. The best result demonstrates sol-gel technology but this route is very complicated. An alternative technology for preparation of ceramic precursors is the treatment of the oxide batch with high mechanical energy [4]. Such a treatment produces combination of mechanical (fine milling with formation of various defects, homogenization) and chemical (split bonds with formation of active centers—free radicals, ion-radicals, etc.) effects resulting in higher reactivity of the activated batch.

Morphological Transformation between Nanocoils and Nanoribbons via Defragmentation Structural Rearrangement or Fragmentation-recombination Mechanism

NASA Astrophysics Data System (ADS)

Zhang, Yibin; Zheng, Yingxuan; Xiong, Wei; Peng, Cheng; Zhang, Yifan; Duan, Ran; Che, Yanke; Zhao, Jincai

2016-06-01

Kinetic control over the assembly pathways towards novel metastable functional materials or far-from-equilibrium systems has been much less studied compared to the thermodynamic equilibrium self-assembly. Herein, we report the distinct morphological transformation between nanocoils and nanoribbons in the self-assembly of unsymmetric perylene diimide (PDI) molecules. We demonstrate that the morphological transformation of the kinetically trapped assemblies into the thermodynamically stable forms proceeds via two distinct mechanisms, i.e., a direct structural rearrangement (molecule 1 or 2) and a fragmentation-recombination mechanism (molecule 4), respectively. The subtle interplay of the steric hindrance of the bulky substituents and the flexibility of the linker structure between the bulky moiety and the perylene core was demonstrated to enable the effective modulation of the energetic landscape of the assemblies and thus modulation of the assembly pathways. Herein, our work presents a new approach to control the self-assembly pathways and thereby can be used to achieve novel far-from-equilibrium systems.

Vibrational and mechanical properties of single layer MXene structures: a first-principles investigation

NASA Astrophysics Data System (ADS)

Yorulmaz, Uğur; Özden, Ayberk; Perkgöz, Nihan K.; Ay, Feridun; Sevik, Cem

2016-08-01

MXenes, carbides, nitrides and carbonitrides of early transition metals are the new members of two dimensional materials family given with a formula of {{{M}}}n+1 X n . Recent advances in chemical exfoliation and CVD growth of these crystals together with their promising performance in electrochemical energy storage systems have triggered the interest in these two dimensional structures. In this work, we employ first principles calculations for n = 1 structures of Sc, Ti, Zr, Mo and Hf pristine MXenes and their fully surface terminated forms with F and O. We systematically investigated the dynamical and mechanical stability of both pristine and fully terminated MXene structures to determine the possible MXene candidates for experimental realization. In conjunction with an extensive stability analysis, we report Raman and infrared active mode frequencies for the first time, providing indispensable information for the experimental elaboration of MXene field. After determining dynamically stable MXenes, we provide their phonon dispersion relations, electronic and mechanical properties.

Vibrational and mechanical properties of single layer MXene structures: a first-principles investigation.

PubMed

Yorulmaz, Uğur; Özden, Ayberk; Perkgöz, Nihan K; Ay, Feridun; Sevik, Cem

2016-08-19

MXenes, carbides, nitrides and carbonitrides of early transition metals are the new members of two dimensional materials family given with a formula of [Formula: see text] X n . Recent advances in chemical exfoliation and CVD growth of these crystals together with their promising performance in electrochemical energy storage systems have triggered the interest in these two dimensional structures. In this work, we employ first principles calculations for n = 1 structures of Sc, Ti, Zr, Mo and Hf pristine MXenes and their fully surface terminated forms with F and O. We systematically investigated the dynamical and mechanical stability of both pristine and fully terminated MXene structures to determine the possible MXene candidates for experimental realization. In conjunction with an extensive stability analysis, we report Raman and infrared active mode frequencies for the first time, providing indispensable information for the experimental elaboration of MXene field. After determining dynamically stable MXenes, we provide their phonon dispersion relations, electronic and mechanical properties.

A Diffusive Homeostatic Signal Maintains Neural Heterogeneity and Responsiveness in Cortical Networks

PubMed Central

Sweeney, Yann; Hellgren Kotaleski, Jeanette; Hennig, Matthias H.

2015-01-01

Gaseous neurotransmitters such as nitric oxide (NO) provide a unique and often overlooked mechanism for neurons to communicate through diffusion within a network, independent of synaptic connectivity. NO provides homeostatic control of intrinsic excitability. Here we conduct a theoretical investigation of the distinguishing roles of NO-mediated diffusive homeostasis in comparison with canonical non-diffusive homeostasis in cortical networks. We find that both forms of homeostasis provide a robust mechanism for maintaining stable activity following perturbations. However, the resulting networks differ, with diffusive homeostasis maintaining substantial heterogeneity in activity levels of individual neurons, a feature disrupted in networks with non-diffusive homeostasis. This results in networks capable of representing input heterogeneity, and linearly responding over a broader range of inputs than those undergoing non-diffusive homeostasis. We further show that these properties are preserved when homeostatic and Hebbian plasticity are combined. These results suggest a mechanism for dynamically maintaining neural heterogeneity, and expose computational advantages of non-local homeostatic processes. PMID:26158556

Nesprin provides elastic properties to muscle nuclei by cooperating with spectraplakin and EB1

PubMed Central

Wang, Shuoshuo; Reuveny, Adriana

2015-01-01

Muscle nuclei are exposed to variable cytoplasmic strain produced by muscle contraction and relaxation, but their morphology remains stable. Still, the mechanism responsible for maintaining myonuclear architecture, and its importance, is currently elusive. Herein, we uncovered a unique myonuclear scaffold in Drosophila melanogaster larval muscles, exhibiting both elastic features contributed by the stretching capacity of MSP300 (nesprin) and rigidity provided by a perinuclear network of microtubules stabilized by Shot (spectraplakin) and EB1. Together, they form a flexible perinuclear shield that protects myonuclei from intrinsic or extrinsic forces. The loss of this scaffold resulted in significantly aberrant nuclear morphology and subsequently reduced levels of essential nuclear factors such as lamin A/C, lamin B, and HP1. Overall, we propose a novel mechanism for maintaining myonuclear morphology and reveal its critical link to correct levels of nuclear factors in differentiated muscle fibers. These findings may shed light on the underlying mechanism of various muscular dystrophies. PMID:26008743

Wearable, wireless gas sensors using highly stretchable and transparent structures of nanowires and graphene

NASA Astrophysics Data System (ADS)

Park, Jihun; Kim, Joohee; Kim, Kukjoo; Kim, So-Yun; Cheong, Woon Hyung; Park, Kyeongmin; Song, Joo Hyeb; Namgoong, Gyeongho; Kim, Jae Joon; Heo, Jaeyeong; Bien, Franklin; Park, Jang-Ung

2016-05-01

Herein, we report the fabrication of a highly stretchable, transparent gas sensor based on silver nanowire-graphene hybrid nanostructures. Due to its superb mechanical and optical characteristics, the fabricated sensor demonstrates outstanding and stable performances even under extreme mechanical deformation (stable until 20% of strain). The integration of a Bluetooth system or an inductive antenna enables the wireless operation of the sensor. In addition, the mechanical robustness of the materials allows the device to be transferred onto various nonplanar substrates, including a watch, a bicycle light, and the leaves of live plants, thereby achieving next-generation sensing electronics for the `Internet of Things' area.Herein, we report the fabrication of a highly stretchable, transparent gas sensor based on silver nanowire-graphene hybrid nanostructures. Due to its superb mechanical and optical characteristics, the fabricated sensor demonstrates outstanding and stable performances even under extreme mechanical deformation (stable until 20% of strain). The integration of a Bluetooth system or an inductive antenna enables the wireless operation of the sensor. In addition, the mechanical robustness of the materials allows the device to be transferred onto various nonplanar substrates, including a watch, a bicycle light, and the leaves of live plants, thereby achieving next-generation sensing electronics for the `Internet of Things' area. Electronic supplementary information (ESI) available. See DOI: 10.1039/c6nr01468b

Mechanical Isolation of Highly Stable Antimonene under Ambient Conditions.

PubMed

Ares, Pablo; Aguilar-Galindo, Fernando; Rodríguez-San-Miguel, David; Aldave, Diego A; Díaz-Tendero, Sergio; Alcamí, Manuel; Martín, Fernando; Gómez-Herrero, Julio; Zamora, Félix

2016-08-01

Antimonene fabricated by mechanical exfoliation is highly stable under atmospheric conditions over periods of months and even when immersed in water. Density functional theory confirms the experiments and predicts an electronic gap of ≈1 eV. These results highlight the use of antimonene for optoelectronics applications. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Mineral assemblage transformation of a metakaolin-based waste form after geopolymer encapsulation

NASA Astrophysics Data System (ADS)

Williams, Benjamin D.; Neeway, James J.; Snyder, Michelle M. V.; Bowden, Mark E.; Amonette, James E.; Arey, Bruce W.; Pierce, Eric M.; Brown, Christopher F.; Qafoku, Nikolla P.

2016-05-01

Mitigation of hazardous and radioactive waste can be improved through conversion of existing waste to a more chemically stable and physically robust waste form. One option for waste conversion is the fluidized bed steam reforming (FBSR) process. The resulting FBSR granular material was encapsulated in a geopolymer matrix referred to here as Geo-7. This provides mechanical strength for ease in transport and disposal. However, it is necessary to understand the phase assemblage evolution as a result of geopolymer encapsulation. In this study, we examine the mineral assemblages formed during the synthesis of the multiphase ceramic waste form. The FBSR granular samples were created from waste simulant that was chemically adjusted to resemble Hanford tank waste. Another set of samples was created using Savannah River Site Tank 50 waste simulant in order to mimic a blend of waste collected from 68 Hanford tank. Waste form performance tests were conducted using the product consistency test (PCT), the Toxicity Characteristic Leaching Procedure (TCLP), and the single-pass flow-through (SPFT) test. X-ray diffraction analyses revealed the structure of a previously unreported NAS phase and indicate that monolith creation may lead to a reduction in crystallinity as compared to the primary FBSR granular product.

Thermodynamics and kinetics of vesicles formation processes.

PubMed

Guida, Vincenzo

2010-12-15

Vesicles are hollow aggregates, composed of bilayers of amphiphilic molecules, dispersed into and filled with a liquid solvent. These aggregates can be formed either as equilibrium or as out of equilibrium meta-stable structures and they exhibit a rich variety of different morphologies. The surprising richness of structures, the vast range of industrial applications and the presence of vesicles in a number of biological systems have attracted the interest of numerous researchers and scientists. In this article, we review both the thermodynamics and the kinetics aspects of the phenomena of formation of vesicles. We start presenting the thermodynamics of bilayer membranes formation and deformation, with the aim of deriving the conditions for the existence of equilibrium vesicles. Specifically, we use the results from continuum thermodynamics to discuss the possibility of formation of stable equilibrium vesicles, from both mixed amphiphiles and single component systems. We also link the bilayer membrane properties to the molecular structure of the starting amphiphiles. In the second part of this article, we focus on the dynamics and kinetics of vesiculation. We review the process of vesicles formation both from planar lamellar phase under shear and from isotropic micelles. In order to clarify the physical mechanisms of vesicles formation, we continuously draw a parallel between emulsification and vesiculation processes. Specifically, we compare the experimental results, the driving forces and the relative scaling laws identified for the two processes. Describing the dynamics of vesicles formation, we also discuss why non equilibrium vesicles can be formed by kinetics control and why they are meta-stable. Understanding how to control the properties, the stability and the formation process of vesicles is of fundamental importance for a vast number of industrial applications. Copyright © 2009. Published by Elsevier B.V.

METHOD OF COATING GRAPHITE WITH STABLE METAL CARBIDES AND NITRIDES

DOEpatents

Gurinsky, D.H.

1959-10-27

A method is presented for forming protective stable nitride and carbide compounds on the surface of graphite. This is accomplished by contacting the graphite surface with a fused heavy liquid metal such as bismuth or leadbismuth containing zirconium, titanium, and hafnium dissolved or finely dispersed therein to form a carbide and nitride of at least one of the dissolved metals on the graphite surface.

Polyfibroblast: A Self-Healing and Galvanic Protection Additive

DTIC Science & Technology

2011-07-25

3 Key Accomplishments 3.1 Silane Formulation Processability Silane coupling agents may be added to the existing microcapsules either in low...constrained by the need to form stable microcapsules . To this end, we explored a number of recipes in which the following silane coupling agents were...Isocyanatopropyltrimethoxy silane (ITS). • Glycidoxypropyltrimethoxy silane (GPS) As expected, the lowest concentrations most readily formed stable microcapsules . The

Formation and stability of synaptic receptor domains.

PubMed

Haselwandter, Christoph A; Calamai, Martino; Kardar, Mehran; Triller, Antoine; da Silveira, Rava Azeredo

2011-06-10

Neurotransmitter receptor molecules, concentrated in postsynaptic domains along with scaffold and a number of other molecules, are key regulators of signal transmission across synapses. Combining experiment and theory, we develop a quantitative description of synaptic receptor domains in terms of a reaction-diffusion model. We show that interactions between only receptors and scaffolds, together with the rapid diffusion of receptors on the cell membrane, are sufficient for the formation and stable characteristic size of synaptic receptor domains. Our work reconciles long-term stability of synaptic receptor domains with rapid turnover and diffusion of individual receptors, and suggests novel mechanisms for a form of short-term, postsynaptic plasticity.

Smoldering and Flame Resistant Textiles via Conformal Barrier Formation.

PubMed

Zammarano, Mauro; Cazzetta, Valeria; Nazaré, Shonali; Shields, J Randy; Kim, Yeon Seok; Hoffman, Kathleen M; Maffezzoli, Alfonso; Davis, Rick

2016-12-07

A durable and flexible silicone-based backcoating (halogen free) is applied to the backside of an otherwise smoldering-prone and flammable fabric. When exposed to fire, cyclic siloxanes (produced by thermal decomposition of the backcoating) diffuse through the fabric in the gas phase. The following oxidation of the cyclic siloxanes forms a highly conformal and thermally stable coating that fully embeds all individual fibers and shields them from heat and oxidation. As a result, the combustion of the fabric is prevented. This is a novel fire retardant mechanism that discloses a powerful approach towards textiles and multifunctional flexible materials with combined smoldering/flaming ignition resistance and fire-barrier properties.

Thread bonds in molecules

NASA Astrophysics Data System (ADS)

Ivlev, B.

2017-07-01

Unusual chemical bonds are proposed. Each bond is characterized by the thread of a small radius, 10-11 cm, extended between two nuclei in a molecule. An analogue of a potential well, of the depth of MeV scale, is formed within the thread. This occurs due to the local reduction of zero point electromagnetic energy. This is similar to formation of the Casimir well. The electron-photon interaction only is not sufficient for formation of thread state. The mechanism of electron mass generation is involved in the close vicinity, 10-16 cm, of the thread. Thread bonds are stable and cannot be created or destructed in chemical or optical processes.

Helical self-organization and hierarchical self-assembly of an oligoheterocyclic pyridine-pyridazine strand into extended supramolecular fibers.

PubMed

Cuccia, Louis A; Ruiz, Eliseo; Lehn, Jean-Marie; Homo, Jean-Claude; Schmutz, Marc

2002-08-02

The synthesis and characterization of an alternating pyridine-pyridazine strand comprising thirteen heterocycles are described. Spontaneous folding into a helical secondary structure is based on a general molecular self-organization process enforced by the conformational information encoded within the primary structure of the molecular strand itself. Conformational control based on heterocyclic "helicity codons" illustrates a strategy for designing folding properties into synthetic oligomers (foldamers). Strong intermolecular interactions of the highly ordered lock-washer subunits of compound 3 results in hierarchical supramolecular self-assembly into protofibrils and fibrils. Compound 3 also forms mechanically stable two-dimensional Langmuir-Blodgett and cast thin films.

Defective neutrophil chemotaxis in juvenile periodontitis.

PubMed Central

Clark, R A; Page, R C; Wilde, G

1977-01-01

Neutrophil chemotaxis was evaluated in nine patients with juvenile periodontitis, with normal subjects and patients with the adult form of periodontitis as controls. Defective chemotactic responses were observed in neutrophils from seven of nine juvenile patients, and a reduced level of complement-derived chemotactic activity was demonstrated in serum from four patients. These determinations were normal in all the patients with adult periodontitis. Serum from five of the juvenile patients contained a heat-stable, non-dialyzable factor that markedly inhibited the chemotaxis of normal neutrophils. Thus the characteristic tissue destruction seen in juvenile periodontitis may be, at least in part, a consequence of a failure of host defense mechanisms. PMID:591063

A superhard sp3 microporous carbon with direct bandgap

NASA Astrophysics Data System (ADS)

Pan, Yilong; Xie, Chenlong; Xiong, Mei; Ma, Mengdong; Liu, Lingyu; Li, Zihe; Zhang, Shuangshuang; Gao, Guoying; Zhao, Zhisheng; Tian, Yongjun; Xu, Bo; He, Julong

2017-12-01

Carbon allotropes with distinct sp, sp2, and sp3 hybridization possess various different properties. Here, a novel all-sp3 hybridized tetragonal carbon, namely the P carbon, was predicted by the evolutionary particle swarm structural search. It demonstrated a low density among all-sp3 carbons, due to the corresponding distinctive microporous structure. P carbon is thermodynamically stable than the known C60 and could be formed through the single-walled carbon nanotubes (SWCNTs) compression. P carbon is a direct bandgap semiconductor displaying a strong and superhard nature. The unique combination of electrical and mechanical properties constitutes P carbon a potential superhard material for semiconductor industrial fields.

Synthesis and characterization of thermally stable and/or conductive polymers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gajiwala, H.M.

1992-01-01

Eight new thermally stable polyimides were synthesized from two tricyclic heterocyclic diamines: thionine which has a phenothiazine moiety and proflavine which has an acridine unit. The polymerization reactions were optimized with respect to solvents, reaction time, reaction temperature, solid contents, etc., and their structure property relationships were studied. All these soluble polyimides have nice film forming properties. One of the polyimides containing the acridine moiety, appears to have a tendency to form a liquid crystalline state when its solution is passed through a fine capillary. All of these polyimides were thermally stable in air up to 500-550[degrees]C and up tomore » 600[degrees]C in a nitrogen atmosphere. They have refractive indices in the range of 1.65 to 1.85 and have relatively low value of permittivity. Two other thermally stable polymers, viz., polybenzimidazole and the ladder polymer having the phenazine moiety in the backbone were also synthesized. For these polymerization reactions, tetraamino derivative of phenazine was synthesized from the commercially available diamino, dinitro derivative of benzene. The polybenzimidazole was prepared via the azomethine pathway. This polymer had an intrinsic viscosity of 0.94 in methanesulfonic acid. The nice film forming polybenzimidazole polymer was found to be thermally stable up to 400[degrees]C. The ladder type of a polymer was synthesized by condensation polymerization between tetraaminophenazine and dihydroxybenzophenone in polyphosphoric acid at an elevated temperature. The completely conjugated ladder polymer was found to be semiconducting on doping with iodine. This polymer was highly crystalline as demonstrated by its X-ray diffraction pattern. A morphology study of the polymer indicated that the material has a tendency to form dendritic crystals. The polymer was thermally stable up to about 400[degrees]C in air.« less

Half-Heusler Alloys as Promising Thermoelectric Materials

NASA Astrophysics Data System (ADS)

Page, Alexander A.

This thesis describes Ph.D. research on the half-Heusler class of thermoelectric materials. Half-Heusler alloys are a versatile class of materials that have been studied for use in photovoltaics, phase change memory, and thermoelectric power generation. With respect to thermoelectric power generation, new approaches were recently developed in order to improve the thermoelectric figure of merit, ZT, of half-Heusler alloys. Two of the strategies discussed in this work are adding excess Ni within MNiSn (M = Ti, Zr, or Hf) compounds to form full-Heusler nanostructures and using isoelectronic substitution of Ti, Zr, and Hf in MNiSn compounds to create microscale grain boundaries. This work uses computational simulations based on density functional theory, combined with the cluster expansion method, to predict the stable phases of pseudo-binary and pseudo-ternary composition systems. Statistical mechanics methods were used to calculate temperature-composition phase diagrams that relate the equilibrium phases. It is shown that full-Heusler nanostructures are predicted to remain stable even at high temperatures, and the microscale grain boundaries observed in (Ti,Zr,Hf)NiSn materials are found to be thermodynamically unstable at equilibrium. A new strategy of combining MNiSn materials with ZrNiPb has also recently emerged, and theoretical and experimental work show that a solid solution of the two materials is stable.

Oxidation of a new Biogenic VOC: Chamber Studies of the Atmospheric Chemistry of Methyl Chavicol

NASA Astrophysics Data System (ADS)

Bloss, William; Alam, Mohammed; Adbul Raheem, Modinah; Rickard, Andrew; Hamilton, Jacqui; Pereira, Kelly; Camredon, Marie; Munoz, Amalia; Vazquez, Monica; Vera, Teresa; Rodenas, Mila

2013-04-01

The oxidation of volatile organic compounds (VOCs) leads to formation of ozone and SOA, with consequences for air quality, health, crop yields, atmospheric chemistry and radiative transfer. Recent observations have identified Methyl Chavicol ("MC": Estragole; 1-allyl-4-methoxybenzene, C10H12O) as a major BVOC above pine forests in the USA, and oil palm plantations in Malaysian Borneo. Palm oil cultivation, and hence MC emissions, may be expected to increase with societal food and bio fuel demand. We present the results of a series of simulation chamber experiments to assess the atmospheric fate of MC. Experiments were performed in the EUPHORE facility, monitoring stable product species, radical intermediates, and aerosol production and composition. We determine rate constants for reaction of MC with OH and O3, and ozonolysis radical yields. Stable product measurements (FTIR, PTRMS, GC-SPME) are used to determine the yields of stable products formed from OH- and O3- initiated oxidation, and to develop an understanding of the initial stages of the MC degradation chemistry. A surrogate mechanism approach is used to simulate MC degradation within the MCM, evaluated in terms of ozone production measured in the chamber experiments, and applied to quantify the role of MC in the real atmosphere.

A Very Stable High Throughput Taylor Cone-jet in Electrohydrodynamics

PubMed Central

Morad, M. R.; Rajabi, A.; Razavi, M.; Sereshkeh, S. R. Pejman

2016-01-01

A stable capillary liquid jet formed by an electric field is an important physical phenomenon for formation of controllable small droplets, power generation and chemical reactions, printing and patterning, and chemical-biological investigations. In electrohydrodynamics, the well-known Taylor cone-jet has a stability margin within a certain range of the liquid flow rate (Q) and the applied voltage (V). Here, we introduce a simple mechanism to greatly extend the Taylor cone-jet stability margin and produce a very high throughput. For an ethanol cone-jet emitting from a simple nozzle, the stability margin is obtained within 1 kV for low flow rates, decaying with flow rate up to 2 ml/h. By installing a hemispherical cap above the nozzle, we demonstrate that the stability margin could increase to 5 kV for low flow rates, decaying to zero for a maximum flow rate of 65 ml/h. The governing borders of stability margins are discussed and obtained for three other liquids: methanol, 1-propanol and 1-butanol. For a gravity-directed nozzle, the produced cone-jet is more stable against perturbations and the axis of the spray remains in the same direction through the whole stability margin, unlike the cone-jet of conventional simple nozzles. PMID:27917956

Bismuth-embedded SBA-15 mesoporous silica for radioactive iodine capture and stable storage

NASA Astrophysics Data System (ADS)

Yang, Jae Hwan; Cho, Yong-Jun; Shin, Jin Myeong; Yim, Man-Sung

2015-10-01

Efficient capture and stable storage of the long-lived iodine-129 (129I), released as off-gas from nuclear fuel reprocessing, have been of significant concern in the waste management field. In this study, bismuth-embedded SBA-15 mesoporous silica was firstly applied for iodine capture and storage. SBA-15 was functionalized with thiol (-SH) groups, followed by bismuth adsorption with Bi-S bonding, which was thermally treated to form Bi2S3 within SBA-15. The bismuth-embedded SBA-15s demonstrated high iodine loading capacities (up to 540 mg-I/g-sorbent), which benefitted from high surface area and porosity of SBA-15 as well as the formation of thermodynamically stable BiI3 compound. Iodine physisorption was effectively suppressed due to the large pores present in SBA-15, resulting in chemisorption as a main mechanism for iodine confinement. Furthermore, a chemically durable iodine-bearing material was made with a facile post-sorption process, during which the iodine-incorporated phase was changed from BiI3 to chemically durable Bi5O7I. Thus, our results showed that both efficient capture and stabilization of 129I would be possible with the bismuth-embedded SBA-15, in contrast to other sorbents mainly focused on iodine capture.

Exploration of the Townsend regime by discharge light emission in a gas discharge device

NASA Astrophysics Data System (ADS)

Hilal Yucel, Kurt

2014-01-01

The Townsend discharge mechanism has been explored in a planar microelectronic gas discharge device (MGDD) with different applied voltages U and interelectrode distance d under various pressures in air. The anode and the cathode of the MGDD are formed by a transparent SnO2 covered glass and a GaAs semiconductor, respectively. In the experiments, the discharge is found to be unstable just below the breakdown voltage Ub, whereas the discharge passes through a homogeneous stable Townsend mode beyond the breakdown voltage. The measurements are made by an electrical circuit and a CCD camera by recording the currents and light emission (LE) intensities. The intensity profiles, which are converted from the 3D light emission images along the semiconductor diameter, have been analysed for different system parameters. Different instantaneous conductivity σt regimes are found below and beyond the Townsend region. These regimes govern the current and spatio-temporal LE stabilities in the plasma system. It has been proven that the stable LE region increases up to 550 Torr as a function of pressure for small d. If the active area of the semiconductor becomes larger and the interlectrode distance d becomes smaller, the stable LE region stays nearly constant with pressure.

Stabilization of primary mobile radiation defects in MgF2 crystals

NASA Astrophysics Data System (ADS)

Lisitsyn, V. M.; Lisitsyna, L. A.; Popov, A. I.; Kotomin, E. A.; Abuova, F. U.; Akilbekov, A.; Maier, J.

2016-05-01

Non-radiative decay of the electronic excitations (excitons) into point defects (F-H pairs of Frenkel defects) is main radiation damage mechanism in many ionic (halide) solids. Typical time scale of the relaxation of the electronic excitation into a primary, short-lived defect pair is about 1-50 ps with the quantum yield up to 0.2-0.8. However, only a small fraction of these primary defects are spatially separated and survive after transformation into stable, long-lived defects. The survival probability (or stable defect accumulation efficiency) can differ by orders of magnitude, dependent on the material type; e.g. ∼10% in alkali halides with f.c.c. or b.c.c. structure, 0.1% in rutile MgF2 and <0.001% in fluorides MeF2 (Me: Ca, Sr, Ba). The key factor determining accumulation of stable radiation defects is stabilization of primary defects, first of all, highly mobile hole H centers, through their transformation into more complex immobile defects. In this talk, we present the results of theoretical calculations of the migration energies of the F and H centers in poorely studied MgF2 crystals with a focus on the H center stabilization in the form of the interstitial F2 molecules which is supported by presented experimental data.

Dynamics of a discrete chain of bi-stable elements: A biomimetic shock absorbing mechanism

NASA Astrophysics Data System (ADS)

Cohen, T.; Givli, S.

2014-03-01

A biomimetic shock absorbing mechanism, inspired by the bi-stable elongation behavior of the giant protein titin, is examined. A bi-stable element, composed of three mass particles with monotonous interaction forces, is suggested to facilitate an internal degree of freedom of finite mass which contributes significantly to dissipation upon unlocking of an internal link. An essential feature of the suggested element is that it undergoes reversible rapture and therefore retrieves its initial configuration once unloaded. The quasistatic and dynamic behaviors are investigated showing similarity to the common tri-linear bi-stable response, with two steady phases separated by a spinodal region. The dynamic behavior of a chain of elements is also examined, for several loading scenarios, showing that the suggested mechanism serves as an efficient shock absorber in a sub-critical dampening environment, as compared with a simple mass on spring system. Propagation of shock waves and refraction waves in an element chain is observed and the effect of natural imperfections is considered.

Binding Mechanisms of Intrinsically Disordered Proteins: Theory, Simulation, and Experiment

PubMed Central

Mollica, Luca; Bessa, Luiza M.; Hanoulle, Xavier; Jensen, Malene Ringkjøbing; Blackledge, Martin; Schneider, Robert

2016-01-01

In recent years, protein science has been revolutionized by the discovery of intrinsically disordered proteins (IDPs). In contrast to the classical paradigm that a given protein sequence corresponds to a defined structure and an associated function, we now know that proteins can be functional in the absence of a stable three-dimensional structure. In many cases, disordered proteins or protein regions become structured, at least locally, upon interacting with their physiological partners. Many, sometimes conflicting, hypotheses have been put forward regarding the interaction mechanisms of IDPs and the potential advantages of disorder for protein-protein interactions. Whether disorder may increase, as proposed, e.g., in the “fly-casting” hypothesis, or decrease binding rates, increase or decrease binding specificity, or what role pre-formed structure might play in interactions involving IDPs (conformational selection vs. induced fit), are subjects of intense debate. Experimentally, these questions remain difficult to address. Here, we review experimental studies of binding mechanisms of IDPs using NMR spectroscopy and transient kinetic techniques, as well as the underlying theoretical concepts and numerical methods that can be applied to describe these interactions at the atomic level. The available literature suggests that the kinetic and thermodynamic parameters characterizing interactions involving IDPs can vary widely and that there may be no single common mechanism that can explain the different binding modes observed experimentally. Rather, disordered proteins appear to make combined use of features such as pre-formed structure and flexibility, depending on the individual system and the functional context. PMID:27668217

Cognitive Adaptations for n-person Exchange: The Evolutionary Roots of Organizational Behavior.

PubMed

Tooby, John; Cosmides, Leda; Price, Michael E

2006-03-01

Organizations are composed of stable, predominantly cooperative interactions or n -person exchanges. Humans have been engaging in n -person exchanges for a great enough period of evolutionary time that we appear to have evolved a distinct constellation of species-typical mechanisms specialized to solve the adaptive problems posed by this form of social interaction. These mechanisms appear to have been evolutionarily elaborated out of the cognitive infrastructure that initially evolved for dyadic exchange. Key adaptive problems that these mechanisms are designed to solve include coordination among individuals, and defense against exploitation by free riders. Multi-individual cooperation could not have been maintained over evolutionary time if free riders reliably benefited more than contributors to collective enterprises, and so outcompeted them. As a result, humans evolved mechanisms that implement an aversion to exploitation by free riding, and a strategy of conditional cooperation, supplemented by punitive sentiment towards free riders. Because of the design of these mechanisms, how free riding is treated is a central determinant of the survival and health of cooperative organizations. The mapping of the evolved psychology of n -party exchange cooperation may contribute to the construction of a principled theoretical foundation for the understanding of human behavior in organizations.

Cognitive Adaptations for n-person Exchange: The Evolutionary Roots of Organizational Behavior

PubMed Central

Tooby, John; Cosmides, Leda; Price, Michael E.

2013-01-01

Organizations are composed of stable, predominantly cooperative interactions or n-person exchanges. Humans have been engaging in n-person exchanges for a great enough period of evolutionary time that we appear to have evolved a distinct constellation of species-typical mechanisms specialized to solve the adaptive problems posed by this form of social interaction. These mechanisms appear to have been evolutionarily elaborated out of the cognitive infrastructure that initially evolved for dyadic exchange. Key adaptive problems that these mechanisms are designed to solve include coordination among individuals, and defense against exploitation by free riders. Multi-individual cooperation could not have been maintained over evolutionary time if free riders reliably benefited more than contributors to collective enterprises, and so outcompeted them. As a result, humans evolved mechanisms that implement an aversion to exploitation by free riding, and a strategy of conditional cooperation, supplemented by punitive sentiment towards free riders. Because of the design of these mechanisms, how free riding is treated is a central determinant of the survival and health of cooperative organizations. The mapping of the evolved psychology of n-party exchange cooperation may contribute to the construction of a principled theoretical foundation for the understanding of human behavior in organizations. PMID:23814325

Cocrystal dissociation in the presence of water: a general approach for identifying stable cocrystal forms.

PubMed

Eddleston, Mark D; Madusanka, Nadeesh; Jones, William

2014-09-01

In previous studies, cocrystals have been shown to be susceptible to dissociation at high humidity because of differences in the solubilities of the two coformer molecules, especially when these molecules can form hydrates. Contrastingly, however, the propensity of the pharmaceutically active compound caffeine to hydrate formation is reduced by cocrystallization with oxalic acid. Here, the stability of the oxalic acid cocrystal of caffeine is investigated from a thermodynamic perspective through the use of aqueous slurries of caffeine hydrate and oxalic acid dihydrate. Conversion to the anhydrous caffeine-oxalic acid cocrystal occurred under these conditions confirming that this form is thermodynamically stable in an aqueous environment. The slurry methodology was further developed as a general approach to screening for cocrystals that are not susceptible to dissociation at high humidity. In this manner, cocrystals of the hydrate-forming molecules theophylline, carbamazepine, and piroxicam that are stable at high humidity, indefinitely avoiding hydrate formation, were identified. © 2014 Wiley Periodicals, Inc. and the American Pharmacists Association.

Ribosomal RNA maturation in Schizosaccharomyces pombe is dependent on a large ribonucleoprotein complex of the internal transcribed spacer 1.

PubMed

Lalev, A I; Abeyrathne, P D; Nazar, R N

2000-09-08

The interdependency of steps in the processing of pre-rRNA in Schizosaccharomyces pombe suggests that RNA processing, at least in part, acts as a quality control mechanism which helps assure that only functional RNA is incorporated into mature ribosomes. To determine further the role of the transcribed spacer regions in rRNA processing and to detect interactions which underlie the interdependencies, the ITS1 sequence was examined for its ability to form ribonucleoprotein complexes with cellular proteins. When incubated with protein extract, the spacer formed a specific large RNP. This complex was stable to fractionation by agarose or polyacrylamide gel electrophoresis. Modification exclusion analyses indicated that the proteins interact with a helical domain which is conserved in the internal transcribed spacers. Mutagenic analyses confirmed an interaction with this sequence and indicated that this domain is critical to the efficient maturation of the precursor RNA. The protein constituents, purified by affinity chromatography using the ITS1 sequence, retained an ability to form stable RNP. Protein analyses of gel purified complex, prepared with affinity-purified proteins, indicated at least 20 protein components ranging in size from 20-200 kDa. Peptide mapping by Maldi-Toff mass spectroscopy identified eight hypothetical RNA binding proteins which included four different RNA-binding motifs. Another protein was putatively identified as a pseudouridylate synthase. Additional RNA constituents were not detected. The significance of this complex with respect to rRNA maturation and interdependence in rRNA processing is discussed. Copyright 2000 Academic Press.

Crystal nucleation and metastable bcc phase in charged colloids: A molecular dynamics study

NASA Astrophysics Data System (ADS)

Ji, Xinqiang; Sun, Zhiwei; Ouyang, Wenze; Xu, Shenghua

2018-05-01

The dynamic process of homogenous nucleation in charged colloids is investigated by brute-force molecular dynamics simulation. To check if the liquid-solid transition will pass through metastable bcc, simulations are performed at the state points that definitely lie in the phase region of thermodynamically stable fcc. The simulation results confirm that, in all of these cases, the preordered precursors, acting as the seeds of nucleation, always have predominant bcc symmetry consistent with Ostwald's step rule and the Alexander-McTague mechanism. However, the polymorph selection is not straightforward because the crystal structures formed are not often determined by the symmetry of intermediate precursors but have different characters under different state points. The region of the state point where bcc crystal structures of large enough size are formed during crystallization is narrow, which gives a reasonable explanation as to why the metastable bcc phase in charged colloidal suspensions is rarely detected in macroscopic experiments.

Solid phase microextraction device using aerogel

DOEpatents

Miller, Fred S.; Andresen, Brian D.

2005-06-14

A sample collection substrate of aerogel and/or xerogel materials bound to a support structure is used as a solid phase microextraction (SPME) device. The xerogels and aerogels may be organic or inorganic and doped with metals or other compounds to target specific chemical analytes. The support structure is typically formed of a glass fiber or a metal wire (stainless steel or kovar). The devices are made by applying gel solution to the support structures and drying the solution to form aerogel or xerogel. Aerogel particles may be attached to the wet layer before drying to increase sample collection surface area. These devices are robust, stable in fields of high radiation, and highly effective at collecting gas and liquid samples while maintaining superior mechanical and thermal stability during routine use. Aerogel SPME devices are advantageous for use in GC/MS analyses due to their lack of interfering background and tolerance of GC thermal cycling.

Method for preparing a solid phase microextraction device using aerogel

DOEpatents

Miller, Fred S [Bethel Island, CA; Andresen, Brian D [Livermore, CA

2006-10-24

A sample collection substrate of aerogel and/or xerogel materials bound to a support structure is used as a solid phase microextraction (SPME) device. The xerogels and aerogels may be organic or inorganic and doped with metals or other compounds to target specific chemical analytes. The support structure is typically formed of a glass fiber or a metal wire (stainless steel or kovar). The devices are made by applying gel solution to the support structures and drying the solution to form aerogel or xerogel. Aerogel particles may be attached to the wet layer before drying to increase sample collection surface area. These devices are robust, stable in fields of high radiation, and highly effective at collecting gas and liquid samples while maintaining superior mechanical and thermal stability during routine use. Aerogel SPME devices are advantageous for use in GC/MS analyses due to their lack of interfering background and tolerance of GC thermal cycling.

Exploring structural properties of small carbon clusters Cn (n = 1, 2, 3) using molecular mechanics and energy minimization

NASA Astrophysics Data System (ADS)

Miswan, M. A.; Gopir, G.; Anas, M. M.

2016-11-01

Geometry optimization is one of the most widely used methods to study in carbon cluster Cn to understand its structural properties. The total energy for each of the structures was calculated using Octopus software with conjugate gradient Broyden-Fletcher-Goldfarb-Shanno (CG-BFGS). Our calculation and other studies indicate that the linear forms are the most stable structures. However, the C3 isomers have equal probability to form, as the differences in our calculation of total energy are statistically insignificant. Despite there are two cohort of total energy, the calculations are acceptable due to the energy ratio between C3 to C2 and C2 to C1 are comparable to others work. Meanwhile, the bond properties of the C2 and C3 bonds also gives significant difference between our work and previous study.

The changing world of G protein-coupled receptors: from monomers to dimers and receptor mosaics with allosteric receptor-receptor interactions.

PubMed

Fuxe, Kjell; Marcellino, Daniel; Borroto-Escuela, Dasiel Oscar; Frankowska, Malgorzata; Ferraro, Luca; Guidolin, Diego; Ciruela, Francisco; Agnati, Luigi F

2010-10-01

Based on indications of direct physical interactions between neuropeptide and monoamine receptors in the early 1980s, the term receptor-receptor interactions was introduced and later on the term receptor heteromerization in the early 1990s. Allosteric mechanisms allow an integrative activity to emerge either intramolecularly in G protein-coupled receptor (GPCR) monomers or intermolecularly via receptor-receptor interactions in GPCR homodimers, heterodimers, and receptor mosaics. Stable heteromers of Class A receptors may be formed that involve strong high energy arginine-phosphate electrostatic interactions. These receptor-receptor interactions markedly increase the repertoire of GPCR recognition, signaling and trafficking in which the minimal signaling unit in the GPCR homomers appears to be one receptor and one G protein. GPCR homomers and GPCR assemblies are not isolated but also directly interact with other proteins to form horizontal molecular networks at the plasma membrane.

Pattern selection in solidification

NASA Technical Reports Server (NTRS)

Langer, J. S.

1984-01-01

Directional solidification of alloys produces a wide variety of cellular or lamellar structures which, depending upon growth conditions, may be reproducibly regular or may behave chaotically. It is not well understood how these patterns are selected and controlled or even whether there ever exist sharp selection mechanisms. A related phenomenon is the spatial propagation of a pattern into a system which has been caused to become unstable against pattern-forming deformations. This phenomenon has some features in common with the propagation of sidebranching modes in dendritic solidification. In a class of one-dimensional models, the nonlinear system can be shown to select the propagating mode in which the leading edge of the pattern is just marginally stable. This stability principle, when applicable, predicts both the speed of propagation and the geometrical characteristics of the pattern which forms behind the moving front. A boundary-layer model for fully two or three dimensional solidification problems appears to exhibit similar mathematical behavior.

Stable Formamidinium-Based Perovskite Solar Cells via In Situ Grain Encapsulation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhu, Kai; Li, Zhen; Yang, Ye

Formamidinium (FA)-based lead iodide perovskites have emerged as the most promising light-absorber materials in the prevailing perovskite solar cells (PSCs). However, they suffer from the phase-instability issue in the ambient atmosphere, which is holding back the realization of the full potential of FA-based PSCs in the context of high efficiency and stability. Herein, the tetraethylorthosilicate hydrolysis process is integrated with the solution crystallization of FA-based perovskites, forming a new film structure with individual perovskite grains encapsulated by amorphous silica layers that are in situ formed at the nanoscale. The silica not only protects perovskite grains from the degradation but alsomore » enhances the charge-carrier dynamics of perovskite films. The underlying mechanism is discussed using a joint experiment-theory approach. Through this in situ grain encapsulation method, PSCs show an efficiency close to 20% with an impressive 97% retention after 1000-h storage under ambient conditions.« less

Self-healing of cracks in Ag joining layer for die-attachment in power devices

NASA Astrophysics Data System (ADS)

Chen, Chuantong; Nagao, Shijo; Suganuma, Katsuaki; Jiu, Jinting; Zhang, Hao; Sugahara, Tohru; Iwashige, Tomohito; Sugiura, Kazuhiko; Tsuruta, Kazuhiro

2016-08-01

Sintered silver (Ag) joining has attracted significant interest in power devices modules for its ability to form stable joints with a porous interconnection layer. A function for the self-healing of cracks in sintered porous Ag interlayers at high temperatures is discovered and reported here. A crack which was prepared on a Ag joining layer was closed after heating at 200 °C in air. The tensile strength of pre-cracked Ag joining layer specimens recovers to the value of non-cracked specimens after heating treatment. Transmission electron microscopy (TEM) was used to probe the self-healing mechanism. TEM images and electron diffraction patterns show that a large quantity of Ag nanoparticles formed at the gap with the size less than 10 nm, which bridges the crack in the self-healing process. This discovery provides additional motivation for the application of Ag as an interconnection material for power devices at high temperature.

Laboratory Experiments on the Low-temperature Formation of Carbonaceous Grains in the ISM

NASA Astrophysics Data System (ADS)

Fulvio, Daniele; Góbi, Sándor; Jäger, Cornelia; Kereszturi, Ákos; Henning, Thomas

2017-11-01

The life cycle of cosmic dust grains is far from being understood and the origin and evolution of interstellar medium (ISM) grains is still under debate. In the ISM, the cosmic dust destruction rate is faster than the production rate by stellar sources. However, observations of ISM refractory matter suggest that to maintain a steady amount of cosmic grains, some supplementary production mechanism takes place. In this context, we aimed to study possible reformation mechanisms of cosmic grains taking place at low temperature directly in the ISM. The low-temperature condensation of carbonaceous materials has been investigated in experiments mimicking the ISM conditions. Gas-phase carbonaceous precursors created by laser ablation of graphite were forced to accrete on cold substrates (T ≈ 10 K) representing surviving dust grains. The growing and evolution of the condensing carbonaceous precursors have been monitored by MIR and UV spectroscopy under a number of experimental scenarios. For the first time, the possibility to form ISM carbonaceous grains in situ is demonstrated. The condensation process is governed by carbon chains that first condense into small carbon clusters and finally into more stable carbonaceous materials, of which structural characteristics are comparable to the material formed in gas-phase condensation experiments at very high temperature. We also show that the so-formed fullerene-like carbonaceous material is transformed into a more ordered material under VUV processing. The cold condensation mechanisms discussed here can give fundamental clues to fully understand the balance between the timescale for dust injection, destruction, and reformation in the ISM.

From toothpaste to topological insulators and materials for valleytronics: The journeys of fluorinated tin

NASA Astrophysics Data System (ADS)

Barraza-Lopez, Salvador; Rivero, Pablo; Yan, Jia-An; Garcia-Suarez, Victor Manuel; Ferrer, Jaime

2015-03-01

Tin fluoride has a vast literature. This material is stable in bulk form at room temperature and has commercial applications that include fluorinated toothpaste. Bulk tin fluoride has a pair of fluorine atoms bridging two tin atoms. In the recent past the electronic properties of 2D tin with honeycomb structure have been discussed thus generating a wealth of literature that emphasizes its non-topologically-trivial electronic properties due to the combination of a Dirac-like dispersion and a strong spin-orbit coupling given its large atomic mass. Nevertheless the stability of such freestanding structures has been contested recently. As it turns out, the most stable form of fluorinated tin does not possess a graphane-like structure either. In the most stable phase to be discussed here, fluorine atoms tilt away from (graphane-like) positions over/below tin atoms; in an atomistic arrangement similar to the one seen on their parent bulk structure. Electronic properties depend on atomistic coordination, and the most stable form of fluorinated tin does not possess non-trivial topological properties. Nevertheless it represents a new paradigm for valleytronics in 2D.

A Manual for a Laboratory Information Management System (LIMS) For Light Stable Isotopes - Version 7.0

DTIC Science & Technology

1998-01-01

A MANUAL FOR A LABORATORY INFORMATION MANAGEMENT SYSTEM (LIMS) FOR LIGHT STABLE ISOTOPES— VERSION 7.0 U.S. GEOLOGICAL SURVEY Open-File Report 98-284...Standard Form 298 (Rev. 8-98) Prescribed by ANSI Std Z39-18 A MANUAL FOR A LABORATORY INFORMATION MANAGEMENT SYSTEM (LIMS) FOR LIGHT STABLE...Europa Scientific ..................................................120 1 A MANUAL FOR A LABORATORY INFORMATION MANAGEMENT SYSTEM (LIMS) FOR LIGHT STABLE

Microbial stabilization and mass reduction of wastes containing radionuclides and toxic metals

DOEpatents

Francis, A.J.; Dodge, C.J.; Gillow, J.B.

1991-09-10

A process is provided to treat wastes containing radionuclides and toxic metals with Clostridium sp. BFGl to release a large fraction of the waste solids into solution and convert the radionuclides and toxic metals to a more concentrated and stable form with concurrent volume and mass reduction. The radionuclides and toxic metals being in a more stable form are available for recovery, recycling and disposal. 18 figures.

Microbial stabilization and mass reduction of wastes containing radionuclides and toxic metals

DOEpatents

Francis, Arokiasamy J.; Dodge, Cleveland J.; Gillow, Jeffrey B.

1991-01-01

A process is provided to treat wastes containing radionuclides and toxic metals with Clostridium sp. BFGl to release a large fraction of the waste solids into solutin and convert the radionuclides and toxic metals to a more concentrated and stable form with concurrent volume and mass reduction. The radionuclides and toxic metals being in a more stable form are available for recovery, recycling and disposal.

Precise side-chain conformation analysis of L-phenylalanine in α-helical polypeptide by quantum-chemical calculation and 13C CP-MAS NMR measurement

NASA Astrophysics Data System (ADS)

Niimura, Subaru; Suzuki, Junya; Kurosu, Hiromichi; Yamanobe, Takeshi; Shoji, Akira

2010-04-01

To clarify the positive role of side-chain conformation in the stability of protein secondary structure (main-chain conformation), we successfully calculated the optimization structure of a well-defined α-helical octadecapeptide composed of L-alanine (Ala) and L-phenylalanine (Phe) residues, H-(Ala) 8-Phe-(Ala) 9-OH, based on the molecular orbital calculation with density functional theory (DFT/B3LYP/6-31G(d)). From the total energy and the precise secondary structural parameters such as main-chain dihedral angles and hydrogen-bond parameters of the optimized structure, we confirmed that the conformational stability of an α-helix is affected dominantly by the side-chain conformation ( χ1) of the Phe residue in this system: model A ( T form: around 180° of χ1) is most stable in α-helix and model B ( G + form: around -60° of χ1) is next stable, but model C ( G - form: around 60° of χ1) is less stable. In addition, we demonstrate that the stable conformation of poly( L-phenylalanine) is an α-helix with the side-chain T form, by comparison of the carbonyl 13C chemical shift measured by 13C CP-MAS NMR and the calculated one.

The candidate histocompatibility locus of a Basal chordate encodes two highly polymorphic proteins.

PubMed

Nydam, Marie L; Netuschil, Nikolai; Sanders, Erin; Langenbacher, Adam; Lewis, Daniel D; Taketa, Daryl A; Marimuthu, Arumugapradeep; Gracey, Andrew Y; De Tomaso, Anthony W

2013-01-01

The basal chordate Botryllus schlosseri undergoes a natural transplantation reaction governed by a single, highly polymorphic locus called the fuhc. Our initial characterization of this locus suggested it encoded a single gene alternatively spliced into two transcripts: a 555 amino acid-secreted form containing the first half of the gene, and a full-length, 1008 amino acid transmembrane form, with polymorphisms throughout the ectodomain determining outcome. We have now found that the locus encodes two highly polymorphic genes which are separated by a 227 bp intergenic region: first, the secreted form as previously described, and a second gene encoding a 531 amino acid membrane-bound gene containing three extracellular immunoglobulin domains. While northern blotting revealed only these two mRNAs, both PCR and mRNA-seq detect a single capped and polyadenylated transcript that encodes processed forms of both genes linked by the intergenic region, as well as other transcripts in which exons of the two genes are spliced together. These results might suggest that the two genes are expressed as an operon, during which both genes are co-transcribed and then trans-spliced into two separate messages. This type of transcriptional regulation has been described in tunicates previously; however, the membrane-bound gene does not encode a typical Splice Leader (SL) sequence at the 5' terminus that usually accompanies trans-splicing. Thus, the presence of stable transcripts encoding both genes may suggest a novel mechanism of regulation, or conversely may be rare but stable transcripts in which the two mRNAs are linked due to a small amount of read-through by RNA polymerase. Both genes are highly polymorphic and co-expressed on tissues involved in histocompatibility. In addition, polymorphisms on both genes correlate with outcome, although we have found a case in which it appears that the secreted form may be major allorecognition determinant.

A phenomenological description of BslA assemblies across multiple length scales

PubMed Central

Morris, Ryan J.; Bromley, Keith M.; Stanley-Wall, Nicola

2016-01-01

Intrinsically interfacially active proteins have garnered considerable interest recently owing to their potential use in a range of materials applications. Notably, the fungal hydrophobins are known to form robust and well-organized surface layers with high mechanical strength. Recently, it was shown that the bacterial biofilm protein BslA also forms highly elastic surface layers at interfaces. Here we describe several self-assembled structures formed by BslA, both at interfaces and in bulk solution, over a range of length scales spanning from nanometres to millimetres. First, we observe transiently stable and highly elongated air bubbles formed in agitated BslA samples. We study their behaviour in a range of solution conditions and hypothesize that their dissipation is a consequence of the slow adsorption kinetics of BslA to an air–water interface. Second, we describe elongated tubules formed by BslA interfacial films when shear stresses are applied in both a Langmuir trough and a rheometer. These structures bear a striking resemblance, although much larger in scale, to the elongated air bubbles formed during agitation. Taken together, this knowledge will better inform the conditions and applications of how BslA can be used in the stabilization of multi-phase materials. This article is part of the themed issue ‘Soft interfacial materials: from fundamentals to formulation’. PMID:27298433

An Investigation into the Polymorphism and Crystallization of Levetiracetam and the Stability of its Solid Form.

PubMed

Xu, Kailin; Xiong, Xinnuo; Guo, Liuqi; Wang, Lili; Li, Shanshan; Tang, Peixiao; Yan, Jin; Wu, Di; Li, Hui

2015-12-01

Levetiracetam (LEV) crystals were prepared using different solvents at different temperatures. The LEV crystals were systematically characterized by X-ray powder diffraction (XRPD) and morphological analysis. The results indicated that many kinds of crystal habits exist in a solid form of LEV. To investigate the effects of LEV concentration, crystallization temperature, and crystallization type on crystallization and solid phase transformation of LEV, multiple methods were performed for LEV aqueous solution to determine if a new solid form exists in solid-state LEV. However, XRPD data demonstrate that the LEV solid forms possess same spatial arrangements that are similar to the original solid form. This result indicates that the LEV concentration, crystallization temperature, and crystallization type in aqueous solution have no influence on the crystallization and solid phase transformation of LEV. Moreover, crystallization by sublimation, melt cooling, and quench cooling, as well as mechanical effect, did not result in the formation of new LEV solid state. During melt cooling, the transformation of solid form LEV is a direct process from melting amorphous phase to the original LEV crystal phase, and the conversion rate is very quick. In addition, stability investigation manifested that LEV solid state is very stable under various conditions. © 2015 Wiley Periodicals, Inc. and the American Pharmacists Association.

Ordering mechanisms of periodic stripe arrays on boron-doped Si(100)

NASA Astrophysics Data System (ADS)

Ermanoski, Ivan; Kellogg, Gary; Bartelt, Norman

2009-03-01

We have used low energy electron microscopy to determine the factors that control the degree of order in self-assembled periodic stripe arrays on the atomically flat Si(100) with high boron doping. The stripes consist of extremely elongated vacancy islands of single atomic height, formed at ˜900C, confined in micrometer-sized pits. ``Perfect'' arrays of parallel stripes (in pits of up to ˜10um in size) were formed by allowing various defects to heal over relatively long periods of time. Sublimation was compensated for by an external Si doser, allowing observation of stripe evolution over the course of hours, with no net loss or gain of Si from the area of interest. Stripe formation and ordering mechanisms include spontaneous nucleation and growth of new islands, longitudinal splitting, as well as coarsening due to surface diffusion. Stripe periodicity depends on temperature, allowing for control of this property. Stripes are stable in a range of ˜100C, outside of which they assume the familiar shape of elongated islands, shaped by the anisotropy in step energy. Stripe order can be preserved to room temperature by quenching. References: [1] J.-F. Nielsen et al., Appl. Phys. Lett. 79 (2001) 3857

Nondestructive natural gas hydrate recovery driven by air and carbon dioxide.

PubMed

Kang, Hyery; Koh, Dong-Yeun; Lee, Huen

2014-10-14

Current technologies for production of natural gas hydrates (NGH), which include thermal stimulation, depressurization and inhibitor injection, have raised concerns over unintended consequences. The possibility of catastrophic slope failure and marine ecosystem damage remain serious challenges to safe NGH production. As a potential approach, this paper presents air-driven NGH recovery from permeable marine sediments induced by simultaneous mechanisms for methane liberation (NGH decomposition) and CH₄-air or CH₄-CO₂/air replacement. Air is diffused into and penetrates NGH and, on its surface, forms a boundary between the gas and solid phases. Then spontaneous melting proceeds until the chemical potentials become equal in both phases as NGH depletion continues and self-regulated CH4-air replacement occurs over an arbitrary point. We observed the existence of critical methane concentration forming the boundary between decomposition and replacement mechanisms in the NGH reservoirs. Furthermore, when CO₂ was added, we observed a very strong, stable, self-regulating process of exchange (CH₄ replaced by CO₂/air; hereafter CH₄-CO₂/air) occurring in the NGH. The proposed process will work well for most global gas hydrate reservoirs, regardless of the injection conditions or geothermal gradient.

Nondestructive natural gas hydrate recovery driven by air and carbon dioxide

PubMed Central

Kang, Hyery; Koh, Dong-Yeun; Lee, Huen

2014-01-01

Current technologies for production of natural gas hydrates (NGH), which include thermal stimulation, depressurization and inhibitor injection, have raised concerns over unintended consequences. The possibility of catastrophic slope failure and marine ecosystem damage remain serious challenges to safe NGH production. As a potential approach, this paper presents air-driven NGH recovery from permeable marine sediments induced by simultaneous mechanisms for methane liberation (NGH decomposition) and CH4-air or CH4-CO2/air replacement. Air is diffused into and penetrates NGH and, on its surface, forms a boundary between the gas and solid phases. Then spontaneous melting proceeds until the chemical potentials become equal in both phases as NGH depletion continues and self-regulated CH4-air replacement occurs over an arbitrary point. We observed the existence of critical methane concentration forming the boundary between decomposition and replacement mechanisms in the NGH reservoirs. Furthermore, when CO2 was added, we observed a very strong, stable, self-regulating process of exchange (CH4 replaced by CO2/air; hereafter CH4-CO2/air) occurring in the NGH. The proposed process will work well for most global gas hydrate reservoirs, regardless of the injection conditions or geothermal gradient. PMID:25311102

Development of Cefotaxime Impregnated Chitosan as Nano-antibiotics: De Novo Strategy to Combat Biofilm Forming Multi-drug Resistant Pathogens

PubMed Central

Jamil, Bushra; Habib, Huma; Abbasi, Shahid A.; Ihsan, Ayesha; Nasir, Habib; Imran, Muhammad

2016-01-01

Frequent incidents of antibiotic-resistant biofilm forming pathogens in community-associated and hospital-acquired infections have become a global concern owing to failure of conventional therapies. Nano-antibiotics (NABs) are de novo tools to overcome the multi-drug resistant mechanisms employed by the superbugs. Inhibition of biofilm formation is one of those strategies to curb multi drug resistance phenomenon. In the current study, the anti-biofilm and antibacterial potential of newly synthesized cefotaxime loaded chitosan based NABs have been investigated. Both bare and cefotaxime loaded NABs were prepared by ionotropic gelation method. They were found carrying positive zeta potential of more than +50 mV, indicating highly stable nano-dispersion. Moreover, microscopic studies revealed their size as less than 100 nm. NABs were tested against clinical isolates of multi drug resistant Klebsiella pneumoniae, Pseudomonas aeruginosa, Escherichia coli, and methicillin resistant Staphylococcus aureus and wherein they demonstrated broad-spectrum anti-biofilm and anti-pathogenic activity. Thus, in vitro synergistic action of cephalosporin drugs and chitosan polymer at nano-scale in contrast to free antibiotics can be an improved broad-spectrum strategy to thwart resistance mechanisms in both Gram-positive and Gram-negative resistant pathogens. PMID:27047457

Human collagen produced in plants: more than just another molecule.

PubMed

Shoseyov, Oded; Posen, Yehudit; Grynspan, Frida

2014-01-01

Consequential to its essential role as a mechanical support and affinity regulator in extracellular matrices, collagen constitutes a highly sought after scaffolding material for regeneration and healing applications. However, substantiated concerns have been raised with regard to quality and safety of animal tissue-extracted collagen, particularly in relation to its immunogenicity, risk of disease transmission and overall quality and consistency. In parallel, contamination with undesirable cellular factors can significantly impair its bioactivity, vis-a-vis its impact on cell recruitment, proliferation and differentiation. High-scale production of recombinant human collagen Type I (rhCOL1) in the tobacco plant provides a source of an homogenic, heterotrimeric, thermally stable "virgin" collagen which self assembles to fine homogenous fibrils displaying intact binding sites and has been applied to form numerous functional scaffolds for tissue engineering and regenerative medicine. In addition, rhCOL1 can form liquid crystal structures, yielding a well-organized and mechanically strong membrane, two properties indispensable to extracellular matrix (ECM) mimicry. Overall, the shortcomings of animal- and cadaver-derived collagens arising from their source diversity and recycled nature are fully overcome in the plant setting, constituting a collagen source ideal for tissue engineering and regenerative medicine applications.

Radiation creation of cation defects in alkali halide crystals: Review and today's concept (Review Article)

NASA Astrophysics Data System (ADS)

Lushchik, A.; Lushchik, Ch.; Vasil'chenko, E.; Popov, A. I.

2018-04-01

Irradiation of alkali halide crystals creates pairs of Frenkel defects both in anion and cation sublattices. However, the particular nonimpact creation mechanisms (related to the decay of different electronic excitations) of cation Frenkel pairs are still unclear. At helium temperatures, there is yet no direct evidences of the creation of stable (long-lived) elemental cation defects. On the other hand, a number of complex structural defects containing cation vacancies and/or interstitials, were detected after irradiation of alkali halides at higher temperatures. Besides already proved mechanism related to the association of H and VK centers into trihalide molecules, the following possibilities of cation interstitial-vacancy pair creation are analyzed as well: (i) a direct decay of cation or anion excitons, (ii) the transformation of anion Frenkel pairs, formed at the decay of anion excitons or e-h recombination, into cation ones.

Interfacial complexation in microfluidic droplets for single-step fabrication of microcapsule

NASA Astrophysics Data System (ADS)

Kaufman, Gilad; Nejati, Siamak; Sarfati, Raphael; Boltyanskiy, Rostislav; Williams, Danielle; Liu, Wei; Schloss, Ashley; Regan, Lynn; Yan, Elsa; Dufrense, Eric; Loewenberg, Michael; Osuji, Chinedum

We present microfluidic interfacial complexation in emulsion droplets as a simple single-step approach for fabricating a large variety of stable monodisperse microcapsules with tailored mechanical properties, protein binding and controlled release behavior. We rely on electrostatic interactions and hydrogen bonding to direct the assembly of complementary species at oil-water droplet interfaces to form microcapsules with polyelectrolyte shells, composite polyelectrolyte-nanoparticle shells, and copolymer-nanofiber shells. Additionally, we demonstrate the formation of microcapsules by adsorption of an amphiphilic bacterial hydrophobin, BslA, at oil-in-water and water-in-oil droplets, and protein capture on these capsules using engineered variants of the hydrophobin. We discuss the composition dependence of mechanical properties, shell thickness and release behavior, and regimes of stability for microcapsule fabrication. Nanoparticle based microcapsules display an intriguing plastic deformation response which enables the formation of large aspect ratio asperities by pipette aspiration of the shell.

Electronic Structure, Mechanical and Dynamical Stability of Hexagonal Subcarbides M2C (M = Tc, Ru, Rh, Pd, Re, Os, Ir, and Pt): Ab Initio Calculations

NASA Astrophysics Data System (ADS)

Suetin, D. V.; Shein, I. R.

2018-02-01

Ab initio calculations were used to study the properties of a series of hexagonal (Fe2N-like) subcarbides M2C, where M = Tc, Ru, Rh, Pd, Re, Os, Ir, and Pt, and to calculate their equilibrium structural parameters, electronic properties, phase stability, elastic constants, compression modulus, shear modulus, Young's modulus, compressibility, Pugh's indicator, Poisson ratio, elastic anisotropy indices, and also hardness, Debye temperature, sound velocity, and low-temperature heat capacity. It is found based on these results that all the subcarbides are mechanically stable; however, their formation energies E form are positive with respect to a mixture of d-metal and graphite. In addition, the calculation of the phonon spectra of these subcarbides shows the existence of negative modes, which indicates their dynamical instability. Thus, a successful synthesis of these subcarbides at normal conditions is highly improbable.

Infrared Spectroscopic Study on Structural Change and Interfacial Interaction in Rubber Composites Filled with Silica-Kaolin Hybrid Fillers

NASA Astrophysics Data System (ADS)

Chen, Y.; Guan, J.; Hu, H.; Gao, H.; Zhang, L.

2016-07-01

A series of natural rubber/styrene butadiene rubber/polybutadiene rubber composites was prepared with nanometer silica and micron kaolin by a dry modification process, mechanical compounding, and mold vulcanization. Fourier transform infrared spectroscopy and a scanning electron microscope were used to investigate the structural changes and interfacial interactions in composites. The results showed that the "seesaw" structure was formed particularly with the incorporation of silica particles in the preparation process, which would be beneficial to the dispersibility of fillers in the rubber matrix. The kaolinite platelets were generally arranged in directional alignment. Kaolinite with smaller particle size and low-defect structure was more stable in preparation, but kaolinite with larger particle size and high defect structure tended to change the crystal structure. The composite prepared in this research exhibited excellent mechanical and thermal properties.

Nanopatched Graphene with Molecular Self-Assembly Toward Graphene-Organic Hybrid Soft Electronics.

PubMed

Kang, Boseok; Lee, Seong Kyu; Jung, Jaehyuck; Joe, Minwoong; Lee, Seon Baek; Kim, Jinsung; Lee, Changgu; Cho, Kilwon

2018-06-01

Increasing the mechanical durability of large-area polycrystalline single-atom-thick materials is a necessary step toward the development of practical and reliable soft electronics based on these materials. Here, it is shown that the surface assembly of organosilane by weak epitaxy forms nanometer-thick organic patches on a monolayer graphene surface and dramatically increases the material's resistance to harsh postprocessing environments, thereby increasing the number of ways in which graphene can be processed. The nanopatched graphene with the improved mechanical durability enables stable operation when used as transparent electrodes of wearable strain sensors. Also, the nanopatched graphene applied as an electrode modulates the molecular orientation of deposited organic semiconductor layers, and yields favorable nominal charge injection for organic transistors. These results demonstrate the potential for use of self-assembled organic nanopatches in graphene-based soft electronics. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

The sarcomeric cytoskeleton: from molecules to motion.

PubMed

Gautel, Mathias; Djinović-Carugo, Kristina

2016-01-01

Highly ordered organisation of striated muscle is the prerequisite for the fast and unidirectional development of force and motion during heart and skeletal muscle contraction. A group of proteins, summarised as the sarcomeric cytoskeleton, is essential for the ordered assembly of actin and myosin filaments into sarcomeres, by combining architectural, mechanical and signalling functions. This review discusses recent cell biological, biophysical and structural insight into the regulated assembly of sarcomeric cytoskeleton proteins and their roles in dissipating mechanical forces in order to maintain sarcomere integrity during passive extension and active contraction. α-Actinin crosslinks in the Z-disk show a pivot-and-rod structure that anchors both titin and actin filaments. In contrast, the myosin crosslinks formed by myomesin in the M-band are of a ball-and-spring type and may be crucial in providing stable yet elastic connections during active contractions, especially eccentric exercise. © 2016. Published by The Company of Biologists Ltd.

Selfishness as second-order altruism

PubMed Central

Eldakar, Omar Tonsi; Wilson, David Sloan

2008-01-01

Selfishness is seldom considered a group-beneficial strategy. In the typical evolutionary formulation, altruism benefits the group, selfishness undermines altruism, and the purpose of the model is to identify mechanisms, such as kinship or reciprocity, that enable altruism to evolve. Recent models have explored punishment as an important mechanism favoring the evolution of altruism, but punishment can be costly to the punisher, making it a form of second-order altruism. This model identifies a strategy called “selfish punisher” that involves behaving selfishly in first-order interactions and altruistically in second-order interactions by punishing other selfish individuals. Selfish punishers cause selfishness to be a self-limiting strategy, enabling altruists to coexist in a stable equilibrium. This polymorphism can be regarded as a division of labor, or mutualism, in which the benefits obtained by first-order selfishness help to “pay” for second-order altruism. PMID:18448681

CARBON-RICH MOLECULAR CHAINS IN PROTOPLANETARY AND PLANETARY ATMOSPHERES: QUANTUM MECHANISMS AND ELECTRON ATTACHMENT RATES FOR ANION FORMATION

DOE Office of Scientific and Technical Information (OSTI.GOV)

Carelli, F.; Grassi, T.; Gianturco, F. A.

The elementary mechanisms through which molecular polyynes could form stable negative ions after interacting with free electrons in planetary atmospheres (e.g., Titan's) are analyzed using quantum scattering calculations and quantum structure methods. The case of radical species and of nonpolar partners are analyzed via specific examples for both the C{sub n}H and HC{sub n}H series, with n values from 4 to 12. We show that attachment processes to polar radicals are dominating the anionic production and that the mediating role of dipolar scattering states is crucial to their formation. The corresponding attachment rates are presented as calculated upper limits tomore » their likely values and are obtained down to the low temperatures of interest. The effects of the computed rates, when used in simple evolutionary models, are also investigated and presented in detail.« less

CMG–Pol epsilon dynamics suggests a mechanism for the establishment of leading-strand synthesis in the eukaryotic replisome

PubMed Central

Janska, Agnieszka; Goswami, Panchali; Renault, Ludovic; Abid Ali, Ferdos; Kotecha, Abhay; Costa, Alessandro

2017-01-01

The replisome unwinds and synthesizes DNA for genome duplication. In eukaryotes, the Cdc45–MCM–GINS (CMG) helicase and the leading-strand polymerase, Pol epsilon, form a stable assembly. The mechanism for coupling DNA unwinding with synthesis is starting to be elucidated, however the architecture and dynamics of the replication fork remain only partially understood, preventing a molecular understanding of chromosome replication. To address this issue, we conducted a systematic single-particle EM study on multiple permutations of the reconstituted CMG–Pol epsilon assembly. Pol epsilon contains two flexibly tethered lobes. The noncatalytic lobe is anchored to the motor of the helicase, whereas the polymerization domain extends toward the side of the helicase. We observe two alternate configurations of the DNA synthesis domain in the CMG-bound Pol epsilon. We propose that this conformational switch might control DNA template engagement and release, modulating replisome progression. PMID:28373564

Simulations of Fluid Nitromethane Under Extreme Conditions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fried, L E; Reed, E J; Manaa, M R

2003-07-15

We report density functional molecular dynamics simulations to determine the early chemical events of hot (T = 3000 K) and dense (1.97 g/cm{sup 3}, V/V{sub 0} = 0.68) nitromethane (CH{sub 3}NO{sub 2}). The first step in the decomposition process is an intermolecular proton abstraction mechanism that leads to the formation of CH{sub 3}NO{sub 2}H and the aci ion H{sub 2}CNO{sub 2}{sup -}, in support of evidence from static high-pressure and shock experiments. An intramolecular hydrogen transfer that transforms nitromethane into the aci acid form, CH{sub 2}NO{sub 2}H, accompanies this event. This is the first confirmation of chemical reactivity with bondmore » selectivity for an energetic material near the condition of fully reacted specimen. We also report the decomposition mechanism followed up to the formation of H{sub 2}O as the first stable product.« less

Molecular mechanical studies of proflavine and acridine orange intercalation.

PubMed Central

Dearing, A; Weiner, P; Kollman, P A

1981-01-01

Previous workers have reported that proflavine and acridine orange form various structurally different complexes with the dinucleoside phosphates rCpG and dCpG, with uniform C3'-endo and mixed C3'-endo (3'-5') C2'-endo sugar puckers being observed. We present theoretical calculations, based on the method of molecular mechanics, which support the experimental observations. The results suggest that the mixed C3'-edo (3'-5') C2'-endo pucker conformation isi intrinsically more stable than the uniform C3'-endo conformation, but that the additional stabilisation gained from specific, hydrogen bonding, interactions between nucleic acid and solvent, or intramolecularly within the nucleic acid, can lead to the adoption of the latter conformation, or of variants between the two. The role played by hydrogen bonding between amino-groups and nucleic acid phosphate appears more subtle than previously supposed. PMID:7232221

Examination of the Mechanism of Human Brain Aspartoacylase through the Binding of an Intermediate Analogue†‡

PubMed Central

Le Coq, Johanne; Pavlovsky, Alexander; Malik, Radhika; Sanishvili, Ruslan; Xu, Chengfu; Viola, Ronald E.

2009-01-01

Canavan disease is a fatal neurological disorder caused by the malfunctioning of a single metabolic enzyme, aspartoacylase, that catalyzes the deacetylation of N-acetyl-l-aspartate to produce l-aspartate and acetate. The structure of human brain aspartoacylase has been determined in complex with a stable tetrahedral intermediate analogue, N-phosphonomethyl-l-aspartate. This potent inhibitor forms multiple interactions between each of its heteroatoms and the substrate binding groups arrayed within the active site. The binding of the catalytic intermediate analogue induces the conformational ordering of several substrate binding groups, thereby setting up the active site for catalysis. The highly ordered binding of this inhibitor has allowed assignments to be made for substrate binding groups and provides strong support for a carboxypeptidase-type mechanism for the hydrolysis of the amide bond of the substrate, N-acetyl-l-aspartate. PMID:18293939

Examination of the mechanism of human brain aspartoacylase through the binding of an intermediate analogue.

PubMed

Le Coq, Johanne; Pavlovsky, Alexander; Malik, Radhika; Sanishvili, Ruslan; Xu, Chengfu; Viola, Ronald E

2008-03-18

Canavan disease is a fatal neurological disorder caused by the malfunctioning of a single metabolic enzyme, aspartoacylase, that catalyzes the deacetylation of N-acetyl-L-aspartate to produce L-aspartate and acetate. The structure of human brain aspartoacylase has been determined in complex with a stable tetrahedral intermediate analogue, N-phosphonomethyl-L-aspartate. This potent inhibitor forms multiple interactions between each of its heteroatoms and the substrate binding groups arrayed within the active site. The binding of the catalytic intermediate analogue induces the conformational ordering of several substrate binding groups, thereby setting up the active site for catalysis. The highly ordered binding of this inhibitor has allowed assignments to be made for substrate binding groups and provides strong support for a carboxypeptidase-type mechanism for the hydrolysis of the amide bond of the substrate, N-acetyl- l-aspartate.

Multistable wireless micro-actuator based on antagonistic pre-shaped double beams

NASA Astrophysics Data System (ADS)

Liu, X.; Lamarque, F.; Doré, E.; Pouille, P.

2015-07-01

This paper presents a monolithic multistable micro-actuator based on antagonistic pre-shaped double beams. The designed micro-actuator is formed by two rows of bistable micro-actuators providing four stable positions. The bistable mechanism for each row is a pair of antagonistic pre-shaped beams. This bistable mechanism has an easier pre-load operation compared to the pre-compressed bistable beams method. Furthermore, it solves the asymmetrical force output problem of parallel pre-shaped bistable double beams. At the same time, the geometrical limit is lower than parallel pre-shaped bistable double beams, which ensures a smaller stroke of the micro-actuator with the same dimensions. The designed micro-actuator is fabricated using laser cutting machine on medium density fiberboard (MDF). The bistability and merits of antagonistic pre-shaped double beams are experimentally validated. Finally, a contactless actuation test is performed using 660 nm wavelength laser heating shape memory alloy (SMA) active elements.

Biomimetic Silk Scaffolds with an Amorphous Structure for Soft Tissue Engineering.

PubMed

Sang, Yonghuan; Li, Meirong; Liu, Jiejie; Yao, Yuling; Ding, Zhaozhao; Wang, Lili; Xiao, Liying; Lu, Qiang; Fu, Xiaobing; Kaplan, David L

2018-03-21

Fine tuning physical cues of silk fibroin (SF) biomaterials to match specific requirements for different soft tissues would be advantageous. Here, amorphous SF nanofibers were used to fabricate scaffolds with better hierarchical extracellular matrix (ECM) mimetic microstructures than previous silk scaffolds. Kinetic control was introduced into the scaffold forming process, resulting in the direct production of water-stable scaffolds with tunable secondary structures and thus mechanical properties. These biomaterials remained with amorphous structures, offering softer properties than prior scaffolds. The fine mechanical tunability of these systems provides a feasible way to optimize physical cues for improved cell proliferation and enhanced neovascularization in vivo. Multiple physical cues, such as partly ECM mimetic structures and optimized stiffness, provided suitable microenvironments for tissue ingrowth, suggesting the possibility of actively designing bioactive SF biomaterials. These systems suggest a promising strategy to develop novel SF biomaterials for soft tissue repair and regenerative medicine.

Instability in a system of two interacting liquid films: Formation of liquid bridges between solid surfaces

NASA Astrophysics Data System (ADS)

Forcada, Mikel L.

1993-01-01

A theoretical study of systems composed of two solid-supported liquid films that are subject to a mutual attractive interaction reveals the existence of a mechanical instability: for distances closer than a certain threshold value, the system composed by two separate liquid films has no stable equilibrium configurations, and the system collapses to form a single liquid body. The sudden condensation of a connecting liquid bridge when two solid surfaces are brought to close proximity inside an undersaturated medium has been observed experimentally using the surface-force apparatus [see, e.g., Christenson et al., Phys. Rev. B 39, 11750 (1989)]. In this paper, these results are explained as follows: first, liquid films condense on the surfaces; then, if the distance is short enough, the films jump to contact, because of a mechanical instability due to attractive interactions.

Childhood Adversity and Epigenetic Regulation of Glucocorticoid Signaling Genes: Associations in Children and Adults

PubMed Central

Tyrka, Audrey R.; Ridout, Kathryn K.; Parade, Stephanie H.

2017-01-01

Early childhood experiences have lasting effects on development, including the risk for psychiatric disorders. Research examining the biologic underpinnings of these associations has revealed the impact of childhood maltreatment on the physiologic stress response and activity of the hypothalamic pituitary adrenal (HPA) axis. A growing body of literature supports the hypothesis that environmental exposures mediate their biological effects via epigenetic mechanisms. Methylation, which is thought to be the most stable form of epigenetic change, is a likely mechanism by which early life exposures has lasting effects. In this review, we present recent evidence related to epigenetic regulation of genes involved in HPA axis regulation, namely the glucocorticoid receptor gene (NR3C1) and FK506 binding protein 51 (FKBP5), after childhood adversity and associations with risk for psychiatric disorders. Implications for the development of interventions and future research are discussed. PMID:27691985

Stable swarming using adaptive long-range interactions

NASA Astrophysics Data System (ADS)

Gorbonos, Dan; Gov, Nir S.

2017-04-01

Sensory mechanisms in biology, from cells to humans, have the property of adaptivity, whereby the response produced by the sensor is adapted to the overall amplitude of the signal, reducing the sensitivity in the presence of strong stimulus, while increasing it when it is weak. This property is inherently energy consuming and a manifestation of the nonequilibrium nature of living organisms. We explore here how adaptivity affects the effective forces that organisms feel due to others in the context of a uniform swarm, in both two and three dimensions. The interactions between the individuals are taken to be attractive and long-range and of power-law form. We find that the effects of adaptivity inside the swarm are dramatic, where the effective forces decrease (or remain constant) with increasing swarm density. Linear stability analysis demonstrates how this property prevents collapse (Jeans instability), when the forces are adaptive. Adaptivity therefore endows swarms with a natural mechanism for self-stabilization.

Structure-based cleavage mechanism of Thermus thermophilus Argonaute DNA guide strand-mediated DNA target cleavage

PubMed Central

Sheng, Gang; Zhao, Hongtu; Wang, Jiuyu; Rao, Yu; Tian, Wenwen; Swarts, Daan C.; van der Oost, John; Patel, Dinshaw J.; Wang, Yanli

2014-01-01

We report on crystal structures of ternary Thermus thermophilus Argonaute (TtAgo) complexes with 5′-phosphorylated guide DNA and a series of DNA targets. These ternary complex structures of cleavage-incompatible, cleavage-compatible, and postcleavage states solved at improved resolution up to 2.2 Å have provided molecular insights into the orchestrated positioning of catalytic residues, a pair of Mg2+ cations, and the putative water nucleophile positioned for in-line attack on the cleavable phosphate for TtAgo-mediated target cleavage by a RNase H-type mechanism. In addition, these ternary complex structures have provided insights into protein and DNA conformational changes that facilitate transition between cleavage-incompatible and cleavage-compatible states, including the role of a Glu finger in generating a cleavage-competent catalytic Asp-Glu-Asp-Asp tetrad. Following cleavage, the seed segment forms a stable duplex with the complementary segment of the target strand. PMID:24374628

Review of thermal properties of graphite composite materials

NASA Technical Reports Server (NTRS)

Kourtides, D. A.

1987-01-01

Flammability, thermal, and selected mechanical properties of composites fabricated with epoxy and other thermally stable resin matrices are described. Properties which were measured included limiting-oxygen index, smoke evolution, thermal degradation products, total-heat release, heat-release rates, mass loss, flame spread, ignition resistance, thermogravimetric analysis, and selected mechanical properties. The properties of 8 different graphite composite panels fabricated using four different resin matrices and two types of graphite reinforcement are described. The resin matrices included: XU71775/H795, a blend of vinyl polystyryl pyridine and bismaleimide; H795, a bismaleimide; Cycom 6162, a phenolic; and PSP 6022M, a polystyryl pyridine. The graphite fiber used was AS-4 in the form of either tape or fabric. The properties of these composites were compared with epoxy composites. It was determined that the blend of vinyl polystyryl pyridine and bismaleimide (XU71775/H795) with the graphite tape was the optimum design giving the lowest heat release rate.

Stable engineered vascular networks from human induced pluripotent stem cell-derived endothelial cells cultured in synthetic hydrogels

PubMed Central

Zanotelli, Matthew R.; Ardalani, Hamisha; Zhang, Jue; Hou, Zhonggang; Nguyen, Eric H.; Swanson, Scott; Nguyen, Bao Kim; Bolin, Jennifer; Elwell, Angela; Bischel, Lauren L.; Xie, Angela W.; Stewart, Ron; Beebe, David J.; Thomson, James A.; Schwartz, Michael P.; Murphy, William L.

2016-01-01

Here, we describe an in vitro strategy to model vascular morphogenesis where human induced pluripotent stem cell-derived endothelial cells (iPSC-ECs) are encapsulated in peptide-functionalized poly(ethylene glycol) (PEG) hydrogels, either on standard well plates or within a passive pumping polydimethylsiloxane (PDMS) tri-channel microfluidic device. PEG hydrogels permissive towards cellular remodeling were fabricated using thiol-ene photopolymerization to incorporate matrix metalloproteinase (MMP)-degradable crosslinks and CRGDS cell adhesion peptide. Time lapse microscopy, immunofluorescence imaging, and RNA sequencing (RNA-Seq) demonstrated that iPSC-ECs formed vascular networks through mechanisms that were consistent with in vivo vasculogenesis and angiogenesis when cultured in PEG hydrogels. Migrating iPSC-ECs condensed into clusters, elongated into tubules, and formed polygonal networks through sprouting. Genes upregulated for iPSC-ECs cultured in PEG hydrogels relative to control cells on tissue culture polystyrene (TCP) surfaces included adhesion, matrix remodeling, and Notch signaling pathway genes relevant to in vivo vascular development. Vascular networks with lumens were stable for at least 14 days when iPSC-ECs were encapsulated in PEG hydrogels that were polymerized within the central channel of the microfluidic device. Therefore, iPSC-ECs cultured in peptide-functionalized PEG hydrogels offer a defined platform for investigating vascular morphogenesis in vitro using both standard and microfluidic formats. PMID:26945632

Conformational and hydration properties modulate ice recognition by type I antifreeze protein and its mutants.

PubMed

Chakraborty, Sandipan; Jana, Biman

2017-05-10

The mechanism of ice recognition by antifreeze protein (AFP) is a topic of recent interest. Here, using equilibrium simulations and free energy calculations, we provide structural rationale to the observed experimental anomalies on type I AFP (wfAFP isoform HPLC6) and its mutants as well as probe the molecular origin of ice recognition by them. Our results clearly demonstrate that the interplay between the conformational and hydration properties dictates the ice binding ability of type I AFP and its mutants. We find that HPLC6 exists as a highly stable long helix which adsorbs on the ice surface through the ordered water cages around the CH 3 group of threonine (THR) residues, rather than directly binding to the ice surface via threonine (THR) through hydrogen bonding. Upon mutating THR with serine (SER), the straight helix conformation of HPLC6 disappears and the most stable conformation is a kinked helix devoid of ice binding ability. Free energy calculations reveal that there is a dynamic equilibrium between straight and bent helical conformations in the case of a valine (VAL) mutant. The straight long helical form of the VAL mutant also has the ability to form an ordered water cage structure around the CH 3 groups of the VAL residues and thereby efficiently adsorbs on an ice plane similar to the wild type AFP.

Co-crystal formation between two organic solids on the surface of Titan

NASA Astrophysics Data System (ADS)

Cable, M. L.; Vu, T. H.; Maynard-Casely, H. E.; Hodyss, R. P.

2017-12-01

Laboratory experiments of Titan molecular materials, informed by modeling, can help us to understand the complex and dynamic surface processes occurring on this moon at cryogenic temperatures. We previously demonstrated that two common organic materials on Titan, ethane and benzene, form a unique and stable co-crystalline structure at Titan surface temperatures. We have now characterized a second co-crystal that is stable on Titan, this time between two solids: acetylene and ammonia. The co-crystal forms within minutes at Titan surface temperature, as evidenced by new Raman spectral features in the lattice vibration and C-H bending regions. In addition, a red shift of the C-H stretching mode suggests that the acetylene-ammonia co-crystal is stabilized by a network of C-H···N interactions. Thermal stability studies indicate that this co-crystal remains intact to >110 K, and experiments with liquid methane and ethane reveal the co-crystal to be resistant to fluvial or pluvial exposure. Non-covalently bound structures such as these co-crystals point to far more complex surface interactions than previously believed on Titan. New physical and mechanical properties (deformation, plasticity, density, etc.), differences in storage of key species (i.e., ethane versus methane), variations in surface transport and new chemical gradients can all result in diverse surface features and chemistries of astrobiological interest.

Cross-linked polyimides for integrated optics

NASA Astrophysics Data System (ADS)

Singer, Kenneth D.; Kowalczyk, Tony C.; Nguyen, Hung D.; Beuhler, Allyson J.; Wargowski, David A.

1997-01-01

We have investigated a promising class of polyimide materials for both passive and active electro-optic devices, namely crosslinkable polyimides. These fluorinated polyimides are soluble in the imidized form and are both thermally and photo-crosslinkable leading to easy processability into waveguide structures and the possibility of stable electro-optic properties. We have fabricated channel and slab waveguides and investigated the mechanism of optical propagation loss using photothermal deflection spectroscopy and waveguide loss spectroscopy, and found the losses to arise from residual absorption due to the formation of charge transfer states. The absorption is inhibited by fluorination leading to propagation losses as low as 0.3 dB/cm in the near infrared. Because of the ability to photocrosslink, channel waveguides are fabricated using a simple wet-etch process. Channel waveguides so formed are observed to have no excess loss over slab structures. Solubility followed by thermal cross-linking allows the formation of multilayer structures. We have produced electro-optic polymers by doping with the nonlinear optical chromophores, DCM and DADC; and a process of concurrent poling and thermal crosslinking. Multilayer structures have been investigated and poling fields optimized in the active layer by doping the cladding with an anti-static agent. The high glass-transition temperature and cross-linking leads to very stable electro-optic properties. We are currently building electro-optic modulators based on these materials. Progress and results in this area also are reported.

Monolithic amplifier with stable, high resistance feedback element and method for fabricating the same

DOEpatents

O'Connor, Paul

1998-08-11

A monolithic amplifier includes a stable, high resistance feedback circuit and a dynamic bias circuit. The dynamic bias circuit is formed with active elements matched to those in the amplifier and feedback circuit to compensate for variations in the operating and threshold voltages thereby maintaining a stable resistance in the feedback circuit.

Molecular dynamics study of di-CF4 based reverse micelles in supercritical CO2.

PubMed

Liu, Bing; Tang, Xinpeng; Fang, Wenjing; Li, Xiaoqi; Zhang, Jun; Zhang, Zhiliang; Shen, Yue; Yan, Youguo; Sun, Xiaoli; He, Jianying

2016-10-26

Reverse micelles (RMs) in supercritical CO 2 (scCO 2 ) are promising alternatives for organic solvents, especially when both polar and non-polar components are involved. Fluorinated surfactants, particularly double-chain fluorocarbon surfactants, are able to form well-structured RMs in scCO 2 . The inherent self-assembly mechanisms of surfactants in scCO 2 are still subject to discussion. In this study, molecular dynamics simulations are performed to investigate the self-aggregation behavior of di-CF4 based RMs in scCO 2 , and stable and spherical RMs are formed. The dynamics process and the self-assembly structure in the RMs reveal a three-step mechanism to form the RMs, that is, small RMs, rod-like RMs and fusion of the rod-like RMs. Hydrogen-bonds between headgroups and water molecules, and salt bridges linking Na + ions, headgroups and water molecules enhance the interfacial packing efficiency of the surfactant. The results show that di-CF4 molecules have a high surfactant coverage at the RM interface, implying a high CO 2 -philicity. This mainly results from bending of the short chain (C-COO-CH 2 -(CF2) 3 -CF3) due to the flexible carboxyl group. The microscopic insight provided in this study is helpful in understanding surfactant self-assembly phenomena and designing new CO 2 -philic surfactants.

Conformational analysis of glutamic acid: a density functional approach using implicit continuum solvent model.

PubMed

Turan, Başak; Selçuki, Cenk

2014-09-01

Amino acids are constituents of proteins and enzymes which take part almost in all metabolic reactions. Glutamic acid, with an ability to form a negatively charged side chain, plays a major role in intra and intermolecular interactions of proteins, peptides, and enzymes. An exhaustive conformational analysis has been performed for all eight possible forms at B3LYP/cc-pVTZ level. All possible neutral, zwitterionic, protonated, and deprotonated forms of glutamic acid structures have been investigated in solution by using polarizable continuum model mimicking water as the solvent. Nine families based on the dihedral angles have been classified for eight glutamic acid forms. The electrostatic effects included in the solvent model usually stabilize the charged forms more. However, the stability of the zwitterionic form has been underestimated due to the lack of hydrogen bonding between the solute and solvent; therefore, it is observed that compact neutral glutamic acid structures are more stable in solution than they are in vacuum. Our calculations have shown that among all eight possible forms, some are not stable in solution and are immediately converted to other more stable forms. Comparison of isoelectronic glutamic acid forms indicated that one of the structures among possible zwitterionic and anionic forms may dominate over the other possible forms. Additional investigations using explicit solvent models are necessary to determine the stability of charged forms of glutamic acid in solution as our results clearly indicate that hydrogen bonding and its type have a major role in the structure and energy of conformers.

Activation of intentional mechanisms through utilization of nonsymbolic movements in aphasia rehabilitation.

PubMed

Richards, Katherine; Singletary, Floris; Rothi, Leslie J Gonzalez; Koehler, Shirley; Crosson, Bruce

2002-01-01

Intentional mechanisms play an important role in complex self-initiated actions, such as language and gesturing. Deficits demonstrated in nonfluent aphasia may be a result of a disconnection between or damage to the initiation (intention) and production mechanisms in the left hemisphere. In chronic nonfluent aphasias, damaged language production mechanisms in the left hemisphere may switch to homologous regions in the right hemisphere while the initiation mechanisms remain active in the left hemisphere. A treatment was developed to prime right-hemisphere initiation mechanisms with movements of the nondominant hand, thereby bringing initiation into the right hemisphere where the language production mechanisms have been shifted. Three subjects with stable, chronic nonfluent aphasias were trained in daily sessions with a therapist to perform a complex nonsymbolic movement sequence with their nondominant hand to initiate naming trials of simple line drawings. Naming probes were administered during pre treatment baseline sessions and before each treatment session. All three subjects demonstrated a stable baseline and a significant increase over baseline performance in the percentage correct on naming probes during the treatment. Findings indicate that more extensive investigations of this newly developed treatment are justified and suggest that activation of right-hemisphere initiation mechanisms may enhance word production accuracy in stable, chronic nonfluent aphasias.

A classical view on nonclassical nucleation.

PubMed

Smeets, Paul J M; Finney, Aaron R; Habraken, Wouter J E M; Nudelman, Fabio; Friedrich, Heiner; Laven, Jozua; De Yoreo, James J; Rodger, P Mark; Sommerdijk, Nico A J M

2017-09-19

Understanding and controlling nucleation is important for many crystallization applications. Calcium carbonate (CaCO 3 ) is often used as a model system to investigate nucleation mechanisms. Despite its great importance in geology, biology, and many industrial applications, CaCO 3 nucleation is still a topic of intense discussion, with new pathways for its growth from ions in solution proposed in recent years. These new pathways include the so-called nonclassical nucleation mechanism via the assembly of thermodynamically stable prenucleation clusters, as well as the formation of a dense liquid precursor phase via liquid-liquid phase separation. Here, we present results from a combined experimental and computational investigation on the precipitation of CaCO 3 in dilute aqueous solutions. We propose that a dense liquid phase (containing 4-7 H 2 O per CaCO 3 unit) forms in supersaturated solutions through the association of ions and ion pairs without significant participation of larger ion clusters. This liquid acts as the precursor for the formation of solid CaCO 3 in the form of vaterite, which grows via a net transfer of ions from solution according to z Ca 2+ + z CO 3 2- → z CaCO 3 The results show that all steps in this process can be explained according to classical concepts of crystal nucleation and growth, and that long-standing physical concepts of nucleation can describe multistep, multiphase growth mechanisms.

(2+1) -dimensional stable spatial Raman solitons

NASA Astrophysics Data System (ADS)

Shverdin, M. Y.; Yavuz, D. D.; Walker, D. R.

2004-03-01

We analyze the formation, propagation, and interaction of stable two-frequency (2+1) -dimensional solitons, formed in a Raman media driven near maximum molecular coherence. The propagating light is trapped in the two transverse dimensions.

The a(4) Scheme-A High Order Neutrally Stable CESE Solver

NASA Technical Reports Server (NTRS)

Chang, Sin-Chung

2009-01-01

The CESE development is driven by a belief that a solver should (i) enforce conservation laws in both space and time, and (ii) be built from a nondissipative (i.e., neutrally stable) core scheme so that the numerical dissipation can be controlled effectively. To provide a solid foundation for a systematic CESE development of high order schemes, in this paper we describe a new high order (4-5th order) and neutrally stable CESE solver of a 1D advection equation with a constant advection speed a. The space-time stencil of this two-level explicit scheme is formed by one point at the upper time level and two points at the lower time level. Because it is associated with four independent mesh variables (the numerical analogues of the dependent variable and its first, second, and third-order spatial derivatives) and four equations per mesh point, the new scheme is referred to as the a(4) scheme. As in the case of other similar CESE neutrally stable solvers, the a(4) scheme enforces conservation laws in space-time locally and globally, and it has the basic, forward marching, and backward marching forms. Except for a singular case, these forms are equivalent and satisfy a space-time inversion (STI) invariant property which is shared by the advection equation. Based on the concept of STI invariance, a set of algebraic relations is developed and used to prove the a(4) scheme must be neutrally stable when it is stable. Numerically, it has been established that the scheme is stable if the value of the Courant number is less than 1/3

Experimental research in the phase change materials based on paraffin and expanded perlite

NASA Astrophysics Data System (ADS)

Jiesheng, Liu; Faping, Li; Xiaoqiang, Gong; Rongtang, Zhang

2018-06-01

In this study, paraffin (PA)/expanded perlite (EP) form-stable phase change material (PCM) was first fabricated using the direct impregnation method without vacuum treatment. Absorptive capacity results showed that the PA/EP composite can obtain good absorptive capacity with the temperature 80 °C and the time 2 h. Compared with the water absorption of EP, the decrease in the water absorption of PA/EP form-stable proved that the absorption of PA into porous EP has been carried out successfully. Scanning electron microscope (SEM) and Fourier transform infrared (FT-IR) results show that paraffin can be well impregnated into EP pores and has good compatibility with it. Differential scanning calorimetry (DSC) results reveal that paraffin/EP composite PCM has melting temperature and latent heat of 53.6 °C and 91.3 J/g, respectively. The durability cycles results suggest that form-stable PA/EP PCM shows good durability.

Functional strategies of tropical dry forest plants in relation to growth form and isotopic composition

NASA Astrophysics Data System (ADS)

Santiago, L. S.; Silvera, K.; Andrade, J. L.; Dawson, T. E.

2017-11-01

Tropical dry forests (TDFs) undergo a substantial dry season in which plant species must endure several months of drought. Although TDFs support a diverse array of plant growth forms, it is not clear how they vary in mechanisms for coping with seasonal drought. We measured organic tissue stable isotopic composition of carbon (δ13C) and nitrogen (δ15N) across six plant growth forms including epiphytes, terrestrial succulents, trees, shrubs, herbs, and vines, and oxygen (δ18O) of four growth forms, to distinguish among patterns of resource acquisition and evaluate mechanisms for surviving annual drought in a lowland tropical dry forest in Yucatan, Mexico. Terrestrial succulent and epiphyte δ13C was around -14‰, indicating photosynthesis through the Crassulacean acid metabolism pathway, and along with one C4 herb were distinct from mean values of all other growth forms, which were between -26 and -29‰ indicating C3 photosynthesis. Mean tissue δ15N across epiphytes was -4.95‰ and was significantly lower than all other growth forms, which had values around +3‰. Tissue N concentration varied significantly among growth forms with epiphytes and terrestrial succulents having significantly lower values of about 1% compared to trees, shrubs, herbs and vines, which were around 3%. Tissue C concentration was highest in trees, shrubs and vines, intermediate in herbs and epiphytes and lowest in terrestrial succulents. δ18O did not vary among growth forms. Overall, our results suggest several water-saving aspects of resource acquisition, including the absolute occurrence of CAM photosynthesis in terrestrial succulents and epiphytes, high concentrations of leaf N in some species, which may facilitate CO2 drawdown by photosynthetic enzymes for a given stomatal conductance, and potentially diverse N sources ranging from atmospheric N in epiphytes with extremely depleted δ15N values, and a large range of δ15N values among trees, many of which are legumes and dry season deciduous.

The topological pressure-temperature phase diagram and crystal structures of the dimorphic system spiperone.

PubMed

Robert, B; Perrin, M-A; Coquerel, G; Céolin, R; Rietveld, I B

2016-03-01

The topological pressure-temperature phase diagram for the dimorphism of spiperone, a potent neuroleptic drug, has been constructed using literature data and improved crystal structures obtained with new crystallographic data from single-crystal X-ray diffraction at various temperatures. It is inferred that form II, which is the more dense form and exhibits the lower melting temperature, becomes the more stable phase under pressure. Under ambient conditions, form I is more stable. Copyright © 2015 Académie Nationale de Pharmacie. Published by Elsevier Masson SAS. All rights reserved.

Polymer compositions, polymer films and methods and precursors for forming same

DOEpatents

Klaehn, John R; Peterson, Eric S; Orme, Christopher J

2013-09-24

Stable, high performance polymer compositions including polybenzimidazole (PBI) and a melamine-formaldehyde polymer, such as methylated, poly(melamine-co-formaldehyde), for forming structures such as films, fibers and bulky structures. The polymer compositions may be formed by combining polybenzimidazole with the melamine-formaldehyde polymer to form a precursor. The polybenzimidazole may be reacted and/or intertwined with the melamine-formaldehyde polymer to form the polymer composition. For example, a stable, free-standing film having a thickness of, for example, between about 5 .mu.m and about 30 .mu.m may be formed from the polymer composition. Such films may be used as gas separation membranes and may be submerged into water for extended periods without crazing and cracking. The polymer composition may also be used as a coating on substrates, such as metal and ceramics, or may be used for spinning fibers. Precursors for forming such polymer compositions are also disclosed.

Influence of early diagenesis on the vertical distribution of metal forms in sediments of Bohai Bay, China.

PubMed

Lu, Xueqiang; Zhang, Yan; Liu, Honglei; Xing, Meinan; Shao, Xiaolong; Zhao, Feng; Li, Xiaojuan; Liu, Qiongqiong; Yu, Dan; Yuan, Xuezhu; Yuan, Min

2014-11-15

The influence of early diagenesis on the vertical distribution of metal forms in the sediments of Bohai Bay was discussed in this paper. The results showed that the concentrations were: Al > Fe ≈ Ca > Mn > Cr > Zn > Cu > Pb > Cd. In vertical distribution, the forms of Cr and Pb were stable from the top to the bottom. However, the exchangeable forms and acid-extracted forms of Cd, Cu and Zn presented an obvious declining trend. The metals would be transformed to more stable forms during the early-diagenesis process. Further analysis found that early diagenesis can change the sedimentary environment, affecting pH, oxidation-reduction potential (ORP), total dissolved solid (TDS) and the structure of organic matter (OM), all main factors influencing metal forms in the sediments of Bohai Bay. Copyright © 2014 Elsevier Ltd. All rights reserved.

Interfacial engineering of solution-processed Ni nanochain-SiO{sub x} (x < 2) cermets towards thermodynamically stable, anti-oxidation solar selective absorbers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yu, Xiaobai; Wang, Xiaoxin; Liu, Jifeng, E-mail: Jifeng.Liu@dartmouth.edu

Cermet solar thermal selective absorber coatings are an important component of high-efficiency concentrated solar power (CSP) receivers. The oxidation of the metal nanoparticles in cermet solar absorbers is a great challenge for vacuum-free operation. Recently, we have demonstrated that oxidation is kinetically retarded in solution processed, high-optical-performance Ni nanochain-SiO{sub x} cermet system compared to conventional Ni-Al{sub 2}O{sub 3} system when annealed in air at 450–600 °C for several hours. However, for long-term, high-temperature applications in CSP systems, thermodynamically stable antioxidation behavior is highly desirable, which requires new mechanisms beyond kinetically reducing the oxidation rate. Towards this goal, in this paper, wemore » demonstrate that pre-operation annealing of Ni nanochain-SiO{sub x} cermets at 900 °C in N{sub 2} forms the thermodynamically stable orthorhombic phase of NiSi at the Ni/SiO{sub x} interfaces, leading to self-terminated oxidation at 550 °C in air due to this interfacial engineering. In contrast, pre-operation annealing at a lower temperature of 750 °C in N{sub 2} (as conducted in our previous work) cannot achieve interfacial NiSi formation directly, and further annealing in air at 450–600 °C for >4 h only leads to the formation of the less stable (metastable) hexagonal phase of NiSi. Therefore, the high-temperature pre-operation annealing is critical to form the desirable orthorhombic phase of NiSi at Ni/SiO{sub x} interfaces towards thermodynamically stable antioxidation behavior. Remarkably, with this improved interfacial engineering, the oxidation of 80-nm-diameter Ni nanochain-SiO{sub x} saturates after annealing at 550 °C in air for 12 h. Additional annealing at 550 °C in air for as long as 20 h (i.e., 32 h air annealing at >550 °C in total) has almost no further impact on the structural or optical properties of the coatings, the latter being very sensitive to any interfacial changes due to the localized surface plasmon resonances of the metal nanostructures. This phenomenon holds true for Ni nanoparticle diameter down to 40 nm in Ni-SiO{sub x} system, where the optical response remains stable for 53 h at 550 °C in air. The oxidation vs. time curve also shows saturation behavior deviating from the kinetic Deal-Grove oxidation model. These results strongly suggest a promising approach to thermodynamically stable, anti-oxidation Ni/SiO{sub x} cermet absorbers via interfacial engineering.« less

Monolithic amplifier with stable, high resistance feedback element and method for fabricating the same

DOEpatents

O`Connor, P.

1998-08-11

A monolithic amplifier includes a stable, high resistance feedback circuit and a dynamic bias circuit. The dynamic bias circuit is formed with active elements matched to those in the amplifier and feedback circuit to compensate for variations in the operating and threshold voltages thereby maintaining a stable resistance in the feedback circuit. 11 figs.

Salmonella L-forms: formation in human bile in vitro and isolation culture from patients' gallbladder samples by a non-high osmotic isolation technique.

PubMed

Wang, D N; Wu, W J; Wang, T; Pan, Y Z; Tang, K L; She, X L; Ding, W J; Wang, H

2015-05-01

Bacterial L-forms have always been considered as osmotic-pressure-sensitive cell-wall-deficient bacteria and isolation culture of L-forms must use media with high osmotic pressure. However, isolation culture of stable L-forms formed in humans and animals is very difficult because they have adapted to the physiological osmotic pressure condition of the host. We use a non-high osmotic isolation technique to isolate stable L-forms of Salmonella Typhi and Salmonella Paratyphi A from bile-inducer cultures in vitro and from patients' gallbladder specimens. Multiplex PCR assay for Salmonella-specific genes and nucleotide sequencing are used to identify the Salmonella L-forms in stable L-form isolates. Using this method, we confirmed that Salmonella Paratyphi A and Salmonella Typhi cannot be isolated from bile-inducer cultures cultured for 6 h or 48 h, but the L-forms can be isolated from 1 h to 45 days. In the 524 gallbladder samples, the positive rate for bacterial forms was 19.7% and the positive rate for Salmonella spp. was 0.6% by routine bacteriological methods. The positive rate for bacterial L-forms was 75.4% using non-high osmotic isolation culture. In the L-form isolates, the positive rate of Salmonella invA gene was 3.1%. In these invA-positive L-form isolates, four were positive for the invA and flic-d genes of Salmonella Typhi, and ten were positive for the invA and flic-a genes of Salmonella Paratyphi A. Copyright © 2014 European Society of Clinical Microbiology and Infectious Diseases. Published by Elsevier Ltd. All rights reserved.

Two-step membrane binding by the bacterial SRP receptor enable efficient and accurate Co-translational protein targeting.

PubMed

Hwang Fu, Yu-Hsien; Huang, William Y C; Shen, Kuang; Groves, Jay T; Miller, Thomas; Shan, Shu-Ou

2017-07-28

The signal recognition particle (SRP) delivers ~30% of the proteome to the eukaryotic endoplasmic reticulum, or the bacterial plasma membrane. The precise mechanism by which the bacterial SRP receptor, FtsY, interacts with and is regulated at the target membrane remain unclear. Here, quantitative analysis of FtsY-lipid interactions at single-molecule resolution revealed a two-step mechanism in which FtsY initially contacts membrane via a Dynamic mode, followed by an SRP-induced conformational transition to a Stable mode that activates FtsY for downstream steps. Importantly, mutational analyses revealed extensive auto-inhibitory mechanisms that prevent free FtsY from engaging membrane in the Stable mode; an engineered FtsY pre-organized into the Stable mode led to indiscriminate targeting in vitro and disrupted FtsY function in vivo. Our results show that the two-step lipid-binding mechanism uncouples the membrane association of FtsY from its conformational activation, thus optimizing the balance between the efficiency and fidelity of co-translational protein targeting.

Preparation of Polyurethane/Graphite Composite Films with Stable Mechanical Property and Wear Resistance Underwater.

PubMed

Wang, Miaomiao; Wang, Zubin; Chen, Qirong; Meng, Xiangfu; Heng, Liping

2018-06-01

The wear resistance and stable mechanical properties affect the service life of the underwater functional materials to a certain extent. Unfortunately, the current study of underwater functional materials is rarely related to these aspects. Herein, we successfully designed and prepared polyurethane/graphite nanosheet (PU/GN) composite materials, which exhibited excellent wear resistance and stable mechanical properties underwater. The PU/GN composite films were prepared by evaporating a mixed solution of PU and GN on concave hexagonal honeycomb silicon templates. The mechanical properties of the composite films were determined by tensile test, and the wear resistance was evaluated by comparing the surface morphology before and after grind. By adjusting the content of graphite in the composite films, we found that the composite films containing 23 wt% GN had higher tensile strength and superior wear resistance. Moreover, this composite film showed an outstanding stability when expose to water. The impressive results along with simple preparation process made PU/GN composite films had potential applications in robust underwater functional materials.

A full genomic characterization of the development of a stable Small Colony Variant cell-type by a clinical Staphylococcus aureus strain.

PubMed

Bui, Long M G; Kidd, Stephen P

2015-12-01

A key to persistent and recurrent Staphylococcus aureus infections is its ability to adapt to diverse and toxic conditions. This ability includes a switch into a biofilm or to the quasi-dormant Small Colony Variant (SCV). The development and molecular attributes of SCVs have been difficult to study due to their rapid reversion to their parental cell-type. We recently described the unique induction of a matrix-embedded and stable SCV cell-type in a clinical S. aureus strain (WCH-SK2) by growing the cells with limiting conditions for a prolonged timeframe. Here we further study their characteristics. They possessed an increased viability in the presence of antibiotics compared to their non-SCV form. Their stability implied that there had been genetic changes; we therefore determined both the genome sequence of WCH-SK2 and its stable SCV form at a single base resolution, employing Single Molecular Real-Time (SMRT) sequencing that enabled the methylome to also be determined. The genetic features of WCH-SK2 have been identified; the SCCmec type, the pathogenicity and genetic islands and virulence factors. The genetic changes that had occurred in the stable SCV form were identified; most notably being in MgrA, a global regulator, and RsbU, a phosphoserine phosphatase within the regulatory pathway of the sigma factor SigB. There was a shift in the methylomes of the non-SCV and stable SCV forms. We have also shown a similar induction of this cell-type in other S. aureus strains and performed a genetic comparison to these and other S. aureus genomes. We additionally map RNAseq data to the WCH-SK2 genome in a transcriptomic analysis of the parental, SCV and stable SCV cells. The results from this study represent the unique identification of a suite of epigenetic, genetic and transcriptional factors that are implicated in the switch in S. aureus to its persistent SCV form. Copyright © 2015 Elsevier B.V. All rights reserved.

Specifically Formed Corona on Silica Nanoparticles Enhances Transforming Growth Factor β1 Activity in Triggering Lung Fibrosis.

PubMed

Wang, Zhenzhen; Wang, Chunming; Liu, Shang; He, Wei; Wang, Lintao; Gan, JingJing; Huang, Zhen; Wang, Zhenheng; Wei, Haoyang; Zhang, Junfeng; Dong, Lei

2017-02-28

A corona is a layer of macromolecules formed on a nanoparticle surface in vivo. It can substantially change the biological identity of nanomaterials and possibly trigger adverse responses from the body tissues. Dissecting the role of the corona in the development of a particular disease may provide profound insights for understanding toxicity of nanomaterials in general. In our present study, we explored the capability of different silica nanoparticles (SiNPs) to induce silicosis in the mouse lung and analyzed the composition of coronas formed on these particles. We found that SiNPs of certain size and surface chemistry could specifically recruit transforming growth factor β1 (TGF-β1) into their corona, which subsequently induces the development of lung fibrosis. Once embedded into the corona on SiNPs, TGF-β1 was remarkably more stable than in its free form, and its fibrosis-triggering activity was significantly prolonged. Our study meaningfully demonstrates that a specific corona component on a certain nanoparticle could initiate a particular pathogenic process in a clinically relevant disease model. Our findings may shed light on the understanding of molecular mechanisms of human health risks correlated with exposure to small-scale substances.

Contact bubble bilayers with flush drainage.

PubMed

Iwamoto, Masayuki; Oiki, Shigetoshi

2015-03-16

Planar lipid bilayers have been used to form stable bilayers into which membrane proteins are reconstituted for measurements of their function under an applied membrane potential. Recently, a lipid bilayer membrane is formed by the apposition of two monolayers that line an oil-electrolyte interface. Here, a bilayer membrane system is developed with picoliter bubbles under mechanically and chemically manipulable conditions. A water bubble lined with a phospholipid monolayer is blown from a glass pipette into an oil phase. Two blowing pipettes are manipulated, and bubbles (each with a diameter of ~ 50 μm) are held side by side to form a bilayer, which is termed a contact bubble bilayer. With the electrode implemented in the blowing pipette, currents through the bilayer are readily measured. The intra-bubble pressure is varied with the pressure-controller, leading to various sizes of the bubble and the membrane area. A rapid solution exchange system is developed by introducing additional pressure-driven injection pipettes, and the blowing pipette works as a drain. The solution is exchanged within 20 ms. Also, an asymmetric membrane with different lipid composition of each leaflet is readily formed. Example applications of this versatile method are presented to characterize the function of ion channels.

Contact Bubble Bilayers with Flush Drainage

PubMed Central

Iwamoto, Masayuki; Oiki, Shigetoshi

2015-01-01

Planar lipid bilayers have been used to form stable bilayers into which membrane proteins are reconstituted for measurements of their function under an applied membrane potential. Recently, a lipid bilayer membrane is formed by the apposition of two monolayers that line an oil-electrolyte interface. Here, a bilayer membrane system is developed with picoliter bubbles under mechanically and chemically manipulable conditions. A water bubble lined with a phospholipid monolayer is blown from a glass pipette into an oil phase. Two blowing pipettes are manipulated, and bubbles (each with a diameter of ~ 50 μm) are held side by side to form a bilayer, which is termed a contact bubble bilayer. With the electrode implemented in the blowing pipette, currents through the bilayer are readily measured. The intra-bubble pressure is varied with the pressure-controller, leading to various sizes of the bubble and the membrane area. A rapid solution exchange system is developed by introducing additional pressure-driven injection pipettes, and the blowing pipette works as a drain. The solution is exchanged within 20 ms. Also, an asymmetric membrane with different lipid composition of each leaflet is readily formed. Example applications of this versatile method are presented to characterize the function of ion channels. PMID:25772819

Molecular structure and vibrational assignment of dimethyl oxaloacetate

NASA Astrophysics Data System (ADS)

Tayyari, Sayyed Faramarz; Salemi, Sirous; Tabrizi, Mansoureh Zahedi; Behforouz, Mohammad

2004-06-01

A complete conformational analysis of the keto and chelated enol forms of dimethyl oxaloacetate (DMOA), a β-dicarbonyl compound, was carried out by ab initio calculations, at the density functional theory (DFT) level. In addition to nine stable enol conformers, which are stabilized by intramolecular hydrogen bonds, twelve stable keto conformers were also obtained. The considerably higher energy of the keto compared to that of the most stable enol conformer makes the presence of keto form, at least in the gas phase, unlikely. Theoretical calculations in the solution, using the Onsager Method, suggest two coexisting enol conformers in the solution. This finding is in agreement with the experimental data. The hydrogen bond strength of the most stable conformer of DMOA is compared with that of acetylacetone (AA). Harmonic vibrational frequencies of this stable enol form and its deuterated analog were also calculated and compared with the experimental data. According to the theoretical calculations, the enolated proton in dimethyl oxaloacetate moves in an asymmetric single minimum potential with a hydrogen bond strength of 31.1 kJ/mol, 35.3 kJ/mol less than that of AA. This weakening of hydrogen bond is consistent with the frequency shifts for OH/OD stretching, OH/OD out-of-plane bending and O⋯O stretching modes. The calculated O ⋯O distance is about 0.07-0.08 Å longer than that of its parent AA.

System of multifunctional laser polarimetry of phase and amplitude anisotropy in the diagnosis of endometriosis

NASA Astrophysics Data System (ADS)

Ushenko, Yu. O.; Dubolazov, O. V.; Olar, O. V.

2015-11-01

The theoretical background of azimuthally stable method Jones matrix mapping of histological sections of biopsy of uterine neck on the basis of spatial-frequency selection of the mechanisms of linear and circular birefringence is presented. The comparative results of measuring the coordinate distributions of complex degree of mutual anisotropy formed by polycristalline networks of blood plasma layers of donors (group 1) and patients with endometriosis (group 2). The values and ranges of change of the statistical (moments of the 1st - 4th order) parameters of complex degree of mutual anisotropy coordinate distributions are studied. The objective criteria of diagnostics of the pathology and differentiation of its severity degree are determined.

Multifunctional polarization tomography of optical anisotropy of biological layers in diagnosis of endometriosis

NASA Astrophysics Data System (ADS)

Ushenko, O. G.; Koval, L. D.; Dubolazov, O. V.; Ushenko, Yu. O.; Savich, V. O.; Sidor, M. I.; Marchuk, Yu. F.

2015-09-01

The theoretical background of azimuthally stable method Jones matrix mapping of histological sections of biopsy of uterine neck on the basis of spatial-frequency selection of the mechanisms of linear and circular birefringence is presented. The comparative results of measuring the coordinate distributions of complex degree of mutual anisotropy formed by polycristalline networks of blood plasma layers of donors (group 1) and patients with endometriosis (group 2). The values and ranges of change of the statistical (moments of the 1st - 4th order) parameters of complex degree of mutual anisotropy coordinate distributions are studied. The objective criteria of diagnostics of the pathology and differentiation of its severity degree are determined.

Interaction of elaiophylin with model bilayer membrane

NASA Astrophysics Data System (ADS)

Genova, J.; Dencheva-Zarkova, M.

2017-01-01

Elaiophylin is a new macrodiolide antibiotic, which is produced by the Streptomyces strains [1]. It displays biological activities against Gram-positive bacteria and fungi. The mode of action of this antibiotic has been attributed to an alteration of the membrane permeability. When this antibiotic is inserted into the bilayer membranes destabilization of the membrane and formation of ion-penetrable channels is observed. The macrodiolide antibiotic forms stable cation selective ion channels in synthetic lipid bilayer membranes. The aim of this work was to study the interactions of Elaiophylin with model bilayer membranes and to get information on the mechanical properties of lipid bilayers in presence of this antibiotic. Patch-clamp technique [2] were used in the study

Stabilization of domain walls between traveling waves by nonlinear mode coupling in Taylor-Couette flow.

PubMed

Heise, M; Hoffmann, Ch; Abshagen, J; Pinter, A; Pfister, G; Lücke, M

2008-02-15

We present a new mechanism that allows the stable existence of domain walls between oppositely traveling waves in pattern-forming systems far from onset. It involves a nonlinear mode coupling that results directly from the nonlinearities in the underlying momentum balance. Our work provides the first observation and explanation of such strongly nonlinearly driven domain walls that separate structured states by a phase generating or annihilating defect. Furthermore, the influence of a symmetry breaking externally imposed flow on the wave domains and the domain walls is studied. The results are obtained for vortex waves in the Taylor-Couette system by combining numerical simulations of the full Navier-Stokes equations and experimental measurements.

The Heat and Mass Transfer Processes at the Cooling of Strong Heated Sphere in a Cold Liquid

NASA Astrophysics Data System (ADS)

Puzina, Yu Yu

2017-10-01

Some new experimental results of continuum mechanics problems in two-phase systems are described. The processes of heat and mass transfer during cooling of strong heated sphere in the subcooled liquid are studied. Due to high level of heater temperature the stable vapor film is formed on the sphere surface. Calculation of steady-state transport processes at vapor - water interface is carried out using methods of molecular-kinetic theory. Heat transfer in vapor by thermal conductivity and natural convection in liquid are considered. Pressure balance is provided by hydrostatic pressure and non-equilibrium boundary condition. The results of the calculations are analyzed by comparison with previous data and experimental results.

A facile sol-gel synthesis of impurity-free nanocrystalline titania.

PubMed

Vinogradov, Alexandr V; Ermakova, Al'ena V; Butman, Mikhail F; Hey-Hawkins, Evamarie; Vinogradov, Vladimir V

2014-06-14

This paper reports an original technique that provides a highly pure crystalline sol of titania with controllable particle size by ultrasonic activation of the hydrolysis products of titanium isopropoxide in an aqueous medium at a near-neutral pH, which is potentially promising in impurity-sensitive electronics and biochemical engineering. Optimal conditions (H2O/TIP ratio, sonication time, etc.) for preparation of stable nanocrystalline titania sol were adopted. A new mechanism of regulation of aggregation and polycondensation under ultrasonic irradiation is proposed. Entrapment of human serum albumin (HSA) in the formed porous titania matrix results in high thermal stability of the protein dopants: the denaturation temperature of HSA is shifted by 31 °C.

Chemical evolution of the Earth: Equilibrium or disequilibrium process?

NASA Technical Reports Server (NTRS)

Sato, M.

1985-01-01

To explain the apparent chemical incompatibility of the Earth's core and mantle or the disequilibrium process, various core forming mechanisms have been proposed, i.e., rapid disequilibrium sinking of molten iron, an oxidized core or protocore materials, and meteorite contamination of the upper mantle after separation from the core. Adopting concepts used in steady state thermodynamics, a method is devised for evaluating how elements should distribute stable in the Earth's interior for the present gradients of temperature, pressure, and gravitational acceleration. Thermochemical modeling gives useful insights into the nature of chemical evolution of the Earth without overly speculative assumptions. Further work must be done to reconcile siderophile elements, rare gases, and possible light elements in the outer core.

Preparation of Stable Amyloid-β Oligomers Without Perturbative Methods.

PubMed

Kotler, Samuel A; Ramamoorthy, Ayyalusamy

2018-01-01

Soluble amyloid-β (Aβ) oligomers have become a focal point in the study of Alzheimer's disease due to their ability to elicit cytotoxicity. A number of recent studies have concentrated on the structural characterization of soluble Aβ oligomers to gain insight into their mechanism of toxicity. Consequently, providing reproducible protocols for the preparation of such oligomers is of utmost importance. The method presented in this chapter details a protocol for preparing an Aβ oligomer, with a primarily disordered secondary structure, without the need for chemical modification or amino acid substitution. Due to the stability of these disordered Aβ oligomers and the reproducibility with which they form, they are amenable for biophysical and high-resolution structural characterization.

Synthesis of Difluoroaminoxy-, Difluoroamino- or Fluorodiazonium-Containing Materials.

DTIC Science & Technology

1987-01-30

the olefin. The cyclic nitroso compounds underwent thermal decomposition at 165 OC in Pyrex glass to form colorless nitro derivatives. 1,2...absence of glass , (perfluorocvcloaikvl)difluoroamines, e.g., (DNF2 , formed. All of the new compounds are stable at 25 "C and are hvdrolvticallv stable...extended periods in Pyrex glass at 25 OC. Strong vibrational bands in the Raman spectra at 7󈧶 cm r were assigned to v__ H. Carbonvl fluoride as a

Resolving phase stability in the Ti-O binary with first-principles statistical mechanics methods

NASA Astrophysics Data System (ADS)

Gunda, N. S. Harsha; Puchala, Brian; Van der Ven, Anton

2018-03-01

The Ti-O system consists of a multitude of stable and metastable oxides that are used in wide ranging applications. In this work we investigate phase stability in the Ti-O binary from first principles. We perform a systematic search for ground state structures as a function of oxygen concentration by considering oxygen-vacancy and/or titanium-vacancy orderings over four parent crystal structures: (i) hcp Ti, (ii) ω -Ti, (iii) rocksalt, and (iv) hcp oxygen containing interstitial titanium. We explore phase stability at finite temperature using cluster expansion Hamiltonians and Monte Carlo simulations. The calculations predict a high oxygen solubility in hcp Ti and the stability of suboxide phases that undergo order-disorder transitions upon heating. Vacancy ordered rocksalt phases are also predicted at low temperature that disorder to form an extended solid solution at high temperatures. Predicted stable and metastable phase diagrams are qualitatively consistent with experimental observations, however, important discrepancies are revealed between first-principles density functional theory predictions of phase stability and the current understanding of phase stability in this system.

Laser-diode pumped self-mode-locked praseodymium visible lasers with multi-gigahertz repetition rate.

PubMed

Zhang, Yuxia; Yu, Haohai; Zhang, Huaijin; Di Lieto, Alberto; Tonelli, Mauro; Wang, Jiyang

2016-06-15

We demonstrate efficient laser-diode pumped multi-gigahertz (GHz) self-mode-locked praseodymium (Pr³⁺) visible lasers with broadband spectra from green to deep red for the first time to our knowledge. With a Pr³⁺-doped GdLiF₄ crystal, stable self-mode-locked visible pulsed lasers at the wavelengths of 522 nm, 607 nm, 639 nm, and 720 nm have been obtained with the repetition rates of 2.8 GHz, 3.1 GHz, 3.1 GHz, and 3.0 GHz, respectively. The maximum output power was 612 mW with the slope efficiency of 46.9% at 639 nm. The mode-locking mechanism was theoretically analyzed. The stable second-harmonic mode-locking with doubled repetition frequency was also realized based on the Fabry-Perot effect formed in the laser cavity. In addition, we find that the polarization directions were turned with lasing wavelengths. This work may provide a new way for generating efficient ultrafast pulses with high- and changeable-repetition rates in the visible range.

AN MHD AVALANCHE IN A MULTI-THREADED CORONAL LOOP

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hood, A. W.; Cargill, P. J.; Tam, K. V.

For the first time, we demonstrate how an MHD avalanche might occur in a multithreaded coronal loop. Considering 23 non-potential magnetic threads within a loop, we use 3D MHD simulations to show that only one thread needs to be unstable in order to start an avalanche even when the others are below marginal stability. This has significant implications for coronal heating in that it provides for energy dissipation with a trigger mechanism. The instability of the unstable thread follows the evolution determined in many earlier investigations. However, once one stable thread is disrupted, it coalesces with a neighboring thread andmore » this process disrupts other nearby threads. Coalescence with these disrupted threads then occurs leading to the disruption of yet more threads as the avalanche develops. Magnetic energy is released in discrete bursts as the surrounding stable threads are disrupted. The volume integrated heating, as a function of time, shows short spikes suggesting that the temporal form of the heating is more like that of nanoflares than of constant heating.« less

The Researches on I-beam of different web’s shapes

NASA Astrophysics Data System (ADS)

Shuang, Chao; Zhou, Dong Hua

2018-05-01

When the ratio of height to thickness of girder web is relatively high, generally the local stability of web is enhanced by setting up stiffeners. But setting up stiffeners not only increase the use of material, but also increases the welding work. Therefore, the web can be processed into trapezoid, curve, triangles and rectangle to improve its stability. In order to study the mechanical behavior of the web with different shapes and its local stable bearing capacity, the finite element analysis software ANSYS was used to analyze the six I-beam, and the stress characteristics under different web forms were obtained. The results show that the local stability bearing capacity of the I-beam is improved, especially the shape of the trapezoidal web and the shape of the curved web have a significant effect on the local stability of the I-beam. Finally, based on the study of the local stability of the trapezoidal web and the curved web, the influence of their geometrical dimensions on the local stable bearing capacity is also studied.

Characteristics and carbon stable isotopes of fluids in the Southern Kerala granulites and their bearing on the source of CO2

NASA Technical Reports Server (NTRS)

Santosh, M.; Jackson, D. H.; Mattey, D. P.; Harris, N. B. W.

1988-01-01

Carbon dioxide-rich inclusions commonly occur in the banded charnockites and khondalites of southern Kerala as well as in the incipient charnockites formed by desiccation of gneisses along oriented zones. The combined high density fluid inclusion isochores and the range of thermometric estimates from mineral assemblages indicate entrapment pressures in the range of 5.4 to 6.1 Kbar. The CO2 equation of state barometry closely compares with the 5 plus or minus 1 Kbar estimate from mineral phases for the region. The isochores for the high density fluid inclusions in all the three rock types pass through the P-T domain recorded by phase equilibria, implying that carbon dioxide was the dominating ambient fluid species during peak metamorphic conditions. In order to constrain the source of fluids and to evaluate the mechanism of desiccation, researchers undertook detailed investigations of the carbon stable isotope composition of entrapped fluids. Researchers report here the results of preliminary studies in some of the classic localities in southern Kerala namely, Ponmudi, Kottavattom, Manali and Kadakamon.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Jingcheng; Wang, Yu; Li, Bin, E-mail: libin@mail.ustc.edu.cn, E-mail: bwang@ustc.edu.cn

We investigate the modification of electronic properties of single cobalt phthalocyanine (CoPc) molecule by an extra Co atom co-adsorbed on Au (111) surface using scanning tunneling microscopy (STM), joint with density functional theory (DFT) calculations. By manipulating CoPc molecules using the STM tip to contact individually adsorbed Co atom, two types of relatively stable complexes can be formed, denoted as CoPc-Co(I) and CoPc-Co(II). In CoPc-Co(I), the Co atom is at an intramolecular site close to aza-N atom of CoPc, which induces significant modifications of the electronic states of CoPc, such as energy shifts and splitting of nonlocal molecular orbitals. However,more » in CoPc-Co(II) where the Co atom is underneath a benzene lobe of CoPc, it only slightly modifies the electronic states of CoPc, and mainly local characteristics of specific molecular orbitals are affected, even though CoPc-Co(II) is more stable than CoPc-Co(I). Our DFT calculations give consistent results with the experiments, and related analyses based on the molecular orbital theory reveal mechanism behind the experimental observations.« less

Reversible capture and release of Cl 2 and Br 2 with a redox-active metal–organic framework

DOE PAGES

Tulchinsky, Yuri; Hendon, Christopher H.; Lomachenko, Kirill A.; ...

2017-03-28

Extreme toxicity, corrosiveness, and volatility pose serious challenges for the safe storage and transportation of elemental chlorine and bromine, which play critical roles in the chemical industry. Solid materials capable of forming stable nonvolatile compounds upon reaction with elemental halogens may partially mitigate these challenges by allowing safe halogen release on demand. Here we demonstrate that elemental halogens quantitatively oxidize coordinatively unsaturated Co(II) ions in a robust azolate metal-organic framework (MOF) to produce stable and safe-to-handle Co(III) materials featuring terminal Co(III)-halogen bonds. Thermal treatment of the oxidized MOF causes homolytic cleavage of the Co(III)-halogen bonds, reduction to Co(II), and concomitantmore » release of elemental halogens. The reversible chemical storage and thermal release of elemental halogens occur with no significant losses of structural integrity, as the parent cobaltous MOF retains its crystallinity and porosity even after three oxidation/reduction cycles. Finally, these results highlight a material operating via redox mechanism that may find utility in the storage and capture of other noxious and corrosive gases.« less

Computational study of stability of an H-H-type pseudoknot motif.

PubMed

Wang, Jun; Zhao, Yunjie; Wang, Jian; Xiao, Yi

2015-12-01

Motifs in RNA tertiary structures are important to their structural organizations and biological functions. Here we consider an H-H-type pseudoknot (HHpk) motif that consists of two hairpins connected by a junction loop and with kissing interactions between the two hairpin loops. Such a tertiary structural motif is recurrently found in RNA tertiary structures, but is difficult to predict computationally. So it is important to understand the mechanism of its formation and stability. Here we investigate the stability of the HHpk tertiary structure by using an all-atom molecular dynamics simulation. The results indicate that the HHpk tertiary structure is stable. However, it is found that this stability is not due to the helix-helix packing, as is usually expected, but is maintained by the combined action of the kissing hairpin loops and junctions, although the former plays the main role. Stable HHpk motifs may form structural platforms for the molecules to realize their biological functions. These results are useful for understanding the construction principle of RNA tertiary structures and structure prediction.

Penta-graphene: A new carbon allotrope

DOE PAGES

Zhang, Shunhong; Zhou, Jian; Wang, Qian; ...

2015-02-02

A 2D metastable carbon allotrope, penta-graphene, composed entirely of carbon pentagons and resembling the Cairo pentagonal tiling, is proposed in this paper. State-of-the-art theoretical calculations confirm that the new carbon polymorph is not only dynamically and mechanically stable, but also can withstand temperatures as high as 1000 K. Due to its unique atomic configuration, penta-graphene has an unusual negative Poisson’s ratio and ultrahigh ideal strength that can even outperform graphene. Furthermore, unlike graphene that needs to be functionalized for opening a band gap, penta-graphene possesses an intrinsic quasi-direct band gap as large as 3.25 eV, close to that of ZnOmore » and GaN. Equally important, penta-graphene can be exfoliated from T12-carbon. When rolled up, it can form pentagon-based nanotubes which are semiconducting, regardless of their chirality. When stacked in different patterns, stable 3D twin structures of T12-carbon are generated with band gaps even larger than that of T12-carbon. Finally, the versatility of penta-graphene and its derivatives are expected to have broad applications in nanoelectronics and nanomechanics.« less

Stable monolayer honeycomb-like structures of RuX2 (X =S,Se)

NASA Astrophysics Data System (ADS)

Ersan, Fatih; Cahangirov, Seymur; Gökoǧlu, Gökhan; Rubio, Angel; Aktürk, Ethem

2016-10-01

Recent studies show that several metal oxides and dichalcogenides (M X2) , which exist in nature, can be stable in two-dimensional (2D) form and each year several new M X2 structures are explored. The unstable structures in H (hexagonal) or T (octahedral) forms can be stabilized through Peierls distortion. In this paper, we propose new 2D forms of RuS2 and RuSe2 materials. We investigate in detail the stability, electronic, magnetic, optical, and thermodynamic properties of 2D Ru X2 (X =S,Se) structures from first principles. While their H and T structures are unstable, the distorted T structures (T'-Ru X2) are stable and have a nonmagnetic semiconducting ground state. The molecular dynamic simulations also confirm that T'-Ru X2 systems are stable even at 500 K without any structural deformation. T'-RuS2 and T'-RuSe2 have indirect band gaps with 0.745 eV (1.694 eV with HSE) and 0.798 eV (1.675 eV with HSE) gap values, respectively. We also examine their bilayer and trilayer forms and find direct and smaller band gaps. We find that AA stacking is more favorable than the AB configuration. The new 2D materials obtained can be good candidates with striking properties for applications in semiconductor electronic, optoelectronic devices, and sensor technology.

Signatures of primordial black hole dark matter

NASA Astrophysics Data System (ADS)

Belotsky, K. M.; Dmitriev, A. E.; Esipova, E. A.; Gani, V. A.; Grobov, A. V.; Khlopov, M. Yu.; Kirillov, A. A.; Rubin, S. G.; Svadkovsky, I. V.

2014-11-01

The nonbaryonic dark matter of the Universe is assumed to consist of new stable forms of matter. Their stability reflects symmetry of micro-world and mechanisms of its symmetry breaking. In the early Universe heavy metastable particles can dominate, leaving primordial black holes (PBHs) after their decay, as well as the structure of particle symmetry breaking gives rise to cosmological phase transitions, from which massive black holes (BHs) and/or their clusters can originate. PBHs can be formed in such transitions within a narrow interval of masses about 1017g and, avoiding severe observational constraints on PBHs, can be a candidate for the dominant form of dark matter. PBHs in this range of mass can give solution of the problem of reionization in the Universe at the redshift z 5-10. Clusters of massive PBHs can serve as a nonlinear seeds for galaxy formation, while PBHs evaporating in such clusters can provide an interesting interpretation for the observations of point-like gamma-ray sources. Analysis of possible PBH signatures represents a universal probe for super-high energy physics in the early Universe in studies of indirect effects of the dark matter.

Nematic DNA Thermotropic Liquid Crystals with Photoresponsive Mechanical Properties.

PubMed

Zhang, Lei; Maity, Sourav; Liu, Kai; Liu, Qing; Göstl, Robert; Portale, Giuseppe; Roos, Wouter H; Herrmann, Andreas

2017-09-01

Over the last decades, water-based lyotropic liquid crystals of nucleic acids have been extensively investigated because of their important role in biology. Alongside, solvent-free thermotropic liquid crystals (TLCs) from DNA are gaining great interest, owing to their relevance to DNA-inspired optoelectronic applications. Up to now, however, only the smectic phase of DNA TLCs has been reported. The development of new mesophases including nematic, hexagonal, and cubic structures for DNA TLCs remains a significant challenge, which thus limits their technological applications considerably. In this work, a new type of DNA TLC that is formed by electrostatic complexation of anionic oligonucleotides and cationic surfactants containing an azobenzene (AZO) moiety is demonstrated. DNA-AZO complexes form a stable nematic mesophase over a temperature range from -7 to 110 °C and retain double-stranded DNA structure at ambient temperature. Photoisomerization of the AZO moieties from the E- to the Z-form alters the stiffness of the DNA-AZO hybrid materials opening a pathway toward the development of DNA TLCs as stimuli-responsive biomaterials. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Superlubricity behavior with phosphoric acid-water network induced by rubbing.

PubMed

Li, Jinjin; Zhang, Chenhui; Luo, Jianbin

2011-08-02

In present work, a superlubricity phenomenon of phosphoric acid (H(3)PO(4)) was found under ambient conditions. An ultralow friction coefficient of about 0.004 between glass/Si(3)N(4) and sapphire/sapphire tribopairs was obtained under the lubrication of a phosphoric acid aqueous solution (pH 1.5) at high contact pressure (the maximum pressure can reach about 1.65 GPa) after a running-in period of about 600 s. The experimental results indicate that the superlow friction state was very stable for more than 3 h. In such a state, solidlike films formed on the two sliding surfaces, which are hydrates of phosphoric acid with a hydrogen-bonded network according to the Raman spectrum. The superlubricity mechanism is mainly attributed to the hydrogen bond effect that forms a hydrated water layer with low shearing strength, and the dipole-dipole effects that form an interfacial Coulomb repulsion force also make some contributions to low friction. This work may help us to introduce a new approach to superlubricity and may lead to the wide application of superlubricity in future technological and biomedical areas.

Theoretical study on Curcumin: A comparison of calculated spectroscopic properties with NMR, UV vis and IR experimental data

NASA Astrophysics Data System (ADS)

Benassi, Rois; Ferrari, Erika; Lazzari, Sandra; Spagnolo, Ferdinando; Saladini, Monica

2008-12-01

The main target of this study is a high-level computational analysis of Curcumin, employing DFT approach with two different sets of basis functions (B3LYP/6-31G ∗ and B3LYP/6-311G ∗∗). Accurate quantum mechanical studies, both in vacuum and in methanol medium, are carried out with the aim to analyze the conformational equilibria, to find the most stable equilibrium structure and to define the nature of the molecular orbitals, fundamental to explain Curcumin binding characteristic. Our theoretical calculations, performed at B3LYP/6-31G ∗ and B3LYP/6-311G ∗∗ levels both in vacuum and in methanol medium, confirm that the keto-enolic forms are more stable than the di-keto one, whose extremely low population suggests that this structure should not influence Curcumin properties. Keto-enolic form C results the most stable, independently on calculation level and solvent (methanol) effect. HOMO and LUMO molecular orbitals are calculated for all the structures with the two sets of basis with very similar results. MEPs show that the negative charge is localized on the oxygen atoms, which, in the keto-enolic forms, point in the same direction enabling metal coordination. NMR, UV-vis and FT-IR experimental data are employed in the comparison with electronic and conformational properties of Curcumin resulting from theoretical calculations. The two different calculation levels (B3LYP/6-31G ∗ and B3LYP/6-311G ∗∗) give very similar results. Good linear correlations between the experimental 1H and 13C NMR chemical shifts ( δexp), in methanol- d4 (MeOD) and DMSO- d6 (DMSO), and calculated magnetic isotropic shielding tensors ( σcalc) are found ( δexp = a · σcalc + b). A good prediction of UV-vis experimental maximum absorption ( λmax) on the basis of conformer populations is obtained. A linear relation with a good correlation coefficient is observed plotting the FT-IR experimental wavenumbers vs . the calculated ones, allowing to predict FT-IR spectra.

Stable, non-dissipative, and conservative flux-reconstruction schemes in split forms

NASA Astrophysics Data System (ADS)

Abe, Yoshiaki; Morinaka, Issei; Haga, Takanori; Nonomura, Taku; Shibata, Hisaichi; Miyaji, Koji

2018-01-01

A stable, non-dissipative, and conservative flux-reconstruction (FR) scheme is constructed and demonstrated for the compressible Euler and Navier-Stokes equations. A proposed FR framework adopts a split form (also known as the skew-symmetric form) for convective terms. Sufficient conditions to satisfy both the primary conservation (PC) and kinetic energy preservation (KEP) properties are rigorously derived by polynomial-based analysis for a general FR framework. It is found that the split form needs to be expressed in the PC split form or KEP split form to satisfy each property in discrete sense. The PC split form is retrieved from existing general forms (Kennedy and Gruber [33]); in contrast, we have newly introduced the KEP split form as a comprehensive form constituting a KEP scheme in the FR framework. Furthermore, Gauss-Lobatto (GL) solution points and g2 correction function are required to satisfy the KEP property while any correction functions are available for the PC property. The split-form FR framework to satisfy the KEP property, eventually, is similar to the split-form DGSEM-GL method proposed by Gassner [23], but which, in this study, is derived solely by polynomial-based analysis without explicitly using the diagonal-norm SBP property. Based on a series of numerical tests (e.g., Sod shock tube), both the PC and KEP properties have been verified. We have also demonstrated that using a non-dissipative KEP flux, a sixteenth-order (p15) simulation of the viscous Taylor-Green vortex (Re = 1 , 600) is stable and its results are free of unphysical oscillations on relatively coarse mesh (total number of degrees of freedom (DoFs) is 1283).

Civilian gunshot wounds to the atlantoaxial spine: a report of 10 cases treated using a multidisciplinary approach.

PubMed

Syre, Peter; Rodriguez-Cruz, Leonardo; Desai, Rajiv; Greene, Karl A; Hurst, Robert; Schuster, James; Malhotra, Neil R; Marcotte, Paul

2013-12-01

Gunshot wounds to the atlantoaxial spine are uncommon injuries and rarely require treatment, as a bullet traversing this segment often results in a fatal injury. Additionally, these injuries are typically biomechanically stable. The authors report a series of 10 patients with gunshot wounds involving the lateral mass and/or bodies of the atlantoaxial complex. Their care is discussed and conclusions are drawn from these cases to identify the optimal treatment for these injuries. A retrospective review was conducted of patients presenting to the emergency rooms of 3 institutions with gunshot wounds involving the atlantoaxial spine. Mechanism of injury and neurological status were obtained, as was the extent of the osteoligamentous, vascular, and neurological injuries. Nonoperative and operative treatment, complications, and clinical and radiographic outcome were recorded. The data were then analyzed to determine the neurological and biomechanical prognosis of these injuries, the utility of the various diagnostic modalities in the acute management of the injuries, and the nature and effectiveness of the nonoperative and operative treatment modalities. Ten patients with gunshot wounds involving the lateral mass and/or bodies of the atlantoaxial complex were identified. All but 2 patients sustained a vertebral artery injury. Each patient was evaluated using cervical radiographs, CT scans, and vascular imaging, 8 in the form of digital subtraction angiography and 2 with high-resolution CT angiography. Uncomplicated patients were treated conservatively using cervical collar immobilization, local wound care, and antibiotics. One patient was treated using a halo for instability and 1 underwent posterior fusion following a posterolateral decompression for delayed myelopathy. One patient underwent transoral resection of a bullet fragment. One patient underwent embolization for a symptomatic arteriovenous fistula and a second patient underwent a neck exploration and a jugular vein ligation. None of the patients received anticoagulation therapy. The mean follow-up duration was 13 months. All but 2 patients regained their previous functional status and all ultimately attained a mechanically stable spine. These 10 patients represent a rare form of cervical spine penetrating injury. Unilateral gunshot wounds to the atlantoaxial complex are usually stable and the need for acute surgical intervention is rare. Unilateral vertebral artery injury is well tolerated and any information provided by angiography does not alter the acute management of the patient. Vascular complications from gunshot wounds can be managed effectively by endovascular techniques.

Lack of contribution of covalent benzo[a]pyrene-7,8-quinone-DNA adducts in benzo[a]pyrene-induced mouse lung tumorigenesis.

PubMed

Nesnow, Stephen; Nelson, Garret; Padgett, William T; George, Michael H; Moore, Tanya; King, Leon C; Adams, Linda D; Ross, Jeffrey A

2010-07-30

Benzo[a]pyrene (B[a]P) is a potent human and rodent lung carcinogen. This activity has been ascribed in part to the formation of anti-trans-7,8-dihydroxy-7,8-dihydroB[a]P-9,10-epoxide (BPDE)-DNA adducts. Other carcinogenic mechanisms have been proposed: (1) the induction of apurinic sites from radical cation processes, and (2) the metabolic formation of B[a]P-7,8-quinone (BPQ) that can form covalent DNA adducts or reactive oxygen species which can damage DNA. The studies presented here sought to examine the role of stable BPQ-DNA adducts in B[a]P-induced mouse lung tumorigenesis. Male strain A/J mice were injected intraperitoneally once with BPQ or trans-7,8-dihydroxy-7,8-dihydroB[a]P (BP-7,8-diol) at 30, 10, 3, or 0mg/kg. Lungs and livers were harvested after 24h, the DNA extracted and subjected to (32)P-postlabeling analysis. Additional groups of mice were dosed once with BPQ or BP-7,8-diol each at 30 mg/kg and tissues harvested 48 and 72 h later, or with B[a]P (50mg/kg, a tumorigenic dose) and tissues harvested 72 h later. No BPQ or any other DNA adducts were observed in lung or liver tissues 24, 48, or 72 h after the treatment with 30 mg/kg BPQ. BP-7,8-diol gave BPDE-DNA adducts at all time points in both tissues and B[a]P treatment gave BPDE-DNA adducts in the lung. In each case, no BPQ-DNA adducts were detected. Mouse body weights significantly decreased over time after BPQ or BP-7,8-diol treatments suggesting that systemic toxicity was induced by both agents. Model studies with BPQ and N-acetylcysteine suggested that BPQ is rapidly inactivated by sulfhydryl-containing compounds and not available for DNA adduction. We conclude that under these treatment conditions BPQ does not form stable covalent DNA adducts in the lungs or livers of strain A/J mice, suggesting that stable BPQ-covalent adducts are not a part of the complex of mechanisms involved in B[a]P-induced mouse lung tumorigenesis. (c) 2010 Elsevier Ireland Ltd. All rights reserved.

Mineral assemblage transformation of a metakaolin-based waste form after geopolymer encapsulation

DOE PAGES

Williams, Benjamin D.; Neeway, James J.; Snyder, Michelle M. V.; ...

2015-12-23

We can improve mitigation of hazardous and radioactive waste through conversion of existing waste to a more chemically stable and physically robust waste form. One option for waste conversion is the fluidized bed steam reforming (FBSR) process. The resulting FBSR granular material was encapsulated in a geopolymer matrix referred to here as Geo-7. This provides mechanical strength for ease in transport and disposal. But, it is necessary to understand the phase assemblage evolution as a result of geopolymer encapsulation. In this study, we examine the mineral assemblages formed during the synthesis of the multiphase ceramic waste form. The FBSR granularmore » samples were created from waste simulant that was chemically adjusted to resemble Hanford tank waste. Another set of samples was created using Savannah River Site Tank 50 waste simulant in order to mimic a blend of waste collected from 68 Hanford tank. Waste form performance tests were conducted using the product consistency test (PCT), the Toxicity Characteristic Leaching Procedure (TCLP), and the single-pass flow-through (SPFT) test. Finally, X-ray diffraction analyses revealed the structure of a previously unreported NAS phase and indicate that monolith creation may lead to a reduction in crystallinity as compared to the primary FBSR granular product.« less

Reactive molecular dynamics simulations of the mechanical properties of various phosphorene allotropes.

PubMed

Le, Minh-Quy

2018-05-11

Although various phosphorene allotropes have been theoretically predicted to be stable at 0 K, the mechanical properties and fracture mechanism at room temperature remain unclear for many of them. We investigate through reactive molecular dynamics simulations at room temperature the mechanical properties of phosphorene allotropes including: five sheets with hexagonal structures (β-, γ-, δ-, θ-, and α-phosphorene), one sheet with 4-8 membered rings (4-8-P), and two sheets with 5-7 membered rings. High, moderate and slight anisotropies in their mechanical properties are observed, depending on their crystal structures. Their Young's moduli and tensile strength are approximately in the range from 7.3% through 25%, and from 8.6% through 22% of those of graphene, respectively. At the early stage of fracture, eye-shaped cracks are formed by local bond breaking and perpendicular to the tensile direction in hexagonal and 4-8-P sheets. Complete fractures take place with straight cracks in these hexagonal sheets under tension along the zigzag direction and under tension along the square edge direction in the 4-8-P sheet. Crack meandering and branching are observed during the tension of α-, β-, and γ-phosphorene along the armchair direction; and along the square diagonal direction in the 4-8-P sheet. Under uniaxial tension of two phosphorene sheets with 5-7 atom rings, 12 and 10 membered rings are formed by merging two neighbor heptagons, and a heptagon and its neighbor pentagon, respectively. These 12 and 10 membered rings coalesce subsequently, causing the failure of these two sheets. The results are of great importance in the design of these novel phosphorene allotropes.

Reactive molecular dynamics simulations of the mechanical properties of various phosphorene allotropes

NASA Astrophysics Data System (ADS)

Le, Minh-Quy

2018-05-01

Although various phosphorene allotropes have been theoretically predicted to be stable at 0 K, the mechanical properties and fracture mechanism at room temperature remain unclear for many of them. We investigate through reactive molecular dynamics simulations at room temperature the mechanical properties of phosphorene allotropes including: five sheets with hexagonal structures (β-, γ-, δ-, θ-, and α-phosphorene), one sheet with 4-8 membered rings (4-8-P), and two sheets with 5-7 membered rings. High, moderate and slight anisotropies in their mechanical properties are observed, depending on their crystal structures. Their Young’s moduli and tensile strength are approximately in the range from 7.3% through 25%, and from 8.6% through 22% of those of graphene, respectively. At the early stage of fracture, eye-shaped cracks are formed by local bond breaking and perpendicular to the tensile direction in hexagonal and 4-8-P sheets. Complete fractures take place with straight cracks in these hexagonal sheets under tension along the zigzag direction and under tension along the square edge direction in the 4-8-P sheet. Crack meandering and branching are observed during the tension of α-, β-, and γ-phosphorene along the armchair direction; and along the square diagonal direction in the 4-8-P sheet. Under uniaxial tension of two phosphorene sheets with 5-7 atom rings, 12 and 10 membered rings are formed by merging two neighbor heptagons, and a heptagon and its neighbor pentagon, respectively. These 12 and 10 membered rings coalesce subsequently, causing the failure of these two sheets. The results are of great importance in the design of these novel phosphorene allotropes.

Carbonic Anhydrase, Calcification Dynamics and Stable Isotope Vital Effects: Deep Sea Corals and Beyond

NASA Astrophysics Data System (ADS)

Chen, S.; Gagnon, A. C.; Adkins, J. F.

2017-12-01

The stable isotope compositions of biogenic carbonates have been used for paleoceanographic and paleoclimatic reconstructions for decades, and produced some of the most iconic records in the field. However, we still lack a fully mechanistic understanding of the stable isotope proxies, especially the biological overprint on the environmental signals termed "vital effects". A ubiquitous feature of stable isotope vital effects in marine calcifying organisms is a strong correlation between δ18O and δ13C in a range of values that are depleted from equilibrium. Two mechanisms have been proposed to explain this correlation, one based on kinetic isotope effects during CO2(aq)-HCO3- inter-conversion, the other based on equilibrium isotope exchange during pH dependent speciation of the dissolved inorganic carbon pool. Neither mechanism explains all the stable isotope features observed in biogenic carbonates. Here we present a fully kinetic model of biomineralization and its isotope effects using deep sea corals as a test organism. A key component of our model is the consideration of the enzyme carbonic anhydrase in catalyzing the CO2(aq)-HCO3- inter-conversion reactions in the extracellular calcifying fluid (ECF). We find that the amount of carbonic anhydrase not only modulates the carbonate chemistry of the calcifying fluid, but also helps explain the slope of the δ18O-δ13C correlation. With this model, we are not only able to fit deep sea coral data, but also explain the stable isotope vital effects of other calcifying organisms. This fully kinetic model of stable isotope vital effects and the underlying calcification dynamics may also help us better understand mechanisms of other paleoceanographic tracers in biogenic carbonates, including boron isotopes and trace metal proxies.

Mechanochemically Reduced SiO2 by Ti Incorporation as Lithium Storage Materials.

PubMed

Kim, Kyungbae; Moon, Janghyuk; Lee, Jaewoo; Yu, Ji-Sang; Cho, Maenghyo; Cho, Kyeongjae; Park, Min-Sik; Kim, Jae-Hun; Kim, Young-Jun

2015-09-21

This study presents a simple and effective method of reducing amorphous silica (a-SiO2 ) with Ti metal through high-energy mechanical milling for improving its reactivity when used as an anode material in lithium-ion batteries. Through thermodynamic calculations, it is determined that Ti metal can easily take oxygen atoms from a-SiO2 by forming a thermodynamically stable SiO2-x /TiOx composite, meaning that electrochemically inactive a-SiO2 is partially reduced by the addition of Ti metal powder during milling. This mechanically reduced SiO2-x /TiOx composite anode exhibits a greatly improved electrochemical reactivity, with a reversible capacity of more than 700 mAh g(-1) and excellent cycle performance over 100 cycles. Furthermore, an enhancement in the mechanical and thermal stability of the composite during cycling can be mainly attributed to the in situ formation of the SiO2-x /TiOx phase. These findings provide new insight into the rational design of robust, high-capacity, Si-based anode materials, as well as their reaction mechanism. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Precursor polymer compositions comprising polybenzimidazole

DOEpatents

Klaehn, John R.; Peterson, Eric S.; Orme, Christopher J.

2015-07-14

Stable, high performance polymer compositions including polybenzimidazole (PBI) and a melamine-formaldehyde polymer, such as methylated, poly(melamine-co-formaldehyde), for forming structures such as films, fibers and bulky structures. The polymer compositions may be formed by combining polybenzimidazole with the melamine-formaldehyde polymer to form a precursor. The polybenzimidazole may be reacted and/or intertwined with the melamine-formaldehyde polymer to form the polymer composition. For example, a stable, free-standing film having a thickness of, for example, between about 5 .mu.m and about 30 .mu.m may be formed from the polymer composition. Such films may be used as gas separation membranes and may be submerged into water for extended periods without crazing and cracking. The polymer composition may also be used as a coating on substrates, such as metal and ceramics, or may be used for spinning fibers. Precursors for forming such polymer compositions are also disclosed.

Ultra-Stable Oscillators for Probe Radio Science Investigations

NASA Technical Reports Server (NTRS)

Asmar, Sami

2012-01-01

An Ultra-Stable Oscillator (USO) is: A frequency reference, and A clock It is stable, small, and sensitive. It is a science and an art form. It is flown on spacecraft/probes. It]is utilized at ground stations alone or as a cleanup loop. It eliminates lock-up time on uplink for occultation egress & effect of media on uplink signal. It has enabled significant planetary science investigations.

Stable, concentrated solutions of high molecular weight polyaniline and articles therefrom

DOEpatents

Mattes, Benjamin R.; Wang, Hsing-Lin

2000-01-01

Stable, concentrated solutions of high molecular weight polyaniline. In order to process high quality fibers and other articles possessing good mechanical properties, it is known that solution concentrations of the chosen polymer should be in the range from 15-30% (w/w). Moreover, it is desirable to use the highest molecular weight consistent with the solubility properties of the polymer. However, such solutions are inherently unstable, forming gels before processing can be achieved. The present invention describes the addition gel inhibitors (GIs) to the polymer solution, thereby permitting high concentrations (>15% (w/w)) of high molecular weight ((M.sub.w)>120,000, and (M.sub.n)>30,000) emeraldine base (EB) polyaniline to be dissolved. Secondary amines have been used for this purpose in concentrations which are small compared to those which might otherwise be used in a cosolvent role therefor. The resulting solutions are useful for generating excellent fibers, films, coatings and other objects, since the solutions are stable for significant time periods, and the GIs are present in too small concentrations to cause polymer deterioration. It is demonstrated that the GIs found to be useful do not act as cosolvents, and that gelation times of the solutions are directly proportional to the concentration of GI. In particular, there is a preferred concentration of GI, which if exceeded causes structural and electrical conductivity degradation of resulting articles. Heating of the solutions significantly improves solubility.

The structure and stability of orbits in Hoag-like ring systems

NASA Astrophysics Data System (ADS)

Bannikova, Elena Yu

2018-05-01

Ring galaxies are amazing objects exemplified by the famous case of Hoag's Object. Here the mass of the central galaxy may be comparable to the mass of the ring, making it a difficult case to model mechanically. In a previous paper, it was shown that the outer potential of a torus (ring) can be represented with good accuracy by the potential of a massive circle with the same mass. This approach allows us to simplify the problem of the particle motion in the gravitational field of a torus associated with a central mass by replacing the torus with a massive circle. In such a system, there is a circle of unstable equilibrium that we call `Lagrangian circle' (LC). Stable circular orbits exist only in some region limited by the last possible circular orbit related to the disappearance of the extrema of the effective potential. We call this orbit `the outermost stable circular orbit' (OSCO) by analogy with the innermost stable circular orbit (ISCO) in the relativistic case of a black hole. Under these conditions, there is a region between OSCO and LC where the circular motion is not possible due to the competition between the gravitational forces by the central mass and the ring. As a result, a gap in the matter distribution can form in Hoag-like system with massive rings.

Functional bacterial amyloid increases Pseudomonas biofilm hydrophobicity and stiffness

PubMed Central

Zeng, Guanghong; Vad, Brian S.; Dueholm, Morten S.; Christiansen, Gunna; Nilsson, Martin; Tolker-Nielsen, Tim; Nielsen, Per H.; Meyer, Rikke L.; Otzen, Daniel E.

2015-01-01

The success of Pseudomonas species as opportunistic pathogens derives in great part from their ability to form stable biofilms that offer protection against chemical and mechanical attack. The extracellular matrix of biofilms contains numerous biomolecules, and it has recently been discovered that in Pseudomonas one of the components includes β-sheet rich amyloid fibrils (functional amyloid) produced by the fap operon. However, the role of the functional amyloid within the biofilm has not yet been investigated in detail. Here we investigate how the fap-based amyloid produced by Pseudomonas affects biofilm hydrophobicity and mechanical properties. Using atomic force microscopy imaging and force spectroscopy, we show that the amyloid renders individual cells more resistant to drying and alters their interactions with hydrophobic probes. Importantly, amyloid makes Pseudomonas more hydrophobic and increases biofilm stiffness 20-fold. Deletion of any one of the individual members of in the fap operon (except the putative chaperone FapA) abolishes this ability to increase biofilm stiffness and correlates with the loss of amyloid. We conclude that amyloid makes major contributions to biofilm mechanical robustness. PMID:26500638

Functional bacterial amyloid increases Pseudomonas biofilm hydrophobicity and stiffness.

PubMed

Zeng, Guanghong; Vad, Brian S; Dueholm, Morten S; Christiansen, Gunna; Nilsson, Martin; Tolker-Nielsen, Tim; Nielsen, Per H; Meyer, Rikke L; Otzen, Daniel E

2015-01-01

The success of Pseudomonas species as opportunistic pathogens derives in great part from their ability to form stable biofilms that offer protection against chemical and mechanical attack. The extracellular matrix of biofilms contains numerous biomolecules, and it has recently been discovered that in Pseudomonas one of the components includes β-sheet rich amyloid fibrils (functional amyloid) produced by the fap operon. However, the role of the functional amyloid within the biofilm has not yet been investigated in detail. Here we investigate how the fap-based amyloid produced by Pseudomonas affects biofilm hydrophobicity and mechanical properties. Using atomic force microscopy imaging and force spectroscopy, we show that the amyloid renders individual cells more resistant to drying and alters their interactions with hydrophobic probes. Importantly, amyloid makes Pseudomonas more hydrophobic and increases biofilm stiffness 20-fold. Deletion of any one of the individual members of in the fap operon (except the putative chaperone FapA) abolishes this ability to increase biofilm stiffness and correlates with the loss of amyloid. We conclude that amyloid makes major contributions to biofilm mechanical robustness.

Electrochemical Behavior of Quinoxalin-2-one Derivatives at Mercury Electrodes and Its Analytical Use

PubMed Central

Zimpl, Milan; Skopalova, Jana; Jirovsky, David; Bartak, Petr; Navratil, Tomas; Sedonikova, Jana; Kotoucek, Milan

2012-01-01

Derivatives of quinoxalin-2-one are interesting compounds with potential pharmacological activity. From this point of view, understanding of their electrochemical behavior is of great importance. In the present paper, a mechanism of electrochemical reduction of quinoxalin-2-one derivatives at mercury dropping electrode was proposed. Pyrazine ring was found to be the main electroactive center undergoing a pH-dependent two-electron reduction process. The molecule protonization of nitrogen in the position 4 precedes the electron acceptance forming a semiquinone radical intermediate which is relatively stable in acidic solutions. Its further reduction is manifested by separated current signal. A positive mesomeric effect of the nonprotonized amino group in the position 7 of the derivative III accelerates the semiquinone reduction yielding a single current wave. The suggested reaction mechanism was verified by means of direct current polarography, differential pulse, cyclic and elimination voltammetry, and coulometry with subsequent GC/MS analysis. The understanding of the mechanism was applied in developing of analytical method for the determination of the studied compounds. PMID:22666117

Designing superhard metals: The case of low borides

NASA Astrophysics Data System (ADS)

Liang, Yongcheng; Qin, Ping; Jiang, Haitao; Zhang, Lizhen; Zhang, Jing; Tang, Chun

2018-04-01

The search for new superhard materials has usually focused on strong covalent solids. It is, however, a huge challenge to design superhard metals because of the low resistance of metallic bonds against the formation and movement of dislocations. Here, we report a microscopic mechanism of enhancing hardness by identifying highly stable thermodynamic phases and strengthening weak slip planes. Using the well-known transition-metal borides as prototypes, we demonstrate that several low borides possess unexpectedly high hardness whereas high borides exhibit an anomalous hardness reduction. Such an unusual phenomenon originates from the peculiar bonding mechanisms in these compounds. Furthermore, the low borides have close compositions, similar structures, and degenerate formation energies. This enables facile synthesis of a multiphase material that includes a large number of interfaces among different borides, and these interfaces form nanoscale interlocks that strongly suppress the glide dislocations within the metal bilayers, thereby drastically enhancing extrinsic hardness and achieving true superhard metals. Therefore, this study not only elucidates the unique mechanism responsible for the anomalous hardening in this class of borides but also offers a valid alchemy to design novel superhard metals with multiple functionalities.

Phenol-Catalyzed Discharge in the Aprotic Lithium-Oxygen Battery.

PubMed

Gao, Xiangwen; Jovanov, Zarko P; Chen, Yuhui; Johnson, Lee R; Bruce, Peter G

2017-06-01

Discharge in the lithium-O 2 battery is known to occur either by a solution mechanism, which enables high capacity and rates, or a surface mechanism, which passivates the electrode surface and limits performance. The development of strategies to promote solution-phase discharge in stable electrolyte solutions is a central challenge for development of the lithium-O 2 battery. Here we show that the introduction of the protic additive phenol to ethers can promote a solution-phase discharge mechanism. Phenol acts as a phase-transfer catalyst, dissolving the product Li 2 O 2 , avoiding electrode passivation and forming large particles of Li 2 O 2 product-vital requirements for high performance. As a result, we demonstrate capacities of over 9 mAh cm -2 areal , which is a 35-fold increase in capacity compared to without phenol. We show that the critical requirement is the strength of the conjugate base such that an equilibrium exists between protonation of the base and protonation of Li 2 O 2 . © 2017 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.

A QM/MM study of the absorption spectrum of harmane in water solution and interacting with DNA: the crucial role of dynamic effects.

PubMed

Etienne, Thibaud; Very, Thibaut; Perpète, Eric A; Monari, Antonio; Assfeld, Xavier

2013-05-02

We present a time-dependent density functional theory computation of the absorption spectra of one β-carboline system: the harmane molecule in its neutral and cationic forms. The spectra are computed in aqueous solution. The interaction of cationic harmane with DNA is also studied. In particular, the use of hybrid quantum mechanics/molecular mechanics methods is discussed, together with its coupling to a molecular dynamics strategy to take into account dynamic effects of the environment and the vibrational degrees of freedom of the chromophore. Different levels of treatment of the environment are addressed starting from purely mechanical embedding to electrostatic and polarizable embedding. We show that a static description of the spectrum based on equilibrium geometry only is unable to give a correct agreement with experimental results, and dynamic effects need to be taken into account. The presence of two stable noncovalent interaction modes between harmane and DNA is also presented, as well as the associated absorption spectrum of harmane cation.

DNA binding by FOXP3 domain-swapped dimer suggests mechanisms of long-range chromosomal interactions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen, Y.; Chen, C.; Zhang, Z.

2015-01-07

FOXP3 is a lineage-specific transcription factor that is required for regulatory T cell development and function. In this study, we determined the crystal structure of the FOXP3 forkhead domain bound to DNA. The structure reveals that FOXP3 can form a stable domain-swapped dimer to bridge DNA in the absence of cofactors, suggesting that FOXP3 may play a role in long-range gene interactions. To test this hypothesis, we used circular chromosome conformation capture coupled with high throughput sequencing (4C-seq) to analyze FOXP3-dependent genomic contacts around a known FOXP3-bound locus, Ptpn22. Our studies reveal that FOXP3 induces significant changes in the chromatinmore » contacts between the Ptpn22 locus and other Foxp3-regulated genes, reflecting a mechanism by which FOXP3 reorganizes the genome architecture to coordinate the expression of its target genes. Our results suggest that FOXP3 mediates long-range chromatin interactions as part of its mechanisms to regulate specific gene expression in regulatory T cells.« less

Solution processed aluminum paper for flexible electronics.

PubMed

Lee, Hye Moon; Lee, Ha Beom; Jung, Dae Soo; Yun, Jung-Yeul; Ko, Seung Hwan; Park, Seung Bin

2012-09-11

As an alternative to vacuum deposition, preparation of highly conductive papers with aluminum (Al) features is successfully achieved by the solution process consisting of Al precursor ink (AlH(3){O(C(4)H(9))(2)}) and low temperature stamping process performed at 110 °C without any serious hydroxylation and oxidation problems. Al features formed on several kinds of paper substrates (calendar, magazine, and inkjet printing paper substrates) are less than ~60 nm thick, and their electrical conductivities were found to be as good as thermally evaporated Al film or even better (≤2 Ω/□). Strong adhesion of Al features to paper substrates and their excellent flexibility are also experimentally confirmed by TEM observation and mechanical tests, such as tape and bending tests. The solution processed Al features on paper substrates show different electrical and mechanical performance depending on the paper type, and inkjet printing paper is found to be the best substrate with high and stable electrical and mechanical properties. The Al conductive papers produced by the solution process may be applicable in disposal paper electronics.

Molecular dynamics simulations of graphoepitaxy of organic semiconductors, sexithiophene, and pentacene: Molecular-scale mechanisms of organic graphoepitaxy

NASA Astrophysics Data System (ADS)

Ikeda, Susumu

2018-03-01

Molecular dynamics (MD) simulations of the organic semiconductors α-sexithiophene (6T) and pentacene were carried out to clarify the mechanism of organic graphoepitaxy at the molecular level. First, the models of the grooved substrates were made and the surfaces of the inside of the grooves were modified with -OH or -OSi(CH3)3, making the surfaces hydrophilic or hydrophobic. By the MD simulations of 6T, it was found that three stable azimuthal directions exist (0, ˜45, and 90° the angle that the c-axis makes with the groove), being consistent with experimental results. MD simulations of deposition processes of 6T and pentacene were also carried out, and pentacene molecules showed the spontaneous formation of herringbone packing during deposition. Some pentacene molecules stood on the surface and formed a cluster whose a-axis was parallel to the groove. It is expected that a deep understanding of the molecular-scale mechanisms will lead graphoepitaxy to practical applications, improving the performance of organic devices.

Structural analysis and modeling reveals new mechanisms governing ESCRT-III spiral filament assembly

PubMed Central

Shen, Qing-Tao; Schuh, Amber L.; Zheng, Yuqing; Quinney, Kyle; Wang, Lei; Hanna, Michael; Mitchell, Julie C.; Otegui, Marisa S.; Ahlquist, Paul; Cui, Qiang

2014-01-01

The scission of biological membranes is facilitated by a variety of protein complexes that bind and manipulate lipid bilayers. ESCRT-III (endosomal sorting complex required for transport III) filaments mediate membrane scission during the ostensibly disparate processes of multivesicular endosome biogenesis, cytokinesis, and retroviral budding. However, mechanisms by which ESCRT-III subunits assemble into a polymer remain unknown. Using cryogenic electron microscopy (cryo-EM), we found that the full-length ESCRT-III subunit Vps32/CHMP4B spontaneously forms single-stranded spiral filaments. The resolution afforded by two-dimensional cryo-EM combined with molecular dynamics simulations revealed that individual Vps32/CHMP4B monomers within a filament are flexible and able to accommodate a range of bending angles. In contrast, the interface between monomers is stable and refractory to changes in conformation. We additionally found that the carboxyl terminus of Vps32/CHMP4B plays a key role in restricting the lateral association of filaments. Our findings highlight new mechanisms by which ESCRT-III filaments assemble to generate a unique polymer capable of membrane remodeling in multiple cellular contexts. PMID:25202029

Mechanism of the Intramolecular Claisen Condensation Reaction Catalyzed by MenB, a Crotonase Superfamily Member†

PubMed Central

Li, Huei-Jiun; Li, Xiaokai; Liu, Nina; Zhang, Huaning; Truglio, James J.; Mishra, Shambhavi; Kisker, Caroline; Garcia-Diaz, Miguel; Tonge, Peter J.

2014-01-01

MenB, the 1,4-dihydroxy-2-naphthoyl-CoA synthase from the bacterial menaquinone biosynthesis pathway, catalyzes an intramolecular Claisen condensation (Dieckmann reaction) in which the electrophile is an unactivated carboxylic acid. Mechanistic studies on this crotonase family member have been hindered by partial active site disorder in existing MenB X-ray structures. In the current work the 2.0 Å structure of O-succinylbenzoyl-aminoCoA (OSB-NCoA) bound to the MenB from Escherichia coli provides important insight into the catalytic mechanism by revealing the position of all active site residues. This has been accomplished by the use of a stable analogue of the O-succinylbenzoyl-CoA (OSB-CoA) substrate in which the CoA thiol has been replaced by an amine. The resulting OSB-NCoA is stable and the X-ray structure of this molecule bound to MenB reveals the structure of the enzyme-substrate complex poised for carbon-carbon bond formation. The structural data support a mechanism in which two conserved active site Tyr residues, Y97 and Y258, participate directly in the intramolecular transfer of the substrate α-proton to the benzylic carboxylate of the substrate, leading to protonation of the electrophile and formation of the required carbanion. Y97 and Y258 are also ideally positioned to function as the second oxyanion hole required for stabilization of the tetrahedral intermediate formed during carbon-carbon bond formation. In contrast, D163, which is structurally homologous to the acid-base catalyst E144 in crotonase, is not directly involved in carbanion formation and may instead play a structural role by stabilizing the loop that carries Y97. When similar studies were performed on the MenB from Mycobacterium tuberculosis, a twisted hexamer was unexpectedly observed, demonstrating the flexibility of the interfacial loops that are involved in the generation of the novel tertiary and quaternary structures found in the crotonase superfamily. This work reinforces the utility of using a stable substrate analogue as a mechanistic probe in which only one atom has been altered leading to a decrease in α-proton acidity. PMID:21830810

Mechanism of the intramolecular Claisen condensation reaction catalyzed by MenB, a crotonase superfamily member.

PubMed

Li, Huei-Jiun; Li, Xiaokai; Liu, Nina; Zhang, Huaning; Truglio, James J; Mishra, Shambhavi; Kisker, Caroline; Garcia-Diaz, Miguel; Tonge, Peter J

2011-11-08

MenB, the 1,4-dihydroxy-2-naphthoyl-CoA synthase from the bacterial menaquinone biosynthesis pathway, catalyzes an intramolecular Claisen condensation (Dieckmann reaction) in which the electrophile is an unactivated carboxylic acid. Mechanistic studies on this crotonase family member have been hindered by partial active site disorder in existing MenB X-ray structures. In the current work the 2.0 Å structure of O-succinylbenzoyl-aminoCoA (OSB-NCoA) bound to the MenB from Escherichia coli provides important insight into the catalytic mechanism by revealing the position of all active site residues. This has been accomplished by the use of a stable analogue of the O-succinylbenzoyl-CoA (OSB-CoA) substrate in which the CoA thiol has been replaced by an amine. The resulting OSB-NCoA is stable, and the X-ray structure of this molecule bound to MenB reveals the structure of the enzyme-substrate complex poised for carbon-carbon bond formation. The structural data support a mechanism in which two conserved active site Tyr residues, Y97 and Y258, participate directly in the intramolecular transfer of the substrate α-proton to the benzylic carboxylate of the substrate, leading to protonation of the electrophile and formation of the required carbanion. Y97 and Y258 are also ideally positioned to function as the second oxyanion hole required for stabilization of the tetrahedral intermediate formed during carbon-carbon bond formation. In contrast, D163, which is structurally homologous to the acid-base catalyst E144 in crotonase (enoyl-CoA hydratase), is not directly involved in carbanion formation and may instead play a structural role by stabilizing the loop that carries Y97. When similar studies were performed on the MenB from Mycobacterium tuberculosis, a twisted hexamer was unexpectedly observed, demonstrating the flexibility of the interfacial loops that are involved in the generation of the novel tertiary and quaternary structures found in the crotonase superfamily. This work reinforces the utility of using a stable substrate analogue as a mechanistic probe in which only one atom has been altered leading to a decrease in α-proton acidity.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jung, Hyeyoung; Allan, Phoebe K.; Hu, Yan-Yan

Metallic germanium is a promising anode material in secondary lithium-ion batteries (LIBs) due to its high theoretical capacity (1623 mAh/g) and low operating voltage, coupled with the high lithium-ion diffusivity and electronic conductivity of lithiated Ge. Here, the lithiation mechanism of micron-sized Ge anodes has been investigated with X-ray diffraction (XRD), pair distribution function (PDF) analysis, and in-/ex-situ high-resolution Li-7 solid-state nuclear magnetic resonance (NMR), utilizing the structural information and spectroscopic fingerprints obtained by characterizing a series of relevant Li(x)Gey model compounds. In contrast to previous work, which postulated the formation of Li9Ge4 upon initial lithiation, we show that crystallinemore » Ge first reacts to form a mixture of amorphous and crystalline Li7Ge3 (space group P32(1)2). Although Li7Ge3 was proposed to be stable in a recent theoretical study of the Li-Ge phase diagram (Morris, A. J.; Grey, C. P.; Pickard, C. J. Phys. Rev. B: Condens. Matter Mater. Phys. 2014, 90, 054111), it had not been identified in prior experimental studies. Further lithiation results in the transformation of Li7Ge3, via a series of disordered phases with related structural motifs, to form a phase that locally resembles Li7Ge2, a process that involves the gradual breakage of the Ge-Ge bonds in the Ge-Ge dimers (dumbbells) on lithiation. Crystalline Li15Ge4 then grows, with an overlithiated phase, Li15+delta Ge4, being formed at the end of discharge. This study provides comprehensive experimental evidence, by using techniques that probe short-, medium-, and long-range order, for the structural transformations that occur on electrochemical lithiation of Ge; the results are consistent with corresponding theoretical studies regarding stable lithiated LixGey phases.« less

α-Actinin/titin interaction: A dynamic and mechanically stable cluster of bonds in the muscle Z-disk

PubMed Central

Grison, Marco; Merkel, Ulrich; Kostan, Julius; Djinović-Carugo, Kristina; Rief, Matthias

2017-01-01

Stable anchoring of titin within the muscle Z-disk is essential for preserving muscle integrity during passive stretching. One of the main candidates for anchoring titin in the Z-disk is the actin cross-linker α-actinin. The calmodulin-like domain of α-actinin binds to the Z-repeats of titin. However, the mechanical and kinetic properties of this important interaction are still unknown. Here, we use a dual-beam optical tweezers assay to study the mechanics of this interaction at the single-molecule level. A single interaction of α-actinin and titin turns out to be surprisingly weak if force is applied. Depending on the direction of force application, the unbinding forces can more than triple. Our results suggest a model where multiple α-actinin/Z-repeat interactions cooperate to ensure long-term stable titin anchoring while allowing the individual components to exchange dynamically. PMID:28096424