Effets thermoelectrique et thermomagnetique du yttrium barium copper oxide monocristallin

NASA Astrophysics Data System (ADS)

Ghamlouche, Hassan

1998-09-01

Des la decouverte des supraconducteurs a haute temperature critique, les recherches se sont intensifiees afin de comprendre les mecanismes qui sont a l'origine des proprietes de ces materiaux L'etat mixte, tout comme l'etat supraconducteur pur et l'etat normal, a fait l'objet de nombreux travaux de recherche. En particulier, la structure des vortex a l'etat mixte, et leur mouvement sous l'effet d'une force quelconque, etaient et restent le centre de preoccupation. Les effets thermoelectrique (Seebeck) et thermomagnetique (Nernst) sont parmi les differentes mesures qui peuvent donner de l'information sur les etats des vortex a l'etat mixte. L'avantage essentiel de ces deux effets est l'absence d'un courant electrique applique. Ce dernier peut donner des perturbations indesirables durant les mesures. D'autre pari, nous avons utilise la methode CA (Courant Alternatif) pour effectuer nos mesures. Cette methode est caracterisee par une meilleure resolution par rapport a la methode CC (Courant Continu) conventionnelle. Nous avons etudie autant des echantillons macles que des echantillons sans macles. D'abord nous avons teste notre montage a champ magnetique nul. Nous avons alors montre que le pic rapporte par certains dans l'effet Seebeck a la transition supraconductrice ne correspond pas a une realite physique mais a un artefact experimental. On avait associe ce pic aux fluctuations. Par la suite, nous avons mis en evidence et etudie pour la premiere fois avec les effets Seebeck et Nernst le phenomene de la fusion du reseau de vortex grace a des mesures sur les echantillons sans macles. Cette etude s'est faite pour deux concentrations d'oxygene differentes et pour un gradient de temperature parallele, consecutivement, aux deux axes cristallographiques dans le plan ab. Finalement, nous avons etudie l'effet des plans de maclage sur le mouvement des vortex. Ceci a ete realise en appliquant le gradient de temperature selon trois directions differentes (0, 45 et 90°) avec les plans de maclage. Nous avons observe, pour le premier angle un mouvement libre du vortex, pour le second angle une contribution de l'effet Nernst a l'effet Seebeck et pour la troisieme direction un phenomene d'activation. Dans ce dernier cas, les plans de maclage font un obstacle qui s'oppose au mouvement des vortex. De ce qui precede, nous concluons qu'avec la bonne resolution de notre technique nous sommes capables d'observer des phenomenes que la technique CC ne met pas en relief. D'autre part, la variete d'echantillons que nous avons etudies et les phenomenes que nous avons observes valorisent la presente etude.

Destructive Clustering of Metal Nanoparticles in Chalcogenide and Oxide Glassy Matrices.

PubMed

Shpotyuk, M V; Shpotyuk, O I; Cebulski, J; Kozyukhin, S

2016-12-01

The energetic χ-criterion is developed to parameterize difference in the origin of high-order optical non-linearity associated with metallic atoms (Cu, Ag, Au) embedded destructively in oxide- and chalcogenide glasses. Within this approach, it is unambiguously proved that covalent-bonded networks of soft semiconductor chalcogenides exemplified by binary As(Ge)-S(Se) glasses differ essentially from those typical for hard dielectric oxides like vitreous silica by impossibility to accommodate pure agglomerates of metallic nanoparticles. In an excellence according to known experimental data, it is suggested that destructive clustering of nanoparticles is possible in Cu-, Ag-, and Au-ion-implanted dielectric oxide glass media, possessing a strongly negative χ-criterion. Some recent speculations trying to ascribe equally this ability to soft chalcogenide glasses despite an obvious difference in the corresponding bond dissociation energies have been disclosed and criticized as inconclusive.

Effets de la taille finie du milieu non-linéaire sur le bruit quantique spatial généré par un oscillateur paramétrique optique confocal

NASA Astrophysics Data System (ADS)

Lopez, L.; Gatti, A.; Maitre, A.; Treps, N.; Gigan, S.; Fabre, C.

2004-11-01

Nous nous intéressons au comportement spatial des fluctuations quantiques à la sortie d'un oscillateur paramétrique optique dégénéré en modes transverses, sous le seuil. En vue de futures expériences, nous étudions les effets de la diffraction dans le milieu paramétrique sur le bruit quantique spatial. Nous montrons que l'on voit apparaître une aire de cohérence de taille finie pour les effets quantiques transverses.

Cure kinetics, morphologies, and mechanical properties of thermoplastic/MWCNT modified multifunctional glassy epoxies prepared via continuous reaction methods

NASA Astrophysics Data System (ADS)

Cheng, Xiaole

The primary goal of this dissertation is to develop a novel continuous reactor method to prepare partially cured epoxy prepolymers for aerospace prepreg applications with the aim of replacing traditional batch reactors. Compared to batch reactors, the continuous reactor is capable of solubilizing and dispersing a broad range of additives including thermoplastic tougheners, stabilizers, nanoparticles and curatives and advancing epoxy molecular weights and viscosities while reducing energy consumption. In order to prove this concept, polyethersulfone (PES) modified 4, 4'-diaminodiphenylsulfone (44DDS)/tetraglycidyl-4, 4'-diaminodiphenylmethane (TGDDM) epoxy prepolymers were firstly prepared using both continuous reactor and batch reactor methods. Kinetic studies confirmed the chain extension reaction in the continuous reactor is similar to the batch reactor, and the molecular weights and viscosities of prepolymers were readily controlled through reaction kinetics. Atomic force microscopy (AFM) confirmed similar cured network morphologies for formulations prepared from batch and continuous reactors. Additionally tensile strength, tensile modulus and fracture toughness analyses concluded mechanical properties of cured epoxy matrices produced from both reactors were equivalent. Effects of multifunctional epoxy compositions on thermoplastics phase-separated morphologies were systematically studied using a combination of AFM with nanomechanical mapping, spectroscopic and calorimetric techniques to provide new insights to tailor cured reaction induced phase separation (CRIPS) in multifunctional epoxy blend networks. Furthermore, how resultant crosslinked glassy polymer network and phase-separated morphologies correlated with mechanical properties are discussed in detail. Multiwall carbon nanotube (MWCNT)/TGDDM epoxy prepolymers were further prepared by combining the successful strategies for advancing epoxy chemistries and dispersing nanotubes using the continuous reactor. Optical microscopy (OM) and scanning electron microscopy (SEM) were used to characterize the MWCNT dispersion states and stabilization in epoxy prepolymer matrix after continuous process and during curing cycles. Additionally, electrical conductivities and mechanical properties of final cured MWCNT/TGDDM composites were measured and discussed in view of their corresponding MWCNT dispersion states. Ternary blends of MWCNT reinforced thermoplastic/epoxy prepolymers were prepared by the continuous reactor. Influence of MWCNT on the CRIPS mechanism and the cured morphologies were systematically investigated using SEM and rheological analysis. Incorporation of MWCNT in thermoplastic/epoxy matrices can lead to a morphological transformation from phase inverted, to co-continuous, and to droplet dispersed morphology. In additional, dynamic mechanical analysis revealed the heterogeneity of MWCNT dispersion in thermoplastic/thermosets systems.

Bush v. Bin Laden: Effect of State Emotion on Perceived Threat is Mediated by Emotion Towards the Threat Agent (Bush vs. Ben Laden: l’Effet de l’Emotion etat sur la Menace Percue est Mediatisees par l’Emotion vis-a-vis de l’Agent Menacant)

DTIC Science & Technology

2009-07-01

auteurs discu- tent des implications des resultats pour les theories qui postulent un effet de I’emotion sur la perception du risque et pour com...effect of global negative emotion on perceived threat . The authors discuss implications of the findings for theories that postulate an effect of... auteurs ont mene une etude perception j emotion j experimentale afin d’examiner les effets d’etats emotionnels Specifi- ques (peur et colere) et globaux

Prediction de l’Eclatement Tourbillonnaire sur les Ailes Delta d’Avions Militaires (CFD Prediction of Vortex Breakdown on Delta Wings for Military Aircraft)

DTIC Science & Technology

2003-03-01

moins développé que le tourbillon expérimental. En moyenne, par effet de compensation entre la région de bord d’attaque et la région proche de ...que les effets d’anisotropie de la turbulence. Un premier élément de réponse peut être obtenu en utilisant un modèle de turbulence un plus élaboré, tel...que l’EARSM (Explicit Algebraïc Reynolds Stress Model) qui prend en compte les effets de rotation et d’anisotropie [Ref 6]. Nous verrons au paragraphe

Le Laser A Argon Ionise : Applications Therapeutiques

NASA Astrophysics Data System (ADS)

Brunetaud, J. M.; Mosquet, L.; Mordon, S.; Rotteleur, G.

1984-03-01

Le laser a argon ionise est un laser a emission continue, reglee en general en multiraies de 487 a 544 nm. Le rayonnement de ce laser est bien absorbe par les tissus vivants, avec une action preferentielle au niveau des pigments rouges (hemoglobine, myoglobine) et noirs (melanine). Le laser a argon est princi-palement utilise en therapeutique pour ses effets thermiques : en fonction du choix des parametres (puissance optique, surface exposee, temps d'exposition) on peut obtenir une coagulation (temperature optimale au niveau des tissus 60° - 80°) ou une volatisation (temperature superieure a 100°). Si la zone volatilisee est tres etroite (inferieure a 0,5 mm) on obtient un effet de coupe. Par rapport aux deux autres lasers egalement utilises pour leurs effets thermiques (CO2 et Nd. YAG) l'argon a des effets intermediaires : la coagulation sera plus superficielle qu'avec le Nd. YAG et la volatisation plus profonde qu'avec le CO2. Lors de la coupe, la necrose sur les berges sera egalement plus importante qu'avec le CO2.

Effets Josephson generalises entre antiferroaimants et entre supraconducteurs antiferromagnetiques

NASA Astrophysics Data System (ADS)

Chasse, Dominique

L'effet Josephson est generalement presente comme le resultat de l'effet tunnel coherent de paires de Cooper a travers une jonction tunnel entre deux supraconducteurs, mais il est possible de l'expliquer dans un contexte plus general. Par exemple, Esposito & al. ont recemment demontre que l'effet Josephson DC peut etre decrit a l'aide du boson pseudo-Goldstone de deux systemes couples brisant chacun la symetrie abelienne U(1). Puisque cette description se generalise de facon naturelle a des brisures de symetries continues non-abeliennes, l'equivalent de l'effet Josephson devrait donc exister pour des types d'ordre a longue portee differents de la supraconductivite. Le cas de deux ferroaimants itinerants (brisure de symetrie 0(3)) couples a travers une jonction tunnel a deja ete traite dans la litterature Afin de mettre en evidence la generalite du phenomene et dans le but de faire des predictions a partir d'un modele realiste, nous etudions le cas d'une jonction tunnel entre deux antiferroaimants itinerants. En adoptant une approche Similaire a celle d'Ambegaokar & Baratoff pour une jonction Josephson, nous trouvons un courant d'aimantation alternee a travers la jonction qui est proportionnel a sG x sD ou fG et sD sont les vecteurs de Neel de part et d'autre de la jonction. La fonction sinus caracteristique du courant Josephson standard est donc remplacee.ici par un produit vectoriel. Nous montrons que, d'un point de vue microscopique, ce phenomene resulte de l'effet tunnel coherent de paires particule-trou de spin 1 et de vecteur d'onde net egal au vecteur d'onde antiferromagnetique Q. Nous trouvons egalement la dependance en temperature de l'analogue du courant critique. En presence d'un champ magnetique externe, nous obtenons l'analogue de l'effet Josephson AC et la description complete que nous en donnons s'applique aussi au cas d'une jonction tunnel entre ferroaimants (dans ce dernier cas, les traitements anterieurs de cet effet AC s'averent incomplets). Nous considerons ensuite le cas d'une jonction tunnel entre deux materiaux au sein desquels l'antiferromagnetisme itinerant et la supraconductivite de type d coexistent de facon homogene. Nous obtenons a nouveau un courant d'aimantation alternee proportionnel a sG x sD, mais l'amplitude de l'analogue du courant critique est modulee par l'energie Josephson de la jonction E oc cos Acp, ou Acp est la difference de phase entre les deux parametres d'ordre supraconducteurs. Symetriquement, le courant Josephson supraconducteur est proportionnel a sin Acp, mais le courant critique est module par l'energie de couplage entre les moments magnetiques alternes ES cx SG· SD.

Effet de la teneur en carbone sur la resistance du CA6NM a la propagation des fissures de fatigue

NASA Astrophysics Data System (ADS)

Akhiate, Aziz

L'amelioration des performances des roues de turbines hydrauliques a fait l'objet de plusieurs etudes. Dans ce memoire, on s'est interesse a l'effet de la teneur en carbone du materiau de base de type CA6NM des aubes de turbines sur la microstructure et les proprietes mecaniques en general et en particulier sur le comportement en fatigue propagation. De maniere a bien atteindre cet objectif, on a choisi trois differentes nuances d'acier a faible 0.018% C, moyenne 0.033% C et elevee 0.067% C teneurs en carbone. Le 0.018% C et 0.067% C ont ete fabriques par le meme facturier et ils ont subi des traitements thermiques differents. De meme, le 0.033% C a subi des traitements thermiques differents des deux autres apres avoir ete coule par un autre fabricant. Afin d'effacer l'historique des traitements thermiques prealablement effectues et d'avoir la meme taille de grains parents austenitiques (GPA), on a austenitise les trois nuances d'acier a la meme temperature 1040°C, a differentes periodes suivant la teneur en carbone. Apres avoir homogeneise la GPA, on a entame le revenu. Le carbone a une influence sur la microstructure revenue notamment la quantite d'austenite de reversion ainsi que sur sa stabilite thermique et mecanique. Pour mettre en evidence l'effet de la teneur en carbone, on a trouve raisonnable d'isoler les effets relies a la temperature de revenu, en particulier la formation d'austenite de reversion. En effet, on a choisi deux temperatures de revenu. La premiere temperature est a 550°C pendant 2h imposee aux trois materiaux afin d'avoir une microstructure sans austenite de reversion. La deuxieme temperature choisie est a 610°C pour avoir un maximum et une identique quantite d'austenite de reversion sans presence de martensite fraiche. A la lumiere de ces deux microstructures, nous pouvons etablir une relation entre les proprietes mecaniques du CA6NM et la teneur en carbone, ainsi qu'entre les effets de la presence ou non d'austenite de reversion sur les proprietes mecaniques. Les resultats montrent que l'effet de la teneur en carbone est plus significatif sur les proprietes mecaniques monotones de traction et de resilience des alliages sans austenite de reversion. En effet, la limite d'elasticite, la resistance a la traction et la durete augmentent avec la teneur en carbone par contre l'allongement diminue. D'autre part, l'augmentation de la temperature et de la duree de revenu diminuent leur durete.

Thermal insulation for high temperature microwave sintering operations and method thereof

DOEpatents

Holcombe, Cressie E.; Dykes, Norman L.; Morrow, Marvin S.

1995-01-01

Superior microwave transparent thermal insulations for high temperature microwave sintering operations were prepared. One embodiment of the thermal insulation comprises granules of boron nitride coated with a very thin layer of glassy carbon made by preparing a glassy carbon precursor and blending it with boron nitride powder to form a mixture. The blended mixture is granulated to form a grit which is dried and heated to form the granules of boron nitride coated with a glassy carbon. Alternatively, grains of glassy carbon are coated with boron nitride by blending a mixture of a slurry comprising boron nitride, boric acid binder, and methyl alcohol with glassy carbon grains to form a blended mixture. The blended mixture is dried to form grains of glassy carbon coated with boron nitride. In addition, a physical mixture of boron nitride powder and glassy carbon grains has also been shown to be an excellent thermal insulation material for microwave processing and sintering.

Method of preparing thermal insulation for high temperature microwave sintering operations

DOEpatents

Holcombe, Cressie E.; Dykes, Norman L.; Morrow, Marvin S.

1996-01-01

Superior microwave transparent thermal insulations for high temperature microwave sintering operations were prepared. One embodiment of the thermal insulation comprises granules of boron nitride coated with a very thin layer of glassy carbon made by preparing a glassy carbon precursor and blending it with boron nitride powder to form a mixture. The blended mixture is granulated to form a grit which is dried and heated to form the granules of boron nitride coated with a glassy carbon. Alternatively, grains of glassy carbon are coated with boron nitride by blending a mixture of a slurry comprising boron nitride, boric acid binder, and methyl alcohol with glassy carbon grains to form a blended mixture. The blended mixture is dried to form grains of glassy carbon coated with boron nitride. In addition, a physical mixture of boron nitride powder and glassy carbon grains has also been shown to be an excellent thermal insulation material for microwave processing and sintering.

Crystallization of the glassy grain boundary phase in silicon nitride ceramics

NASA Technical Reports Server (NTRS)

Drummond, Charles H., III

1991-01-01

The role was studied of the intergranular glassy phase in silicon nitride as-processed with yttria as a sintering aid. The microstructure, crystallization, and viscosity of the glassy phase were areas studied. Crystallization of the intergranular glassy phase to more refractory crystalline phases should improve the high temperature mechanical properties of the silicon nitride. The addition of a nucleating agent will increase the rate of crystallization. The measurement of the viscosity of the glassy phase will permit the estimation of the high temperature deformation of the silicon nitride.

Method of preparing thermal insulation for high temperature microwave sintering operations

DOEpatents

Holcombe, C.E.; Dykes, N.L.; Morrow, M.S.

1996-07-16

Superior microwave transparent thermal insulations for high temperature microwave sintering operations were prepared. One embodiment of the thermal insulation comprises granules of boron nitride coated with a very thin layer of glassy carbon made by preparing a glassy carbon precursor and blending it with boron nitride powder to form a mixture. The blended mixture is granulated to form a grit which is dried and heated to form the granules of boron nitride coated with a glassy carbon. Alternatively, grains of glassy carbon are coated with boron nitride by blending a mixture of a slurry comprising boron nitride, boric acid binder, and methyl alcohol with glassy carbon grains to form a blended mixture. The blended mixture is dried to form grains of glassy carbon coated with boron nitride. In addition, a physical mixture of boron nitride powder and glassy carbon grains has also been shown to be an excellent thermal insulation material for microwave processing and sintering. 1 fig.

Thermal insulation for high temperature microwave sintering operations and method thereof

DOEpatents

Holcombe, C.E.; Dykes, N.L.; Morrow, M.S.

1995-09-12

Superior microwave transparent thermal insulations for high temperature microwave sintering operations were prepared. One embodiment of the thermal insulation comprises granules of boron nitride coated with a very thin layer of glassy carbon made by preparing a glassy carbon precursor and blending it with boron nitride powder to form a mixture. The blended mixture is granulated to form a grit which is dried and heated to form the granules of boron nitride coated with a glassy carbon. Alternatively, grains of glassy carbon are coated with boron nitride by blending a mixture of a slurry comprising boron nitride, boric acid binder, and methyl alcohol with glassy carbon grains to form a blended mixture. The blended mixture is dried to form grains of glassy carbon coated with boron nitride. In addition, a physical mixture of boron nitride powder and glassy carbon grains has also been shown to be an excellent thermal insulation material for microwave processing and sintering. 1 fig.

Prévalence et caractéristiques des effets indésirables des antihypertenseurs chez les patients suivis en ambulatoire au Centre Hospitalier Universitaire Yalgado Ouédraogo

PubMed Central

Millogo, Georges Rosario Christian; Zongo, Ragomzingba Frank Edgard; Benao, Anita; Youl, Estelle Noëla Hoho; Bassoleth, Blaise Alexandre Bazona; Ouédraogo, Moussa; Zabsonré, Patrice; Guissou, Innocent Pierre

2018-01-01

La prise en charge médicamenteuse de l'hypertension artérielle (HTA) entraine des effets indésirables qui peuvent être gênants et ainsi influencer l'observance du patient. Nous avons étudié ces effets indésirables dans le service de cardiologie du Centre hospitalier universitaire Yalgado Ouédraogo afin de déterminer leurs fréquences et leurs caractéristiques. Il s'agissait d'une étude transversale de juillet à septembre 2015 chez les patients suivis en ambulatoire pour HTA. Les données ont été obtenues à partir de l'interrogatoire, des carnets de suivi des patients et des fiches de consultations. Au total 278 patients ont été inclus. La population d'étude incluait 69,1% de femmes. L'âge moyen était de 52,2 ans avec des extrêmes de 23 et 86 ans. Quatre vingt et sept virgule huit pourcent (87,8%) vivaient en milieu urbain. Le tabagisme, la dyslipidémie et les antécédents familiaux d'HTA représentaient respectivement 9%, 35,6% et 57,2%. Au plan thérapeutique, 43,2% étaient sous monothérapie, 35,6% sous bithérapie à l'initiation du traitement. Les inhibiteurs calciques (59,7%) étaient la classe thérapeutique la plus utilisée. La prévalence globale des effets indésirables était de 60,1%. Les inhibiteurs calciques étaient impliqués dans 53,6% suivis des diurétiques (48,6%) dans la survenue de l'effet indésirable. La prévalence spécifique par molécule était 28,1% pour l'amlodipine et 24,5% pour l'hydrochlorothiazide. La diurèse excessive (13,7%), la toux (12,9%) et les vertiges (11,5%) étaient les effets indésirables les plus fréquemment évoqués par les patients. Le système nerveux central et périphérique et le système ostéo-musculaire étaient les systèmes les plus atteints. Les effets indésirables sont un déterminant majeur de l'adhésion aux traitements antihypertenseur, car leur impact sur la vie quotidienne des patients peut s'avérer significatif. PMID:29875965

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

Tan, Guoqiang; Wu, Feng; Zhan, Chun

The development of safe, stable, and long-life Li-ion batteries is being intensively pursued to enable the electrification of transportation and intelligent grid applications. Here, we report a new solid-state Li-ion battery technology, using a solid nanocomposite electrolyte composed of porous silica matrices with in situ immobilizing Li+ conducting ionic liquid, anode material of MCMB, and cathode material of LiCoO 2, LiNi 1/3Co 1/3Mn 1/3O 2, or LiFePO 4. An injection printing method is used for the electrode/electrolyte preparation. Solid nanocomposite electrolytes exhibit superior performance to the conventional organic electrolytes with regard to safety and cycle-life. They also have a transparentmore » glassy structure with high ionic conductivity and good mechanical strength. Solid-state full cells tested with the various cathodes exhibited high specific capacities, long cycling stability, and excellent high temperature performance. This solid-state battery technology will provide new avenues for the rational engineering of advanced Li-ion batteries and other electrochemical devices.« less

Effect of sodium chloride on the glass transition of condensed starch systems.

PubMed

Chuang, Lillian; Panyoyai, Naksit; Shanks, Robert; Kasapis, Stefan

2015-10-01

The present investigation deals with the structural properties of condensed potato starch-sodium chloride systems undergoing a thermally induced glass transition. Sample preparation included hot pressing at 120°C for 7 min to produce extensive starch gelatinisation. Materials covered a range of moisture contents from 3.6% to 18.8%, which corresponded to relative humidity values of 11% and 75%. Salt addition was up to 6.0% in formulations. Instrumental work was carried out with dynamic mechanical analysis in tension, modulated differential scanning calorimetry, Fourier transform infrared spectroscopy, scanning electron microscopy and wide angle X-ray diffraction. Experimental conditions ensured the development of amorphous matrices that exhibited thermally reversible glassy consistency. Both moisture content and addition of sodium chloride affected the mechanical strength and glass transition temperature of polymeric systems. Sodium ions interact with chemical moieties of the polysaccharide chain to alter considerably structural properties, as compared to the starch-water matrix. Copyright © 2015. Published by Elsevier Ltd.

Detailed characterization of mechanical properties and molecular mobility within dry seed glasses: relevance to the physiology of dry biological systems.

PubMed

Ballesteros, Daniel; Walters, Christina

2011-11-01

Slow movement of molecules in glassy matrices controls the kinetics of chemical and physical reactions in dry seeds. Variation in physiological activity among seeds suggests that there are differences in mobility among seed glasses. Testing this hypothesis is difficult because few tools are available to measure molecular mobility within dry seeds. Here, motional properties within dry pea cotyledons were assessed using dynamic mechanical analysis. The technique detected several molecular relaxations between -80 and +80°C and gave a more detailed description of water content-temperature effects on molecular motion than previously understood from studies of glass formation in seeds at glass transition (Tg). Diffusive movement is delimited by the α relaxation, which appears to be analogous to Tg. β and γ relaxations were also detected at temperatures lower than α relaxations, clearly demonstrating intramolecular motion within the glassy matrix of the pea cotyledon. Glass transitions, or the mechanical counterpart α relaxation, appear to be less relevant to seed aging during dry storage than previously thought. On the other hand, β relaxation occurs at temperature and moisture conditions typically used for seed storage and has established importance for physical aging of synthetic polymer glasses. Our data show that the nature and extent of molecular motion varies considerably with moisture and temperature, and that the hydrated conditions used for accelerated aging experiments and ultra-dry conditions sometimes recommended for seed storage give greater molecular mobility than more standard seed storage practices. We believe characterization of molecular mobility is critical for evaluating how dry seeds respond to the environment and persist through time. Published 2011. This article is a US Government work and is in the public domain in the USA.

Diffusivity measurements of volatile organics in levitated viscous aerosol particles

NASA Astrophysics Data System (ADS)

Bastelberger, Sandra; Krieger, Ulrich K.; Luo, Beiping; Peter, Thomas

2017-07-01

Field measurements indicating that atmospheric secondary organic aerosol (SOA) particles can be present in a highly viscous, glassy state have spurred numerous studies addressing low diffusivities of water in glassy aerosols. The focus of these studies is on kinetic limitations of hygroscopic growth and the plasticizing effect of water. In contrast, much less is known about diffusion limitations of organic molecules and oxidants in viscous matrices. These may affect atmospheric chemistry and gas-particle partitioning of complex mixtures with constituents of different volatility. In this study, we quantify the diffusivity of a volatile organic in a viscous matrix. Evaporation of single particles generated from an aqueous solution of sucrose and small amounts of volatile tetraethylene glycol (PEG-4) is investigated in an electrodynamic balance at controlled relative humidity (RH) and temperature. The evaporative loss of PEG-4 as determined by Mie resonance spectroscopy is used in conjunction with a radially resolved diffusion model to retrieve translational diffusion coefficients of PEG-4. Comparison of the experimentally derived diffusivities with viscosity estimates for the ternary system reveals a breakdown of the Stokes-Einstein relationship, which has often been invoked to infer diffusivity from viscosity. The evaporation of PEG-4 shows pronounced RH and temperature dependencies and is severely depressed for RH ≲ 30 %, corresponding to diffusivities < 10-14 cm2 s-1 at temperatures < 15 °C. The temperature dependence is strong, suggesting a diffusion activation energy of about 300 kJ mol-1. We conclude that atmospheric volatile organic compounds can be subject to severe diffusion limitations in viscous organic aerosol particles. This may enable an important long-range transport mechanism for organic material, including pollutant molecules such as polycyclic aromatic hydrocarbons (PAHs).

Development of a Molecularly Imprinted Polymer-Based Sensor for the Electrochemical Determination of Triacetone Triperoxide (TATP)

PubMed Central

Mamo, Samuel Kassahun; Gonzalez-Rodriguez, Jose

2014-01-01

The explosive triacetone triperoxide (TATP), which can be prepared from commercially readily available reagents following an easy synthetic procedure, is one of the most common components of improvised explosive devices (IEDs). Molecularly-imprinted polymer (MIP) electrochemical sensors have proved useful for the determination of different compounds in different matrices with the required sensitivity and selectivity. In this work, a highly sensitive and selective molecularly imprinted polymer with electrochemical capabilities for the determination of TATP has been developed. The molecular imprinting has been performed via electropolymerisation onto a glassy carbon electrode surface by cyclic voltammetry from a solution of pyrrole functional monomer, TATP template and LiClO4. Differential Pulse Voltammetry of TATP, with LiClO4 as supporting electrolyte, was performed in a potential range of −2.0 V to +1.0 V (vs. Ag/AgCl). Three-factor two-level factorial design was used to optimise the monomer concentration at 0.1 mol·L−1, template concentration at 100 mmol·L−1 and the number of cyclic voltammetry scan cycles to 10. The molecularly imprinted polymer-modified glassy carbon electrode demonstrated good performance at low concentrations for a linear range of 82–44,300 μg·L−1 and a correlation coefficient of r2 = 0.996. The limits of detection (LoD) and quantification (LoQ) achieved were 26.9 μg·L−1 and 81.6 μg·L−1, respectively. The sensor demonstrated very good repeatability with precision values (n = 6, expressed as %RSD) of 1.098% and 0.55% for 1108 and 2216 μg·L−1, respectively. It also proved selective for TATP in the presence of other explosive substances such as PETN, RDX, HMX, and TNT. PMID:25490589

Observation de l'interaction entre atome et surface en cellule de vapeur submicrométrique

NASA Astrophysics Data System (ADS)

Dutier, G.; Saltiel, S.; Bloch, D.; Ducloy, M.; Papoyan, A.; Sarkisyan, D.

2002-06-01

Sur une cellule de vapeur d'épaisseur submicrométrique ( 300 nm), les spectres d'absorption linéaire se révèlent très peu sensibles à l'effet Doppler (les effets transitoires favorisent fortement les atomes lents), et font apparaître les effets de l'interaction van der Waals à longue portée entre atome-surface. L'étude, entreprise d'abord sur la raie de résonance D1 de Cs, est poursuivie sur une transition à deux photons vers le niveau Cs 6(D{3/2}) résonnant avec la surface de YAG de la fenêtre. Elle ouvre diverses perspectives, notamment la détection d'états liés par un puits de potentiel induit par la surface.

Shock-wave studies of anomalous compressibility of glassy carbon

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

Molodets, A. M., E-mail: molodets@icp.ac.ru; Golyshev, A. A.; Savinykh, A. S.

2016-02-15

The physico-mechanical properties of amorphous glassy carbon are investigated under shock compression up to 10 GPa. Experiments are carried out on the continuous recording of the mass velocity of compression pulses propagating in glassy carbon samples with initial densities of 1.502(5) g/cm{sup 3} and 1.55(2) g/cm{sup 3}. It is shown that, in both cases, a compression wave in glassy carbon contains a leading precursor with amplitude of 0.135(5) GPa. It is established that, in the range of pressures up to 2 GPa, a shock discontinuity in glassy carbon is transformed into a broadened compression wave, and shock waves are formedmore » in the release wave, which generally means the anomalous compressibility of the material in both the compression and release waves. It is shown that, at pressure higher than 3 GPa, anomalous behavior turns into normal behavior, accompanied by the formation of a shock compression wave. In the investigated area of pressure, possible structural changes in glassy carbon under shock compression have a reversible character. A physico-mechanical model of glassy carbon is proposed that involves the equation of state and a constitutive relation for Poisson’s ratio and allows the numerical simulation of physico-mechanical and thermophysical properties of glassy carbon of different densities in the region of its anomalous compressibility.« less

Mesure Objective De L'attenuation et De L'effet D'occlusion Des Protecteurs Auditifs a Partir Des Potentiels Evoques Stationnaires et Multiples =

NASA Astrophysics Data System (ADS)

Valentin, Olivier

Selon l'Organisation mondiale de la sante, le nombre de travailleurs exposes quotidiennement a des niveaux de bruit prejudiciables a leur audition est passe de 120 millions en 1995 a 250 millions en 2004. Meme si la reduction du bruit a la source devrait etre toujours privilegiee, la solution largement utilisee pour lutter contre le bruit au travail reste la protection auditive individuelle. Malheureusement, le port des protecteurs auditifs n'est pas toujours respecte par les travailleurs car il est difficile de fournir un protecteur auditif dont le niveau d'attenuation effective est approprie a l'environnement de travail d'un individu. D'autre part, l'occlusion du canal auditif induit une modification de la perception de la parole, ce qui cree un inconfort incitant les travailleurs a retirer leurs protecteurs. Ces deux problemes existent parce que les methodes actuelles de mesure de l'effet d'occlusion et de l'attenuation sont limitees. Les mesures objectives basees sur des mesures microphoniques intra-auriculaires ne tiennent pas compte de la transmission directe du son a la cochlee par conduction osseuse. Les mesures subjectives au seuil de l'audition sont biaisees a cause de l'effet de masquage aux basses frequences induit par le bruit physiologique. L'objectif principal de ce travail de these de doctorat est d'ameliorer la mesure de l'attenuation et de l'effet d'occlusion des protecteurs auditifs intra-auriculaires. L'approche generale consiste a : (i) verifier s'il est possible de mesurer l'attenuation des protecteurs auditifs grâce au recueil des potentiels evoques stationnaires et multiples (PEASM) avec et sans protecteur auditif (protocole 1), (ii) adapter cette methodologie pour mesurer l'effet d'occlusion induit par le port de protecteur auditifs intra-auriculaires (protocole 2), et (iii) valider chaque protocole par l'intermediaire de mesures realisees sur sujets humains. Les resultats du protocole 1 demontrent que les PEASM peuvent etre utilises pour mesurer objectivement l'attenuation des protecteurs auditifs : les resultats obtenus a 500 Hz et 1 kHz demontrent que l'attenuation mesuree a partir des PEASM est relativement equivalente a l'attenuation calculee par la methode REAT, ce qui est en accord avec ce qui etait attendu puisque l'effet de masquage induit par le bruit physiologique aux basses frequences est relativement negligeable a ces frequences. Les resultats du protocole 2 demontrent que les PEASM peuvent etre egalement utilises pour mesurer objectivement l'effet d'occlusion induit par le port de protecteurs auditifs : l'effet d'occlusion mesure a partir des PEASM a 500 Hz est plus eleve que celui calcule par l'intermediaire de la methode subjective au seuil de l'audition, ce qui est en accord avec ce qui etait attendu puisqu'en dessous d'1 kHz, l'effet de masquage induit par le bruit physiologique aux basses frequences est source de biais pour les resultats obtenus par la methode subjective car il y a surestimation des seuils de l'audition en basse frequence lors du port de protecteurs auditifs. Toutefois, les resultats obtenus a 250 Hz sont en contradiction avec les resultats attendus. D'un point de vue scientifique, ce travail de these a permis de realiser deux nouvelles methodes innovantes pour mesurer objectivement l'attenuation et l'effet d'occlusion des protecteurs auditifs intra-auriculaires par electroencephalographie. D'un point de vue sante et securite au travail, les avancees presentees dans cette these pourraient aider a concevoir des protecteurs auditifs plus performants. En effet, si ces deux nouvelles methodes objectives etaient normalisees pour caracteriser les protecteurs auditifs intra-auriculaires, elles pourraient permettre : (i) de mieux apprehender l'efficacite reelle de la protection auditive et (ii) de fournir une mesure de l'inconfort induit par l'occlusion du canal auditif lors du port de protecteurs. Fournir un protecteur auditif dont l'efficacite reelle est adaptee a l'environnement de travail et dont le confort est optimise permettrait, sur le long terme, d'ameliorer les conditions des travailleurs en minimisant le risque lie a la degradation de leur appareil auditif. Les perspectives de travail proposees a la fin de cette these consistent principalement a : (i) exploiter ces deux methodes avec une gamme frequentielle plus etendue, (ii) explorer la variabilite intra-individuelle de chacune des methodes, (iii) comparer les resultats des deux methodes avec ceux obtenus par l'intermediaire de la methode "Microphone in Real Ear" (MIRE) et (iv) verifier la compatibilite de chacune des methodes avec tous les types de protecteurs auditifs. De plus, pour la methode de mesure de l'effet d'occlusion utilisant les PEASM, une etude complementaire est necessaire pour lever la contradiction observee a 250 Hz.

Evaluation of grapevine as a host for the glassy-winged sharpshooter

USDA-ARS?s Scientific Manuscript database

Grapevine was evaluated as a feeding and oviposition host for the glassy-winged sharpshooter. Two sets of experiments were conducted. The first set compared performance and preference of glassy-winged sharpshooter females for grapevine (cv. Chardonnay) versus cowpea (Vigna unguiculata cultivar black...

Development of the Ni-based Metallic glassy bipolar plates for Proton Exchange Membrane Fuel Cell (PEMFC)

NASA Astrophysics Data System (ADS)

Yamaura, S.; Yokoyama, M.; Kimura, H. M.; Inoue, A.

2009-01-01

Alloy optimization in the Ni80-xCrxP16B4 (x = 9-30 at%) alloy system was conducted in order to achieve low Tg, Tx and a large ΔTx. From this study, the Ni65Cr15P16B4 glassy alloy was found to be the optimal alloy. The static and potentiodynamic corrosion behaviours of this alloy were measured. As a result of polarization measurements, it was found that the current density of the non-polished glassy alloy sample was smaller than that of a SUS316L sample. By contrast, the current density of the surface-polished glassy sample was slightly larger than that of the SUS316L sample in the voltage range of 0.3-0.8 V. A bipolar plate was successfully produced by hot-pressing the glassy alloy sheet in a supercooled liquid state. The I-V characteristics of a single cell with the glassy bipolar plates were measured.

Photon energy upconverting nanopaper: a bioinspired oxygen protection strategy.

PubMed

Svagan, Anna J; Busko, Dmitry; Avlasevich, Yuri; Glasser, Gunnar; Baluschev, Stanislav; Landfester, Katharina

2014-08-26

The development of solid materials which are able to upconvert optical radiation into photons of higher energy is attractive for many applications such as photocatalytic cells and photovoltaic devices. However, to fully exploit triplet-triplet annihilation photon energy upconversion (TTA-UC), oxygen protection is imperative because molecular oxygen is an ultimate quencher of the photon upconversion process. So far, reported solid TTA-UC materials have focused mainly on elastomeric matrices with low barrier properties because the TTA-UC efficiency generally drops significantly in glassy and semicrystalline matrices. To overcome this limit, for example, combine effective and sustainable annihilation upconversion with exhaustive oxygen protection of dyes, we prepare a sustainable solid-state-like material based on nanocellulose. Inspired by the structural buildup of leaves in Nature, we compartmentalize the dyes in the liquid core of nanocellulose-based capsules which are then further embedded in a cellulose nanofibers (NFC) matrix. Using pristine cellulose nanofibers, a sustainable and environmentally friendly functional nanomaterial with ultrahigh barrier properties is achieved. Also, an ensemble of sensitizers and emitter compounds are encapsulated, which allow harvesting of the energy of the whole deep-red sunlight region. The films demonstrate excellent lifetime in synthetic air (20.5/79.5, O2/N2)-even after 1 h operation, the intensity of the TTA-UC signal decreased only 7.8% for the film with 8.8 μm thick NFC coating. The lifetime can be further modulated by the thickness of the protective NFC coating. For comparison, the lifetime of TTA-UC in liquids exposed to air is on the level of seconds to minutes due to fast oxygen quenching.

Boundary Layer Simulation and Control in Wind Tunnels

DTIC Science & Technology

1988-04-01

de l’art dans le domaine de la simulation de la couche limite, ou le nombre de Reynolds n’est pas ou ne peut pas etre simule, examine les effets ...pour la definition de certains essais en soufflerie oil les effets visqueux sont d’une importance particuliere. CONTENTS Page PREFACE iii 1...transition associated with cylindrical bodies at high incidence in subsonic flow. Other relevant references are given therein. Figures 11 a-b, from Ref

Effects of nymphal diet and adult feeding on allocation of resources to glassy-winged sharpshooter egg production

USDA-ARS?s Scientific Manuscript database

The glassy-winged sharpshooter is an invasive insect capable of transmitting the bacterial pathogen Xylella fastidiosa. Pre-oviposition periods of laboratory reared glassy-winged sharpshooters are variable. Here, two questions were addressed: does nymphal diet affect pre-oviposition period and how d...

New model system in radiation cryochemistry:. hyperquenched glassy water

NASA Astrophysics Data System (ADS)

Bednarek, Janusz; Plonka, Andrzej; Hallbrucker, Andreas; Mayer, Erwin

1999-08-01

Radicals generated by high-energy irradiation of liquid water, short-lived at ambient temperature, can be studied at cryogenic temperatures after irradiating water and dilute aqueous solutions in their glassy states which can be obtained by so-called hyperquenching of the liquids at cooling rates of ˜10 6-10 7 K s -1. In the glassy states of hyperquenched dilute aqueous solutions there is no problem with phase separation and radiolysis of glassy water is quite distinct from radiolysis of polycrystalline ice obtained from liquid water on slow-cooling in liquid nitrogen.

Simulation studies of glassy nanoclusters

NASA Astrophysics Data System (ADS)

Bowles, Richard

2015-03-01

Glassy materials are amorphous solids usually formed by rapidly cooling a liquid below its equilibrium freezing temperature, trapping the particles in a liquid-like structure at the glass transition temperature. While appearing throughout nature and industry, these systems continue to challenge the way we think about the dynamics and thermodynamics of condensed matter and a fundamental understanding of the glass state remains elusive. This talk describes molecular simulation studies of glassy behaviour in binary Lennard-Jones nanoclusters. We show that the relaxation dynamics of the clusters is nonuniform and the core of the cluster goes through a glass transition at higher temperatures than at the surface. As the nanoclusters are cooled, they also exhibit a fragile-strong crossover in their dynamics and we explore how this phenomena is linked to the potential energy landscape of the clusters. Finally, we compare the properties of nanoclusters formed through vapour condensation, directly to the glassy state, with those of glassy clusters formed through traditional supercooling. The condensation clusters are shown to form ultra-stable glassy states analogous to the ultra-stable glasses formed by thin film vapour deposition onto a cold substrate. In all, our work suggests that nanoscale clusters exhibit some unique glassy features, while also offering potential insights into the fundamental nature of the glass transition.

Effets Seebeck et Nernst dans les cuprates: Etude de la reconstruction de la surface de Fermi sous champ magnetique intense

NASA Astrophysics Data System (ADS)

Laliberte, Francis

2010-06-01

Ce memoire presente des mesures de transport thermoelectrique, les effets Seebeck et Nernst, dans une serie d'echantillons de supraconducteurs a haute temperature critique. Des resultats obtenus recemment au Laboratoire National des Champs Magnetiques Intenses a Grenoble sur La1.7Eu0.2Sr0.1 CuO4, La1.675Eu0.2Sr0.125CuO 4, La1.64Eu0.2Sr0.16CuO4, La1.74Eu0.1Sr0.16CuO4 et La 1.4Nd0.4Sr0.2CuO4 sont analyses. Une attention particuliere est accordee aux equations de la theorie semi-classique du transport et leur validite est verifiee. La procedure experimentale et les materiaux utilises pour concevoir les montages de mesures sont expliques en detail. Enfin, un chapitre est dedie a l'explication et l'interpretation des resultats de transport thermoelectrique sur YBa2Cu3O6+delta publies au cours de l'hiver 2010 dans les revues Nature et Physical Review Letters. Les donnees d'effet Seebeck dans les echantillons de La 1.8-x,Eu0.2SrxCuO 4, ou un changement de signe est observe, permettent de conclure a la presence d'une poche d'electrons dans la surface de Fermi qui domine le transport a basse temperature dans la region sous-dopee du diagramme de phase. Cette conclusion est similaire a celle obtenue par des mesures d'effet Hall dans YBa 2Cu3O6+delta et elle cadre bien dans un scenario de reconstruction de la surface de Fermi. Les donnees d'effet Nernst recueillies indiquent que la contribution des fluctuations supraconductrices est limitee a un modeste intervalle de temperature au-dessus de la temperature critique.

Silicon-tin oxynitride glassy composition and use as anode for lithium-ion battery

DOEpatents

Neudecker, Bernd J.; Bates, John B.

2001-01-01

Disclosed are silicon-tin oxynitride glassy compositions which are especially useful in the construction of anode material for thin-film electrochemical devices including rechargeable lithium-ion batteries, electrochromic mirrors, electrochromic windows, and actuators. Additional applications of silicon-tin oxynitride glassy compositions include optical fibers and optical waveguides.

Effects of xylem-sap composition on glassy-winged sharpshooter egg maturation on high and low quality host plants

USDA-ARS?s Scientific Manuscript database

Glassy-winged sharpshooters must feed as adults to produce mature eggs. Cowpea and sunflower are both readily accepted by the glassy-winged sharpshooter for feeding, but egg production on sunflower was reported to be lower than egg production on cowpea. To better understand the role of adult diet in...

Observation of glassy state relaxation during annealing of frozen sugar solutions by X-ray computed tomography.

PubMed

Nakagawa, Kyuya; Tamiya, Shinri; Do, Gabsoo; Kono, Shinji; Ochiai, Takaaki

2018-06-01

Glassy phase formation in a frozen product determines various properties of the freeze-dried products. When an aqueous solution is subjected to freezing, a glassy phase forms as a consequence of freeze-concentration. During post-freezing annealing, the relaxation of the glassy phase and the ripening of ice crystals (i.e. Ostwald ripening) spontaneously occur, where the kinetics are controlled by the annealing and glass transition temperatures. This study was motivated to observe the progress of glassy state relaxation separate from ice coarsening during annealing. X-ray computed tomography (CT) was used to observe a frozen and post-freezing annealed solutions by using monochromatized X-ray from the synchrotron radiation. CT images were successfully obtained, and the frozen matrix were analyzed based on the gray level values that were equivalent to the linear X-ray attenuation coefficients of the observed matters. The CT images obtained from rapidly frozen sucrose and dextrin solutions with different concentrations gave clear linear relationships between the linear X-ray attenuation coefficients values and the solute concentrations. It was confirmed that the glassy state relaxation progressed as increasing annealing time, and this trend was larger in the order of the glass transition temperature of the maximally freeze-concentrated phase. The sucrose-water system required nearly 20 h of annealing time at -5 °C for the completion of the glassy phase relaxation, whereas dextrin-water systems required much longer periods because of their higher glass transition temperatures. The trends of ice coarsening, however, did not perfectly correspond to the trends of the relaxation, suggesting that the glassy phase relaxation and Ostwald ripening would jointly control the ice crystal growth/ripening kinetics, and the dominant mechanism differed by the annealing stage. Copyright © 2018 Elsevier B.V. All rights reserved.

Glassy nature and glass-to-crystal transition in the binary metallic glass CuZr

NASA Astrophysics Data System (ADS)

Wei, Zi-Yang; Shang, Cheng; Zhang, Xiao-Jie; Liu, Zhi-Pan

2017-06-01

The prediction for the stability of glassy material is a key challenge in physical science. Here, we report a theoretical framework to predict the glass stability based on stochastic surface walking global optimization and reaction pathway sampling. This is demonstrated by revealing for the first time the global potential energy surface (PES) of two systems, CuZr binary metallic glass and nonglassy pure Cu systems, and establishing the lowest energy pathways linking glassy/amorphous structures with crystalline structures. The CuZr system has a significant number of glassy structures on PES that are ˜0.045 eV /atom above the crystal structure. Two clear trends are identified from global PES in the glass-to-crystal transition of the CuZr system: (i) the local Zr-Cu coordination (nearest neighbor) increases, and (ii) the local Zr bonding environment becomes homogeneous. This allows us to introduce quantitative structural and energetics conditions to distinguish the glassy structures from the crystalline structures. Because of the local Zr-Cu exchange in the glass-to-crystal transition, a high reaction barrier (>0.048 eV /atom ) is present to separate the glassy structures and the crystals in CuZr. By contrast, the Cu system, although it does possess amorphous structures that appear at much higher energy (˜0.075 eV /atom ) with respect to the crystal structure, has very low reaction barriers for the crystallization of amorphous structures, i.e. <0.011 eV /atom . The quantitative data on PES now available from global optimization techniques deepens our understanding on the microscopic nature of glassy material and might eventually facilitate the design of stable glassy materials.

Capturing Gases in Carbon Honeycomb

NASA Astrophysics Data System (ADS)

Krainyukova, Nina V.

2017-04-01

In our recent paper (Krainyukova and Zubarev in Phys Rev Lett 116:055501, 2016. doi: 10.1103/PhysRevLett.116.055501) we reported the observation of an exceptionally stable honeycomb carbon allotrope obtained by deposition of vacuum-sublimated graphite. A family of structures can be built from absolutely dominant {sp}2-bonded carbon atoms, and may be considered as three-dimensional graphene. Such structures demonstrate high absorption capacity for gases and liquids. In this work we show that the formation of honeycomb structures is highly sensitive to the carbon evaporation temperature and deposition rates. Both parameters are controlled by the electric current flowing through thin carbon rods. Two distinctly different regimes were found. At lower electric currents almost pure honeycomb structures form owing to sublimation. At higher currents the surface-to-bulk rod melting is observed. In the latter case densification of the carbon structures and a large contribution of glassy graphite emerge. The experimental diffraction patterns from honeycomb structures filled with absorbed gases and analyzed by the advanced method are consistent with the proposed models for composites which are different for Ar, Kr and Xe atoms in carbon matrices.

Fast and long-range triplet exciton diffusion in metal-organic frameworks for photon upconversion at ultralow excitation power.

PubMed

Mahato, Prasenjit; Monguzzi, Angelo; Yanai, Nobuhiro; Yamada, Teppei; Kimizuka, Nobuo

2015-09-01

The conversion of low-energy light into photons of higher energy based on sensitized triplet-triplet annihilation upconversion (TTA-UC) has emerged as a promising wavelength-shifting methodology because it permits UC at excitation powers as low as the solar irradiance. However, its application has been significantly hampered by the slow diffusion of excited molecules in solid matrices. Here, we introduce metal-organic frameworks (MOFs) that promote TTA-UC by taking advantage of triplet exciton migration among fluorophores that are regularly aligned with spatially controlled chromophore orientations. We synthesized anthracene-containing MOFs with different molecular orientations, and the analysis of TTA-UC emission kinetics unveiled a high triplet diffusion rate with a micrometre-scale diffusion length. Surface modification of MOF nanocrystals with donor molecules and their encapsulation in glassy poly(methyl methacrylate) (PMMA) allowed the construction of molecular-diffusion-free solid-state upconverters, which lead to an unprecedented maximization of overall UC quantum yield at excitation powers comparable to or well below the solar irradiance.

Giant Faraday Rotation through Ultrasmall Fe0 n Clusters in Superparamagnetic FeO-SiO2 Vitreous Films.

PubMed

Nakatsuka, Yuko; Pollok, Kilian; Wieduwilt, Torsten; Langenhorst, Falko; Schmidt, Markus A; Fujita, Koji; Murai, Shunsuke; Tanaka, Katsuhisa; Wondraczek, Lothar

2017-04-01

Magnetooptical (MO) glasses and, in particular, Faraday rotators are becoming key components in lasers and optical information processing, light switching, coding, filtering, and sensing. The common design of such Faraday rotator materials follows a simple path: high Faraday rotation is achieved by maximizing the concentration of paramagnetic ion species in a given matrix material. However, this approach has reached its limits in terms of MO performance; hence, glass-based materials can presently not be used efficiently in thin film MO applications. Here, a novel strategy which overcomes this limitation is demonstrated. Using vitreous films of x FeO·(100 - x )SiO 2 , unusually large Faraday rotation has been obtained, beating the performance of any other glassy material by up to two orders of magnitude. It is shown that this is due to the incorporation of small, ferromagnetic clusters of atomic iron which are generated in line during laser deposition and rapid condensation of the thin film, generating superparamagnetism. The size of these clusters underbids the present record of metallic Fe incorporation and experimental verification in glass matrices.

Constitutive modeling of glassy shape memory polymers

NASA Astrophysics Data System (ADS)

Khanolkar, Mahesh

The aim of this research is to develop constitutive models for non-linear materials. Here, issues related for developing constitutive model for glassy shape memory polymers are addressed in detail. Shape memory polymers are novel material that can be easily formed into complex shapes, retaining memory of their original shape even after undergoing large deformations. The temporary shape is stable and return to the original shape is triggered by a suitable mechanism such heating the polymer above a transition temperature. Glassy shape memory polymers are called glassy because the temporary shape is fixed by the formation of a glassy solid, while return to the original shape is due to the melting of this glassy phase. The constitutive model has been developed to capture the thermo-mechanical behavior of glassy shape memory polymers using elements of nonlinear mechanics and polymer physics. The key feature of this framework is that a body can exist stress free in numerous natural configurations, the underlying natural configuration of the body changing during the process, with the response of the body being elastic from these evolving natural configurations. The aim of this research is to formulate a constitutive model for glassy shape memory polymers (GSMP) which takes in to account the fact that the stress-strain response depends on thermal expansion of polymers. The model developed is for the original amorphous phase, the temporary glassy phase and transition between these phases. The glass transition process has been modeled using a framework that was developed recently for studying crystallization in polymers and is based on the theory of multiple natural configurations. Using the same frame work, the melting of the glassy phase to capture the return of the polymer to its original shape is also modeled. The effect of nanoreinforcement on the response of shape memory polymers (GSMP) is studied and a model is developed. In addition to modeling and solving boundary value problems for GSMP's, problems of importance for CSMP, specifically a shape memory cycle (Torsion of a Cylinder) is solved using the developed crystallizable shape memory polymer model. To solve complex boundary value problems in realistic geometries a user material subroutine (UMAT) for GSMP model has been developed for use in conjunction with the commercial finite element software ABAQUS. The accuracy of the UMAT has been verified by testing it against problems for which the results are known.

A Survey of Serious Aircraft Accidents Involving Fatigue Fracture. Volume 2. Rotary-Wing Aircraft (Etude sur des Accidents Importants d’Avions du aux Effets des Fractures de Fatigue. Volume 2. Effets sur des Helicopteres).

DTIC Science & Technology

1983-04-01

Convention on International Civil Aviation, Second Edition , March 1966. 5. WORLD AIRLINE ACCIDENT SUMMARY. Civil Aviation Authority, (Great Britain...people who either provided information, or who suggested other sources of information for the current edition of this survey. E.M.R. Alexander Civil...Waverley, New Zealand. F-28C Tail rotor drive shaft. Fatigue strength reduc- ed by softened condition & surface decarbur- isation. AISA 4130 steel. Ref: NZ

Interphase and particle dispersion correlations in polymer nanocomposites

NASA Astrophysics Data System (ADS)

Senses, Erkan

Particle dispersion in polymer matrices is a major parameter governing the mechanical performance of polymer nanocomposites. Controlling particle dispersion and understanding aging of composites under large shear and temperature variations determine the processing conditions and lifetime of composites which are very important for diverse applications in biomedicine, highly reinforced materials and more importantly for the polymer composites with adaptive mechanical responses. This thesis investigates the role of interphase layers between particles and polymer matrices in two bulk systems where particle dispersion is altered upon deformation in repulsive composites, and good-dispersion of particles is retained after multiple oscillatory shearing and aging cycles in attractive composites. We demonstrate that chain desorption and re-adsorption processes in attractive composites under shear can effectively enhance the bulk microscopic mechanical properties, and long chains of adsorbed layers lead to a denser entangled interphase layer. We further designed experiments where particles are physically adsorbed with bimodal lengths of homopolymer chains to underpin the entanglement effect in interphases. Bimodal adsorbed chains are shown to improve the interfacial strength and used to modulate the elastic properties of composites without changing the particle loading, dispersion state or polymer conformation. Finally, the role of dynamic asymmetry (different mobilities in polymer blends) and chemical heterogeneity in the interphase layer are explored in systems of poly(methyl methacrylate) adsorbed silica nanoparticles dispersed in poly(ethylene oxide) matrix. Such nanocomposites are shown to exhibit unique thermal-stiffening behavior at temperatures above glass transitions of both polymers. These interesting findings suggest that the mobility of the surface-bound polymer is essential for reinforcement in polymer nanocomposites, contrary to existing glassy layer theories for polymers on attractive particle surfaces. The shown thermally-induced stiffening behavior is reversible and makes this interfacial mechanism highly attractive in developing new active, remotely controllable engineered materials from non-responsive components.

SPM investigation of local aging effects in glassy polymers

NASA Astrophysics Data System (ADS)

Crider, Philip

2005-03-01

We investigate the cooperative and heterogeneous nature of glassy dynamics by nanometer-scale probing in a glassy polymer, Polyvinyl-Actetate (PVAc), with a Scanning Force Microscope (SFM). Using ultra-high-vacuum (UHV) Scanning Capacitive Force Microscopy techniques, nanometer-scale capacitive responses are probed. Dielectric relaxation near the glass transition is investigated, and scanning capabilities are utilized to analyze spatial response on a nanometer scale. The results of these studies may yield insight into the understanding of temperature-dependent cooperative length scales, local aging properties, and energy landscape properties of evolving dipole clusters on a mesoscopic scale. Results are used to test the validity and relevance of current models of glassy dynamics.

Les effets des interfaces sur les proprietes magnetiques et de transport des multicouches nickel/iron et cobalt/silver

NASA Astrophysics Data System (ADS)

Veres, Teodor

Cette these est consacree a l'etude de l'evolution structurale des proprietes magnetiques et de transport des multicouches Ni/Fe et nanostructures a base de Co et de l'Ag. Dans une premiere partie, essentiellement bibliographique, nous introduisons quelques concepts de base relies aux proprietes magnetiques et de transport des multicouches metalliques. Ensuite, nous presentons une breve description des methodes d'analyse des resultats. La deuxieme partie est consacree a l'etude des proprietes magnetiques et de transport des multicouches ferromagnetiques/ferromagnetiques Ni/Fe. Nous montrerons qu'une interpretation coherente de ces proprietes necessite la prise en consideration des effets des interfaces. Nous nous attacherons a mettre en evidence, a evaluer et a etudier les effets de ces interfaces ainsi que leur evolution, et ce, suite a des traitements thermiques tel que le depot a temperature elevee et l'irradiation ionique. Les analyses correlees de la structure et de la magnetoresistance nous permettront d'emettre des conclusions sur l'influence des couches tampons entre l'interface et le substrat ainsi qu'entre les couches elles-memes sur le comportement magnetique des couches F/F. La troisieme partie est consacree aux systemes a Magneto-Resistance Geante (MRG) a base de Co et Ag. Nous allons etudier l'evolution de la microstructure suite a l'irradiation avec des ions Si+ ayant une energie de 1 MeV, ainsi que les effets de ces changements sur le comportement magnetique. Cette partie debutera par l'analyse des proprietes d'une multicouche hybride, intermediaire entre les multicouches et les materiaux granulaires. Nous analyserons a l'aide des mesures de diffraction, de relaxation superparamagnetique et de magnetoresistance, les evolutions structurales produites par l'irradiation ionique. Nous etablirons des modeles qui nous aideront a interpreter les resultats pour une serie des multicouches qui couvrent un large eventail de differents comportements magnetiques et ceci en fonction de l'epaisseur de la couche magnetique de Co. Nous verrons que dans ces systemes les effets de l'irradiation ionique sont fortement influences par l'energie de surface ainsi que par l'enthalpie de formation, largement positive pour le systeme Co/Ag.

Thermodynamic behavior of glassy state of structurally related compounds.

PubMed

Kaushal, Aditya Mohan; Bansal, Arvind Kumar

2008-08-01

Thermodynamic properties of amorphous pharmaceutical forms are responsible for enhanced solubility as well as poor physical stability. The present study was designed to investigate the differences in thermodynamic parameters arising out of disparate molecular structures and associations for four structurally related pharmaceutical compounds--celecoxib, valdecoxib, rofecoxib, and etoricoxib. Conventional and modulated temperature differential scanning calorimetry were employed to study glass forming ability and thermodynamic behavior of the glassy state of model compounds. Glass transition temperature of four glassy compounds was in a close range of 327.6-331.8 K, however, other thermodynamic parameters varied considerably. Kauzmann temperature, strength parameter and fragility parameter showed rofecoxib glass to be most fragile of the four compounds. Glass forming ability of the compounds fared similar in the critical cooling rate experiments, suggesting that different factors were determining the glass forming ability and subsequent behavior of the compounds in glassy state. A comprehensive understanding of such thermodynamic facets of amorphous form would help in rationalizing the approaches towards development of stable glassy pharmaceuticals.

Comment on ``Glassy Potts model: A disordered Potts model without a ferromagnetic phase''

NASA Astrophysics Data System (ADS)

Carlucci, Domenico M.

1999-10-01

We report the equivalence of the ``glassy Potts model,'' recently introduced by Marinari et al. and the ``chiral Potts model'' investigated by Nishimori and Stephen. Both models do not exhibit any spontaneous magnetization at low temperature, differently from the ordinary glass Potts model. The phase transition of the glassy Potts model is easily interpreted as the spin-glass transition of the ordinary random Potts model.

Electrical properties of carbon nanotubes modified GaSe glassy system

NASA Astrophysics Data System (ADS)

Khan, Hana; Khan, Zubair M. S. H.; Islam, Shama; Rahman, Raja Saifu; Husain, M.; Zulfequar, M.

2018-05-01

In this paper we report the investigation of the effect of Carbon Nanotubes (CNT) addition on the electrical properties of GaSe Glassy system. Dielectric constant and dielectric loss of GaSe glassy system are found to increase on CNT addition. The conductivity of GaSe glasy systems is also found to increase on CNT addition. This behavior is attributed to the excellent conduction properties of Carbon Nanotube.

Magnetic resonance imaging and image analysis for assessment of HPMC matrix tablets structural evolution in USP Apparatus 4.

PubMed

Kulinowski, Piotr; Dorożyński, Przemysław; Młynarczyk, Anna; Węglarz, Władysław P

2011-05-01

The purpose of the study was to present a methodology for the processing of Magnetic Resonance Imaging (MRI) data for the quantification of the dosage form matrix evolution during drug dissolution. The results of the study were verified by comparison with other approaches presented in literature. A commercially available, HPMC-based quetiapine fumarate tablet was studied with a 4.7T MR system. Imaging was performed inside an MRI probe-head coupled with a flow-through cell for 12 h in circulating water. The images were segmented into three regions using threshold-based segmentation algorithms due to trimodal structure of the image intensity histograms. Temporal evolution of dry glassy, swollen glassy and gel regions was monitored. The characteristic features were observed: initial high expansion rate of the swollen glassy and gel layers due to initial water uptake, dry glassy core disappearance and maximum area of swollen glassy region at 4 h, and subsequent gel layer thickness increase at the expense of swollen glassy layer. The temporal evolution of an HPMC-based tablet by means of noninvasive MRI integrated with USP Apparatus 4 was found to be consistent with both the theoretical model based on polymer disentanglement concentration and experimental VIS/FTIR studies.

Assessment of the effect of No Stay, Bent Stay or Straight Stay when the Clothe the Soldier Rucksack is Worn with the Fragmentation Vest

DTIC Science & Technology

2006-02-01

effets de différents renforts de sac à dos (renforts droits, renforts courbés et aucun renfort) sur la...supérieures au seuil de tolérance de la peau et des muscles sous-jacents, et elles pourraient causer des lésions sur la peau et des ecchymoses. Assessment...présente évaluation portait sur cette pratique et visait à déterminer les effets de différents renforts de sac à dos (renforts droits, renforts courbés

A Survey of Serious Aircraft Accidents Involving Fatigue Fracture. Volume 1. Fixed-Wing Aircraft (Etude sur des Accidents Importants d’Avions du aux Effets des Fractures de Fatigue. Volume 1. Effets sur des Avions).

DTIC Science & Technology

1983-04-01

Bureau of Standards. NTS3 National Transportation Safety Board (USA). NTSB AAR NTSB Aircraft Accident Report. NZ AAR New Zealand Aircraft Accident Report...NZ AI New Zealand Accident Investigation Bureau. 0 -5- RAN Royal Australian Navy RAAI Royal Australian Air Force RAF Royal Air Force, UK S Substantial...Ice land Iraq Ireland Jamaica (1966 -1981) Japan (1973 - Feb. 81) Kenya Lethoso Malaysia Ma law i Mal ta Mexico Netherlands New Zealand Norway

Evaluation d'impact sur la santé et évaluation d'impact sur l'équité en santé : éventail de pratiques et questions de recherche.

PubMed

Villeval, Mélanie; Bidault, Elsa; Lang, Thierry

2016-09-01

L'Evaluation d'Impact sur la Santé (EIS) se développe au niveau international et est encore au stade émergent en France. Elle vise à évaluer les effets positifs et négatifs potentiels d'un projet, d'un programme ou d'une politique sur la santé. L'objectif est de produire des recommandations en direction des décideurs, afin d'en maximiser les effets positifs et d'en diminuer les effets négatifs. L'EIS est un moyen particulièrement intéressant d'action sur les déterminants de la santé au-delà des comportements individuels et du système de santé. Les politiques de logement, de transport, de solidarité, économiques, etc. ont, en effet, des impacts souvent non prévus sur la santé. Au-delà des effets sur la santé, l'EIS doit aussi permettre d'apprécier la distribution de ces effets dans la population.Si la préoccupation pour l'équité en santé est centrale dans l'EIS, elle reste cependant difficilement traduite en pratique. Face à cette difficulté, des démarches d'évaluation d'impact ont été développées pour renforcer la prise en compte de l'équité à chaque étape de l'EIS ou « Equity Focused Health Impact Assessment », ou prendre en compte les impacts sur les inégalités de santé de façon spécifique. Ainsi, l'Evaluation de l'Impact sur l'Equité en Santé (EIES) semble, par exemple, particulièrement intéressante pour évaluer l'impact sur les inégalités de projets dans le champ sanitaire.L'EIS et l'EIES posent de nombreuses questions de recherche, notamment autour de la réunion, dans une même démarche, du politique, du citoyen et de l'expert. La participation des populations vulnérables potentiellement affectées par la politique évaluée est une valeur centrale de l'EIS, mais pose des questions d'acceptabilité sociale. La collaboration avec les décideurs politiques est également un enjeu majeur. Les difficultés méthodologiques, notamment de quantification des impacts, peuvent constituer des freins à la promotion de la démarche auprès des décideurs. © The Author(s) 2015.

Graphene Reinforced Glassy Carbon (GRGC) Beam Windows

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

Renomeron, Lynda L.

Secondary particle beams require beam windows that isolate the target (usually in air) from the primary particle beam vacuum. Advanced beam window solutions are needed that can withstand anticipated increases in beam power and intensity that will result in higher thermal shock on the window and increased oxidative erosion rates on the air-side caused by increased temperatures. Carbon-based windows, in particular, glassy carbon windows are of interest to minimize interaction with the beam. The attractive properties of glassy carbon are: 1. Low atomic number 2. Low thermal expansion 3. High strength and low Young's modulus 4. Low gas permeability andmore » low outgassing for ultrahigh vacuum use The one liability of glassy carbon is its low thermal conductivity, nominally 5 W/mK, which will exacerbate temperature rise, oxidation, and thermal shock concerns as beam powers increase. TA&T proposes the development of graphene reinforced glassy carbon (GRGC) composites to increase the thermal conductivity and address this Achilles heel of glassy carbon. Graphene as a reinforcing phase has shown the capability to increase the thermal conductivity of the matrix material by up to two orders of magnitude. For beam windows this would substantially increase heat spreading away from the beam zone of the window and improve thermal shock resistance, and reduce maximum temperature and air-side oxidation of the window. Increased thermal conductivity would also improve the effectiveness of edge-cooling schemes to minimize temperature increase. In the Phase I effort, graphene oxide (GO) particles were dispersed into glassy carbon precursor at different content levels and cast into solid shapes. The goal was to determine the effect of graphene concentration on the mechanical properties (flexure strength), and thermal (thermal conductivity). The Phase I results indicated that addition of graphene did have a significant effect on thermal conductivity; however the microstructural properties of the composite need further improvement. The Phase II work is designed to address the processing issues found during Phase I, so as to fully realize the benefits of GO within the glassy carbon In addition to enabling improved windows for high energy particle beam experiments, the reinforced glassy carbon material will find various other applications such as thruster bodies for rocket propulsion, more durable carbon-based electrodes for electrochemistry applications, bi-polar plates for advanced batteries, catalyst support structures, and structural bio-implants.« less

Seasonal population dynamics of Homalodisca vitripennis (Hemiptera: Cicadellidae) in sweet orange trees maintained under continuous deficit irrigation.

PubMed

Krugner, Rodrigo; Groves, Russell L; Johnson, Marshall W; Flores, Arnel P; Hagler, James R; Morse, Joseph G

2009-06-01

A 2-yr study was conducted in a citrus orchard (Citrus sinensis L. Osbeck cultivar Valencia) to determine the influence of plant water stress on the population dynamics of glassy-winged sharpshooter, Homalodisca vitripennis (Germar). Experimental treatments included irrigation at 100% of the crop evapotranspiration rate (ET(c)) and continuous deficit-irrigation regimens at 80 and 60% ET(c). Microclimate and plant conditions monitored included temperature and humidity in the tree canopy, leaf surface temperature, water potential, and fruit quality and yield. Glassy-winged sharpshooter population densities and activity were monitored weekly by a combination of visual inspections, beat net sampling, and trapping. Glassy-winged sharpshooter populations were negatively affected by severe plant water stress; however, population densities were not linearly related to decreasing water availability in plants. Citrus trees irrigated at 60% ET(c) had significantly warmer leaves, lower xylem water potential, and consequently hosted fewer glassy-winged sharpshooter eggs, nymphs, and adults than trees irrigated at 80% ET(c). Citrus trees irrigated at 100% ET(c) hosted similar numbers of glassy-winged sharpshooter stages as trees irrigated at 60% ET(c) and a lower number of glassy-winged sharpshooter nymphs than the 80% ET(c) treatment, specifically during the nymphal density peak in mid-April to early July. Irrigation treatments did not affect populations of monitored natural enemies. Although the adult glassy-winged sharpshooter population was reduced, on average, by 50% in trees under severe water stress, the total number of fruit and number of fruit across several fruit grade categories were significantly lower in the 60% ET(c) than in the 80 and 100% ET(c) irrigation treatments.

Pair distribution function analysis of sulfide glassy electrolytes for all-solid-state batteries: Understanding the improvement of ionic conductivity under annealing condition.

PubMed

Shiotani, Shinya; Ohara, Koji; Tsukasaki, Hirofumi; Mori, Shigeo; Kanno, Ryoji

2017-08-01

In general, the ionic conductivity of sulfide glasses decreases with their crystallization, although it increases for a few sulphide glasses owing to the crystallization of a highly conductive new phase (e.g., Li 7 P 3 S 11 : 70Li 2 S-30P 2 S 5 ). We found that the ionic conductivity of 75Li 2 S-25P 2 S 5 sulfide glass, which consists of glassy and crystalline phases, is improved by optimizing the conditions of the heat treatment, i.e., annealing. A different mechanism of high ionic conductivity from the conventional mechanism is expected in the glassy phase. Here, we report the glassy structure of 75Li 2 S-25P 2 S 5 immediately before the crystallization by using the differential pair distribution function (d-PDF) analysis of high-energy X-ray diffraction. Even though the ionic conductivity increases during the optimum annealing, the d-PDF analysis indicated that the glassy structure undergoes no structural change in the sulfide glass-ceramic electrolyte at a crystallinity of 33.1%. We observed the formation of a nanocrystalline phase in the X-ray and electron diffraction patterns before the crystallization, which means that Bragg peaks were deformed. Thus, the ionic conductivity in the mixture of glassy and crystalline phases is improved by the coexistence of the nanocrystalline phase.

Disconnecting structure and dynamics in glassy thin films

PubMed Central

Sussman, Daniel M.; Cubuk, Ekin D.; Liu, Andrea J.

2017-01-01

Nanometrically thin glassy films depart strikingly from the behavior of their bulk counterparts. We investigate whether the dynamical differences between a bulk and thin film polymeric glass former can be understood by differences in local microscopic structure. Machine learning methods have shown that local structure can serve as the foundation for successful, predictive models of particle rearrangement dynamics in bulk systems. By contrast, in thin glassy films, we find that particles at the center of the film and those near the surface are structurally indistinguishable despite exhibiting very different dynamics. Next, we show that structure-independent processes, already present in bulk systems and demonstrably different from simple facilitated dynamics, are crucial for understanding glassy dynamics in thin films. Our analysis suggests a picture of glassy dynamics in which two dynamical processes coexist, with relative strengths that depend on the distance from an interface. One of these processes depends on local structure and is unchanged throughout most of the film, while the other is purely Arrhenius, does not depend on local structure, and is strongly enhanced near the free surface of a film. PMID:28928147

Optical and mechanical behaviors of glassy silicone networks derived from linear siloxane precursors

NASA Astrophysics Data System (ADS)

Jang, Heejun; Seo, Wooram; Kim, Hyungsun; Lee, Yoonjoo; Kim, Younghee

2016-01-01

Silicon-based inorganic polymers are promising materials as matrix materials for glass fiber composites because of their good process ability, transparency, and thermal property. In this study, for utilization as a matrix precursor for a glass-fiber-reinforced composite, glassy silicone networks were prepared via hydrosilylation of linear/pendant Si-H polysiloxanes and the C=C bonds of viny-lterminated linear/cyclic polysiloxanes. 13C nuclear magnetic resonance spectroscopy was used to determine the structure of the cross-linked states, and a thermal analysis was performed. To assess the mechanical properties of the glassy silicone networks, we performed nanoindentation and 4-point bending tests. Cross-linked networks derived from siloxane polymers are thermally and optically more stable at high temperatures. Different cross-linking agents led to final networks with different properties due to differences in the molecular weights and structures. After stepped postcuring, the Young's modulus and the hardness of the glassy silicone networks increased; however, the brittleness also increased. The characteristics of the cross-linking agent played an important role in the functional glassy silicone networks.

Voltammetric pH sensing using carbon electrodes: glassy carbon behaves similarly to EPPG.

PubMed

Lu, Min; Compton, Richard G

2014-09-21

Developing and building on recent work based on a simple sensor for pH determination using unmodified edge plane pyrolytic graphite (EPPG) electrodes, we present a voltammetric method for pH determination using a bare unmodified glassy carbon (GC) electrode. By exploiting the pH sensitive nature of quinones present on carbon edge-plane like sites within the GC, we show how GC electrodes can be used to measure pH. The electro-reduction of surface quinone groups on the glassy carbon electrode was characterised using cyclic voltammetry (CV) and optimised with square-wave voltammetry (SWV) at 298 K and 310 K. At both temperatures, a linear correlation was observed, corresponding to a 2 electron, 2 proton Nernstian response over the aqueous pH range 1.0 to 13.1. As such, unmodified glassy carbon electrodes are seen to be pH dependent, and the Nernstian response suggests its facile use for pH sensing. Given the widespread use of glassy carbon electrodes in electroanalysis, the approach offers a method for the near-simultaneous measurement and monitoring of pH during such analyses.

Aryl Diazonium Chemistry for the Surface Functionalization of Glassy Biosensors.

PubMed

Zheng, Wei; van den Hurk, Remko; Cao, Yong; Du, Rongbing; Sun, Xuejun; Wang, Yiyu; McDermott, Mark T; Evoy, Stephane

2016-03-14

Nanostring resonator and fiber-optics-based biosensors are of interest as they offer high sensitivity, real-time measurements and the ability to integrate with electronics. However, these devices are somewhat impaired by issues related to surface modification. Both nanostring resonators and photonic sensors employ glassy materials, which are incompatible with electrochemistry. A surface chemistry approach providing strong and stable adhesion to glassy surfaces is thus required. In this work, a diazonium salt induced aryl film grafting process is employed to modify a novel SiCN glassy material. Sandwich rabbit IgG binding assays are performed on the diazonium treated SiCN surfaces. Fluorescently labelled anti-rabbit IgG and anti-rabbit IgG conjugated gold nanoparticles were used as markers to demonstrate the absorption of anti-rabbit IgG and therefore verify the successful grafting of the aryl film. The results of the experiments support the effectiveness of diazonium chemistry for the surface functionalization of SiCN surfaces. This method is applicable to other types of glassy materials and potentially can be expanded to various nanomechanical and optical biosensors.

Aryl Diazonium Chemistry for the Surface Functionalization of Glassy Biosensors

PubMed Central

Zheng, Wei; van den Hurk, Remko; Cao, Yong; Du, Rongbing; Sun, Xuejun; Wang, Yiyu; McDermott, Mark T.; Evoy, Stephane

2016-01-01

Nanostring resonator and fiber-optics-based biosensors are of interest as they offer high sensitivity, real-time measurements and the ability to integrate with electronics. However, these devices are somewhat impaired by issues related to surface modification. Both nanostring resonators and photonic sensors employ glassy materials, which are incompatible with electrochemistry. A surface chemistry approach providing strong and stable adhesion to glassy surfaces is thus required. In this work, a diazonium salt induced aryl film grafting process is employed to modify a novel SiCN glassy material. Sandwich rabbit IgG binding assays are performed on the diazonium treated SiCN surfaces. Fluorescently labelled anti-rabbit IgG and anti-rabbit IgG conjugated gold nanoparticles were used as markers to demonstrate the absorption of anti-rabbit IgG and therefore verify the successful grafting of the aryl film. The results of the experiments support the effectiveness of diazonium chemistry for the surface functionalization of SiCN surfaces. This method is applicable to other types of glassy materials and potentially can be expanded to various nanomechanical and optical biosensors. PMID:26985910

Electrical resistivity in Zr48Nb8Cu12Fe8Be24 glassy and crystallized alloys

NASA Astrophysics Data System (ADS)

Bai, H. Y.; Tong, C. Z.; Zheng, P.

2004-02-01

The electrical resistivity of Zr48Nb8Cu12Fe8Be24 bulk metallic glassy and crystallized alloys in the temperature range of 4.2-293 K is investigated. It is found that the resistivity in glassy and crystallized states shows opposite temperature coefficients. For the metallic glass, the resistivity shows a negative logarithmic dependence at temperatures below 16 K, whereas it has more normal behavior for the crystallized alloy. At higher temperatures, the resistivity in both glassy and crystallized alloys shows dependence upon both T and T2, but the signs of the T and T2 terms are opposite. The results are interpreted in terms of scattering from two-level tunneling states in glasses and the generalized Ziman diffraction model.

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.

Electrochemical synthesis of gold nanoparticles on the surface of multi-walled carbon nanotubes with glassy carbon electrode and their application

NASA Astrophysics Data System (ADS)

Song, Y. Z.; Li, X.; Song, Y.; Cheng, Z. P.; Zhong, H.; Xu, J. M.; Lu, J. S.; Wei, C. G.; Zhu, A. F.; Wu, F. Y.; Xu, J.

2013-01-01

Gold nanoparticles on the surface of multi-walled carbon nanotubes with glassy carbon electrode were prepared using electrochemical synthesis method. The thin films of gold Nanoparticles/multi-walled carbon nanotubes were characterized by scanning electron microscopy, powder X-ray diffraction, and cyclic voltammetry. Electrochemical behavior of adrenaline hydrochloride at gold nanoparticles/multi-walled carbon nanotube modified glassy carbon electrode was investigated. A simple, sensitive, and inexpensive method for determination of adrenaline hydrochloride was proposed.

Les effets bénéfiques de l'accompagnement du patient cancéreux: particularités du Maroc

PubMed Central

Lkhoyaali, Sihame; Aitelhaj, Meryem; Errihani, Hassan

2014-01-01

Au Maroc la majorité des patients âgés cancéreux sont pris en charge par leurs proches l'accompagnement des patients est à l'origine de conséquences émotionnelles psychiques et financières négatives mais en contrepartie il est à l'origine de plusieurs effets bénéfiques à savoir un resserrement des liens familiaux, une surestime du soi et il est la source d'un bien-être affectif et spirituel qui permet de faire face à la maladie. PMID:25722766

Development of a Dynamic Biomechanical Model for Load Carriage: Phase IV Part C1: Assessment of Pressure Measurement Systems on Flat Surfaces for use in Human Load Carriage

DTIC Science & Technology

2005-08-01

iv Sommaire Les études sur les effets de la pression de contact produite par une charge d’un sac à dos sont essentielles, étant...mobilité des soldats et amenuiser leur capacité de combat. Afin de mieux comprendre les effets de la pression d’un sac à dos sur le confort et la... de mesure de pression qui pourraient être utilisés pour établir les valeurs de tolérance de la peau aux pressions durant le transport d’une charge

Consequences experimentales des effets des fluctuations du vide sur la fluorescence parametrique et la generation du second harmonique en milieu confine

NASA Astrophysics Data System (ADS)

Robichaud, Luc

Les fluctuations du vide, qui consistent en l'apparition momentanee de particules, ce qui est permit par le principe d'incertitude de Heisenberg, joue un role primordial dans les processus photoniques, en particulier les processus non-lineaires. Par la manipulation de ces fluctuations du vide a l'aide de confinement optique, on retrouve deux phenomenes particuliers : l'intensification de la fluorescence parametrique (Walker, 2008) et l'inhibition de la generation du second harmonique (Collette, 2013). Dans ce travail, on presente les resultats dans le cas classique ; c'est-a-dire sans fluctuations du vide et confinement. Par la suite, on presente les effets des fluctuations du vide et du confinement, ce qui mene aux deux effets mentionnes. Dans le cas de la fluorescence parametrique, le bruit quantique sur le champ interne et externe est calcule, le role du desaccord de phase dans le modele est expose et une generalisation tridimensionnelle est etudiee afin de generaliser la conception du modele d'un cas unidimensionnel a un cas tridimensionnel planaire. Dans le cas de la generation du second harmonique, les difficultes d'un modele purement tridimensionnel sont exposees et ensuite le cas limite planaire est etudie.

Low-temperature electron-spin relaxation in the crystalline and glassy states of solid ethanol

NASA Astrophysics Data System (ADS)

Kveder, Marina; Merunka, Dalibor; Jokić, Milan; Rakvin, Boris

2008-03-01

X -band electron paramagnetic resonance spectroscopy was used to study the spectral properties of a nitroxide spin probe in ethanol glass and crystalline ethanol, at 5-11.5K . The different anisotropy of molecular packing in the two host matrices was evidenced by different rigid limit values for maximal hyperfine splitting in the signal of the spin probe. The significantly shorter phase memory time Tm for the spin probe dissolved in crystalline ethanol, as compared to ethanol glass, was discussed in terms of contribution from spectral diffusion. The effect of low-frequency dynamics was manifested in the temperature dependence of Tm and in the difference between the data measured at different spectral positions. This phenomenon was addressed within the framework of the slow-motional isotropic diffusion model [S. Lee and S. Z. Tang, Phys. Rev. B 31, 1308 (1985)] predicting the spin probe dynamics within the millisecond range, at very low temperatures. The shorter spin-lattice relaxation time of the spin probe in ethanol glass was interpreted in terms of enhanced energy exchange between the spin system and the lattice in the glass matrix due to boson peak excitations.

Magnetic resonance microscopy for assessment of morphological changes in hydrating hydroxypropylmethyl cellulose matrix tablets in situ.

PubMed

Kulinowski, Piotr; Młynarczyk, Anna; Dorożyński, Przemysław; Jasiński, Krzysztof; Gruwel, Marco L H; Tomanek, Bogusław; Węglarz, Władysław P

2012-12-01

To resolve contradictions found in morphology of hydrating hydroxypropylmethyl cellulose (HPMC) matrix as studied using Magnetic Resonance Imaging (MRI) techniques. Until now, two approaches were used in the literature: either two or three regions that differ in physicochemical properties were identified. Multiparametric, spatially and temporally resolved T(2) MR relaxometry in situ was applied to study the hydration progress in HPMC matrix tablets using a 11.7 T MRI system. Two spin-echo based pulse sequences-one of them designed to specifically study short T(2) signals-were used. Two components in the T(2) decay envelope were estimated and spatial distributions of their parameters, i.e. amplitudes and T(2) values, were obtained. Based on the data, five different regions and their temporal evolution were identified: dry glassy, hydrated solid like, two interface layers and gel layer. The regions were found to be separated by four evolving fronts identified as penetration, full hydration, total gelification and apparent erosion. The MRI results showed morphological details of the hydrating HPMC matrices matching compound theoretical models. The proposed method will allow for adequate evaluation of controlled release polymeric matrix systems loaded with drug substances of different solubility.

Influence of phosphate glass recrystallization on the stability of a waste matrix to leaching

NASA Astrophysics Data System (ADS)

Yudintsev, S. V.; Pervukhina, A. M.; Mokhov, A. V.; Malkovsky, V. I.; Stefanovsky, S. V.

2017-04-01

In Russia, highly radioactive liquid wastes from recycling of spent fuel of nuclear reactors are solidified into Na-Al-P glass for underground storage. The properties of the matrix including the radionuclide fixation will change with time due to crystallization. This is supported by the results of study of the interaction between glassy matrices, products of their crystallization, and water. The concentration of Cs in a solution at the contact of a recrystallized sample increased by three orders of magnitude in comparison with an experiment with glass. This difference is nearly one order of magnitude for Sr, Ce, and Nd (simulators of actinides) and U due to their incorporation into phases with low solubility in water. Based on data on the compositional change of solutions after passing through filters of various diameters, it is concluded that Cs occurs in the dissolved state in runs with a glass and recrystallized matrix. At the same time, Sr, lanthanides, and U occur in the dissolved state and in the composition of colloids in runs with glass, and mostly in colloid particles after contact with the recrystallized sample. These results should be regarded for substantiation of safety for geological waste storage.

Synthesis of netlike gold nanoparticles using ampicillin as a stabilizing reagent and its application

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

Song, Y.Z., E-mail: singyuanzhi@sina.com; Zhou, J.F.; Song, Y., E-mail: songyang@mail.buct.edu.cn

Graphical abstract: Electrochemical deposition of netlike gold nanoparticles (GNPs) on the surface of glassy carbon electrode and preparation of netlike GNPs in aqueous solution using ampicillin as a stabilizing reagent were proposed. The catalytic properties of netlike gold nanoparticles on the glassy carbon electrode for dopamine were demonstrated. The results indicate that the netlike gold nanoparticle modified electrode has an excellent repeatability and reproducibility. Display Omitted Highlights: ► Synthesis of netlike gold nanoparticles using ampicillin as a stabilizing reagent. ► Excellent repeatability and reproducibility of netlike gold nanoparticle modified glassy carbon electrode. ► The catalytic properties of netlike gold nanoparticlemore » for dopamine. -- Abstract: Electrochemical deposition of netlike gold nanoparticles on the surface of glassy carbon electrode and preparation of netlike GNPs in aqueous solution using ampicillin as a stabilizing reagent were proposed. The netlike gold nanoparticles were characterized by scanning electron microscope, transmission electron microscope, infrared spectrometer, UV spectrophotometer, powder X-ray diffractometer and electrochemical analyzer. The catalysis of the netlike gold nanoparticles on the glassy carbon electrode for dopamine was demonstrated. The results indicate that the gold nanoparticle modified electrode has an excellent repeatability and reproducibility.« less

Disentangling the Role of Entanglement Density and Molecular Alignment in the Mechanical Response of Glassy Polymers

NASA Astrophysics Data System (ADS)

O'Connor, Thomas; Robbins, Mark

Glassy polymers are a ubiquitous part of modern life, but much about their mechanical properties remains poorly understood. Since chains in glassy states are hindered from exploring their conformational entropy, they can't be understood with common entropic network models. Additionally, glassy states are highly sensitive to material history and nonequilibrium distributions of chain alignment and entanglement can be produced during material processing. Understanding how these far-from equilibrium states impact mechanical properties is analytically challenging but essential to optimizing processing methods. We use molecular dynamics simulations to study the yield and strain hardening of glassy polymers as separate functions of the degree of molecular alignment and inter-chain entanglement. We vary chain alignment and entanglement with three different preparation protocols that mimic common processing conditions in and out of solution. We compare our results to common mechanical models of amorphous polymers and assess their applicability to different experimental processing conditions. This research was performed within the Center for Materials in Extreme Dynamic Environments (CMEDE) under the Hopkins Extreme Materials Institute at Johns Hopkins University. Financial support was provided by Grant W911NF-12-2-0022.

The Erevan howardite: Petrology of glassy clasts and mineral chemistry

NASA Technical Reports Server (NTRS)

Nazarov, M. A.; Ariskin, A. A.

1993-01-01

The Erevan howardite is a polymict regolith breccia containing xenoliths of carbonaceous chondrites. In this work, we studied glassy clasts, which could be considered as primary quenched melts, and mineral chemistry of the breccia. The study reveals that the Erevan howardite consists of common rocks of the HED suite. However, unique glassy clasts, which are present in some eucritic melts, were identified. The mineral chemistry and the simulation of crystallization of the melts suggest that the compositions of the melts reflect those of some primary lithologies of EPB.

Mechanical reinforcement and segmental dynamics of polymer nanocomposites

NASA Astrophysics Data System (ADS)

Gong, Shushan

The addition of nanofiller into a polymer matrix will dramatically change the physical properties of polymer. The introduction of nanofiller makes the polymer more applicable in many industries, such as automobile tires, coatings, semiconductors, and packaging. The altered properties are not the simple combination of the characters from the two components. The interactions in polymer nanocomposites play an important role in determining the physical properties. This dissertation focuses on the mechanical properties of polymer nanocomposites (silica/poly-2-vinylpyridine) above their glass transition temperature Tg, as a model for automobile tires, which utilize small silica particles in crosslinked rubber far above Tg. We also investigate the impacts of the interaction between particle filler and polymer matrix on the altered mechanical properties. Dielectric relaxation spectroscopy (DRS) is used to study the glassy bound polymer layers formed around the particles. The results show evidence of the existence of immobilized polymer layers at the surface of each nanoparticle. At the same time, the thickness of the immobilized polymer layers is quantified and formed to be around 2 nm. Then we consider particles with glassy bound polymer layers are bridged together (either rubbery bridge or glassy bridge) by polymer chains and form small clusters. Clusters finally percolate to form a particle-polymer network as loading fraction increases. Rheology is used to study the network formation, and to predict the boundary of rubbery bridge and glassy bridge regimes. The distance between particles determines the type of polymer bridging. The particle spacing larger than Kuhn length makes flexible (rubbery) bridge with rheology described by a flexible Rouse model for percolation. When the spacing is shorter than the Kuhn length (~ 1nm), stiffer bridge forms instead, which is called glassy bridge. The mechanical differences between rubbery bridge and glassy bridge, and the effect of Mw on the formation of glassy bridge, are also discussed.

Glassy composition for hermetic seals

DOEpatents

Wilder, Jr., James A.

1980-01-01

The invention relates to a glassy composition adaptable for sealing to aluminum-based alloys to form a hermetically-sealed insulator body. The composition may either be employed as a glass or, after devitrifying heat treatment, as a glass-ceramic.

Boson peak as a probe of quantum effects in a glassy state of biomolecules: the case of L-cysteine.

PubMed

Lima, T A; Ishikawa, M S; Martinho, H S

2014-02-01

Some physical properties of hydrated biomolecules, e.g., the occurrence of a boson peak, have been recognized to resemble those of glassy states. The present work shows that quantum fluctuations play a fundamental role in describing the glassy state of biomolecules, particularly at lower hydration levels. There is a linear relationship between the quantumness and the slope of the temperature dependence of the boson peak frequency, which is used to classify the extent of quantum contributions to the glassy state of glasses in general. Lastly, we demonstrate that the boson peak two-band spectral structure that is observed in some cases can be directly linked to the anisotropy of the elastic properties of the material. The amino acid L-cysteine is studied in detail. The findings are compared with previously reported data for other macromolecules.

Non-Equilibrium Water-Glassy Polymer Dynamics

NASA Astrophysics Data System (ADS)

Davis, Eric; Minelli, Matteo; Baschetti, Marco; Sarti, Giulio; Elabd, Yossef

2012-02-01

For many applications (e.g., medical implants, packaging), an accurate assessment and fundamental understanding of the dynamics of water-glassy polymer interactions is of great interest. In this study, sorption and diffusion of pure water in several glassy polymers films, such as poly(styrene) (PS), poly(methyl methacrylate) (PMMA), poly(lactide) (PLA), were measured over a wide range of vapor activities and temperatures using several experimental techniques, including quartz spring microbalance (QSM), quartz crystal microbalance (QCM), and time-resolved Fourier transform infrared-attenuated total reflectance (FTIR-ATR) spectroscopy. Non-Fickian behavior (diffusion-relaxation phenomena) was observed by all three techniques, while FTIR-ATR spectroscopy also provides information about the distribution of the states of water and water transport mechanisms on a molecular-level. Specifically, the states of water are significantly different in PS compared to PMMA and PLA. Additionally, a purely predictive non-equilibrium lattice fluid (NELF) model was applied to predict the sorption isotherms of water in these glassy polymers.

Conformers, infrared spectrum and UV-induced photochemistry of matrix-isolated furfuryl alcohol.

PubMed

Araujo-Andrade, C; Gómez-Zavaglia, A; Reva, I D; Fausto, R

2012-03-08

The infrared spectra of furfuryl alcohol (2-furanmethanol, FFA) were investigated for FFA monomers isolated in low-temperature argon matrices. The structural interpretation of the obtained experimental spectra was assisted by analysis of the molecule's conformational landscape. According to the DFT(B3LYP)/6-311++G(d,p) calculations, five different minimum energy structures were found on the potential energy surface of the molecule. They can be defined by the orientation of the OCCO and CCOH dihedral angles: GG', GG, TG, TT, GT (G = +gauche, G' = -gauche, T = trans) and have a symmetry equivalent configuration: GG' = G'G, GG = G'G', TG = TG', GT = G'T. When zero-point energies are taken into account, only three (GG', GG, and TT) out of the five unique minima correspond to stable structures. The most stable conformer GG' (OCCO, 72.7°; CCOH, -59.3°), which in gas phase at room temperature accounts for ∼65% of the total population, was the only form isolated in the argon matrices at 14 K. The other two relevant forms convert into conformer GG' during matrix deposition. The low temperature glassy and crystalline states of FFA were also obtained and their infrared spectra assigned, suggesting the sole existence of the GG' conformer also in these phases. The photochemical behavior of FFA induced in situ, by tunable UV-laser, was also studied. The longest wavelength resulting in photochemical changes in the structure of the irradiated sample was found to be λ = 229 nm. Such UV irradiation of the matrix-isolated FFA led to production of formaldehyde and different isomeric C(4)H(4)O species. Cycloprop-2-ene-1-carbaldehyde and buta-2,3-dienal (two conformers) are the main initial C(4)H(4)O photoproducts formed upon short-time excitation at λ = 229 nm. But-3-ynal (two conformers) was the principal photoproduct resulting from prolonged excitation at λ= 229 nm, being consumed upon irradiation at shorter wavelengths (λ < 227.5 nm). Vinyl ketene is produced from FFA in the trans conformation and undergoes isomerization to the cis form upon irradiation at λ < 227.5 nm. Cyclopropene, propyne, allene, and CO were also identified in the irradiated matrices (in particular at the later stages of irradiation), suggesting that the photoproduced aldehydes partially decarbonylate during the performed photochemical experiments.

Gravitational lensing in observational cosmology

NASA Astrophysics Data System (ADS)

Nottale, L.

This paper reviews some previous theoretical and observational results concerning the various effects of gravitational lensing, and also presents still unpublished results in this field. The theoretical section deals with the Optical Scalar Equation (OSE) approach. We recall the form of these equations, which relate the deformations of the cross sectional area of a light beam to the material and energetic distribution it encounters, via the two basic contributions to lensing, the matter or Ricci term and the shear term. The introduction of a new distance, the optical distance, allows to write the OSE in a simplified way from which new solutions are easily derived. We demonstrate here that a general form may be obtained for the amplification formula in the exact relativistic treatment, provided the Universe is assumed to be Friedmannian in the mean. New results are also presented concerning the probability distribution of amplifications, the relation from matter term to shear terms (the first ones give the mean of the second ones) and the problem of energy conservation. We recall how our method let to an analytical formula yielding the amplification by any number of lenses placed anywhere along the line of sight and present new general solutions for lensing by large scale density inhomogeneities. The gravitational redshift effects are also considered, either due to the crossing by photons of inhomogeneities, or intrinsic to them ; generalized solutions to the last problem are given. Some observational evidence concerning various lensing effects, either statistical or applying to individual sources, are considered. We first recall how the dependence of the amplification formula on the various physical parameters points towards the optimisation of lensing by very rich clusters of galaxies lying at redshifts around 0.7, which may give rise to very large amplifications for reasonable values of the density parameter. Recent results concerning a statistical effect of amplification of Brightest Cluster Galaxies by foreground clusters are analysed, including the discussion of a selection effect precisely due to gravitational luminosity amplification. It results in an artificial increase of the deceleration parameter of the Universe measured from the Hubble diagram of these objects. We recall our proposal that the sample of distant 3C radiogalaxies of redshift > 1 is strongly perturbed by lensing effects, mostly by foreground clusters of galaxies (i.e. only the luminosity is changed without image multiplication), but also for some objects by galaxies, producing gravitational mirages. The case of 3C324, for which definite evidence for multiple imaging has been recently obtained, is described, including detailed modelling of the lensing configuration. We present a highly significant statistical effect of lensing on absorption line QSOs due to matter lying at the absorption redshifts. Microlensing is also considered, and we recall our recent proposal that the variability of some among the OVV QSOs turning to BL Lac at maximum brightness, like the eruptive object 0846 +51W1, is a consequence of microlensing by stars or compact objects constituting foreground galaxy halos. Finally, discrepant redshift associations are considered. We recall how the case of anomalous quintets of galaxies have been explained by the gravitational lensing effects of quartets halos on background galaxies. Then we present evidence that the Arp QSO-galaxy associations may be the result of the combined lensing effects of several superposed galaxies, groups and clusters. Cet article présente une revue de certains résultats théoriques et observationnels concernant les divers effets de lentille gravitationnelle, complétée par des résultats nouveaux non encore publiés. Dans la partie théorique, nous considérons essentiellement l'approche relativiste employant les équations scalaires optiques. La forme de ces équations est rappelée : elles relient les diverses déformations subies par la section d'un faisceau lumineux au cours de sa propagation, à la distribution matérielle et énergétique qu'il rencontre sur son trajet entre la source et l'observateur. Les deux contributions aux effets d'optique apparaissant dans ces équations (et leurs solutions) sont les termes de matière et les termes de cisaillement. Nous montrons comment une nouvelle distance peut être introduite, la distance optique, en fonction de laquelle les équations se simplifient et de nouvelles solutions analytiques peuvent être établies. En particulier, nous démontrons que la formule d'amplification gravitationnelle peut s'écrire sous une forme très générale sous la simple hypothèse que l'Univers est en moyenne de type Friedmann-Robertson-Walker. De nouveaux résultats sont aussi présentés concernant la distribution de probabilité des amplifications, les rapports entre termes de matière et termes de cisaillement (les premiers donnant la moyenne des seconds), et le problème de la conservation de l'énergie. Nous rappelons comment une formule analytique peut être obtenue pour des amplifications multiples et présentons des solutions nouvelles au problème de l'amplification par des hétérogénéités à très grande échelle. Enfin, les effets de décalages spectraux gravitationnels sont aussi considérés, qu'ils soient dus à des effets de traversée d'excès de densité, ou intrinsèques à ceux-ci ; dans ce dernier cas, une généralisation de solutions déjà connues est proposée. On considère ensuite le problème de la mise en évidence observationnelle des divers effets d'optique gravitationnelle, qu'ils soient de nature statistique ou qu'ils concernent des objets individuels. A la suite d'une analyse décrivant la dépendance de la formule d'amplification en fonction des différents paramètres y intervenant, nous insistons tout particulièrement sur le rôle cosmologique que jouent probablement les amas de galaxies très riches de décalages spectraux autour de 0,7 qui peuvent donner lieu à des amplifications quasi-infinies. La mise en évidence récente d'un effet statistique d'amplification par des amas d'avant-plan sur les galaxies les plus brillantes des amas est rappelée, ainsi que celle d'un important effet de sélection observationnel, précisément dû aux amplifications, qui augmente artificiellement la valeur de q0 mesurée à partir du diagramme de Hubble. L'extrapolation de cet effet à des objets plus lointains nous a conduit à proposer que les radiogalaxies lointaines du catalogue 3C de z < 1 étaient fortement affectées par les effets de lentille gravitationnelle, essentiellement par les amas (qui les amplifient la plupart du temps sans multiplication d'image), mais aussi dans certains cas par des galaxies qui peuvent alors provoquer des effets de mirage. Le cas de 3C324, pour lequel des preuves observationelles de multiplication d'image ont été récemment obtenues, est analysé en particulier ; un modèle détaillé en est présenté. Un autre effet statistique récemment démontré concerne les quasars à raies d'absorption, dont la luminosité est fortement corrélée à l'amplification prédite par de la matière située aux décalages spectraux d'absorption. On considère également les effets de microlentille : nous rappelons notre proposition récente que la variabilité de certains OVVs tels que le BL Lac éruptif 0846 + 51W1 est une conséquence du passage d'étoiles ou d'objets compacts du halo de galaxies intervenantes devant les régions centrales d'un quasar. Le lien entre effets d'optique gravitationnelle et associations de décalages spectraux discordants est évoqué. Le cas des quintets de galaxies discordant a été récemment expliqué par les effets (amplification, agrandissement, changement de densité superficielle d'objets lointains) des halos de groupes compacts de galaxies. Nous démontrons pour finir que les associations QSOsgalaxies de Arp peuvent s'expliquer par les effets de lentille gravitationnelle combinés de plusieurs galaxies, groupes et amas vus en superposition.

Development of a Dynamic Biomechanical Model for Load Carriage: Phase V: Development of the Biomechanical Model by Means of the Portable Measurement System

DTIC Science & Technology

2005-05-01

Résumé La performance opérationnelle des soldats dépend d’un certain nombre de facteurs, dont la charge de travail physiologique, les effets ...particulièrement à la charge de travail physiologique et aux effets biomécaniques, et à perfectionner la mise au point d’un modèle biomécanique dynamique (DBM...on a créé une couche de peau possédant des propriétés appropriées pour le modèle de torse et on a réalisé la modélisation de tous les composants

Playback interference of glassy-winged sharp shooter communication

USDA-ARS?s Scientific Manuscript database

Animal communication is vital to reproduction, particularly for securing a mate. Insects commonly communicate by exchanging vibrational signals that are transmitted through host plants. The glassy-winged sharpshooter (GWSS), Homalodisca vitripennis, is an important vector of Xylella fastidiosa, a pl...

Mating interference of glassy-winged sharpshooters, Homalodisca vitripennis

USDA-ARS?s Scientific Manuscript database

Animal signaling is a complex behavior that is influenced by abiotic and biotic factors of the environment. Glassy-winged sharpshooters (GWSS), Homalodisca vitripennis (Hemiptera: Cicadellidae), primarily use vibrational signaling for courtship. Because GWSS is a major pest, transmitting the plant ...

Nucleation and growth of thin films of the organic conductor TTF-iodide over glassy carbon. Electrochemical and spectroelectrochemical study.

PubMed

Gómez, L; Rodríguez-Amaro, R

2009-04-21

On the basis of the electrochemical and spectroelectrochemical behavior of thin films of TTF over a glassy carbon electrode in iodide media, a new, more complete mechanism for the electrode processes involved is proposed. The voltammetric and chronoamperometric results for the films can be explained in light of a recently developed nucleation-growth model involving a layer-by-layer mechanism. Also, their in situ UV-vis spectral data expand the available knowledge about the overall mechanism and the nature of the compound formed over the glassy carbon electrode.

Molecular dynamics and crystallization phenomenon of supercooled and glassy DNA and RNA nucleosides: β-adenosine, β-thymidine, and β-uridine

NASA Astrophysics Data System (ADS)

Adrjanowicz, K.; Wojnarowska, Z.; Grzybowska, K.; Hawelek, L.; Kaminski, K.; Paluch, M.; Kasprzycka, A.; Walczak, K.

2011-11-01

Nucleosides are chemical compounds that have an extremely important biological role; they can be found in all types of living organisms. They are crucial components from which DNA and RNA acids are built. In addition, nucleosides are key regulators of many physiological processes. In this paper, the molecular dynamics in the liquid and glassy state of three selected nucleosides, β-adenosine, β-thymidine, and β-uridine, was investigated by means of dielectric spectroscopy. Our results revealed multiple relaxation processes associated with different types of molecular motions. Besides the primary α relaxation, two secondary modes in the glassy states of examined compounds were identified. Crystallization progress monitored by dielectric spectroscopy and x-ray diffraction technique at isostructural relaxation conditions revealed that the examined nucleosides possess completely different tendencies to recrystallize from the liquid as well as the glassy state. We have also made an attempt to predict the time scale of molecular motion below the glass transition temperatures of the respective nucleosides to discuss their potential stability at room temperature over prolonged storage time. Finally, combination of molecular mobility studies with evaluation of thermodynamic parameters from calorimetric measurements allowed us to discuss the fundamental roles of both kinetic and thermodynamic factors in governing the physical stability of the glassy state.

Comparaison des effets des irradiations γ, X et UV dans les fibres optiques

NASA Astrophysics Data System (ADS)

Girard, S.; Ouerdane, Y.; Baggio, J.; Boukenter, A.; Meunier, J.-P.; Leray, J.-L.

2005-06-01

Les fibres optiques présentent de nombreux avantages incitant à les intégrer dans des applications devant résister aux environnements radiatifs associés aux domaines civil, spatial ou militaire. Cependant, leur exposition à un rayonnement entraîne la création de défauts ponctuels dans la silice amorphe pure ou dopée qui constitue les différentes parties de la fibre optique. Ces défauts causent, en particulier, une augmentation transitoire de l'atténuation linéique des fibres optiques responsable de la dégradation voire de la perte du signal propagé dans celles-ci. Dans cet article, nous comparons les effets de deux types d'irradiation: une impulsion X et une dose γ cumulée. Les effets de ces irradiations sont ensuite comparés avec ceux induits par une insolation ultraviolette (244 nm) sur les propriétés d'absorption des fibres optiques. Nous montrons qu'il existe des similitudes entre ces différentes excitations et qu'il est possible, sous certaines conditions, d'utiliser celles-ci afin d'évaluer la capacité de certaines fibres optiques à fonctionner dans un environnement nucléaire donné.

Antisuperconductors: Properties of Layered Compounds with Coupling

NASA Astrophysics Data System (ADS)

Carton, J.-P.; Lammert, P. E.; Prost, J.

1995-11-01

In this note, we consider properties of a hypothetical superconductor composed of Josephson-coupled microscopic layers with tunneling energy minimized at a phase difference of π. The non-zero phase offset in the ground state engenders an intriguing interplay between the superconductive ordering and structural lattice defects. Unusual magnetic properties are expected in the case of highly disordered crystals, which are consistent with observations of a “paramagnetic Meissner” or “Wohlleben” effect in high-T_c cuprate superconductors. Dans cette note, nous considérons les propriétés d'un supraconducteur hypothétique composé de couches microscopiques, couplées par effet Josephson, mais dont l'énergie de couplage est minimisée pour une différence de phase de π. L'état de base a des propriétés fascinantes dues à l'effet combiné de l'ordre supraconducteur et des défauts structuraux du cristal. Dans le cas de cristaux très désordonnés, on attend des propriétés magnétiques exceptionnelles, qui sont compatibles avec les observations dans quelques supraconducteurs cuprate haute-T_c d'un effet “Meissner paramagnétique” ou “Wohlleben”.

Etude par resistivite electrique du comportement d'un alliage amorphe Fe 40Ni 38Mo 4B 18 deforme par traction

NASA Astrophysics Data System (ADS)

Hoang, Long Phan; Sacovy, Paulette; Delaplace, Jean

1983-02-01

Des rubans d'alliages amorphes Metglas du type Fe 40Ni 38Mo 4B 18 à l'état brut de trempe ont été déformés par traction à la température ambiante et l'on a suivi les variations de la résistance électrique des échantillons au cours de la déformation. Il ressort de ces essais que la déformation plastique qui est de l'ordre de 0.5% avant rupture ne se produit pas de faĉon homogène dans l'échantillon. Les mesures électriques effectuées au cours de la déformation mettent en évidence dans le domaine élastique un effet d'élastorésistance, relativement important ( K ≠ 1); elles montrent que dans le domaine plastique la déformation permanente des échantillons s'accompagne d'une diminution de la résistivité électrique du matériau. Deux hypothèses sont discutées pour expliquer cet effet inattendu, l'un qui fait appel à l'existence de volumes libres, l'autre qui suppose une cristallisation localisée du matériau sous l'effet de la contrainte.

Mating behavior and vibrational mimicry in the glassy-winged sharpshooter, Homalodisca vitripennis

USDA-ARS?s Scientific Manuscript database

Vibrational communication is widespread in insects, particularly in leafhoppers where the pair formation process is mediated by species-specific vibrational signals. One important pest using vibrational communication, glassy-winged sharpshooter (GWSS), Homalodisca vitripennis, is a vector of Xylella...

Electronic structure and bonding of intergranular glassy films in polycrystalline Si3 N4 : Ab initio studies and classical molecular dynamics simulations

NASA Astrophysics Data System (ADS)

Rulis, P.; Chen, J.; Ouyang, L.; Ching, W.-Y.; Su, X.; Garofalini, S. H.

2005-06-01

The electronic structure and bonding of a realistic model of an intergranular glassy film (IGF) was studied with multiple computational methods. The model has a Si-O-N glassy region sandwiched between crystalline basal planes of β-Si3N4 and contains a total of 798 atoms. It was constructed with periodic boundary conditions via classical molecular dynamics (MD) techniques using an accurate multibody atomic potential. The model was then further relaxed by the VASP (Vienna ab initio simulation package) program. It is shown that the VASP-relaxed structure reduces the total energy from the MD-relaxed structure by only 47.38eV , validating the accuracy of the multiatom potential used. The calculated electronic structure shows the IGF model to be an insulator with a sizable gap of almost 3eV . Quasidefectlike states can be identified near the band edges arising from the more strained Si-N and Si-O bonds at the interface. Calculation of the Mulliken effective charge and bond order values indicates that the bonds in the glassy region and at the interface can be enhanced and weakened by distortions in the bond length and bond angle. The states at the top of the valence band are derived mostly from the crystalline part of the Si-N bonding while the states at the bottom of the conduction band are dominated by the Si-O bonding in the glassy region. Calculation of the electrostatic potential across the interface shows an average band offset of about 1.5eV between the crystalline β-Si3N4 and the glassy Si-O-N region which could be related to the space charge model for IGF.

Nanoparticules d'or: De l'imagerie par resonance magnetique a la radiosensibilisation

NASA Astrophysics Data System (ADS)

Hebert, Etienne M.

Cette thèse approfondit l'étude de nanoparticules d'or de 5 nm de diamètre recouvertes de diamideéthanethioldiethylènetriaminepentacétate de gadolinium (DTDTPA:Gd), un agent de contraste pour l'imagerie par résonance magnétique (IRM). En guise de ciblage passif, la taille des nanoparticules a été contrôlée afin d'utiliser le réseau de néovaisseaux poreux et perméable des tumeurs. De plus les tumeurs ont un drainage lymphatique déficient qui permet aux nanoparticules de demeurer plus longtemps dans le milieu interstitiel de la tumeur. Les expériences ont été effectuées sur des souris Balb/c femelles portant des tumeurs MC7-L1. La concentration de nanoparticules a pu être mesurée à l'IRM in vivo. La concentration maximale se retrouvait à la fin de l'infusion de 10 min. La concentration s'élevait à 0.3 mM dans la tumeur et de 0.12 mM dans le muscle environnant. Les nanoparticules étaient éliminées avec une demi-vie de 22 min pour les tumeurs et de 20 min pour le muscle environnant. Les nanoparticules ont été fonctionnalisées avec le peptide Tat afin de leur conférer des propriétés de ciblage actif La rétention de ces nanoparticules a ainsi été augmentée de 1600 %, passant d'une demi-vie d'élimination de 22 min à 350 min. La survie des souris a été mesurée à l'aide de courbes Kaplan-Meier et d'un modèle mathématique évalue l'efficacité de traitements. Le modèle nous permet, à l'aide de la vitesse de croissance des tumeurs et de l'efficacité des traitements, de calculer la courbe de survie des spécimens. Un effet antagoniste a été observé au lieu de l'effet synergétique attendu entre une infusion de Au@DTDTPA:Gd et l'irradiation aux rayons X. L'absence d'effet synergétique a été attribuée à l'épaisseur du recouvrement de DTDTPA:Gd qui fait écran aux électrons produits par l'or. De plus, le moyen d'ancrage du recouvrement utilise des thiols qui peuvent s'avérer être des capteurs de radicaux. De plus, contrairement a ce qui était escompté, un effet chimiothérapeutique de ces nanoparticules a été observé in vitro et in vivo. Par contre, le mécanisme précis de cet effet est encore à être expliquer, mais on sait déjà que les nanoparticules d'or affectent les fonctions des macrophages ainsi que l'angiogenèse. MOTS-CLÉS : Radiosensibilisateur, Nanoparticules d'or, Agent de contraste pour l'IRM, Électrons de basses énergies, Kaplan-Meier, Effet chimiothérapeutique.

Parametrisation D'effets Non-Standard EN Phenomenologie Electrofaible

NASA Astrophysics Data System (ADS)

Maksymyk, Ivan

Cette these pat articles porte sur la parametrisation d'effets non standard en physique electrofaible. Dans chaque analyse, nous avons ajoute plusieurs operateurs non standard au lagrangien du modele standard electrofaible. Les operateurs non standard decrivent les nouveaux effets decoulant d'un modele sous-jacent non-specefie. D'emblee, le nombre d'operateurs non standard que l'on peut inclure dans une telle analyse est illimite. Mais pour une classe specifique de modeles sous-jacents, les effets non standard peuvent etre decrits par un nombre raisonnable d'operateurs. Dans chaque analyse nous avons developpe des expressions pour des observables electrofaibles, en fonction des coefficients des operateurs nouveaux. En effectuant un "fit" statistique sur un ensemble de donnees experimentales precises, nous avons obtenu des contraintes phenomenologiques sur ces coefficients. Dans "Model-Independent Global Constraints on New Physics", nous avons adopte des hypotheses tres peu contraignantes relatives aux modeles sous-jacents. Nous avons tronque le lagrangien effectif a la dimension cinq (inclusivement). Visant la plus grande generalite possible, nous avons admis des interactions qui ne respectent pas les symetries discretes (soit C, P et CP) ainsi que des interactions qui ne conservent pas la saveur. Le lagrangien effectif contient une quarantaine d'operateurs nouveaux. Nous avons determine que, pour la plupart des coefficients des nouveaux operateurs, les contraintes sont assez serrees (2 ou 3%), mais il y a des exceptions interessantes. Dans "Bounding Anomalous Three-Gauge-Boson Couplings", nous avons determine des contraintes phenomenologiques sur les deviations des couplages a trois bosons de jauge par rapport aux interactions prescrites par le modele standard. Pour ce faire, nous avons calcule les contributions indirectes des CTBJ non standard aux observables de basse energie. Puisque le lagrangien effectif est non-renormalisable, certaines difficultes techniques se posent: pour regulariser les integrales de Feynman les chercheurs se sont generalement servi de la methode de coupure, mais cette methode peut mener a des resultats incorrects. Nous avons opte pour une technique alternative: la regularisation dimensionnelle et la "soustraction minimale avec decouplage". Dans "Beyond S, T and U" nous presentons le formalisme STUVWX, qui est une extension du formalisme STU de Peskin et Takeuchi. Ces formalismes sont bases sur l'hypothese que la theorie sous-jacente se manifeste au moyen de self -energies de bosons de jauge. Ce type d'effet s'appelle 'oblique'. A la base du formalisme STU se trouve la supposition que l'echelle de la nouvelle physique, M, est beaucoup plus grande que q, l'echelle a laquelle on effectue des mesures. Il en resulte que les effets obliques se parametrisent par les trois variables S, T et U. Par contre, dans le formalisme STUVWX, nous avons admis la possibilite que M~ q. Dans "A Global Fit to Extended Oblique Parameters", nous avons effectue deux fits statistiques sur un ensemble de mesures electrofaibles de haute precision. Dans le premier fit, nous avons pose V=W=X=0, obtenant ainsi des contraintes pour l'ensemble {S,T,U}. Dans le second fit, nous avons inclus tous les six parametres.

Grapevines respond to glassy-winged sharpshooter (Homalodisca vitripennis) oviposition by increasing local and systemic terpenoid levels

USDA-ARS?s Scientific Manuscript database

Grapevines (Vitis vinifera) have been observed to respond to oviposition by glassy-winged sharpshooters [Homalodisca vitripennis (Germar)(Hemiptera: Cicadellidae)] by producing volatile compounds that attract egg parasitoids such as Gonatocerus ashmeadi Girault (Hymenoptera: Mymaridae). Recent work ...

Glassy-winged sharpshooter can use a mechanical mechanism to inoculate Xylella fastidiosa into grapevines

USDA-ARS?s Scientific Manuscript database

Xylem-feeding leafhoppers such as the glassy-winged sharpshooter, Homalodisca vitripennis (Cicadellidae: Cicadellinae), are thought to inoculate the bacterium Xylella fastidiosa (Xf) from colonies bound to cuticle of the sharpshooter’s functional foregut (precibarium and cibarium). The mechanism of ...

Substrate-borne vibrational signals in intraspecific communication of glassy-winged sharpshooters (GWSS)

USDA-ARS?s Scientific Manuscript database

Exploitation of vibrational signals for suppressing glassy-winged sharpshooter (GWSS) populations could prove to be a useful tool. However, existing knowledge on GWSS vibrational communication is insufficient to implement a management program for this pest in California. Therefore, the objective of ...

The Quench Control of Water Estimates in Convergent Margin Magmas

NASA Astrophysics Data System (ADS)

Gavrilenko, M.; Krawczynski, M.; Ruprecht, P.

2017-12-01

Mineral-hosted glassy melt inclusions (MIs) have been used to quantify magma volatile contents for several decades. Despite the growing number of volatile studies utilizing MIs, it has not been tested whether there is a physical limit on how much dissolved volatiles a glassy MI can contain. We explored the limits of MIs as hydrous magma recorders in an experimental study, showing that there is a limit of dissolved H2O that glassy MIs cannot exceed. These results show there is potential bias in the glassy MI data set; they can only faithfully record pre-eruptive H2O contents in the upper-most part of the Earth's crust where H2O-solubility is low. The current MI database cannot be used to robustly estimate the full range of arc magmas and therefore assess volatile budgets in primitive or evolved compositions. Such magmas may contain much larger amounts of H2O than currently recognized and the diversity of magma evolutionary pathways in subduction zones is likely being significantly underappreciated.

A Thermodynamic Theory of Solid Viscoelasticity. Part 3: Nonlinear Glassy Viscoelasticity, Stability Constraints, Specifications

NASA Technical Reports Server (NTRS)

Freed, Alan; Leonov, Arkady I.

2002-01-01

This paper, the last in the series, continues developing the nonlinear constitutive relations for non-isothermal, compressible, solid viscoelasticity. We initially discuss a single integral approach, more suitable for the glassy state of rubber-like materials, with basic functionals involved in the thermodynamic description for this type of viscoelasticity. Then we switch our attention to analyzing stability constraints, imposed on the general formulation of the nonlinear theory of solid viscoelasticity. Finally, we discuss specific (known from the literature or new) expressions for material functions that are involved in the constitutive formulations of both the rubber-like and glassy-like, complementary parts of the theory.

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.

Interplay between local dynamics and mechanical reinforcement in glassy polymer nanocomposites

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

Holt, Adam P.; Bocharova, Vera; Cheng, Shiwang

The modification of polymer dynamics in the presence of strongly interacting nanoparticles has been shown to significantly change themacroscopic properties above the glass transition temperature of polymer nanocomposites (PNCs). However, much less attention has been paid to changes in the dynamics of glassy PNCs. Analysis of neutron and light scattering data presented herein reveals a surprising enhancement of local dynamics, e.g., fast picosecond and secondary relaxations, in glassy PNCs accompanied with a strengthening of mechanical modulus. Here we ascribe this counter-intuitive behavior to the complex interplay between chain packing and stretching within the interfacial layer formed at the polymer-nanoparticle interface.

Interplay between local dynamics and mechanical reinforcement in glassy polymer nanocomposites

DOE PAGES

Holt, Adam P.; Bocharova, Vera; Cheng, Shiwang; ...

2017-11-17

The modification of polymer dynamics in the presence of strongly interacting nanoparticles has been shown to significantly change themacroscopic properties above the glass transition temperature of polymer nanocomposites (PNCs). However, much less attention has been paid to changes in the dynamics of glassy PNCs. Analysis of neutron and light scattering data presented herein reveals a surprising enhancement of local dynamics, e.g., fast picosecond and secondary relaxations, in glassy PNCs accompanied with a strengthening of mechanical modulus. Here we ascribe this counter-intuitive behavior to the complex interplay between chain packing and stretching within the interfacial layer formed at the polymer-nanoparticle interface.

Diamond fiber field emitters

DOEpatents

Blanchet-Fincher, Graciela B.; Coates, Don M.; Devlin, David J.; Eaton, David F.; Silzars, Aris K.; Valone, Steven M.

1996-01-01

A field emission electron emitter comprising an electrode formed of at least one diamond, diamond-like carbon or glassy carbon composite fiber, said composite fiber having a non-diamond core and a diamond, diamond-like carbon or glassy carbon coating on said non-diamond core, and electronic devices employing such a field emission electron emitter.

Detection and typing of Xylella fastidiosa from glassy-winged sharpshooter for Pierce’s disease epidemiology

USDA-ARS?s Scientific Manuscript database

Epidemiology of Pierce’s disease of grape, caused by the bacterial pathogen Xylella fastidiosa (Xf), is largely dependent on populations of insect vectors such as the invasive glassy-winged sharpshooter (GWSS) (Homalodisca vitripennis). In the grape-growing regions of the southern San Joaquin Valley...

Glassy-winged sharpshooter oviposition effects on foliar grapevine and red-tipped photinia terpenoid levels

USDA-ARS?s Scientific Manuscript database

The glassy-winged sharpshooter (GWSS), Homalodisca vitripennis (Germar) (Hemiptera: Cicadellidae), is an important vector of Xylella fastidiosa, the bacterium that causes Pierce's disease of grapevine and is a threat to grape production throughout the United States. Female GWSS deposit egg masses be...

Broadband nanoindentation of glassy polymers: Part II. Viscoplasticity

Treesearch

Joseph E. Jakes; Rod S. Lakes; Don S. Stone

2012-01-01

The relationship between hardness and flow stress in glassy polymers is examined. Materials studied include poly(methylmethacrylate), polystyrene, and polycarbonate. Properties are strongly rate dependent, so broadband nanoindentation creep (BNC) is used to measure hardness across a broad range of indentation strain rates (10-4 to 10 s

Broadband nanoindentation of glassy polymers: Part I Viscoelasticity

Treesearch

Joesph E. Jakes; Rod S. Lakes; Don S. Stone

2012-01-01

Protocols are developed to assess viscoelastic moduli from unloading slopes in Berkovich nanoindentation across four orders of magnitude in time scale (0.01-100 s unloading time). Measured viscoelastic moduli of glassy polymers poly(methyl methacrylate), polystyrene, and polycarbonate follow the same trends with frequency (1/unloading time) as viscoelastic moduli...

Exploring glassy-winged sharpshooter microbiota using deep 16S rRNA sequencing from individual insects

USDA-ARS?s Scientific Manuscript database

The glassy-winged sharpshooter (GWSS) is an invasive insect species that transmits Xylella fastidiosa, the bacterium causing Pierce’s disease of grapevine and other leaf scorch diseases. X. fastidiosa has been shown to colonize the anterior foregut (cibarium and precibarium) of sharpshooters, where ...

Glassy-winged sharpshooter Microbiota explored using deep 16S rRNA sequencing from individual insects

USDA-ARS?s Scientific Manuscript database

The glassy-winged sharpshooter (GWSS) is an invasive insect species that transmits Xylella fastidiosa, the bacterium causing Pierce’s disease of grapevine and other leaf scorch diseases. X. fastidiosa has been shown to colonize the anterior foregut (cibarium and precibarium) of sharpshooters, where ...

Mating vibrational signal transmission through and between plants of an agricultural pest, the Glassy-Winged Sharpshooter

USDA-ARS?s Scientific Manuscript database

The agricultural pest, glassy-winged sharpshooter (GWSS), Homalodisca vitripennis, relies primarily on successful vibrational communication across its home plant. Males and females engage in a vibrational duet to identify correct species, attractiveness of mate, and location on the plant. The signal...

Design of a candidate vibrational signal for mating disruption against the glassy-winged sharpshooter, Homalodisca Vitripennis

USDA-ARS?s Scientific Manuscript database

The glassy-winged sharpshooter (GWSS), Homalodisca vitripennis, is an important pest of grapevines due to its ability to transmit Xylella fastidiosa, the causal agent of Pierce’s disease. GWSS mating communication is based on vibrational signals; therefore, vibrational mating disruption could be an ...

Playback of natural vibrational signals in vineyard trellis for mating disruption of glassy-winged sharpshooter

USDA-ARS?s Scientific Manuscript database

The glassy-winged sharpshooter, Homalodisca vitripennis (Germar) (Hemiptera: Cicadellidae), is a vector of Xylella fastidiosa, an important bacterial pathogen of several crops in the Americas and Europe. Mating communication of this and many other cicadellid pests involves the exchange of substrate-...

Egg maturation by the glassy-winged sharpshooter (Hemiptera: Cicadellidae); a vector of Xylella fastidiosa

USDA-ARS?s Scientific Manuscript database

Rates of spread of insect-transmitted plant pathogens are a function of vector abundance. Despite this, factors affecting population growth rates of insects that transmit plant pathogens have received limited attention. The glassy-winged sharpshooter (Homalodisca vitripennis) feeds on xylem-sap and ...

Graphitization of Glassy Carbon after Compression at Room Temperature

NASA Astrophysics Data System (ADS)

Shiell, T. B.; McCulloch, D. G.; McKenzie, D. R.; Field, M. R.; Haberl, B.; Boehler, R.; Cook, B. A.; de Tomas, C.; Suarez-Martinez, I.; Marks, N. A.; Bradby, J. E.

2018-05-01

Glassy carbon is a technologically important material with isotropic properties that is nongraphitizing up to ˜3000 °C and displays complete or "superelastic" recovery from large compression. The pressure limit of these properties is not yet known. Here we use experiments and modeling to show permanent densification, and preferred orientation occurs in glassy carbon loaded to 45 GPa and above, where 45 GPa represents the limit to the superelastic and nongraphitizing properties of the material. The changes are explained by a transformation from its s p2 rich starting structure to a s p3 rich phase that reverts to fully s p2 bonded oriented graphite during pressure release.

The superconducting state parameters of glassy superconductors

NASA Astrophysics Data System (ADS)

Vora, Aditya M.

2011-11-01

We present theoretical investigations of the superconducting state parameters (SSPs), i.e. the electron-phonon coupling strength, λ, Coulomb pseudopotential, μ*, transition temperature, Tc, isotope effect exponent, α, and effective interaction strength, N0V, of glassy superconductors by employing Ashcroft's well know empty core model potential for the first time using five screening functions proposed by Hartree (H), Taylor, Ichimaru-Utsumi (IU), Farid et al and Sarkar et al. The Tc obtained from the H and IU screening functions is found to be in excellent agreement with available experimental data. Also, the present results confirm the superconducting phase in bulk metallic glass superconductors. A strong dependency of the SSPs of the glassy superconductors on the 'Z' valence is found.

Elastic properties of aspirin in its crystalline and glassy phases studied by micro-Brillouin scattering

NASA Astrophysics Data System (ADS)

Ko, Jae-Hyeon; Lee, Kwang-Sei; Ike, Yuji; Kojima, Seiji

2008-11-01

The acoustic waves propagating along the direction perpendicular to the (1 0 0) cleavage plane of aspirin crystal were investigated using micro-Brillouin spectroscopy from which C11, C55 and C66 were obtained. The temperature dependence of the longitudinal acoustic waves could be explained by normal anharmonic lattice models, while the transverse acoustic waves showed an abnormal increase in the hypersonic attenuation at low temperatures indicating their coupling to local remnant dynamics. The sound velocity as well as the attenuation of the longitudinal acoustic waves of glassy aspirin showed a substantial change at ˜235 K confirming a transition from glassy to supercooled liquid state in vitreous aspirin.

Microstructure and mechanical behavior of metallic glass fiber-reinforced Al alloy matrix composites

PubMed Central

Wang, Z.; Georgarakis, K.; Nakayama, K. S.; Li, Y.; Tsarkov, A. A.; Xie, G.; Dudina, D.; Louzguine-Luzgin, D. V.; Yavari, A. R.

2016-01-01

Metallic glass-reinforced metal matrix composites are an emerging class of composite materials. The metallic nature and the high mechanical strength of the reinforcing phase offers unique possibilities for improving the engineering performance of composites. Understanding the structure at the amorphous/crystalline interfaces and the deformation behavior of these composites is of vital importance for their further development and potential application. In the present work, Zr-based metallic glass fibers have been introduced in Al7075 alloy (Al-Zn-Mg-Cu) matrices using spark plasma sintering (SPS) producing composites with low porosity. The addition of metallic glass reinforcements in the Al-based matrix significantly improves the mechanical behavior of the composites in compression. High-resolution TEM observations at the interface reveal the formation of a thin interdiffusion layer able to provide good bonding between the reinforcing phase and the Al-based matrix. The deformation behavior of the composites was studied, indicating that local plastic deformation occurred in the matrix near the glassy reinforcements followed by the initiation and propagation of cracks mainly through the matrix. The reinforcing phase is seen to inhibit the plastic deformation and retard the crack propagation. The findings offer new insights into the mechanical behavior of metal matrix composites reinforced with metallic glasses. PMID:27067824

Preparation and characterization of PANI@G/CWO nanocomposite for enhanced 2-nitrophenol sensing

NASA Astrophysics Data System (ADS)

Khan, Anish; Khan, Aftab Aslam Parwaz; Rahman, Mohammed M.; Asiri, Abdullah M.; Inamuddin; Alamry, Khalid A.; Hameed, Salem A.

2018-03-01

A new material by polymer insertion via graphene oxide into cerium tungstate was prepared by very simple oxidation-reduction method. Aniline polymerization was done on the surface of graphene oxide (GO) which was reduced to graphene (G) simultaneously mixed with separately prepared inorganic matrices of cerium tungstate (Ce2(WO4)3 (CWO)). PANI@G/CWO was characterized by various spectroscopic methods as SEM, FTIR, TGA, XRD and XPS to confirm its possibilities. Selective 2-nitrophenol sensor was fabricated on flat glassy carbon electrode (GCE) and PANI@G/CWO nanocomposites in the form of thin layer. It was found excellent sensitivity as well as long life spam with broad dynamic concentration range (LDR) that showed efficient electrochemical performance towards 2-nitrophenol on fabricated chemical sensor by PANI@G/CWO. The linear calibration curve (r2 = 0.9914) with wide range of 2-nitrophenol concentration (1.0 nM-1.0 mM) was found having the detection limit of 0.87 nM while the sensitivity of the sensor was around 1.229 μ A μM-1 cm-2. It was introduced a new route for the development of a versatile phenolic sensor based on PANI@G/CWO nanocomposites by I-V method that is proved more selective and sensitive for environmental toxic materials.

Organization of Nucleotides in Different Environments and the Formation of Pre-Polymers

NASA Astrophysics Data System (ADS)

Himbert, Sebastian; Chapman, Mindy; Deamer, David W.; Rheinstädter, Maikel C.

2016-08-01

RNA is a linear polymer of nucleotides linked by a ribose-phosphate backbone. Polymerization of nucleotides occurs in a condensation reaction in which phosphodiester bonds are formed. However, in the absence of enzymes and metabolism there has been no obvious way for RNA-like molecules to be produced and then encapsulated in cellular compartments. We investigated 5‧-adenosine monophosphate (AMP) and 5‧-uridine monophosphate (UMP) molecules confined in multi-lamellar phospholipid bilayers, nanoscopic films, ammonium chloride salt crystals and Montmorillonite clay, previously proposed to promote polymerization. X-ray diffraction was used to determine whether such conditions imposed a degree of order on the nucleotides. Two nucleotide signals were observed in all matrices, one corresponding to a nearest neighbour distance of 4.6 Å attributed to nucleotides that form a disordered, glassy structure. A second, smaller distance of 3.4 Å agrees well with the distance between stacked base pairs in the RNA backbone, and was assigned to the formation of pre-polymers, i.e., the organization of nucleotides into stacks of about 10 monomers. Such ordering can provide conditions that promote the nonenzymatic polymerization of RNA strands under prebiotic conditions. Experiments were modeled by Monte-Carlo simulations, which provide details of the molecular structure of these pre-polymers.

Permeation of Mixed Penetrants through Glassy Polymer Membranes.

DTIC Science & Technology

1985-03-15

and LOPE. Also, ESCA was used in conjunction with plasma etching to determine the effects of the gas phase fluorine concentration and fluorination...at 35 3C. ARD-AISS5 65 PERMEATION OF MIXED PENETRANTS THROUGH GLASSY POLYMER 213 MENBRANES (U) NORTH CAROLINA STATE UNIV AT RALEIGH R T CHERN ET AL. 15

Anterior foregut microbiota of the glassy-winged sharpshooter explored using deep 16S rRNA gene sequencing from individual insects

USDA-ARS?s Scientific Manuscript database

The glassy-winged sharpshooter (GWSS) is an invasive insect species that transmits Xylella fastidiosa, the bacterium causing Pierce’s disease of grapevine and other leaf scorch diseases. X. fastidiosa has been shown to colonize the anterior foregut (cibarium and precibarium) of sharpshooters, where ...

Effects of energy reserves and diet on glassy-winged sharpshooter egg maturation

USDA-ARS?s Scientific Manuscript database

Effects of stored energy and diet quality on glassy-winged sharpshooter egg maturation were evaluated. To evaluate effects of diet quality on egg maturation, egg load weights of females at the end of a 6-day feeding period on cowpea or grapevine were compared. To estimate energy reserves available a...

Evaluation of a method to quantify glassy-winged sharpshooter (Hemiptera: Cicadellidae) egg maturation during a feeding assay

USDA-ARS?s Scientific Manuscript database

Methods to improve an assay relating adult feeding to egg maturation by the glassy-winged sharpshooter (Hemiptera: Cicadellidae) were evaluated. The assay consisted of confining adult females to cowpea stems in parafilm enclosures and quantifying adult feeding and egg maturation. Adult feeding was...

Salivary enzymes are injected into xylem by the glassy-winged sharpshooter, a vector of Xylella fastidiosa

USDA-ARS?s Scientific Manuscript database

Certain hemipteran insects such as the glassy-winged sharpshooter, Homalodisca vitripennis, subsist entirely on xylem fluid, notwithstanding the poor nutrition of such food. Among many adaptations enabling xylem-feeding are aspects of the insect’s salivation that may also allow these insects to tra...

Graphene oxide-mediated electrochemistry of glucose oxidase on glassy carbon electrodes.

PubMed

Castrignanò, Silvia; Valetti, Francesca; Gilardi, Gianfranco; Sadeghi, Sheila J

2016-01-01

Glucose oxidase (GOD) was immobilized on glassy carbon electrodes in the presence of graphene oxide (GO) as a model system for the interaction between GO and biological molecules. Lyotropic properties of didodecyldimethylammonium bromide (DDAB) were used to stabilize the enzymatic layer on the electrode surface resulting in a markedly improved electrochemical response of the immobilized GOD. Transmission electron microscopy images of the GO with DDAB confirmed the distribution of the GO in a two-dimensional manner as a foil-like material. Although it is known that glassy carbon surfaces are not ideal for hydrogen peroxide detection, successful chronoamperometric titrations of the GOD in the presence of GO with β-d-glucose were performed on glassy carbon electrodes, whereas no current response was detected upon β-d-glucose addition in the absence of GO. The GOD-DDAB-GO system displayed a high turnover efficiency and substrate affinity as a glucose biosensor. The simplicity and ease of the electrode preparation procedure of this GO/DDAB system make it a good candidate for immobilizing other biomolecules for fabrication of amperometric biosensors. © 2015 International Union of Biochemistry and Molecular Biology, Inc.

Rb-Sr and Sm-Nd Isotopic Studies of Lunar Green and Orange Glasses

NASA Technical Reports Server (NTRS)

Shih, C.-Y.; Nyquist, L. E.; Reese, Y.

2012-01-01

Lunar volcanic glassy beads have been considered as quenched basaltic magmas derived directly from deep lunar mantle during fire-fountaining eruptions [1]. Since these sub-mm size glassy melt droplets were cooled in a hot gaseous medium during free flight [2], they have not been subject to mineral fractionations. Thus, they represent primary magmas and are the best samples for the investigation of the lunar mantle. Previously, we presented preliminary Rb- Sr and Sm-Nd isotopic results for green and orange glassy samples from green glass clod 15426,63 and orange soil 74220,44, respectively [3]. Using these isotopic data, initial Sr-87/Sr-86 and Nd ratios for these pristine mare glass sources can be calculated from their respective crystallization ages previously determined by other age-dating techniques. These isotopic data were used to evaluate the mineralogy of the mantle sources. In this report, we analyzed additional glassy samples in order to further characterize isotopic signatures of their source regions. Also, we'll postulate a relationship between these two major mare basalt source mineralogies in the context of lunar magma ocean dynamics.

Study of optical properties of vacuum evaporated carbon nanotube containing Se80Te16Cu4 thin films

NASA Astrophysics Data System (ADS)

Upadhyay, A. N.; Tiwari, R. S.; Singh, Kedar

2016-08-01

Thin films of Se80Te16Cu4 glassy alloy and 3 wt.% of carbon nanotubes (CNTs) containing Se80Te16Cu4 glassy composite were deposited on clean glass substrate by thermal evaporation technique. The scanning electron microscope and energy dispersive x-ray analysis were performed to investigate the surface morphology and elemental composition of as synthesised samples. The reflectance and transmittance spectra of as-deposited thin films were recorded (200-1100 nm) by using UV/VIS/NIR spectrophotometer. The optical band gap and optical constants such as absorption coefficient (α), refractive index (n) and extinction coefficient (k) of Se80Te16Cu4 and 3 wt.% CNTs-Se80Te16Cu4 glassy composite thin films were calculated. It is observed that optical properties alter due to CNTs incorporation in Se80Te16Cu4 glassy alloy. Effect on optical properties due to CNTs incorporation can be explained in terms of concentration of unsaturated bonds/defects in the localised states.

Effect of osmotic dehydration pretreatment and glassy state storage on the quality attributes of frozen mangoes under long-term storage.

PubMed

Zhao, Jin-Hong; Xiao, Hong-Wei; Ding, Yang; Nie, Ying; Zhang, Yu; Zhu, Zhen; Tang, Xuan-Ming

2017-05-01

Changes in the quality of frozen mango cuboids were investigated during long-term glassy state storage with and without osmotic dehydration pretreatment. The mango cuboids were dehydrated in mixed solutions (sucrose: glucose: fructose in a ratio of 3.6:1:3) of different concentrations (30, 40, and 50% (wt/wt)) prior to freezing and then stored at -55 °C (in the glassy state) for 6 months. The results revealed that compared with the untreated samples, osmotic pretreatment decreased total color difference (reduced by 15.6-62.3%), drip loss (reduced by 8.2-29.5%) and titration acidity (reduced by 1.3-9.4%), while increasing hardness (increased by 48.8-82.3%), vitamin C content (increased by 72.5-120.6%) and total soluble solids (increased by 21.8-53.7%) of frozen mangoes after 6 months. Dehydration with a sugar concentration of 40% was considered as the optimal pretreatment condition. In addition, a storage temperature of -55 °C provided better retention of quality than rubbery state storage at -18 °C. With prolonged storage time, the quality of frozen mangoes continued to change, even in the glassy state. However, the changes in quality of the osmotic-dehydrated samples were less than those of the untreated samples. The current work indicates that osmotic pretreatment and glassy state storage significantly improved the quality of frozen mangoes during long-term storage.

Systemes Fermioniques a Basse Dimension D'espace: Supraconductivite, Effet Hall Quantique et Statistique Fractionnaire

NASA Astrophysics Data System (ADS)

Sakhi, Said

Cette these est constituee de trois sujets de recherche distincts. Les deux premiers articles traitent du phenomene de supraconductivite dans un modele bidimensionnel, dans le troisieme article on etudie l'action effective d'un systeme electronique soumis a l'effet d'un champ magnetique (systeme de Hall) et le dernier article examine la quantification d'un systeme de particules identiques en deux dimensions d'espace et la possibilite des anyons. Le modele qu'on analyse dans les deux premiers articles est un systeme fermionique dont les particules chargees et de masse nulle interagissent entre elles avcc un couplage attractif et fort. L'analyse de l'action effective decrivant la physique a basse energie nous permet d'examiner la structure de l'espace de phase. A temperature nulle, le parametre d'ordre du systeme prend une valeur moyenne non nulle. Consequemment, la symetrie continue U(1) du modele est spontanement brisee et il en resulte l'apparition d'un mode de Goldstone. En presence d'un champ electromagnetique externe, ce mode disparait et le champ de jauge acquiert une masse donc l'effet Meissner caracteristique d'un supraconducteur. Bien que le modele ne soit pas renormalisable dans le sens perturbatif, on montre qu'il l'est dans le cadre du developpement en 1/N ou N est le nombre d'especes fermioniques. En outre, on montre que l'inclusion des effets thermiques change radicalement le mecanisme de supraconductivite. En effet, on montre que la brisure spontanee de la symetrie U(1) n'est plus possible a temperature finie a cause de tres severes divergences infrarouges. Par contre, la dynamique des tourbillons (vortex) existant dans le plan devient essentielle. On montre que le phenomene de supraconductivite resulte du confinement de ces objets topologiques et que la temperature critique s'identifie a celle de Kosterlitz -Thouless. Ce mecanisme de supraconductivite presente l'avantage d'aboutir a un rapport gap a la temperature critique plus eleve que celui du modele de BCS et la non violation de la symetrie par renversement du temps et de l'espace contrairement au modele anyonique. Dans le troisieme article, on a developpe une methode systematique pour calculer les determinants fermioniques en presence d'un champ magnetique perpendiculaire au plan de confinement des particules. Aussi bien les effets thermiques que ceux dus aux impuretes sont pris en consideration dans cette methode. La technique est illustree dans le cas du systeme de Hall quantique. Finalement, dans le dernier article, on discute la quantification d'un systeme de particules identiques dans le plan. Apres avoir correctement defini l'espace de phase classique du systeme, l'analyse fait ressortir deux parametres fondamentaux denotes par theta et alpha. Le premier parametre theta est associe a l'intensite du flux magnetique localise au vertex du cone et definit la statistique des particules. Pour des valeurs arbitraires de theta on parle d'anyons. L'autre parametre alpha est associe a l'extension auto-adjointe de l'hamiltonien et ressort de l'unitarite de la theorie. On montre par un exemple explicite que alpha peut etre vu comme le vestige d'une interaction a tres courte distance (haute energie) entre les particules du systeme. Finalement, on montre que le groupe de symetrie du systeme avec extension auto -adjointe n'est plus SO(2,1) car le generateur de dilatation de ce groupe n'est plus compatible avec un parametre alpha arbitraire. (Abstract shortened by UMI.).

L'effet Hall Quantique

NASA Astrophysics Data System (ADS)

Samson, Thomas

Nous proposons une methode permettant d'obtenir une expression pour la conductivite de Hall de structures electroniques bidimensionnelles et nous examinons celle -ci a la limite d'une temperature nulle dans le but de verifier l'effet Hall quantique. Nous allons nous interesser essentiellement a l'effet Hall quantique entier et aux effets fractionnaires inferieurs a un. Le systeme considere est forme d'un gaz d'electrons en interaction faible avec les impuretes de l'echantillon. Le modele du gaz d'electrons consiste en un gaz bidimensionnel d'electrons sans spin expose perpendiculairement a un champ magnetique uniforme. Ce dernier est decrit par le potentiel vecteur vec{rm A} defini dans la jauge de Dingle ou jauge symetrique. Conformement au formalisme de la seconde quantification, l'hamiltonien de ce gaz est represente dans la base des etats a un-corps de Dingle |n,m> et exprime ainsi en terme des operateurs de creation et d'annihilation correspondants a_sp{ rm n m}{dag} et a _{rm n m}. Nous supposons de plus que les electrons du niveau fondamental de Dingle interagissent entre eux via le potentiel coulombien. La methode utilisee fait appel a une equation mai tresse a N-corps, de nature quantique et statistique, et verifiant le second principe de la thermodynamique. A partir de celle-ci, nous obtenons un systeme d'equations differentielles appele hierarchie d'equations quantique dont la resolution nous permet de determiner une equation a un-corps, dite de Boltzmann quantique, et dictant l'evolution de la moyenne statistique de l'operateur non-diagonal a _sp{rm n m}{dag } a_{rm n}, _{rm m}, sous l'action du champ electrique applique vec{rm E}(t). C'est sa solution Tr(p(t) a _sp{rm n m}{dag} a_{rm n},_ {rm m}), qui definit la relation de convolution entre la densite courant de Hall vec{rm J}_{rm H }(t) et le champ electrique vec {rm E}(t) dont la transformee de Laplace-Fourier du noyau nous fournit l'expression de la conductivite de Hall desiree. Pour une valeur de facteur d'occupation (nombre d'electrons/degenerescence des etats de Dingle) superieure a un, c'est-a-dire en absence d'interaction electron-electron, il nous sera facile d'evaluer cette conductivite a la limite d'une temperature nulle et de demontrer qu'elle tend vers l'une des valeurs quantiques qe^2/h conformement a l'effet Hall quantique entier. Cependant, pour une valeur du facteur d'occupation inferieure a un, c'est-a-dire en presence d'interaction electron-electron, nous ne pourrons evaluer cette limite et obtenir les resultats escomptes a cause de l'impossibilite de determiner l'un des termes impliques. Neanmoins, ce dernier etant de nature statistique, il pourra etre aisement mis en fonction du propagateur du gaz d'electrons dont on doit maintenant determiner une expression en regime effet Hall quantique fractionnaire. Apres avoir demontre l'impuissance de la theorie des perturbations, basee sur le theoreme de Wick et la technique des diagrammes de Feynman, a accomplir cette tache correctement, nous proposons une seconde methode. Celle -ci fait appel au formalisme de l'integrale fonctionnelle et a l'utilisation d'une transformation de Hubbard-Stratonovich generalisee permettant de substituer a l'interaction a deux-corps une interaction effective a un-corps. L'expression finale obtenue bien que non completement resolue, devrait pouvoir etre estimee par une bonne approximation analytique ou au pire numeriquement.

"Non-equilibrium" block copolymer micelles with glassy cores: a predictive approach based on theory of equilibrium micelles.

PubMed

Nagarajan, Ramanathan

2015-07-01

Micelles generated in water from most amphiphilic block copolymers are widely recognized to be non-equilibrium structures. Typically, the micelles are prepared by a kinetic process, first allowing molecular scale dissolution of the block copolymer in a common solvent that likes both the blocks and then gradually replacing the common solvent by water to promote the hydrophobic blocks to aggregate and create the micelles. The non-equilibrium nature of the micelle originates from the fact that dynamic exchange between the block copolymer molecules in the micelle and the singly dispersed block copolymer molecules in water is suppressed, because of the glassy nature of the core forming polymer block and/or its very large hydrophobicity. Although most amphiphilic block copolymers generate such non-equilibrium micelles, no theoretical approach to a priori predict the micelle characteristics currently exists. In this work, we propose a predictive approach for non-equilibrium micelles with glassy cores by applying the equilibrium theory of micelles in two steps. In the first, we calculate the properties of micelles formed in the mixed solvent while true equilibrium prevails, until the micelle core becomes glassy. In the second step, we freeze the micelle aggregation number at this glassy state and calculate the corona dimension from the equilibrium theory of micelles. The condition when the micelle core becomes glassy is independently determined from a statistical thermodynamic treatment of diluent effect on polymer glass transition temperature. The predictions based on this "non-equilibrium" model compare reasonably well with experimental data for polystyrene-polyethylene oxide diblock copolymer, which is the most extensively studied system in the literature. In contrast, the application of the equilibrium model to describe such a system significantly overpredicts the micelle core and corona dimensions and the aggregation number. The non-equilibrium model suggests ways to obtain different micelle sizes for the same block copolymer, by the choices we can make of the common solvent and the mode of solvent substitution. Published by Elsevier Inc.

Pressure-induced transformations in computer simulations of glassy water.

PubMed

Chiu, Janet; Starr, Francis W; Giovambattista, Nicolas

2013-11-14

Glassy water occurs in at least two broad categories: low-density amorphous (LDA) and high-density amorphous (HDA) solid water. We perform out-of-equilibrium molecular dynamics simulations to study the transformations of glassy water using the ST2 model. Specifically, we study the known (i) compression-induced LDA-to-HDA, (ii) decompression-induced HDA-to-LDA, and (iii) compression-induced hexagonal ice-to-HDA transformations. We study each transformation for a broad range of compression/decompression temperatures, enabling us to construct a "P-T phase diagram" for glassy water. The resulting phase diagram shows the same qualitative features reported from experiments. While many simulations have probed the liquid-state phase behavior, comparatively little work has examined the transitions of glassy water. We examine how the glass transformations relate to the (first-order) liquid-liquid phase transition previously reported for this model. Specifically, our results support the hypothesis that the liquid-liquid spinodal lines, between a low-density and high-density liquid, are extensions of the LDA-HDA transformation lines in the limit of slow compression. Extending decompression runs to negative pressures, we locate the sublimation lines for both LDA and hyperquenched glassy water (HGW), and find that HGW is relatively more stable to the vapor. Additionally, we observe spontaneous crystallization of HDA at high pressure to ice VII. Experiments have also seen crystallization of HDA, but to ice XII. Finally, we contrast the structure of LDA and HDA for the ST2 model with experiments. We find that while the radial distribution functions (RDFs) of LDA are similar to those observed in experiments, considerable differences exist between the HDA RDFs of ST2 water and experiment. The differences in HDA structure, as well as the formation of ice VII (a tetrahedral crystal), are a consequence of ST2 overemphasizing the tetrahedral character of water.

Pressure-induced transformations in computer simulations of glassy water

NASA Astrophysics Data System (ADS)

Chiu, Janet; Starr, Francis W.; Giovambattista, Nicolas

2013-11-01

Glassy water occurs in at least two broad categories: low-density amorphous (LDA) and high-density amorphous (HDA) solid water. We perform out-of-equilibrium molecular dynamics simulations to study the transformations of glassy water using the ST2 model. Specifically, we study the known (i) compression-induced LDA-to-HDA, (ii) decompression-induced HDA-to-LDA, and (iii) compression-induced hexagonal ice-to-HDA transformations. We study each transformation for a broad range of compression/decompression temperatures, enabling us to construct a "P-T phase diagram" for glassy water. The resulting phase diagram shows the same qualitative features reported from experiments. While many simulations have probed the liquid-state phase behavior, comparatively little work has examined the transitions of glassy water. We examine how the glass transformations relate to the (first-order) liquid-liquid phase transition previously reported for this model. Specifically, our results support the hypothesis that the liquid-liquid spinodal lines, between a low-density and high-density liquid, are extensions of the LDA-HDA transformation lines in the limit of slow compression. Extending decompression runs to negative pressures, we locate the sublimation lines for both LDA and hyperquenched glassy water (HGW), and find that HGW is relatively more stable to the vapor. Additionally, we observe spontaneous crystallization of HDA at high pressure to ice VII. Experiments have also seen crystallization of HDA, but to ice XII. Finally, we contrast the structure of LDA and HDA for the ST2 model with experiments. We find that while the radial distribution functions (RDFs) of LDA are similar to those observed in experiments, considerable differences exist between the HDA RDFs of ST2 water and experiment. The differences in HDA structure, as well as the formation of ice VII (a tetrahedral crystal), are a consequence of ST2 overemphasizing the tetrahedral character of water.

Sunset Crater, AZ: Evolution of a highly explosive basaltic eruption as indicated by granulometry and clast componentry

NASA Astrophysics Data System (ADS)

Allison, C. M.; Clarke, A. B.; Pioli, L.; Alfano, F.

2011-12-01

Basaltic scoria cone volcanoes are the most abundant volcanic edifice on Earth and occur in all tectonic settings. Basaltic magmas have lower viscosities, higher temperatures, and lower volatile contents than silicic magmas, and therefore generally have a lower potential for explosive activity. However, basaltic eruptions display great variability in eruptive style, from mild lava flows to more energetic explosions with large plumes. The San Francisco Volcanic Field (SFVF) in northern Arizona, active from 6 Ma-present, consists of over 600 volcanoes, mostly alkali basalt scoria cones, and five silicic centers [Wood and Kienle (1990), Cambridge University Press]. The eruption of Sunset Crater in the SFVF during the Holocene was an anomalously large basaltic explosive eruption, consisting of eight tephra-bearing phases and three lava flows [Amos (1986), MS thesis, ASU]. Typical scoria cone-forming eruptions have volumes <0.1km3 DRE, while the Sunset Crater deposit is at least 0.6km3 DRE [Amos (1986)]. The phases vary in size and style; the beginning stages of explosive activity (phases 1-2) were considerably smaller than phases 3-5, classified as subplinian. Due to its young age, the eruptive material is fresh and the deposit is well-preserved. We sampled the first five tephra units at 25 locations, ranging from 6 km to 20 km from the vent, concentrating our efforts in the downwind direction (E and SE of the vent) along the primary dispersal axes of several phases. Notable variations among the first five phases were found from evaluation of juvenile clast componentry, with each phase containing some proportion of red, grey, and glassy to iridescent clasts. The red and grey clasts are sub-rounded to rounded with high sphericity, while the other clasts are highly angular and slightly elongate, with blue-black to gold glassy and iridescent surfaces. The glassy and iridescent clasts likely represent fresh, juvenile ejecta, which were quenched rapidly, whereas the red and grey rounded clasts may be the result of recycling of the cone or vent-fill material. Alternatively, the differences among the populations may represent lateral variations in conduit flow conditions. In general, phases associated with large volumes and large dispersal areas tend to contain larger proportions of the glassy/iridescent clasts. Phase 1 has a large proportion of glassy clasts. Phase 2 has approximately half red and half grey clasts, as well as a small fraction of glassy material. Phase 3, which is the phase with the largest dispersal area, has a similar proportion of glassy clasts as phase 1. Phase 4, the largest by volume at ~0.11km3 DRE [Amos (1986)], has the highest proportion of glassy clasts. Phase 5 is comparable to phase 4 (similar fractions of each clast type), although the glassy surface changes from gold to black as clast size decreases. Each phase is well- to very well-sorted. Future work will include textural analysis of bubbles and crystals to understand the ascent and cooling history of the different clast types, and also to better interpret differences in abundance as related to variations in eruption or vent dynamics.

L’effet du yoga chez les patients atteints de cancer

PubMed Central

Côté, Andréanne; Daneault, Serge

2012-01-01

Résumé Objectif Déterminer si le yoga thérapeutique améliore la qualité de vie de patients atteints de cancer. Sources des données Recherche effectuée avec la base de données MEDLINE (1950–2010) en utilisant les mots-clés yoga, cancer et quality of life. Sélection des études Priorité accordée aux études cliniques randomisées contrôlées évaluant l’effet du yoga sur différents symptômes susceptibles de se présenter chez des patients atteints de cancer en Amérique du Nord. Synthèse Quatre études cliniques randomisées contrôlées ont d’abord été analysées, puis 2 études sans groupe-contrôle. Trois études réalisées en Inde et au Proche-Orient ont également apporté des éléments intéressants au plan méthodologique. Les interventions proposées comprenaient des séances de yoga d’une durée et d’une fréquence variables. Les paramètres mesurés variaient également d’une étude à l’autre. Plusieurs symptômes ont connu des améliorations significatives avec le yoga (meilleure qualité du sommeil, diminution des symptômes anxieux ou dépressifs, amélioration du bien-être spirituel, etc.). Il a aussi semblé que la qualité de vie, dans sa globalité ou dans certaines de ses composantes spécifiques, s’améliorait. Conclusion La variété des effets bénéfiques produits, l’absence d’effet secondaire et le rapport coût-bénéfice avantageux du yoga thérapeutique en fait une intervention intéressante à suggérer par les médecins de famille aux patients atteints de cancer. Certaines lacunes méthodologiques ont pu diminuer la puissance statistique des études présentées, à commencer par la taille restreinte des échantillons et par l’assiduité variable des patients soumis à l’intervention. Il est également possible que les échelles de mesure utilisées ne convenaient pas à ce type de situation et de clientèle pour qu’en soit dégagé un effet significatif. Toutefois, les commentaires favorables des participants recueillis au cours des études et leur degré d’appréciation et de bien-être donnent à penser qu’il faille poursuivre les recherches pour mieux en comprendre les mécanismes.

Differences in Stylet Penetration Behaviors of Glassy-winged Sharpshooters on Xylella-Resistant Vitis candicans vs. Susceptible Vitis vinifera cv. ‘Chardonnay’

USDA-ARS?s Scientific Manuscript database

Electrical penetration graph (EPG) monitoring was used to compare stylet penetration behaviors of glassy-winged sharpshooter (GWSS), a vector of Xylella fastidiosa (Xf), on Xf-resistant Vitis candicans grape vs. susceptible V. vinifera cv. ‘Chardonnay.’ Frequency of occurrence of X waves (represent...

Anomalous glassy dynamics in simple models of dense biological tissue

NASA Astrophysics Data System (ADS)

Sussman, Daniel M.; Paoluzzi, M.; Marchetti, M. Cristina; Manning, M. Lisa

2018-02-01

In order to understand the mechanisms for glassy dynamics in biological tissues and shed light on those in non-biological materials, we study the low-temperature disordered phase of 2D vertex-like models. Recently it has been noted that vertex models have quite unusual behavior in the zero-temperature limit, with rigidity transitions that are controlled by residual stresses and therefore exhibit very different scaling and phenomenology compared to particulate systems. Here we investigate the finite-temperature phase of two-dimensional Voronoi and Vertex models, and show that they have highly unusual, sub-Arrhenius scaling of dynamics with temperature. We connect the anomalous glassy dynamics to features of the potential energy landscape associated with zero-temperature inherent states.

Gels from soft hairy nanoparticles in polymeric matrices

NASA Astrophysics Data System (ADS)

Vlassopoulos, Dimitris

2013-03-01

Hairy particles represent a huge class of soft colloids with tunable interactions and properties. Advances in synthetic chemistry have enabled obtaining well-characterized such systems for specific needs. In this talk we present two model hairy soft particles with diameters of the order of tens of nanometers, star polymers and polymerically grafted spherical particles. In particular, we discuss design strategies for dispersing them in polymeric matrices and eventually creating and breaking gels. Control parameters are the matrix molar mass, the grafting density (or functionality) and the size of the grafts (or arms). The linear viscoelastic properties and slow time evolution of the gels are examined in view of the existing knowledge from colloidal gels consisting of micron-sized particles, and compared. In the case of stars we start from a concentrated glassy suspension in molecular solvent and add homopolymer at increasing concentration, and as a result of the induced osmotic pressure the stars shrink and a depletion gel is formed. For the grafted colloidal particles, they are added at low concentration to a polymer matrix, and it has been shown that under certain conditions the anisotropy of interactions gives rise to network formation. We then focus on the nonlinear rheological response and in particular the effect of shear flow in inducing a solid to liquid transition. Our studies show that the yielding process is gradual and shares many common features with that of flocculated colloidal suspensions, irrespectively of the shape of the building block of the gel. Whereas shear can melt such a gel, it cannot break it into its constituent blocks and hence fully disperse the hairy nanoparticles. On the other hand, the hairy particles are intrinsically hybrid. We show how this important feature is reflected on the heating of the gels. In that case, the mismatch of thermal expansion coefficients of core and shell appears to play a role on the particle response as it imposes and internal strain on the particle, which in turn changes the shell conformation and under some conditions can lead to thermal melting of the gel. These alternative avenues for manipulating the gel-to-liquid transition have potential implications in directing the properties of hairy nanoparticles and their assemblies in viscoelastic matrices. Parts of this work reflect collaboration with D. Truzzolillo (FORTH), J. F. Moll and S. K.Kumar (Columbia). R. H. Colby (Penn State), M. Gauthier (Waterloo) and B. C. Benicewicz (Univ. South Carolina).

Le rôle médiateur du fonctionnement familial dans la relation entre l’adversité familiale et l’adaptation sociale des enfants d’âge préscolaire1

PubMed Central

Felli, M. C.; Parent, S.; Zelazo, P. D.; Tremblay, R. E.; Séguin, J. R.

2017-01-01

Résumé À la petite enfance, l’adaptation sociale de l’enfant dépend en partie des risques auxquels il est exposé dans son environnement. Toutefois, les mécanismes par lesquels les facteurs de risque opèrent leurs influences sur l’adaptation sociale de l’enfant sont peu documentés. Ainsi, cette étude examine dans un premier temps l’effet principal de l’adversité familiale, un cumul de facteurs de risque, sur les problèmes de comportement intériorisés et extériorisés, ainsi que sur la sécurité d’attachement des enfants d’âge préscolaire. Dans un deuxième temps, elle évalue le rôle médiateur du fonctionnement familial dans le lien entre l’adversité familiale et les problèmes de comportement de même qu’entre l’adversité familiale et la sécurité d’attachement des enfants d’âge préscolaire. Les 572 participants à l’étude (n=572) sont âgés entre cinq et 42 mois lors des mesures de l’adversité familiale et de 42 mois lors de la mesure des problèmes de comportement et du fonctionnement familial. Quatre-vingt d’entre eux (n=80) ont fait l’objet d’une mesure de sécurité d’attachement à 48 mois. Les résultats indiquent, d’abord, un effet principal de l’adversité familiale sur les problèmes de comportement intériorisés et extériorisés. Un effet médiateur significatif du fonctionnement familial est ensuite rapporté dans le lien entre l’adversité familiale et les problèmes de comportement intériorisés et extériorisés. Aucun effet significatif n’est observé pour la sécurité d’attachement des enfants de 48 mois. PMID:28567062

Dielectric relaxation studies in super-cooled liquid and glassy phases of anti-cancerous alkaloid: Brucine

NASA Astrophysics Data System (ADS)

Afzal, Aboothahir; Shahin Thayyil, M.; Sulaiman, M. K.; Kulkarni, A. R.

2018-05-01

Brucine has good anti-tumor effects, on both liver cancer and breast cancer. It has bioavailability of 40.83%. Since the bioavailability of the drug is low, an alternative method to increase its bioavailability and solubility is by changing the drug into glassy form. We used Differential Scanning Calorimetry (DSC) for studying the glass forming ability of the drug. Brucine was found to be a very good glass former glass transition temperature 365 K. Based on the DSC analysis we have used broadband dielectric spectroscopy (BDS) for studying the drug in the super cooled and glassy state. BDS is an effective tool to probe the molecular dynamics in the super cooled and glassy state. Molecular mobility is found to be present even in the glassy state of this active pharmaceutical ingredient (API) which is responsible for the instability. Our aim is to study the factors responsible for instability of this API in amorphous form. Cooling curves for dielectric permittivity and dielectric loss revealed the presence of structural (α) and secondary relaxations (β and γ). Temperature dependence of relaxation time is fitted by Vogel-Fulcher-Tammann equation and found the values of activation energy of the α relaxation, fragility and glass transition temperature. Paluch's anti correlation is also verified, that the width of the α-loss peak at or near the glass transition temperature Tg is strongly anticorrelated with the polarity of the molecule. The larger the dielectric relaxation strength Δɛ (Tg) of the system, the narrower is the α-loss peak (higher value of βKWW).

Evidence for the absence of enzymatic reactions in the glassy state. A case study of xanthophyll cycle pigments in the desiccation-tolerant moss Syntrichia ruralis

PubMed Central

Fernández-Marín, Beatriz; Kranner, Ilse; Sebastián, María San; Artetxe, Unai; Laza, José Manuel; Vilas, José Luis; Pritchard, Hugh W.; Nadajaran, Jayanthi; Míguez, Fátima; Becerril, José María; García-Plazaola, José Ignacio

2013-01-01

Desiccation-tolerant plants are able to withstand dehydration and resume normal metabolic functions upon rehydration. These plants can be dehydrated until their cytoplasm enters a ‘glassy state’ in which molecular mobility is severely reduced. In desiccation-tolerant seeds, longevity can be enhanced by drying and lowering storage temperature. In these conditions, they still deteriorate slowly, but it is not known if deteriorative processes include enzyme activity. The storage stability of photosynthetic organisms is less studied, and no reports are available on the glassy state in photosynthetic tissues. Here, the desiccation-tolerant moss Syntrichia ruralis was dehydrated at either 75% or <5% relative humidity, resulting in slow (SD) or rapid desiccation (RD), respectively, and different residual water content of the desiccated tissues. The molecular mobility within dry mosses was assessed through dynamic mechanical thermal analysis, showing that at room temperature only rapidly desiccated samples entered the glassy state, whereas slowly desiccated samples were in a ‘rubbery’ state. Violaxanthin cycle activity, accumulation of plastoglobules, and reorganization of thylakoids were observed upon SD, but not upon RD. Violaxanthin cycle activity critically depends on the activity of violaxanthin de-epoxidase (VDE). Hence, it is proposed that enzymatic activity occurred in the rubbery state (after SD), and that in the glassy state (after RD) no VDE activity was possible. Furthermore, evidence is provided that zeaxanthin has some role in recovery apparently independent of its role in non-photochemical quenching of chlorophyll fluorescence. PMID:23761488

Isothermal enthalpy relaxation of glassy 1,2,6-hexanetriol

NASA Astrophysics Data System (ADS)

Fransson, Å.; Bäckström, G.

The isothermal enthalpy relaxation of glassy 1,2,6-hexanetriol has been measured at six temperatures. The relaxation time and the distribution parameters extracted from fits of the Williams-Watts relaxation function are compared with parameters obtained by other techniques and on other substances. A detailed comparison of the Williams-Watts and the Davidson-Cole relaxation functions is presented.

Effects of kaolin particle film and imidacloprid on glassy-winged sharpshooter (Homalodisca vitripennis) (Hemiptera: Cicadellidae)populations and the prevention of spread of Xylella fastidiosa in grape

USDA-ARS?s Scientific Manuscript database

The glassy-winged sharpshooter (GWSS), Homalodisca coagulata (Say), was introduced into California and soon became a major pest of important agronomic, horticultural, landscape, ornamental crops and native trees in California. This pest feeds readily on grape and, in doing so, transmits X. fastidio...

Internal stresses, dislocation mobility and ductility

NASA Astrophysics Data System (ADS)

Saada, G.

1991-06-01

The description of plastic deformation must take into account individual mechanisms and heterogeneity of plastic strain. Influence of dislocation interaction with forest dislocations and of cross slip are connected with the organization of dipole walls. The latter are described and their development is explained as a consequence of edge effects. Applications are discussed. La description de la déformation plastique doit prendre en compte les interactions individuelles des dislocations et l'hétérogénéité à grande échelle de la déformation plastique. Les interactions des dislocations mobiles avec la forêt de dislocations, le glissement dévié, ont pour effet la création de parois dipolaires. Celles-ci sont décrites et leur développement est appliqué à partir des effets de bord.

Water clustering in glassy polymers.

PubMed

Davis, Eric M; Elabd, Yossef A

2013-09-12

In this study, water solubility and water clustering in several glassy polymers, including poly(methyl methacrylate) (PMMA), poly(styrene) (PS), and poly(vinylpyrrolidone) (PVP), were measured using both quartz spring microbalance (QSM) and Fourier transform infrared-attenuated total reflectance (FTIR-ATR) spectroscopy. Specifically, QSM was used to determine water solubility, while FTIR-ATR spectroscopy provided a direct, molecular-level measurement of water clustering. The Flory-Huggins theory was employed to obtain a measure of water-polymer interaction and water solubility, through both prediction and regression, where the theory failed to predict water solubility in both PMMA and PVP. Furthermore, a comparison of water clustering between direct FTIR-ATR spectroscopy measurements and predictions from the Zimm-Lundberg clustering analysis produced contradictory results. The failure of the Flory-Huggins theory and Zimm-Lundberg clustering analysis to describe water solubility and water clustering, respectively, in these glassy polymers is in part due to the equilibrium constraints under which these models are derived in contrast to the nonequilibrium state of glassy polymers. Additionally, FTIR-ATR spectroscopy results were compared to temperature-dependent diffusivity data, where a correlation between the activation energy for diffusion and the measured water clustering was observed.

Glassy materials for lithium batteries: electrochemical properties and devices performances

NASA Astrophysics Data System (ADS)

Duclot, Michel; Souquet, Jean-Louis

Amorphous or glassy materials may be used as electrolyte or electrode materials for lithium primary or secondary batteries. A first generation proceeded from classical coin cells in which the organic electrolyte was replaced by a high lithium conductive glassy electrolyte. The solid components were assembled under isostatic pressure. The main advantages of such cells are a good storage stability and ability to operate until 200°C. Nevertheless, the high resistivity of the glassy electrolyte below room temperature and a limited depth for charge and discharge cycles makes these cells not competitive compared to conventional lithium-ion batteries. More promising, are the thin films solid state microbatteries realised by successive depositions of electrodes and electrolyte. The low resistance of the electrolyte amorphous layer allows cycling at temperatures as low as -10°C. The total thickness of thin film batteries, including packaging is less than 100 μm. A capacity of about 100 μAh cm -2 with over 10 4 charge-discharge cycles at 90% in depth of discharge is well suited for energy independent smart cards or intelligent labels, which represent for these devices a large and unrivalled market.

Evaluation of the relevance of the glassy state as stability criterion for freeze-dried bacteria by application of the Arrhenius and WLF model.

PubMed

Aschenbrenner, Mathias; Kulozik, Ulrich; Foerst, Petra

2012-12-01

The aim of this work was to describe the temperature dependence of microbial inactivation for several storage conditions and protective systems (lactose, trehalose and dextran) in relation to the physical state of the sample, i.e. the glassy or non-glassy state. The resulting inactivation rates k were described by applying two models, Arrhenius and Williams-Landel-Ferry (WLF), in order to evaluate the relevance of diffusional limitation as a protective mechanism. The application of the Arrhenius model revealed a significant decrease in activation energy E(a) for storage conditions close to T(g). This finding is an indication that the protective effect of a surrounding glassy matrix can, at least, partly be ascribed to its inherent restricted diffusion and mobility. The application of the WLF model revealed that the temperature dependence of microbial inactivation above T(g) is significantly weaker than predicted by the universal coefficients. Thus, it can be concluded that microbial inactivation is not directly linked with the mechanical relaxation behavior of the surrounding matrix as it was reported for viscosity and crystallization phenomena in case of disaccharide systems. Copyright © 2012. Published by Elsevier Inc.

Free-Volume Nanostructurization in Ga-Modified As2Se3 Glass.

PubMed

Shpotyuk, Ya; Ingram, A; Shpotyuk, O; Dziedzic, A; Boussard-Pledel, C; Bureau, B

2016-12-01

Different stages of intrinsic nanostructurization related to evolution of free-volume voids, including phase separation, crystalline nuclei precipitation, and growth, were studied in glassy As2Se3 doped with Ga up to 5 at. %, using complementary techniques of positron annihilation lifetime spectroscopy, X-ray powder diffraction, and scanning electron microscopy with energy-dispersive X-ray analysis. Positron lifetime spectra reconstructed in terms of a two-state trapping model testified in favor of a native void structure of g-As2Se3 modified by Ga additions. Under small Ga content (below 3 at. %), the positron trapping in glassy alloys was dominated by voids associated with bond-free solid angles of bridging As2Se4/2 units. This void agglomeration trend was changed on fragmentation with further Ga doping due to crystalline Ga2Se3 nuclei precipitation and growth, these changes being activated by employing free volume from just attached As-rich glassy matrix with higher content of As2Se4/2 clusters. Respectively, the positron trapping on free-volume voids related to pyramidal AsSe3/2 units (like in parent As2Se3 glass) was in obvious preference in such glassy crystalline alloys.

Application of nickel zinc ferrite/graphene nanocomposite as a modifier for fabrication of a sensitive electrochemical sensor for determination of omeprazole in real samples.

PubMed

Afkhami, Abbas; Bahiraei, Atousa; Madrakian, Tayyebeh

2017-06-01

In the present study, a simple and highly sensitive sensor for the determination of omeprazole based on nickel-zinc ferrite/graphene modified glassy carbon electrode is reported. The morphology and electro analytical performance of the fabricated sensor were characterized with X-ray diffraction spectrometry, Fourier transform infrared spectrometry, scanning electron microscopy, electrochemical impedance spectroscopy, cyclic voltammetry, differential pulse voltammetry and operation of the sensor. Results were compared with those achieved at the graphene modified glassy carbon electrode and bare glassy carbon electrode. Under the optimized experimental conditions, linear response was over the range of 0.03-100.0µmolL -1 . The lower detection limit was found to be 0.015µmolL -1 . The effect of different interferences on the anodic current response of OMZ was investigated. By measuring the concentrations of omeprazole in plasma and pharmaceutical samples, the practical application of the modified electrode was evaluated. This revealed that the nickel-zinc ferrite/graphene modified glassy carbon electrode shows excellent analytical performance for the determination of omeprazole with a very low detection limit, high sensitivity, and very good accuracy. Copyright © 2017 Elsevier Inc. All rights reserved.

Thermodynamic Modeling of Gas Transport in Glassy Polymeric Membranes.

PubMed

Minelli, Matteo; Sarti, Giulio Cesare

2017-08-19

Solubility and permeability of gases in glassy polymers have been considered with the aim of illustrating the applicability of thermodynamically-based models for their description and prediction. The solubility isotherms are described by using the nonequilibrium lattice fluid (NELF) (model, already known to be appropriate for nonequilibrium glassy polymers, while the permeability isotherms are described through a general transport model in which diffusivity is the product of a purely kinetic factor, the mobility coefficient, and a thermodynamic factor. The latter is calculated from the NELF model and mobility is considered concentration-dependent through an exponential relationship containing two parameters only. The models are tested explicitly considering solubility and permeability data of various penetrants in three glassy polymers, PSf, PPh and 6FDA-6FpDA, selected as the reference for different behaviors. It is shown that the models are able to calculate the different behaviors observed, and in particular the permeability dependence on upstream pressure, both when it is decreasing as well as when it is increasing, with no need to invoke the onset of additional plasticization phenomena. The correlations found between polymer and penetrant properties with the two parameters of the mobility coefficient also lead to the predictive ability of the transport model.

Annealing effect on thermal conductivity and microhardness of carbon nanotube containing Se80Te16Cu4 glassy composites

NASA Astrophysics Data System (ADS)

Upadhyay, A. N.; Tiwari, R. S.; Singh, Kedar

2018-02-01

This study deals with the effect of thermal annealing on structural/microstructural, thermal and mechanical behavior of pristine Se80Te16Cu4 and carbon nanotubes (CNTs) containing Se80Te16Cu4 glassy composites. Pristine Se80Te16Cu4, 3 and 5 wt%CNTs-Se80Te16Cu4 glassy composites are annealed in the vicinity of glass transition temperature to onset crystallization temperature (340-380 K). X-ray diffraction (XRD) pattern revealed formation of polycrystalline phases of hexagonal CuSe and trigonal selenium. The indexed d-values in XRD patterns are in well conformity with the d-values obtained after the indexing of the ring pattern of selected area electron diffraction pattern of TEM images. The SEM investigation exhibited that the grain size of the CNTs containing Se80Te16Cu4 glassy composites increased with increasing annealing temperature and decreased at further higher annealing temperature. Thermal conductivity, microhardness exhibited a substantial increase with increasing annealing temperature of 340-360 K and slightly decreases for 380 K. The variation of thermal conductivity and microhardness can be explained by cross-linking formation and voids reduction.

Thermodynamic Modeling of Gas Transport in Glassy Polymeric Membranes

PubMed Central

Minelli, Matteo; Sarti, Giulio Cesare

2017-01-01

Solubility and permeability of gases in glassy polymers have been considered with the aim of illustrating the applicability of thermodynamically-based models for their description and prediction. The solubility isotherms are described by using the nonequilibrium lattice fluid (NELF) (model, already known to be appropriate for nonequilibrium glassy polymers, while the permeability isotherms are described through a general transport model in which diffusivity is the product of a purely kinetic factor, the mobility coefficient, and a thermodynamic factor. The latter is calculated from the NELF model and mobility is considered concentration-dependent through an exponential relationship containing two parameters only. The models are tested explicitly considering solubility and permeability data of various penetrants in three glassy polymers, PSf, PPh and 6FDA-6FpDA, selected as the reference for different behaviors. It is shown that the models are able to calculate the different behaviors observed, and in particular the permeability dependence on upstream pressure, both when it is decreasing as well as when it is increasing, with no need to invoke the onset of additional plasticization phenomena. The correlations found between polymer and penetrant properties with the two parameters of the mobility coefficient also lead to the predictive ability of the transport model. PMID:28825619

Effets de l'humidite sur la propagation du delaminage dans un composite carbone/epoxy sollicite en mode mixte I/II

NASA Astrophysics Data System (ADS)

LeBlanc, Luc R.

Les materiaux composites sont de plus en plus utilises dans des domaines tels que l'aerospatiale, les voitures a hautes performances et les equipements sportifs, pour en nommer quelques-uns. Des etudes ont demontre qu'une exposition a l'humidite nuit a la resistance des composites en favorisant l'initiation et la propagation du delaminage. De ces etudes, tres peu traitent de l'effet de l'humidite sur l'initiation du delaminage en mode mixte I/II et aucune ne traite des effets de l'humidite sur le taux de propagation du delaminage en mode mixte I/II dans un composite. La premiere partie de cette these consiste a determiner les effets de l'humidite sur la propagation du delaminage lors d'une sollicitation en mode mixte I/II. Des eprouvettes d'un composite unidirectionnel de carbone/epoxy (G40-800/5276-1) ont ete immergees dans un bain d'eau distillee a 70°C jusqu'a leur saturation. Des essais experimentaux quasi-statiques avec des chargements d'une gamme de mixites des modes I/II (0%, 25%, 50%, 75% et 100%) ont ete executes pour determiner les effets de l'humidite sur la resistance au delaminage du composite. Des essais de fatigue ont ete realises, avec la meme gamme de mixite des modes I/II, pour determiner 1'effet de 1'humidite sur l'initiation et sur le taux de propagation du delaminage. Les resultats des essais en chargement quasi-statique ont demontre que l'humidite reduit la resistance au delaminage d'un composite carbone/epoxy pour toute la gamme des mixites des modes I/II, sauf pour le mode I ou la resistance au delaminage augmente apres une exposition a l'humidite. Pour les chargements en fatigue, l'humidite a pour effet d'accelerer l'initiation du delaminage et d'augmenter le taux de propagation pour toutes les mixites des modes I/II. Les donnees experimentales recueillies ont ete utilisees pour determiner lesquels des criteres de delaminage en statique et des modeles de taux de propagation du delaminage en fatigue en mode mixte I/II proposes dans la litterature representent le mieux le delaminage du composite etudie. Une courbe de regression a ete utilisee pour determiner le meilleur ajustement entre les donnees experimentales et les criteres de delaminage en statique etudies. Une surface de regression a ete utilisee pour determiner le meilleur ajustement entre les donnees experimentales et les modeles de taux de propagation en fatigue etudies. D'apres les ajustements, le meilleur critere de delaminage en statique est le critere B-K et le meilleur modele de propagation en fatigue est le modele de Kenane-Benzeggagh. Afin de predire le delaminage lors de la conception de pieces complexes, des modeles numeriques peuvent etre utilises. La prediction de la longueur de delaminage lors des chargements en fatigue d'une piece est tres importante pour assurer qu'une fissure interlaminaire ne va pas croitre excessivement et causer la rupture de cette piece avant la fin de sa duree de vie de conception. Selon la tendance recente, ces modeles sont souvent bases sur l'approche de zone cohesive avec une formulation par elements finis. Au cours des travaux presentes dans cette these, le modele de progression du delaminage en fatigue de Landry & LaPlante (2012) a ete ameliore en y ajoutant le traitement des chargements en mode mixte I/II et en y modifiant l'algorithme du calcul de la force d'entrainement maximale du delaminage. Une calibration des parametres de zone cohesive a ete faite a partir des essais quasi-statiques experimentaux en mode I et II. Des resultats de simulations numeriques des essais quasi-statiques en mode mixte I/II, avec des eprouvettes seches et humides, ont ete compares avec les essais experimentaux. Des simulations numeriques en fatigue ont aussi ete faites et comparees avec les resultats experimentaux du taux de propagation du delaminage. Les resultats numeriques des essais quasi-statiques et de fatigue ont montre une bonne correlation avec les resultats experimentaux pour toute la gamme des mixites des modes I/II etudiee.

Study of the physical properties of Ge-S-Ga glassy alloy

NASA Astrophysics Data System (ADS)

Rana, Anjli; Sharma, Raman

2018-05-01

In the present work, we have studied the effect of Ga doping on the physical properties of Ge20S80-xGax glassy alloy. The basic physical parameters which have important role in determining the structure and strength of the material viz. average coordination number, lone-pair electrons, mean bond energy, glass transition temperature, electro negativity, probabilities for bond distribution and cohesive energy have been computed theoretically for Ge-S-Ga glassy alloy. Here, the glass transition temperature and mean bond energy have been investigated using the Tichy-Ticha approach. The cohesive energy has been calculated by using chemical bond approach (CBA) method. It has been found that while average coordination number increases, all the other parameters decrease with the increase in Ga content in Ge-S-Ga system.

Loss of halogens from crystallized and glassy silicic volcanic rocks

USGS Publications Warehouse

Noble, D.C.; Smith, V.C.; Peck, L.C.

1967-01-01

One hundred and sixty-four F and Cl analyses of silicic welded tuffs and lavas and glass separates are presented. Comparison of the F and Cl contents of crystallized rocks with those of nonhydrated glass and hydrated glassy rocks from the same rock units shows that most of the halogens originally present were lost on crystallization. An average of about half of the F and four-fifths of the Cl originally present was lost. Analyses of hydrated natural glasses and of glassy rocks indicate that in some cases significant amounts of halogens may be removed from or added to hydrated glass through prolonged contact with ground water. The data show that the original halogen contents of the groundmass of a silicic volcanic rock can be reliably determined only from nonhydrated glass. ?? 1967.

Electrochemiluminescence of luminol at the titanate nanotubes modified glassy carbon electrode.

PubMed

Xu, Guifang; Zeng, Xiaoxue; Lu, Shuangyan; Dai, Hong; Gong, Lingshan; Lin, Yanyu; Wang, Qingping; Tong, Yuejin; Chen, Guonan

2013-01-01

A new strategy for the construction of a sensitive and stable electrochemiluminescent platform based on titanate nanotubes (TNTs) and Nafion composite modified electrode for luminol is described, TNTs contained composite modified electrodes that showed some photocatalytic activity toward luminol electrochemiluminescence emission, and thus could dramatically enhance luminol light emission. This extremely sensitive and stable platform allowed a decrease of the experiment electrochemiluminescence luminol reagent. In addition, in luminol solution at low concentrations, we compared the capabilities of a bare glassy carbon electrode with the TNT composite modified electrode for hydrogen peroxide detection. The results indicated that compared with glassy carbon electrode this platform was extraordinarily sensitive to hydrogen peroxide. Therefore, by combining with an appropriate enzymatic reaction, this platform would be a sensitive matrix for many biomolecules.

Plastic flow modeling in glassy polymers

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

Clements, Brad

2010-12-13

Glassy amorphous and semi-crystalline polymers exhibit strong rate, temperature, and pressure dependent polymeric yield. As a rule of thumb, in uniaxial compression experiments the yield stress increases with the loading rate and applied pressure, and decreases as the temperature increases. Moreover, by varying the loading state itself complex yield behavior can be observed. One example that illustrates this complexity is that most polymers in their glassy regimes (i.e., when the temperature is below their characteristic glass transition temperature) exhibit very pronounced yield in their uniaxial stress stress-strain response but very nebulous yield in their uniaxial strain response. In uniaxial compression,more » a prototypical glassy-polymer stress-strain curve has a stress plateau, often followed by softening, and upon further straining, a hardening response. Uniaxial compression experiments of this type are typically done from rates of 10{sup -5} s{sup -1} up to about 1 s{sup -1}. At still higher rates, say at several thousands per second as determined from Split Hopkinson Pressure Bar experiments, the yield can again be measured and is consistent with the above rule of thumb. One might expect that that these two sets of experiments should allow for a successful extrapolation to yet higher rates. A standard means to probe high rates (on the order of 105-107 S-I) is to use a uniaxial strain plate impact experiment. It is well known that in plate impact experiments on metals that the yield stress is manifested in a well-defined Hugoniot Elastic Limit (HEL). In contrast however, when plate impact experiments are done on glassy polymers, the HEL is arguably not observed, let alone observed at the stress estimated by extrapolating from the lower strain rate experiments. One might argue that polymer yield is still active but somehow masked by the experiment. After reviewing relevant experiments, we attempt to address this issue. We begin by first presenting our recently developed glassy polymer model. While polymers are well known for their non-equilibrium deviatoric behavior we have found the need for incorporating both equilibrium and non-equilibrium volumetric behavior into our theory. Experimental evidence supporting the notion of non-equilibrium volumetric behavior will be summarized. Our polymer yield model accurately captures the stress plateau, softening and hardening and its yield stress predictions agree well with measured values for several glassy polymers including PMMA, PC, and an epoxy resin. We then apply our theory to plate impact experiments in an attempt to address the questions associated with high rate polymer yield in uniaxial strain configurations.« less

Invasive Threats to the American Homeland

DTIC Science & Technology

2004-04-01

The second example is the glassy-winged sharpshooter, an invasive insect that hosts the bacterium Xylella Fastidiosa . The insect was first de- tected... Xylella Fastidiosa causes Pierce’s Disease in grapes, which infects and kills the grapevine. The glassy-winged sharpshooter transmits and spreads the...netic processes.” Adversaries of the United States may modify the genetics of an invasive species to increase its competitiveness, virulence , lethality

Reduced electronegativity difference as a factor leading to the formation of Al-based glassy alloys with a large supercooled liquid region of 50 K

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

Louzguine-Luzgin, Dmitri V.; Inoue, Akihisa; Botta, Walter Jose

2006-01-02

The influence of the electronegativity difference among the constituent elements on the stability of the supercooled liquid in two Al-based glassy alloys is studied. A record-large value of the supercooled liquid region of about 50 K is obtained based on the electronegativity difference concept within a certain composition range.

Caracterisation de la cohesion de l'interface AMF/polymere dans une structure deformable adaptative

NASA Astrophysics Data System (ADS)

Fischer-Rousseau, Charles

Les structures déformables adaptatives (SDA) sont appelées à jouer un rôle important en aéronautique entre autres. Les alliages à mémoire de forme (AMF) sont un des candidats les plus prometteurs. Beaucoup de travail reste toutefois à faire avant que ces structures rencontrent les exigences élevées reliées à leur intégration dans un contexte aéronautique. Des travaux de recherche ont montré que la résistance à la décohésion de l’interface AMF/polymère peut être un élément limitant dans la performance des SDA. Dans ce travail, l’effet sur la résistance à la décohésion de l’interface AMF/polymère de divers traitements de surface, géométries de fil et types de polymère est évalué. La géométrie du fil est modifiée par une combinaison spécifique de laminage à froid et de recuit postdéformation qui maintient les propriétés de mémoire de forme tout en permettant de réduire l’aire de la section transversale du fil. Le traitement thermomécanique le plus prometteur est proposé. Une nouvelle méthode d’évaluation de la résistance à la décohésion est développée. Plutôt que de tester les fils en arrachement et de mesurer la force maximale, les tests en contraction sont basés sur la capacité des fils d’AMF à se contracter s’ils ont été encastrés dans un état tiré et qu’ils sont chauffés par effet Joule. L’hypothèse qu’on pose est que ces tests sont une meilleure approximation des conditions rencontrées dans une SDA, où les fils se contractent plutôt qu’ils sont arrachés par une force externe à la structure. Bien qu’une décohésion partielle ait été observée pour tous les échantillons, l’aire de la surface où il y a décohésion tait plus grande pour les échantillons avec une pré-déformation plus grande. Le front de décohésion a semblé cesser de progresser après les cycles de chauffage initiaux lorsque la vitesse de chauffage était faible. Un modèle numérique simulant la réponse thermique transitoire du polymère et du fil d’AMF lors d’un chauffage par effet Joule est programmé à l’aide du logiciel ANSYS. Le comportement du modèle est validé avec des résultats expérimentaux où des thermocouples encastrés dans l’échantillon permettent des mesures locales de la température. Les résultats calculés sont en accord avec les résultats expérimentaux d’un point de vue qualitatif, mais accusent des différences significatives d’un point de vue quantitatif. La mesure du champ de déformation à l’interface du fil et du polymère dans une SDA permettrait de développer et valider un modèle numérique prenant en compte l’effet mémoire de forme d’un fil encastré dans une matrice polymère. Dans ce but, une machine de traction miniature permettant l’analyse par microspectrométrie Raman in situ est présentée. Elle a une capacité de 1 kN et un déplacement maximal de 20 mm dans une enveloppe de conception totale de 160 mm de diamètre. La machine est conçue pour que le milieu de l’échantillon soit immobile grâce au fait que le mouvement des deux extrémités soit symétrique. Les résultats montrent que du travail supplémentaire est nécessaire avant de pouvoir encastrer des fils d’AMF dans une structure déformable adaptative. Mots-clés: décohésion, structure active, alliage à mémoire de forme, AMF, tests d’arrachement.

A characteristic energy scale in glasses

NASA Astrophysics Data System (ADS)

Lerner, Edan; Bouchbinder, Eran

2018-06-01

Intrinsically generated structural disorder endows glassy materials with a broad distribution of various microscopic quantities—such as relaxation times and activation energies—without an obvious characteristic scale. At the same time, macroscopic glassy responses—such as Newtonian (linear) viscosity and nonlinear plastic deformation—are widely interpreted in terms of a characteristic energy scale, e.g., an effective temperature-dependent activation energy in Arrhenius relations. Nevertheless, despite its fundamental importance, such a characteristic energy scale has not been robustly identified. Inspired by the accumulated evidence regarding the crucial role played by disorder- and frustration-induced soft quasilocalized excitations in determining the properties and dynamics of glasses, we propose that the bulk average of the glass response to a localized force dipole defines such a characteristic energy scale. We show that this characteristic glassy energy scale features remarkable properties: (i) It increases dramatically in underlying inherent structures of equilibrium supercooled states approaching the glass transition temperature Tg, significantly surpassing the corresponding increase in the macroscopic shear modulus, dismissing the common view that structural variations in supercooled liquids upon vitrification are minute. (ii) Its variation with annealing and system size is very similar in magnitude and form to that of the energy of the softest non-phononic vibrational mode, thus establishing a nontrivial relation between a rare glassy fluctuation and a bulk average response. (iii) It exhibits striking dependence on spatial dimensionality and system size due to the long-ranged fields associated with quasilocalization, which are speculated to be related to peculiarities of the glass transition in two dimensions. In addition, we identify a truly static growing lengthscale associated with the characteristic glassy energy scale and discuss possible connections between the increase of this energy scale and the slowing down of dynamics near the glass transition temperature. Open questions and future directions are discussed.

Glassy selenium at high pressure: Le Chatelier's principle still works

NASA Astrophysics Data System (ADS)

Brazhkin, V. V.; Tsiok, O. B.

2017-10-01

Selenium is the only easily vitrified elementary substance. Numerous experimental studies of glassy Se (g -Se) at high pressures show a large spread in the data on the compressibility and electrical resistivity of g -Se. Furthermore, H. Liu et al. [Proc. Natl. Acad. Sci. USA 105, 13229 (2008), 10.1073/pnas.0806857105] have arrived at the surprising conclusion that the volume of glass increases during pressure-induced crystallization. We have performed high-precision measurements of the specific volume and electrical resistivity of glassy selenium (g -Se) at high hydrostatic pressures up to 9 GPa. The measured bulk modulus at normal pressure is B =(9.0 5 ±0.15 ) GPa and its pressure derivative is BP'=6.4 ±0.2 . In the pressure range P <3 GPa, glassy selenium has an anomalously large negative second derivative of the bulk modulus. The electrical resistivity of g -Se decreases almost exponentially with increasing pressure and reaches 20 Ω cm at a pressure of 8.75 GPa. The inelastic behavior and weak relaxation of the volume for g -Se begin at pressures above 3.5 GPa; the volume and logarithm of the electrical resistivity relax significantly (logarithmically with the time) at pressures above 8 GPa. Bulk measurements certainly indicate that the volume of g -Se glass in the crystallization pressure range is larger than the volumes of both appearing crystalline phases (by 2% and 4%). Therefore, the "volume expansion phenomenon" suggested in [H. Liu et al., Proc. Natl. Acad. Sci. USA 105, 13229 (2008), 10.1073/pnas.0806857105] is not observed, and the pressure-induced crystallization of glassy selenium is consistent with the laws of thermodynamics.

A characteristic energy scale in glasses.

PubMed

Lerner, Edan; Bouchbinder, Eran

2018-06-07

Intrinsically generated structural disorder endows glassy materials with a broad distribution of various microscopic quantities-such as relaxation times and activation energies-without an obvious characteristic scale. At the same time, macroscopic glassy responses-such as Newtonian (linear) viscosity and nonlinear plastic deformation-are widely interpreted in terms of a characteristic energy scale, e.g., an effective temperature-dependent activation energy in Arrhenius relations. Nevertheless, despite its fundamental importance, such a characteristic energy scale has not been robustly identified. Inspired by the accumulated evidence regarding the crucial role played by disorder- and frustration-induced soft quasilocalized excitations in determining the properties and dynamics of glasses, we propose that the bulk average of the glass response to a localized force dipole defines such a characteristic energy scale. We show that this characteristic glassy energy scale features remarkable properties: (i) It increases dramatically in underlying inherent structures of equilibrium supercooled states approaching the glass transition temperature T g , significantly surpassing the corresponding increase in the macroscopic shear modulus, dismissing the common view that structural variations in supercooled liquids upon vitrification are minute. (ii) Its variation with annealing and system size is very similar in magnitude and form to that of the energy of the softest non-phononic vibrational mode, thus establishing a nontrivial relation between a rare glassy fluctuation and a bulk average response. (iii) It exhibits striking dependence on spatial dimensionality and system size due to the long-ranged fields associated with quasilocalization, which are speculated to be related to peculiarities of the glass transition in two dimensions. In addition, we identify a truly static growing lengthscale associated with the characteristic glassy energy scale and discuss possible connections between the increase of this energy scale and the slowing down of dynamics near the glass transition temperature. Open questions and future directions are discussed.

Temperature-programed time-of-flight secondary ion mass spectrometry study of 1-butyl-3-methylimidazolium trifluoromethanesulfonate during glass-liquid transition, crystallization, melting, and solvation

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

Souda, Ryutaro; Guenster, Jens; CiC Ceramic Institute Clausthal GmbH, D-38678 Clausthal-Zellerfeld

2008-09-07

For this study, time-of-flight secondary ion mass spectrometry was used to analyze the molecular orientation of 1-butyl-3-methylimidazolium trifluoromethanesulfonate ([bmim][OTf]) and its interaction with the adsorbed Na and LiI species at temperatures of 150-300 K. A glassy [bmim][OTf] film crystallizes at around 230 K, as observed from the increase in the [bmim]{sup +} yield. LiI and Na adsorbed on the glassy film are solvated, whereas they tend to form islands on a crystalline film. The crystalline surface inertness is ascribable to the termination with the CF{sub 3} and C{sub 4}H{sub 9} groups, whereas the exposure of polar SO{sub 3} and imidazolemore » groups at the glassy film results in the solvation. Surface layering occurs during solvation of LiI on the glassy film in such a way that the [bmim]{sup +} ([OTf]{sup -}) moiety is exposed to the vacuum (oriented to the bulk). The LiI adsorbed on the glassy film is incorporated into the bulk at temperatures higher than 200 K because of the glass-liquid transition. No further uptake of LiI is observed during crystallization, providing a contrast to the results of normal molecular solids such as water and ethanol. The surface layers of the crystal melt at temperatures below the bulk melting point, as confirmed from the dissolution of adsorbed LiI, but the melting layer retains a short-range order similar to the crystal. The [bmim][OTf] can be regarded as a strongly correlated liquid with the combined liquid property and crystal-type local structure. The origin of this behavior is discussed.« less

Inhomogeneous magnesium hydride synthesized by low temperature ion implantation: weak localization effect

NASA Astrophysics Data System (ADS)

Nédellec, P.; Dumoulin, L.; Burger, J. P.; Bernas, H.; Köstler, H.; Traverse, A.

1993-11-01

Metastable MgHx hydride was prepared by H ion implantation into Mg films at 5 K. The resistivity and magnetoresistance temperature dependence reveal weak localization effects due to atomic disorder. At low hydrogen concentrations, x le 0.3, the conductivity varies as σ sim log(T), typical of two-dimensional weak localization behaviour. The resistivity is also very sensitive to the sample inhomogeneity, due to H diffusion, which can be modelled by introducing a temperature-dependent geometrical percolating factor G. At higher H concentrations, 0.7 le x le 3, after annealing at 20 K, 50 K and 110 K, the samples also exhibit weak localization but with three-dimensional behaviour i.e. a σ sim sqrt{T}. Our analysis is consistent with the existence of an inhomogeneous system formed by a mixture of two phases with contrasted conduction properties, one of which is a well-behaved metal, while the other displays the localization properties. The results lead us to identify the former phase to a non percolating superconducting phase at low temperature. Des films d'hydrure MgHx sont préparés, hors de l'équilibre thermodynamique, par implantation d'ions H dans des films de Mg maintenus à 5 K. La mesure de la résistance et de la magnétorésistance en fonction de la température met en évidence des effets importants de localisation électronique due au désordre atomique. Pour les faibles concentrations d'hydrogène, x le 0,3, la conductivité varie comme σ sim log(T), variation caractéristique d'un comportement dominé par les effets de localisation électronique faible à 2 dimensions. La résistivité est très sensible aux effets d'inhomogénéité, liés à la diffusion de H. Nous avons modélisé ces effets en introduisant un coefficient géométrique variant avec la température. Pour les concentrations plus élevées (0, 7 le x le 3), après un recuit à 20 K, 50 K et 110 K, les films montrent également des effets de localisation mais la conductivité varie maintenant comme σ sim sqrt{T}, caractéristique d'un comportement tridimensionnel. L'analyse des résultats est compatible avec l'hypothèse d'un système inhomogène formé du mélange de deux phases avec des propriétés électriques contrastées : un “mauvais métal" et un “bon métal" qui, à basse température, pourrait présenter un état supraconducteur non percolant.

Des recommandations probantes pour surveiller l’innocuité des antipsychotiques de deuxième génération chez les enfants et les adolescents

PubMed Central

Pringsheim, Tamara; Panagiotopoulos, Constadina; Davidson, Jana; Ho, Josephine

2012-01-01

HISTORIQUE : Au Canada, l’utilisation d’antipsychotiques, notamment les antipsychotiques de deuxième génération (ADG), a augmenté de façon considérable depuis cinq ans chez les enfants ayant des troubles de santé mentale. Ces médicaments ont le potentiel de causer de graves complications métaboliques et neurologiques lorsqu’on les utilise de manière chronique. OBJECTIF : Synthétiser les données probantes relatives aux effets secondaires métaboliques et neurologiques précis associés à l’usage d’ADG chez les enfants et fournir des recommandations probantes sur la surveillance de ces effets secondaires. MÉTHODOLOGIE : Les auteurs ont procédé à une analyse systématique des essais cliniques contrôlés des ADG auprès d’enfants. Ils ont fait des recommandations à l’égard de la surveillance de l’innocuité des ADG d’après un modèle de classification fondé sur le système GRADE (système de notation de l’évaluation et de l’élaboration des recommandations). Lorsque les données probantes n’étaient pas suffisantes, ils fondaient leurs recommandations sur le consensus et l’avis d’experts. Un groupe consensuel multidisciplinaire a analysé toutes les données probantes pertinentes et est parvenu à un consensus à l’égard des recommandations. RÉSULTATS : Les recommandations probantes portant sur la surveillance de l’innocuité des ADG figurent dans les présentes lignes directrices. Les auteurs indiquent la qualité des recommandations relatives à des examens physiques et tests de laboratoire précis à l’égard de chaque ADG à des moments déterminés. CONCLUSION : De multiples essais aléatoires et contrôlés ont permis d’évaluer l’efficacité de bon nombre des ADG utilisés pour traiter les troubles de santé mentale en pédiatrie. Toutefois, leurs avantages ne sont pas sans risques : on observe à la fois des effets secondaires métaboliques et neurologiques chez les enfants traités au moyen d’ADG. Le risque de prise de poids, d’augmentation de l’indice de masse corporelle et de taux lipidiques anormaux est plus élevé à l’utilisation d’olanzapine, suivie de la clozapine et de la quétiapine. Quant au risque d’effets secondaires neurologiques des traitements, il est plus élevé à l’utilisation de rispéridone, d’olanzapine et d’aripiprazole. Des interventions de surveillance pertinentes des effets secondaires amélioreront la qualité des soins des enfants traités à l’aide de ces médicaments. PMID:24082813

Etude des melanges co-continus d'acide polylactique et d'amidon thermoplastique (PLA/TPS)

NASA Astrophysics Data System (ADS)

Chavez Garcia, Maria Graciela

Les melanges co-continus sont des melanges polymeriques ou chaque composant se trouve dans une phase continue. Pour cette raison, les caracteristiques de chacun des composants se combinent et il en resulte un materiau avec une morphologie et des proprietes particulieres. L'acide polylactique (PLA) et l'amidon thermoplastique (TPS) sont des biopolymeres qui proviennent de ressources renouvelables et qui sont biodegradables. Dans ce projet, differents melanges de PLA et TPS a une haute concentration de TPS ont ete prepares dans une extrudeuse bi-vis afin de generer des structures co-continues. Grace a la technique de lixiviation selective, le TPS est enleve pour creer une structure poreuse de PLA qui a pu etre analysee au moyen de la microtomographie R-X et de la microscopie electronique a balayage MEB. L'analyse des images 2D et 3D confirme la presence de la structure co-continue dans les melanges dont la concentration en TPS. se situe entre 66% et 80%. L'effet de deux plastifiants, le glycerol seul et le melange de glycerol et de sorbitol, dans la formulation de TPS est etudie dans ce travail. De plus, nous avons evalue l'effet du PLA greffe a l'anhydride maleique (PLAg) en tant que compatibilisant. On a trouve que la phase de TPS obtenue avec le glycerol est plus grande. L'effet de recuit sur la taille de phases est aussi analyse. Grace aux memes techniques d'analyse, on a etudie l'effet du procede de moulage par injection sur la morphologie. On a constate que les pieces injectees presentent une microstructure heterogene et differente entre la surface et le centre de la piece. Pres de la surface, une peau plus riche en PLA est presente et les phases de TPS y sont allongees sous forme de lamelles. Plus au centre de la piece, une morphologie plus cellulaire est observee pour chaque phase continue. L'effet des formulations sur les proprietes mecaniques a aussi ete etudie. Les pieces injectees dont la concentration de TPS est plus grande presentent une moindre resistance a la traction. La presence du compatibilisant dans la region co-continue affecte negativement cette resistance. En considerant que l'amidon est un biomateriau abondant, moins cher et plus rapidement biodegradable, son ajout dans le PLA presente l'avantage de reduire le cout tout en augmentant la vitesse de degradation du PLA. De plus, une structure continue poreuse de PLA produit par la technique de lixiviation selective a des applications potentielles soit comme materiau a degradation rapide ou encore, une fois la phase TPS retiree, comme substrat a porosite ouverte pour la fabrication de membranes, de supports cellulaires ou de filtres. Mots-cles : melanges immiscibles, acide polylactique, amidon thermoplastique, morphologie cocontinue, lixiviation selective, microtomographie R-X, materiau rigide poreux biodegradable.

Influence of Packing on Low Energy Vibrations of Densified Glasses

NASA Astrophysics Data System (ADS)

Carini, Giovanni, Jr.; Carini, Giuseppe; D'Angelo, Giovanna; Tripodo, Gaspare; Di Marco, Gaetano; Vasi, Cirino; Gilioli, Edmondo

2013-12-01

A comparative study of Raman scattering and low temperature specific heat capacity has been performed on samples of B2O3, which have been high-pressure quenched to go through different glassy phases having growing density to the crystalline state. It has revealed that the excess volume characterizing the glassy networks favors the formation of specific glassy structural units, the boroxol rings, which produce the boson peak, a broad band of low energy vibrational states. The decrease of boroxol rings with increasing pressure of synthesis is associated with the progressive depression of the excess low energy vibrations until their full disappearance in the crystalline phase, where the rings are missing. These observations prove that the additional soft vibrations in glasses arise from specific units whose formation is made possible by the poor atomic packing of the network.

Glassy dynamics of landscape evolution

PubMed Central

Ortiz, Carlos P.; Jerolmack, Douglas J.

2018-01-01

Soil creeps imperceptibly downhill, but also fails catastrophically to create landslides. Despite the importance of these processes as hazards and in sculpting landscapes, there is no agreed-upon model that captures the full range of behavior. Here we examine the granular origins of hillslope soil transport by discrete element method simulations and reanalysis of measurements in natural landscapes. We find creep for slopes below a critical gradient, where average particle velocity (sediment flux) increases exponentially with friction coefficient (gradient). At critical gradient there is a continuous transition to a dense-granular flow rheology. Slow earthflows and landslides thus exhibit glassy dynamics characteristic of a wide range of disordered materials; they are described by a two-phase flux equation that emerges from grain-scale friction alone. This glassy model reproduces topographic profiles of natural hillslopes, showing its promise for predicting hillslope evolution over geologic timescales. PMID:29686102

Comportement instationnaire des thermoéléments à effet Peltier multi-étages

NASA Astrophysics Data System (ADS)

Monchoux, F.; Zély, D.; Cordier, A.

1995-01-01

The analysis of thermoelectric phenomena is possible based on non-equilibrium thermodynamics. Integration of the thermal balance equation leads to an analytical solution for the non-stationnary behaviour. The influence to Thomson effect is commmented. The model, introduced in the complete software TRNSYS, permits the modelling of complex systems including such elements in their thermal regulation. La thermodynamique des processus irréversibles permet l'analyse des phénomènes thermoélectriques. Par intégration de l'équation de bilan thermique, on a obtenu une solution analytique pour le régime non stationnaire donnant la température en tous points et le flux absorbé. On a analysé l'influence de l'effet Thomson. Le modèle a été inclu dans le code plus général TRNSYS qui permet la modélisation de systèmes complexes.

Equation of state of heated glassy carbon

NASA Technical Reports Server (NTRS)

Sekine, Toshimori; Ahrens, Thomas J.

1991-01-01

New Hugoniot data are presented for glassy carbon preheated to 1550 K and shocked to 20 GPa. The high-temperature Hugoniot is very similar to the principal Hugoniot. This results argues against the diffusional mechanism for the shock-induced transformaton of amorphous carbon to diamond, although the present results are obviously limited to below 20 GPa. This study provides the first Higoniot data for carbon preheated to significantly high temperatures.

AC Current Driven Dynamic Vortex State in YBa2Cu3O7-x (Postprint)

DTIC Science & Technology

2012-02-01

coexisting steady states of driven vortex motion with different characteristics: a quasi-static disordered glassy state in the sample interior and a...coexisting, vortex, plastic, dynamic, calculations, disordered , hysteretic, model, films, edges 16. SECURITY CLASSIFICATION OF: 17. LIMITATION OF...characteris- tics: a quasi-static disordered glassy state in the sample interior and a dynamic state of plastic motion near the edges. Finite- element

To enhance the efficiency of a power supply circuit by the use of Fe-P-B-Nb-type ultralow loss glassy metal core

NASA Astrophysics Data System (ADS)

Matsumoto, H.; Urata, A.; Yamada, Y.; Makino, A.

2009-04-01

The inductor in a power supply is required to be capable of dealing satisfactorily with the high-current supply and to improve the power loss characteristic. A novel glassy metal powder with a chemical composition Fe77P7B13Nb3 features both a high saturated magnetic flux density of 1.3 T and a low coercive force of 2.0 A/m, which has a stable amorphous structure suitable for glassy metal composite cores. Hence there is no magnetic saturation even under a high-current supply, and it is confirmed to have significantly low magnetic loss resulting from the low coercive force. As a result of using the glassy metal alloy Fe77P7B13Nb3 powder in an inductor core, we have achieved improvement in power supply efficiency by up to roughly 2.0%. Moreover, the reduction in the standby power requirement by the improvement in the power supply efficiency in the low load current case, where the core loss occupies a high ratio in the entire loss, can be expected. Additionally, heat generation in a core is suppressed by using the low loss powder, and it becomes easy to design a temperature rise in the entire power supply circuit.

Scalable Nanostructured Carbon Electrode Arrays for Enhanced Dopamine Detection.

PubMed

Demuru, Silvia; Nela, Luca; Marchack, Nathan; Holmes, Steven J; Farmer, Damon B; Tulevski, George S; Lin, Qinghuang; Deligianni, Hariklia

2018-04-27

Dopamine is a neurotransmitter that modulates arousal and motivation in humans and animals. It plays a central role in the brain "reward" system. Its dysregulation is involved in several debilitating disorders such as addiction, depression, Parkinson's disease, and schizophrenia. Dopamine neurotransmission and its reuptake in extracellular space takes place with millisecond temporal and nanometer spatial resolution. Novel nanoscale electrodes are needed with superior sensitivity and improved spatial resolution to gain an improved understanding of dopamine dysregulation. We report on a scalable fabrication of dopamine neurochemical probes of a nanostructured glassy carbon that is smaller than any existing dopamine sensor and arrays of more than 6000 nanorod probes. We also report on the electrochemical dopamine sensing of the glassy carbon nanorod electrode. Compared with a carbon fiber, the nanostructured glassy carbon nanorods provide about 2× higher sensitivity per unit area for dopamine sensing and more than 5× higher signal per unit area at low concentration of dopamine, with comparable LOD and time response. These glassy carbon nanorods were fabricated by pyrolysis of a lithographically defined polymeric nanostructure with an industry standard semiconductor fabrication infrastructure. The scalable fabrication strategy offers the potential to integrate these nanoscale carbon rods with an integrated circuit control system and with other complementary metal oxide semiconductor (CMOS) compatible sensors.

Quantifying glassy and crystalline basalt partitioning in the oceanic crust

NASA Astrophysics Data System (ADS)

Moore, Rachael; Ménez, Bénédicte

2016-04-01

The upper layers of the oceanic crust are predominately basaltic rock, some of which hosts microbial life. Current studies of microbial life within the ocean crust mainly focus on the sedimentary rock fraction, or those organisms found within glassy basalts while the potential habitability of crystalline basalts are poorly explored. Recently, there has been recognition that microbial life develops within fractures and grain boundaries of crystalline basalts, therefore estimations of total biomass within the oceanic crust may be largely under evaluated. A deeper understanding of the bulk composition and fractionation of rocks within the oceanic crust is required before more accurate estimations of biomass can be made. To augment our understanding of glassy and crystalline basalts within the oceanic crust we created two end-member models describing basalt fractionation: a pillow basalt with massive, or sheet, flows crust and a pillow basalt with sheeted dike crust. Using known measurements of massive flow thickness, dike thickness, chilled margin thickness, pillow lava size, and pillow lava glass thickness, we have calculated the percentage of glassy versus crystalline basalts within the oceanic crust for each model. These models aid our understanding of textural fractionation within the oceanic crust, and can be applied with bioenergetics models to better constrain deep biomass estimates.

Degradation behavior of carbon nanotubes/phenol-furfuryl alcohol multifunctional composites with aerospace application

NASA Astrophysics Data System (ADS)

Conejo, L. S.; Costa, M. L.; Oishi, S. S.; Botelho, E. C.

2017-10-01

Lightweight and highly conductive composite associated with good impact and tribological properties could be used in the aerospace industry to replace metal for an aircraft skin and still provide effective shielding against electromagnetic interference (EMI). Also, phenol-furfuryl alcohol resins (PFA) are excellent candidates to replace existing thermoset matrices used for obtaining glassy carbon, both in its pure form and reinforced with nanoscale structures. The synthesis of PFA allow obtaining a resin with better properties than that showed by conventional phenolic resins and with synthesis and cure processes more controlled than observed for the furfuryl alcohol resin. This work has as main purpose the synthesis and thermal characterization of PFA resin and its nanostructured composites with different concentrations of carbon nanotubes (0, 0.1, 0.5 and 1.0 wt%). PFA resin was synthesized with 1:2:1 molar ratio of phenol/formaldehyde/furfuryl alcohol, according to the more appropriate condition obtained previously. The specimens were evaluated by thermogravimetry (TGA) to knowledge of the temperature of thermal degradation, either by actual analyses as simulated by simulation heating rate conversion software (known as Highway Simulation). The introduction of CNT in PFA sample does not affect its thermal stability. The values of residual weight found for samples with CNT additions are close to the values of the phenolic resin in the literature (about 60% residual weight).

Textural variations and impact history of the Millbillillie eucrite

NASA Technical Reports Server (NTRS)

Yamaguchi, Akira; Takeda, Hiroshi; Bogard, Donald D.; Garrison, Daniel

1994-01-01

We have investigated 10 new specimens of the Millbillillie eucrite to study its textures and mineral compositions by electron probe microanalyser and scanning electron microscope. Although originally described as having fine-grained texture, the new specimens show diversity of texture. The compositions (Mg/Fe ratios) of the host pigeonites and augite lamellae are homogeneous, respectively, in spite of the textural variation. In addition to their chemical homogeneity, pyroxenes in coarse and fine-grained clasts are partly inverted to orthopyroxene. Chemical zoning of plagioclase during crystal growth is preserved. This eucrite includes areas of granulitic breccias and impact melts. Large scale textures show a subparallel layering suggesting incomplete mixing and deposition of impact melt and lithic fragments. An Ar-39-Ar-40 age determination for a coarse-grained clast indicates a strong degassing event at 3.55 +/- 0.02 Ga. We conclude that Millbillillie is among the most equilibriated eucrites produced by thermal annealing after impact brecciation. According to the classificcation of impact breccias, Millbillillie can be classified as a mixture of granulitic breccias and impact melts. The last significant thermal event is characterized by network-like glassy veins that run through clasts and matrices. Consideration of textual observations and requirements for Ar-degassing suggests that the Ar-39-Ar-40 age could in principle date either the earlier brecciation and annealing event or the event which produced the veins.

L'etude de l'InP et du GaP suite a l'implantation ionique de Mn et a un recuit thermique

NASA Astrophysics Data System (ADS)

Bucsa, Ioan Gigel

Cette these est dediee a l'etude des materiaux InMnP et GaMnP fabriques par implantation ionique et recuit thermique. Plus precisement nous avons investigue la possibilite de former par implantation ionique des materiaux homogenes (alliages) de InMnP et GaMnP contenant de 1 a 5 % atomiques de Mn qui seraient en etat ferromagnetique, pour des possibles applications dans la spintronique. Dans un premier chapitre introductif nous donnons les motivations de cette recherche et faisons une revue de la litterature sur ce sujet. Le deuxieme chapitre decrit les principes de l'implantation ionique, qui est la technique utilisee pour la fabrication des echantillons. Les effets de l'energie, fluence et direction du faisceau ionique sur le profil d'implantation et la formation des dommages seront mis en evidence. Aussi dans ce chapitre nous allons trouver des informations sur les substrats utilises pour l'implantation. Les techniques experimentales utilisees pour la caracterisation structurale, chimique et magnetique des echantillons, ainsi que leurs limitations sont presentees dans le troisieme chapitre. Quelques principes theoriques du magnetisme necessaires pour la comprehension des mesures magnetiques se retrouvent dans le chapitre 4. Le cinquieme chapitre est dedie a l'etude de la morphologie et des proprietes magnetiques des substrats utilises pour implantation et le sixieme chapitre, a l'etude des echantillons implantes au Mn sans avoir subi un recuit thermique. Notamment nous allons voir dans ce chapitre que l'implantation de Mn a plus que 1016 ions/cm 2 amorphise la partie implantee du materiau et le Mn implante se dispose en profondeur sur un profil gaussien. De point de vue magnetique les atomes implantes se trouvent dans un etat paramagnetique entre 5 et 300 K ayant le spin 5/2. Dans le chapitre 7 nous presentons les proprietes des echantillons recuits a basses temperatures. Nous allons voir que dans ces echantillons la couche implantee est polycristalline et les atomes de Mn sont toujours dans un etat paramagnetique. Dans les chapitres 8 et 9, qui sont les plus volumineux, nous presentons les resultats des mesures sur les echantillons recuits a hautes temperatures: il s'agit d'InP et du GaP implantes au Mn, dans le chapitre 8 et d'InP co-implante au Mn et au P, dans le chapitre 9. D'abord, dans le chapitre 8 nous allons voir que le recuit a hautes temperatures mene a une recristallisation epitaxiale du InMnP et du GaMnP; aussi la majorite des atomes de Mn se deplacent vers la surface a cause d'un effet de segregation. Dans les regions de la surface, concentres en Mn, les mesures XRD et TEM identifient la formation de MnP et d'In cristallin. Les mesures magnetiques identifient aussi la presence de MnP ferromagnetique. De plus dans ces mesures on trouve qu'environ 60 % du Mn implante est en etat paramagnetique avec la valeur du spin reduite par rapport a celle trouvee dans les echantillons non-recuits. Dans les echantillons InP co-implantes au Mn et au P la recristallisation est seulement partielle mais l'effet de segregation du Mn a la surface est beaucoup reduit. Dans ce cas plus que 50 % du Mn forme des particules MnP et le restant est en etat paramagnetique au spin 5/2, dilue dans la matrice de l'InP. Finalement dans le dernier chapitre, 10, nous presentons les conclusions principales auxquels nous sommes arrives et discutons les resultats et leurs implications. Mots cles: implantation ionique, InP, GaP, amorphisation, MnP, segregation, co-implantation, couche polycristalline, paramagnetisme, ferromagnetisme.

A Novel Method for Electroplating Ultra-High-Strength Glassy Metals

NASA Technical Reports Server (NTRS)

Ramsey, Brian; Engelhaupt, Darell; Six, N. Frank (Technical Monitor)

2002-01-01

A novel method for electroplating ultra-high-strength glassy metals, nickel-phosphorous and nickel-cobalt-phosphorous, has been developed at NASA Marshall Space Flight Center, cooperatively with the University of Alabama in Huntsville. Traditionally, thin coatings of these metals are achieved via electroless deposition. Benefits of the new electrolytic process include thick, low-stress deposits, free standing shapes, lower plating temperature, low maintenance, and safer operation with substantially lower cost.

Highly Selective Membranes For The Separation Of Organic Vapors Using Super-Glassy Polymers

DOEpatents

Pinnau, Ingo; Lokhandwala, Kaaeid; Nguyen, Phuong; Segelke, Scott

1997-11-18

A process for separating hydrocarbon gases of low boiling point, particularly methane, ethane and ethylene, from nitrogen. The process is performed using a membrane made from a super-glassy material. The gases to be separated are mixed with a condensable gas, such as a C.sub.3+ hydrocarbon. In the presence of the condensable gas, improved selectivity for the low-boiling-point hydrocarbon gas over nitrogen is achieved.

Low substrate temperature deposition of diamond coatings derived from glassy carbon

DOEpatents

Holcombe, C.E. Jr.; Seals, R.D.

1995-09-26

A process is disclosed for depositing a diamond coating on a substrate at temperatures less than about 550 C. A powder mixture of glassy carbon and diamond particles is passed through a high velocity oxy-flame apparatus whereupon the powders are heated prior to impingement at high velocity against the substrate. The powder mixture contains between 5 and 50 powder volume percent of the diamond particles, and preferably between 5 and 15 powder volume percent. The particles have a size from about 5 to about 100 micrometers, with the diamond particles being about 5 to about 30 micrometers. The flame of the apparatus provides a velocity of about 350 to about 1000 meters per second, with the result that upon impingement upon the substrate, the glassy carbon is phase transformed to diamond as coaxed by the diamond content of the powder mixture. 2 figs.

Relation between the Dynamics of Glassy Clusters and Characteristic Features of their Energy Landscape

NASA Astrophysics Data System (ADS)

De, Sandip; Schaefer, Bastian; Sadeghi, Ali; Sicher, Michael; Kanhere, D. G.; Goedecker, Stefan

2014-02-01

Based on a recently introduced metric for measuring distances between configurations, we introduce distance-energy (DE) plots to characterize the potential energy surface of clusters. Producing such plots is computationally feasible on the density functional level since it requires only a few hundred stable low energy configurations including the global minimum. By using standard criteria based on disconnectivity graphs and the dynamics of Lennard-Jones clusters, we show that the DE plots convey the necessary information about the character of the potential energy surface and allow us to distinguish between glassy and nonglassy systems. We then apply this analysis to real clusters at the density functional theory level and show that both glassy and nonglassy clusters can be found in simulations. It turns out that among our investigated clusters only those can be synthesized experimentally which exhibit a nonglassy landscape.

Scalable Synthesis of Cholesteric Glassy Liquid Crystals

DOE PAGES

Wallace, Jason U.; Shestopalov, Alexander; Kosc, Tanya; ...

2018-03-15

Capable of non-absorbing circular polarization of unpolarized incident light, cholesteric glassy liquid crystals consisting of hybrid chiral-nematic pendants to volume-excluding cores are potentially useful for the fabrication of various robust optical devices. As illustrated in this study, the well-oriented glassy film of enantiomeric Bz3ChN, with a glass transition at 73 °C and a cholesteric-to-isotropic transition at 295 °C, exhibits a selective reflection band centered at approximately 410 nm, an exceptional set of properties well suited for optical device exploration. To enable sustainable, large-scale synthesis of this material class for widespread applications, a productive strategy has been established, requiring a meremore » three-step scheme with an overall yield, atom economy, and reaction mass efficiency at 34%, 33% and 12%, respectively. Lastly, while amenable to improvements, the resultant green chemistry metrics are encouraging as the first attempt.« less

Understanding soft glassy materials using an energy landscape approach

NASA Astrophysics Data System (ADS)

Hwang, Hyun Joo; Riggleman, Robert A.; Crocker, John C.

2016-09-01

Many seemingly different soft materials--such as soap foams, mayonnaise, toothpaste and living cells--display strikingly similar viscoelastic behaviour. A fundamental physical understanding of such soft glassy rheology and how it can manifest in such diverse materials, however, remains unknown. Here, by using a model soap foam consisting of compressible spherical bubbles, whose sizes slowly evolve and whose collective motion is simply dictated by energy minimization, we study the foam's dynamics as it corresponds to downhill motion on an energy landscape function spanning a high-dimensional configuration space. We find that these downhill paths, when viewed in this configuration space, are, surprisingly, fractal. The complex behaviour of our model, including power-law rheology and non-diffusive bubble motion and avalanches, stems directly from the fractal dimension and energy function of these paths. Our results suggest that ubiquitous soft glassy rheology may be a consequence of emergent fractal geometry in the energy landscapes of many complex fluids.

Glassy dynamics of landscape evolution.

PubMed

Ferdowsi, Behrooz; Ortiz, Carlos P; Jerolmack, Douglas J

2018-05-08

Soil creeps imperceptibly downhill, but also fails catastrophically to create landslides. Despite the importance of these processes as hazards and in sculpting landscapes, there is no agreed-upon model that captures the full range of behavior. Here we examine the granular origins of hillslope soil transport by discrete element method simulations and reanalysis of measurements in natural landscapes. We find creep for slopes below a critical gradient, where average particle velocity (sediment flux) increases exponentially with friction coefficient (gradient). At critical gradient there is a continuous transition to a dense-granular flow rheology. Slow earthflows and landslides thus exhibit glassy dynamics characteristic of a wide range of disordered materials; they are described by a two-phase flux equation that emerges from grain-scale friction alone. This glassy model reproduces topographic profiles of natural hillslopes, showing its promise for predicting hillslope evolution over geologic timescales. Copyright © 2018 the Author(s). Published by PNAS.

Relationship between microstructure and tribological behavior of CFRC composites

NASA Astrophysics Data System (ADS)

de Souza, Maria Aparecida Miranda; Pardini, Luiz Claudio

2017-12-01

Carbon fiber reinforced carbon (CFRC) composites were initially introduced in spacecraft propulsion area and quickly started to be applied in aircraft braking systems, replacing conventional metallic systems, thanks to their excellent tribological properties. Each company develops their own CFRC composite production system, the information is unique to each manufacturer, and little is reported in the literature. In this work, tribological characterizations of three commercial CFRC composites are performed using a pin-on-disc tribometer. The results showed that the pairs assembled with pyrolytic matrix composites of rough or smooth laminar texture with graphitization index between 18 and 40% has an average COF between 0.15 and 0.25, while the pairs assembled with mixed pairs, pyrolytic matrix and glassy matrix, or pair of glassy matrix display average COF between 0.10 and 0.15. Wear which can reach a rate 9 times higher to the tribological pair of glassy composite when compared to a pyrolytic composite.

Unraveling the Mechanism of Nanoscale Mechanical Reinforcement in Glassy Polymer Nanocomposites

DOE PAGES

Cheng, Shiwang; Bocharova, Vera; Belianinov, Alex; ...

2016-05-20

The mechanical reinforcement of polymer nanocomposites (PNCs) above the glass transition temperature, T g, has been extensively researched. However, not much is known about the origin of this effect below T g. In this paper, we unravel the mechanism of PNC reinforcement within the glassy state by directly probing nanoscale mechanical properties with atomic force microscopy and macroscopic properties with Brillouin light scattering. Our results unambiguously show that the "glassy" Young's modulus in the interfacial polymer layer of PNCs is two-times higher than in the bulk polymer, which results in significant reinforcement below T g. We ascribe this phenomenon tomore » a high stretching of the chains within the interfacial layer. Since the interfacial chain packing is essentially temperature independent, these findings provide a new insight into the mechanical reinforcement of PNCs also above T g.« less

Compressed glassy carbon: An ultrastrong and elastic interpenetrating graphene network

PubMed Central

Hu, Meng; He, Julong; Zhao, Zhisheng; Strobel, Timothy A.; Hu, Wentao; Yu, Dongli; Sun, Hao; Liu, Lingyu; Li, Zihe; Ma, Mengdong; Kono, Yoshio; Shu, Jinfu; Mao, Ho-kwang; Fei, Yingwei; Shen, Guoyin; Wang, Yanbin; Juhl, Stephen J.; Huang, Jian Yu; Liu, Zhongyuan; Xu, Bo; Tian, Yongjun

2017-01-01

Carbon’s unique ability to have both sp2 and sp3 bonding states gives rise to a range of physical attributes, including excellent mechanical and electrical properties. We show that a series of lightweight, ultrastrong, hard, elastic, and conductive carbons are recovered after compressing sp2-hybridized glassy carbon at various temperatures. Compression induces the local buckling of graphene sheets through sp3 nodes to form interpenetrating graphene networks with long-range disorder and short-range order on the nanometer scale. The compressed glassy carbons have extraordinary specific compressive strengths—more than two times that of commonly used ceramics—and simultaneously exhibit robust elastic recovery in response to local deformations. This type of carbon is an optimal ultralight, ultrastrong material for a wide range of multifunctional applications, and the synthesis methodology demonstrates potential to access entirely new metastable materials with exceptional properties. PMID:28630918

The influence of Ge on optical and thermo- mechanical properties of S-Se chalcogenide glasses

NASA Astrophysics Data System (ADS)

Samudrala, Kavitha; Babu Devarasetty, Suresh

2018-05-01

S-Se-Ge glasses were prepared by melt quenching method to investigate the effect of Germanium on thermo-mechanical and optical properties of chalcogenide glasses. The glassy nature of the samples has been verified by x-ray diffraction and DSC studies that the samples are glassy in nature. The optical band gap of the samples was estimated by the absorption spectrum fitting method. The optical band gap increased from 1.61 ev for x = 0 sample to 1.90 ev for x = 40 sample and is explained in terms of cohesive energies. The basic thermo-mechanical parameters such as micro-hardness, Volume (Vh) and formation energy (Eh) of micro voids in the glassy network, as well as the modulus of Elasticity (E) have been calculated for prepared glasses.in present glasses. The variation in these parameters with Ge content correlated with heat of atomization of alloys.

Low substrate temperature deposition of diamond coatings derived from glassy carbon

DOEpatents

Holcombe, Jr., Cressie E.; Seals, Roland D.

1995-01-01

A process for depositing a diamond coating on a substrate at temperatures less than about 550.degree. C. A powder mixture of glassy carbon and diamond particles is passed through a high velocity oxy-flame apparatus whereupon the powders are heated prior to impingement at high velocity against the substrate. The powder mixture contains between 5 and 50 powder volume percent of the diamond particles, and preferably between 5 and 15 powder volume percent. The particles have a size from about 5 to about 100 micrometers, with the diamond particles being about 5 to about 30 micrometers. The flame of the apparatus provides a velocity of about 350 to about 1000 meters per second, with the result that upon impingement upon the substrate, the glassy carbon is phase transformed to diamond as coaxed by the diamond content of the powder mixture.

Bulk Fe-based metallic glass with extremely soft ferromagnetic properties

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

Shen, T. D.; Harms, U. S.; Schwarz, R. B.

2001-01-01

The authors have investigated the DC and AC magnetic properties of a bulk glassy Fe{sub 65.5}Cr{sub 4}Mo{sub 4}Ga{sub 4}P{sub 12}B{sub 5.5}C{sub 5} alloy. In the annealed state the alloy has coercivity H{sub C} and maximum DC permeability {mu}{sub m} of approximately 0.4 A/m (5 mOe) and 2.8 x 10{sup 5}, comparable to those found in annealed zero-magnetostriction Co-based alloys. The low H{sub C} found in the bulk glassy alloy is attributed to the low ratio of surface-roughness to sample thickness, and low residual internal-stress. The total power loss in the annealed bulk glass is about one order of magnitude lowermore » than that of rapidly quenched Fe-based glassy ribbons. This is attributed to a low anomalous eddy-current loss.« less

The viscoelastic behavior of notched glassy polymers

NASA Technical Reports Server (NTRS)

Crook, R. A.; Letton, Alan

1993-01-01

In the bulk, glassy polymers exhibit a nonlinear viscoelastic response during deformation. Stress or strain induced damage (i.e. crazing, microshear banding) results in the production of nonrecoverable work and observed nonlinearity. Stress or strain dependent shift factors have been used to mathematically model the mechanical behavior of these polymers. Glassy polymers that have been notched, may exhibit very different load displacement response compared to the same material under bulk deformation. If a sharp notch is introduced into the body then loaded, the load displacement trace may appear to be single-valued in the absence of viscoelasticity and crack growth. This suggests the volume of damaged material is small compared to the overall dimensions of the specimen. The ability to produce a single-valued load-load-line displacement trace through the use of the Correspondence Principle may prove to be useful for fracture of viscoelastic materials.

Scalable Synthesis of Cholesteric Glassy Liquid Crystals

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

Wallace, Jason U.; Shestopalov, Alexander; Kosc, Tanya

2018-03-08

Capable of non-absorbing circular polarization of unpolarized incident light, cholesteric glassy liquid crystals consisting of hybrid chiral-nematic pendants to volume-excluding cores are potentially useful for the fabrication of various robust optical devices. As illustrated in this study, the well-oriented glassy film of enantiomeric Bz3ChN, with a glass transition at 73 oC and a cholesteric-to-isotropic transition at 295 oC, exhibits a selective reflection band centered at approximately 410 nm, an exceptional set of properties well suited for optical device exploration. To enable sustainable, large-scale synthesis of this material class for widespread applications, a productive strategy has been established, requiring a meremore » three-step scheme with an overall yield, atom economy, and reaction mass efficiency at 34, 33 and 12 %, respectively. While amenable to improvements, the resultant green chemistry metrics are encouraging as the first attempt.« less

The behavior of biogenic silica-rich rocks and volcanic tuffs as pozzolanic additives in cement

NASA Astrophysics Data System (ADS)

Fragoulis, Dimitris; Stamatakis, Michael; Anastasatou, Marianthi

2015-04-01

Cements currently produced, include a variety of pozzolanic materials, aiming for lower clinker addition and utilization of vast deposits of certain raw materials and/or mining wastes and byproducts. The major naturally occurring pozzolanic materials include glassy tuffs, zeolitic tuffs, diatomites and volcanic lavas rich in glassy phase, such as perlites. Therefore, based on the available raw materials in different locations, the cement composition might vary according to the accessibility of efficient pozzolanic materials. In the present investigation, the behavior of pozzolanic cements produced with representative samples of the aforementioned materials was studied, following the characterization of the implemented pozzolanas with respect to their chemical and mineralogical characteristics. Laboratory cements were produced by co-grinding 75% clinker, 5% gypsum and 20% pozzolana, for the same period of time (45 min). Regarding pozzolanic materials, four different types of pozzolanas were utilized namely, diatomite, perlite, zeolite tuff and glassy tuff. More specifically, two diatomite samples originated from Australia and Greece, with high and low reactive silica content respectively, two perlite samples originated from Turkey and from Milos Island, Greece, with different reactive silica contents, a zeolite tuff sample originated from Turkey and a glassy tuff sample originated from Milos Island, Greece. The above pozzolana samples, which were ground in the laboratory ball mill for cement production performed differently during grinding and that was reflected upon the specific surface area (cm2/gr) values. The perlites and the glassy tuff were the hardest to grind, whereas, the zeolite tuff and the Australian diatomite were the easiest ones. However, the exceedingly high specific surface area of the Australian diatomite renders cement difficult to transport and tricky to use for concrete manufacturing, due to the high water demand of the cement mixture. Regarding late compressive strength, the worst performing cement was the one with the lowest reactive silica content with biogenic opal-A as the only reactive pozzolana constituent. Cements produced with perlites, raw materials consisting mainly of a glassy phase, were characterized by higher strength and a rather ordinary specific surface area. Cements produced with Turkish zeolite tuff and Milos glassy tuff exhibited higher late compressive strength than those mentioned above. The highest strength was achieved by the implementation of Australian diatomite for cement production. Its 28 day strength exceeded that of the control mixture consisting of 95% clinker and 5% gypsum. That could be attributed to both, high specific surface of cement and reactive SiO2 of diatomite. Therefore, a preliminary assessment regarding late strength of pozzolanic cements could be obtained by the consideration of two main parameters, namely: specific surface area of cement and reactive silica content of pozzolana.

Solute induced relaxation in glassy polymers: Experimental measurements and nonequilibrium thermodynamic model

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

Minelli, Matteo; Doghieri, Ferruccio

2014-05-15

Data for kinetics of mass uptake from vapor sorption experiments in thin glassy polymer samples are here interpreted in terms of relaxation times for volume dilation. To this result, both models from non-equilibrium thermodynamics and from mechanics of volume relaxation contribute. Different kind of sorption experiments have been considered in order to facilitate the direct comparison between kinetics of solute induced volume dilation and corresponding data from process driven by pressure or temperature jumps.

Crystallization of the glassy phase of grain boundaries in silicon nitride

NASA Technical Reports Server (NTRS)

Jefferson, D. A.; Thomas, J. M.; Wen, S.

1984-01-01

Three types of hot-pressed silicon nitride specimens (containing 5wt% Y2O3 and 2wt% Al2O3 additives) which were subjected to different temperature heat treatments were studied by X-ray diffraction, X-ray microanalysis and high resolution electron microscopy. The results indicated that there were phase changes in the grain boundaries after heat treatment and the glassy phase at the grain boundaries was crystallized by heat treatment.

Thermodynamics of water sorption in high performance glassy thermoplastic polymers

PubMed Central

Scherillo, Giuseppe; Petretta, Mauro; Galizia, Michele; La Manna, Pietro; Musto, Pellegrino; Mensitieri, Giuseppe

2014-01-01

Sorption thermodynamics of water in two glassy polymers, polyetherimide (PEI) and polyetheretherketone (PEEK), is investigated by coupling gravimetry and on line FTIR spectroscopy in order to gather information on the total amount of sorbed water as well as on the different species of water molecules absorbed within the polymers, addressing the issue of cross- and self-interactions occurring in the polymer/water systems. Water sorption isotherms have been determined at temperatures ranging from 30 to 70°C while FTIR spectroscopy has been performed only at 30°C. The experimental analysis provided information on the groups present on the polymer backbones involved in hydrogen bonding interactions with absorbed water molecules. Moreover, it also supplied qualitative indications about the different “populations” of water molecules present within the PEEK and a quantitative assessment of these “populations” in the case of PEI. The results of the experimental analysis have been interpreted using an equation of state theory based on a compressible lattice fluid model for the Gibbs energy of the polymer-water mixture, developed by extending to the case of out of equilibrium glassy polymers a previous model intended for equilibrium rubbery polymers. The model accounts for the non-equilibrium nature of glassy polymers as well as for mean field and for hydrogen bonding interactions, providing a satisfactory quantitative interpretation of the experimental data. PMID:24860802

Vesicle Size Distribution as a Novel Nuclear Forensics Tool

DOE PAGES

Donohue, Patrick H.; Simonetti, Antonio

2016-09-22

The first nuclear bomb detonation on Earth involved a plutonium implosion-type device exploded at the Trinity test site (33°40'38.28"N, 106°28'31.44"W), White Sands Proving Grounds, near Alamogordo, New Mexico. Melting and subsequent quenching of the local arkosic sand produced glassy material, designated “Trinitite”. In cross section, Trinitite comprises a thin (1–2 mm), primarily glassy surface above a lower zone (1–2 cm) of mixed melt and mineral fragments from the precursor sand. Multiple hypotheses have been put forward to explain these well-documented but heterogeneous textures. In this study, we report the first quantitative textural analysis of vesicles in Trinitite to constrain theirmore » physical and thermal history. Vesicle morphology and size distributions confirm the upper, glassy surface records a distinct processing history from the lower region, that is useful in determining the original sample surface orientation. Specifically, the glassy layer has lower vesicle density, with larger sizes and more rounded population in cross-section. This vertical stratigraphy is attributed to a two-stage evolution of Trinitite glass from quench cooling of the upper layer followed by prolonged heating of the subsurface. Finally, defining the physical regime of post-melting processes constrains the potential for surface mixing and vesicle formation in a post-detonation environment.« less

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

Kaminski, K.; Adrjanowicz, K.; Paluch, M.

Time-dependent isothermal dielectric measurements were carried out deeply in the glassy state on two very important saccharides: sucrose and trehalose. In both compounds two prominent secondary relaxation processes were identified. The faster one is an inherent feature of the whole family of carbohydrates. The slower one can also be detected in oligo- and polysaccharides. It was shown earlier that the {beta} process is the Johari-Goldstein (JG) relaxation coupled to motions of the glycosidic linkage, while the {gamma} relaxation originates from motions of the exocyclic hydroxymethyl unit. Recently, it was shown that the JG relaxation process can be used to determinemore » structural relaxation times in the glassy state [R. Casalini and C. M. Roland, Phys. Rev. Lett. 102, 035701 (2009)]. In this paper we present the results of an analysis of the data obtained during aging using two independent approaches. The first was proposed by Casalini and Roland, and the second one is based on the variation of the dielectric strength of the secondary relaxation process during aging [J. K. Vij and G. Power, J. Non-Cryst. Solids 357, 783 (2011)]. Surprisingly, we found that the estimated structural relaxation times in the glassy state of both saccharides are almost the same, independent of the type of secondary mode. This finding calls into question the common view that secondary modes of intramolecular origin do not provide information about the dynamics of the glassy state.« less

Synthesis and characterization of Ag+ ion conducting glassy electrolytes

NASA Astrophysics Data System (ADS)

Chandra, Angesh; Bhatt, Alok; Chandra, Archana

2013-07-01

Synthesis and characterization of new Ag+ ion conducting glassy systems: x[0.75AgI:0.25AgC1]: (1 - x)[Ag2O:P2O5], where 0.1 < x < 1 in molar weight fraction, are reported. The present glassy electrolytes have been synthesized by melt-quench technique using a high-speed twin roller-quencher. An alternate host salt: "quenched [0.75AgI:0.25AgC1] mixed system/solid solution", has been used in place of the traditional host AgI. The compositional dependence conductivity studies on the glassy systems: x[0.75AgI:0.25AgC1]:(1 - x)[Ag2O:P2O5] as well as xAgI:(1 - x)[Ag2O:P2O5] prepared identically, indicated that the composition at x = 0.75 exhibited the highest room temperature conductivity (σ ~ 5.5 x 10-3 S cm-1). The composition: 0.75[0.75AgI:0.25AgC1]:0.25[Ag2O:P2O5] has been referred to as optimum conducting composition (OCC). The some basic ion transport parameters viz. ionic conductivity (σ), ionic mobility (μ), mobile ion concentration (n), ionic drift velocity (vd), ion transference number (tion) and activation energy (Ea) values have been characterized with the help of various experimental techniques. A solid state battery was fabricated and its basic cell parameters calculated.

Exceptional effect of glassy lithium fluorophosphate on Mn-rich olivine cathode material for high-performance Li ion batteries

NASA Astrophysics Data System (ADS)

Kim, Jongsoon; Kim, Hyungsub; Myung, Seung-Taek; Yoo, Jung-Keun; Lee, Seongsu

2018-01-01

Mn-rich olivine LiFe0.3Mn0.7PO4 is homogenously encapsulated by an ∼3-nm-thick conductive nanolayer composed of the glassy lithium fluorophosphate through simple non-stoichiometric synthesis using additives of small amounts of LiF and a phosphorus source. The coating of the glassy lithium fluorophosphate nanolayer is clearly verified using transmission electron microscopy and X-ray photoelectron spectroscopy. It enables significant decrease in charge transfer resistance of LiFe0.3Mn0.7PO4 and improvement of its sluggish Li diffusion. At a rate of 10C, the LiFe0.3Mn0.7PO4 encapsulated by conductive glassy lithium fluorophosphate (LiFe0.3Mn0.7PO4-GLFP) electrode delivers a capacity of ∼130 mAh g-1, which is ∼77% of its theoretical capacity (∼170 mAh g-1) and ∼1.5 times higher than that of the pristine counterpart at 10C. Furthermore, LiFe0.3Mn0.7PO4-GLFP achieves outstanding cycle stability (∼75% retention of its initial capacity over 500 cycles at 1C). The proposed olivine LiFe0.3Mn0.7PO4-GLFP battery is thus expected to be a promising candidate for large-scale energy storage applications.

Origin of the glass-like dynamics in molecular metals κ-(BEDT-TTF)2X: implications from fluctuation spectroscopy and ab initio calculations

NASA Astrophysics Data System (ADS)

Müller, Jens; Hartmann, Benedikt; Rommel, Robert; Brandenburg, Jens; Winter, Stephen M.; Schlueter, John A.

2015-08-01

We have studied the low-frequency dynamics of the charge carriers in different organic charge-transfer salts κ-(BEDT-TTF)2X with polymeric anions X by using resistance noise spectroscopy. Our aim is to investigate the structural, glass-like transition caused by the conformational degrees of freedom of the BEDT-TTF molecules’ terminal ethylene groups. Although of fundamental importance for studies of the electronic ground-state properties, the phenomenology of the glassy dynamics has been minimally investigated and its origin is not understood. Our systematic studies of fluctuation spectroscopy of various different compounds reveal a universal, pronounced maximum in the resistance noise power spectral density related to the glass transition. The energy scale of this process can be identified with the activation energy of the glass-like ethylene endgroup structural dynamics as determined from thermodynamic and NMR measurements. For the first time for this class of ‘plastic crystals’, we report a typical glassy property of the relaxation time, namely a Vogel-Fulcher-Tammann law, and are able to determine the degree of fragility of the glassy system. Supporting ab initio calculations provide an explanation for the origin and phenomenology of the glassy dynamics in different systems in terms of a simple two-level model, where the relevant energy scales are determined by the coupling of the ethylene endgroups to the anions.

Microwave enhanced electroanalysis of formulations: processes in micellar media at glassy carbon and at platinum electrodes.

PubMed

Ghanem, Mohamed A; Compton, Richard G; Coles, Barry A; Canals, Antonio; Marken, Frank

2005-10-01

The direct electroanalysis of complex formulations containing alpha-tocopherol (vitamin E) is possible in micellar solution and employing microwave-enhanced voltammetry. In the presence of microwave radiation substantial heating and current enhancement effects have been observed at 330 microm diameter glassy carbon electrodes placed into a micellar aqueous solution and both hydrophilic and highly hydrophobic redox systems are detected. For the water soluble Fe(CN)(6)(3-/4-) redox system in micellar aqueous solutions of 0.1 M NaCl and 0.1 M sodium dodecylsulfate (SDS) at low to intermediate microwave power, thermal effects and convection effects are observed. At higher microwave power, thermal cavitation is induced and dominates the mass transport at the electrode surface. For the micelle-soluble redox systems tert-butylferrocene and 2,5-di-tert-butyl-1,4-benzoquinone, strong and concentration dependent current responses are observed only in the presence of microwave radiation. For the oxidation of micelle-soluble alpha-tocopherol current responses at glassy carbon electrodes are affected by adsorption and desorption processes whereas at platinum electrodes, analytical limiting currents are obtained over a wide range of alpha-tocopherol concentrations. However, for the determination of alpha-tocopherol in a commercial formulation interference from proteins is observed at platinum electrodes and direct measurements are possible only over a limited concentration range and at glassy carbon electrodes.

In-Vivo Characterization of Glassy Carbon Micro-Electrode Arrays for Neural Applications and Histological Analysis of the Brain Tissue

NASA Astrophysics Data System (ADS)

Vomero, Maria

The aim of this work is to fabricate and characterize glassy carbon Microelectrode Arrays (MEAs) for sensing and stimulating neural activity, and conduct histological analysis of the brain tissue after the implant to determine long-term performance. Neural applications often require robust electrical and electrochemical response over a long period of time, and for those applications we propose to replace the commonly used noble metals like platinum, gold and iridium with glassy carbon. We submit that such material has the potential to improve the performances of traditional neural prostheses, thanks to better charge transfer capabilities and higher electrochemical stability. Great interest and attention is given in this work, in particular, to the investigation of tissue response after several weeks of implants in rodents' brain motor cortex and the associated materials degradation. As part of this work, a new set of devices for Electrocorticography (ECoG) has been designed and fabricated to improve durability and quality of the previous generation of devices, designed and manufactured by the same research group in 2014. In-vivo long-term impedance measurements and brain activity recordings were performed to test the functionality of the neural devices. In-vitro electrical characterization of the carbon electrodes, as well as the study of the adhesion mechanisms between glassy carbon and different substrates is also part of the research described in this book.

Effects of Xylem-Sap Composition on Glassy-Winged Sharpshooter (Hemiptera: Cicadellidae) Egg Maturation on High- and Low-Quality Host Plants.

PubMed

Sisterson, Mark S; Wallis, Christopher M; Stenger, Drake C

2017-04-01

Glassy-winged sharpshooters must feed as adults to produce mature eggs. Cowpea and sunflower are both readily accepted by the glassy-winged sharpshooter for feeding, but egg production on sunflower was reported to be lower than egg production on cowpea. To better understand the role of adult diet in egg production, effects of xylem-sap chemistry on glassy-winged sharpshooter egg maturation was compared for females confined to cowpea and sunflower. Females confined to cowpea consumed more xylem-sap than females held on sunflower. In response, females held on cowpea produced more eggs, had heavier bodies, and greater lipid content than females held on sunflower. Analysis of cowpea and sunflower xylem-sap found that 17 of 19 amino acids were more concentrated in cowpea xylem-sap than in sunflower xylem-sap. Thus, decreased consumption of sunflower xylem-sap was likely owing to perceived lower quality, with decreased egg production owing to a combination of decreased feeding and lower return per unit volume of xylem-sap consumed. Examination of pairwise correlation coefficients among amino acids indicated that concentrations of several amino acids within a plant species were correlated. Principal component analyses identified latent variables describing amino acid composition of xylem-sap. For females held on cowpea, egg maturation was affected by test date, volume of excreta produced, and principal components describing amino acid composition of xylem-sap. Principal component analyses aided in identifying amino acids that were positively or negatively associated with egg production, although determining causality with respect to key nutritional requirements for glassy-winged sharpshooter egg production will require additional testing. Published by Oxford University Press on behalf of Entomological Society of America 2017. This work is written by US Government employees and is in the public domain in the US.

Persistent optical hole-burning spectroscopy of nano-confined dye molecules in liquid at room temperature: Spectral narrowing due to a glassy state and extraordinary relaxation in a nano-cage

NASA Astrophysics Data System (ADS)

Murakami, Hiroshi

2018-04-01

Persistent optical hole-burning spectroscopy has been conducted for a dye molecule within a very small (˜1 nm) reverse micelle at room temperature. The spectra show a spectral narrowing due to site-selective excitation. This definitely demonstrates that the surroundings of the dye molecule are in a glassy state regardless of a solution at room temperature. On the other hand, the hole-burning spectra exhibit large shifts from excitation frequencies, and their positions are almost independent of excitation frequencies. The hole-burning spectra have been theoretically calculated by taking account of a vibronic absorption band of the dye molecule under the assumption that the surroundings of the dye molecule are in a glassy state. The calculated results agree with the experimental ones that were obtained for the dye molecule in a polymer glass for comparison, where it has been found that the ratio of hole-burning efficiencies of vibronic- to electronic-band excitations is quite high. On the other hand, the theoretical results do not explain the large spectral shift from the excitation frequency and small spectral narrowing observed in the hole-burning spectra measured for the dye-containing reverse micelle. It is thought that the spectral shift and broadening occur within the measurement time owing to the relaxation process of the surroundings that are hot with the thermal energy deposited by the dye molecule optically excited. Furthermore, the relaxation should be temporary because the cooling of the inside of the reverse micelle takes place with the dissipation of the excess thermal energy to the outer oil solvent, and so the surroundings of the dye molecule return to the glassy state and do not attain the thermal equilibrium. These results suggest that a very small reverse micelle provides a unique reaction field in which the diffusional motion can be controlled by light in a glassy state.

Étude comparative des techniques d'analyse par fluorescence X à dispersion d'énergie (ED-XRF) et à dispersion de longueur d'onde (WD-XRF), et par spectrométrie d'émission atomique à source plasma couplée par induction (ICP-AES)

NASA Astrophysics Data System (ADS)

Rahmani, A.; Benyaïch, F.; Bounakhla, M.; Bilal, E.; Moutte, J.; Gruffat, J. J.; Zahry, F.

2004-11-01

Dans ce travail, nous présentons une étude comparative des techniques d'analyse par fluorescence X à dispersion d'énergie (ED-XRF) et à dispersion de longueur d'onde (WD-XRF), et par spectrométrie d'émission atomique à source plasma couplée par induction (ICP-AES). Les résultats de la calibration des spectromètres à dispersion d'énergie, à excitation par sources radioactives (55Fe, 109Cd et 241Am) et à excitation secondaire (cible secondaire Mo et Cu) du Centre National pour l'Energie, les Sciences et les Techniques Nucléaires (CNESTEN, Rabat, Maroc) sur des échantillons étalons de références de l'Agence International de l'Energie Atomique (AIEA) et du Community Bureau of Référence (BCR) ont été comparés aux résultats d'analyse des mêmes échantillons étalons par la spectrométrie X à dispersion de longueur d'onde (WD-XRF) et par spectrométrie d'émission atomique à source plasma couplé par induction (ICP-AES) au département GENERIC du centre SPIN à l'Ecole des Mines de Saint-Etienne (France). Les trois techniques d'analyse utilisées donnent des résultats comparables pour le dosage des éléments majeurs, alors que pour les traces on note des déviations importantes à cause des effets de matrice qui sont difficiles à corriger dans le cas de la fluorescence X.

Effets non lineaires transversaux dans les guides d'ondes plans

NASA Astrophysics Data System (ADS)

Dumais, Patrick

Les effets non lineaires transversaux dus a l'effet Kerr optique non resonant sont etudies dans deux types de guides a geometrie plane. D'abord (au chapitre 2), l'emission de solitons spatiaux d'un guide de type canal est etudie historiquement, analytiquement et numeriquement dans le but d'en faire la conception et la fabrication, en AlGaAs, dans la region spectrale en deca de la moitie de la bande interdite de ce materiau, soit autour de 1,5 microns. Le composant, tel que concu, comporte une structure de multipuits quantiques. Le desordonnement local de cette structure permet une variation locale du coefficient Kerr dans le guide, ce qui mene a l'emission d'un soliton spatial au-dela d'une puissance optique de seuil. L'observation experimentale d'un changement en fonction de l'intensite du profil de champ a la sortie du guide realise est presentee. Deuxiemement (au chapitre 3) une technique de mesure du coefficient Kerr dans un guide plan est presentee. Cette technique consiste a mesurer le changement de transmission au travers d'un cache place a la sortie du guide en fonction de l'intensite crete a l'entree du guide plan. Une methode pour determiner les conditions optimales pour la sensibilite de la mesure est presentee, illustree de plusieurs exemples. Finalement, la realisation d'un oscillateur parametrique optique basee sur un cristal de niobate de lithium a domaines periodiquement inverses est presentee. La theorie des oscillateurs parametriques optiques est exposee avec une emphase sur la generation d'impulsions intenses a des longueurs d'onde autour de 1,5 microns a partir d'un laser Ti:saphir, dans le but d'obtenir une source pour faire les experiences sur l'emission solitonique.

Electrochemical and spectroelectrochemical behavior of the TCNQ(0/)(-) couple on a glassy carbon electrode. Layer-by-layer nucleation and growth.

PubMed

Gómez, L; Rodríguez-Amaro, R

2006-08-15

On the basis of the electrochemical results obtained for thin films of 7,7,8,8- tetracyanoquinodimethane (TCNQ) on a glassy carbon electrode, the reduction and oxidation of the [TCNQ](0/)(-) couple in KCl aqueous media occurs via a mechanism involving layer-by-layer nucleation and growth. In situ recorded UV-visible spectroelectrochemical data allow two different crystal structures for the oxidized form of TCNQ to be discriminated.

Tunable PhoXonic Band Gap Materials from Self-Assembly of Block Copolymers and Colloidal Nanocrystals (NBIT Phase II)

DTIC Science & Technology

2013-12-12

their application in sensors and as displays. We found that the thermochromic behavior of a lamellar block copolymer poly(styrene-b-2-vinylpyridine...the solution pH. The findings of this work provide the basis for understanding and controlling the properties of thermochromic block copolymers...by the glassy PS layers . The glassy layers completely constrain the lateral expansion of the P2VP gel block and the dislocation defect network that

Scanning Electron Microscopy and Petrography of Glassy Particles Produced by Lava Fountain Eruptions. Ph.D. Thesis - Final Report

NASA Technical Reports Server (NTRS)

Ladle, G. H.

1978-01-01

A conceptual model of a lava fountain consists of a vent, spatter ramparts, fountain column, downwind plume and associated pumice deposits. Glassy particles produced by lava fountain eruptions consist primarily of sideromelane glass and minor to moderate amounts of vesicles and crystals. Particles are classified on the basis of morphology as: (1) spherical, (2) elongate, (3) glass-coated mineral grain, (4) shard, (5) reticulite, (6) composite particle, and (7) lithic fragment.

Dynamical singularities of glassy systems in a quantum quench.

PubMed

Obuchi, Tomoyuki; Takahashi, Kazutaka

2012-11-01

We present a prototype of behavior of glassy systems driven by quantum dynamics in a quenching protocol by analyzing the random energy model in a transverse field. We calculate several types of dynamical quantum amplitude and find a freezing transition at some critical time. The behavior is understood by the partition-function zeros in the complex temperature plane. We discuss the properties of the freezing phase as a dynamical chaotic phase, which are contrasted to those of the spin-glass phase in the static system.

Ab initio tensile experiment on a model of an intergranular glassy film in β-Si3N4 with prismatic surfaces

NASA Astrophysics Data System (ADS)

Ching, W. Y.; Rulis, Paul; Ouyang, Lizhi; Misra, A.

2009-02-01

We report the results of a large-scale ab initio simulation of an intergranular glassy film (IGF) model in β-Si3N4. It is shown that the stress-strain behavior under uniaxial load in the model with prismatic surfaces and few defective bonds is very different from an earlier IGF model with basal planes. The results are explained by the fundamental electronic structure of the model.

Significantly enhanced memory effect in metallic glass by multistep training

NASA Astrophysics Data System (ADS)

Li, M. X.; Luo, P.; Sun, Y. T.; Wen, P.; Bai, H. Y.; Liu, Y. H.; Wang, W. H.

2017-11-01

The state of metastable equilibrium glass can carry an imprint of the past and exhibit memory effect. As a hallmark of glassy dynamics, memory effect can affect glassy behavior as it evolves further upon time. Even though the physical picture of the memory effect has been well studied, it is unclear whether a glass can recall as many pieces of information as possible, and if so, how the glass will accordingly behave. We report that by fractionizing temperature interval, inserting multistep aging protocols, and optimizing the time of each temperature step, i.e., by imposing a multistep "training" on a prototypical P d40N i10C u30P20 metallic glass, the memory of the trained glass can be significantly strengthened, marked by a pronounced augment in potential energy. These findings provide a new guide for regulating the energy state of glass by enhancing the nonequilibrium behaviors of the memory effect and offer an opportunity to develop a clearer physical picture of glassy dynamics.

Composition-dependent metallic glass alloys correlate atomic mobility with collective glass surface dynamics.

PubMed

Nguyen, Duc; Zhu, Zhi-Guang; Pringle, Brian; Lyding, Joseph; Wang, Wei-Hua; Gruebele, Martin

2016-06-22

Glassy metallic alloys are richly tunable model systems for surface glassy dynamics. Here we study the correlation between atomic mobility, and the hopping rate of surface regions (clusters) that rearrange collectively on a minute to hour time scale. Increasing the proportion of low-mobility copper atoms in La-Ni-Al-Cu alloys reduces the cluster hopping rate, thus establishing a microscopic connection between atomic mobility and dynamics of collective rearrangements at a glass surface made from freshly exposed bulk glass. One composition, La60Ni15Al15Cu10, has a surface resistant to re-crystallization after three heating cycles. When thermally cycled, surface clusters grow in size from about 5 glass-forming units to about 8 glass-forming units, evidence of surface aging without crystal formation, although its bulk clearly forms larger crystalline domains. Such kinetically stable glass surfaces may be of use in applications where glassy coatings stable against heating are needed.

Temperature-dependent microindentation data of an epoxy composition in the glassy region

NASA Astrophysics Data System (ADS)

Minster, Jiří; Králík, Vlastimil

2015-02-01

The short-term instrumented microindentation technique was applied for assessing the influence of temperature in the glassy region on the time-dependent mechanical properties of an average epoxy resin mix near to its native state. Linear viscoelasticity theory with the assumption of time-independent Poisson ratio value forms the basis for processing the experimental results. The sharp standard Berkovich indenter was used to measure the local mechanical properties at temperatures 20, 24, 28, and 35 °C. The short-term viscoelastic compliance histories were defined by the Kohlrausch-Williams-Watts double exponential function. The findings suggest that depth-sensing indentation data of thermorheologically simple materials influenced by different temperatures in the glassy region can also be used, through the time-temperature superposition, to extract viscoelastic response functions accurately. This statement is supported by the comparison of the viscoelastic compliance master curve of the tested material with data derived from standard macro creep measurements under pressure on the material in a conformable state.

Glassy aging with modified Kohlrausch-Williams-Watts form

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

Sen Gupta, Bhaskar; Das, Shankar P.

2007-12-15

In this paper, we address the question of whether aging in the nonequilibrium glassy state is controlled by the equilibrium {alpha}-relaxation process, which occurs at temperatures above T{sub g}. Recently, Lunkenheimer et al. [Phys. Rev. Lett. 95, 055702 (2005)] proposed a model for the glassy aging data of dielectric relaxation using a modified Kohlrausch-Williams-Watts form exp[-(t{sub age}/{tau}{sub age}){sup {beta}{sub age}}]. The aging time t{sub age} dependence of the relaxation time {tau}{sub age} is defined by these authors through a functional relation involving the corresponding frequency {nu}(t{sub age})=1/(2{pi}{tau}{sub age}), but the stretching exponent {beta}{sub age} is the same as {beta}{sub {alpha}},more » the {alpha}-relaxation stretching exponent. We present here an alternative functional form for {tau}{sub age}(t{sub age}) directly involving the relaxation time itself. The proposed model fits the data of Lunkenheimer et al. perfectly with a stretching exponent {beta}{sub age} different from {beta}{sub {alpha}}.« less

Prediction of Process-Induced Distortions in L-Shaped Composite Profiles Using Path-Dependent Constitutive Law

NASA Astrophysics Data System (ADS)

Ding, Anxin; Li, Shuxin; Wang, Jihui; Ni, Aiqing; Sun, Liangliang; Chang, Lei

2016-10-01

In this paper, the corner spring-in angles of AS4/8552 L-shaped composite profiles with different thicknesses are predicted using path-dependent constitutive law with the consideration of material properties variation due to phase change during curing. The prediction accuracy mainly depends on the properties in the rubbery and glassy states obtained by homogenization method rather than experimental measurements. Both analytical and finite element (FE) homogenization methods are applied to predict the overall properties of AS4/8552 composite. The effect of fiber volume fraction on the properties is investigated for both rubbery and glassy states using both methods. And the predicted results are compared with experimental measurements for the glassy state. Good agreement is achieved between the predicted results and available experimental data, showing the reliability of the homogenization method. Furthermore, the corner spring-in angles of L-shaped composite profiles are measured experimentally and the reliability of path-dependent constitutive law is validated as well as the properties prediction by FE homogenization method.

Molecular glasses of azobenzene for holographic data storage applications

NASA Astrophysics Data System (ADS)

Zarins, Elmars; Balodis, Karlis; Ruduss, Armands; Kokars, Valdis; Ozols, Andris; Augustovs, Peteris; Saharovs, Dmitrijs

2018-05-01

A series of D-N=N-A type molecular glasses where the electron acceptor part (A) contains several electron withdrawing substituents, but the electron donating part (D) of the glassy azochromophores contains amorphous phase promoting non-conjugated bulky triphenyl or hydroxyl groups have been synthesized and investigated. Results showed that the azodye physical properties depend not only on the incorporated electron withdrawing substituents but are also influenced by the bonding type of covalently attached bulky moieties. Synthesized glassy azocompounds showed glass transition temperatures up to 106 °C and thermal stability up to 312 °C. The ability to form holographic gratings in spin-cast thin films of the glassy azodyes was investigated using 532 nm and 633 nm lasers obtaining diffraction efficiency up to 57%, self-diffraction efficiency up to 15% and photosensitivity as high as 3.7 J/(cm2%). Surface relief grating (SRG) depths reached 1.1 μm and in some cases even exceeded the thickness of the films.

A 3D Microfluidic Chip for Electrochemical Detection of Hydrolysed Nucleic Bases by a Modified Glassy Carbon Electrode

PubMed Central

Vlachova, Jana; Tmejova, Katerina; Kopel, Pavel; Korabik, Maria; Zitka, Jan; Hynek, David; Kynicky, Jindrich; Adam, Vojtech; Kizek, Rene

2015-01-01

Modification of carbon materials, especially graphene-based materials, has wide applications in electrochemical detection such as electrochemical lab-on-chip devices. A glassy carbon electrode (GCE) modified with chemically alternated graphene oxide was used as a working electrode (glassy carbon modified by graphene oxide with sulphur containing compounds and Nafion) for detection of nucleobases in hydrolysed samples (HCl pH = 2.9, 100 °C, 1 h, neutralization by NaOH). It was found out that modification, especially with trithiocyanuric acid, increased the sensitivity of detection in comparison with pure GCE. All processes were finally implemented in a microfluidic chip formed with a 3D printer by fused deposition modelling technology. As a material for chip fabrication, acrylonitrile butadiene styrene was chosen because of its mechanical and chemical stability. The chip contained the one chamber for the hydrolysis of the nucleic acid and another for the electrochemical detection by the modified GCE. This chamber was fabricated to allow for replacement of the GCE. PMID:25621613

Characterization and calibration of a viscoelastic simplified potential energy clock model for inorganic glasses

DOE PAGES

Chambers, Robert S.; Tandon, Rajan; Stavig, Mark E.

2015-07-07

In this study, to analyze the stresses and strains generated during the solidification of glass-forming materials, stress and volume relaxation must be predicted accurately. Although the modeling attributes required to depict physical aging in organic glassy thermosets strongly resemble the structural relaxation in inorganic glasses, the historical modeling approaches have been distinctly different. To determine whether a common constitutive framework can be applied to both classes of materials, the nonlinear viscoelastic simplified potential energy clock (SPEC) model, developed originally for glassy thermosets, was calibrated for the Schott 8061 inorganic glass and used to analyze a number of tests. A practicalmore » methodology for material characterization and model calibration is discussed, and the structural relaxation mechanism is interpreted in the context of SPEC model constitutive equations. SPEC predictions compared to inorganic glass data collected from thermal strain measurements and creep tests demonstrate the ability to achieve engineering accuracy and make the SPEC model feasible for engineering applications involving a much broader class of glassy materials.« less

A neutron-X-ray, NMR and calorimetric study of glassy Probucol synthesized using containerless techniques

NASA Astrophysics Data System (ADS)

Weber, J. K. R.; Benmore, C. J.; Tailor, A. N.; Tumber, S. K.; Neuefeind, J.; Cherry, B.; Yarger, J. L.; Mou, Q.; Weber, W.; Byrn, S. R.

2013-10-01

Acoustic levitation was used to trap 1-3 mm diameter drops of Probucol and other pharmaceutical materials in containerless conditions. Samples were studied in situ using X-ray diffraction and ex situ using neutron diffraction, NMR and DSC techniques. The materials were brought into non-equilibrium states by supersaturating solutions or by supercooling melts. The glass transition and crystallization temperatures of glassy Probucol were 29 ± 1 and 71 ± 1 °C respectively. The glassy form was stable with a shelf life of at least 8 months. A neutron/X-ray difference function of the glass showed that while molecular sub-groups remain rigid, many of the hydrogen correlations observed in the crystal become smeared out in the disordered material. The glass is principally comprised of slightly distorted Form I Probucol molecules with disordered packing rather than large changes in the individual molecular structure. Avoiding surface contact-induced nucleation provided access to highly non-equilibrium phases and enabled synthesis of phase-pure glasses.

Cooperativity in glassy dynamics investigated by higher-harmonic dielectric spectroscopy

NASA Astrophysics Data System (ADS)

Bauer, Thomas; Lunkenheimer, Peter; Loidl, Alois; Experimental Physics V Team

2014-03-01

In recent years, due to experimental advances initiated by hole burning experiments, nonlinear dielectric spectroscopy has gained increasing interest in the field of glass-forming matter. For example, refining the technique of high-field permittivity measurements, we found a surprising lack of nonlinearity in the so-called excess wing region, that could not be accessed by this method before. In the present contribution, we report new, detailed measurements of the third-order nonlinear dielectric susceptibility χ3 of four glass-forming liquids for a broad temperature range. We find a significant hump in χ3(ν) , from which we deduce the number of correlated molecules Ncorr. We detect a continuous increase of Ncorr on approaching the glass-transition temperature. Comparing these results with the temperature-dependent apparent energy barriers in these systems, our experiments finally prove the old notion that intermolecular correlations of glassy systems are responsible for the non-canonical temperature development of glassy dynamics. This work was supported by the Deutsche Forschungsgemeinschaft via Research Unit FOR1394.

The glassy random laser: replica symmetry breaking in the intensity fluctuations of emission spectra

PubMed Central

Antenucci, Fabrizio; Crisanti, Andrea; Leuzzi, Luca

2015-01-01

The behavior of a newly introduced overlap parameter, measuring the correlation between intensity fluctuations of waves in random media, is analyzed in different physical regimes, with varying amount of disorder and non-linearity. This order parameter allows to identify the laser transition in random media and describes its possible glassy nature in terms of emission spectra data, the only data so far accessible in random laser measurements. The theoretical analysis is performed in terms of the complex spherical spin-glass model, a statistical mechanical model describing the onset and the behavior of random lasers in open cavities. Replica Symmetry Breaking theory allows to discern different kinds of randomness in the high pumping regime, including the most complex and intriguing glassy randomness. The outcome of the theoretical study is, eventually, compared to recent intensity fluctuation overlap measurements demonstrating the validity of the theory and providing a straightforward interpretation of qualitatively different spectral behaviors in different random lasers. PMID:26616194

A thermo-chemo-mechanically coupled constitutive model for curing of glassy polymers

NASA Astrophysics Data System (ADS)

Sain, Trisha; Loeffel, Kaspar; Chester, Shawn

2018-07-01

Curing of a polymer is the process through which a polymer liquid transitions into a solid polymer, capable of bearing mechanical loads. The curing process is a coupled thermo-chemo-mechanical conversion process which requires a thorough understanding of the system behavior to predict the cure dependent mechanical behavior of the solid polymer. In this paper, a thermodynamically consistent, frame indifferent, thermo-chemo-mechanically coupled continuum level constitutive framework is proposed for thermally cured glassy polymers. The constitutive framework considers the thermodynamics of chemical reactions, as well as the material behavior for a glassy polymer. A stress-free intermediate configuration is introduced within a finite deformation setting to capture the formation of the network in a stress-free configuration. This work considers a definition for the degree of cure based on the chemistry of the curing reactions. A simplified version of the proposed model has been numerically implemented, and simulations are used to understand the capabilities of the model and framework.

A 3D microfluidic chip for electrochemical detection of hydrolysed nucleic bases by a modified glassy carbon electrode.

PubMed

Vlachova, Jana; Tmejova, Katerina; Kopel, Pavel; Korabik, Maria; Zitka, Jan; Hynek, David; Kynicky, Jindrich; Adam, Vojtech; Kizek, Rene

2015-01-22

Modification of carbon materials, especially graphene-based materials, has wide applications in electrochemical detection such as electrochemical lab-on-chip devices. A glassy carbon electrode (GCE) modified with chemically alternated graphene oxide was used as a working electrode (glassy carbon modified by graphene oxide with sulphur containing compounds and Nafion) for detection of nucleobases in hydrolysed samples (HCl pH = 2.9, 100 °C, 1 h, neutralization by NaOH). It was found out that modification, especially with trithiocyanuric acid, increased the sensitivity of detection in comparison with pure GCE. All processes were finally implemented in a microfluidic chip formed with a 3D printer by fused deposition modelling technology. As a material for chip fabrication, acrylonitrile butadiene styrene was chosen because of its mechanical and chemical stability. The chip contained the one chamber for the hydrolysis of the nucleic acid and another for the electrochemical detection by the modified GCE. This chamber was fabricated to allow for replacement of the GCE.

Biogas desulfurization and biogas upgrading using a hybrid membrane system--modeling study.

PubMed

Makaruk, A; Miltner, M; Harasek, M

2013-01-01

Membrane gas permeation using glassy membranes proved to be a suitable method for biogas upgrading and natural gas substitute production on account of low energy consumption and high compactness. Glassy membranes are very effective in the separation of bulk carbon dioxide and water from a methane-containing stream. However, the content of hydrogen sulfide can be lowered only partially. This work employs process modeling based upon the finite difference method to evaluate a hybrid membrane system built of a combination of rubbery and glassy membranes. The former are responsible for the separation of hydrogen sulfide and the latter separate carbon dioxide to produce standard-conform natural gas substitute. The evaluation focuses on the most critical upgrading parameters like achievable gas purity, methane recovery and specific energy consumption. The obtained results indicate that the evaluated hybrid membrane configuration is a potentially efficient system for the biogas processing tasks that do not require high methane recoveries, and allows effective desulfurization for medium and high hydrogen sulfide concentrations without additional process steps.

Diazonium Chemistry for the Bio-Functionalization of Glassy Nanostring Resonator Arrays

PubMed Central

Zheng, Wei; Du, Rongbing; Cao, Yong; Mohammad, Mohammad A.; Dew, Steven K.; McDermott, Mark T.; Evoy, Stephane

2015-01-01

Resonant glassy nanostrings have been employed for the detection of biomolecules. These devices offer high sensitivity and amenability to large array integration and multiplexed assays. Such a concept has however been impaired by the lack of stable and biocompatible linker chemistries. Diazonium salt reduction-induced aryl grafting is an aqueous-based process providing strong chemical adhesion. In this work, diazonium-based linker chemistry was performed for the first time on glassy nanostrings, which enabled the bio-functionalization of such devices. Large arrays of nanostrings with ultra-narrow widths down to 10 nm were fabricated employing electron beam lithography. Diazonium modification was first developed on SiCN surfaces and validated by X-ray photoelectron spectroscopy. Similarly modified nanostrings were then covalently functionalized with anti-rabbit IgG as a molecular probe. Specific enumeration of rabbit IgG was successfully performed through observation of downshifts of resonant frequencies. The specificity of this enumeration was confirmed through proper negative control experiments. Helium ion microscopy further verified the successful functionalization of nanostrings. PMID:26263989

Diazonium Chemistry for the Bio-Functionalization of Glassy Nanostring Resonator Arrays.

PubMed

Zheng, Wei; Du, Rongbing; Cao, Yong; Mohammad, Mohammad A; Dew, Steven K; McDermott, Mark T; Evoy, Stephane

2015-07-30

Resonant glassy nanostrings have been employed for the detection of biomolecules. These devices offer high sensitivity and amenability to large array integration and multiplexed assays. Such a concept has however been impaired by the lack of stable and biocompatible linker chemistries. Diazonium salt reduction-induced aryl grafting is an aqueous-based process providing strong chemical adhesion. In this work, diazonium-based linker chemistry was performed for the first time on glassy nanostrings, which enabled the bio-functionalization of such devices. Large arrays of nanostrings with ultra-narrow widths down to 10 nm were fabricated employing electron beam lithography. Diazonium modification was first developed on SiCN surfaces and validated by X-ray photoelectron spectroscopy. Similarly modified nanostrings were then covalently functionalized with anti-rabbit IgG as a molecular probe. Specific enumeration of rabbit IgG was successfully performed through observation of downshifts of resonant frequencies. The specificity of this enumeration was confirmed through proper negative control experiments. Helium ion microscopy further verified the successful functionalization of nanostrings.

Relationship between local structure and relaxation in out-of-equilibrium glassy systems

DOE PAGES

Schoenholz, Samuel S.; Cubuk, Ekin D.; Kaxiras, Efthimios; ...

2016-12-27

The dynamical glass transition is typically taken to be the temperature at which a glassy liquid is no longer able to equilibrate on experimental timescales. Consequently, the physical properties of these systems just above or below the dynamical glass transition, such as viscosity, can change by many orders of magnitude over long periods of time following external perturbation. During this progress toward equilibrium, glassy systems exhibit a history dependence that has complicated their study. In previous work, we bridged the gap between structure and dynamics in glassy liquids above their dynamical glass transition temperatures by introducing a scalar field calledmore » “softness,” a quantity obtained using machine-learning methods. Softness is designed to capture the hidden patterns in relative particle positions that correlate strongly with dynamical rearrangements of particle positions. Here we show that the out-of-equilibrium behavior of a model glass-forming system can be understood in terms of softness. We first demonstrate that the evolution of behavior following a temperature quench is a primarily structural phenomenon: The structure changes considerably, but the relationship between structure and dynamics remains invariant. We then show that the relaxation time can be robustly computed from structure as quantified by softness, with the same relation holding both in equilibrium and as the system ages. Together, these results show that the history dependence of the relaxation time in glasses requires knowledge only of the softness in addition to the usual state variables.« less

Shear-transformation-zone theory of linear glassy dynamics.

PubMed

Bouchbinder, Eran; Langer, J S

2011-06-01

We present a linearized shear-transformation-zone (STZ) theory of glassy dynamics in which the internal STZ transition rates are characterized by a broad distribution of activation barriers. For slowly aging or fully aged systems, the main features of the barrier-height distribution are determined by the effective temperature and other near-equilibrium properties of the configurational degrees of freedom. Our theory accounts for the wide range of relaxation rates observed in both metallic glasses and soft glassy materials such as colloidal suspensions. We find that the frequency-dependent loss modulus is not just a superposition of Maxwell modes. Rather, it exhibits an α peak that rises near the viscous relaxation rate and, for nearly jammed, glassy systems, extends to much higher frequencies in accord with experimental observations. We also use this theory to compute strain recovery following a period of large, persistent deformation and then abrupt unloading. We find that strain recovery is determined in part by the initial barrier-height distribution, but that true structural aging also occurs during this process and determines the system's response to subsequent perturbations. In particular, we find by comparison with experimental data that the initial deformation produces a highly disordered state with a large population of low activation barriers, and that this state relaxes quickly toward one in which the distribution is dominated by the high barriers predicted by the near-equilibrium analysis. The nonequilibrium dynamics of the barrier-height distribution is the most important of the issues raised and left unresolved in this paper.

Generation of fine hydromagmatic ash by growth and disintegration of glassy rinds

USGS Publications Warehouse

Mastin, L.G.

2007-01-01

The deposits of mafic hydromagmatic eruptions are more fine grained and variable in vesicularity than dry magmatic deposits. Blocky, equant shapes of many hydromagmatic clasts also contrast with droplet, thread, and bubble wall morphology of dry magmatic fragments. Small (

Development and Validation of Chronopotentiometric Method for Imidacloprid Determination in Pesticide Formulations and River Water Samples

PubMed Central

Đurović, Ana; Stojanović, Zorica; Kravić, Snežana; Grahovac, Nada; Bursić, Vojislava; Vuković, Gorica; Suturović, Zvonimir

2016-01-01

A new electrochemical method for determination of imidacloprid using chronopotentiometry on thin film mercury and glassy carbon electrode was presented. The most important experimental parameters of chronopotentiometry were examined and optimized with respect to imidacloprid analytical signal. Imidacloprid provided well-defined reduction peak in Britton-Robinson buffer on thin film mercury electrode at −1.0 V (versus Ag/AgCl (KCl, 3.5 mol/L)) and on glassy carbon electrode at −1.2 V (versus Ag/AgCl (KCl, 3.5 mol/L)). The reduction time was linearly proportional to concentrations from 0.8 to 30.0 mg/L on thin film mercury electrode and from 7.0 to 70.0 mg/L on glassy carbon electrode. The detection limits were 0.17 mg/L and 0.93 mg/L for thin film mercury and glassy carbon electrode, respectively. The estimation of method precision as a function of repeatability and reproducibility showed relative standard deviations values lower than 3.73%. Recovery values from 97.3 to 98.1% confirmed the accuracy of the proposed method, while the constancy of the transition time with deliberated small changes in the experimental parameters indicated a very good robustness. A minor influence of possible interfering compounds proved good selectivity of the method. Developed method was applied for imidacloprid determination in commercial pesticide formulations and river water samples. PMID:27042181

Relationship between local structure and relaxation in out-of-equilibrium glassy systems.

PubMed

Schoenholz, Samuel S; Cubuk, Ekin D; Kaxiras, Efthimios; Liu, Andrea J

2017-01-10

The dynamical glass transition is typically taken to be the temperature at which a glassy liquid is no longer able to equilibrate on experimental timescales. Consequently, the physical properties of these systems just above or below the dynamical glass transition, such as viscosity, can change by many orders of magnitude over long periods of time following external perturbation. During this progress toward equilibrium, glassy systems exhibit a history dependence that has complicated their study. In previous work, we bridged the gap between structure and dynamics in glassy liquids above their dynamical glass transition temperatures by introducing a scalar field called "softness," a quantity obtained using machine-learning methods. Softness is designed to capture the hidden patterns in relative particle positions that correlate strongly with dynamical rearrangements of particle positions. Here we show that the out-of-equilibrium behavior of a model glass-forming system can be understood in terms of softness. To do this we first demonstrate that the evolution of behavior following a temperature quench is a primarily structural phenomenon: The structure changes considerably, but the relationship between structure and dynamics remains invariant. We then show that the relaxation time can be robustly computed from structure as quantified by softness, with the same relation holding both in equilibrium and as the system ages. Together, these results show that the history dependence of the relaxation time in glasses requires knowledge only of the softness in addition to the usual state variables.

An Analysis of the Max-Min Texture Measure.

DTIC Science & Technology

1982-01-01

PANC 33 D2 Confusion Matrices for Scene A, IR 34 D3 Confusion Matrices for Scene B, PANC 35 D4 Confusion Matrices for Scene B, IR 36 D5 Confusion...Matrices for Scene C, PANC 37 D6 Confusion Matrices for Scene C, IR 38 D7 Confusion Matrices for Scene E, PANC 39 D8 Confusion Matrices for Scene E, IR 40...D9 Confusion Matrices for Scene H, PANC 41 DIO Confusion Matrices for Scene H, JR 42 3 .D 10CnuinMtie o cn ,IR4 AN ANALYSIS OF THE MAX-MIN TEXTURE

Periodic GMP Matrices

NASA Astrophysics Data System (ADS)

Eichinger, Benjamin

2016-07-01

We recall criteria on the spectrum of Jacobi matrices such that the corresponding isospectral torus consists of periodic operators. Motivated by those known results for Jacobi matrices, we define a new class of operators called GMP matrices. They form a certain Generalization of matrices related to the strong Moment Problem. This class allows us to give a parametrization of almost periodic finite gap Jacobi matrices by periodic GMP matrices. Moreover, due to their structural similarity we can carry over numerous results from the direct and inverse spectral theory of periodic Jacobi matrices to the class of periodic GMP matrices. In particular, we prove an analogue of the remarkable ''magic formula'' for this new class.

A Thermodynamic Theory Of Solid Viscoelasticity. Part 1: Linear Viscoelasticity.

NASA Technical Reports Server (NTRS)

Freed, Alan D.; Leonov, Arkady I.

2002-01-01

The present series of three consecutive papers develops a general theory for linear and finite solid viscoelasticity. Because the most important object for nonlinear studies are rubber-like materials, the general approach is specified in a form convenient for solving problems important for many industries that involve rubber-like materials. General linear and nonlinear theories for non-isothermal deformations of viscoelastic solids are developed based on the quasi-linear approach of non-equilibrium thermodynamics. In this, the first paper of the series, we analyze non-isothermal linear viscoelasticity, which is applicable in a range of small strains not only to all synthetic polymers and bio-polymers but also to some non-polymeric materials. Although the linear case seems to be well developed, there still are some reasons to implement a thermodynamic derivation of constitutive equations for solid-like, non-isothermal, linear viscoelasticity. The most important is the thermodynamic modeling of thermo-rheological complexity , i.e. different temperature dependences of relaxation parameters in various parts of relaxation spectrum. A special structure of interaction matrices is established for different physical mechanisms contributed to the normal relaxation modes. This structure seems to be in accord with observations, and creates a simple mathematical framework for both continuum and molecular theories of the thermo-rheological complex relaxation phenomena. Finally, a unified approach is briefly discussed that, in principle, allows combining both the long time (discrete) and short time (continuous) descriptions of relaxation behaviors for polymers in the rubbery and glassy regions.

Fundamental considerations in the effect of molecular weight on the glass transition of the gelatin/cosolute system.

PubMed

Jiang, Bin; Kasapis, Stefan; Kontogiorgos, Vassilis

2012-05-01

Four molecular fractions of gelatin produced by alkaline hydrolysis of collagen were investigated in the presence of cosolute to record the mechanical properties of the glass transition in high-solid preparations. Dynamic oscillatory and stress relaxation moduli in shear were recorded from 40°C to temperatures as low as -60°C. The small-deformation behavior of these linear polymers was separated by the method of reduced variables into a basic function of time alone and a basic function of temperature alone. The former allowed the reduction of isothermal runs into a master curve covering 17 orders of magnitude in the time domain. The latter follows the passage from the rubbery plateau through the glass transition region to the glassy state seen in the variation of shift factor, a(T) , as a function of temperature. The mechanical glass transition temperature (T(g) ) is pinpointed at the operational threshold of the free volume theory and the predictions of the reaction rate theory. Additional insights into molecular dynamics are obtained via the coupling model of cooperativity, which introduces the concept of coupling constant or interaction strength of local segmental motions that govern structural relaxation at the vicinity of T(g) . The molecular weight of the four gelatin fractions appears to have a profound effect on the transition temperature or coupling constant of vitrified matrices, as does the protein chemistry in relation to that of amorphous synthetic polymers or gelling polysaccharides. © 2011 Wiley Periodicals, Inc.

Photostabilization studies of antihypertensive 1,4-dihydropyridines using polymeric containers.

PubMed

De Luca, Michele; Ioele, Giuseppina; Spatari, Claudia; Ragno, Gaetano

2016-05-30

1,4-dihydropyridine antihypertensives (DHPs) are almost all dispensed in solid pharmaceutical formulations for their easy lability when exposed to light. This paper reports a study on the photoprotective effect of containers in different glassy or polymeric matrices with regard to four known DHPs when in solutions. The samples were subjected to forced degradation by means of a Xenon lamp, in accordance with the international rules on drug stability evaluation. The simultaneous determination of the drugs and their photoproducts was carried out by applying the multivariate curve resolution (MCR) methodology to the spectral data recorded along the irradiation test. This technique was able to determine the kinetic parameters and resolve the spectra of the photoproducts. The time required to reduce by 10% the concentration of the drug (t0.1) was adopted as a criterion to compare the protective ability of the containers. A significant photoprotection for all drugs tested was obtained by the use of polyethylene terephthalate (PET) containers. The best result was achieved for the felodipine solution in blue PET transparent bottle of 0.6mm thickness, reaching an almost complete stabilization up to six hours under stressing irradiation. In contrast, the glass containers, whether or not coloured, did not provide a satisfactory photoprotection of the drugs, showing in any case t0.1 values under 24min. These results can be a good opportunity to design new photoprotective pharmaceutical packaging for DHPs in liquid dosage form. Copyright © 2016 Elsevier B.V. All rights reserved.

Molecularly imprinted electrochemical biosensor based on Fe@Au nanoparticles involved in 2-aminoethanethiol functionalized multi-walled carbon nanotubes for sensitive determination of cefexime in human plasma.

PubMed

Yola, Mehmet Lütfi; Eren, Tanju; Atar, Necip

2014-10-15

The molecular imprinting technique depends on the molecular recognition. It is a polymerization method around the target molecule. Hence, this technique creates specific cavities in the cross-linked polymeric matrices. In present study, a sensitive imprinted electrochemical biosensor based on Fe@Au nanoparticles (Fe@AuNPs) involved in 2-aminoethanethiol (2-AET) functionalized multi-walled carbon nanotubes (f-MWCNs) modified glassy carbon (GC) electrode was developed for determination of cefexime (CEF). The results of X-ray photoelectron spectroscopy (XPS) and reflection-absorption infrared spectroscopy (RAIRS) confirmed the formation of the developed surfaces. CEF imprinted film was constructed by cyclic voltammetry (CV) for 9 cycles in the presence of 80 mM pyrrole in phosphate buffer solution (pH 6.0) containing 20mM CEF. The developed electrochemical biosensor was validated according to the International Conference on Harmonisation (ICH) guideline and found to be linear, sensitive, selective, precise and accurate. The linearity range and the detection limit were obtained as 1.0 × 10(-10)-1.0 × 10(-8)M and 2.2 × 10(-11)M, respectively. The developed CEF imprinted sensor was successfully applied to real samples such as human plasma. In addition, the stability and reproducibility of the prepared molecular imprinted electrode were investigated. The excellent long-term stability and reproducibility of the prepared CEF imprinted electrodes make them attractive in electrochemical sensors. Copyright © 2014 Elsevier B.V. All rights reserved.

Processing and Properties of Fire Resistant EPDM Rubber-Based Ceramifiable Composites

NASA Astrophysics Data System (ADS)

Anyszka, Rafał; Bieliński, Dariusz M.; Pędzich, Zbigniew; Zarzecka-Napierała, Magdalena; Imiela, Mateusz; Rybiński, Przemysław

2017-10-01

Low softening point temperature glassy frit, reinforcing silica, wollastonite and dicumyl peroxide were incorporated into ethylene-propylene-diene (EPDM) rubber matrix in different amounts in order to obtain ceramifiable composites. Kinetics of vulcanization of the mixes was measured. Mechanical properties, micromorphology, thermal properties and combustibility of the vulcanizates were studied as well as compression strength of the ceramic residue obtained after heat treatment. Studies show that optimal amount of glassy frit from the point of view of ceramification effectiveness in dispersed mineral phase is 40 % wt.

Study of the overall behavior of thin films of the 7,7,8,8-tetracyanoquinodimethane neutral/anion couple on glassy carbon electrodes in the presence of cesium ion.

PubMed

Gómez, L; Rodríguez-Amaro, R

2008-10-07

The overall electrochemistry of 7,7,8,8-tetracyanoquinodimethane thin films on glassy carbon electrodes in media containing Cs+ ions is explained in light of a layer-by-layer nucleation and growth model, and kinetic data for the processes involved are reported. Using in situ UV-vis spectroelectrochemistry allowed available mechanistic knowledge on such processes to be expanded and the presence of various intermediates in the redox reactions confirmed.

Positronics of radiation-induced effects in chalcogenide glassy semiconductors

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

Shpotyuk, O.; Kozyukhin, S. A., E-mail: sergkoz@igic.ras.ru; Shpotyuk, M.

2015-03-15

Using As{sub 2}S{sub 3} and AsS{sub 2} glasses as an example, the principal possibility of using positron annihilation spectroscopy methods for studying the evolution of the free volume of hollow nanoobjects in chalcogenide glassy semiconductors exposed to radiation is shown. The results obtained by measurements of the positron annihilation lifetime and Doppler broadening of the annihilation line in reverse chronological order are in full agreement with the optical spectroscopy data in the region of the fundamental absorption edge, being adequately described within coordination defect-formation and physical-aging models.

Process for microwave sintering boron carbide

DOEpatents

Holcombe, C.E.; Morrow, M.S.

1993-10-12

A method of microwave sintering boron carbide comprises leaching boron carbide powder with an aqueous solution of nitric acid to form a leached boron carbide powder. The leached boron carbide powder is coated with a glassy carbon precursor to form a coated boron carbide powder. The coated boron carbide powder is consolidated in an enclosure of boron nitride particles coated with a layer of glassy carbon within a container for microwave heating to form an enclosed coated boron carbide powder. The enclosed coated boron carbide powder is sintered within the container for microwave heating with microwave energy.

Process for microwave sintering boron carbide

DOEpatents

Holcombe, Cressie E.; Morrow, Marvin S.

1993-01-01

A method of microwave sintering boron carbide comprises leaching boron carbide powder with an aqueous solution of nitric acid to form a leached boron carbide powder. The leached boron carbide powder is coated with a glassy carbon precursor to form a coated boron carbide powder. The coated boron carbide powder is consolidated in an enclosure of boron nitride particles coated with a layer of glassy carbon within a container for microwave heating to form an enclosed coated boron carbide powder. The enclosed coated boron carbide powder is sintered within the container for microwave heating with microwave energy.

Electronic Transport Behaviors due to Charge Density Waves in Ni-Nb-Zr-H Glassy Alloys

NASA Astrophysics Data System (ADS)

Fukuhara, Mikio; Umemori, Yoshimasa

2013-11-01

The amorphous Ni-Nb-Zr-H glassy alloy containing subnanometer-sized icosahedral Zr5 Nb5Ni3 clusters exhibited four types of electronic phenomena: a metal/insulator transition, an electric current-induced voltage oscillation (Coulomb oscillation), giant capacitor behavior and an electron avalanche with superior resistivity. These findings could be excluded by charge density waves that the low-dimensional component of clusters, in which the atoms are lined up in chains along the [130] direction, plays important roles in various electron transport phenomena.

Effetive methods in educating extension agents and farmers on conservation farming technology

USDA-ARS?s Scientific Manuscript database

Adoption of new technologies requires transfer of information from developers to end users. Efficiency of the transfer process influences the rate of adoption and ultimate impact of the technology. Various channels are used to transfer technology from researchers to farmers. Two commonly used ones ...

Future of Software Engineering Standards

NASA Technical Reports Server (NTRS)

Poon, Peter T.

1997-01-01

In the new millennium, software engineering standards are expected to continue to influence the process of producing software-intensive systems which are cost-effetive and of high quality. These sytems may range from ground and flight systems used for planetary exploration to educational support systems used in schools as well as consumer-oriented systems.

Effet Bauschinger lors de la plasticité cyclique de l'aluminium pur monocristallin

NASA Astrophysics Data System (ADS)

Alhamany, A.; Chicois, J.; Fougères, R.; Hamel, A.

1992-08-01

This paper is concerned with the study of microscopic mechanisms which control the cyclic deformation of pure aluminium and especially with the analysis of the Bauschinger effect which appears in aluminium single crystals deformed by cyclic straining. Fatigue tests are performed on Al single crystals with the crystal axis parallel to [ overline{1}23] at room temperature, at plastic shear strain amplitudes in the range from 10^{-4} to 3× 10^{-3}. Mechanical saturation is not obtained at any strain level. Instead, a hardening-softening-secondary hardening sequence is found. The magnitude of the Bauschinger effect as the difference between yield stresses in traction and in compression, changes all along the fatigue loop and during the fatigue test. The Bauschinger effect disappears at two points of the fatigue loop, one in the traction part, the other in the compression one. At these points, the Bauschinger effect is inverted. Dislocation arrangement evolutions with fatigue conditions can explain the cyclic behaviour of Al single crystals. An heterogeneous dislocation distribution can be observed in the cyclically strained metal : dislocation tangles, long dislocation walls and dislocation cell walls, separated by dislocation poor channels appear in the material as a function of the cycle number. The long range internal stress necessary to ensure the compatibility of deformation between the hard and soft regions controls the observed Bauschinger effect. Ce travail s'inscrit dans le cadre de l'étude des mécanismes microsocopiques intervenant lors de la déformation cyclique de l'aluminium pur et concerne en particulier l'analyse de l'effet Bauschinger apparaissant au cours de la solliciation cyclique des monocristaux. L'étude a été menée à température ambiante sur des monocristaux d'aluminium pur orientés pour un glissement simple (axe [ overline{1}23] ), à des amplitudes de déformation plastique comprise entre 10^{-4} et quelques 10^{-3}. Nous n'avons pas obtenu de véritable saturation mécanique. Nous sommes en présence d'une séquence durcissement-adoucissement-durcissement secondaire. L'amplitude de l'effet Bauschinger considéré comme la différence entre les limites élastiques en traction et en compression mesurées selon une procédure appropriée, évolue le long d'une boucle de fatigue, s'annule pour deux points particuliers l'un en traction l'autre en compression. De part et d'autre de ces points, le signe de l'effet Bauschinger est inversé. Les microstructures des états fatigués sont caractérisés par une répartition hétérogène des dislocations constituée d'amas, de murs ou des parois, suivant le degré de déformation cyclique, séparés par des zones à faible densité de dislocations. Les contraintes internes liées aux incompatibilités de déformation résultant de cette répartition hétérogène des dislocations sont à l'origine de l'effet Bauschinger observé dans les monocristaux. Ces contraintes et l'évolution de la quantité de cellules de dislocations avec la fatigue expliquent le durcissement secondaire.

Fungible Correlation Matrices: A Method for Generating Nonsingular, Singular, and Improper Correlation Matrices for Monte Carlo Research.

PubMed

Waller, Niels G

2016-01-01

For a fixed set of standardized regression coefficients and a fixed coefficient of determination (R-squared), an infinite number of predictor correlation matrices will satisfy the implied quadratic form. I call such matrices fungible correlation matrices. In this article, I describe an algorithm for generating positive definite (PD), positive semidefinite (PSD), or indefinite (ID) fungible correlation matrices that have a random or fixed smallest eigenvalue. The underlying equations of this algorithm are reviewed from both algebraic and geometric perspectives. Two simulation studies illustrate that fungible correlation matrices can be profitably used in Monte Carlo research. The first study uses PD fungible correlation matrices to compare penalized regression algorithms. The second study uses ID fungible correlation matrices to compare matrix-smoothing algorithms. R code for generating fungible correlation matrices is presented in the supplemental materials.

A novel highly selective and sensitive detection of serotonin based on Ag/polypyrrole/Cu2O nanocomposite modified glassy carbon electrode.

PubMed

Selvarajan, S; Suganthi, A; Rajarajan, M

2018-06-01

A silver/polypyrrole/copper oxide (Ag/PPy/Cu 2 O) ternary nanocomposite was prepared by sonochemical and oxidative polymerization simple way, in which Cu 2 O was decorated with Ag nanoparticles, and covered by polyprrole (PPy) layer. The as prepared materials was characterized by UV-vis-spectroscopy (UV-vis), FT-IR, X-ray diffraction (XRD), thermo-gravimetric analysis (TGA), scanning electron microscopy (SEM) with EDX, high resolution transmission electron microscopy (HR-TEM) and X-ray photoelectron spectroscopy (XPS). Sensing of serotonin (5HT) was evaluated electrocatalyst using polypyrrole/glassy carbon electrode (PPy/GCE), polypyrrole/copper oxide/glassy carbon electrode (PPy/Cu 2 O/GCE) and silver/polypyrrole/copper oxide/glassy carbon electrode (Ag/PPy/Cu 2 O/GCE). The Ag/PPy/Cu 2 O/GCE was electrochemically treated in 0.1MPBS solution through cyclic voltammetry (CV) and differential pulse voltammetry (DPV). The peak current response increases linearly with 5-HT concentration from 0.01 to 250 µmol L -1 and the detection limit was found to be 0.0124 μmol L -1 . It exhibits high electrocatalytic activity, satisfactory repeatability, stability, fast response and good selectivity against potentially interfering species, which suggests its potential in the development of sensitive, selective, easy-operation and low-cost serotonin sensor for practical routine analyses. The proposed method is potential to expand the possible applied range of the nanocomposite material for detection of various concerned electro active substances. Copyright © 2018 Elsevier B.V. All rights reserved.

A geochemical approach to constraining the formation of glassy fallout debris from nuclear tests

DOE PAGES

Bonamici, Chloë E.; Kinman, William S.; Fournelle, John H.; ...

2016-12-15

Reprocessed earth material is a glassy nuclear fallout debris from near-surface nuclear tests. A geochemical approach to analysis of glassy fallout is uniquely suited to determine the means of reprocessing and shed light on the mechanisms of fallout formation. An improved understanding of fallout formation is of interest both for its potential to guide post-detonation nuclear forensic investigations and in the context of possible affinities between glassy debris and other glasses generated by high-energy natural events, such as meteorite impacts and lightning strikes. Our study presents a large major-element compositional dataset for glasses within aerodynamic fallout from the Trinity nuclearmore » test (“trinitite”) and a geochemically based analysis of the glass compositional trends. Silica-rich and alkali-rich trinitite glasses show compositions and textures consistent with formation through melting of individual mineral grains—quartz and alkali feldspar, respectively—from the test-site sediment. Furthermore, the volumetrically dominant glass phase—called the CaMgFe glass—shows extreme major-element compositional variability. Compositional trends in the CaMgFe glass are most consistent with formation through volatility-controlled condensation from compositionally heterogeneous plasma. Radioactivity occurs only in CaMgFe glass, indicating that co-condensation of evaporated bulk ground material and trace device material was the main mechanism of radioisotope incorporation into trinitite. CaMgFe trinitite glasses overlap compositionally with basalts, rhyolites, fulgurites, tektites, and microtektites but display greater compositional diversity than all of these naturally formed glasses. Indeed, the most refractory CaMgFe glasses compositionally resemble early solar system condensates—specifically, CAIs.« less

A geochemical approach to constraining the formation of glassy fallout debris from nuclear tests

NASA Astrophysics Data System (ADS)

Bonamici, Chloë E.; Kinman, William S.; Fournelle, John H.; Zimmer, Mindy M.; Pollington, Anthony D.; Rector, Kirk D.

2017-01-01

Glassy nuclear fallout debris from near-surface nuclear tests is fundamentally reprocessed earth material. A geochemical approach to analysis of glassy fallout is uniquely suited to determine the means of reprocessing and shed light on the mechanisms of fallout formation. An improved understanding of fallout formation is of interest both for its potential to guide post-detonation nuclear forensic investigations and in the context of possible affinities between glassy debris and other glasses generated by high-energy natural events, such as meteorite impacts and lightning strikes. This study presents a large major-element compositional dataset for glasses within aerodynamic fallout from the Trinity nuclear test ("trinitite") and a geochemically based analysis of the glass compositional trends. Silica-rich and alkali-rich trinitite glasses show compositions and textures consistent with formation through melting of individual mineral grains—quartz and alkali feldspar, respectively—from the test-site sediment. The volumetrically dominant glass phase—called the CaMgFe glass—shows extreme major-element compositional variability. Compositional trends in the CaMgFe glass are most consistent with formation through volatility-controlled condensation from compositionally heterogeneous plasma. Radioactivity occurs only in CaMgFe glass, indicating that co-condensation of evaporated bulk ground material and trace device material was the main mechanism of radioisotope incorporation into trinitite. CaMgFe trinitite glasses overlap compositionally with basalts, rhyolites, fulgurites, tektites, and microtektites but display greater compositional diversity than all of these naturally formed glasses. Indeed, the most refractory CaMgFe glasses compositionally resemble early solar system condensates—specifically, CAIs.

Laser micromilling of convex microfluidic channels onto glassy carbon for glass molding dies

NASA Astrophysics Data System (ADS)

Tseng, Shih-Feng; Chen, Ming-Fei; Hsiao, Wen-Tse; Huang, Chien-Yao; Yang, Chung-Heng; Chen, Yu-Sheng

2014-06-01

This study reports the fabrication of convex microfluidic channels on glassy carbon using an ultraviolet laser processing system to produce glass molding dies. The laser processing parameters, including various laser fluences and scanning speeds of galvanometers, were adjusted to mill a convex microchannel on a glassy carbon substrate to identify the effects of material removal. The machined glassy carbon substrate was then applied as a glass molding die to fabricate a glass-based microfluidic biochip. The surface morphology, milled width and depth, and surface roughness of the microchannel die after laser micromilling were examined using a three-dimensional confocal laser scanning microscope. This study also investigates the transcription rate of microchannels after the glass molding process. To produce a 180 μm high microchannel on the GC substrate, the optimal number of milled cycles, laser fluence, and scanning speed were 25, 4.9 J/cm2, and 200 mm/s, respectively. The width, height, and surface roughness of milled convex microchannels were 119.6±0.217 μm, 180.26±0.01 μm, and 0.672±0.08 μm, respectively. These measured values were close to the predicted values and suitable for a glass molding die. After the glass molding process, a typical glass-based microchannel chip was formed at a molding temperature of 660 °C and the molding force of 0.45 kN. The transcription rates of the microchannel width and depth were 100% and 99.6%, respectively. Thus, the proposed approach is suitable for performing in chemical, biochemical, or medical reactions.

Potential applications of cold sprayed Cu50Ti20Ni30 metallic glassy alloy powders for antibacterial protective coating in medical and food sectors.

PubMed

El-Eskandrany, M Sherif; Al-Azmi, Ahmed

2016-03-01

Mechanical alloying was utilized for synthesizing of metallic glassy Cu50Ti20Ni30 alloy powders, using a low energy ball milling technique. The metallic glassy powders obtained after 100 h of ball milling had an average particle size of 1.7 mm in diameter and possessed excellent thermal stability, indexed by a relatively high glass transition temperature (358.3 °C) with a wide supercooled liquid region (61 °C). This amorphous phase crystallized into Ti2Cu and CuTiNi2 ordered phases through two overlapped crystallization temperatures at 419.3 °C and 447.5 °C, respectively. The total enthalpy change of crystallization was -4.8 kJ/mol. The glassy powders were employed as feedstock materials to double-face coating the surface of SUS 304 substrate, using cold spraying process under helium gas pressure at 400 °C. This coating material had an extraordinary high nanohardness value of 3.1 GPa. Moreover, it showed a high resistance to wear with a low value of the coefficient of friction ranging from 0.45 to 0.45. Biofilms were grown on 20-mm(2) SUS304 sheets coated coupons inoculated with 1.5 × 10(8) CFU ml(-1)E. coli. Significant biofilm inhibition (p The inhibition of biofilm formation by nanocrystalline powders of Cu-based provides a practical approach to achieve the inhibition of biofilms formation. Copyright © 2015 Elsevier Ltd. All rights reserved.

Spatial and mesoscopic fluctuations in glassy dynamics

NASA Astrophysics Data System (ADS)

Chamon, Claudio C.; Cugliandolo, Leticia F.

2004-05-01

One of the striking properties of a glassy system is that many material properties depend on its age, i.e., the time since the system entered its glassy phase. In this this talk we shall review some recent progress (work in collaboration with H. E. Castillo, P. Charbonneau, J. L. Iguain, M. P. Kennett, D. R. Reichman and M. Sellitto) in understanding local aging, through the study of local observable quantities, which reveal that there are spatial heterogeneities and fluctuations in the aging process of macroscopic systems. We show that a number of universal properties are shared by many non-equilibrium systems, both with and without quenched disorder, such as the 3D Edwards-Anderson model and some kinetically constrained non-interacting 2D and 3D spin models, for example. Similar scaling relations are found for mesoscopic sample-to-sample fluctuations of global quantities in small size systems. We discuss how the emergence of a symmetry in aging systems, time-reparametrization invariance, could be responsible for the observed universal behavior of the local and mesoscopic non-equilibrium fluctuations.

Structural modifications of polymethacrylates: impact on thermal behavior and release characteristics of glassy solid solutions.

PubMed

Claeys, Bart; De Coen, Ruben; De Geest, Bruno G; de la Rosa, Victor R; Hoogenboom, Richard; Carleer, Robert; Adriaensens, Peter; Remon, Jean Paul; Vervaet, Chris

2013-11-01

Polymethacrylates such as Eudragit® polymers are well established as drug delivery matrix. Here, we synthesize several Eudragit E PO (n-butyl-, dimethylaminoethyl-, methyl-methacrylate-terpolymer) analogues via free radical polymerization. These polymers are processed via hot melt extrusion, followed by injection molding and evaluated as carriers to produce immediate release solid solution tablets. Three chemical modifications increased the glass transition temperature of the polymer: (a) substitution of n-butyl by t-butyl groups, (b) reduction of the dimethylaminoethyl methacrylate (DMAEMA) content, and (c) incorporation of a bulky isobornyl repeating unit. These structural modifications revealed the possibility to increase the mechanical stability of the tablets via altering the polymer Tg without influencing the drug release characteristics and glassy solid solution forming properties. The presence of DMAEMA units proved to be crucial with respect to API/polymer interaction (essential in creating glassy solid solutions) and drug release characteristics. Moreover, these chemical modifications accentuate the need for a more rational design of (methacrylate) polymer matrix excipients for drug formulation via hot melt extrusion and injection molding. Copyright © 2013 Elsevier B.V. All rights reserved.

Deuterium Isotope Effects During HMX Combustion: Chemical Kinetic Burn Rate Control Mechanism Verified

DTIC Science & Technology

1989-01-01

experience de gen dieses Experiments. Der 10 KDIE-Wert legt nahe. dab die combustion statique. La valeur de l’effet isotopique primaire laisse...anomaler combustion globale. Des 6tudes publifes par ailleurs confirment cette KDIE-Wert bei 10,4 MPa wirL angegeben. Diese KDIE-Experimente hypoth~se

Effets pathogènes d'un faible débit de dose : la relation « dose effet »

NASA Astrophysics Data System (ADS)

Masse, Roland

2002-10-01

There is no evidence of pathogenic effects in human groups exposed to less than 100 mSv at low dose-rate. The attributed effects are therefore the result of extrapolations from higher doses. The validity of such extrapolations is discussed from the point of view of epidemiology as well as cellular and molecular biology. The Chernobyl accident resulted in large excess of thyroid cancers in children; it also raised the point that some actual sanitary effects among distressed populations might be a direct consequence of low doses. Studies under the control of UN have not confirmed this point identifying no dose-effect relationship and " severe socio-economic and psychological pressures… poverty, poor diet and living conditions, and lifestyle factors" as the main cause for depressed health. Some hypothesis are considered for explaining the dose-dependence and high prevalence of non-cancer causes of death among human groups exposed to more than 300 mSv. To cite this article: R. Masse, C. R. Physique 3 (2002) 1049-1058.

Fiabilité des structures mécaniques adaptatives: effet de la panne des actionneurs ou des capteurs sur la stabilité

NASA Astrophysics Data System (ADS)

Fall, H.; Charon, W.; Kouta, R.

2002-12-01

Ces dernières décennies, des activités significatives dans le monde étaient dirigées autour du contrôle actif. Le but de ces recherches était essentiellement d'améliorer les performances, la fiabilité et la sécurité des systèmes. Notamment dans le cas des structures soumises à des vibrations aléatoires. D'importants travaux ont été consacré à l'utilisation des “matériaux intelligents” comme capteurs et actionneurs. Cette article propose l'analyse de la fiabilité des systèmes mécaniques en étudiant les pannes des actionneurs ou des capteurs. L'effet de ces pannes sur la stabilité et la performance du système y est démontré. Les méthodologies de conception y sont rappelées. Des exemples numériques sont fournis à travers le contrôle d'un panneau sous chargement dynamique pour illustrer la méthode proposée.

Hydrogen and Sulfur from Hydrogen Sulfide. 5. Anodic Oxidation of Sulfur on Activated Glassy Carbon

DTIC Science & Technology

1988-12-05

electrolyses of H S can probably be carried out at high rates with modest cell voltages in the range 1-1.5 V. The variation in anode current densities...of H2S from solutions of NaSH in aqueous NaOH was achieved using suitably ac- tivated glassy carbon anodes. Thus electrolyses of H2S can probably be...passivation by using a basic solvent at 850C. Using an H2S-saturated 6M NaOH solution, they conducted electrolyses for extended periods at current densities

Hydration reactivity of crystalline and vitrified diopside under hydrothermal conditions

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

Grzeszczyk, S.; Szuba, J.

1990-07-01

Hydration reactivity of diopside in both the crystalline and amorphous (glassy) phase was studied under hydrothermal conditions. Samples were treated in an autoclave at 200{degrees}C in saturated vapor for 24 and 72 h. The progress of hydration was determined by X-ray powder diffractometry and IR spectroscopy. Results indicate that crystalline diopside possessed poor hydraulic activity. However, once vitrified it proved to be much more reactive. The principal hydration products found for the glassy diopside after 24 and 72 h of treatment were calcium silicate hydrate (xonotlite) and magnesium silicate hydrates (chrysotile and tremolite).

Microanalytical study of some cosmic dust discovered in sea-floor sediments in China

NASA Technical Reports Server (NTRS)

Shijie, Z.; Hanchang, P.; Zhong, Y.

1984-01-01

The study of cosmic dust can provide useful data in the investigation of the origin of the Earth and the evolution of celestial bodies. Three types of cosmic dust (ferriginous, siliceous, and glassy) were discovered in the seafloor sediments near China. Their chemical composition and microstructure were examined by X-ray diffraction, fractography, and electron microscopy. The major mineral in an iron-containing cosmic dust is magnetite. The silicate spheres contain sundry metals and metal oxides. Glassy microtektites are similar in composition to tektites, and are found in all the major meteorite areas worldwide.

Glass-(nAg, nCu) biocide coatings on ceramic oxide substrates.

PubMed

Esteban-Tejeda, Leticia; Malpartida, Francisco; Díaz, Luis Antonio; Torrecillas, Ramón; Rojo, Fernando; Moya, José Serafín

2012-01-01

The present work was focused on obtaining biocide coatings constituted by a glassy soda-lime matrix containing silver or copper nanoparticles on ceramic (alumina and zirconia based) substrates. Both glassy coatings showed a high biocide activity against Gram-, Gram+ bacteria and yeast, reducing cell numbers more than three logarithms. Silver nanoparticles had a significantly higher biocide activity than copper nanoparticles, since the lixiviation levels required to reduce cell numbers more than 3 logarithms was of almost 1-2 µg/cm(2) in the case of silver nanoparticles, and 10-15 µg/cm(2) for the copper nanoparticles.

Glassy dynamics of dense particle assemblies on a spherical substrate.

PubMed

Vest, Julien-Piera; Tarjus, Gilles; Viot, Pascal

2018-04-28

We study by molecular dynamics simulation a dense one-component system of particles confined on a spherical substrate. We more specifically investigate the evolution of the structural and dynamical properties of the system when changing the control parameters, the temperature and the curvature of the substrate. We find that the dynamics become glassy at low temperature, with a strong slowdown of the relaxation and the emergence of dynamical heterogeneity. The prevalent local 6-fold order is frustrated by curvature and we analyze in detail the role of the topological defects in the statics and the dynamics of the particle assembly.

CMV matrices in random matrix theory and integrable systems: a survey

NASA Astrophysics Data System (ADS)

Nenciu, Irina

2006-07-01

We present a survey of recent results concerning a remarkable class of unitary matrices, the CMV matrices. We are particularly interested in the role they play in the theory of random matrices and integrable systems. Throughout the paper we also emphasize the analogies and connections to Jacobi matrices.

Basal Cell Carcinoma With Matrical Differentiation: Clinicopathologic, Immunohistochemical, and Molecular Biological Study of 22 Cases.

PubMed

Kyrpychova, Liubov; Carr, Richard A; Martinek, Petr; Vanecek, Tomas; Perret, Raul; Chottová-Dvořáková, Magdalena; Zamecnik, Michal; Hadravsky, Ladislav; Michal, Michal; Kazakov, Dmitry V

2017-06-01

Basal cell carcinoma (BCC) with matrical differentiation is a fairly rare neoplasm, with about 30 cases documented mainly as isolated case reports. We studied a series of this neoplasm, including cases with an atypical matrical component, a hitherto unreported feature. Lesions coded as BCC with matrical differentiation were reviewed; 22 cases were included. Immunohistochemical studies were performed using antibodies against BerEp4, β-catenin, and epithelial membrane antigen (EMA). Molecular genetic studies using Ion AmpliSeq Cancer Hotspot Panel v2 by massively parallel sequencing on Ion Torrent PGM were performed in 2 cases with an atypical matrical component (1 was previously subjected to microdissection to sample the matrical and BCC areas separately). There were 13 male and 9 female patients, ranging in age from 41 to 89 years. Microscopically, all lesions manifested at least 2 components, a BCC area (follicular germinative differentiation) and areas with matrical differentiation. A BCC component dominated in 14 cases, whereas a matrical component dominated in 4 cases. Matrical differentiation was recognized as matrical/supramatrical cells (n=21), shadow cells (n=21), bright red trichohyaline granules (n=18), and blue-gray corneocytes (n=18). In 2 cases, matrical areas manifested cytologic atypia, and a third case exhibited an infiltrative growth pattern, with the tumor metastasizing to a lymph node. BerEP4 labeled the follicular germinative cells, whereas it was markedly reduced or negative in matrical areas. The reverse pattern was seen with β-catenin. EMA was negative in BCC areas but stained a proportion of matrical/supramatrical cells. Genetic studies revealed mutations of the following genes: CTNNB1, KIT, CDKN2A, TP53, SMAD4, ERBB4, and PTCH1, with some differences between the matrical and BCC components. It is concluded that matrical differentiation in BCC in most cases occurs as multiple foci. Rare neoplasms manifest atypia in the matrical areas. Immunohistochemical analysis for BerEP4, EMA, and β-catenin can be helpful in limited biopsy specimens. From a molecular biological prospective, BCC and matrical components appear to share some of the gene mutations but have differences in others, but this observation must be validated in a large series.

Effets de la pollution de l’air sur la santé

PubMed Central

Abelsohn, Alan; Stieb, Dave M.

2011-01-01

Résumé Objectif Faire connaître aux médecins de famille les effets de la pollution atmosphérique sur la santé et indiquer quels conseils donner aux patients vulnérables pour qu’ils soient moins exposés. Sources de l’information On a consulté MEDLINE à l’aide des termes relatifs à la pollution atmosphérique et à ses effets indésirables. On a révisé les articles en anglais publiés entre janvier 2008 et décembre 2009. La plupart des études contenaient des preuves de niveau II. Principal message Au Canada, la pollution de l’air extérieur cause une morbidité et une mortalité importantes. Elle peut affecter le système respiratoire (exacerbation de l’asthme et de la maladie pulmonaire obstructive chronique) et le système cardiovasculaire (déclencher l’arythmie, l’insuffisance cardiaque et les AVC). La cote air santé (CAS) est un nouvel outil de communication mis au point par Santé Canada et Environnement Canada qui indique sur une échelle de 1 à 10, le risque pour la santé causé par la pollution atmosphérique. La CAS est largement diffusée dans les médias et cet outil pourrait être utile au médecin de famille pour inciter les patients à haut risque (comme ceux qui souffrent d’asthme, de maladie pulmonaire obstructive chronique ou d’insuffisance cardiaque) à réduire leur exposition à la pollution atmosphérique. Conclusion Le médecin de famille peut se servir de la CAS et de ses messages sur la santé pour enseigner aux asthmatiques et aux autres patients à risque élevé la façon de réduire les risques pour la santé causés par la pollution atmosphérique.

Le rôle du soutien parental dans la relation entre la victimisation homophobe, l’homophobie intériorisée et la détresse psychologique chez les jeunes de minorités sexuelles (JMS) : une approche de médiation modérée

PubMed Central

Bergeron, Félix-Antoine; Blais, Martin; Hébert, Martine

2016-01-01

Résumé Cet article explore le rôle modérateur du soutien parental dans les relations entre la victimisation homophobe, l’homophobie intériorisée et la détresse psychologique chez des jeunes de minorités sexuelles (JMS), que l’on dit aussi lesbiennes, gais, bisexuels ou en questionnement. Il vise à 1) documenter la prévalence des différentes formes de victimisation homophobe vécue par les JMS, et ce, selon le genre et l’âge et 2) à explorer l’effet modérateur du soutien parental dans la relation entre la victimisation homophobe, l’homophobie intériorisée et la détresse psychologique. Un échantillon de 228 JMS âgés de 14 à 22 ans, non exclusivement hétérosexuels, recrutés en milieu communautaire dans le cadre de l’enquête sur le Parcours Amoureux des Jeunes (PAJ) du Québec a été analysé. L’impact de la victimisation homophobe, du soutien parental, de l’homophobie intériorisée sur la détresse psychologique est exploré par un modèle de régression linéaire avec effets de médiation modérée. Le rôle modérateur du soutien parental est confirmé dans la relation entre la victimisation homophobe et la détresse psychologique. Ces variables peuvent constituer des leviers pour prévenir les effets négatifs des préjudices homophobes sur la santé mentale des JMS. PMID:26966851

Etude thermo-hydraulique de l'ecoulement du moderateur dans le reacteur CANDU-6

NASA Astrophysics Data System (ADS)

Mehdi Zadeh, Foad

Etant donne la taille (6,0 m x 7,6 m) ainsi que le domaine multiplement connexe qui caracterisent la cuve des reacteurs CANDU-6 (380 canaux dans la cuve), la physique qui gouverne le comportement du fluide moderateur est encore mal connue de nos jours. L'echantillonnage de donnees dans un reacteur en fonction necessite d'apporter des changements a la configuration de la cuve du reacteur afin d'y inserer des sondes. De plus, la presence d'une zone intense de radiations empeche l'utilisation des capteurs courants d'echantillonnage. En consequence, l'ecoulement du moderateur doit necessairement etre etudie a l'aide d'un modele experimental ou d'un modele numerique. Pour ce qui est du modele experimental, la fabrication et la mise en fonction de telles installations coutent tres cher. De plus, les parametres de la mise a l'echelle du systeme pour fabriquer un modele experimental a l'echelle reduite sont en contradiction. En consequence, la modelisation numerique reste une alternative importante. Actuellement, l'industrie nucleaire utilise une approche numerique, dite de milieu poreux, qui approxime le domaine par un milieu continu ou le reseau des tubes est remplace par des resistances hydrauliques distribuees. Ce modele est capable de decrire les phenomenes macroscopiques de l'ecoulement, mais ne tient pas compte des effets locaux ayant un impact sur l'ecoulement global, tel que les distributions de temperatures et de vitesses a proximite des tubes ainsi que des instabilites hydrodynamiques. Dans le contexte de la surete nucleaire, on s'interesse aux effets locaux autour des tubes de calandre. En effet, des simulations faites par cette approche predisent que l'ecoulement peut prendre plusieurs configurations hydrodynamiques dont, pour certaines, l'ecoulement montre un comportement asymetrique au sein de la cuve. Ceci peut provoquer une ebullition du moderateur sur la paroi des canaux. Dans de telles conditions, le coefficient de reactivite peut varier de maniere importante, se traduisant par l'accroissement de la puissance du reacteur. Ceci peut avoir des consequences majeures pour la surete nucleaire. Une modelisation CFD (Computational Fluid Dynamics) detaillee tenant compte des effets locaux s'avere donc necessaire. Le but de ce travail de recherche est de modeliser le comportement complexe de l'ecoulement du moderateur au sein de la cuve d'un reacteur nucleaire CANDU-6, notamment a proximite des tubes de calandre. Ces simulations servent a identifier les configurations possibles de l'ecoulement dans la calandre. Cette etude consiste ainsi a formuler des bases theoriques a l'origine des instabilites macroscopiques du moderateur, c.-a-d. des mouvements asymetriques qui peuvent provoquer l'ebullition du moderateur. Le defi du projet est de determiner l'impact de ces configurations de l'ecoulement sur la reactivite du reacteur CANDU-6.

Proprietes ionochromes et photochromes de derives du polythiophene

NASA Astrophysics Data System (ADS)

Levesque, Isabelle

La synthese et la caracterisation de derives regioreguliers du polythiophene ont ete effectuees en solution et sur des films minces. La spectroscopie UV-visible de ces derives a permis de constater qu'ils peuvent posseder des proprietes chromiques particulieres selon le stimulus auquel ils sont soumis. Par exemple, une augmentation de la temperature permet en effet aux polymeres de passer d'une couleur violette a jaune, et ce, a l'etat solide aussi bien qu'en solution. Ces proprietes chromiques semblent regies par une transition conformationnelle (plane a non-plane) de la chaine principale. Ce travail avait pour but de mieux comprendre l'influence de l'organisation des chaines laterales sur les transitions chromiques. Deux derives synthetises possedant des chaines laterales sensibles aux cations alcalins se sont averes etre ionochromes en plus d'etre thermochromes. Il s'agit d'un polymere comportant des chaines laterales de type oligo(oxyethylene) et d'un autre comportant un groupement ether couronne specifique aux ions lithium. Les effets chromiques observes sont expliques par des interactions non-covalentes des cations avec les atomes d'oxygene des chaines laterales dans le cas du premier polymere, et par l'insertion de l'ion Li + dans la cavite de l'ether couronne dans le cas du second polymere. Ces interactions semblent provoquer une diminution de l'organisation induisant ainsi une torsion de la chaine principale. Les deux polymeres semblent specifiques a certains cations et pourraient donc servir comme detecteurs optiques. La specificite aux ions Li+ du second polymere pourrait aussi permettre la conduction ionique, en plus de la conductivite electronique caracteristique des polythiophenes, ce qui pourrait s'averer utile dans le cas de batteries legeres entierement faites de polymeres et de sels de lithium. D'autres derives comportant des chaines laterales de type azobenzene se sont averes etre photochromes en plus d'etre thermochromes. Le groupement lateral a la possibilite de changer de configuration de la forme trans a la forme cis lorsqu'il est soumis a une irradiation dans le domaine de l'ultraviolet ce qui provoque, selon toute evidence, un effet marque sur l'organisation des chaines laterales. Cela induit alors une torsion de la chaine principale thiophene entrainant une diminution de conjugaison marquee. Ces effets peuvent etre exploites entre autres dans l'ecriture optique. Il s'est avere que le polymere irradie peu conjugue peut etre force a retourner a son etat initial conjugue tres rapidement par un traitement electrochimique simple. En conclusion, on a pu prouver qu'une modification dans l'organisation des chaines laterales par un stimulus exterieur affecte considerablement la conformation de la chaine principale. Cela porte a croire que les chaines laterales stabilisent une conformation particuliere des polythiophenes.

A Brief Historical Introduction to Matrices and Their Applications

ERIC Educational Resources Information Center

Debnath, L.

2014-01-01

This paper deals with the ancient origin of matrices, and the system of linear equations. Included are algebraic properties of matrices, determinants, linear transformations, and Cramer's Rule for solving the system of algebraic equations. Special attention is given to some special matrices, including matrices in graph theory and electrical…

Laminin active peptide/agarose matrices as multifunctional biomaterials for tissue engineering.

PubMed

Yamada, Yuji; Hozumi, Kentaro; Aso, Akihiro; Hotta, Atsushi; Toma, Kazunori; Katagiri, Fumihiko; Kikkawa, Yamato; Nomizu, Motoyoshi

2012-06-01

Cell adhesive peptides derived from extracellular matrix components are potential candidates to afford bio-adhesiveness to cell culture scaffolds for tissue engineering. Previously, we covalently conjugated bioactive laminin peptides to polysaccharides, such as chitosan and alginate, and demonstrated their advantages as biomaterials. Here, we prepared functional polysaccharide matrices by mixing laminin active peptides and agarose gel. Several laminin peptide/agarose matrices showed cell attachment activity. In particular, peptide AG73 (RKRLQVQLSIRT)/agarose matrices promoted strong cell attachment and the cell behavior depended on the stiffness of agarose matrices. Fibroblasts formed spheroid structures on the soft AG73/agarose matrices while the cells formed a monolayer with elongated morphologies on the stiff matrices. On the stiff AG73/agarose matrices, neuronal cells extended neuritic processes and endothelial cells formed capillary-like networks. In addition, salivary gland cells formed acini-like structures on the soft matrices. These results suggest that the peptide/agarose matrices are useful for both two- and three-dimensional cell culture systems as a multifunctional biomaterial for tissue engineering. Copyright © 2012 Elsevier Ltd. All rights reserved.

A wrinkling-based method for investigating glassy polymer film relaxation as a function of film thickness and temperature.

PubMed

Chung, Jun Young; Douglas, Jack F; Stafford, Christopher M

2017-10-21

We investigate the relaxation dynamics of thin polymer films at temperatures below the bulk glass transition T g by first compressing polystyrene films supported on a polydimethylsiloxane substrate to create wrinkling patterns and then observing the slow relaxation of the wrinkled films back to their final equilibrium flat state by small angle light scattering. As with recent relaxation measurements on thin glassy films reported by Fakhraai and co-workers, we find the relaxation time of our wrinkled films to be strongly dependent on film thickness below an onset thickness on the order of 100 nm. By varying the temperature between room temperature and T g (≈100 °C), we find that the relaxation time follows an Arrhenius-type temperature dependence to a good approximation at all film thicknesses investigated, where both the activation energy and the relaxation time pre-factor depend appreciably on film thickness. The wrinkling relaxation curves tend to cross at a common temperature somewhat below T g , indicating an entropy-enthalpy compensation relation between the activation free energy parameters. This compensation effect has also been observed recently in simulated supported polymer films in the high temperature Arrhenius relaxation regime rather than the glassy state. In addition, we find that the film stress relaxation function, as well as the height of the wrinkle ridges, follows a stretched exponential time dependence and the short-time effective Young's modulus derived from our modeling decreases sigmoidally with increasing temperature-both characteristic features of glassy materials. The relatively facile nature of the wrinkling-based measurements in comparison to other film relaxation measurements makes our method attractive for practical materials development, as well as fundamental studies of glass formation.

Kinetic analysis of the non-isothermal crystallization process, magnetic and mechanical properties of FeCoBSiNb and FeCoBSiNbCu bulk metallic glasses

NASA Astrophysics Data System (ADS)

Ramasamy, Parthiban; Stoica, Mihai; Taghvaei, A. H.; Prashanth, K. G.; Ravi Kumar, Eckert, Jürgen

2016-02-01

The crystallization kinetics of [(Fe0.5Co0.5)0.75B0.2Si0.05]96Nb4 and {[(Fe0.5Co0.5)0.75B0.2Si0.05]0.96Nb0.04}99.5Cu0.5 bulk metallic glasses were evaluated using differential scanning calorimetry under non-isothermal condition. The fully glassy rods with diameters up to 2 mm were obtained by copper mold injection casting. Both glasses show good thermal stability, but the addition of only 0.5% Cu completely changes the crystallization behavior. The average activation energy required for crystallization decreases from 645 kJ/mol to 425 kJ/mol after Cu addition. Upon heating, the Cu-free alloy forms only the metastable Fe23B6 phase. In contrast, two well-separated exothermic events are observed for the Cu-added bulk glassy samples. First, the (Fe,Co) phase nucleates and then (Fe,Co)2B and/or (Fe,Co)3B crystallize from the remaining glassy matrix. The Cu-added alloy exhibits a lower coercivity and a higher magnetic saturation than the base alloy, both in as-cast as well as in annealed condition. Besides, the Cu-added glassy sample with 2 mm diameter exhibits a maximum compressive fracture strength of 3913 MPa together with a plastic strain of 0.6%, which is highest plastic strain ever reported for 2 mm diameter ferromagnetic bulk metallic glass sample. Although Cu addition improves the magnetic and mechanical properties of the glass, it affects the glass-forming ability of the base alloy.

A wrinkling-based method for investigating glassy polymer film relaxation as a function of film thickness and temperature

NASA Astrophysics Data System (ADS)

Chung, Jun Young; Douglas, Jack F.; Stafford, Christopher M.

2017-10-01

We investigate the relaxation dynamics of thin polymer films at temperatures below the bulk glass transition Tg by first compressing polystyrene films supported on a polydimethylsiloxane substrate to create wrinkling patterns and then observing the slow relaxation of the wrinkled films back to their final equilibrium flat state by small angle light scattering. As with recent relaxation measurements on thin glassy films reported by Fakhraai and co-workers, we find the relaxation time of our wrinkled films to be strongly dependent on film thickness below an onset thickness on the order of 100 nm. By varying the temperature between room temperature and Tg (≈100 °C), we find that the relaxation time follows an Arrhenius-type temperature dependence to a good approximation at all film thicknesses investigated, where both the activation energy and the relaxation time pre-factor depend appreciably on film thickness. The wrinkling relaxation curves tend to cross at a common temperature somewhat below Tg, indicating an entropy-enthalpy compensation relation between the activation free energy parameters. This compensation effect has also been observed recently in simulated supported polymer films in the high temperature Arrhenius relaxation regime rather than the glassy state. In addition, we find that the film stress relaxation function, as well as the height of the wrinkle ridges, follows a stretched exponential time dependence and the short-time effective Young's modulus derived from our modeling decreases sigmoidally with increasing temperature—both characteristic features of glassy materials. The relatively facile nature of the wrinkling-based measurements in comparison to other film relaxation measurements makes our method attractive for practical materials development, as well as fundamental studies of glass formation.

Solution processable 2-(trityloxy)ethyl and tert-butyl group containing amorphous molecular glasses of pyranylidene derivatives with light-emitting and amplified spontaneous emission properties

NASA Astrophysics Data System (ADS)

Zarins, Elmars; Vembris, Aivars; Misina, Elina; Narels, Martins; Grzibovskis, Raitis; Kokars, Valdis

2015-11-01

Small organic molecules with incorporated 4H-pyran-4-ylidene (pyranylidene) fragment as the π-conjugation system which bonds the electron acceptor fragment (A) with electron donor part (D) in the molecule - also well known as derivatives of 4-(dicyano-methylene)-2-methyl-6-[p-(dimethylamino)styryl]-4H-pyran (DCM) laser dye-have attracted considerable attention of scientists as potential new generation materials for organic photonics and molecular electronics due to their low-cost fabrication possibility, flexibility and low-weight. Six glassy derivatives of 4H-pyran-4-ylidene (pyranylidene) with attached bulky 2-(trityloxy)ethyl and tert-butyl groups are described in this report. Almost all of the synthesized compounds form good optical quality transparent amorphous films from volatile organic solvents and could be obtained in good yields up to 75%. Their light emission in solution and thin solid films is in the range of 600-700 nm, they are thermally stable and show glass transition in the range of 108-158 °C. The amplified spontaneous emission threshold values of the neat films of the glassy pyranylidene derivatives vary from 155 to 450 μJ/cm2 and their HOMO and LUMO energy levels are between of those of tris(8-hydroxy quinolinato) aluminum (Alq3). The photoluminescence quantum yields of the glassy compounds are in the range from 1% to about 7.7% and their electroluminescence properties have been investigated. Therefore, glassy pyranylidene derivatives could be a very potential low-cost solution processable materials for Alq3 hosted light-amplification and light-emitting application studies.

Alteration mineralogy, mineral chemistry and stable isotope geochemistry of the Eocene pillow lavas from the Trabzon area, NE Turkey

NASA Astrophysics Data System (ADS)

Abdioğlu Yazar, Emel

2018-02-01

The Eocene subaqueous volcanic units in NE Turkey developed as pillow, closely packed pillow, isolated pillow, pillow breccia, hyaloclastite breccia and rare peperitic facies with red micritic limestones. They are locally set on volcaniclastic sandstone and claystone alternations and gradually pass to tuffs and volcanic breccias. The pillow lava samples generally exhibit intersertal, intergranular, microlitic porphyritic, variolitic, vesicular and glomeroporphyritic and glassy textures with clinopyroxene (Wo47-52En40-45Fs6-8), plagioclase (An10 to An96), olivine (Fo79-87) and Fe-Ti oxides (Usp0-0.27). Saponite, interlayered chlorite/saponite, rare beidellite and calcite were determined after olivine, rarely after plagioclase as well as in the glassy groundmass. Illite was restricted to plagioclase and the glassy groundmass. Na-Ca zeolites, chlorites/saponites, beidellite, dolomite and calcite occur as void infillings and in the glassy groundmass. Mineralogical, lithochemical and isotopic interpretations as well as thermometric calculations reveal a low-temperature seawater alteration in a semi-closed environment for the alteration of primary minerals and volcanic glass in addition to sealed vesicles and open systems for crosscutting veins. Due to the short exposure time intervals of seawater to rocks, the total chemistry of the rocks is not fully changed and most of the elements seem to be immobile, remaining in the system as a result of precipitation in voids and cracks. Thermometric estimations indicate that, the temperature of heated seawater is approximately 160 °C at the highest point especially in the vesicles, and decreases to approximately 85 °C due to circulation, resulting in alterations of the primary phases and volcanic glass.

Contribution a l'etude et au developpement de nouvelles poudres de fonte

NASA Astrophysics Data System (ADS)

Boisvert, Mathieu

L'obtention de graphite libre dans des pieces fabriquees par metallurgie des poudres (M/P) est un defi auquel plusieurs chercheurs se sont attardes. En effet, la presence de graphite apres frittage ameliore l'usinabilite des pieces, permettant donc de reduire les couts de production, et peut aussi engendrer une amelioration des proprietes tribologiques. L'approche utilisee dans cette these pour tenter d'obtenir du graphite libre apres frittage est par l'utilisation de nouvelles poudres de fontes atomisees a l'eau. L'atomisation a l'eau etant un procede de production de poudres relativement peu couteux qui permet de grandes capacites de production, le transfert des decouvertes de ce doctorat vers des applications industrielles sera donc economiquement plus favorable. En plus de l'objectif d'obtenir du graphite libre apres frittage, un autre aspect important des travaux est le controle de la morphologie du graphite libre apres frittage. En effet, il est connu dans la litterature des fontes coulees/moulees que la morphologie du graphite influencera les proprietes des fontes, ce qui est aussi vrai pour les pieces de M/P. Les fontes ductiles, pour lesquelles le graphite est sous forme de nodules spheroidaux isoles les uns des autres, possedent des proprietes mecaniques superieures aux fontes grises pour lesquelles le graphite est sous forme lamellaire et continu dans la matrice. Les resultats presentes dans cette these montrent qu'il est possible, dans des melanges contenant des poudres de fontes, d'avoir un controle sur la morphologie du graphite et donc sur les proprietes des pieces. Le controle de la morphologie du graphite a principalement ete realise par le type de frittage et le phenomene de diffusion " uphill " du carbone cause par des gradients en silicium. En effet, pour les frittages en phase solide, tous les nodules de graphite sont presents a l'interieur des grains de poudre apres frittage. Pour les frittages en phase liquide, l'intensite de la diffusion " uphill " permet de conserver plus ou moins de graphite nodulaire a l'interieur des regions riches en silicium, alors que le reste du graphite precipite sous forme lamellaire/vermiculaire dans les regions interparticulaires. L'etude des poudres de fontes et la recherche des mecanismes regissant la morphologie du graphite dans les fontes coulees/moulees nous ont amenes a produire des poudres de fontes traitees au magnesium avant l'atomisation. Plusieurs resultats fondamentaux ont ete obtenus de la caracterisation des poudres traitees au magnesium et de leur comparaison avec des poudres de chimies similaires non traitees au magnesium. D'abord, il a ete possible d'observer des bifilms d'oxyde de silicium dans la structure du graphite primaire d'une poudre de fonte grise hypereutectique. Il s'agit des premieres images montrant la structure double de ces defauts, venant ainsi appuyer la theorie elaboree par le professeur John Campbell. Ensuite, il a ete montre que le traitement au magnesium forme une atmosphere protectrice gazeuse autogeneree qui empeche l'oxydation de la surface du bain liquide et donc, la formation et l'entrainement des bifilms. Le role du magnesium sur la morphologie du graphite est de diminuer le soufre en solution en formant des precipites de sulfure de magnesium et ainsi d'augmenter l'energie d'interface graphite-liquide. En reponse a cette grande energie d'interface graphite-liquide, le graphite cherche a minimiser son ratio surface/volume, ce qui favorise la formation de graphite spheroidal. De plus, deux types de germination ont ete observes dans la poudre de fonte hypereutectique traitee au magnesium. Le premier type est une germination heterogene sur un nombre limite de particules faites de magnesium, d'aluminium, de silicium et d'oxygene. Le deuxieme type est une germination homogene des nodules dans certaines regions du liquide plus riches en silicium. L'observation du centre reel tridimensionnel, en microscopie electronique en transmission en haute resolution, d'un des nodules ayant subi une germination homogene a permis de confirmer que le mode de croissance du graphite spheroidal se produit selon le modele de la croissance en feuille de chou. (Abstract shortened by ProQuest.).

Miscellaneous methods for measuring matric or water potential

USGS Publications Warehouse

Scanlon, Bridget R.; Andraski, Brian J.; Bilskie, Jim; Dane, Jacob H.; Topp, G. Clarke

2002-01-01

A variety of techniques to measure matric potential or water potential in the laboratory and in the field are described in this section. The techniques described herein require equilibration of some medium whose matric or water potential can be determined from previous calibration or can be measured directly. Under equilibrium conditions the matric or water potential of the medium is equal to that of the soil. The techniques can be divided into: (i) those that measure matric potential and (ii) those that measure water potential (sum of matric and osmotic potentials). Matric potential is determined when the sensor matrix is in direct contact with the soil, so salts are free to diffuse in or out of the sensor matrix, and the equilibrium measurement therefore reflects matric forces acting on the water. Water potential is determined when the sensor is separated from the soil by a vapor gap, so salts are not free to move in or out of the sensor, and the equilibrium measurement reflects the sum of the matric and osmotic forces acting on the water.Seven different techniques are described in this section. Those that measure matric potential include (i) heat dissipation sensors, (ii) electrical resistance sensors, (iii) frequency domain and time domain sensors, and (iv) electro-optical switches. A method that can be used to measure matric potential or water potential is the (v) filter paper method. Techniques that measure water potential include (vi) the Dew Point Potentiameter (Decagon Devices, Inc., Pullman, WA1) (water activity meter) and (vii) vapor equilibration.The first four techniques are electronically based methods for measuring matric potential. Heat dissipation sensors and electrical resistance sensors infer matric potential from previously determined calibration relations between sensor heat dissipation or electrical resistance and matric potential. Frequency-domain and timedomain matric potential sensors measure water content, which is related to matric potential of the sensor through calibration. Electro-optical switches measure changes in light transmission through thin, nylon filters as they absorb or desorb water in response to changes in matric potential. Heat dissipation sensors and electrical resistance sensors are used primarily in the field to provide information on matric potential. Frequency domain matric potential sensors are new and have not been widely used. Time domain matric potential sensors and electro-optical switches are new and have not been commercialized. For the fifth technique, filter paper is used as the standard matrix. The filter paper technique measures matric potential when the filter paper is in direct contact with soil or water potential when separated from soil by a vapor gap. The Dew Point Potentiameter calculates water potential from the measured dew point and sample temperature. The vapor equilibration technique involves equilibration of soil samples with salt solutions of known osmotic potential. The filter paper, Dew Point Potentiameter, and vapor equilibration techniques are generally used in the laboratory to measure water potential of disturbed field samples or to measure water potential for water retention functions.

Taking Up Space: Museum Exploration in the Twenty-First Century

ERIC Educational Resources Information Center

Sutton, Tiffany

2007-01-01

Museums have become a crucible for questions of the role that traditional art and art history should play in contemporary art. Friedrich Nietzsche argued in the nineteenth century that museums can be no more than mausoleums for effete (fine) art. Over the course of the twentieth century, however, curators dispelled such blanket pessimism by…

Issues and Prospects of Effetive Implementation of New Secondary School Curriculum in Nigeria

ERIC Educational Resources Information Center

Ahmadi, Ali A.; Lukman, Ajibola A.

2015-01-01

This paper digs into the issues surrounding effective implementation of new secondary school curriculum in Nigeria. This is based on the feeling that 21st century education is characterized with a dramatic technological revolution. The paper therefore portrays education in the 21st century as a total departure from the factory-model education of…

Optics of a Double Focussing Magnetic Sector by Fringe Effect; OPTIQUE D'UN SECTEUR MAGNETIQUE A DOUBLE FOCALISATION PAR EFFET DE FRANCES

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

Krafft, J.

1960-01-01

A general study is made of the optical elements of a double-fccusing magnetic sector by the fringe effect, with a view to its application to the monochromation of the proton, deuteron, or triton beam of the 1.4 Mev accelerator. (auth)

Investigations into the Power MOSFET SEGR Phenomenon and its Physical Mechanism

NASA Technical Reports Server (NTRS)

Swift, G. M.; Edmonds, L. E.; Miyahira, T.; Nichols, D. K.; Johnston, A. H.

1997-01-01

The state of understanding of the destructive SEGR event in power MOSFETs is relatively mature with large published efforts, both experimental and theoretical. However, gasps remain in the uderstanding of the phenomenon, including unexplained anomalies, emperical-only dependencies on some important device and incident ion physical parameters, and limited insight into latent effets.

Genetic code, hamming distance and stochastic matrices.

PubMed

He, Matthew X; Petoukhov, Sergei V; Ricci, Paolo E

2004-09-01

In this paper we use the Gray code representation of the genetic code C=00, U=10, G=11 and A=01 (C pairs with G, A pairs with U) to generate a sequence of genetic code-based matrices. In connection with these code-based matrices, we use the Hamming distance to generate a sequence of numerical matrices. We then further investigate the properties of the numerical matrices and show that they are doubly stochastic and symmetric. We determine the frequency distributions of the Hamming distances, building blocks of the matrices, decomposition and iterations of matrices. We present an explicit decomposition formula for the genetic code-based matrix in terms of permutation matrices, which provides a hypercube representation of the genetic code. It is also observed that there is a Hamiltonian cycle in a genetic code-based hypercube.

Aluminum phthalocyanine tetrasulfonate in MCF-10F, human breast epithelial cells: a hole burning study.

PubMed Central

Milanovich, N; Reinot, T; Hayes, J M; Small, G J

1998-01-01

Laser-induced holes are burned in the absorption spectrum of aluminum phthalocyanine tetrasulfonate (APT) in MCF-10F, human breast epithelial cells. The hole burning mechanism is shown to be nonphotochemical. The fluorescence excitation spectra and hole spectra are compared with those of APT in hyperquenched glassy films of water, ethanol, and methanol. The results show that the APT is in an acidic, aqueous environment with a hydrogen-bonded network similar to that of glassy water, but showing the influence of other cellular components. Pressure shifts of holes allow the local compressibility about the APT to be determined. PMID:9591692

Catalytic carbide formation at aluminium-carbon interfaces

NASA Technical Reports Server (NTRS)

Maruyama, B.; Rabenberg, L.; Ohuchi, F. S.

1990-01-01

X-ray photoelectron spectroscopy investigations of the reaction of several monolayer-thick films of aluminum with glassy carbon substrates are presented. The influence of molecular oxygen and water vapor on the rate of reaction is examined. It is concluded that water vapor catalyzed the formation of aluminum carbide from aluminum and carbon by forming active sites which weakened carbon-carbon bonds at the glassy carbon surface, thus assisting their cleavage. The rate of carbide formation for undosed and molecular oxygen-dosed examples was less as neither metallic aluminum nor oxygen-formed alumina could bond to the carbon atom with sufficient strength to dissociate it quickly.

Dielectric relaxation studies in Se{sub 90}Cd{sub 8}Sb{sub 2} glassy alloy

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

Shukla, Nitesh; Rao, Vandita; Dwivedi, D. K.

2016-05-06

Se{sub 90}Cd{sub 8}Sb{sub 2} chalcogenide semiconducting alloy was prepared by melt quench technique. The prepared glassy alloy has been characterized by techniques such as scanning electron microscopy (SEM) and energy dispersive X-ray (EDAX).Dielectric properties of Se{sub 90}Cd{sub 8}Sb{sub 2} chalcogenide semiconductor have been studied using impedance spectroscopic technique in the frequency range 5×10{sup 2}Hz - 1×10{sup 5}Hz and in temperature range 303-318K. It is found that dielectric constant ε′ and dielectric loss factor ε″ are dependent on frequency and temperature.

Glucose biosensing using glassy carbon electrode modified with polyhydroxy-C60, glucose oxidase and ionic-liquid.

PubMed

Yang, Tian; Yang, Xiao-Lu; Zhang, Yu-Shuai; Xiao, BaoLin; Hong, Jun

2014-01-01

Direct electrochemistry of glucose oxidase (GOD) was achieved when an ionic liquid/GOD-Polyhydroxy-C60 functional membrane was confined on a glassy carbon electrode (GCE). The cyclic voltammograms (CVs) of the modified GCE showed a pair of redox peaks with a formal potential (E°') of - 329 ± 2 mV. The heterogeneous electron transfer constant (k(s)) was 1.43 s-1. The modified GCE response to glucose was linear in the range from 0.02 to 2.0 mM. The detection limit was 1 μM. The apparent Michaelis-Menten constant (K(m)(app)) was 1.45 mM.

A molecular dynamics study of cooling rate during solidification of metal nanoparticles

NASA Astrophysics Data System (ADS)

Shibuta, Yasushi; Suzuki, Toshio

2011-01-01

The effect of the cooling rate on the solidification behavior of metal nanoparticles is investigated by molecular dynamics simulation. The structure of molybdenum nanoparticles varies with the cooling rate. That is, single-crystalline, polycrystalline then glassy nanoparticles are obtained as the cooling rate is increased from 2.0 × 10 10 to 1.0 × 10 13 K/s. The solidification point decreases with increasing cooling rate then drops rapidly at a cooling rate on the order of 10 12 K/s. These results are summarized in a continuous cooling transformation (CCT) diagram, in which regions corresponding the liquid, single-crystalline, polycrystalline and glassy structures appear.

Atomistic interpretation of the ac-dc crossover frequency in crystalline and glassy ionic conductors

NASA Astrophysics Data System (ADS)

Marple, M. A. T.; Avila-Paredes, H.; Kim, S.; Sen, S.

2018-05-01

A comprehensive analysis of the ionic dynamics in a wide variety of crystalline and glassy ionic conductors, obtained in recent studies using a combination of electrochemical impedance and nuclear magnetic resonance spectroscopic techniques, is presented. These results demonstrate that the crossover frequency, between the frequency-independent dc conductivity and the frequency-dependent ac conductivity, corresponds to the time scale of "successful" diffusive hops of the mobile ions between the trapping sites in the structure. These inter-site hops are typically compound in nature and consist of several elementary hops in the intervening region between the neighboring trapping sites.

Cooperativity and Heterogeneity in Plastic Crystals Studied by Nonlinear Dielectric Spectroscopy

NASA Astrophysics Data System (ADS)

Michl, M.; Bauer, Th.; Lunkenheimer, P.; Loidl, A.

2015-02-01

The glassy dynamics of plastic-crystalline cyclo-octanol and ortho-carborane, where only the molecular reorientational degrees of freedom freeze without long-range order, is investigated by nonlinear dielectric spectroscopy. Marked differences to canonical glass formers show up: While molecular cooperativity governs the glassy freezing, it leads to a much weaker slowing down of molecular dynamics than in supercooled liquids. Moreover, the observed nonlinear effects cannot be explained with the same heterogeneity scenario recently applied to canonical glass formers. This supports ideas that molecular relaxation in plastic crystals may be intrinsically nonexponential. Finally, no nonlinear effects were detected for the secondary processes in cyclo-octanol.

Atomistic interpretation of the ac-dc crossover frequency in crystalline and glassy ionic conductors.

PubMed

Marple, M A T; Avila-Paredes, H; Kim, S; Sen, S

2018-05-28

A comprehensive analysis of the ionic dynamics in a wide variety of crystalline and glassy ionic conductors, obtained in recent studies using a combination of electrochemical impedance and nuclear magnetic resonance spectroscopic techniques, is presented. These results demonstrate that the crossover frequency, between the frequency-independent dc conductivity and the frequency-dependent ac conductivity, corresponds to the time scale of "successful" diffusive hops of the mobile ions between the trapping sites in the structure. These inter-site hops are typically compound in nature and consist of several elementary hops in the intervening region between the neighboring trapping sites.

Heterogeneous dynamics of ionic liquids: A four-point time correlation function approach

NASA Astrophysics Data System (ADS)

Liu, Jiannan; Willcox, Jon A. L.; Kim, Hyung J.

2018-05-01

Many ionic liquids show behavior similar to that of glassy systems, e.g., large and long-lasted deviations from Gaussian dynamics and clustering of "mobile" and "immobile" groups of ions. Herein a time-dependent four-point density correlation function—typically used to characterize glassy systems—is implemented for the ionic liquids, choline acetate, and 1-butyl-3-methylimidazolium acetate. Dynamic correlation beyond the first ionic solvation shell on the time scale of nanoseconds is found in the ionic liquids, revealing the cooperative nature of ion motions. The traditional solvent, acetonitrile, on the other hand, shows a much shorter length-scale that decays after a few picoseconds.

Laboratory simulation of infrared astrophysical features. Ph.D. Thesis; [emission spectra of comets

NASA Technical Reports Server (NTRS)

Rose, L. A.

1977-01-01

Intermediate resolution emission spectroscopy was used to study a group of 9 terrestrial silicates, 1 synthetic silicate, 6 meteorites and 2 lunar soils; comparisons were made with the intermediate resolution spectra of Comet Kohoutek in order to determine which materials best simulate the 10um astrophysical feature. Mixtures of silicates which would yield spectra matching the spectrum of the comet in the 10um region include: (1) A hydrous layer lattice silicate in combination with a high temperature condensate; (2) an amorphous magnesium silicate in combination with a high temperature condensate and (3) glassy olivine and glassy anorthite in approximately equal proportions.

The valence bond glass phase

NASA Astrophysics Data System (ADS)

Tarzia, M.; Biroli, G.

2008-06-01

We show that a new glassy phase can emerge in the presence of strong magnetic frustration and quantum fluctuations. It is a valence bond glass (VBG). We study its properties solving the Hubbard-Heisenberg model on a Bethe lattice within the large-N limit introduced by Affleck and Marston. We work out the phase diagram that contains Fermi liquid, dimer and valence bond glass phases. This new glassy phase has no electronic or spin gap (although a pseudo-gap is observed), it is characterized by long-range critical valence bond correlations and is not related to any magnetic ordering. As a consequence, it is quite different from both valence bond crystals and spin glasses.

Some aspects of the thermal history of lunar glass.

NASA Technical Reports Server (NTRS)

Cooper, A. R.; Varshneya, A. K.; Sarkar, S. K.; Swift, J.; Klein, L.; Yen, F.

1972-01-01

Electron microprobe examination revealed that glassy lunar fragments had inclusions as well as boundaries between mineral glasses of different compositions. Glassy lunar spherules showed detectable heterogeneity less marked than that of the fragments. The room-temperature refractive indices and densities of the spherules are changed by heat-treating them at 500 to 700 C. The large increases (as much as 2% in density and 0.7% in index of refraction) are difficult to explain on the basis of classical glass-transition phenomena alone unless extremely rapid cooling rates are assumed. Further, the spherules darkened significantly when they were heated in air or a medium vacuum above 625 C.

Lubricant rheology applied to elastohydrodynamic lubrication

NASA Technical Reports Server (NTRS)

Winer, W. O.; Sanborn, D. M.

1977-01-01

Viscosity measurements in a high pressure rheometer, elastohydrodynamic simulator studies (including the development of a temperature measuring technique), and analytical fluid modeling for elastohydrodynamic contacts are described. The more recent research which is described concerns infrared temperature measurements in elastohydrodynamic contacts and the exploration of the glassy state of lubricants. A correlation, of engineering significance, was made between transient surface temperature measurements and surface roughness profiles. Measurements of glass transitions of lubricants and the study of the effect of rate processes on materials lead to the conclusion that typical lubricants go into the glassy state as they pass through the contact region of typical elastohydrodynamic contacts.

Effects of minor Cu and Si additions on glass forming ability and mechanical properties of Co-Fe-Ta-B Bulk metallic glass

NASA Astrophysics Data System (ADS)

Yazici, Ziya Ozgur; Hitit, Aytekin; Yalcin, Yilmaz; Ozgul, Metin

2016-01-01

Effect of Cu and Si substitutions for Co and B on the glass forming ability (GFA) of Co(43-x)CuxFe20Ta5.5B(31.5-x)Siy (x=0-1.5 and y=5-10) were systematically investigated by X-ray diffraction, optical microscopy, scanning electron microscopy, and differential scanning calorimetry. In order to evaluate the contribution of copper and silicon, appropriate amounts of copper and silicon were individually introduced to the base alloy composition. By using the effects of copper and silicon together, significant enhancement was obtained and the critical casting thickness (CCT) of the base alloy was increased three times from 2 mm to 6 mm. Moreover, mechanical properties of the alloys were examined by compression tests and Vickers hardness measurements. The compression test results revealed that the glassy alloys having enhanced GFA shows high strength of about 3500-4000 MPa. In addition, existence of (Co,Fe)2B and (Co,Fe)20.82Ta2.18B6 crystalline phases in glassy matrix influences the hardnesses of the alloys compared to monolitic glassy structure having hardness of about 1200 Hv.

Gold nanoparticles embedded electropolymerized thin film of pyrimidine derivative on glassy carbon electrode for highly sensitive detection of l-cysteine.

PubMed

Kannan, Ayyadurai; Sevvel, Ranganathan

2017-09-01

This paper demonstrates the fabrication of novel gold nanoparticles incorporated poly (4-amino-6-hydroxy-2-mercaptopyrimidine) (Nano-Au/Poly-AHMP) film modified glassy carbon electrode and it is employed for highly sensitive detection of l-cysteine (CYS). The modified electrode was characterized by scanning electron microscope (SEM), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). SEM images of modified electrode revealed the homogeneous distribution of gold nanoparticles on poly (4-amino-6-hydroxy-2-mercaptopyrimidine) thin film modified glassy carbon electrode. The modified electrode was successfully utilized for highly selective and sensitive determination of l-cysteine at physiological pH7.0. The present electrochemical sensor successfully resolved the voltammetric signals of ascorbic acid (AA) and l-cysteine with peak separation of 0.510V. To the best of our knowledge, this is the first report of larger peak separation between AA and CYS. Wide linear concentration ranges (2μM-500μM), low detection limit (0.020μM), an excellent reproducibility and stability are achieved for cysteine sensing with this Nano-Au/Poly-AHMP/GCE. Copyright © 2017 Elsevier B.V. All rights reserved.

Tellurium-nanowire-coated glassy carbon electrodes for selective and sensitive detection of dopamine.

PubMed

Tsai, Hsiang-Yu; Lin, Zong-Hong; Chang, Huan-Tsung

2012-05-15

Tellurium-nanowire-coated glassy carbon electrodes (TNGCEs) have been fabricated and employed for selective and sensitive detection of dopamine (DA). TNGCEs were prepared by direct deposition of tellurium nanowires, 600 ± 150 nm in length and 16 ± 3 nm in diameter, onto glassy carbon electrodes, which were further coated with Nafion to improve their selectivity and stability. Compared to the GCE, the TNGCE is more electroactive (by approximately 1.9-fold) for DA, and its selectivity toward DA over ascorbic acid (AA) and uric acid (UA) is also greater. By applying differential pulse voltammetry, at a signal-to-noise ratio of 3, the TNGCE provides a limit of detection of 1 nM for DA in the presence of 0.5mM AA and UA. Linearity (R(2)=0.9955) of the oxidation current at 0.19 V against the concentration of DA is found over the range 5 nM-1 μM. TNGCEs have been applied to determine the concentration of dopamine to be 0.59 ± 0.07 μM in PC12 cells. Copyright © 2012 Elsevier B.V. All rights reserved.

Tin, Bismuth, and Tin-Bismuth Alloy Electrodeposition from Chlorometalate Salts in Deep Eutectic Solvents.

PubMed

Vieira, Luciana; Burt, Jennifer; Richardson, Peter W; Schloffer, Daniel; Fuchs, David; Moser, Alwin; Bartlett, Philip N; Reid, Gillian; Gollas, Bernhard

2017-06-01

The electrodeposition of tin, bismuth, and tin-bismuth alloys from Sn II and Bi III chlorometalate salts in the choline chloride/ethylene glycol (1:2 molar ratio) deep eutectic solvent was studied on glassy carbon and gold by cyclic voltammetry, rotating disc voltammetry, and chronoamperometry. The Sn II -containing electrolyte showed one voltammetric redox process corresponding to Sn II /Sn 0 . The diffusion coefficient of [SnCl 3 ] - , detected as the dominating species by Raman spectroscopy, was determined from Levich and Cottrell analyses. The Bi III -containing electrolyte showed two voltammetric reduction processes, both attributed to Bi III /Bi 0 . Dimensionless current/time transients revealed that the electrodeposition of both Sn and Bi on glassy carbon proceeded by 3D-progressive nucleation at a low overpotential and changed to instantaneous at higher overpotentials. The nucleation rate of Bi on glassy carbon was considerably smaller than that of Sn. Elemental Sn and Bi were electrodeposited on Au-coated glass slides from their respective salt solutions, as were Sn-Bi alloys from a 2:1 Sn II /Bi III solution. The biphasic Sn-Bi alloys changed from a Bi-rich composition to a Sn-rich composition by making the deposition potential more negative.

In Situ Nanocalorimetric Investigations of Plasma Assisted Deposited Poly(ethylene oxide)-like Films by Specific Heat Spectroscopy.

PubMed

Madkou, Sherif; Melnichu, Iurii; Choukourov, Andrei; Krakovsky, Ivan; Biederman, Hynek; Schönhals, Andreas

2016-04-28

In recent years, highly cross-linked plasma polymers have started to unveil their potential in numerous biomedical applications in thin-film form. However, conventional diagnostic methods often fail due to their diverse molecular dynamics conformations. Here, glassy dynamics and the melting transition of thin PEO-like plasma assisted deposited (ppPEO) films (thickness 100 nm) were in situ studied by a combination of specific heat spectroscopy, utilizing a pJ/K sensitive ac-calorimeter chip, and composition analytical techniques. Different cross-linking densities were obtained by different plasma powers during the deposition of the films. Glassy dynamics were observed for all values of the plasma power. It was found that the glassy dynamics slows down with increasing the plasma power. Moreover, the underlying relaxation time spectra broaden indicating that the molecular motions become more heterogeneous with increasing plasma power. In a second set of the experiment, the melting behavior of the ppPEO films was studied. The melting temperature of ppPEO was found to decrease with increasing plasma power. This was explained by a decrease of the order in the crystals due to formation of chemical defects during the plasma process.

High temperature deformation of hot-pressed polycrystalline orthoenstatite. Ph.D. Thesis

NASA Technical Reports Server (NTRS)

Dehghan-Banadaki, A.

1983-01-01

Artificial hot pressed polycrystalline samples were prepared from purified powder of Bamble, Norway, orthoenstatite, (Mg0.86Fe0.14)SiO3. The uniaxial creep behavior of the polycrystalline orthoenstatite was studied over stress ranges of 10-180 MPa and temperatures of 1500-1700 K (0.82-0.93 T sub m) under two different oxygen fugacities, namely equilibrium (Mo-MoO2 buffer) and a reducing (graphite heating element) atmosphere, respectively. An intergranular glassy phase of different compositions with a cavitational creep deformation were observed. In the Mo-MoO2 buffer atmosphere with PO2 approx. 10 to the minus 11 power - 10 to the minus 13 power atmospheres, the results of an analytical electron microscopy analysis indicate that the glassy phases are richer in Ca and Al due to the residual impurities after hot pressing. In the reducing atmosphere with an oxygen fugacity of PO2 approx. 10 to the minus 3 power - 10 to the minus 25 power atmospheres, the results of analytical electron microscopy analysis indicate that the glassy phase is almost pure silica with the presence of free iron precipitate on grain facets and at triple junctions due to the reduction of bulk materials.

Electrochemical behavior of an antiviral drug acyclovir at fullerene-C(60)-modified glassy carbon electrode.

PubMed

Shetti, Nagaraj P; Malode, Shweta J; Nandibewoor, Sharanappa T

2012-12-01

Electrochemical oxidation of acyclovir at fullerene-C(60)-modified glassy carbon electrode has been investigated using cyclic and differential pulse voltammetry. In pH 7.4 phosphate buffer, acyclovir showed an irreversible oxidation peak at about 0.96V. The cyclic voltammetric results showed that fullerene-C(60)-modified glassy carbon electrode can remarkably enhance electrocatalytic activity towards the oxidation of acyclovir. The electrocatalytic behavior was further exploited as a sensitive detection scheme for the acyclovir determination by differential pulse voltammetry. Effects of anodic peak potential (E(p)/V), anodic peak current (I(p)/μA) and heterogeneous rate constant (k(0)) have been discussed. Under optimized conditions, the concentration range and detection limit were 9.0×10(-8) to 6.0×10(-6)M and 1.48×10(-8)M, respectively. The proposed method was applied to acyclovir determination in pharmaceutical samples and human biological fluids such as urine and blood plasma as a real sample. This method can also be employed in quality control and routine determination of drugs in pharmaceutical formulations. Copyright © 2012 Elsevier B.V. All rights reserved.

Determination of mutagenic amines in water and food samples by high pressure liquid chromatography with amperometric detection using a multiwall carbon nanotubes-glassy carbon electrode.

PubMed

Bueno, Ana María; Marín, Miguel Ángel; Contento, Ana María; Ríos, Ángel

2016-02-01

A chromatographic method, using amperometric detection, for the sensitive determination of six representative mutagenic amines was developed. A glassy carbon electrode (GCE), modified with multiwall carbon nanotubes (GCE-CNTs), was prepared and its response compared to a conventional glassy carbon electrode. The chromatographic method (HPLC-GCE-CNTs) allowed the separation and the determination of heterocyclic aromatic amines (HAAs) classified as mutagenic amines by the International Agency for Research of Cancer. The new electrode was systematically studied in terms of stability, sensitivity, and reproducibility. Statistical analysis of the obtained data demonstrated that the modified electrode provided better sensitivity than the conventional unmodified ones. Detection limits were in the 3.0 and 7.5 ng/mL range, whereas quantification limits ranged between 9.5 and 25.0 ng/mL were obtained. The applicability of the method was demonstrated by the determination of the amines in several types of samples (water and food samples). Recoveries indicate very good agreement between amounts added and those found for all HAAs (recoveries in the 92% and 105% range). Copyright © 2015 Elsevier Ltd. All rights reserved.

Square-wave stripping voltammetric determination of caffeic acid on electrochemically reduced graphene oxide-Nafion composite film.

PubMed

Filik, Hayati; Çetintaş, Gamze; Avan, Asiye Aslıhan; Aydar, Sevda; Koç, Serkan Naci; Boz, İsmail

2013-11-15

An electrochemical sensor composed of Nafion-graphene nanocomposite film for the voltammetric determination of caffeic acid (CA) was studied. A Nafion graphene oxide-modified glassy carbon electrode was fabricated by a simple drop-casting method and then graphene oxide was electrochemically reduced over the glassy carbon electrode. The electrochemical analysis method was based on the adsorption of caffeic acid on Nafion/ER-GO/GCE and then the oxidation of CA during the stripping step. The resulting electrode showed an excellent electrocatalytical response to the oxidation of caffeic acid (CA). The electrochemistry of caffeic acid on Nafion/ER-GO modified glassy carbon electrodes (GCEs) were studied by cyclic voltammetry and square-wave adsorption stripping voltammetry (SW-AdSV). At optimized test conditions, the calibration curve for CA showed two linear segments: the first linear segment increased from 0.1 to 1.5 and second linear segment increased up to 10 µM. The detection limit was determined as 9.1×10(-8) mol L(-1) using SW-AdSV. Finally, the proposed method was successfully used to determine CA in white wine samples. Copyright © 2013 Elsevier B.V. All rights reserved.

Radiation-induced defect centers in glass ceramics

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

Tsai, T.E.; Friebele, E.J.; Griscom, D.L.

1989-01-15

Electron spin resonance (ESR) was used to characterize the radiation-induced defect centers in low-thermal-expansion glass ceramics, including two types of Zerodur and Astrositall. The observed ESR spectra can be associated with different types of defect centers: a Zn/sup +/ center, several types of oxygen hole centers (OHCs), an aluminum-oxygen hole center (Al-OHC), an Fe/sup 3 +/ center, Ti/sup 3 +/ and Zr/sup 3 +/ centers, and three types of As centers. An Sb/sup 4 +/ center, which is not observed in Zerodur, is tentatively identified in Astrositall. From the effect of crystallization on the observed defect concentrations in Zerodur andmore » computer simulation of the spectral lines of some of the centers, we infer that among the nine defect centers observed in the Zerodurs, the As-associated centers are located in the glassy phase and/or at the interface between the glassy and crystalline phases, Zn/sup +/ and Al-OHC are in the crystalline phase, and the rest (including most of the OHCs) are in the glassy phase. Radiation-induced compaction in these materials appears to be related to the generation of OHCs in the glass phase.« less

Reaction of Rhyolitic Magma to its Interception by the IDDP-1 Well, Krafla, 2009

NASA Astrophysics Data System (ADS)

Saubin, É.; Kennedy, B.; Tuffen, H.; Villeneuve, M.; Watson, T.; Nichols, A. R.; Schipper, I.; Cole, J. W.; Mortensen, A. K.; Zierenberg, R. A.

2017-12-01

The unexpected encounter of rhyolitic magma during IDDP-1 geothermal borehole drilling at Krafla, Iceland in 2009, temporarily created the world's hottest geothermal well. This allowed new questions to be addressed. i) How does magma react to drilling? ii) Are the margins of a magma chamber suitable for long-term extraction of supercritical fluids? To investigate these questions, we aim to reconstruct the degassing and deformation behaviour of the enigmatic magma by looking for correlations between textures in rhyolitic material retrieved from the borehole and the recorded drilling data. During drilling, difficulties were encountered in two zones, at 2070 m and below 2093 m depth. Drilling parameters are consistent with the drill bit encountering a high permeability zone and the contact zone of a magma chamber, respectively. Magma was intercepted three times between 2101-2104.4 m depth, which culminated in an increase in standpipe pressure followed by a decrease in weight on bit interpreted as representing the ascent of magma within the borehole. Circulation returned one hour after the last interception, carrying cuttings of glassy particles, felsite with granophyre and contaminant clasts from drilling, which were sampled as a time-series for the following 9 hours. The nature of glassy particles in this time-series varied through time, with a decrease in the proportion of vesicular clasts and a commensurate increase in dense glassy clasts, transitioning from initially colourless to brown glass. Componentry data show a sporadic decrease in felsite (from 34 wt. %), an increase in glassy particles during the first two hours (from 63 wt. % to 94 wt. %) and an increase in contaminant clasts towards the end of the cutting retrieval period. These temporal variations are probably related to the magma body architecture and interactions with the borehole. Transition from vesicular to dense clasts suggests a change in the degassing process that could be related to an early degassing phase caused by drilling-induced decompressions followed by a fast ascent after the last magma interception. Additional data in terms of shape of clasts, vesicularity, density and water content within glassy particles will link textural data to drilling history in order to investigate degassing history, origin of clasts and quenching pressure.

Cell-adhesive RGD peptide-displaying M13 bacteriophage/PLGA nanofiber matrices for growth of fibroblasts.

PubMed

Shin, Yong Cheol; Lee, Jong Ho; Jin, Linhua; Kim, Min Jeong; Oh, Jin-Woo; Kim, Tai Wan; Han, Dong-Wook

2014-01-01

M13 bacteriophages can be readily fabricated as nanofibers due to non-toxic bacterial virus with a nanofiber-like shape. In the present study, we prepared hybrid nanofiber matrices composed of poly(lactic-co-glycolic acid, PLGA) and M13 bacteriophages which were genetically modified to display the RGD peptide on their surface (RGD-M13 phage). The surface morphology and chemical composition of hybrid nanofiber matrices were characterized by scanning electron microscopy (SEM) and Raman spectroscopy, respectively. Immunofluorescence staining was conducted to investigate the existence of M13 bacteriophages in RGD-M13 phage/PLGA hybrid nanofibers. In addition, the attachment and proliferation of three different types of fibroblasts on RGD-M13 phage/PLGA nanofiber matrices were evaluated to explore how fibroblasts interact with these matrices. SEM images showed that RGD-M13 phage/PLGA hybrid matrices had the non-woven porous structure, quite similar to that of natural extracellular matrices, having an average fiber diameter of about 190 nm. Immunofluorescence images and Raman spectra revealed that RGD-M13 phages were homogeneously distributed in entire matrices. Moreover, the attachment and proliferation of fibroblasts cultured on RGD-M13 phage/PLGA matrices were significantly enhanced due to enriched RGD moieties on hybrid matrices. These results suggest that RGD-M13 phage/PLGA matrices can be efficiently used as biomimetic scaffolds for tissue engineering applications.

Bayes linear covariance matrix adjustment

NASA Astrophysics Data System (ADS)

Wilkinson, Darren J.

1995-12-01

In this thesis, a Bayes linear methodology for the adjustment of covariance matrices is presented and discussed. A geometric framework for quantifying uncertainties about covariance matrices is set up, and an inner-product for spaces of random matrices is motivated and constructed. The inner-product on this space captures aspects of our beliefs about the relationship between covariance matrices of interest to us, providing a structure rich enough for us to adjust beliefs about unknown matrices in the light of data such as sample covariance matrices, exploiting second-order exchangeability and related specifications to obtain representations allowing analysis. Adjustment is associated with orthogonal projection, and illustrated with examples of adjustments for some common problems. The problem of adjusting the covariance matrices underlying exchangeable random vectors is tackled and discussed. Learning about the covariance matrices associated with multivariate time series dynamic linear models is shown to be amenable to a similar approach. Diagnostics for matrix adjustments are also discussed.

Caracterisation de l'effet du vieillissement en milieu aqueux sur les proprietes mecaniques de composites a matrice elastomere

NASA Astrophysics Data System (ADS)

Favre, Audrey

Rubber composites are widely used in several engineering fields, such as automotive, and more recently for inflatable dams and other innovative underwater applications. These rubber materials are composed by an elastomeric matrix while the reinforcing phase is a synthetic fabric. Since these components are expected to operate several years in water environment, their durability must be guaranteed. The use of rubber materials immersed in water is not new, in fact, these materials have been studied for almost one century. However, the knowledge on reinforced rubber composites immersed several years in water is still limited. In this work, investigations on reinforced rubbers were carried out in the framework of a research project in partnership with Alstom and Hydro-Quebec. The objective of this study was to identify rubber composites that could be used under water for long periods. Various rubber composites with ethylene-propylene-diene monomer (EPDM), silicone, EPDM/silicone and polychloroprene (Neoprene) matrices reinforced with E-glass fabric were studied. Thus, these materials were exposed to an accelerated ageing at 85 °C underwater for periods varying from 14 to 365 days. For comparison purposes, they were also immersed and aged one year at room temperature (21 °C). The impact of accelerated aging was estimated through three different characterization methods. Scanning electron microscopy (SEM) was first used to assess the quality of fiber-matrix interface. Then, water absorption tests were performed to quantify the rate of water absorption during immersion. Finally the evolution of the mechanical properties was followed by the determination of Young's modulus (E) and ultimate stress (sigmau) using a dedicated traction test. This analysis allowed to point out that the quality of the fiber-matrix interface was the main factor influencing the drop of the mechanical properties and their durability. Moreover, it was noticed that this interface could be improved by using appropriate coupling agent as confirmed by the silicone composite with treated fabric. It was also observed that fiber-matrix interface could be a place where high stresses were localized because of differential swelling leading to an important loss of mechanical properties. The results revealed very different behaviors from one composite to another. The accelerated aging of EPDM/silicone and Neoprene composites led to a rapid diminution of mechanical properties in only 14 days. Conversely, silicone composites showed a 20 % increase of mechanical properties after 75 days of immersion. EPDM composites exhibited an important variability from one sample to another. It can be concluded from this study that composites made from silicone matrix with treated E-glass result in a better durability underwater. Keywords: composite elastomer, accelerated ageing, immersion in the water

The Cultivation of Ivy. A Saga of the College in America.

ERIC Educational Resources Information Center

Thelin, John R

The popular image of the Ivy League is one of a slightly awesome bastion of the well-born, well-bred, and soon-to-be-powerful or, less charitably, a haven for "the effete, unAmerican, and hopelessly bookish." This pervasive idea of collegiate personality is analyzed, tracing the evolution of the Ivy League from an incongruous array of…

Human Benchmarking of Expert Systems. Literature Review

DTIC Science & Technology

1990-01-01

effetiveness of the development procedures used in order to predict whether the aplication of similar approaches will likely have effective and...they used in their learning and problem solving. We will describe these approaches later. Reasoning. Reasoning usually includes inference. Because to ... in the software engineering process. For example, existing approaches to software evaluation in the military are based on a model of conventional

Symetrie en energie des spectres de l'onde de densite de charge dans le 2-hydrogene seleniure de niobium

NASA Astrophysics Data System (ADS)

Behmand, Behnaz

Les mecanismes qui menent a la supraconductivite dans les supraconducteurs a haute temperature critique sont encore aujourd'hui mal compris contrairement a ceux dans les supraconducteurs conventionnels. Dans les hauts-Tc, certaines modulations de la densite d'etats electroniques coexistant avec la phase supraconductrice ont ete observees, ce qui engendre des questionnements sur leur role dans la supraconductivite. En fait, plusieurs types de modulation de la densite d'etats electroniques existent, comme par exemple l'onde de densite de charge et l'onde de densite de paires. Ces deux modulations, d'origines differentes et mesurables avec la technique de spectroscopie par effet tunnel, peuvent etre differenciees avec une etude de leur symetrie. Ce memoire consistera donc a presenter l'etude de la symetrie de l'onde de densite de charge dans le 2H-NbSe2 qui est presente dans la phase supraconductrice a 300 mK. Par contre, certaines difficultes liees au principe de mesure, soit l'effet de normalisation, nuisent a l'identification de cette symetrie. La methode, pour contourner ce probleme sera alors l'element clef de ce travail.

Accident D’Electrisation et Hemorragie Cerebro-Meningee : A Propos D’une Observation

PubMed Central

Chaibdraa, A.; Medjellakh, M.S.; Saouli, A.; Bentakouk, M.C.

2008-01-01

Summary L'électrisation est un évènement accidentel qui diffère des autres pathologies occasionnant des brûlures graves, à cause de ses spécificités qui traduisent d'une part la destruction du revêtement cutané, mais également les effets directs ou indirects du courant électrique sur tout tissu de l'organisme rencontré lors de son passage, en particulier le tissu nerveux. Les manifestations neurologiques centrales sont nombreuses, en relation avec les effets de l'électricité sur le parenchyme cérébral ou une lésion associée à l'électrisation. Nous rapportons l'observation d'une hémorragie cérébro-meningée survenant au 3ème jour d'une électrisation grave. Cette complication est bien documentée dans la littérature traitant des accidents d'électrisation post-foudroiement. N'ayant pas rencontré de cas similaire publié lors des accidents dus au courant industriel, nous présentons cette observation, qui soulève le problème du mécanisme physiopathologique de survenue, difficile à trancher. PMID:21991125

Nouvelles approches en theorie du champ moyen dynamique: le cas du pouvoir thermoelectrique et celui de l'effet orbital d'un champ magnetique

NASA Astrophysics Data System (ADS)

Arsenault, Louis-Francois

Les applications reliees a la generation d'energie motivent la recherche de materiaux ayant un fort pouvoir thermoelectrique (S). De plus, S nous renseigne sur certaines proprietes fondamentales des materiaux, comme, par exemple, la transition entre l'etat coherent et incoherent des quasi-particules lorsque la temperature augmente. Empiriquement, la presence de fortes interactions electron-electron peut mener a un pouvoir thermoelectrique geant. Nous avons donc etudie le modele le plus simple qui tient compte de ces fortes interactions, le modele de Hubbard. La theorie du champ moyen dynamique (DMFT) est tout indiquee dans ce cas. Nous nous sommes concentres sur un systeme tridimensionnel (3d) cubique a face centree (fcc), et ce, pour plusieurs raisons. A) Ce type de cristal est tres commun dans la nature. B) La DMFT donne de tres bons resultats en 3d et donc ce choix sert aussi de preuve de principe de la methode. C) Finalement, a cause de la frustration electronique intrinseque au fcc, celui-ci ne presente pas de symetrie particule-trou, ce qui est tres favorable a l'apparition d'une grande valeur de S. Ce travail demontre que lorsque le materiau est un isolant a demi-remplissage a cause des fortes interactions (isolant de Mott), il est possible d'obtenir de grands pouvoirs thermoelectriques en le dopant legerement. C'est un resultat pratique important. Du point de vue methodologique, nous avons montre comment la limite de frequence infinie de S et l'approche dite de Kelvin, qui considere la limite de frequence nulle avant la limite thermodynamique pour S, donnent des estimations fiables de la vraie limite continue (DC) dans les domaines de temperature appropriee. Ces deux approches facilitent grandement les calculs en court-circuit ant la necessite de recourir a de problematiques prolongements analytiques. Nous avons trouve que la methode de calcul a frequence infinie fonctionne bien lorsque les echelles d'energie sont relativement faibles. En d'autres termes, cette approche donne une bonne representation de S lorsque le systeme devient coherent. Les calculs montrent aussi que la formule Kelvin est precise lorsque la fonction spectrale des electrons devient incoherente, soit a plus haute temperature. Dans la limite Kelvin, S est essentiellement l'entropie par particule, tel que propose il y a longtemps. Nos resultats demontrent ainsi que la vision purement entropique de S est la bonne dans le regime incoherent, alors que dans le regime coherent, l'approche a frequence infinie est meilleure. Nous avons utilise une methode a la fine pointe, soit le Monte-Carlo quantique en temps continu pour resoudre la DMFT. Pour permettre une exploration rapide du diagramme de phase, nous avons du developper une nouvelle version de la methode des perturbations iterees pour qu'elle soit applicable aussi a forte interaction au-dela de la valeur critique de la transition de Mott. Un autre sujet a aussi ete aborde. L'effet orbital du champ magnetique dans les systemes electroniques fortement correles est une question tres importante et peu developpee. Cela est d'autant plus essentiel depuis la decouverte des oscillations quantiques dans les supraconducteurs a haute temperature (haut- Tc). Par desir de developper une methode la moins biaisee possible, nous avons derive la DMFT lorsqu'un champ se couplant a l'operateur energie cinetique par la substitution de Peierls est present. Ce type d'approche est necessaire pour comprendre entre autres l'effet de la physique de Mott sur des phenomenes tels que les oscillations quantiques. Nous avons obtenu un resultat tres important en demontrant rigoureusement que la relation d'auto-coherence de la DMFT et le systeme intermediaire d'impurete quantique restent les memes. L'effet du champ peut etre contenu dans la fonction de Green locale, ce qui constitue la grande difference avec le cas habituel. Ceci permet de continuer a utiliser les solutionneurs d'impuretes standards, qui sont de plus en plus puissants. Nous avons aussi developpe la methode pour le cas d'un empilement de plans bidimensionnels selon z, ce qui permet d'etudier l'effet orbital du champ dans des nanostructures et meme dans les materiaux massifs, si le nombre de plans est suffisant pour obtenir la limite tridimensionnelle. Mots cles : Pouvoir thermoelectrique, Theorie du Champ Moyen Dynamique, Modele de Hubbard, Effet orbital du champ magnetique, Electrons fortement correles, Materiaux quantiques, Theorie des perturbations iterees

Use of job-exposure matrices to estimate occupational exposure to pesticides: A review.

PubMed

Carles, Camille; Bouvier, Ghislaine; Lebailly, Pierre; Baldi, Isabelle

2017-03-01

The health effects of pesticides have been extensively studied in epidemiology, mainly in agricultural populations. However, pesticide exposure assessment remains a key methodological issue for epidemiological studies. Besides self-reported information, expert assessment or metrology, job-exposure matrices still appear to be an interesting tool. We reviewed all existing matrices assessing occupational exposure to pesticides in epidemiological studies and described the exposure parameters they included. We identified two types of matrices, (i) generic ones that are generally used in case-control studies and document broad categories of pesticides in a large range of jobs, and (ii) specific matrices, developed for use in agricultural cohorts, that generally provide exposure metrics at the active ingredient level. The various applications of these matrices in epidemiological studies have proven that they are valuable tools to assess pesticide exposure. Specific matrices are particularly promising for use in agricultural cohorts. However, results obtained with matrices have rarely been compared with those obtained with other tools. In addition, the external validity of the given estimates has not been adequately discussed. Yet, matrices would help in reducing misclassification and in quantifying cumulated exposures, to improve knowledge about the chronic health effects of pesticides.

Stochastic local operations and classical communication (SLOCC) and local unitary operations (LU) classifications of n qubits via ranks and singular values of the spin-flipping matrices

NASA Astrophysics Data System (ADS)

Li, Dafa

2018-06-01

We construct ℓ -spin-flipping matrices from the coefficient matrices of pure states of n qubits and show that the ℓ -spin-flipping matrices are congruent and unitary congruent whenever two pure states of n qubits are SLOCC and LU equivalent, respectively. The congruence implies the invariance of ranks of the ℓ -spin-flipping matrices under SLOCC and then permits a reduction of SLOCC classification of n qubits to calculation of ranks of the ℓ -spin-flipping matrices. The unitary congruence implies the invariance of singular values of the ℓ -spin-flipping matrices under LU and then permits a reduction of LU classification of n qubits to calculation of singular values of the ℓ -spin-flipping matrices. Furthermore, we show that the invariance of singular values of the ℓ -spin-flipping matrices Ω 1^{(n)} implies the invariance of the concurrence for even n qubits and the invariance of the n-tangle for odd n qubits. Thus, the concurrence and the n-tangle can be used for LU classification and computing the concurrence and the n-tangle only performs additions and multiplications of coefficients of states.

Matrix computations in MACSYMA

NASA Technical Reports Server (NTRS)

Wang, P. S.

1977-01-01

Facilities built into MACSYMA for manipulating matrices with numeric or symbolic entries are described. Computations will be done exactly, keeping symbols as symbols. Topics discussed include how to form a matrix and create other matrices by transforming existing matrices within MACSYMA; arithmetic and other computation with matrices; and user control of computational processes through the use of optional variables. Two algorithms designed for sparse matrices are given. The computing times of several different ways to compute the determinant of a matrix are compared.

Complex symmetric matrices with strongly stable iterates

NASA Technical Reports Server (NTRS)

Tadmor, E.

1985-01-01

Complex-valued symmetric matrices are studied. A simple expression for the spectral norm of such matrices is obtained, by utilizing a unitarily congruent invariant form. A sharp criterion is provided for identifying those symmetric matrices whose spectral norm is not exceeding one: such strongly stable matrices are usually sought in connection with convergent difference approximations to partial differential equations. As an example, the derived criterion is applied to conclude the strong stability of a Lax-Wendroff scheme.

Drug delivery to macrophages for the therapy of cancer and infectious diseases.

PubMed

Kirsh, R; Bugelski, P J; Poste, G

1987-01-01

The mechanisms by which mononuclear phagocytes discriminate between self and nonself, recognize foreign materials, senescent, damaged, old, or effete cells, and tumor cells are unknown. However, regardless of the mechanism(s) involved, once activated by the appropriate signal(s), macrophages are able to selectively recognize and destroy neoplastic cells in vitro and in vivo. Liposomes injected intravenously, in common with other particulate or polymeric matrices, localize preferentially in organs with high mononuclear phagocyte activity and in circulating blood monocytes. This behavior allows microparticulates to serve as a convenient system for the selective delivery of encapsulated drugs to cells of the mononuclear phagocyte series in vivo. Liposomes are a particularly attractive experimental system because of their capacity to incorporate a wide variety of water-soluble and lipid-soluble drugs. At this time, however, there is no reason to assume that a liposome-based drug delivery system will offer any significant therapeutic advantage compared to other microparticulate drug delivery systems. As in commercial development of any pharmaceutical preparation, considerations of cost-of-goods, shelf life, and acceptance of the formulation and dosing regimen by both physicians and patients will be of major importance in determining success and widespread clinical use. Liposomes containing macrophage-activating agents are highly effective at augmenting macrophage-mediated tumoricidal activity in vitro eradicating tumor metastasis in vivo, as well as protecting animals from a wide variety of microbial and viral infections. Although the demands of solving the scientific and technical problems associated with liposome development are substantial, the rapid rate of progress in biology and in pharmaceutical sciences enhances the prospect of success for at least several aspects of liposome-mediated drug delivery. The next few years will be crucial in determining whether the commercial development of liposomes is feasible or whether they will join the ranks of other drug carrier designs that have failed to fulfill their initial promise.

Calculation of controllability and observability matrices for special case of continuous-time multi-order fractional systems.

PubMed

Hassanzadeh, Iman; Tabatabaei, Mohammad

2017-03-28

In this paper, controllability and observability matrices for pseudo upper or lower triangular multi-order fractional systems are derived. It is demonstrated that these systems are controllable and observable if and only if their controllability and observability matrices are full rank. In other words, the rank of these matrices should be equal to the inner dimension of their corresponding state space realizations. To reduce the computational complexities, these matrices are converted to simplified matrices with smaller dimensions. Numerical examples are provided to show the usefulness of the mentioned matrices for controllability and observability analysis of this case of multi-order fractional systems. These examples clarify that the duality concept is not necessarily true for these special systems. Copyright © 2017 ISA. Published by Elsevier Ltd. All rights reserved.

Evidence for a glassy state in strongly driven carbon

DOE PAGES

Brown, C. R. D.; Gericke, D. O.; Cammarata, M.; ...

2014-06-09

Here, we report results of an experiment creating a transient, highly correlated carbon state using a combination of optical and x-ray lasers. Scattered x-rays reveal a highly ordered state with an electrostatic energy significantly exceeding the thermal energy of the ions. Strong Coulomb forces are predicted to induce nucleation into a crystalline ion structure within a few picoseconds. However, we observe no evidence of such phase transition after several tens of picoseconds but strong indications for an over-correlated fluid state. The experiment suggests a much slower nucleation and points to an intermediate glassy state where the ions are frozen closemore » to their original positions in the fluid.« less

The high temperature creep deformation of Si3N4-6Y2O3-2Al2O3

NASA Technical Reports Server (NTRS)

Todd, J. A.; Xu, Zhi-Yue

1988-01-01

The creep properties of silicon nitride containing 6 wt percent yttria and 2 wt percent alumina have been determined in the temperature range 1573 to 1673 K. The stress exponent, n, in the equation epsilon dot varies as sigma sup n, was determined to be 2.00 + or - 0.15 and the true activation energy was found to be 692 + or - 25 kJ/mol. Transmission electron microscopy studies showed that deformation occurred in the grain boundary glassy phase accompanied by microcrack formation and cavitation. The steady state creep results are consistent with a diffusion controlled creep mechanism involving nitrogen diffusion through the grain boundary glassy phase.

Glassiness versus Order in Densely Frustrated Josephson Arrays

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

Gupta, P.; Teitel, S.; Gingras, M.J.

1998-01-01

We carry out extensive Monte Carlo simulations of the Coulomb gas dual to the uniformly frustrated two-dimensional XY model, for a sequence of frustrations f converging to the irrational (3{minus}{radical}(5))/ 2. We find in these systems a sharp first order equilibrium phase transition to an ordered vortex structure at a T{sub c} which varies only slightly with f . This ordered vortex structure remains, in general, phase incoherent until a lower vortex pinning transition T{sub p}(f) that varies with f. We argue that the glassy behaviors reported for this model in earlier simulations are dynamic effects. {copyright} {ital 1997} {italmore » The American Physical Society}« less

Rheological observation of glassy dynamics of dilute polymer solutions near the coil-stretch transition in elongational flows.

PubMed

Sridhar, T; Nguyen, D A; Prabhakar, R; Prakash, J Ravi

2007-04-20

It has long been conjectured that the macroscopic dynamics of dilute polymer solutions may exhibit a glasslike slowdown caused by ergodicity breaking, in the vicinity of the coil-stretch transition in elongational flows. We report experimental observations using a filament stretching rheometer that confirm the existence of such glassy states. It is observed that different time-dependent elongational strain-rate profiles lead to a pronounced history dependence and aging effects within a narrow range of strain rates. The results have a direct bearing on the analysis and design of processes employing dilute polymer solutions, such as ink-jet printing, surface coating, and turbulent-drag reduction.

Elastic Heterogeneity in Metallic Glasses

NASA Astrophysics Data System (ADS)

Dmowski, W.; Iwashita, T.; Chuang, C.-P.; Almer, J.; Egami, T.

2010-11-01

When a stress is applied on a metallic glass it deforms following Hook’s law. Therefore it may appear obvious that a metallic glass deforms elastically. Using x-ray diffraction and anisotropic pair-density function analysis we show that only about (3)/(4) in volume fraction of metallic glasses deforms elastically, whereas the rest of the volume is anelastic and in the experimental time scale deform without resistance. We suggest that this anelastic portion represents residual liquidity in the glassy state. Many theories, such as the free-volume theory, assume the density of defects in the glassy state to be of the order of 1%, but this result shows that it is as much as a quarter.

Melt processing of Bi--2212 superconductors using alumina

DOEpatents

Holesinger, Terry G.

1999-01-01

Superconducting articles and a method of forming them, where the superconducting phase of an article is Bi.sub.2 Sr.sub.2 CaCu.sub.2 O.sub.y (Bi-2212). Alumina is combined with Bi-2212 powder or Bi-2212 precursor powder and, in order to form an intimate mixture, the mixture is melted and rapidly cooled to form a glassy solid. The glassy solid is comminuted and the resulting powder is combined with a carrier. An alternative to melting is to form the mixture of nanophase alumina and material having a particle size of less than about 10 microns. The powder, with the carrier, is melt processed to form a superconducting article.

Ion beam promoted lithium absorption in glassy polymeric carbon

NASA Astrophysics Data System (ADS)

Ila, D.; Zimmerman, R. L.; Jenkins, G. M.; Maleki, H.; Poker, D. B.

1995-12-01

Glassy Polymeric Carbon (GPC) samples prepared from a precursor possess accessible pore volume that depends on the heat treatment temperature. We have shown that lithium percolates without diffusion into the accessible pores of GPC samples immersed in a molten lithium salt bath at 700°C. Ion bombardment with 10 MeV Au atoms increases the total pore volume available for lithium occupation even for samples normally impermeable to lithium. The lithium concentration depth profile is measured using Li7(p,2α) nuclear reaction analysis. We will report on lithium percolation into GPC prepared at temperatures between 500°C and 1000°C and activated by a 10 MeV gold ion bombardment.

The effect of hydrogen content on ballistic transport behaviors in the Ni-Nb-Zr-H glassy alloys.

PubMed

Fukuhara, Mikio; Umemori, Yoshimasa

2012-01-01

The electronic transport behaviors of (Ni(0.39)Nb(0.25)Zr(0.35))(100-) (x)H(x) (0 ≤ x < 23.5) glassy alloys with subnanostructural icosahedral Zr(5)Nb(5)Ni(3) clusters have been studied as a function of hydrogen content. These alloys show semiconducting, electric current-induced voltage (Coulomb) oscillation and ballistic transport behaviors. Coulomb oscillation and ballistic transport occur at hydrogen contents between 6.7 and 13.5 at% and between 13.5 and 21.2 at%, respectively. These results suggest that the localization effect of hydrogen in the clusters plays an important role in various electron transport phenomena.

Electric resistivity and thermoelectricity of Ni-Nb-Zr and Ni-Nb-Zr-H glassy alloys

NASA Astrophysics Data System (ADS)

Fukuhara, Mikio; Inoue, Akihisa

2010-09-01

Electric resistivity ρ and thermoelectric power S of Ni 36Nb 24Zr 40 and (Ni 0.36Nb 0.24Zr 0.4) 90H 10 glassy alloys were investigated in temperature region between 1.5 and 300 K. After resistivity curves of both alloys increase gradually with decreasing temperature down to around 6 K, they dropped suddenly and then reached zero resistivity at 2.1 K, leading to superconductivity. Linear curve with negative TCR of ρ vs T2 and slight increase of S/ T in temperature region down to around 6 K clearly reveal Fermi-liquid phenomenon in electronic state for both alloys independent of hydrogen content.

The Effect of Hydrogen Content on Ballistic Transport Behaviors in the Ni-Nb-Zr-H Glassy Alloys

PubMed Central

Fukuhara, Mikio; Umemori, Yoshimasa

2012-01-01

The electronic transport behaviors of (Ni0.39Nb0.25Zr0.35)100−xHx (0 ≤ x < 23.5) glassy alloys with subnanostructural icosahedral Zr5Nb5Ni3 clusters have been studied as a function of hydrogen content. These alloys show semiconducting, electric current-induced voltage (Coulomb) oscillation and ballistic transport behaviors. Coulomb oscillation and ballistic transport occur at hydrogen contents between 6.7 and 13.5 at% and between 13.5 and 21.2 at%, respectively. These results suggest that the localization effect of hydrogen in the clusters plays an important role in various electron transport phenomena. PMID:22312246

Hollow fiber membranes and methods for forming same

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

Bhandari, Dhaval Ajit; McCloskey, Patrick Joseph; Howson, Paul Edward

2016-03-22

The invention provides improved hollow fiber membranes having at least two layers, and methods for forming the same. The methods include co-extruding a first composition, a second composition, and a third composition to form a dual layer hollow fiber membrane. The first composition includes a glassy polymer; the second composition includes a polysiloxane; and the third composition includes a bore fluid. The dual layer hollow fiber membranes include a first layer and a second layer, the first layer being a porous layer which includes the glassy polymer of the first composition, and the second layer being a polysiloxane layer whichmore » includes the polysiloxane of the second composition.« less

Dispersion of the refractive index of a samarium-doped Se{sup 95}Te{sup 5} chalcogenide glassy semiconductor

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

Atayeva, S. U., E-mail: seva-atayeva@mail.ru; Mekhtiyeva, S. I.; Isayev, A. I.

2015-07-15

The transmission spectrum of a Se{sup 95}Te{sup 5} chalcogenide glassy semiconductor doped with samarium (0.05, 0.1, 0.25, 0.5, and 1 at %) is studied; the Swanepoel method and the single-oscillator model are used to determine the oscillator energy E{sup 0}, dispersion energy E{sup d}, optical width of the band gap E{sup g}, and linear (n) and nonlinear (n{sup 2}) refractive indices. The changes in the values of these parameters as a result of doping are attributed to modification of the local structure and to a change in the concentration of defect states.

Fibrillation auriculaire et activité physique

PubMed Central

Bosomworth, N. John

2015-01-01

Résumé Objectif Examiner les données probantes portant sur les effets de divers niveaux d’activité physique sur l’incidence de fibrillation auriculaire (FA) dans la population générale et chez les athlètes d’endurance. Sources des données Une recherche a initialement été menée sur PubMed à l’aide des titres MeSH ou des mots-de-texte anglais (avec descripteur de zone de recherche TIAB [title and abstract]) atrial fibrillation et exercise ou physical activity ou athlet* ou sport*, sans filtre additionnel. Le système GRADE (grading of recommendations, assessment, development, and evaluation) a été utilisé pour tirer les conclusions au sujet de la qualité et du niveau de preuve. Sélection des études Aucune étude d’intervention n’est ressortie de la recherche. Les études d’observation ont alors été jugées acceptables et, bien que des études prospectives de cohortes à long terme de plus grande envergure auraient été préférables, des essais cas-témoins ou transversaux ont aussi été inclus dans cette révision. Synthèse Les données disponibles laissent croire à un lien proportionnel à la dose entre l’exercice plus intense et l’incidence réduite de FA chez les femmes. Il en va de même pour les hommes dont le niveau d’activité physique est de faible à modéré. Chez les hommes seulement, l’activité intense est associée à un risque accru de FA et ce, dans la plupart des études, mais pas la totalité d’entre elles. Ce risque est modéré, le rapport de risque instantané étant de 1,29 dans l’une des études de meilleure qualité. Le risque de FA chez la plupart des personnes régulièrement actives est plus faible que le risque observé dans la population sédentaire appariée. Conclusion La fibrillation auriculaire est probablement moins fréquente à mesure que le niveau d’activité physique augmente, la relation dose-réponse étant démontrable. À toutes les intensités, l’exercice doit être encouragé pour ses effets sur le bien-être physique et la réduction de la mortalité. Chez les hommes qui pratiquent des activités vigoureuses, les effets bénéfiques sur la FA pourraient disparaître et le risque pourrait surpasser celui observé dans la population sédentaire; cependant les données probantes à cet effet ne sont ni robustes ni constantes. Ces hommes devraient être mis au courant de cette hausse modeste du risque s’ils choisissent de poursuivre leurs activités physiques vigoureuses.

Almost commuting self-adjoint matrices: The real and self-dual cases

NASA Astrophysics Data System (ADS)

Loring, Terry A.; Sørensen, Adam P. W.

2016-08-01

We show that a pair of almost commuting self-adjoint, symmetric matrices is close to a pair of commuting self-adjoint, symmetric matrices (in a uniform way). Moreover, we prove that the same holds with self-dual in place of symmetric and also for paths of self-adjoint matrices. Since a symmetric, self-adjoint matrix is real, we get a real version of Huaxin Lin’s famous theorem on almost commuting matrices. Similarly, the self-dual case gives a version for matrices over the quaternions. To prove these results, we develop a theory of semiprojectivity for real C*-algebras and also examine various definitions of low-rank for real C*-algebras.

Electrochemical behavior of triflusal, aspirin and their metabolites at glassy carbon and boron doped diamond electrodes.

PubMed

Enache, Teodor Adrian; Fatibello-Filho, Orlando; Oliveira-Brett, Ana Maria

2010-08-01

The electrochemical behavior of triflusal (TRF) and aspirin (ASA), before and after hydrolysis in water and in alkaline medium using two different electrode surfaces, glassy carbon and boron doped diamond, was study by differential pulse voltammetry over a wide pH range. The hydrolysis products are 2-(hydroxyl)-4-(trifluoromethyl)-benzoic acid (HTB) for triflusal and salicylic acid (SA) for aspirin, which in vivo represent their main metabolites. The hydrolysis processes were also followed by spectrophotometry. The UV results showed complete hydrolysis after one hour for TRF and after two hours for ASA in alkaline solution. The glassy carbon electrode enables only indirect determination of TRF and ASA through the electrochemical detection of their hydrolysis products HTB and SA, respectively. The oxidation processes of HTB and SA are pH dependent and involve different numbers of electrons and protons. Moreover, the difference between the oxidation peak potential of SA and HTB was equal to 100 mV in the studied pH range from 1 to 8 due to the CF3 of the aromatic ring of HTB molecule. Due to its wider oxidation potential range, the boron doped diamond electrode was used to study the direct oxidation of TRF and ASA, as well as of their respective metabolites HTB and SA.

Structural and surface changes in glassy carbon due to strontium implantation and heat treatment

NASA Astrophysics Data System (ADS)

Odutemowo, O. S.; Malherbe, J. B.; Prinsloo, L. C.; Njoroge, E. G.; Erasmus, R.; Wendler, E.; Undisz, A.; Rettenmayr, M.

2018-01-01

There are still questions around the microstructure of glassy carbon (GC), like the observation of the micropores. These were proposed to explain the low density of GC. This paper explains the effect of ion bombardment (200 keV Sr+, 1 × 1016 Sr+/cm2 at RT) on the microstructure of GC. TEM and AFM show that micropores in pristine GC are destroyed leading to densification of GC from 1.42 g/cm3 to 2.03 g/cm3. The amorphisation of glassy carbon was also not complete with graphitic strands embedded within the GC. These were relatively few, as Raman analysis showed that the Sr implantation resulted in a typical amorphous Raman spectrum. Annealing of the sample at 900 °C only resulted in a slight recovery of the GC structure. AFM and SEM analysis showed that the surface of the sample became rougher after Sr implantation. The roughness increased after the sample was annealed at 600 °C due to segregation of Sr towards the surface of the GC. SEM measurements of a sample with both implanted and un-implanted edges after annealing at 900 °C, showed that the high temperature heat treatment did not affect the surface topography of un-irradiated GC.

Local thermal energy as a structural indicator in glasses.

PubMed

Zylberg, Jacques; Lerner, Edan; Bar-Sinai, Yohai; Bouchbinder, Eran

2017-07-11

Identifying heterogeneous structures in glasses-such as localized soft spots-and understanding structure-dynamics relations in these systems remain major scientific challenges. Here, we derive an exact expression for the local thermal energy of interacting particles (the mean local potential energy change caused by thermal fluctuations) in glassy systems by a systematic low-temperature expansion. We show that the local thermal energy can attain anomalously large values, inversely related to the degree of softness of localized structures in a glass, determined by a coupling between internal stresses-an intrinsic signature of glassy frustration-anharmonicity and low-frequency vibrational modes. These anomalously large values follow a fat-tailed distribution, with a universal exponent related to the recently observed universal [Formula: see text] density of states of quasilocalized low-frequency vibrational modes. When the spatial thermal energy field-a "softness field"-is considered, this power law tail manifests itself by highly localized spots, which are significantly softer than their surroundings. These soft spots are shown to be susceptible to plastic rearrangements under external driving forces, having predictive powers that surpass those of the normal modes-based approach. These results offer a general, system/model-independent, physical/observable-based approach to identify structural properties of quiescent glasses and relate them to glassy dynamics.

Effect of instantaneous and continuous quenches on the density of vibrational modes in model glasses.

PubMed

Lerner, Edan; Bouchbinder, Eran

2017-08-01

Computational studies of supercooled liquids often focus on various analyses of their "underlying inherent states"-the glassy configurations at zero temperature obtained by an infinitely fast (instantaneous) quench from equilibrium supercooled states. Similar protocols are also regularly employed in investigations of the unjamming transition at which the rigidity of decompressed soft-sphere packings is lost. Here we investigate the statistics and localization properties of low-frequency vibrational modes of glassy configurations obtained by such instantaneous quenches. We show that the density of vibrational modes grows as ω^{β} with β depending on the parent temperature T_{0} from which the glassy configurations were instantaneously quenched. For quenches from high temperature liquid states we find β≈3, whereas β appears to approach the previously observed value β=4 as T_{0} approaches the glass transition temperature. We discuss the consistency of our findings with the theoretical framework of the soft potential model, and contrast them with similar measurements performed on configurations obtained by continuous quenches at finite cooling rates. Our results suggest that any physical quench at rates sufficiently slower than the inverse vibrational time scale-including all physically realistic quenching rates of molecular or atomistic glasses-would result in a glass whose density of vibrational modes is universally characterized by β=4.

Volcanic Rocks As Targets For Astrobiology Missions

NASA Astrophysics Data System (ADS)

Banerjee, N.

2010-12-01

Almost two decades of study highlight the importance of terrestrial subaqueous volcanic rocks as microbial habitats, particularly in glass produced by the quenching of basaltic lava upon contact with water. On Earth, microbes rapidly begin colonizing glassy surfaces along fractures and cracks exposed to water. Microbial colonization of basaltic glass leads to enhanced alteration through production of characteristic granular and/or tubular bioalteration textures. Infilling of formerly hollow alteration textures by minerals enable their preservation through geologic time. Basaltic rocks are a major component of the Martian crust and are widespread on other solar system bodies. A variety of lines of evidence strongly suggest the long-term existence of abundant liquid water on ancient Mars. Recent orbiter, lander and rover missions have found evidence for the presence of transient liquid water on Mars, perhaps persisting to the present day. Many other solar system bodies, notably Europa, Enceladus and other icy satellites, may contain (or have once hosted) subaqueous basaltic glasses. The record of terrestrial glass bioalteration has been interpreted to extend back ~3.5 billion years and is widespread in modern oceanic crust and its ancient metamorphic equivalents. The terrestrial record of glass bioalteration strongly suggests that glassy or formerly glassy basaltic rocks on extraterrestrial bodies that have interacted with liquid water are high-value targets for astrobiological exploration.

Molecular dynamics in supercooled liquid and glassy states of antibiotics: azithromycin, clarithromycin and roxithromycin studied by dielectric spectroscopy. Advantages given by the amorphous state.

PubMed

Adrjanowicz, K; Zakowiecki, D; Kaminski, K; Hawelek, L; Grzybowska, K; Tarnacka, M; Paluch, M; Cal, K

2012-06-04

Antibiotics are chemical compounds of extremely important medical role. Their history can be traced back more than one hundred years. Despite the passing time and significant progress made in pharmacy and medicine, treatment of many bacterial infections without antibiotics would be completely impossible. This makes them particularly unique substances and explains the unflagging popularity of antibiotics within the medical community. Herein, using dielectric spectroscopy we have studied the molecular mobility in the supercooled liquid and glassy states of three well-known antibiotic agents: azithromycin, clarithromycin and roxithromycin. Dielectric studies revealed a number of relaxation processes of different molecular origin. Besides the primary α-relaxation, observed above the respective glass transition temperatures of antibiotics, two secondary relaxations in the glassy state were identified. Interestingly, the fragility index as well as activation energies of the secondary processes turned out to be practically the same for all three compounds, indicating probably much the same molecular dynamics. Long-term stability of amorphous antibiotics at room temperature was confirmed by X-ray diffraction technique, and calorimetric studies were performed to evaluate the basic thermodynamic parameters. Finally, we have also checked the experimental solubility advantages given by the amorphous form of the examined antibiotics.

A user-friendly model for spray drying to aid pharmaceutical product development.

PubMed

Grasmeijer, Niels; de Waard, Hans; Hinrichs, Wouter L J; Frijlink, Henderik W

2013-01-01

The aim of this study was to develop a user-friendly model for spray drying that can aid in the development of a pharmaceutical product, by shifting from a trial-and-error towards a quality-by-design approach. To achieve this, a spray dryer model was developed in commercial and open source spreadsheet software. The output of the model was first fitted to the experimental output of a Büchi B-290 spray dryer and subsequently validated. The predicted outlet temperatures of the spray dryer model matched the experimental values very well over the entire range of spray dryer settings that were tested. Finally, the model was applied to produce glassy sugars by spray drying, an often used excipient in formulations of biopharmaceuticals. For the production of glassy sugars, the model was extended to predict the relative humidity at the outlet, which is not measured in the spray dryer by default. This extended model was then successfully used to predict whether specific settings were suitable for producing glassy trehalose and inulin by spray drying. In conclusion, a spray dryer model was developed that is able to predict the output parameters of the spray drying process. The model can aid the development of spray dried pharmaceutical products by shifting from a trial-and-error towards a quality-by-design approach.

Mediatorless solar energy conversion by covalently bonded thylakoid monolayer on the glassy carbon electrode.

PubMed

Lee, Jinhwan; Im, Jaekyun; Kim, Sunghyun

2016-04-01

Light reactions of photosynthesis that take place in thylakoid membranes found in plants or cyanobacteria are among the most effective ways of utilizing light. Unlike most researches that use photosystem I or photosystem II as conversion units for converting light to electricity, we have developed a simple method in which the thylakoid monolayer was covalently immobilized on the glassy carbon electrode surface. The activity of isolated thylakoid membrane was confirmed by measuring evolving oxygen under illumination. Glassy carbon surfaces were first modified with partial or full monolayers of carboxyphenyl groups by reductive C-C coupling using 4-aminobenzoic acid and aniline and then thylakoid membrane was bioconjugated through the peptide bond between amine residues of thylakoid and carboxyl groups on the surface. Surface properties of modified surfaces were characterized by cyclic voltammetry, contact angle measurements, and electrochemical impedance spectroscopy. Photocurrent of 230 nA cm(-2) was observed when the thylakoid monolayer was formed on the mixed monolayer of 4-carboxylpheny and benzene at applied potential of 0.4V vs. Ag/AgCl. A small photocurrent resulted when the 4-carboxyphenyl full monolayer was used. This work shows the possibility of solar energy conversion by directly employing the whole thylakoid membrane through simple surface modification. Copyright © 2015 Elsevier B.V. All rights reserved.

Structural characterization and aging of glassy pharmaceuticals made using acoustic levitation.

PubMed

Benmore, Chris J; Weber, J K R; Tailor, Amit N; Cherry, Brian R; Yarger, Jeffery L; Mou, Qiushi; Weber, Warner; Neuefeind, Joerg; Byrn, Stephen R

2013-04-01

Here, we report the structural characterization of several amorphous drugs made using the method of quenching molten droplets suspended in an acoustic levitator. (13) C NMR, X-ray, and neutron diffraction results are discussed for glassy cinnarizine, carbamazepine, miconazole nitrate, probucol, and clotrimazole. The (13) C NMR results did not find any change in chemical bonding induced by the amorphization process. High-energy X-ray diffraction results were used to characterize the ratio of crystalline to amorphous material present in the glasses over a period of 8 months. All the glasses were stable for at least 6 months except carbamazepine, which has a strong tendency to crystallize within a few months. Neutron and X-ray pair distribution function analyses were applied to the glassy materials, and the results were compared with their crystalline counterparts. The two diffraction techniques yielded similar results in most cases and identified distinct intramolecular and intermolecular correlations. The intramolecular scattering was calculated based on the crystal structure and fit to the measured X-ray structure factor. The resulting intermolecular pair distribution functions revealed broad-nearest and next-nearest neighbor molecule-molecule correlations. © 2013 Wiley Periodicals, Inc. and the American Pharmacists Association J Pharm Sci 102:1290-1300, 2013. Copyright © 2013 Wiley Periodicals, Inc.

Tin, Bismuth, and Tin–Bismuth Alloy Electrodeposition from Chlorometalate Salts in Deep Eutectic Solvents

PubMed Central

Vieira, Luciana; Burt, Jennifer; Richardson, Peter W.; Schloffer, Daniel; Fuchs, David; Moser, Alwin; Bartlett, Philip N.; Reid, Gillian

2017-01-01

Abstract The electrodeposition of tin, bismuth, and tin–bismuth alloys from SnII and BiIII chlorometalate salts in the choline chloride/ethylene glycol (1:2 molar ratio) deep eutectic solvent was studied on glassy carbon and gold by cyclic voltammetry, rotating disc voltammetry, and chronoamperometry. The SnII‐containing electrolyte showed one voltammetric redox process corresponding to SnII/Sn0. The diffusion coefficient of [SnCl3]−, detected as the dominating species by Raman spectroscopy, was determined from Levich and Cottrell analyses. The BiIII‐containing electrolyte showed two voltammetric reduction processes, both attributed to BiIII/Bi0. Dimensionless current/time transients revealed that the electrodeposition of both Sn and Bi on glassy carbon proceeded by 3D‐progressive nucleation at a low overpotential and changed to instantaneous at higher overpotentials. The nucleation rate of Bi on glassy carbon was considerably smaller than that of Sn. Elemental Sn and Bi were electrodeposited on Au‐coated glass slides from their respective salt solutions, as were Sn–Bi alloys from a 2:1 SnII/BiIII solution. The biphasic Sn–Bi alloys changed from a Bi‐rich composition to a Sn‐rich composition by making the deposition potential more negative. PMID:28638772

Impedimetric PSA aptasensor based on the use of a glassy carbon electrode modified with titanium oxide nanoparticles and silk fibroin nanofibers.

PubMed

Benvidi, Ali; Banaei, Maryam; Tezerjani, Marzieh Dehghan; Molahosseini, Hosein; Jahanbani, Shahriar

2017-12-14

This article describes an impedimetric aptasensor for the prostate specific antigen (PSA), a widely accepted prostate cancer biomarker. A glassy carbon electrode (GCE) was modified with titanium oxide nanoparticles (TiO 2 ) and silk fibroin nanofiber (SF) composite. The aptasensor was obtained by immobilizing a PSA-binding aptamer on the AuNP-modified with 6-mercapto-1-hexanol. The single fabrication steps were characterized by cyclic voltammetry and electrochemical impedance spectroscopy. The assay has two linear response ranges (from 2.5 fg.mL -1 to 25 pg.mL -1 , and from 25 pg.mL -1 to 25 ng.mL -1 ) and a 0.8 fg.mL -1 detection limit. After optimization of experimental conditions, the sensor is highly selective for PSA over bovine serum albumin and lysozyme. It was successfully applied to the detection of PSA in spiked serum samples. Graphical abstract Schematic of the fabrication of an aptasensor for the prostate specific antigen (PSA). It is based on the use of a glassy carbon electrode modified with gold nanoparticles and titanium oxide-silk fibroin. The immobilization process of aptamer and interaction with PSA were followed by electrochemical impedance spectroscopy technique.

Electrochemical reduction of nalidixic acid at glassy carbon electrode modified with multi-walled carbon nanotubes.

PubMed

Patiño, Yolanda; Pilehvar, Sanaz; Díaz, Eva; Ordóñez, Salvador; De Wael, Karolien

2017-02-05

The aqueous phase electrochemical degradation of nalidixic acid (NAL) is studied in this work, using cyclic voltammetry (CV) and differential pulse voltammetry (DPV) as instrumental techniques. The promotional effect of multi-walled carbon nanotubes (MWCNT) on the performance of glassy carbon electrodes is demonstrated, being observed that these materials catalyze the NAL reduction. The effect of surface functional groups on MWCNT -MWCNT-COOH and MWCNT-NH 2 -was also studied. The modification of glassy carbon electrode (GCE) with MWCNT leads to an improved performance for NAL reduction following the order of MWCNT>MWCNT-NH 2 >MWCNT-COOH. The best behavior at MWCNT-GCE is mainly due to both the increased electrode active area and the enhanced MWCNT adsorption properties. The NAL degradation was carried out under optimal conditions (pH=5.0, deposition time=20s and volume of MWCNT=10μL) using MWCNT-GCE obtaining an irreversible reduction of NAL to less toxic products. Paramaters as the number of DPV cycles and the volume/area (V/A) ratio were optimized for maximize pollutant degradation. It was observed that after 15 DPV scans and V/A=8, a complete reduction was obtained, obtaining two sub-products identified by liquid chromatography-mass spectrometry (LC-MS). Copyright © 2016 Elsevier B.V. All rights reserved.

Effect of instantaneous and continuous quenches on the density of vibrational modes in model glasses

NASA Astrophysics Data System (ADS)

Lerner, Edan; Bouchbinder, Eran

2017-08-01

Computational studies of supercooled liquids often focus on various analyses of their "underlying inherent states"—the glassy configurations at zero temperature obtained by an infinitely fast (instantaneous) quench from equilibrium supercooled states. Similar protocols are also regularly employed in investigations of the unjamming transition at which the rigidity of decompressed soft-sphere packings is lost. Here we investigate the statistics and localization properties of low-frequency vibrational modes of glassy configurations obtained by such instantaneous quenches. We show that the density of vibrational modes grows as ωβ with β depending on the parent temperature T0 from which the glassy configurations were instantaneously quenched. For quenches from high temperature liquid states we find β ≈3 , whereas β appears to approach the previously observed value β =4 as T0 approaches the glass transition temperature. We discuss the consistency of our findings with the theoretical framework of the soft potential model, and contrast them with similar measurements performed on configurations obtained by continuous quenches at finite cooling rates. Our results suggest that any physical quench at rates sufficiently slower than the inverse vibrational time scale—including all physically realistic quenching rates of molecular or atomistic glasses—would result in a glass whose density of vibrational modes is universally characterized by β =4 .

An Easily Fabricated Electrochemical Sensor Based on a Graphene-Modified Glassy Carbon Electrode for Determination of Octopamine and Tyramine

PubMed Central

Zhang, Yang; Zhang, Meiqin; Wei, Qianhui; Gao, Yongjie; Guo, Lijuan; Al-Ghanim, Khalid A.; Mahboob, Shahid; Zhang, Xueji

2016-01-01

A simple electrochemical sensor has been developed for highly sensitive detection of octopamine and tyramine by electrodepositing reduced graphene oxide (ERGO) nanosheets onto the surface of a glassy carbon electrode (GCE). The electrocatalytic oxidation of octopamine and tyramine is individually investigated at the surface of the ERGO modified glassy carbon electrode (ERGO/GCE) by using cyclic voltammetry (CV) and differential pulse voltammetry (DPV). Several essential factors including the deposition cycle of reduced graphene oxide nanosheets and the pH of the running buffer were investigated in order to determine the optimum conditions. Furthermore, the sensor was applied to the quantification of octopamine and tyramine by DPV in the concentration ranges from 0.5 to 40 μM and 0.1 to 25 μM, respectively. In addition, the limits of detection of octopamine and tyramine were calculated to be 0.1 μM and 0.03 μM (S/N = 3), respectively. The sensor showed good reproducibility, selectivity and stability. Finally, the sensor successfully detected octopamine and tyramine in commercially available beer with satisfactory recovery ranges which were 98.5%–104.7% and 102.2%–103.1%, respectively. These results indicate the ERGO/GCE based sensor is suitable for the detection of octopamine and tyramine. PMID:27089341

Construction of an electrochemical sensor based on the electrodeposition of Au-Pt nanoparticles mixtures on multi-walled carbon nanotubes film for voltammetric determination of cefotaxime.

PubMed

Shahrokhian, Saeed; Rastgar, Shokoufeh

2012-06-07

Mixtures of gold-platinum nanoparticles (Au-PtNPs) are fabricated consecutively on a multi-walled carbon nanotubes (MWNT) coated glassy carbon electrode (GCE) by the electrodeposition method. The surface morphology and nature of the hybrid film (Au-PtNPs/MWCNT) deposited on glassy carbon electrodes is characterized by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) techniques. The modified electrode is used as a new and sensitive electrochemical sensor for the voltammetric determination of cefotaxime (CFX). The electrochemical behavior of CFX is investigated on the surface of the modified electrode using linear sweep voltammetry (LSV). The results of voltammetric studies exhibited a considerable improvement in the oxidation peak current of CFX compared to glassy carbon electrodes individually coated with MWCNT or Au-PtNPs. Under the optimized conditions, the modified electrode showed a wide linear dynamic range of 0.004-10.0 μM with a detection limit of 1.0 nM for the voltammetric determination of CFX. The modified electrode was successfully applied for the accurate determination of trace amounts of CFX in pharmaceutical and clinical preparations.

Temperature and frequency response of conductivity in Ag2S doped chalcogenide glassy semiconductor

NASA Astrophysics Data System (ADS)

Ojha, Swarupa; Das, Anindya Sundar; Roy, Madhab; Bhattacharya, Sanjib

2018-06-01

The electric conductivity of chalcogenide glassy semiconductor xAg2S-(1-x)(0.5S-0.5Te) has been presented here as a function of temperature and frequency. Formation of different nanocrystallites has been confirmed from X-ray diffraction study. It is also noteworthy that average size of nanocrystallites decreases with the increase of dislocation density. Dc conductivity data have been interpreted using Mott's model and Greaves's model in low and high temperature regions respectively. Ac conductivity above the room temperature has been analyzed using Meyer-Neldel (MN) conduction rule. It is interestingly noted that Correlated Barrier Hopping (CBH) model is the most appropriate conduction mechanism for x = 0.35, where pairs of charge carrier are considered to hop over the potential barrier between the sites via thermal activation. To interpret experimental data for x = 0.45, modified non-overlapping small polaron tunnelling (NSPT) model is supposed to be appropriate model due to tunnelling through grain boundary. The conductivity spectra at various temperatures have been analyzed using Almond-West Formalism (power law model). Scaling of conductivity spectra reveals that electrical relaxation process of charge carriers (polaron) is temperature independent but depends upon the composition of the present chalcogenide glassy system.

Mechanism of drug release from polymethacrylate-based extrudates and milled strands prepared by hot-melt extrusion.

PubMed

Albers, Jessica; Alles, Rainer; Matthée, Karin; Knop, Klaus; Nahrup, Julia Schulze; Kleinebudde, Peter

2009-02-01

The aim of the study was the formulation of solid dispersions of the poorly water-soluble drug celecoxib and a polymethacrylate carrier by hot-melt extrusion. The objectives were to elucidate the mechanism of drug release from obtained extrudates and milled strands addicted to the solid-state properties of the solid dispersions and to examine and eliminate stability problems occurring under storage, exposure of mechanical stress, and in vitro dissolution. Transparent extrudates containing up to 60% drug could be prepared with a temperature setting below the melting point of celecoxib. XRPD and DSC measurements indicated the formation of a glassy solid solution, where the drug is molecularly dispersed in the carrier. The amorphous state of the glassy solid solution could be maintained during the exposure of mechanical stress in a milling process, and was stable under storage for at least 6 months. Solid-state properties and SEM images of extrudates after dissolution indicated a carrier-controlled dissolution, whereby the drug is molecularly dispersed within the concentrated carrier layer. The glassy solid solution showed a 58-fold supersaturation in 0.1 N HCl within the first 10 min, which was followed by a recrystallization process. Recrystallization could be inhibited by an external addition of HPMC.

Decision Matrices: Tools to Enhance Middle School Engineering Instruction

ERIC Educational Resources Information Center

Gonczi, Amanda L.; Bergman, Brenda G.; Huntoon, Jackie; Allen, Robin; McIntyre, Barb; Turner, Sheri; Davis, Jen; Handler, Rob

2017-01-01

Decision matrices are valuable engineering tools. They allow engineers to objectively examine solution options. Decision matrices can be incorporated in K-12 classrooms to support authentic engineering instruction. In this article we provide examples of how decision matrices have been incorporated into 6th and 7th grade classrooms as part of an…

19 CFR 10.90 - Master records and metal matrices.

Code of Federal Regulations, 2011 CFR

2011-04-01

... 19 Customs Duties 1 2011-04-01 2011-04-01 false Master records and metal matrices. 10.90 Section... Master Records, and Metal Matrices § 10.90 Master records and metal matrices. (a) Consumption entries... made, of each master record or metal matrix covered thereby. (c) A bond on Customs Form 301, containing...

19 CFR 10.90 - Master records and metal matrices.

Code of Federal Regulations, 2013 CFR

2013-04-01

... 19 Customs Duties 1 2013-04-01 2013-04-01 false Master records and metal matrices. 10.90 Section... Master Records, and Metal Matrices § 10.90 Master records and metal matrices. (a) Consumption entries... made, of each master record or metal matrix covered thereby. (c) A bond on Customs Form 301, containing...

19 CFR 10.90 - Master records and metal matrices.

Code of Federal Regulations, 2014 CFR

2014-04-01

... 19 Customs Duties 1 2014-04-01 2014-04-01 false Master records and metal matrices. 10.90 Section... Master Records, and Metal Matrices § 10.90 Master records and metal matrices. (a) Consumption entries... made, of each master record or metal matrix covered thereby. (c) A bond on Customs Form 301, containing...

19 CFR 10.90 - Master records and metal matrices.

Code of Federal Regulations, 2012 CFR

2012-04-01

... 19 Customs Duties 1 2012-04-01 2012-04-01 false Master records and metal matrices. 10.90 Section... Master Records, and Metal Matrices § 10.90 Master records and metal matrices. (a) Consumption entries... made, of each master record or metal matrix covered thereby. (c) A bond on Customs Form 301, containing...

19 CFR 10.90 - Master records and metal matrices.

Code of Federal Regulations, 2010 CFR

2010-04-01

... 19 Customs Duties 1 2010-04-01 2010-04-01 false Master records and metal matrices. 10.90 Section... Master Records, and Metal Matrices § 10.90 Master records and metal matrices. (a) Consumption entries... made, of each master record or metal matrix covered thereby. (c) A bond on Customs Form 301, containing...

Crosslinked type II collagen matrices: preparation, characterization, and potential for cartilage engineering.

PubMed

Pieper, J S; van der Kraan, P M; Hafmans, T; Kamp, J; Buma, P; van Susante, J L C; van den Berg, W B; Veerkamp, J H; van Kuppevelt, T H

2002-08-01

The limited intrinsic repair capacity of articular cartilage has stimulated continuing efforts to develop tissue engineered analogues. Matrices composed of type II collagen and chondroitin sulfate (CS), the major constituents of hyaline cartilage, may create an appropriate environment for the generation of cartilage-like tissue. In this study, we prepared, characterized, and evaluated type 11 collagen matrices with and without CS. Type II collagen matrices were prepared using purified, pepsin-treated, type II collagen. Techniques applied to prepare type I collagen matrices were found unsuitable for type II collagen. Crosslinking of collagen and covalent attachment of CS was performed using 1-ethyl-3-(3-dimethyl aminopropyl)carbodiimide. Porous matrices were prepared by freezing and lyophilization, and their physico-chemical characteristics (degree of crosslinking, denaturing temperature, collagenase-resistance, amount of CS incorporated) established. Matrices were evaluated for their capacity to sustain chondrocyte proliferation and differentiation in vitro. After 7 d of culture, chondrocytes were mainly located at the periphery of the matrices. In contrast to type I collagen, type II collagen supported the distribution of cells throughout the matrix. After 14 d of culture, matrices were surfaced with a cartilagenous-like layer, and occasionally clusters of chondrocytes were present inside the matrix. Chondrocytes proliferated and differentiated as indicated by biochemical analyses, ultrastructural observations, and reverse transcriptase PCR for collagen types I, II and X. No major differences were observed with respect to the presence or absence of CS in the matrices.

Cocos nucifera Linn. (Palmae) husk fiber ethanolic extract: antioxidant capacity and electrochemical investigation.

PubMed

Oliveira, Monika Bezerra dos Santos; Valentim, Iara Barros; de Vasconcelos, Camila Calado; Omena, Cristhiane Maria Bazílio; Bechara, Etelvino José Henriques; da Costa, João Gomes; Freitas, Mikael de Lima; Sant'Ana, Antônio Euzébio Goulart; Goulart, Marília Oliveira Fonseca

2013-02-01

The present study aims to determine the antioxidant capacity of the ethanolic extracts of husk fiber of four coconut (Cocos nucifera L.) varieties (yellow dwarf, green dwarf, giant and hybrid) and to evaluate the electrochemical behavior of these extracts on a glassy carbon electrode and on a modified glassy carbon electrode. The highest values of total phenolic content were obtained for the hybrid (531 ± 24 mg GAE g(-1) dry extract) and yellow dwarf (501 ± 29 mg GAE g(-1) dry extract) varieties and the lowest was for the green dwarf variety with 58 ± 9 mg GAE g(-1) dry extract. The ability of the extracts to scavenge DPPH˙ radicals was in the order of giant > yellow dwarf > hybrid > green dwarf and the IC50 values varied from 8.6 to 55.9 μg mL(-1). All varieties showed reducing potential by the use of FRAP and CUPRAC methods, with the lowest performance obtained for the green dwarf variety. Additionally, through the use of mimetic biomembranes, ethanolic extracts of coconut husk were shown to protect lipids against oxidative damage independent of the variety. The main antioxidants identified in the extract of yellow dwarf variety by UPLC-MS were quercetin and catechin. Cyclic voltammetric studies of the ethanolic extracts on glassy carbon electrode confirmed the presence of easily oxidized compounds, and the high antioxidant capacity of the varieties. This capacity was expressed as mg quercetin equivalents g(-1) dry extract and ranged from 25.9 up to 53.5 mg QE g(-1). A poly-xanthurenic acid (poly-Xa)/multi-walled carbon nanotube (MWCNT) / glassy carbon modified electrode (poly-Xa/MWCNT/GCE) was used for this purpose. Our findings suggest that these extracts are potentially important antioxidant supplements for the everyday human diet, pharmaceutical and cosmetic industries, thereby aggregating value to the enormous amount of waste from the coconut industry, mostly used for burning purposes.

Heating-induced glass-glass and glass-liquid transformations in computer simulations of water.

PubMed

Chiu, Janet; Starr, Francis W; Giovambattista, Nicolas

2014-03-21

Water exists in at least two families of glassy states, broadly categorized as the low-density (LDA) and high-density amorphous ice (HDA). Remarkably, LDA and HDA can be reversibly interconverted via appropriate thermodynamic paths, such as isothermal compression and isobaric heating, exhibiting first-order-like phase transitions. We perform out-of-equilibrium molecular dynamics simulations of glassy water using the ST2 model to study the evolution of LDA and HDA upon isobaric heating. Depending on pressure, glass-to-glass, glass-to-crystal, glass-to-vapor, as well as glass-to-liquid transformations are found. Specifically, heating LDA results in the following transformations, with increasing heating pressures: (i) LDA-to-vapor (sublimation), (ii) LDA-to-liquid (glass transition), (iii) LDA-to-HDA-to-liquid, (iv) LDA-to-HDA-to-liquid-to-crystal, and (v) LDA-to-HDA-to-crystal. Similarly, heating HDA results in the following transformations, with decreasing heating pressures: (a) HDA-to-crystal, (b) HDA-to-liquid-to-crystal, (c) HDA-to-liquid (glass transition), (d) HDA-to-LDA-to-liquid, and (e) HDA-to-LDA-to-vapor. A more complex sequence may be possible using lower heating rates. For each of these transformations, we determine the corresponding transformation temperature as function of pressure, and provide a P-T "phase diagram" for glassy water based on isobaric heating. Our results for isobaric heating dovetail with the LDA-HDA transformations reported for ST2 glassy water based on isothermal compression/decompression processes [Chiu et al., J. Chem. Phys. 139, 184504 (2013)]. The resulting phase diagram is consistent with the liquid-liquid phase transition hypothesis. At the same time, the glass phase diagram is sensitive to sample preparation, such as heating or compression rates. Interestingly, at least for the rates explored, our results suggest that the LDA-to-liquid (HDA-to-liquid) and LDA-to-HDA (HDA-to-LDA) transformation lines on heating are related, both being associated with the limit of kinetic stability of LDA (HDA).

Heating-induced glass-glass and glass-liquid transformations in computer simulations of water

NASA Astrophysics Data System (ADS)

Chiu, Janet; Starr, Francis W.; Giovambattista, Nicolas

2014-03-01

Water exists in at least two families of glassy states, broadly categorized as the low-density (LDA) and high-density amorphous ice (HDA). Remarkably, LDA and HDA can be reversibly interconverted via appropriate thermodynamic paths, such as isothermal compression and isobaric heating, exhibiting first-order-like phase transitions. We perform out-of-equilibrium molecular dynamics simulations of glassy water using the ST2 model to study the evolution of LDA and HDA upon isobaric heating. Depending on pressure, glass-to-glass, glass-to-crystal, glass-to-vapor, as well as glass-to-liquid transformations are found. Specifically, heating LDA results in the following transformations, with increasing heating pressures: (i) LDA-to-vapor (sublimation), (ii) LDA-to-liquid (glass transition), (iii) LDA-to-HDA-to-liquid, (iv) LDA-to-HDA-to-liquid-to-crystal, and (v) LDA-to-HDA-to-crystal. Similarly, heating HDA results in the following transformations, with decreasing heating pressures: (a) HDA-to-crystal, (b) HDA-to-liquid-to-crystal, (c) HDA-to-liquid (glass transition), (d) HDA-to-LDA-to-liquid, and (e) HDA-to-LDA-to-vapor. A more complex sequence may be possible using lower heating rates. For each of these transformations, we determine the corresponding transformation temperature as function of pressure, and provide a P-T "phase diagram" for glassy water based on isobaric heating. Our results for isobaric heating dovetail with the LDA-HDA transformations reported for ST2 glassy water based on isothermal compression/decompression processes [Chiu et al., J. Chem. Phys. 139, 184504 (2013)]. The resulting phase diagram is consistent with the liquid-liquid phase transition hypothesis. At the same time, the glass phase diagram is sensitive to sample preparation, such as heating or compression rates. Interestingly, at least for the rates explored, our results suggest that the LDA-to-liquid (HDA-to-liquid) and LDA-to-HDA (HDA-to-LDA) transformation lines on heating are related, both being associated with the limit of kinetic stability of LDA (HDA).

Crystallization kinetics of Mg–Cu–Yb–Ca–Ag metallic glasses

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

Tsarkov, Andrey A., E-mail: tsarkov@misis.ru; WPI Advanced Institute for Materials Research, Tohoku University, Katahira 2-1-1, Aoba-Ku, Sendai 980-8577; Zanaeva, Erzhena N.

The paper presents research into a Mg–Cu–Yb system based metallic glassy alloys. Metallic glasses were prepared using induction melting and further injection on a spinning copper wheel. The effect of alloying by Ag and Ca on the glass forming ability and the kinetics of crystallization of Mg–Cu–Yb system based alloys were studied. The differential scanning calorimeter and X-ray diffractometer were used to investigate the kinetics of crystallization and the phase composition of the samples. An indicator of glass forming ability, effective activation energy of crystallization, and enthalpy of mixing were calculated. An increase of the Ca and Ag content hasmore » a positive effect on the glass forming ability, the effective activation energy of crystallization, and the enthalpy of mixing. The highest indicators of the glass forming ability and the thermal stability were found for alloys that contain both alloying elements. The Ag addition suppresses precipitation of the Mg{sub 2}Cu phase during crystallization. A dual-phase glassy-nanocrystalline Mg structure was obtained in Mg{sub 65}Cu{sub 25}Yb{sub 10} and Mg{sub 59.5}Cu{sub 22.9}Yb{sub 11}Ag{sub 6.6} alloys after annealing. Bulk samples with a composite glassy-crystalline structure were obtained in Mg{sub 59.5}Cu{sub 22.9}Yb{sub 11}Ag{sub 6.6} and Mg{sub 64}Cu{sub 21}Yb{sub 9.5}Ag{sub 5.5} alloys. A thermodynamic database for the Mg–Cu–Yb–Ca–Ag system was created to compare the process of crystallization of alloys with polythermal sections of the Mg–Cu–Yb–Ca–Ag phase diagram. - Highlights: • New alloy compositions based on Mg–Cu–Yb system were developed and investigated. • Increasing content of Ag and Ca leads to improving GFA. • Bulk samples with a composite glassy-crystalline structure were obtained. • Thermodynamic database for Mg–Cu–Yb–Ca–Ag system was created.« less

Structural state diagram of concentrated suspensions of jammed soft particles in oscillatory shear flow

NASA Astrophysics Data System (ADS)

Khabaz, Fardin; Cloitre, Michel; Bonnecaze, Roger T.

2018-03-01

In a recent study [Khabaz et al., Phys. Rev. Fluids 2, 093301 (2017), 10.1103/PhysRevFluids.2.093301], we showed that jammed soft particle glasses (SPGs) crystallize and order in steady shear flow. Here we investigate the rheology and microstructures of these suspensions in oscillatory shear flow using particle-dynamics simulations. The microstructures in both types of flows are similar, but their evolutions are very different. In both cases the monodisperse and polydisperse suspensions form crystalline and layered structures, respectively, at high shear rates. The crystals obtained in the oscillatory shear flow show fewer defects compared to those in the steady shear. SPGs remain glassy for maximum oscillatory strains less than about the yield strain of the material. For maximum strains greater than the yield strain, microstructural and rheological transitions occur for SPGs. Polydisperse SPGs rearrange into a layered structure parallel to the flow-vorticity plane for sufficiently high maximum shear rates and maximum strains about 10 times greater than the yield strain. Monodisperse suspensions form a face-centered cubic (FCC) structure when the maximum shear rate is low and hexagonal close-packed (HCP) structure when the maximum shear rate is high. In steady shear, the transition from a glassy state to a layered one for polydisperse suspensions included a significant induction strain before the transformation. In oscillatory shear, the transformation begins to occur immediately and with different microstructural changes. A state diagram for suspensions in large amplitude oscillatory shear flow is found to be in close but not exact agreement with the state diagram for steady shear flow. For more modest amplitudes of around one to five times the yield strain, there is a transition from a glassy structure to FCC and HCP crystals, at low and high frequencies, respectively, for monodisperse suspensions. At moderate frequencies, the transition is from glassy to HCP via an intermediate FCC phase.

Evaluation de L’Effet du Vieillissement des Equipages sur les Consequences du Decalage Horaire (Evaluation of Crew Members Aging on Jet-Lag Consequences)

DTIC Science & Technology

2000-08-01

Ergonomia , 1987, 30, 13 79- physique que psychologique. Cela tend A damontrer que 1393. dans des conditions militaires op~rationnelles, les 2...melatonin. Ergonomia , 1987, 30, 1379- 1393. 2 - BLOIS R, FEINBERG I., GAILLARD J.M., KUPFER D.J. and WEBB W.B. Sleep in normal and pathological aging

Electromagnetic Noise Interference and Compatibility

DTIC Science & Technology

1975-11-01

RADIO INTERFERENCE by C.Fengler 7 LES CHARGES ELECTROSTATIQUES ET LES PERTURBATIONS QU’ELLES ENTRAINENT DANS LES LIAISONS RADIOELECTRIQUES par...PAR LA TRANSMISSION DANS UN SYSTFJE INTEGRE AEROPORTE par r,.David et M.Vanneizel 31 Not available at time of priating Reference DIGITAL DATA...TRANSMISSION IN AIRCRAFT: EMC-PROBLEMS AND POSSIBLE SOLUTIONS by R.Rode 32 GENERATIONS El EFFETS DES TENSIONS PARASITES DE CONDUCTION ET DE RAVONNEMENT ENTRE

Impuretés et systèmes corrélés. Des chaînes aux cuprates supraconducteurs

NASA Astrophysics Data System (ADS)

Bobroff, J.

2005-01-01

Impurities and correlated systems Discovery of high TC superconductors has opened the new field of strongly correlated fermions physics. In these compounds, mostly transition metal oxides, strong correlations between electrons affect sharply their electronic properties. In order to determine accurately these correlations and their possible link with superconductivity, we study the effect of local defects such as non magnetic impurities. In fact, in the more simple case of insulating spin chains and ladders, these impurities induce a staggered magnetism in their neighborhood which reveals the underlying electronic correlations. Similar effects are observed in high TC superconductors, using local probes such as nuclear magnetic resonance. These observations allow to get a better understanding of both normal and superconducting state of these oxides, both full of surprises. La découverte des supraconducteurs à haute température critique a ouvert la voie à une nouvelle physique, celle des fermions fortement corrélés. Dans ces systèmes, le plus souvent des oxydes de métaux de transition, les fortes corrélations entre électrons affectent profondément leurs propriétés électroniques et induisent de nouveaux états originaux : liquides de spins, supraconductivité, etc. Pour mesurer ces corrélations et ainsi déterminer leur lien éventuel avec la supraconductivité, nous proposons d'étudier l'effet de défauts ponctuels tels que des impuretés non magnétiques. En effet, dans le cas plus simple de chaînes ou d'échelles de spin isolantes, ces impuretés induisent dans leur voisinage immédiat un magnétisme alterné révélateur des corrélations électroniques. Des effets semblables sont observés dans les supraconducteurs à haute température critique, grâce à des sondes locales comme la résonance magnétique nucléaire. Ces observations permettent de mieux comprendre à la fois l'état normal et supraconducteur de ces oxydes, tous deux riches en surprises.

Les hémodialysés HVC sont-ils vraiment des patients difficiles à traiter?

PubMed Central

Krati, Khadija; Cherquaoui, Hind; Oubaha, Sofia; Samlani, Zouhour

2015-01-01

L'hépatite C demeure la principale infection virale chez l'hémodialysé, dont la prise en charge thérapeutique ainsi que la gestion de ses effets secondaires restent difficiles. Il s'agit d'une étude rétrospective portant sur tous les patients atteints d'hépatite C chronique ayant une insuffisance rénale chronique sous hémodialyse, suivis au service de gastroentérologie au CHU Mohamed VI de Marrakech sur une période de Janvier 2004 à Décembre 2014. Sur un total de 355 cas d'hépatite virale C, 13 patients étaient hémodialysés (3,66%). Dix patients ont été traités, soit 76,94% des cas. Le traitement n’était pas indiqué chez 2 patients ayant une fibrose minime sans cytolyse. Il était contre-indiqué chez une patiente multitarée. Deux malades ont eu une réponse virologique rapide et 5 une réponse virologique précoce. Le taux de réponse virologique soutenue était de 40%, 30% des patients étaient non répondeurs. Le traitement fut arrêté chez 2 patientes pour effets secondaires sévères. Un seul patient a été candidat à une transplantation rénale. En analyse multivariée, la réponse virologique soutenue a été significativement associée à certains facteurs prédictifs de bonne réponse thérapeutique: Age jeune ≤40 ans (P=0,0057), fibrose minime F1-F2 (P=0,03), génotype non 1 (P=0,0064), charge virale préthérapeutique <800000 UI/ml (P=0,013), et l'absence d'arrêt thérapeutique (P=0,028). La gestion efficace des effets secondaires du traitement de HVC permet d'obtenir chez l'hémodialysé un taux de réponse virologique soutenue avoisinant celui de la population générale. PMID:27022433

Durcissement superficiel de la fonte grise Ft25 induit par un traitement de surface dans le moule

NASA Astrophysics Data System (ADS)

Bouitna, Mohamed; Boutarek-Zaourar, Naïma; Mansour, Samir; Chentouf, Samir Mourad; Mossang, Eric

2018-02-01

L'objectif de cette étude est la consolidation en surface de la fonte grise lamellaire Ft25 par un dépôt riche en manganèse en développant une méthode combinant en une seule opération l'élaboration et le traitement de surface dans le moule. Les effets de la granulométrie du ferro-manganèse (80 % Mn + 20 % Fe), ainsi que l'épaisseur des pièces en fontes sur les couches formées ont été étudiés. On a retenu trois granulométries du ferro-manganèse de 0,18 mm, 0,25 mm et 0,5 mm pour le traitement des pièces en fontes présentant des épaisseurs de 25 mm, 100 mm et 200 mm. Parmi les résultats obtenus, on distingue une consolidation des propriétés en surface induite par la formation d'une couche riche en manganèse continue et homogène. L'effet de la granulométrie du ferro-manganèse sur l'épaisseur de la couche traitée a été mis en évidence. La variation de l'épaisseur des couches formées diminue avec l'augmentation de la granulométrie du ferro-manganèse. Pour une pièce de 100 mm d'épaisseur, la couche formée est estimée à 350 μm pour une granulométrie de 0,18 alors qu'elle n'est que de 180 μm pour une granulométrie de 0,5. L'effet de l'épaisseur de la pièce n'est en revanche pas assez prononcé sur la taille des couches formées. Une amélioration nette de la résistance, à l'usure de la fonte traitée en relation avec les transformations en surface, a été mise en évidence.

Les neuropathies liées au VIH/SIDA: une étude clinique chez les patients infectés par le VIH au Centre d'Excellence VIH/SIDA de l'Université de Lubumbashi

PubMed Central

Kabongo, Joe Katabwa; Kaputu-Kalala-Malu, Célestin; Luboya, Oscar; Mutombo, Valerien; Ntambwe, Abel; Mapatano, Mala Ali; Mukendi, Kavulu Mayamba

2015-01-01

Introduction En vue d'améliorer la prise en charge des patients souffrant de neuropathie (NP) associées à l'infection HIV, nous avons essayé de déterminer le profil clinique des personnes souffrant de NP au cours du suivi thérapeutique de leur infection HIV. Méthodes Il s'agit d'une étude transversale (n= 101) menée au centre d'excellence depuis 1 an. Notre analyse est essentiellement clinique. Par un examen clinique minutieux, nous avons recherché tous les symptômes et signes cliniques des NP. Subjectivement, les douleurs dominent le tableau. Pour affiner leur diagnostic, nous avons utilisé l’échelle DN4 (Diagnostic des douleurs neuropathiques) et l’échelle EVA (Evaluation de la gravité des douleurs). Nous avons ensuite analysé nos données en fonction de certains autres facteurs épidémiologiques tels que le taux des CD4, le traitement anti-HIV etc. Résultats Les 101 patients représentent 3,12% de la cohorte générale; 53,3% des patients présentent une abolition des réflexes ostéotendineux des membres inférieurs; 77,89% présentent une hypoesthésie thermo algique en chaussette et en gants; 25% ont présenté une amyotrophie des membres inférieurs; 76,5% ont été soumis à un traitement antirétroviral contenant la stavudine; 11,7% ont pris la didanosine (DDI) et Abacavir (ABC). 84% ont une moyenne de CD4 de 292 cel/mm3. Conclusion La NP altère la qualité de vie de nos patients et diminue l'adhérence au traitement antirétroviral. Plusieurs facteurs sont incriminés dans la survenue de la NP, l'effet direct des antirétroviraux, l'effet inflammatoire dysimmunitaire, l'effet infectieux lié aux infections opportunistes. D'autres facteurs seront recherchés et analysés ultérieurement. PMID:26185582

Matrices. New Topics for Secondary School Mathematics: Materials and Software.

ERIC Educational Resources Information Center

North Carolina School of Science and Mathematics. Dept. of Mathematics and Computer Science.

This material on matrices is part of "Introduction to College Mathematics" (ICM), designed to prepare high school students who have students who have completed algebra II for the variety of mathematics they will encounter in college and beyond. The concept goals of this unit are to use matrices to model real-world phenomena, to use matrices as…

Generalized matrix summability of a conjugate derived Fourier series.

PubMed

Mursaleen, M; Alotaibi, Abdullah

2017-01-01

The study of infinite matrices is important in the theory of summability and in approximation. In particular, Toeplitz matrices or regular matrices and almost regular matrices have been very useful in this context. In this paper, we propose to use a more general matrix method to obtain necessary and sufficient conditions to sum the conjugate derived Fourier series.

Rhotrix Vector Spaces

ERIC Educational Resources Information Center

Aminu, Abdulhadi

2010-01-01

By rhotrix we understand an object that lies in some way between (n x n)-dimensional matrices and (2n - 1) x (2n - 1)-dimensional matrices. Representation of vectors in rhotrices is different from the representation of vectors in matrices. A number of vector spaces in matrices and their properties are known. On the other hand, little seems to be…

Commutative semigroups of real and complex matrices. [with use of the jordan form

NASA Technical Reports Server (NTRS)

Brown, D. R.

1974-01-01

The computation of divergence is studied. Covariance matrices to be analyzed admit a common diagonalization, or even triangulation. Sufficient conditions are given for such phenomena to take place, the arguments cover both real and complex matrices, and are not restricted to Hermotian or other special forms. Specifically, it is shown to be sufficient that the matrices in question commute in order to admit a common triangulation. Several results hold in the case that the matrices in question form a closed and bounded set, rather than only in the finite case.

Field matric potential sensor

DOEpatents

Hubbell, Joel M.; Sisson, James B.

2001-01-01

A method of determining matric potential of a sample, the method comprising placing the sample in a container, the container having an opening; and contacting the sample with a tensiometer via the opening. An apparatus for determining matric potential of a sample, the apparatus comprising a housing configured to receive a sample; a portable matric potential sensing device extending into the housing and having a porous member; and a wall closing the housing to insulate the sample and at least a portion of the matric potential sensing device including the porous member.

The underexposed role of food matrices in probiotic products: Reviewing the relationship between carrier matrices and product parameters.

PubMed

Flach, Joost; van der Waal, Mark B; van den Nieuwboer, Maurits; Claassen, Eric; Larsen, Olaf F A

2017-06-13

Probiotic microorganisms are increasingly incorporated into food matrices in order to confer proposed health benefits on the consumer. It is important that the health benefits, sensory properties, shelf-life and probiotic gastrointestinal tract (GIT) survival of these products are carefully balanced as they determine functionality and drive consumer acceptance. The strain-specific effects of probiotic species are imperative in this process but carrier matrices may play a pivotal role as well. This study therefore recapitulates the wealth of knowledge on carrier matrices and their interaction with probiotic strains. The most substantiated carrier matrices, factors that influence probiotic functionality and matrix effects on shelf-life, GIT survival and clinical efficacy are reviewed. Results indicate that carrier matrices have a significant impact on the quality of probiotic products. Matrix components, such as proteins, carbohydrates and flavoring agents are shown to alter probiotic efficacy and viability. In vivo studies furthermore revealed strain-dependent matrix effects on the GIT survival of probiotic bacteria. However, only a limited number of studies have specifically addressed the effects of carrier matrices on the aforementioned product-parameters; most studies seem to focus solely on the strain-specific effects of probiotic microorganisms. This hampers the innovation of probiotic products. More human studies, comparing not only different probiotic strains but different carrier matrices as well, are needed to drive the innovation cycle.

Electrospun Zein/PCL Fibrous Matrices Release Tetracycline in a Controlled Manner, Killing Staphylococcus aureus Both in Biofilms and Ex Vivo on Pig Skin, and are Compatible with Human Skin Cells.

PubMed

Alhusein, Nour; Blagbrough, Ian S; Beeton, Michael L; Bolhuis, Albert; De Bank, Paul A

2016-01-01

To investigate the destruction of clinically-relevant bacteria within biofilms via the sustained release of the antibiotic tetracycline from zein-based electrospun polymeric fibrous matrices and to demonstrate the compatibility of such wound dressing matrices with human skin cells. Zein/PCL triple layered fibrous dressings with entrapped tetracycline were electrospun. The successful entrapment of tetracycline in these dressings was validated. The successful release of bioactive tetracycline, the destruction of preformed biofilms, and the viability of fibroblast (FEK4) cells were investigated. The sustained release of tetracycline from these matrices led to the efficient destruction of preformed biofilms from Staphylococcus aureus MRSA252 in vitro, and of MRSA252 and ATCC 25923 bacteria in an ex vivo pig skin model using 1 × 1 cm square matrices containing tetracycline (30 μg). Human FEK4 cells grew normally in the presence of these matrices. The ability of the zein-based matrices to destroy bacteria within increasingly complex in vitro biofilm models was clearly established. An ex vivo pig skin assay showed that these matrices, with entrapped tetracycline, efficiently kill bacteria and this, combined with their compatibility with a human skin cell line suggest these matrices are well suited for applications in wound healing and infection control.

Core-shell alginate-ghatti gum modified montmorillonite composite matrices for stomach-specific flurbiprofen delivery.

PubMed

Bera, Hriday; Ippagunta, Sohitha Reddy; Kumar, Sanoj; Vangala, Pavani

2017-07-01

Novel alginate-arabic gum (AG) gel membrane coated alginate-ghatti gum (GG) modified montmorillonite (MMT) composite matrices were developed for intragastric flurbiprofen (FLU) delivery by combining floating and mucoadhesion mechanisms. The clay-biopolymer composite matrices containing FLU as core were accomplished by ionic-gelation technique. Effects of polymer-blend (alginate:GG) ratios and crosslinker (CaCl 2 ) concentrations on drug entrapment efficiency (DEE, %) and cumulative drug release after 8h (Q 8h , %) were studied to optimize the core matrices by a 3 2 factorial design. The optimized matrices (F-O) demonstrated DEE of 91.69±1.43% and Q 8h of 74.96±1.56% with minimum errors in prediction. The alginate-AG gel membrane enveloped optimized matrices (F-O, coated) exhibited superior buoyancy, better ex vivo mucoadhesion and slower drug release rate. The drug release profile of FLU-loaded uncoated and coated optimized matrices was best fitted in Korsmeyer-Peppas model with anomalous diffusion and case-II transport driven mechanism, respectively. The uncoated and coated matrices containing FLU were also characterized for drug-excipients compatibility, drug crystallinity, thermal behaviour and surface morphology. Thus, the newly developed alginate-AG gel membrane coated alginate-GG modified MMT composite matrices are appropriate for intragastric delivery of FLU over an extended period of time with improved therapeutic benefits. Copyright © 2017 Elsevier B.V. All rights reserved.

Glassy phases and driven response of the phase-field-crystal model with random pinning.

PubMed

Granato, E; Ramos, J A P; Achim, C V; Lehikoinen, J; Ying, S C; Ala-Nissila, T; Elder, K R

2011-09-01

We study the structural correlations and the nonlinear response to a driving force of a two-dimensional phase-field-crystal model with random pinning. The model provides an effective continuous description of lattice systems in the presence of disordered external pinning centers, allowing for both elastic and plastic deformations. We find that the phase-field crystal with disorder assumes an amorphous glassy ground state, with only short-ranged positional and orientational correlations, even in the limit of weak disorder. Under increasing driving force, the pinned amorphous-glass phase evolves into a moving plastic-flow phase and then, finally, a moving smectic phase. The transverse response of the moving smectic phase shows a vanishing transverse critical force for increasing system sizes.

Energy barriers, entropy barriers, and non-Arrhenius behavior in a minimal glassy model.

PubMed

Du, Xin; Weeks, Eric R

2016-06-01

We study glassy dynamics using a simulation of three soft Brownian particles confined to a two-dimensional circular region. If the circular region is large, the disks freely rearrange, but rearrangements are rarer for smaller system sizes. We directly measure a one-dimensional free-energy landscape characterizing the dynamics. This landscape has two local minima corresponding to the two distinct disk configurations, separated by a free-energy barrier that governs the rearrangement rate. We study several different interaction potentials and demonstrate that the free-energy barrier is composed of a potential-energy barrier and an entropic barrier. The heights of both of these barriers depend on temperature and system size, demonstrating how non-Arrhenius behavior can arise close to the glass transition.

Communication: Effect of density on the physical aging of pressure-densified polymethylmethacrylate

NASA Astrophysics Data System (ADS)

Casalini, R.; Roland, C. M.

2017-09-01

The rate of physical aging of glassy polymethylmethacrylate (PMMA), followed from the change in the secondary relaxation with aging, is found to be independent of the density, the latter controlled by the pressure during glass formation. Thus, the aging behavior of the secondary relaxation is the same whether the glass is more compacted or less dense than the corresponding equilibrium liquid. This equivalence in aging of glasses formed under different pressures indicates that local packing is the dominant variable governing the glassy dynamics. The fact that pressure densification yields different glass structures is at odds with a model for non-associated materials having dynamic properties exhibited by PMMA, such as density scaling of the relaxation time and isochronal superposition of the relaxation dispersion.

Analysis of elemental maps from glaze to body of ancient Chinese Jun and Ru porcelain by micro-X-ray fluorescence

NASA Astrophysics Data System (ADS)

Cheng, Lin; Li, Rongwu; Pan, Qiuli; Li, Guoxia; Zhao, Weijuan; Liu, Zhiguo

2009-01-01

The reasons how the middle layer of Ru and Jun porcelain between the glaze and body came into being are still not completely understood. Here, elemental maps from the glaze to the body of pieces of ancient Chinese Ru and Jun porcelain were analyzed by micro-X-ray fluorescence. The results show the middle layer was probably formed by the chemical composition of the glaze turning into glassy states and undergoing complex physical-chemical reactions with the body. However, the middle layer of Jun porcelain was formed by the chemical composition of the glaze turning into glassy states and then infiltrating the body at high temperatures during the firing process.

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

Dmowski, W.; Gierlotka, S.; Wang, Z.

Through high-energy x-ray diffraction and atomic pair density function analysis we find that Zr-based metallic alloy, heated to the supercooled liquid state under hydrostatic pressure and then quenched to room temperature, exhibits a distinct glassy structure. The PDF indicates that the Zr-Zr distances in this glass are significantly reduced compared to those quenched without pressure. Annealing at the glass transition temperature at ambient pressure reverses structural changes and the initial glassy state is recovered. This result suggests that pressure causes a liquid-to-liquid phase transition in this metallic alloy supercooled melt. Such a pressure induced transition is known for covalent liquids,more » but has not been observed for metallic liquids. The High Pressure Quenched glasses are stable in ambient conditions after decompression.« less

Unusual strain glassy phase in Fe doped Ni2Mn1.5In0.5

NASA Astrophysics Data System (ADS)

Nevgi, R.; Priolkar, K. R.

2018-01-01

Fe doped Ni2Mn1.5In0.5, particularly, Ni2Mn1.4Fe0.1In0.5, despite having an incommensurate, modulated 7M martensitic structure at room temperature exhibits frequency dependent behavior of storage modulus and loss which obeys the Vogel-Fulcher law as well as shows ergodicity breaking between zero field cooled and field cooled strain measurements just above the transition temperature. Both frequency dependence and ergodicity breaking are characteristics of a strain glassy phase and occur due to the presence of strain domains which are large enough to present signatures of long range martensitic order in diffraction but are non-interacting with other strain domains due to the presence of Fe impurities.

Nonmonotonic Aging and Memory in a Frictional Interface

NASA Astrophysics Data System (ADS)

Dillavou, Sam; Rubinstein, Shmuel M.

2018-06-01

We measure the static frictional resistance and the real area of contact between two solid blocks subjected to a normal load. We show that following a two-step change in the normal load the system exhibits nonmonotonic aging and memory effects, two hallmarks of glassy dynamics. These dynamics are strongly influenced by the discrete geometry of the frictional interface, characterized by the attachment and detachment of unique microcontacts. The results are in good agreement with a theoretical model we propose that incorporates this geometry into the framework recently used to describe Kovacs-like relaxation in glasses as well as thermal disordered systems. These results indicate that a frictional interface is a glassy system and strengthen the notion that nonmonotonic relaxation behavior is generic in such systems.

Electrocatalytic oxidation of hydrazine and hydroxylamine by graphene oxide-Pd nanoparticle-modified glassy carbon electrode.

PubMed

Lee, Eunhee; Kim, Daekun; You, Jung-Min; Kim, Seul Ki; Yun, Mira; Jeon, Seungwon

2012-12-01

Pd nanoparticle catalysts supported by thiolated graphene oxide (tGO) on a glassy carbon electrode (GCE), and denoted as tGO-Pd/GCE, are used in this study for the electrochemical determination of hydroxylamine and hydrazine. The physicochemical properties of tGO-Pd were characterized by transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and electrochemical impedance spectroscopy (EIS). They showed strong catalytic activity toward the oxidation of hydroxylamine and hydrazine. Cyclic voltammetry (CV) and amperometry were used to characterize the sensors' performances. The detection limits of hydroxylamine and hydrazine by tGO-Pd/GCE were 0.31 and 0.25 microM (s/n = 3), respectively. The sensors' sensitivity, selectivity, and stability were also investigated.

Soft modes in the perceptron model for jamming.

NASA Astrophysics Data System (ADS)

Franz, Silvio

I will show how a well known neural network model \\x9Dthe perceptro provides a simple solvable model of glassy behavior and jamming. The glassy minima of the energy function of this model can be studied in full analytic detail. This allows the identification of two kind of soft modes the first ones associated to the existence a marginal glass phase and a hierarchical structure of the energy landscape, the second ones associated to isostaticity and marginality of jamming. These results highlight the universality of the spectrum of normal modes in disordered systems, and open the way toward a detailed analytical understanding of the vibrational spectrum of low-temperature glasses. This work was supported by a Grant from the Simons Foundation (454941 to Silvio Franz).

The hydrophilic-to-hydrophobic transition in glassy silica is driven by the atomic topology of its surface

NASA Astrophysics Data System (ADS)

Yu, Yingtian; Krishnan, N. M. Anoop; Smedskjaer, Morten M.; Sant, Gaurav; Bauchy, Mathieu

2018-02-01

The surface reactivity and hydrophilicity of silicate materials are key properties for various industrial applications. However, the structural origin of their affinity for water remains unclear. Here, based on reactive molecular dynamics simulations of a series of artificial glassy silica surfaces annealed at various temperatures and subsequently exposed to water, we show that silica exhibits a hydrophilic-to-hydrophobic transition driven by its silanol surface density. By applying topological constraint theory, we show that the surface reactivity and hydrophilic/hydrophobic character of silica are controlled by the atomic topology of its surface. This suggests that novel silicate materials with tailored reactivity and hydrophilicity could be developed through the topological nanoengineering of their surface.

Understanding glass-forming ability through sluggish crystallization of atomically thin metallic glassy films

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

Sun, Y. T.; Cao, C. R.; Huang, K. Q.

2014-08-04

The glass-forming ability (GFA) of an alloy, closely related to its ability to resist crystallization, is a crucial issue in condensed matter physics. So far, the studies on GFA are mostly statistical and empirical guides. Benefiting from the ultrahigh thermal stability of ultrathin metallic glassy film and high resolution spherical aberration-corrected transmission electron microscope, the crystallization of atomically thin ZrCu and its microalloyed ZrCuAl glasses with markedly different GFA was investigated at the atomic scale. We find the Zr diffusivity estimated from the density of nuclei is dramatically decreased by adding of Al, which is the major reason for themore » much better GFA of the ZrCuAl metallic glass.« less

Ultrapermeable, reverse-selective nanocomposite membranes.

PubMed

Merkel, T C; Freeman, B D; Spontak, R J; He, Z; Pinnau, I; Meakin, P; Hill, A J

2002-04-19

Polymer nanocomposites continue to receive tremendous attention for application in areas such as microelectronics, organic batteries, optics, and catalysis. We have discovered that physical dispersion of nonporous, nanoscale, fumed silica particles in glassy amorphous poly(4-methyl-2-pentyne) simultaneously and surprisingly enhances both membrane permeability and selectivity for large organic molecules over small permanent gases. These highly unusual property enhancements, in contrast to results obtained in conventional filled polymer systems, reflect fumed silica-induced disruption of polymer chain packing and an accompanying subtle increase in the size of free volume elements through which molecular transport occurs, as discerned by positron annihilation lifetime spectroscopy. Such nanoscale hybridization represents an innovative means to tune the separation properties of glassy polymeric media through systematic manipulation of molecular packing.

Glassy phase in quenched disordered crystalline membranes

NASA Astrophysics Data System (ADS)

Coquand, O.; Essafi, K.; Kownacki, J.-P.; Mouhanna, D.

2018-03-01

We investigate the flat phase of D -dimensional crystalline membranes embedded in a d -dimensional space and submitted to both metric and curvature quenched disorders using a nonperturbative renormalization group approach. We identify a second-order phase transition controlled by a finite-temperature, finite-disorder fixed point unreachable within the leading order of ɛ =4 -D and 1 /d expansions. This critical point divides the flow diagram into two basins of attraction: that associated with the finite-temperature fixed point controlling the long-distance behavior of disorder-free membranes and that associated with the zero-temperature, finite-disorder fixed point. Our work thus strongly suggests the existence of a whole low-temperature glassy phase for quenched disordered crystalline membranes and, possibly, for graphene and graphene-like compounds.

Decomposition mechanism of an artemisinin-type compound via hemin-electrocatalysis.

PubMed

Chen, H Y; Chen, Y; Zhu, S M; Bian, N S; Shan, F; Li, Y

1999-01-01

The interaction between a typical derivative of artemisinin and hemin was investigated by electrochemical and spectroelectrochemical methods. This derivative can be reduced via hemin-catalysis at the glassy carbon electrode, the cathodic overpotential is decreased by ca. 650 mV. A HPLC method for separating the products of the catalytic reaction was established. They were identified either in H(2)O-CH(3)CN solution or in tetrahydrofuran, respectively. The structures of these products show that the hemin-catalyzed decomposition of an artemisinin-type compound on the glassy carbon or reticulated vitreous carbon electrode can be achieved by both electrochemical reduction and rearrangement. The conclusion that the reaction of artemisinin with hemin is a critical step in the antimalarial mechanism of artemisinin can be drawn.

Novel value-added uses for sweet potato juice and flour in polyphenol- and protein-enriched functional food ingredients.

PubMed

Grace, Mary H; Truong, An N; Truong, Van-Den; Raskin, Ilya; Lila, Mary Ann

2015-09-01

Blackcurrant, blueberry, and muscadine grape juices were efficiently sorbed, concentrated, and stabilized into dry granular ingredient matrices which combined anti-inflammatory and antioxidant fruit polyphenols with sweet potato functional constituents (carotenoids, vitamins, polyphenols, fibers). Total phenolics were highest in blackcurrant-orange sweet potato ingredient matrices (34.03 mg/g), and lowest in muscadine grape-yellow sweet potato matrices (10.56 mg/g). Similarly, anthocyanins were most concentrated in blackcurrant-fortified orange and yellow sweet potato matrices (5.40 and 6.54 mg/g, respectively). Alternatively, other protein-rich edible matrices (defatted soy flour, light roasted peanut flour, and rice protein concentrate) efficiently captured polyphenols (6.09-9.46 mg/g) and anthocyanins (0.77-1.27 mg/g) from purple-fleshed sweet potato juice, with comparable efficiency. Antioxidant activity correlated well with total phenolic content. All formulated ingredient matrices stabilized and preserved polyphenols for up to 24 weeks, even when stored at 37°C. Complexation with juice-derived polyphenols did not significantly alter protein or carbohydrate profiles of the matrices. Sensory evaluation of the ingredient matrices suggested potential uses for a wide range of functional food products.

Inference for High-dimensional Differential Correlation Matrices.

PubMed

Cai, T Tony; Zhang, Anru

2016-01-01

Motivated by differential co-expression analysis in genomics, we consider in this paper estimation and testing of high-dimensional differential correlation matrices. An adaptive thresholding procedure is introduced and theoretical guarantees are given. Minimax rate of convergence is established and the proposed estimator is shown to be adaptively rate-optimal over collections of paired correlation matrices with approximately sparse differences. Simulation results show that the procedure significantly outperforms two other natural methods that are based on separate estimation of the individual correlation matrices. The procedure is also illustrated through an analysis of a breast cancer dataset, which provides evidence at the gene co-expression level that several genes, of which a subset has been previously verified, are associated with the breast cancer. Hypothesis testing on the differential correlation matrices is also considered. A test, which is particularly well suited for testing against sparse alternatives, is introduced. In addition, other related problems, including estimation of a single sparse correlation matrix, estimation of the differential covariance matrices, and estimation of the differential cross-correlation matrices, are also discussed.

On Fluctuations of Eigenvalues of Random Band Matrices

NASA Astrophysics Data System (ADS)

Shcherbina, M.

2015-10-01

We consider the fluctuations of linear eigenvalue statistics of random band matrices whose entries have the form with i.i.d. possessing the th moment, where the function u has a finite support , so that M has only nonzero diagonals. The parameter b (called the bandwidth) is assumed to grow with n in a way such that . Without any additional assumptions on the growth of b we prove CLT for linear eigenvalue statistics for a rather wide class of test functions. Thus we improve and generalize the results of the previous papers (Jana et al., arXiv:1412.2445; Li et al. Random Matrices 2:04, 2013), where CLT was proven under the assumption . Moreover, we develop a method which allows to prove automatically the CLT for linear eigenvalue statistics of the smooth test functions for almost all classical models of random matrix theory: deformed Wigner and sample covariance matrices, sparse matrices, diluted random matrices, matrices with heavy tales etc.

An Approximate Approach to Automatic Kernel Selection.

PubMed

Ding, Lizhong; Liao, Shizhong

2016-02-02

Kernel selection is a fundamental problem of kernel-based learning algorithms. In this paper, we propose an approximate approach to automatic kernel selection for regression from the perspective of kernel matrix approximation. We first introduce multilevel circulant matrices into automatic kernel selection, and develop two approximate kernel selection algorithms by exploiting the computational virtues of multilevel circulant matrices. The complexity of the proposed algorithms is quasi-linear in the number of data points. Then, we prove an approximation error bound to measure the effect of the approximation in kernel matrices by multilevel circulant matrices on the hypothesis and further show that the approximate hypothesis produced with multilevel circulant matrices converges to the accurate hypothesis produced with kernel matrices. Experimental evaluations on benchmark datasets demonstrate the effectiveness of approximate kernel selection.

Homology search with binary and trinary scoring matrices.

PubMed

Smith, Scott F

2006-01-01

Protein homology search can be accelerated with the use of bit-parallel algorithms in conjunction with constraints on the values contained in the scoring matrices. Trinary scoring matrices (containing only the values -1, 0, and 1) allow for significant acceleration without significant reduction in the receiver operating characteristic (ROC) score of a Smith-Waterman search. Binary scoring matrices (containing the values 0 and 1) result in some reduction in ROC score, but result in even more acceleration. Binary scoring matrices and five-bit saturating scores can be used for fast prefilters to the Smith-Waterman algorithm.

Methods for Quantum Circuit Design and Simulation

DTIC Science & Technology

2010-03-01

cannot be deter- mined given the one output. Reversible gates, expressed mathematically, are unitary matrices. 16 3.3.1 PAULI Gates/Matrices Three...common single-qubit gates are expressed mathematically as Pauli matrices, which are 2x2 matrices. A 2x2 quantum gate can be applied to a single quantum...bit (a 2x1 column vector). The Pauli matrices are expressed as follows: X =   0 1 1 0   Y =   0 −i i 0   Z =   1 0 0 −1   (3.10) where i

An automated procedure for calculating system matrices from perturbation data generated by an EAI Pacer and 100 hybrid computer system

NASA Technical Reports Server (NTRS)

Milner, E. J.; Krosel, S. M.

1977-01-01

Techniques are presented for determining the elements of the A, B, C, and D state variable matrices for systems simulated on an EAI Pacer 100 hybrid computer. An automated procedure systematically generates disturbance data necessary to linearize the simulation model and stores these data on a floppy disk. A separate digital program verifies this data, calculates the elements of the system matrices, and prints these matrices appropriately labeled. The partial derivatives forming the elements of the state variable matrices are approximated by finite difference calculations.

Polytetramethylene glycol-modified polycyanurate matrices reinforced with nanoclays: synthesis and thermomechanical performance

NASA Astrophysics Data System (ADS)

Anthoulis, G. I.; Kontou, E.; Fainleib, A.; Bei, I.

2009-03-01

The outstanding improvement in the physical properties of cyanate esters (CEs) compared with those of competitor resins, such as epoxies, has attracted appreciable attention recently. Cyanate esters undergo thermal polycyclotrimerization to give polycyanurates (PCNs). However, like most thermo setting resins, the main draw back of CEs is brittleness. To over come this disadvan tage, CEs can be toughened by the introduction of polytetramethylene glycol (PTMG), a hydroxyl-terminated polyether. How ever, PTMG has a detrimental impact on Young's modulus. To simultaneously enhance both the ductility and the stiffness of CE, we added PTMG and an organoclay (mont morillonite, MMT) to it. A series of PCN/PTMG/MMT nanocomposites with a constant PTMG weight ratio was pre pared, and the resulting nanophase morphology, i.e., the degree of filler dispersion and distribution in the composite and the thermomechanical properties, in terms of glass-transition behaviour, Young's modulus, tensile strength, and elongation at break, were examined using the scanning elec tron micros copy (SEM), a dynamic mechanical analysis (DMA), and stress-strain measurements, re spectively. It was found that, at a content of MMT below 2 wt.%, MMT nanoparticles were distributed uniformly in the matrix, suggesting a lower degree of agglomeration for these materials. In the glassy state, the significant increase in the storage modulus revealed a great stiffening effect of MMT due to its high Young's modulus. The modification with PTMG led to a 233% greater elongation at break compared with that of neat PCN. The nanocomposites exhibited an invariably higher Young's modulus than PCN/PTMG for all the volume factors of organoclay examined, with the 2 wt.% material displaying the most pronounced in crease in the modulus, in agreement with micros copy results.

Chemical speciation of U, Fe, and Pu in melt glass from nuclear weapons testing

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

Pacold, J. I.; Lukens, W. W.; Booth, C. H.

Nuclear weapons testing generates large volumes of glassy materials that influence the transport of dispersed actinides in the environment and may carry information on the composition of the detonated device. We determine the oxidation state of U and Fe (which is known to buffer the oxidation state of actinide elements and to affect the redox state of groundwater) in samples of melt glass collected from three U.S. nuclear weapons tests. For selected samples, we also determine the coordination geometry of U and Fe, and we report the oxidation state of Pu from one melt glass sample. We find significant variationsmore » among the melt glass samples and, in particular, find a clear deviation in one sample from the expected buffering effect of Fe(II)/Fe(III) on the oxidation state of uranium. In the first direct measurement of Pu oxidation state in a nuclear test melt glass, we obtain a result consistent with existing literature that proposes Pu is primarily present as Pu(IV) in post-detonation material. In addition, our measurements imply that highly mobile U(VI) may be produced in significant quantities when melt glass is quenched rapidly following a nuclear detonation, though these products may remain immobile in the vitrified matrices. The observed differences in chemical state among the three samples show that redox conditions can vary dramatically across different nuclear test conditions. The local soil composition, associated device materials, and the rate of quenching are all likely to affect the final redox state of the glass. The resulting variations in glass chemistry are significant for understanding and interpreting debris chemistry and the later environmental mobility of dispersed material.« less

Chemical speciation of U, Fe, and Pu in melt glass from nuclear weapons testing

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

Pacold, J. I.; Lukens, W. W.; Booth, C. H.

We report that nuclear weapons testing generates large volumes of glassy materials that influence the transport of dispersed actinides in the environment and may carry information on the composition of the detonated device. We determine the oxidation state of U and Fe (which is known to buffer the oxidation state of actinide elements and to affect the redox state of groundwater) in samples of melt glass collected from three U.S. nuclear weapons tests. For selected samples, we also determine the coordination geometry of U and Fe, and we report the oxidation state of Pu from one melt glass sample. Wemore » find significant variations among the melt glass samples and, in particular, find a clear deviation in one sample from the expected buffering effect of Fe(II)/Fe(III) on the oxidation state of uranium. In the first direct measurement of Pu oxidation state in a nuclear test melt glass, we obtain a result consistent with existing literature that proposes Pu is primarily present as Pu(IV) in post-detonation material. In addition, our measurements imply that highly mobile U(VI) may be produced in significant quantities when melt glass is quenched rapidly following a nuclear detonation, though these products may remain immobile in the vitrified matrices. The observed differences in chemical state among the three samples show that redox conditions can vary dramatically across different nuclear test conditions. The local soil composition, associated device materials, and the rate of quenching are all likely to affect the final redox state of the glass. Lastly, the resulting variations in glass chemistry are significant for understanding and interpreting debris chemistry and the later environmental mobility of dispersed material.« less

Chemical speciation of U, Fe, and Pu in melt glass from nuclear weapons testing

DOE PAGES

Pacold, J. I.; Lukens, W. W.; Booth, C. H.; ...

2016-05-18

We report that nuclear weapons testing generates large volumes of glassy materials that influence the transport of dispersed actinides in the environment and may carry information on the composition of the detonated device. We determine the oxidation state of U and Fe (which is known to buffer the oxidation state of actinide elements and to affect the redox state of groundwater) in samples of melt glass collected from three U.S. nuclear weapons tests. For selected samples, we also determine the coordination geometry of U and Fe, and we report the oxidation state of Pu from one melt glass sample. Wemore » find significant variations among the melt glass samples and, in particular, find a clear deviation in one sample from the expected buffering effect of Fe(II)/Fe(III) on the oxidation state of uranium. In the first direct measurement of Pu oxidation state in a nuclear test melt glass, we obtain a result consistent with existing literature that proposes Pu is primarily present as Pu(IV) in post-detonation material. In addition, our measurements imply that highly mobile U(VI) may be produced in significant quantities when melt glass is quenched rapidly following a nuclear detonation, though these products may remain immobile in the vitrified matrices. The observed differences in chemical state among the three samples show that redox conditions can vary dramatically across different nuclear test conditions. The local soil composition, associated device materials, and the rate of quenching are all likely to affect the final redox state of the glass. Lastly, the resulting variations in glass chemistry are significant for understanding and interpreting debris chemistry and the later environmental mobility of dispersed material.« less

Chemical speciation of U, Fe, and Pu in melt glass from nuclear weapons testing

NASA Astrophysics Data System (ADS)

Pacold, J. I.; Lukens, W. W.; Booth, C. H.; Shuh, D. K.; Knight, K. B.; Eppich, G. R.; Holliday, K. S.

2016-05-01

Nuclear weapons testing generates large volumes of glassy materials that influence the transport of dispersed actinides in the environment and may carry information on the composition of the detonated device. We determine the oxidation state of U and Fe (which is known to buffer the oxidation state of actinide elements and to affect the redox state of groundwater) in samples of melt glass collected from three U.S. nuclear weapons tests. For selected samples, we also determine the coordination geometry of U and Fe, and we report the oxidation state of Pu from one melt glass sample. We find significant variations among the melt glass samples and, in particular, find a clear deviation in one sample from the expected buffering effect of Fe(II)/Fe(III) on the oxidation state of uranium. In the first direct measurement of Pu oxidation state in a nuclear test melt glass, we obtain a result consistent with existing literature that proposes Pu is primarily present as Pu(IV) in post-detonation material. In addition, our measurements imply that highly mobile U(VI) may be produced in significant quantities when melt glass is quenched rapidly following a nuclear detonation, though these products may remain immobile in the vitrified matrices. The observed differences in chemical state among the three samples show that redox conditions can vary dramatically across different nuclear test conditions. The local soil composition, associated device materials, and the rate of quenching are all likely to affect the final redox state of the glass. The resulting variations in glass chemistry are significant for understanding and interpreting debris chemistry and the later environmental mobility of dispersed material.

The parent body controls on cosmic spherule texture: Evidence from the oxygen isotopic compositions of large micrometeorites

NASA Astrophysics Data System (ADS)

van Ginneken, M.; Gattacceca, J.; Rochette, P.; Sonzogni, C.; Alexandre, A.; Vidal, V.; Genge, M. J.

2017-09-01

High-precision oxygen isotopic compositions of eighteen large cosmic spherules (>500 μm diameter) from the Atacama Desert, Chile, were determined using IR-laser fluorination - Isotope Ratio Mass spectrometry. The four discrete isotopic groups defined in a previous study on cosmic spherules from the Transantarctic Mountains (Suavet et al., 2010) were identified, confirming their global distribution. Approximately 50% of the studied cosmic spherules are related to carbonaceous chondrites, 38% to ordinary chondrites and 12% to unknown parent bodies. Approximately 90% of barred olivine (BO) cosmic spherules show oxygen isotopic compositions suggesting they are related to carbonaceous chondrites. Similarly, ∼90% porphyritic olivine (Po) cosmic spherules are related to ordinary chondrites and none can be unambiguously related to carbonaceous chondrites. Other textures are related to all potential parent bodies. The data suggests that the textures of cosmic spherules are mainly controlled by the nature of the precursor rather than by the atmospheric entry parameters. We propose that the Po texture may essentially be formed from a coarse-grained precursor having an ordinary chondritic mineralogy and chemistry. Coarse-grained precursors related to carbonaceous chondrites (i.e. chondrules) are likely to either survive atmospheric entry heating or form V-type cosmic spherules. Due to the limited number of submicron nucleation sites after total melting, ordinary chondrite-related coarse-grained precursors that suffer higher peak temperatures will preferentially form cryptocrystalline (Cc) textures instead of BO textures. Conversely, the BO textures would be mostly related to the fine-grained matrices of carbonaceous chondrites due to the wide range of melting temperatures of their constituent mineral phases, allowing the preservation of submicron nucleation sites. Independently of the nature of the precursors, increasing peak temperatures form glassy textures.

Synthesis and electrochemical detection of a thiazolyl-indole natural product isolated from the nosocomial pathogen Pseudomonas aeruginosa.

PubMed

Buzid, Alyah; Muimhneacháin, Eoin Ó; Reen, F Jerry; Hayes, Phyllis E; Pardo, Leticia M; Shang, Fengjun; O'Gara, Fergal; Sperry, Jonathan; Luong, John H T; Glennon, Jeremy D; McGlacken, Gerard P

2016-09-01

Pseudomonas aeruginosa is a Gram-negative opportunistic pathogen, capable of surviving in a broad range of natural environments and quickly acquiring resistance. It is associated with hospital-acquired infections, particularly in patients with compromised immunity, and is the primary cause of morbidity and mortality in cystic fibrosis (CF) patients. P. aeruginosa is also of nosocomial importance on dairy farms and veterinary hospitals, where it is a key morbidity factor in bovine mastitis. P. aeruginosa uses a cell-cell communication system consisting of signalling molecules to coordinate bacterial secondary metabolites, biofilm formation, and virulence. Simple and sensitive methods for the detection of biomolecules as indicators of P. aeruginosa infection would be of great clinical importance. Here, we report the synthesis of the P. aeruginosa natural product, barakacin, which was recently isolated from the bovine ruminal strain ZIO. A simple and sensitive electrochemical method was used for barakacin detection using a boron-doped diamond (BDD) and glassy carbon (GC) electrodes, based on cyclic voltammetry (CV) and differential pulse voltammetry (DPV). The influence of electrolyte pH on the peak potential and peak currents was also investigated. At pH 2.0, the peak current was linearly dependent on barakacin concentration (in the range used, 1-10 μM), with correlation coefficients greater than 0.98 on both electrodes. The detection limit (S/N = 3) on the BDD electrode was 100-fold lower than that obtained on the GC electrode. The optimized method using the BDD electrode was extended to bovine (cow feces) and human (sputum of a CF patient) samples. Spiked barakacin was easily detected in these matrices at a limit of 0.5 and 0.05 μM, respectively. Graphical abstract Electrochemical detection of barakacin.

NATO Human Resources (Manpower) Management (Gestion des ressources humaines (effectifs) de l’OTAN)

DTIC Science & Technology

2012-02-01

performances , la gestion des récompenses et du salaire, et la motivation du personnel. En conséquence, il faut que la gestion des ressources humaines...importance au fil du temps. Les ressources humaines, chargées à l’origine de l’embauche, du licenciement, de la paie et de la gestion des ...les effets des systèmes d’évaluation des performances ;

Afterrise: Deep Body Temperature Following Exercise

DTIC Science & Technology

1992-03-01

Egalement, les effets de la posture et des v~tements durant la recuperation et la temperature de la salle de recuperation furent examines. Cinq hommes se...chemise a manches courtes). Les temperatures rectales et de la peau furent mesurees A chaque minute durant les exercices et la r~cup~ration affectaient...overgarment. RESUME Cette etude fut entreprise pour documenter l’augmentation continue de la temperature rectale apres exercice dans la chaleur

Impact of Technologies on Learning in the Workplace. Final Report = L'effet des technologies d'apprentissage sur l'apprentissage a vie en milieu de travail.

ERIC Educational Resources Information Center

Dugas, Tim; Green, Lyndsay; Leckie, Norm

The use of learning technologies in the workplace and their impact on lifelong learning were examined. Data were collected from three sources: the literature on learning technologies and labor market trends affecting the adoption, implementation, and success of learning technologies in the workplace; case studies of 8 Canadian firms with 100 or…

Prevention des Toxicomanies Aupres des Filles avec des Problemes de Comportement: Effets a Court Terme (Prevention of Drug Addiction in Girls with Behavior Problems: Short-Term Effects).

ERIC Educational Resources Information Center

Vitaro, Frank; And Others

1992-01-01

This article, written in French, describes and evaluates the first phase of a program to prevent drug addiction among 110 fifth-grade girls with behavior problems in Montreal (Quebec, Canada). Evaluation of the instructional program showed positive results for student knowledge level, attitudes, and behaviors and supported program continuation…

Possibilité d'une nouvelle technologie de traitement des minerais de fer de l'Ouenza par radiométrie

NASA Astrophysics Data System (ADS)

Idres, A.; Bounouala, M.

2005-05-01

En l'absence d'une technologie fiable de traitement des haldes de minerais de fer, les caractéristiques minéralogiques et chimiques complexes et les effets néfastes des résidus miniers posent réellement un problème environnemental. A cet effet, une étude minéralogique et chimique du minerai de fer a été menée en utilisant des techniques multiples (microscopie optique, DRX, FX, MEB). En tenant compte de la nature des résidus, des échantillons représentatifs ont été testés par séparation radiométrique. Plusieurs paramètres ont été caractérisés tels que la vitesse de la bande transporteuse, le temps d'émission des rayons gamma et la granulométrie d'alimentation du procédé. Les résultats ainsi obtenus par cette méthode de séparation sont très significatifs en récupération et en teneur fer. Cependant, cette nouvelle technologie permet d'une part une meilleure valorisation des minerais de fer et d'autre part une réduction du tonnage stocké sur le carreau de la mine.

Effets tardifs d'une irradiation corporelle totale sur le métabolisme intraneuronal de la dopamine et de la sérotonine

NASA Astrophysics Data System (ADS)

Joubert, C.; Jacquet, N.; Lambert, F.; Martin, S.; Martin, C.

1998-04-01

Whole-body irradiation leads to delayed cognitive dysfunction which could result from perturbations of neurotransmission, specially the dopaminergic and the serotoninergic one. The aim of this study was to determine the concentrations of dopamine (DA), serotonin (5-HT) and their metabolites in three cerebral areas of rats, one month after (neutron-gamma) irradiation at 3.38Gy. An increase of DA, 5-HT, and their catabolites was observed. These effects are weak but observed in older rats. Au cours des mois suivant une irradiation corporell totale peuvent se manifester des troubles comportementaux qui pourraient être la conséquence d'altérations de la neuraotransmission, plus particulièrement de la transmission dopaminergique ou sérotoninergique. Nous avons recherché les variations des taux de dopamine (DA), de sérotonine (5-HT) et de leurs métabolites dans 3structures cérébrales 1 mois après une irradiation (neutron-gamma) à la dose de 3,38Gy. Les résultats préliminaires mettent en évidence une augmentation des taux de DA, de 5-HT et de leurs catabolites ; ces effets sont plus discrets mais similaires à ceux observés chez des animaux plus âgés.

Effet d'un champ magnétique uniforme sur les instabilités de Rayleigh-Bénard avec effet Soret

NASA Astrophysics Data System (ADS)

Ben Sassi, Mokhtar; Kaddeche, Slim; Abdennadher, Ali; Henry, Daniel; Hadid, Hamda Ben; Mojtabi, Abdelkader

2016-01-01

The effect of both magnitude and orientation of a uniform magnetic field on the critical transition occurring within an electrically conducting binary fluid layer, stratified in temperature and concentration, taking into account the Soret effect, is investigated numerically. For such a configuration, the results show that the critical thresholds corresponding to an arbitrary orientated magnetic field can be derived from those obtained for a vertical magnetic field and that the axes of the marginal cells are aligned with the horizontal component of the magnetic field. Moreover, an analytical study is conducted to investigate the impact of the magnetic field on long-wavelength instabilities. The effect of the magnetic field on such instabilities reveals a new phenomenon consisting in major changes of the unstable modes that lose their unicellular nature to regain their multi-roll characteristic, as it is the case without magnetic field for ψ <ψℓ0 = 131 Le / (34 - 131 Le). For a binary fluid characterized by a Lewis number Le and a separation factor ψ >ψℓ0, the value of the Hartmann number Haℓ (ψ , Le) corresponding to that transition responsible for a significant change in mass and heat transfer can be determined from the analytical relations derived in this work.

Invertible flexible matrices

NASA Astrophysics Data System (ADS)

Justino, Júlia

2017-06-01

Matrices with coefficients having uncertainties of type o (.) or O (.), called flexible matrices, are studied from the point of view of nonstandard analysis. The uncertainties of the afore-mentioned kind will be given in the form of the so-called neutrices, for instance the set of all infinitesimals. Since flexible matrices have uncertainties in their coefficients, it is not possible to define the identity matrix in an unique way and so the notion of spectral identity matrix arises. Not all nonsingular flexible matrices can be turned into a spectral identity matrix using Gauss-Jordan elimination method, implying that that not all nonsingular flexible matrices have the inverse matrix. Under certain conditions upon the size of the uncertainties appearing in a nonsingular flexible matrix, a general theorem concerning the boundaries of its minors is presented which guarantees the existence of the inverse matrix of a nonsingular flexible matrix.

Statistical potential-based amino acid similarity matrices for aligning distantly related protein sequences.

PubMed

Tan, Yen Hock; Huang, He; Kihara, Daisuke

2006-08-15

Aligning distantly related protein sequences is a long-standing problem in bioinformatics, and a key for successful protein structure prediction. Its importance is increasing recently in the context of structural genomics projects because more and more experimentally solved structures are available as templates for protein structure modeling. Toward this end, recent structure prediction methods employ profile-profile alignments, and various ways of aligning two profiles have been developed. More fundamentally, a better amino acid similarity matrix can improve a profile itself; thereby resulting in more accurate profile-profile alignments. Here we have developed novel amino acid similarity matrices from knowledge-based amino acid contact potentials. Contact potentials are used because the contact propensity to the other amino acids would be one of the most conserved features of each position of a protein structure. The derived amino acid similarity matrices are tested on benchmark alignments at three different levels, namely, the family, the superfamily, and the fold level. Compared to BLOSUM45 and the other existing matrices, the contact potential-based matrices perform comparably in the family level alignments, but clearly outperform in the fold level alignments. The contact potential-based matrices perform even better when suboptimal alignments are considered. Comparing the matrices themselves with each other revealed that the contact potential-based matrices are very different from BLOSUM45 and the other matrices, indicating that they are located in a different basin in the amino acid similarity matrix space.

The Development of Novel Nanodiamond Based MALDI Matrices for the Analysis of Small Organic Pharmaceuticals

NASA Astrophysics Data System (ADS)

Chitanda, Jackson M.; Zhang, Haixia; Pahl, Erica; Purves, Randy W.; El-Aneed, Anas

2016-10-01

The utility of novel functionalized nanodiamonds (NDs) as matrices for matrix-assisted laser desorption ionization-mass spectrometry (MALDI-MS) is described herein. MALDI-MS analysis of small organic compounds (<1000 Da) is typically complex because of interferences from numerous cluster ions formed when using conventional matrices. To expand the use of MALDI for the analysis of small molecules, novel matrices were designed by covalently linking conventional matrices (or a lysine moiety) to detonated NDs. Four new functionalized NDs were evaluated for their ionization capabilities using five pharmaceuticals with varying molecular structures. Two ND matrices were able to ionize all tested pharmaceuticals in the negative ion mode, producing the deprotonated ions [M - H]-. Ion intensity for target analytes was generally strong with enhanced signal-to-noise ratios compared with conventional matrices. The negative ion mode is of great importance for biological samples as interference from endogenous compounds is inherently minimized in the negative ion mode. Since the molecular structures of the tested pharmaceuticals did not suggest that negative ion mode would be preferable, this result magnifies the importance of these findings. On the other hand, conventional matrices primarily facilitated the ionization as expected in the positive ion mode, producing either the protonated molecules [M + H]+ or cationic adducts (typically producing complex spectra with numerous adduct peaks). The data presented in this study suggests that these matrices may offer advantages for the analysis of low molecular weight pharmaceuticals/metabolites.

The Development of Novel Nanodiamond Based MALDI Matrices for the Analysis of Small Organic Pharmaceuticals.

PubMed

Chitanda, Jackson M; Zhang, Haixia; Pahl, Erica; Purves, Randy W; El-Aneed, Anas

2016-10-01

The utility of novel functionalized nanodiamonds (NDs) as matrices for matrix-assisted laser desorption ionization-mass spectrometry (MALDI-MS) is described herein. MALDI-MS analysis of small organic compounds (<1000 Da) is typically complex because of interferences from numerous cluster ions formed when using conventional matrices. To expand the use of MALDI for the analysis of small molecules, novel matrices were designed by covalently linking conventional matrices (or a lysine moiety) to detonated NDs. Four new functionalized NDs were evaluated for their ionization capabilities using five pharmaceuticals with varying molecular structures. Two ND matrices were able to ionize all tested pharmaceuticals in the negative ion mode, producing the deprotonated ions [M - H](-). Ion intensity for target analytes was generally strong with enhanced signal-to-noise ratios compared with conventional matrices. The negative ion mode is of great importance for biological samples as interference from endogenous compounds is inherently minimized in the negative ion mode. Since the molecular structures of the tested pharmaceuticals did not suggest that negative ion mode would be preferable, this result magnifies the importance of these findings. On the other hand, conventional matrices primarily facilitated the ionization as expected in the positive ion mode, producing either the protonated molecules [M + H](+) or cationic adducts (typically producing complex spectra with numerous adduct peaks). The data presented in this study suggests that these matrices may offer advantages for the analysis of low molecular weight pharmaceuticals/metabolites. Graphical Abstract ᅟ.

Analysis of electrical property changes of skin by oil-in-water emulsion components

PubMed Central

Jeong, CB; Han, JY; Cho, JC; Suh, KD; Nam, GW

2013-01-01

Synopsis ObjectivesAs the ‘Dry Skin Cycle’ produces continuous deterioration, cosmetic xerosis (flaky, dry skin) is one of the major concerns to most consumers. The purpose of this study was to investigate the moisturizing effect of oil-in-water (O/W) emulsion components. There are numerous types of oils, waxes, polyols and surfactants used as ingredients in skincare products. However, the moisturizing effect of each ingredient and understanding each use to make an effective moisturizing products are still not well understood. Methods To provide answers to these questions, we investigated the moisturizing effect of widely used 41 components (four different classes) in a simple O/W emulsion using capacitance methods. 106 different single oils, and combinations of oil with oil, wax, humectants, and surfactant were formulated and tested. Results In this study, we found that most of the O/W emulsion components had hydration effects on the skin. (i) The average relative water content increase (RWCI) rate of a single oil-based emulsion was 11.8 ± 5.2% (SE) and 7.9 ± 6.0% (SE) at 3 and 6 h, respectively. (ii) An oil combination emulsion showed an average RWCI rate similar to that of a single oil-based emulsion, 12.6 ± 6.0% (SE) and 12.1 ± 6.4% (SE) at 3 and 6 h, respectively (iii) A combination of waxes with oil showed an average RWCI rate of 16 ± 5.6% (SE) and 12.4 ± 4.5% (SE) at 3 and 6 h, respectively. (iv) Humectant combinations showed the highest average RWCI rate 28 ± 7.3% (SE) and 22.2 ± 7.5% (SE) at 3 and 6 h, respectively (v) Surfactant combinations had an average RWCI of 10.8 ± 4.5% (SE) and 6.0 ± 4.0% (SE) at 3 and 6 h, respectively. Conclusion Interestingly, it was difficult to find moisturizing power differences among samples in the same group. Only the humectants group showed significant differences among samples. Glycerine and urea showed significant skin hydration effects compared with other humectants. We also found a significant moisturizing effect by analysing the chemical functional groups; amide class had a higher hydration effect than betaines and disaccharides in humectants combination. Résumé Objectif Puisque le «cycle de la peau sèche” produit une détérioration continue, la xérose cosmétique (squameuse, peau sèche) est l’une des préoccupations majeures pour la plupart des consommateurs. Le but de cette étude était d’étudier l’effet hydratant des composants d’émulsions H / E. Il existe de nombreux types d’huiles, des cires, de polyols, et des tensioactifs utilisés comme ingrédients dans les produits de soins de la peau. Cependant, l’effet hydratant de chaque ingrédient et de leur utilisation dans des produits hydratants efficaces ne sont pas encore bien compris. MethodesPour apporter des réponses à ces questions, nous avons étudié l’effet hydratant des 41 éléments (4 classes différentes) largement utilisés dans une émulsion simple O/W en utilisant des méthodes de capacitance. 106 huiles individuelles différentes et des combinaisons d’huile avec de l’huile, de la cire, des humectants, et de tensioactifs ont été formulées et testées. ResultatsDans cette étude, nous avons constaté que la plupart des composants des émulsions huile-dans-eau (H/E) possédaient des effets d’hydratation de la peau. (i) Le taux moyen d’augmentation d’eau (RWCI = relative water content increase) d’une émulsion à base d’une seule huile était de 11,8 ± 5,2% (SE) et de 7,9 ± 6,0% (SE) à 3 et 6 h, respectivement. (ii) Une émulsion de combinaison d’huile montrait une RWCI similaire à celle d’une émulsion à base d’huile unique, 12,6 ± 6,0% (SE) et 12,1 ± 6,4% (SE) à 3 et 6 h, respectivement. (iii) Une combinaison des cires avec de l’huile présentait une RWCI de 16 ± 5,6% (SE) et 12,4 ± 4,5% (SE) à 3 et 6 h, respectivement. (iv) Les combinaisons d’humectant ont montré la plus forte augmentation avec +28 ± 7,3% (SE) et 22,2 ± 7,5% (SE) à 3 et 6 h, respectivement. (v) Les combinaisons de tensioactifs ont une RWCI moyenne de 10,8 ± 4,5% (SE) et de 6,0 ± 4,0% (SE) à 3 et 6 h, respectivement. ConclusionFait intéressant, il était difficile de trouver des différences de pouvoir d’hydratation entre les échantillons dans le même groupe. Seul le groupe des humectants a montré des différences significatives entre les échantillons. La glycérine et l’urée ont montré des effets significatifs sur l’hydratation de la peau par rapport aux autres humectants. Nous avons également constaté un effet hydratant important en analysant les groupes fonctionnels chimiques; la classe “amide” a eu un effet d’hydratation plus élevé que les bétaînes et disaccharides dans les combinaisons des humectants. PMID:23621673

Extraction and Analysis of Sulfur Mustard (HD) from Various Food Matrices by Gas ChromatographyMass Spectrometry

DTIC Science & Technology

2016-01-01

EXTRACTION AND ANALYSIS OF SULFUR MUSTARD (HD) FROM VARIOUS FOOD MATRICES BY GAS CHROMATOGRAPHY–MASS...Sulfur Mustard (HD) from Various Food Matrices by Gas Chromatography–Mass Spectrometry 5a. CONTRACT NUMBER 5b. GRANT NUMBER 5c. PROGRAM ELEMENT...spectrometry was used to analyze sulfur mustard (HD) in various food matrices. The development of a solid-phase extraction method using a normal

Novel value-added uses for sweet potato juice and flour in polyphenol- and protein-enriched functional food ingredients

PubMed Central

Grace, Mary H; Truong, An N; Truong, Van-Den; Raskin, Ilya; Lila, Mary Ann

2015-01-01

Blackcurrant, blueberry, and muscadine grape juices were efficiently sorbed, concentrated, and stabilized into dry granular ingredient matrices which combined anti-inflammatory and antioxidant fruit polyphenols with sweet potato functional constituents (carotenoids, vitamins, polyphenols, fibers). Total phenolics were highest in blackcurrant-orange sweet potato ingredient matrices (34.03 mg/g), and lowest in muscadine grape-yellow sweet potato matrices (10.56 mg/g). Similarly, anthocyanins were most concentrated in blackcurrant-fortified orange and yellow sweet potato matrices (5.40 and 6.54 mg/g, respectively). Alternatively, other protein-rich edible matrices (defatted soy flour, light roasted peanut flour, and rice protein concentrate) efficiently captured polyphenols (6.09–9.46 mg/g) and anthocyanins (0.77–1.27 mg/g) from purple-fleshed sweet potato juice, with comparable efficiency. Antioxidant activity correlated well with total phenolic content. All formulated ingredient matrices stabilized and preserved polyphenols for up to 24 weeks, even when stored at 37°C. Complexation with juice-derived polyphenols did not significantly alter protein or carbohydrate profiles of the matrices. Sensory evaluation of the ingredient matrices suggested potential uses for a wide range of functional food products. PMID:26405527

The performance of the Congruence Among Distance Matrices (CADM) test in phylogenetic analysis

PubMed Central

2011-01-01

Background CADM is a statistical test used to estimate the level of Congruence Among Distance Matrices. It has been shown in previous studies to have a correct rate of type I error and good power when applied to dissimilarity matrices and to ultrametric distance matrices. Contrary to most other tests of incongruence used in phylogenetic analysis, the null hypothesis of the CADM test assumes complete incongruence of the phylogenetic trees instead of congruence. In this study, we performed computer simulations to assess the type I error rate and power of the test. It was applied to additive distance matrices representing phylogenies and to genetic distance matrices obtained from nucleotide sequences of different lengths that were simulated on randomly generated trees of varying sizes, and under different evolutionary conditions. Results Our results showed that the test has an accurate type I error rate and good power. As expected, power increased with the number of objects (i.e., taxa), the number of partially or completely congruent matrices and the level of congruence among distance matrices. Conclusions Based on our results, we suggest that CADM is an excellent candidate to test for congruence and, when present, to estimate its level in phylogenomic studies where numerous genes are analysed simultaneously. PMID:21388552

Chemical resistance and cleanability of glazed surfaces

NASA Astrophysics Data System (ADS)

Hupa, Leena; Bergman, Roger; Fröberg, Linda; Vane-Tempest, Stina; Hupa, Mikko; Kronberg, Thomas; Pesonen-Leinonen, Eija; Sjöberg, Anna-Maija

2005-06-01

Adhesion of soil on glazed surfaces and their cleanability depends on chemical composition, phase composition, and roughness of the surface. The surface can be glossy consisting mainly of a smooth glassy phase. A matt and rough surface consists of a glassy phase and one or more crystalline phases. The origin and composition of the crystalline phases affect the chemical resistance and the cleanability of the surface. Fifteen experimental glossy and matt glazes were soaked in a slightly alkaline cleaning agent solution. The surfaces were spin-coated with sebum, i.e. a soil component typical for sanitary facilities. After wiping out the soil film in a controlled manner, the surface conditions and the soil left were evaluated with colour measurements, SEM/EDXA and COM. The results show that wollastonite-type crystals in the glaze surfaces were attacked in aqueous solutions containing typical cleaning agents. This corrosion led to significant decrease in the cleanability of the surface. The other crystal types observed, i.e. diopside and quartz crystals were not corroded, and the cleanability of glazes containing only these crystals was not changed in the cleaning agent exposures. Also the glassy phase was found to be attacked in some formulations leading to a somewhat decreased cleanability. The repeated soiling and cleaning procedures indicated that soil is accumulated on rough surfaces and surfaces which were clearly corroded by the cleaning agent.

A rapid electrochemical monitoring platform for sensitive determination of thiamethoxam based on β-cyclodextrin-graphene composite.

PubMed

Zhai, XingChen; Zhang, Hua; Zhang, Min; Yang, Xin; Gu, Cheng; Zhou, GuoPeng; Zhao, HaiTian; Wang, ZhenYu; Dong, AiJun; Wang, Jing

2017-08-01

A rapid monitoring platform for sensitive voltammetric detection of thiamethoxam residues is reported in the present study. A β-cyclodextrin-reduced graphene oxide composite was used as a reinforcing material in electrochemical determination of thiamethoxam. Compared with bare glassy carbon electrodes, the reduction peak currents of thiamethoxam at reduced graphene oxide/glassy carbon electrode and β-cyclodextrin-reduced graphene oxide/glassy carbon electrode were increased by 70- and 124-fold, respectively. The experimental conditions influencing voltammetric determination of thiamethoxam, such as the amount of β-cyclodextrin-reduced graphene oxide, solution pH, temperature, and accumulation time, were optimized. The reduction mechanism and binding affinity of this material is also discussed. Under optimal conditions, the reduction peak currents increased linearly between 0.5 µM and 16 µM concentration of thiamethoxam. The limit of detection was 0.27 µM on the basis of a signal-to-noise ratio of 3. When the proposed method was applied to brown rice in a recovery test, the recoveries were between 92.20% and 113.75%. The results were in good concordance with the high-performance liquid chromatography method. The proposed method therefore provides a promising and effective platform for sensitive and rapid determination of thiamethoxam. Environ Toxicol Chem 2017;36:1991-1997. © 2017 SETAC. © 2017 SETAC.

Metallic and nonmetallic shine in luster: An elastic ion backscattering study

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

Pradell, T.; Climent-Font, A.; Molera, J.

2007-05-15

Luster is a metal glass nanocomposite layer first produced in the Middle East in early Islamic times (9th AD) made of metal copper or silver nanoparticles embedded in a silica-based glassy matrix. These nanoparticles are produced by ion exchange between Cu{sup +} and Ag{sup +} and alkaline ions from the glassy matrix and further growth in a reducing atmosphere. The most striking property of luster is its capability of reflecting light like a continuous metal layer and it was unexpectedly found to be linked to one single production parameter: the presence of lead in the glassy matrix composition. The purposemore » of this article is to describe the characteristics and differences of the nanoparticle layers developed on lead rich and lead free glasses. Copper luster layers obtained using the ancient recipes and methods are analyzed by means of elastic ion backscattering spectroscopy associated with other analytical techniques. The depth profile of the different elements is determined, showing that the luster layer formed in lead rich glasses is 5-6 times thinner and 3-4 times Cu richer. Therefore, the metal nanoparticles are more densely packed in the layer and this fact is related to its higher reflectivity. It is shown that lead influences the structure of the metal nanoparticle layer through the change of the precipitation kinetics.« less

Local thermal energy as a structural indicator in glasses

NASA Astrophysics Data System (ADS)

Zylberg, Jacques; Lerner, Edan; Bar-Sinai, Yohai; Bouchbinder, Eran

2017-07-01

Identifying heterogeneous structures in glasses—such as localized soft spots—and understanding structure-dynamics relations in these systems remain major scientific challenges. Here, we derive an exact expression for the local thermal energy of interacting particles (the mean local potential energy change caused by thermal fluctuations) in glassy systems by a systematic low-temperature expansion. We show that the local thermal energy can attain anomalously large values, inversely related to the degree of softness of localized structures in a glass, determined by a coupling between internal stresses—an intrinsic signature of glassy frustration—anharmonicity and low-frequency vibrational modes. These anomalously large values follow a fat-tailed distribution, with a universal exponent related to the recently observed universal ω4ω4 density of states of quasilocalized low-frequency vibrational modes. When the spatial thermal energy field—a “softness field”—is considered, this power law tail manifests itself by highly localized spots, which are significantly softer than their surroundings. These soft spots are shown to be susceptible to plastic rearrangements under external driving forces, having predictive powers that surpass those of the normal modes-based approach. These results offer a general, system/model-independent, physical/observable-based approach to identify structural properties of quiescent glasses and relate them to glassy dynamics.

Highly Stable Glassy Carbon Interfaces for Long-Term Neural Stimulation and Low-Noise Recording of Brain Activity

PubMed Central

Vomero, Maria; Castagnola, Elisa; Ciarpella, Francesca; Maggiolini, Emma; Goshi, Noah; Zucchini, Elena; Carli, Stefano; Fadiga, Luciano; Kassegne, Sam; Ricci, Davide

2017-01-01

We report on the superior electrochemical properties, in-vivo performance and long term stability under electrical stimulation of a new electrode material fabricated from lithographically patterned glassy carbon. For a direct comparison with conventional metal electrodes, similar ultra-flexible, micro-electrocorticography (μ-ECoG) arrays with platinum (Pt) or glassy carbon (GC) electrodes were manufactured. The GC microelectrodes have more than 70% wider electrochemical window and 70% higher CTC (charge transfer capacity) than Pt microelectrodes of similar geometry. Moreover, we demonstrate that the GC microelectrodes can withstand at least 5 million pulses at 0.45 mC/cm2 charge density with less than 7.5% impedance change, while the Pt microelectrodes delaminated after 1 million pulses. Additionally, poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT-PSS) was selectively electrodeposited on both sets of devices to specifically reduce their impedances for smaller diameters (<60 μm). We observed that PEDOT-PSS adhered significantly better to GC than Pt, and allowed drastic reduction of electrode size while maintaining same amount of delivered current. The electrode arrays biocompatibility was demonstrated through in-vitro cell viability experiments, while acute in vivo characterization was performed in rats and showed that GC microelectrode arrays recorded somatosensory evoked potentials (SEP) with an almost twice SNR (signal-to-noise ratio) when compared to the Pt ones. PMID:28084398

Raman Spectroscopy of Isotopic Water Diffusion in Ultraviscous, Glassy, and Gel States in Aerosol by Use of Optical Tweezers.

PubMed

Davies, James F; Wilson, Kevin R

2016-02-16

The formation of ultraviscous, glassy, and amorphous gel states in aqueous aerosol following the loss of water results in nonequilibrium dynamics due to the extended time scales for diffusive mixing. Existing techniques for measuring water diffusion by isotopic exchange are limited by contact of samples with the substrate, and methods applied to infer diffusion coefficients from mass transport in levitated droplets requires analysis by complex coupled differential equations to derive diffusion coefficients. We present a new technique that combines contactless levitation with aerosol optical tweezers with isotopic exchange (D2O/H2O) to measure the water diffusion coefficient over a broad range (Dw ≈ 10(-12)-10(-17) m(2)·s(-1)) in viscous organic liquids (citric acid, sucrose, and shikimic acid) and inorganic gels (magnesium sulfate, MgSO4). For the organic liquids in binary and ternary mixtures, Dw depends on relative humidity and follows a simple compositional Vignes relationship. In MgSO4 droplets, water diffusivity decreases sharply with water activity and is consistent with predictions from percolation theory. These measurements show that, by combining micrometer-sized particle levitation (a contactless measurement with rapid mixing times) with an established probe of water diffusion, Dw can be simply and directly quantified for amorphous and glassy states that are inaccessible to existing methods.

A glassy carbon electrode modified with poly(2,4-dinitrophenylhydrazine) for simultaneous detection of dihydroxybenzene isomers.

PubMed

Lopa, Nasrin Siraj; Rahman, Md Mahbubur; Jang, Hohyoun; Sutradhar, Sabuj Chandra; Ahmed, Faiz; Ryu, Taewook; Kim, Whangi

2017-12-06

2,4-Dinitrophenylhydrazine (DNPH) was electropolymerized on the surface of an anodized glassy carbon electrode by cyclic voltammetry. The anodized electrode has a highly electroactive surface due to the creation of chemically functionalized graphitic nanoparticles, and this facilitates the formation of poly-DNPH via radical polymerization. Poly-DNPH displays excellent redox activity due to the presence of nitro groups on its backbone. These catalyze the electro-oxidation of hydroquinone (HQ) and catechol (CT). The peak-to-peak separation is around 109 mV, while a bare GCE cannot resolve the peaks (located at 165 and 274 mV vs. Ag/AgCl). Sensitivity is also enhanced to ∼1.20 and 1.19 μA·cm -2 ·μM -1 , respectively. The sensor has a linear response that covers the 20-250 μM concentration range for both HQ and CT, with 0.75 and 0.76 μM detection limits, respectively, at simultaneous detection. Commonly present species do not interfere. Graphical abstract A novel conducting poly(2,4-dinitrophenylhydrazine)-modified anodized glassy carbon electrode (pDNPH/AGCE) was developed by electrochemical method. The electro-catalytic activity of pDNPH/AGCE sensor was investigated for the selective and simultaneous electrochemical detection of hydroquinone (HQ) and catechol (CT), which revealed high sensitivities and low detection limits with excellent stability.

A User-Friendly Model for Spray Drying to Aid Pharmaceutical Product Development

PubMed Central

Grasmeijer, Niels; de Waard, Hans; Hinrichs, Wouter L. J.; Frijlink, Henderik W.

2013-01-01

The aim of this study was to develop a user-friendly model for spray drying that can aid in the development of a pharmaceutical product, by shifting from a trial-and-error towards a quality-by-design approach. To achieve this, a spray dryer model was developed in commercial and open source spreadsheet software. The output of the model was first fitted to the experimental output of a Büchi B-290 spray dryer and subsequently validated. The predicted outlet temperatures of the spray dryer model matched the experimental values very well over the entire range of spray dryer settings that were tested. Finally, the model was applied to produce glassy sugars by spray drying, an often used excipient in formulations of biopharmaceuticals. For the production of glassy sugars, the model was extended to predict the relative humidity at the outlet, which is not measured in the spray dryer by default. This extended model was then successfully used to predict whether specific settings were suitable for producing glassy trehalose and inulin by spray drying. In conclusion, a spray dryer model was developed that is able to predict the output parameters of the spray drying process. The model can aid the development of spray dried pharmaceutical products by shifting from a trial-and-error towards a quality-by-design approach. PMID:24040240

Electron transfer with self-assembled copper ions at Au-deposited biomimetic films: mechanistic ‘anomalies’ disclosed by temperature- and pressure-assisted fast-scan voltammetry

NASA Astrophysics Data System (ADS)

Khoshtariya, Dimitri E.; Dolidze, Tinatin D.; Tretyakova, Tatyana; van Eldik, Rudi

2015-06-01

It has been suggested that electron transfer (ET) processes occurring in complex environments capable of glass transitions, specifically in biomolecules, under certain conditions may experience the medium’s nonlinear response and nonergodic kinetic patterns. The interiors of self-assembled organic films (SAMs) deposited on solid conducting platforms (electrodes) are known to undergo glassy dynamics as well, hence they may also exhibit the abovementioned ‘irregularities’. We took advantage of Cu2+ ions as redox-active probes trapped in the Au-deposited  -COOH-terminated SAMs, either L-cysteine, or 3-mercaptopropionic acid diluted by the inert 2-mercaptoethanol, to systematically study the impact of glassy dynamics on ET using the fast-scan voltammetry technique and its temperature and high-pressure extensions. We found that respective kinetic data can be rationalized within the extended Marcus theory, taking into account the frictionally controlled (adiabatic) mechanism for short-range ET, and complications due to the medium’s nonlinear response and broken ergodicity. This combination shows up in essential deviations from the conventional energy gap (overpotential) dependence and in essentially nonlinear temperature (Arrhenius) and high-pressure patterns, respectively. Biomimetic aspects for these systems are also discussed in the context of recently published results for interfacial ET involving self-assembled blue copper protein (azurin) placed in contact with a glassy environment.

Raman Spectroscopy of Isotopic Water Diffusion in Ultraviscous, Glassy, and Gel States in Aerosol by Use of Optical Tweezers

DOE PAGES

Davies, James F.; Wilson, Kevin R.

2016-01-11

The formation of ultraviscous, glassy, and amorphous gel states in aqueous aerosol following the loss of water results in nonequilibrium dynamics due to the extended time scales for diffusive mixing. Existing techniques for measuring water diffusion by isotopic exchange are limited by contact of samples with the substrate, and methods applied to infer diffusion coefficients from mass transport in levitated droplets requires analysis by complex coupled differential equations to derive diffusion coefficients. Here, we present a new technique that combines contactless levitation with aerosol optical tweezers with isotopic exchange (D 2O/H 2O) to measure the water diffusion coefficient over amore » broad range (D w ≈ 10 -12-10 -17 m 2s -1) in viscous organic liquids (citric acid, sucrose, and shikimic acid) and inorganic gels (magnesium sulfate, MgSO 4). For the organic liquids in binary and ternary mixtures, D w depends on relative humidity and follows a simple compositional Vignes relationship. In MgSO 4 droplets, water diffusivity decreases sharply with water activity and is consistent with predictions from percolation theory. These measurements show that, by combining micrometer-sized particle levitation (a contactless measurement with rapid mixing times) with an established probe of water diffusion, D w can be simply and directly quantified for amorphous and glassy states that are inaccessible to existing methods.« less

Diffusion of liquid polystyrene into glassy poly(phenylene oxide) characterized by DSC

NASA Astrophysics Data System (ADS)

Li, Linling; Wang, Xiaoliang; Zhou, Dongshan; Xue, Gi

2013-03-01

We report a diffusion study on the polystyrene/poly(phenylene oxide) (PS/PPO) mixture consisted by the PS and PPO nanoparticles. Diffusion of liquid PS into glassy PPO (l-PS/g-PPO) is promoted by annealing the PS/PPO mixture at several temperatures below Tg of the PPO. By tracing the Tgs of the PS-rich domain behind the diffusion front using DSC, we get the relationships of PS weight fractions and diffusion front advances with the elapsed diffusion times at different diffusion temperatures using the Gordon-Taylor equation and core-shell model. We find that the plots of weight fraction of PS vs. elapsed diffusion times at different temperatures can be converted to a master curve by Time-Temperature superposition, and the shift factors obey the Arrhenius equation. Besides, the diffusion front advances of l-PS into g-PPO show an excellent agreement with the t1/2 scaling law at the beginning of the diffusion process, and the diffusion coefficients of different diffusion temperatures also obey the Arrhenius equation. We believe the diffusion mechanism for l-PS/g-PPO should be the Fickean law rather than the Case II, though there are departures of original linearity at longer diffusion times due to the limited liquid supply system. Diffusion of liquid polystyrene into glassy poly(phenylene oxide) characterized by DSC

Enzymatic biosensor based on entrapment of d-amino acid oxidase on gold nanofilm/MWCNTs nanocomposite modified glassy carbon electrode by sol-gel network: Analytical applications for d-alanine in human serum.

PubMed

Shoja, Yalda; Rafati, Amir Abbas; Ghodsi, Javad

2017-05-01

Sensing and determination of d-alanine is studied by using an enzymatic biosensor which was constructed on the basis of d-amino acid oxidase (DAAO) immobilization by sol-gel film onto glassy carbon electrode surface modified with nanocomposite of gold nanofilm (Au-NF) and multiwalled carbon nanotubes (MWCNTs). The Au-NF/MWCNT nanocomposite was prepared by applying the potentiostatic technique for electrodeposition of Au-NF on the MWCNT immobilized on glassy carbon electrode surface. The modified electrode is investigated by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), linear sweep voltammetry (LSV) and cyclic voltammetry(CV) techniques. The linear sweep voltammetry was used for determination of d-alanine and the results showed an excellent linear relationship between biosensor response and d-alanine concentration ranging from 0.25μM to 4.5μM with correction coefficient of 0.999 (n=20). Detection limit for the fabricated sensor was calculated about 20nM (for S/N=3) and sensitivity was about 56.1μAμM -1 cm -2 . The developed biosensor exhibited rapid and accurate response to d-alanine, a good stability (4 weeks) and an average recovery of 98.9% in human serum samples. Copyright © 2017 Elsevier Inc. All rights reserved.

Electrochemical Determination of Caffeine Content in Ethiopian Coffee Samples Using Lignin Modified Glassy Carbon Electrode.

PubMed

Amare, Meareg; Aklog, Senait

2017-01-01

Lignin film was deposited at the surface of glassy carbon electrode potentiostatically. In contrast to the unmodified glassy carbon electrode, an oxidative peak with an improved current and overpotential for caffeine at modified electrode showed catalytic activity of the modifier towards oxidation of caffeine. Linear dependence of peak current on caffeine concentration in the range 6 × 10 -6 to 100 × 10 -6  mol L -1 with determination coefficient and method detection limit (LoD = 3 s/slope) of 0.99925 and 8.37 × 10 -7  mol L -1 , respectively, supplemented by recovery results of 93.79-102.17% validated the developed method. An attempt was made to determine the caffeine content of aqueous coffee extracts of Ethiopian coffees grown in four coffee cultivating localities (Wonbera, Wolega, Finoteselam, and Zegie) and hence to evaluate the correlation between users preference and caffeine content. In agreement with reported works, caffeine contents (w/w%) of 0.164 in Wonbera coffee; 0.134 in Wolega coffee; 0.097 in Finoteselam coffee; and 0.089 in Zegie coffee were detected confirming the applicability of the developed method for determination of caffeine in a complex matrix environment. The result indicated that users' highest preference for Wonbera and least preference for Zegie cultivated coffees are in agreement with the caffeine content.

In situ AFM investigation of slow crack propagation mechanisms in a glassy polymer

NASA Astrophysics Data System (ADS)

George, M.; Nziakou, Y.; Goerke, S.; Genix, A.-C.; Bresson, B.; Roux, S.; Delacroix, H.; Halary, J.-L.; Ciccotti, M.

2018-03-01

A novel experimental technique based on in situ AFM monitoring of the mechanisms of damage and the strain fields associated to the slow steady-state propagation of a fracture in glassy polymers is presented. This micron-scale investigation is complemented by optical measurements of the sample deformation up to the millimetric macroscopic scale of the sample in order to assess the proper crack driving conditions. These multi-scale observations provide important insights towards the modeling of the fracture toughness of glassy polymers and its relationship with the macromolecular structure and non-linear rheological properties. This novel technique is first tested on a standard PMMA thermoplastic in order to both evaluate its performance and the richness of this new kind of observations. Although the fracture propagation in PMMA is well known to proceed through crazing in the bulk of the samples, our observations provide a clear description and quantitative evaluation of a change of fracture mechanism towards shear yielding fracture accompanied by local necking close to the free surface of the sample, which can be explained by the local change of stress triaxiality. Moreover, this primary surface necking mechanism is shown to be accompanied by a network of secondary grooves that can be related to surface crazes propagating towards the interior of the sample. This overall scenario is validated by post-mortem fractographic investigations by scanning electron microscopy.

Thermal rejuvenation in metallic glasses

NASA Astrophysics Data System (ADS)

Saida, Junji; Yamada, Rui; Wakeda, Masato; Ogata, Shigenobu

2017-12-01

Structural rejuvenation in metallic glasses by a thermal process (i.e. through recovery annealing) was investigated experimentally and theoretically for various alloy compositions. An increase in the potential energy, a decrease in the density, and a change in the local structure as well as mechanical softening were observed after thermal rejuvenation. Two parameters, one related to the annealing temperature, Ta/Tg, and the other related to the cooling rate during the recovery annealing process, Vc/Vi, were proposed to evaluate the rejuvenation phenomena. A rejuvenation map was constructed using these two parameters. Since the thermal history of metallic glasses is reset above 1.2Tg, accompanied by a change in the local structure, it is essential that the condition of Ta/Tg ≥ 1.2 is satisfied during annealing. The glassy structure transforms into a more disordered state with the decomposition of icosahedral short-range order within this temperature range. Therefore, a new glassy structure (rejuvenation) depending on the subsequent quenching rate is generated. Partial rejuvenation also occurs in a Zr55Al10Ni5Cu30 bulk metallic glass when annealing is performed at a low temperature (Ta/Tg 1.07) followed by rapid cooling. This behavior probably originates from disordering in the weakly bonded (loosely packed) region. This study provides a novel approach to improving the mechanical properties of metallic glasses by controlling their glassy structure.

New Scenario of Dynamical Heterogeneity in Supercooled Liquid and Glassy States of 2D Monatomic System.

PubMed

Van Hoang, Vo; Teboul, Victor; Odagaki, Takashi

2015-12-24

Via analysis of spatiotemporal arrangements of atoms based on their dynamics in supercooled liquid and glassy states of a 2D monatomic system with a double-well Lennard-Jones-Gauss (LJG) interaction potential, we find a new scenario of dynamical heterogeneity. Atoms with the same or very close mobility have a tendency to aggregate into clusters. The number of atoms with high mobility (and size of their clusters) increases with decreasing temperature passing over a maximum before decreasing down to zero. Position of the peak moves toward a lower temperature if mobility of atoms in clusters is lower together with an enhancement of height of the peak. In contrast, the number of atoms with very low mobility or solidlike atoms (and size of their clusters) has a tendency to increase with decreasing temperature and then it suddenly increases in the vicinity of the glass transition temperature leading to the formation of a glassy state. A sudden increase in the number of strongly correlated solidlike atoms in the vicinity of a glass transition temperature (Tg) may be an origin of a drastical increase in viscosity of the glass-forming systems approaching the glass transition. In fact, we find that the diffusion coefficient decays exponentially with a fraction of solidlike atoms exhibiting a sudden decrease in the vicinity of the glass transition region.

High temperature polymerization monitoring of an epoxy resin using ultrasound

NASA Astrophysics Data System (ADS)

Maréchal, P.; Ghodhbani, N.; Duflo, H.

2018-05-01

In this study, the real time ultrasonic monitoring is investigated to quantify changes in physical and mechanical properties during the manufacture of composite structures. In this context, an experimental transmission was developed with the aim of characterizing a high temperature polymerization reaction and post-curing properties using an ultrasonic method. First, the monitoring of ultrasonic parameters of a thermosetting resin is carried out in a device reproducing the experimental conditions for manufacturing a composite material with a process known as RTM, that is to say an isothermal polymerization at T = 160°C. During this curing, the resin is changing from its initial viscous liquid state to its final viscous solid state. Between those states, a glassy transition stage is observed, during which the physical properties are strongly changing, i.e. an increase of the ultrasonic velocity up to its steady value and a transient increase of the ultrasonic attenuation. Second, the ultrasonic inspection of the thermosetting resin is performed during a heating and cooling process to study the temperature sensitivity after curing. This type of characterization leads to identifying the ultrasonic properties dependence before, during and after the glassy transition temperature Tg . Eventually, this study is composed of two complementary parts: the first is useful for the curing optimization, while the second one is fruitful for the post-processing characterization in a temperature range including the glassy transition temperature Tg .

EFFECT OF PRE-ALLOYING CONDITION ON THE BULK AMORPHOUS ALLOY ND(60)FE(30)AL(10).

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

OCONNOR,A.S.; LEWIS,L.H.; MCCALLUM,R.W.

Bulk metallic glasses are materials that require only modest cooling rates to obtain amorphous solids directly from the melt. Nd{sub 60}Fe{sub 30}Al{sub 10} has been reported to be a ferromagnetic bulk metallic glass that exhibits high coercivity, a combination unlike conventional Nd-based amorphous magnetic alloys. To clarify the relationship between short-range order and high coercivity in glassy Nd{sub 60}Fe{sub 30}Al{sub 10}, experiments were performed to verify the existence of a homogeneous liquid state prior to rapid solidification. Alloys were prepared by various pre-alloying routes and then melt-spun. Arc-melted alloys were prepared for melt spinning using three different protocols involving: (1)more » alloying all three elements at once, (2) forming a Nd-Fe alloy which was subsequently alloyed with Al, and (3) forming a Fe-Al alloy for subsequent alloying with Nd. XRD, DTA, and magnetic measurement data from the resultant ribbons indicate significant differences in both the glassy fraction and the crystalline phase present in the as-spun material. These observed differences are attributed to the presence of highly stable nanoscopic aluminide-and/or silicide-phases, or motes, present in the melt prior to solidification. These motes would affect the short-range order and coercivity of the resultant glassy state and are anticipated to provide heterogeneous nucleation sites for crystallization.« less

Molecular Factors Governing the Liquid and Glassy States Recrystallization of Celecoxib in Binary Mixtures with Excipients of Different Molecular Weights.

PubMed

Grzybowska, K; Chmiel, K; Knapik-Kowalczuk, J; Grzybowski, A; Jurkiewicz, K; Paluch, M

2017-04-03

Transformation of poorly water-soluble crystalline pharmaceuticals to the amorphous form is one of the most promising strategies to improve their oral bioavailability. Unfortunately, the amorphous drugs are usually thermodynamically unstable and may quickly return to their crystalline form. A very promising way to enhance the physical stability of amorphous drugs is to prepare amorphous compositions of APIs with certain excipients which can be characterized by significantly different molecular weights, such as polymers, acetate saccharides, and other APIs. By using different experimental techniques (broadband dielectric spectroscopy, differential scanning calorimetry, X-ray diffraction) we compare the effect of adding the large molecular weight polymer-polyvinylpyrrolidone (PVP K30)-and the small molecular weight excipient-octaacetylmaltose (acMAL)-on molecular dynamics as well as the tendency to recrystallization of the amorphous celecoxib (CEL) in the amorphous solid dispersions: CEL-PVP and CEL-acMAL. The physical stability investigations of the binary systems were performed in both the supercooled liquid and glassy states. We found that acMAL is a better inhibitor of recrystallization of amorphous CEL than PVP K30 deep in the glassy state (T < T g ). In contrast, PVP K30 is a better crystallization inhibitor of CEL than acMAL in the supercooled liquid state (at T > T g ). We discuss molecular factors governing the recrystallization of amorphous CEL in examined solid dispersions.

Classical mutual information in mean-field spin glass models

NASA Astrophysics Data System (ADS)

Alba, Vincenzo; Inglis, Stephen; Pollet, Lode

2016-03-01

We investigate the classical Rényi entropy Sn and the associated mutual information In in the Sherrington-Kirkpatrick (S-K) model, which is the paradigm model of mean-field spin glasses. Using classical Monte Carlo simulations and analytical tools we investigate the S-K model in the n -sheet booklet. This is achieved by gluing together n independent copies of the model, and it is the main ingredient for constructing the Rényi entanglement-related quantities. We find a glassy phase at low temperatures, whereas at high temperatures the model exhibits paramagnetic behavior, consistent with the regular S-K model. The temperature of the paramagnetic-glassy transition depends nontrivially on the geometry of the booklet. At high temperatures we provide the exact solution of the model by exploiting the replica symmetry. This is the permutation symmetry among the fictitious replicas that are used to perform disorder averages (via the replica trick). In the glassy phase the replica symmetry has to be broken. Using a generalization of the Parisi solution, we provide analytical results for Sn and In and for standard thermodynamic quantities. Both Sn and In exhibit a volume law in the whole phase diagram. We characterize the behavior of the corresponding densities, Sn/N and In/N , in the thermodynamic limit. Interestingly, at the critical point the mutual information does not exhibit any crossing for different system sizes, in contrast with local spin models.

Virial expansion for almost diagonal random matrices

NASA Astrophysics Data System (ADS)

Yevtushenko, Oleg; Kravtsov, Vladimir E.

2003-08-01

Energy level statistics of Hermitian random matrices hat H with Gaussian independent random entries Higeqj is studied for a generic ensemble of almost diagonal random matrices with langle|Hii|2rangle ~ 1 and langle|Hi\

Inference for High-dimensional Differential Correlation Matrices *

PubMed Central

Cai, T. Tony; Zhang, Anru

2015-01-01

Motivated by differential co-expression analysis in genomics, we consider in this paper estimation and testing of high-dimensional differential correlation matrices. An adaptive thresholding procedure is introduced and theoretical guarantees are given. Minimax rate of convergence is established and the proposed estimator is shown to be adaptively rate-optimal over collections of paired correlation matrices with approximately sparse differences. Simulation results show that the procedure significantly outperforms two other natural methods that are based on separate estimation of the individual correlation matrices. The procedure is also illustrated through an analysis of a breast cancer dataset, which provides evidence at the gene co-expression level that several genes, of which a subset has been previously verified, are associated with the breast cancer. Hypothesis testing on the differential correlation matrices is also considered. A test, which is particularly well suited for testing against sparse alternatives, is introduced. In addition, other related problems, including estimation of a single sparse correlation matrix, estimation of the differential covariance matrices, and estimation of the differential cross-correlation matrices, are also discussed. PMID:26500380

Deterministic matrices matching the compressed sensing phase transitions of Gaussian random matrices

PubMed Central

Monajemi, Hatef; Jafarpour, Sina; Gavish, Matan; Donoho, David L.; Ambikasaran, Sivaram; Bacallado, Sergio; Bharadia, Dinesh; Chen, Yuxin; Choi, Young; Chowdhury, Mainak; Chowdhury, Soham; Damle, Anil; Fithian, Will; Goetz, Georges; Grosenick, Logan; Gross, Sam; Hills, Gage; Hornstein, Michael; Lakkam, Milinda; Lee, Jason; Li, Jian; Liu, Linxi; Sing-Long, Carlos; Marx, Mike; Mittal, Akshay; Monajemi, Hatef; No, Albert; Omrani, Reza; Pekelis, Leonid; Qin, Junjie; Raines, Kevin; Ryu, Ernest; Saxe, Andrew; Shi, Dai; Siilats, Keith; Strauss, David; Tang, Gary; Wang, Chaojun; Zhou, Zoey; Zhu, Zhen

2013-01-01

In compressed sensing, one takes samples of an N-dimensional vector using an matrix A, obtaining undersampled measurements . For random matrices with independent standard Gaussian entries, it is known that, when is k-sparse, there is a precisely determined phase transition: for a certain region in the (,)-phase diagram, convex optimization typically finds the sparsest solution, whereas outside that region, it typically fails. It has been shown empirically that the same property—with the same phase transition location—holds for a wide range of non-Gaussian random matrix ensembles. We report extensive experiments showing that the Gaussian phase transition also describes numerous deterministic matrices, including Spikes and Sines, Spikes and Noiselets, Paley Frames, Delsarte-Goethals Frames, Chirp Sensing Matrices, and Grassmannian Frames. Namely, for each of these deterministic matrices in turn, for a typical k-sparse object, we observe that convex optimization is successful over a region of the phase diagram that coincides with the region known for Gaussian random matrices. Our experiments considered coefficients constrained to for four different sets , and the results establish our finding for each of the four associated phase transitions. PMID:23277588

Amino acid "little Big Bang": representing amino acid substitution matrices as dot products of Euclidian vectors.

PubMed

Zimmermann, Karel; Gibrat, Jean-François

2010-01-04

Sequence comparisons make use of a one-letter representation for amino acids, the necessary quantitative information being supplied by the substitution matrices. This paper deals with the problem of finding a representation that provides a comprehensive description of amino acid intrinsic properties consistent with the substitution matrices. We present a Euclidian vector representation of the amino acids, obtained by the singular value decomposition of the substitution matrices. The substitution matrix entries correspond to the dot product of amino acid vectors. We apply this vector encoding to the study of the relative importance of various amino acid physicochemical properties upon the substitution matrices. We also characterize and compare the PAM and BLOSUM series substitution matrices. This vector encoding introduces a Euclidian metric in the amino acid space, consistent with substitution matrices. Such a numerical description of the amino acid is useful when intrinsic properties of amino acids are necessary, for instance, building sequence profiles or finding consensus sequences, using machine learning algorithms such as Support Vector Machine and Neural Networks algorithms.

Etude du champ magnetique dans les nuages moleculaires

NASA Astrophysics Data System (ADS)

Houde, Martin

2001-12-01

Ce travail est une étude du champ magnétique duns l'environnement circumstellaire des étoiles jeunes. Il a pour origine la certitude qu'avait l'auteur qu'il se devait d'être possible de détecter la présence d'un champ magnétique, et de possiblement le caractériser, par le biais d'observations de profils spectraux d'espèces moléculaires ioniques. Il en découle donc qu'un des buts principaux était de prouver que cela est effectivement possible. La thèse comporte alors des éléments théoriques et expérimentaux qui sont à la fois complémentaires et intimement liés. L'aspect théorique est basé sur l'interaction mutuelle que des particules neutres et chargées peuvent avoir l'une sur l'autre daps un plasma faiblement ionisé comme ceux existants daps les nuages moléculaires sites de formation stellaire. Il appert que la présence d'un champ magnétique a un effet direct sur le comportement des ions (via la force de Lorentz) et indirect sur les molécules neutres (via les nombreuses collisions entre les deux types de particules). Une telle interaction est, comme il est maintenant bien connu, présente dans les premières étapes de la formation dune étoile. Il s'agit bien sûr de la diffusion ambipolaire. Nous montrerons qu'il existe cependant un autre type de diffusion, jusqu'ici inconnue, qui se manifeste plus tard au tours de l'évolution des nuages moléculaires. Celle-ci peut avoir un effet dramatique sur l'apparence des profils spectraux (de rotation moléculaire) des espèces ioniques lorsque comparés à ceux qu'exhibent des espèces neutres coexistantes. Mais pour ce faire, il doit y avoir existence de mouvements organisés (des flots ou jets) de matière ou encore la présence de turbulence dans les régions considérées. Une distribution de vélocité du type maxwellienne ne révèlera pas la présence du champ magnétique. Les observations, qui ont pour but de confirmer la théorie, se situent dans le domaine des longueurs d'ondes millimétriques et sous- millimétriques. Plusieurs espèces moléculaires furent détectées dans un échantillon significatif de nuages moléculaires. L'effet prédit fut confirmé et ce peu importe si les raies observées sont opaques ou transparentes. Dans le dernier chapitre, nous considérerons une application intéressante où nous utiliserons la manifestation de cet effet (ou son manque) pour vérifier l'alignement préférentiel des flots bipolaires, qui accompagnent souvent la présence de proto- étoiles, avec le champ magnétique local.

Quantification of VX Nerve Agent in Various Food Matrices by Solid-Phase Extraction Ultra-Performance Liquid ChromatographyTime-of-Flight Mass Spectrometry

DTIC Science & Technology

2016-04-01

QUANTIFICATION OF VX NERVE AGENT IN VARIOUS FOOD MATRICES BY SOLID-PHASE EXTRACTION ULTRA-PERFORMANCE...TITLE AND SUBTITLE Quantification of VX Nerve Agent in Various Food Matrices by Solid-Phase Extraction Ultra-Performance Liquid Chromatography... food matrices. The mixed-mode cation exchange (MCX) sorbent and Quick, Easy, Cheap, Effective, Rugged, and Safe (QuEChERS) methods were used for

Novel image compression-encryption hybrid algorithm based on key-controlled measurement matrix in compressive sensing

NASA Astrophysics Data System (ADS)

Zhou, Nanrun; Zhang, Aidi; Zheng, Fen; Gong, Lihua

2014-10-01

The existing ways to encrypt images based on compressive sensing usually treat the whole measurement matrix as the key, which renders the key too large to distribute and memorize or store. To solve this problem, a new image compression-encryption hybrid algorithm is proposed to realize compression and encryption simultaneously, where the key is easily distributed, stored or memorized. The input image is divided into 4 blocks to compress and encrypt, then the pixels of the two adjacent blocks are exchanged randomly by random matrices. The measurement matrices in compressive sensing are constructed by utilizing the circulant matrices and controlling the original row vectors of the circulant matrices with logistic map. And the random matrices used in random pixel exchanging are bound with the measurement matrices. Simulation results verify the effectiveness, security of the proposed algorithm and the acceptable compression performance.

Intrinsic character of Stokes matrices

NASA Astrophysics Data System (ADS)

Gagnon, Jean-François; Rousseau, Christiane

2017-02-01

Two germs of linear analytic differential systems x k + 1Y‧ = A (x) Y with a non-resonant irregular singularity are analytically equivalent if and only if they have the same eigenvalues and equivalent collections of Stokes matrices. The Stokes matrices are the transition matrices between sectors on which the system is analytically equivalent to its formal normal form. Each sector contains exactly one separating ray for each pair of eigenvalues. A rotation in S allows supposing that R+ lies in the intersection of two sectors. Reordering of the coordinates of Y allows ordering the real parts of the eigenvalues, thus yielding triangular Stokes matrices. However, the choice of the rotation in x is not canonical. In this paper we establish how the collection of Stokes matrices depends on this rotation, and hence on a chosen order of the projection of the eigenvalues on a line through the origin.

Surveying the quantum group symmetries of integrable open spin chains

NASA Astrophysics Data System (ADS)

Nepomechie, Rafael I.; Retore, Ana L.

2018-05-01

Using anisotropic R-matrices associated with affine Lie algebras g ˆ (specifically, A2n(2), A2n-1 (2) , Bn(1), Cn(1), Dn(1)) and suitable corresponding K-matrices, we construct families of integrable open quantum spin chains of finite length, whose transfer matrices are invariant under the quantum group corresponding to removing one node from the Dynkin diagram of g ˆ . We show that these transfer matrices also have a duality symmetry (for the cases Cn(1) and Dn(1)) and additional Z2 symmetries that map complex representations to their conjugates (for the cases A2n-1 (2) , Bn(1) and Dn(1)). A key simplification is achieved by working in a certain "unitary" gauge, in which only the unbroken symmetry generators appear. The proofs of these symmetries rely on some new properties of the R-matrices. We use these symmetries to explain the degeneracies of the transfer matrices.

Amperometric biosensor based on glassy carbon electrode modified with long-length carbon nanotube and enzyme

NASA Astrophysics Data System (ADS)

Furutaka, Hajime; Nemoto, Kentaro; Inoue, Yuki; Hidaka, Hiroki; Muguruma, Hitoshi; Inoue, Hitoshi; Ohsawa, Tatsuya

2016-05-01

An amperometric biosensor based on a glassy carbon electrode modified with long-length multiwalled carbon nanotubes (MWCNTs) and enzyme nicotinamide-adenine-dinucleotide-dependent glucose dehydrogenase (GDH) is presented. We demonstrate the effect of the MWCNT length on the amperometric response of the enzyme biosensor. The long length of MWCNT is 200 µm (average), whereas the normal length of MWCNT is 1 µm (average). The response of the long MWCNT-GDH electrode is 2 times more sensitive than that of the normal-length MWCNT-GDH electrode in the concentration range from 0.25-35 mM. The result of electrochemical impedance spectroscopy measurements suggest that the long-length MWCNT-GDH electrode formed a better electron transfer network than the normal-length one.

Manufacturing of glassy thin shell for adaptive optics: results achieved

NASA Astrophysics Data System (ADS)

Poutriquet, F.; Rinchet, A.; Carel, J.-L.; Leplan, H.; Ruch, E.; Geyl, R.; Marque, G.

2012-07-01

Glassy thin shells are key components for the development of adaptive optics and are part of future & innovative projects such as ELT. However, manufacturing thin shells is a real challenge. Even though optical requirements for the front face - or optical face - are relaxed compared to conventional passive mirrors, requirements concerning thickness uniformity are difficult to achieve. In addition, process has to be completely re-defined as thin mirror generates new manufacturing issues. In particular, scratches and digs requirement is more difficult as this could weaken the shell, handling is also an important issue due to the fragility of the mirror. Sagem, through REOSC program, has recently manufactured different types of thin shells in the frame of European projects: E-ELT M4 prototypes and VLT Deformable Secondary Mirror (VLT DSM).

Raman non-coincidence effect of boroxol ring: The interplay between repulsion and attraction forces in the glassy, supercooled and liquid state

NASA Astrophysics Data System (ADS)

Kalampounias, Angelos G.; Papatheodorou, George N.

2018-06-01

Temperature dependent Raman spectra of boric oxide have been measured in a temperature range covering the glassy, supercooled and liquid state. The shift of the isotropic band assigned to boroxol rings relative to the anisotropic component upon heating the glass is measured and attributed to the Raman non-coincidence effect. The measured shift is associated with the competition between attraction and repulsion forces with increasing temperature. The relation of dephasing and orientational relaxation times to the non-coincidence effect of the condensed phases has been examined. We discuss our results in the framework of the current phenomenological status of the field in an attempt to separate the attraction and repulsion contributions corresponding to the observed non-coincidence effect.

Supercooled and glassy water: Metastable liquid(s), amorphous solid(s), and a no-man's land

NASA Astrophysics Data System (ADS)

Handle, Philip H.; Loerting, Thomas; Sciortino, Francesco

2017-12-01

We review the recent research on supercooled and glassy water, focusing on the possible origins of its complex behavior. We stress the central role played by the strong directionality of the water-water interaction and by the competition between local energy, local entropy, and local density. In this context we discuss the phenomenon of polyamorphism (i.e., the existence of more than one disordered solid state), emphasizing both the role of the preparation protocols and the transformation between the different disordered ices. Finally, we present the ongoing debate on the possibility of linking polyamorphism with a liquid-liquid transition that could take place in the no-man's land, the temperature-pressure window in which homogeneous nucleation prevents the investigation of water in its metastable liquid form.

Pressure Induced Liquid-to-Liquid Transition in Zr-based Supercooled Melts and Pressure Quenched Glasses.

PubMed

Dmowski, W; Gierlotka, S; Wang, Z; Yokoyama, Y; Palosz, B; Egami, T

2017-07-26

Through high-energy x-ray diffraction and atomic pair density function analysis we find that Zr-based metallic alloy, heated to the supercooled liquid state under hydrostatic pressure and then quenched to room temperature, exhibits a distinct glassy structure. The PDF indicates that the Zr-Zr distances in this glass are significantly reduced compared to those quenched without pressure. Annealing at the glass transition temperature at ambient pressure reverses structural changes and the initial glassy state is recovered. This result suggests that pressure causes a liquid-to-liquid phase transition in this metallic alloy supercooled melt. Such a pressure induced transition is known for covalent liquids, but has not been observed for metallic liquids. The High Pressure Quenched glasses are stable in ambient conditions after decompression.

Enhanced amperometric detection of metronidazole in drug formulations and urine samples based on chitosan protected tetrasulfonated copper phthalocyanine thin-film modified glassy carbon electrode.

PubMed

Meenakshi, S; Pandian, K; Jayakumari, L S; Inbasekaran, S

2016-02-01

An enhanced electrocatalytic reduction of metronidazole antibiotic drug molecule using chitosan protected tetrasulfonated copper phthalocyanine (Chit/CuTsPc) thin-film modified glassy carbon electrode (GCE) has been developed. An irreversible reduction occurs at -0.47V (vs. Ag/AgCl) using Chit/CuTsPc modified GCE. A maximum peak current value is obtained at pH1 and the electrochemical reduction reaction is a diffusion controlled one. The detection limit is found to be 0.41nM from differential pulse voltammetry (DPV) method. This present investigation method is adopted for electrochemical detection of metronidazole in drug formulation and urine samples by using DPV method. Copyright © 2015 Elsevier B.V. All rights reserved.

Pressure-induced positive electrical resistivity coefficient in Ni-Nb-Zr-H glassy alloy

NASA Astrophysics Data System (ADS)

Fukuhara, M.; Gangli, C.; Matsubayashi, K.; Uwatoko, Y.

2012-06-01

Measurements under hydrostatic pressure of the electrical resistivity of (Ni0.36Nb0.24Zr0.40)100-xHx (x = 9.8, 11.5, and 14) glassy alloys have been made in the range of 0-8 GPa and 0.5-300 K. The resistivity of the (Ni0.36Nb0.24Zr0.40)86H14 alloy changed its sign from negative to positive under application of 2-8 GPa in the temperature range of 300-22 K, coming from electron-phonon interaction in the cluster structure under pressure, accompanied by deformation of the clusters. In temperature region below 22 K, the resistivity showed negative thermal coefficient resistance by Debye-Waller factor contribution, and superconductivity was observed at 1.5 K.

ac impedance analysis of a Ni-Nb-Zr-H glassy alloy with femtofarad capacitance tunnels

NASA Astrophysics Data System (ADS)

Fukuhara, M.; Seto, M.; Inoue, A.

2010-01-01

A Nyquist diagram of a (Ni0.36Nb0.24Zr0.40)90H10 glassy alloy shows a semitrue circle, indicating that it is a conducting material with a total capacitance of 17.8 μF. The Bode plots showing the dependencies of its real and imaginary impedances, and phase on frequency suggest a simpler equivalent circuit having a resistor in parallel with a capacitor. Dividing the total capacitance (17.8 μF) by the capacitance of a single tunnel (0.9 fF), we deduced that this material has a high number of dielectric tunnels, which can be regarded as regular prisms separated from the electric-conducting distorted icosahedral Zr5Ni5Nb3 clusters by an average of 0.225 nm.

Poly(amidosulfonic acid) modified glassy carbon electrode for determination of isoniazid in pharmaceuticals.

PubMed

Yang, Gongjun; Wang, Cunxiao; Zhang, Rui; Wang, Chenying; Qu, Qishu; Hu, Xiaoya

2008-06-01

Amidosulfonic acid was electropolymerized by cyclic voltammetry onto the surface of glassy carbon electrode (GCE) to fabricate the chemically modified electrode, which showed high stability, good selectivity and reproducibility for determination of isoniazid. The modified electrode showed an excellent electrocatalytical effect on the oxidation of isoniazid. Under the optimum conditions, there was a good linear relationship between anodic peak current and isoniazid concentration in the range of 5.0 x 10(-8)- 1.0 x 10(-5) M, and a detection limit of 1.0 x 10(-8) M (S/N = 3) was obtained after 120 s at the accumulation potential of - 0.2 V (vs. SCE). This developed method had been applied to the direct determination of isoniazid in injection and tablet samples with satisfactory results.

Efficient linear algebra routines for symmetric matrices stored in packed form.

PubMed

Ahlrichs, Reinhart; Tsereteli, Kakha

2002-01-30

Quantum chemistry methods require various linear algebra routines for symmetric matrices, for example, diagonalization or Cholesky decomposition for positive matrices. We present a small set of these basic routines that are efficient and minimize memory requirements.

ESTIMATION OF FUNCTIONALS OF SPARSE COVARIANCE MATRICES.

PubMed

Fan, Jianqing; Rigollet, Philippe; Wang, Weichen

High-dimensional statistical tests often ignore correlations to gain simplicity and stability leading to null distributions that depend on functionals of correlation matrices such as their Frobenius norm and other ℓ r norms. Motivated by the computation of critical values of such tests, we investigate the difficulty of estimation the functionals of sparse correlation matrices. Specifically, we show that simple plug-in procedures based on thresholded estimators of correlation matrices are sparsity-adaptive and minimax optimal over a large class of correlation matrices. Akin to previous results on functional estimation, the minimax rates exhibit an elbow phenomenon. Our results are further illustrated in simulated data as well as an empirical study of data arising in financial econometrics.

ESTIMATION OF FUNCTIONALS OF SPARSE COVARIANCE MATRICES

PubMed Central

Fan, Jianqing; Rigollet, Philippe; Wang, Weichen

2016-01-01

High-dimensional statistical tests often ignore correlations to gain simplicity and stability leading to null distributions that depend on functionals of correlation matrices such as their Frobenius norm and other ℓr norms. Motivated by the computation of critical values of such tests, we investigate the difficulty of estimation the functionals of sparse correlation matrices. Specifically, we show that simple plug-in procedures based on thresholded estimators of correlation matrices are sparsity-adaptive and minimax optimal over a large class of correlation matrices. Akin to previous results on functional estimation, the minimax rates exhibit an elbow phenomenon. Our results are further illustrated in simulated data as well as an empirical study of data arising in financial econometrics. PMID:26806986

Study of lnter-Molecular Dynamics within Alkylsiloxane Self-Assembled Monolayer and Elastomer Systems

NASA Astrophysics Data System (ADS)

Roman, Michael

In this work, molecular motion, and in particular, glassy relaxations are studied in two novel experimental systems. Both experimental systems offer a significant degree of control over molecule-molecule, or group-group (where group refers to a portion of a molecule), interactions by controlling density and the type of inter-molecular interaction. Both systems have rigid elements that decrease the tendency of bulk materials to spontaneously change their density with temperature. Thus, density can be maintained and controlled and the effect of density and temperature can be (at least in part) de-convolved. The goal of this work is to experimentally observe the transition from simple, local relaxations to glassy dynamics as density is increased and to understand how this transition differs as the inter-molecular interactions are altered. In both approaches, the system is fabricated from individual parts where the nature, spacing, and particular arrangement of the parts can be controlled and the resultant changes in molecular motion can be observed. Building up a custom system from parts enables fundamental investigation into the glass transition (as discussed above) and also makes possible the development of materials that have engineered responses as a function of temperature. As a short-hand, we refer to the two systems as the monolayer or SAM (short for Self-Assembled Monolayer) and elastomer approaches. In Chapters 4-7 we discuss results from the monolayer approach. Chapter 8 summarizes results from the elastomer approach. In particular, Chapter 4 introduces you to dielectric spectroscopy and briefly summarizes the previous work by former students in the Clarke group which identified the local and glass relaxations in silane monolayers of substituted alkyl chains as analogous to the local and glassy relaxations in polymeric systems containing phase segregated alkyl chains, and similar to the local and glass modes in poly(ethylene). The remainder of Chapter 4 summarizes my own work to clearly delineate the transition from non-interacting behavior at low density (a partially-filled monolayer) to glassy behavior (with or without the presence of a local mode) as density is increased. In Chapter 5, I determined that this transition is highly robust to sample preparation technique. In Chapter 6, the effect of different inter-molecular interactions (dipole strength) on this transition and the resultant glassy state is discussed. Chapter 7 discusses changes in the local modes and the distribution of local and glass modes in the system as a function of terminal dipole strength. In chapter 8, elastomers are studied and the effect of backbone composition and distance between crosslinks is shown. This elastomer system can serve as a new substrate on which similar experiments as conducted with mono layers can be undertaken.

Waterlike glass polyamorphism in a monoatomic isotropic Jagla model.

PubMed

Xu, Limei; Giovambattista, Nicolas; Buldyrev, Sergey V; Debenedetti, Pablo G; Stanley, H Eugene

2011-02-14

We perform discrete-event molecular dynamics simulations of a system of particles interacting with a spherically-symmetric (isotropic) two-scale Jagla pair potential characterized by a hard inner core, a linear repulsion at intermediate separations, and a weak attractive interaction at larger separations. This model system has been extensively studied due to its ability to reproduce many thermodynamic, dynamic, and structural anomalies of liquid water. The model is also interesting because: (i) it is very simple, being composed of isotropically interacting particles, (ii) it exhibits polyamorphism in the liquid phase, and (iii) its slow crystallization kinetics facilitate the study of glassy states. There is interest in the degree to which the known polyamorphism in glassy water may have parallels in liquid water. Motivated by parallels between the properties of the Jagla potential and those of water in the liquid state, we study the metastable phase diagram in the glass state. Specifically, we perform the computational analog of the protocols followed in the experimental studies of glassy water. We find that the Jagla potential calculations reproduce three key experimental features of glassy water: (i) the crystal-to-high-density amorphous solid (HDA) transformation upon isothermal compression, (ii) the low-density amorphous solid (LDA)-to-HDA transformation upon isothermal compression, and (iii) the HDA-to-very-high-density amorphous solid (VHDA) transformation upon isobaric annealing at high pressure. In addition, the HDA-to-LDA transformation upon isobaric heating, observed in water experiments, can only be reproduced in the Jagla model if a free surface is introduced in the simulation box. The HDA configurations obtained in cases (i) and (ii) are structurally indistinguishable, suggesting that both processes result in the same glass. With the present parametrization, the evolution of density with pressure or temperature is remarkably similar to the corresponding experimental measurements on water. Our simulations also suggest that the Jagla potential may reproduce features of the HDA-VHDA transformations observed in glassy water upon compression and decompression. Snapshots of the system during the HDA-VHDA and HDA-LDA transformations reveal a clear segregation between LDA and HDA but not between HDA and VHDA, consistent with the possibility that LDA and HDA are separated by a first order transformation as found experimentally, whereas HDA and VHDA are not. Our results demonstrate that a system of particles with simple isotropic pair interactions, a Jagla potential with two characteristic length scales, can present polyamorphism in the glass state as well as reproducing many of the distinguishing properties of liquid water. While most isotropic pair potential models crystallize readily on simulation time scales at the low temperatures investigated here, the Jagla potential is an exception, and is therefore a promising model system for the study of glass phenomenology.

A Study on the Application of the Extended Matrices Based on TRIZ in Constructing a Collaborative Model of Enterprise Network

NASA Astrophysics Data System (ADS)

Yang, Yan; Shao, Yunfei; Tang, Xiaowo

Based on mass related literature on enterprise network, the key influence factors are reduced to Trust, Control, Relationship and Interaction. Meanwhile, the specific contradiction matrices, judgment matrices and strategy collections based on TRIZ are constructed which make the connotation of contradiction matrices in TRIZ extended. Finally they are applied to the construction of the collaborative model on enterprise network based on Multi Agent System (MAS).

Stimulating effect of graphene oxide on myogenesis of C2C12 myoblasts on RGD peptide-decorated PLGA nanofiber matrices.

PubMed

Shin, Yong Cheol; Lee, Jong Ho; Kim, Min Jeong; Hong, Suck Won; Kim, Bongju; Hyun, Jung Keun; Choi, Yu Suk; Park, Jong-Chul; Han, Dong-Wook

2015-01-01

In the field of biomedical engineering, many studies have focused on the possible applications of graphene and related nanomaterials due to their potential for use as scaffolds, coating materials and delivery carriers. On the other hand, electrospun nanofiber matrices composed of diverse biocompatible polymers have attracted tremendous attention for tissue engineering and regenerative medicine. However, their combination is intriguing and still challenging. In the present study, we fabricated nanofiber matrices composed of M13 bacteriophage with RGD peptide displayed on its surface (RGD-M13 phage) and poly(lactic-co-glycolic acid, PLGA) and characterized their physicochemical properties. In addition, the effect of graphene oxide (GO) on the cellular behaviors of C2C12 myoblasts, which were cultured on PLGA decorated with RGD-M13 phage (RGD/PLGA) nanofiber matrices, was investigated. Our results revealed that the RGD/PLGA nanofiber matrices have suitable physicochemical properties as a tissue engineering scaffold and the growth of C2C12 myoblasts were significantly enhanced on the matrices. Moreover, the myogenic differentiation of C2C12 myoblasts was substantially stimulated when they were cultured on the RGD/PLGA matrices in the presence of GO. In conclusion, these findings propose that the combination of RGD/PLGA nanofiber matrices and GO can be used as a promising strategy for skeletal tissue engineering and regeneration.

Electrospun Poly(lactic acid-co-glycolic acid) Scaffolds for Skin Tissue Engineering

PubMed Central

Kumbar, Sangamesh G.; Nukavarapu, Syam Prasad; James, Roshan; Nair, Lakshmi S.; Laurencin, Cato T.

2008-01-01

Electrospun fiber matrices composed of scaffolds of varying fiber diameters were investigated for potential application of severe skin loss. Few systematic studies have been performed to examine the effect of varying fiber diameter electrospun fiber matrices for skin regeneration. The present study reports the fabrication of poly[lactic acid-co-glycolic acid] (PLAGA) matrices with fiber diameters of 150–225, 200–300, 250–467, 500–900, 600–1200, 2500–3000 and 3250–6000 nm via electrospinning. All fiber matrices found to have a tensile modulus from 39.23 ± 8.15 to 79.21 ± 13.71 MPa which falls in the range for normal human skin. Further, the porous fiber matrices have porosity between 38–60 % and average pore diameters between 10–14µm. We evaluated the efficacy of these biodegradable fiber matrices as skin substitutes by seeding them with human skin fibroblasts (hSF). Human skin fibroblasts acquired a well spread morphology and showed significant progressive growth on fiber matrices in the 350–1100 nm diameter range. Collagen type III gene expression was significantly up-regulated in hSF seeded on matrices with fiber diameters in the range of 350–1100 nm. Based on the need, the proposed fiber skin substitutes can be successfully fabricated and optimized for skin fibroblast attachment and growth. PMID:18639927

Redistribution of Sr and rare earth elements in the matrices of CV3 carbonaceous chondrites during aqueous alteration in their parent body

NASA Astrophysics Data System (ADS)

Jogo, Kaori; Ito, Motoo; Nakamura, Tomoki; Kobayashi, Sachio; Lee, Jong Ik

2018-03-01

We measured the abundances of Sr and rare earth elements (REEs) in the matrices of five CV3 carbonaceous chondrites: Meteorite Hills (MET) 00430, MET 01070, La Paz ice field (LAP) 02206, Asuka (A) 881317 and Roberts Massif (RBT) 04143. In the MET 00430 and MET 01074 matrices, the Sr/CI and light REE (LREE, La-Nd)/CI ratios positively correlate with the amounts of Ca-rich secondary minerals, which formed during aqueous alteration in the CV3 chondrite parent body. In contrast, in the LAP 02206 and RBT 04143 matrices, although the Sr/CI ratios correlate with the amounts of Ca-rich secondary minerals, the LREE/CI ratios vary independently from the amounts of any secondary minerals. This suggests that the LREE/CI ratios in these matrices were produced prior to the parent body alteration, probably in the solar nebula. The LREE/CI ratios of the LAP 02206 and RBT 04143 matrices reveal the mixing process of matrix minerals prior to the accretion of the CV3 chondrite parent body. The mixing degrees of matrix minerals might be different between these two matrices. Because solid materials would be mixed over time according to the radial diffusion model of a turbulent disk, the matrix minerals consisting of LAP 02206 and RBT 04143 matrices might be incorporated into their parent body with different timing.

Motion Cues in Flight Simulation and Simulator Induced Sickness

DTIC Science & Technology

1988-06-01

asseusod in a driving simulator by means of a response surface methodology central-composite design . The most salient finding of the study was that visual...across treatment conditions. For an orthogonal response surface methodology (IBM) design with only tro independent variables. it can be readily shown that...J.E.Fowikes 8 SESSION III - ETIOLOGICAL FACTORS IN SIMULATOR-INDUCED AFTER EFFETS THE USE OF VE& IIBULAR MODELS FOR DESIGN AND EVALUATION OF FLIGHT

Engineering Aerodynamics

DTIC Science & Technology

1986-12-01

effective Reynolds Number5 to include the effet Of turbulence, which was supported in a convincing manner by the same ratio of 2.4 betwveen the Reynolds...iLIFT DEVICIS 143 methods incorl)orating various forms of flas) are shown on Figure 59. The other two methods, Boundary Layer Control and the Magnus ...Class Airship Hlull with Varying Lengths of Cylindric Midships," N.A.CA. Technical Report No. 138 (1922). 276 ENGINEERING AERODYNAMICS [Ch. 9 -- - - 2.0

Environmental Exposure and Design Criteria for Offshore Oil and Gas Structures

DTIC Science & Technology

1980-05-01

reliability ar_alysis. Because there are no clear lines of demarcation between them, these methods are often used in varying combinations. Sound ...cludes that OCSEA-P not now effe.tively contribute...to the accrual of sound scientific information adequate for OCS management." One reason for such a...procedures for resolving differences need to be developed. Sound and timely assessments of environmental exposure risks will require: 1) adequate levels of

A Snowball's Chance? Communities and Families Working To Prevent Youth Crime = Effet de boule de neige? Les communautes et les familles collaborent a la prevention de la criminalite chez les jeunes.

ERIC Educational Resources Information Center

Theilheimer, Ish, Ed.; Eisner, Kathy, Ed.

1996-01-01

This issue of the Canadian quarterly "Transitions," in French and English language versions, examines the prevention of youth crime, with a specific focus on activities, trends, and research dealing with Canadian families. Major articles in this issue are: (1) "A Snowball's Chance? Communities and Families Working to Prevent Youth…

Superomniphobic Surfaces for Military Applications: Nano- and Micro-Fabrication Methods. Chapter 1: Lithographic Fabrication of Surfaces with Different Microgeometries and Investigation of Their Wetting Behaviour

DTIC Science & Technology

2011-01-01

plus important, comparativement à une échelle plus large. Les résultats indiquent qu’un effet de cette nature est attribuable à des facteurs...par un angle de contact à l’avancement plus petit et un angle de contact au retrait plus important, comparativement à une échelle plus large. Les...Methods ............................................................................................................ 10 3.1 Experimental Design

Recherche universitaire et priorites nationales: l'effet du financement public sur la recherche energie solaire au Canada (University Research and National Priorities: The Effect of Public Financing on Solar Energy Research in Canada).

ERIC Educational Resources Information Center

Dalpe, Robert; Gingras, Yves

1990-01-01

The role of two main sources of university research financing in solar energy is examined to assess whether they oriented research in the direction of government programs. The strongest relationship appears to be in journal publication patterns. This scientific community has acquired the capacity to tap varying sources. (Author/MSE)

Analysing generator matrices G of similar state but varying minimum determinants

NASA Astrophysics Data System (ADS)

Harun, H.; Razali, M. F.; Rahman, N. A. Abdul

2016-10-01

Since Tarokh discovered Space-Time Trellis Code (STTC) in 1998, a considerable effort has been done to improve the performance of the original STTC. One way of achieving enhancement is by focusing on the generator matrix G, which represents the encoder structure for STTC. Until now, researchers have only concentrated on STTCs of different states in analyzing the performance of generator matrix G. No effort has been made on different generator matrices G of similar state. The reason being, it is difficult to produce a wide variety of generator matrices G with diverse minimum determinants. In this paper a number of generator matrices G with minimum determinant of four (4), eight (8) and sixteen (16) of the same state (i.e., 4-PSK) have been successfully produced. The performance of different generator matrices G in term of their bit error rate and signal-to-noise ratio for a Rayleigh fading environment are compared and evaluated. It is found from the MATLAB simulation that at low SNR (<8), the BER of generator matrices G with smaller minimum determinant is comparatively lower than those of higher minimum determinant. However, at high SNR (>14) there is no significant difference between the BER of these generator matrices G.

Arrowheaded enhanced multivariance products representation for matrices (AEMPRM): Specifically focusing on infinite matrices and converting arrowheadedness to tridiagonality

NASA Astrophysics Data System (ADS)

Özdemir, Gizem; Demiralp, Metin

2015-12-01

In this work, Enhanced Multivariance Products Representation (EMPR) approach which is a Demiralp-and-his- group extension to the Sobol's High Dimensional Model Representation (HDMR) has been used as the basic tool. Their discrete form have also been developed and used in practice by Demiralp and his group in addition to some other authors for the decomposition of the arrays like vectors, matrices, or multiway arrays. This work specifically focuses on the decomposition of infinite matrices involving denumerable infinitely many rows and columns. To this end the target matrix is first decomposed to the sum of certain outer products and then each outer product is treated by Tridiagonal Matrix Enhanced Multivariance Products Representation (TMEMPR) which has been developed by Demiralp and his group. The result is a three-matrix- factor-product whose kernel (the middle factor) is an arrowheaded matrix while the pre and post factors are invertable matrices decomposed of the support vectors of TMEMPR. This new method is called as Arrowheaded Enhanced Multivariance Products Representation for Matrices. The general purpose is approximation of denumerably infinite matrices with the new method.

What Controls the Low Ice Number Concentration in the Upper Tropical Troposphere?

NASA Astrophysics Data System (ADS)

Penner, J.; Zhou, C.; Lin, G.; Liu, X.; Wang, M.

2015-12-01

Cirrus clouds in the tropical tropopause play a key role in regulating the moisture entering the stratosphere through their dehydrating effect. Low ice number concentrations and high supersaturations were frequently were observed in these clouds. However, low ice number concentrations are inconsistent with cirrus cloud formation based on homogeneous freezing. Different mechanisms have been proposed to explain this discrepancy, including the inhibition of homogeneous freezing by pre-existing ice crystals and/or glassy organic aerosol heterogeneous ice nuclei (IN) and limiting the formation of ice number from high frequency gravity waves. In this study, we examined the effect from three different parameterizations of in-cloud updraft velocities, the effect from pre-existing ice crystals, the effect from different water vapor deposition coefficients (α=0.1 or 1), and the effect from 0.1% of secondary organic aerosol (SOA) acting as glassy heterogeneous ice nuclei (IN) in CAM5. Model simulated ice crystal numbers are compared against an aircraft observational dataset. Using grid resolved large-scale updraft velocity in the ice nucleation parameterization generates ice number concentrations in better agreement with observations for temperatures below 205K while using updraft velocities based on the model-generated turbulence kinetic energy generates ice number concentrations in better agreement with observations for temperatures above 205K. A larger water vapor deposition coefficient (α=1) can efficiently reduce the ice number at temperatures below 205K but less so at higher temperatures. Glassy SOA IN are most effective at reducing the ice number concentrations when the effective in-cloud updraft velocities are moderate (~0.05-0.2 m s-1). Including the removal of water vapor on pre-existing ice can also effectively reduce the ice number and diminish the effects from the additional glassy SOA heterogeneous IN. We also re-evaluate whether IN seeding in cirrus cloud is a viable mechanism for cooling. A significant amount of negative climate forcing can only be achieved if we restrict the updraft velocity in regions of background cirrus formation to moderate values (~0.05-0.2 m s-1).

Water Retention in Mature and Immature Lunar Regolith

NASA Astrophysics Data System (ADS)

Flom, A. J.; Kramer, G. Y.; Combe, J. P.

2017-12-01

The study of water and hydroxyl (HOH/OH) in lunar regolith and how it is retained has important implications for understanding how the Solar System and the Moon were formed. As a "hydration" phenomenon, understanding the process may provide a vital resource in space exploration. This study looks at how the amount of surface HOH/OH changes over time (eons) in lunar regolith. This is done by comparing the spectral absorption feature in the 3 micron area in Moon Mineralogy Mapper (M3) data [1]. This area of the spectrum is affected by thermal emission and it is known that the initial M3 correction for this is was not sufficient. To correct for this, a new thermal correction has been done on the data using a surface roughness model. With this correction, the 3 micron area spectral absorption feature between mature regolith (that has been exposed to weathering processes on the surface) against immature regolith (in fresh crater ejecta which has been mostly unaffected by these processes) [2]. It is commonly believed that HOH/OH is being formed due to hydrogen atoms from the solar wind interacting with oxygen in lunar minerals. There are a couple competing hypotheses about the process that dominates retaining this HOH/OH once it forms. The first suggests that the exposed oxygen atoms on freshly fractured mineral surfaces facilitate adsorption of protons. Alternately, a second proposes that HOH/OH is trapped in vesicles in the glassy parts of more mature regolith. The first hypothesis would lead to the mature regolith having a weaker HOH/OH absorption than immature regolith, because its weathered glassy coating would prevent it from capturing hydrogen atoms as efficiently. The second hypothesis would lead to the mature regolith having a stronger absorption because the glassy component of the regolith increases with maturity, and therefore so do the vesicles in that glassy coating. This study looks at fresh craters across Crisium, South Pole Aitken, and Reiner Gamma in order to identify a trend across many different terrains and compare these two hypotheses. References [1] Pieters, C. M. et al. (2009) Science 326 [2] Kramer, G.Y. and Combe, J-P. (2016) LPSC 47

Formulation, caracterisation, modelisation et prevision du comportement thermomecanique des pieces plastiques et composites de fibres de bois : Application aux engrenages =

NASA Astrophysics Data System (ADS)

Mijiyawa, Faycal

Cette etude permet d'adapter des materiaux composites thermoplastiques a fibres de bois aux engrenages, de fabriquer de nouvelles generations d'engrenages et de predire le comportement thermique de ces engrenages. Apres une large revue de la litterature sur les materiaux thermoplastiques (polyethylene et polypropylene) renforces par les fibres de bois (bouleau et tremble), sur la formulation et l'etude du comportement thermomecanique des engrenages en plastique-composite; une relation a ete etablie avec notre presente these de doctorat. En effet, beaucoup d'etudes sur la formulation et la caracterisation des materiaux composites a fibres de bois ont ete deja realisees, mais aucune ne s'est interessee a la fabrication des engrenages. Les differentes techniques de formulation tirees de la litterature ont facilite l'obtention d'un materiau composite ayant presque les memes proprietes que les materiaux plastiques (nylon, acetal...) utilises dans la conception des engrenages. La formulation des materiaux thermoplastiques renforces par les fibres de bois a ete effectuee au Centre de recherche en materiaux lignocellulosiques (CRML) de l'Universite du Quebec a Trois-Rivieres (UQTR), en collaboration avec le departement de Genie Mecanique, en melangeant les composites avec deux rouleaux sur une machine de type Thermotron-C.W. Brabender (modele T-303, Allemand) ; puis des pieces ont ete fabriquees par thermocompression. Les thermoplastiques utilises dans le cadre de cette these sont le polypropylene (PP) et le polyethylene haute densite (HDPE), avec comme renfort des fibres de bouleau et de tremble. A cause de l'incompatibilite entre la fibre de bois et le thermoplastique, un traitement chimique a l'aide d'un agent de couplage a ete realise pour augmenter les proprietes mecaniques des materiaux composites. Pour les composites polypropylene/bois : (1) Les modules elastiques et les contraintes a la rupture en traction des composites PP/bouleau et PP/tremble evoluent lineairement en fonction du taux de fibres, avec ou sans agent de couplage (Maleate de polypropylene MAPP). De plus, l'adherence entre les fibres de bois et le plastique est amelioree en utilisant seulement 3 % MAPP, entrainant donc une augmentation de la contrainte maximale bien qu'aucun effet significatif ne soit observe sur le module d'elasticite. (2) Les resultats obtenus montrent que, en general, les proprietes en traction des composites polypropylene/bouleau, polypropylene/tremble et polypropylene/bouleau/ tremble sont tres semblables. Les composites plastique-bois (WPCs), en particulier ceux contenant 30 % et 40 % de fibres, ont des modules elastiques plus eleves que certains plastiques utilises dans l'application des engrenages (ex. Nylon). Pour les composites polyethylene/bois, avec 3%Maleate de polyethylene (MAPE): (1) Tests de traction : le module elastique passe de 1.34 GPa a 4.19 GPa pour le composite HDPE/bouleau, alors qu'il passe de 1.34 GPa a 3.86 GPa pour le composite HDPE/tremble. La contrainte maximale passe de 22 MPa a 42.65 MPa pour le composite HDPE/bouleau, alors qu'elle passe de 22 MPa a 43.48 MPa pour le composite HDPE/tremble. (2) Tests de flexion : le module elastique passe de 1.04 GPa a 3.47 GPa pour le composite HDPE/bouleau et a 3.64 GPa pour le composite HDPE/tremble. La contrainte maximale passe de 23.90 MPa a 66.70 MPa pour le composite HDPE/bouleau, alors qu'elle passe a 59.51 MPa pour le composite HDPE/tremble. (3) Le coefficient de Poisson determine par impulsion acoustique est autour de 0.35 pour tous les composites HDPE/bois. (4) Le test de degradation thermique TGA nous revele que les materiaux composites presentent une stabilite thermique intermediaire entre les fibres de bois et la matrice HDPE. (5) Le test de mouillabilite (angle de contact) revele que l'ajout de fibres de bois ne diminue pas de facon significative les angles de contact avec de l'eau parce que les fibres de bois (bouleau ou tremble) semblent etre enveloppees par la matrice sur la surface des composites, comme le montrent des images prises au microscope electronique a balayage MEB. (6) Le modele de Lavengoof-Goettler predit mieux le module elastique du composite thermoplastique/bois. (7) Le HDPE renforce par 40 % de bouleau est mieux adapte pour la fabrication des engrenages, car le retrait est moins important lors du refroidissement au moulage. La simulation numerique semble mieux predire la temperature d'equilibre a la vitesse de 500 tr/min; alors qu'a 1000 tr/min, on remarque une divergence du modele. (Abstract shortened by ProQuest.). None None None None None None None None

The method of similar operators in the study of the spectra of the adjacency matrices of graphs

NASA Astrophysics Data System (ADS)

Kozlukov, Serge

2018-03-01

The method of similar operators [1, 2, 3] is used to investigate spectral properties of a certain class of matrices in the context of graphs [4, 5]. Specifically, we consider the adjacency matrix of an “almost-complete graph”. Then we generalize the result to allow the matrices obtained as combinations of the Kronecker products [6, 7] and the small-norm perturbations. We derive the estimates of the spectra and the eigenvectors of such matrices.

Extraction Methodological Contributions Toward Ultra-Performance Liquid ChromatographyTime-of-Flight Mass Spectrometry: Quantification of Free GB from Various Food Matrices

DTIC Science & Technology

2016-02-01

SPECTROMETRY: QUANTIFICATION OF FREE GB FROM VARIOUS FOOD MATRICES ECBC-TR-1351 Sue Y. Bae Mark D. Winemiller RESEARCH AND TECHNOLOGY DIRECTORATE...Flight Mass Spectrometry: Quantification of Free GB from Various Food Matrices 5a. CONTRACT NUMBER 5b. GRANT NUMBER 5c. PROGRAM ELEMENT NUMBER...methylphosphonofluoridate (sarin, GB) in various food matrices. The development of a solid-phase extraction method using a normal-phase silica gel column for

Bunch-Kaufman factorization for real symmetric indefinite banded matrices

NASA Technical Reports Server (NTRS)

Jones, Mark T.; Patrick, Merrell L.

1989-01-01

The Bunch-Kaufman algorithm for factoring symmetric indefinite matrices was rejected for banded matrices because it destroys the banded structure of the matrix. Herein, it is shown that for a subclass of real symmetric matrices which arise in solving the generalized eigenvalue problem using Lanczos's method, the Bunch-Kaufman algorithm does not result in major destruction of the bandwidth. Space time complexities of the algorithm are given and used to show that the Bunch-Kaufman algorithm is a significant improvement over LU factorization.

EMQIT: a machine learning approach for energy based PWM matrix quality improvement.

PubMed

Smolinska, Karolina; Pacholczyk, Marcin

2017-08-01

Transcription factor binding affinities to DNA play a key role for the gene regulation. Learning the specificity of the mechanisms of binding TFs to DNA is important both to experimentalists and theoreticians. With the development of high-throughput methods such as, e.g., ChiP-seq the need to provide unbiased models of binding events has been made apparent. We present EMQIT a modification to the approach introduced by Alamanova et al. and later implemented as 3DTF server. We observed that tuning of Boltzmann factor weights, used for conversion of calculated energies to nucleotide probabilities, has a significant impact on the quality of the associated PWM matrix. Consequently, we proposed to use receiver operator characteristics curves and the 10-fold cross-validation to learn best weights using experimentally verified data from TRANSFAC database. We applied our method to data available for various TFs. We verified the efficiency of detecting TF binding sites by the 3DTF matrices improved with our technique using experimental data from the TRANSFAC database. The comparison showed a significant similarity and comparable performance between the improved and the experimental matrices (TRANSFAC). Improved 3DTF matrices achieved significantly higher AUC values than the original 3DTF matrices (at least by 0.1) and, at the same time, detected notably more experimentally verified TFBSs. The resulting new improved PWM matrices for analyzed factors show similarity to TRANSFAC matrices. Matrices had comparable predictive capabilities. Moreover, improved PWMs achieve better results than matrices downloaded from 3DTF server. Presented approach is general and applicable to any energy-based matrices. EMQIT is available online at http://biosolvers.polsl.pl:3838/emqit . This article was reviewed by Oliviero Carugo, Marek Kimmel and István Simon.

Biodegradable organic acid-crosslinked alkali-treated gelatins with anti-thrombogenic and endothelialization properties

PubMed Central

Inoue, Motoki; Sasaki, Makoto; Taguchi, Tetsushi

2012-01-01

Gelatins were crosslinked with organic acids and treated with alkali to impart to them endothelialization and anti-thrombogenic properties. These matrices were characterized by biochemical and physicochemical techniques. The amounts of residual amino groups in the matrices decreased with increasing crosslinker concentration. The matrices with the highest crosslinking densities showed excellent endothelial cell adhesion and proliferation. In addition, the adhesion of platelets and formation of fibrin networks on the matrices were suppressed with increasing crosslinker concentration. The matrices also exhibited excellent biodegradability, and the degradation rate decreased with increasing crosslinking density. All the organic acid-crosslinked alkali-treated gelatins showed excellent anti-thrombogenic and endothelialization properties, superior to those of glutaraldehyde-crosslinked alkali-treated gelatins. PMID:27877542