Search

In this work, Bi.sub.2O.sub.3 nanoparticles (NPs) were used for the construction of a modified carbon paste electrode for the non-enzymatic determination of uric acid in human urine samples by differential pulse voltammetry as the quantitative analytical technique which was optimized using a Box-Behnken design. Bi.sub.2O.sub.3-NPs/CPE sensor showed an excellent performance for uric acid oxidation presenting two linear ranges of 5-300 and 300-1000 [mu]M. The good reproducibility, repeatability, low interference in the presence of other chemical species, and statistical evaluation demonstrated that the proposed methodology is as reliable as the enzymatic spectrophotometric technique for the quantification of uric acid in human urine samples. Bi.sub.2O.sub.3 nanostructures resulted in a good modifier for the development of an effective non-enzymatic electrochemical methodology for the determination of uric acid in physiological samples., Author(s): Daniel Hernández-Ramírez [sup.1] , Luis Humberto Mendoza-Huizar [sup.1] , Carlos Andrés Galán-Vidal [sup.1] , Guadalupe Yoselin Aguilar-Lira [sup.1] , Luz Elena Rebolledo-Perales [sup.1] , Giaan Arturo Álvarez-Romero [sup.1] Author [...]

The aim of this study is to develop an electroanalytical method for the determination of serotonin, a very important neurotransmitter for neuroscience in food products, with an electrochemically produced sulfur-doped graphene oxide modified pencil graphite electrode (EGO/PGE). The S-doped graphene oxide electrode was fabricated by chronoamperometry, a fast, environmentally friendly, and, more importantly, functional group doping technique in one step. Techniques such as atomic force microscopy, electrochemical impedance spectroscopy, cyclic voltammetry, energy-dispersive X-ray spectroscopy, scanning electron microscopy, and Fourier-transform infrared spectroscopy were used for the structural and morphological characterization of the produced sensor. The limit of detection and limit of quantitation were calculated as 0.026 and 0.09 [micro]M, respectively, using differential pulse voltammetry under optimum experimental conditions with the prepared EGO/PGE. Recovery tests were performed by spiking different concentrations into walnut and milk samples to investigate the applicability of the developed method in food samples. Good results between 93.1 and 105.8% were obtained in recovery studies. These results showed that the developed S-doped graphene oxide modified pencil graphite electrode platform was practically applicable in food samples due to its simplicity, low cost, fast response time, easy manufacturing, good selectivity, and high sensitivity., Author(s): Zeynep Serbest [sup.1] , Ozge Gorduk [sup.1] , Yucel Sahin [sup.1] Author Affiliations: (1) grid.38575.3c, 0000 0001 2337 3561, Yildiz Technical University, Faculty of Arts and Science, Department of [...]

For catalytic reactions, temperature has a great influence on reaction rate and reaction mechanism. The oxidation processes of soot precursors (C6H6) at different temperatures are simulated using reactive force field molecular dynamics to investigate the effect of temperature on the oxidation process. The reaction products at different temperatures and the effect of temperature are discussed. The results show that the intermediate species C3 and C4 are more and existed longer at 1400 K than at 2000 K, while hardly existed at 2000 K, indicating that as the temperature increases, the oxidation reaction takes place more completely and the products formed are more stable. The effect of temperature on the oxidation mechanism is then explored; the results show that the main reaction pathway at 1400 K is basically the same as that at 2000 K, while the final product contains less hydrogen and more oxygen atoms at 2000 K. The C6 components with two, three, and four oxygen atoms are found easier to be decomposed at both 1400 and 2000 K. It shows that temperature mainly afects the catalytic reaction process by afecting the hydrogen and oxygen content of the decomposed C6 component. This may be helpful to understand the effect of temperature on the C6H6 oxidation from the perspective of basic research. Key words: temperature, soot precursors, catalytic reaction, oxidation mechanism, ReaxFF MD Dans le contexte des reactions catalytiques, la temperature a une grande influence sur la vitesse et le mecanisme de reaction. Nous avons simule les processus d'oxydation des precurseurs de suie (C6H6) a diferentes temperatures a l'aide de la dynamique moleculaire (MD pour molecular dynamics) dans le cadre de laquelle nous avons employe un potentiel de champ de force (FF pour force field) reactif (ReaxFF MD) afin d'etudier l'efet de la temperature sur le processus d'oxydation. Nous discutons des produits de reaction a diferentes temperatures et de l'efet de la temperature. Les resultats montrent que les especes intermediaires en C3 et en C4 ont ete produites en plus grande quantite et ont existe plus longtemps a 1400 K qu'a 2000 K, temperature a laquelle elles etaient pratiquement absentes. Nous pouvons conclure d'apres ces observations que lorsque la temperature augmente, la reaction d'oxydation procede de maniere plus complete et que le produit forme est plus stable. Nous avons ensuite explore l'efet de la temperature sur le mecanisme d'oxydation. Les resultats montrent que la voie de reaction principale a 1400 K est fondamentalement la meme qu'a 2000 K, mais que le produit final contient moins d'atomes d'hydrogene et plus d'atomes d'oxygene a 2000 K. On constate egalement que les composants en C6 contenant 2, 3 et 4 atomes d'oxygene sont plus faciles a decomposer tant a 1400 K qu'a 2000 K, et que la temperature influence le processus de reaction catalytique principalement en modifiant la teneur en hydrogene et en oxygene du composant en C6 decompose. Ces observations peuvent etre utiles pour comprendre l'efet de la temperature sur l'oxydation du C6H6 dans une perspective de recherche fondamentale. [Traduit par la Redaction] Mots-cles : temperature, precurseurs de suie, reaction catalytique, mecanisme d'oxydation, ReaxFF MD, 1. Introduction The oxidation mechanism of soot is an active topic in the field of combustion. Understanding the detailed oxidation process of soot not only is important from the fundamental [...]

Acyclovir and valacyclovir are oxidized on a glassy carbon electrode (GCE) with immobilized reduced graphene oxide coated with a polyglycine film. We selected the conditions for forming a polymer film, reducing graphene oxide on the GCE, and recording the maximum catalytic current on the composite surface. A procedure was developed for the selective voltammetric determination of acyclovir and valacyclovir on an electrode with a reduced graphene oxide-polyglycine film composite. A method is proposed for the amperometric detection of guanine-based antiviral drugs with this modified electrode under the conditions of flow-injection analysis. The dependence of the analytical signal on the concentration of acyclovir and valacyclovir is linear up to 5 x 10.sup.-6 M in the static mode and up to 1 x 10.sup.-7 M in the flow-injection system. The developed voltammetric method for determining acyclovir and valacyclovir was tested in the analysis of pharmaceutical preparations., Author(s): L. G. Shaidarova [sup.1] , A. V. Gedmina [sup.1] , A. A. Poadnyak [sup.1] , I. A. Chelnokova [sup.1] , H. C. Budnikov [sup.1] Author Affiliations: (1) grid.77268.3c, 0000 [...]

In this study, bacterial cellulose (BC) hydrogels were cultured from a kombucha SCOBY starter. The scanning electron microscopy (SEM) results indicated that the dried BC exhibited an interpenetrating fibrous mat. The BC films harvested for 5, 10, and 15 days were 15-19, 14.4-24, and 30-31 pm thick, respectively. Then, BC/graphene oxide (GO) composite films were prepared via the exhaust dyeing method. GO sheets penetrated the BC matrix, resulting in the formation of a BC/GO composite, as revealed by the SEM analysis results. The mechanical properties of the composite films were investigated. Compared with virgin BC, the tensile strength of the composite films was higher, while the %E at break was lower, resulting in a significant increase in the Young's modulus. The X-ray diffraction results indicated that an increase in the dyeing time (0.5-2 h) gradually induced cellulose crystalline conformation, which in turn affected the swelling ability, mechanical properties, and electrical properties of the BC/GO composite films. After the reduction of GO to reduced GO (rGO), flexible conductive BC/rGO films were obtained, as confirmed by their resistivity values. Thus, flexible conductive composite films with excellent mechanical properties were successfully fabricated. KEYWORDS bacterial cellulose/graphene oxide composites, dyeing method, mechanical and electrical properties, 1 | INTRODUCTION Polymer nanocomposites such as synthetic polymer/ graphene nanocomposites and biopolymer-based nanocomposites such as natural rubber/graphene, synthetic rubber/ bacterial cellulose (BC), nanocellulose aerogel/graphene, BC/Ti[O.sub.2,] and BC/nanoclay composites have [...]

Water freezing is ubiquitous and affects areas as diverse as climate, the chemical industry, cryobiology and materials science. Ice nucleation is the controlling step in water freezing.sup.1-5 and has, for nearly a century, been assumed to require the formation of a critical ice nucleus.sup.6-10. But there has been no direct experimental evidence for the existence of such a nucleus, owing to its transient and nanoscale nature.sup.6,7. Here we report ice nucleation in water droplets containing graphene oxide nanosheets of controlled sizes and show that they have a notable impact on ice nucleation only above a certain size that varies with the degree of supercooling of the droplets. We infer from our experimental data and theoretical calculations that the critical size of the graphene oxide reflects the size of the critical ice nucleus, which in the case of sufficiently large graphene oxides sits on their surface and gives rise to ice formation behaviour consistent with classical nucleation theory. By contrast, when the graphene oxide size is smaller than that of the critical ice nucleus, pinning at the periphery of the graphene oxide deforms the ice nucleus as it grows. This gives rise to a much higher free-energy barrier for nucleation and suppresses the promoting effect of the graphene oxide.sup.11. The results provide experimental information on the existence and temperature-dependent size of the critical ice nucleus, which has previously only been explored theoretically and through simulations.sup.12-16. As pinning of a pre-critical nucleus at a nanoparticle edge is not specific to the ice nucleus on graphene oxides, we expect that our approach could be extended to probe the critical nuclei in other nucleation processes. Nucleation experiments with water droplets containing differently sized graphene oxide nanosheets provide an experimental indication of the temperature-dependent size of the critical ice nucleus., Author(s): Guoying Bai [sup.1] [sup.2] , Dong Gao [sup.3] , Zhang Liu [sup.1] , Xin Zhou [sup.4] [sup.5] [sup.6] , Jianjun Wang [sup.1] [sup.6] [sup.7] Author Affiliations: (1) Key Laboratory [...]

This work experimentally and theoretically investigates the use of the symmetrical cyclic trifunctional initiator diethyl ketone triperoxide (DEKTP) in the bulk polymerization of styrene (St). The study focused on temperatures of 150 to 200°C, considering chemical initiation by both sequential and total decomposition reactions. The experimental work consisted of a series of isothermal batch polymerizations at higher temperatures, 150 and 200°C, with an initiator concentration of 0.01 mol/L. The mathematical model is based on a kinetic mechanism that includes thermal and chemical initiation (both sequential and total decomposition reactions), propagation, transfer to monomer, termination by combination and re-initiation reactions. Experimental and theoretical results show that the decomposition mechanism of the initiator is modified by the reaction temperature and can be modeled as a set of two parallel reactions with different temperature dependences. The developed mathematical model simulates the bulk polymerization of St in the presence of DEKTP for a wide temperature range (120-200°C). It was found that due to these two decomposition mechanisms, the system may behave as a 'dead-end' polymerization system above a certain temperature, yielding low molecular weights and a limiting conversion value. Simulation results indicate the value of this temperature to be about 185°C., INTRODUCTION The use of multifunctional initiators in the bulk polymerization of styrene (St) allows obtaining both high reaction rates and molecular weights, as well as enhanced mechanical properties compared to [...]

Protein radicals are implicated in oxidative stress and are associated with a wide range of diseases and disorders. In the present work, we describe the specific application of a newly synthesized nitrone spin trap, Bio-SS-DMPO, for the detection of these highly reactive species by mass spectrometry (MS). Bio-SS-DMPO is a biotinylated analogue of the spin-trap 5,5-dimethyi-1-pyrroline-N-oxide (DMPO) that allows for specific capture of the protein(s)/peptide(s) labeled by the spin-trap on a (strept)avidin-bound solid matrix. The disulfide bond in the linker arm joining biotin to DMPO can be cleaved to release captured spin-adduct peptide from the solid matrix. This (strept)avidin-based affinity purification reduces the complexity of the samples prior to MS analyses, thereby facilitating the location of the sites of spin trap addition. In addition, the biotin moiety on the spin-trap can efficiently be probed with (strept)avidin-conjugated reporter. This offers an effective means to visualize the presence of DMPO-adducted proteins in intact cells. 10.1021/ac1023183

This article presents results of detailed and direct real-time observations of the wide variety of Sn[O.sub.2] nanobelt motions induced by ac dielectrophoresis (DEP) in an innovative microfluidic setup. High ac electric fields were generated on a gold microelectrode (~20 [micro]m electrode gap) array, patterned on a glass substrate and covered by a ~10 [micro]m tall polydimethylsiloxane (PDMS) microchannel. Ethanol suspended Sn[O.sub.2] nanobelts were introduced into the microchannel, and the DEP experiments were performed. Negative DEP (repulsion) of the nanobelts was observed in the low-frequency range (< 100 kHz) of the applied electric field, which caused rigid body motion as well as deformation of the nanobelts. The negative DEP effect observed in ethanol is unusual and contrary to what is predicted by the Clausius--Mossotti factor (using bulk Sn[O.sub.2] conductivity and permittivity values) of the dipole approximation theory. In the high-frequency range (~1-10 MHz), positive DEP (attraction) of the nanobelts was observed. Pearl chain formation involving short nanobelts and particles was also observed in the two DEP regimes. 10.1021/ac901287z

The core of the current granular perpendicular magnetic recording (PMR) media is the granular oxide magnetic layer (GOML). We observe that a fcc NiW seed layer, followed by a hcp Ru layer sputtered under low pressure (LP-Ru) and then by a hcp Ru layer sputtered under high pressure (HP-Ru) provides an excellent structural template for the granular oxide magnetic layer (GOML). Microstructure and magnetic properties of the GOML can be tailored through process conditions and alloy compositions to maximize the recording performance of the perpendicular magnetic recording media. Exchange coupled composite (ECC) media design provides significant improvement in overwrite (OW) and signal-to-noise ratio (So NR) for perpendicular magnetic recording media. Recording performance of the ECC media needs to be optimized with consideration of the magnetic properties and thicknesses of both the exchange control layer (ECL) and the cap magnetic layer (CML). At their respective optimum, the recording performance of the ECC media is mostly dependent upon the properties of the GOML and CML. This study indicates that a dual magnetic cap layer structure consisting of low-Ms and high-Ms sublayers can combine the benefits provided by the two types of cap magnetic materials. Index Terms--Dual magnetic cap layer, exchange control layer, exchange coupled composite media, granular oxide magnetic layer, perpendicular magnetic recording media.

Proteomics-based analysis of signaling cascades relies on a growing suite of affinity resins and methods aimed at efficient enrichment of phosphorylated peptides from complex biological mixtures. Given the heterogeneity of phosphopeptides and the overlap in chemical properties between phospho- and unmodified peptides, it is likely that the use of multiple resins will provide the best combination of specificity, yield, and coverage for large-scale proteomics studies. Recently titanium and zirconium dioxides have been used successfully for enrichment of phosphopeptides. Here we report the first demonstration that niobium pentoxide ([Nb.sub.2][O.sub.5]) provides for efficient enrichment and recovery (~50-100%) of phosphopeptides from simple mixtures and facilitates identification of several hundred putative sites of phosphorylation from cell lysate. Comparison of phosphorylated peptides identified from [Nb.sub.2][O.sub.5] and Ti[O.sub.2] with sequences in the PhosphoELM database suggests a useful degree of divergence in the selectivity of these metal oxide resins. Collectively our data indicate that [Nb.sub.2][O.sub.5] provides efficient enrichment for phosphopeptides and offers a complementary approach for large-scale phosphoproteomics studies.

We demonstrate a multicore multidopant fiber which, when pumped with a single pump source around ~800 nm, emits a more than one octave-spanning fluorescence spectrum ranging from 925 to 2300 nm. The fiber preform is manufactured from granulated oxides and the individual cores are doped with five different rare earths, i.e., [Nd.sup.3+], [Yb.sup.3+], [Er.sup.3+], [Ho.sup.3+], and [Tm.sup.3+]. OCIS codes: 060.2280, 060.2290, 060.2400, 160.5690, 300.2530, 300.6340.

Cu([In.sub.1-x][Ga.sub.x])[Se.sub.2] (CIGS)-based thin film solar cells fabricated using transparent conducting oxide (TCO) front and back contacts were investigated. The cell performance of substrate-type CIGS devices using TCO back contacts was almost the same as that of conventional CIGS solar cells with metallic Mo back contacts when the CIGS deposition temperatures were below 500[degrees]C for Sn[O.sub.2]:F and 520[degrees]C for ITO. CIGS thin film solar cells fabricated with ITO back contacts had ah efficiency of 15.2% without anti-reflection coatings. However, the cell performance deteriorated at deposition temperatures above 520[degrees]C. This is attributed to the increased resistivity of the TCO's due to the removal of fluorine from Sn[O.sub.2] or undesirable formation of a [Ga.sub.2][O.sub.3] thin layer at the CIGS/ITO interface. The formation of [Ga.sub.2][O.sub.3] was eliminated by inserting an intermediate layer such as Mo between ITO and CIGS. Furthermore, bifacial CIGS thin film solar cells were demonstrated as being one of the applications of semi-transparent CIGS devices. The cell performance of bifacial devices was improved by controlling the thickness of the CIGS absorber layer. Superstrate-type CIGS thin film solar cells with ah efficiency of 12.8% were fabricated using a ZnO:Al front contact. Key techniques include the use of a graded band gap Cu[(In,Ga).sub.3][Se.sub.5] phase absorber layer and a ZnO buffer layer along with the inclusion of [Na.sub.2]S during CIGS deposition. Keywords: Cu(In,Ga)[Se.sub.2]; Bifacial solar cells; Transparent conducting oxides; Superstrate solar cells

Optical coatings with enhanced roughness offer promising prospects for ultrahydrophobic transparent surfaces with controlled scatter losses. Our approach links roughness characteristics with both wetting behavior and scattering. Experiments with rough oxide layers yielded surfaces with a high water contact angle. OCIS codes: 240.5770, 310.1620, 310.6860, 310.6870.

We have investigated the magnetoresistance properties of spin valves in the current-perpendicular-to-plane (CPP) mode. Conventional single spin-valve (SV) film shows resistance area product RA = 81 m[OMEGA][micro][m.sup.2], and resistance change area product [DELTA] RA = 0.35 m[OMEGA][micro][m.sup.2]. For a CPP element of a single SV with oxide layers, [DELTA] RA dramatically increased to 9.0 m[OMEGA][micro][m.sup.2]. Micromagnetics simulation revealed that the readback performance of the CPP head with low-impedance conventional SV film was much affected by sense current. On the other hand, the medium impedance CPP head, such as the SV film with oxide layers, shows several advantages compared with the low impedance head, such as higher output voltage, less influence by magnetic field of the sense current, and narrower core width. Index Terms--Current perpendicular to plane, magnetic heads, micromagnetics simulation, oxide layer, spin valve.

SrRuO3 conductive metallic oxide thin film was grown by laser ablation at temperatures over 400 deg C, and characterized.

Periodic artificial pinning centers in oxide-superconductors were determined using lithographic methods.

Developments in the chemical sensor technology field have paved a way for a new emerging technique, the chemical sensor arrays, which yield responses to different analytes simultaneously. This review discusses different types of sensors in this class including metal oxide and electrochemical devices, polymer-based systems, and acoustic wave oscilltors.

A gate oxide B-mode dielectric breakdown failure elimination technique destroys pre-electrode formation weak spots, occurring due to crystal defects. A rotating water in a brush scrubber gives pure water which charges the gate oxide. The gate oxide achieves saturation near its inherent breakdown voltage. Experiments reveal that very few saturated samples suffer B-mode failure.

Low temperature substrate hot-electron injection experiments indicate that oxide trap generation can be detected only after the occupation of traps by new electrons. The rate of interface generation at room temperature depends on the exponentiality of the oxygen field. At low temperatures, the primary degradation mechanism, related to release and migration of the substrates, is independent of temperature. The density of the hydrogen atoms is reduced by post-growth annealing in nitrogen.

Co-Ce-O films were synthesized by a newly developed electrochemical method called the 'metal-oxide co-electrodeposition method,' i.e., the simultaneous deposition of Co and Ce[O.sub.2] from a reaction solution containing COS[O.sub.4], Ce[Cl.sub.3], and glycine. Giycine acts as the complexing agent for [Co.sup.2+] and was effective in avoiding the precipitation of Co[(OH).sub.2]. The Co-Ce-O films prepared had a smooth surface. The Co content in the deposited films was subject to change from 0 to 100 vol.%, depending on the concentration of the COS[O.sub.4] in the reaction solution. Coercivity and sheet resistivity decrease suddenly at 22 vol.% Co. Therefore, the nano-size structure of the films may be changed at this concentration. Index Terms--Co-Ce-O, glycine, metal-oxide co-electrodeposition, metal-oxide granular film.

A series of nitrogen-sulfuroxides produced during the reaction of nitrogen and sulfur oxides were simultaneously detected using an ion-pair chromatographic procedure with an acetonitrile gradient. These oxides include nitrilotrisulfonate, imidodisulfonate, hydroxilaminedisulfonate, N-nitrosohydroxylamine-N-sulfonate,hydroxylaminesulfonate and aminosulfonate. The method would allow future investigation of the effect of metal ions on hydrolysis and their possible rolein atmospheric oxidation processes.

A detailed Rietveld analysis of x-ray powder diffraction data of Pb(Zr(sub x)Ti(sub 1-x))O(sub 3) (PZT) compositions across the morphotropic phase boundary (MPB) region is presented. It was found that the structure of PZT is pure tetragonal for x

Silicon and oxide membranes were fabricated using an ion-cut layer transfer process, which is suitable for sub-micron-thick membrane fabrication with good thickness uniformity and surface micro-roughness. After hydrogen ions were implanted into a silicon water, the implanted wafer was bonded to another wafer that has patterned cavities of various shapes and sizes. The bonded pair was then heated until hydrogen-induced silicon layer cleavage occurred along the implanted hydrogen peak concentration, resulting in the transfer of the silicon layer from one wafer to the other. Using this technique, we have been able to form sealed cavities and channels of various shapes and sizes up to 50- [micro] m wide, with a 1.6- [micro] m-thick silicon membrane. As a process variation, we have also fabricated silicon dioxide membranes for optically transparent applications. [506] Index Terms--Ion-cut, layer transfer, micro channels, oxide membrane, sealed cavities, silicon membrane, wafer bonding.

Microscopic pH electrodes were produced by deposition of hydrous iridium oxide onto carbon fiber microelectrodes. The electrodes exhibit two linear regions of potentiometric response between pH 2-6 and pH 6-12. The electrodes respond to pH changes within 50 ms, and an equilibrium value is reached within 30 s. By using these electrodes as probes in the scanning electrochemical microscope, dynamic pH changes occurring at or near a surface can be measured and pH maps of the surface can be generated. Vertical pH profiles and images of pH were obtained at substrates where electrochemical (oxidation and reduction of [H.sub.2][O.sub.2], hydrogen evolution) or enzymatic (glucose oxidase) reactions involving proton transfers occur.

Many oxide materials are strongly correlated systems exhibiting a broad spectrum of physical properties such as superconductivity, ferromagnetic order, ferroelectricity, transparency to visible light, semiconducting behavior (often associated with transparency [...]

Manganese oxide thin films are described, with fast ion-exchange characteristics.