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Sharp Peak (sharp + peak)
Selected AbstractsCoherent random lasers from weakly scattering polymer films embedded with superfine silver nanoparticlesPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue S1 2009Xiangeng Meng Abstract Random lasers with coherent feedback have been obtained in highly transparent polymer films embedded with silver (Ag) nanoparticles. The hybrid materials were fabricated via in situ synthesis, through which Ag nanoparticles were precipitated by heat treatment. Sharp peaks with linewidth of ,0.3 nm emerge on a broad emission background when the pump energy reaches a threshold. Random lasers with coherent feedback induced by Ag nanoparticles have been little reported, and hence, we believe that this work brings about an important aspect to random lasers. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Enhancement of crystalline perfection by organic dopants in ZTS, ADP and KHP crystals as investigated by high-resolution XRD and SEMJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 6 2006S. Parthiban To reveal the influence of complexing agents on crystalline perfection, tristhiourea zinc(II) sulfate (ZTS), ammonium dihydrogen phosphate (ADP) and potassium hydrogen phthalate (KHP) crystals grown by slow-evaporation solution growth technique using low concentrations (5 × 10,3M) of dopants like ethylenediamminetetraacetic acid (EDTA) and 1,10-phenanthroline (phen) were characterized by high-resolution X-ray diffractometry (XRD) and scanning electron microscopy (SEM). High-resolution diffraction curves (DCs) recorded for ZTS and ADP crystals doped with EDTA show that the specimen contains an epilayer, as observed by the additional peak in the DC, whereas undoped specimens do not have such additional peaks. On etching the surface layer, the additional peak due to the epilayer disappears and a very sharp DC is obtained, with full width at half-maximum (FWHM) of less than 10,arcsec, as expected from the plane wave dynamical theory of X-ray diffraction for an ideally perfect crystal. SEM micrographs also confirm the existence of an epilayer in doped specimens. The ZTS specimen has a layer with a rough surface morphology, having randomly oriented needles, whereas the ADP specimen contains a layer with dendric structure. In contrast to ADP and ZTS crystals, the DC of phen-doped KHP shows no additional peak, but it is quite broad (FWHM = 28,arcsec) with a high value of integrated intensity, , (area under the DC). The broadness of the DC and the high value of , indicate the formation of a mosaic layer on the surface of the crystal. However, similar to ADP and ZTS, the DC recorded after etching the surface layer of the KHP specimen shows a very sharp peak with an FWHM of 8 arcsec. An SEM photograph of phen-doped KHP shows deep cracks on the surface, confirming the mosaicity. After removing the surface layer, the SEM pictures reveal a smooth surface. A similar trend is observed with other complexing agents, like oxalic acid, bipy and picolinic acid. However, only typical examples are described in the present article where the effects were observed prominently. The investigations on ZTS, ADP and KHP crystals, employing high-resolution XRD and SEM studies, revealed that some organic dopants added to the solution during the growth lead to the formation of a surface layer, due to complexation of these dopants with the trace metal ion impurities present in the solution, which prevents the entry of impurities, including the solvent, into the crystal, thereby assisting crystal growth with high crystalline perfection. The influence of organic dopants on the second harmonic generation efficiency is also investigated. [source] Synthesis and characterizations of nanosized iron(II) hydroxide and iron(II) hydroxide/poly(vinyl alcohol) nanocompositeJOURNAL OF APPLIED POLYMER SCIENCE, Issue 3 2010M. Fathima Parveen Abstract Nanosized Fe(OH)2 was synthesized by a coprecipitation method. Peaks between 500 and 1250 cm,1 in Fourier transform infrared (FTIR) spectroscopy confirmed the presence of metal hydroxide stretching. X-ray diffraction showed the suppressed crystalline system of Fe(OH)2/aniline (ANI) due to the presence of a higher weight percentage of the dispersing agent, ANI. Thermogravimetric analysis implied that 75.5 wt % of residue remained up to 800°C. High resolution transmission electron microscope (HRTEM) analysis of Fe(OH)2/ANI revealed that its size ranged from 10 to 50 nm with a rodlike morphology. Scanning electron microscopy implied that pristine Fe(OH)2 had a nanotriangular platelet morphology, and a higher weight percentage of dispersing agent intercalated with Fe(OH)2 had a spheroid with an agglomerated structure. The (UV,visible) spectrum implied the presence of Fe2+ ions at 326 nm and the existence of an amino group intercalated with Fe(OH)2 showed a sharp peak at 195 nm, the intensity of which increased with increasing intercalated dispersing agent weight percentage. Photoluminescence showed that ANI-intercalated Fe(OH)2 showed a lesser intensity than the pristine Fe(OH)2. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source] Uptake and Dispersion of Metformin in the Isolated Perfused Rat LiverJOURNAL OF PHARMACY AND PHARMACOLOGY: AN INTERNATI ONAL JOURNAL OF PHARMACEUTICAL SCIENCE, Issue 8 2000CHEN-HSI CHOU Although metformin is a widely used oral antihyperglycaemic, the exact mechanisms of its cellular uptake and action remain obscure. In this study the hepatic extraction and disposition kinetics of metformin were investigated by use of an isolated in-situ rat liver preparation. The liver was perfused in single-pass mode with protein-free Krebs bicarbonate medium at a flow rate of 20mLmin,1. During constant infusion with 1 mgL,1 metformin hydrochloride the hepatic uptake of metformin approached equilibrium within 10 min. The steady-state availability, F, determined from the ratio of outflow concentration to input concentration, was 0.99±0.02 (mean±s.d., n=4). The outflow profile of metformin resulting from a bolus injection of 25 ,g into the portal vein, had a sharp peak then a slower declining terminal phase. The mean transit time (MTT; 49.5±14.5, n = 6) and normalized variance (CV2; 4.13±0.05) of the hepatic transit times of metformin were estimated by numerical integration from the statistical moments of the outflow data. The volume of distribution of metformin in the liver (1.58±0.28 mL (g liver),1) was estimated from its MTT. The volume of distribution is greater than the water space of liver, indicating that metformin enters the hepatic aqueous space and becomes distributed among cellular components. The magnitude of CV2 for metformin is greater than for the vascular marker sucrose, suggesting that distribution of metformin into hepatic tissue is not instantaneous. In conclusion, hepatic uptake of metformin is rate-limited by a permeability barrier. Although metformin is accumulated in the liver, the organ does not extract it. [source] 3D models of radiatively driven colliding winds in massive O + O star binaries , III.MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2010Thermal X-ray emission ABSTRACT The X-ray emission from the wind,wind collision in short-period massive O + O star binaries is investigated. The emission is calculated from 3D hydrodynamical models which incorporate gravity, the driving of the winds, orbital motion of the stars and radiative cooling of the shocked plasma. Changes in the amount of stellar occultation and circumstellar attenuation introduce phase-dependent X-ray variability in systems with circular orbits, while strong variations in the intrinsic emission also occur in systems with eccentric orbits. The X-ray emission in eccentric systems can display strong hysteresis, with the emission softer after periastron than at corresponding orbital phases prior to periastron, reflecting the physical state of the shocked plasma at these times. Our simulated X-ray light curves bear many similarities to observed light curves. In systems with circular orbits the light curves show two minima per orbit, which are identical (although not symmetric) if the winds are identical. The maxima in the light curves are produced near quadrature, with a phase delay introduced due to the aberration and curvature of the wind collision region. Circular systems with unequal winds produce minima of different depths and duration. In systems with eccentric orbits the maxima in the light curves may show a very sharp peak (depending on the orientation of the observer), followed by a precipitous drop due to absorption and/or cooling. We show that the rise to maximum does not necessarily follow a 1/dsep law. Our models further demonstrate that the effective circumstellar column can be highly energy dependent. Therefore, spectral fits which assume energy-independent column(s) are overly simplified and may compromise the interpretation of observed data. To better understand observational analyses of such systems we apply Chandra and Suzaku response files, plus Poisson noise, to the spectra calculated from our simulations and fit these using standard xspec models. We find that the recovered temperatures from two- or three-temperature mekal fits are comparable to those from fits to the emission from real systems with similar stellar and orbital parameters/nature. We also find that when the global abundance is thawed in the spectral fits, subsolar values are exclusively returned, despite the calculations using solar values as input. This highlights the problem of fitting oversimplified models to data, and of course is of wider significance than just the work presented here. Further insight into the nature of the stellar winds and the wind,wind collision region in particular systems will require dedicated hydrodynamical modelling, the results of which will follow in due course. [source] Synthesis and properties of magnetite/poly (aniline-co-8-amino-2-naphthalenesulfonic acid) (SPAN) nanocompositesPOLYMERS FOR ADVANCED TECHNOLOGIES, Issue 1 2007Kakarla Raghava Reddy Abstract Composites were prepared by incorporating magnetite (Fe3O4) nanoparticles into the matrix of a sulfonated polyaniline (SPAN) [poly(aniline-co-8-amino-2-naphthalenesulfonic acid) PANSA] through chemical oxidative polymerization of a mixture of aniline and 8-amino-2-naphthalenesulfonic acid in the presence of magnetite nanoparticles. The composite, magnetite/SPAN(PANSA) was characterized by means of transmission electron microscopy (TEM), X-ray diffraction (XRD), elemental analysis (EA), Fourier transform infrared (FT-IR) spectra, UV-vis spectroscopy, thermogravimetric analysis (TGA), conductivity and magnetic properties measurements. TEM image shows that magnetite nanoparticles were finely distributed into the SPAN matrix. XRD pattern of the nanocomposite reveals the presence of additional crystalline order through the appearance of a sharp peak at ,43° and 71°. Conductivity of the nanocomposite (0.23,S/cm) is much higher than pristine copolymer (1.97,×,10,2,S/cm). The results of FT-IR and UV-visible spectroscopy reveal the presence of molecular level interactions between SO groups in SPAN and magnetite nanoparticles in the composite. Copyright © 2006 John Wiley & Sons, Ltd. [source] Quasi-particle peak due to magnetic order in strongly correlated electron systemsANNALEN DER PHYSIK, Issue 8 2010T.A. Zaleski Abstract We study the electron spectral function of the antiferromagnetically ordered phase of the three dimensional Hubbard model, using recently formulated low-energy theory based on the 2D half-filled Hubbard model which describes both collective spin and charge fluctuations for arbitrary value of the Coulomb repulsion U. The model then is solved by a saddle-point approximation within the CP1 representation for the Neel field. The single-particle properties are obtained by writing the fermion field in terms of a U(1) phase, Schwinger boson SU(2) fields and a pseudofermion variables. We demonstrate that the appearance of a sharp peak in the electron spectral function in the antiferromagnetic state points to the emergence of the bosonic mode, which is associated with spin ordering. [source] Aspects of the modelling of the radial distribution function for small nanoparticlesJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 6 2007Vladimir I. Korsunskiy An approach to modelling radial distribution functions (RDFs) of nanoparticle samples over a wide range of interatomic distances is presented. Two different types of contribution to the model RDF are calculated. The first explicitly reflects the structure of the nanoparticle parts with more or less crystalline atomic structure. It can be calculated precisely and contains comparatively sharp peaks, which are produced by the set of discrete interatomic distances. The second includes RDF contributions from distances between weakly correlated atoms positioned within different nanoparticles or within different parts of a nanoparticle model. The calculation is performed using the approximation of a uniform distribution of atoms and utilizes the ideas of the characteristic functions of the particle shape known in small-angle scattering theory. This second RDF contribution is represented by slowly varying functions of interatomic distance r. The relative magnitude of this essential part of the model RDF increases with increasing r compared with the part that represents the ordered structure. The method is applied to test several spherical and core/shell models of semiconductor nanoparticles stabilized with organic ligands. The experimental RDFs of ZnSe and CdSe/ZnS nanoparticle samples were obtained by high-energy X-ray diffraction at beamline BW5, HASYLAB, DESY. The ZnSe nanoparticles have a spherical core with approximately 26,Å diameter and zincblende structure. The RDF of the CdSe/ZnS nanoparticle sample shows resolved peaks of the first- and the second-neighbour distances characteristic for CdSe (2.62 and 4.27,Å) and for ZnS (2.33 and 3.86,Å) and for the first time clearly confirms the presence of CdSe and ZnS nanophases in such objects. The diameters of the CdSe and ZnS spherical cores are estimated as 27 and 15,Å. CdSe and ZnS are present in the sample for the most part as independent nanoparticles. A smaller amount of ZnS forms an irregularly shaped shell around the CdSe cores, which consists of small independently oriented ZnS particles. [source] Observation of new defect levels in nanodiamond membranesPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 11 2005R. Kravets Abstract This paper reports on a new set of defect features in thin membrane nanodiamond. The samples were stud-ied using Fourier transform photocurrent spectroscopy. We have observed four dominant new peaks in nanocrystalline diamond: two sharp peaks at 0.36 and 0.40 eV and broad bands at 0.27 and 0.57 eV. The first of these peaks is suggested to originate from a currently unknown bulk impurity; the other three are surface-related and are especially prone to surface effects such as absorption/desorption over time. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Magnetic impurity transition in a (d,+,s)-wave superconductorPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 3 2010L. S. BorkowskiArticle first published online: 8 FEB 2010 Abstract We consider the superconducting state of symmetry with finite concentration of Anderson impurities in the limit . The model consists of a BCS-like term in the Hamiltonian and the Anderson impurity treated in the self-consistent large- N mean field approximation. Increasing impurity concentration or lowering the ratio drives the system through a transition from a state with two sharp peaks at low energies and exponentially small density of states at the Fermi level to one with . This transition is discontinuous if the energy of the impurity resonance is the smallest energy scale in the problem. [source] Spontaneous emission from semiconductor nanocrystals in coupled spherical microcavitiesPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 2 2005Yu. P. Rakovich Abstract We report on the coherent coupling of whispering gallery modes (WGM) in a photonic molecule formed from two melamine-formaldehyde spherical microcavities coated with a thin shell of light-emitting CdTe nanocrystals (NCs). Utilizing different excitation conditions the splitting of the WGM resonances originating from bonding and anti-bonding branches of the photonic states is observed and fine structure consisting of very sharp peaks resulting from lifting of the WGM degeneracy has been detected. Time-resolved measurements showed a slight increase in the spontaneous emission rate of NCs in a photonic molecule when compared to the spontaneous emission rate for NCs coating a single microsphere. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Zones and sublattices of integral latticesACTA CRYSTALLOGRAPHICA SECTION A, Issue 6 2004A. Janner Methods are presented for an analysis of zones and sublattices of integral lattices, whose relevance is revealed by sharp peaks in the frequency distribution of hexagonal and tetragonal lattices, as a function of the axial ratio . Starting from a few examples, zone symmetries, lattice,sublattice relations and integral scaling transformations are derived for hexagonal lattices with axial ratios , , and 1 (the isometric case) and for the related and tetragonal lattices. Sublattices and zones connected by linear rational transformations lead to rational equivalence classes of integral lattices. For properties like the axial ratio and the point-group symmetry (lattice holohedry), rational equivalence can be extended so that also metric tensors differing by an integral factor become equivalent. These two types of equivalence classes are determined for the lattices mentioned above. [source] | ||||||||||||||||