meV

Distribution by Scientific Domains
Distribution within Physics and Astronomy


Selected Abstracts


Relationship between Slow Coronary Flow and Left Atrial Appendage Blood Flow Velocities

ECHOCARDIOGRAPHY, Issue 1 2007
Recep Demirbag M.D.
Aims: This study was undertaken to assess whether slow coronary flow (SCF)is related to low left atrial appendage (LAA) blood flow velocities. Methods: Study subjects consist of 44 patients with SCF and 11 volunteer subjects with normal coronary angiogram. The diagnosis of SCF was made using the TIMI frame count method. The blood flow velocities were obtained by placing a pulsed-wave Doppler sample volume inside the proximal third of the LAA. Results: The mean LAA emptying velocities (MEV)were significantly lower in patients than control subjects (34.5 9.9 cm/sec vs 84.0 12.1 cm/sec; P < 0.001). In bivariate analysis, significant correlation was found between MEV, and systolic pulmonary venous flow, mean TIMI frame count, deceleration time, and isovolumetric relaxation time (P < 0.05). By multiple linear regression analysis, mean TIMI frame count (=,0.865, P < 0.001) was identified as independent predictors of MEV. Conclusion: This study indicates that SCF phenomenon may be related to low LAA blood flows. [source]


On the construction of multivariate extreme value models via copulas

ENVIRONMETRICS, Issue 2 2010
F. Durante
Abstract Copulas represent a fundamental tool for constructing multivariate probability distributions. Exploiting recent theoretical developments concerning the construction of copulas, we outline several methods for generating multivariate extreme value (MEV) laws having a suitable number of parameters, a feature of great importance in applications. The corresponding random vectors can be efficiently simulated, and easily fitted to empirical data. The use of multivariate return periods for extreme events is also discussed. A practical illustration involving maxima sampled via a network of non-independent gauge stations is presented. Copyright 2009 John Wiley & Sons, Ltd. [source]


Microwave-Assisted Hydrothermal Synthesis of Structurally and Morphologically Controlled Sodium Niobates by Using Niobic Acid as a Precursor

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 8 2008
Amauri J. Paula
Abstract There are many advantages to using a microwave as a source of heat in hydrothermal reactions. Because it is a quick and homogeneous way to crystallize ceramic powders, it was used in this work for the production of antiferroelectric sodium niobate (NaNbO3) in a cubic-like form and its intermediary phase, disodium diniobate hydrate (Na2Nb2O6.H2O), with a fiber morphology. The syntheses were carried out by treating niobic acid (Nb2O5nH2O) with NaOH. By changing the reaction time and the concentration of the reactants, particles with different structures and different morphologies could be obtained. The structural evolution of the products of this reaction was elucidated on the basis of the arrangement of the NbO6 octahedral units. Conclusive results were obtained with morphological and structural characterizations through XRD, TEM, MEV, and NMR and Raman spectroscopy. ( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source]


MS and clinically isolated syndromes: Shared specificity but diverging clonal patterns of virus-specific IgG antibodies produced in vivo and by CSF B cells in vitro

EUROPEAN JOURNAL OF NEUROLOGY, Issue 10 2009
G. Skorstad
Background:, Intrathecal synthesis of oligoclonal IgG antibodies against measles virus (MeV), varicella zoster virus (VZV) and herpes simplex virus type-1 (HSV-1) is a characteristic feature multiple sclerosis (MS). Methods:, We have used isoelectric focusing-immunoblot to define the clonal patterns of IgG and of IgG antibodies to MeV, VZV and HSV-1 in supernatants of in vitro cultures of peripheral blood lymphocytes (PBL) and cerebrospinal fluid (CSF) cells and in sera and CSF from three patients with MS and three patients with clinically isolated syndromes (CIS) suspective of demyelinating disease. Results:,In vitro synthesis of IgG by PBL was not detected in any patient. In contrast, in vitro synthesis by CSF cells of oligoclonal IgG and oligoclonal IgG antibodies to one or two of the three viruses tested was observed in all six patients. The clonal patterns of the in vitro synthesized IgG and virus specific IgG differed to varying extent from those synthesized intrathecally in vivo. However, in each patient, the in vitro and in vivo intrathecally produced antibodies displayed specificity for the same viruses. The addition of B cell activating factor (BAFF) had no effect on the amounts or clonal patterns of either total IgG or virus-specific IgG produced by CSF cells in vitro. Conclusion:, Virus specific B cells capable of spontaneous IgG synthesis are clonally expanded in the CSF of patients with MS. The B-cell repertoire in CSF samples is only partially representative of the intrathecal B-cell repertoire. [source]


Inversion of time-dependent nuclear well-logging data using neural networks

GEOPHYSICAL PROSPECTING, Issue 1 2008
Laura Carmine
ABSTRACT The purpose of this work was to investigate a new and fast inversion methodology for the prediction of subsurface formation properties such as porosity, salinity and oil saturation, using time-dependent nuclear well logging data. Although the ultimate aim is to apply the technique to real-field data, an initial investigation as described in this paper, was first required; this has been carried out using simulation results from the time-dependent radiation transport problem within a borehole. Simulated neutron and ,-ray fluxes at two sodium iodide (NaI) detectors, one near and one far from a pulsed neutron source emitting at ,14 MeV, were used for the investigation. A total of 67 energy groups from the BUGLE96 cross section library together with 567 property combinations were employed for the original flux response generation, achieved by solving numerically the time-dependent Boltzmann radiation transport equation in its even parity form. Material property combinations (scenarios) and their correspondent teaching outputs (flux response at detectors) are used to train the Artificial Neural Networks (ANNs) and test data is used to assess the accuracy of the ANNs. The trained networks are then used to produce a surrogate model of the expensive, in terms of computational time and resources, forward model with which a simple inversion method is applied to calculate material properties from the time evolution of flux responses at the two detectors. The inversion technique uses a fast surrogate model comprising 8026 artificial neural networks, which consist of an input layer with three input units (neurons) for porosity, salinity and oil saturation; and two hidden layers and one output neuron representing the scalar photon or neutron flux prediction at the detector. This is the first time this technique has been applied to invert pulsed neutron logging tool information and the results produced are very promising. The next step in the procedure is to apply the methodology to real data. [source]


Tuning and Enhancing Photoluminescence of Light-Emitting Polymer Nanotubes through Electron-Beam Irradiation

ADVANCED FUNCTIONAL MATERIALS, Issue 4 2009
Young Ki Hong
A new method for the tuning and enhancing photoluminescence (PL) characteristics of light emitting poly (3-methylthiopnehe) (P3MT) nanotubes through E-beam irradiation under atmospheric environments is reported. An E-beam generated from a linear electron accelerator (1 MeV, 1.6,,1013,8.0,,1016 electrons cm,2) is irradiated onto P3MT nanotubes including an Al2O3 template. From laser confocal microscope (LCM) PL experiments, significant enhancements in the PL intensity,up to about 90 times of an isolated single strand of the E-beam irradiated P3MT nanotubes,are observed. The luminescent color of the P3MT nanotubes changes from green to red color depending on the variation of E-beam dosage. These results might originate from the de-doping effect and the conformational modification through E-beam irradiations. Conformational changes of the E-beam irradiated P3MT nanotubes are confirmed by LCM single Raman and ultraviolet-visible (UV/Vis) absorption spectra. From UV/Vis absorption spectra, it is observed that the ,,,* transition peak and the doping induced bipolaron peaks of the P3MT nanotubes dramatically vary with E-beam irradiating conditions. [source]


Formation of Nanoislands on Conducting Poly(3,4-ethylenedioxythiophene) Films by High-Energy - Ion Irradiation: Applications as Field Emitters and Capacitor Electrodes,

ADVANCED FUNCTIONAL MATERIALS, Issue 9 2005
J. Joo
Abstract Nanoislands have been fabricated on the surface of conducting poly(3,4-ethylenedioxythiophene) (PEDOT) films doped with poly(4-styrenesulfonate) (PSS) using high-energy (,,1,3,MeV) Cl2+ ion irradiation. Scanning electron microscopy and atomic force microscopy confirm the direct formation of nanoislands with diameters ranging from 50,to 300,nm and heights ranging from 40,to 120,nm. From our analysis, we propose that the formation of nanoislands might be due to micelle formation of the polymeric stabilizer poly(sodium 4-styrenesulfonate) (PSS-Na) surrounding the nuclei in the PEDOT/PSS via the high-energy-ion irradiation. We observe similar results for high-energy-ion irradiated polyaniline doped with PSS-Na. On using the nanoislands as nanotip emitters of a field-emission display, an increase in the current density of about five orders of magnitude is observed. Cyclic voltammetry of the PEDOT/PSS electrode with the nanoislands as the electrode shows enhanced capacitance compared with that of the PEDOT/PSS film that contains no nanostructure. [source]


Small-angle X-ray scattering measurements of helium-bubble formation in borosilicate glass

JOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 5 2006
Alexander Y. Terekhov
Small-angle X-ray scattering (SAXS) measurements have been performed to study helium-bubble formation in borosilicate glass. Helium was introduced by He+ implantation over an energy range of 1 to 2,MeV to give a uniform distribution over ,1,m depth. The implanted dose was varied from 9 1013 to 2.8 1016,ions,cm,2, corresponding to a local concentration range of 40 to 11200 atomic parts per million (a.p.p.m.) averaged over the implantation depth. The SAXS response was fit with the Percus,Yevick hard-sphere interaction potential to account for interparticle interference. The fits yield helium-bubble radii and helium-bubble volume fractions that vary from 5 to 15, and from 10,3 to 10,1, respectively, as the dose increased from 9 1013 to 2.8 1016,cm,2. The SAXS data are also consistent with maximum helium solubility with respect to bubble formation between 40 and 200 a.p.p.m. in the borosilicate glass matrix. [source]


Effect of neutron irradiation on the structural, mechanical, and thermal properties of jute fiber

JOURNAL OF APPLIED POLYMER SCIENCE, Issue 1 2008
E. Sinha
Abstract This article describes the effect of neutron irradiation on jute fiber (Corchorus olitorius). The jute fibers (4.0 tex) were irradiated by fast neutrons with an energy of 4.44 MeV at different fluences ranging from 2 109 to 2 1013 n/cm2. An important aspect of neutron irradiation is that the fast neutrons can produce dense ionization at deep levels in the materials. Structural analysis of the raw and irradiated fibers were studied by small-angle X-ray scattering (SAXS), X-ray diffraction (XRD), scanning electron microscopy (SEM), and Fourier transform infrared spectroscopy. Thermal analysis carried out on the raw and irradiated fibers showed that the thermal stability of the fibers decreased after irradiation. The mechanical properties of the jute fibers were found to decrease after irradiation. The SAXS study showed that the average periodicity transverse to the layer decreased after irradiation, which may have been due to the shrinkage of cellulosic particles constituting the fiber. The residual compressive stress developed in the fiber after irradiation resulted in a decrease in crystallite size as supported by our XRD analysis. Observation with SEM did not indicate any change produced in the surface morphology of the fiber due to irradiation. 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source]


Modification induced by alpha particle irradiationin Makrofol polycarbonate

JOURNAL OF APPLIED POLYMER SCIENCE, Issue 6 2008
S. A. Nouh
Abstract Makrofol DE 1-1 CC polycarbonate samples were exposed to alpha particles of initial energies at levels between 5.1 and 34 MeV. The modifications induced in polycarbonate samples due to the alpha particle irradiation have been studied through different characterization techniques such as X-ray diffraction (XRD), infrared spectroscopy, intrinsic viscosity, and color difference studies. The infrared spectroscopy indicated that the intensities of the characteristic absorption bands decrease with increasing the deposited alpha energy in the range 5.1,8.4 MeV, indicating that the degradation is the dominant mechanism at this range. At the same time, an increase in the OH groups was observed at the same energy range 5.1,8.4 MeV due to the degradation of carbonate group and the H abstraction from the polymer backbone to form hydroxyl groups. The degradation reported by IR spectroscopy enhanced the degree of ordering in the degraded samples as revealed by XRD technique. Additionally, this degradation decreases the intrinsic viscosity from 0.56 to 0.43 at 35C, indicating a decrease in the average molecular mass. The non irradiated Polycarbonate polymer is nearly colorless. It showed significant darkness sensitivity towards alpha particle irradiation, indicated by an increase in the color intercept L* from 33.6 to 36.7. 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source]


Deposition of 90YPO4 and 144CePO4 radioisotopes on polymer surfaces for radiation delivery devices

JOURNAL OF BIOMEDICAL MATERIALS RESEARCH, Issue 2 2002
Xin Qu
Abstract Intravascular irradiation with , emitters inhibits restenosis in arteries after balloon angioplasty or stent implantation. Yttrium-90 (90Y, T1/2=64 h) and cerium-144 (144Ce, T1/2=286 d) emit beta particles (Emax=2.28,3.50 MeV) having an ideal energy range for brachytherapy delivery system. In this article, a previously reported method for depositing 32P on poly(ethylene terephtalate) (PET) surfaces is generalized and modifications that allow deposition of other ,-emitting radioisotopes, such as 90Y and 144Ce, are demonstrated. PET films were first coated with chitosan hydrogel and then adsorbed different amounts of phosphoric acid (PA) in aqueous solutions. Yttrium was deposited onto the surface as YPO4 after the films were immersed in YCl3 solutions. 1 ,Ci 90YCl3 (210,9 g) was used in each sample as a tracer for measuring the deposition efficiency, which is defined as the percentage of YCl3 deposited on the surface compared to the amount of YCl3 in solutions before the deposition. In order to improve the safety of brachytherapy treatments, polyurethanes were used to seal the deposited radioisotopes on the surface to minimize the leakage of the isotopes into the patients. The generality of this method presented here for a wide variety of particular radioisotopic components allows design of a broad range of versatile radioisotope sources. 2002 Wiley Periodicals, Inc. J Biomed Mater Res (Appl Biomater) 63: 98,105, 2002; DOI 10.1002/jbm.10095 [source]


Preparation and animal biodistribution of 166Ho labeled DOTA for possible use in intravascular radiation therapy (IVRT)

JOURNAL OF LABELLED COMPOUNDS AND RADIOPHARMACEUTICALS, Issue 3 2003
Tapas Das
Owing to its favorable decay characteristics (T1/2=27 h, E,(max)=1.85 MeV, E,=81 keV) and its availability with a specific activity of 3.7,4.4 GBq/mg from a moderate flux reactor, 166Ho can be considered as a potential radionuclide for intravascular radiation therapy (IVRT) using liquid-filled balloons. In the present work, studies on the use of 166Ho labeled 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) as a possible agent for IVRT for the prevention of restenosis has been initiated. 166Ho was obtained by irradiating natural Ho2O3 powder and DOTA was synthesized by a multistep procedure. The optimum protocol of radiolabeling of DOTA with 166Ho was achieved by varying different reaction parameters. The complex was found to retain its stability for 7 days at room temperature. Bioevaluation studies carried out in Wistar rats showed that >95% of the injected activity was excreted within 3 h p.i. with almost no retention in any major organ. Both radiochemical and biological studies showed that 166Ho labeled DOTA can be further explored as a potential agent for IVRT. Copyright 2002 John Wiley & Sons, Ltd. [source]


Monoenergetic electron beam generation in a laser-driven plasma acceleration

LASER PHYSICS LETTERS, Issue 2 2006
M. Adachi
Abstract We obtained a 7-MeV monoenergetic electron beam from a plasma with the electron density ne of 1.5 1020 cm,3 produced by a 2-TW 50-fs laser pulse. In both higher and lower sides of the density region of 4 1019 4 1020 cm,3, energy spectra of electrons were bi-Maxwellian distribution function whose maximum electron energy and effective electron temperature were 30 MeV and approximately MeV, respectively. Observed first Stokes satellites in the forward scattering light spectra, and the density dependences of maximum electron energy and the effective temperature suggest that electrons are first accelerated by SMLWFA and are further accelerated by direct laser acceleration (DLA) in the ne region of more than 2 1020 cm,3; a cascade acceleration by SMLWFA and DLA. A Stokes satellite peak observed with the monoenergetic beam suggests that the monoenergetic beam would be accelerated by SMLWFA. ( 2006 by Astro, Ltd. Published exclusively by WILEY-VCH Verlag GmbH & Co. KGaA) [source]


Modification of the gamma-ray spectra by internal absorption in optically violently variable blazars: the example cases of 3C 273 and 3C 279

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2008
J. Sitarek
ABSTRACT Recent observations with the low-threshold Cherenkov telescopes proved that sub-TeV ,-rays are able to arrive from active galaxies at relatively large distances in spite of the expected severe absorption in the extragalactic background light (EBL). We calculate the ,-ray spectra at TeV energies from two example optically violently variable quasars, 3C 273 and 3C 279, assuming that ,-rays are injected in the inner parts of the jets launched by the accretion discs. It is assumed that ,-rays in the broad energy range (from MeV up to TeV) are produced in these blazars with a power-law spectrum with the spectral index as observed from these objects by the EGRET telescope at GeV energies. We take into account the internal absorption of these ,-rays by considering a number of models for the radiation field surrounding the jet. The classical picture of a relativistic blob in a jet for the injection of primary ,-rays is considered, with the injection rate of ,-rays as observed by the EGRET telescope in the GeV energy range. The results of calculations are compared with positive detection and the upper limits on the sub-TeV ,-ray fluxes from these two sources. It is concluded that, even with the Stecker EBL model, the level of ,-ray emission from 3C 279 is close to the recent measurements in the sub-TeV ,-ray energies, provided that the injected ,-ray spectrum extends from the GeV energies over the next two decades with this same spectral index. We also suggest that a flare with a time-scale of a few days from 3C 273 could be detected by the MAGIC II stereo telescopes. [source]


Extragalactic MeV ,-ray emission from cocoons of young radio galaxies

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2007
M. Kino
ABSTRACT Strong ,-ray emission from cocoons of young radio galaxies is predicted for the first time. Considering the process of adiabatic injection of the shock dissipation energy and mass of the relativistic jet in active nuclei into the cocoon, while assuming thermalizing electron plasma interactions, we find that the thermal electron temperature of the cocoon is typically predicted to be of the order of , MeV, and is determined only by the bulk Lorentz factor of the relativistic jet. Together with the time-dependent dynamics of the cocoon expansion, we find that young cocoons can yield thermal bremsstrahlung emissions at energies ,MeV. [source]


The GRB early optical flashes from internal shocks: application to GRB 990123, GRB 041219a and GRB 060111b

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2007
D. M. Wei
ABSTRACT With the successful launch of the Swift Gamma-ray Burst Explorer, it is widely expected that the prompt optical flashes like GRB 990123 would be easily detected. However, the observations show that for a number of Gamma-ray bursts (GRBs) no early optical flash has been detected, which indicates that the reverse shock emission must be suppressed. Here we explore the possibility that the optical flash may arise from the internal shock emission. For GRB 990123 and GRB 060111b, although their optical emission are not correlated with the gamma-ray emission, we propose here that their optical and gamma-ray emission may arise from different internal shocks (which can be formed by collision of different shells), and find that, under certain circumstances, the optical flashes of GRB 990123 and GRB 060111b can well be explained by the internal shock model. For GRB 041219a, the prompt optical emission was correlated with the gamma-ray emission, which can also be explained by the internal shock model if we assume the optical emission was the low-energy extension of the gamma-ray emission, and we find its redshift is about z, 0.2. As for GRB 050904, we have shown in previous paper that the optical flash was produced by synchrotron radiation and the X-ray flare was produced by the synchrotron,self-Compton (SSC) mechanism. Therefore we conclude that the early optical flashes of GRBs can usually arise from the internal shock emission. Meanwhile in our model since the shells producing the optical flashes would be easily disrupted by other shells, so we suggest that the bright optical flash should not be common in GRBs. In addition, we also discussed the SSC emission in the internal shock model, and find that for different values of parameters, there would be several kinds of high-energy emission (at ,100 keV, ,10 MeV or GeV) accompanying the optical flash. For a burst like GRB 990123, a GeV flare with fluence about 10,8 erg cm,2 s,1 is expected, which might be detected by the GLAST satellite. [source]


Fullerene C60 and hybrid C60/Ti films as substrates for adhesion and growth of bone cells

PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 9 2008
Marta Vandrovcova
Abstract Thin films of fullerenes C60, Ti or binary C60/Ti composites (ratio C60versus Ti 1:1) were deposited on microscopic glass coverslips in a continuous or micropatterned form. The latter was created using a metallic mask with rectangular openings, and contained prominences from 108 2 nm to 362 5 nm in height. Some micropatterned C60 and C60/Ti films were irradiated with Au+ ions (energy 1.8 MeV, fluence 2 1014 cm,2), which led to the conversion of some C60 molcules into amorphous carbon (a-C). The films were then seeded with human osteoblast-like MG 63 cells (,17,000 cells/cm2). One and 3 days after seeding, the cells reached numbers which were usually similar or even higher in comparison with the values on control glass coverslips and standard cell culture polystyrene dishes. On micropatterned layers, the cells adhered and grew preferentially in grooves among the prominences (,57% to 90% of cells). On day 3 after seeding, this preferential colonization of the grooves disappeared in the ion-irradiated layers, which could be explained by a conversion of C60 into amorphous carbon and increased hydrophilia of the layer. Thus, all tested films gave good support to the adhesion and growth of bone-derived MG 63 cells. In addition, microstructured C60 and C60/Ti films containing prominences and grooves on their surface could be applied for regionally-selective cell adhesion and directed growth of cells. ( 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


Radiation-induced structural transformations in a silicon layer of SOI

PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 8 2007
K. D. Shcherbachev
Abstract The differences in the secondary processes proceeding in the silicon layer of SOI and reference bulk silicon wafers are revealed by using High-Resolution X-ray diffraction and Rutherford Backscattering spectroscopy methods. The damage depth profiles in the implanted layers described by both strain and static Debye,Waller factor profiles, were reconstructed from the diffraction patterns using an autofitting procedure, based on a genetic algorithm. The contribution of diffuse scattering was excluded using the triple-crystal diffractometry technique. The defect density profiles were obtained from the RBS/Channelling measurements, which were carried out using 4He+ beam at 2.0 MeV. The DICADA code, based on the theoretical description of dechanneling was used to interpret the RBS/C data. Accumulation kinetics, spatial distribution, and concentration of radiation-induced defects in the topmost silicon layer of SOI and a bulk silicon were shown to be essentially different. The influence of the fields was shown to lead to the loss of crystallinity of the thin surface layer of silicon in SOI due to accumulation of vacancy-type defects and increase of concentration of interstitial atoms near the internal interphase boundary "Si,SiO2". ( 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


Study of the influence of ,-particles irradiation on AlGaAs/GaAs heterojunction structures

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 12 2008
P. Georgakakos
Abstract Aim of the present work is to study the influence of the radiation of ,-particles (5 MeV) in Schottky diodes on CaAs/AlGaAs/GaAs heterojunction structures. The investigation was performed by means of current-voltage and capacitance-voltage characteristics in 300 K temperature. The dependence of ideality factor, barrier height, carrier concentration and series resistance as a function of radiation fluence was determined. ( 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


Europium-doped barium halide X-ray scintillators

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 3 2007
J. Selling
Abstract Single crystals of europium-doped barium chloride, bromide, and iodide were investigated under x-ray and ,-ray excitation. The Eu2+ -related x-ray excited luminescence is at 402, 404, and 425 nm for the chloride, bromide, and iodide, respectively. BaCl2:Eu2+ has the most promising scintillation properties of the systems investigated. The light yield is about 20,000 2,000 photons per MeV of absorbed ,-ray energy, the energy resolution for the 662 keV photopeak is 9% 1%, and the scintillation decay time is (390 40) ns. ( 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


High and low energy proton irradiation effects on AlGaN/GaN HFETs

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 6 2006
G. Sonia
Abstract AlGaN/GaN heterojunction field effect transistors (HFETs) have been irradiated with protons at 68 MeV and 2 MeV with fluences up to 1013 cm,2 in order to simulate operation in space. Hall effect measurements, dc characteristics and RF load pull measurements at 2 GHz do not reveal significant changes indicating the suitability of the transistors for reliable operation in space. ( 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


Prevention of malignant seeding at drain sites by hypofractionated radiotherapy in patients with pleural mesothelioma

ASIA-PACIFIC JOURNAL OF CLINICAL ONCOLOGY, Issue 3 2010
Pinar KARA
Abstract Aim: Unlike most other malignancies, malignant pleural mesothelioma (MPM) has a tendency to recur along tracks of chest wall instrumentation. We investigated the efficiency of hypofractionated radiotherapy for prevention of malignant seeding. Methods: Twenty-one (six female, 15 male) patients diagnosed with pleural mesothelioma who had chest wall instrumentation and were treated with prophylactic radiotherapy were investigated retrospectively. All patients underwent surgery or thoracoscopy and/or talc pleurodesis, for diagnosis, staging procedures or as a treatment. All were treated with electron (12 MeV) external beam radiation therapy (21 Gy in three fractions over 3 days), directed to the instrumentation pathway after the invasive procedure. After completion of radiotherapy, four of 21 patients had also undergone chemotherapy. Results: Nineteen of 21 patients were followed-up for a median period of 13 months (1,24 months) and two patients were lost just after the first month of the follow-up period. None of the followed patients had tumor progression in the treated area. Radiotherapy was well tolerated. The most common side-effect was grade 1 erythema (Radiation Therapy Oncology Group [RTOG] scale), noted in 13 treated patients. Conclusion: Our experience showed that prophylactic radiotherapy to prevent malignant seeding in malignant mesothelioma at invasive procedure sites was effective and well tolerated in preventing malignant seeding, painful metastases after surgery or instrumentation in patients with pleural mesothelioma. Larger multicenter prospective trials are still needed to validate this treatment approach utility for it to be recommended routinely. [source]


High energy emission from AGN cocoons in clusters of galaxies

ASTRONOMISCHE NACHRICHTEN, Issue 2-3 2009
M. Kino
Abstract Gamma-ray emission from cocoons of young radio galaxies is predicted. Considering the process of adiabatic injection of the shock dissipation energy and mass of the relativistic jet into the cocoon, we find that the thermal electron temperature of the cocoon is typically predicted to be of the order of ,MeV, and is determined only by the bulk Lorentz factor of the jet. Together with the time-dependent dynamics of the cocoon expansion, we find that young cocoons can yield thermal bremsstrahlung emissions at energies ,MeV. Hotter cocoons (i.e., GeV) for younger sources are also discussed ( 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


Heavy-ion-induced bystander killing of human lung cancer cells: Role of gap junctional intercellular communication

CANCER SCIENCE, Issue 4 2009
Kosaku Harada
The aim of the present study was to clarify the mechanisms of cell death induced by heavy-ion irradiation focusing on the bystander effect in human lung cancer A549 cells. In microbeam irradiation, each of 1, 5, and 25 cells under confluent cell conditions was irradiated with 1, 5, or 10 particles of carbon ions (220 MeV), and then the surviving fraction of the population was measured by a clonogenic assay in order to investigate the bystander effect of heavy-ions. In this experiment, the limited number of cells (0.0001,0.002%, 5,25 cells) under confluent cell conditions irradiated with 5 or 10 carbon ions resulted in an exaggerated 8,14% increase in cell death by clonogenic assay. However, these overshooting responses were not observed under exponentially growing cell conditions. Furthermore, these responses were inhibited in cells treated with an inhibitor of gap junctional intercellular communication (GJIC), whereas they were markedly enhanced by the addition of a stimulator of GJIC. The present results suggest that bystander cell killing by heavy-ions was induced mainly by direct cell-to-cell communication, such as GJIC, which might play important roles in bystander responses. (Cancer Sci 2009; 100: 684,688) [source]


Structural, electrical and optical properties of Ge implanted GaSe single crystals grown by Bridgman technique

CRYSTAL RESEARCH AND TECHNOLOGY, Issue 12 2006
H. Karaa
Abstract Structural, optical and electrical properties of Ge implanted GaSe single crystal have been studied by means of X-Ray Diffraction (XRD), temperature dependent conductivity and photoconductivity (PC) measurements for different annealing temperatures. It was observed that upon implanting GaSe with Ge and applying annealing process, the resistivity is reduced from 2.1 109 to 6.5 105 ,-cm. From the temperature dependent conductivities, the activation energies have been found to be 4, 34, and 314 meV for as-grown, 36 and 472 meV for as-implanted and 39 and 647 meV for implanted and annealed GaSe single crystals at 500C. Calculated activation energies from the conductivity measurements indicated that the transport mechanisms are dominated by thermal excitation at different temperature intervals in the implanted and unimplanted samples. By measuring photoconductivity (PC) measurement as a function of temperature and illumination intensity, the relation between photocurrent (IPC) and illumination intensity (,) was studied and it was observed that the relation obeys the power law, IPC ,,n with n between 1 and 2, which is indication of behaving as a supralinear character and existing continuous distribution of localized states in the band gap. As a result of transmission measurements, it was observed that there is almost no considerable change in optical band gap of samples with increasing annealing temperatures for as-grown GaSe; however, a slight shift of optical band gap toward higher energies for Ge-implanted sample was observed with increasing annealing temperatures. ( 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


The Influence of Film Morphology in High-Mobility Small-Molecule:Polymer Blend Organic Transistors

ADVANCED FUNCTIONAL MATERIALS, Issue 14 2010
Jeremy Smith
Abstract Organic field-effect transistors (OFETs) based upon blends of small molecular semiconductors and polymers show promise for high performance organic electronics applications. Here the charge transport characteristics of high mobility p-channel organic transistors based on 2,8-difluoro-5,11-bis(triethylsilylethynyl) anthradithiophene:poly(triarylamine) blend films are investigated. By simple alteration of the film processing conditions two distinct film microstructures can be obtained: one characterized by small spherulitic grains (SG) and one by large grains (LG). Charge transport measurements reveal thermally activated hole transport in both SG and LG film microstructures with two distinct temperature regimes. For temperatures >115,K, gate voltage dependent activation energies (EA) in the range of 25,60 meV are derived. At temperatures <115,K, the activation energies are smaller and typically in the range 5,30 meV. For both film microstructures hole transport appears to be dominated by trapping at the grain boundaries. Estimates of the trap densities suggests that LG films with fewer grain boundaries are characterized by a reduced number of traps that are less energetically disordered but deeper in energy than for small SG films. The effects of source and drain electrode treatment with self-assembled monolayers (SAMs) on current injection is also investigated. Fluorinated thiol SAMs were found to alter the work function of gold electrodes by up to ,1,eV leading to a lower contact resistance. However, charge transport analysis suggests that electrode work function is not the only parameter to consider for efficient charge injection. [source]


Variable Temperature Mobility Analysis of n-Channel, p-Channel, and Ambipolar Organic Field-Effect Transistors

ADVANCED FUNCTIONAL MATERIALS, Issue 1 2010
Joseph A. Letizia
Abstract The temperature dependence of field-effect transistor (FET) mobility is analyzed for a series of n-channel, p-channel, and ambipolar organic semiconductor-based FETs selected for varied semiconductor structural and device characteristics. The materials (and dominant carrier type) studied are 5,5,,,-bis(perfluorophenacyl)-2,2,:5,,2,:5,,2,,,-quaterthiophene (1, n-channel), 5,5,,,-bis(perfluorohexyl carbonyl)-2,2,:5,,2,:5,,2,,,-quaterthiophene (2, n-channel), pentacene (3, p-channel); 5,5,,,-bis(hexylcarbonyl)-2,2,:5,,2,:5,,2,,,-quaterthiophene (4, ambipolar), 5,5,,,-bis-(phenacyl)-2,2,: 5,,2,:5,,2,,,-quaterthiophene (5, p-channel), 2,7-bis((5-perfluorophenacyl)thiophen-2-yl)-9,10-phenanthrenequinone (6, n-channel), and poly(N -(2-octyldodecyl)-2,2,-bithiophene-3,3,-dicarboximide) (7, n-channel). Fits of the effective field-effect mobility (eff) data assuming a discrete trap energy within a multiple trapping and release (MTR) model reveal low activation energies (EAs) for high-mobility semiconductors 1,3 of 21, 22, and 30,meV, respectively. Higher EA values of 40,70,meV are exhibited by 4,7 -derived FETs having lower mobilities (eff). Analysis of these data reveals little correlation between the conduction state energy level and EA, while there is an inverse relationship between EA and eff. The first variable-temperature study of an ambipolar organic FET reveals that although n-channel behavior exhibits EA,=,27,meV, the p-channel regime exhibits significantly more trapping with EA,=,250,meV. Interestingly, calculated free carrier mobilities (0) are in the range of ,0.2,0.8,cm2,V,1 s,1 in this materials set, largely independent of eff. This indicates that in the absence of charge traps, the inherent magnitude of carrier mobility is comparable for each of these materials. Finally, the effect of temperature on threshold voltage (VT) reveals two distinct trapping regimes, with the change in trapped charge exhibiting a striking correlation with room temperature eff. The observation that EA is independent of conduction state energy, and that changes in trapped charge with temperature correlate with room temperature eff, support the applicability of trap-limited mobility models such as a MTR mechanism to this materials set. [source]


Control of Charge Transport in Iridium(III) Complex-Cored Carbazole Dendrimers by Generation and Structural Modification

ADVANCED FUNCTIONAL MATERIALS, Issue 2 2009
Salvatore Gambino
Abstract Here, the charge transporting properties of a family of highly phosphorescent iridium(III) complex-cored carbazole dendrimers designed to have improved charge transport by incorporating carbazole units into the dendrons are studied. Firstly, the effect of the dendrimer generation and the role of dendron for materials with one dendron per ligand of the core are considered. It is shown, in contrast to previously reported light-emitting dendrimers, that in this case the carbazolyl-based dendrons have an active role in charge transport. Next, the effect on the charge transport of attaching two dendrons per ligand to the dendrimer core is explored. In this latter case, for the so called "double dendron" material a highly non-dispersive charge transport behavior is observed, together with a time-of-flight mobility of the order of 10,3,cm2 V,1,s,1. Furthermore the lowest energetic disorder parameter (,) ever reported for a solution-processed conjugated organic material is found, ,,< ,20 meV. [source]


Shielding Nanowires and Nanotubes with Imogolite: A Route to Nanocables

ADVANCED MATERIALS, Issue 43 2009
Agnieszka Kuc
The use of an imogolite (aluminosilicate) sheath to protect a conducting core consisting of a carbon nanotube (CNT) or nanowire from mechanical and chemical attacks is proposed. The cross-sectional structure of such a nanocable is shown in the figure. The most stable CNT@ imogolite nanocable is calculated to have a tube,tube distance of 2.8, and an insertion energy of ca. 60,meV per carbon atom. [source]


Hartree,Fock exchange fitting basis sets for H to Rn ,

JOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 2 2008
Florian Weigend
Abstract For elements H to Rn (except Lanthanides), a series of auxiliary basis sets fitting exchange and also Coulomb potentials in Hartree,Fock treatments (RI-JK-HF) is presented. A large set of small molecules representing nearly each element in all its common oxidation states was used to assess the quality of these auxiliary bases. For orbital basis sets of triple zeta valence and quadruple zeta valence quality, errors in total energies arising from the RI-JK approximation are below ,1 meV per atom in molecular compounds. Accuracy of RI-JK-approximated HF wave functions is sufficient for being used for post-HF treatments like Mller,Plesset perturbation theory, MP2. Compared to nonapproximated treatments, RI-JK-HF leads to large computational savings for quadruple zeta valence orbital bases and, in case of small to midsize systems, to significant savings for triple zeta valence bases. 2007 Wiley Periodicals, Inc. J Comput Chem, 2008 [source]