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Search Results: 1 - 10 of 410944 matches for " Stephen M. Schindler "
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Properties of Pt Schottky Type Contacts On High-Resistivity CdZnTe Detectors
Aleksey E. Bolotnikov,Steven E. Boggs,C. M. Hubert Chen,Walter R. Cook,Fiona A. Harrison,Stephen M. Schindler
Physics , 2001, DOI: 10.1016/S0168-9002(01)01506-6
Abstract: In this paper we present studies of the I-V characteristics of CdZnTe detectors with Pt contacts fabricated from high-resistivity single crystals grown by the high-pressure Brigman process. We have analyzed the experimental I-V curves using a model that approximates the CZT detector as a system consisting of a reversed Schottky contact in series with the bulk resistance. Least square fits to the experimental data yield 0.78-0.79 eV for the Pt-CZT Schottky barrier height, and <20 V for the voltage required to deplete a 2 mm thick CZT detector. We demonstrate that at high bias the thermionic current over the Schottky barrier, the height of which is reduced due to an interfacial layer between the contact and CZT material, controls the leakage current of the detectors. In many cases the dark current is not determined by the resistivity of the bulk material, but rather the properties of the contacts; namely by the interfacial layer between the contact and CZT material.
Effects of Bulk and Surface Conductivity on the Performance of CdZnTe Pixel Detectors
Aleksey E. Bolotnikov,C. M. Hubert Chen,Walter R. Cook,Fiona A. Harrison,Irfan Kuvvetli,Stephen M. Schindler
Physics , 2001, DOI: 10.1109/TNS.2002.801673
Abstract: We studied the effects of bulk and surface conductivity on the performance of high-resistivity CdZnTe (CZT) pixel detectors with Pt contacts. We emphasize the difference in mechanisms of the bulk and surface conductivity as indicated by their different temperature behaviors. In addition, the existence of a thin (10-100 A) oxide layer on the surface of CZT, formed during the fabrication process, affects both bulk and surface leakage currents. We demonstrate that the measured I-V dependencies of bulk current can be explained by considering the CZT detector as a metal-semiconductor-metal system with two back-to-back Schottky-barrier contacts. The high surface leakage current is apparently due to the presence of a low-resistivity surface layer that has characteristics which differ considerably from those of the bulk material. This surface layer has a profound effect on the charge collection efficiency in detectors with multi-contact geometry; some fraction of the electric field lines originated on the cathode intersects the surface areas between the pixel contacts where the charge produced by an ionizing particle gets trapped. To overcome this effect we place a grid of thin electrodes between the pixel contacts; when the grid is negatively biased, the strong electric field in the gaps between the pixels forces the electrons landing on the surface to move toward the contacts, preventing the charge loss. We have investigated these effects by using CZT pixel detectors indium bump bonded to a custom-built VLSI readout chip.
Hedgehog signaling patterns the outgrowth of unpaired skeletal appendages in zebrafish
Yavor Hadzhiev, Zsolt Lele, Simone Schindler, Stephen W Wilson, Per Ahlberg, Uwe Str?hle, Ferenc Müller
BMC Developmental Biology , 2007, DOI: 10.1186/1471-213x-7-75
Abstract: Here we provide molecular description of the initial ontogeny of the median fins in zebrafish and present several independent lines of evidence that Sonic hedgehog signaling emanating from the embryonic midline is essential for establishment and outgrowth of the caudal fin primordium. However, gene expression analysis shows that the primordium of the adult caudal fin does not harbor a Sonic hedgehog-expressing domain equivalent to the Shh secreting zone of polarizing activity (ZPA) of paired appendages.Our results suggest that Hedgehog proteins can regulate skeletal appendage outgrowth independent of a ZPA and demonstrates an unexpected mechanism for mediating Shh signals in a median fin primordium. The median fins evolved before paired fins in early craniates, thus the patterning of the median fins may be an ancestral mechanism that controls the outgrowth of skeletogenic appendages in vertebrates.Living primitive chordates like Branchiostoma and the agnathan hagfishes have a very simple, non-differentiated caudal fin fringe, whereas lampreys are characterized by separate and differentiated caudal and dorsal median fins [1]. Recent analyses concur that the fossil jawless vertebrates ("ostracoderms"), which have differentiated median fins and either no or one pair (pectoral) fins, form the stem group of the Gnathostomata. This phylogenetic pattern implies that median fins appeared before paired fins [2]. The mechanisms patterning median fins may be ancestral to those used by the paired fins and limbs [3]. Gnathostomes primitively have paired pectoral and pelvic fins, as well as unpaired caudal, anal and at least one dorsal fin, which together is the ancestral morphology well matched by zebrafish [1].The development of paired appendages such as wings, fins and limbs has been intensively studied and many details about the underlying molecular mechanisms are known (reviewed in [4]). For instance, the signaling molecule Sonic hedgehog (Shh) is a morphogen [5] that emanat
Droplet traffic in microfluidic networks: A simple model for understanding and designing
M. Schindler,A. Ajdari
Physics , 2007, DOI: 10.1103/PhysRevLett.100.044501
Abstract: We propose a simple model to analyze the traffic of droplets in microfluidic ``dual networks''. Such functional networks which consist of two types of channels, namely those accessible or forbidden to droplets, often display a complex behavior characteristic of dynamical systems. By focusing on three recently proposed configurations, we offer an explanation for their remarkable behavior. Additionally, the model allows us to predict the behavior in different parameter regimes. A verification will clarify fundamental issues, such as the network symmetry, the role of the driving conditions, and of the occurrence of reversible behavior. The model lends itself to a fast numerical implementation, thus can help designing devices, identifying parameter windows where the behavior is sufficiently robust for a devices to be practically useful, and exploring new functionalities.
Hadronic parity violation in effective field theory
M. R. Schindler
Physics , 2013,
Abstract: The application of effective field theories to hadronic parity violation in two- and three-nucleon systems is described. These methods provide several important advantages over the traditionally used meson-exchange models, e.g., model independence and the possibility to reliably estimate theoretical errors. We focus on the so-called "pionless" theory and describe calculations of various two- and three-nucleon observables. The role of parity-violating three-nucleon interactions is also discussed.
Data of hydraulic properties of North East and North Central German soils
U. Schindler ,L. Müller
Earth System Science Data (ESSD) & Discussions (ESSDD) , 2010, DOI: 10.5194/essd-2-189-2010
Abstract: The paper presents a data base of soil physical and hydrological properties of North East and North Central German soils. Included are measured data of the soil water retention curve and the unsaturated hydraulic conductivity function. Information on geo-reference, soil type and horizon are given. Soil hydraulic functions were measured with the evaporation method. The applied measurement technique is described and information to actual innovations and advanced technology is given. Additional soil physical data like particle size distribution, dry bulk density, organic matter content and other variables are presented. The data base includes original measurement results of 278 organic and of 497 mineral soil samples from 103 sites. The mineral soils cover a wide range of texture classes and dry bulk densities. The organic soils and samples represent different states of decomposition and mineralization. Furthermore hydraulic functions are included of soils anthropogenically altered by deep plough sand covering measures.
Data of hydraulic properties of North East and Central German soils
U. Schindler,L. Müller
Earth System Science Data Discussions , 2010, DOI: 10.5194/essdd-3-131-2010
Abstract: The paper presents a data base of soil hydrological properties of North East and Central German soils. Included are measured data of the soil water retention curve and the unsaturated hydraulic conductivity function. Information to geo reference, soil type and horizon are given. Additional soil physical data like particle size distribution, dry bulk density, organic matter content and other variables are presented and its measurement is methodically described. The data base includes original measurement results of 278 organic and of 497 mineral soil samples from 103 sites. The mineral soils cover a wide range of texture classes and dry bulk densities. The organic soils and samples vary in dependence on the degree of decomposition and mineralization, the dry bulk density and the total porosity.
Anisotropic elasticity in confocal studies of colloidal crystals
M. Schindler,A. C. Maggs
Physics , 2011, DOI: 10.1140/epje/i2011-11115-7
Abstract: We consider the theory of fluctuations of a colloidal solid observed in a confocal slice. For a cubic crystal we study the evolution of the projected elastic properties as a function of the anisotropy of the crystal using numerical methods based on the fast Fourier transform. In certain situations of high symmetry we find exact analytic results for the projected fluctuations.
Sampling eigenmodes in colloidal solids
A. C. Maggs,M. Schindler
Physics , 2014, DOI: 10.1209/0295-5075/109/48005
Abstract: We study the properties of correlation matrices widely used in the characterisation of vibrational modes in colloidal materials. We show that the eigenvectors in the middle of the spectrum are strongly mixed, but that at both the top and the bottom of the spectrum it is possible to extract a good approximation to the true eigenmodes of an elastic system.
X-ray analysis of Abell 2634 and its central galaxy 3C465
Sabine Schindler,M. Almudena Prieto
Physics , 1997,
Abstract: An analysis of a ROSAT/PSPC observation of the galaxy cluster A2634 is presented. The cluster has a luminosity of $7.9\pm0.1\times10^{43}$erg/s in the ROSAT band (0.1-2.4 keV). The temperature profile decreases from about 3 keV in the outer parts to 1.2 keV in the centre. Within a radius of 1.5 Mpc the gas mass of the cluster is 0.51$\times 10^{14}\msol$ and the total mass amounts to $4.1^{+2.6}_{-1.8}\times 10^{14}\msol$. The X-ray morphology shows two peculiar features -- a strongly peaked emission in the centre and an excess emission in the south-west. The central emission probably originates from a weak cooling flow, the SW emission is possibly associated with higher density regions in pressure equilibrium with the intra-cluster medium. This region of excess emission is somewhat embraced by the wide-angle radio tails associated with 3C465 suggesting that the overpressure of the relativistic particles has displaced the thermal gas.
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