261 resultados para Fisher, Ray


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X-ray Photoelectron Spectroscopy (XPS) plays a central role in the investigation of electronic properties as well as compositional analysis of almost every conceivable material. However, a very short inelastic mean free path (IMFP) and the limited photon flux in standard laboratory conditions render this technique very much surface sensitive. Thus, the electronic structure buried below several layers of a heterogeneous sample is not accessible with usual photoemission techniques. An obvious way to overcome this limitation is to use a considerably higher energy photon source, as this increases the IMFP of the photo-ejected electron, thereby making the technique more depth and bulk sensitive. Due to this obvious advantage, Hard X-ray Photo Electron Spectroscopy (HAXPES) is rapidly becoming an extremely powerful tool for chemical, elemental, compositional and electronic characterization of bulk systems, more so with reference to systems characterized by the presence of buried interfaces and other types of chemical heterogeneity. The relevance of such an investigative tool becomes evident when we specifically note the ever-increasing importance of heterostructures and interfaces in the context of a wide range of device applications, spanning electronic, magnetic, optical and energy applications. The interest in this nondestructive, element specific HAXPES technique has grown rapidly in the past few years; we discuss critically its extensive use in the study of depth resolved electronic properties of nanocrystals, multilayer superlattices and buried interfaces, revealing their internal structures. We specifically present a comparative discussion, with examples, on two most commonly used methods to determine internal structures of heterostructured systems using XPS. (C) 2015 Elsevier B.V. All rights reserved.

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A ray tracing based path length calculation is investigated for polarized light transport in a pixel space. Tomographic imaging using polarized light transport is promising for applications in optical projection tomography of small animal imaging and turbid media with low scattering. Polarized light transport through a medium can have complex effects due to interactions such as optical rotation of linearly polarized light, birefringence, diattenuation and interior refraction. Here we investigate the effects of refraction of polarized light in a non-scattering medium. This step is used to obtain the initial absorption estimate. This estimate can be used as prior in Monte Carlo (MC) program that simulates the transport of polarized light through a scattering medium to assist in faster convergence of the final estimate. The reflectance for p-polarized (parallel) and s-polarized (perpendicular) are different and hence there is a difference in the intensities that reach the detector end. The algorithm computes the length of the ray in each pixel along the refracted path and this is used to build the weight matrix. This weight matrix with corrected ray path length and the resultant intensity reaching the detector for each ray is used in the algebraic reconstruction (ART) method. The proposed method is tested with numerical phantoms for various noise levels. The refraction errors due to regions of different refractive index are discussed, the difference in intensities with polarization is considered. The improvements in reconstruction using the correction so applied is presented. This is achieved by tracking the path of the ray as well as the intensity of the ray as it traverses through the medium.

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Soil shrinkage curve represents a decrease of total porosity or an increase of bulk density with water loss. However, our knowledge of the dynamics of pores and their geometry during soil shrinkage is scarce, partially due to lack of reliable methods for determining soil pores in relation to change in soil water. This study aimed to investigate the dynamics of macropores (>30 mu m) of paddy soils during shrinkage. Two, paddy soils, which were sampled from one paddy field cultivated for 20 years (YPF) and the other one for over 100 years (OPF), represented difference in crack geometry in the field. Macropore parameters (volume, connectivity, and orientation of pores) and soil shrinkage parameters were determined on the same undisturbed soil cores by X-ray microtomography and shrinkage curve, respectively. Macroporosity was on average four times larger in the YPF than in the OPF whereas the shrinkage capacity was lower in the YPF as compared to the OPF (0.09 vs. 0.15 COLE). Soil shrinkage increased the volume of pores by 3.7% in the YPF and by 1.6% in the OPF as well as their connectivity. The formation of macropores occurred mostly in the proportional shrinkage phase. As a result, the slope of the proportional shrinkage phase was smaller in the YPF (0.65) than in the OPF (0.89). New macropores were cracks and extended pre-existing pores in the range of 225-1215 pm size without any preferential orientation. This work provides image evidences that in paddy soils with high shrinkage capacity more macropores are generated in the soil presenting a smaller proportional shrinkage slope. (C) 2015 Elsevier B.V. All rights reserved.

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Cu2SnS3 thins films were deposited onto In2O3: Sn coated soda lime glass substrates by spin coating technique. The films have been structurally characterized using x-ray Diffraction (XRD) and Atomic Force Microscopy (AFM). The morphology of the films was studied using Field Emission Scanning Electron Microscopy (FESEM). The optical properties of the films were determined using UV-vis-NIR spectrophotometer. The electrical properties were measured using Hall effect measurements. The energy band offsets at the Cu2SnS3/In2O3: Sn interface were calculated using x-ray photoelectron spectroscopy (XPS). The valence band offset was found to be -3.4 +/- 0.24 eV. From the valence band offset value, the conduction band offset is calculated to be -1.95 +/- 0.34 eV. The energy band alignment indicates a type-II misaligned heterostructure formation.

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We study the diffuse X-ray luminosity (L-X) of star-forming galaxies using two-dimensional axisymmetric hydrodynamical simulations and analytical considerations of supernovae-(SNe-) driven galactic outflows. We find that the mass loading of the outflows, a crucial parameter for determining the X-ray luminosity, is constrained by the availability of gas in the central star-forming region, and a competition between cooling and expansion. We show that the allowed range of the mass loading factor can explain the observed scaling of L-X with star formation rate (SFR) as L-X alpha SFR2 for SFR greater than or similar to 1 M-circle dot yr(-1), and a flatter relation at low SFRs. We also show that the emission from the hot circumgalactic medium (CGM) in the halo of massive galaxies can explain the large scatter in the L-X-SFR relation for low SFRs (less than or similar to few M-circle dot yr(-1)). Our results suggest that galaxies with small SFRs and large diffuse X-ray luminosities are excellent candidates for the detection of the elusive CGM.

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Cu2SnS3 thins films were deposited onto In2O3: Sn coated soda lime glass substrates by spin coating technique. The films have been structurally characterized using x-ray Diffraction (XRD) and Atomic Force Microscopy (AFM). The morphology of the films was studied using Field Emission Scanning Electron Microscopy (FESEM). The optical properties of the films were determined using UV-vis-NIR spectrophotometer. The electrical properties were measured using Hall effect measurements. The energy band offsets at the Cu2SnS3/In2O3: Sn interface were calculated using x-ray photoelectron spectroscopy (XPS). The valence band offset was found to be -3.4 +/- 0.24 eV. From the valence band offset value, the conduction band offset is calculated to be -1.95 +/- 0.34 eV. The energy band alignment indicates a type-II misaligned heterostructure formation.