The
I–
V relations found for the system metal|semiconductor|metal with chemically inert electrodes are not always as one would expect from the common theory of semiconductivity. The problem can be ...traced back to motion of ionic defects, i.e. the acceptors (or donors) in the semiconductor. We here discuss the parameters, equations and physical constraints that have to be taken into consideration when evaluating the
I–
V relations of that system in the presence of motion of the ionic defects. For comparison another model, that of electron hopping in the band of dopant impurity states, is also discussed.
I–
V relations and the defect distributions depend on three main factors: the contact potentials at the semiconductor/metal-electrode, the thickness of the sample and the degree of ionization of the dopant. A variety of
I–
V relations are obtained for different values of the controlling parameters. This explains the diversity in the
I–
V relations reported for systems of the form metal|semiconductor|metal.
We examine the hydrodynamic response of the inviscid small shearing box model of a midplane section of a rotationally supported astrophysical disk. We formulate an energy functional ${\cal E}$ for ...the general nonlinear problem. We find that the fate of disturbances is related to the conservation of this quantity which, in turn, depends on the boundary conditions utilized: ${\cal E}$ is conserved for channel boundary conditions, while it is not conserved, in general, for shearing box conditions. Linearized disturbances subject to channel boundary conditions have normal-modes described by Bessel Functions and are qualitatively governed by a quantity Σ, which is a measure of the ratio between the azimuthal and vertical wavelengths. Inertial oscillations ensue if Σ > 1 – otherwise disturbances must be treated generally as an initial value problem. We reflect upon these results and offer a speculation.
A device of the form metal1 |semiconductor| metal2 is discussed, in which the semiconductor is assumed to be p-type, donors are not present, yet electron hopping in the impurity band is possible due ...to partial occupancy. The two electrodes (metal1 and metal2) are assumed to be asymmetric (contact potentials wise) one leading to depletion and the other one with zero contact potential. The defect distribution and I-V relations are solved numerically assuming steady state. The effects of sample thickness, ionization-recombination reaction constant, recombination rate and hopping mobility are discussed. Different thicknesses, from nano to macro, are considered. The results are compared with a classical model in which the acceptors are fully ionized and no hopping is possible. The classical model is equivalent to a device with a Schottky junction on one side. The question of the existence of regions with local neutrality (l.n.) is discussed, and the concentration profile there is solved for the cases of strict l.n. and quasi-local neutrality.
The aim of this study is to compare the therapeutic effect of a single intravitreal bevacizumab (IVB) injection in eyes with diabetic macular oedema (DMO) of different patterns determined by optical ...coherence tomography (OCT).
Medical records of patients who had a single IVB injection for DMO were analysed retrospectively. Eyes with a clinically significant DMO and a central foveal thickness (CFT) of 250 μm or more determined by OCT were included in the analysis. Best-corrected visual acuity (BCVA), CFT and total macular volume values before and after the injection were recorded. Eyes were divided into sponge-like diffuse retinal thickening (DRT), cystoid macular oedema (CMO) and serous retinal detachment (SRD) groups according to the morphology on OCT.
A total of 92 eyes (42 with DRT, 31 with CMO and 19 with SRD) were included in the study. There was no statistically significant variation between three groups regarding the change in BCVA (P=0.695). CMO and SRD groups had greater reductions in their mean CFT, and the amount of reduction showed statistically significant variation between three groups (P=0.048). However, no statistically significant difference was found between groups in terms of percentage of change in CFT (P=0.278).
CMO and SRD subtypes are associated with a greater reduction in the CFT than the DRT subtype. Although the change in BCVA was not significantly different between groups, the DRT group showed markedly better visual improvement in proportion to the decrease in CFT.
TOPOGRAPHIC MAPPING OF PLUTO AND CHARON USING NEW HORIZONS DATA Schenk, P. M.; Beyer, R. A.; Moore, J. M. ...
International archives of the photogrammetry, remote sensing and spatial information sciences.,
01/2016, Letnik:
XLI-B4
Journal Article, Conference Proceeding
Recenzirano
Odprti dostop
New Horizons 2015 flyby of the Pluto system has resulted in high-resolution topographic maps of Pluto and Charon, the most distant objects so mapped. DEM’s over ~30% of each object were produced at ...100-300 m vertical and 300-800 m spatial resolutions, in hemispheric maps and high-resolution linear mosaics. Both objects reveal more relief than was observed at Triton. The dominant 800-km wide informally named Sputnik Planum bright ice deposit on Pluto lies in a broad depression 3 km deep, flanked by dispersed mountains 3-5 km high. Impact craters reveal a wide variety of preservation states from pristine to eroded, and long fractures are several km deep with throw of 0-2 km. Topography of this magnitude suggests the icy shell of Pluto is relatively cold and rigid. Charon has global relief of at least 10 km, including ridges of 2-3 km and troughs of 3-5 km of relief. Impact craters are up to 6 km deep. Vulcan Planum consists of rolling plains and forms a topographic moat along its edge, suggesting viscous flow.
Abstract
The New Horizons spacecraft encountered the Kuiper Belt object (KBO) Arrokoth (486958), originally designated as 2014 MU
69
and formerly called “Ultima Thule,” on 2019 January 01. At 43.3 au ...from the Sun and 44.4 au from Earth, this was the most distant spacecraft reconnaissance of a solar system body to date. The Radio Science Experiment (REX) on New Horizons performed radiometry measurements of the KBO's thermal emission at
λ
= 4.2 cm in two observation slots, one before (dayside) and one after (nightside) the point of closest approach. Owing to the small size of the target, the intensity of the thermal emission was expected to be only marginally detectable. The KBO was not detected on approach because of unexpectedly large variations in the REX system temperature. A brightness temperature
T
b
= 29 ± 5 K was derived for the nightside observation, considerably less than the predicted equilibrium temperature of ∼50 K derived for Arrokoth on the dayside. A model explaining this day−night contrast is used to constrain the global values of emissivity, thermal inertia, and electrical skin depth of the KBO. In particular, models with small values of thermal inertia and small values of electrical skin depth are excluded. Relatively high values of the effective radio emissivity (
E
eff
> 0.8) provide better agreement with the REX observation.
The Cold Classical Kuiper Belt, a class of small bodies in undisturbed orbits beyond Neptune, is composed of primitive objects preserving information about Solar System formation. In January 2019, ...the New Horizons spacecraft flew past one of these objects, the 36-kilometer-long contact binary (486958) Arrokoth (provisional designation 2014 MU
). Images from the flyby show that Arrokoth has no detectable rings, and no satellites (larger than 180 meters in diameter) within a radius of 8000 kilometers. Arrokoth has a lightly cratered, smooth surface with complex geological features, unlike those on previously visited Solar System bodies. The density of impact craters indicates the surface dates from the formation of the Solar System. The two lobes of the contact binary have closely aligned poles and equators, constraining their accretion mechanism.
GEOLOGICAL MAPPING OF PLUTO AND CHARON USING NEW HORIZONS DATA Moore, J. M.; Spencer, J. R.; McKinnon, W. B. ...
International archives of the photogrammetry, remote sensing and spatial information sciences.,
01/2016, Letnik:
XLI-B4
Journal Article, Conference Proceeding
Recenzirano
Odprti dostop
Pluto and Charon exhibit strikingly different surface appearances, despite their similar densities and presumed bulk compositions. Systematic mapping has revealed that much of Pluto’s surface can be ...attributed to surface-atmosphere interactions and the mobilization of volatile ices by insolation. Many mapped valley systems appear to be the consequence of glaciation involving nitrogen ice. Other geological activity requires or required internal heating. The convection and advection of volatile ices in Sputnik Planum can be powered by present-day radiogenic heat loss. On the other hand, the prominent mountains at the western margin of Sputnik Planum, and the strange, multi-km-high mound features to the south, probably composed of H2O, are young geologically as inferred by light cratering and superposition relationships. Their origin, and what drove their formation so late in Solar System history, is under investigation. The dynamic remolding of landscapes by volatile transport seen on Pluto is not unambiguously evident in the mapping of Charon. Charon does, however, display a large resurfaced plain and globally engirdling extensional tectonic network attesting to its early endogenic vigor.
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