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We discuss efforts to explain the dust distribution, as it was derived from the F-coronal brightness, mainly how to explain a constant number density near the Sun. It is shown that silicate particles have temperatures below the blackbody temperature if the impurity from absorbing material amounts to less than 0.1% in volume. This effect is especially significant for porous particles and may explain why particles can approach to less than 3 R⊙ from the Sun. Another effect may arise from particles on high eccentricity orbits and from the influence of collisional fragments. Whereas on the one hand heat resistant silicate particles may cause a stable dust cloud in the solar vicinity, on the other hand dynamical effects may cause a variation of the number density in the corona in short time scales.
Child maltreatment is a major risk factor for psychopathology, including reactive attachment disorder (RAD).
To examine whether neural activity during reward processing was altered in children and adolescents with RAD.
Sixteen children and adolescents with RAD and 20 typically developing (TD) individuals performed tasks with high and low monetary rewards while undergoing functional magnetic resonance imaging.
Significantly reduced activity in the caudate and nucleus accumbens was observed during the high monetary reward condition in the RAD group compared with the TD group (P=0.015, family-wise error-corrected cluster level). Significant negative correlations between bilateral striatal activity and avoidant attachment were observed in the RAD and TD groups.
Striatal neural reward activity in the RAD group was markedly decreased. The present results suggest that dopaminergic dysfunction occurs in the striatum of children and adolescents with RAD, leading towards potential future risks for psychopathology.
Cognitive–behavioral therapy (CBT) is thought to be useful for chronic pain, with the pathology of the latter being closely associated with cognitive–emotional components. However, there are few resting-state functional magnetic resonance imaging (R-fMRI) studies. We used the independent component analysis method to examine neural changes after CBT and to assess whether brain regions predict treatment response.
We performed R-fMRI on a group of 29 chronic pain (somatoform pain disorder) patients and 30 age-matched healthy controls (T1). Patients were enrolled in a weekly 12-session group CBT (T2). We assessed selected regions of interest that exhibited differences in intrinsic connectivity network (ICN) connectivity strength between the patients and controls at T1, and compared T1 and T2. We also examined the correlations between treatment effects and rs-fMRI data.
Abnormal ICN connectivity of the orbitofrontal cortex (OFC) and inferior parietal lobule within the dorsal attention network (DAN) and of the paracentral lobule within the sensorimotor network in patients with chronic pain normalized after CBT. Higher ICN connectivity strength in the OFC indicated greater improvements in pain intensity. Furthermore, ICN connectivity strength in the dorsal posterior cingulate cortex (PCC) within the DAN at T1 was negatively correlated with CBT-related clinical improvements.
We conclude that the OFC is crucial for CBT-related improvement of pain intensity, and that the dorsal PCC activation at pretreatment also plays an important role in improvement of clinical symptoms via CBT.
We report on the first results from our pilot observation of nearby galaxies with Hyper Suprime-Cam. We have observed two galaxies with mass similar to that of the Milky Way Galaxy and measured the abundance of their satellite galaxies in order to address the missing satellite problem outside of the Local Group. We find that (1) the abundance of dwarf galaxies is smaller by a factor of two than the prediction from one of the current hydro-dynamical simulations and (2) there is a large halo to halo scatter. Our results highlight the importance of a statistical sample of nearby galaxies to address the missing satellite problem.
We present the results from the state-of-the-art wide-field survey of the M81 galaxy group that we are conducting with Hyper Suprime-Cam on Subaru Telescope. Our photometry reaches about 2 mag below the tip of the red giant branch (RGB) and reveals the spatial distribution of both old and young stars over an area of 5°2 around the M81. The young main-sequence (MS) stars closely follow the HI distribution and can be found in a stellar stream between M81 and NGC 3077 and in numerous outlying stellar associations. Our survey also reveals for the first time the very extended (>2 × R25) halos of RGB stars around M81, M82, and NGC 3077, as well as faint tidal streams that link these systems. The gravitational interactions between M81, M82 and NGC 3077 galaxies induced star formation in tidally stripped gas, and also significantly perturbed the older stellar components leading to disturbed halo morphologies.
The charge transport properties critically depend on the degree of ordering of the chains in the solid state as well as on the density of chemical or structural defects. In general, goodelectronic performance requires strong electronic coupling between adjace nt molecules in the solid-state that yield strong intermolecular π-overlap. Herein, we newly designed and synthesized organic semiconducting materials having both aryl (Ar) and perfluoroaryl (FAr) as substituents for organic electronics along with molecular packing control. Regarding this molecular design, we hypothesized and expected that the Ar and FAr substituents would induce well-defined π-π stacking structure of charge transport units for high performance organic electronics devices.
In this study, we propose copper oxide (CuOx) edge-termination for GaN-based Schottky barrier diodes (SBDs) with low turn-on voltage. CuOx fabricated by thermal oxidization of sputtered Cu film at 275°C consisted mainly of Cu2O which is known as a p-type semiconductor. We applied CuOx edge-termination to GaN SBDs with tantalum (Ta) Schottky electrode which has low work function of 4.25 eV. The experimental results of current-voltage characteristics insisted that CuOx edge-termination structure was effective to increase breakdown voltage of GaN SBDs with keeping low turn-on voltage of 0.29 V at 10 A/cm2.
Growth process of microcrystalline silicon (μc-Si:H) using plasma-enhanced chemicalvapor- deposition method under high-rate-growth condition has been studied for the control of optoelectronic properties in the resulting materials. We have found two important things for the spatial-defect distribution in the resulting μc-Si:H through a precise dangling-bond-density measurement, e. g., (1) dangling-bond defects are uniformly distributed in the bulk region of μc- Si:H films independent of their crystallite size and (2) large number of dangling bonds are located at the surface of μc-Si:H especially when the film is deposited at high growth rate. Starting procedure of film growth has been investigated as an important process to control the dangling-bond-defect density in the bulk region of resulting μc-Si:H through the change in the electron temperature by the presence of particulates produced at the starting period of the plasma. Deposition of Si-compress thin layer on μc-Si:H grown at high rate followed by thermal annealing has been proposed as an effective method to reduce the defect density at the surface of resulting μc-Si:H. Utilizing the starting-procedure-controlling method and the compress-layerdeposition method together with several interface-controlling methods, we have demonstrated the fabrication of high conversion-efficiency (9.27%) substrate-type (n-i-p) μc-Si:H solar cells whose intrinsic μc-Si:H layer is deposited at high growth rate of 2.3 nm/sec.
We have fabricated zincblende GaAs nanocrystals by means of Ga+ and As+ coimplantation into SiO2 matrices. A broad photoluminescence band is observed in the visible spectral region. Under selective excitation at energies within the visible luminescence band, GaAs-related phonon structures are observed at low temperatures. The photoluminescence mechanism in GaA/SiO2 nanocomposites is discussed.
The structural and optical properties of CdS/CdTe(S) interface region of 2-μm thick CdS/CdTe solar cells have been studied in conjunction with photovoltaic performances of the solar cells. The properties are found to be crucially influenced by the annealing temperature and oxygen concentration of the CdCl2 treatment. An increase in VOC and F.F. found in the solar cells with the CdCl2 treatment at < 360°C is interpreted as due to suppression of interdiffusion of sulfur and tellurium at the CdS/CdTe(S) interface. On the other hand, the electromodulated photoluminescence with UV light excitation (UVE-EMPL) study reveals that the increasing VOC due to increasing oxygen concentration to 5% is likely to be caused by an increase in the built-in electric field in n+-CdTe1−xSx just adjacent to the CdS/CdTe(S) interface. As a result of the modification of the process parameters, we have achieved the conversion efficiency of 13.6% (VOC: 0.817V, JSC: 23.0 mA/cm2, F.F.: 0.725) using 2.3-μm thick PV active layer without anti-reflection coating.
Practical use of amorphous silicon stacked-junction color detectors in large-area arrays requires periodic readout of the photo-charge stored in the capacitance of the device by a transient technique of sensing. In any stacked-junction devices, color information is obtained by the “self-biasing” process: during an integration time, the three junctions independently lose charge; during the readout pulse, the capacitances of the three junctions in electrical series are re-charged. Equilibrium is reached after a few cycles, when the charge integrated in a cycle by each junction is the same, and equals the readout charge. The amount of charge is determined by the reverse biased junction and accounts for the light intensity.
Dimensioning the amorphous silicon Thin Film Transistor (TFT) used as a pixel switch for the detector is a critical part of the project of a color imager. The actual design determines the self-bias process duration and the readout accuracy. The typical large thickness difference between the detector junctions makes the constraints for the switching process extremely demanding: since a greater capacitance is expected in the thinner top junction detecting blue radiation, the on-resistance must be reduced. Since the front junction does not ensure full rejection of green and red light, a calculation must be performed to extract the information on blue radiation. This requires further precision in the readout process.
In this work we present a simulation study of the self-biasing process. Both a-Si:H TFT and the a-Si:H p-i-n-i-p two-color detectors are simulated by a finite-elements two-dimensional simulator ensuring a correct modeling of both the devices. Simulations allow to study in detail the timing and the accuracy of the self-biasing process. Including electrostatic capacitance and trapped charge, a set of design rules for the TFT is achieved in terms of on-state design. Similar considerations can be extended to the case of ATCD three-color detectors.
We have developed a physically-based analytical model of the static current-voltage characteristics of hydrogenated amorphous silicon (a-Si:H) inverted staggered thin film transistors (TFTs) in the reverse (leakage) regime (VG<0,VD>0). We studied analytically (based on measurement data) the dependence of the leakage current on process parameters (i.e. the deposition-temperature-dependent phosphorus diffusion profile in the a-Si:H active layer), geometrical parameters (i.e. a-Si:H thickness, source/drain overlap areas), and operating conditions (i.e. VG, VD). The derived analytical model is implemented in HSPICE. The simulated and measured results are in good agreement with a discrepancy of less than 5%.
The structure of undoped Si:H films deposited at a high rate of 6-9 Å/s in an RF (13.56 MHz) plasma from hydrogen-silane gas mixtures at various substrate temperatures was studied using TEM (with in-situ annealing), XRD, Raman spectroscopy, optical absorption and hydrogen effusion. It is found that under our conditions the amorphous to crystalline transition occurs in a relatively narrow range of parameters, influenced mainly by hydrogen dilution and to a lesser degree by the substrate temperature. In the crystalline range the material is found to be nanocrystalline (average grain size 20 nm) and the crystals are essentially stable up to 800°C annealing. The crystal structure of a mixed amorphousnanocrystalline phase of samples deposited near the edge of crystallinity is also found to be rather stable. Nanocrystalline Si films deposited under these latter deposition conditions reveal in hydrogen effusion a relatively compact material and show high solar cell efficiencies (6-8%) when incorporated as i-layers in pin solar cells.
The preparation of μc-Si films from SiH4-H2 mixtures by electron-cyclotron resonance (ECR) CVD at deposition temperatures ≤ 400°C on foreign substrates is reported. Deposition conditions were identified for which Si films with a high degree of crystallinity were grown as was confirmed by Raman spectroscopy. A factorial analysis was carried out, for which the influence of deposition temperature, microwave power, hydrogen dilution and total pressure on film growth were investigated. Samples of optimized crystallinity were prepared in a lowpressure and high-hydrogen dilution regime. In-plane grain sizes were measured by TEM and found to be on the order of 10 - 12 nm. Next to the optimization of crystallinity several sources of impurity contamination during film deposition were identified and eliminated. Intrinsic μc-Si layers could be prepared under these conditions that exhibited a dark conductivity σd of 2 × 10-7 S/cm and photosensitivity σph/σd of 150. It is concluded that ECR CVD is capable of producing intrinsic layers with electronic properties as necessary for use in state-of-the-art n-i-p μc-Si solar cells.
We have performed computer calculations to explore effects of the p/i interface on the open-circuit voltage in a-Si:H based pin solar cells. The principal conclusions are that interface limitation can occur for values of VOC significantly below the built-in potential VBI of a cell, and that the effects can be understood in terms of thermionic emission of electrons from the intrinsic layer into the p-layer. We compare measurements of VOC and electroabsorption estimates of VBI with the model calculations. We conclude that p/i interface limitation is important for current a-Si:H based cells, and that the conduction band offset between the p and i layers is as important as the built-in potential for future improvements to VOC.
The patterned nc-Si/a-SiNx:H superlattices were fabricated by using laser interference crystallization method and investigated with atomic force microscope (AFM), micro-Raman spectroscope, cross-section transmission electron microscope (TEM) and high resolution electron microscope (HREM). We found that after laser irradiation, self-assembled Si nanocrystallites (nc-Si) are formed within the initial a-Si:H sublayers, moreover, in the plane parallel to the surface of the films, these nc-Si orderly distribute in the certain regions with the same periodicity of 2.0 µm as phase shifting mask grating. Based on the structural analyses, the crystallization mechanism and the origin of the self-assembled phenomena are briefly discussed.
The post-initial growth dynamic scaling exponent β, which describes the surface roughness evolution in time, is determined for a-Si:H growth using in situ single wavelength (632.8 nm) rotating compensator ellipsometry. β is measured as function of the substrate temperature for three different growth rates 2, 5 and 22 Ås-1 under conditions where SiH3 dominantly contributes to growth. β (≤ 0.5) decreases with increasing substrate temperature and does not strongly depend on the growth rate within the range of growth rates. A roughness evolution model is proposed, based upon a random generation of active growth sites and a subsequent site dependent surface diffusion process. The measured β temperature dependence can be simulated with an activated site hopping activation energy of about 1.0 eV. This activation energy is much higher than what would be expected from a model based upon the diffusion of physisorbed silyl SiH3 radical and suggests therefore another mechanism which is responsible for the surface smoothening during a-Si:H growth.
Gas-phase and surface reactions of transported species decomposed on the catalyzer were investigated in catalytic CVD (Cat-CVD), often called hot-wire CVD, using a specially designed reactor tube. The phenomena were comparatively studied using H2- or He-diluted SiH4. It turned out that the control of gas flow through the catalyzer between the gas showerhead and the substrate is a key factor to obtain high uniformity in not only the film thickness but also the crystallinity for Si films prepared by Cat-CVD using the gas pressure above about 10 Pa and the gas-flow velocity faster than several m/s.
Efficient hydrogenated amorphous silicon (a-Si:H) n-i-p solar cells have been fabricated with all doped and undoped a-Si:H layers deposited by hot-wire chemical vapor deposition (HWCVD). The total deposition time of all layers, except the top ITO-contact, is less than 4 minutes. On an untextured stainless steel (SS) substrate, an initial efficiency of 7.12% is reached, with a stable efficiency of 5.4% after 1000 hours 1 sun light soaking. This initial efficiency is reached by incorporating into the p/i interface about 60 Å of intrinsic a-Si:H “edge” material grown under conditions near the transition to microcrystallinity. This edge layer increases the cell's fill factor from 0.60 to 0.68 and the best open-circuit voltage is about 0.88 V. Using textured Ag/ZnOcoated SS supplied by United Solar Corporation, preliminary results of an all-HWCVD solar cell give an initial efficiency of 8.7 %.
A new technique for direct determination of the density of electronic states (DOS) in disordered semiconductors is described. It involves Laplace transformation of transient photocurrent data I(t) followed by the numerical solution of the system of linear algebraic equations obtained from the Fredholm integral of the first kind, for a DOS represented by a series of discrete levels. No approximations are used in the solution, and no prior assumptions as to the form of the DOS are made. The fidelity of this method is assessed and compared with existing techniques by application to computer-simulated I(t) data generated from single-level and continuous DOS profiles, and to experimental data.