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Two-dimensional particle-in-cell (PIC) simulations have been used to investigate the interaction between a laser pulse and a foil exposed to an external strong longitudinal magnetic field. Compared with that in the absence of the external magnetic field, the divergence of proton with the magnetic field in radiation pressure acceleration (RPA) regimes has improved remarkably due to the restriction of the electron transverse expansion. During the RPA process, the foil develops into a typical bubble-like shape resulting from the combined action of transversal ponderomotive force and instabilities. However, the foil prefers to be in a cone-like shape by using the magnetic field. The dependence of proton divergence on the strength of magnetic field has been studied, and an optimal magnetic field of nearly 60 kT is achieved in these simulations.
Good canopy structure is essential for optimal maize (Zea mays L.) production. However, creating appropriate maize canopy structure can be difficult, because the characteristics of individual plants are altered by changes in plant age, density and interactions with neighbouring plants. The objective of the current study was to find a reliable method for building good maize canopy structure by analysing changes in canopy structure, light distribution and grain yield (GY). A modern maize cultivar (ZhengDan958) was planted at 12 densities ranging from 1.5 to 18 plants/m2 at two field locations in Xinjiang, China. At the silking stage (R1), plant and ear height increased with plant density as well as leaf area index (LAI), whereas leaf area per plant decreased logarithmically. The fraction of light intercepted by the plant (F) increased with increasing plant density, but the light extinction coefficient (K) decreased linearly from 0.61 to 0.39. Taking the optimum value of F (95%) as an example, and using measured values of K for each plant density at R1 and the equation from Beer's law, the corresponding (theoretical) LAI for each plant density was calculated and optimum plant density (9.72 plants/m2) obtained by calculating the difference between theoretical LAIs and actual observations. Further analysis showed that plant density ranging from 10.64 to 11.55 plants/m2 yielded a stable GY range. Therefore, taking into account the persistence time for maximum LAI, the plant density required to obtain an ideal GY maize canopy structure should be increased by 10–18% from 9.72 plants/m2.
We report the discovery in the Greenland ice sheet of a discrete layer of free nanodiamonds (NDs) in very high abundances, implying most likely either an unprecedented influx of extraterrestrial (ET) material or a cosmic impact event that occurred after the last glacial episode. From that layer, we extracted n-diamonds and hexagonal diamonds (lonsdaleite), an accepted ET impact indicator, at abundances of up to about 5×106 times background levels in adjacent younger and older ice. The NDs in the concentrated layer are rounded, suggesting they most likely formed during a cosmic impact through some process similar to carbon-vapor deposition or high-explosive detonation. This morphology has not been reported previously in cosmic material, but has been observed in terrestrial impact material. This is the first highly enriched, discrete layer of NDs observed in glacial ice anywhere, and its presence indicates that ice caps are important archives of ET events of varying magnitudes. Using a preliminary ice chronology based on oxygen isotopes and dust stratigraphy, the ND-rich layer appears to be coeval with ND abundance peaks reported at numerous North American sites in a sedimentary layer, the Younger Dryas boundary layer (YDB), dating to 12.9 ± 0.1 ka. However, more investigation is needed to confirm this association.
An outbreak of acute hepatitis recently occurred in a nursing home in Zhejiang Province, China. The objectives of this study were to confirm the outbreak and identify the aetiology, source and transmission patterns. All residents and staff in or near the nursing home during the period from 1 October 2014 to 21 May 2015 were investigated regarding hygiene and for epidemiological information including water and food (eating meat especially pork products). Serum and stool specimens were collected for detection of hepatitis E virus (HEV) antibodies using ELISA and RNA using RT–PCR. Samples that were RNA positive were genotyped. Of 185 senior residents and 24 staff in the nursing home, there were 37 laboratory-confirmed cases during the outbreak. Of these cases, 12 patients (three deaths) were symptomatic with jaundice, a common clinical symptom for hepatitis E infection. HEV strains were isolated from three cases and they formed a single cluster within genotype 4d. A case-control study was conducted to investigate potential risk factors for the outbreak and the results revealed that cases more often washed their dishes and rinsed their mouths using tap water than the controls (P < 0·05). Based on hygiene investigation and meteorological information, it is likely that HEV-infected sewage and faeces contaminated the water network on rainy days. Collectively, these results suggest that the outbreak of HEV genotype 4 infection was most likely caused by contaminated tap water rather than food.
The herbicide chlorsulfuron is commonly applied to cereals and may persist in alkaline soil long enough to damage subsequent sensitive crops. Sewage water, a potential source of the heavy metal cadmium (Cd), is used to irrigate agricultural soils in many developing countries. The current work evaluated the effects of the residual herbicide chlorsulfuron and Cd on maize seedlings, with particular attention to the mechanism of their action on plant growth. Maize seeds were planted in soil that had been sprayed with chlorsulfuron and Cd, after which residues in both seedlings and the soil were measured. The chlorsulfuron dose was correlated with the amount of residue found in seedlings but not in the soil. In all, 39 metabolites were identified in seedlings using the Automated Mass spectral Deconvolution and Identification System software program and the retention index method. The combination of chlorsulfuron and Cd significantly reduced multiple metabolites in the shikimate pathway, malic acid and citric acid production in the tricarboxylic acid cycle, and lactic acid, glucose, aspartic acid, asparagine and 3-glycerophosphoric acid production. In addition, chlorsulfuron caused an increase in multiple amino acids, including tyrosine, methionine and asparagine, and a marked decrease in caffeic and cinnamic acids (the secondary metabolites derived from the shikimate pathway and galactose). Finally, chlorsulfuron and Cd stress markedly increased shikimate acid, decreased 3-glycerophosphoric acid and caused negative correlations between the amounts of phenylalanine and tyrosine and those of quinic- and cinnamic-acid. In conclusion, chlorsulfuron and Cd did not have a synergistic effect on maize seedlings; rather, the combination of these pollutants had an antagonistic effect on some amino acids.
The oxidation of GaN epilayers in dry oxygen has been studied. The 1-µm-thick GaN epilayers grown on (0001) sapphire substrates by Rapid-Thermal-Processing/Low Pressure Metalorganic Chemical Vapor Deposition were used in this work. The oxidation of GaN in dry oxygen was performed at various temperatures for different time. The oxide was identified as the monoclinic β-Ga2O3 by a θ−2θ scan X-ray diffraction (XRD). The scanning electron microscope observation shows a rough oxide surface and an expansion of the volume. XRD data also showed that the oxidation of GaN began to occur at 800°C. The GaN diffraction peaks disappeared at 1050°C for 4 h or at 1100°C for 1 h, which indicates that the GaN epilayers has been completely oxidized. From these results, it was found that the oxidation of GaN in dry oxygen was not layer-by-layer and limited by the interfacial reaction and diffusion mechanism at different temperatures.
We report a study on the wetting and spreading of hydrazine-CZTS solution on a series of solid surfaces. The work of adhesion between a hydrazine solution and soda-lime glass, Si, graphite, ITO, SnO2, ZnO, CdS, In2S3, Cu, Au, Ag, Al, Ni, Mo, and carbon single-walled nanotubes was calculated using observed contact angles and the areas of the interface. The surface roughness of drop-casted CZTS precursor films was lower on surfaces with better hydrazine wettability. This suggests that the surface roughness of solution-processed films can be controlled by altering the wetting behavior of the solution on the substrate.
A novel approach to fabricate CuIn(S,Se)2 (CIS) thin films through ultrasonically spraying a hydrazine-based precursor solution onto a heated substrate is reported. The effects of the composition of the precursor solutions and the deposition temperature on the CIS film properties were investigated by comparing thin films fabricated using aqueous metal salt solution, anhydrous hydrazine solution, and hydrazine hydrate solution at various deposition temperatures. Crystallite size and texture coefficient in the preferred (112) orientation in the sprayed films increased when the aqueous solution was replaced by hydrazine-based solutions. Additionally, the hydrazine-based precursor solutions resulted in films with better surface smoothness and compositional uniformity than those fabricated using water-based solutions and the hydrazine hydrate solution resulting in the smoothest, most uniform films. The sprayed films were used to fabricate preliminary solar cells that demonstrated a modest photovoltaic response. With optimization, the synthesis of high-quality CIS films by spray pyrolysis from a hydrazine hydrate solution could demonstrate the potential for a low-cost, high-throughput manufacturing process.
The nonlinear characteristics of a simply-supported three-layer circular piezoelectric plate-like power harvester near resonance are examined in the paper, where the energy-scavenging structure consists of two properly poled piezoceramic layers separated by a central metallic layer. The structure is subjected to a uniform harmonic pressure on the upper surface. Nonlinear effects of large deflection near resonance to induce the incidental in-plane extension are considered. Results on output powers are presented, which exhibit multi-valuedness and jump phenomena.
The oxidation of GaN epilayers in dry oxygen has been studied. The 1-μm-thick GaN epilayers grown on (0001) sapphire substrates by Rapid-Thermal-Processing/Low Pressure Metalorganic Chemical Vapor Deposition were used in this work. The oxidation of GaN in dry oxygen was performed at various temperatures for different time. The oxide was identified as the monoclinic β-Ga2O3 by a θ-2θ scan X-ray diffraction (XRD). The scanning electron microscope observation shows a rough oxide surface and an expansion of the volume. XRD data also showed that the oxidation of GaN began to occur at 800°C. The GaN diffraction peaks disappeared at 1050°C for 4 h or at 1100°C for 1 h, which indicates that the GaN epilayers has been completely oxidized. From these results, it was found that the oxidation of GaN in dry oxygen was not layer-by-layer and limited by the interfacial reaction and diffusion mechanism at different temperatures.
Polymer/TiO2 composite solar cells (CSCs) are currently being investigated by academic research groups and industrial companies due to the prospect of achieving good power conversion efficiencies and lifetime stability at a low production cost. We present data of the initial period of operation (up to several hours) of such devices, which show that during this period the CSCs operate in a non-steady state regime. The transient behaviour is accounted for using an equivalent circuit model (ECM) of the photovoltaic device with time-dependent resistors.
Co(SiGe)x contacts have been formed on low defect density, relaxed Si0.7Ge0.3 layers by conventional self-aligned contact processing techniques. Test structures measuring the contact metal sheet resistance indicate that the resistivity is high for anneal temperatures from 450°C to 750°C. The lowest sheet resistivity was 100 Ω/□, about 10 times the resistivity of a comparable amount of CoSi2. Contact resistivities, measured by the transmission line method, were as low as 2 × 10−5 Ω cm2. There is a large discrepancy between contact resistivities measured by transmission line and 4 point Kelvin test structures that may be due to the fabricated contact sizes.
The formation of interfacial oxide between high-k and Si creates a two-layer dielectric in the MOS structure. In this paper, we present a model to describe electrical breakdown in the two-layer dielectric. Depending on the thickness ratio of the two dielectric layers, electrical breakdown can occur either in one dielectric after the other or simultaneously. In the case of one-by-one breakdown, the current through the two-layer dielectric shows three regimes with applied voltage: tunneling through two layers, tunneling through one layer, and breakdown for both layers. Our model has been compared with experimental data obtained from the HfOx/SiO2 MOS structure, and a good agreement is achieved. This model can be used to estimate either the thickness, breakdown field, or dielectric constant of each of the two dielectric layers. It can also predict the overall breakdown voltage for different combinations of dielectric layers. When combined with C-V measurements, more information about the two-layer dielectric is obtained.
Porous methylsilsesquioxane (p-MSQ) films (JSR LKD 5109) were treated with
alkyldimethylmonochlorosilanes having chain lengths of one, four, and eight
carbon atoms dissolved in supercritical carbon dioxide at 150-300 atm and
50-60°C to repair oxygen ashing damage. Fourier transform infrared (FTIR)
spectroscopy showed that trimethylchlorosilane (TMCS),
butyldimethylchlorosilane (BDMCS), and octyldimethylchlorosilane (ODMCS)
reacted with silanol groups on the surfaces of the pores producing covalent
Si-O-Si bonds. Selfcondensation between alkylsilanols produced a residue on
the surface, which was partially removed using a pure scCO2
rinse. The hydrophobicity of the blanket p-MSQ surface was recovered after
silylation treatment as shown by contact angles >85°. The initial
dielectric constant of 2.4 ± 0.1 increased to 3.5 ± 0.1 after oxygen plasma
ashing and was reduced to 2.6 ± 0.1 by TMCS, 2.8 ± 0.1 by BDMCS, and 3.2 by
The elastic strain in 2 MeV He ion-bombarded pseudomorphic or lattice-relaxd GaInAs is found to vary by 13% over tlhe beam dose range, 5x1012 - 5×1015 cm-2, with a minimum at 5×1013 cm-2. The data suggest a beam-induced annealing effect at lower doses and the build-up of radiation damage at higher doses, which are also indicated by the phonon line shift data. The phonon shift and the elastic strain in lattice-relaxed GaInAs, bombarded with 15 MeV Cl ions, are approximately the same as in an ion-bombarded bulk GaAs. The lattice mismatch in parallel constant decreases for a sample with a lower misfit and increases for a sample with higher misfit with increasing beam dose. The phonon shift in a pseudomorphic GaInAs bombarded with 15 MeV Cl ions is smaller than in the relaxed samples by a factor of two.
A series of Graded-Index Waveguide Separate-Confinement Heterostructure Quantum Well (GRINSCH-QW) laser diodes were grown by MBE at the systematically varied substrate temperatures. The threshold current of laser diodes were found to depend strongly on the growth temperature. The structure and electrical characteristics of the laser diodes were studied by double-crystal x-ray diffraction, I-V-T, C-V and deep level transient spectroscopy (DLTS). The interface recombination is found to be the dominant carrier transport process in the high threshold current laser diodes and is closely related to the presence of the high concentration of deep traps and interface states. In the low threshold current laser diodes, diffusion process is found to be the dominant carrier transport process.
Dc magnetic field, temperature, and magnetic history dependencies of the millimeter-wave surface resistance have been measured in high quality grain-aligned and in polycrystalline YBa2Cu3Ox bulk material. The measurements were carried at 75 GHz using the endplate of the cavity replacement method. The data is interpreted in terms of the presence of intra- and inter-grain types of weak links. The values of characteristic critical fields of the bulk and the weak link junctions are determined and discussed.
In addition to being successfully used for ion implantation, the plasma source ion implantation (PSII) technique has been used to produce diamond-like carbon films. Homogeneous, adherent films were obtained on silicon and stainless steel substrates under 2 kV pulse bias voltages and 50 mtorr methane plasma pressure. Chemical composition analysis was made using Auger electron microscopy. Fretting wear tests and scratch tests were performed to study the tribological and adherent properties. Cross sectional TEM samples were prepared. The interfacial microstrucutres and chemical compositions were analyzed using transmission electron microscopy and scanning transmission electron microscopy.