Plasma jets are widely investigated both in the laboratory and in nature. Astrophysical objects such as black holes, active galactic nuclei and young stellar objects commonly emit plasma jets in various forms. With the availability of data from plasma jet experiments resembling astrophysical plasma jets, classification of such data would potentially aid in not only investigating the underlying physics of the experiments but also the study of astrophysical jets. In this work we use deep learning to process all of the laboratory plasma images from the Caltech Spheromak Experiment spanning two decades. We found that cosine similarity can aid in feature selection, classify images through comparison of feature vector direction and be used as a loss function for the training of AlexNet for plasma image classification. We also develop a simple vector direction comparison algorithm for binary and multi-class classification. Using our algorithm we demonstrate 93 % accurate binary classification to distinguish unstable columns from stable columns and 92 % accurate five-way classification of a small, labelled data set which includes three classes corresponding to varying levels of kink instability.

With the increasing usage of Al alloys in vehicle manufacture, it is necessary to join dissimilar Al alloys with lap joint. However, hot cracking is a challenging issue due to the chemical composition and thermal tension, which greatly determines the reliability of automobile operation. Among different Al alloys, the series 5000 (Al–Mg) and 6000 (Al–Mg–Si) are widely used. To better understand the hot cracking behavior, various stack ups of AA5754 and AA6013 were laser welded to investigate the effects of process parameters on hot cracking formation. The chemical composition, microstructure, fusion ratio, and fracture morphology of the weld joint were also examined. The results showed that the order of material stacking affected weld's susceptibility to hot cracking significantly, and the critical process parameters were obtained for tested conditions which could effectively reduce hot cracking. The findings from this work provide guidance for hot cracking prevention in laser welding of dissimilar Al alloys.

The fracture behavior of precracked nanocrystals with grain size gradients is simulated using the molecular dynamics method. A large grain size gradient is found to elevate resistance to crack propagation and transform the fracture mode from intergranular to intragranular when the crack is obstructed by a coarse grain. But the intragranular crack is nipped in its bud due to the difficulty of intragranular fracture. However, intergranular fractures can be always kept in nanocrystals with a small grain size gradient. Both the Schmid factors for the slip systems of grains near the crack tip and the critical stress intensity factors are calculated, and energy partitioning is conducted to analyze the mechanisms behind this phenomenon. The research exhibits the key role of grain size gradient in improving the antifracture ability of nanocrystals.

Light-induced metastability of amorphous/microcrystalline (micromorph) silicon tandem solar cell, in which the microcrystalline bottom cell was deposited in a single-chamber system, has been studied under a white light for more than 1000 hours. Two different light-induced metastable behaviors were observed. The first type was the conventional light-induced degradation, where the open-circuit voltage (Voc), fill factor (FF), and short-circuit current density (Jsc) were degraded, hence the efficiency was degraded as well. This phenomenon was observed mainly in the tandem cells with a bottom cell limited current mismatch. The second type was with a light-induced increase in Voc, which sometimes resulted in an increase in efficiency. The second type of light-induced metastability was observed in the tandem cells with a top cell limited current mismatch. The possible mechanisms for these phenomena are discussed.

In this article, we present a study of boron-doped hydrogenated nanocrystalline silicon (nc-Si: H) films by very high frequency-plasma enhanced chemical vapor deposition (VHF-PECVD) using high deposition pressure. Electrical, structural and optical properties of the films were investigated. Dark conductivity as high as 2.75S/cm of p-type nc-Si: H prepared at 2.5Torr pressure has been achieved at a deposition rate of 1.75Å/s for 25nm thin film. By controlling boron and phosphorus contamination, single junction nc-Si: H solar cells incorporated p-layers prepared under high pressure and low pressure, respectively, were deposited. It has been proven that nanocrystalline silicon solar cells with incorporation of p layer prepared at high pressure has resulted in enhanced open circuit voltage, short circuit current density and subsequently high conversion efficiency. Through the optimization of the bottom solar cell and application of ZnO/Al back reflector, 10.59% initial conversion efficiency of micromorph tandem solar cell (1.027cm2) with an open circuit voltage of 1.3864V, has been fabricated, where the bottom solar cell using a high pressure p layer was deposited in a single chamber.

The clogging of the Submerged Entry Nozzle (SEN) duringbillet continuous casting of mid-carbon steel is studied.Clogging materials and inclusions in steel samples taken atladles, tundish and billets are investigated. The total oxygen onthe whole section of the billet is measured. Steel cleanliness atunsteady casting states, including cast start, ladle change, SENchange, cast end, and the special unsteady pouring periodinduced by SEN clogging, are studied. Fluid flow and inclusionmotion and entrapment to SEN surface are also simulated.

The influence of the density of gap states and the band gap width of the intrinsic a-Si:H active layer on the characteristics of a-Si PIN/OLED coupling pair was analyzed by a-Si:H PIN/OLED CAD simulation model. The CAD simulation model was carried out based on a-Si PIN Hack & Shur model and OLED TCL transport model. At the same band gap width, for the intrinsic a-Si:H active layer with the higher density of gap states, the reverse current of a-Si PIN trended to be saturated at the higher reverse bias voltage. As a result, I-V curve of a-Si PIN/OLED around the turn point Vt became smoother with the increase of the density of gap states. At the same state density, the light induced current of a-Si PIN increased against the band gap width, assuming the input light had the same spectrum as AM1.5 solar light. Thus the luminance emitted from OLED increased with the decrease of the band gap width because OLED belongs to the light-emitting device controlled by current. The simulation results also showed that the influence of the state density intensified with the increase of the band gap of a-Si:H.

Nanostructured and thick SiC coatings have been successfully deposited on Si and graphite substrates by thermal plasma physical vapor deposition (TPPVD) using ultrafine SiC powder as a starting material. The control of processing parameters such as substrate temperature, composition of plasma gases, permits to the deposition of SiC coatings with a variety of microstructures and with various morphologies from dense to columnar. The maximum deposition rate reached 200 nm/s. Seebeck coefficient up to −480 μV/K was obtained for the non-doped coatings with stoichiometric composition. Nitrogen doping to the coatings made it possible to decrease the electrical resistivity from 10-2∼10-3 to 10-4∼10-5 Ωm and showing the maximum power factor of 1.0×10-3 Wm-1K-2 at 973 K.

By using the transient-null-current method, we have measured the internal electric field profiles Ei(x) near the p/i interface for two groups of solar cells: (a) a-Si:H p-i-n solar cells with varied i-layer thicknesses, and (b) a-SiGe:H cells with varied Ge content. When using an exponential function of Ei(x) to fit the experimental results, we obtained the field strength at the p/i interface E0, the screening length Lo, and the density of defect states Nd in the i-layer. The thinner the i-layer, the stronger the field strength obtained. For i-layer thickness increasing from 0.1 to 0.5 μm, the field strength E0 decreases from 1.15×105 to 2.0×104 V/cm; Lo decreases from 0.89 to 0.14 μm; and Nd is 3-4×1016 (cm3eV)−1. For the a-SiGe:H cells, as the Ge content increases from 40 to 55 %, E0 increases from 9.3×104 to 1.2×105 V/cm. The correlation of the internal electric field parameters with the cell‘s performance is discussed.