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This letter focuses on the streamer-to-spark transitions generated by microsecond pulsed discharges (±20 kV of amplitude, 150 μs of pulse width) in deionized water to provide a quantitative insight into the underwater breakdown process. The discharge channel during underwater electrical breakdown is generally considered as a homogenous blackbody radiator by the arc model. However, we report an unsymmetrical structure of negative breakdown channel in water which shows great discrepancy from the frequently observed uniform structure. An improved two-stage analytical model is proposed to quantitatively estimate the parameter variations of the discharge channels, e.g. radius, temperature, pressure. The calculated results show that the discrepancy in parameters of different parts of negative discharge channel is tremendous. Specifically, during negative electrical breakdown, the region of discharge channel near ground electrode owns greatest values in characteristic parameters (e.g. T max = 22 300 K, P max = 0.145 GPa and v max = 219 m s−1), which are far above the counterparts of main body of channel. By introducing field ionization and impact ionization mechanisms during the propagation of the streamer, we explain the rapid expansion of positive discharge channel and the regions of negative channel near the needle tip as well as the ground electrode. Besides, the deposited homocharges at the gas–liquid interface weaken the ionizations in main body of negative breakdown channel, and hence causing the formation of the unsymmetrical structure.

An improved multi-target tracking algorithm for automotive radar is proposed in this paper. In the application of automotive radar, in addition to the motion generated by the target maneuver, the maneuver of the radar-equipped vehicle will also cause the target to move relative to the radar. A single motion model for the target cannot accurately describe the motion state of the target relative to the radar. To solve the above problems, the nonlinear state equations of various motion models and their process noise covariance matrix are derived, and the Interacting Multiple Model (IMM) algorithm, the Joint Probabilistic Data Association (JPDA) algorithm and the Unscented Kalman Filter with Doppler measurement (DUKF) are combined. At the same time, the correlation coefficient of range measurement error and velocity measurement error of Frequency Modulated Continuous Wave (FMCW) radar is derived, and the relationship between it and FMCW radar parameters is studied. By simulation, its influence on target tracking is assessed, final results indicate the reference value for the application of automotive radar in intelligent driving.

Student Evaluations of Teaching (SET) have been adopted worldwide as a standard practice to enhance teaching and learning quality. However, improvement efforts are threatened by various problems involving ordinal scores and interpretive frameworks restricted to individual item sets and uninformed by a well-defined invariant construct. In this study, an approach to framing SET items according to theory rather than personal or subjective decisions is described. A sample of 920 students from the University of Macau participating in this study provided responses to 42 SET items. Applying a scientific model of measurement, the data collected were analysed and interpreted. Justification between theoretical and measurement analysis informed the creation of a theoretical SET construct map. That map and the associated item hierarchy were used as reference sources for configuring SET reports and recommendations. A new coherent paradigm for SET documentation is proposed for further study.

High-performance photodetector arrays are desired to achieve integrated devices for various technological applications. Film based photodetectors have shown great potential as photodetector arrays because they are compatible with traditional complementary metal oxide semiconductor (CMOS) electronics. Herein, high-mobility graphene/single-crystal ZnS nanowire film hybrids based photodetector arrays have been successfully achieved. With 3 orders of magnitude higher conductance compared with ZnS nanoparticle films, single-crystal ZnS nanowire films are expected to enable a larger portion of photo-generated carriers to move to graphene channel via charge transfer mechanism. As a result, the as-produced graphene/ZnS nanowire film hybrids based devices possess a high photocurrent of 320 µA, a high responsivity of 2.6 × 106 A W−1, a high detectivity of 8.0 × 1012 Jones, and a low detectable light intensity of 1 µW cm−2. Moreover, the integrated graphene/ZnS nanowire film hybrids based photodetector arrays are demonstrated as high-performance image sensors with good uniformity.

This paper discusses the effects of several geometric parameters in DC and RF performances of AlGaN/GaN high electron mobility transistors (HEMTs) grown on high-resistivity silicon substrates. Those parameters include the dependency of gate length (L g), gate cap length (L cap) and gate-to-source distance (L gs). It is shown that decreasing L g and L gs can both improve maximum drain current and transconductance behaviors. The fabricated 50 μm wide GaN-HEMT exhibits the maximum drain current of 1 A mm−1 at V g = 2 V and maximum extrinsic transconductance G mmax of 240 mS mm−1. Besides, decreasing L g and L cap also provides the improvement on current gain frequency (fT ) and maximum oscillation cut off frequency (f MAX). The fT of 40 GHz and f MAX of 55 GHz at V ds = 5 V are demonstrated by GaN-HEMT device featuring L g of 200 nm, L cap of 300 nm and L gs of 1.2 μm, which can realize the compact solid-state power amplifier used in S and C band. However, gate-to-source distance has little effect on RF performance of AlGaN/GaN HEMTs. Those results compared in our study are not only very essential for accurate GaN-based HEMT device modeling and fabrication, but are also vital to better understanding of their device physics.

Conservation practices can be greatly enhanced and influenced by scientific analysis and art historical insights. In the same respect, scientific data can be contextualized and substantiated by findings from visual examination and historical research. Such collaboration can contribute to the field of conservation in multiple ways: by assisting the conservator to investigate treatment options, discover artists' materials and techniques, determine date of manufacture, and investigate conservation treatment materials. Several technical studies conducted by the author and her collaborators employed micro-x-ray fluorescence (μ-XRF), Raman Spectroscopy, Fourier-transform infrared spectrometry (FTIR), and scanning electron microscopy with energy dispersive x-ray spectroscopy (SEM-EDS) and polarized light microscopy (PLM). These techniques were used on the following previously published projects such as a Japanese painting at the Museum of Fine Arts at Boston, Thai manuscripts at the Arthur M. Sackler Museum at Harvard University, and Chinese export paintings on pith at the Winterthur Museum. Although these studies have been published in the past, they are worthy examples to illustrate how collaborations between conservator, scientist, and art historian complement one another. This presentation will also touch upon ethics in sampling of fine art materials and several online databases such as Infrared and Raman User Group (IRUG) and Conservation and Art Materials Encyclopedia Online (CAMEO), which have proven to be very helpful in the field of conservation.

An on-chip approach for fabricating ferromagnetic/semiconductor-nanotip heterojunctions is demonstrated. The high-density array of Si nanotips (SiNTs) is employed as a template for depositing La(0.7)Sr(0.3)MnO(3) (LSMO) rods with a pulsed-laser deposition method. Compared with the planar LSMO/Si thin film, the heterojunction shows a large enhancement of room temperature magnetoresistance (MR) ratio up to 20% under 0.5 T and a bias current of 20 µA. The MR ratio is found to be tunable, which increases with increasing external bias and the aspect ratios of the nanotips. Electric-field-induced metallization, in conjunction with nanotip geometry, is proposed to be the origin for the giant MR ratio.