The Very Large Array Sky Survey (VLASS) is a synoptic, all-sky radio sky survey with a unique combination of high angular resolution (≈2 5), sensitivity (a 1σ goal of 70 μJy/beam in the coadded data), full linear Stokes polarimetry, time domain coverage, and wide bandwidth (2-4 GHz). The first observations began in 2017 September, and observing for the survey will finish in 2024. VLASS will use approximately 5500 hr of time on the Karl G. Jansky Very Large Array (VLA) to cover the whole sky visible to the VLA (decl. >−40°), a total of 33 885deg 2. The data will be taken in three epochs to allow the discovery of variable and transient radio sources. The survey is designed to engage radio astronomy experts, multi-wavelength astronomers, and citizen scientists alike. By utilizing an "on the fly" interferometry mode, the observing overheads are much reduced compared to a conventional pointed survey. In this paper, we present the science case and observational strategy for the survey, and also results from early survey observations.

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Preventing broken-rail-caused derailments is a high priority for the rail industry and government. The current practice is to periodically inspect rails using non-destructive technologies such as ultrasonic rail inspection. Determining the optimal inspection frequency is a critical decision in railway infrastructure management. The objective of this paper is to develop an analytical framework to address the trade-offs among various factors related to rail defect inspection frequency, in order to maximize rail transportation safety and efficiency.

Impact of sidewall recombination on the quantum efficiency of dry etched InGaAs/InP semiconductor wires Appl.InGaAs/InP quantum wires with widths ranging from 200 to 40 nm have been fabricated using high-resolution electron-beam lithography and CH&z reactive-ion etching. The excitation intensity dependence of the photoluminescence (PL) energies and line shapes for relatively wide wires (-100 nm) exhibits the effects of band filling in k space and band-gap renormalization due to many-body effects in dense electron-hole plasmas (EHP). In the narrowest wires studied (-40 nm), the effects of sidewall surface recombination limit the attainable EHP density. In addition, the results show a blue shift of PL energies when wire width decreases below 100 nm.