On the dynamic tensile strength of Zirconium

Despite its fundamental nature, the process of dynamic tensile failure (spall) is poorly understood. Spall initiation via cracks, voids, etc, before subsequent coalesce, is known to be highly microstructure-dependant. In particular, the availability of slip planes and other methods of plastic deformation controls the onset (or lack thereof) of spall. While studies have been undertaken into the spall response of BCC and FCC materials, less attention has paid to the spall response of highly anisotropic HCP materials. Here the dynamic behaviour of zirconium is investigated via plate-impact experiments, with the aim of building on an ongoing in-house body of work investigating these highly complex materials. In particular, in this paper the effect of impact stress on spall in a commercially sourced Zr rod is considered, with apparent strain-rate softening highlighted

Strongly Localized State of a Photon at the Intersection of the Phase Slips in 2D Photonic Crystal with Low Contrast of Dielectric Constant

Two-dimensional photonic crystal with a rectangular symmetry and low contrast (< 1) of the dielectric constant is considered. We demonstrate that, despite the {\em absence} of a bandgap, strong localization of a photon can be achieved for certain ``magic'' geometries of a unit cell by introducing two $\pi/2$ phase slips along the major axes. Long-living photon mode is bound to the intersection of the phase slips. We calculate analytically the lifetime of this mode for the simplest geometry -- a square lattice of cylinders of a radius, $r$. We find the magic radius, $r_c$, of a cylinder to be 43.10 percent of the lattice constant. For this value of $r$, the quality factor of the bound mode exceeds $10^6$. Small ($\sim 1$) deviation of $r$ from $r_c$ results in a drastic damping of the bound mode.Comment: 6 pages, 2 figure

Talent management: the good, the bad, and the possible

In this essay we offer a critical investigation of talent management practices (TMP), which is an increasingly influential concept in contemporary organisations. We try to show how these organisational practices could have both a negative and a positive ethical impact on those identified as ‘talent’ within organisations. A critical analysis of how talent is defined, and how this impacts on individuals’ capacities for ethical reflection, allows us to highlight the ethical ambiguity inherent in talent management. We then highlight examples of some ‘bad’ consequences of TM, and explore some ‘good’ counter-examples. To highlight what may be ‘possible’ in talent management, we propose a more constructive relationship between talent management and ethics based on two dimensions: 1) the acceptance of ambiguity and personal struggle and 2) the development of more qualitative approaches to performance that could enable a better understanding of and sensitivity towards the broader context within which organisations function

Estimating oceanic primary production using vertical irradiance and chlorophyll profiles from ocean gliders in the North Atlantic

An autonomous underwater vehicle (Seaglider) has been used to estimate marine primary production (PP) using a combination of irradiance and fluorescence vertical profiles. This method provides estimates for depth-resolved and temporally evolving PP on fine spatial scales in the absence of ship-based calibrations. We describe techniques to correct for known issues associated with long autonomous deployments such as sensor calibration drift and fluorescence quenching. Comparisons were made between the Seaglider, stable isotope (13C), and satellite estimates of PP. The Seaglider-based PP estimates were comparable to both satellite estimates and stable isotope measurements

Shock waves in two-dimensional granular flow: effects of rough walls and polydispersity

We have studied the two-dimensional flow of balls in a small angle funnel, when either the side walls are rough or the balls are polydisperse. As in earlier work on monodisperse flows in smooth funnels, we observe the formation of kinematic shock waves/density waves. We find that for rough walls the flows are more disordered than for smooth walls and that shock waves generally propagate more slowly. For rough wall funnel flow, we show that the shock velocity and frequency obey simple scaling laws. These scaling laws are consistent with those found for smooth wall flow, but here they are cleaner since there are fewer packing-site effects and we study a wider range of parameters. For pipe flow (parallel side walls), rough walls support many shock waves, while smooth walls exhibit fewer or no shock waves. For funnel flows of balls with varying sizes, we find that flows with weak polydispersity behave qualitatively similar to monodisperse flows. For strong polydispersity, scaling breaks down and the shock waves consist of extended areas where the funnel is blocked completely.Comment: 11 pages, 15 figures; accepted for PR

Improving snow albedo processes in WRF/SSiB regional climate model to assess impact of dust and black carbon in snow on surface energy balance and hydrology over western U.S.

Two important factors that control snow albedo are snow grain growth and presence of light‐absorbing impurities (aerosols) in snow. However, current regional climate models do not include such processes in a physically based manner in their land surface models. We improve snow albedo calculations in the Simplified Simple Biosphere (SSiB) land surface model coupled with the Weather Research and Forecasting (WRF) regional climate model (RCM), by incorporating the physically based SNow ICe And Radiative (SNICAR) scheme. SNICAR simulates snow albedo evolution due to snow aging and presence of aerosols in snow. The land surface model is further modified to account for deposition, movement, and removal by meltwater of such impurities in the snowpack. This paper presents model development technique, validation with in situ observations, and preliminary results from RCM simulations investigating the impact of such impurities in snow on surface energy and water budgets. By including snow‐aerosol interactions, the new land surface model is able to realistically simulate observed snow albedo, snow grain size, dust in snow, and surface water and energy balances in offline simulations for a location in western U.S. Preliminary results with the fully coupled RCM show that over western U.S., realistic aerosol deposition in snow induces a springtime average radiative forcing of 16 W/m2 due to a 6% albedo reduction, a regional surface warming of 0.84°C, and a snowpack reduction of 11 mm.Key PointsIncluding snow aging and aerosols in snow improves offline and WRF snow simulationsDust and black/organic carbon exerts nontrivial radiative forcing in western U.S.RCM simulation shows temperature increase and snow mass loss from aerosols in snowPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/111782/1/jgrd52045.pd

Mutator Dynamics on a Smooth Evolutionary Landscape

We investigate a model of evolutionary dynamics on a smooth landscape which features a ``mutator'' allele whose effect is to increase the mutation rate. We show that the expected proportion of mutators far from equilibrium, when the fitness is steadily increasing in time, is governed solely by the transition rates into and out of the mutator state. This results is a much faster rate of fitness increase than would be the case without the mutator allele. Near the fitness equilibrium, however, the mutators are severely suppressed, due to the detrimental effects of a large mutation rate near the fitness maximum. We discuss the results of a recent experiment on natural selection of E. coli in the light of our model.Comment: 4 pages, 3 figure

Lasing oscillation in a three-dimensional photonic crystal nanocavity with a complete bandgap

We demonstrate lasing oscillation in a three-dimensional photonic crystal nanocavity. The laser is realized by coupling a cavity mode, which is localized in a complete photonic bandgap and exhibits the highest quality factor of ~38,500, with high-quality semiconductor quantum dots. We show a systematic change in the laser characteristics, including the threshold and the spontaneous emission coupling factor by controlling the crystal size, which consequently changes the strength of photon confinement in the third dimension. This opens up many interesting possibilities for realizing future ultimate light sources and three-dimensional integrated photonic circuits and for more fundamental studies of physics in the field of cavity quantum electrodynamics.Comment: 14 pages, 4 figure

Effects of different needles and substrates on CuInS2 deposited by electrostatic spray deposition

Copper indium disulphide (CuInS2) thin films were deposited using the electrostatic spray deposition method. The effects of applied voltage and solution flow rate on the aerosol cone shape, film composition, surface morphology and current conversion were investigated. The effect of aluminium substrates and transparent fluorine doped tin oxide (SnO2:F) coated glass substrates on the properties of as-deposited CuInS2 films were analysed. An oxidation process occurs during the deposition onto the metallic substrates which forms an insulating layer between the photoactive film and substrate. The effects of two different spray needles on the properties of the as-deposited films were also studied. The results reveal that the use of a stainless steel needle results in contamination of the film due to the transfer of metal impurities through the spray whilst this is not seen for the glass needle. The films were characterised using a number of different analytical techniques such as X-ray diffraction, scanning electron microscopy, Rutherford back-scattering and secondary ion mass spectroscopy and opto-electronic measurements

Linear and nonlinear optical spectroscopy of a strongly-coupled microdisk-quantum dot system

A fiber taper waveguide is used to perform direct optical spectroscopy of a microdisk-quantum-dot system, exciting the system through the photonic (light) channel rather than the excitonic (matter) channel. Strong coupling, the regime of coherent quantum interactions, is demonstrated through observation of vacuum Rabi splitting in the transmitted and reflected signals from the cavity. The fiber coupling method also allows the examination of the system's steady-state nonlinear properties, where saturation of the cavity-QD response is observed for less than one intracavity photon.Comment: adjusted references, added minor clarification