Concentration dependence of the fluorescence decay profile in transition metal doped chalcogenide glass

In this paper we present the fluorescence decay profiles of vanadium and titanium doped gallium lanthanum sulphide (GLS) glass at various doping concentrations between 0.01 and 1% (molar). We demonstrate that below a critical doping concentration the fluorescence decay profile can be fitted with the stretched exponential function: exp[-(t/τ)β], where τ is the fluorescence lifetime and β is the stretch factor. At low concentrations the lifetime for vanadium and titanium doped GLS was 30µs and 67µs respectively. We validate the use of the stretched exponential model and discuss the possible microscopic phenomenon it arises from. We also demonstrate that above a critical doping concentration of around 0.1% (molar) the fluorescence decay profile can be fitted with the double exponential function: a*exp-(t/τ1)+ b*exp-(t/τ2), where τ1 and τ2 are characteristic fast and slow components of the fluorescence decay profile, for vanadium the fast and slow components are 5µs and 30µs respectively and for titanium they are 15µs and 67µs respectively. We also show that the fluorescence lifetime of vanadium and titanium at low concentrations in the oxide rich host; gallium lanthanum oxy-sulphide (GLSO) is 43µs and 97µs respectively, which is longer than that in GLS. From this we deduce that vanadium and titanium fluorescing ions preferentially substitute into high efficiency oxide sites until at a critical concentration they become saturated and low efficiency sulphide sites start to be filled

``Plug and play'' systems for quantum cryptography

We present a time-multiplexed interferometer based on Faraday mirrors, and apply it to quantum key distribution. The interfering pulses follow exactly the same spatial path, ensuring very high stability and self balancing. Use of Faraday mirrors compensates automatically any birefringence effects and polarization dependent losses in the transmitting fiber. First experimental results show a fringe visibility of 0.9984 for a 23km-long interferometer, based on installed telecom fibers.Comment: LaTex, 6 pages, with 2 Postscript figures, Submitted to Applied Physics Letter

Distinct forms of synaptic inhibition and neuromodulation regulate calretinin positive neuron excitability in the spinal cord dorsal horn

The dorsal horn (DH) of the spinal cord contains a heterogenous population of neurons that process incoming sensory signals before information ascends to the brain. We have recently characterized calretinin-expressing (CR+) neurons in the DH and shown that they can be divided into excitatory and inhibitory subpopulations. The excitatory population receives high-frequency excitatory synaptic input and expresses delayed firing action potential discharge, whereas the inhibitory population receives weak excitatory drive and exhibits tonic or initial bursting discharge. Here, we characterize inhibitory synaptic input and neuromodulation in the two CR+ populations, in order to determine how each is regulated. We show that excitatory CR+ neurons receive mixed inhibition from GABAergic and glycinergic sources, whereas inhibitory CR+ neurons receive inhibition, which is dominated by glycine. Noradrenaline and serotonin produced robust outward currents in excitatory CR+ neurons, predicting an inhibitory action on these neurons, but neither neuromodulator produced a response in CR+ inhibitory neurons. In contrast, enkephalin (along with selective mu and delta opioid receptor agonists) produced outward currents in inhibitory CR+ neurons, consistent with an inhibitory action but did not affect the excitatory CR+ population. Our findings show that the pharmacology of inhibitory inputs and neuromodulator actions on CR+ cells, along with their excitatory inputs can define these two subpopulations further, and this could be exploited to modulate discrete aspects of sensory processing selectively in the DH

Investigation of ultrafast spin dynamics in a Ni thin film

Copyright © 2002 American Institute of PhysicsOptically induced ultrafast demagnetization has been studied in a polycrystalline nickel thin film by means of a magneto-optical pump-probe technique. The time and magnetic field dependence of the effect have been explored by measuring changes in the reflectivity, and the rotation and ellipticity associated with the linear magneto-optical Kerr effect. We find that, contrary to an earlier report, there is no significant difference in the time dependence of the rotation and ellipticity signals. Furthermore, we observe dynamic hysteresis loops with strange shapes which we believe result from a slow magnetic reorientation induced by average heating effects. These observations emphasize the importance of studying ultrafast demagnetization at saturation

Genetic differentiation, reproductive mode, and gene flow in the brooding coral Pocillopora damicornis along the Great Barrier Reef, Australia

The widespread and morphologically variable coral Pocillopora damicornis has been reported to exhibit huge variation in life-history traits (e.g. mode of reproduction, growth rate, longevity and dispersal) both locally and regionally throughout the Indo-Pacific Ocean. Dispersal may be achieved by the settlement of sexually or asexually generated brooded planula larvae, by broadcast spawning or more locally through asexual fragmentation of large colonies. In the present study, we conducted a hierarchical survey of allozyme variation within and among reef-crest sites on 3 mid-shelf reefs separated by up to 1200 km on the Great Barrier Reef (GBR), Australia. Our objective was to use allozyme data (1) to quantify local and regional patterns of variation in P. damicornis (along the northeastern coast of Australia), (2) to determine the relative contribution of sexual versus asexual production of planulae in P. damicornis, and (3) to estimate levels of gene flow among adjacent sites (>5 km apart) and among reefs separated by 500 to 1200 km. High levels of genotypic diversity in our samples of P. damicornis imply that dispersive propagules in this species are produced sexually rather than asexually along the length of the GBR. Corals at all sites displayed the same level of multi-locus genotypic diversity expected for randomly mating, sexually derived populations, and the majority of individual colonies possessed unique 7-locus genotypes. We also detected consistent deficits of heterozygotes within each collection (from 3 local sites on each of the 3 widely spaced reefs). This pattern is consistent with the predicted effects of sexual reproduction associated with some localised dispersal of gametes or larvae (although other explanations cannot be excluded). Furthermore, each reef was genetically subdivided, suggesting that larval recruitment was localised and that these populations are slightly inbred: hierarchical analysis of the standardised genetic variances (FST)(estimated as Weir & Cockerham's Θ) revealed that, although there was only moderate variation among all 9 sites (FST = 0.055 ± 0.029), more variation was found among sites within reefs (FSL= 0.035 ± 0.04 to 0.088 ± 0.033) than among distant reefs (FLT= 0.008 ± 0.014). This homogeneity of gene frequencies across widely separated reefs implies that reefs are connected by high levels of gene flow (Nem = ca 31) and that local populations of P. damicornis separated by >1000 km can interbreed sufficiently to maintain a consistent suite of life-history characters

Bioinformatics tools for analysing viral genomic data

The field of viral genomics and bioinformatics is experiencing a strong resurgence due to high-throughput sequencing (HTS) technology, which enables the rapid and cost-effective sequencing and subsequent assembly of large numbers of viral genomes. In addition, the unprecedented power of HTS technologies has enabled the analysis of intra-host viral diversity and quasispecies dynamics in relation to important biological questions on viral transmission, vaccine resistance and host jumping. HTS also enables the rapid identification of both known and potentially new viruses from field and clinical samples, thus adding new tools to the fields of viral discovery and metagenomics. Bioinformatics has been central to the rise of HTS applications because new algorithms and software tools are continually needed to process and analyse the large, complex datasets generated in this rapidly evolving area. In this paper, the authors give a brief overview of the main bioinformatics tools available for viral genomic research, with a particular emphasis on HTS technologies and their main applications. They summarise the major steps in various HTS analyses, starting with quality control of raw reads and encompassing activities ranging from consensus and de novo genome assembly to variant calling and metagenomics, as well as RNA sequencing

Declining grouper spawning aggregations in Western Province, Solomon Islands, signal the need for a modified management approach

Globally, groupers (Epinephelidae) that form fish spawning aggregations (FSAs) are highly vulnerable to overfishing and often require site-specific approaches to management. Over 5-years (2009-2013), we conducted underwater visual censuses (UVC) at a well-known spawning site at Njari Island, Gizo, Western Province, Solomon Islands, that supports aggregations of squaretail coralgrouper (Plectropomus areolatus), camouflage grouper (Epinephelus polyphekadion) and brown-marbled grouper (E. fuscoguttatus). Findings show that while there were species-specific variations in the duration and timing of the spawning season, aggregation densities peaked from March to June, representing the main spawning season for all three species. For P. areolatus, gonad analysis from samples taken from 2008 to 2011 confirmed reproductive activity in support of density trends observed through UVC. Over the 5-year UVC monitoring period, FSA densities declined for P. areolatus and E. polyphekadion. Conversely, following the first year of monitoring, E. fuscoguttatus densities increased. These inter-specific differences may reflect variable responses to fishing as shown elsewhere, or for example, differences in recruitment success. In response to known declines in FSAs of these species, in 2018 the Solomon Islands government placed a nationwide ban on these species' harvest and sale between October and January. As this study shows, this ban does not encompass the peak aggregation period at Njari and will offer limited protection to other FSAs of these species that are known to vary in reproductive seasonality across the Solomon Islands. A more biologically meaningful and practical management strategy would be to implement a nationwide ban on the harvest and sale of these groupers each month between full and new moons when these FSAs form consistently throughout the country. Since effective management of FSAs typically requires a combined approach, spatial management that protects both spawning sites and reproductive migratory corridors is warranted

Determination of the Thickness of Al2O3 Barriers in Magnetic Tunnel Junctions

Copyright © 2002 American Institute of PhysicsThe barrier thickness in magnetic spin-dependent tunnel junctions with Al2O3 barriers has been measured using grazing incidence x-ray reflectivity and by fitting the tunneling current to the Simmons model. We have studied the effect of glow discharge oxidation time on the barrier structure, revealing a substantial increase in Al2O3 thickness with oxidation. The greater thickness of barrier measured using grazing incidence x-ray reflectivity compared with that obtained by fitting current density–voltage to the Simmons electron tunneling model suggests that electron tunneling is localized to specific regions across the barrier, where the thickness is reduced by fluctuations due to nonconformal roughness