Laser Based Underwater Communication Systems

We report on recent progress in the field of visible light communications including direct modulation of blue laser devices at data rates beyond 10 Gbit/s, and the transmission of 2.5 Gbit/s OOK data through water. We also discuss the advantages of operating with single mode laser devices and matched filtering at the receiver in the context of applications with significant solar background. The system performance for two types of direct-detection receivers, a PIN detector and less conventional silicon Photomultiplier technology will be presented

Background complexity can mitigate poor camouflage

Avoiding detection through camouflage is often key to survival. However, an animal's appearance is not the only factor affecting conspicuousness: background complexity also alters detectability. This has been experimentally demonstrated for both artificially patterned backgrounds in the lab and natural backgrounds in the wild, but only for targets that already match the background well. Do habitats of high visual complexity provide concealment to even relatively poorly-camouflaged animals? Using artificial prey which differed in their degrees of background matching to tree bark, we were able to determine their survival, under bird predation, with respect to the natural complexity of the background. The latter was quantified using low-level vision metrics of feature congestion (or 'visual clutter') adapted for bird vision. Higher background orientation clutter (edges with varying orientation) reduced the detectability of all but the poorest background-matching camouflaged treatments; higher background luminance clutter (varying achromatic lightness) reduced average mortality for all treatments. Our results suggest that poorer camouflage can be mitigated by more complex backgrounds, with implications for both camouflage evolution and habitat preferences.Data file is: Rowe_at_al_data.txt Format: tab-delimited text Created: 24/03/2021 Description of variables (columns) Block "Experimental block (different part of study site on different dates): factor with 27 levels, 1 to 27." Treatment "Experimental treatment (varied average luminance): factor with 9 levels (1 = darkest, 9 = lightest)." Replicate "Replicate number, factor with 10 levels, nested within Block and Treatment." Censored "Binary code: 1 = bird predation, 0 = disappearance for any other reason (e.g. invertebrate predation) or survival to the end of the trial." Day "Day of disappearance: numeric, taking values 0 to 5. 0 indicates the replicate was lost before deployment (n=3)." Notes Plain text description of fate of target. contrast.fc Luminance contrast metric of feature congestion. colour.fc Colour contrast metric of feature congestion. orientation.fc Edge orientation metric of feature congestion. Funding provided by: Biotechnology & Biological Sciences Research Council, UKCrossref Funder Registry ID: http://dx.doi.org/10.13039/501100000268Award Number: BB/S00873X/

A Spectroscopic Survey of a Sample of Active M Dwarfs

A moderate resolution spectroscopic survey of Fleming's sample of 54 X-ray selected M dwarfs with photometric distances less than 25 pc is presented. Radial and rotation velocities have been measured by fits to the H-alpha profiles. Radial velocities have been measured by cross correlation. Artificial broadening of an observed spectrum has produced a relationship between H-alpha FWHM and rotation speed, which we use to infer rotation speeds for the entire sample by measurement of the H-alpha emission line. We find 3 ultra-fast rotators (UFRs, vsini > 100km/s), and 8 stars with 30 < vsini < 100 km/s. The UFRs have variable emission. Cross-correlation velocities measured for ultra-fast rotators (UFRs) are shown to depend on rotation speed and the filtering used. The radial velocity dispersion of the sample is 17 km/s. A new double emission line spectroscopic binary with a period of 3.55 days has been discovered, and another known one is in the sample. Three other objects are suspected spectroscopic binaries, and at least six are visual doubles. The only star in the sample observed to have significant lithium is a known TW Hya Association member, TWA 8A. These results show that there are a number of young (< 10^8 yr) and very young (< 10^7 yr) low mass stars in the immediate solar neighbourhood. The H-alpha activity strength does not depend on rotation speed. Our fast rotators are less luminous than similarly fast rotators in the Pleiades. They are either younger than the Pleiades, or gained angular momentum in a different way.Comment: 38 pages incl. 14 figures and 4 tables, plus 12 pages of table for electronic journal only; LaTeX, aastex.cls. Accepted 07/18/02 for publication in The Astronomical Journa

Narratives of self and identity in women's prisons: stigma and the struggle for self-definition in penal regimes

A concern with questions of selfhood and identity has been central to penal practices in women's prisons, and to the sociology of women's imprisonment. Studies of women's prisons have remained preoccupied with women prisoners’ social identities, and their apparent tendency to adapt to imprisonment through relationships. This article explores the narratives of women in two English prisons to demonstrate the importance of the self as a site of meaning for prisoners and the central place of identity in micro-level power negotiations in prisons

Renal revascularization in Takayasu arteritis–induced renal artery stenosis

AbstractPurposeThis study was undertaken to define the long-term effects of renal revascularization on blood pressure, and renal and cardiac function in patients with Takayasu arteritis–induced renal artery stenosis (TARAS).MethodsTwenty-seven patients (25 women; mean age, 27 years) with TARAS underwent intervention. Primary, primary assisted, and secondary patency rates were determined, and the late effects on blood pressure, renal and cardiac function, and survival were analyzed.ResultsAll patients had hypertension (mean blood pressure, 167/99 mm Hg; 2.5 antihypertensive medications per patient). Mean estimated glomerular filtration rate in patients not receiving hemodialysis was 76 mL/min, and in five patients serum creatinine concentration was greater than 1.5 mg/dL. Three patients were hemodialysis-dependent, and two had intractable congestive heart failure. Forty interventions were performed, including 32 aortorenal bypass procedures, two repeat implantations, four nephrectomies, and two transluminal angioplasty procedures. Postoperative morbidity was 19%. There were no deaths. During follow-up (mean, 68 months), three graft stenoses, all due to intimal hyperplasia, and three graft occlusions occurred. Two of three graft stenoses were successfully revised. At 1, 3, and 5 years of follow-up, primary patency was 87%, 79%, and 79%, respectively; primary assisted patency was 93%, 89%, 89%, respectively; and secondary patency was 93%, 89%, and 89%, respectively. Intervention resulted in a decrease in blood pressure to a mean of 132/79 mm Hg (P < .0001), and the need for antihypertensive medications was reduced to one per patient (P < .01). Mean glomerular filtration rate increased to 88 mL/min (P < .005), and two patients no longer required hemodialysis. Congestive heart failure resolved in both patients, and did not recur. There were three deaths during follow-up, with 5-year and 10-year actuarial survival of 96% and 80%, respectively.ConclusionsRenal revascularization to treat TARAS is durable, has a salutary effect on blood pressure, and enhances long-term renal and cardiac function. This response establishes renal revascularization as a successful and durable intervention for TARAS, and a benchmark to which other therapies should be compared

InGaN/GaN Laser Diodes and their Applications

Gallium nitride (GaN) laser diodes are becoming popular sources not only for lighting but for applications ranging from communications to quantum. This paper presents the use of a commercial, off-the-shelf laser diode, with an emission wavelength of 450 nm, for visible light communication, both in free space and for underwater scenarios. Data rates up to 15 Gbit/s have been achieved by making use of orthogonal frequency division multiplexing (OFDM). In addition, distributed feedback (DFB) lasers have been realised emitting at a single wavelength which lend themselves towards applications where high spectral purity is crucial such as atomic clocks or filtered free space transmission systems. These devices have the grating structure etched into the sidewall of the ridge and work is ongoing to measure the linewidth of these lasers with the intended application of cooling Sr+ ions

FAD binding, cobinamide binding and active site communication in the corrin reductase (CobR)

Adenosylcobalamin, the coenzyme form of vitamin B12, is one Nature's most complex coenzyme whose de novo biogenesis proceeds along either an anaerobic or aerobic metabolic pathway. The aerobic synthesis involves reduction of the centrally chelated cobalt metal ion of the corrin ring from Co(II) to Co(I) before adenosylation can take place. A corrin reductase (CobR) enzyme has been identified as the likely agent to catalyse this reduction of the metal ion. Herein, we reveal how Brucella melitensis CobR binds its coenzyme FAD (flavin dinucleotide) and we also show that the enzyme can bind a corrin substrate consistent with its role in reduction of the cobalt of the corrin ring. Stopped-flow kinetics and EPR reveal a mechanistic asymmetry in CobR dimer that provides a potential link between the two electron reduction by NADH to the single electron reduction of Co(II) to Co(I)

Delays Associated with Elementary Processes in Nuclear Reaction Simulations

Scatterings, particularly those involving resonances, and other elementary processes do not happen instantaneously. In the context of semiclassical nuclear reaction simulations, we consider delays associated with an interaction for incident quantum wave-packets. As a consequence, we express delays associated with elementary processes in terms of elements of the scattering matrix and phase shifts for elastic scattering. We show that, to within the second order in density, the simulation must account for delays in scattering consistently with the mean field in order to properly model thermodynamic properties such as pressure and free-energy density. The delays associated with nucleon-nucleon and pion-nucleon scattering in free space are analysed with their nontrivial energy dependence. Finally, an example of s-channel scattering of massless partons is studied, and scattering schemes in nuclear reaction simulations are investigated in the context of scattering delays.Comment: 45 pages, 5 uuencoded Postscript figure

Messing with nature? Exploring public perceptions of geoengineering in the UK

Anthropogenic influence on the climate – and possible societal responses to it – offers a unique window through which to examine the way people think about and relate to the natural world. This paper reports data from four, one-day deliberative workshops conducted with members of the UK public during early 2012. The workshops focused on geoengineering – the deliberate, large-scale manipulation of the planetary environment – as one of three possible responses to climate change (alongside mitigation and adaptation). Here, we explore one of the most pervasive and wide-ranging themes to emerge from the workshops: whether geoengineering represented an unprecedented human intervention into ‘nature’, and what the moral consequences of this might be. Using the concept of ‘messing with nature’ as an analytical lens, we explore public perceptions of geoengineering. We also reflect on why ‘messing with nature’ was such a focal point for debate and disagreement, and whether the prospect of geoengineering may reveal new dimensions to the way that people think about the natural world, and their relationship to it

Evidence for seasonal cycles in deep-sea fish abundances: A great migration in the deep SE Atlantic?

Animal migrations are of global ecological significance, providing mechanisms for the transport of nutrients and energy between distant locations. In much of the deep sea (>200 m water depth), the export of nutrients from the surface ocean provides a crucial but seasonally variable energy source to seafloor ecosystems. Seasonal faunal migrations have been hypothesized to occur on the deep seafloor as a result, but have not been documented. Here, we analyse a 7.5‐year record of photographic data from the Deep‐ocean Environmental Long‐term Observatory Systems seafloor observatories to determine whether there was evidence of seasonal (intra‐annual) migratory behaviours in a deep‐sea fish assemblage on the West African margin and, if so, identify potential cues for the behaviour. Our findings demonstrate a correlation between intra‐annual changes in demersal fish abundance at 1,400 m depth and satellite‐derived estimates of primary production off the coast of Angola. Highest fish abundances were observed in late November with a smaller peak in June, occurring approximately 4 months after corresponding peaks in primary production. Observed changes in fish abundance occurred too rapidly to be explained by recruitment or mortality, and must therefore have a behavioural driver. Given the recurrent patterns observed, and the established importance of bottom‐up trophic structuring in deep‐sea ecosystems, we hypothesize that a large fraction of the fish assemblage may conduct seasonal migrations in this region, and propose seasonal variability in surface ocean primary production as a plausible cause. Such trophic control could lead to changes in the abundance of fishes across the seafloor by affecting secondary production of prey species and/or carrion availability for example. In summary, we present the first evidence for seasonally recurring patterns in deep‐sea demersal fish abundances over a 7‐year period, and demonstrate a previously unobserved level of dynamism in the deep sea, potentially mirroring the great migrations so well characterized in terrestrial systems