893 research outputs found
Reciprocity-Enhanced Optical Communication Through Atmospheric TurbulenceâPart II: Communication Architectures and Performance
Free-space optical (FSO) communication provides rapidly deployable, dynamic communication links that are capable of very high data rates compared with those of radio-frequency systems. As such, FSO communication is ideal for mobile platforms, for platforms that require the additional security afforded by the narrow divergence of a laser beam, and for systems that must be deployed in a relatively short time frame. In clear-weather conditions the data rate and utility of FSO communication links are primarily limited by fading caused by microscale atmospheric temperature variations that create parts-per-million refractive-index fluctuations known as atmospheric turbulence. Typical communication techniques to overcome turbulence-induced fading, such as interleavers with sophisticated codes, lose viability as the data rate is driven higher or the delay tolerance is driven lower. This paper, along with its companion [J. Opt. Commun. Netw. 4, 947 (2012)], present communication systems and techniques that exploit atmospheric reciprocity to overcome turbulence that are viable for high data rate and low delay tolerance systems. Part I proves that reciprocity is exhibited under rather general conditions and derives the optimal power-transfer phase compensation for far-field operation. Part II presents capacity-achieving architectures that exploit reciprocity to overcome the complexity and delay issues that limit state-of-the-art FSO communications.United States. National Aeronautics and Space Administration (Air Force Contract #FA8721-05-C-0002
Calciphylaxis following kidney transplantation: a case report
Introduction: Calciphylaxis occurring after kidney transplantation is rare and rarely reported. It results in chronic non-healing wounds and is associated with a poor prognosis and is often fatal. We present a case of proximal lower limb calciphylaxis that occurred early after kidney transplantation. The patient had no classic associated risk factors. He had previously had a total parathyroidectomy but had normal serum calcium-phosphate product and parathyroid hormone levels. The clinical outcome of this case was favorable and highlights some fundamental issues relating to management.
Case prsentation: A 70-year-old British Caucasian man with end-stage renal failure secondary to IgA nephropathy presented six months post kidney transplantation with cutaneous calciphylaxis lesions involving the medial aspect of the thigh bilaterally.
Conclusion: To the best of our knowledge, this is the first reported case of rapid onset cutaneous calciphylaxis occurring soon after kidney transplantation that was associated with a favorable outcome. Cutaneous calciphylaxis lesions should be promptly managed with meticulous wound care, antimicrobial therapy and the correction of calcium-phosphate product where indicated
The secret world of shrimps: polarisation vision at its best
Animal vision spans a great range of complexity, with systems evolving to
detect variations in optical intensity, distribution, colour, and polarisation.
Polarisation vision systems studied to date detect one to four channels of
linear polarisation, combining them in opponent pairs to provide
intensity-independent operation. Circular polarisation vision has never been
seen, and is widely believed to play no part in animal vision. Polarisation is
fully measured via Stokes' parameters--obtained by combined linear and circular
polarisation measurements. Optimal polarisation vision is the ability to see
Stokes' parameters: here we show that the crustacean \emph{Gonodactylus
smithii} measures the exact components required. This vision provides optimal
contrast-enhancement, and precise determination of polarisation with no
confusion-states or neutral-points--significant advantages. We emphasise that
linear and circular polarisation vision are not different modalities--both are
necessary for optimal polarisation vision, regardless of the presence of
strongly linear or circularly polarised features in the animal's environment.Comment: 10 pages, 6 figures, 2 table
"Women's rights, the European Court and Supranational Constitutionalism"
This analysis examines supranational constitutionalism in the European Union. In particular, the study focuses on the role of the European Court of Justice in the creation of womenâs rights. I examine the interaction between the Court and member state governments in legal integration, and also the integral role that womenâs advocates â both individual activists and groups â have played in the development of EU social provisions. The findings suggest that this litigation dynamic can have the effect of fueling the integration process by creating new rights that may empower social actors and EU organizations, with the ultimate effect of diminishing member state government control over the scope and direction of EU law. This study focuses specifically on gender equality law, yet provides a general framework for examining the case law in subsequent legal domains, with the purpose of providing a more nuanced understanding of supranational governance and constitutionalism
Late-onset Tay-Sachs disease
We discuss the assessment and differential diagnoses of a young adult Hungarian man with a 1-year history of a progressive and symmetric amyotrophic lateral sclerosis-like syndrome, along with irregular action tremor and stimulus-sensitive myoclonus of the arms. MR scan of the brain showed isolated cerebellar atrophy and formal neuropsychometric testing identified significant subclinical deficits in attention, processing speed and memory. We suspected a form of GM2 gangliosidosis, and white cell enzyme analysis showed markedly reduced enzymatic activity of β-hexosaminidase A. Genetic testing subsequently revealed two heterozygous pathogenic mutations in the HEXA gene (c.1499delT p.(Leu500fs) and c.805G>A p.(Gly269Ser)), confirming the very rare diagnosis of adult-onset Tay-Sachs disease
Single photon quantum non-demolition in the presence of inhomogeneous broadening
Electromagnetically induced transparency (EIT) has been often proposed for
generating nonlinear optical effects at the single photon level; in particular,
as a means to effect a quantum non-demolition measurement of a single photon
field. Previous treatments have usually considered homogeneously broadened
samples, but realisations in any medium will have to contend with inhomogeneous
broadening. Here we reappraise an earlier scheme [Munro \textit{et al.} Phys.
Rev. A \textbf{71}, 033819 (2005)] with respect to inhomogeneities and show an
alternative mode of operation that is preferred in an inhomogeneous
environment. We further show the implications of these results on a potential
implementation in diamond containing nitrogen-vacancy colour centres. Our
modelling shows that single mode waveguide structures of length in single-crystal diamond containing a dilute ensemble of NV
of only 200 centres are sufficient for quantum non-demolition measurements
using EIT-based weak nonlinear interactions.Comment: 21 pages, 9 figures (some in colour) at low resolution for arXiv
purpose
A 'resource allocator' for transcription based on a highly fragmented T7 RNA polymerase
Synthetic genetic systems share resources with the host, including machinery for transcription and translation. Phage RNA polymerases (RNAPs) decouple transcription from the host and generate high expression. However, they can exhibit toxicity and lack accessory proteins (Ď factors and activators) that enable switching between different promoters and modulation of activity. Here, we show that T7 RNAP (883 amino acids) can be divided into four fragments that have to be coâexpressed to function. The DNAâbinding loop is encoded in a Câterminal 285âaa âĎ fragmentâ, and fragments with different specificity can direct the remaining 601âaa âcore fragmentâ to different promoters. Using these parts, we have built a resource allocator that sets the core fragment concentration, which is then shared by multiple Ď fragments. Adjusting the concentration of the core fragment sets the maximum transcriptional capacity available to a synthetic system. Further, positive and negative regulation is implemented using a 67âaa Nâterminal âÎą fragmentâ and a null (inactivated) Ď fragment, respectively. The Îą fragment can be fused to recombinant proteins to make promoters responsive to their levels. These parts provide a toolbox to allocate transcriptional resources via different schemes, which we demonstrate by building a system which adjusts promoter activity to compensate for the difference in copy number of two plasmids.United States. Office of Naval Research (N00014â13â1â0074)National Institutes of Health (U.S.) (5R01GM095765)National Science Foundation (U.S.) (Synthetic Biology Engineering Research Center (SA5284â11210))United States. Dept. of Defense (National Defense Science and Engineering Graduate Fellowship (NDSEG) Program))Hertz Foundation (Fellowship
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