Transient Resonant Spiking in Degenerate Four Wave Mixing in Saturable Absorbers

We show that under certain conditions the time evolution of the conjugate reflectivity for degenerate four wave mixing in saturable absorbers can exhibit a resonant spike after a time equal to the molecular relaxation time of the system

Optical Bistability in Semiconductor Injection Lasers

This paper reviews optical bistability in semiconductor lasers, with particular reference to the potential switching speeds of the systems demonstrated to date. Devices which switch by redistributing a nearly constant number of carriers within the active region should be faster, though less stable, than systems whose transitions are attended by changes in carrier numbers. One system of the former type, the self-focused coupled cavity laser, is analysed in some detail and is compared with the twin stripe laser and the Fabry-Perot laser amplifier

A Model for the Diffuse γ-Ray Spectrum

A model is proposed to describe the observed shelf in the cosmic diffuse radiation spectrum just above 1 MeV. This model is based on induced positronium annihilation, which at incident photon energy 2 mc^2 gives rise to enhancement of the radiative field. It is proposed that this amplification may occur in double radio sources or other accreting objects. Recent observation of γ-ray line emission from the double radio sources SS 433 at 1.2 and 1.5 MeV is in good agreement with the proposed model

Fordism: a review essay

Fordism is a central concept in American labour history. This essay, the first survey of the range of historiographical and sociological approaches deployed to understand Fordism, suggests that Fordism and Americanism are inseparably intertwined. Previous scholarship has emphasised that the technological and managerial efficiency of Fordist practice were a hallmark of twentieth century Americanism. Historians of labour have demonstrated that these aspects manifested as a relentless system of control in the workplace that paradoxically helped to unify worker resistance. Historians of capitalism have tended to used Fordism to refer to an ethos underpinning mid-twentieth century capitalist development marked by a balance between mass production and mass consumption. They identify increased social provisions and class compromise between labour and management as features that made Fordism attractive to states rebuilding their economies following the Second World War. New transnational histories of Fordism have begun to bridge the gap between these two main interpretations to show how Fordist practice and ethos were exported together internationally as part of an ideological project to modernise nations in America's image. This essay concludes by assessing the usefulness of Fordism to historians and suggesting avenues for future research

Evaluation of early and late presentation of patients with ocular mucous membrane pemphigoid to two major tertiary referral hospitals in the United Kingdom

PURPOSE: Ocular mucous membrane pemphigoid (OcMMP) is a sight-threatening autoimmune disease in which referral to specialists units for further management is a common practise. This study aims to describe referral patterns, disease phenotype and management strategies in patients who present with either early or established disease to two large tertiary care hospitals in the United Kingdom.\ud \ud PATIENTS AND METHODS: In all, 54 consecutive patients with a documented history of OcMMP were followed for 24 months. Two groups were defined: (i) early-onset disease (EOD:<3 years, n=26, 51 eyes) and (ii) established disease (EstD:>5 years, n=24, 48 eyes). Data were captured at first clinic visit, and at 12 and 24 months follow-up. Information regarding duration, activity and stage of disease, visual acuity (VA), therapeutic strategies and clinical outcome were analysed.\ud \ud RESULTS: Patients with EOD were younger and had more severe conjunctival inflammation (76% of inflamed eyes) than the EstD group, who had poorer VA (26.7%=VA<3/60, P<0.01) and more advanced disease. Although 40% of patients were on existing immunosuppression, 48% required initiation or switch to more potent immunotherapy. In all, 28% (14) were referred back to the originating hospitals for continued care. Although inflammation had resolved in 78% (60/77) at 12 months, persistence of inflammation and progression did not differ between the two phenotypes. Importantly, 42% demonstrated disease progression in the absence of clinically detectable inflammation.\ud \ud CONCLUSIONS: These data highlight that irrespective of OcMMP phenotype, initiation or escalation of potent immunosuppression is required at tertiary hospitals. Moreover, the conjunctival scarring progresses even when the eye remains clinically quiescent. Early referral to tertiary centres is recommended to optimise immunosuppression and limit long-term ocular damage.\ud \u

SMARCB1 regulates the hypoxic stress response in sickle cell trait during the pathogenesis of renal medullary carcinoma.

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Towards an Intelligent Tutor for Mathematical Proofs

Computer-supported learning is an increasingly important form of study since it allows for independent learning and individualized instruction. In this paper, we discuss a novel approach to developing an intelligent tutoring system for teaching textbook-style mathematical proofs. We characterize the particularities of the domain and discuss common ITS design models. Our approach is motivated by phenomena found in a corpus of tutorial dialogs that were collected in a Wizard-of-Oz experiment. We show how an intelligent tutor for textbook-style mathematical proofs can be built on top of an adapted assertion-level proof assistant by reusing representations and proof search strategies originally developed for automated and interactive theorem proving. The resulting prototype was successfully evaluated on a corpus of tutorial dialogs and yields good results.Comment: In Proceedings THedu'11, arXiv:1202.453

Genetic Diversity in the SIR Model of Pathogen Evolution

We introduce a model for assessing the levels and patterns of genetic diversity in pathogen populations, whose epidemiology follows a susceptible-infected-recovered model (SIR). We model the population of pathogens as a metapopulation composed of subpopulations (infected hosts), where pathogens replicate and mutate. Hosts transmit pathogens to uninfected hosts. We show that the level of pathogen variation is well predicted by analytical expressions, such that pathogen neutral molecular variation is bounded by the level of infection and increases with the duration of infection. We then introduce selection in the model and study the invasion probability of a new pathogenic strain whose fitness (R0(1+s)) is higher than the fitness of the resident strain (R0). We show that this invasion probability is given by the relative increment in R0 of the new pathogen (s). By analyzing the patterns of genetic diversity in this framework, we identify the molecular signatures during the replacement and compare these with those observed in sequences of influenza A