The Cerenkov effect revisited: from swimming ducks to zero modes in gravitational analogs

We present an interdisciplinary review of the generalized Cerenkov emission of radiation from uniformly moving sources in the different contexts of classical electromagnetism, superfluid hydrodynamics, and classical hydrodynamics. The details of each specific physical systems enter our theory via the dispersion law of the excitations. A geometrical recipe to obtain the emission patterns in both real and wavevector space from the geometrical shape of the dispersion law is discussed and applied to a number of cases of current experimental interest. Some consequences of these emission processes onto the stability of condensed-matter analogs of gravitational systems are finally illustrated.Comment: Lecture Notes at the IX SIGRAV School on "Analogue Gravity" in Como, Italy from May 16th-21th, 201

A history of high-power laser research and development in the United Kingdom

The first demonstration of laser action in ruby was made in 1960 by T. H. Maiman of Hughes Research Laboratories, USA. Many laboratories worldwide began the search for lasers using different materials, operating at different wavelengths. In the UK, academia, industry and the central laboratories took up the challenge from the earliest days to develop these systems for a broad range of applications. This historical review looks at the contribution the UK has made to the advancement of the technology, the development of systems and components and their exploitation over the last 60 years

Analysis of the aerodynamic performance of a morphing wing-tip demonstrator using a novel nonlinear vortex lattice method

This paper presents the novel nonlinear formulation of the Vortex Lattice Method approach for calculating the aerodynamic properties of lifting surfaces. The mathematical model is constructed by using two-dimensional viscous analyses of the wing span-wise sections, according to strip theory, and then coupling the strip viscous forces with the forces generated by the vortex rings distributed on the wing camber surface, calculated with a fully three-dimensional vortex lifting law. The numerical results obtained with the proposed method are validated with experimental data and show good agreement in predicting both the lift and pitching moment, as well as in predicting the wing drag. The technology demonstrator was modeled after an aircraft wing tip section, and was fitted with a composite material upper skin whose shape can be morphed, as a function of the flight condition, by four electrical actuators placed inside the wing structure. The nonlinear VLM results were compared with balance forces/moments measurements taken during subsonic wind tunnel tests performed at the National Research Council Canada.Peer reviewed: YesNRC publication: Ye

Fertilidade em garanhões avaliada através do exame andrológico Fertility in stallions as accessed by the breeding soundness examination

O presente trabalho teve por objetivo discutir aspectos da fertilidade de garanhões e sua relação com o exame andrológico. Numa primeira análise, 10 garanhões usados em monta natural exclusivamente, tiveram seus índices reprodutivos relacionados a qualidade do seu sêmen. Num segundo grupo, foram considerados 14 garanhões cujos acasalamentos eram, alternadamente, inseminação artificial e/ou monta natural. No terceiro estudo, foram relacionados garanhões específicos, pertencentes aos dois grupos anteriores, sabidamente subférteis em que os índices de fertilidade foram relacionados a características do sêmen ou manejo. Quando os garanhões são submetidos a monta natural dentro de um programa de manejo racional existe uma significativa relação entre qualidade de sêmen e fertilidade (P <0,01). O mesmo não se verifica quando há interferência de manejo (homem), usando inseminação artificial e modificando condições naturais (inseminação artificial inadequadamente empregada reduzindo a fertilidade e. adequadamente empregada, melhorando a fertilidade de garanhões subférteis). A análise de exames andrológicos individuais evidencia falares intrínsecos e extrínsecos (manejo) afetando a fertilidade.<br>This paper discuss certain aspects of the fertility in stallions and its relationship to the Breeding Soundness Examination. In afirst analysis, 10 stallions that were bred only naturally had their reproductive standards correlated to the sêmen quality. In a second step, we consider 14 stallions that were bred either by artificial insemination and for naturally. In a third study, certain subfertile stallions, belonging to the previous two groups, had their fertility standards correlated to sêmen quality and management procedures. A significam association (P<0.01) was observed between sêmen quality (sperm morphology) and fertility, when stallions were bred naturally under appropriate management procedures. This relationship was not observed when artificial insemination was included in the management, because it can improve the fertility of subfertile stallions or be detrimental to normal stallions when misused used. The individual analysis of the subfertile stallions allowed to determine if the cause the infertility can befrom intrinsic or extrinsic (management) factors

An exploratory comparison of e-commerce adoption in large and small enterprises

This study compares the reasons why small and large companies are adopting electronic commerce (e-commerce) and compares the benefits realized from the adoption of e-commerce by these two groups of companies. Two surveys that were undertaken contemporaneously on the use of e-commerce by small and large companies in the UK were used as the empirical basis for this study. The study found that the use of e-commerce for responding to competitors, providing enhanced customer services and improving relations with suppliers was driving the uptake by smaller businesses to a greater extent than by their larger counterparts. Only in the area of improved operational efficiency did larger businesses express greater interest in adopting e-commerce. The study also found that smaller businesses believed that they had achieved greater benefits from their e-commerce services than had the larger firms in all areas explored