Vortex dynamos

We investigate the kinematic dynamo properties of interacting vortex tubes. These flows are of great importance in geophysical and astrophysical fluid dynamics: for a large range of systems, turbulence is dominated by such coherent structures. We obtain a dynamically consistent 2(2)-(1)-dimensional velocity field of the form (u(x, y, t), upsilon(x, y, t), w(x, y, t)) by solving the z-independent Navier-Stokes equations in the presence of helical forcing. This system naturally forms vortex tubes via an inverse cascade. It has chaotic Lagrangian properties and is therefore a candidate for fast dynamo action. The kinematic dynamo properties of the flow are calculated by determining the growth rate of a small-scale seed field. The growth rate is found to have a complicated dependence on Reynolds number Re and magnetic Reynolds number Rm, but the flow continues to act as a dynamo for large Re and Rm. Moreover the dynamo is still efficient even in the limit Re much greater than Rm, providing Rm is large enough, because of the formation of coherent structures

Numerical solution of scattering problems using a Riemann--Hilbert formulation

A fast and accurate numerical method for the solution of scalar and matrix Wiener--Hopf problems is presented. The Wiener--Hopf problems are formulated as Riemann--Hilbert problems on the real line, and a numerical approach developed for these problems is used. It is shown that the known far-field behaviour of the solutions can be exploited to construct numerical schemes providing spectrally accurate results. A number of scalar and matrix Wiener--Hopf problems that generalize the classical Sommerfeld problem of diffraction of plane waves by a semi-infinite plane are solved using the approach

Short- and Long- Time Transport Structures in a Three Dimensional Time Dependent Flow

Lagrangian transport structures for three-dimensional and time-dependent fluid flows are of great interest in numerous applications, particularly for geophysical or oceanic flows. In such flows, chaotic transport and mixing can play important environmental and ecological roles, for examples in pollution spills or plankton migration. In such flows, where simulations or observations are typically available only over a short time, understanding the difference between short-time and long-time transport structures is critical. In this paper, we use a set of classical (i.e. Poincar\'e section, Lyapunov exponent) and alternative (i.e. finite time Lyapunov exponent, Lagrangian coherent structures) tools from dynamical systems theory that analyze chaotic transport both qualitatively and quantitatively. With this set of tools we are able to reveal, identify and highlight differences between short- and long-time transport structures inside a flow composed of a primary horizontal contra-rotating vortex chain, small lateral oscillations and a weak Ekman pumping. The difference is mainly the existence of regular or extremely slowly developing chaotic regions that are only present at short time.Comment: 9 pages, 9 figure

Inelastic Sum Rules

The history and present status of several sum rules for deep-inelastic lepton scattering are reviewed, with particular attention to the discovery of scaling, partons, quarks and QCD. Two outstanding issues are then discussed in more detail: the singlet (Ellis-Jaffe) nucleon spin sum rule and the Drell-Hearn-Gerasimov-Iddings sum rule

The Exemplary Life of Dimitrios Vikelas (1835-1908)

This paper describes the "satisfying curve" of Dimitrios Vikelas' life journey, starting from Syros in 1835, moving via Constantinople, Odessa, and Syros again, to London, Paris and finally Athens. It explores Vikelas' multiple aspects, as merchant, writer, traveller, lecturer and essayist, Olympic founder, educationalist, book collector and philanthropist, all of which were united in the public-spirited man of letters (logios). It sets Vikelas in the context of the Greek commercial diaspora, the world of the London expatriate Greek community, and the dynamic society of late nineteenth-century Athens, beginning in the 1870s to act as a magnet to Greek expatriates. The author stresses two qualities of Vikelas: his belief in the idea of a progressive Greek state marked by advances in education, culture, tourism and standards of public life; and the self-awareness and experience which inform his autobiographical writings, not only his memoir My Life but also his last such work, The War of 1897

A politician and his books: the Venizelos library in Chania

Eleftherios Venizelos loved books. He collected them, read them, andannotated them. With few exceptions, the most important being his translation of Thucydides into modern Greek, he did not write them. Books were an important part of his life, and he continued until the end to buy them. His collection of books is of historical and psychological interest. After his death in 1936, the books were transferred from his apartment in Paris and his wife’s house in Athens to the Venizelos family house in Halepa, near Chania in Crete. After many vicissitudes, especially during the German occupation of Crete, they came to rest in Chania Municipal Library, where they remain today. This paper explores Venizelos’ reading habits and preferences through this collection, showing that he used books both for professional information, for pleasure, and to improve his knowledge of foreign languages, in particular English. He was familiar with the great authors from Homer to Shakespeare; with philosophy from Aristotle to Bergson; with poetry, fiction, but especially with political thought, history and literature. It is good that the collection remains in the hands in the Municipal Library in the city where Venizelos lived and worked

From concrete quarks to QCD: a personal perspective

The simple story line that ‘Gell-Mann and Zweig invented quarks in 1964 and the quark model was generally accepted after 1968 when deep inelastic electron scattering experiments at SLAC showed that they are real’ contains elements of the truth, but is not true. This paper describes the origins and development of the quark model until it became generally accepted in the mid-1970s, as witnessed by a spectator and some-time participant who joined the field as a graduate student in October 1964. It aims to ensure that the role of Petermann is not overlooked, and Zweig and Bjorken get the recognition they deserve, and to clarify the role of Serber

The Exemplary Life of Dimitrios Vikelas (1835-1908)

This paper describes the "satisfying curve" of Dimitrios Vikelas' life journey, starting from Syros in 1835, moving via Constantinople, Odessa, and Syros again, to London, Paris and finally Athens. It explores Vikelas' multiple aspects, as merchant, writer, traveller, lecturer and essayist, Olympic founder, educationalist, book collector and philanthropist, all of which were united in the public-spirited man of letters (logios). It sets Vikelas in the context of the Greek commercial diaspora, the world of the London expatriate Greek community, and the dynamic society of late nineteenth-century Athens, beginning in the 1870s to act as a magnet to Greek expatriates. The author stresses two qualities of Vikelas: his belief in the idea of a progressive Greek state marked by advances in education, culture, tourism and standards of public life; and the self-awareness and experience which inform his autobiographical writings, not only his memoir My Life but also his last such work, The War of 1897

Obtaining self-samples to diagnose curable sexually transmitted infections: a systematic review of patients' experiences

BACKGROUND: Routine screening is key to sexually transmitted infection (STI) prevention and control. Previous studies suggest that clinic-based screening programmes capture only a small proportion of people with STIs. Self-sampling using non- or minimally invasive techniques may be beneficial for those reluctant to actively engage with conventional sampling methods. We systematically reviewed studies of patients' experiences of obtaining self-samples to diagnose curable STIs. METHODS: We conducted an electronic search of MEDLINE, EMBASE, CINAHL, PsychINFO, BNI, and Cochrane Database of Systematic Reviews to identify relevant articles published in English between January 1980 and March 2014. Studies were included if participants self-sampled for the diagnosis of a curable STI and had specifically sought participants' opinions of their experience, acceptability, preferences, or willingness to self-sample. RESULTS: The initial search yielded 558 references. Of these, 45 studies met the inclusion criteria. Thirty-six studies assessed patients' acceptability and experiences of self-sampling. Pooled results from these studies shows that self-sampling is a highly acceptable method with 85% of patients reporting the method to be well received and acceptable. Twenty-eight studies reported on ease of self-sampling; the majority of patients (88%) in these studies found self-sampling an "easy" procedure. Self-sampling was favoured compared to clinician sampling, and home sampling was preferred to clinic-based sampling. Females and older participants were more accepting of self-sampling. Only a small minority of participants (13%) reported pain during self-sampling. Participants were willing to undergo self-sampling and recommend others. Privacy and safety were the most common concerns. CONCLUSION: Self-sampling for diagnostic testing is well accepted with the majority having a positive experience and willingness to use again. Standardization of self-sampling procedures and rigorous validation of outcome measurement will lead to better comparability across studies. Future studies need to conduct rigorous economic evaluations of self-sampling to inform policy development for the management of STI