A note on the appearance of self-dual Yang-Mills fields in integrable hierarchies

A family of mappings from the solution spaces of certain generalized Drinfeld-Sokolov hierarchies to the self-dual Yang-Mills system on R^{2,2} is described. This provides an extension of the well-known relationship between self-dual connections and integrable hierarchies of AKNS and Drinfeld-Sokolov type

Catching NGC4051 in the low state with XMM-Newton

The Narrow Line Seyfert 1 galaxy NGC4051 shows unusual low flux states, lasting several months, when the 2-10 keV X-ray spectrum becomes unusually hard (photon index<1) while the spectrum at lower X-ray energies is dominated by a large soft excess. A Chandra TOO of the low state has shown that the soft excess and hard components are variable and well-correlated. The variability of the hard component rules out an origin in a distant reflector. Here we present results from a recent XMM-Newton TOO of NGC4051 in the low state, which allows a much more detailed examination of the nature of the hard and soft spectral components in the low state. We demonstrate that the spectral shape in the low state is consistent with the extrapolation of the spectral pivoting observed at higher fluxes. The XMM-Newton data also reveals the warm absorbing gas in emission, as the drop in the primary continuum flux unmasks prominent emission lines from a range of ion species.Comment: 4 pages, 4 figures. Proc. of the meeting: "The Restless High-Energy Universe" (Amsterdam, The Netherlands), E.P.J. van den Heuvel, J.J.M. in 't Zand, and R.A.M.J. Wijers Ed

Training in oesophageal surgery – The gold standard: A prospective study

AbstractIntroductionCompetency in complex oesophagogastric surgery, within the current climate of changes to medical training and reduced hours, requires repeated, focused, hands-on training. We describe the training methods for oesophagectomy in our institution.MethodsAll oesophageal resections under the care of one consultant surgeon are regarded as training cases. When trainees start they are shown the first resection; subsequently, the trainees then perform every case with the consultant scrubbed. Consultant input consists of retraction and tips in difficult situations. All data were collected on a prospective database.ResultsTwo hundered and seventy patients (215 males, median age=64 years) underwent primary oesophagectomy under the consultant, between January 2000 and May 2007. Fifteen resections (6%) were performed solely by the consultant. ASA grading was: I=15, II=154, III=95, IV=5, and unrecorded=1. In-hospital mortality and clinically apparent leak rate was 1.9% (5 deaths) and 6.2% (n=17), respectively. Reoperation was required in 15 patients (5.5%). The median length of hospital stay was 14 days (range=8–95 days). Median lymph node yield was 13 (range=0–64).ConclusionsTrainees under supervision can competently perform an oesophagectomy without compromising patient care. An early hands-on approach leads to a rapid ascent of the learning curve and is essential in today's climate of limited training opportunity

Evaluation of a Live-Attenuated Foot-and-Mouth Disease Virus as a Vaccine Candidate

AbstractA variant of foot-and-mouth disease virus (FMDV) lacking the leader (L) coding region (A12-LLV2) was previously constructed and shown to be less virulent in cattle than its wild-type parent (A12-IC). In this study, cattle were tested for their clinical and immunological responses to subcutaneous inoculation with A12-LLV2 or A12-IC or to intramuscular vaccination with chemically inactivated A12-IC. Five weeks postinoculation animals were challenged by intradermal inoculation in the tongue with a virulent cattle-passaged virus. A12-LLV2-inoculated animals showed no clinical signs of disease and developed a neutralizing antibody response by 4 days postinoculation, whereas a companion control bovine did not seroconvert. After challenge, two of three inoculated animals did not develop lesions, but showed mild signs of infection. The third inoculated animal developed some lesions, but these were less severe than in the uninoculated control animal, which showed classical FMD. All animals inoculated with A12-IC developed a fever, two showed typical FMD lesions, and the companion control seroconverted, indicating that it had acquired infection by contact. The A12-IC-inoculated animals and the control were protected from challenge. Animals vaccinated with inactivated virus showed no clinical signs of disease and developed a neutralizing antibody response, and the control did not seroconvert. Upon challenge none of the vaccinated animals developed lesions, one developed a fever, and the control developed FMD. These experiments demonstrate the potential of a rationally designed live-attenuated FMDV vaccine

Hidden Symmetries and Integrable Hierarchy of the N=4 Supersymmetric Yang-Mills Equations

We describe an infinite-dimensional algebra of hidden symmetries of N=4 supersymmetric Yang-Mills (SYM) theory. Our derivation is based on a generalization of the supertwistor correspondence. Using the latter, we construct an infinite sequence of flows on the solution space of the N=4 SYM equations. The dependence of the SYM fields on the parameters along the flows can be recovered by solving the equations of the hierarchy. We embed the N=4 SYM equations in the infinite system of the hierarchy equations and show that this SYM hierarchy is associated with an infinite set of graded symmetries recursively generated from supertranslations. Presumably, the existence of such nonlocal symmetries underlies the observed integrable structures in quantum N=4 SYM theory.Comment: 24 page

Darboux Transformations for a Lax Integrable System in 2n2n-Dimensions

A $2n$-dimensional Lax integrable system is proposed by a set of specific spectral problems. It contains Takasaki equations, the self-dual Yang-Mills equations and its integrable hierarchy as examples. An explicit formulation of Darboux transformations is established for this Lax integrable system. The Vandermonde and generalized Cauchy determinant formulas lead to a description for deriving explicit solutions and thus some rational and analytic solutions are obtained.Comment: Latex, 14 pages, to be published in Lett. Math. Phy

Camera trap distance sampling for terrestrial mammal population monitoring: lessons learnt from a UK case study

Accurate and precise density estimates are crucial for effective species management and conservation. However, efficient monitoring of mammal densities over large spatial and temporal scales is challenging. In the United Kingdom, published density estimates for many mammals, including species considered to be common, are imprecise. Camera trap distance sampling (CTDS) can estimate densities of multiple species at a time and has been used successfully in a small number of studies. However, CTDS has typically been used over relatively homogeneous landscapes, often over large time scales, making monitoring changes (by repeating surveys) difficult. In this study, we deployed camera traps at 109 sites across an area of 2725 km2 of varied habitat in North-East England, United Kingdom. The 4-month survey generated 51 447 photos of wild mammal species. Data were sufficient for us to use CTDS to estimate the densities of eight mammal species across the whole-survey area and within four specific habitats. Both survey-wide and habitat-specific density estimates largely fell within previously published density ranges and our estimates were amongst the most precise produced for these species to date. Lower precision for some species was typically due to animals being missed by the camera at certain distances, highlighting the need for careful consideration of practical and methodological decisions, such as how high to set cameras and where to left-truncate data. Although CTDS is a promising methodology for determining densities of multiple species from one survey, species-specific decisions are still required and these cannot always be generalized across species types and locations. Taking the United Kingdom as a case study, our study highlights the potential for CTDS to be used on a national scale, although the scale of the task suggests that it would need to be integrated with a citizen science approach

Crossover and scaling in a two-dimensional field-tuned superconductor

Using an analysis similar to that of Imry and Wortis, it is shown that the apparent first order superconductor to metal transition, which has been claimed to exist at low values of the magnetic field in a two-dimensional field-tuned system at zero temperature,can be consistentlyinterpreted as a sharp crossover from a strong superconductor to an inhomogeneous state, which is a weak superconductor. The true zero-temperature superconductor to insulator transition within the inhomogenous state is conjectured to be that of randomly diluted XY model. An explaination of the observed finite temperature approximate scaling of resistivity close to the critical point is speculated within this model.Comment: 5 pages, 2 figures, corrected and modified according to referee Report

Analytic and Asymptotic Methods for Nonlinear Singularity Analysis: a Review and Extensions of Tests for the Painlev\'e Property

The integrability (solvability via an associated single-valued linear problem) of a differential equation is closely related to the singularity structure of its solutions. In particular, there is strong evidence that all integrable equations have the Painlev\'e property, that is, all solutions are single-valued around all movable singularities. In this expository article, we review methods for analysing such singularity structure. In particular, we describe well known techniques of nonlinear regular-singular-type analysis, i.e. the Painlev\'e tests for ordinary and partial differential equations. Then we discuss methods of obtaining sufficiency conditions for the Painlev\'e property. Recently, extensions of \textit{irregular} singularity analysis to nonlinear equations have been achieved. Also, new asymptotic limits of differential equations preserving the Painlev\'e property have been found. We discuss these also.Comment: 40 pages in LaTeX2e. To appear in the Proceedings of the CIMPA Summer School on "Nonlinear Systems," Pondicherry, India, January 1996, (eds) B. Grammaticos and K. Tamizhman

Geochemical characterization of the mining district of Linares (Jaen, Spain) by means of XRF and ICP-AES

Linares (Jaen, Spain) has been subjected to an intense mining and metallurgic activity during 2500 years. Basically, lead and silver have been extracted from galena; as well as copper and zinc. Different studies have been conducted to evaluate trace element concentrations to obtain relationships with anthropogenic and geologic factors. The analytical results of these studies have been obtained with ICP-AES. This analytical technique is relatively expensive and inaccessible in zones with scarce economic means. In this study, XRF analyses have been conducted and the obtained results are presented, as well as a comparison with the previously obtained ICP results. In both cases, a cluster analysis has been made to try to identify the same relations in the target area. 5 groups have been identified, mainly related with lithology. Only 10 of the 122 grid squares (each one of 1 km2) are classified in different groups if the cluster analysis is conducted with XRF results or ICP results. ICP classifies better where these grid squares are located, mostly, in contact zones of different lithologies