The Casimir spectrum revisited

We examine the mathematical and physical significance of the spectral density sigma(w) introduced by Ford in Phys. Rev. D38, 528 (1988), defining the contribution of each frequency to the renormalised energy density of a quantum field. Firstly, by considering a simple example, we argue that sigma(w) is well defined, in the sense of being regulator independent, despite an apparently regulator dependent definition. We then suggest that sigma(w) is a spectral distribution, rather than a function, which only produces physically meaningful results when integrated over a sufficiently large range of frequencies and with a high energy smooth enough regulator. Moreover, sigma(w) is seen to be simply the difference between the bare spectral density and the spectral density of the reference background. This interpretation yields a simple `rule of thumb' to writing down a (formal) expression for sigma(w) as shown in an explicit example. Finally, by considering an example in which the sign of the Casimir force varies, we show that the spectrum carries no manifest information about this sign; it can only be inferred by integrating sigma(w).Comment: 10 pages, 4 figure

Non-unitary representations of the SU(2) algebra in the Dirac equation with a Coulomb potential

A novel realization of the classical SU(2) algebra is introduced for the Dirac relativistic hydrogen atom defining a set of operators that, besides, allow the factorization of the problem. An extra phase is needed as a new variable in order to define the algebra. We take advantage of the operators to solve the Dirac equation using algebraic methods. To acomplish this, a similar path to the one used in the angular momentum case is employed; hence, the radial eigenfuntions calculated comprise non unitary representations of the algebra. One of the interesting properties of such non unitary representations is that they are not labeled by integer nor by half-integer numbers as happens in the usual angular momentum representation.Comment: 20 pages 1 eps figure in a single zipped file, submitted to J. Math. Phy

Heat Capacity Measurements in Pulsed Magnetic Fields

The new NHMFL 60T quasi-continuous magnet produces a flat-top field for a period of 100 ms at 60 Tesla, and for longer time at lower fields, e.g. 0.5 sec at 35 Tesla. We have developed for the first time the capability to measure heat capacity at very high magnetic fields in the NHMFL 60 T quasi-continuous magnet at LANL, using a probe built out of various plastic materials. The field plateau allows us to utilize a heat-pulse method to obtain heat capacity data. Proof-of-principle heat capacity experiments were performed on a variety of correlated electron systems. Both magnet performance characteristics and physical properties of various materials studied hold out a promise of wide application of this new tool.Comment: 6 pages, 3 figures, World Scientific Pub. Co., to be publishe

Estudio serológico de la infección por Salmonella spp. en cerdos de engorde del Noreste de España y factores de riesgo asociados

The results of a serological survey carried out in northeastern Spain to estimate the seroprevalence to Salmonella spp. and to determine potential risk factors are presented. Sera were obtained from farms submitting serum samples to the Regional Diagnostic Laboratory (RDL) for the diagnosis of other infectious diseases included within official eradication/surveillance programs, and farm data collected through a questionnaire. Out of 6,182 pig sera (217 farms) analyzed 1,219 (19.7%) were positive (optical density, OD ≥ 40%). More than 70% of the herds presented ≥ 1 seropositive animal indicating that salmonellosis was widespread. In a multivariable logistic mixed regression model seroprevalence was associated with farms where birds were visible inside the fattening units (OR = 2.1; 95% CI: 1.3-3.2) or that shared workers with other pig farms (OR = 2.5; 95% CI: 1.4-4.7). Seropositivity also increased when farmers used footwear exclusive for the farm (OR = 3.1; 95% CI: 1.3-7.3) or pigs were fed mostly with pellets (OR = 1.7; 95% CI: 1.1-2.6). It was also higher during the fall and winter months. The presence of a changing room and shower in the farm was negatively associated with it (OR = 0.5; 95% CI: 0.3-0.8). Most risk factors could be mitigated through strict hygiene and biosecurity measures, but the high (> 40%) within-herd seroprevalence observed in many herds may challenge the capacity of intervention of animal health authorities.Se presentan los resultados de un estudio serológico realizado en explotaciones porcinas del Noreste de España para estimar la seroprevalencia frente a Salmonella spp. y determinar posibles factores de riesgo asociados. Los sueros se obtuvieron a partir de aquellos enviados por las explotaciones al Laboratorio Regional de Diagnóstico para el diagnóstico de otras enfermedades infecciosas sometidas a erradicación/vigilancia oficial, y los datos sobre las explotaciones se recogieron mediante un cuestionario. De un total de 6.182 sueros de cerdo (217 granjas) analizados 1.219 (19,7%) resultaron positivos (densidad óptica, DO ≥ 40%). Más del 70% de los rebaños presentaron al menos un animal positivo, indicando que la salmonelosis está ampliamente distribuida en la región. Según un modelo multivariable mixto de regresión logística, la seroprevalencia se asoció con granjas en las cuales se veían aves en el interior de las naves (OR = 2,1; IC 95%: 1,3-3,2) y también con granjas que compartían trabajadores (OR = 2,5; IC 95%: 1,4-4,7). Se observó que la seropositividad se incrementaba cuando los trabajadores usaban botas exclusivas en la explotación (OR = 3,1; IC 95%: 1,3-7,3) o al alimentar a los cerdos principalmente con alimento granulado (OR = 1,7; IC 95%: 1,1-2,6). La seroprevalencia también fue superior durante los meses de otoño e invierno. La existencia en las granjas de vestuarios y duchas para el personal se asoció negativamente con la seroprevalencia (OR = 0,5; IC 95%: 0,3-0,8). La mayoría de los factores de riesgo podrían controlarse a través de estrictas medidas de higiene y bioseguridad, pero el gran número de rebaños que presentaron alta seroprevalencia (> 40%) puede poner a prueba la capacidad de intervención de las autoridades sanitarias oficiales

Salmonellosis in wild birds and its relationship with the infection in finishing pigs

The potential relationship between Salmonella infection in wild birds and pigs was investigated. Feces from pigs, wild birds, and bird droppings or other environmental samples from 25 finishing farms were cultured for Salmonella isolation. In 17 (68%) farms Salmonella was isolated. Out of 57 Salmonella isolates found, 32 (56.1%) were Typhimurium. In 6 (24%) farms the same Salmonella serotype was isolated from samples from different origins and similar AR and PFGE patterns were found, which would support the existence of a transmission cycle of Salmonella infection between birds and pigs in this area. Preventing bird access to farm premises is highly recommended

Serological characterization of Salmonella spp. infection in finishing pigs from NE Spain

The seroprevalence of salmonella spp. In finishing pigs in Aragón (NE of Spain) and the potential factors associated with it were assessed. Serum samples were collected directly from the Regional Diagnostic Laboratory (RDL). Only farms submitting a minimum of 30 serum samples to the RDL were included, i.e. exporting and farrow-to-finish farms, and those in the last stages of the Aujezsky\u27s disease eradication program

Resolved images of the protoplanetary disk around HD 100546 with ALMA

The disk around the Herbig Ae/Be star HD 100546 has been extensively studied and it is one of the systems for which there are observational indications of ongoing and/or recent planet formation. However, up until now no resolved image of the millimeter dust emission or the gas has been published. We present the first resolved images of the disk around HD 100546 obtained in Band 7 with the ALMA observatory. The CO (3-2) image reveals a gas disk that extends out to 350 au radius at the 3-sigma level. Surprisingly, the 870um dust continuum emission is compact (radius <60 au) and asymmetric. The dust emission is well matched by a truncated disk with outer radius of $\approx$50 au. The lack of millimeter-sized particles outside the 60 au is consistent with radial drift of particles of this size. The protoplanet candidate, identified in previous high-contrast NACO/VLT L' observations, could be related to the sharp outer edge of the millimeter-sized particles. Future higher angular resolution ALMA observations are needed to determine the detailed properties of the millimeter emission and the gas kinematics in the inner region (<2arcsec). Such observations could also reveal the presence of a planet through the detection of circumplanetary disk material.Comment: 6 pages, 4 figures. Accepted in ApJ

Coherent Radiation from Extensive Air Showers in the Ultra-High Frequency Band

Using detailed Monte Carlo simulations we have characterized the features of the radio emission of inclined air showers in the Ultra-High Frequency band (300 MHz - 3 GHz). The Fourier-spectrum of the radiation is shown to have a sizable intensity well into the GHz frequency range. The emission is mainly due to transverse currents induced by the geomagnetic field and to the excess charge produced by the Askaryan effect. At these frequencies only a significantly reduced volume of the shower around the axis contributes coherently to the signal observed on the ground. The size of the coherently emitting volume depends on frequency, shower geometry and observer position, and is interpreted in terms of the relative time delays. At ground level, the maximum emission at high frequencies is concentrated in an elliptical ring-like region around the intersection of a Cherenkov cone with its vertex at shower maximum and the ground. The frequency spectrum of inclined showers when observed at positions that view shower maximum in the Cherenkov direction, is shown to be in broad agreement with the pulses detected by the Antarctic Impulsive Transient Antenna (ANITA) experiment, making the interpretation that they are due to Ultra-High Energy Cosmic Ray atmospheric showers consistent with our simulations. These results are also of great importance for experiments aiming to detect molecular bremsstrahlung radiation in the GHz range as they present an important background for its detection.Comment: 8 pages, 8 figure

Phonon Thermal Transport of URu2Si2: Broken Translational Symmetry and Strong-Coupling of the Hidden Order to the Lattice

A dramatic increase in the total thermal conductivity (k) is observed in the Hidden Order (HO) state of single crystal URu2Si2. Through measurements of the thermal Hall conductivity, we explicitly show that the electronic contribution to k is extremely small, so that this large increase in k is dominated by phonon conduction. An itinerant BCS/mean-field model describes this behavior well: the increase in kappa is associated with the opening of a large energy gap at the Fermi Surface, thereby decreasing electron-phonon scattering. Our analysis implies that the Hidden Order parameter is strongly coupled to the lattice, suggestive of a broken symmetry involving charge degrees of freedom.Comment: 17 pages including figures, updated author institutions and acknowledgement