Planar Josephson Tunnel Junctions in a Transverse Magnetic Field

Traditionally, since the discovery of the Josephson effect in 1962, the magnetic diffraction pattern of planar Josephson tunnel junctions has been recorded with the field applied in the plane of the junction. Here we discuss the static junction properties in a transverse magnetic field where demagnetization effects imposed by the junction geometry and configuration of the electrodes are important. Measurements of the critical current versus magnetic field in planar Nb-based high-quality junctions with different geometry, size and critical current density show that it is advantageous to use a transverse magnetic field rather than an in-plane field to suppress the Josephson tunnel current and Fiske resonances in practical applications.Comment: 5 pages, 2 figures, submitted to Journal of Applied Physic

The role of temperature in the magnetic irreversibility of type-I Pb superconductors

Evidence of how temperature takes part in the magnetic irreversibility in the intermediate state of a cylinder and various disks of pure type-I superconducting lead is presented. Isothermal measurements of first magnetization curves and magnetic hysteresis cycles are analyzed in a reduced representation that defines an equilibrium state for flux penetration in all the samples and reveals that flux expulsion depends on temperature in the disks but not in the cylinder. The magnetic field at which irreversibility sets in along the descending branch of the hysteresis cycle and the remnant magnetization at zero field are found to decrease with temperature in the disks. The contributions to irreversibility of the geometrical barrier and the energy minima associated to stress defects that act as pinning centers on normal-superconductor interfaces are discussed. The differences observed among the disks are ascribed to the diverse nature of the stress defects in each sample. The pinning barriers are suggested to decrease with the magnetic field to account for these results

Universal restrictions to the conversion of heat into work derived from the analysis of the Nernst theorem as a uniform limit

We revisit the relationship between the Nernst theorem and the Kelvin-Planck statement of the second law. We propose that the exchange of entropy uniformly vanishes as the temperature goes to zero. The analysis of this assumption shows that is equivalent to the fact that the compensation of a Carnot engine scales with the absorbed heat so that the Nernst theorem should be embedded in the statement of the second law. ----- Se analiza la relaci{\'o}n entre el teorema de Nernst y el enunciado de Kelvin-Planck del segundo principio de la termodin{\'a}mica. Se{\~n}alamos el hecho de que el cambio de entrop{\'\i}a tiende uniformemente a cero cuando la temperatura tiende a cero. El an{\'a}lisis de esta hip{\'o}tesis muestra que es equivalente al hecho de que la compensaci{\'o}n de una m{\'a}quina de Carnot escala con el calor absorbido del foco caliente, de forma que el teorema de Nernst puede derivarse del enunciado del segundo principio.Comment: 8pp, 4 ff. Original in english. Also available translation into spanish. Twocolumn format. RevTe

Performance of discrete heat engines and heat pumps in finite time

The performance in finite time of a discrete heat engine with internal friction is analyzed. The working fluid of the engine is composed of an ensemble of noninteracting two level systems. External work is applied by changing the external field and thus the internal energy levels. The friction induces a minimal cycle time. The power output of the engine is optimized with respect to time allocation between the contact time with the hot and cold baths as well as the adiabats. The engine's performance is also optimized with respect to the external fields. By reversing the cycle of operation a heat pump is constructed. The performance of the engine as a heat pump is also optimized. By varying the time allocation between the adiabats and the contact time with the reservoir a universal behavior can be identified. The optimal performance of the engine when the cold bath is approaching absolute zero is studied. It is found that the optimal cooling rate converges linearly to zero when the temperature approaches absolute zero.Comment: 45 pages LaTeX, 25 eps figure

The Human Ecology and Geography of Burning in an Unstable Savanna Environment

According to new ecological theories, many savannas are inherently in disequilibrium and can flip from tree-dominated to grass-dominated landscapes depending upon the disturbance regime. In particular, a shift in a fire regime to a more frequent and intensive one can radically alter the tree-to-grass ratio in a given savanna. Drawing upon the ecological buffering model we argue that savanna persistence requires a relatively stable fire regime. We hypothesize that anthropogenic burning practices perform this function by producing a regular annual spatiotemporal pattern of fire that is linked to vegetation type. We test this hypothesis using a study of two areas, one in Mali and the other Burkina Faso. We use two sources of satellite data to produce an 11-year time series of the spatiotemporal pattern of fires and an example of the annual burned area pattern these fires produce. We combine the analysis of satellite imagery with interviews of rural inhabitants who set fires to understand the logic underlying the patterns of fire. Analysis of a time series of imagery reveals a strikingly regular annual spatiotemporal pattern of burning for both study areas, which cannot be explained by the regional climatic pattern alone. We conclude that the regularity of the annual fire regime in West Africa is a human-ecological phenomenon closely linked to vegetation type and controlled by people\u27s burning practices. We argue that the anthropogenic burning regime serves to buffer the savanna and maintain its ecological stability

Notes on the Third Law of Thermodynamics.I

We analyze some aspects of the third law of thermodynamics. We first review both the entropic version (N) and the unattainability version (U) and the relation occurring between them. Then, we heuristically interpret (N) as a continuity boundary condition for thermodynamics at the boundary T=0 of the thermodynamic domain. On a rigorous mathematical footing, we discuss the third law both in Carath\'eodory's approach and in Gibbs' one. Carath\'eodory's approach is fundamental in order to understand the nature of the surface T=0. In fact, in this approach, under suitable mathematical conditions, T=0 appears as a leaf of the foliation of the thermodynamic manifold associated with the non-singular integrable Pfaffian form $\delta Q_{rev}$. Being a leaf, it cannot intersect any other leaf $S=$ const. of the foliation. We show that (N) is equivalent to the requirement that T=0 is a leaf. In Gibbs' approach, the peculiar nature of T=0 appears to be less evident because the existence of the entropy is a postulate; nevertheless, it is still possible to conclude that the lowest value of the entropy has to belong to the boundary of the convex set where the function is defined.Comment: 29 pages, 2 figures; RevTex fil

Manifestation of the electromagnetic proximity effect in superconductor-ferromagnet thin film structures

Using the newly emerged theory model of an electromagnetic proximity effect, we demonstrate that it provides a good description of our previously reported anomalous Meissner screening observed in thin film superconductor-ferromagnet proximity structures. Using the low energy muon spin rotation measurement technique, we further investigate this new theory by probing directly the flux screening in various superconductor-ferromagnet proximity structures. We examine its main characteristics and find in general good agreement between theory and experiment. Understanding and control of this new proximity effect is an important step forward toward a new generation of superconducting spintronic devices

‘It’s Kinda Punishment’: Tandem Logics and Penultimate Power in the Penal Voluntary Sector for Canadian Youth

This paper draws on original empirical research in Ontario, Canada which analyses penal voluntary sector practice with youth in conflict with the law. I illustrate how youth penal voluntary sector practice (YPVS) operates alongside, or in tandem with the statutory criminal justice system. I argue that examining the PVS and the statutory criminal justice system simultaneously, or in tandem, provides fuller understandings of PVS inclusionary (and exclusionary) control practices (Tomczak and Thompson 2017). I introduce the concept of penultimate power, which demonstrates the ability of PVS workers to trigger criminal justice system response toward a young person in conflict with the law. My novel concepts of tandem logics and penultimate power are useful for understanding PVS practice, explaining how seemingly contradictory approaches across state and ‘community’ organizations not only co-exist, but depend upon the tandem relationship between the PVS and the statutory criminal justice system

Clinical characteristics and airway inflammation profile of COPD persistent sputum producers

SummaryBackgroundCOPD patients with chronic bronchitis include a subgroup with persistent sputum production on most or every day. We hypothesized that COPD patients with persistent sputum production have a different profile of airway inflammation, and more severe clinical characteristics.ObjectiveTo compare the airway inflammation profile and clinical characteristics of COPD persistent and non-persistent sputum producers.MethodsCOPD persistent sputum producers (n = 26) and non-persistent sputum producers (n = 26) underwent sputum induction and pulmonary function tests. Exacerbation history was recorded; the St. George's Respiratory Questionnaire, Modified Medical Research Council Dyspnoea scale and COPD Assessment Tool were completed. 33 COPD patients provided sputum for bacteriology.ResultsPersistent sputum producers had lower post-bronchodilator FEV1% predicted (p = 0.01), diffusion capacity (p = 0.04), 6 min walk test distance (p = 0.05), and higher closing volume (p = 0.01), BODE index (p = 0.01), rate of bacterial colonization (p = 0.004) and exacerbations (p = 0.03) compared to non-persistent sputum producers. The mean SGRQ and CAT scores were higher in persistent sputum producers (p = 0.01 and 0.03 respectively). Sputum neutrophil and eosinophil total cell counts were higher in persistent sputum producers (p = 0.02 and 0.05 respectively). Sputum levels of eotaxin (p = 0.02), MCP-1 (p = 0.02), TNF-α (p = 0.03) and IL-6 (p = 0.05) were higher in persistent sputum producers.ConclusionCOPD persistent sputum producers have more severe clinical characteristics and increased concentrations of some inflammatory mediators in the airways

A Search for Dark Higgs Bosons

Recent astrophysical and terrestrial experiments have motivated the proposal of a dark sector with GeV-scale gauge boson force carriers and new Higgs bosons. We present a search for a dark Higgs boson using 516 fb-1 of data collected with the BABAR detector. We do not observe a significant signal and we set 90% confidence level upper limits on the product of the Standard Model-dark sector mixing angle and the dark sector coupling constant.Comment: 7 pages, 5 postscript figures, published version with improved plots for b/w printin