Possible first order transition in the two-dimensional Ginzburg-Landau model induced by thermally fluctuating vortex cores

We study the two-dimensional Ginzburg-Landau model of a neutral superfluid in the vicinity of the vortex unbinding transition. The model is mapped onto an effective interacting vortex gas by a systematic perturbative elimination of all fluctuating degrees of freedom (amplitude {\em and} phase of the order parameter field) except the vortex positions. In the Coulomb gas descriptions derived previously in the literature, thermal amplitude fluctuations were neglected altogether. We argue that, if one includes the latter, the vortices still form a two- dimensional Coulomb gas, but the vortex fugacity can be substantially raised. Under the assumption that Minnhagen's generic phase diagram of the two- dimensional Coulomb gas is correct, our results then point to a first order transition rather than a Kosterlitz-Thouless transition, provided the Ginzburg-Landau correlation length is large enough in units of a microscopic cutoff length for fluctuations. The experimental relevance of these results is briefly discussed. [Submitted to J. Stat. Phys.]Comment: 36 pages, LaTeX, 6 figures upon request, UATP2-DB1-9

Entropy and Spin Susceptibility of s-wave Type-II Superconductors near Hc2H_{c2}

A theoretical study is performed on the entropy $S_{\rm s}$ and the spin susceptibility $\chi_{\rm s}$ near the upper critical field $H_{c2}$ of s-wave type-II superconductors with arbitrary impurity concentrations. The changes of these quantities through $H_{c2}$ may be expressed as $[S_{\rm s}(T,B)-S_{\rm s}(T,0)]/[S_{\rm n}(T)-S_{\rm s}(T,0)]=1-\alpha_{S}(1-B/H_{c2})\approx (B/H_{c2})^{\alpha_{S}}$, for example, where $B$ is the average flux density and $S_{\rm n}$ denotes entropy in the normal state. It is found that the slopes $\alpha_{S}$ and $\alpha_{\chi}$ at T=0 are identical, connected directly with the zero-energy density of states, and vary from 1.72 in the dirty limit to $0.5\sim 0.6$ in the clean limit. This mean-free-path dependence of $\alpha_{S}$ and $\alpha_{\chi}$ at T=0 is quantitatively the same as that of the slope $\alpha_{\rho}(T=0)$ for the flux-flow resistivity studied previously. The result suggests that $S_{\rm s}(B)$ and $\chi_{\rm s}(B)$ near T=0 are convex downward (upward) in the dirty (clean) limit, deviating substantially from the linear behavior $\propto B/H_{c2}$. The specific-heat jump at $H_{c2}$ also shows fairly large mean-free-path dependence.Comment: 8 pages, 5 figure

Ginzburg-Landau theory of vortices in a multi-gap superconductor

The Ginzburg-Landau functional for a two-gap superconductor is derived within the weak-coupling BCS model. The two-gap Ginzburg-Landau theory is, then, applied to investigate various magnetic properties of MgB2 including an upturn temperature dependence of the transverse upper critical field and a core structure of an isolated vortex. Orientation of vortex lattice relative to crystallographic axes is studied for magnetic fields parallel to the c-axis. A peculiar 30-degree rotation of the vortex lattice with increasing strength of an applied field observed by neutron scattering is attributed to the multi-gap nature of superconductivity in MgB2.Comment: 11 page

Density Functional for Anisotropic Fluids

We propose a density functional for anisotropic fluids of hard body particles. It interpolates between the well-established geometrically based Rosenfeld functional for hard spheres and the Onsager functional for elongated rods. We test the new approach by calculating the location of the the nematic-isotropic transition in systems of hard spherocylinders and hard ellipsoids. The results are compared with existing simulation data. Our functional predicts the location of the transition much more accurately than the Onsager functional, and almost as good as the theory by Parsons and Lee. We argue that it might be suited to study inhomogeneous systems.Comment: To appear in J. Physics: Condensed Matte

The stable isotope composition of organic and inorganic fossils in lake sediment records: current understanding, challenges, and future directions

This paper provides an overview of stable isotope analysis (H, C, N, O, Si) of the macro and microscopic remains from aquatic organisms found in lake sediment records and their application in (palaeo)environmental science. Aquatic organisms, including diatoms, macrophytes, invertebrates, and fish, can produce sufficiently robust remains that preserve well as fossils and can be identified in lake sediment records. Stable isotope analyses of these remains can then provide valuable insights into habitat-specific biogeochemistry, feeding ecology, but also on climatic and hydrological changes in and around lakes. Since these analyses focus on the remains of known and identified organisms, they can provide more specific and detailed information on past ecosystem, food web and environmental changes affecting different compartments of lake ecosystems than analyses on bulk sedimentary organic matter or carbonate samples. We review applications of these types of analyses in palaeoclimatology, palaeohydrology, and palaeoecology. Interpretation of the environmental ‘signal’ provided by taxon-specific stable isotope analysis requires a thorough understanding of the ecology and phenology of the organism groups involved. Growth, metabolism, diet, feeding strategy, migration, taphonomy and several other processes can lead to isotope fractionation or otherwise influence the stable isotope signatures of the remains from aquatic organisms. This paper includes a review of the (modern) calibration, culturing and modeling studies used to quantify the extent to which these factors influence stable isotope values and provides an outlook for future research and methodological developments for the different examined fossil groups

The Shapes of Flux Domains in the Intermediate State of Type-I Superconductors

In the intermediate state of a thin type-I superconductor magnetic flux penetrates in a disordered set of highly branched and fingered macroscopic domains. To understand these shapes, we study in detail a recently proposed "current-loop" (CL) model that models the intermediate state as a collection of tense current ribbons flowing along the superconducting-normal interfaces and subject to the constraint of global flux conservation. The validity of this model is tested through a detailed reanalysis of Landau's original conformal mapping treatment of the laminar state, in which the superconductor-normal interfaces are flared within the slab, and of a closely-related straight-lamina model. A simplified dynamical model is described that elucidates the nature of possible shape instabilities of flux stripes and stripe arrays, and numerical studies of the highly nonlinear regime of those instabilities demonstrate patterns like those seen experimentally. Of particular interest is the buckling instability commonly seen in the intermediate state. The free-boundary approach further allows for a calculation of the elastic properties of the laminar state, which closely resembles that of smectic liquid crystals. We suggest several new experiments to explore of flux domain shape instabilities, including an Eckhaus instability induced by changing the out-of-plane magnetic field, and an analog of the Helfrich-Hurault instability of smectics induced by an in-plane field.Comment: 23 pages, 22 bitmapped postscript figures, RevTex 3.0, submitted to Phys. Rev. B. Higher resolution figures may be obtained by contacting the author

Technical assessment of compressed hydrogen storage tank systems for automotive applications.

The performance and cost of compressed hydrogen storage tank systems has been assessed and compared to the U.S. Department of Energy (DOE) 2010, 2015, and ultimate targets for automotive applications. The on-board performance and high-volume manufacturing cost were determined for compressed hydrogen tanks with design pressures of 350 bar ({approx}5000 psi) and 700 bar ({approx}10,000 psi) capable of storing 5.6 kg of usable hydrogen. The off-board performance and cost of delivering compressed hydrogen was determined for hydrogen produced by central steam methane reforming (SMR). The main conclusions of the assessment are that the 350-bar compressed storage system has the potential to meet the 2010 and 2015 targets for system gravimetric capacity but will not likely meet any of the system targets for volumetric capacity or cost, given our base case assumptions. The 700-bar compressed storage system has the potential to meet only the 2010 target for system gravimetric capacity and is not likely to meet any of the system targets for volumetric capacity or cost, despite the fact that its volumetric capacity is much higher than that of the 350-bar system. Both the 350-bar and 700-bar systems come close to meeting the Well-to-Tank (WTT) efficiency target, but fall short by about 5%. These results are summarized

Observations of the microphysical evolution of convective clouds in the southwest of the United Kingdom

The COnvective Precipitation Experiment (COPE) was designed to investigate the origins of heavy convective precipitation over the southwestern UK, a region that experiences flash flooding due to heavy precipitation from slow-moving convective systems. In this study, the microphysical and dynamical characteristics of developing turrets during 4 days in July and August 2013 are analyzed. In situ cloud microphysical measurements from the University of Wyoming King Air and vertically pointing W-band radar measurements from Wyoming Cloud Radar are examined, together with data from the ground-based NXPol radar. The 4 days presented here cover a range of environmental conditions in terms of wind shear and instability, resulting in a similarly wide variability in observed ice crystal concentrations, both across days as well as between clouds on individual days. The highest concentration of ice was observed on the days in which there was an active warm-rain process supplying precipitation-sized liquid drops. The high ice concentrations observed ( > 100L−1) are consistent with the production of secondary ice particles through the Hallett–Mossop process. Turrets that ascended through remnant cloud layers above the 0°C level had higher ice particle concentrations, suggesting that entrainment of ice particles from older clouds or previous thermals may have acted to aid in the production of secondary ice through the Hallett–Mossop process. Other mechanisms such as the shattering of frozen drops may be more important for producing ice in more isolated clouds

Timeliness of contact tracing among flight passengers for influenza A/H1N1 2009

<p>Abstract</p> <p>Background</p> <p>During the initial containment phase of influenza A/H1N1 2009, close contacts of cases were traced to provide antiviral prophylaxis within 48 h after exposure and to alert them on signs of disease for early diagnosis and treatment. Passengers seated on the same row, two rows in front or behind a patient infectious for influenza, during a flight of ≥ 4 h were considered close contacts. This study evaluates the timeliness of flight-contact tracing (CT) as performed following national and international CT requests addressed to the Center of Infectious Disease Control (CIb/RIVM), and implemented by the Municipal Health Services of Schiphol Airport.</p> <p>Methods</p> <p>Elapsed days between date of flight arrival and the date passenger lists became available (contact details identified - CI) was used as proxy for timeliness of CT. In a retrospective study, dates of flight arrival, onset of illness, laboratory diagnosis, CT request and identification of contacts details through passenger lists, following CT requests to the RIVM for flights landed at Schiphol Airport were collected and analyzed.</p> <p>Results</p> <p>24 requests for CT were identified. Three of these were declined as over 4 days had elapsed since flight arrival. In 17 out of 21 requests, contact details were obtained within 7 days after arrival (81%). The average delay between arrival and CI was 3,9 days (range 2-7), mainly caused by delay in diagnosis of the index patient after arrival (2,6 days). In four flights (19%), contacts were not identified or only after > 7 days. CI involving Dutch airlines was faster than non-Dutch airlines (<it>P </it>< 0,05). Passenger locator cards did not improve timeliness of CI. In only three flights contact details were identified within 2 days after arrival.</p> <p>Conclusion</p> <p>CT for influenza A/H1N1 2009 among flight passengers was not successful for timely provision of prophylaxis. CT had little additional value for alerting passengers for disease symptoms, as this information already was provided during and after the flight. Public health authorities should take into account patient delays in seeking medical advise and laboratory confirmation in relation to maximum time to provide postexposure prophylaxis when deciding to install contact tracing measures. International standardization of CT guidelines is recommended.</p