The electronic specific heat in the pairing pseudogap regime

When pairing correlations in a quasi two dimensional electron system induce a pseudogap in the single particle density of states, the specific heat must also contain a sizeable pair contribution. The theoretically calculated specific heat for such a system is compared to the experimental results of Loram and his collaborators for underdoped YBa_2Cu_3O_{6+x} and La_{2-x}Sr_{x}CuO_4 samples. The size and doping dependence of the extracted pseudogap energy scale for both materials is comparable to the values obtained from a variety of other experiments.Comment: 4 pages, 5 eps figure

Immunohistochemical detection of haemoglobin subunit epsilon (HBE) in the developing mouse placenta

Introduction: Haemoglobin is a widely studied protein due to its important roles in physiology and pathology. Aberrant expression of haemoglobins, including primitive globins, have been reported in various sites and disease states and may have utility in some instances as diagnostic and/or prognostic markers. Despite this, robust detection of haemoglobin epsilon in the placenta during development by immunohistochemistry has not been well documented. Aim: To evaluate a polyclonal antibody against human haemoglobin subunit epsilon (HBE) by immunohistochemistry during primitive erythropoiesis in the developing mouse placenta. Methods and results: An immunohistochemistry protocol was developed using a commercially available anti-human haemoglobin subunit epsilon antibody on the mouse placenta at embryonic day 11.5. Strong and specific cytoplasmic staining was observed in primitive erythroid cells within the blood cell islands. By contrast, the placenta endothelium, mesothelium and mesoderm were all immunonegative for epsilon haemoglobin. Conclusions: An immunohistochemistry protocol for the specific detection of epsilon haemoglobin was successfully developed using mouse placenta tissue. This assay has utility as a tool for the study of erythropoiesis during development and/or detecting the ectopic expression of epsilon globins in disease states such as cancer

Point-contact Andreev reflection spectroscopy of heavy-fermion-metal/superconductor junctions

Our previous point-contact Andreev reflection studies of the heavy-fermion superconductor CeCoIn$_5$ using Au tips have shown two clear features: reduced Andreev signal and asymmetric background conductance [1]. To explore their physical origins, we have extended our measurements to point-contact junctions between single crystalline heavy-fermion metals and superconducting Nb tips. Differential conductance spectra are taken on junctions with three heavy-fermion metals, CeCoIn$_5$, CeRhIn$_5$, and YbAl$_3$, each with different electron mass. In contrast with Au/CeCoIn$_5$ junctions, Andreev signal is not reduced and no dependence on effective mass is observed. A possible explanation based on a two-fluid picture for heavy fermions is proposed. [1] W. K. Park et al., Phys. Rev. B 72 052509 (2005); W. K. Park et al., Proc. SPIE-Int. Soc. Opt. Eng. 5932 59321Q (2005); W. K. Park et al., Physica C (in press) (cond-mat/0606535).Comment: 2 pages, 2 figures, submitted to the SCES conference, Houston, Texas, USA, May 13-18, 200

Mechanisms of Spontaneous Current Generation in an Inhomogeneous d-Wave Superconductor

A boundary between two d-wave superconductors or an s-wave and a d-wave superconductor generally breaks time-reversal symmetry and can generate spontaneous currents due to proximity effect. On the other hand, surfaces and interfaces in d-wave superconductors can produce localized current-carrying states by supporting the T-breaking combination of dominant and subdominant order parameters. We investigate spontaneous currents in the presence of both mechanisms and show that at low temperature, counter-intuitively, the subdominant coupling decreases the amplitude of the spontaneous current due to proximity effect. Superscreening of spontaneous currents is demonstrated to be present in any d-d (but not s-d) junction and surface with d+id' order parameter symmetry. We show that this supercreening is the result of contributions from the local magnetic moment of the condensate to the spontaneous current.Comment: 4 pages, 5 figures, RevTe

Vacuum fluctuations and topological Casimir effect in Friedmann-Robertson-Walker cosmologies with compact dimensions

We investigate the Wightman function, the vacuum expectation values of the field squared and the energy-momentum tensor for a massless scalar field with general curvature coupling parameter in spatially flat Friedmann-Robertson-Walker universes with an arbitrary number of toroidally compactified dimensions. The topological parts in the expectation values are explicitly extracted and in this way the renormalization is reduced to that for the model with trivial topology. In the limit when the comoving lengths of the compact dimensions are very short compared to the Hubble length, the topological parts coincide with those for a conformal coupling and they are related to the corresponding quantities in the flat spacetime by standard conformal transformation. In the opposite limit of large comoving lengths of the compact dimensions, in dependence of the curvature coupling parameter, two regimes are realized with monotonic or oscillatory behavior of the vacuum expectation values. In the monotonic regime and for nonconformally and nonminimally coupled fields the vacuum stresses are isotropic and the equation of state for the topological parts in the energy density and pressures is of barotropic type. In the oscillatory regime, the amplitude of the oscillations for the topological part in the expectation value of the field squared can be either decreasing or increasing with time, whereas for the energy-momentum tensor the oscillations are damping.Comment: 20 pages, 2 figure

Noninteracting dark matter

Since an acceptable dark matter candidate may interact only weakly with ordinary matter and radiation, it is of interest to consider the limiting case where the dark matter interacts only with gravity and itself, the matter originating by the gravitational particle production at the end of inflation. We use the bounds on the present dark mass density and the measured large-scale fluctuations in the thermal cosmic background radiation to constrain the two parameters in a self-interaction potential that is a sum of quadratic and quartic terms in a single scalar dark matter field that is minimally coupled to gravity. In quintessential inflation, where the temperature at the end of inflation is relatively low, the field starts acting like cold dark matter relatively late, shortly before the epoch of equal mass densities in matter and radiation. This could have observable consequences for galaxy formation. We respond to recent criticisms of the quintessential inflation scenario, since these issues also apply to elements of the noninteracting dark matter picture.Comment: 37 pages, 3 figure

Local and macroscopic tunneling spectroscopy of Y(1-x)CaxBa2Cu3O(7-d) films: evidence for a doping dependent is or idxy component in the order parameter

Tunneling spectroscopy of epitaxial (110) Y1-xCaxBa2Cu3O7-d films reveals a doping dependent transition from pure d(x2-y2) to d(x2-y2)+is or d(x2-y2)+idxy order parameter. The subdominant (is or idxy) component manifests itself in a splitting of the zero bias conductance peak and the appearance of subgap structures. The splitting is seen in the overdoped samples, increases systematically with doping, and is found to be an inherent property of the overdoped films. It was observed in both local tunnel junctions, using scanning tunneling microscopy (STM), and in macroscopic planar junctions, for films prepared by either RF sputtering or laser ablation. The STM measurements exhibit fairly uniform splitting size in [110] oriented areas on the order of 10 nm2 but vary from area to area, indicating some doping inhomogeneity. U and V-shaped gaps were also observed, with good correspondence to the local faceting, a manifestation of the dominant d-wave order parameter

Quasiclassical description of transport through superconducting contacts

We present a theoretical study of transport properties through superconducting contacts based on a new formulation of boundary conditions that mimics interfaces for the quasiclassical theory of superconductivity. These boundary conditions are based on a description of an interface in terms of a simple Hamiltonian. We show how this Hamiltonian description is incorporated into quasiclassical theory via a T-matrix equation by integrating out irrelevant energy scales right at the onset. The resulting boundary conditions reproduce results obtained by conventional quasiclassical boundary conditions, or by boundary conditions based on the scattering approach. This formalism is well suited for the analysis of magnetically active interfaces as well as for calculating time-dependent properties such as the current-voltage characteristics or as current fluctuations in junctions with arbitrary transmission and bias voltage. This approach is illustrated with the calculation of Josephson currents through a variety of superconducting junctions ranging from conventional to d-wave superconductors, and to the analysis of supercurrent through a ferromagnetic nanoparticle. The calculation of the current-voltage characteristics and of noise is applied to the case of a contact between two d-wave superconductors. In particular, we discuss the use of shot noise for the measurement of charge transferred in a multiple Andreev reflection in d-wave superconductors

Project manager-to-project allocations in practice: an empirical study of the decision-making practices of a multi-project based organization

Empirical studies that examine how managers make project manager-to-project (PM2P) allocation decisions in multi-project settings are currently limited. Such decisions are crucial to organizational success. An empirical study of the PM2P practice, conducted in the context of Botswana, revealed ineffective processes in terms of optimality in decision-making. A conceptual model to guide effective PM2P practices was developed. The focus of this study is on deploying the model as a lens to study the PM2P practices of a large organization, with a view to identify and illustrate strengths and weaknesses. A case study was undertaken in the mining industry, where core activities in terms of projects are underground mineral explorations at identified geographical regions. A semi-structured interview protocol was used to collect data from 15 informants, using an enumeration. Integrated analysis of both data types (using univariate descriptive analysis for the quantitative data, content and thematic analysis for the qualitative data) revealed strengths in PM2P practices, demonstrated by informants’ recognition of some important criteria to be considered. The key weaknesses were exemplified by a lack of effective management tools and techniques to match project managers to projects. The findings provide a novel perspective through which improvements in working practices can be made

Inflation and Preheating in NO models

We study inflationary models in which the effective potential of the inflaton field does not have a minimum, but rather gradually decreases at large $\phi$. In such models the inflaton field does not oscillate after inflation, and its effective mass becomes vanishingly small, so the standard theory of reheating based on the decay of the oscillating inflaton field does not apply. For a long time the only mechanism of reheating in such non-oscillatory (NO) models was based on gravitational particle production in an expanding universe. This mechanism is very inefficient. We will show that it may lead to cosmological problems associated with large isocurvature fluctuations and overproduction of dangerous relics such as gravitinos and moduli fields. We also note that the setting of initial conditions for the stage of reheating in these models should be reconsidered. All of these problems can be resolved in the context of the recently proposed scenario of instant preheating if there exists an interaction ${g^2} \phi^2\chi^2$ of the inflaton field $\phi$ with another scalar field $\chi$. We show that the mechanism of instant preheating in NO models is much more efficient than the usual mechanism of gravitational particle production even if the coupling constant $g^2$ is extremely small, $10^{-14} \ll g^2 \ll 1$.Comment: 10 pages, revte