Superconductors with Magnetic Impurities: Instantons and Sub-gap States

When subject to a weak magnetic impurity potential, the order parameter and quasi-particle energy gap of a bulk singlet superconductor are suppressed. According to the conventional mean-field theory of Abrikosov and Gor'kov, the integrity of the energy gap is maintained up to a critical concentration of magnetic impurities. In this paper, a field theoretic approach is developed to critically analyze the validity of the mean field theory. Using the supersymmetry technique we find a spatially homogeneous saddle-point that reproduces the Abrikosov-Gor'kov theory, and identify instanton contributions to the density of states that render the quasi-particle energy gap soft at any non-zero magnetic impurity concentration. The sub-gap states are associated with supersymmetry broken field configurations of the action. An analysis of fluctuations around these configurations shows how the underlying supersymmetry of the action is restored by zero modes. An estimate of the density of states is given for all dimensionalities. To illustrate the universality of the present scheme we apply the same method to study `gap fluctuations' in a normal quantum dot coupled to a superconducting terminal. Using the same instanton approach, we recover the universal result recently proposed by Vavilov et al. Finally, we emphasize the universality of the present scheme for the description of gap fluctuations in d-dimensional superconducting/normal structures.Comment: 18 pages, 9 eps figure

Whipworm genome and dual-species transcriptome analyses provide molecular insights into an intimate host-parasite interaction.

Whipworms are common soil-transmitted helminths that cause debilitating chronic infections in man. These nematodes are only distantly related to Caenorhabditis elegans and have evolved to occupy an unusual niche, tunneling through epithelial cells of the large intestine. We report here the whole-genome sequences of the human-infective Trichuris trichiura and the mouse laboratory model Trichuris muris. On the basis of whole-transcriptome analyses, we identify many genes that are expressed in a sex- or life stage-specific manner and characterize the transcriptional landscape of a morphological region with unique biological adaptations, namely, bacillary band and stichosome, found only in whipworms and related parasites. Using RNA sequencing data from whipworm-infected mice, we describe the regulated T helper 1 (TH1)-like immune response of the chronically infected cecum in unprecedented detail. In silico screening identified numerous new potential drug targets against trichuriasis. Together, these genomes and associated functional data elucidate key aspects of the molecular host-parasite interactions that define chronic whipworm infection

Robust multi-disciplinary design and optimisation of a reusable launch vehicle

For various technical reasons, no fully reusable launch vehicle has ever been successfully constructed or operated. Nonetheless, a range of reusable hypersonic vehicles is currently being considered as a viable alternative to the expensive but more conventional expendable rocket systems that are currently being used to gain access to space. This paper presents a methodology that has been developed for the rapid and efficient preliminary design of such vehicles. The methodology that is presented uses multi-disciplinary design optimization coupled with an integrated set of reduced-order models to estimate the characteristics of the vehicle's aero-thermodynamic, propulsion, thermal protection and internal system architecture, as well as to estimate its overall mass. In the present work, the methodology has been applied to the multi-disciplinary modelling and optimization of a reusable hybrid rocket- and ramjet-powered launch vehicle during both the ascent and re-entry phases of its mission

Mission-Integrated Exergy Analysis for Hypersonic Vehicles: Methodology and Application

Recently developed theoretical work in which energy (the first law of thermodynamics) and entropy (the second law of thermodynamics) considerations are consistently applied to aerospace vehicles is used to provide a detailed exergy (availability) and performance analysis for an airbreathing hypersonic vehicle. An acceleration and climb mission at constant freestream dynamic pressure is performed with detailed instantaneous and time-integrated audits of entropy generation in and over the vehicle and in the vehicle wake. Entropy generation in the vehicle wake ranges from five to eight times the total entropy generation in and over the vehicle. The impact of irreversibility occurring in and over the vehicle itself on the total entropy generation in the wake is a small fraction of the overall wake losses. Fifteen percent of the overall energy input during the mission actually goes into productive acceleration and climb. The remainder is associated with the generation of entropy due to irreversibility in and over the vehicle and in the vehicle wake. The propulsion system is responsible for almost all entropy generation associated solely with the vehicle (excluding the overwhelmingly dominant contribution of the vehicle wake), and entropy generation in the combustor alone represents 85% of the total propulsion system loss

Influence of boundary layer transition on the trajectory optimisation of a reusable launch vehicle

Based on flight experience from the Space Shuttle programme, it is well known that mis-prediction of the effects of boundary layer transition represents one of the highest technical risks when designing a Reusable Launch Vehicle. Indeed, mis-prediction of the boundary layer behaviour at hypersonic speeds could impinge on the overall survivability of a given design, whereas excessive conservatism in the analyses could result in an overweight vehicle not capable of attaining orbit with a useful payload mass on-board. From the standpoint of conceptual design, it is therefore of paramount importance to develop engineering means of predicting the effects of uncertainty in the behaviour of the boundary layer on the vehicle as far as transition is concerned. Indeed, a robust preliminary analysis should ensure thermal survival of the spaceplane structure and give a measure of confidence in the ability of the conceptual vehicle to maintain sufficiently good controllability during re-entry in the presence of possibly asymmetric boundary layer transition. A reduced-order model has been used to evaluate the sensitivity of a particular design of hypersonic reusable launch vehicle to the uncertainty in predicting its aero-thermodynamic behavior that results from variability in the onset of boundary layer transition on its surface, especially when optimising the re-entry trajectory of the vehicle. The results of the simulations presented here seem to suggest that the effects of boundary layer transition on the vehicle's performance during re-entry might largely be ameliorated through careful aerodynamic design and appropriate scheduling of the control surface deflections along the vehicle's trajectory

Minimum-Fuel Ascent of a Hypersonic Vehicle Using Surrogate Optimization

Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/140593/1/1.c032617.pd