Anomalous Behavior of the Upper Critical Field in Extreme Type-II Superconductors at Low Temperatures

We present a detailed numerical calculation of the upper critical field $H_{c2}(T)$ for a bulk extreme type-II superconductor. Particular emphasis is placed on the high-field, low-temperature regime of the HT-phase diagram. In this regime it is necessary to go beyond the standard semi-classical theory and include the effects of Landau quantization of the electronic motion on the superconducting state. The presence of Landau level quantization induces an upward curvature in $H_{c2}(T)$ at $\sim 10$ of $T_{c0}$ for those superconducting systems in which the slope of $H_{c2}(T)$ at $T_{c0}$ is $\geq$ 0.2 Tesla/Kelvin. We construct a simple analytical model that can account for this behavior based on the renormalization of the BCS coupling constant by the off-diagonal pairing of electrons on Landau levels.Comment: 13 pages, Revtex, 3 ps figures, to appear in Physica

Low-Temperature Specific Heat of an Extreme-Type-II Superconductor at High Magnetic Fields

We present a detailed study of the quasiparticle contribution to the low-temperature specific heat of an extreme type-II superconductor at high magnetic fields. Within a T-matrix approximation for the self-energies in the mixed state of a homogeneous superconductor, the electronic specific heat is a linear function of temperature with a linear-$T$ coefficient $\gamma_s(H)$ being a nonlinear function of magnetic field $H$. In the range of magnetic fields H\agt (0.15-0.2)H_{c2} where our theory is applicable, the calculated $\gamma_s(H)$ closely resembles the experimental data for the borocarbide superconductor YNi$_2$B$_2$C.Comment: 7 pages, 2 figures, to appear in Physical Review

A Simple Model For the Intermolecular Interactions in Halogene Crystals

A simple effective atom-atom intermolecular potential for halogene solids (F2, Cl-, Br2 and 12) is proposed. The centers of inter action of the effective potential (6-exp type) are shifted from\u27 the atomic sites in order to reduce anisotropy of the intermolecular distances. The calculated results of the static properties for fluorine and chlorine are in good agreement with the experimental results. The calculated results for bromine and iodine crystals are less satisfactory. The limitations of the atom-atom model for description of the dynamical properties of halogene solids are also briefly discusse

A Simple Model For the Intermolecular Interactions in Halogene Crystals

A simple effective atom-atom intermolecular potential for halogene solids (F2, Cl-, Br2 and 12) is proposed. The centers of inter action of the effective potential (6-exp type) are shifted from\u27 the atomic sites in order to reduce anisotropy of the intermolecular distances. The calculated results of the static properties for fluorine and chlorine are in good agreement with the experimental results. The calculated results for bromine and iodine crystals are less satisfactory. The limitations of the atom-atom model for description of the dynamical properties of halogene solids are also briefly discusse

Quasiparticle spectrum of a type-II superconductor in a high magnetic field with randomly pinned vortices

We show that gapless superconductivity of a strongly type-II superconductor in a high magnetic field prevails in the presence of disorder, suggesting a topological nature. We calculate the density of states of the Bogoliubov-de Gennes quasiparticles for a two-dimensional inhomogeneous system in both cases of weak and strong disorder. In the limit of very weak disorder, the effect is very small and the density of states is not appreciably changed. As the disorder increases, the density of states at low energies increases and the ratio of the low-energy density of states to its maximum increases significantly

Density of states of a type-II superconductor in a high magnetic field: Impurity effects

We have calculated the density of states $N(\omega)$ of a dirty but homogeneous superconductor in a high magnetic field. We assume a dilute concentration of scalar impurities and find how $N(\omega)$ behaves as one crosses from the weak scattering to the strong scattering limit. At low energies, $N(\omega)\sim \omega ^2$ for small values of the impurity concentration and scattering strength. When the disorder becomes stronger than some critical value, a finite density of states is created at the Fermi surface. These results are a consequence of the gapless nature of the quasiparticle excitation spectrum in a high magnetic field.Comment: 20 pages in RevTeX, 4 figures, to appear in Phys. Rev. B (July 1, 1997

Particle Filter for Fault Diagnosis and Robust Navigation of Underwater Robot

This article has been accepted for inclusion in a future issue of this journal. Content is final as presented, with the exception of pagination. © IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other users, including reprinting/ republishing this material for advertising or promotional purposes, creating new collective works for resale or redistribution to servers or lists, or reuse of any copyrighted components of this work in other works.A particle filter (PF)-based robust navigation with fault diagnosis (FD) is designed for an underwater robot, where 10 failure modes of sensors and thrusters are considered. The nominal underwater robot and its anomaly are described by a switching-mode hidden Markov model. By extensively running a PF on the model, the FD and robust navigation are achieved. Closed-loop full-scale experimental results show that the proposed method is robust, can diagnose faults effectively, and can provide good state estimation even in cases where multiple faults occur. Comparing with other methods, the proposed method can diagnose all faults within a single structure, it can diagnose simultaneous faults, and it is easily implemented

Differences in forms and frequency of peer violence between primary and secondary school students

Rad omogućava razumijevanje vršnjačkog nasilja, njegovih pojavnih oblika kao i detaljnu analizu razlika u oblicima i učestalosti vršnjačkog nasilja između učenika osnovnih i srednjih škola, dobivenih provedenim istraživanjem. Nasilje među djecom definira se kao opetovana ili trajna izloženost učenika negativnim postupcima jednoga učenika ili više njih, a naglasak je u radu stavljen na oblike i uzroke nasilnog ponašanja kao i na sve sudionike kruga nasilja. U radu su detaljno opisane karakteristike nasilnika, žrtve i promatrača kako bi se pravovremenim uočavanjem navedenih karakteristika moglo spriječiti nasilničko ponašanje, a samim tim u umanjiti negativne posljedice.Work enables understanding of peer violence and it's manifestations as well as a detailed analysis of differences in forms and frequency of peer violence between primary and secondary school students obtained through the research. Violence among children is defined as repeated or permanent exposure of students to the negative actions of one or more students, and the emphasis is placed on the forms and causes of violent behavior, as well as on all participants in the circle of violence. The paper describes in detail the characteristics of the abuser, the victim and the observer, so that timely identification of these characteristics can prevent violent behavior and thus reduce the negative consequences

Absence of Persistent Magnetic Oscillations in Type-II Superconductors

We report on a numerical study intended to examine the possibility that magnetic oscillations persist in type II superconductors beyond the point where the pairing self-energy exceeds the normal state Landau level separation. Our work is based on the self-consistent numerical solution for model superconductors of the Bogoliubov-deGennes equations for the vortex lattice state. In the regime where the pairing self-energy is smaller than the cyclotron energy, magnetic oscillations resulting from Landau level quantization are suppressed by the broadening of quasiparticle Landau levels due to the non-uniform order parameter of the vortex lattice state, and by splittings of the quasiparticle bands. Plausible arguments that the latter effect can lead to a sign change of the fundamental harmonic of the magnetic oscillations when the pairing self-energy is comparable to the cyclotron energy are shown to be flawed. Our calculations indicate that magnetic oscillations are strongly suppressed once the pairing self-energy exceeds the Landau level separation.Comment: 7 pages, revtex, 7 postscript figure