Some Characteristics of Polar Bears Killed during Conflicts with Humans in the Northwest Territories, 1976-86

We examined 265 cases where polar bears were killed in the Northwest Territories as a result of bear-human encounters between 1 July 1976 and 30 June 1986. Age and sex of the bears, time of year and general circumstances of the cases were characterized. Subadult animals constituted 53% of the aged sample, and males accounted for 70% of the sexed bears. Subadult males represented 40% of known age and sex bears. Problem kills occurred throughout the year but were most frequent in the ice-free season (August-November). In 222 cases where circumstances surrounding the death were known, 63% were associated with Inuit on the land, 18% with settlements, 15% were industrial sites and 4% with research activities. Most problem kills (87%) were not included in the quota harvest. This mortality in excess of the quota may adversely affect some populations. Therefore, wherever possible we encourage the inclusion of problem bears on community quotas.Key words: polar bear (Ursus maritimus), problem bears, bear-human encounters, Arctic, Northwest TerritoriesMots clés: ours polaire (Ursus maririmus), ours-problèmes, rencontres entre l’homme et l’ours, Arctique, Territoires du Nord-Oues

On the controllability of bimodal piecewise linear systems

This paper studies controllability of bimodal systems that consist of two linear dynamics on each side of a given hyperplane. We show that the controllability properties of these systems can be inferred from those of linear systems for which the inputs are constrained in a certain way. Inspired by the earlier work on constrained controllability of linear systems, we derive necessary and sufficient conditions for a bimodal piecewise linear system to be controllable.Natl Sci Fdn; Univ Penn, Sch Engn & Appl Sci

The influence of the aortic valve angle on the hemodynamic features of the thoracic aorta

Since the first observation of a helical flow pattern in aortic blood flow, the existence of helical blood flow has been found to be associated with various pathological conditions such as bicuspid aortic valve, aortic stenosis, and aortic dilatation. However, an understanding of the development of helical blood flow and its clinical implications are still lacking. In our present study, we hypothesized that the direction and angle of aortic inflow can influence helical flow patterns and related hemodynamic features in the thoracic aorta. Therefore, we investigated the hemodynamic features in the thoracic aorta and various aortic inflow angles using patient-specific vascular phantoms that were generated using a 3D printer and time-resolved, 3D, phase-contrast magnetic resonance imaging (PC-MRI). The results show that the rotational direction and strength of helical blood flow in the thoracic aorta largely vary according to the inflow direction of the aorta, and a higher helical velocity results in higher wall shear stress distributions. In addition, right-handed rotational flow conditions with higher rotational velocities imply a larger total kinetic energy than left-handed rotational flow conditions with lower rotational velocities.115Ysciescopu

Kinetic energy driven superconductivity in doped cuprates

Within the t-J model, the mechanism of superconductivity in doped cuprates is studied based on the partial charge-spin separation fermion-spin theory. It is shown that dressed holons interact occurring directly through the kinetic energy by exchanging dressed spinon excitations, leading to a net attractive force between dressed holons, then the electron Cooper pairs originating from the dressed holon pairing state are due to the charge-spin recombination, and their condensation reveals the superconducting ground-state. The electron superconducting transition temperature is determined by the dressed holon pair transition temperature, and is proportional to the concentration of doped holes in the underdoped regime. With the common form of the electron Cooper pair, we also show that there is a coexistence of the electron Cooper pair and antiferromagnetic short-range correlation, and hence the antiferromagnetic short-range fluctuation can persist into the superconducting state. Our results are qualitatively consistent with experiments.Comment: 6 pages, Revtex, two figures are included, corrected typo

Generalized canonical quantization of bosonic string model in massive background fields

A method of constructing a canonical gauge invariant quantum formulation for a non-gauge classical theory depending on a set of parameters is advanced and then applied to the theory of closed bosonic string interacting with massive background fields. It is shown that within the proposed formulation the correct linear equations of motion for background fields arise.Comment: 4 pages, LaTeX, talk given by I.L. Buchbinder at the Second Conference on Constrained Dynamics and Quantum Gravity, S. Margherita Ligure, September 17-21 199

Moment of Inertia and Quadrupole Response Function of a Trapped Superfluid

We derive an explicit relationship between the moment of inertia and the quadrupole response function of an interacting gas confined in a harmonic trap. The relationship holds for both Bose and Fermi systems and is well suited to reveal the effects of irrotationality of the superfluid motion. Recent experimental results on the scissors mode are used to extract the value of the moment of inertia of a trapped Bose gas and to point out the deviations from the rigid value due to superfluidity.Comment: 6 page

Localized Tachyons and the Quantum McKay Correspondence

The condensation of closed string tachyons localized at the fixed point of a C^d/\Gamma orbifold can be studied in the framework of renormalization group flow in a gauged linear sigma model. The evolution of the Higgs branch along the flow describes a resolution of singularities via the process of tachyon condensation. The study of the fate of D-branes in this process has lead to a notion of a ``quantum McKay correspondence.'' This is a hypothetical correspondence between fractional branes in an orbifold singularity in the ultraviolet with the Coulomb and Higgs branch branes in the infrared. In this paper we present some nontrivial evidence for this correspondence in the case C^2/Z_n by relating the intersection form of fractional branes to that of ``Higgs branch branes,'' the latter being branes which wrap nontrivial cycles in the resolved space.Comment: 25 pages; harvma

Dynamical Gauge Conditions for the Einstein Evolution Equations

The Einstein evolution equations have been written in a number of symmetric hyperbolic forms when the gauge fields--the densitized lapse and the shift--are taken to be fixed functions of the coordinates. Extended systems of evolution equations are constructed here by adding the gauge degrees of freedom to the set of dynamical fields, thus forming symmetric hyperbolic systems for the combined evolution of the gravitational and the gauge fields. The associated characteristic speeds can be made causal (i.e. less than or equal to the speed of light) by adjusting 14 free parameters in these new systems. And 21 additional free parameters are available, for example to optimize the stability of numerical evolutions. The gauge evolution equations in these systems are generalizations of the ``K-driver'' and ``Gamma-driver'' conditions that have been used with some success in numerical black hole evolutions.Comment: New appendix on constraint evolution adde

Quasiparticles as composite objects in the RVB superconductor

We study the nature of the superconducting state, the origin of d-wave pairing, and elementary excitations of a resonating valence bond (RVB) superconductor. We show that the phase string formulation of the t-J model leads to confinement of bare spinon and holon excitations in the superconducting state, though the vacuum is described by the RVB state. Nodal quasiparticles are obtained as composite excitations of spinon and holon excitations. The d-wave pairing symmetry is shown to arise from short range antiferromagnetic correlations