Proper Motion of the Crab Pulsar Revisited

It has been suggested that the Crab pulsar's proper motion is well aligned with the symmetry axis of the pulsar wind nebula. We have re-visited this question, examining over 6 years of F547M WFPC2 chip 3 images to obtain a best-fit value of $\mu_\ast = 14.9 \pm 0.8$mas/yr at PA 278\arcdeg \pm 3\arcdeg. At 26\arcdeg\pm 3\arcdeg to the nebula axis, this substantially relaxes constraints on the birth kick of this pulsar. Such misalignment allows the momentum to be imparted over $\sim$1s timescales.Comment: 10 pages, 3 figures, accepted for publication in Ap

Stability of conductance oscillations in monatomic sodium wires

We study the stability of conductance oscillations in monatomic sodium wires with respect to structural variations. The geometry, the electronic structure and the electronic potential of sodium wires suspended between two sodium electrodes are obtained from self-consistent density functional theory calculations. The conductance is calculated within the framework of the Landauer-B\"utttiker formalism, using the mode-matching technique as formulated recently in a real-space finite-difference scheme [Phys. Rev. B \textbf{70}, 195402 (2004)]. We find a regular even-odd conductance oscillation as a function of the wire length, where wires comprising an odd number of atoms have a conductance close to the quantum unit $G_0=e^2/\pi\hbar$, and even-numbered wires have a lower conductance. The conductance of odd-numbered wires is stable with respect to geometry changes in the wire or in the contacts between the wire and the electrodes; the conductance of even-numbered wires is more sensitive. Geometry changes affect the spacing and widths of the wire resonances. In the case of odd-numbered wires the transmission is on-resonance, and hardly affected by the resonance shapes, whereas for even-numbered wires the transmission is off-resonance and sensitive to the resonance shapes. Predicting the amplitude of the conductance oscillation requires a first-principles calculation based upon a realistic structure of the wire and the leads. A simple tight-binding model is introduced to clarify these results.Comment: 16 pages, 20 figure

Grand Circus Park

Printed on image below title: "Copyrighted Nov. 10, 1914 by F. L. Wychoff, 48 Adams Ave. West."Copyright deposit; F. L. Wychoff; November 11, 1914; DLC/PP-1914:44851

Structural characterization of Lu0.7Y0..3AlO3 single crystal by Raman spectroscopy

Lutetium yttrium orthoaluminate perovskite [Lu0.7Y0.3AlO3 (LuYAP)] crystals show great potential as fast response and highefficiency scintillators as an alternative to LuAlO3 (LuAP) crystals. This paper aims to offer a complete analysis of the vibrational modes of the LuYAP crystal by means of polarized Raman spectroscopy in the temperature range of 20-290 K and confronting the experimental results with numerical methods inorder to characterize the crystal structure.Furthermore, an interpretation of the data in terms of vibrating molecular structures is suggested and the results are successfully confronted with the vibrational modes of similar perovskite crystal