Two and three electrons in a quantum dot: 1/|J| - expansion

We consider systems of two and three electrons in a two-dimensional parabolic quantum dot. A magnetic field is applied perpendicularly to the electron plane of motion. We show that the energy levels corresponding to states with high angular momentum, J, and a low number of vibrational quanta may be systematically computed as power series in 1/|J|. These states are relevant in the high-B limit.Comment: LaTeX, 15 pages,6 postscript figure

Collisionless reconnection: The sub-microscale mechanism of magnetic field line interaction

Magnetic field lines are quantum objects carrying one quantum $\Phi_0=2\pi\hbar/e$ of magnetic flux and have finite radius $\lambda_m$. Here we argue that they possess a very specific dynamical interaction. Parallel field lines reject each other. When confined to a certain area they form two-dimensional lattices of hexagonal structure. We estimate the filling factor of such an area. Antiparallel field lines, on the other hand, attract each other. We identify the physical mechanism as being due to the action of the gauge potential field which we determine quantum mechanically for two parallel and two antiparallel field lines. The distortion of the quantum electrodynamic vacuum causes a cloud of virtual pairs. We calculate the virtual pair production rate from quantum electrodynamics and estimate the virtual pair cloud density, pair current and Lorentz force density acting on the field lines via the pair cloud. These properties of field line dynamics become important in collisionless reconnection, consistently explaining why and how reconnection can spontaneously set on in the field-free centre of a current sheet below the electron-inertial scale.Comment: 13 journal pages, 6 figures, submitted to Ann. Geophy

Probing the geometry and motion of AGN coronae through accretion disc emissivity profiles

To gain a better understanding of the inner disc region that comprises active galactic nuclei it is necessary to understand the pattern in which the disc is illuminated (the emissivity profile) by X-rays emitted from the continuum source above the black hole (corona). The differences in the emissivity profiles produced by various corona geometries are explored via general relativistic ray tracing simulations. Through the analysis of various parameters of the geometries simulated it is found that emissivity profiles produced by point source and extended geometries such as cylindrical slabs and spheroidal coronae placed on the accretion disc are distinguishable. Profiles produced by point source and conical geometries are not significantly different, requiring an analysis of reflection fraction to differentiate the two geometries. Beamed point and beamed conical sources are also simulated in an effort to model jet-like coronae, though the differences here are most evident in the reflection fraction. For a point source we determine an approximation for the measured reflection fraction with the source height and velocity. Simulating spectra from the emissivity profiles produced by the various geometries produce distinguishable differences. Overall spectral differences between the geometries do not exceed 15 per cent in the most extreme cases. It is found that emissivity profiles can be useful in distinguishing point source and extended geometries given high quality spectral data of extreme, bright sources over long exposure times. In combination with reflection fraction, timing, and spectral analysis we may use emissivity profiles to discern the geometry of the X-ray source.Comment: 15 pages, 12 figures. Accepted for publication in MNRA

Separator development and testing of nickel-hydrogen cells

The components, design, and operating characteristics of Ni-H2 cells batteries were improved. A separator development program was designed to develop a separator that is resistant to penetration by oxygen and loose active material from then nickel electrode, while retraining the required chemical and thermal stability, reservoir capability, and high ionic conductivity. The performance of the separators in terms of cell operating voltage was to at least match that of state-of-the-art separators while eliminating the separator problems. The separators were submitted to initial screening tests and those which successfully completed the tests were built into Ni-H2 cells for short term testing. The separators with the best performance are tested for long term performance and life

Constraints on the braneworld from compact stars

According to the braneworld idea, ordinary matter is confined on a 3-dimensional space (brane) that is embedded in a higher-dimensional space-time where gravity propagates. In this work, after reviewing the limits coming from general relativity, finiteness of pressure and causality on the brane, we derive observational constraints on the braneworld parameters from the existence of stable compact stars. The analysis is carried out by solving numerically the brane-modified Tolman-Oppenheimer-Volkoff equations, using different representative equations of state to describe matter in the star interior. The cases of normal dense matter, pure quark matter and hybrid matter are considered.Comment: 13 pages, 11 figures, 2 tables; new EoS considered, references and comments adde

Spin reorientation transition in the incommensurate stripe-ordered phase of La3/2Sr1/2NiO4

The spin ordering of La3/2Sr1/2NiO4 was investigated by magnetization measurements, and by unpolarized- and polarized-neutron diffraction. Spin ordering with an incommensurability epsilon ~ 0.445 is observed below T_so ~ 80 K. On cooling, a spin reorientation is observed at 57 +/- 1 K, with the spin axes rotating from 52 +/- 4 degrees to 78 +/- 3 degrees. This is the first time a spin reorientation has been observed in a La2-xSrxNiO4+delta compound having incommensurate stripe order.Comment: REVTex 4. 4 pages including 4 figures. Minor changes to text. Accepted to be published in Physical Review

Cross-linked polyvinyl alcohol films as alkaline battery separators

Cross-linking methods were investigated to determine their effect on the performance of polyvinyl alcohol (PVA) films as alkaline battery separators. The following types of cross-linked PVA films are discussed: (1) PVA-dialdehyde blends post-treated with an acid or acid periodate solution (two-step method) and (2) PVA-dialdehyde blends cross-linked during film formation (drying) by using a reagent with both aldehyde and acid functionality (one-step method). Laboratory samples of each cross-linked type of film were prepared and evaluated in standard separator screening tests. The pilot-plant batches of films were prepared and compared to measure differences due to the cross-linking method. The pilot-plant materials were then tested in nickel oxide - zinc cells to compare the two methods with respect to performance characteristics and cycle life. Cell test results are compared with those from tests with Celgard