Hall current effects in dynamic magnetic reconnection solutions

The impact of Hall current contributions on flow driven planar magnetic merging solutions is discussed. The Hall current is important if the dimensionless Hall parameter (or normalized ion skin depth) satisfies cH>η where η is the inverse Lundquist number for the plasma. A dynamic analysis of the problem shows, however, that the Hall current initially manifests itself, not by modifying the planar reconnection field, but by inducing a non-reconnecting perpendicular "separator" component in the magnetic field. Only if the stronger condition c2/H > η is satisfied can Hall currents be expected to affect the planar merging. These analytic predictions are then tested by performing a series of numerical experiments in periodic geometry, using the full system of planar magnetohydrodynamic (MHD) equations. The numerical results confirm that the nature of the merging changes dramatically when the Hall coupling satisfies c2/H > η. In line with the analytic treatment of sheared reconnection, the coupling provided by the Hall term leads to the emergence of multiple current layers that can enhance the global Ohmic dissipation at the expense of the reconnection rate. However, the details of the dissipation depend critically on the symmetries of the simulation, and when the merging is "head-on" (i.e., comprises fourfold symmetry) the reconnection rate can be enhanced

Measurement of Quantum Fluctuations in Geometry

A particular form for the quantum indeterminacy of relative spacetime position of events is derived from the limits of measurement possible with Planck wavelength radiation. The indeterminacy predicts fluctuations from a classically defined geometry in the form of ``holographic noise'' whose spatial character, absolute normalization, and spectrum are predicted with no parameters. The noise has a distinctive transverse spatial shear signature, and a flat power spectral density given by the Planck time. An interferometer signal displays noise due to the uncertainty of relative positions of reflection events. The noise corresponds to an accumulation of phase offset with time that mimics a random walk of those optical elements that change the orientation of a wavefront. It only appears in measurements that compare transverse positions, and does not appear at all in purely radial position measurements. A lower bound on holographic noise follows from a covariant upper bound on gravitational entropy. The predicted holographic noise spectrum is estimated to be comparable to measured noise in the currently operating interferometer GEO600. Because of its transverse character, holographic noise is reduced relative to gravitational wave effects in other interferometer designs, such as LIGO, where beam power is much less in the beamsplitter than in the arms.Comment: 7 pages, 2 figures, LaTeX. Extensive rewrite of original version, including more detailed analysis. Main result is the same but the estimate of noise in strain units for GEO600, showing 1/f behavior at low f and flat at high f, is improved. To appear in Phys. Rev.

MULTIDIMENSIONAL OUTPUT INDICES

This abstract describes alternative output aggregates that provide both cross-sectional and temporal comparisons appropriate for the analysis of panel data sets. Several of these multidimensional output indices are constructed using detailed data on agricultural production to illustrate the effects of fixing price weights over time, employing sample average price weights, and choosing between alternative approximations of Divisia indices.Research Methods/ Statistical Methods,

Believability and Attitudes toward Alcohol Warning Label Information: The Role of Persuasive Communications Theory

Based on tenets of persuasive communications theory, five recently proposed alcohol warning labels are examined for their differential impact on label believability and attitudes. While all warnings are rated as believable, the ones regarding birth defects and driving impairment are perceived to be significantly more believable than the others. In addition, persons with more favorable attitudes toward alcohol consumption tend to disbelieve specific instance hazards (e.g., birth defects, driving impairment and drug combination warnings), while disliking longterm risks of alcohol consumption and abuse (e.g., hypertension, liver disease, cancer and addiction warnings). Implications for public policy and researchers are discussed

Characterization of quantum well structures using a photocathode electron microscope

Present day integrated circuits pose a challenge to conventional electronic and mechanical test methods. Feature sizes in the submicron and nanometric regime require radical approaches in order to facilitate electrical contact to circuits and devices being tested. In addition, microwave operating frequencies require careful attention to distributed effects when considering the electrical signal paths within and external to the device under test. An alternative testing approach which combines the best of electrical and optical time domain testing is presented, namely photocathode electron microscope quantitative voltage contrast (PEMQVC)

PATTERNS OF AGRICULTURAL DEVELOPMENT IN THE UNITED STATES

International Development,

Addressing the needs of international postgraduate students: the role of social capital

Self-evidently, international students are likely to have considerable informational and social needs when coming to study in the UK. This paper reports the findings of a small study of such needs among international postgraduate students in the School of Health Sciences. It was an interview study, with twelve students participating. Though the study was designed to support the creation of an online resource, the findings suggest that meeting those needs satisfactorily requires a multi-faceted approach. Both face-to-face and online processes are needed to help students to develop the social capital necessary to success in undertaking the course, getting to know the university, and adjusting to life in England