Generalizing Boolean Satisfiability II: Theory

This is the second of three planned papers describing ZAP, a satisfiability engine that substantially generalizes existing tools while retaining the performance characteristics of modern high performance solvers. The fundamental idea underlying ZAP is that many problems passed to such engines contain rich internal structure that is obscured by the Boolean representation used; our goal is to define a representation in which this structure is apparent and can easily be exploited to improve computational performance. This paper presents the theoretical basis for the ideas underlying ZAP, arguing that existing ideas in this area exploit a single, recurring structure in that multiple database axioms can be obtained by operating on a single axiom using a subgroup of the group of permutations on the literals in the problem. We argue that the group structure precisely captures the general structure at which earlier approaches hinted, and give numerous examples of its use. We go on to extend the Davis-Putnam-Logemann-Loveland inference procedure to this broader setting, and show that earlier computational improvements are either subsumed or left intact by the new method. The third paper in this series discusses ZAPs implementation and presents experimental performance results

Generalizing Boolean Satisfiability III: Implementation

This is the third of three papers describing ZAP, a satisfiability engine that substantially generalizes existing tools while retaining the performance characteristics of modern high-performance solvers. The fundamental idea underlying ZAP is that many problems passed to such engines contain rich internal structure that is obscured by the Boolean representation used; our goal has been to define a representation in which this structure is apparent and can be exploited to improve computational performance. The first paper surveyed existing work that (knowingly or not) exploited problem structure to improve the performance of satisfiability engines, and the second paper showed that this structure could be understood in terms of groups of permutations acting on individual clauses in any particular Boolean theory. We conclude the series by discussing the techniques needed to implement our ideas, and by reporting on their performance on a variety of problem instances

A comparison between Pa alpha and H alpha emission: The relation between HII region mean reddening, local gas density and metallicity

We measure reddenings to HII regions in NGC 2903, NGC 1512, M51, NGC 4449 and NGC 6946 from Hubble Space Telescope Pa alpha and H alpha images. Extinctions range from A_V ~ 5 - 0 depending upon the galaxy. For the galaxies with HST images in both lines, NGC 2903, NGC 1512 and M51, the Pa alpha and H alpha emission are almost identical in morphology which implies that little emission from bright HII regions is hidden from view by regions of comparatively high extinction. The scatter in the measured extinctions is only +- 0.5 mag. We compare the reddenings we measure in five galaxies using the Pa alpha to H alpha ratios to those measured previously from the Balmer decrement in the LMC and as a function of radius in M101 and M51. We find that luminosity weighted mean extinctions of these ensembles of HI regions are correlated with gas surface density and metallicity. The correlation is consistent with the mean extinction depending on dust density where the dust to gas mass ratio scales with the metallicity. This trend is expected if HII regions tend to be located near the mid-plane of a gas disk and emerge from their parent molecular clouds soon after birth. In environments with gas densities below a few hundred Msol/pc^2 star formation rates estimated from integrated line fluxes and mean extinctions are likely to be fairly accurate.Comment: accepted for publication in A

A Survey of Women in Academia and the role of a Multidisciplinary Professional Society

The Society of Women Engineers (SWE) is a global professional society of over 30,000 members with a mission to “Stimulate women to achieve full potential in careers as engineers and leaders, expand the image of the engineering profession as a positive force in improving the quality of life, and demonstrate the value of diversity”1. SWE is an organization that is deeply rooted in industry. The founding members were employed by firms that are a result of the industrial revolution, and thus the focus of its membership is on those that work for industry, consultants, and often themselves. This focus has unintentionally left a large population of its membership, the academic population, underrepresented and misunderstood. Early discussion at the board level in the mid 2000’s indicated a willingness for a paradigm shift. However, the representation of academics on the board and other leadership roles has been lacking. This can be attributed to the lower numbers of this group relative to the whole, as well as the requirements of tenure that do not support the time and dedication to such an endeavor. A small but influential group of members, including a former board member, and a few involved at various levels of the society have been working toward increasing opportunities for women in academia (WIA). Some of the initiatives have been the societal support of the WIA committee, the addition of professional development opportunities targeting women in academic careers, providing recognition and awards, and aiding in networking opportunities. These all lead toward career advancement, making SWE more attractive to women engineers in the academe. To further our understanding of available opportunities and those opportunities that will make membership and active participation more attractive to members in academia, a survey was developed. Information gathered by the survey include demographics, perceived needs, and potential contributions the individual could make in furthering the creation of professional development opportunities for this population. This work is intended to share the results of this survey, using descriptive statistics, further developing our understanding of this underserved population within SWE

ASCA Observation of the New Transient X-ray Pulsar XTE J0111.2-7317 in the Small Magellanic Cloud

The new transient X-ray pulsar XTE J0111.2-7317 was observed with Advanced Satellite for Cosmology and Astrophysics (ASCA) on 1998 November 18, a few days after its discovery with the Proportional Counter Array onboard the Rossi X-ray Timing Explorer. The source was detected at a flux level of 3.6x10^-10 erg cm^-2 s^-1 in the 0.7--10.0 keV band, which corresponds to the X-ray luminosity of 1.8x10^38 erg s^-1, if a distance of 65 kpc for this pulsar in the Small Magellanic Cloud is assumed. Nearly sinusoidal pulsations with a period of 30.9497 +/- 0.0004 s were unambiguously detected during the ASCA observation. The pulsed fraction is low and slightly energy dependent with average value of \~27%. The energy spectrum shows a large soft excess below ~2 keV when fitted to a simple power-law type model. The soft excess is eliminated if the spectrum is fitted to an ``inversely broken power-law'' model, in which photon indices below and above a break energy of 1.5 keV are 2.3 and 0.8, respectively. The soft excess can also be described by a blackbody or a thermal bremsstrahlung when the spectrum above ~2 keV is modeled by a power-law. In these models, however, the thermal soft component requires a very large emission zone, and hence it is difficult to explain the observed pulsations at energies below 2 keV. A bright state of the source enables us to identify a weak iron line feature at 6.4 keV with an equivalent width of 50 +/- 14 eV. Pulse phase resolved spectroscopy revealed a slight hardening of the spectrum and marginal indication of an increase in the iron line strength during the pulse maximum.Comment: 8 pages, 5 Figures, to be published in ApJ. Also available at http://www-cr.scphys.kyoto-u.ac.jp/member/jun/job

Constraints on Intervening Stellar Populations Toward the Large Magellanic Cloud

The suggestion by Zaritsky & Lin that a vertical extension of the red clump feature in color-magnitude diagrams of the Large Magellanic Cloud (LMC) is consistent with a significant population of foreground stars to the LMC that could account for the observed microlensing optical depth has been challenged by various investigators. We respond by (1) examining each of the challenges presented and (2) presenting new photometric and spectroscopic data. We conclude that although the CMD data do not mandate the existence of a foreground population, they are entirely consistent with a foreground population associated with the LMC that contributes significantly (~ 50%) to the observed microlensing optical depth. From our new data, we conclude that <~ 40% of the VRC stars are young, massive red clump stars because (1) synthetic color-magnitude diagrams created using the star formation history derived indepdently from HST data suggest that < 50% of the VRC stars are young, massive red clump stars, (2) the angular distribution of the VRC stars is more uniform than that of the young (age < 1 Gyr) main sequence stars, and (3) the velocity dispersion of the VRC stars in the region of the LMC examined by ZL is inconsistent with the expectation for a young disk population. Each of these arguments is predicated on assumptions and the conclusions are uncertain. Therefore, an exact determination of the contribution to the microlensing optical depth by the various hypothesized foreground populations, and the subsequent conclusions regarding the existence of halo MACHOs, requires a detailed knowledge of many complex astrophysical issues, such as the IMF, star formation history, and post-main sequence stellar evolution. (abridged)Comment: Scheduled for publication in AJ in May 199

Magellanic Cloud Structure from Near-IR Surveys I: The Viewing Angles of the LMC

We present a detailed study of the viewing angles of the LMC disk plane. We find that our viewing direction differs considerably from the commonly accepted values, which has important implications for the structure of the LMC. The discussion is based on an analysis of spatial variations in the apparent magnitude of features in the near-IR color-magnitude diagrams extracted from the DENIS and 2MASS surveys. Sinusoidal brightness variations with a peak-to-peak amplitude of approximately 0.25 mag are detected as function of position angle, for both AGB and RGB stars. This is naturally interpreted as the result of distance variations, due to one side of the LMC plane being closer to us than the opposite side. The best fitting geometric model of an inclined plane yields an inclination angle i = 34.7 +/- 6.2 degrees and line-of-nodes position angle Theta = 122.5 +/- 8.3 degrees. There is tentative evidence that the LMC disk plane may be warped. Traditional methods to estimate the position angle of the line of nodes have used either the major axis position angle Theta_maj of the spatial distribution of tracers on the sky, or the position angle Theta_max of the line of maximum gradient in the velocity field, given that for a circular disk Theta_maj = Theta_max = Theta. The present study does not rely on the assumption of circular symmetry, and is considerably more accurate than previous studies of its kind. We find that the actual position angle of the line of nodes differs considerably from both Theta_maj and Theta_max, for which measurements have fallen in the range 140-190 degrees. This indicates that the intrinsic shape of the LMC disk is not circular, but elliptical, as discussed further in Paper II. [Abridged]Comment: Astronomical Journal, in press. 44 pages, LaTeX, with 8 PostScript figures. Contains minor revisions with respect to previously posted version. Check out http://www.stsci.edu/~marel/lmc.html for a large scale (23x21 degree) stellar number-density image of the LMC constructed from RGB and AGB stars in the 2MASS and DENIS surveys. The paper is available with higher resolution figures from http://www.stsci.edu/~marel/abstracts/abs_R31.htm

Generation of single-mode SU(1,1) intelligent states and an analytic approach to their quantum statistical properties

We discuss a scheme for generation of single-mode photon states associated with the two-photon realization of the SU(1,1) algebra. This scheme is based on the process of non-degenerate down-conversion with the signal prepared initially in the squeezed vacuum state and with a measurement of the photon number in one of the output modes. We focus on the generation and properties of single-mode SU(1,1) intelligent states which minimize the uncertainty relations for Hermitian generators of the group. Properties of the intelligent states are studied by using a ``weak'' extension of the analytic representation in the unit disk. Then we are able to obtain exact analytical expressions for expectation values describing quantum statistical properties of the SU(1,1) intelligent states. Attention is mainly devoted to the study of photon statistics and linear and quadratic squeezing.Comment: to appear in Quantum Semiclass. Opt., LaTeX, epsf style, 21 pages including 5 Postscript figures. More information on http://www.technion.ac.il/~brif/science.htm

Factorisation of analytic representations in the unit disk and number-phase statistics of a quantum harmonic oscillator

The inner-outer part factorisation of analytic representations in the unit disk is used for an effective characterisation of the number-phase statistical properties of a quantum harmonic oscillator. It is shown that the factorisation is intimately connected to the number-phase Weyl semigroup and its properties. In the Barut-Girardello analytic representation the factorisation is implemented as a convolution. Several examples are given which demonstrate the physical significance of the factorisation and its role for quantum statistics. In particular, we study the effect of phase-space interference on the factorisation properties of a superposition state.Comment: to appear in J. Phys. A, LaTeX, 13 pages, no figures. More information on http://www.technion.ac.il/~brif/science.htm

Probing the Space of Toric Quiver Theories

We demonstrate a practical and efficient method for generating toric Calabi-Yau quiver theories, applicable to both D3 and M2 brane world-volume physics. A new analytic method is presented at low order parametres and an algorithm for the general case is developed which has polynomial complexity in the number of edges in the quiver. Using this algorithm, carefully implemented, we classify the quiver diagram and assign possible superpotentials for various small values of the number of edges and nodes. We examine some preliminary statistics on this space of toric quiver theories