Hidden symmetry in the presence of fluxes

We derive the most general first order symmetry operator for the Dirac equation coupled to arbitrary fluxes. Such an operator is given in terms of an inhomogenous form omega which is a solution to a coupled system of first order partial differential equations which we call the generalized conformal Killing-Yano system. Except trivial fluxes, solutions of this system are subject to additional constraints. We discuss various special cases of physical interest. In particular, we demonstrate that in the case of a Dirac operator coupled to the skew symmetric torsion and U(1) field, the system of generalized conformal Killing-Yano equations decouples into the homogenous conformal Killing-Yano equations with torsion introduced in [arXiv:0905.0722] and the symmetry operator is essentially the one derived in [arXiv:1002.3616]. We also discuss the Dirac field coupled to a scalar potential and in the presence of 5-form and 7-form fluxes.Comment: 13 pages, no figure

The Electrodynamics of Inhomogeneous Rotating Media and the Abraham and Minkowski Tensors II: Applications

Applications of the covariant theory of drive-forms are considered for a class of perfectly insulating media. The distinction between the notions of "classical photons" in homogeneous bounded and unbounded stationary media and in stationary unbounded magneto-electric media is pointed out in the context of the Abraham, Minkowski and symmetrized Minkowski electromagnetic stress-energy-momentum tensors. Such notions have led to intense debate about the role of these (and other) tensors in describing electromagnetic interactions in moving media. In order to address some of these issues for material subject to the Minkowski constitutive relations, the propagation of harmonic waves through homogeneous and inhomogeneous, isotropic plane-faced slabs at rest is first considered. To motivate the subsequent analysis on accelerating media two classes of electromagnetic modes that solve Maxwell's equations for uniformly rotating homogeneous polarizable media are enumerated. Finally it is shown that, under the influence of an incident monochromatic, circularly polarized, plane electromagnetic wave, the Abraham and symmetrized Minkowski tensors induce different time-averaged torques on a uniformly rotating materially inhomogeneous dielectric cylinder. We suggest that this observation may offer new avenues to explore experimentally the covariant electrodynamics of more general accelerating media.Comment: 29 pages, 4 figures. Accepted for publication in Proc. Roy. Soc.

An excess of damped Lyman alpha galaxies near QSOs

We present a sample of 33 damped Lyman alpha systems (DLAs) discovered in the Sloan Digital Sky Survey (SDSS) whose absorption redshifts (z_abs) are within 6000 km/s of the QSO's systemic redshift (z_sys). Our sample is based on 731 2.5 < z_sys < 4.5 non-broad-absorption-line (non-BAL) QSOs from Data Release 3 (DR3) of the SDSS. We estimate that our search is ~100 % complete for absorbers with N(HI) >= 2e20 cm^-2. The derived number density of DLAs per unit redshift, n(z), within v < 6000 km/s is higher (3.5 sigma significance) by almost a factor of 2 than that of intervening absorbers observed in the SDSS DR3, i.e. there is evidence for an overdensity of galaxies near the QSOs. This provides a physical motivation for excluding DLAs at small velocity separations in surveys of intervening 'field' DLAs. In addition, we find that the overdensity of proximate DLAs is independent of the radio-loudness of the QSO, consistent with the environments of radio-loud and radio-quiet QSOs being similar.Comment: Accepted for publication in MNRAS (13 pages, 6 figures

Small Engine Component Technology (SECT)

A study of small gas turbine engines was conducted to identify high payoff technologies for year-2000 engines and to define companion technology plans. The study addressed engines in the 186 to 746 KW (250 to 1000 shp) or equivalent thrust range for rotorcraft, commuter (turboprop), cruise missile (turbojet), and APU applications. The results show that aggressive advancement of high payoff technologies can produce significant benefits, including reduced SFC, weight, and cost for year-2000 engines. Mission studies for these engines show potential fuel burn reductions of 22 to 71 percent. These engine benefits translate into reductions in rotorcraft and commuter aircraft direct operating costs (DOC) of 7 to 11 percent, and in APU-related DOCs of 37 to 47 percent. The study further shows that cruise missile range can be increased by as much as 200 percent (320 percent with slurry fuels) for a year-2000 missile-turbojet system compared to a current rocket-powered system. The high payoff technologies were identified and the benefits quantified. Based on this, technology plans were defined for each of the four engine applications as recommended guidelines for further NASA research and technology efforts to establish technological readiness for the year 2000

Young Muslim women's experiences of Islam and physical education in Greece and Britain: a comparative study

Previous research suggests that Muslim women can experience particular problems when taking physical education (PE) lessons, for example with dress codes, mixed-teaching and exercise during Ramadan; and they can face restrictions in extra-curricular activities for cultural and religious reasons. The area is under-researched and there is little evidence of comparative studies that explore similarities and differences in cross-national experiences, which is the aim of this paper. Two studies conducted in Greece and Britain that explored the views of Muslim women on school experiences of physical education are compared. Both studies focused on diaspora communities, Greek Turkish girls and British Asian women, living in predominantly non-Muslim countries. Growing concerns about global divisions between 'Muslims and the West' make this a particularly pertinent study. Qualitative data were collected by interviews with 24 Greek Muslim women, and 20 British Muslim women. \ud <P> \ud Physical education has national curriculum status and a similar rationale in both countries but with different cultures of formality and tradition, which impacted on pupils' experiences. Data suggested that Greek and British groups held positive views towards physical education but were restricted on their participation in extra-curricular activities. For the British women religious identity and consciousness of Islamic requirements were more evident than for the Greek women. Differences in stages of acculturation, historical and socio-cultural contexts contributed to less problematic encounters with physical education for Greek Muslims who appeared more closely assimilated into the dominant culture

Maxwell's Equations in a Uniformly Rotating Dielectric Medium and the Wilson-Wilson Experiment

This note offers a conceptually straightforward and efficient way to formulate and solve problems in the electromagnetics of moving media based on a representation of Maxwell's equations in terms of differential forms on spacetime together with junction conditions at moving interfaces. This framework is used to address a number of issues that have been discussed recently in this journal about the theoretical description underlying the interpretation of the Wilson-Wilson experiment.Comment: 16 pages, 2 figure

Characterization of 1.55-μm pulses from a self-seeded gain-switched Fabry-Pérot laser diode using frequency-resolved optical gating

The intensity and frequency chirp of picosecond pulses from a self-seeded gain-switched Fabry-Perot laser diode have been directly measured using the technique of frequency-resolved optical gating. Measurements over an output sidemode suppression ratio (SMSR) range of 15-35 dB show that higher SMSR's are associated with an increasingly linear frequency chirp across the output pulses. This complete pulse characterization allows the conditions for optimum pulse compression to be determined accurately, and indicates that transform-limited, pedestal free pulses can be obtained at an SMSR of 35 dB

Debye Potentials for Maxwell and Dirac Fields from a Generalisation of the Killing-Yano Equation

By using conformal Killing-Yano tensors, and their generalisations, we obtain scalar potentials for both the source-free Maxwell and massless Dirac equations. For each of these equations we construct, from conformal Killing-Yano tensors, symmetry operators that map any solution to another.Comment: 35 pages, plain Te

Killing-Yano Forms of a Class of Spherically Symmetric Space-Times II: A Unified Generation of Higher Forms

Killing-Yano (KY) two and three forms of a class of spherically symmetric space-times that includes the well-known Minkowski, Schwarzschild, Reissner-Nordstrom, Robertson-Walker and six different forms of de Sitter space-times as special cases are derived in a unified and exhaustive manner. It is directly proved that while the Schwarzschild and Reissner-Nordstrom space-times do not accept any KY 3-form and they accept only one 2-form, the Robertson-Walker space-time admits four KY 2-forms and only one KY 3-form. Maximal number of KY-forms are obtained for Minkowski and all known forms of de Sitter space-times. Complete lists comprising explicit expressions of KY-forms are given.Comment: 28 page

The Redshift Distribution of FIRST Radio Sources at 1 mJy

We present spectra for a sample of radio sources from the FIRST survey, and use them to define the form of the redshift distribution of radio sources at mJy levels.We targeted 365 sources and obtained 46 redshifts (13 per cent of the sample). We find that our sample is complete in redshift measurement to R $\sim 18.6$, corresponding to $z\sim 0.2$. Early-type galaxies represent the largest subset (45 per cent) of the sample and have redshifts 0.15\la z \la 0.5 ; late-type galaxies make up 15 per cent of the sample and have redshifts 0.05\la z \la 0.2; starbursting galaxies are a small fraction ($\sim 6$ per cent), and are very nearby (z\la 0.05). Some 9 per cent of the population have Seyfert1/quasar-type spectra, all at z\ga 0.8, and there are 4 per cent are Seyfert2 type galaxies at intermediate redshifts ($z\sim 0.2$). Using our measurements and data from the Phoenix survey, we obtain an estimate for $N(z)$ at $S_{1.4 \rm {GHz}}\ge 1$ mJy and compare this with model predictions. At variance with previous conclusions, we find that the population of starbursting objects makes up \la 5 per cent of the radio population at S $\sim 1$ mJy.Comment: 20 pages, sumbitted to MNRA