A deep Giant Metre-wave Radio Telescope 610-MHz survey of the 1^HXMM–Newton/Chandra survey field

We present the results of a deep 610-MHz survey of the 1^HXMM–Newton/Chandra survey area with the Giant Metre-wave Radio Telescope. The resulting maps have a resolution of ~7 arcsec and an rms noise limit of 60 μJy. To a 5σ detection limit of 300 μJy, we detect 223 sources within a survey area of 64 arcmin in diameter. We compute the 610-MHz source counts and compare them to those measured at other radio wavelengths. The well-known flattening of the Euclidean-normalized 1.4-GHz source counts below ~2 mJy, usually explained by a population of starburst galaxies undergoing luminosity evolution, is seen at 610 MHz. The 610-MHz source counts can be modelled by the same populations that explain the 1.4-GHz source counts, assuming a spectral index of −0.7 for the starburst galaxies and the steep spectrum active galactic nucleus (AGN) population. We find a similar dependence of luminosity evolution on redshift for the starburst galaxies at 610 MHz as is found at 1.4 GHz (i.e. 'Q'= 2.45^(+0.3)_(−0.4))

Gravitational Theory with a Dynamical Time

A gravitational theory involving a vector field $\chi^{\mu}$, whose zero component has the properties of a dynamical time, is studied. The variation of the action with respect to $\chi^{\mu}$ gives the covariant conservation of an energy momentum tensor $T^{\mu \nu}_{(\chi)}$. Studying the theory in a background which has killing vectors and killing tensors we find appropriate shift symmetries of the field $\chi^{\mu}$ which lead to conservation laws. The energy momentum that is the source of gravity $T^{\mu \nu}_{(G)}$ is different but related to $T^{\mu \nu}_{(\chi)}$ and the covariant conservation of $T^{\mu \nu}_{(G)}$ determines in general the vector field $\chi^{\mu}$. When $T^{\mu \nu}_{(\chi)}$ is chosen to be proportional to the metric, the theory coincides with the Two Measures Theory, which has been studied before in relation to the Cosmological Constant Problem. When the matter model consists of point particles, or strings, the form of $T^{\mu \nu}_{(G)}$, solutions for $\chi^{\mu}$ are found. For the case of a string gas cosmology, we find that the Milne Universe can be a solution, where the gas of strings does not curve the spacetime since although $T^{\mu \nu}_{(\chi)} \neq 0$, $T^{\mu \nu}_{(G)}= 0$, as a model for the early universe, this solution is also free of the horizon problem. There may be also an application to the "time problem" of quantum cosmology.Comment: 21 pages, discussions extended, some more explicit proofs included, more references include

Proof of the Generalized Second Law for Quasistationary Semiclassical Black Holes

A simple direct explicit proof of the generalized second law of black hole thermodynamics is given for a quasistationary semiclassical black hole.Comment: 12 pages, LaTeX, report Alberta-Thy-10-93 (revision of paper in response to Phys. Rev. Lett. referees' comments, which suffered a series of long delays

Numerical modeling of dynamic powder compaction using the Kawakita equation of state

Dynamic powder compaction is analyzed using the assumption that the powder behaves, while it is being compacted, like a hydrodynamic fluid in which deviatoric stress and heat conduction effects can be ignored throughout the process. This enables techniques of computational fluid dynamics such the equilibrium flux method to be used as a modeling tool. The equation of state of the powder under compression is assumed to be a modified version of the Kawakita loading curve. Computer simulations using this model are performed for conditions matching as closely as possible with those from experiments by Page and Killen [Powder Metall. 30, 233 (1987)]. The numerical and experimental results are compared and a surprising degree of qualitative agreement is observed

Does Positronium Form in the Universe ?

Positronium (the bound state of electron and positron) has been thought to be formed after proton decay ($>10^{34}$yr) through collisional recombination and then decays by pair annihilation, thereby changing the matter content of the universe. We revisit the issue of the formation of positronium in the long-term future of the universe in light of recent indication that the universe is dominated by dark energy and dark matter. We find that if the equation of state of dark energy $w$ is less than -1/3 (including the cosmological constant $w=-1$), then the formation of positronium would not be possible, while it is possible through bound-bound transitions for -1/3\siml w\siml-0.2, or through collisional recombination for w\simg-0.2. The radiation from \epm pair annihilation cannot dominate over \epm, while that from proton decay will dominate over baryon and \epm for a while but not over dark matter.Comment: 13 pages, to appear in JCA

Cosmological Measures without Volume Weighting

Many cosmologists (myself included) have advocated volume weighting for the cosmological measure problem, weighting spatial hypersurfaces by their volume. However, this often leads to the Boltzmann brain problem, that almost all observations would be by momentary Boltzmann brains that arise very briefly as quantum fluctuations in the late universe when it has expanded to a huge size, so that our observations (too ordered for Boltzmann brains) would be highly atypical and unlikely. Here it is suggested that volume weighting may be a mistake. Volume averaging is advocated as an alternative. One consequence may be a loss of the argument that eternal inflation gives a nonzero probability that our universe now has infinite volume.Comment: 15 pages, LaTeX, added references for constant-H hypersurfaces and also an idea for minimal-flux hypersurface

The ducky^{2J} Mutation in Cacna2d2 Results in Reduced Spontaneous Purkinje Cell Activity and Altered Gene Expression

The mouse mutant ducky and its allele ducky^{2J} represent a model for absence epilepsy characterized by spike-wave seizures and cerebellar ataxia. These mice have mutations in Cacna2d2, which encodes the α₂δ-2 calcium channel subunit. Of relevance to the ataxic phenotype, α₂δ-2 mRNA is strongly expressed in cerebellar Purkinje cells (PCs). The Cacna2d2du2J mutation results in a 2 bp deletion in the coding region and a complete loss of α₂δ-2 protein. Here we show that du^{2J}/du^{2J} mice have a 30% reduction in somatic calcium current and a marked fall in the spontaneous PC firing rate at 22°C, accompanied by a decrease in firing regularity, which is not affected by blocking synaptic input to PCs. At 34°C, du^{2J}/du^{2J} PCs show no spontaneous intrinsic activity. DU^{2J}/du^{2J} mice also have alterations in the cerebellar expression of several genes related to PC function. At postnatal day 21, there is an elevation of tyrosine hydroxylase mRNA and a reduction in tenascin-C gene expression. Although du^{2J}/+ mice have a marked reduction in α₂δ-2 protein, they show no fall in PC somatic calcium currents or increase in cerebellar tryrosine hydroxylase gene expression. However, du^{2J}/+ PCs do exhibit a significant reduction in firing rate, correlating with the reduction in α₂δ-2. A hypothesis for future study is that effects on gene expression occur as a result of a reduction in somatic calcium currents, whereas effects on PC firing occur as a long-term result of loss of α₂δ-2 and/or a reduction in calcium currents and calcium-dependent processes in regions other than the soma

Bremsstrahlung neutrinos from electron-electron scattering in a relativistic degenerate electron plasma

We present a calculation of neutrino pair bremsstrahlung due to electron-electron scattering in a relativistic degenerate plasma of electrons. Proper treatment of the in-medium photon propagator, i.e., inclusion of Debye screening of the longitudinal part and Landau damping of the transverse part, leads to a neutrino emissivity which is several orders of magnitude larger than when Debye screening is imposed for the tranverse part. Our results show that this in-medium process can compete with other sources of neutrino radiation and can, in some cases, even be the dominant neutrino emission mechanism. We also discuss the natural extension to quark-quark bremsstrahlung in gapped and ungapped quark matter.Comment: 15 pages, 7 figure

The Luminosity Function Evolution of Soft X--ray selected AGN in the RIXOS survey

A sample of 198 soft X--ray selected active galactic nuclei (AGN) from the ROSAT International X--ray Optical Survey (RIXOS), is used to investigate the X--ray luminosity function and its evolution. RIXOS, with a flux limit of 3E-14 erg s-1 cm-2 (0.5 to 2.0 keV), samples a broad range in redshift over 20 deg^2 of sky, and is almost completely identified; it is used in combination with the Einstein Extended Medium Sensitivity Survey (EMSS), to give a total sample of over 600 AGN. We find the evolution of AGN with redshift to be consistent with pure luminosity evolution (PLE) models in which the rate of evolution slows markedly or stops at high redshifts z>1.8. We find that this result is not affected by the inclusion, or exclusion, of narrow emission line galaxies at low redshift in the RIXOS and EMSS samples, and is insensitive to uncertainties in the conversion between flux values measured with ROSAT and Einstein. We confirm, using a model independent Ve/Va test, that our survey is consistent with no evolution at high redshifts.Comment: 10 pages, LaTeX file, PS figures and mn.sty. Accepted in MNRA

Distributing the burdens of climate change

Global climate change raises many questions for environmental political theorists. This article focuses on the question of identifying the agents that should bear the financial burden of preventing dangerous climate change. Identifying in a fair way the agents that should take the lead in climate mitigation and adaptation, as well as the precise burdens that these parties must bear, will be a key aspect of the next generation of global climate policies. After a critical review of a number of rival approaches to burden sharing, the paper argues that only a principled and philosophically robust reconciliation of three approaches to burden sharing (‘contribution to problem’, ‘ability to pay’ and ‘beneficiary pays’) can generate a satisfactory mix of theoretical coherence and practical application