Intrinsic Variability and Field Statistics for the Vela Pulsar: 3. Two-Component Fits and Detailed Assessment of Stochastic Growth Theory

The variability of the Vela pulsar (PSR B0833-45) corresponds to well-defined field statistics that vary with pulsar phase, ranging from Gaussian intensity statistics off-pulse to approximately power-law statistics in a transition region and then lognormal statistics on-pulse, excluding giant micropulses. These data are analyzed here in terms of two superposed wave populations, using a new calculation for the amplitude statistics of two vectorially-combined transverse fields. Detailed analyses show that the approximately power-law and lognormal distributions observed are fitted well at essentially all on-pulse phases by Gaussian-lognormal and double-lognormal combinations, respectively. These good fits, plus the smooth but significant variations in fit parameters across the source, provide strong evidence that the approximately power-law statistics observed in the transition region are not intrinsic. Instead, the data are consistent with normal pulsar emission having lognormal statistics at all phases. This is consistent with generation in an inhomogeneous source obeying stochastic growth theory (SGT) and with the emission mechanism being purely linear (either direct or indirect). A nonlinear mechanism is viable only if it produces lognormal statistics when suitably ensemble-averaged. Variations in the SGT fit parameters with phase imply that the radiation is relatively more variable near the pulse edges than near the center, as found in earlier work. In contrast, Vela's giant micropulses come from a very restricted phase range and have power-law statistics with indices ($6.7 \pm 0.6$) not inconsistent with nonlinear wave collapse. These results imply that normal pulses have a different source and generation mechanism than giant micropulses, as suggested previously on other grounds.Comment: 10 pages and 14 figures. Accepted by Monthly Notices of the Royal Astronomical Society in April 200

Plant root proliferation in nitrogen-rich patches confers competitive advantage

Plants respond to environmental heterogeneity, particularly below ground, where spectacular root proliferations in nutrient-rich patches may occur. Such 'foraging' responses apparently maximize nutrient uptake and are now prominent in plant ecological theory. Proliferations in nitrogen-rich patches are difficult to explain adaptively, however. The high mobility of soil nitrate should limit the contribution of proliferation to N capture. Many experiments on isolated plants show only a weak relation between proliferation and N uptake. We show that N capture is associated strongly with proliferation during interspecific competition for finite, locally available, mixed N sources, precisely the conditions under which N becomes available to plants on generally infertile soils. This explains why N-induced root proliferation is an important resource-capture mechanism in N-limited plant communities and suggests that increasing proliferation by crop breeding or genetic manipulation will have a limited impact on N capture by well-fertilized monocultures

AOIPS 3 User's guide. Volume 1: Overview and software utilization

This is Volume I of the Atmospheric and Oceanographic Information Processing System (AOIPS) User's Guide. AOIPS 3 is the version of the AOIPS software as of April 1989. The AOIPS software was developed jointly by the Goddard Space Flight Center and General Sciences Corporation. Volume 1 is intended to provide the user with an overall guide to the AOIPS system. It introduces the user to AOIPS system concepts, explains how programs are related and the necessary order of program execution, and provides brief descriptions derived from on-line help for every AOIPS program. It is intended to serve as a reference for information such as: program function, inmput/output variable descriptions, program limitations, etc. AOIPS is an interactive meteorological processing system with capabilities to ingest and analyze the many types of meteorological data. AOIPS includes several applications in areas of relevance to meteorological research. AOIPS is partitioned into four applications components: satellite data analysis, radar data analysis, aircraft data analysis, and utilities

Full major-shell calculation for states that were degenerate in a single-j-shell calculation

A full fp calculation is performed for states which were degenerate in a single-j-shell calculation in which isospin-zero two-body matrix elements were set to zero energy. Most of the splitting in a complete shell calculation (but not all) comes from the T=0 part of the interaction.Comment: 5 pages, RevTeX4. Submitted to Physical Review

Sub-millimetre observations of hyperluminous infrared galaxies

We present sub-mm photometry for 11 Hyperluminous Infrared Galaxies (HLIRGs) and use radiative transfer models for starbursts and AGN to investigate the IR emission. In all sources both a starburst and AGN are required to explain the IR emission. The mean starburst fraction is 35%, with a range spanning 80% starburst dominated to 80% AGN dominated. In all cases the starburst dominates at rest-frame wavelengths >50 microns, with star formation rates >500 solar masses per year. The trend of increasing AGN fraction with increasing IR luminosity seen in IRAS galaxies peaks in HLIRGs, and is not higher than the fraction seen in bright ULIRGs. The AGN and starburst luminosities correlate, suggesting that a common physical factor, plausibly the dust masses, governs their luminosities. Our results suggest that the HLIRG population is comprised both of ULIRG-like galaxy mergers, and of young galaxies going through their maximal star formation periods whilst harbouring an AGN. The coeval AGN and starburst activity in our sources implies that starburst and AGN activity, and the peak starburst and AGN luminosities, can be coeval in active galaxies generally. When extrapolated to high-z our sources have comparable sub-mm fluxes to sub-mm survey sources. At least some sub-mm survey sources are therefore likely to be comprised of similar galaxy populations to those found in the HLIRG population. It is also plausible from these results that high-z sub-mm sources harbour heavily obscured AGN. The differences in X-ray and sub-mm properties between HLIRGs at z~1 and sub-mm sources at z~3 implies evolution between the two epochs. Either the mean AGN obscuration level is greater at z~3 than at z~1, or the fraction of IR-luminous sources at z~3 that contain AGN is smaller than that at z~1.Comment: 15 pages. Accepted for publication in MNRA

Some exact solutions with torsion in 5-D Einstein-Gauss-Bonnet gravity

Exact solutions with torsion in Einstein-Gauss-Bonnet gravity are derived. These solutions have a cross product structure of two constant curvature manifolds. The equations of motion give a relation for the coupling constants of the theory in order to have solutions with nontrivial torsion. This relation is not the Chern-Simons combination. One of the solutions has a $AdS_2\times S^3$ structure and is so the purely gravitational analogue of the Bertotti-Robinson space-time where the torsion can be seen as the dual of the covariantly constant electromagnetic field.Comment: 19 pages, LaTex, no figures. References added, notation clarified. Accepted for publication on Physical Review

The star-formation history of the universe - an infrared perspective

A simple and versatile parameterized approach to the star formation history allows a quantitative investigation of the constraints from far infrared and submillimetre counts and background intensity measurements. The models include four spectral components: infrared cirrus (emission from interstellar dust), an M82-like starburst, an Arp220-like starburst and an AGN dust torus. The 60 $\mu$m luminosity function is determined for each chosen rate of evolution using the PSCz redshift data for 15000 galaxies. The proportions of each spectral type as a function of 60 $\mu$m luminosity are chosen for consistency with IRAS and SCUBA colour-luminosity relations, and with the fraction of AGN as a function of luminosity found in 12 $\mu$m samples. The luminosity function for each component at any wavelength can then be calculated from the assumed spectral energy distributions. With assumptions about the optical seds corresponding to each component and, for the AGN component, the optical and near infrared counts can be accurately modelled. A good fit to the observed counts at 0.44, 2.2, 15, 60, 90, 175 and 850 $\mu$m can be found with pure luminosity evolution in all 3 cosmological models investigated: $\Omega_o$ = 1, $\Omega_o$ = 0.3 ($\Lambda$ = 0), and $\Omega_o$ = 0.3, $\Lambda$ = 0.7. All 3 models also give an acceptable fit to the integrated background spectrum. Selected predictions of the models, for example redshift distributions for each component at selected wavelengths and fluxes, are shown. The total mass-density of stars generated is consistent with that observed, in all 3 cosmological models.Comment: 20 pages, 25 figures. Accepted for publication in ApJ. Full details of models can be found at http://astro.ic.ac.uk/~mrr/countmodel

Design of a "Digital Atlas Vme Electronics" (DAVE) Module

ATLAS-SCT has developed a new ATLAS trigger card, 'Digital Atlas Vme Electronics' ("DAVE"). The unit is designed to provide a versatile array of interface and logic resources, including a large FPGA. It interfaces to both VME bus and USB hosts. DAVE aims to provide exact ATLAS CTP (ATLAS Central Trigger Processor) functionality, with random trigger, simple and complex deadtime, ECR (Event Counter Reset), BCR (Bunch Counter Reset) etc. being generated to give exactly the same conditions in standalone running as experienced in combined runs. DAVE provides additional hardware and a large amount of free firmware resource to allow users to add or change functionality. The combination of the large number of individually programmable inputs and outputs in various formats, with very large external RAM and other components all connected to the FPGA, also makes DAVE a powerful and versatile FPGA utility cardComment: 8 pages, 4 figures, TWEPP-2011; E-mail: [email protected]