The Distribution of X-ray Dips with Orbital Phase in Cygnus X-1

We present results of a comprehensive study of the distribution of absorption dips with orbital phase in Cygnus X-1. Firstly, the distribution was obtained using archival data from all major X-ray observatories and corrected for the selection effect that phase zero (superior conjunction of the black hole) has been preferentially observed. Dip occurrence was seen to vary strongly with orbital phase \phi, with a peak at \phi ~ 0.95, i.e. was not symmetric about phase zero. Secondly, the RXTE ASM has provided continuous coverage of the Low State of Cygnus X-1 since Sept. 1996, and we have selected dip data based on increases in hardness ratio. The distribution, with much increased numbers of dip events, confirms that the peak is at \phi ~ 0.95, and we report the discovery of a second peak at \phi ~ 0.6. We attribute this peak to absorption in an accretion stream from the companion star HDE 226868. We have estimated the ionization parameter at different positions showing that radiative acceleration of the wind is suppressed by photoionization in particular regions in the binary system. To obtain the variation of column density with phase, we make estimates of neutral wind density for the extreme cases that acceleration of the wind is totally suppressed, or not suppressed at all. An accurate description will lie between these extremes. In each case, a strong variation of column density with orbital phase resulted, similar to the variation of dip occurrence. This provides evidence that formation of the blobs in the wind which lead to absorption dips depends on the density of the neutral component in the wind, suggesting possible mechanisms for blob growth.Comment: 9 pages, Latex, 7 ps figures. accepted by MNRA

Carbohydrate effects on the inducement of the arginine deiminase pathway enzymes in wine lactic acid bacteria : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Microbiology at Massey University

Pages i-ii not in originalCharacterised by a fermentative sugar metabolism resulting in lactic acid as a major end product, the lactic acid bacteria (LAB) may be isolated from a broad range of sources. Dairy products, fermented vegetables, meats and baking products such as sourdough bread involve these organisms in a consistent and intentional manner in present times, no matter how accidental or fortuitous their initial involvement may have been. Alcoholic beverages such as beer, cider and, most pertinently here, wine are also affected by the presence of particular LAB. As conditions differ between nutrient environments so do the LAB found in wine differ to those isolated elsewhere - being both ethanol tolerant to the degree where growth is capable in 10% v/v ethanol and aciduric, able to maintain an active presence at acidic levels as great as pH 4 or less. This ability to remain viable during the primary yeast fermentation of juice into wine leads to these LAB being of no small practical interest in the wine industry. The process of malolactic fermentation (MLF) involves the wine LAB altering the law materials present in the juice and wine further, increasing the intricacies of the winemaking and final product. Primarily encouraged due to its effect of reducing wine acidity, MLF also alters flavour and aroma in what is generally thought to be an advantageous manner when applied correctly. Another factor thought to be of significance is an increase in biological stability. Found, for example, among the lactobacilli, pediococci and leuconostocs, the wine LAB are classed as either homofermentative or heterofermentative. Homofermenters commonly produce two moles of lactic acid per mole of glucose fermented, while heterofermenters form one mole each of lactic acid and carbon dioxide and varied quantities of ethanol and acetic acid from one mole of glucose. Natural or chance occurrences of wine LAB, whether as part of the microbiological community on the raw materials or from other sources - such as inoculation from contaminated equipment - were the original manner in which these organisms were introduced into the vinification equation. With the predilection towards quality control, standardisation and safety in the present day, the use of pure microbial starter cultures to initiate MLF has become increasingly widespread. In order to optimise the manipulation of wine LAB in both the laboratory and industry a thorough insight into their physiology and metabolism is an obvious necessity. Certain areas of interest have undergone more intensive study than others, with, for example, the catabolism of carbohydrates in both wine (Davis et al., 1986) and model wine systems (Liu et al., 1995a) having had a considerable amount of research compared to less primary sources of energy such as nitrogen metabolism

Managers Handbook for Software Development

Methods and aids for the management of software development projects are presented. The recommendations are based on analyses and experiences with flight dynamics software development. The management aspects of organizing the project, producing a development plan, estimation costs, scheduling, staffing, preparing deliverable documents, using management tools, monitoring the project, conducting reviews, auditing, testing, and certifying are described

New XMM-Newton analysis of three bright X-ray sources in M31 globular clusters, including a new black hole candidate

We present detailed analysis of three globular cluster X-ray sources in the XMM-Newton extended survey of M31. The X-ray counterpart to the M31 globular cluster Bo 45 (XBo 45) was observed with XMM-Newton on 2006 December 26. Its combined pn+MOS 0.3--10 keV lightcurve exhibited a r.m.s variability of ~10%, and its 0.3--7.0 keV emission spectrum was well described by an absorbed power law with photon index 1.44$\pm$0.12. Its variability and emission is characteristic of low mass X-ray binaries (LMXBs) in the low-hard state, whether the accretor is a neutron star or black hole. Such behaviour is typically observed at luminosities \la10% Eddington. However, XBo 45 exhibited this behaviour at an unabsorbed, 0.3--10 keV luminosity of 2.5$\pm0.2\times 10^{38}$ erg s$^{-1}$, or{~140%} Eddington for a 1.4 $M_{\odot}$ neutron star accreting hydrogen. Hence, we identify XBo 45 as a new candidate black hole LMXB. XBo 45 appears to have been consistently bright for ~30 years, consistent with theoretical prediction for a globular cluster black hole binary formed via tidal capture. Bo 375 was observed in the 2007, January 2 XMM-Newton observation, and has a two-component spectrum that is typical for a bright neutron star LMXB. Bo 135 was observed in the same field as Bo 45, and could contain either a black hole or neutron star.Comment: Accepted by ApJ, 16 pages, 5 figures. This version includes the final changes made at the request of the refere

Developing a quality assurance metric: a panoptic view

This article is a post-print of the published article that may be accessed at the link below. Copyright @ 2006 Sage Publications.There are a variety of techniques that lecturers can use to get feedback on their teaching - for example, module feedback and coursework results. However, a question arises about how reliable and valid are the content that goes into these quality assurance metrics. The aim of this article is to present a new approach for collecting and analysing qualitative feedback from students that could be used as the first stage in developing more reliable quality assurance metrics. The approach, known as the multi-dimensional crystal view, is based on the belief that individuals have different views on the benefits that the embedded process in a system can have on the behaviour of the system. The results of this study indicate that in the context of evaluation and feedback methods, the multi-dimensional approach appears to provide the opportunity for developing more effective student feedback mechanisms

The Structure and X-ray Recombination Emission of a Centrally Illuminated Accretion Disk Atmosphere and Corona

We model an accretion disk atmosphere and corona photoionized by a central X-ray continuum source. We calculate the opacity and radiation transfer for an array of disk radii, to obtain the two-dimensional structure of the disk and its X-ray recombination emission. The atmospheric structure is insensitive to the viscosity alpha. We find a feedback mechanism between the disk structure and the central illumination, which expands the disk and increases the solid angle subtended by the atmosphere. We model the disk of a neutron star X-ray binary. We map the temperature, density, and ionization structure of the disk, and we simulate the high resolution spectra observable with the Chandra and XMM-Newton grating spectrometers. The X-ray emission lines from the disk atmosphere are detectable, especially for high-inclination binary systems. The grating observations of two classes of X-ray binaries already reveal important spectral similarities with our models. The line spectrum is very sensitive to the structure of each atmospheric layer, and it probes the heating mechanisms in the disk. The model spectrum is dominated by double-peaked lines of H-like and He-like ions, plus weak Fe L. Species with a broad range of ionization levels coexist at each radius: from Fe XXVI in the hot corona, to C VI at the base of the atmosphere. The choice of stable solutions affects the spectrum, since a thermal instability is present in the regime where the X-ray recombination emission is most intense.Comment: 32 pages, incl. 26 figures, accepted for publication in Ap

X-ray Emission Properties of Large Scale Jets, Hotspots and Lobes in Active Galactic Nuclei

We examine a systematic comparison of jet-knots, hotspots and radio lobes recently observed with Chandra and ASCA. This report will discuss the origin of their X-ray emissions and investigate the dynamics of the jets. The data was compiled at well sampled radio (5GHz) and X-ray frequencies (1keV) for more than 40 radio galaxies. We examined three models for the X-ray production: synchrotron (SYN), synchrotron self-Compton (SSC) and external Compton on CMB photons (EC). For the SYN sources -- mostly jet-knots in nearby low-luminosity radio galaxies -- X-ray photons are produced by ultrarelativistic electrons with energies 10-100 TeV that must be accelerated in situ. For the other objects, conservatively classified as SSC or EC sources, a simple formulation of calculating the ``expected'' X-ray fluxes under an equipartition hypothesis is presented. We confirmed that the observed X-ray fluxes are close to the expected ones for non-relativistic emitting plasma velocities in the case of radio lobes and majority of hotspots, whereas considerable fraction of jet-knots is too bright at X-rays to be explained in this way. We examined two possibilities to account for the discrepancy in a framework of the inverse-Compton model: (1) magnetic field is much smaller than the equipartition value, and (2) the jets are highly relativistic on kpc/Mpc scales. We concluded, that if the inverse-Compton model is the case, the X-ray bright jet-knots are most likely far from the minimum-power condition. We also briefly discuss the other possibility, namely that the observed X-ray emission from all of the jet-knots is synchrotron in origin.Comment: 20 pages, 10 figures, accepted for publication in the Astrophysical Journal, vol.62

Kripke Semantics for Martin-L\"of's Extensional Type Theory

It is well-known that simple type theory is complete with respect to non-standard set-valued models. Completeness for standard models only holds with respect to certain extended classes of models, e.g., the class of cartesian closed categories. Similarly, dependent type theory is complete for locally cartesian closed categories. However, it is usually difficult to establish the coherence of interpretations of dependent type theory, i.e., to show that the interpretations of equal expressions are indeed equal. Several classes of models have been used to remedy this problem. We contribute to this investigation by giving a semantics that is standard, coherent, and sufficiently general for completeness while remaining relatively easy to compute with. Our models interpret types of Martin-L\"of's extensional dependent type theory as sets indexed over posets or, equivalently, as fibrations over posets. This semantics can be seen as a generalization to dependent type theory of the interpretation of intuitionistic first-order logic in Kripke models. This yields a simple coherent model theory, with respect to which simple and dependent type theory are sound and complete

Surfaces roughness effects on the transmission of Gaussian beams by anisotropic parallel plates

Influence of the plate surfaces roughness in precise ellipsometry experiments is studied. The realistic case of a Gaussian laser beam crossing a uniaxial platelet is considered. Expression for the transmittance is determined using the first order perturbation theory. In this frame, it is shown that interference takes place between the specular transmitted beam and the scattered field. This effect is due to the angular distribution of the Gaussian beam and is of first order in the roughness over wavelength ratio. As an application, a numerical simulation of the effects of quartz roughness surfaces at normal incidence is provided. The interference term is found to be strongly connected to the random nature of the surface roughness.Comment: 18 pages, Journal of Physics D: Applied Physics, volume 36, issue 21, pages 2697 - 270

Providing Self-Aware Systems with Reflexivity

We propose a new type of self-aware systems inspired by ideas from higher-order theories of consciousness. First, we discussed the crucial distinction between introspection and reflexion. Then, we focus on computational reflexion as a mechanism by which a computer program can inspect its own code at every stage of the computation. Finally, we provide a formal definition and a proof-of-concept implementation of computational reflexion, viewed as an enriched form of program interpretation and a way to dynamically "augment" a computational process.Comment: 12 pages plus bibliography, appendices with code description, code of the proof-of-concept implementation, and examples of executio