Multifrequency nature of the 0.75 mHz feature in the X-ray light curves of the nova V4743 Sgr

We present timing analyses of eight X-ray light curves and one optical/UV light curve of the nova V4743 Sgr (2002) taken by CHANDRA and XMM on days after outburst: 50 (early hard emission phase), 180, 196, 302, 371, 526 (super soft source, SSS, phase), and 742 and 1286 (quiescent emission phase). We have studied the multifrequency nature and time evolution of the dominant peak at ~0.75 mHz using the standard Lomb-Scargle method and a 2-D sine fitting method. We found a double structure of the peak and its overtone for days 180 and 196. The two frequencies were closer together on day 196, suggesting that the difference between the two peaks is gradually decreasing. For the later observations, only a single frequency can be detected, which is likely due to the exposure times being shorter than the beat period between the two peaks, especially if they are moving closer together. The observations on days 742 and 1286 are long enough to detect two frequencies with the difference found for day 196, but we confidently find only a single frequency. We found significant changes in the oscillation frequency and amplitude. We have derived blackbody temperatures from the SSS spectra, and the evolution of changes in frequency and blackbody temperature suggests that the 0.75-mHz peak was modulated by pulsations. Later, after nuclear burning had ceased, the signal stabilised at a single frequency, although the X-ray frequency differs from the optical/UV frequency obtained consistently from the OM onboard XMM and from ground-based observations. We believe that the late frequency is the white dwarf rotation and that the ratio of spin/orbit period strongly supports that the system is an intermediate polar.Comment: 17 pages, 22 figures, 7 tables, accepted for publication in MNRA

Development of a Methodology for Modelling Consumers’ Low Input Food Purchases

This paper explains the development of a methodology to model consumers’ purchases of low input and organic foods. The focus of the research design is the need to create value and satisfaction that exceeds consumers’ expectations and induces loyalty. The adopted analytical framework adopts a structural equation model (SEM) in the context of consumer loyalty research to explore the determinants of consumer loyalty in terms of constructs of perceived quality, perceived risk, sacrifice, perceived value and satisfaction. A General Model is proposed that permits the specification of nested models and hence, tests for the suitability of preferred models. The primary research instrument is a questionnaire applied to four products in five countries. The questionnaire collects data to inform the SEM and in addition, includes measures of attitudes to foods in general, and attitudes to, and beliefs about organic food

Nonequilibrium distribution functions for quantum transport: universality and approximation for the steady state regime

We derive a general expression for the electron nonequilibrium (NE) distribution function in the context of steady state quantum transport through a two-terminal nanodevice with interaction. The central idea for the use of NE distributions for open quantum systems is that both the NE and many-body (MB) effects are taken into account in the statistics of the finite size system connected to reservoirs. We develop an alternative scheme to calculate the NE steady state properties of such systems. The method, using NE distribution and spectral functions, presents several advantages, and is equivalent to conventional steady-state NE Green's functions (NEGF) calculations when the same level of approximation for the MB interaction is used. The advantages of our method resides in the fact that the NE distribution and spectral functions have better analytic behaviour for numerical calculations. Furthermore our approach offer the possibility of introducing further approximations, not only at the level of the MB interaction as in NEGF, but also at the level of the functional form used for the NE distributions. For the single level model with electron-phonon coupling we have considered, such approximations provide a good representation of the exact results, for either the NE distributions themselves or the transport properties. We also derive the formal extensions of our method for systems consisting of several electronic levels and several vibration modes.Comment: paper accepted for publication in Phys. Rev. B (fig 4 now correct

Early Super Soft Source spectra in RS Oph

Recent Swift X-ray monitoring campaigns of novae have revealed extreme levels of variability during the early super-soft-source (SSS) phase. The first time this was observed was during the 2006 outburst of the recurrent nova RS Oph which was also extensively covered by grating observations with XMM-Newton and Chandra. I focus here on an XMM-Newton observation taken on day 26.1, just before Swift confirmed the start of the SSS phase, and a Chandra observation taken on day 39.7. The first observation probes the evolution of the shock emission produced by the collision of the nova ejecta with the stellar wind of the companion. The second observation contains bright SSS emission longwards of 15A while at short wavelengths, the shock component can be seen to have hardly changed. On top of the SSS continuum, additional emission lines are clearly seen, and I show that they are much stronger than those seen on day 26.1, indicating line pumping caused by the SSS emission. The lightcurve on day 39.7 is highly variable on short time scales while the long-term Swift light curve was still variable. In 2007, we have shown that brightness variations are followed by hardness variations, lagging behind 1000 seconds. I show now that the hardness variations are owed to variations in the depth of the neutral hydrogen column density of order 25%, particularly affecting the oxygen K-shell ionization edge at 0.5 keV.Comment: Accepted for Acta Polytechnica. 4 pages, 4 figures, conference proceedings PALERMO WORKSHOP 201

An investigation into the use of CCTV footage to improve likeness in facial composites

Facial composites are an important investigative tool and have been used in numerous high-profile cases (e.g. Yorkshire Ripper). Despite this, a great deal of research has indicated that composites often portray very poor facial resemblance to the suspect/target. While some of the difficulties with the older composite systems (e.g. Photofit and Identikit) were due to system design (see e.g. Ellis, Shepherd & Davies, 1975; Davies, Ellis & Shepherd, 1978; Laughery & Fowler (1980), the hit rate for composites constructed with more modern systems (e.g. E-FIT and PROfit) can still be very low (e.g. Frowd et al. 2005). While research has indicated that composite likeness can be improved at test by combining composites from multiple witnesses (e.g. Bennet, Brace, Pike, & Kemp 1999; Bruce, Ness, Hancock, Newman, & Rarity, 2002; Ness, 2003) research on improving composites during construction has produced mixed results

POPULATION AND THE ENVIRONMENT: FRAMEWORKS FOR ANALYSIS

This working paper is one of a series the EPAT/MUCIA Population and Environmental and Natural Resources team is producing. It examines major ways of thinking about the population-environment relationship over the past two centuries. The paper begins with Malthus and reviews developments to the present. Then it examines in detail six current frameworks or models for analyzing population-environment relationships. The six models include Bongaarts', Clark's, and Harrison's attempts to identify the relative impact of population growth on a limited number of forms of environmental degradation. It also examines the more complex Meadows, Meadows, and Randers WORLD3 dynamic model of the global system and International Institute of Applied Systems Analysis (IIASA) population-environment model now being applied to Mauritius. A basic finding of these models is that population growth can have a major impact on the environment. However, the impact is never simple and direct, and human organization always moderates its effect. Further, we cannot expect that slowing population growth will alleviate environmental pressures in the near term. Finally, achieving sustainable development will require a combined attack on population growth, consumption, and a variety of other human patterns of production.Resource /Energy Economics and Policy,

The supersoft X-ray source in V5116 Sgr I. The high resolution spectra

Classical novae occur on the surface of an accreting white dwarf in a binary system. After ejection of a fraction of the envelope and when the expanding shell becomes optically thin to X-rays, a bright source of supersoft X-rays arises, powered by residual H burning on the surface of the white dwarf. While the general picture of the nova event is well established, the details and balance of accretion and ejection processes in classical novae are still full of unknowns. The long-term balance of accreted matter is of special interest for massive accreting white dwarfs, which may be promising supernova Ia progenitor candidates. V5116 Sgr was observed as a bright and variable supersoft X-ray source by XMM-Newton 610~days after outburst. The light curve showed a periodicity consistent with the orbital period. During one third of the orbit the luminosity was a factor of seven brighter than during the other two thirds of the orbital period. In the present work we aim to disentangle the X-ray spectral components of V5116 Sgr and their variability. We present the high resolution spectra obtained with XMM-Newton RGS and Chandra LETGS/HRC-S in March and August 2007. The grating spectrum during the periods of high-flux shows a typical hot white dwarf atmosphere dominated by absorption lines of N VI and N VII. During the low-flux periods, the spectrum is dominated by an atmosphere with the same temperature as during the high-flux period, but with several emission features superimposed. Some of the emission lines are well modeled with an optically thin plasma in collisional equilibrium, rich in C and N, which also explains some excess in the spectra of the high-flux period. No velocity shifts are observed in the absorption lines, with an upper limit set by the spectral resolution of 500 km/s, consistent with the expectation of a non-expanding atmosphere so late in the evolution of the post-nova.Comment: 12 pages, 15 figures, 4 tables; accepted for publication in Astronomy and Astrophysic