Accelerating expansion and change of signature

We show that some types of sudden singularities admit a natural explanation in terms of regular changes of signature on brane-worlds in AdS$_{5}$. The present accelerated expansion of the Universe and its possible ending at a sudden singularity may therefore simply be an indication that our braneworld is about to change its Lorentzian signature to an Euclidean one, while remaining fully regular. An explicit example of this behaviour satisfying the weak and strong energy conditions is presented.Comment: LaTeX, 4 pages. Uses the eas.cls class. To appear in the proceedings of the Spanish Relativity Meeting ERE'0

An investigation into the use of 3G mobile communications to provide telehealth services in rural KwaZulu-Natal

This article has been made available through the Brunel Open Access Publishing Fund.Abstract Background: We investigated the use of third-generation (3G) mobile communications to provide telehealth services in remote health clinics in rural KwaZulu-Natal, South Africa. Materials and Methods: We specified a minimal set of services as our use case that would be representative of typical activity and to provide a baseline for analysis of network performance. Services included database access to manage chronic disease, local support and management of patients (to reduce unnecessary travel to the hospital), emergency care (up to 8 h for an ambulance to arrive), e-mail, access to up-to-date information (Web), and teleclinics. We made site measurements at a representative set of health clinics to determine the type of coverage (general packet radio service [GPRS]/3G), its capabilities to support videoconferencing (H323 and Skype™ [Microsoft, Redmond, WA]) and audio (Skype), and throughput for transmission control protocol (TCP) to gain a measure of application performance. Results: We found that none of the remote health clinics had 3G service. The GPRS service provided typical upload speed of 44 kilobits per second (Kbps) and download speed of 64 Kbps. This was not sufficient to support any form of videoconferencing. We also observed that GPRS had significant round trip time (RTT), in some cases in excess of 750 ms, and this led to slow start-up for TCP applications. Conclusions: We found audio was always so broken as to be unusable and further observed that many applications such as Web access would fail under conditions of very high RTT. We found some health clinics were so remote that they had no mobile service. 3G, where available, had measured upload speed of 331 Kbps and download speed of 446 Kbps and supported videoconferencing and audio at all sites, but we frequently experienced 3G changing to GPRS. We conclude that mobile communications currently provide insufficient coverage and capability to provide reliable clinical services and would advocate dedicated wireless services where reliable communication is essential and use of store and forward for mobile applications.The Royal Society, United Kingdom

Gender Demographics and Perception in Librarianship

This article is an examination of the history of gender demographics in the field of librarianship. The historic development and subsequent feminization of librarianship continues to influence the gender wage gap and the disproportionate leadership bias in the field today. This article examines the stereotyping of librarians and the cyclical effect of genderizing the profession. Consideration of current trends and data in librarian demographics demonstrates a consistent decrease in gender diversity, accompanied by a troubling lack of women leaders and executives. Additionally, this article explores options for combating the gender perceptions that negatively impact women in library and information science fields, including management and negotiation training in graduate programs, increased emphasis on technological skills, and professional organization advocacy

Spacetime Ehlers group: Transformation law for the Weyl tensor

The spacetime Ehlers group, which is a symmetry of the Einstein vacuum field equations for strictly stationary spacetimes, is defined and analyzed in a purely spacetime context (without invoking the projection formalism). In this setting, the Ehlers group finds its natural description within an infinite dimensional group of transformations that maps Lorentz metrics into Lorentz metrics and which may be of independent interest. The Ehlers group is shown to be well defined independently of the causal character of the Killing vector (which may become null on arbitrary regions). We analyze which global conditions are required on the spacetime for the existence of the Ehlers group. The transformation law for the Weyl tensor under Ehlers transformations is explicitly obtained. This allows us to study where, and under which circumstances, curvature singularities in the transformed spacetime will arise. The results of the paper are applied to obtain a local characterization of the Kerr-NUT metric.Comment: LaTeX, 25 pages, no figures, uses Amstex. Accepted for publication in Classical and Quantum Gravit

The adsorption of sulfur by microporous materials

The sorption of sulfur by the zeolites NaX (= 13X) and CaA (= 5A) and an activated charcoal prepared from sugar was investigated at temperatures between 150 and 350°C and relative sulfur pressures between 10−4 and 10−1. The adsorbate-adsorbate interaction indicated by the S-shaped isotherm for the zeolite NaX points to physical or chemical interaction of sulfur molecules in neighboring supercages. In CaA adsorbate-adsorbate interaction between sulfur species in different supercages is negligible. Below 200°C the rate of sulfur uptake by the zeolite CaA is determined by the diffusion rate of a sulfur species through the zeolitic framework. In activated charcoal a strong adsorbate-adsorbent interaction is present and part of the sulfur is chemisorbed at 350°C. The differences in the density of the adsorbed sulfur determined with three different methods indicate that even at full saturation of the micropore volume with sulfur, there is still some residual adsorption volume

The mechanism of pyridine hydrogenolysis on molybdenum-containing catalysts : III. Cracking, hydrocracking, dehydrogenation and disproportionation of pentylamine

The conversion of pentylamine on a MoO3-Al2O3 catalyst was studied between 250 and 350 °C, at various hydrogen pressures. The reactions observed were cracking to pentene and ammonia, hydrocracking to pentane and ammonia, dehydrogenation to pentanimine and butylcarbonitrile, and disproportionation to ammonia and dipentylamine.\ud \ud The equilibrium between pentylamine, dipentylamine and ammonia appeared to be established under most of the experimental conditions. The equilibrium constant is about 9 at 250 °C and about 5 at 320 °C. The disproportionation reaction is zero order in hydrogen and of −1 order in the initial pentylamine pressure.\ud \ud Dehydrogenation was observed at low hydrogen pressures, and especially at higher temperatures; the reaction is first order in pentylamine.\ud \ud Both cracking and hydrocracking take place, mainly above 300 °C. Hydrocracking appears to be half order in hydrogen; the rate of cracking is almost independent of the hydrogen pressure. The hydrocarbon formation is of zero order in pentylamine or dipentylamine.\ud \ud The same type of reactions (except hydrocracking) take place on alumina, but with a far lower reaction rate