A complete sample of 21-cm absorbers at z~1.3: Giant Metrewave Radio Telescope Survey Using MgII Systems

We present the results of a systematic Giant Metrewave Radio Telescope (GMRT) survey of 21-cm absorption in a representative and unbiased sample of 35 strong MgII systems in the redshift range: zabs~1.10-1.45, 33 of which have W_r>1 \AA. The survey using ~400hrs of telescope time has resulted in 9 new 21-cm detections and stringent 21-cm optical depth upper limits (median 3-sigma optical depth per 10 km/s of 0.017) for the remaining 26 systems. This is by far the largest number of 21-cm detections from any single survey of intervening absorbers. Prior to our survey no intervening 21-cm system was known in the above redshift range and only one system was known in the redshift range 0.7<z<1.5. We discuss the relation between the detectability of 21-cm absorption and various properties of UV absorption lines. We show that if MgII systems are selected with the following criteria, MgII doublet ratio <1.3 and W_r(MgI)/W_r(MgII)>0.3, then a detection rate of 21-cm absorption up to 90% can be achieved. We estimate n_{21}, the number per unit redshift of 21-cm absorbers with W_r(Mg(II)>W_o and integrated optical depth Tau_{21}>Tau_o and show that n_{21} decreases with increasing redshift. In particular, for W_o=1.0 \AA and Tau_o>0.3 km\s, n_{21} falls by a factor 4 from =0.5 to =1.3. The evolution seems to be stronger for stronger MgII systems. Using a subsample of systems for which high frequency VLBA images are available, we show that the effect is not related to the structure of the background radio sources and is most probably due to the evolution of the cold neutral medium filling factor in MgII systems. We find no correlation between the velocity spread of the 21-cm absorption feature and W_r(MgII) at z~1.3.Comment: 22 pages, 8 tables, 12 figures, accepted for publication in MNRA

Search for cold gas in z>2 damped Lyman-alpha systems: 21-cm and H_2 absorption

(Abridged) We present the results of a systematic GBT and GMRT survey for 21-cm absorption in a sample of 10 DLAs at 2<z_abs<3.4. Analysis of L-band VLBA images of the background QSOs are also presented. We detect 21-cm absorption in only one DLA (at z_abs = 3.1745 towards J1337+3152). Combining our data with the data from the literature (a sample of 28 DLAs) and assuming the measured core fraction at milliarcsecond scale to represent the gas covering factor, we find that the HI gas in DLAs at z> 2 is predominantly constituted by WNM. The detection rate of 21-cm absorption seems to be higher for systems with higher N(HI) or metallicity. However, no clear correlation is found between the integrated 21-cm optical depth (or spin temperature) and either N(HI), metallicity or velocity spread of the low ionization species. There are 13 DLAs in our sample for which high resolution optical spectra covering the expected wavelength range of H_2 absorption are available. We report the detection of H_2 molecules in the z_abs = 3.3871 21-cm absorber towards J0203+1134 (PKS 0201+113). In 8 cases, neither H_2 nor 21-cm absorption are detected. The lack of 21-cm and H_2 absorption in these systems can be explained if most of the HI in these DLAs originate from low density high temperature gas. In one case we have a DLA with 21-cm absorption not showing H_2 absorption. In two cases, both species are detected but do not originate from the same velocity component. In the remaining 2 cases 21-cm absorption is not detected despite the presence of H_2 with evidence for the presence of cold gas. All this is consistent with the idea that the H_2 components seen in DLAs are compact (with sizes of < 15 pc) and contain only a small fraction (i.e typically <10%) of the total N(HI) measured in the DLAs.Comment: Accepted for publication in MNRA

Radiation pattern of a classical dipole in a photonic crystal: photon focusing

The asymptotic analysis of the radiation pattern of a classical dipole in a photonic crystal possessing an incomplete photonic bandgap is presented. The far-field radiation pattern demonstrates a strong modification with respect to the dipole radiation pattern in vacuum. Radiated power is suppressed in the direction of the spatial stopband and strongly enhanced in the direction of the group velocity, which is stationary with respect to a small variation of the wave vector. An effect of radiated power enhancement is explained in terms of \emph{photon focusing}. Numerical example is given for a square-lattice two-dimensional photonic crystal. Predictions of asymptotic analysis are substantiated with finite-difference time-domain calculations, revealing a reasonable agreement.Comment: Submitted to Phys. Rev.

The origin and prevention of pandemics.

Despite the fact that most emerging diseases stem from the transmission of pathogenic agents from animals to humans, the factors that mediate this process are still ill defined. What is known, however, is that the interface between humans and animals is of paramount importance in the process. This review will discuss the importance of the human-animal interface to the disease emergence process. We also provide an overview of factors that are believed to contribute to the origin and global spread of emerging infectious diseases and offer suggestions that may serve as future prevention strategies, such as social mobilization, public health education, behavioral change, and communication strategies. Because there exists no comprehensive global surveillance system to monitor zoonotic disease emergence, the intervention measures discussed herein may prove effective temporary alternatives

Phase separation and rotor self-assembly in active particle suspensions

Adding a non-adsorbing polymer to passive colloids induces an attraction between the particles via the `depletion' mechanism. High enough polymer concentrations lead to phase separation. We combine experiments, theory and simulations to demonstrate that using active colloids (such as motile bacteria) dramatically changes the physics of such mixtures. First, significantly stronger inter-particle attraction is needed to cause phase separation. Secondly, the finite size aggregates formed at lower inter-particle attraction show unidirectional rotation. These micro-rotors demonstrate the self assembly of functional structures using active particles. The angular speed of the rotating clusters scales approximately as the inverse of their size, which may be understood theoretically by assuming that the torques exerted by the outermost bacteria in a cluster add up randomly. Our simulations suggest that both the suppression of phase separation and the self assembly of rotors are generic features of aggregating swimmers, and should therefore occur in a variety of biological and synthetic active particle systems.Comment: Main text: 6 pages, 5 figures. Supplementary information: 5 pages, 4 figures. Supplementary movies available from httP://www.pnas.org/lookup/suppl/doi:10.1073/pnas.1116334109/-/DCSupplementa

Inflation-Produced Magnetic Fields in R^n F^2 and I F^2 models

We re-analyze the production of seed magnetic fields during Inflation in (R/m^2)^n F_{\mu \nu}F^{\mu \nu} and I F_{\mu \nu}F^{\mu \nu} models, where n is a positive integer, R the Ricci scalar, m a mass parameter, and I \propto \eta^\alpha a power-law function of the conformal time \eta, with \alpha a positive real number. If m is the electron mass, the produced fields are uninterestingly small for all n. Taking m as a free parameter we find that, for n \geq 2, the produced magnetic fields can be sufficiently strong in order to seed dynamo mechanism and then to explain galactic magnetism. For \alpha \gtrsim 2, there is always a window in the parameters defining Inflation such that the generated magnetic fields are astrophysically interesting. Moreover, if Inflation is (almost) de Sitter and the produced fields almost scale-invariant (\alpha \simeq 4), their intensity can be strong enough to directly explain the presence of microgauss galactic magnetic fields.Comment: 5 pages, 2 figures. Minor revisions. References added. Accepted for publication in Phys. Rev.

C IV and other metal absorption line systems in 18 z=4 quasars

We present a modest survey of quasar metal line absorption systems at redshifts 2.3-4.5. Relatively high signal-to-noise ratio (similar to25 pixel(-1)) spectra of 18 quasars at 2 Angstrom FWHM resolution show many absorption systems with strong metal lines in the region redward of the Lyalpha emission lines. We conducted a systematic search and found 55 C IV doublets, 19 Si IV doublets, three Mg II doublets, and seven N v doublets. The present data alone hint that the number of C IV absorption doublets per unit redshift, N(z), decreases with increasing redshift for 2.3 0.3 Angstrom are approximately 55% of all C IV systems with W > 0.15 Angstrom, but by z similar or equal to 4 that percentage is less than 37%. Similar conclusions were reached by Sargent, Boksenberg, & Steidel and by Steidel, primarily at lower redshifts. However, we measure approximately twice the density of C IV systems at 2.3 0.15 Angstrom that was reported by Steidel. The probability that our sample and previous samples come from the same distribution is only similar to2%. But this could be a statistical accident because it is an a posteriori comparison. We believe that the systems that we report are real, and we have no other explanation for this difference. For Si IV absorption lines, there is a 1 sigma hint of evolution with the same sense. In contrast, Lyalpha and Mg II systems are known to show evolution of the opposite sense with more absorbers at larger redshifts. The physical cause of this difference may be a mixture of ionization and chemical evolution effects.ArticleASTRONOMICAL JOURNAL. 123(4):1847-1863 (2002)journal articl

From dictatorship to a reluctant democracy: Stroke therapists talking about self-management

This article is made available through the Brunel Open Access Publishing Fund.Purpose: Self-management is being increasingly promoted within chronic conditions including stroke. Concerns have been raised regarding professional ownership of some programmes, yet little is known of the professional’s experience. This paper aims to present the views of trained therapists about the utility of a specific self-management approach in stroke rehabilitation. Method: Eleven stroke therapists trained in the self-management approach participated in semi-structured interviews. These were audio recorded, transcribed verbatim and analysed thematically. Results: Two overriding themes emerged. The first was the sense that in normal practice therapists act as ‘‘benign dictators’’, committed to help their patients, but most comfortable when they, the professional, are in control. Following the adoption of the self-management approach therapists challenged themselves to empower stroke survivors to take control of their own recovery. However, therapists had to confront many internal and external challenges in this transition of power resulting in the promotion of a somewhat ‘‘reluctant democracy’’. Conclusions: This study illustrates that stroke therapists desire a more participatory approach to rehabilitation. However, obstacles challenged the successful delivery of this goal. If self-management is an appropriate model to develop in post stroke pathways, then serious consideration must be given to how and if these obstacles can be overcome

Wild primate populations in emerging infectious disease research: the missing link?

Wild primate populations, an unexplored source of information regarding emerging infectious disease, may hold valuable clues to the origins and evolution of some important pathogens. Primates can act as reservoirs for human pathogens. As members of biologically diverse habitats, they serve as sentinels for surveillance of emerging pathogens and provide models for basic research on natural transmission dynamics. Since emerging infectious diseases also pose serious threats to endangered and threatened primate species, studies of these diseases in primate populations can benefit conservation efforts and may provide the missing link between laboratory studies and the well-recognized needs of early disease detection, identification, and surveillance