1834 research outputs found
Sort by
Polarization of the Sunyaev-Zel'dovich effect: relativistic imprint of thermal and non-thermal plasma
No full textAbridged] Inverse Compton scattering of CMB fluctuations off cosmic electron plasma generates a polarization of the associated Sunyaev-Zel'dovich (SZ) effect. This signal has been studied so far mostly in the non-relativistic regime and for a thermal electron population and, as such, has limited astrophysical applications. Partial attempts to extend this calculation for a thermal electron plasma in the relativistic regime have been done but cannot be applied to a general relativistic electron distribution. Here we derive a general form of the SZ effect polarization valid in the full relativistic approach for both thermal and non-thermal electron plasmas, as well as for a generic combination of various electron population co-spatially distributed in the environments of galaxy clusters or radiogalaxy lobes. We derive the spectral shape of the Stokes parameters induced by the IC scattering of every CMB multipole, focusing on the CMB quadrupole and octupole that provide the largest detectable signals in galaxy clusters. We found that the CMB quadrupole induced Stoke parameter Q is always positive with a maximum amplitude at 216 GHz which increases slightly with increasing cluster temperature. The CMB octupole induced Q spectrum shows, instead, a cross-over frequency which depends on the cluster electron temperature, or on the minimum momentum p_1 as well as on the power-law spectral index of a non-thermal electron population. We discuss some possibilities to disentangle the quadrupole-induced Q spectrum from the octupole-induced one which allow to measure these quantities through the SZ effect polarization. We finally apply our model to the realistic case of the Bullet cluster and derive the visibility windows of the total, quandrupole-induced and octupole-induced Stoke parameter Q in the frequency ranges accessible to SKA, ALMA, MILLIMETRON and CORE++ experiments.National Research Foundation (South Africa
AGILE Observations of the Gravitational-wave Event GW150914
No full textWe report the results of an extensive search through the AGILE data for a gamma-ray counterpart to the LIGO gravitational-wave (GW) event GW150914. Currently in spinning mode, AGILE has the potential of cover 80% of the sky with its gamma-ray instrument, more than 100 times a day. It turns out that AGILE came within a minute of the event time of observing the accessible GW150914 localization region. Interestingly, the gamma-ray detector exposed ~65% of this region during the 100 s time intervals centered at −100 and +300 s from the event time. We determine a 2σ flux upper limit in the band 50 MeV–10 GeV, UL = 1.9 × 10−8 erg cm−2 s−1, obtained ~300 s after the event. The timing of this measurement is the fastest ever obtained for GW150914, and significantly constrains the electromagnetic emission of a possible high-energy counterpart. We also carried out a search for a gamma-ray precursor and delayed emission over five timescales ranging from minutes to days: in particular, we obtained an optimal exposure during the interval −150/−30 s. In all these observations, we do not detect a significant signal associated with GW150914. We do not reveal the weak transient source reported by Fermi-GBM 0.4 s after the event time. However, even though a gamma-ray counterpart of the GW150914 event was not detected, the prospects for future AGILE observations of GW sources are decidedly promising.National Research Foundation (South Africa
Intentionally introduced terrestrial invertebrates: patterns, risks, and options for management
No full textOur understanding and management of pathways of alien species introductions has improved significantly in the past few years. However, little attention has been paid in most parts of the world to the risks posed by the intentional introduction of alien terrestrial invertebrates which are not intended for use in biological control. We review the species and pathways involved in this intentional trade, and discuss key factors that mediate different aspects of risk. A total of 20 different intentions for the introduction of terrestrial invertebrates were identified. Uses and trade patterns have changed over time and further changes are likely in the future. In particular, invertebrates used in the pet trade, and as human food and animal feed are likely to increase in relevance. We assess priorities for future research and regulation based on the perceived “risk” of the uses including propagule pressure, security of captivity and ease of regulation. Regarding risk assessment, we examine three options: (a) using an existing generic protocol developed for a broad range of taxa; (b) developing a new protocol, possibly by adapting a protocol developed for other taxa; and (c) adopting the approach applied for biological control, i.e. structured experiments and observations. This review highlights the diversity of uses and associated threats of intentional terrestrial invertebrate introductions. It provides recommendations on how to tackle and prevent related issues and can therefore serve as a guideline for future work. We argue that the most suitable option for risk assessment might depend on the type or organism and the level of knowledge of the organism, as well as the intended use.National Research Foundation (South Africa
The social determinants of health and the role of the health care system: a case study of the significance of good governance in public hospitals in South Africa
No full textIncreasingly international and national policies are being directed at actions for the social determinants of health and for an integrated approach to health care provision, not only in terms of institutional co-operation but also stakeholder involvement. A key component of both these policies is the development of good governance principles in all health care agencies and organizations. A neglected dimension in these debates has been the role of the public hospital which remains a vital and expensive dimension of service provision. In a case study of a public hospital in South Africa, this paper charts the readiness of its management principles and activities to provide quality health care linked to population health and to contribute to the non-medical determinant of health. Using Taylor’s principles of good governance, we conclude that there is a mixture of good and not so good governance activity. The paper concludes by examining the external constraints on the public hospital and by providing suggestions for future activities.National Research Foundation (South Africa
National Health Insurance: South Africa’s most progressive reform to date
No full textAlthough the National Health Insurance (NHI) White Paper takes a socialist approach to universal health care, how will it be implemented in South Africa’s neo-liberal environment? Additionally, support from key stakeholders including citizens and doctors is necessary as is decentralisation and proper funding,National Research Foundation (South Africa
Op-Ed: Twenty questions for Adam Habib
No full textHere, then, are the questions for Habib:
1. Who owns these firms, what is their history, and what profits do they make?
2. How are their security personnel recruited and trained?
3. Are they members of a union, which one?
4. What is the command structure?
5. What physical force are they permitted to use in the most extreme circumstances? Physical contact, batons, pepper spray, tear gas, rubber bullets?
6. In terms of rank, who gives the commands to use such force?
7. Do the firms film their interventions? With what equipment?
8. To what extent do the security firms have regard for the Constitution’s provision for a right to protest peacefully and unarmed?
9. Do the uniformed security personnel wear name tags so that they can be identified?
10. If there is evidence of improper conduct, because security personnel touched women’s breasts for instance, what is the procedure for taking disciplinary action?
11. What is the gender profile of the security personnel?
12. How much are these security personnel paid?
13. Who advised the university about the appointment of the particular companies employed?
14. How much do they cost?
15. What deliverables are expected of them?
16. What is the time frame specified in contracts?
17. At an operational level, to whom are they answerable within the university?
18. Are they permitted to use violence that might cause bodily harm without reference to the university?
19. Under what circumstances would the Public Order Police intervene?
20. Do they engage in intelligence gathering or is that left to State Security and SAPS?National Research Foundation (South Africa
Seasonal reproduction in the Arabian spiny mouse, Acomys dimidiatus (Rodentia: Muridae) from Saudi Arabia: the role of rainfall and temperature
No full textIn deserts where unpredictable rainfall arises and a large variation in temperature occurs, this poses severe energetic and water related constraints on reproduction in small mammals and makes the use of photoperiod as cue for reproduction unreliable. In the present study, the gonad morphometrics, gonadal histology and endocrine profiles of the Arabian spiny mouse (Acomys dimidiatus) were studied over 12 consecutive months in a field population from western Saudi Arabia in an attempt to assess the seasonality of reproduction and gain insights into the environmental cues that may trigger reproduction in this species. Although sperm was present throughout the year, most reproductive parameters exhibited a seasonal pattern with a minimum in winter in both sexes and pregnancies were observed from spring to autumn. Whereas testes volume, the number of corpora lutea and progesterone levels were correlated with temperature, all other reproductive parameters were correlated with rainfall. Thus, it appears that A. dimidiatus ceases to breed during winter and uses rainfall as an environmental cue to initiate reproduction in the study area. However, the species appears to have the ability to reproduce throughout the year, if favourable conditions arise.National Research Foundation (South Africa
The distribution of mucous secreting cells in the gastrointestinal tracts of three small rodents from the Saudi-Arabian Peninsula: Acomys dimidiatus, Meriones rex and Meriones lybicus
No full textThe proportion of mucin phenotypes (which form the protective biofilm of the gastrointestinal tract) differs between intestinal regions. This study examines the distribution of mucin secreting cells in the gastrointestinal tracts of the Eastern spiny mouse (Acomys dimidiatus), King jird (Meriones rex) and Libyan jird (Meriones libycus), which inhabit the dry and hot deserts of Saudi Arabia. Intestinal tract samples were processed to wax and tissue sections stained with Alcian Blue-Periodic Acid Schiff (AB-PAS) and High Iron Diamine-Alcian Blue (HID-AB) in order to determine different mucin phenotypes by quantitative analysis. Mixed mucin secreting cells (combined neutral and acid) was the predominant mucin secreting cell type observed throughout the gastrointestinal tract in all species. Acid mucin secreting goblet cells were mainly located in the colon. A. dimidiatus presented with significantly more total sialo than sulfomucin secreting cells while the opposite was true for both Meriones species. The distribution of mucin secreting cells is therefore similar to previously reported results for small mammals not living under arid conditions.National Research Foundation (South Africa
Digging for answers: contributions of density- and frequency-dependent factors on ectoparasite burden in a social mammal
No full textDue to the density-dependent nature of parasite transmission parasites are generally assumed to constrain the evolution of sociality. However, evidence for a correlation between group size and parasite burden is equivocal, particularly for mammals. Host contact rates may be modified by mobility of the host and parasite as well as social barriers. In the current study, we used the common mole-rat (Cryptomys hottentotus hottentotus), a social subterranean rodent, as a model system to investigate the effect of host density and frequency of contact rates on ectoparasite burdens. To address these factors we used a study species that naturally varies in population densities and intergroup contact rates across its geographic range. We found that ectoparasite prevalence, abundance and species richness decreased with increasing host density at a regional scale. At the same time, measures of parasite burden increased with intergroup contact rates. Ectoparasite burdens decreased with colony size at the group level possibly as a result of increased grooming rates. Equating group size with population density might be too simplistic an approach when assessing parasite distributions in social mammals. Our data suggest that frequency-dependent mechanisms may play a much greater role at a population level than density-dependent mechanisms in determining parasite distributions in social species. We suggest that future studies should explicitly consider behavioural mechanisms that may affect parasite distributionNational Research Foundation (South Africa
Transport characteristics of n-ZnO/p-Si heterojunction as determined from temperature dependent current–voltage measurements
No full textZinc oxide (ZnO) nanorods have been synthesized by a two-step chemical bath deposition process on silicon substrates having different dopant densities and orientations. Scanning electron microscopy and X-ray diffraction analysis reveal that the orientation of the Si substrate does not affect the orientation, distribution or crystallinity of the nanostructures. The electrical properties of the ZnO/Si heterojunction are also investigated by current–voltage (I–V) measurements. The ideality factor is found to be 2.6 at 295 K, indicating that complex current transport mechanisms are at play. Temperature dependent I–V characteristics have been used to determine the dominant transport mechanism. The experimental results suggest that in the low bias region the current is dominated by a trap assisted multi-step tunneling process.National Research Foundation (South Africa