A Cosmic Ray Positron Anisotropy due to Two Middle-Aged, Nearby Pulsars?

Geminga and B0656+14 are the closest pulsars with characteristic ages in the ran ge of 100 kyr to 1 Myr. They both have spindown powers of the order 3e34 erg/s at present. The winds of these pulsars had most probably powered pulsar wind nebulae (PWNe) that broke up less than about 100 kyr after the birth of the pulsars. Assuming that leptonic particles accelerated by the pulsars were confined in th e PWNe and were released into the interstellar medium (ISM) on breakup of the PW Ne, we show that, depending on the pulsar parameters, both pulsars make a non-ne gligible contribution to the local cosmic ray (CR) positron spectrum, and they m ay be the main contributors above several GeV. The relatively small angular dist ance between Geminga and B0656+14 thus implies an anisotropy in the local CR po sitron flux at these energies. We calculate the contribution of these pulsars to the locally observed CR electr on and positron spectra depending on the pulsar birth period and the magnitude o f the local CR diffusion coefficient. We further give an estimate of the expecte d anisotropy in the local CR positron flux. Our calculations show that within the framework of our model, the local CR posit ron spectrum imposes constraints on pulsar parameters for Geminga and B0656+14, notably the pulsar period at birth, and also the local interstellar diffusion co efficient for CR leptons.Comment: accepted for publication in ApJ

Quantitative and qualitative analysis of sterols/sterolins and hypoxoside contents of three Hypoxis (African potato) spp.

The glycoside, hypoxoside, identified and isolated from the corms of the African potato (Hypoxis hemerocallidea) has shown promising anticancer activities. The African potato is used as an Africantraditional medicine for its nutritional and medicinal properties. Most research has been carried out on H. hemerocallidea (formerly known as H. rooperi), with very little or nothing on other Hypoxis spp. Thinlayer chromatography (TLC) was used to confirm the presence of sterols/sterolins, whereas a GC method was developed to identify and quantify sterols (especially β-sitosterol) in chloroform extracts of H. hemerocallidea, H. stellipilis and H. sobolifera var. sobolifera. High performance liquid chromatography (HPLC) was used to identify and quantify hypoxoside content in these Hypoxis spp. TLC results showed that H. sobolifera var. sobolifera contained the most sterols and sterolins compared to the other two Hypoxis spp. Gas chromatography (GC) results show that β-sitosterol and campesterol were the two main phytosterols present in the Hypoxis extracts. H. sobolifera var. sobolifera and H. hemerocallidea contained the most β-sitosterol and hypoxoside, respectively. H. sobolifera and H. hemerocallidea contained 74.69 µg of β-sitosterol and 12.27 µg of hypoxoside per 5 mg of chloroform extracts, respectively. These results show a significant difference in the sterol/sterolin and hypoxoside contents between species of the genus Hypoxis, which may influence their degree of biological activities

Unidentified Galactic High-Energy Sources as Ancient Pulsar Wind Nebulae in the light of new high energy observations and the new code

In a Pulsar Wind Nebula (PWN), the lifetime of inverse Compton (IC) emitting electrons exceeds the lifetime of its progenitor pulsar (as well as its shell-type remnant), but it also exceeds the age of those that emit via synchrotron radiation. Therefore, during its evolution, the PWN can remain bright in IC so that its GeV-TeV gamma-ray flux remains high for timescales much larger (for 10^5 - 10^6 yrs) than the pulsar lifetime and the X-ray PWN lifetime. In this scenario, the magnetic field in the cavity induced by the wind of the progenitor star plays a crucial role. This scenario is in line with the discovery of several unidentified or "dark" sources in the TeV gamma-ray band without X-ray counterparts; and it is also finding confirmation in the recent discoveries at GeV gamma rays. Moreover, these consequences could be also important for reinterpreting the detection of starburst galaxies in the TeV gamma-ray band when considering a leptonic origin of the gamma-ray signal. Both theoretical aspects and their observational proofs will be discussed, as well as the first results of our new modeling code.Comment: Proceedings of the 5th International Symposium on High-Energy Gamma-Ray Astronomy (Gamma2012

Gamma-rays from millisecond pulsars in Globular Clusters

Globular clusters (GCs) with their ages of the order of several billion years contain many final products of evolution of stars such as: neutron stars, white dwarfs and probably also black holes. These compact objects can be at present responsible for the acceleration of particles to relativistic energies. Therefore, gamma-ray emission is expected from GCs as a result of radiation processes occurring either in the inner magnetosperes of millisecond pulsars or in the vicinity of accreting neutron stars and white dwarfs or as a result of interaction of particles leaving the compact objects with the strong radiation field within the GC. Recently, GeV gamma-ray emission has been detected from several GCs by the new satellite observatory Fermi. Also Cherenkov telescopes reported interesting upper limits at the TeV energies which start to constrain the content of GCs. We review the results of these gamma-ray observations in the context of recent scenarios for their origin.Comment: 20 pages, 9 figures, will be published in Astrophysics and Space Science Series (Springer), eds. N. Rea and D.F. Torre

Turnover, account value and diversification of real traders: evidence of collective portfolio optimizing behavior

Despite the availability of very detailed data on financial market, agent-based modeling is hindered by the lack of information about real trader behavior. This makes it impossible to validate agent-based models, which are thus reverse-engineering attempts. This work is a contribution to the building of a set of stylized facts about the traders themselves. Using the client database of Swissquote Bank SA, the largest on-line Swiss broker, we find empirical relationships between turnover, account values and the number of assets in which a trader is invested. A theory based on simple mean-variance portfolio optimization that crucially includes variable transaction costs is able to reproduce faithfully the observed behaviors. We finally argue that our results bring into light the collective ability of a population to construct a mean-variance portfolio that takes into account the structure of transaction costsComment: 26 pages, 9 figures, Fig. 8 fixe

Prospects for Observations of Pulsars and Pulsar Wind Nebulae with CTA

The last few years have seen a revolution in very-high gamma-ray astronomy (VHE; E>100 GeV) driven largely by a new generation of Cherenkov telescopes (namely the H.E.S.S. telescope array, the MAGIC and MAGIC-II large telescopes and the VERITAS telescope array). The Cherenkov Telescope Array (CTA) project foresees a factor of 5 to 10 improvement in sensitivity above 0.1 TeV, extending the accessible energy range to higher energies up to 100 TeV, in the Galactic cut-off regime, and down to a few tens GeV, covering the VHE photon spectrum with good energy and angular resolution. As a result of the fast development of the VHE field, the number of pulsar wind nebulae (PWNe) detected has increased from one PWN in the early '90s to more than two dozen firm candidates today. Also, the low energy threshold achieved and good sensitivity at TeV energies has resulted in the detection of pulsed emission from the Crab Pulsar (or its close environment) opening new and exiting expectations about the pulsed spectra of the high energy pulsars powering PWNe. Here we discuss the physics goals we aim to achieve with CTA on pulsar and PWNe physics evaluating the response of the instrument for different configurations.Comment: accepted for publication in Astroparticle Physic

Integrative conjugative elements of the ICEPan family play a potential role in Pantoea ananatis ecological diversification and antibiosis

Pantoea ananatis is a highly versatile enterobacterium isolated from diverse environmental sources. The ecological diversity of this species may be attributed, in part, to the acquisition of mobile genetic elements. One such element is an Integrative and Conjugative Element (ICE). By means of in silico analyses the ICE elements belonging to a novel family, ICEPan, were identified in the genome sequences of five P. ananatis strains and characterized. PCR screening showed that ICEPan is prevalent among P. ananatis strains isolated from different environmental sources and geographic locations. Members of the ICEPan family share a common origin with ICEs of other enterobacteria, as well as conjugative plasmids of Erwinia spp. Aside from core modules for ICEPan integration, maintenance and dissemination, the ICEPan contain extensive non-conserved islands coding for proteins that may contribute toward various phenotypes such as stress response and antibiosis, and the highly diverse ICEPan thus plays a major role in the diversification of P. ananatis. An island is furthermore integrated within an ICEPan DNA repair-encoding locus umuDC and we postulate its role in stress-induced dissemination and/or expression of the genes on this island

Diagnosis, monitoring and treatment of tuberous sclerosis complex: A South African consensus response to international guidelines

Tuberous sclerosis complex (TSC) is a genetic disorder with multi-system manifestations and a high burden of disease. In 2013, an international panel of TSC experts revised the guidelines for the diagnosis, surveillance and treatment of the disorder. In South Africa (SA), a local multidisciplinary group of healthcare professionals and TSC researchers reviewed the international guidelines to generate an SA consensus clinical update on the identification, diagnosis, treatment and lifelong monitoring of individuals who live with TSC. We strongly endorse dissemination and use of the international guidelines for the assessment, monitoring and treatment of TSC. In addition, we strongly support access to genetic testing and to mTOR (mammalian target of rapamycin) inhibitors to treat subependymal giant cell astrocytomas not amenable to surgery and renal angiomyolipomas larger than 3 cm, and as adjunctive treatment for refractory focal seizures. We await with interest results from mTOR inhibitor trials of skin and TSC-associated neuropsychiatric disorders (TAND). With regard to training, we recommend the inclusion of TSC in undergraduate and postgraduate medical and health sciences curricula, and the promotion of other continuing professional development events to raise awareness about TSC. We also support the development of a TSC user/carer/parent organisation to provide an informal support network for families across SA. We acknowledge that some progress has been made in recent years in SA, but much remains to be done. We hope that this SA onsensus clinical update based on the international guidelines will make a positive contribution to increase knowledge and improve clinical care for all patients who live with TSC in SA, and their families

Deploying design science research in graduate computing studies in South Africa

Design science research is a relatively recent paradigm, which has enjoyed more acceptance in information systems than in computer science. Yet researchers are increasingly accepting this new paradigm where artifacts are to be developed to solve a problem, and the knowledge that is derived during the process is recorded and contributes to the field of knowledge. It is also particularly applicable in a developing world context. In this paper we present two case studies, demonstrating how two postgraduate students used design science research during their research. We reflect on the lessons learned and explain how design science research can be an attractive option for graduate student research at masters and doctoral level in both Information Systems and Computer Science