Quasi-Local Linear Momentum in Black-Hole Binaries

We propose a quasi-local formula for the linear momentum of black-hole horizons inspired by the formalism of quasi-local horizons. We test this formula using two complementary configurations: (i) by calculating the large orbital linear momentum of the two black holes in an unequal-mass, zero-spin, quasi-circular binary and (ii) by calculating the very small recoil momentum imparted to the remnant of the head-on collision of an equal-mass, anti-aligned-spin binary. We obtain results consistent with the horizon trajectory in the orbiting case, and consistent with the net radiated linear momentum for the much smaller head-on recoil velocity.Comment: 5 pages, 3 figures, revtex

Non-symmetric trapped surfaces in the Schwarzschild and Vaidya spacetimes

Marginally trapped surfaces (MTSs) are commonly used in numerical relativity to locate black holes. For dynamical black holes, it is not known generally if this procedure is sufficiently reliable. Even for Schwarzschild black holes, Wald and Iyer constructed foliations which come arbitrarily close to the singularity but do not contain any MTSs. In this paper, we review the Wald-Iyer construction, discuss some implications for numerical relativity, and generalize to the well known Vaidya spacetime describing spherically symmetric collapse of null dust. In the Vaidya spacetime, we numerically locate non-spherically symmetric trapped surfaces which extend outside the standard spherically symmetric trapping horizon. This shows that MTSs are common in this spacetime and that the event horizon is the most likely candidate for the boundary of the trapped region.Comment: 4 pages, 3 figures; v2: minor modifications; v3: clarified conclusion

Stroke outcomes in a socio-economically disadvantaged urban community

Aims. To determine survival, disability and functional outcomes of stroke patients following their discharge from an acute stroke unit in an urban community with limited rehabilitative resources. Methods. Stroke patients were recruited from a district hospital in Cape Town and followed-up for 6 months. Clinical characteristics, demographic and socioeconomic data, and disability and function as measured by modified Rankin Score (mRS), modified Barthel Index (mBI) at recruitment and 3 follow-up visits, were recorded. Results. The study included 196 patients. Median age was 60 (IQR 51 - 69) years, 135 (68.9%) were female, 57.7% black, 42.3% coloured, and 45 (23%) died within 6 months. At discharge, median mBI score was 7 (IQR 3 - 12) and median mRS 4 (IQR 3 - 5). In the multivariate regression models, only function (mBI OR 0.88, 95% confidence interval (CI) 0.79 - 0.96, p<0.0001) and disability (mRS 0R 2.34, 95%CI 1.20 - 4.54, p<0.0001) were independently associated with risk of death. Shack housing was independently associated with moderate or severe disability (odds ratio 3.42, 95%CI 1.22 - 9.59, p=0.02). Despite limited rehabilitation resources, 67% of survivors had mild to moderate disability at 6 months. Conclusion. Apart from initial stroke severity, risk factors for poor survival were a severe disability category and the presence of impaired swallowing at discharge. Shack housing was independently associated with poor functional outcomes. These findings should be helpful in allocating home-based care and inpatient rehabilitation resources to high-risk groups to improve outcomes

“I don’t use a condom (with my regular partner) because I know that I’m faithful, but with everyone else I do”: The cultural and socioeconomic determinants of sexual partner concurrency in young South Africans

Finding ways to reduce the high rates of sexual partner concurrency is increasingly believed to be vital to controlling HIV spread in southern Africa. We describe the frequency and correlates of sexual partner concurrency in a representative sample of 3 324 young South Africans aged 14-25. Of the 2 468 individuals who were sexually active 21% had engaged in concurrent sexual partnerships. Multivariate analysis revealed that concurrency was more common with males, Africans, those who knew their partner had anotherpartner, early age of sexual debut, four or more lifetime sexual partners, alcohol consumption, and self-perception of being at high risk for acquisition of HIV. If the respondent’s partner knew his or her friends (termed high structural embeddedness) this was associated with a 52% reduction in concurrency rates. There are significant differences in both the rates of concurrency and the risk factors underpinning these in the different racial/ethnic groups. Analysis of these underlying determinants suggests that cultural rather than socioeconomic factors predominate, which has important implications for the design and targeting of prevention efforts

Contribution à l'étude du régime alimentairedu barbeau (Barbus barbus callensis Valenciennes, 1842) d'un cours d'eau du Moyen-Atlas (Maroc) : Oued Boufekrane

L'étude du régime alimentaire du barbeau (Barbus barbus callensis Valenciennes, 1842) de l'Oued Boufekrane a été réalisée sur 1 021 poissons, capturés entre janvier 1998 et juin 1999. Cette espèce présente un rythme saisonnier d'activité alimentaire. Ainsi, avec des faibles taux de vacuité, l'été et le printemps sont les saisons de forte activité alimentaire. Cette dernière diminue durant l'automne et l'hiver. Le caractère omnivore du barbeau est vérifié ; son régime alimentaire se compose essentiellement de larves d'Insectes et de débris de végétaux. Les jeunes individus (moins de 13 cm de longueur) ont une tendance zoophage, dominée par les larves de Diptères et d'Éphéméroptères. En revanche, les plus âgés présentent une tendance phytophage qui reflète l'opportunisme de ce poisson et explique ainsi, son adaptation aux conditions trophiques du milieu, caractérisées par une pauvreté en benthos.The diet of the barbel (Barbus barbus callensis Vallenciennes, 1842) in Boufekrane stream was studied on 1021 fish catched between January 1998 and June 1999.This species presented a seasonal rhythm. So, with the low rate of vacuity index, the summer and the spring were the seasons of intense alimentary activity. This activity regressed during automn and winter. The omnivorous character of the barbel was verified. The diet was composed essentially from insect larvae and plant's sherd. The young barbel (length is less than 13 cm) have zoophagous tendency. Their diet was dominated by Diptera and Ephemeroptera larvae. But, the old ones present a phytophagous tendency the opportunism of this species and the plasicity of its diet. This behavior explain the adaptability of this species to trophic conditions in the stream which contained low density of benthic fauna

DISTINCT PHENOTYPIC CHANGES BY PACAP AND VIP IN LIPOPOLYSACCHARIDE STIMULATED BV2 MICROGLIAL CELLS

Background: Aberrant microglial activation plays a key role in the progressive neuronal loss seen in many neurodegenerative diseases. PACAP and VIP are two neuropeptides that elicit robust immunosuppressive functions within the CNS. However, the underlying mechanisms through which these peptides regulate microglia activities are not clear. Aim & Objectives: Using lipopolysaccharide (LPS) to induce BV2 microglial cell polarisation, we aimed at testing whether and how administration of either PACAP or VIP could differentially affect microglial pro-inflammatory profile, polarisation state and morphological appearance to elicit immunosuppressive effects. Methods: Quantitative real-time PCR, Western blot, Griess reactions, immunofluorescence and morphological analyses were conducted in order to determine the effects of PACAP and VIP in BV2 microglial cells exposed or not to 1µg/ml LPS. Results: Our data demonstrated that both PACAP and VIP reduce the expression of pro-inflammatory mediators in LPS-stimulated BV2 cells. We also found that exogenous administration of PACAP and VIP rescued the dysregulations of the endogenous PACAP/VIP levels and attenuated the expression of microglial activation markers caused by LPS. Interestingly, despite the similar anti-inflammatory activities of PACAP and VIP, PACAP mainly reduced the number of M1 polarised cells, whereas VIP acted by increasing the subpopulation of cells exhibiting an ‘intermediate’ phenotype/bipolar-shaped (p<0.001 vs. control), at the expenses of resting/rounded cells. Conclusion: PACAP and VIP both possess immunosuppressive effects in activated BV2 microglial cells, but these effects seem to involve the differential shift of certain cell subpopulations towards distinctive phenotypes

Analisis Sifat Mekanik Komposit Serat Sabut Kelapa sebagai Material Alternatif Pengganti Kayu untuk Pembuatan Kapal Tradisional

Recently, it has been difficult to get the wood as a material to construct the traditional ships. Alternatively, the wood can be substituted by composite materials such as the composite of coco fiber. The coco fiber composites have potential to construct a fishing boat. In this research produced the composite plates and investigation of their value of tensile strength and flexural strength. The composite composition was used 70% polyester and 30% coco fiber. Production of the composite plates used Vacuum Assisted Resin Infusion (VARI) method by variation of the direction of fibers (random, continous and woven). Based on the research result that was produced the composite plates sizes of 400 x 400 x 8 mm and the value of tensile strengths of composite coco fiber for random fiber direction of 12.8572 N/mm2, continuous fiber direction of 15.4436 N/mm2 and woven direction of 12.1797 N/mm2. The value of flexural strengths for random fiber direction was 97.3220 N/mm2, continuous fiber direction of 96.1347 N/mm2 and woven fiber direction of 80.3922 N/mm2. In conclusion, the value of the highest tensile strength and the highest flexural strength were a continuous fiber direction and a random fiber direction, respectively

Clinical characteristics and outcomes of familial and idiopathic dilated cardiomyopathy in Cape Town: A comparative study of 120 cases followed up over 14 years

Background. It is not known whether there are differences in clinical characteristics and outcomes of patients with familial and idiopathic dilated cardiomyopathy (DCM) in an African setting. Purpose. To compare the clinical characteristics and outcomes of familial and idiopathic DCM. Methods. We performed a retrospective study of familial and idiopathic DCM at Groote Schuur Hospital, Cape Town, between 1 February 1996 and 31 December 2009. Clinical, electrocardiographic (ECG) and imaging characteristics were compared, in addition to treatment and survival. Results. Eighty patients with idiopathic DCM and 40 familial cases were studied. ECG T-wave inversion was significantly more frequent in familial DCM (87.5%) than in idiopathic cases (68.8%) (p=0.014), whereas idiopathic patients had a higher prevalence of pathological Q waves (32.5%) than familial cases (12.5%) (p=0.028). Cardiac chambers were significantly more dilated with poorer systolic function in idiopathic than familial cases. A mortality rate of 40% after a median follow-up of 5 years was, however, similar in both groups. The presence of New York Heart Association functional class III and IV symptoms was an independent predictor of mortality (odds ratio (OR) 3.85, 95% confidence interval (CI) 1.30 - 48.47, p&lt;0.001), while heart transplantation was an independent predictor of survival (OR 4.72, 95% CI 1.31 - 72.60, p=0.026) in both groups. Digoxin use without serum monitoring was a significant predictor of mortality in idiopathic DCM (OR 1.62, 95% CI 1.04 - 3.98, p=0.037). Conclusion. Patients with idiopathic DCM have greater cardiac dysfunction than those with familial disease, but mortality is similarly high in both groups. Digoxin use without drug level monitoring may be associated with increased mortality in idiopathic DCM

Frequency and clinical genetics of familial dilated cardiomyopathy in Cape Town: Implications for the evaluation of patients with unexplained cardiomyopathy

Background. Studies from Europe and North America suggest that 20 - 50% of patients with dilated cardiomyopathy (DCM) may have familial disease. There is little information on the frequency and clinical genetics of familial DCM in Africa. Purpose. To determine the frequency and probable mode of inheritance of familial DCM in patients referred for investigation of the cause of DCM at a tertiary centre in Cape Town. Methods. We conducted a retrospective analysis of consecutive patients diagnosed with DCM between 1 February 1996 and 31 December 2009 to determine the frequency of familial disease. Results. Of 109 unrelated patients with DCM, 29 (26.6%) had familial disease. Their mean age of onset of cardiomyopathy (28.01 (standard deviation (SD) 15.33) years) was significantly younger than that for non-familial cases (39.1 (SD 12.6) years) (p=0.001). Male predominance (N=21, 72.4%) and racial distribution (15 (48.3%) coloured patients, 10 (34.5%) black Africans, 4 (13.8%) white individuals, and 1 (3.4%) of Indian descent) of familial DCM probands were similar to the non-familial cases. Of the 29 patients with familial DCM, 2 (7%) had at least one relative diagnosed with peripartum cardiomyopathy. Pedigree analysis of the 29 families was consistent with autosomal dominant inheritance in 72.4%, autosomal recessive inheritance in 17.2% and X-linked recessive inheritance in 10.4%. Conclusions. Familial DCM affects at least a quarter of African patients with DCM, presents at a young age, is associated with peripartum cardiomyopathy, and follows an autosomal dominant pattern of inheritance in the majority of families. Family screening for familial DCM is indicated in all cases of unexplained DCM, including patients with peripartum cardiomyopathy

Transitional intermittency in boundary layers subjected to pressure gradient

Results are reported from an extensive series of experiments on boundary layers in which the location of pressure gradient and transition onset could be varied almost independently, by judicious use of tunnel wall liners and transition-fixing devices. The experiments show that the transition zone is sensitive to the pressure gradient especially near onset, and can be significantly asymmetric; no universal similarity appears valid in general. Observed intermittency distributions cannot be explained on the basis of the hypothesis, often made, that the spot propagates at speeds proportional to the local free-stream velocity but is otherwise unaffected by the pressure gradient