Homology and Derived Series of Groups II: Dwyer's Theorem

We give new information about the relationship between the low-dimensional homology of a group and its derived series. This yields information about how the low-dimensional homology of a topological space constrains its fundamental group. Applications are given to detecting when a set of elements of a group generates a subgroup ``large enough'' to map onto a non-abelian free solvable group, and to concordance and grope cobordism of links. We also greatly generalize several key homological results employed in recent work of Cochran-Orr-Teichner, in the context of classical knot concordance. In 1963 J. Stallings established a strong relationship between the low-dimensional homology of a group and its lower central series quotients. In 1975 W. Dwyer extended Stallings' theorem by weakening the hypothesis on the second homology groups. The naive analogues of these theorems for the derived series are false. In 2003 the second author introduced a new characteristic series, associated to the derived series, called the torsion-free derived series. The authors previously established a precise analogue, for the torsion-free derived series, of Stallings' theorem. Here our main result is the analogue of Dwyer's theorem for the torsion-free derived series. We also prove a version of Dwyer's theorem for the rational lower central series. We apply these to give new results on the Cochran-Orr-Teichner filtration of the classical link concordance group.Comment: 26 pages. In this version, we have included a new proof of part of the main theorem. The new proof is somewhat simpler and stays entirely in the world of group homology and homological algebra rather than using Eilenberg-Mac Lane spaces. Other minor corrections. This is the final version to appear in Geometry & Topolog

The nonperturbative closed string tachyon vacuum to high level

We compute the action of closed bosonic string field theory at quartic order with fields up to level ten. After level four, the value of the potential at the minimum starts oscillating around a nonzero negative value, in contrast with the proposition made in [5]. We try a different truncation scheme in which the value of the potential converges faster with the level. By extrapolating these values, we are able to give a rather precise value for the depth of the potential.Comment: 24 pages. v2: typos corrected, clarified extrapolation in scheme B, and added extrapolated tachyon and dilaton vev's at the end of Section

Social constructions of gender roles, gender-based violence and HIV/AIDS in two communities of the Western Cape, South Africa

The links between gender roles, gender-based violence and HIV/AIDS risk are complex and culturally specific. In this qualitative study we investigated how women and men in two black communities in the Western Cape, South Africa, constructed their gender identities and roles, how they understood gender-based violence, and what they believed about the links between gender relations and HIV risk. First we conducted 16 key informant interviews with members of relevant stakeholder organisations. Then we held eight focus group discussions with community members in single-sex groups. Key findings included the perception that although traditional gender roles were still very much in evidence, shifts in power between men and women were occurring. Also, gender-based violence was regarded as a major problem throughout communities, and was seen to be fuelled by unemployment, poverty and alcohol abuse. HIV/AIDS was regarded as particularly a problem of African communities, with strong themes of stigma, discrimination, and especially ‘othering' evident. Developing effective HIV/AIDS interventions in these communities will require tackling the overlapping as well as divergent constructions of gender, gender violence and HIV which emerged in the study. Keywords: gender roles, gender-based violence, HIV/AIDS, South Africa. RÉSUMÉ Les liens entre les rôles de genre, la violence contre les femmes et le risque du VIH/SIDA sont complexes et culturellement particuliers. Dans cette étude qualitative, nous avons examiné: comment des hommes et des femmes ont construit des identités et les rôles de genre dans deux communautés noires du Cap de l'Ouest, en Afrique du Sud, comment ont-ils compris la violence contre les femmes et ce qu'ils croyaient des liens entre les relations de sexes et le risque du VIH. Dans un premier temps, nous avons mené 16 entretiens principaux d'informateurs auprès des membres des organismes dépositaires. Ensuite, nous avons eu huit discussions des groupes de foyer avec des membres de la communauté en deux groupes différents, un pour les femmes un autre pour les hommes. Les résultats de recherche ont inclus la perception que: même si les rôles de genre traditionnels restent toujours évidents, il y a aussi le déplacement de pouvoir entre les hommes et les femmes. De plus, la violence contre les femmes était vue comme un problème majeur à travers les communautés et d'être aggravée par le chômage, la pauvreté et l'abus d'alcool. Le VIH/SIDA était considéré particulièrement comme un problème des communautés africaines avec des thèmes fortes de stigmatisation, de discrimination et surtout le ‘othering' évidents. Le développement des interventions efficaces du VIH/SIDA dans ces communautés va exiger une maîtrise des constructions de genre qui se recouvrent partiellement et qui sont divergentes également, la violence contre les femmes et le VIH qui ont apparu dans cette étude. Mot clés: les rôles de genre, la violence contre les femmes, le VIH/SIDA, l'Afrique du Sud

On field theory quantization around instantons

With the perspective of looking for experimentally detectable physical applications of the so-called topological embedding, a procedure recently proposed by the author for quantizing a field theory around a non-discrete space of classical minima (instantons, for example), the physical implications are discussed in a ``theoretical'' framework, the ideas are collected in a simple logical scheme and the topological version of the Ginzburg-Landau theory of superconductivity is solved in the intermediate situation between type I and type II superconductors.Comment: 27 pages, 5 figures, LaTe

Boundary Conformal Field Theory and Ribbon Graphs: a tool for open/closed string dualities

We construct and fully characterize a scalar boundary conformal field theory on a triangulated Riemann surface. The results are analyzed from a string theory perspective as tools to deal with open/closed string dualities.Comment: 40 pages, 7 figures; typos correcte

Matrix Model for Discretized Moduli Space

We study the algebraic geometrical background of the Penner--Kontsevich matrix model with the potential N\alpha \tr {\bigl(- \fr 12 \L X\L X +\log (1-X)+X\bigr)}. We show that this model describes intersection indices of linear bundles on the discretized moduli space right in the same fashion as the Kontsevich model is related to intersection indices (cohomological classes) on the Riemann surfaces of arbitrary genera. The special role of the logarithmic potential originated from the Penner matrix model is demonstrated. The boundary effects which was unessential in the case of the Kontsevich model are now relevant, and intersection indices on the discretized moduli space of genus $g$ are expressed through Kontsevich's indices of the genus $g$ and of the lower genera

Effect of age on intraoperative cerebrovascular autoregulation and near-infrared spectroscopy-derived cerebral oxygenation

Background Age is an important risk factor for perioperative cerebral complications such as stroke, postoperative cognitive dysfunction, and delirium. We explored the hypothesis that intraoperative cerebrovascular autoregulation is less efficient and brain tissue oxygenation lower in elderly patients, thus, increasing the vulnerability of elderly brains to systemic insults such as hypotension. Methods We monitored intraoperative cerebral perfusion in 50 patients aged 18-40 and 77 patients >65 yr at two Swiss university hospitals. Mean arterial pressure (MAP) was measured continuously using a plethysmographic method. An index of cerebrovascular autoregulation (Mx) was calculated based on changes in transcranial Doppler flow velocity due to changes in MAP. Cerebral oxygenation was assessed by the tissue oxygenation index (TOI) using near-infrared spectroscopy. End-tidal CO2, O2, and sevoflurane concentrations and peripheral oxygen saturation were recorded continuously. Standardized anaesthesia was administered in all patients (thiopental, sevoflurane, fentanyl, atracurium). Results Autoregulation was less efficient in patients aged >65 yr [by 0.10 (se 0.04; P=0.020)] in a multivariable linear regression analysis. This difference was not attributable to differences in MAP, end-tidal CO2, or higher doses of sevoflurane. TOI was not significantly associated with age, sevoflurane dose, or Mx but increased with increasing flow velocity [by 0.09 (se 0.04; P=0.028)] and increasing MAP [by 0.11 (se 0.05; P=0.043)]. Conclusions Our results do not support the hypothesis that older patients' brains are more vulnerable to systemic insults. The difference of autoregulation between the two groups was small and most likely clinically insignifican

Estimates of measles case fatality ratios: a comprehensive review of community-based studies.

BACKGROUND: Global deaths from measles have decreased notably in past decades, due to both increases in immunization rates and decreases in measles case fatality ratios (CFRs). While some aspects of the reduction in measles mortality can be monitored through increases in immunization coverage, estimating the level of measles deaths (in absolute terms) is problematic, particularly since incidence-based methods of estimation rely on accurate measures of measles CFRs. These ratios vary widely by geographic and epidemiologic context and even within the same community from year-to-year. METHODS: To understand better the variations in CFRs, we reviewed community-based studies published between 1980 and 2008 reporting age-specific measles CFRs. RESULTS: The results of the search consistently document that measles CFRs are highest in unvaccinated children under age 5 years; in outbreaks; the lowest CFRs occur in vaccinated children regardless of setting. The broad range of case and death definitions, study populations and geography highlight the complexities in extrapolating results for global public health planning. CONCLUSIONS: Values for measles CFRs remain imprecise, resulting in continued uncertainty about the actual toll measles exacts