Mantle melting as a function of water content beneath back-arc basins

Subduction zone magmas are characterized by high concentrations of H_(2)O, presumably derived from the subducted plate and ultimately responsible for melting at this tectonic setting. Previous studies of the role of water during mantle melting beneath back-arc basins found positive correlations between the H_(2)O concentration of the mantle (H_(2)O_o ) and the extent of melting (F), in contrast to the negative correlations observed at mid-ocean ridges. Here we examine data compiled from six back-arc basins and three mid-ocean ridge regions. We use TiO_2 as a proxy for F, then use F to calculate H_(2)O_o from measured H_(2)O concentrations of submarine basalts. Back-arc basins record up to 0.5 wt % H_(2)O or more in their mantle sources and define positive, approximately linear correlations between H_(2)O_o and F that vary regionally in slope and intercept. Ridge-like mantle potential temperatures at back-arc basins, constrained from Na-Fe systematics (1350°–1500°C), correlate with variations in axial depth and wet melt productivity (∼30–80% F/wt % H_(2)O_o ). Water concentrations in back-arc mantle sources increase toward the trench, and back-arc spreading segments with the highest mean H_(2)O_o are at anomalously shallow water depths, consistent with increases in crustal thickness and total melt production resulting from high H_(2)O. These results contrast with those from ridges, which record low H_(2)O_o (<0.05 wt %) and broadly negative correlations between H_(2)O_o and F that result from purely passive melting and efficient melt focusing, where water and melt distribution are governed by the solid flow field. Back-arc basin spreading combines ridge-like adiabatic melting with nonadiabatic mantle melting paths that may be independent of the solid flow field and derive from the H_(2)O supply from the subducting plate. These factors combine significant quantitative and qualitative differences in the integrated influence of water on melting phenomena in back-arc basin and mid-ocean ridge settings

Dual Geometric Worm Algorithm for Two-Dimensional Discrete Classical Lattice Models

We present a dual geometrical worm algorithm for two-dimensional Ising models. The existence of such dual algorithms was first pointed out by Prokof'ev and Svistunov \cite{ProkofevClassical}. The algorithm is defined on the dual lattice and is formulated in terms of bond-variables and can therefore be generalized to other two-dimensional models that can be formulated in terms of bond-variables. We also discuss two related algorithms formulated on the direct lattice, applicable in any dimension. These latter algorithms turn out to be less efficient but of considerable intrinsic interest. We show how such algorithms quite generally can be "directed" by minimizing the probability for the worms to erase themselves. Explicit proofs of detailed balance are given for all the algorithms. In terms of computational efficiency the dual geometrical worm algorithm is comparable to well known cluster algorithms such as the Swendsen-Wang and Wolff algorithms, however, it is quite different in structure and allows for a very simple and efficient implementation. The dual algorithm also allows for a very elegant way of calculating the domain wall free energy.Comment: 12 pages, 6 figures, Revtex

Occupational segregation, gender essentialism and male primacy as major barriers to equity in HIV/AIDS caregiving: Findings from Lesotho

<p>Abstract</p> <p>Background</p> <p>Gender segregation of occupations, which typically assigns caring/nurturing jobs to women and technical/managerial jobs to men, has been recognized as a major source of inequality worldwide with implications for the development of robust health workforces. In sub-Saharan Africa, gender inequalities are particularly acute in HIV/AIDS caregiving (90% of which is provided in the home), where women and girls make up the informal (and mostly unpaid) workforce. Men's and boy's entry into HIV/AIDS caregiving in greater numbers would both increase the equity and sustainability of national and community-level HIV/AIDS caregiving and mitigate health workforce shortages, but notions of gender essentialism and male primacy make this far from inevitable.</p> <p>In 2008 the Capacity Project partnered with the Lesotho Ministry of Health and Social Welfare in a study of the gender dynamics of HIV/AIDS caregiving in three districts of Lesotho to account for men's absence in HIV/AIDS caregiving and investigate ways in which they might be recruited into the community and home-based care (CHBC) workforce.</p> <p>Methods</p> <p>The study used qualitative methods, including 25 key informant interviews with village chiefs, nurse clinicians, and hospital administrators and 31 focus group discussions with community health workers, community members, ex-miners, and HIV-positive men and women.</p> <p>Results</p> <p>Study participants uniformly perceived a need to increase the number of CHBC providers to deal with the heavy workload from increasing numbers of patients and insufficient new entries. HIV/AIDS caregiving is a gender-segregated job, at the core of which lie stereotypes and beliefs about the appropriate work of men and women. This results in an inequitable, unsustainable burden on women and girls. Strategies are analyzed for their potential effectiveness in increasing equity in caregiving.</p> <p>Conclusions</p> <p>HIV/AIDS and human resources stakeholders must address occupational segregation and the underlying gender essentialism and male primacy if there is to be more equitable sharing of the HIV/AIDS caregiving burden and any long-term solution to health worker shortages. Policymakers, activists and programmers must redress the persistent disadvantages faced by the mostly female caregiving workforce and the gendered economic, psychological, and social impacts entailed in HIV/AIDS caregiving. Research on gender desegregation of HIV/AIDS caregiving is needed.</p

Occupational segregation, gender essentialism and male primacy as major barriers to equity in HIV/AIDS caregiving: Findings from Lesotho

<p>Abstract</p> <p>Background</p> <p>Gender segregation of occupations, which typically assigns caring/nurturing jobs to women and technical/managerial jobs to men, has been recognized as a major source of inequality worldwide with implications for the development of robust health workforces. In sub-Saharan Africa, gender inequalities are particularly acute in HIV/AIDS caregiving (90% of which is provided in the home), where women and girls make up the informal (and mostly unpaid) workforce. Men's and boy's entry into HIV/AIDS caregiving in greater numbers would both increase the equity and sustainability of national and community-level HIV/AIDS caregiving and mitigate health workforce shortages, but notions of gender essentialism and male primacy make this far from inevitable.</p> <p>In 2008 the Capacity Project partnered with the Lesotho Ministry of Health and Social Welfare in a study of the gender dynamics of HIV/AIDS caregiving in three districts of Lesotho to account for men's absence in HIV/AIDS caregiving and investigate ways in which they might be recruited into the community and home-based care (CHBC) workforce.</p> <p>Methods</p> <p>The study used qualitative methods, including 25 key informant interviews with village chiefs, nurse clinicians, and hospital administrators and 31 focus group discussions with community health workers, community members, ex-miners, and HIV-positive men and women.</p> <p>Results</p> <p>Study participants uniformly perceived a need to increase the number of CHBC providers to deal with the heavy workload from increasing numbers of patients and insufficient new entries. HIV/AIDS caregiving is a gender-segregated job, at the core of which lie stereotypes and beliefs about the appropriate work of men and women. This results in an inequitable, unsustainable burden on women and girls. Strategies are analyzed for their potential effectiveness in increasing equity in caregiving.</p> <p>Conclusions</p> <p>HIV/AIDS and human resources stakeholders must address occupational segregation and the underlying gender essentialism and male primacy if there is to be more equitable sharing of the HIV/AIDS caregiving burden and any long-term solution to health worker shortages. Policymakers, activists and programmers must redress the persistent disadvantages faced by the mostly female caregiving workforce and the gendered economic, psychological, and social impacts entailed in HIV/AIDS caregiving. Research on gender desegregation of HIV/AIDS caregiving is needed.</p

The Role of MED31 in the Regulation of Mesenchymal Stem Cell State

Joseph Straub, Matthew Busby, Michael Osmun, Erik Beadle, and Jamie Newman are part of the School of Biological Sciences at Louisiana Tech University. Joseph Straub, Erik Beadle, and Jamie Newman are part of the Molecular Science and Nanotechnology department at Louisiana Tech University. Bruce Bunnell is a apart of the Tulane Center for Stem Cell Research and Regenerative Medicine at Tulane University

Generalized Geometric Cluster Algorithm for Fluid Simulation

We present a detailed description of the generalized geometric cluster algorithm for the efficient simulation of continuum fluids. The connection with well-known cluster algorithms for lattice spin models is discussed, and an explicit full cluster decomposition is derived for a particle configuration in a fluid. We investigate a number of basic properties of the geometric cluster algorithm, including the dependence of the cluster-size distribution on density and temperature. Practical aspects of its implementation and possible extensions are discussed. The capabilities and efficiency of our approach are illustrated by means of two example studies.Comment: Accepted for publication in Phys. Rev. E. Follow-up to cond-mat/041274

Prevalence of sacral dysmorphia in a prospective trauma population: Implications for a "safe" surgical corridor for sacro-iliac screw placement

<p>Abstract</p> <p>Background</p> <p>Percutaneous sacro-iliac (SI) screw fixation represents a widely used technique in the management of unstable posterior pelvic ring injuries and sacral fractures. The misplacement of SI-screws under fluoroscopic guidance represents a critical complication for these patients. This study was designed to determine the prevalence of sacral dysmorphia and the radiographic anatomy of surgical S1 and S2 corridors in a representative trauma population.</p> <p>Methods</p> <p>Prospective observational cohort study on a consecutive series of 344 skeletally mature trauma patients of both genders enrolled between January 1, 2007, to September 30, 2007, at a single academic level 1 trauma center. Inclusion criteria included a pelvic CT scan as part of the initial diagnostic trauma work-up. The prevalence of sacral dysmorphia was determined by plain radiographic pelvic films and CT scan analysis. The anatomy of sacral corridors was analyzed on 3 mm reconstruction sections derived from multislice CT scan, in the axial, coronal, and sagittal plane. "Safe" potential surgical corridors at S1 and S2 were calculated based on these measurements.</p> <p>Results</p> <p>Radiographic evidence of sacral dysmorphia was detected in 49 patients (14.5%). The prevalence of sacral dysmorphia was not significantly different between male and female patients (12.2% <it>vs</it>. 19.2%; <it>P </it>= 0.069). In contrast, significant gender-related differences were detected with regard to radiographic analysis of surgical corridors for SI-screw placement, with female trauma patients (<it>n </it>= 99) having significantly narrower corridors at S1 and S2 in all evaluated planes (axial, coronal, sagittal), compared to male counterparts (<it>n </it>= 245; <it>P </it>< 0.01). In addition, the mean S2 body height was higher in dysmorphic compared to normal sacra, albeit without statistical significance (<it>P </it>= 0.06), implying S2 as a safe surgical corridor of choice in patients with sacral dysmorphia.</p> <p>Conclusions</p> <p>These findings emphasize a high prevalence of sacral dysmorphia in a representative trauma population and imply a higher risk of SI-screw misplacement in female patients. Preoperative planning for percutaneous SI-screw fixation for unstable pelvic and sacral fractures must include a detailed CT scan analysis to determine the safety of surgical corridors.</p

Mantle Melting as a Function of Water Content beneath the Mariana Arc

Subduction zone magmas are characterized by high concentrations of pre-eruptive H_2O, presumably as a result of an H_2Oflux originating from the dehydrating, subducting slab. The extent of mantle melting increases as a function of increasing water content beneath back-arc basins and is predicted to increase in a similar manner beneath arc volcanoes. Here, we present new data for olivine-hosted, basaltic melt inclusions from the Mariana arc that reveal pre-eruptive H_2O contents of ~1•5-6•0 wt %, which are up to three times higher than concentrations reported for the Mariana Trough back-arc basin. Major element systematics of arc and back-arc basin basalts indicate that the back-arc basin melting regime does not simply mix with wet, arc-derived melts to produce the observed range of back-arc magmatic H_2O concentrations. Simple melting models reveal that the trend of increasing extents of melting with increasing H_2O concentrations of the mantle source identified in the Mariana Trough generally extends beneath the Mariana volcanic front to higher mantle water contents and higher extents of melting. In detail, however, each Mariana volcano may define a distinct relationship between extent of melting and the H_2O content of the mantle source. We develop a revised parameterization of hydrous melting, incorporating terms for variable pressure and mantle fertility, to describe the distinct relationships shown by each arc volcano. This model is used in combination with thermobarometry constraints to show that hydrous melts equilibrate at greater depths (34-87 km) and temperatures (>1300°C) beneath the Mariana arc than beneath the back-arc basin (21-37 km), although both magma types can form from a mantle of similar potential temperature (~1350°C).The difference lies in where the melts form and equilibrate. Arc melts are dominated by those that equilibrate within the hot core of the mantle wedge, whereas back-arc melts are dominated by those that equilibrate within the shallow zone of decompression melting beneath the spreading center. Despite higher absolute melting temperatures (>1300°C), Mariana arc melts reflect lower melt productivity as a result of wet melting conditions and a more refractory mantle source

The public procurement of information systems: dialectics in requirements specification

When acquiring information systems, public entities face a dilemma. On the one hand, they want to procure the system that best suits their needs, which often requires lengthy dialogues with vendors. At the same time, they are restricted by government regulations that mandate limited dialogue in the interests of transparency and equal opportunities for all vendors. To examine how public entities deal with this, we followed three procurement projects in Norway. We show that this dilemmamanifests itself as a dialectic between the thesis of getting the systemrequirements right and the antithesis of strictly adhering to regulations. Public entities search for a resolution of this dialectic through two syntheses: selecting an appropriate tendering procedure, and learning how to specify requirements through networks of peer public entities. Our findings reveal that the syntheses are possible because the dialectic is actually complimentary, both the thesis and the antithesis are needed to create the joint outcome that satisfies both. The resolution of the dialectic unfolds differently over time. Our study contributes to the relatively neglected stream of IS research on dialectics that explicitly searches for a synthesis while revealing the complementarity of the dialectic. We show how time plays a nuanced role in the resolution of the dialectic situation