Stability of the quantum supermembrane in a manifold with boundary

We point out an effect which may stabilize a supersymmetric membrane moving on a manifold with boundary, and lead to a light-cone Hamiltonian with a discrete spectrum of eigenvalues. The analysis is carried out explicitly for a closed supermembrane in the regularized $SU(N)$ matrix model version.Comment: 10 pages, harvmac (references added, minor changes

One-loop four-graviton amplitude in eleven-dimensional supergravity

We find explicit expression for the one-loop four-graviton amplitude in eleven-dimensional supergravity compactified on a circle. Represented in terms of the string coupling (related to the compactification radius) it takes the form of an infinite sum of perturbative string loop corrections. We also compute the amplitude in the case of compactification on a 2-torus which is given by an SL(2,Z) invariant expansion in powers of the torus area. We discuss the structure of quantum corrections in eleven-dimensional theory and their relation to string theory.Comment: 14 pages, harvmac. Remarks on the amplitude in uncompactified D=11 space and on explicit structure of R^4 terms adde

Relation of arterial geometry to luminal narrowing and histologic markers for plaque vulnerability: the remodeling paradox

AbstractObjective. To relate local arterial geometry with markers that are thought to be related to plaque rupture.Background. Plaque rupture often occurs at sites with minor luminal stenosis and has retrospectively been characterized by colocalization of inflammatory cells. Recent studies have demonstrated that luminal narrowing is related with the mode of atherosclerotic arterial remodeling.Methods. We obtained 1,521 cross section slices at regular intervals from 50 atherosclerotic femoral arteries. Per artery, the slices with the largest and smallest lumen area, vessel area and plaque area were selected for staining on the presence of macrophages (CD68), T-lymphocytes (CD45RO), smooth muscle cells (alpha-actin) and collagen.Results. Inflammation of the cap or shoulder of the plaque was observed in 33% of all cross sections. Significantly more CD68 and CD45RO positive cells, more atheroma, less collagen and less alpha-actin positive staining was observed in cross sections with the largest plaque area and largest vessel area vs. cross sections with the smallest plaque area and smallest vessel area, respectively. No difference in the number of inflammatory cells was observed between cross sections with the largest and smallest lumen area.Conclusion. Intraindividually, pathohistologic markers previously reported to be related to plaque vulnerability were associated with a larger plaque area and vessel area. In addition, inflammation of the cap and shoulder of the plaque was a common finding in the atherosclerotic femoral artery

Collinear helium under periodic driving: stabilization of the asymmetric stretch orbit

The collinear eZe configuration of helium, with the electrons on opposite sides of the nucleus, is studied in the presence of an external electromagnetic (laser or microwave) field. We show that the classically unstable "asymmetric stretch" orbit, on which doubly excited intrashell states of helium with maximum interelectronic angle are anchored, can be stabilized by means of a resonant driving where the frequency of the electromagnetic field equals the frequency of Kepler-like oscillations along the orbit. A static magnetic field, oriented parallel to the oscillating electric field of the driving, can be used to enforce the stability of the configuration with respect to deviations from collinearity. Quantum Floquet calculations within a collinear model of the driven two-electron atom reveal the existence of nondispersive wave packets localized on the stabilized asymmetric stretch orbit, for double excitations corresponding to principal quantum numbers of the order of N > 10.Comment: 13 pages, 12 figure

Linear response within the projection-based renormalization method: Many-body corrections beyond the random phase approximation

The explicit evaluation of linear response coefficients for interacting many-particle systems still poses a considerable challenge to theoreticians. In this work we use a novel many-particle renormalization technique, the so-called projector-based renormalization method, to show how such coefficients can systematically be evaluated. To demonstrate the prospects and power of our approach we consider the dynamical wave-vector dependent spin susceptibility of the two-dimensional Hubbard model and also determine the subsequent magnetic phase diagram close to half-filling. We show that the superior treatment of (Coulomb) correlation and fluctuation effects within the projector-based renormalization method significantly improves the standard random phase approximation results.Comment: 17 pages, 7 figures, revised versio

Constraints on Three-Neutrino Mixing from Atmospheric and Reactor Data

Observations of atmospheric neutrinos are usually analyzed using the simplifying approximation that either $\nu_\mu \leftrightarrow \nu_\tau$ or $\nu_e \leftrightarrow \nu_\mu$ two-flavor mixing is relevant. Here we instead consider the data using the simplifying approximation that only one neutrino mass scale is relevant. This approximation is the minimal three-flavor notation that includes the two relevant two-flavor approximations. The constraints in the parameter space orthogonal to the usual, two-flavor analyses are studied.Comment: 15 pages, preprint IUHET-26

Students with global experiences during medical school are more likely to work in settings that focus on the underserved: an observational study from a public U.S. institution

Background: Global health interest has grown among medical students over the past 20 years, and most medical schools offer global health opportunities. Studies suggest that completing global health electives during medical school may increase the likelihood of working with underserved populations in a clinical or research capacity. This study aimed to assess the association of global electives in medical school on subsequently working in global health and with underserved populations in the United States (U.S.), additionally considering students’ interests and experiences prior to medical school. We also examined whether respondents perceived benefits gained from global electives. Methods: We surveyed medical school graduates (classes of 2011-2015) from a large public medical school in the U.S. to describe current practice settings and previous global health experience. We evaluated work, volunteer, and educational experiences preceding medical school, socioeconomic status, race and ethnicity using American Medical College Application Service (AMCAS) data. We assessed the association between students’ backgrounds, completing global health electives in medical school and current work in global health or with underserved populations in the U.S. Results: In the 5 to 8 years post-graduation, 78% of 161 respondents reported work, research, or teaching with a focus on global or underserved U.S. populations. Completing a global health elective during medical school (p = 0.0002) or during residency (p = 0.06) were positively associated with currently working with underserved populations in the U.S. and pre-medical school experiences were marginally associated (p = 0.1). Adjusting for pre-medical school experiences, completing a global health elective during medical school was associated with a 22% greater prevalence of working with an underserved population. Perceived benefits from global electives included improved cultural awareness, language skills, public health and research skills, and ability to practice in technology-limited settings. Conclusion: Medical school graduates who participated in global electives as students were more likely than their peers to pursue careers with underserved populations, independent of experiences prior to medical school. We hypothesize that by offering global health experiences, medical schools can enhance the interests and skills of graduates that will make them more likely and better prepared to work with underserved populations in the U.S. and abroad

Social Entrepreneurship and Broader Theories: Shedding New Light on the “Bigger Picture”

This article documents the results of a research workshop bringing together six perspectives on social entrepreneurship. The idea was to challenge existing concepts of the economy, the firm, and entrepreneurship in order to shed new light on social entrepreneurship and on our existing theoretical frameworks. The first two contributions use a macro-perspective and discuss the notion of adaptive societies and the tragedies of disharmonization, respectively. Taking a management perspective, the next two focus on the limits of conventional assumptions in management theory, particularly human capital theory and resource-based view. The final two contributions follow an entrepreneurship perspective highlighting the usefulness of mobilization theory and the business model lens to social entrepreneurship. Despite this diversity, all contributions share the fact that they challenge narrow definitions of the unit of analysis in social entrepreneurship; they illustrate the aspect of social embeddedness, and they argue for an open-but-disciplined diversity of theories in social entrepreneurship research

Hydrodynamic Synchronisation of Model Microswimmers

We define a model microswimmer with a variable cycle time, thus allowing the possibility of phase locking driven by hydrodynamic interactions between swimmers. We find that, for extensile or contractile swimmers, phase locking does occur, with the relative phase of the two swimmers being, in general, close to 0 or pi, depending on their relative position and orientation. We show that, as expected on grounds of symmetry, self T-dual swimmers, which are time-reversal covariant, do not phase-lock. We also discuss the phase behaviour of a line of tethered swimmers, or pumps. These show oscillations in their relative phases reminiscent of the metachronal waves of cilia.Comment: 17 pages, 8 figure