The gauge algebra of double field theory and Courant brackets

We investigate the symmetry algebra of the recently proposed field theory on a doubled torus that describes closed string modes on a torus with both momentum and winding. The gauge parameters are constrained fields on the doubled space and transform as vectors under T-duality. The gauge algebra defines a T-duality covariant bracket. For the case in which the parameters and fields are T-dual to ones that have momentum but no winding, we find the gauge transformations to all orders and show that the gauge algebra reduces to one obtained by Siegel. We show that the bracket for such restricted parameters is the Courant bracket. We explain how these algebras are realised as symmetries despite the failure of the Jacobi identity.Comment: 25 pages, LaTe

The first use of Fulton's K for assessing and comparing the conditions of inter-tidal fish populations

Fulton's K condition factor was applied, for the first time, to inter-tidal specimens of the shanny (Lipophrys pholis) and long-spined scorpion fish (Taurulus bubalis) from two English rocky shore and two Welsh rocky shore sites during summer 2010 and winter 2011. As both species contribute to the diet of commercial species such as cod (Gadus morhua) and near-threatened species such as the European otter (Lutra lutra), their condition may affect that of these predators. Fulton's K found that inter-tidal Welsh fish maintained a ‘good’ condition between seasons, whereas the inter-tidal English fish were in a poorer condition during winter. Although condition also changed amongst the sites on each coast, further studies are needed into fish morphologies, environmental parameters, prey availabilities and abundances, and fish specimen sex and maturities

Background independent action for double field theory

Double field theory describes a massless subsector of closed string theory with both momentum and winding excitations. The gauge algebra is governed by the Courant bracket in certain subsectors of this double field theory. We construct the associated nonlinear background-independent action that is T-duality invariant and realizes the Courant gauge algebra. The action is the sum of a standard action for gravity, antisymmetric tensor, and dilaton fields written with ordinary derivatives, a similar action for dual fields with dual derivatives, and a mixed term that is needed for gauge invariance.Comment: 45 pages, v2: minor corrections, refs. added, to appear in JHE

Home-made fish traps reduce the capture of small shannies (Lipophrys pholis) compared to using hand-nets in the UK

A replicated, controlled study in 2011-2012 found that using home-made fish traps reduced the capture of unwanted, small shannies Lipophrys pholis compared to using conventional hand-nets in intertidal habitats

Generalized Kahler geometry and gerbes

We introduce and study the notion of a biholomorphic gerbe with connection. The biholomorphic gerbe provides a natural geometrical framework for generalized Kahler geometry in a manner analogous to the way a holomorphic line bundle is related to Kahler geometry. The relation between the gerbe and the generalized Kahler potential is discussed.Comment: 28 page

Duality Twists, Orbifolds, and Fluxes

We investigate compactifications with duality twists and their relation to orbifolds and compactifications with fluxes. Inequivalent compactifications are classified by conjugacy classes of the U-duality group and result in gauged supergravities in lower dimensions with nontrivial Scherk-Schwarz potentials on the moduli space. For certain twists, this mechanism is equivalent to introducing internal fluxes but is more general and can be used to stabilize some of the moduli. We show that the potential has stable minima with zero energy precisely at the fixed points of the twist group. In string theory, when the twist belongs to the T-duality group, the theory at the minimum has an exact CFT description as an orbifold. We also discuss more general twists by nonperturbative U-duality transformations.Comment: 30 pages, harvmac, references and brief comments on gauged supergravity adde

Variation in prescribing for anxiety and depression: a reflection of health inequalities, cultural differences or variations in access to care?

BACKGROUND: There are large variations in mental health prescribing in UK populations. However the underlying reasons for these differences, which may be related to differences in prevalence, cultural expectations or practical difficulties in access to treatment, remain uncertain. METHODS: Linear modelling was used to investigate whether population characteristics or access to primary care account for variations in mental health prescribing across 39 deprived neighbourhoods. RESULTS: The proportion of sampled respondents whose first language was not English and the ratio of general practitioners to population explained 61% of variation. Deprivation and mental health status were not significant predictors of prescribing in these relatively deprived communities. CONCLUSION: These findings suggest that mental health prescribing, within deprived areas, as well as reflecting cultural and social differences in prescribing, may also be a proxy measure of access to care

Null Brane Intersections

We study pairs of planar D-branes intersecting on null hypersurfaces, and other related configurations. These are supersymmetric and have finite energy density. They provide open-string analogues of the parabolic orbifold and null-fluxbrane backgrounds for closed superstrings. We derive the spectrum of open strings, showing in particular that if the D-branes are shifted in a spectator dimension so that they do not intersect, the open strings joining them have no asymptotic states. As a result, a single non-BPS excitation can in this case catalyze a condensation of massless modes, changing significantly the underlying supersymmetric vacuum state. We argue that a similar phenomenon can modify the null cosmological singularity of the time-dependent orbifolds. This is a stringy mechanism, distinct from black-hole formation and other strong gravitational instabilities, and one that should dominate at weak string coupling. A by-product of our analysis is a new understanding of the appearance of 1/4 BPS threshold bound states, at special points in the moduli space of toroidally-compactified type-II string theory.Comment: Tex file, uses harvmac, 24 pages with 5 figures. Corrected typos and added references. Final version to appear in JHE

Prioritization of Features for Mobile Apps for Families in a Federal Nutrition Program for Low-Income Women, Infants, and Children: User-Centered Design Approach

Background: The Special Supplemental Nutrition Assistance Program for Women, Infants, and Children (WIC) is a federal nutrition program that provides nutritious food, education, and health care referrals to low-income women, infants, and children up to the age of 5 years. Although WIC is associated with positive health outcomes for each participant category, modernization and efficiency are needed at the clinic and shopping levels to increase program satisfaction and participation rates. New technologies, such as electronic benefits transfer (EBT), online nutrition education, and mobile apps, can provide opportunities to improve the WIC experience for participants. Objective: This formative study applies user-centered design principles to inform the layout and prioritization of features in mobile apps for low-income families participating in the WIC program. Methods: To identify and prioritize desirable app features, caregivers (N=22) of the children enrolled in WIC participated in individual semistructured interviews with a card sorting activity. Interviews were transcribed verbatim and analyzed using constant comparative analysis for themes. App features were ranked and placed into natural groupings by each participant. The sum and average of the rankings were calculated to understand which features were prioritized by the users. Natural groupings of features were labeled according to participant descriptions. Results: Natural groupings focused on the following categories: clinics/appointments, shopping/stores, education/assessments, location, and recipes/food. Themes from the interviews triangulated the results from the ranking activity. The priority app features were balance checking, an item scanner, and appointment scheduling. Other app features discussed and ranked included appointment reminders, nutrition training and quizzes, shopping lists, clinic and store locators, recipe gallery, produce calculator, and dietary preferences/allergies. Conclusions: This study demonstrates how a user-centered design process can aid the development of an app for low-income families participating in WIC to inform the effective design of the app features and user interface

{\AA}ngstr\"om-resolved Interfacial Structure in Organic-Inorganic Junctions

Charge transport processes at interfaces which are governed by complex interfacial electronic structure play a crucial role in catalytic reactions, energy storage, photovoltaics, and many biological processes. Here, the first soft X-ray second harmonic generation (SXR-SHG) interfacial spectrum of a buried interface (boron/Parylene-N) is reported. SXR-SHG shows distinct spectral features that are not observed in X-ray absorption spectra, demonstrating its extraordinary interfacial sensitivity. Comparison to electronic structure calculations indicates a boron-organic separation distance of 1.9 {\AA}, wherein changes as small as 0.1 {\AA} result in easily detectable SXR-SHG spectral shifts (ca. 100s of meV). As SXR-SHG is inherently ultrafast and sensitive to individual atomic layers, it creates the possibility to study a variety of interfacial processes, e.g. catalysis, with ultrafast time resolution and bond specificity.Comment: 19 page