298 research outputs found
Conformal Invariance and Duality in Self-Dual Gravity and (2,1) Heterotic String Theory
A system of gravity coupled to a 2-form gauge field, a dilaton and Yang-Mills
fields in dimensions arises from the (2,1) sigma model or string. The
field equations imply that the curvature with torsion and Yang-Mills field
strength are self-dual in four dimensions, or satisfy generalised self-duality
equations in dimensions. The Born-Infeld-type action describing this
system is simplified using an auxiliary metric and shown to be classically Weyl
invariant only in four dimensions. A dual form of the action is found (no
isometries are required). In four dimensions, the dual geometry is self-dual
gravity without torsion coupled to a scalar field. In dimensions, the
dual geometry is hermitian and determined by a form potential ,
generalising the K\"{a}hler potential of the four dimensional case, with the
fundamental 2-form given by . The
coupling to Yang-Mills is through a term and leads to
a Uhlenbeck-Yau field equation .Comment: LaTeX, 14 pages, no figures. One reference added and interpretation
revised; version to appear in Physics Letters
Accessing Opportunities for Household Provisioning Post-COVID-19
In this project, we used a mixed-methods study to collect critical information to evaluate the extent to which people modified their shopping behavior, either by choice or necessity, to meet their provisioning needs during the COVID-19 crisis and the following recovery. First, four waves of a cross-sectional survey were administered online to a representative sample of households in Arizona, Florida, Michigan, Oregon, and Washington. This longitudinal, comparative study responded directly to a critical research gap and advanced behavioral science by providing a rich survey dataset to support and test theories of behavioral change and technology adoption. Second, focus groups were conducted with older adults in Oregon to discuss their arc of technology adoption for grocery shopping. Focus groups were also conducted with two sets of mentors who provide assistance to family members and friends with online food purchases to understand what kinds of interventions might be necessary to broaden access to e-commerce and delivery platforms for vulnerable populations. This report presents high-level descriptive statistics from these surveys comparing results by wave and/or by state. The findings from the focus groups with older adults and mentors are also described. The findings of this research are critical for emergency planning but also for understanding the ever-changing mechanism used to access retail and service opportunities (whether in-person vs. online), and the opportunities for future interventions to remedy barriers to accessing food that are relevant after the pandemic recovery
Activities of National Hellenic Documentation Centre and the National Network of Scientific and Technological Libraries
Περιέχει το πλήρες κείμενοThe mission of National (Hellenic) Documentation Centre (NDC)is to ensure the flow of the scientific and technological information to the Hellenic scientific community. This is achieved by establishing online access to 17 international hosts and 1.300 databases, acting as the major information intermediary in the country offering bibliographic references to 10.000 scientst per year, producing 8 national databases and hosting 40 databases produced by other national or international organisations. Concerning libraries NDC supports them by developing and disseminating ABEKT, the most popular library automation software in the country numbering more than 700 copies installed, developing, in close collaboration with 206 libraries, the Union Catalogue of Periodicals including 22.790 unique journal titles, creating and coordinating the National Network of Hellenic Scientific Libraries with 107 libraries supporting interlibrary loan through the online document ordering system provided by the host computer of NDC, developing its own digital library having access to more than 230 electronic journals via internet and about 1.000 installed locally, organising seminars, workshops and information days focusing on the electronic information services and technologies
Epidemiology of Methicillin-resistant and Methicillin-sensitive Staphylococcus aureus infections in Lebanon
Background. Methicillin-resistant Staphylococcus aureus (MRSA) is a prevalent pathogen associated with significant morbidity and mortality. In Lebanon, MRSA rates have recently started to rise. We aimed to determine risk factors for acquiring MRSA and Methicillin-sensitive Staphylococcus aureus (MSSA) infections and identify independent risk factors for in-hospital mortality among patients with S. aureus infection. Methods. We used a case-case-control study design that included patients with infections and compared them to uninfected controls. Two multivariable regression models were constructed to determine variables associated with acquiring MRSA and MSSA infections. We explored independent predictors of mortality in the overall population compared with the MRSA subgroup. Results. 356 patients with S. aureus infections were identified and compared to 208 uninfected controls. A recent history of surgery and underlying diabetes were independent risk factors for acquiring both infections. Having a urinary catheter for more than 6 days and steroid therapy were unique risk factors for MRSA infection (aOR 28.1, 95% CI 3.5-223.6 and 3.7, 95% CI 1.6-8.7, respectively). Risk factors exclusively associated with MRSA infection included ICU admission, acute renal failure, and malignancy. Conclusions. Risk factors associated with MRSA infection are distinct from those associated with MSSA infection. This can be used to risk stratify patients and will aid in choosing empirical antibiotic therapy
Momentum modes of M5-branes in a 2d space
We study M5 branes by considering the selfdual strings parallel to a plane.
With the internal oscillation frozen, each selfdual string gives a 5d SYM
field. All selfdual strings together give a 6d field with 5 scalars, 3 gauge
degrees of freedom and 8 fermionic degrees of freedom in adjoint representation
of U(N). Selfdual strings with the same orientation have the SYM-type
interaction. For selfdual strings with the different orientations, which could
also be taken as the unparallel momentum modes of the 6d field on that plane or
the (p,q) (r,s) strings on D3 with (p,q)\neq (r,s), the [i,j]+[j,k]\rightarrow
[i,k] relation is not valid, so the coupling cannot be written in terms of the
standard N \times N matrix multiplication. 3-string junction, which is the
bound state of the unparallel [i,j] [j,k] selfdual strings, may play a role
here.Comment: 37 pages, 5 figures, to appear in JHEP; v2: reference adde
String Multiplets from an Invariant 2-Brane
We study a three-dimensional gauge theory obtained from the dimensional
reduction of a D4-brane worldvolume theory in the background of space-time
moduli. An SL(3) symmetry in this theory, which acts on fields as well as
coupling constants, is identified. By comparing the energies with the string
tensions, we show that certain 1/2 supersymmetric classical solutions of this
theory can be identified as SL(3,Z) multiplets of type II strings in eight
dimensions. Results are then generalized to the non-linear Born-Infeld action.
We also discuss the possibility of 1/8 BPS states in this theory and their
representations in terms of string networks.Comment: 17 pages, Latex, minor correction
Dynamics of BPS States in the Dirac-Born-Infeld Theory
The Dirac-Born-Infeld action with transverse scalar fields is considered to
study the dynamics of various BPS states. We first describe the characteristic
properties of the so-called 1/2 and 1/4 BPS states on the D3 brane, which can
be interpreted as F/D-strings ending on a D3-brane in Type IIB string theory
picture. We then study the response of the BPS states to low energy excitations
of massless fields on the brane, the scalar fields representing the shape
fluctuation of the brane and U(1) gauge fields describing the open string
excitations on the D-brane. This leads to an identification of interactions
between BPS states including the static potentials and the kinetic
interactions.Comment: 19 pages, 4 figures References added, Typographical errors are
correcte
The No-Triangle Hypothesis for N=8 Supergravity
We study the perturbative expansion of N=8 supergravity in four dimensions
from the viewpoint of the ``no-triangle'' hypothesis, which states that
one-loop graviton amplitudes in N=8 supergravity only contain scalar box
integral functions. Our computations constitute a direct proof at six-points
and support the no-triangle conjecture for seven-point amplitudes and beyond.Comment: 43page
The geometry of N=4 twisted string
We compare N=2 string and N=4 topological string within the framework of the
sigma model approach. Being classically equivalent on a flat background, the
theories are shown to lead to different geometries when put in a curved space.
In contrast to the well studied Kaehler geometry characterising the former
case, in the latter case a manifold has to admit a covariantly constant
holomorphic two-form in order to support an N=4 twisted supersymmetry. This
restricts the holonomy group to be a subgroup of SU(1,1) and leads to a
Ricci--flat manifold. We speculate that, the N=4 topological formalism is an
appropriate framework to smooth down ultraviolet divergences intrinsic to the
N=2 theory.Comment: 20 pages, LaTe
Chern-Simons Vortices in Supergravity
We study supersymmetric vortex solutions in three-dimensional abelian gauged
supergravity. First, we construct the general U(1)-gauged D=3, N=2 supergravity
whose scalar sector is an arbitrary Kahler manifold with U(1) isometry. This
construction clarifies the connection between local supersymmetry and the
specific forms of some scalar potentials previously found in the literature --
in particular, it provides the locally supersymmetric embedding of the abelian
Chern-Simons Higgs model. We show that the Killing spinor equations admit
rotationally symmetric vortex solutions with asymptotically conical geometry
which preserve half of the supersymmetry.Comment: 26 pages, LaTeX2
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