2,754 research outputs found
Explaining the Electroweak Scale and Stabilizing Moduli in M Theory
In a recent paper \cite{Acharya:2006ia} it was shown that in theory vacua
without fluxes, all moduli are stabilized by the effective potential and a
stable hierarchy is generated, consistent with standard gauge unification. This
paper explains the results of \cite{Acharya:2006ia} in more detail and
generalizes them, finding an essentially unique de Sitter (dS) vacuum under
reasonable conditions. One of the main phenomenological consequences is a
prediction which emerges from this entire class of vacua: namely gaugino masses
are significantly suppressed relative to the gravitino mass. We also present
evidence that, for those vacua in which the vacuum energy is small, the
gravitino mass, which sets all the superpartner masses, is automatically in the
TeV - 100 TeV range.Comment: 73 pages, 39 figures, Minor typos corrected, Figures and References
adde
Geometric structure of the generic static traversable wormhole throat
Traversable wormholes have traditionally been viewed as intrinsically
topological entities in some multiply connected spacetime. Here, we show that
topology is too limited a tool to accurately characterize a generic traversable
wormhole: in general one needs geometric information to detect the presence of
a wormhole, or more precisely to locate the wormhole throat. For an arbitrary
static spacetime we shall define the wormhole throat in terms of a
2-dimensional constant-time hypersurface of minimal area. (Zero trace for the
extrinsic curvature plus a "flare-out" condition.) This enables us to severely
constrain the geometry of spacetime at the wormhole throat and to derive
generalized theorems regarding violations of the energy conditions-theorems
that do not involve geodesic averaging but nevertheless apply to situations
much more general than the spherically symmetric Morris-Thorne traversable
wormhole. [For example: the null energy condition (NEC), when suitably weighted
and integrated over the wormhole throat, must be violated.] The major technical
limitation of the current approach is that we work in a static spacetime-this
is already a quite rich and complicated system.Comment: 25 pages; plain LaTeX; uses epsf.sty (four encapsulated postscript
figures
Experimental and numerical analysis of mold filling in rotational molding
This work focuses on the development of a numerical mold filling simulation for the rotational molding process. In the rotational molding process, a dry fiber preform is placed in a mold and impregnated with a thermoset matrix under rotation. Additionally, metallic load introduction elements can be inserted into the mold and joined with co-curing or form-fit, resulting in hybrid drive shafts or tie rods. The numerical model can be used to simulate the impregnation of the preform. Based on the resin transfer molding process, an OpenFOAM solver is extended for the rotational molding process. Permeability, kinetic and curing models are selected and adapted to the materials used. A wireless measurement solution with a capacitive sensor is developed to validate the model. Comparisons between measurements and numerically calculated impregnation times to reach the capacitive sensor with the matrix show good quality of the developed model. The average deviation between calculated result and measured mean values in the experiment is 43.8% the maximum deviation is 65.8% . The model can therefore be used to predict the impregnation progress and the curing state
Polynomial Hamiltonian form of General Relativity
Phase space of General Relativity is extended to a Poisson manifold by
inclusion of the determinant of the metric and conjugate momentum as additional
independent variables. As a result, the action and the constraints take a
polynomial form. New expression for the generating functional for the Green
functions is proposed. We show that the Dirac bracket defines degenerate
Poisson structure on a manifold, and a second class constraints are the Casimir
functions with respect to this structure. As an application of the new
variables, we consider the Friedmann universe.Comment: 33 pages, 1 figure, corrected reference
Opioid initiation and injection transition in rural northern New England: A mixed-methods approach
BACKGROUND: In rural northern New England, located in the northeastern United States, the overdose epidemic has accelerated with the introduction of fentanyl. Opioid initiation and transition to opioid injection have been studied in urban settings. Little is known about opioid initiation and transition to injection drug use in rural northern New England.
METHODS: This mixed-methods study characterized opioid use and drug injection in 11 rural counties in Massachusetts, Vermont, and New Hampshire between 2018 and 2019. People who use drugs completed audio computer-assisted self-interview surveys on substance use and risk behaviors (n = 589) and shared personal narratives through in-depth interviews (n = 22). The objective of the current study is to describe initiation of opioid use and drug injection in rural northern New England.
RESULTS: Median age of first injection was 22 years (interquartile range 18-28 years). Key themes from in-depth interviews that led to initiating drug injection included normalization of drug use in families and communities, experiencing trauma, and abrupt discontinuation of an opioid prescription. Other factors that led to a transition to injecting included lower cost, increased effect/ rush, greater availability of heroin/ fentanyl, and faster relief of withdrawal symptoms with injection.
CONCLUSIONS: Trauma, normalization of drug use, over-prescribing of opioids, and abrupt discontinuation challenge people who use drugs in rural northern New England communities. Inadequate opioid tapering may increase transition to non-prescribed drug use. The extent and severity of traumatic experiences described highlights the importance of enhancing trauma-informed care in rural areas
Stable Topologies of Event Horizon
In our previous work, it was shown that the topology of an event horizon (EH)
is determined by the past endpoints of the EH. A torus EH (the collision of two
EH) is caused by the two-dimensional (one-dimensional) set of the endpoints. In
the present article, we examine the stability of the topology of the EH. We see
that a simple case of a single spherical EH is unstable. Furthermore, in
general, an EH with handles (a torus, a double torus, ...) is structurally
stable in the sense of catastrophe theory.Comment: 21 pages, revtex, five figures containe
Gaussian coordinate systems for the Kerr metric
We present the whole class of Gaussian coordinate systems for the Kerr
metric. This is achieved through the uses of the relationship between Gaussian
observers and the relativistic Hamilton-Jacobi equation. We analyze the
completeness of this coordinate system. In the appendix we present the
equivalent JEK formulation of General Relativity -- the so-called
quasi-Maxwellian equations -- which acquires a simpler form in the Gaussian
coordinate system. We show how this set of equations can be used to obtain the
internal metric of the Schwazschild solution, as a simple example. We suggest
that this path can be followed to the search of the internal Kerr metric
Birmingham’s Eastside story: making steps towards sustainability?
Sustainability has come to play a dominant discursive role in the UK planning system, particularly relating to urban regeneration. The purpose of this paper is to evaluate the role that sustainability plays in a major regeneration
programme, known as Eastside, currently underway in Birmingham, the UK. That this ÂŁ6 billion redevelopment is now widely talked about by such key players as Birmingham City Council and the Regional Development Agency, Advantage West Midlands, as having a central sustainability agenda points to the growing importance of the ideal of sustainability in planning and regeneration agendas. In this paper, we investigate in detail how and why sustainability has become part of the planning discourse for Eastside and critically evaluate what impact, if any, this is having on public policy decision-making
Flux-Line Lattice Structures in Untwinned YBa2Cu3O
A small angle neutron scattering study of the flux-line lattice in a large
single crystal of untwinned YBa2Cu3O is presented. In fields parallel to the
c-axis, diffraction spots are observed corresponding to four orientations of a
hexagonal lattice, distorted by the a-b anisotropy. A value for the anisotropy,
the penetration depth ratio, of 1.18(2) was obtained. The high quality of the
data is such that second order diffraction is observed, indicating a well
ordered FLL. With the field at 33 degrees to c a field dependent re-orientation
of the lattice is observed around 3T.Comment: 4 pages, 4 figure
Microbial Ecology of Ballast Water During a Transoceanic Voyage and the Effects of Open-Ocean Exchange
The only procedure used frequently to reduce the risk of invasion by ballast-mediated biota is open-ocean exchange of ballast water, a procedure in which vessels release coastal water and replace it with oceanic water. Limited information exists concerning the effects of transport upon the aquatic microbial community throughout transit and following open-ocean exchange, A transoceanic voyage aboard a commercial bulk carrier afforded us the opportunity to sample the microbial community in exchanged and unexchanged ballast-water holds during the journey from Hadera, Israel to Baltimore, USA. Five days following the exchange process, all microbial metrics tested (i.e. bacteria concentration, virus-like particle density, chl a and phaeopigment concentration, and microbial biomass) had decreased 1.6- to 34-fold from initial values, With respect to microbial measures, no significant differences existed between exchanged and unexchanged holds on Day 15, the final day of sampling. We stress that we quantified differences in total microorganism abundance and biomass, not species composition, and more research is necessary to determine the changes that nonindigenous microorganisms, including potential pathogens, may effect in receiving waters
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