573 research outputs found
On dilaton dependence of type II superstring action
The supersymmetric action of type IIA D=10 superstring in N=2a, D=10
supergravity background can be derived by double dimensional reduction of the
action of supermembrane coupled to D=11 supergravity. We demonstrate that the
background Ramond-Ramond fields appear in the resulting superstring action with
an extra factor of exponential of the dilaton.Comment: 6 pages, harvmac (references added
Initial Data and Coordinates for Multiple Black Hole Systems
We present here an alternative approach to data setting for spacetimes with
multiple moving black holes generalizing the Kerr-Schild form for rotating or
non-rotating single black holes to multiple moving holes. Because this scheme
preserves the Kerr-Schild form near the holes, it selects out the behaviour of
null rays near the holes, may simplify horizon tracking, and may prove useful
in computational applications. For computational evolution, a discussion of
coordinates (lapse function and shift vector) is given which preserves some of
the properties of the single-hole Kerr-Schild form
Constraints on Automorphic Forms of Higher Derivative Terms from Compactification
By dimensionally reducing the higher derivative corrections of
ten-dimensional IIB theory on a torus we deduce constraints on the E_{n+1}
automorphic forms that occur in d=10-n dimensions. In particular we argue that
these automorphic forms involve the representation of E_{n+1} with fundamental
weight \lambda^{n+1}, which is also the representation to which the string
charges in d dimensions belong. We also consider a similar calculation for the
reduction of higher derivative terms in eleven-dimensional M-theory.Comment: Minor corrections, to appear in JHE
Dynamics of M-Theory Cosmology
A complete global analysis of spatially-flat, four-dimensional cosmologies
derived from the type IIA string and M-theory effective actions is presented. A
non--trivial Ramond-Ramond sector is included. The governing equations are
written as a dynamical system. Asymptotically, the form fields are dynamically
negligible, but play a crucial role in determining the possible intermediate
behaviour of the solutions (i.e. the nature of the equilibrium points). The
only past-attracting solution (source in the system) may be interpreted in the
eleven-dimensional setting in terms of flat space. This source is unstable to
the introduction of spatial curvature.Comment: 13 pages, 4 Postscript figures, uses graphics.sty, submitted to Phys.
Rev.
Grazing Collisions of Black Holes via the Excision of Singularities
We present the first simulations of non-headon (grazing) collisions of binary
black holes in which the black hole singularities have been excised from the
computational domain. Initially two equal mass black holes are separated a
distance and with impact parameter . Initial data are
based on superposed, boosted (velocity ) solutions of single black
holes in Kerr-Schild coordinates. Both rotating and non-rotating black holes
are considered. The excised regions containing the singularities are specified
by following the dynamics of apparent horizons. Evolutions of up to are obtained in which two initially separate apparent horizons are present
for . At that time a single enveloping apparent horizon forms,
indicating that the holes have merged. Apparent horizon area estimates suggest
gravitational radiation of about 2.6% of the total mass. The evolutions end
after a moderate amount of time because of instabilities.Comment: 2 References corrected, reference to figure update
Stable characteristic evolution of generic 3-dimensional single-black-hole spacetimes
We report new results which establish that the accurate 3-dimensional
numerical simulation of generic single-black-hole spacetimes has been achieved
by characteristic evolution with unlimited long term stability. Our results
cover a selection of distorted, moving and spinning single black holes, with
evolution times up to 60,000M.Comment: 4 pages, 3 figure
Investigating the New Landscapes of Welfare: Housing Policy, Politics and the Emerging Research Agenda
As debates about housing form an increasingly important arena of political controversy, much has been written about the new fissures that have appeared as governments not only struggle to reduce public expenditure deficits but also attempt to address problems such as affordability and homelessness. It is widely anticipated that new conflicts will be played out in the private rental market as access to homeownership becomes unrealistic and the supply of social housing diminishes. However, what other tensions might surface; that hitherto have not been subject to the critical gaze of housing research? In this paper, we provide some thoughts on the nascent policy issues as well as the ideological schisms that are likely to develop in coming years, offering suggestions as to how the focus of housing policy research might be reoriented towards a “politics” framework to capture and better understand the conflicts that are likely to arise
Role of ALD Al2O3 Surface Passivation on the Performance of p-Type Cu2O Thin Film Transistors
High-performance p- type oxide thin film transistors (TFTs) have great potential for many semiconductor applications. However, these devices typically suffer from low hole mobility and high off-state currents. We fabricated p-type TFTs with a phase-pure polycrystalline Cu2O semiconductor channel grown by atomic layer deposition (ALD). The TFT switching characteristics were improved by applying a thin ALD Al2O3 passivation layer on the Cu2O channel, followed by vacuum annealing at 300 degrees C. Detailed characterization by transmission electron microscopy-energy dispersive X-ray analysis and X-ray photoelectron spectroscopy shows that the surface of Cu2O is reduced following Al2O3 deposition and indicates the formation of a 1-2 nm thick CuAlO2 interfacial layer. This, together with field-effect passivation caused by the high negative fixed charge of the ALD Al2O3, leads to an improvement in the TFT performance by reducing the density of deep trap states as well as by reducing the accumulation of electrons in the semiconducting layer in the device off-state.Peer reviewe
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