5,984 research outputs found
E11 must be a symmetry of strings and branes
We construct the non-linear realisation of the semi-direct product of E11 and
its vector representation in five and eleven dimensions and find the dynamical
equations it predicts at low levels. Restricting these results to contain only
the usual fields of supergravity and the generalised space-time to be the usual
space-time we find the equations of motion of the five and eleven dimensional
maximal supergravity theories. Since this non-linear realisation contains
effects that are beyond the supergravity approximation and are thought to be
present in an underlying theory we conclude that the low energy effective
action of string and branes must possess an E11 symmetry.Comment: 17 pages, The eleven dimensional results are given in more detail and
are shown to be uniquely determined. Typographical and transcription errors
are also correcte
Generalised vielbeins and non-linear realisations
We briefly review why the non-linear realisation of the semi-direct product
of a group with one of its representations leads to a field theory defined on a
generalised space-time equipped with a generalised vielbein. We give formulae,
which only involve matrix multiplication, for the generalised vielbein, the
Cartan forms and their transformations. We consider the generalised space-time
introduced in 2003 in the context of the non-linear realisation of the
semi-direct product of E(11) and its first fundamental representation. For this
latter theory we give explicit expressions for the generalised vielbein up to
and including the levels associated with the dual graviton in four, five and
eleven dimensions and for the IIB theory in ten dimensions. We also compute the
generalised vielbein, up to the analogous level, for the non-linear realisation
of the semi-direct product of very extended SL(2) with its first fundamental
representation, which is a theory associated with gravity in four dimensions.Comment: 42 page
Accelerator dynamics of a fractional kicked rotor
It is shown that the Weyl fractional derivative can quantize an open system.
A fractional kicked rotor is studied in the framework of the fractional
Schrodinger equation. The system is described by the non-Hermitian Hamiltonian
by virtue of the Weyl fractional derivative. Violation of space symmetry leads
to acceleration of the orbital momentum. Quantum localization saturates this
acceleration, such that the average value of the orbital momentum can be a
direct current and the system behaves like a ratchet. The classical counterpart
is a nonlinear kicked rotor with absorbing boundary conditions.Comment: Submitted for publication in Phys. Rev.
A Graph-Based Semantics Workbench for Concurrent Asynchronous Programs
A number of novel programming languages and libraries have been proposed that
offer simpler-to-use models of concurrency than threads. It is challenging,
however, to devise execution models that successfully realise their
abstractions without forfeiting performance or introducing unintended
behaviours. This is exemplified by SCOOP---a concurrent object-oriented
message-passing language---which has seen multiple semantics proposed and
implemented over its evolution. We propose a "semantics workbench" with fully
and semi-automatic tools for SCOOP, that can be used to analyse and compare
programs with respect to different execution models. We demonstrate its use in
checking the consistency of semantics by applying it to a set of representative
programs, and highlighting a deadlock-related discrepancy between the principal
execution models of the language. Our workbench is based on a modular and
parameterisable graph transformation semantics implemented in the GROOVE tool.
We discuss how graph transformations are leveraged to atomically model
intricate language abstractions, and how the visual yet algebraic nature of the
model can be used to ascertain soundness.Comment: Accepted for publication in the proceedings of FASE 2016 (to appear
Titan Science with the James Webb Space Telescope (JWST)
The James Webb Space Telescope (JWST), scheduled for launch in 2018, is the
successor to the Hubble Space Telescope (HST) but with a significantly larger
aperture (6.5 m) and advanced instrumentation focusing on infrared science
(0.6-28.0 m ). In this paper we examine the potential for scientific
investigation of Titan using JWST, primarily with three of the four
instruments: NIRSpec, NIRCam and MIRI, noting that science with NIRISS will be
complementary. Five core scientific themes are identified: (i) surface (ii)
tropospheric clouds (iii) tropospheric gases (iv) stratospheric composition and
(v) stratospheric hazes. We discuss each theme in depth, including the
scientific purpose, capabilities and limitations of the instrument suite, and
suggested observing schemes. We pay particular attention to saturation, which
is a problem for all three instruments, but may be alleviated for NIRCam
through use of selecting small sub-arrays of the detectors - sufficient to
encompass Titan, but with significantly faster read-out times. We find that
JWST has very significant potential for advancing Titan science, with a
spectral resolution exceeding the Cassini instrument suite at near-infrared
wavelengths, and a spatial resolution exceeding HST at the same wavelengths. In
particular, JWST will be valuable for time-domain monitoring of Titan, given a
five to ten year expected lifetime for the observatory, for example monitoring
the seasonal appearance of clouds. JWST observations in the post-Cassini period
will complement those of other large facilities such as HST, ALMA, SOFIA and
next-generation ground-based telescopes (TMT, GMT, EELT).Comment: 50 pages, including 22 figures and 2 table
Can greater muscularity in larger individuals resolve the 3/4 power-law controversy when modelling maximum oxygen uptake?
BACKGROUND: The power function relationship, MR = a.m(b), between metabolic rate (MR) and body mass m has been the source of much controversy amongst biologists for many years. Various studies have reported mass exponents (b) greater than the anticipated 'surface-area' exponent 0.67, often closer to 0.75 originally identified by Kleiber. AIM: The study aimed to provide a biological explanation for these 'inflated' exponents when modelling maximum oxygen uptake (max), based on the observations from this and previous studies that larger individuals develop disproportionately more muscle mass in the arms and legs. RESEARCH DESIGN AND SUBJECTS: A cross-sectional study of 119 professional soccer players from Croatia aged 18-34 was carried out. RESULTS: Here we confirm that the power function relationship between max and body mass of the professional soccer players results in an 'inflated' mass exponent of 0.75 (95% confidence interval from 0.56 to 0.93), but also the larger soccer players have disproportionately greater leg muscle girths. When the analysis was repeated incorporating the calf and thigh muscle girths rather than body mass as predictor variables, the analysis not only explained significantly more of the variance in max, but the sum of the exponents confirmed a surface-area law. CONCLUSIONS: These findings confirm the pitfalls of fitting body-mass power laws and suggest using muscle-girth methodology as a more appropriate way to scale or normalize metabolic variables such as max for individuals of different body sizes
Dynamic Scaling of an Adsorption-Diffusion Process on Fractals
A dynamic scaling of a diffusion process involving the Langmuir type
adsorption is studied. We find dynamic scaling functions in one and two
dimensions and compare them with direct numerical simulations, and we further
study the dynamic scaling law on fractal surfaces. The adsorption-diffusion
process obeys the fracton dynamics on the fractal surfaces.Comment: 9 pages, 7 figure
Massive Ellipticals at High Redshift: NICMOS Imaging of Z~1 Radio Galaxies
We present deep, continuum images of eleven high-redshift (0.811 < z < 1.875)
3CR radio galaxies observed with NICMOS. Our images probe the rest-frame
optical light where stars are expected to dominate the galaxy luminosity. The
rest-frame UV light of eight of these galaxies demonstrates the well-known
``alignment effect''. Most of the radio galaxies have rounder, more symmetric
morphologies at rest-frame optical wavelengths. Here we show the most direct
evidence that in most cases the stellar hosts are normal elliptical galaxies
with de Vaucouleurs law light profiles. For a few galaxies very faint traces of
the UV-bright aligned component are also visible in the infrared images. We
derive both the effective radius and surface-brightness for nine of eleven
sample galaxies by fitting surface-brightness models to them. We find their
sizes are similar to those of local FRII radio source hosts and are in general
larger than other local galaxies. The derived host galaxy luminosities are very
high and lie at the bright end of luminosity functions constructed at similar
redshifts. The galaxies in our sample are also brighter than the rest-frame
size--surface-brightness locus defined by the low-redshift sources. Passive
evolution roughly aligns the z ~ 1 galaxies with the low-redshift samples. The
optical host is sometimes centered on a local minimum in the rest-frame UV
emission, suggesting the presence of substantial dust obscuration. We also see
good evidence of nuclear point sources in three galaxies. Overall, our results
are consistent with the hypothesis that these galaxies have already formed the
bulk of their stars at redshifts greater than z >~ 2, and that the AGN
phenomenon takes place within otherwise normal, perhaps passively evolving,
galaxies. (abridged)Comment: 28 pages, 14 figures, accepted to ApJ. Uses AASTEX and emulateapj
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