1,329 research outputs found
Dual Isomonodromic Deformations and Moment Maps to Loop Algebras
The Hamiltonian structure of the monodromy preserving deformation equations
of Jimbo {\it et al } is explained in terms of parameter dependent pairs of
moment maps from a symplectic vector space to the dual spaces of two different
loop algebras. The nonautonomous Hamiltonian systems generating the
deformations are obtained by pulling back spectral invariants on Poisson
subspaces consisting of elements that are rational in the loop parameter and
identifying the deformation parameters with those determining the moment maps.
This construction is shown to lead to ``dual'' pairs of matrix differential
operators whose monodromy is preserved under the same family of deformations.
As illustrative examples, involving discrete and continuous reductions, a
higher rank generalization of the Hamiltonian equations governing the
correlation functions for an impenetrable Bose gas is obtained, as well as dual
pairs of isomonodromy representations for the equations of the Painleve
transcendents and .Comment: preprint CRM-1844 (1993), 28 pgs. (Corrected date and abstract.
Direct measurement of facet temperature up to melting point and cod in high-power 980-nm semiconductor diode lasers
Sun exposure behaviour, seasonal vitamin D deficiency, and relationship to bone health in adolescents
YesContext: Vitamin D is essential for bone health in adolescence, where there is rapid bone mineral
content accrual. As cutaneous sun-exposure provides vitamin D, there is no recommended oral intake
for UK adolescents.
Objective: Assess seasonal vitamin D status and its contributors in white Caucasian adolescents, and
examine bone health in those found deficient.
Design: Prospective cohort study.
Setting: Six schools in Greater Manchester, UK.
Participants: 131 adolescents, 12–15 years.
Intervention(s): Seasonal assessment of circulating 25-hydroxyvitamin D (25OHD), personal sunexposure
and dietary vitamin D. Adolescents deficient (25OHD <10 ng/mL/25 nmol/L) in ≥one
season underwent dual-energy X-ray absorptiometry (lumbar spine, femoral neck), with bone mineral
apparent density (BMAD) correction for size, and peripheral quantitative computed tomography
(distal radius) for volumetric (v)BMD.
Main Outcome Measure: Serum 25OHD; BMD.
Results: Mean 25OHD was highest in September: 24.1 (SD 6.9) ng/mL and lowest in January: 15.5
(5.9) ng/mL. Over the year, 16% were deficient in ≥one season and 79% insufficient (25OHD <20
ng/mL/50 nmol/L) including 28% in September. Dietary vitamin D was low year-round while
personal sun-exposure was seasonal and predominantly across the school week. Holidays accounted
for 17% variation in peak 25OHD (p<0.001). Nineteen adolescents underwent bone assessment,
which showed low femoral neck BMAD versus matched reference data (p=0.0002), 3 with Z≤ -2.0
distal radius trabecular vBMD.
Conclusions: Sun-exposure levels failed to provide adequate vitamin D, ~one-quarter adolescents
insufficient even at summer-peak. Seasonal vitamin D deficiency was prevalent and those affected
had low BMD. Recommendations on vitamin D acquisition are indicated in this age-group.The Bupa Foundation (Grant number TBF-M10-017)
Duality Invariance of Cosmological Perturbation Spectra
I show that cosmological perturbation spectra produced from quantum
fluctuations in massless or self-interacting scalar fields during an
inflationary era remain invariant under a two parameter family of
transformations of the homogeneous background fields. This relates slow-roll
inflation models to solutions which may be far from the usual slow-roll limit.
For example, a scale-invariant spectrum of perturbations in a minimally
coupled, massless field can be produced by an exponential expansion with
, or by a collapsing universe with .Comment: 5 pages, Latex with Revtex. Hamiltonian formulation added and
discussion expanded. Version to appear in Phys Rev
Search for Exotic Mesons in pi- P Interactions at 18 GeV/c
The recent search for non mesons in interactions at
Brookhaven National Laboratory is summarized. Many final states such as , , , , , ,
which are favored decay modes of exotics, are under investigation.Comment: 9 pages, PostScript, Presented at the International School of Nuclear
Physics, Erice, Sicily, Italy, September 199
Hagedorn transition and chronology protection in string theory
We conjecture chronology is protected in string theory due to the
condensation of light winding strings near closed null curves. This
condensation triggers a Hagedorn phase transition, whose end-point target space
geometry should be chronological. Contrary to conventional arguments,
chronology is protected by an infrared effect. We support this conjecture by
studying strings in the O-plane orbifold, where we show that some winding
string states are unstable and condense in the non-causal region of spacetime.
The one-loop string partition function has infrared divergences associated to
the condensation of these states.Comment: 40 pages, 11 figures. Expanded discussion on evolution of on-shell
modes and added appendi
Elemental signatures of Australopithecus africanus teeth reveal seasonal dietary stress
Reconstructing the detailed dietary behaviour of extinct hominins is challenging1\u2014particularly for a species such as Australopithecus africanus, which has a highly variable dental morphology that suggests a broad diet2,3. The dietary responses of extinct hominins to seasonal fluctuations in food availability are poorly understood, and nursing behaviours even less so; most of the direct information currently available has been obtained from high-resolution trace-element geochemical analysis of Homo sapiens (both modern and fossil), Homo neanderthalensis4 and living apes5. Here we apply high-resolution trace-element analysis to two A. africanus specimens from Sterkfontein Member 4 (South Africa), dated to 2.6\u20132.1 million years ago. Elemental signals indicate that A. africanus infants predominantly consumed breast milk for the first year after birth. A cyclical elemental pattern observed following the nursing sequence\u2014comparable to the seasonal dietary signal that is seen in contemporary wild primates and other mammals\u2014indicates irregular food availability. These results are supported by isotopic evidence for a geographical range that was dominated by nutritionally depauperate areas. Cyclical accumulation of lithium in A. africanus teeth also corroborates the idea that their range was characterized by fluctuating resources, and that they possessed physiological adaptations to this instability. This study provides insights into the dietary cycles and ecological behaviours of A. africanus in response to food availability, including the potential cyclical resurgence of milk intake during times of nutritional challenge (as observed in modern wild orangutans5). The geochemical findings for these teeth reinforce the unique place of A. africanus in the fossil record, and indicate dietary stress in specimens that date to shortly before the extinction of Australopithecus in South Africa about two million years ago
RETRATO SIN IDENTIFICAR [Material gráfico]
Copia digital. Madrid : Ministerio de Educación, Cultura y Deporte, 201
WMAP and Supergravity Inflationary Models
We study a class of N=1 Supergravity inflationary models in which the
evolution of the inflaton dynamics is controlled by a single power in the
inflaton field at the point where the observed density fluctuations are
produced, in the context of the braneworld scenario, in light of WMAP results.
In particular, we find that the bounds on the spectral index and its running
constrain the parameter space both for models where the inflationary potential
is dominated by a quadratic term and by a cubic term in the inflaton field. We
also find that is required for the quadratic model whereas
for the cubic model. Moreover, we have determined an upper bound
on the five-dimensional Planck scale, M_5 \lsim 0.019 M, for the quadratic
model. On the other hand, a running spectral index with on large scales
and on small scales is not possible in either case.Comment: 7 pages, 4 eps figures, references corrected, version to appear in
Phys. Rev.
Inflation at Low Scales: General Analysis and a Detailed Model
Models of inflationary cosmology based on spontaneous symmetry breaking
typically suffer from the shortcoming that the symmetry breaking scale is
driven to nearly the Planck scale by observational constraints. In this paper
we investigate inflationary potentials in a general context, and show that this
difficulty is characteristic only of potentials dominated near their
maxima by terms of order . We find that potentials dominated by terms
of order with \hbox{} can satisfy observational constraints at
an arbitrary symmetry breaking scale. Of particular interest, the spectral
index of density fluctuations is shown to depend only on the order of the
lowest non-vanishing derivative of near the maximum. This result is
illustrated in the context of a specific model, with a broken
symmetry, in which the potential is generated by gauge boson loops.Comment: Submitted to Phys. Rev. D. 32 Pages, REVTeX. No figure
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