162 research outputs found
Evaluation of cholesterol and vitamin E concentrations in adult alpacas and nursing crias
The objective of this study was to determine if serum cholesterol and vitamin E concentrations change with production and physiologic state in alpacas. Blood was collected from 3 groups of alpacas. An adult female group was sampled in the periparturient period and once monthly until their offspring were weaned. Crias born to the females were sampled after birth, then once monthly until weaning. A group consisting of males was sampled once monthly throughout the study period. Serum vitamin E and cholesterol concentrations were measured and vitamin E to cholesterol ratios was calculated. Vitamin E concentrations were similar throughout the different physiologic states. Cria vitamin E concentrations closely correlated to that of their dam. Significant cholesterol concentration fluctuations in crias occurred after 4 weeks of life possibly due to milk fat content. After weaning, the cholesterol concentrations became similar to the adult animals within study. Vitamin E concentrations varied with age in crias as they transitioned from a milk to forage based diet. Cholesterol fluctuated with altered physiologic and metabolic demands, most noticeable in the crias. Further studies are needed to determine if vitamin E to cholesterol ratios would be more appropriate to fully assess the vitamin E status in nursing crias
Untwisting of a Strained Cholesteric Elastomer by Disclination Loop Nucleation
The application of a sufficiently strong strain perpendicular to the pitch
axis of a monodomain cholesteric elastomer unwinds the cholesteric helix.
Previous theoretical analyses of this transition ignored the effects of Frank
elasticity which we include here. We find that the strain needed to unwind the
helix is reduced because of the Frank penalty and the cholesteric state becomes
metastable above the transition. We consider in detail a previously proposed
mechanism by which the topologically stable helical texture is removed in the
metastable state, namely by the nucleation of twist disclination loops in the
plane perpendicular to the pitch axis. We present an approximate calculation of
the barrier energy for this nucleation process which neglects possible spatial
variation of the strain fields in the elastomer, as well as a more accurate
calculation based on a finite element modeling of the elastomer.Comment: 12 pages, 9 figure
Nonabelian D-branes and Noncommutative Geometry
We discuss the nonabelian world-volume action which governs the dynamics of N
coincident Dp-branes. In this theory, the branes' transverse displacements are
described by matrix-valued scalar fields, and so this is a natural physical
framework for the appearance of noncommutative geometry. One example is the
dielectric effect by which Dp-branes may be polarized into a noncommutative
geometry by external fields. Another example is the appearance of
noncommutative geometries in the description of intersecting D-branes of
differing dimensions, such as D-strings ending on a D3- or D5-brane. We also
describe the related physics of giant gravitons.Comment: 21 pages, Latex, ref. adde
Pure states don't wear black
Recently, string theory has provided some remarkable new insights into the
microphysics of black holes. I argue that a simple and important lesson is also
provided with regards to the information loss paradox, namely, pure quantum
states do not form black holes! Thus it seems black hole formation, as well as
evaporation, must be understood within the framework of quantum decoherence.Comment: 6 pages, harvmac.tex, awarded First Prize in the Gravity Research
Foundation Essay Competition, to appear in General Relativity and Gravitatio
String Junctions and Bound States of Intersecting Branes
We study four-dimensional black hole configurations which result from
wrapping M5-branes on a Calabi-Yau manifold, as well as U-dual realizations.
Our aim is to understand the microscopic degrees of freedom responsible for the
existence of bound states of multiple branes. The details depend on the chosen
U-frame; in some cases, they are massless string junctions. We also identify a
perturbative description in which these states correspond to twisted strings of
intersecting D3-branes at an orbifold singularity. In each case, these are the
preponderant states of the spacetime infrared conformal field theory and
account for the entropy of the blackhole.Comment: 14 pages; 2 figures; uses latex with epsf and hyperref package
Strong subadditivity and the covariant holographic entanglement entropy formula
Headrick and Takayanagi showed that the Ryu-Takayanagi holographic
entanglement entropy formula generally obeys the strong subadditivity (SSA)
inequality, a fundamental property of entropy. However, the Ryu-Takayanagi
formula only applies when the bulk spacetime is static. It is not known whether
the covariant generalization proposed by Hubeny, Rangamani, and Takayanagi
(HRT) also obeys SSA. We investigate this question in three-dimensional
AdS-Vaidya spacetimes, finding that SSA is obeyed as long as the bulk spacetime
satisfies the null energy condition. This provides strong support for the
validity of the HRT formula.Comment: 38 page
Early Environmental Origins of Neurodegenerative Disease in Later Life
Parkinson disease (PD) and Alzheimer disease (AD), the two most common neurodegenerative disorders in American adults, are of purely genetic origin in a minority of cases and appear in most instances to arise through interactions among genetic and environmental factors. In this article we hypothesize that environmental exposures in early life may be of particular etiologic importance and review evidence for the early environmental origins of neurodegeneration. For PD the first recognized environmental cause, MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine), was identified in epidemiologic studies of drug abusers. Chemicals experimentally linked to PD include the insecticide rotenone and the herbicides paraquat and maneb; interaction has been observed between paraquat and maneb. In epidemiologic studies, manganese has been linked to parkinsonism. In dementia, lead is associated with increased risk in chronically exposed workers. Exposures of children in early life to lead, polychlorinated biphenyls, and methylmercury have been followed by persistent decrements in intelligence that may presage dementia. To discover new environmental causes of AD and PD, and to characterize relevant gene–environment interactions, we recommend that a large, prospective genetic and epidemiologic study be undertaken that will follow thousands of children from conception (or before) to old age. Additional approaches to etiologic discovery include establishing incidence registries for AD and PD, conducting targeted investigations in high-risk populations, and improving testing of the potential neurologic toxicity of chemicals
Maximum Wavelength of Confined Quarks and Gluons and Properties of Quantum Chromodynamics
Because quarks and gluons are confined within hadrons, they have a maximum
wavelength of order the confinement scale. Propagators, normally calculated for
free quarks and gluons using Dyson-Schwinger equations, are modified by
bound-state effects in close analogy to the calculation of the Lamb shift in
atomic physics. Because of confinement, the effective quantum chromodynamic
coupling stays finite in the infrared. The quark condensate which arises from
spontaneous chiral symmetry breaking in the bound state Dyson-Schwinger
equation is the expectation value of the operator evaluated in the
background of the fields of the other hadronic constituents, in contrast to a
true vacuum expectation value. Thus quark and gluon condensates reside within
hadrons. The effects of instantons are also modified. We discuss the
implications of the maximum quark and gluon wavelength for phenomena such as
deep inelastic scattering and annihilation, the decay of heavy quarkonia, jets,
and dimensional counting rules for exclusive reactions. We also discuss
implications for the zero-temperature phase structure of a vectorial SU()
gauge theory with a variable number of massless fermions.Comment: 6 pages, late
Meson Spectroscopy in AdS/CFT with Flavour
We compute the meson spectrum of an N=2 super Yang-Mills theory with
fundamental matter from its dual string theory on AdS_5 x S_5 with a D7-brane
probe. For scalar and vector mesons with arbitrary R-charge the spectrum is
computed in closed form by solving the equations for D7-brane fluctuations; for
matter with non-zero mass m_q it is discrete, exhibits a mass gap of order m_q
/ sqrt(g_s N) and furnishes representations of SO(5) even though the manifest
global symmetry of the theory is only SO(4). The spectrum of mesons with large
spin J is obtained from semiclassical, rotating open strings attached to the
D7-brane. It displays Regge-like behaviour for J << sqrt(g_s N), whereas for J
>> sqrt(g_s N) it corresponds to that of two non-relativistic quarks bound by a
Coulomb potential. Meson interactions, baryons and `giant gauge bosons' are
briefly discussed.Comment: LaTeX, 39 pages, 4 figures, uses epsf. v2: typos corrected.
references adde
The Noncommutative Bion Core
We examine noncommutative solutions of the nonabelian theory on the
world-volume of N coincident D-strings. These solutions can be interpreted in
terms of noncommutative geometry as funnels describing the nonabelian D-string
expanding out into an orthogonal D3-brane. These configurations are `dual' to
the bion solutions in the abelian world-volume theory of the D3-brane. In the
latter, a charge N magnetic monopole describes N D-strings attached to the
D3-brane with a spike deformation of the world-volume. The noncommutative
D-string solutions give a reliable account of physics at the core of the
monopole, where the bion description is expected to breakdown. In the large N
limit, we find good agreement between the two points of view, including the
energy, couplings to background fields, and the shape of the funnel. We also
study fluctuations traveling along the D-string, again obtaining agreement in
the large N limit. At finite N, our results give a limit on the number of modes
that can travel to infinity along the N D-strings attached to the D3-brane.Comment: 22 pages, refs adde
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