177 research outputs found
The changing face of kuru: a personal perspective
The epidemic of kuru is now known to have been transmitted among the Fore by ritual consumption of infected organs from deceased relatives. As cannibalism was suppressed by government patrol officers during the 1950s, most transmission had ceased by 1957, when the kuru research programme first commenced. As predicted in the 1960s, the epidemic has waned, with progressive ageing of kuru-affected cohorts over the years to 2007. The few cases seen in the twenty-first century, with the longest incubation periods, were almost certainly exposed as children prior to 1960. Although the research programme had almost no role in bringing the kuru epidemic to an end, it did provide important knowledge that was to help the wider world in controlling the later epidemics of iatrogenic and variant Creutzfeldt–Jakob disease and bovine spongiform encephalopathy
Relativistic wave equations for interacting massive particles with arbitrary half-intreger spins
New formulation of relativistic wave equations (RWE) for massive particles
with arbitrary half-integer spins s interacting with external electromagnetic
fields are proposed. They are based on wave functions which are irreducible
tensors of rank n=s-\frac12$) antisymmetric w.r.t. n pairs of indices,
whose components are bispinors. The form of RWE is straightforward and free of
inconsistencies associated with the other approaches to equations describing
interacting higher spin particles
Generalized Brans-Dicke cosmology in the presence of matter and dark energy
We study the Generalized Brans-Dicke cosmology in the presence of matter and
dark energy. Of particular interest for a constant Brans-Dicke parameter, the
de Sitter space has also been investigated.Comment: 9 page
Testing Broken U(1) Symmetry in a Two-Component Atomic Bose-Einstein Condensate
We present a scheme for determining if the quantum state of a small trapped
Bose-Einstein condensate is a state with well defined number of atoms, a Fock
state, or a state with a broken U(1) gauge symmetry, a coherent state. The
proposal is based on the observation of Ramsey fringes. The population
difference observed in a Ramsey fringe experiment will exhibit collapse and
revivals due to the mean-field interactions. The collapse and revival times
depend on the relative strength of the mean-field interactions for the two
components and the initial quantum state of the condensate.Comment: 20 Pages RevTex, 3 Figure
Disappearing Dark Matter in Brane World Cosmology: New Limits on Noncompact Extra Dimensions
We explore cosmological implications of dark matter as massive particles
trapped on a brane embedded in a Randall-Sundrum noncompact higher dimension
space. It is an unavoidable consequence of this cosmology that massive
particles are metastable and can disappear into the bulk dimension. Here, we
show that a massive dark matter particle (e.g. the lightest supersymmetric
particle) is likely to have the shortest lifetime for disappearing into the
bulk. We examine cosmological constraints on this new paradigm and show that
disappearing dark matter is consistent (at the 95% confidence level) with all
cosmological constraints, i.e. present observations of Type Ia supernovae at
the highest redshift, trends in the mass-to-light ratios of galaxy clusters
with redshift, the fraction of X-ray emitting gas in rich clusters, and the
spectrum of power fluctuations in the cosmic microwave background. A best concordance region is identified corresponding to a mean lifetime for
dark matter disappearance of Gyr. The implication
of these results for brane-world physics is discussed.Comment: 7 pages, 7 figures, new cosmological constraints added, accepted for
publication in PR
Multiloop String-Like Formulas for QED
Multiloop gauge-theory amplitudes written in the Feynman-parameter
representation are poised to take advantage of two important developments of
the last decade: the spinor-helicity technique and the superstring
reorganization. The former has been considered in a previous article; the
latter will be elaborated in this paper. We show here how to write multiloop
string-like formulas in the Feynman-parameter representation for any process in
QED, including those involving other non-electromagnetic interactions. The
general connection between the Feynman-parameter approach and the
superstring/first-quantized approach is discussed. In the special case of a
one-loop multi-photon amplitude, these formulas reduce to the ones obtained by
the superstring and the first quantized methods. The string-like formulas
exhibits a simple gauge structure which makes the Ward-Takahashi identity
apparent, and enables the integration-by-parts technique of Bern and Kosower to
be applied, so that gauge-invariant parts can be extracted diagram-by-diagram
with the seagull vertex neglected.Comment: 25 pages in Plain Tex, plus four figures in a postscript file;
McGill/92-5
De Novo Sequence and Copy Number Variants Are Strongly Associated with Tourette Disorder and Implicate Cell Polarity in Pathogenesis.
We previously established the contribution of de novo damaging sequence variants to Tourette disorder (TD) through whole-exome sequencing of 511 trios. Here, we sequence an additional 291 TD trios and analyze the combined set of 802 trios. We observe an overrepresentation of de novo damaging variants in simplex, but not multiplex, families; we identify a high-confidence TD risk gene, CELSR3 (cadherin EGF LAG seven-pass G-type receptor 3); we find that the genes mutated in TD patients are enriched for those related to cell polarity, suggesting a common pathway underlying pathobiology; and we confirm a statistically significant excess of de novo copy number variants in TD. Finally, we identify significant overlap of de novo sequence variants between TD and obsessive-compulsive disorder and de novo copy number variants between TD and autism spectrum disorder, consistent with shared genetic risk
Efeitos do PEG 3350 e de uma solução enteral, associados ou não ao Ringer lactato, e do NaCl 0,9% sobre a glicose, o lactato, o cortisol e a insulina de equinos hígidos
Prospects for Constraining Cosmology with the Extragalactic Cosmic Microwave Background Temperature
Observers have demonstrated that it is now feasible to measure the cosmic
microwave background (CMB) temperature at high redshifts. We explore the
possible constraints on cosmology which might ultimately be derived from such
measurements. Besides providing a consistency check on standard and alternative
cosmologies, possibilities include: constraints on the inhomogeneity and
anisotropy of the universe at intermediate redshift ; an
independent probe of peculiar motions with respect to the Hubble flow; and
constraining the epoch of reionization. We argue that the best possibility is
as a probe of peculiar motions. We show, however, that the current measurement
uncertainty (K) in the local present absolute CMB
temperature imposes intrinsic limits on the use of such CMB temperature
measurements as a cosmological probe. At best, anisotropies at intermediate
redshift could only be constrained at a level of and peculiar
motions could only be determined to an uncertainty of km
s. If the high CMB temperature can only be measured with a precision
comparable to the uncertainty of the local interstellar CMB temperature, then
peculiar motions could be determined to an uncertainty of .Comment: 8 pages 2 Figures, PRD Submitte
Observational Constraints on Dark Radiation in Brane Cosmology
We analyze the observational constraints on brane-world cosmology whereby the
universe is described as a three-brane embedded in a five-dimensional anti-de
Sitter space.
In this brane-universe cosmology, the Friedmann equation is modified by the
appearance of extra terms which derive from existence of the extra dimensions.
In the present work we concentrate on the ``dark radiation'' term which
diminishes with cosmic scale factor as .
We show that, although the observational constraints from primordial
abundances allow only a small contribution when this term is positive, a much
wider range of negative values is allowed. Furthermore, such a negative
contribution can reconcile the tension between the observed primordial \he4
and D abundances.
We also discuss the possible constraints on this term from the power spectrum
of CMB anisotropies in the limit of negligible cosmological perturbation on the
brane world. We show that BBN limits the possible contribution from dark
radiation just before the nucleosynthesis epoch to lie between -65% and
of the background photon energy density. Combining this with the CMB constraint
reduces this range to between -24% and at the confidence
level.Comment: 6 pages, 3 figures, submitted to PRD; this version includes the
referee's suggestions, updated references, and an improved treatment of BBN
model uncertaintie
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