309 research outputs found
Asymptotically hyperbolic manifolds with small mass
For asymptotically hyperbolic manifolds of dimension with scalar
curvature at least equal to the conjectured positive mass theorem
states that the mass is non-negative, and vanishes only if the manifold is
isometric to hyperbolic space. In this paper we study asymptotically hyperbolic
manifolds which are also conformally hyperbolic outside a ball of fixed radius,
and for which the positive mass theorem holds. For such manifolds we show that
the conformal factor tends to one as the mass tends to zero
Asymptotic gluing of asymptotically hyperbolic solutions to the Einstein constraint equations
We show that asymptotically hyperbolic solutions of the Einstein constraint
equations with constant mean curvature can be glued in such a way that their
asymptotic regions are connected.Comment: 37 pages; 2 figure
The ecology of sex explains patterns of helping in arthropod societies
Authors thank the Natural Sciences and Engineering Research Council of Canada (NGD), the Clarendon Fund (NGD) and the Natural Environment Research Council (LR, NE/K009516/1; AG, NE/K009524/1) for funding.Across arthropod societies, sib-rearing (e.g. nursing or nest defence) may be provided by females, by males or by both sexes. According to Hamilton's âhaplodiploidy hypothesisâ, this diversity reflects the relatedness consequences of diploid vs. haplodiploid inheritance. However, an alternative âpreadaptation hypothesisâ instead emphasises an interplay of ecology and the co-option of ancestral, sexually dimorphic traits for sib-rearing. The preadaptation hypothesis has recently received empirical support, but remains to be formalised. Here, we mathematically model the coevolution of sex-specific helping and sex allocation, contrasting these hypotheses. We find that ploidy per se has little effect. Rather, the ecology of sex shapes patterns of helping: sex-specific preadaptation strongly influences who helps; a freely adjustable sex ratio magnifies sex biases and promotes helping; and sib-mating, promiscuity, and reproductive autonomy also modulate the sex and abundance of helpers. An empirical survey reveals that patterns of sex-specific helping in arthropod taxa are consistent with the preadaptation hypothesis.Publisher PDFPeer reviewe
A large class of non constant mean curvature solutions of the Einstein constraint equations on an asymptotically hyperbolic manifold
We construct solutions of the constraint equation with non constant mean
curvature on an asymptotically hyperbolic manifold by the conformal method. Our
approach consists in decreasing a certain exponent appearing in the equations,
constructing solutions of these sub-critical equations and then in letting the
exponent tend to its true value. We prove that the solutions of the
sub-critical equations remain bounded which yields solutions of the constraint
equation unless a certain limit equation admits a non-trivial solution.
Finally, we give conditions which ensure that the limit equation admits no
non-trivial solution.Comment: remark on the equivalence between the existence of a solution to the
Lichnerowicz equation and to the prescribed scalar curvature equation added,
reference [BPB09] added, to appear in Commun. Math. Phy
Expanding running coupling effects in the hard Pomeron
We study QCD hard processes at scales of order k^2 > Lambda^2 in the limit in
which the beta-function coefficient - b is taken to be small, but alphas(k) is
kept fixed. The (nonperturbative) Pomeron is exponentially suppressed in this
limit, making it possible to define purely perturbative high-energy Green's
functions. The hard Pomeron exponent acquires diffusion and running coupling
corrections which can be expanded in the b parameter and turn out to be
dependent on the effective coupling b alphas^2 Y. We provide a general setup
for this b-expansion and we calculate the first few terms both analytically and
numerically.Comment: 36 pages, 15 figures, additional references adde
Genuine Correlations of Like-Sign Particles in Hadronic Z0 Decays
Correlations among hadrons with the same electric charge produced in Z0
decays are studied using the high statistics data collected from 1991 through
1995 with the OPAL detector at LEP. Normalized factorial cumulants up to fourth
order are used to measure genuine particle correlations as a function of the
size of phase space domains in rapidity, azimuthal angle and transverse
momentum. Both all-charge and like-sign particle combinations show strong
positive genuine correlations. One-dimensional cumulants initially increase
rapidly with decreasing size of the phase space cells but saturate quickly. In
contrast, cumulants in two- and three-dimensional domains continue to increase.
The strong rise of the cumulants for all-charge multiplets is increasingly
driven by that of like-sign multiplets. This points to the likely influence of
Bose-Einstein correlations. Some of the recently proposed algorithms to
simulate Bose-Einstein effects, implemented in the Monte Carlo model PYTHIA,
are found to reproduce reasonably well the measured second- and higher-order
correlations between particles with the same charge as well as those in
all-charge particle multiplets.Comment: 26 pages, 6 figures, Submitted to Phys. Lett.
D* Production in Deep Inelastic Scattering at HERA
This paper presents measurements of D^{*\pm} production in deep inelastic
scattering from collisions between 27.5 GeV positrons and 820 GeV protons. The
data have been taken with the ZEUS detector at HERA. The decay channel
(+ c.c.) has been used in the study. The
cross section for inclusive D^{*\pm} production with
and is 5.3 \pms 1.0 \pms 0.8 nb in the kinematic region
{ GeV and }. Differential cross
sections as functions of p_T(D^{*\pm}), and are
compared with next-to-leading order QCD calculations based on the photon-gluon
fusion production mechanism. After an extrapolation of the cross section to the
full kinematic region in p_T(D^{*\pm}) and (D^{*\pm}), the charm
contribution to the proton structure function is
determined for Bjorken between 2 10 and 5 10.Comment: 17 pages including 4 figure
Does congenital deafness affect the structural and functional architecture of primary visual cortex?
Deafness results in greater reliance on the remaining senses. It is unknown whether the cortical architecture of the intact senses is optimized to compensate for lost input. Here we performed widefield population receptive field (pRF) mapping of primary visual cortex (V1) with functional magnetic resonance imaging (fMRI) in hearing and congenitally deaf participants, all of whom had learnt sign language after the age of 10 years. We found larger pRFs encoding the peripheral visual field of deaf compared to hearing participants. This was likely driven by larger facilitatory center zones of the pRF profile concentrated in the near and far periphery in the deaf group. pRF density was comparable between groups, indicating pRFs overlapped more in the deaf group. This could suggest that a coarse coding strategy underlies enhanced peripheral visual skills in deaf people. Cortical thickness was also decreased in V1 in the deaf group. These findings suggest deafness causes structural and functional plasticity at the earliest stages of visual cortex
Size Doesn't Matter: Towards a More Inclusive Philosophy of Biology
notes: As the primary author, OâMalley drafted the paper, and gathered and analysed data (scientific papers and talks). Conceptual analysis was conducted by both authors.publication-status: Publishedtypes: ArticlePhilosophers of biology, along with everyone else, generally perceive life to fall into two broad categories, the microbes and macrobes, and then pay most of their attention to the latter. âMacrobeâ is the word we propose for larger life forms, and we use it as part of an argument for microbial equality. We suggest that taking more notice of microbes â the dominant life form on the planet, both now and throughout evolutionary history â will transform some of the philosophy of biologyâs standard ideas on ontology, evolution, taxonomy and biodiversity. We set out a number of recent developments in microbiology â including biofilm formation, chemotaxis, quorum sensing and gene transfer â that highlight microbial capacities for cooperation and communication and break down conventional thinking that microbes are solely or primarily single-celled organisms. These insights also bring new perspectives to the levels of selection debate, as well as to discussions of the evolution and nature of multicellularity, and to neo-Darwinian understandings of evolutionary mechanisms. We show how these revisions lead to further complications for microbial classification and the philosophies of systematics and biodiversity. Incorporating microbial insights into the philosophy of biology will challenge many of its assumptions, but also give greater scope and depth to its investigations
Plasma glial fibrillary acidic protein is raised in progranulin-associated frontotemporal dementia
Background There are few validated fluid biomarkers in frontotemporal dementia (FTD). Glial fibrillary acidic protein (GFAP) is a measure of astrogliosis, a known pathological process of FTD, but has yet to be explored as potential biomarker.
Methods Plasma GFAP and neurofilament light chain (NfL) concentration were measured in 469 individuals enrolled in the Genetic FTD Initiative: 114 C9orf72 expansion carriers (74 presymptomatic, 40 symptomatic), 119 GRN mutation carriers (88 presymptomatic, 31 symptomatic), 53 MAPT mutation carriers (34 presymptomatic, 19 symptomatic) and 183 non-carrier controls. Biomarker measures were compared between groups using linear regression models adjusted for age and sex with family membership included as random effect. Participants underwent standardised clinical assessments including the Mini-Mental State Examination (MMSE), Frontotemporal Lobar Degeneration-C linical Dementia Rating scale and MRI. Spearman's correlation coefficient was used to investigate the relationship of plasma GFAP to clinical and imaging measures.
Results Plasma GFAP concentration was significantly increased in symptomatic GRN mutation carriers (adjusted mean difference from controls 192.3 pg/mL, 95% CI 126.5 to 445.6), but not in those with C9orf72 expansions (9.0, -61.3 to 54.6), MAPT mutations (12.7, -33.3 to 90.4) or the presymptomatic groups. GFAP concentration was significantly positively correlated with age in both controls and the majority of the disease groups, as well as with NfL concentration. In the presymptomatic period, higher GFAP concentrations were correlated with a lower cognitive score (MMSE) and lower brain volume, while in the symptomatic period, higher concentrations were associated with faster rates of atrophy in the temporal lobe.
Conclusions Raised GFAP concentrations appear to be unique to GRN-related FTD, with levels potentially increasing just prior to symptom onset, suggesting that GFAP may be an important marker of proximity to onset, and helpful for forthcoming therapeutic prevention trials
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