245 research outputs found
Evolution of dosage compensation under sexual selection differs between X and Z chromosomes.
Complete sex chromosome dosage compensation has more often been observed in XY than ZW species. In this study, using a population genetic model and the chicken transcriptome, we assess whether sexual conflict can account for this difference. Sexual conflict over expression is inevitable when mutation effects are correlated across the sexes, as compensatory mutations in the heterogametic sex lead to hyperexpression in the homogametic sex. Coupled with stronger selection and greater reproductive variance in males, this results in slower and less complete evolution of Z compared with X dosage compensation. Using expression variance as a measure of selection strength, we find that, as predicted by the model, dosage compensation in the chicken is most pronounced in genes that are under strong selection biased towards females. Our study explains the pattern of weak dosage compensation in ZW systems, and suggests that sexual selection plays a major role in shaping sex chromosome dosage compensation
Lake warming favours small-sized planktonic diatom species
Diatoms contribute to a substantial portion of primary production in the oceans and many lakes. Owing to their relatively heavy cell walls and high nutrient requirements, planktonic diatoms are expected to decrease with climate warming because of reduced nutrient redistribution and increasing sinking velocities. Using a historical dataset, this study shows that diatoms were able to maintain their biovolume with increasing stratification in Lake Tahoe over the last decades; however, the diatom community structure changed. Increased stratification and reduced nitrogen to phosphorus ratios selected for small-celled diatoms, particularly within the Cyclotella genus. An empirical model showed that a shift in phytoplankton species composition and cell size was consistent within different depth strata, indicating that altered nutrient concentrations were not responsible for the change. The increase in small-celled species was sufficient to decrease the average diatom size and thus sinking velocity, which strongly influences energy transfer through the food web and carbon cycling. Our results show that within the diverse group of diatoms, small-sized species with a high surface area to volume ratio were able to adapt to a decrease in mixing intensity, supporting the hypotheses that abiotic drivers affect the size structure of planktonic communities and that warmer climate favours small-sized diatom cells
High-resolution magnetic resonance imaging reveals nuclei of the human amygdala: manual segmentation to automatic atlas
Available online 4 May 2017The amygdala is composed of multiple nuclei with unique functions and connections in the limbic system and to the rest of the brain. However, standard in vivo neuroimaging tools to automatically delineate the amygdala into its multiple nuclei are still rare. By scanning postmortem specimens at high resolution (100–150 µm) at 7 T field strength (n = 10), we were able to visualize and label nine amygdala nuclei (anterior amygdaloid, cortico-amygdaloid transition area; basal, lateral, accessory basal, central, cortical medial, paralaminar nuclei). We created an atlas from these labels using a recently developed atlas building algorithm based on Bayesian inference. This atlas, which will be released as part of FreeSurfer, can be used to automatically segment nine amygdala nuclei from a standard resolution structural MR image. We applied this atlas to two publicly available datasets (ADNI and ABIDE) with standard resolution T1 data, used individual volumetric data of the amygdala nuclei as the measure and found that our atlas i) discriminates between Alzheimer's disease participants and age-matched control participants with 84% accuracy (AUC=0.915), and ii) discriminates between individuals with autism and age-, sex- and IQ-matched neurotypically developed control participants with 59.5% accuracy (AUC=0.59). For both datasets, the new ex vivo atlas significantly outperformed (all p < .05) estimations of the whole amygdala derived from the segmentation in FreeSurfer 5.1 (ADNI: 75%, ABIDE: 54% accuracy), as well as classification based on whole amygdala volume (using the sum of all amygdala nuclei volumes; ADNI: 81%, ABIDE: 55% accuracy). This new atlas and the segmentation tools that utilize it will provide neuroimaging researchers with the ability to explore the function and connectivity of the human amygdala nuclei with unprecedented detail in healthy adults as well as those with neurodevelopmental and neurodegenerative disorders.This work was supported by the PHS grant DA023427 and NICHD/
NIH grant F32HD079169 (Z.M.S); Feodor Lynen Postdoctoral Fellowship
of the Alexander von Humboldt Foundation (D.K.); R21(MH106796),
R21 (AG046657) and K01AG28521 (J.C.A.), the National Cancer
Institute (1K25CA181632-01) as well as the Genentech Foundation (M.R.); the European Union's Horizon 2020 Marie Sklodowska-Curie
grant agreement No 654911 (project ”THALAMODEL”) and ERC Starting
Grant agreement No 677697 (project “BUNGEE-TOOLS”); and the
Spanish Ministry of Economy and Competitiveness (MINECO) reference
TEC2014-51882-P (J.E.I.); and the NVIDIA hardware award (M.R. and
J.E.I.). Further support for this research was provided in part by
the National Institute for Biomedical Imaging and Bioengineering
(P41EB015896, R01EB006758, R21EB018907, R01EB019956, R01-
EB013565), the National Institute on Aging (5R01AG008122,
R01AG016495), the National Institute of Diabetes and Digestive and
Kidney Diseases (1-R21-DK-108277-01), the National Institute for
Neurological Disorders and Stroke (R01NS0525851, R21NS072652,
R01NS070963, R01NS083534, 5U01NS086625), the Massachusetts
ADRC (P50AG005134) and was made possible by the resources provided
by Shared Instrumentation Grants 1S10RR023401, 1S10RR019307, and
1S10RR023043. Additional support was provided by the NIH Blueprint
for Neuroscience Research (5U01-MH093765), part of the multi-institutional
Human Connectome Project. In addition, BF has a financial interest
in CorticoMetrics, a company whose medical pursuits focus on brain
imaging and measurement technologies. BF's interests were reviewed and
are managed by Massachusetts General Hospital and Partners HealthCare
in accordance with their conflict of interest policies.
The collection and sharing of the ADNI MRI data used in the
evaluation was funded by the Alzheimer's Disease Neuroimaging
Initiative (ADNI) (National Institutes of Health Grant U01 AG024904)
and DOD ADNI (Department of Defense award number W81XWH-12-2-
0012). ADNI is funded by the National Institute on Aging, the National
Institute of Biomedical Imaging and Bioengineering, and through generous
contributions from the following: Alzheimer's Association;
Alzheimer's Drug Discovery Foundation; BioClinica, Inc.; Biogen Idec
Inc.; Bristol-Myers Squibb Company; Eisai Inc.; Elan Pharmaceuticals,
Inc.; Eli Lilly and Company; F. Hoffmann-La Roche Ltd and its affiliated
company Genentech, Inc.; GE Healthcare; Innogenetics, N.V.; IXICO Ltd.;
Janssen Alzheimer Immunotherapy Research & Development, LLC.;
Johnson & Johnson Pharmaceutical Research & Development LLC.;
Medpace, Inc.; Merck & Co., Inc.; Meso Scale Diagnostics, LLC.;
NeuroRx Research; Novartis Pharmaceuticals Corporation; Pfizer Inc.;
Piramal Imaging; Servier; Synarc Inc.; and Takeda Pharmaceutical
Company. The Canadian Institutes of Health Research is providing funds
to support ADNI clinical sites in Canada. Private sector contributions are
facilitated by the Foundation for the National Institutes of Health (www.
fnih.org). The grantee organization is the Northern California Institute for
Research and Education, and the study is coordinated by the Alzheimer's
Disease Cooperative Study at the University of California, San Diego.
ADNI data are disseminated by the Laboratory for Neuro Imaging at the
University of Southern California
Renormalization Group Approach to Generalized Cosmological models
We revisit here the problem of generalized cosmology using renormalization
group approach. A complete analysis of these cosmologies, where specific models
appear as asymptotic fixed-points, is given here along with their linearized
stability analysis.Comment: 10 pages, to appear in the International Journal of Theoretical
Physic
Centrality Dependence of Charged Particle Multiplicity at Mid-Rapidity in Au+Au Collisions at sqrt(s_NN) = 130 GeV
We present a measurement of the pseudorapidity density of primary charged
particles near mid-rapidity in Au+Au collisions at sqrt(s_NN) = 130 GeV as a
function of the number of participating nucleons. These results are compared to
models in an attempt to discriminate between competing scenarios of particle
production in heavy ion collisions.Comment: 5 pages, 4 figures, revtex (submitted to Phys. Rev. Letters
Orbital state and magnetic properties of LiV_2 O_4
LiV_2 O_4 is one of the most puzzling compounds among transition metal oxides
because of its heavy fermion like behavior at low temperatures. In this paper
we present results for the orbital state and magnetic properties of LiV_2 O_4
obtained from a combination of density functional theory within the local
density approximation and dynamical mean-field theory (DMFT). The DMFT
equations are solved by quantum Monte Carlo simulations. The trigonal crystal
field splits the V 3d orbitals such that the a_{1g} and e_{g}^{pi} orbitals
cross the Fermi level, with the former being slightly lower in energy and
narrower in bandwidth. In this situation, the d-d Coulomb interaction leads to
an almost localization of one electron per V ion in the a_{1g} orbital, while
the e_{g}^{pi} orbitals form relatively broad bands with 1/8 filling. 2The
theoretical high-temperature paramagnetic susceptibility chi(T) follows a
Curie-Weiss law with an effective paramagnetic moment p_{eff}=1.65 in agreement
with the experimental results.Comment: 11 pages, 10 figures, 2 table
Categorizing Different Approaches to the Cosmological Constant Problem
We have found that proposals addressing the old cosmological constant problem
come in various categories. The aim of this paper is to identify as many
different, credible mechanisms as possible and to provide them with a code for
future reference. We find that they all can be classified into five different
schemes of which we indicate the advantages and drawbacks.
Besides, we add a new approach based on a symmetry principle mapping real to
imaginary spacetime.Comment: updated version, accepted for publicatio
Heavy Quarks and Heavy Quarkonia as Tests of Thermalization
We present here a brief summary of new results on heavy quarks and heavy
quarkonia from the PHENIX experiment as presented at the "Quark Gluon Plasma
Thermalization" Workshop in Vienna, Austria in August 2005, directly following
the International Quark Matter Conference in Hungary.Comment: 8 pages, 5 figures, Quark Gluon Plasma Thermalization Workshop
(Vienna August 2005) Proceeding
Single Electrons from Heavy Flavor Decays in p+p Collisions at sqrt(s) = 200 GeV
The invariant differential cross section for inclusive electron production in
p+p collisions at sqrt(s) = 200 GeV has been measured by the PHENIX experiment
at the Relativistic Heavy Ion Collider over the transverse momentum range $0.4
<= p_T <= 5.0 GeV/c at midrapidity (eta <= 0.35). The contribution to the
inclusive electron spectrum from semileptonic decays of hadrons carrying heavy
flavor, i.e. charm quarks or, at high p_T, bottom quarks, is determined via
three independent methods. The resulting electron spectrum from heavy flavor
decays is compared to recent leading and next-to-leading order perturbative QCD
calculations. The total cross section of charm quark-antiquark pair production
is determined as sigma_(c c^bar) = 0.92 +/- 0.15 (stat.) +- 0.54 (sys.) mb.Comment: 329 authors, 6 pages text, 3 figures. Submitted to Phys. Rev. Lett.
Plain text data tables for the points plotted in figures for this and
previous PHENIX publications are (or will be) publicly available at
http://www.phenix.bnl.gov/papers.htm
Nuclear Modification of Electron Spectra and Implications for Heavy Quark Energy Loss in Au+Au Collisions at sqrt(s_NN)=200 GeV
The PHENIX experiment has measured mid-rapidity transverse momentum spectra
(0.4 < p_T < 5.0 GeV/c) of electrons as a function of centrality in Au+Au
collisions at sqrt(s_NN)=200 GeV. Contributions from photon conversions and
from light hadron decays, mainly Dalitz decays of pi^0 and eta mesons, were
removed. The resulting non-photonic electron spectra are primarily due to the
semi-leptonic decays of hadrons carrying heavy quarks. Nuclear modification
factors were determined by comparison to non-photonic electrons in p+p
collisions. A significant suppression of electrons at high p_T is observed in
central Au+Au collisions, indicating substantial energy loss of heavy quarks.Comment: 330 authors, 6 pages text, 3 figures. Submitted to Phys. Rev. Lett.
Plain text data tables for the points plotted in figures for this and
previous PHENIX publications are (or will be) publicly available at
http://www.phenix.bnl.gov/papers.htm
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