221 research outputs found
The Chromatin Remodeler BPTF Activates a Stemness Gene-Expression Program Essential for the Maintenance of Adult Hematopoietic Stem Cells
Self-renewal and differentiation of adult stem cells are tightly regulated partly through configuration of chromatin structure by chromatin remodelers. Using knockout mice, we here demonstrate that bromodomain PHD finger transcription factor (BPTF), a component of the nucleosome remodeling factor (NURF) chromatin-remodeling complex, is essential for maintaining the population size of hematopoietic stem/progenitor cells (HSPCs), including long-term hematopoietic stem cells (HSCs). Bptf-deficient HSCs are defective in reconstituted hematopoiesis, and hematopoietic-specific knockout of Bptf caused profound defects including bone marrow failure and anemia. Genome-wide transcriptome profiling revealed that BPTF loss caused downregulation of HSC-specific gene-expression programs, which contain several master transcription factors (Meis1, Pbx1, Mn1, and Lmo2) required for HSC maintenance and self-renewal. Furthermore, we show that BPTF potentiates the chromatin accessibility of key HSC “stemness” genes. These results demonstrate an essential requirement of the chromatin remodeler BPTF and NURF for activation of “stemness” gene-expression programs and proper function of adult HSCs. Wang and colleagues show that a chromatin remodeler, BPTF, sustains appropriate functions of hematopoietic stem/progenitor cells (HSPCs). BPTF loss causes bone marrow failure and anemia. The authors further define a BPTF-dependent gene-expression program in HSPCs, which contains key HSC stemness factors. These results demonstrate an essential requirement of the BPTF-associated chromatin remodelers for HSC functionality and adult hematopoiesis
A time-series of methane and carbon dioxide production from dairy cows during a period of dietary transition
Emissions from dairy farms are contributing to the increased concentrations of greenhouse gases which are linked to recent climate change. Altering diets has been proposed as a greenhouse gas mitigation strategy in dairy systems. The magnitude of mitigation and the time taken for cows to adapt to new diets has not been comprehensively quantified. Methane (CH4) and carbon dioxide (CO2) produced by dairy cows was measured for six weeks using the sulphur hexafluoride tracer technique following a change in diet; from barley straw and protein supplements to grazed grass. CH4 and CO2 production increased linearly as the animals adapted to their new diets, however, production did not reach an asymptote six weeks into the grazing period. This suggested that metabolic activity and greenhouse gas emissions may not have been at their maximum. There was substantial variation between individuals with high emitting cows producing four times more CH4 than low producing cows. Cows which produced greater amounts of CH4 consistently also produced greater CO2. We demonstrate that feeding regime plays an important role in determining greenhouse gas emissions and we highlight that transition periods in greenhouse gas models and future experiments must be sufficiently large to allow for adaptation
Probing neutrino non-standard interactions with atmospheric neutrino data
We have reconsidered the atmospheric neutrino anomaly in light of the laetst
data from Super-Kamiokande contained events and from Super-Kamiokande and MACRO
up-going muons. We have reanalysed the proposed solution to the atmospheric
neutrino anomaly in terms of non-standard neutrino-matter interactions (NSI) as
well as the standard nu_mu -> nu_tau oscillations (OSC). Our statistical
analysis shows that a pure NSI mechanism is now ruled out at 99%, while the
standard nu_mu -> nu_tau OSC mechanism provides a quite remarkably good
description of the anomaly. We therefore study an extended mechanism of
neutrino propagation which combines both oscillation and non-standard
neutrino-matter interactions, in order to derive limits on flavour-changing
(FC) and non-universal (NU) neutrino interactions. We obtain that the
off-diagonal flavour-changing neutrino parameter epsilon and the diagonal
non-universality neutrino parameter epsilon' are confined to -0.03 < epsilon <
0.02 and |epsilon'| < 0.05 at 99.73% CL. These limits are model independent and
they are obtained from pure neutrino-physics processes. The stability of the
neutrino oscillation solution to the atmospheric neutrino anomaly against the
presence of non-standard neutrino interactions establishes the robustness of
the near-maximal atmospheric mixing and massive-neutrino hypothesis. The best
agreement with the data is obtained for Delta_m^2 = 2.3*10^{-3} eV^2,
sin^2(2*theta) = 1, epsilon = 6.7*10^{-3} and epsilon' = 1.1*10^{-3}, although
the chi^2 function is quite flat in the epsilon and epsilon' directions for
epsilon, epsilon' -> 0.Comment: 26 pages, LaTeX file using REVTeX4, 1 table and 12 figures included.
Added a revised analysis which takes into account the new 1489-day
Super-Kamiokande and final MACRO data. The bound on NSI parameters is
considerably improve
Confusing non-standard neutrino interactions with oscillations at a neutrino factory
Most neutrino mass theories contain non-standard interactions (NSI) of
neutrinos which can be either non-universal (NU) or flavor-changing (FC). We
study the impact of such interactions on the determination of neutrino mixing
parameters at a neutrino factory using the so-called ``golden channels''
\pnu{e}\to\pnu{\mu} for the measurement of \theta_{13}. We show that a certain
combination of FC interactions in neutrino source and earth matter can give
exactly the same signal as oscillations arising due to \theta_{13}. This
implies that information about \theta_{13} can only be obtained if bounds on
NSI are available. Taking into account the existing bounds on FC interactions,
this leads to a drastic loss in sensitivity in \theta_{13}, at least two orders
of magnitude. A near detector at a neutrino factory offers the possibility to
obtain stringent bounds on some NSI parameters. Such near site detector
constitutes an essential ingredient of a neutrino factory and a necessary step
towards the determination of \theta_{13} and subsequent study of leptonic CP
violation.Comment: 23 pages, 5 figures, improved version, accepted for publication in
Phs. Rev. D, references adde
Measurement of the partial widths of the Z into up- and down-type quarks
Using the entire OPAL LEP1 on-peak Z hadronic decay sample, Z -> qbarq gamma
decays were selected by tagging hadronic final states with isolated photon
candidates in the electromagnetic calorimeter. Combining the measured rates of
Z -> qbarq gamma decays with the total rate of hadronic Z decays permits the
simultaneous determination of the widths of the Z into up- and down-type
quarks. The values obtained, with total errors, were Gamma u = 300 ^{+19}_{-18}
MeV and Gamma d = 381 ^{+12}_{-12} MeV. The results are in good agreement with
the Standard Model expectation.Comment: 22 pages, 5 figures, Submitted to Phys. Letts.
Measurement of Rb in e+e- Collisions at 182 - 209 GeV
Measurements of Rb, the ratio of the bbbar cross-section to the qqbar cross-
section in e+e- collisions, are presented. The data were collected by the OPAL
experiment at LEP at centre-of-mass energies between 182 GeV and 209 GeV.
Lepton, lifetime and event shape information is used to tag events containing b
quarks with high efficiency. The data are compatible with the Standard Model
expectation. The mean ratio of the eight measurements reported here to the
Standard Model prediction is 1.055+-0.031+-0.037, where the first error is
statistical and the second systematic.Comment: 21 pages, 5 figures, Submitted to Phys. Letts
A measurement of the tau mass and the first CPT test with tau leptons
We measure the mass of the tau lepton to be 1775.1+-1.6(stat)+-1.0(syst.) MeV
using tau pairs from Z0 decays. To test CPT invariance we compare the masses of
the positively and negatively charged tau leptons. The relative mass difference
is found to be smaller than 3.0 10^-3 at the 90% confidence level.Comment: 10 pages, 4 figures, Submitted to Phys. Letts.
WW Production Cross Section and W Branching Fractions in e+e- Collisions at 189 GeV
From a data sample of 183 pb^-1 recorded at a center-of-mass energy of roots
= 189 GeV with the OPAL detector at LEP, 3068 W-pair candidate events are
selected. Assuming Standard Model W boson decay branching fractions, the W-pair
production cross section is measured to be sigmaWW = 16.30 +- 0.34(stat.) +-
0.18(syst.) pb. When combined with previous OPAL measurements, the W boson
branching fraction to hadrons is determined to be 68.32 +- 0.61(stat.) +-
0.28(syst.) % assuming lepton universality. These results are consistent with
Standard Model expectations.Comment: 22 pages, 5 figures, submitted to Phys. Lett.
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.
Search for R-Parity Violating Decays of Scalar Fermions at LEP
A search for pair-produced scalar fermions under the assumption that R-parity
is not conserved has been performed using data collected with the OPAL detector
at LEP. The data samples analysed correspond to an integrated luminosity of
about 610 pb-1 collected at centre-of-mass energies of sqrt(s) 189-209 GeV. An
important consequence of R-parity violation is that the lightest supersymmetric
particle is expected to be unstable. Searches of R-parity violating decays of
charged sleptons, sneutrinos and squarks have been performed under the
assumptions that the lightest supersymmetric particle decays promptly and that
only one of the R-parity violating couplings is dominant for each of the decay
modes considered. Such processes would yield final states consisting of
leptons, jets, or both with or without missing energy. No significant
single-like excess of events has been observed with respect to the Standard
Model expectations. Limits on the production cross- section of scalar fermions
in R-parity violating scenarios are obtained. Constraints on the supersymmetric
particle masses are also presented in an R-parity violating framework analogous
to the Constrained Minimal Supersymmetric Standard Model.Comment: 51 pages, 24 figures, Submitted to Eur. Phys. J.
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