2,459 research outputs found
Spin dynamics in the single-ion magnet [Er(W5O18)2]9−
In this work we present a detailed NMR and \u3bc+SR investigation of the spin dynamics in the new hydrated sodium salt containing the single-ion magnet [Er(W5O18)2]9-. The H1NMR absorption spectra at various applied magnetic fields present a line broadening on decreasing temperature which indicates a progressive spin freezing of the single-molecule magnetic moments. The onset of quasistatic local magnetic fields, due to spin freezing, is observed also in the muon relaxation curves at low temperature. Both techniques yield a local field distribution of the order of 0.1-0.2 T, which appears to be of dipolar origin. On decreasing the temperature, a gradual loss of the H1NMR signal intensity is observed, a phenomenon known as wipe-out effect. The effect is analyzed quantitatively on the basis of a simple model which relies on the enhancement of the NMR spin-spin, T2-1, relaxation rate due to the slowing down of the magnetic fluctuations. Measurements of spin-lattice relaxation rate T1-1 for H1NMR and of the muon longitudinal relaxation rate \u3bb show an increase as the temperature is lowered. However, while for the NMR case the signal is lost before reaching the very slow fluctuation region, the muon spin-lattice relaxation \u3bb can be followed until very low temperatures and the characteristic maximum, reached when the electronic spin fluctuation frequency becomes of the order of the muon Larmor frequency, can be observed. At high temperatures, the data can be well reproduced with a simple model based on a single correlation time \u3c4=\u3c40exp(\u394/T) for the magnetic fluctuations. However, to fit the relaxation data for both NMR and \u3bc+SR over the whole temperature and magnetic field range, one has to use a more detailed model that takes into account spin-phonon transitions among the Er3+ magnetic sublevels. A good agreement for both proton NMR and \u3bc+SR relaxation is obtained, which confirms the validity of the energy level scheme previously calculated from an effective crystal field Hamiltonian
Regulation of the Na+/K+-ATPase Ena1 Expression by Calcineurin/Crz1 under High pH Stress: A Quantitative Study
[EN] Regulated expression of the Ena1 Na+-ATPase is a crucial event for adaptation to high
salt and/or alkaline pH stress in the budding yeast Saccharomyces cerevisiae. ENA1
expression is under the control of diverse signaling pathways, including that mediated
by the calcium-regulatable protein phosphatase calcineurin and its downstream
transcription factor Crz1. We present here a quantitative study of the expression of
Ena1 in response to alkalinization of the environment and we analyze the contribution
of Crz1 to this response. Experimental data and mathematical models substantiate the
existence of two stress-responsive Crz1-binding sites in the ENA1 promoter and
estimate that the contribution of Crz1 to the early response of the ENA1 promoter is
about 60%. The models suggest the existence of a second input with similar kinetics,
which would be likely mediated by high pH-induced activation of the Snf1 kinase.This work was supported by grants BFU2011-30197-C3-01, BFU2014-54591-C2-1-P and EUI2009-04147 (SysMo2) to JA. (Ministry of Industry and Competitivity, Spain, and Fondo Europeo de Desarrollo Regional [FEDER]). JA is the recipient of an Ajut 2014SGR-4 award (Generalitat de Catalunya). DC was recipient of a predoctoral fellowship from the Spanish Ministry of Education. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.Petrezsélyová, S.; López-Malo, M.; Canadell, D.; Roque, A.; Serra-Cardona, A.; Marques Romero, MC.; Vilaprinyó, E.... (2016). Regulation of the Na+/K+-ATPase Ena1 Expression by Calcineurin/Crz1 under High pH Stress: A Quantitative Study. PLoS ONE. 11(6):e0158424-e0158424. https://doi.org/10.1371/journal.pone.0158424Se0158424e015842411
Equation of state and phonon frequency calculations of diamond at high pressures
The pressure-volume relationship and the zone-center optical phonon frequency
of cubic diamond at pressures up to 600 GPa have been calculated based on
Density Functional Theory within the Local Density Approximation and the
Generalized Gradient Approximation. Three different approaches, viz. a
pseudopotential method applied in the basis of plane waves, an all-electron
method relying on Augmented Plane Waves plus Local Orbitals, and an
intermediate approach implemented in the basis of Projector Augmented Waves
have been used. All these methods and approximations yield consistent results
for the pressure derivative of the bulk modulus and the volume dependence of
the mode Grueneisen parameter of diamond. The results are at variance with
recent precise measurements up to 140 GPa. Possible implications for the
experimental pressure determination based on the ruby luminescence method are
discussed.Comment: 10 pages, 6 figure
Differential branching fraction and angular analysis of the decay B0→K∗0μ+μ−
The angular distribution and differential branching fraction of the decay B 0→ K ∗0 μ + μ − are studied using a data sample, collected by the LHCb experiment in pp collisions at s√=7 TeV, corresponding to an integrated luminosity of 1.0 fb−1. Several angular observables are measured in bins of the dimuon invariant mass squared, q 2. A first measurement of the zero-crossing point of the forward-backward asymmetry of the dimuon system is also presented. The zero-crossing point is measured to be q20=4.9±0.9GeV2/c4 , where the uncertainty is the sum of statistical and systematic uncertainties. The results are consistent with the Standard Model predictions
Observation of two new baryon resonances
Two structures are observed close to the kinematic threshold in the mass spectrum in a sample of proton-proton collision data, corresponding
to an integrated luminosity of 3.0 fb recorded by the LHCb experiment.
In the quark model, two baryonic resonances with quark content are
expected in this mass region: the spin-parity and
states, denoted and .
Interpreting the structures as these resonances, we measure the mass
differences and the width of the heavier state to be
MeV,
MeV,
MeV, where the first and second
uncertainties are statistical and systematic, respectively. The width of the
lighter state is consistent with zero, and we place an upper limit of
MeV at 95% confidence level. Relative
production rates of these states are also reported.Comment: 17 pages, 2 figure
Opposite-side flavour tagging of B mesons at the LHCb experiment
The calibration and performance of the oppositeside
flavour tagging algorithms used for the measurements
of time-dependent asymmetries at the LHCb experiment
are described. The algorithms have been developed using
simulated events and optimized and calibrated with
B
+ →J/ψK
+, B0 →J/ψK
∗0 and B0 →D
∗−
μ
+
νμ decay
modes with 0.37 fb−1 of data collected in pp collisions
at
√
s = 7 TeV during the 2011 physics run. The oppositeside
tagging power is determined in the B
+ → J/ψK
+
channel to be (2.10 ± 0.08 ± 0.24) %, where the first uncertainty
is statistical and the second is systematic
Observation of an Excited Bc+ State
Using pp collision data corresponding to an integrated luminosity of 8.5 fb-1 recorded by the LHCb experiment at center-of-mass energies of s=7, 8, and 13 TeV, the observation of an excited Bc+ state in the Bc+π+π- invariant-mass spectrum is reported. The observed peak has a mass of 6841.2±0.6(stat)±0.1(syst)±0.8(Bc+) MeV/c2, where the last uncertainty is due to the limited knowledge of the Bc+ mass. It is consistent with expectations of the Bc∗(2S31)+ state reconstructed without the low-energy photon from the Bc∗(1S31)+→Bc+γ decay following Bc∗(2S31)+→Bc∗(1S31)+π+π-. A second state is seen with a global (local) statistical significance of 2.2σ (3.2σ) and a mass of 6872.1±1.3(stat)±0.1(syst)±0.8(Bc+) MeV/c2, and is consistent with the Bc(2S10)+ state. These mass measurements are the most precise to date
Measurement of the ratio of branching fractions BR(B0 -> K*0 gamma)/BR(Bs0 -> phi gamma)
The ratio of branching fractions of the radiative B decays B0 -> K*0 gamma
and Bs0 -> phi gamma has been measured using 0.37 fb-1 of pp collisions at a
centre of mass energy of sqrt(s) = 7 TeV, collected by the LHCb experiment. The
value obtained is BR(B0 -> K*0 gamma)/BR(Bs0 -> phi gamma) = 1.12 +/- 0.08
^{+0.06}_{-0.04} ^{+0.09}_{-0.08}, where the first uncertainty is statistical,
the second systematic and the third is associated to the ratio of fragmentation
fractions fs/fd. Using the world average for BR(B0 -> K*0 gamma) = (4.33 +/-
0.15) x 10^{-5}, the branching fraction BR(Bs0 -> phi gamma) is measured to be
(3.9 +/- 0.5) x 10^{-5}, which is the most precise measurement to date.Comment: 15 pages, 1 figure, 2 table
Measurement of the mass and lifetime of the baryon
A proton-proton collision data sample, corresponding to an integrated
luminosity of 3 fb collected by LHCb at and 8 TeV, is used
to reconstruct , decays. Using the , decay mode for calibration, the lifetime ratio and absolute
lifetime of the baryon are measured to be \begin{align*}
\frac{\tau_{\Omega_b^-}}{\tau_{\Xi_b^-}} &= 1.11\pm0.16\pm0.03, \\
\tau_{\Omega_b^-} &= 1.78\pm0.26\pm0.05\pm0.06~{\rm ps}, \end{align*} where the
uncertainties are statistical, systematic and from the calibration mode (for
only). A measurement is also made of the mass difference,
, and the corresponding mass, which
yields \begin{align*} m_{\Omega_b^-}-m_{\Xi_b^-} &= 247.4\pm3.2\pm0.5~{\rm
MeV}/c^2, \\ m_{\Omega_b^-} &= 6045.1\pm3.2\pm 0.5\pm0.6~{\rm MeV}/c^2.
\end{align*} These results are consistent with previous measurements.Comment: 11 pages, 5 figures, All figures and tables, along with any
supplementary material and additional information, are available at
https://lhcbproject.web.cern.ch/lhcbproject/Publications/LHCbProjectPublic/LHCb-PAPER-2016-008.htm
Observation of the decay
The decay is observed for the first
time, using proton-proton collisions collected with the LHCb detector
corresponding to an integrated luminosity of 3fb. A signal yield of
decays is reported with a significance of 6.2 standard deviations.
The ratio of the branching fraction of \B_c \rightarrow J/\psi K^+ K^- \pi^+
decays to that of decays is measured to be
, where the first uncertainty is statistical and the
second is systematic.Comment: 18 pages, 2 figure
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