8,576 research outputs found
Scaling regimes in spherical shell rotating convection
Rayleigh-B\'enard convection in rotating spherical shells can be considered
as a simplified analogue of many astrophysical and geophysical fluid flows.
Here, we use three-dimensional direct numerical simulations to study this
physical process. We construct a dataset of more than 200 numerical models that
cover a broad parameter range with Ekman numbers spanning , Rayleigh numbers within the range and a Prandtl number unity. We investigate the scaling behaviours of
both local (length scales, boundary layers) and global (Nusselt and Reynolds
numbers) properties across various physical regimes from onset of rotating
convection to weakly-rotating convection. Close to critical, the convective
flow is dominated by a triple force balance between viscosity, Coriolis force
and buoyancy. For larger supercriticalities, a subset of our numerical data
approaches the asymptotic diffusivity-free scaling of rotating convection
in a narrow fraction of the parameter space delimited by
. Using a decomposition of the viscous
dissipation rate into bulk and boundary layer contributions, we establish a
theoretical scaling of the flow velocity that accurately describes the
numerical data. In rapidly-rotating turbulent convection, the fluid bulk is
controlled by a triple force balance between Coriolis, inertia and buoyancy,
while the remaining fraction of the dissipation can be attributed to the
viscous friction in the Ekman layers. Beyond , the
rotational constraint on the convective flow is gradually lost and the flow
properties vary to match the regime changes between rotation-dominated and
non-rotating convection. The quantity provides an accurate
transition parameter to separate rotating and non-rotating convection.Comment: 42 pages, 20 figures, 3 tables, accepted for publication in JF
The ATLAS liquid argon hadronic end-cap calorimeter: construction and selected beam test results
ATLAS has chosen for its Hadronic End-Cap Calorimeter (HEC) the copper-liquid
argon sampling technique with flat plate geometry and GaAs pre-amplifiers in
the argon. The contruction of the calorimeter is now approaching completion.
Results of production quality checks are reported and their anticipated impact
on calorimeter performance discussed. Selected results, such as linearity,
electron and pion energy resolution, uniformity of energy response, obtained in
beam tests both of the Hadronic End-Cap Calorimeter by itself, and in the ATLAS
configuration where the HEC is in combination with the Electromagnetic End-Cap
Calorimeter (EMEC) are described.Comment: 4 pages, 2 figures,IPRD04 conferenc
Radiative and Semileptonic B Decays Involving Higher K-Resonances in the Final States
We study the radiative and semileptonic B decays involving a spin-
resonant with parity for and for
in the final state. Using the large energy effective theory (LEET)
techniques, we formulate transition form factors in the large
recoil region in terms of two independent LEET functions
and , the values of
which at zero momentum transfer are estimated in the BSW model. According to
the QCD counting rules, exhibit a dipole
dependence in . We predict the decay rates for ,
and . The
branching fractions for these decays with higher -resonances in the final
state are suppressed due to the smaller phase spaces and the smaller values of
. Furthermore, if the spin of
becomes larger, the branching fractions will be further suppressed due to the
smaller Clebsch-Gordan coefficients defined by the polarization tensors of the
. We also calculate the forward backward asymmetry of the decay, for which the zero is highly insensitive to the
-resonances in the LEET parametrization.Comment: 27 pages, 4 figures, 7 tables;contents and figures corrected, title
and references revise
NNLO vertex corrections to non-leptonic B decays: Tree amplitudes
The colour-suppressed tree amplitude in non-leptonic B decays is particularly
sensitive to perturbative and non-perturbative corrections. We calculate the
two-loop (NNLO) vertex corrections to the colour-suppressed and colour-allowed
tree amplitudes in QCD factorization. Our results are given completely
analytically, including the full dependence on the charm quark mass. We then
update theoretical predictions for a range of interesting observables derived
from pi pi, pi rho, and rho rho final states that do not depend (significantly)
on penguin contributions, and hence are now available with NNLO accuracy. We
observe good agreement with experimental data within experimental and
theoretical errors, except for observables involving the pi^0 pi^0 branching
fraction.Comment: 52 pages, 8 figures, 3 tables. Equations (42) and (84) are contained
in electronic form in the source file of the present submissio
Understanding the newly observed Y(4008) by Belle
Very recently a new enhancement around 4.05 GeV was observed by Belle
experiment. In this short note, we discuss some possible assignments for this
enhancement, i.e. and molecular state. In these two
assignments, Y(4008) can decay into with comparable
branching ratio with that of . Thus one suggests
high energy experimentalists to look for Y(4008) in channel.
Furthermore one proposes further experiments to search missing channel
, and especially and
, which will be helpful to distinguish and
molecular state assignments for this new enhancement.Comment: 4 pages, 5 figures. Typos correcte
Redescription of the rugose coral Macqeea (Rozkowskaella) sandaliformis (Rozkowska, 1980) from the Upper Frasnian of het Holy Cross Mountains (Poland)
The discovery of horseshoe dissepiments at the base of some coralla of Trigonella sandaliformis ROZKOWSKA, 1980, type species of Rozkowskaella WRZOLEK, 1987 from the Upper Frasnian of Poland, leads to consider this taxon as a subgenus of Macgeea WEBSTER, 1889. Moreover, Debnikiella ROZKOWSKA, 1980, whose type species is D. formosa ROZKOWSKA, 1980 also from the Upper Frasnian of Poland, can probably be placed in synonymy with Rozkowskaella. For comparison, a few topotypes of Pachyphyllum solitarium HALL & WHITFIELD, 1873, type species of the genus Macgeea are described
Exciton spin dynamics and photoluminescence polarization of CdSe/CdS dot-in-rod nanocrystals in high magnetic fields
The exciton spin dynamics and polarization properties of the related emission
are investigated in colloidal CdSe/CdS dot-in-rod (DiR) and spherical
core/shell nanocrystal (NC) ensembles by magneto-optical photoluminescence (PL)
spectroscopy in magnetic fields up to 15 T. It is shown that the degree of
circular polarization (DCP) of the exciton emission induced by the magnetic
field is affected by the NC geometry as well as the exciton fine structure and
can provide information on nanorod orientation. A theory to describe the
circular and linear polarization properties of the NC emission in magnetic
field is developed. It takes into account phonon mediated coupling between the
exciton fine structure states as well as the dielectric enhancement effect
resulting from the anisotropic shell of DiR NCs. This theoretical approach is
used to model the experimental results and allows us to explain most of the
measured features. The spin dynamics of the dark excitons is investigated in
magnetic fields by time-resolved photoluminescence. The results highlight the
importance of confined acoustic phonons in the spin relaxation of dark
excitons. The bare core surface as well as the core/shell interface give rise
to an efficient spin relaxation channel, while the surface of core/shell NCs
seems to play only a minor role.Comment: 18 pages, 15 figure
Testing new physics with the electron g-2
We argue that the anomalous magnetic moment of the electron (a_e) can be used
to probe new physics. We show that the present bound on new-physics
contributions to a_e is 8*10^-13, but the sensitivity can be improved by about
an order of magnitude with new measurements of a_e and more refined
determinations of alpha in atomic-physics experiments. Tests on new-physics
effects in a_e can play a crucial role in the interpretation of the observed
discrepancy in the anomalous magnetic moment of the muon (a_mu). In a large
class of models, new contributions to magnetic moments scale with the square of
lepton masses and thus the anomaly in a_mu suggests a new-physics effect in a_e
of (0.7 +- 0.2)*10^-13. We also present examples of new-physics theories in
which this scaling is violated and larger effects in a_e are expected. In such
models the value of a_e is correlated with specific predictions for processes
with violation of lepton number or lepton universality, and with the electric
dipole moment of the electron.Comment: 34 pages, 7 figures. Minor changes and references adde
Radiative and isospin-violating decays of Ds mesons in the hadrogenesis conjecture
The masses and decays of the scalar D_{s0}^*(2317) and axial-vector
D_{s1}^*(2460) charmed strange mesons are calculated consistently in the
hadrogenesis conjecture. These mesons decay either strongly into the
isospin-violating pi^0 D_s and pi^0 D_s^* channels or electromagnetically. They
are generated by coupled-channel dynamics based on the leading order chiral
Lagrangian. The effect of chiral corrections to chiral order Q_\chi^2 is
investigated. We show that taking into account large-N_c relations to determine
the strength of these correction terms implies a measurable signal for an
exotic axial-vector state in the eta D* invariant mass distribution. The
one-loop contribution to the electromagnetic decay amplitudes of scalar and
axial-vector states is calculated. The Lagrangian describing electromagnetic
interactions is obtained by gauging the chiral Lagrangian for hadronic
interactions and adding gauge-invariant correction terms to chiral order
Q_chi^2. In addition the role of light vector meson degrees of freedom is
explored. We confront our results with measured branching ratios. Once the
light vector mesons are included, a natural explanation of all radiative decay
parameters is achieved.Comment: 102 pages, 7 figures, further improved presentatio
Branching ratios and CP asymmetries of decays in the pQCD approach
We calculate the branching ratios and CP violating asymmetries of the four B
\to K \etap decays in the perturbative QCD (pQCD) factorization approach.
Besides the full leading order contributions, the partial next-to-leading order
(NLO) contributions from the QCD vertex corrections, the quark loops, and the
chromo-magnetic penguins are also taken into account. The NLO pQCD predictions
for the CP-averaged branching ratios are , Br(B^\pm \to K^\pm \etar) \approx 51.0 \times 10^{-6},
, and Br(B^0 \to K^0 \etar)
\approx 50.3 \times 10^{-6}. The NLO contributions can provide a 70%
enhancement to the LO Br(B \to K \etar), but a 30% reduction to the LO , which play the key role in understanding the observed pattern of
branching ratios. The NLO pQCD predictions for the CP-violating asymmetries,
such as \acp^{dir} (K^0_S \etar) \sim 2.3% and \acp^{mix}(K^0_S \etar)\sim
63%, agree very well with currently available data. This means that the
deviation \Delta S=\acp^{mix}(K^0_S \etar) - \sin{2\beta} in pQCD approach is
also very small.Comment: 31 pages, 11 ps/eps figures, typos corrected. A little modificatio
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