930 research outputs found
Plumes in stellar convection zones
All numerical simulations of compressible convection reveal the presence of
strong downwards directed flows. Thanks to helioseismology, such plumes have
now been detected also at the top of the solar convection zone, on super-
granular scales. Their properties may be crudely described by adopting Taylor's
turbulent entrainment hypothesis, whose validity is well established under
various conditions. Using this model, one finds that the strong density
stratification does not prevent the plumes from traversing the whole convection
zone, and that they carry upwards a net energy flux (Rieutord & Zahn 1995).
They penetrate to some extent in the adjacent stable region, where they
establish a nearly adiabatic stratification. These plumes have a strong impact
on the dynamics of stellar convection zones, and they play probably a key role
in the dynamo mechanism.Comment: Proceedings of the 14th Florida Workshop in Nonlinear Astronomy and
Physics, "Astrophysical Turbulence and Convection", Eds. J.R. Buchler and H.
Kandrup, to appear in the Annals of the New York Academy of Sciences (15
pages, 3 figures
Solutions to common problems in training learners in general internal medicine ambulatory settings
Persistence of magnetic field driven by relativistic electrons in a plasma
The onset and evolution of magnetic fields in laboratory and astrophysical
plasmas is determined by several mechanisms, including instabilities, dynamo
effects and ultra-high energy particle flows through gas, plasma and
interstellar-media. These processes are relevant over a wide range of
conditions, from cosmic ray acceleration and gamma ray bursts to nuclear fusion
in stars. The disparate temporal and spatial scales where each operates can be
reconciled by scaling parameters that enable to recreate astrophysical
conditions in the laboratory. Here we unveil a new mechanism by which the flow
of ultra-energetic particles can strongly magnetize the boundary between the
plasma and the non-ionized gas to magnetic fields up to 10-100 Tesla (micro
Tesla in astrophysical conditions). The physics is observed from the first
time-resolved large scale magnetic field measurements obtained in a laser
wakefield accelerator. Particle-in-cell simulations capturing the global plasma
and field dynamics over the full plasma length confirm the experimental
measurements. These results open new paths for the exploration and modelling of
ultra high energy particle driven magnetic field generation in the laboratory
Baryon history and cosmic star formation in non-Gaussian cosmological models: numerical simulations
We present the first numerical, N-body, hydrodynamical, chemical simulations
of cosmic structure formation in the framework of non-Gaussian models. We study
the impact of primordial non-Gaussianities on early chemistry (e, H, H+, H-,
He, He+, He++, H2, H2+, D, D+, HD, HeH+), molecular and atomic gas cooling,
star formation, metal (C, O, Si, Fe, Mg, S) enrichment, population III (popIII)
and population II-I (popII) transition, and on the evolution of "visible"
objects. We find that non-Gaussianities can have some consequences on baryonic
structure formation at very early epochs, but the subsequent evolution at later
times washes out any difference among the various models. When assuming
reasonable values for primordial non-Gaussian perturbations, it turns out that
they are responsible for: (i) altering early molecular fractions in the cold,
dense gas phase of ~10 per cent; (ii) inducing small temperature fluctuations
of <~10 per cent during the cosmic evolution of primordial objects; (iii)
influencing the onset of the first star formation events, at z>~15, and of the
popIII/popII transition of up to some 10^7yr; (iv) determining variations of
<~10 per cent in the gas cloud and stellar mass distributions after the
formation of the first structures; (v) causing only mild variations in the
chemical history of the Universe. We stress, though, that purely non-Gaussian
effects might be difficult to address, since they are strictly twisted with
additional physical phenomena (e.g. primordial gas bulk flows, unknown
primordial popIII stellar mass function, etc.) that have similar or stronger
impact on the behaviour of the baryons.Comment: Accepted for publications on MNRAS, on April 13, 2011. Minor
revision
Neutrophil Infiltration of the Colon Is Independent of the FPR1 yet FPR1 Deficient Mice Show Differential Susceptibilities to Acute Versus Chronic Induced Colitis
Measurement of Branching Fraction and Dalitz Distribution for B0->D(*)+/- K0 pi-/+ Decays
We present measurements of the branching fractions for the three-body decays
B0 -> D(*)-/+ K0 pi^+/-B0 -> D(*)-/+ K*+/- using
a sample of approximately 88 million BBbar pairs collected by the BABAR
detector at the PEP-II asymmetric energy storage ring.
We measure:
B(B0->D-/+ K0 pi+/-)=(4.9 +/- 0.7(stat) +/- 0.5 (syst)) 10^{-4}
B(B0->D*-/+ K0 pi+/-)=(3.0 +/- 0.7(stat) +/- 0.3 (syst)) 10^{-4}
B(B0->D-/+ K*+/-)=(4.6 +/- 0.6(stat) +/- 0.5 (syst)) 10^{-4}
B(B0->D*-/+ K*+/-)=(3.2 +/- 0.6(stat) +/- 0.3 (syst)) 10^{-4}
From these measurements we determine the fractions of resonant events to be :
f(B0-> D-/+ K*+/-) = 0.63 +/- 0.08(stat) +/- 0.04(syst) f(B0-> D*-/+ K*+/-) =
0.72 +/- 0.14(stat) +/- 0.05(syst)Comment: 7 pages, 3 figures submitted to Phys. Rev. Let
Measurement of the quasi-elastic axial vector mass in neutrino-oxygen interactions
The weak nucleon axial-vector form factor for quasi-elastic interactions is
determined using neutrino interaction data from the K2K Scintillating Fiber
detector in the neutrino beam at KEK. More than 12,000 events are analyzed, of
which half are charged-current quasi-elastic interactions nu-mu n to mu- p
occurring primarily in oxygen nuclei. We use a relativistic Fermi gas model for
oxygen and assume the form factor is approximately a dipole with one parameter,
the axial vector mass M_A, and fit to the shape of the distribution of the
square of the momentum transfer from the nucleon to the nucleus. Our best fit
result for M_A = 1.20 \pm 0.12 GeV. Furthermore, this analysis includes updated
vector form factors from recent electron scattering experiments and a
discussion of the effects of the nucleon momentum on the shape of the fitted
distributions.Comment: 14 pages, 10 figures, 6 table
Study of e+e- --> pi+ pi- pi0 process using initial state radiation with BABAR
The process e+e- --> pi+ pi- pi0 gamma has been studied at a center-of-mass
energy near the Y(4S) resonance using a 89.3 fb-1 data sample collected with
the BaBar detector at the PEP-II collider. From the measured 3pi mass spectrum
we have obtained the products of branching fractions for the omega and phi
mesons, B(omega --> e+e-)B(omega --> 3pi)=(6.70 +/- 0.06 +/- 0.27)10-5 and
B(phi --> e+e-)B(phi --> 3pi)=(4.30 +/- 0.08 +/- 0.21)10-5, and evaluated the
e+e- --> pi+ pi- pi0 cross section for the e+e- center-of-mass energy range
1.05 to 3.00 GeV. About 900 e+e- --> J/psi gamma --> pi+ pi- pi0 gamma events
have been selected and the branching fraction B(J/psi --> pi+ pi- pi0)=(2.18
+/- 0.19)% has been measured.Comment: 21 pages, 37 postscript figues, submitted to Phys. Rev.
Measurement of the B+ --> p pbar K+ Branching Fraction and Study of the Decay Dynamics
With a sample of 232x10^6 Upsilon(4S) --> BBbar events collected with the
BaBar detector, we study the decay B+ --> p pbar K+ excluding charmonium decays
to ppbar. We measure a branching fraction Br(B+ --> p pbar
K+)=(6.7+/-0.5+/-0.4)x10^{-6}. An enhancement at low ppbar mass is observed and
the Dalitz plot asymmetry suggests dominance of the penguin amplitude in this B
decay. We search for a pentaquark candidate Theta*++ decaying into pK+ in the
mass range 1.43 to 2.00 GeV/c2 and set limits on Br(B+ -->
Theta*++pbar)xBr(Theta*++ --> pK+) at the 10^{-7} level.Comment: 8 pages, 7 postscript figures, submitted to Phys. Rev. D (Rapid
Communications
Search for the W-exchange decays B0 --> Ds(*)- Ds(*)+
We report a search for the decays , , in a sample of 232
million decays to \BBb ~pairs collected with the \babar detector
at the PEP-II asymmetric-energy storage ring. We find no significant
signal and set upper bounds for the branching fractions: and at 90% confidence level.Comment: 8 pages, 2 figures, submitted to PRD-R
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