14,663 research outputs found
Sea-surface circulation, sediment transport, and marine mammal distribution, Alaska continental shelf
There are no author-identified significant results in this report
The 2^-+ assignment for the X(3872)
Very recently the BaBar collaboration has put forward a claim that the
X(3872) is not a 1^++ resonance, as most of the phenomenological work on the
subject was relying on, but rather a 2^-+ one. We examine the consequences of
this quantum number assignment for the solution of the X(3872) puzzle. The
molecular interpretation appears less likely, and the conventional charmonium
interpretation should be reconsidered. There are several well-known
difficulties with this interpretation, to which we add a new one: the
production cross section at CDF is predicted to be much smaller than that
observed. We also confirm, using a relativistic string model, the conclusion
from potential models that the mass of the state is not consistent with
expectations. In the tetraquark interpretation the 2^-+ assignment implies a
rich spectrum of partner states, although the X(3872) may be among the few
which are narrow enough to be observable.Comment: 18 pages, 6 figures, 4 tables; minor style corrections. Version to
appear in PR
The momentum distribution of J/psi in B decays
The discrepancy between theory and data in the momentum distribution of slow
J/psi in B decays has been several times addressed as a puzzle. Using the most
recent results on exclusive B decays into J/psi and heavy kaons or exotic
mesons and reconsidering the non-relativistic-QCD calculation of the color
octet fragmentation component, we show that an improvement in the comparison
between data and theory can be obtained. There is still room for a better fit
to data and this may imply that new exotic mesons of the XYZ kind have yet to
be discovered.Comment: 4 pages, 2 figures, 2 tables. To appear in Physical Review
Spectroscopic Observations of Convective Patterns in the Atmospheres of Metal-Poor Stars
Convective line asymmetries in the optical spectrum of two metal-poor stars,
Gmb1830 and HD140283, are compared to those observed for solar metallicity
stars. The line bisectors of the most metal-poor star, the subgiant HD140283,
show a significantly larger velocity span that the expectations for a
solar-metallicity star of the same spectral type and luminosity class. The
enhanced line asymmetries are interpreted as the signature of the lower metal
content, and therefore opacity, in the convective photospheric patterns. These
findings point out the importance of three-dimensional convective velocity
fields in the interpretation of the observed line asymmetries in metal-poor
stars, and in particular, urge for caution when deriving isotopic ratios from
observed line shapes and shifts using one-dimensional model atmospheres.
The mean line bisector of the photospheric atomic lines is compared with
those measured for the strong Mg I b1 and b2 features. The upper part of the
bisectors are similar, and assuming they overlap, the bottom end of the
stronger lines, which are formed higher in the atmosphere, goes much further to
the red. This is in agreement with the expected decreasing of the convective
blue-shifts in upper atmospheric layers, and compatible with the high velocity
redshifts observed in the chromosphere, transition region, and corona of
late-type stars.Comment: 27 pages, LaTeX; 10 Figures (14 PostScript files); to be published in
The Astrophysical Journa
Integral constraints on the monodromy group of the hyperkahler resolution of a symmetric product of a K3 surface
Let M be a 2n-dimensional Kahler manifold deformation equivalent to the
Hilbert scheme of length n subschemes of a K3 surface S. Let Mon be the group
of automorphisms of the cohomology ring of M, which are induced by monodromy
operators. The second integral cohomology of M is endowed with the
Beauville-Bogomolov bilinear form. We prove that the restriction homomorphism
from Mon to the isometry group O[H^2(M)] is injective, for infinitely many n,
and its kernel has order at most 2, in the remaining cases. For all n, the
image of Mon in O[H^2(M)] is the subgroup generated by reflections with respect
to +2 and -2 classes. As a consequence, we get counter examples to a version of
the weight 2 Torelli question, when n-1 is not a prime power.Comment: Version 3: Latex, 54 pages. Expository change
The educational value of ward rounds for junior trainees
The ward round (WR) is a complex task and medical teachers are often faced with the challenge of finding a balance between service provision and clinical development of learners. The educational value of WRs is an under-researched area. This short communication aims to evaluate the educational role of WRs for junior trainees and provides insight into current practices. It also identifies obstacles to effective teaching/training in this setting and provides suggestions for improving the quality of WR teaching
Photoinduced time-resolved electrodynamics of superconducting metals and alloys
The photoexcited state in superconducting metals and alloys was studied via
pump-probe spectroscopy. A pulsed Ti:sapphire laser was used to create the
non-equilibrium state and the far-infrared pulses of a synchrotron storage
ring, to which the laser is synchronized, measured the changes in the material
optical properties. Both the time- and frequency- dependent photoinduced
spectra of Pb, Nb, NbN, Nb{0.5}Ti{0.5}N, and Pb{0.75}Bi{0.25} superconducting
thin films were measured in the low-fluence regime. The time dependent data
establish the regions where the relaxation rate is dominated either by the
phonon escape time (phonon bottleneck effect) or by the intrinsic quasiparticle
recombination time. The photoinduced spectra measure directly the reduction of
the superconducting gap due to an excess number of quasiparticles created by
the short laser pulses. This gap shift allows us to establish the temperature
range over which the low fluence approximation is valid.Comment: 12 pages with 10 figure
The dynamics of Abell 2634
We have amassed a large sample of velocity data for the cluster of galaxies Abell 2634 which contains the wide-angle tail (WAT) radio source 3C 465. Robust indicators of location and scale and their confidence intervals are used to determine if the cD galaxy, containing the WAT, has a significant peculiar motion. We find a cD peculiar radial velocity of 219 plus or minus 98 km s(exp -1). Further dynamical analyses, including substructure and normality tests, suggest that A 2634 is an unrelaxed cluster whose radio source structure may be bent by the turbulent gas of a recent cluster-subcluster merger
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