312 research outputs found
Equivalent variational approaches to biaxial liquid crystal dynamics
Within the framework of liquid crystal flows, the Qian & Sheng (QS) model for
Q-tensor dynamics is compared to the Volovik & Kats (VK) theory of biaxial
nematics by using Hamilton's variational principle. Under the assumption of
rotational dynamics for the Q-tensor, the variational principles underling the
two theories are equivalent and the conservative VK theory emerges as a
specialization of the QS model. Also, after presenting a micropolar variant of
the VK model, Rayleigh dissipation is included in the treatment. Finally, the
treatment is extended to account for nontrivial eigenvalue dynamics in the VK
model and this is done by considering the effect of scaling factors in the
evolution of the Q-tensor.Comment: 8 pages. Third versio
FSI Rescattering in Decays via States with and
New results going beyond those obtained from isospin and flavor symmetry and
subject to clear experimental tests are obtained for effects of FSI in
decays to charmless strange final states containing neutral flavor-mixed mesons
like , , and . The most general strong-interaction
diagrams containing arbitrary numbers of quarks and gluons are included with
the assumptions that any pair created by gluons must be a flavor
singlet, and that there are no hairpin diagrams in which a final meson contains
a pair from the same gluon vertex. The smallness of
suggests that it might have a large CP violation. A sum rule is derived to test
whether the large requires the addition of an additional glueball
or charm admixture. Further analysis from decay systematics supports this
picture of FSI and raises questions about charm admixture in the
Ontogenetic scaling patterns and functional anatomy of the pelvic limb musculature in emus (Dromaius novaehollandiae)
Emus (Dromaius novaehollandiae) are exclusively terrestrial, bipedal and cursorial ratites with some similar biomechanical characteristics to humans. Their growth rates are impressive, as their body mass increases eighty-fold from hatching to adulthood whilst maintaining the same mode of locomotion throughout life. These ontogenetic characteristics stimulate biomechanical questions about the strategies that allow emus to cope with their rapid growth and locomotion, which can be partly addressed via scaling (allometric) analysis of morphology. In this study we have collected pelvic limb anatomical data (muscle architecture, tendon length, tendon mass and bone lengths) and calculated muscle physiological cross sectional area (PCSA) and average tendon cross sectional area from emus across three ontogenetic stages (n = 17, body masses from 3.6 to 42 kg). The data were analysed by reduced major axis regression to determine how these biomechanically relevant aspects of morphology scaled with body mass. Muscle mass and PCSA showed a marked trend towards positive allometry (26 and 27 out of 34 muscles respectively) and fascicle length showed a more mixed scaling pattern. The long tendons of the main digital flexors scaled with positive allometry for all characteristics whilst other tendons demonstrated a less clear scaling pattern. Finally, the two longer bones of the limb (tibiotarsus and tarsometatarsus) also exhibited positive allometry for length, and two others (femur and first phalanx of digit III) had trends towards isometry. These results indicate that emus experience a relative increase in their muscle force-generating capacities, as well as potentially increasing the force-sustaining capacities of their tendons, as they grow. Furthermore, we have clarified anatomical descriptions and provided illustrations of the pelvic limb muscle–tendon units in emus
Perturbative Prediction for Parton Fragmentation into Heavy Hadron
By expanding functions of parton fragmentation into a heavy hadron in the
inverse of the heavy quark mass we attempt to factorize them into
perturbative- and nonperturbative parts. In our approach the nonperturbative
parts can be defined as matrix elements in heavy quark effective theory, the
shape of the functions is predicted by perturbative QCD. In this work we
neglect effect at order of and calculate the perturbative parts at
one-loop level for heavy quark- and gluon fragmentation. We compare our results
from leading log approximation with experimental results from
colliders and find a deviation below or at 10% level. Adding effect of higher
order in it can be expected to reduce the deviation. The size of
matrix elements appearing at the order we consider for several types of heavy
hadrons is determined.Comment: 21 pages + 3 pages figures, plain te
Delta s density in a proton and unpolarized lepton - polarized proton scatterings
It is shown that the parity--violating deep--inelastic scatterings of
unpolarized charged leptons on polarized protons, , could provide a sensitive
test for the behavior and magnitude of the polarized strange--quark density in
a proton. Below charm threshold these processes are also helpful to uniquely
determine the magnitude of individual polarized parton distributions.Comment: LaTeX file, 12 pages+4 fiigures not included (available upon request
Searching for sub-stellar companion into the LkCa15 proto-planetary disk
Recent sub-millimetric observations at the Plateau de Bure interferometer
evidenced a cavity at ~ 46 AU in radius into the proto-planetary disk around
the T Tauri star LkCa15 (V1079 Tau), located in the Taurus molecular cloud.
Additional Spitzer observations have corroborated this result possibly
explained by the presence of a massive (>= 5 MJup) planetary mass, a brown
dwarf or a low mass star companion at about 30 AU from the star. We used the
most recent developments of high angular resolution and high contrast imaging
to search directly for the existence of this putative companion, and to bring
new constraints on its physical and orbital properties. The NACO adaptive
optics instrument at VLT was used to observe LkCa15 using a four quadrant phase
mask coronagraph to access small angular separations at relatively high
contrast. A reference star at the same parallactic angle was carefully observed
to optimize the quasi-static speckles subtraction (limiting our sensitivity at
less than 1.0). Although we do not report any positive detection of a faint
companion that would be responsible for the observed gap in LkCa15's disk
(25-30 AU), our detection limits start constraining its probable mass,
semi-major axis and eccentricity. Using evolutionary model predictions, Monte
Carlo simulations exclude the presence of low eccentric companions with masses
M >= 6 M Jup and orbiting at a >= 100 AU with significant level of confidence.
For closer orbits, brown dwarf companions can be rejected with a detection
probability of 90% down to 80 AU (at 80% down to 60 AU). Our detection limits
do not access the star environment close enough to fully exclude the presence
of a brown dwarf or a massive planet within the disk inner activity (i.e at
less than 30 AU). Only, further and higher contrast observations should unveil
the existence of this putative companion inside the LkCa15 disk.Comment: 6 pages, 4 figures, accepted for publication in A&
Measuring tiny mass accretion rates onto young brown dwarfs
We present low-resolution Keck I/LRIS spectra spanning from 3200-9000 A of
nine young brown dwarfs and three low-mass stars in the TW Hya Association and
in Upper Sco. The optical spectral types of the brown dwarfs range from
M5.5-M8.75, though two have near-IR spectral types of early L-dwarfs. We report
new accretion rates derived from excess Balmer continuum emission for the
low-mass stars TW Hya and Hen 3-600A and the brown dwarfs 2MASS
J12073347-3932540, UScoCTIO 128, SSSPM J1102-3431, UScoJ160606.29-233513.3,
DENIS-P J160603.9-205644, and Oph J162225-240515B, and upper limits on
accretion for the low-mass star Hen 3-600B and the brown dwarfs UScoCTIO 112,
Oph J162225-240515A, and USco J160723.82-221102.0. For the six brown dwarfs in
our sample that are faintest at short wavelengths, the accretion luminosity or
upper limit is measurable only when the image is binned over large wavelength
intervals. This method extends our sensivity to accretion rate down to ~1e-13
solar masses/year for brown dwarfs. Since the ability to measure an accretion
rate from excess Balmer continuum emission depends on the contrast between
excess continuum emission and the underlying photosphere, for objects with
earlier spectral types the upper limit on accretion rate is much higher.
Absolute uncertainties in our accretion rate measurements of ~3-5 include
uncertainty in accretion models, brown dwarf masses, and distance. The
accretion rate of 2e-12 solar masses/year onto 2MASS J12073347-3932540 is
within 15% of two previous measurements, despite large changes in the H-alpha
flux.Comment: Accepted by ApJ. 23 pages, 5 figures, 3 table
Strangeness Production in pp and pn Reactions at COSY
The COoler SYnchrotron COSY-J\"ulich delivers phase-space cooled, polarized
proton and deuteron beams with momenta up to p=3.65 GeV/c. Various experiments
on hadron-induced strangeness production on proton, neutron and nuclear targets
have been carried out. Here we report about recent results on associated
strangeness production in pp -> KYN (Y= Lambda,Sigma) reactions, on K^+
production in pn collisions, and on K K-bar pair production in pp interactions.
We also briefly discuss possible measurements to disentangle the parity of the
recently discovered pentaquark state Theta^+, the spin dependence of the YN
interaction, as well as planned experiments which aim at the determination of
the a_0-f_0 mixing matrix element, a quantity which is believed to be sensitive
to the nature of the light scalar mesons a_0/f_0(980).Comment: 10 pages, 3 figures; Proc. VIII Int. Conf. on Hypernuclear and
Strange Particle Physics, JLab, Oct. 14 - 18, 200
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