68,152 research outputs found
Reptile scale paradigm: Evo-Devo, pattern formation and regeneration
The purpose of this perspective is to highlight the merit of the reptile integument as an experimental model. Reptiles represent the first amniotes. From stem reptiles, extant reptiles, birds and mammals have evolved. Mammal hairs and feathers evolved from Therapsid and Sauropsid reptiles, respectively. The early reptilian integument had to adapt to the challenges of terrestrial life, developing a multi-layered stratum corneum capable of barrier function and ultraviolet protection. For better mechanical protection, diverse reptilian scale types have evolved. The evolution of endothermy has driven the convergent evolution of hair and feather follicles: both form multiple localized growth units with stem cells and transient amplifying cells protected in the proximal follicle. This topological arrangement allows them to elongate, molt and regenerate without structural constraints. Another unique feature of reptile skin is the exquisite arrangement of scales and pigment patterns, making them testable models for mechanisms of pattern formation. Since they face the constant threat of damage on land, different strategies were developed to accommodate skin homeostasis and regeneration. Temporally, they can be under continuous renewal or sloughing cycles. Spatially, they can be diffuse or form discrete localized growth units (follicles). To understand how gene regulatory networks evolved to produce increasingly complex ectodermal organs, we have to study how prototypic scale-forming pathways in reptiles are modulated to produce appendage novelties. Despite the fact that there are numerous studies of reptile scales, molecular analyses have lagged behind. Here, we underscore how further development of this novel experimental model will be valuable in filling the gaps of our understanding of the Evo-Devo of amniote integuments
The magnetic dipole transitions in the binding system
The magnetic dipole transitions between the vector mesons and their
relevant pseudoscalar mesons (, , , ,
and etc, the binding states of system) of
the family are interesting. To see the `hyperfine' splitting due to
spin-spin interaction is an important topic for understanding the spin-spin
interaction and the spectrum of the the binding system. The
knowledge about the magnetic dipole transitions is also very useful for
identifying the vector boson mesons experimentally, whose masses are
just slightly above the masses of their relevant pseudoscalar mesons
accordingly. Considering the possibility to observe the vector mesons via the
transitions at factory and the potentially usages of the theoretical
estimate on the transitions, we fucus our efforts on calculating the magnetic
dipole transitions, i.e. precisely to calculate the rates for the transitions
such as decays and , and particularly
work in the Behte-Salpeter framework. In the estimate, as a typical example, we
carefully investigate the dependance of the rate
on the mass difference as well.Comment: 10 pages, 2 figures, 1 tabl
Shifting with
Precision measurements at the resonance agree well with the standard
model. However, there is still a hint of a discrepancy, not so much in by
itself (which has received a great deal of attention in the past several years)
but in the forward-backward asymmetry together with . The two
are of course correlated. We explore the possibilty that these and other
effects are due to the mixing of and with one or more heavy quarks.Comment: 11 pages, 1 Figure, LaTex fil
Fitting Precision Electroweak Data with Exotic Heavy Quarks
The 1999 precision electroweak data from LEP and SLC persist in showing some
slight discrepancies from the assumed standard model, mostly regarding and
quarks. We show how their mixing with exotic heavy quarks could result in a
more consistent fit of all the data, including two unconventional
interpretations of the top quark.Comment: 7 pages, no figure, 2 typos corrected, 1 reference update
Analysis of data from NASA B-57B gust gradient program
Statistical analysis of the turbulence measured in flight 6 of the NASA B-57B over Denver, Colorado, from July 7 to July 23, 1982 included the calculations of average turbulence parameters, integral length scales, probability density functions, single point autocorrelation coefficients, two point autocorrelation coefficients, normalized autospectra, normalized two point autospectra, and two point cross sectra for gust velocities. The single point autocorrelation coefficients were compared with the theoretical model developed by von Karman. Theoretical analyses were developed which address the effects spanwise gust distributions, using two point spatial turbulence correlations
Hadronic Production of S-wave and P-wave Charmed Beauty Mesons via Heavy Quark Fragmentation
At hadron colliders the dominant production mechanism of mesons
with large transverse momentum is due to parton fragmentation. We compute the
rates and transverse momentum spectra for production of S-wave and P-wave
mesons at the Tevatron via the direct fragmentation of the bottom
antiquark as well as the Altarelli-Parisi induced gluon fragmentation. Since
all the radially and orbitally excited mesons below the
flavor threshold will cascade into the pseudoscalar ground state through
electromagnetic and/or hadronic transitions, they all contribute to the
inclusive production of . The contributions of the excited S-wave and
P-wave states to the inclusive production of are 58 and 23\%,
respectively, and hence significant.Comment: Changes are made in the Discussio
Turbulence Time Series Data Hole Filling using Karhunen-Loeve and ARIMA methods
Measurements of optical turbulence time series data using unattended
instruments over long time intervals inevitably lead to data drop-outs or
degraded signals. We present a comparison of methods using both Principal
Component Analysis, which is also known as the Karhunen--Loeve decomposition,
and ARIMA that seek to correct for these event-induced and mechanically-induced
signal drop-outs and degradations. We report on the quality of the correction
by examining the Intrinsic Mode Functions generated by Empirical Mode
Decomposition. The data studied are optical turbulence parameter time series
from a commercial long path length optical anemometer/scintillometer, measured
over several hundred metres in outdoor environments.Comment: 8 pages, 9 figures, submitted to ICOLAD 2007, City University,
London, U
The Decays to -wave Charmonium by Improved Bethe-Salpeter Approach
We re-calculate the exclusive semileptonic and nonleptonic decays of
meson to a -wave charmonium in terms of the improved Bethe-Salpeter (B-S)
approach, which is developed recently. Here the widths for the exclusive
semileptonic and nonleptonic decays, the form factors, and the charged lepton
spectrums for the semileptonic decays are precisely calculated. To test the
concerned approach by comparing with experimental measurements when the
experimental data are available, and to have comparisons with the other
approaches the results obtained by the approach and those by some approaches
else as well as the original B-S approach, which appeared in literature, are
comparatively presented and discussed.Comment: 33 pages, 5 figures, 3 table
Investigation of the energy dependence of the orbital light curve in LS 5039
LS 5039 is so far the best studied -ray binary system at
multi-wavelength energies. A time resolved study of its spectral energy
distribution (SED) shows that above 1 keV its power output is changing along
its binary orbit as well as being a function of energy. To disentangle the
energy dependence of the power output as a function of orbital phase, we
investigated in detail the orbital light curves as derived with different
telescopes at different energy bands. We analysed the data from all existing
\textit{INTEGRAL}/IBIS/ISGRI observations of the source and generated the most
up-to-date orbital light curves at hard X-ray energies. In the -ray
band, we carried out orbital phase-resolved analysis of \textit{Fermi}-LAT data
between 30 MeV and 10 GeV in 5 different energy bands. We found that, at
100 MeV and 1 TeV the peak of the -ray emission is
near orbital phase 0.7, while between 100 MeV and 1 GeV it moves
close to orbital phase 1.0 in an orbital anti-clockwise manner. This result
suggests that the transition region in the SED at soft -rays (below a
hundred MeV) is related to the orbital phase interval of 0.5--1.0 but not to
the one of 0.0--0.5, when the compact object is "behind" its companion. Another
interesting result is that between 3 and 20 GeV no orbital modulation is found,
although \textit{Fermi}-LAT significantly (18) detects LS 5039.
This is consistent with the fact that at these energies, the contributions to
the overall emission from the inferior conjunction phase region (INFC, orbital
phase 0.45 to 0.9) and from the superior conjunction phase region (SUPC,
orbital phase 0.9 to 0.45) are equal in strength. At TeV energies the power
output is again dominant in the INFC region and the flux peak occurs at phase
0.7.Comment: 7 pages, 6 figures, accepted for publication in MNRA
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