634 research outputs found
Entropy Change through Rayleigh-B\'enard Convective Transition with Rigid Boundaries
The previous investigation on Rayleigh-B\'enard convection of a dilute
classical gas [T. Kita: J. Phys. Soc. Jpn. {\bf 75} (2006) 124005] is extended
to calculate entropy change of the convective transition with the rigid
boundaries. We obtain results qualitatively similar to those of the stress-free
boundaries. Above the critical Rayleigh number, the roll convection is realized
among possible steady states with periodic structures, carrying the highest
entropy as a function of macroscopic mechanical variables.Comment: 5 pages, 4 figure
Drosophila Chitinase 2 is expressed in chitin producing organs for cuticle formation.
The architecture of the outer body wall cuticle is fundamental to protect arthropods against invading pathogens and numerous other harmful stresses. Such robust cuticles are formed by parallel running chitin microfibrils. Molting and also local wounding leads to dynamic assembly and disassembly of the chitin-matrix throughout development. However, the underlying molecular mechanisms that organize proper chitin-matrix formation are poorly known. Recently we identified a key region for cuticle thickening at the apical cell surface, the cuticle assembly zone, where Obstructor-A (Obst-A) coordinates the formation of the chitin-matrix. Obst-A binds chitin and the deacetylase Serpentine (Serp) in a core complex, which is required for chitin-matrix maturation and preservation. Here we present evidence that Chitinase 2 (Cht2) could be essential for this molecular machinery. We show that Cht2 is expressed in the chitin-matrix of epidermis, trachea, and the digestive system. There, Cht2 is enriched at the apical cell surface and the dense chitin-matrix. We further show that in Cht2 knockdown larvae the assembly zone is rudimentary, preventing normal cuticle formation and pore canal organization. As sequence similarities of Cht2 and the core complex proteins indicate evolutionarily conserved molecular mechanisms, our findings suggest that Cht2 is involved in chitin formation also in other insects
Specific heat and thermal conductivity in the mixed state of MgB2
The specific heat C and the electronic and phononic thermal conductivities
kappa_e and kappa_{ph} are calculated in the mixed state for magnetic fields H
near H_{c2}. The effects of supercurrent flow and Andreev scattering of the
Abrikosov vortex lattice on the quasiparticles are taken into account. The
resulting function C(H) is nearly linear while kappa_e(H) exhibits an upward
curvature near H_{c2}. The slopes decrease with impurity scattering which
improves the agreement with the data on MgB_2. The ratio of phonon relaxation
times tau_n/tau_s = g(omega_0,H) for phonon energy omega_0, which is nearly a
step function at omega_0 = 2Delta for the BCS state, is smeared out and tends
to one for increasing H. This leads to a rapid reduction of kappa_{ph}(H) in
MgB_2 for relatively small fields due to the rapid suppression of the smaller
energy gap.Comment: 8 pages, 4 figures, accepted for publication in Phys. Rev. Letter
MicroRNA regulation of bovine monocyte inflammatory and metabolic networks in an in vivo infection model.
peer-reviewedBovine mastitis is an inflammation-driven disease of the bovine mammary gland that costs the global dairy industry several billion dollars per annum. Because disease susceptibility is a multi-factorial complex phenotype, an integrative biology approach is required to dissect the molecular networks involved. Here, we report such an approach, using next generation sequencing combined with advanced network and pathway biology methods to simultaneously profile mRNA and miRNA expression at multiple time-points (0, 12, 24, 36 and 48h) in both milk and blood FACS-isolated CD14+ monocytes from animals infected in vivo with Streptococcus uberis. More than 3,700 differentially expressed (DE) genes were identified in milk-isolated monocytes (MIMs), a key immune cell recruited to the site of infection during mastitis. Up-regulated genes were significantly enriched for inflammatory pathways, while down-regulated genes were enriched for non-glycolytic metabolic pathways. Monocyte transcriptional changes in the blood, however, were more subtle but highlighted the impact of this infection systemically. Genes up-regulated in blood-isolated-monocytes (BIMs) showed a significant association with interferon and chemokine signalling. Furthermore, twenty-six miRNAs were differentially expressed in MIMs and three in BIMs. Pathway analysis revealed that predicted targets of down-regulated miRNAs were highly enriched for roles in innate immunity (FDR < 3.4E-8) in particular TLR signalling, while up-regulated miRNAs preferentially targeted genes involved in metabolism. We conclude that during S. uberis infection miRNAs are key amplifiers of monocyte inflammatory response networks and repressors of several metabolic pathways.This study was funded in part by Teagasc RMIS 6018 and United States Department of Agriculture ARS funding 3625-32000-102-00. NL is supported by a Teagasc Walsh Fellowship
Specific heat and thermal conductivity in the vortex state of the two-gap superconductor MgB_2
The specific heat coefficient gamma_s(H) and the electronic thermal
conductivity kappa_{es}(H) are calculated for Abrikosov's vortex lattice by
taking into account the effects of supercurrent flow and Andreev scattering.
First we solve the gap equation for the entire range of magnetic fields. We
take into account vertex corrections due to impurity scattering calculated in
the Born approximation. The function gamma_s(H)/gamma_n increases from zero and
becomes approximately linear above H/H_{c2} \sim 0.1. The dependence on
impurity scattering is substantially reduced by the vertex corrections. The
upward curvature of kappa_{es}(H)/kappa_{en}, which is caused by decreasing
Andreev scattering for increasing field, is reduced for increasing impurity
scattering. We also calculate the temperature dependence of the scattering
rates 1/tau_{ps}(H) of a phonon and 1/tau_{es}(H) of a quasiparticle due to
quasiparticle and phonon scattering, respectively. At low temperatures the
ratio tau_{pn}/tau_{ps}(H) increases rapidly to one as H tends to H_{c2} which
yields a rapid drop in the phononic thermal conductivity kappa_{ph}. Our
results are in qualitative agreement with the experiments on the two-gap
superconductor MgB_2.Comment: 12 pages, 5 figures, additions to figures 1, 2, and 3. Accepted by
Phys. Rev.
Whirling Hexagons and Defect Chaos in Hexagonal Non-Boussinesq Convection
We study hexagon patterns in non-Boussinesq convection of a thin rotating
layer of water. For realistic parameters and boundary conditions we identify
various linear instabilities of the pattern. We focus on the dynamics arising
from an oscillatory side-band instability that leads to a spatially disordered
chaotic state characterized by oscillating (whirling) hexagons. Using
triangulation we obtain the distribution functions for the number of pentagonal
and heptagonal convection cells. In contrast to the results found for defect
chaos in the complex Ginzburg-Landau equation and in inclined-layer convection,
the distribution functions can show deviations from a squared Poisson
distribution that suggest non-trivial correlations between the defects.Comment: 4 mpg-movies are available at
http://www.esam.northwestern.edu/~riecke/lit/lit.html submitted to New J.
Physic
On retracts, absolute retracts, and folds in cographs
Let G and H be two cographs. We show that the problem to determine whether H
is a retract of G is NP-complete. We show that this problem is fixed-parameter
tractable when parameterized by the size of H. When restricted to the class of
threshold graphs or to the class of trivially perfect graphs, the problem
becomes tractable in polynomial time. The problem is also soluble when one
cograph is given as an induced subgraph of the other. We characterize absolute
retracts of cographs.Comment: 15 page
Dynamics and Selection of Giant Spirals in Rayleigh-Benard Convection
For Rayleigh-Benard convection of a fluid with Prandtl number \sigma \approx
1, we report experimental and theoretical results on a pattern selection
mechanism for cell-filling, giant, rotating spirals. We show that the pattern
selection in a certain limit can be explained quantitatively by a
phase-diffusion mechanism. This mechanism for pattern selection is very
different from that for spirals in excitable media
Four nearby L dwarfs
We present spectroscopic, photometric and astrometric observations of four
bright L dwarfs identified in the course of the 2MASS near-infrared survey. Our
spectroscopic data extend to wavelengths shortward of 5000\AA in the L0 dwarf
2MASSJ0746+2000 and the L4 dwarf 2MASSJ0036+1840, allowing the identification
of absorption bands due to MgH and CaOH. The atomic resonance lines Ca I
4227\AA and Na I 5890/5896\AA are extremely strong, with the latter having an
equivalent width of 240\AA in the L4 dwarf. By spectral type L5, the D lines
extend over \AA and absorb a substantial fraction of the flux emitted
in the V band, with a corresponding effect on the (V-I) broadband colour. The
KI resonance doublet at 7665/7699\AA increases in equivalent width from
spectral type M3 to M7, but decreases in strength from M7 to L0 before
broadening substantially at later types. These variations are likely driven by
dust formation in these cool atmospheres.Comment: to appear in AJ, January 2000; 27 pages, including 3 tables and 7
figures embedded in the tex
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