17,385 research outputs found
Abnormal Action Potentials Associated with the Shaker Complex Locus of Drosophila
Intracellular recordings of action potentials were made from the cervical giant axon in Shaker (Sh) mutants and normal Drosophila. The mutants showed abnormally long delays in repolarization. The defect is not due to abnormal Ca2+ channels, because it persists in the presence of Co2+, a Ca2+-channel blocker. On the other hand, the K+-channel blocker 4-aminopyridine causes a similar effect in normal animals, suggesting that the Sh mutant may have abnormal K+ conductance. Gene-dosage analysis of Sh shows that the defect is not due to underproduction of an otherwise normal molecule; it may be due to an abnormal molecule produced by the mutated gene. Gel electrophoresis failed to detect an abnormal protein, suggesting that, if Sh codes for a nervous system protein, it is rare. Genetic analysis of the Sh locus indicates three regions. Mutations or chromosome breaks in the two flanking regions cause Sh mutant physiology; the central region shows a "haplolethal effect"--i.e., heterozygous females are lethal
The Variation of Gas Mass Distribution in Galaxy Clusters: Effects of Preheating and Shocks
We investigate the origin of the variation of the gas mass fraction in the
core of galaxy clusters, which was indicated by our work on the X-ray
fundamental plane. The adopted model supposes that the gas distribution
characterized by the slope parameter is related to the preheated temperature.
Comparison with observations of relatively hot (~> 3 keV) and low redshift
clusters suggests that the preheated temperature is about 0.5-2 keV, which is
higher than expected from the conventional galactic wind model and possibly
suggests the need for additional heating such as quasars or gravitational
heating on the largest scales at high redshift. The dispersion of the preheated
temperature may be attributed to the gravitational heating in subclusters. We
calculate the central gas fraction of a cluster from the gas distribution,
assuming that the global gas mass fraction is constant within a virial radius
at the time of the cluster collapse. We find that the central gas density thus
calculated is in good agreement with the observed one, which suggests that the
variation of gas mass fraction in cluster cores appears to be explained by
breaking the self-similarity in clusters due to preheated gas. We also find
that this model does not change major conclusions on the fundamental plane and
its cosmological implications obtained in previous papers, which strongly
suggests that not only for the dark halo but also for the intracluster gas the
core structure preserves information about the cluster formation.Comment: 17 pages, to be published in Ap
A Simple Measurement of Turbulence in Cores of Galaxy Clusters
Using a simple model, we study the effects of turbulence on the motion of
bubbles produced by AGN jet activities in the core of a galaxy cluster. We
focus on the turbulence with scales larger then the size of the bubbles. We
show that for a bubble pair with an age of ~10^8 yr, the projected angle
between the two vectors from the cluster center to the two bubbles should be ~>
90 degree and the ratio of their projected distances from the cluster center
should be ~< 2.5, if the velocity and scale of the turbulence are ~250 km s^-1
and ~20 kpc, respectively. The positions of the bubbles observed in the Perseus
cluster suggest that the turbulent velocity is ~>100 km s^-1 for the cluster.Comment: Accepted for publication in ApJ
Temperature-dependent tensile and shear response of graphite/aluminum
The thermo-mechanical response of unidirectional P100 graphite fiber/6061 aluminum matrix composites was investigated at four temperatures:-150, +75, +250, and +500 F. Two types of tests, off-axis tension and losipescu shear, were used to obtain the desired properties. Good experimental-theoretical correlation was obtained for Exx, vxy, and G12. It is shown that E11 is temperature independent, but E22, v12, and G12 generally decrease with increasing temperature. Compared with rather high longitudinal strength, very low transverse strength was obtained for the graphite/aluminum. The poor transverse strength is believed to be due to the low interfacial bond strength in this material. The strength decrease significantly with increasing temperature. The tensile response at various temperatures is greatly affected by the residual stresses caused by the mismatch in the coefficients of thermal expansion of fibers and matrix. The degradation of the aluminum matrix properties at higher temperatures has a deleterious effect on composite properties. The composite has a very low coefficient of thermal expansion in the fiber direction
Environmental effects on star formation in dwarf galaxies and star clusters
We develop a simple analytical criterion to investigate the role of the
environment on the onset of star formation. We will consider the main external
agents that influence the star formation (i.e. ram pressure, tidal interaction,
Rayleigh-Taylor and Kelvin-Helmholtz instabilities) in a spherical galaxy
moving through an external environment. The theoretical framework developed
here has direct applications to the cases of dwarf galaxies in galaxy clusters
and dwarf galaxies orbiting our Milky Way system, as well as any primordial
gas-rich cluster of stars orbiting within its host galaxy. We develop an
analytic formalism to solve the fluid dynamics equations in a non-inertial
reference frame mapped with spherical coordinates. The two-fluids instability
at the interface between a stellar system and its surrounding hotter and less
dense environment is related to the star formation processes through a set of
differential equations. The solution presented here is quite general, allowing
us to investigate most kinds of orbits allowed in a gravitationally bound
system of stars in interaction with a major massive companion. We present an
analytical criterion to elucidate the dependence of star formation in a
spherical stellar system (as a dwarf galaxy or a globular cluster) on its
surrounding environment useful in theoretical interpretations of numerical
results as well as observational applications. We show how spherical
coordinates naturally enlighten the interpretation of the two-fluids
instability in a geometry that directly applies to astrophysical case. This
criterion predicts the threshold value for the onset of star formation in a
mass vs. size space for any orbit of interest. Moreover, we show for the first
time the theoretical dependencies of the different instability phenomena acting
on a system in a fully analytical way.Comment: ACCEPTED in A&A the 09/09/2014. Changes from ver 1: the non-inertial
linear-response theory for gas instabilities in spherical coordinates is
moved to the Appenidx and will be available only on-lin
Instabilities at [110] Surfaces of d_{x^2-y^2} Superconductors
We compare different scenarios for the low temperature splitting of the
zero-energy peak in the local density of states at (110) surfaces of
d_{x^2-y^2}-wave superconductors, observed by Covington et al.
(Phys.Rev.Lett.79 (1997), 277). Using a tight binding model in the
Bogolyubov-de Gennes treatment we find a surface phase transition towards a
time-reversal symmetry breaking surface state carrying spontaneous currents and
an s+id-wave state. Alternatively, we show that electron correlation leads to a
surface phase transition towards a magnetic state corresponding to a local spin
density wave state.Comment: 4 pages, 5 figure
Reflectance measurement of two-dimensional photonic crystal nanocavities with embedded quantum dots
The spectra of two-dimensional photonic crystal slab nanocavities with
embedded InAs quantum dots are measured by photoluminescence and reflectance.
In comparing the spectra taken by these two different methods, consistency with
the nanocavities' resonant wavelengths is found. Furthermore, it is shown that
the reflectance method can measure both active and passive cavities. Q-factors
of nanocavities, whose resonant wavelengths range from 1280 to 1620 nm, are
measured by the reflectance method in cross polarization. Experimentally,
Q-factors decrease for longer wavelengths and the intensity, reflected by the
nanocavities on resonance, becomes minimal around 1370 nm. The trend of the
Q-factors is explained by the change of the slab thickness relative to the
resonant wavelength, showing a good agreement between theory and experiment.
The trend of reflected intensity by the nanocavities on resonance can be
understood as effects that originate from the PC slab and the underlying air
cladding thickness. In addition to three dimensional finite-difference
time-domain calculations, an analytical model is introduced that is able to
reproduce the wavelength dependence of the reflected intensity observed in the
experiment.Comment: 24 pages, 7 figures, corrected+full versio
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