23,133 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
Valley filter in strain engineered graphene
We propose a simple, yet highly efficient and robust device for producing
valley polarized current in graphene. The device comprises of two distinct
components; a region of uniform uniaxial strain, adjacent to an out-of-plane
magnetic barrier configuration formed by patterned ferromagnetic gates. We show
that when the amount of strain, magnetic field strength, and Fermi level are
properly tuned, the output current can be made to consist of only a single
valley contribution. Perfect valley filtering is achievable within
experimentally accessible parameters.Comment: 4 pages, 3 figures; minor corrections, updated Figs. 2 and 3, added
reference
Effects of Ram-Pressure from Intracluster Medium on the Star Formation Rate of Disk Galaxies in Clusters of Galaxies
Using a simple model of molecular cloud evolution, we have quantitatively
estimated the change of star formation rate (SFR) of a disk galaxy falling
radially into the potential well of a cluster of galaxies. The SFR is affected
by the ram-pressure from the intracluster medium (ICM). As the galaxy
approaches the cluster center, the SFR increases to twice the initial value, at
most, in a cluster with high gas density and deep potential well, or with a
central pressure of because the ram-pressure
compresses the molecular gas of the galaxy. However, this increase does not
affect the color of the galaxy significantly. Further into the central region
of the cluster ( Mpc from the center), the SFR of the disk
component drops rapidly due to the effect of ram-pressure stripping. This makes
the color of the galaxy redder and makes the disk dark. These effects may
explain the observed color, morphology distribution and evolution of galaxies
in high-redshift clusters. By contrast, in a cluster with low gas density and
shallow potential well, or the central pressure of ,
the SFR of a radially infalling galaxy changes less significantly, because
neither ram-pressure compression nor stripping is effective. Therefore, the
color of galaxies in poor clusters is as blue as that of field galaxies, if
other environmental effects such as galaxy-galaxy interaction are not
effective. The predictions of the model are compared with observations.Comment: 19 pages, 9 figures, to appear in Ap
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