829 research outputs found
Pressure-wave formation and collapses of cavitation clouds impinging on solid wall in a submerged water jet
A high-speed water jet ejected into water forms a cavitating water jet accompanied with cavitation clouds in a periodic manner. A powerful impulsive force can be caused at the collapse of unsteady cavitation clouds at the same time when the cavitating water jet impinges against a solid wall. It is known that this force can be widely used in an industrial field such as cleaning, cutting, and peening. In the present experiment, cavitation clouds are observed to investigate the details such as impinging, dividing and collapsing behaviors using a constrained-type test section as well as an opentype test section. The constrained-type test section is used to quasitwo dimensionally observe the behavior of cavitation clouds in the near impinging wall region. The present purpose is to investigate about the behavior of cavitating water jet in the near impinging wall region as well as the relation of cavitation cloud collapse with the formation of pressure wave, the propagation of pressure wave and the cavitation impact. In order to estimate the high speed phenomena such as rapid and consecutive collapses of cavitation clouds and pressure wave formation, the frame difference method for cavitating flow is used in the present image analysis for cavitation cloud. The usefulness of the method is experimentally verified for the behavior analysis of high speed liquid flow accompanied with growth and collapse of bubbly cloud. As a result it is experimentally found that 1) the present image analysis method based on the frame difference method makes possible to grasp the motion of pressure wave propagation in cavitation cloud, 2) local cloud collapse causes a pressure wave which propagates toward the surrounding area and as a result causes secondary collapses in a chain-reaction manner, and 3) cavitation clouds on the impinging wall tend to be peripherally located in an annular zone at the final collapsing stage. The existence of the annular cloudy zone can be related to the ring-like cavitation erosion distribution and the chain-reaction-type propagation of cavitation clouds.http://deepblue.lib.umich.edu/bitstream/2027.42/84263/1/CAV2009-final66.pd
A possible route to spontaneous reduction of the heat conductivity by a temperature gradient driven instability in electron-ion plasmas
We have shown that there exists low-frequency growing modes driven by a
global temperature gradient in electron and ion plasmas, by linear perturbation
analysis within the frame work of plasma Kinetic theory. The driving force of
the instability is the local deviation of the distribution function from the
Maxwell-Boltzmann due to global temperature gradient. Application to the
intracluster medium shows that scattering of the particles due to waves excited
by the instability is possible to reduce mean free paths of electron and ion
down to five to seven order of magnitude than the mean free paths due to
Coulomb collisions. This may provide a hint to explain why hot and cool gas can
co-exist in the intracluster medium in spite of the very short evaporation time
scale due to thermal conduction if the conductivity is the classical Spitzer
value. Our results suggest that the realization of the global thermal
equilibrium is postponed by the local instability which is induced for quicker
realization of local thermal equilibrium state in plasmas. The instability
provides a new possibility to create and grow cosmic magnetic fields without
any seed magnetic field.Comment: Accepted for publication in ApJ: 16 pages, 1figur
Supernova Nucleosynthesis and Extremely Metal-Poor Stars
We investigate hydrodynamical and nucleosynthetic properties of the
jet-induced explosion of a population III star and compare the
abundance patterns of the yields with those of the metal-poor stars. We
conclude that (1) the ejection of Fe-peak products and the fallback of
unprocessed materials can account for the abundance patterns of the extremely
metal-poor (EMP) stars and that (2) the jet-induced explosion with different
energy deposition rates can explain the diversity of the abundance patterns of
the metal-poor stars. Furthermore, the abundance distribution after the
explosion and the angular dependence of the yield are shown for the models with
high and low energy deposition rates and . We also find that the
peculiar abundance pattern of a Si-deficient metal-poor star HE 1424--0241 can
be reproduced by the angle-delimited yield for of
the model with .Comment: 6 pages, 3 figures. To appear in "ORIGIN OF MATTER AND EVOLUTION OF
GALAXIES: From the Dawn of Universe to the Formation of Solar System", AIP
Conf. Proc. 1016 (December 2007, Sapporo), eds. T. Suda, T. Nozawa, et al.
(Melville: AIP
Coevolution of Supermassive Black Holes and Circumnuclear Disks
We propose a new evolutionary model of a supermassive black hole (SMBH) and a
circumnuclear disk (CND), taking into account the mass-supply from a host
galaxy and the physical states of CND. In the model, two distinct accretion
modes depending on gravitational stability of the CND play a key role on
accreting gas to a SMBH. (i) If the CMD is gravitationally unstable, energy
feedback from supernovae (SNe) supports a geometrically thick, turbulent gas
disk. The accretion in this mode is dominated by turbulent viscosity, and it is
significantly larger than that in the mode (ii), i.e., the CMD is supported by
gas pressure. Once the gas supply from the host is stopped, the high accretion
phase () changes to the low one (mode
(ii), ), but there is a delay with yr. Through this evolution, the gas-rich CND turns into the gas poor
stellar disk. We found that not all the gas supplied from the host galaxy
accrete onto the SMBH even in the high accretion phase (mode (i)), because the
part of gas is used to form stars. As a result, the final SMBH mass () is not proportional to the total gas mass supplied from the host
galaxy (); decreases with .This would indicate that it is difficult to form a SMBH with observed at high- QSOs. The evolution of the SMBH and CND would
be related to the evolutionary tracks of different type of AGNs.Comment: 11 pages, 11 figures, accepted for publication in Ap
Discovery of a new pulsating X-ray source with a 1549.1-s period, AX J183220-0840
A new pulsating X-ray source, AX J183220-0840, with a 1549.1-s period was
discovered at R.A.= 18h32m20s and Dec.=-8d40'30'' (J2000,
uncertainty=0.6degree) during an ASCA observation on the Galactic plane. The
source was observed two times, in 1997 and in 1999. A phase-averaged X-ray flux
of 1.1E-11 ergs cm-2 s-1 and pulsation period of 1549.1+/-0.4 s were
consistently obtained from these two observations. The X-ray spectrum was
represented by a flat absorbed power-law with a photon-index of =~0.8 and an
absorption column density of =~1.3E22 cm-2. Also, a signature of iron K-shell
line emission with a centroid of 6.7 keV and an equivalent width of
approximately 450 eV was detected. From the pulsation period and the iron-line
feature, AX J183220-0840 is likely to be a magnetic white dwarf binary with a
complexly absorbed thermal spectrum with a temperature of about 10 keV.Comment: 13 pages, 4 figures, accepted for publication in ApJ Letter
On the origin of the Tully-Fisher relation
We discuss the origin of the Tully-Fisher (TF) relation using the
-body/SPH method, which includes cooling, star formation and stellar
feedback of energy, mass and metals. We consider initially rotating overdense
spheres, and trace formation processes of disk galaxies from to in
the Cold Dark Matter (CDM) cosmology. To clarify the origin of the TF relation,
we simulate formation of 14 galaxies with different masses and spin parameters,
and compute observable values, such as the total magnitude and the line-width.
We find that the simulated galaxies reproduce the slope and scatter of the TF
relation: the slope is originated in the difference of total galactic masses,
and the scatter is produced by the difference of initial spin parameters. As
well as the TF relation, observed features of spiral galaxies, such as the
exponential light-profile and the flat rotation curve, are reproduced in our
simulations, which were assumed {\it a priori} in past semi-analytical
approaches.Comment: 11 pages, including 6 figures, submitted to Ap
Dynamical generation of a nontrivial index on the fuzzy 2-sphere
In the previous paper hep-th/0312199 we studied the 't Hooft-Polyakov (TP)
monopole configuration in the U(2) gauge theory on the fuzzy 2-sphere and
showed that it has a nonzero topological charge in the formalism based on the
Ginsparg-Wilson relation. In this paper, by showing that the TP monopole
configuration is stabler than the U(2) gauge theory without any condensation in
the Yang-Mills-Chern-Simons matrix model, we will present a mechanism for
dynamical generation of a nontrivial index. We further analyze the instability
and decay processes of the U(2) gauge theory and the TP monopole configuration.Comment: Latex2e, 30 pages, 4 figures, the topological charge for a monopole
configuration is corrected, reference added, the final version to appear in
Physical Review D (the typos mentioned in the erratum are corrected
Large Non-perturbative Effects of Small \Delta m^2_{21}/\Delta m^2_{31} and \sin \theta_{13} on Neutrino Oscillation and CP Violation in Matter
In the framework of three generations, we consider the CP violation in
neutrino oscillation with matter effects. At first, we show that the
non-perturbative effects of two small parameters, \Delta m_{21}^2/\Delta
m_{31}^2 and \sin \theta_{13}, become more than 50% in certain ranges of energy
and baseline length. This means that the non-perturbative effects should be
considered in detailed analysis in the long baseline experiments. Next, we
propose a method to include these effects in approximate formulas for
oscillation probabilities. Assuming the two natural conditions,
\theta_{23}=45^\circ and the fact that the matter density is symmetric, a set
of approximate formulas, which involve the non-perturbative effects, has been
derived in all channels.Comment: 25 pages, 4 figures, version to appear in JHE
- …