3,350 research outputs found
Black Strings in Our World
The brane world scenario is a new approach to resolve the problem on how to
compactify the higher dimensional spacetime to our 4-dimensional world. One of
the remarkable features of this scenario is the higher dimensional effects in
classical gravitational interactions at short distances. Due to this feature,
there are black string solutions in our 4-dimensional world. In this paper,
assuming the simplest model of complex minimally coupled scalar field with the
local U(1) symmetry, we show a possibility of black-string formation by merging
processes of type I long cosmic strings in our 4-dimensional world. No fine
tuning for the parameters in the model might be necessary.Comment: 11pages, no figur
Developments of a centimeter-level precise muometric wireless navigation system (MuWNS-V) and its first demonstration using directional information from tracking detectors
Various positioning techniques such as Wi-Fi positioning system have been
proposed to use in situations where satellite navigation is unavailable. One
such system, the muometric positioning system (muPS), was invented for
navigation which operates in locations where even radio waves cannot reach such
as underwater or underground. muPS takes advantage of a key feature of its
probe, cosmic-ray muons, which travel straightforwardly at almost a speed of
light in vacuum regardless of the matter they traverse. Similar to other
positioning techniques, muPS is a technique to determine the position of a
client's muPS receiver within the coordinate defined by reference detectors.
This can be achieved either by using time-of-flight (ToF) or angle of arrival
(AoA) measurements. The latter configuration (AoA), called the Vector-muPS has
recently been invented and the present paper describes the developments of the
first prototype of a vector muometric wireless navigation system (MuWNS-V) with
this new vector-muPS concept and its demonstration. With MuWNS-V, the reference
tracker and the receiver ran wirelessly with fully independent readout systems,
and a positioning accuracy of 3.9 cm (RMS) has been achieved. We also evaluated
the outcome of measuring continuous indoor localization of a moving receiver
with this prototype. Our results indicated that further improvements in
positioning accuracy will be attainable by acquiring higher angular resolution
of the reference trackers. It is anticipated that "sub-cm level" navigation
will be possible for muPS which could be applied to many situations such as
future autonomous mobile robot operations.Comment: 11 pages, 9 figure
Open String on Symmetric Product
We develop some basic properties of the open string on the symmetric product
which is supposed to describe the open string field theory in discrete
lightcone quantization (DLCQ). After preparing the consistency conditions of
the twisted boundary conditions for Annulus/M\"obius/Klein Bottle amplitudes in
generic non-abelian orbifold, we classify the most general solutions of the
constraints when the discrete group is . We calculate the corresponding
orbifold amplitudes from two viewpoints -- from the boundary state formalism
and from the trace over the open string Hilbert space. It is shown that the
topology of the world sheet for the short string and that of the long string in
general do not coincide. For example the annulus sector for the short string
contains all the sectors (torus, annulus, Klein bottle, M\"obius strip) of the
long strings. The boundary/cross-cap states of the short strings are classified
into three categories in terms of the long string, the ordinary boundary and
the cross-cap states, and the ``joint'' state which describes the connection of
two short strings. We show that the sum of the all possible boundary conditions
is equal to the exponential of the sum of the irreducible amplitude -- one body
amplitude of long open (closed) strings. This is typical structure of DLCQ
partition function. We examined that the tadpole cancellation condition in our
language and derived the well-known gauge group .Comment: 56 pages, 11 figures, Late
Dust-to-Gas Ratio and Metallicity in Dwarf Galaxies
We examine the dust-to-gas ratio as a function of metallicity for dwarf
galaxies [dwarf irregular galaxies (dIrrs) and blue compact dwarf galaxies
(BCDGs)]. Using a one-zone model and adopting the instantaneous recycling
approximation, we prepare a set of basic equations which describes processes of
dust formation and destruction in a galaxy. Four terms are included for the
processes: dust formation from heavy elements ejected by stellar mass loss,
dust destruction in supernova remnants, dust destruction in star-forming
regions, and accretion of heavy elements onto preexisting dust grains. Solving
the equations, we compare the result with observational data of nearby dIrrs
and BCDGs. The solution is consistent with the data within the reasonable
ranges of model parameters constrained by the previous examinations. This means
that the model is successful in understanding the dust amount of nearby
galaxies. We also show that the accretion rate of heavy element onto
preexisting dust grains is less effective than the condensation of heavy
elements in dwarf galaxies.Comment: 14 pages LaTeX, 4 figures, to appear in Ap
Evolution of Interstellar Clouds in Local Group Dwarf Spheroidal Galaxies in the Context of Their Star Formation Histories
We consider evolution of interstellar clouds in Local Group dwarf spheroidal
galaxies (dSphs) in the context of their observed star formation histories. The
Local Group dSphs generally experienced initial bursts of star formations in
their formation epochs ( Gyr ago), when hot gas originating from the
supernovae can make the cold interstellar clouds evaporate. We find that the
maximum size of evaporating cloud is 10 pc. Thus, clouds larger than 10 pc can
survive during the initial star formation. These surviving clouds can
contribute to the second star formation to produce ``intermediate-age (
3--10 Gyr ago) stellar populations.'' Assuming that collisions between clouds
induce star formation and that the timescale of the second star formation is a
few Gyr, we estimate the total mass of the clouds. The total mass is about
, which is 1--3 orders of magnitude smaller than the typical
stellar mass of a present dSph. This implies that the initial star formation is
dominant over the second star formation, which is broadly consistent with the
observed star formation histories. However, the variety of the dSphs in their
star formation histories suggests that the effects of environments on the dSphs
may be important.Comment: 14 pages LaTeX, no figures, to appear in Ap
Ion acceleration during internal magnetic reconnection events in TST-2
Characteristics of ion acceleration in the internal magnetic reconnection
events (IRE) have been studied by means of a neutral particle energy analyzer
(NPA) in Tokyo Spherical Tokamak (TST-2). The major and minor radii are 0.38 m
and 0.25m, respectively. The magnetic field strength is 0.3T and the maximum
plasma current is up to 140 kA. The electron and ion temperatures are 0.4-0.5
keV and 0.1 keV, respectively and the electron density is ~1x1019 m-3. The NPA
can be scanned toroidally from q = 74° (cw) to q = 114° (ccw), where q
= 90° corresponds to the perpendicular sightline. The direction of the
plasma current is cw. The NPA signals are digitized at every 50 ms. The NPA is
calibrated in the energy range of 0.1 keV < E < 8.4 keV. When the IRE occurs,
it is observed that the plasma current increases by ~ 20% and the loop voltage
drops from 0.6 V to-5 V for ~ 0.1 ms. The enhanced charge exchange flux is
observed by more than one order of magnitude at ~ 1 keV for this reconnection
phase. The ion temperature increases by 80 eV at IREs. The angle q dependence
of increment of Ti shows that DTi (q = 74°) is higher than that for q =
114°. This observation suggests that an ion is accelerated initially in the
direction of magnetic field lines. The time evolution of the ion distribution
function is simulated with a Fokker-Planck code taking into account the
electric field effects.Comment: 12th International Congress on Plasma Physics, 25-29 October 2004,
Nice (France
Star Formation Efficiency in the Central 1 kpc Region of Early-Type Spiral Galaxies
It has been reported recently that there are some early-type spiral (Sa--Sab)
galaxies having evident star-forming regions which concentrate in their own
central 1-kpc. In such central region, is the mechanism of the star formation
distinct from that in disks of spiral galaxies? To reveal this, we estimate the
star formation efficiency (SFE) in this central 1-kpc star-forming region of
some early-type spiral galaxies, taking account of the condition for this 1-kpc
region to be self-gravitating. Using two indicators of present star formation
rate (H and infrared luminosity), we estimate the SFE to be a few
percents. This is equivalent to the observational SFE in the disks of late-type
spiral (Sb--) galaxies. This coincidence may support the universality of the
mean SFE of spiral galaxies reported in the recent studies. That is, we find no
evidence of distinct mechanism of the star formation in the central 1-kpc
region of early-type galaxies. Also, we examine the structure of the central
star-forming region, and discuss a method for estimating the mass of
star-forming regions.Comment: accepted by A
Phase Diagram of Pressure-Induced Superconductivity in EuFe2As2 Probed by High-Pressure Resistivity up to 3.2 GPa
We have constructed a pressuretemperature () phase diagram of
-induced superconductivity in EuFeAs single crystals, via
resistivity () measurements up to 3.2 GPa. As hydrostatic pressure is
applied, an antiferromagnetic (AF) transition attributed to the FeAs layers at
shifts to lower temperatures, and the corresponding resistive
anomaly becomes undetectable for 2.5 GPa. This suggests that the
critical pressure where becomes zero is about 2.5
GPa. We have found that the AF order of the Eu moments survives up to
3.2 GPa without significant changes in the AF ordering temperature
. The superconducting (SC) ground state with a sharp transition
to zero resistivity at 30 K, indicative of bulk
superconductivity, emerges in a pressure range from 2.5
GPa to 3.0 GPa. At pressures close to but outside the SC phase, the
curve shows a partial SC transition (i.e., zero resistivity is not
attained) followed by a reentrant-like hump at approximately
with decreasing temperature. When nonhydrostatic pressure with a uniaxial-like
strain component is applied using a solid pressure medium, the partial
superconductivity is continuously observed in a wide pressure range from 1.1
GPa to 3.2 GPa.Comment: 7 pages, 6 figures, accepted for publication in Physical Review B,
selected as "Editors' Suggestion
Radiography of the Earth's Core and Mantle with Atmospheric Neutrinos
A measurement of the absorption of neutrinos with energies in excess of 10
TeV when traversing the Earth is capable of revealing its density distribution.
Unfortunately, the existence of beams with sufficient luminosity for the task
has been ruled out by the AMANDA South Pole neutrino telescope. In this letter
we point out that, with the advent of second-generation kilometer-scale
neutrino detectors, the idea of studying the internal structure of the Earth
may be revived using atmospheric neutrinos instead.Comment: 4 pages, LaTeX file using RevTEX4, 2 figures and 1 table included.
Matches published versio
How to detect a possible correlation from the information of a sub-system in quantum mechanical systems
A possibility to detect correlations between two quantum mechanical systems
only from the information of a subsystem is investigated. For generic cases, we
prove that there exist correlations between two quantum systems if the
time-derivative of the reduced purity is not zero. Therefore, an
experimentalist can conclude non-zero correlations between his/her system and
some environment if he/she finds the time-derivative of the reduced purity is
not zero. A quantitative estimation of a time-derivative of the reduced purity
with respect to correlations is also given. This clarifies the role of
correlations in the mechanism of decoherence in open quantum systems.Comment: 7 pages, 1 figur
- …