7,109 research outputs found
Interchain interactions and magnetic properties of Li2CuO2
An effective Hamiltonian is constructed for an insulating cuprate with
edge-sharing chains Li2CuO2.The Hamiltonian contains the nearest and
next-nearest neighboring intrachain and zigzag-type interchain interactions.The
values of the interactions are obtained from the analysis of the magnetic
susceptibility, and this system is found to be described as coupled frustrated
chains.We calculate the dynamical spin correlation function S(q,\omega) by
using the exact diagonalization method, and show that the spectra of
S(q,\omega) are characterized by the zigzag-type interchain interactions. The
results of the recent inelastic neutron scattering experiment are discussed in
the light of the calculated spectra.Comment: 4 pages, 3 figures, RevTe
The Molecular ISM of Dwarf Galaxies on Kiloparsec Scales: A New Survey for CO in Northern, IRAS-detected Dwarf Galaxies
We present a new survey for CO in dwarf galaxies using the Kitt Peak 12m
telescope. We observed the central regions of 121 northern dwarfs with IRAS
detections and no known CO emission. We detect CO in 28 of these galaxies and
marginally detect another 16, increasing by about 50% the number of such
galaxies known to have significant CO emission. The galaxies we detect are
comparable in mass to the LMC, although somewhat brighter in CO and fainter in
the FIR. Within dwarfs, we find that the CO luminosity, L_CO, is most strongly
correlated with the K-band and the far infrared luminosities. There are also
strong correlations with the radio continuum and B-band luminosities, and
linear diameter. We suggest that L_CO and L_K correlate well because the
stellar component of a galaxy dominates the midplane gravitational field and
thus sets the pressure of the atomic gas, which controls the formation of H_2
from HI. We compare our sample with more massive galaxies and find that dwarfs
and large galaxies obey the same relationship between CO and the 1.4 GHz radio
continuum (RC) surface brightness. This relationship is well described by a
Schmidt Law with Sigma_RC proportional to Sigma_CO^1.3. Therefore, dwarf
galaxies and large spirals exhibit the same relationship between molecular gas
and star formation rate (SFR). We find that this result is robust to moderate
changes in the RC-to-SFR and CO-to-H_2 conversion factors. Our data appear to
be inconsistent with large (order of magnitude) variations in the CO-to-H_2
conversion factor in the star forming molecular gas. [abridged]Comment: 28 pages, 14 figures, 5 tables, ApJ accepte
Power Law of Customers' Expenditures in Convenience Stores
In a convenience store chain, a tail of the cumulative density function of
the expenditure of a person during a single shopping trip follows a power law
with an exponent of -2.5. The exponent is independent of the location of the
store, the shopper's age, the day of week, and the time of day.Comment: 9 pages, 5 figures. Accepted for publication in Journal of the
Physical Society of Japan Vol.77No.
Current topics of physiology and pharmacology in the lymphatic system
ArticlePharmacology & therapeutics. 2005;105(2):165-188journal articl
Iron-Based Heavy Quasiparticles in SrFeSb: An Infrared Spectroscopic Study
Temperature-dependent infrared reflectivity spectra of SrFeSb
has been measured. A renormalized Drude peak with a heavy effective mass and a
pronounced pseudogap of 10 meV develops in the optical conductivity spectra at
low temperatures. As the temperature decreases below 100 K, the effective mass
() rapidly increases, and the scattering rate () is quenched.
The temperature dependence of and indicates that the
hybridization between the Fe 3d spins and the charge carriers plays an
important role in determining the physical properties of SrFeSb at
low temperatures. This result is the clear evidence of the iron-based heavy
quasiparticles.Comment: 5 pages, 5 figure
The Low CO Content of the Extremely Metal Poor Galaxy I Zw 18
We present sensitive molecular line observations of the metal-poor blue
compact dwarf I Zw 18 obtained with the IRAM Plateau de Bure interferometer.
These data constrain the CO J=1-0 luminosity within our 300 pc (FWHM) beam to
be L_CO < 1 \times 10^5 K km s^-1 pc^2 (I_CO < 1 K km s^-1), an order of
magnitude lower than previous limits. Although I Zw 18 is starbursting, it has
a CO luminosity similar to or less than nearby low-mass irregulars (e.g. NGC
1569, the SMC, and NGC 6822). There is less CO in I Zw 18 relative to its
B-band luminosity, HI mass, or star formation rate than in spiral or dwarf
starburst galaxies (including the nearby dwarf starburst IC 10). Comparing the
star formation rate to our CO upper limit reveals that unless molecular gas
forms stars much more efficiently in I Zw 18 than in our own galaxy, it must
have a very low CO-to-H_2 ratio, \sim 10^-2 times the Galactic value. We detect
3mm continuum emission, presumably due to thermal dust and free-free emission,
towards the radio peak.Comment: 5 pages in emulateapj style, accepted by the Astrophysical Journa
Star Forming Dense Cloud Cores in the TeV {\gamma}-ray SNR RX J1713.7-3946
RX J1713.7-3946 is one of the TeV {\gamma}-ray supernova remnants (SNRs)
emitting synchrotron X rays. The SNR is associated with molecular gas located
at ~1 kpc. We made new molecular observations toward the dense cloud cores,
peaks A, C and D, in the SNR in the 12CO(J=2-1) and 13CO(J=2-1) transitions at
angular resolution of 90". The most intense core in 13CO, peak C, was also
mapped in the 12CO(J=4-3) transition at angular resolution of 38". Peak C shows
strong signs of active star formation including bipolar outflow and a
far-infrared protostellar source and has a steep gradient with a
r^{-2.20.4} variation in the average density within radius r. Peak C and
the other dense cloud cores are rim-brightened in synchrotron X rays,
suggesting that the dense cloud cores are embedded within or on the outer
boundary of the SNR shell. This confirms the earlier suggestion that the X rays
are physically associated with the molecular gas (Fukui et al. 2003). We
present a scenario where the densest molecular core, peak C, survived against
the blast wave and is now embedded within the SNR. Numerical simulations of the
shock-cloud interaction indicate that a dense clump can indeed survive shock
erosion, since shock propagation speed is stalled in the dense clump.
Additionally, the shock-cloud interaction induces turbulence and magnetic field
amplification around the dense clump that may facilitate particle acceleration
in the lower-density inter-clump space leading to the enhanced synchrotron X
rays around dense cores.Comment: 22 pages, 7 figures, to accepted in The Astrophysical Journal. A full
color version with higher resolution figures is available at
http://www.a.phys.nagoya-u.ac.jp/~sano/ApJ10/ms_sano.pd
Fluctuation-dissipation theorem in an aging colloidal glass
We provide a direct experimental test of the Stokes-Einstein relation as a
special case of the fluctuation-dissipation theorem (FDT) in an aging colloidal
glass. The use of combined active and passive microrheology allows us to
independently measure both the correlation and response functions in this
non-equilibrium situation. Contrary to previous reports, we find no deviations
from the FDT over several decades in frequency (1 Hz-10 kHz) and for all aging
times. In addition, we find two distinct viscoelastic contributions in the
aging glass, including a nearly elastic response at low frequencies that grows
during aging. This is the clearest change in material properties of the system
with aging.Comment: 5 pages,4 figure
Will the starless cores in Chamaeleon I and III turn prestellar?
The nearby Chamaeleon molecular cloud complex is a good laboratory to study
the process of low-mass star formation since it consists of three clouds with
very different properties. Cha III does not show any sign of star formation,
while star formation has been very active in Cha I and may already be
finishing. Our goal is to determine whether star formation can proceed in Cha
III, and to compare the results to our recent survey of Cha I. We used the
Large APEX Bolometer Array (LABOCA) to map Cha III in dust continuum emission
at 870 micron. 29 sources are extracted from the map, all of them being
starless. The starless cores are found down to a visual extinction of 1.9 mag,
in marked contrast with other molecular clouds, including Cha I. Apart from
this difference, the Cha III starless cores share very similar properties with
those found in Cha I. At most two sources have a mass larger than the critical
Bonnor-Ebert mass, which suggests that the fraction of prestellar cores is very
low, even lower than in Cha I. Only the most massive sources are candidate
prestellar cores, in agreement with the correlation found earlier in the Pipe
nebula. The mass distribution of the 85 starless cores of Cha I and III that
are not candidate prestellar cores is consistent with a single power law down
to the 90% completeness limit, with an exponent close to the Salpeter value. A
fraction of the starless cores in Cha I and III may still grow in mass and
become gravitationally unstable. Based on predictions of numerical simulations
of turbulent molecular clouds, we estimate that at most 50% and 20% of the
starless cores of Cha I and III, respectively, may form stars. The LABOCA
survey reveals that Cha III, and Cha I to some extent too, is a prime target to
study the formation of prestellar cores, and thus the onset of star formation.
(abridged).Comment: Accepted for publication in A&A. 22 pages, 16 figures, 4 tables. A
version with high-resolution figures is available on request to the first
autho
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