9,860 research outputs found
Simultaneous dual-frequency radio observations of S5 0716+714: A search for intraday variability with the Korean VLBI Network
This study aims to search for the existence of intraday variability (IDV) of
BL Lac object S5 0716+714 at high radio frequencies for which the interstellar
scintillation effect is not significant. Using the 21-meter radio telescope of
the Korean VLBI Network (KVN), we present results of multi-epoch simultaneous
dual-frequency radio observations. Single-dish observations of S5 0716+714 were
simultaneously conducted at 21.7 GHz (K-band) and 42.4 GHz (Q-band), with a
high cadence of 30-60 minute intervals.We observed four epochs between December
2009 and June 2010. Over the whole set of observation epochs, S5 0716+714
showed significant inter-month variations in flux density at both the K- and
Q-bands, with modulation indices of approximately 19% for the K-band and
approximately 36% for the Q-band. In all epochs, no clear intraday variability
was detected at either frequency. The source shows monotonic flux density
increase in epochs 1 and 3 and monotonic flux density decrease in epochs 2 and
4. In the flux density increasing phases, the flux densities at the Q-band
increase more rapidly. In the decreasing phase, no significant flux density
difference is seen at the two frequencies. The situation could be different
close to flux density peaks that we did not witness in our observations. We
find an inverted spectrum with mean spectral indices of -0.57+-0.13 in epoch 1
and -0.15+-0.11 in epoch 3. On the other hand, we find relatively steep indices
of +0.24+-0.14 and +0.17+-0.18 in epochs 2 and 4, respectively. We conclude
that the frequency dependence of the variability and the change of the spectral
index are caused by source-intrinsic effects rather than by any extrinsic
scintillation effect.Comment: 6 pages and 4 figures and 4 table
Cigarette smoking and food insecurity among low-income families in the United States, 2001
The goal of this research is to quantify the association between food insecurity and smoking among low-income families. This analysis is a retrospective study using data from the 2001 Panel Study of Income Dynamics, a longitudinal study of a representative sample of U.S. men, women, and children and the family units in which they reside. Family income is linked with U.S. poverty thresholds to identify 2,099 families living near or below 200 percent of the federal poverty level. Food insecurity (that is, having insufficient funds to purchase enough food to maintain an active and healthy lifestyle) is calculated from the eighteen core items in the food security module of the U.S. Department of Agriculture. The results indicate that smoking prevalence is higher among low-income families who are food insecure compared to low-income families who are food secure (43.6 percent versus 31.9 percent). Multivariate analysis reveals that smoking is associated with an increase in food insecurity of approximately 6 percentage points. Given our finding that families near the federal poverty level spend a large share of their income on cigarettes, perhaps it would be prudent for food assistance and tobacco control programs to work together to help low-income people quit smoking.
Conformal anomaly and the vector coupling in dense matter
We construct an effective chiral Lagrangian for hadrons implemented by the
conformal invariance and discuss the properties of nuclear matter at high
density. The model is formulated based on two alternative assignment, "naive"
and mirror, of chirality to the nucleons. It is shown that taking the dilaton
limit, in which the mended symmetry of Weinberg is manifest, the vector-meson
Yukawa coupling becomes suppressed and the symmetry energy becomes softer as
one approaches the chiral phase transition. This leads to softer equations of
state (EoS) and could accommodate the EoS without any exotica consistent with
the recent measurement of a neutron star.Comment: v2:10 pages, 2 figures, typos corrected, a rough estimate of m0 adde
Lyman alpha line formation in starbursting galaxies II. Extremely Thick, Dustless, and Static HI Media
The Lya line transfer in an extremely thick medium of neutral hydrogen is
investigated by adopting an accelerating scheme in our Monte Carlo code to skip
a large number of core or resonant scatterings. This scheme reduces computing
time significantly with no sacrifice in the accuracy of the results. We applied
this numerical method to the Lya transfer in a static, uniform, dustless, and
plane-parallel medium. Two types of photon sources have been considered, the
midplane source and the uniformly distributed sources. The emergent profiles
show double peaks and absorption trough at the line-center. We compared our
results with the analytic solutions derived by previous researchers, and
confirmed that both solutions are in good agreement with each other. We
investigated the directionality of the emergent Lya photons and found that limb
brightening is observed in slightly thick media while limb darkening appears in
extremely thick media. The behavior of the directionality is noted to follow
that of the Thomson scattered radiation in electron clouds, because both Lya
wing scattering and Thomson scattering share the same Rayleigh scattering phase
function. The mean number of wing scatterings just before escape is in exact
agreement with the prediction of the diffusion approximation. The Lya photons
constituting the inner part of the emergent profiles follow the relationship
derived from the diffusion approximation. We present a brief discussion on the
application of our results to the formation of Lya broad absorption troughs and
P-Cygni type Lya profiles seen in the UV spectra of starburst galaxies.Comment: 24 papges, 12 figures, The revised version submitted to Ap
A Spectral Line Survey from 138.3 to 150.7 GHZ toward Orion-KL
We present the results of a spectral line survey from 138.3 to 150.7 GHz
toward Orion-KL. The observations were made using the 14 m radio telescope of
Taeduk Radio Astronomy Observatory. Typical system temperatures were between
500 and 700 K, with the sensitivity between K in units of .
A total of 149 line spectra are detected in this survey. Fifty lines have
been previously reported, however we find 99 new detections. Among these new
lines, 32 are `unidentified', while 67 are from molecular transitions with
known identifications. There is no detection of H or He recombination lines.
The identified spectra are from a total of 16 molecular species and their
isotopic variants. In the range from 138.3 to 150.7 GHz, the strongest spectral
line is the J=3-2 transition of CS molecule, followed by transitions of the
, , , and . Spectral lines from
the large organic molecules such as , , , and are prominent; with 80 % of the
identified lines arising from transitions of these molecules. The rotational
temperatures and column densities are derived using the standard rotation
diagram analysis for (), , and with and . These estimates are fairly comparable to the values for the
same molecule in other frequency regions by other studies.Comment: 10 figures, 2 tex files for a manuscript and tables, accepted to Ap
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