50 research outputs found
Physical properties of CO-dark molecular gas traced by C
Neither HI nor CO emission can reveal a significant quantity of so-called
dark gas in the interstellar medium (ISM). It is considered that CO-dark
molecular gas (DMG), the molecular gas with no or weak CO emission, dominates
dark gas. We identified 36 DMG clouds with C emission (data from Galactic
Observations of Terahertz C+ (GOT C+) project) and HINSA features. Based on
uncertainty analysis, optical depth of HI of 1 is a reasonable
value for most clouds. With the assumption of , these clouds
were characterized by excitation temperatures in a range of 20 K to 92 K with a
median value of 55 K and volume densities in the range of
cm to cm with a median value of
cm. The fraction of DMG column density in the cloud ()
decreases with increasing excitation temperature following an empirical
relation +1.0. The relation
between and total hydrogen column density is given by
=. The values of in the
clouds of low extinction group ( mag) are consistent with the
results of the time-dependent, chemical evolutionary model at the age of ~ 10
Myr. Our empirical relation cannot be explained by the chemical evolutionary
model for clouds in the high extinction group ( mag). Compared to
clouds in the low extinction group ( mag), clouds in the high
extinction group ( mag) have comparable volume densities but
excitation temperatures that are 1.5 times lower. Moreover, CO abundances in
clouds of the high extinction group ( mag) are
times smaller than the canonical value in the Milky Way. #[Full version of
abstract is shown in the text.]#Comment: Accepted for publishing in Astronomy & Astrophysics. 13 pages, 8
figure
Adjuvant chemotherapy of megestrol acetate in advanced breast cancer: A meta-analysis
To evaluate the effectiveness and safety of adjuvant chemotherapy of megestrol acetate (MA) in advanced breast cancer, we searched CBM, CNKI, VIP, Wangfang Data and PubMed, and collected randomized controlled trials (RCT) of adjuvant chemotherapy of MA in advanced breast cancer. MA significantly increased treatment efficiency (p=0.0010); improve weight (p<0.0001), appetite (p=0.001) and KPS (p=0.06); ameliorate leucopenia (p=0.02), thrombocytopenia (p=0.02) and hemoglobin (p=0.01); reduce gastrointestinal reaction (p=0.0005) of the patients of adjuvant chemotherapy in advanced breast cancer. MA significantly increased treatment efficiency, improve the nutritional situation, reduce bone marrow suppression, and gastrointestinal reaction of the patients of adjuvant chemotherapy in advanced breast cancer. High-quality RCTs are needed to guidance for preliminary studies of the effective treatment of adjuvant chemotherapy of MA in advanced breast cancer.
Where is OH and Does It Trace the Dark Molecular Gas (DMG)?
Hydroxyl (OH) is expected to be abundant in diffuse interstellar molecular
gas as it forms along with under similar conditions and within a similar
extinction range. We have analyzed absorption measurements of OH at 1665 MHz
and 1667 MHz toward 44 extragalactic continuum sources, together with the J=1-0
transitions of CO, CO , and CO, and the J=2-1 of
CO. The excitation temperature of OH were found to follow a modified
log-normal distribution, ,
the peak of which is close to the temperature of the Galactic emission
background (CMB+synchron). In fact, 90% of the OH has excitation temperature
within 2 K of the Galactic background at the same location, providing a
plausible explanation for the apparent difficulty to map this abundant molecule
in emission. The opacities of OH were found to be small and peak around 0.01.
For gas at intermediate extinctions (A 0.05-2 mag), the detection
rate of OH with detection limit cm is
approximately independent of . We conclude that OH is abundant in the
diffuse molecular gas and OH absorption is a good tracer of `dark molecular gas
(DMG)'. The measured fraction of DMG depends on assumed detection threshold of
the CO data set. The next generation of highly sensitive low frequency radio
telescopes, FAST and SKA, will make feasible the systematic inventory of
diffuse molecular gas, through decomposing in velocity the molecular (e.g. OH
and CH) absorption profiles toward background continuum sources with numbers
exceeding what is currently available by orders of magnitude.Comment: 24 pages, 23 figures. Accepted for publication in ApJ
CRAFTS for Fast Radio Bursts : extending the dispersion-fluence relation with new FRBs detected by FAST
We report three new FRBs discovered by the Five-hundred-meter Aperture Spherical radio Telescope (FAST), namely FRB 181017.J0036+11, FRB 181118, and FRB 181130, through the Commensal Radio Astronomy FAST Survey (CRAFTS). Together with FRB 181123, which was reported earlier, all four FAST-discovered FRBs share the same characteristics of low fluence (1000 pc cm(-3)), consistent with the anticorrelation between DM and fluence of the entire FRB population. FRB 181118 and FRB 181130 exhibit band-limited features. FRB 181130 is prominently scattered (tau(s) 8 ms) at 1.25 GHz. FRB 181017.J0036+11 has full-bandwidth emission with a fluence of 0.042 Jy ms, which is one of the faintest FRB sources detected so far. CRAFTS has started to build a new sample of FRBs that fills the region for more distant and fainter FRBs in the fluence-DME diagram, previously out of reach of other surveys. The implied all-sky event rate of FRBs is 1.24(-0.90)(+1.94) x 5 sky(-1) day(-1) at the 95% confidence interval above 0.0146 Jy ms. We also demonstrate here that the probability density function of CRAFTS FRB detections is sensitive to the assumed intrinsic FRB luminosity function and cosmological evolution, which may be further constrained with more discoveries
CRAFTS for Fast Radio Bursts Extending the dispersion-fluence relation with new FRBs detected by FAST
We report three new FRBs discovered by the Five-hundred-meter Aperture
Spherical radio Telescope (FAST), namely FRB 181017.J0036+11, FRB 181118 and
FRB 181130, through the Commensal Radio Astronomy FAST Survey (CRAFTS).
Together with FRB 181123 that was reported earlier, all four FAST-discovered
FRBs share the same characteristics of low fluence (0.2 Jy ms) and high
dispersion measure (DM, \dmu), consistent with the anti-correlation
between DM and fluence of the entire FRB population. FRB 181118 and FRB 181130
exhibit band-limited features. FRB 181130 is prominently scattered
( ms) at 1.25 GHz. FRB 181017.J0036+11 has full-bandwidth
emission with a fluence of 0.042 Jy ms, which is one of the faintest FRB
sources detected so far. CRAFTS starts to built a new sample of FRBs that fills
the region for more distant and fainter FRBs in the fluence- diagram,
previously out of reach of other surveys. The implied all sky event rate of
FRBs is sky day at the
confidence interval above 0.0146 Jy ms. We also demonstrate here that the
probability density function of CRAFTS FRB detections is sensitive to the
assumed intrinsic FRB luminosity function and cosmological evolution, which may
be further constrained with more discoveries.Comment: 9 Pages, 4 Plots and 1 Table. The Astrophysical Journal Letter
Accepte
A Fast Radio Burst Discovered in FAST Drift Scan Survey
We report the discovery of a highly dispersed fast radio burst (FRB), FRB 181123, from an analysis of ~1500 hr of drift scan survey data taken using the Five-hundred-meter Aperture Spherical radio Telescope (FAST). The pulse has three distinct emission components, which vary with frequency across our 1.0–1.5 GHz observing band. We measure the peak flux density to be... (See full abstract in article)