95 research outputs found
Abundance ratios of OH/CO and HCO+/CO as probes of the cosmic ray ionization rate in diffuse clouds
The cosmic-ray ionization rate (CRIR, ) is one of the key parameters
controlling the formation and destruction of various molecules in molecular
clouds. However, the current most commonly used CRIR tracers, such as H,
OH, and HO, are hard to detect and require the presence of
background massive stars for absorption measurements. In this work, we propose
an alternative method to infer the CRIR in diffuse clouds using the abundance
ratios of OH/CO and HCO/CO. We have analyzed the response of chemical
abundances of CO, OH, and HCO on various environmental parameters of the
interstellar medium in diffuse clouds and found that their abundances are
proportional to . Our analytic expressions give an excellent
calculation of the abundance of OH for 10 s,
which are potentially useful for modelling chemistry in hydrodynamical
simulations. The abundances of OH and HCO were found to monotonically
decrease with increasing density, while the CO abundance shows the opposite
trend. With high-sensitivity absorption transitions of both CO (1--0) and
(2--1) lines from ALMA, we have derived the H number densities () toward 4 line-of-sights (LOSs); assuming a kinetic temperature of
, we find a range of
(0.140.03--1.20.1)10 cm}. By comparing the
observed and modelled HCO/CO ratios, we find that in our diffuse
gas sample is in the { range of 10 10 s. This is 2 times higher
than the average value measured at higher extinction, supporting an attenuation
of CRs as suggested by theoretical models.Comment: 22 pages, 9 figures, accepted by Ap
Increased p38-MAPK is responsible for chemotherapy resistance in human gastric cancer cells
<p>Abstract</p> <p>Background</p> <p>Chemoresistance is one of the main obstacles to successful cancer therapy and is frequently associated with Multidrug resistance (MDR). Many different mechanisms have been suggested to explain the development of an MDR phenotype in cancer cells. One of the most studied mechanisms is the overexpression of P-glycoprotein (P-gp), which is a product of the <it>MDR1 </it>gene. Tumor cells often acquire the drug-resistance phenotype due to upregulation of the <it>MDR1 </it>gene. Overexpression of <it>MDR1 </it>gene has often been reported in primary gastric adenocarcinoma.</p> <p>Methods</p> <p>This study investigated the role of p38-MAPK signal pathway in vincristine-resistant SGC7901/VCR cells. P-gp and MDR1 RNA were detected by Western blot analysis and RT-PCR amplification. Mitgen-activated protein kinases and function of P-gp were demonstrated by Western blot and FACS Aria cytometer analysis. Ap-1 activity and cell apoptosis were detected by Dual-Luciferase Reporter Assay and annexin V-PI dual staining.</p> <p>Results</p> <p>The vincristine-resistant SGC7901/VCR cells with increased expression of the multidrug-resistance 1 (<it>MDR1</it>) gene were resistant to P-gp-related drug and P-gp-unrelated drugs. Constitutive increases of phosphorylated p38-MAPK and AP-1 activities were also found in the drug-resistant cells. Inhibition of p38-MAPK by SB202190 reduced activator protein-1 (AP-1) activity and <it>MDR1 </it>expression levels and increased the sensitivity of SGC7901/VCR cells to chemotherapy.</p> <p>Conclusion</p> <p>Activation of the p38-MAPK pathway might be responsible for the modulation of P-glycoprotein-mediated and P-glycoprotein-unmediated multidrug resistance in the SGC7901/VCR cell line.</p
Dependence of Chemical Abundance on the Cosmic Ray Ionization Rate in IC 348
Ions (e.g., H, HO) have been used extensively to quantify the
cosmic-ray ionization rate (CRIR) in diffuse sightlines. However, measurements
of CRIR in low-to-intermediate density gas environments are rare, especially
when background stars are absent. In this work, we combine molecular line
observations of CO, OH, CH, and HCO in the star-forming cloud IC~348, and
chemical models to constrain the value of CRIR and study the response of the
chemical abundances distribution. The cloud boundary is found to have an
of approximately 4 mag. From the interior to the exterior of the
cloud, the observed CO line intensities drop by an order of magnitude.
The calculated average abundance of CO (assuming C/C = 65)
is (1.20.9) 10, which increases by a factor of 6 from the
interior to the outside regions. The average abundance of CH (3.30.7
10) is in good agreement with previous findings in diffuse and
translucent clouds ( 5 mag). However, we did not find a decline
in CH abundance in regions of high extinction (8 mag) as
previously reported in Taurus. By comparing the observed molecular abundances
and chemical models, we find a decreasing trend of CRIR as
increases. The inferred CRIR of = (4.71.5)
10 s at low is consistent with H measurements
toward two nearby massive stars.Comment: 21 pages, 11 figures. Submitted to Ap
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