Radially Excited States of ηc\eta_c

In the framework of chiral quark model, the mass spectrum of $\eta_c(ns) (n=1,...,6)$ is studied with Gaussian expansion method. With the wave functions obtained in the study of mass spectrum, the open flavor two-body strong decay widths are calculated by using $^3P_0$ model. The results show that the masses of $\eta_c(1S)$ and $\eta_c(2S)$ are consistent with the experimental data. The explanation of X(3940) as $\eta_c(3S)$ is disfavored for X(3940) is a narrow state, $\Gamma=37^{+26}_{-15} \pm 8$ MeV, while the open flavor two-body strong decay width of $\eta_c(3S)$ is about 200 MeV in our calculation. Although the mass of X(4160) is about 100 MeV less than that of $\eta_c(4S)$, the assignment of X(4160) as $\eta_c(4S)$ can not be excluded because the open flavor two-body strong decay width of $\eta_c(4S)$ is consistent with the experimental value of X(4160) and the branching ratios of $\eta_c(4S)$ are compatible with that of X(4160), and the mass of $\eta_c(4S)$ can be shifted downwards by taking into account the coupling effect of the open charm channels. There are still no good candidates to $\eta_c(5S)$ and $\eta_c(6S)$.Comment: 5 page

Two-probe study of hot carriers in reduced graphene oxide

The energy relaxation of carriers in reduced graphene oxide thin films is studied using optical pump-probe spectroscopy with two probes of different colors. We measure the time difference between peaks of the carrier density at each probing energy by measuring a time-resolved differential transmission and find that the carrier density at the lower probing energy peaks later than that at the higher probing energy. Also, we find that the peak time for the lower probing energy shifts from about 92 to 37 fs after the higher probing energy peak as the carrier density is increased from 1.5E12 to 3E13 per square centimeter, while no noticeable shift is observed in that for the higher probing energy. Assuming the carriers rapidly thermalize after excitation, this indicates that the optical phonon emission time decreases from about 50 to about 20 fs and the energy relaxation rate increases from 4 to 10 meV/fs. The observed density dependence is inconsistent with the phonon bottleneck effect.Comment: 10 pages, 4 figure

Femtosecond Pump-Probe Studies of Reduced Graphene Oxide Thin Films

The dynamics of photocarriers in reduced graphene oxide thin films is studied by using ultrafast pump-probe spectroscopy. Time dependent differential transmissions are measured with sample temperatures ranging from 9 to 300 K. At each sample temperature and probe delay, the sign of differential transmission remains positive. A fast energy relaxation of hot carriers is observed, and is found to be independent of sample temperature. Our experiments show that the carrier dynamics in reduced graphene oxide is similar to other types of graphene, and that the differential transmission is caused by phase-state filling of carriers.Comment: 3 pages, 3 figure

Luteinizing hormone induces expression of 11beta-hydroxysteroid dehydrogenase type 2 in rat Leydig cells

<p>Abstract</p> <p>Background</p> <p>Leydig cells are the primary source of testosterone in male vertebrates. The biosynthesis of testosterone in Leydig cells is strictly dependent on luteinizing hormone (LH). On the other hand, it can be directly inhibited by excessive glucocorticoid (Corticosterone, CORT, in rats) which is beyond the protective capability of 11beta-Hydroxysteroid dehydrogenase type 1 (11beta-HSD1) and type 2 (11beta-HSD2; encoded by gene Hsd11b2 in rats) in Leydig cells. Our previous study found that LH increases 11beta-HSD1 expression in rat Leydig cells, but the effect of LH on the expression and activity of 11beta-HSD2 is not investigated yet.</p> <p>Methods</p> <p>The Leydig cells were isolated from male Sprague-Dawley rats (90 days of age). After Leydig cells were incubated either for 24 h with various concentrations of LH (2.5, 5, 10 and 20 ng/mL) or for different time periods (2, 8, 12 and 24 h) with 20 ng/mL LH, the mRNA expression of 11beta-HSD2 was measured by real-time PCR. 11beta-HSD2 protein levels in Leydig cells were assayed by Western Blot and 11beta-HSD2 enzyme activity was determined by calculating the ratio of conversion of [3H]CORT to [3H]11-dehydrocorticosterone by 24 h after stimulation with 20 ng/ml LH. Four reporter gene plasmids containing various lengths of Hsd11b2 promoter region were constructed and transfected into mouse Leydig tumor cells to investigate the effect of LH on Hsd11b2 transcription. A glucocorticoid-responsive reporter gene plasmid, GRE-Luc, was constructed. To evaluate influence of LH on intracellular glucocorticoid level, rat Leydig cells were transfected with GRE-Luc, and luciferase activities were measured after incubation with CORT alone or CORT plus LH.</p> <p>Results</p> <p>We observed dose- and temporal-dependent induction of rat 11beta-HSD2 mRNA expression in Leydig cells subject to LH stimulation. The protein and enzyme activity of 11beta-HSD2 and the luciferase activity of reporter gene driven by promoter regions of Hsd11b2 were increased by LH treatment. LH decreased the glucocorticoid-induced luciferase activity of GRE-Luc reporter gene.</p> <p>Conclusion</p> <p>The results of the present study suggest that LH increases the expression and enzyme activity of 11beta-HSD2, and therefore enhances capacity for oxidative inactivation of glucocorticoid in rat Leydig cells in vitro.</p