Search

It has been suggested that a νp-process can occur when hot, dense, and proton-rich matter is expanding within a strong flux of antineutrinos. In such an environment, proton-rich nuclides can be produced in sequences of proton captures and (n, p) reactions, where the free neutrons are created in situ by |$\overline{\nu }_\mathrm{e}+\mathrm{p} {\rightarrow} \mathrm{n}+\mathrm{e}^+$| reactions. The detailed hydrodynamic evolution determines where the nucleosynthesis path turns off from N  = Z line and how far up the nuclear chart it runs. In this work, the uncertainties on the final isotopic abundances stemming from uncertainties in the nuclear reaction rates were investigated in a large-scale Monte Carlo approach, simultaneously varying more than 10 000 reactions. A large range of model conditions was investigated because a definitive astrophysical site for the νp-process has not yet been identified. The present parameter study provides, for each model, identification of the key nuclear reactions dominating the uncertainty for a given nuclide abundance. As all rates appearing in the νp-process involve unstable nuclei, and thus only theoretical rates are available, the final abundance uncertainties are larger than those for nucleosynthesis processes closer to stability. Nevertheless, most uncertainties remain below a factor of 3 in trajectories with robust nucleosynthesis. More extreme conditions allow production of heavier nuclides but show larger uncertainties because of the accumulation of the uncertainties in many rates and because the termination of nucleosynthesis is not at equilibrium conditions. It is also found that the solar ratio of the abundances of 92Mo and 94Mo could be reproduced within uncertainties. [ABSTRACT FROM AUTHOR]

Abstract   We obtain faster algorithms for problems such as r-dimensional matching and r-set packing when the size k of the solution is considered a parameter. We first establish a general framework for finding and exploiting small problem kernels (of size polynomial in k). This technique lets us combine Alon, Yuster and Zwick’s color-coding technique with dynamic programming to obtain faster fixed-parameter algorithms for these problems. Our algorithms run in time O(n+2 O(k)), an improvement over previous algorithms for some of these problems running in time O(n+k O(k)). The flexibility of our approach allows tuning of algorithms to obtain smaller constants in the exponent. [ABSTRACT FROM AUTHOR]

Taurine has been reported to enhance cholesterol 7α-hydroxylase (CYP7A1) mRNA expression in animal models. However, no in vitro studies of this effect have been reported. The Hep G2 human hepatoma cell line has been recognized as a good model for studying the regulation of human CYP7A1. This work characterizes the effects of taurine on CYP7A1 mRNA levels of Hep G2 cells in a dose- and time-dependent manner. In the dose-dependent experiment, Hep G2 cells were treated with 0, 2, 10 or 20mM taurine in the presence or absence of cholesterol 0.2mM for 48h. In the time-dependent experiment, Hep G2 cells were treated with 0 or 20mM taurine for 4, 24 and 48h with and without cholesterol 0.2mM. Our data revealed that taurine showed time- and dose-response effects on CYP7A1 mRNA levels in Hep G2 cells. However, glycine – a structural analogue of taurine – did not have an effect on CYP7A1 gene expression. These results show that, in agreement to previous studies on animal models, taurine induces the mRNA levels of CYP7A1 in Hep G2 cells, which could enhance cholesterol conversion into bile acids. Also, Hep G2 cell line may be an appropriate model to study the effects of taurine on human cholesterol metabolism. [ABSTRACT FROM AUTHOR]

To clarify the physiological role(s) of metallothionein (MT) in carcinogenesis, we studied the susceptibility of MT-null mice to chemically mediated carcinogenesis in the 7,12-dimethylbenz[a]anthracene (DMBA)/12-O-tetradecanoylphorbol-13-acetate (TPA)-induced two-stage carcinogenesis model. The MT-null mice were subjected to a single topical application of DMBA (50 or 100 µg/mouse) and, 1 week later, to promotion with TPA (10 µg/mouse) twice a week for 20 weeks. At week 21, nearly all of the MT-null mice developed tumors in the skin, in contrast to only 10-40% of wild-type mice. No tumors were observed in MT-null or wild-type mice that were administered TPA alone. By using the PCR-restriction fragment length polymorphism and PCR-single strand conformation polymorphism methods, we found a transversion of A182 to T in codon 61 of c-Ha-ras in the papilloma tissue of MT-null mice and wild-type mice but failed to find any mutations in the c-Ki-ras and c-N-ras genes. In two-stage skin carcinogenesis induction by DMBA/TPA, p53 and p21WAF1/Cip1 expression levels were found to be increased in MT-null mice compared with wild-type mice. As to an earlier change at the promotion stage triggered by TPA application, MT-null mice were found to have both hyperplasia of the epithelium and a marked degree of inflammation in the basal layer, indicating that the induced as well as endogenous MT acted as a protective factor against tumorigenesis. In conclusion, the present study has demonstrated that MT has antitumorigenic potential in both the initiation and promotion stages of the two-stage chemical skin carcinogenesis model. [ABSTRACT FROM AUTHOR]

A spectrally narrowed widely tunable Ce3+: Er3+-codoped fluorozirconate (ZBLAN) fiber laser with a continuous-wave laser diode pumping at 975-nm pumping is demonstrated. Wide tunable range over 120 nm (1490-1610 nm) is attained by using a diffraction grating combined with a tuning mirror in the Ce3+: Er3+-ZBLAN fiber laser cavity. Rate-equation model analysis shows that the tunable range can expand further by using a wavelength-dependent reflectivity cavity mirror. [ABSTRACT FROM PUBLISHER]

We demonstrate the low-noise and high-gain operation of a fluoride Er3+ and Ce3+ codoped fiber (F-ECDF) amplifier with 980-nm pumping. A 980-nm-pumped F-ECDF with a length of only 45 cm exhibits a noise figure of <4.5 dB in the entire C-band and a small signal gain of >20 dB with a gain ripple of <1 dB without any gain-flattening filter in the 1525-1560-nm range. Excitation spectra for the gain and noise figure of an F-ECDF exhibit flat shapes in the 974-982-nm range. We also demonstrate that the gain coefficient reaches 1.4 dB/mW and the power conversion efficiency is 27.4% at 1532 nm for a 2.25-m-long F-ECDF. [ABSTRACT FROM PUBLISHER]