固体激光器的快速电光Q开关驱动电路的实验研究

比较了三种不同的电光调Q驱动电路。电子管式调Q电路工作稳定,退压沿70ns左右,但空间体积大,激光脉冲能量较低;雪崩管串联武调Q电路退压时间大约为20ns,输出激光脉冲能量高,脉宽窄;MOSFET管串联调Q电路,简单可靠,单管耐压高,退压时间为50ns。     

Genome-wide meta-analysis identifies 56 bone mineral density loci and reveals 14 loci associated with risk of fracture

Bone mineral density (BMD) is the most widely used predictor of fracture risk. We performed the largest meta-analysis to date on lumbar spine and femoral neck BMD, including 17 genome-wide association studies and 32,961 individuals of European and east Asian ancestry. We tested the top BMD-associated markers for replication in 50,933 independent subjects and for association with risk of low-trauma fracture in 31,016 individuals with a history of fracture (cases) and 102,444 controls. We identified 56 loci (32 new) associated with BMD at genome-wide significance (P < 5 × 10(-8)). Several of these factors cluster within the RANK-RANKL-OPG, mesenchymal stem cell differentiation, endochondral ossification and Wnt signaling pathways. However, we also discovered loci that were localized to genes not known to have a role in bone biology. Fourteen BMD-associated loci were also associated with fracture risk (P < 5 × 10(-4), Bonferroni corrected), of which six reached P < 5 × 10(-8), including at 18p11.21 (FAM210A), 7q21.3 (SLC25A13), 11q13.2 (LRP5), 4q22.1 (MEPE), 2p16.2 (SPTBN1) and 10q21.1 (DKK1). These findings shed light on the genetic architecture and pathophysiological mechanisms underlying BMD variation and fracture susceptibility.     

Participation of DNA repair in the response to 5-fluorouracil

The anti-metabolite 5-fluorouracil (5-FU) is employed clinically to manage solid tumors including colorectal and breast cancer. Intracellular metabolites of 5-FU can exert cytotoxic effects via inhibition of thymidylate synthetase, or through incorporation into RNA and DNA, events that ultimately activate apoptosis. In this review, we cover the current data implicating DNA repair processes in cellular responsiveness to 5-FU treatment. Evidence points to roles for base excision repair (BER) and mismatch repair (MMR). However, mechanistic details remain unexplained, and other pathways have not been exhaustively interrogated. Homologous recombination is of particular interest, because it resolves unrepaired DNA intermediates not properly dealt with by BER or MMR. Furthermore, crosstalk among DNA repair pathways and S-phase checkpoint signaling has not been examined. Ongoing efforts aim to design approaches and reagents that (i) approximate repair capacity and (ii) mediate strategic regulation of DNA repair in order to improve the efficacy of current anticancer treatments. Received 08 September 2008; received after revision 25 September 2008; accepted 03 October 2008     

The E-site story: the importance of maintaining two tRNAs on the ribosome during protein synthesis

In the sixties James Watson suggested a twosite model for the ribosome comprising the P site for the peptidyl transfer RNA (tRNA) before peptide-bond formation and the A site, where decoding takes place according to the codon exposed there. In the eighties a third tRNA binding site was detected, the E site, which was specific for deacylated tRNA and turned out to be a universal feature of ribosomes. However, despite having three tRNA binding sites, only two tRNAs occupy the ribosome at a time during protein synthesis: at the A and P sites before translocation (PRE state) and at the P and E sites after translocation (POST state). The importance of having two tRNAs in the POST state has been revealed during the last 25 years, showing that the E site contributes two fundamental features: (i) the fact that incorporation of a wrong amino acid is not harmful for the cell (only 1 in about 400 misincorporations destroys the function of a protein) stems from the presence of an E-tRNA; (ii) maintenance of the reading frame is one of the most remarkable achievements of the ribosome, essential for faithful translation of the genetic information. The presence of the POST state E-tRNA prevents loss of the reading frame. Received 14 March 2006; received after revision 8 June 2006; accepted 4 August 2006     

The proportion of marriages ending in divorce

Even though cohabitation has become more prevalent in the last few decades, the majority of the adult population is married, and marriage is associated with a number of factors, such as educational outcom and health. Understanding the marrie population is also an important part of understanding partnering behaviour and family formation and dissolution. The length of marriages and whether they are ended by death or divorce is therefore of interest t demographers and policy maker     

Rheumatoid arthritis susceptibility loci at chromosomes 10p15, 12q13 and 22q13

The WTCCC study identified 49 SNPs putatively associated with rheumatoid arthritis at P = 1 x 10(-4) - 1 x 10(-5) (tier 3). Here we show that three of these SNPs, mapping to chromosome 10p15 (rs4750316), 12q13 (rs1678542) and 22q13 (rs3218253), are also associated (trend P = 4 x 10(-5), P = 4 x 10(-4) and P = 4 x 10(-4), respectively) in a validation study of 4,106 individuals with rheumatoid arthritis and an expanded reference group of 11,238 subjects, confirming them as true susceptibility loci in individuals of European ancestry.