Kinetic modeling of Q-switched high-power ytterbium-doped fiber lasers

We present a kinetic model for Q-switched, cladding-pumped, high-power Yb-doped fiber lasers that are based on the rate equation, in a difference equation form, of ion population and propagation equations for both pumping and signal light. The effects of fiber-laser parameters, such as doping, length, pump power, and repetition rate on pulse characteristics are analyzed. This model is used to analyze the performance of Q-switched multicore fiber lasers and to show the output pulses with enhanced characteristics.     

粒状贝氏体和粒状组织强韧化机制的研究

M-A岛以双相强化方式可有效地提高粒状组织的强度；而对粒状贝氏体起主要作用的是碳的固溶强化和板条亚晶强化，这是造成粒状贝氏体强度高于拉状组织的主要原因。粒状组织的韧性来源于由铁素体断裂强度所决定的裂纹形成功，但粒状贝氏体的韧性主要部分是裂纹扩展功，铁素体板条亚矗厦机械稳定性较高的残案奥氏体对此起主要韧化作用。     

Determination of trace perchlorate in high-salinity water samples by ion chromatography with on-line preconcentration and preelution

A simple, automated system for the determination of trace perchlorate by ion chromatography (IC) with an online preconcentration technique is reported. The sample is preconcentrated, and less strongly held ions preeluted before the analyte is transferred to the principal separation system. This approach provides low limits of detection (LOD) and is particularly robust toward the effect of high concentrations of common anions, such as those present in groundwater samples. It compares favorably with currently promulgated EPA method 314.0. The LOD (S/N = 3) is 0.77 microg/L for a 2-mL reagent water sample and decreases more-or-less proportionately with increasing sample volume, at least up to 20 mL. Even with a sample of conductivity 14.7 mS/cm (approximately that of 0.1 M Na2SO4), the recovery of added perchlorate at the 25.0 microg/L level was still 92%. The concentration of added perchlorate in the range of 1-400 microg/L was linearly correlated to the peak area, with an r2 value of 0.9997. The recovery of perchlorate from artificial samples with different conductivity by the present method compares favorably with those from the currently recommended EPA Method. The ability of this approach to remove matrix interferences suggests that it would be also promising for perchlorate analysis in other challenging samples.     

Silver-induced enhancement of thiochrome-based peroxide measurements

Thiamine is presently one of the most attractive substrates used for sensitive fluorometric measurements of peroxides. Thiochrome (TC), a highly fluorescent product, is formed in enzyme-mediated oxidations. It is assumed that H(2)O(2) is nearly quantitatively converted to TC. The reaction cannot differentiate H(2)O(2) from many other peroxides such as methylhydroperoxide (MHP); to perform differential measurements, H(2)O(2) can first be selectively destroyed by a suitable catalyst such as MnO(2). In substituting Ag(2)O for MnO(2) to accomplish the selective destruction of H(2)O(2), we achieved the stated objective but were puzzled by a 3-fold increase in the MHP response in the presence of Ag(2)O. It was soon discovered that traces of dissolved Ag(+) and Hg(2+) can dramatically increase the yield of TC in this reaction from either H(2)O(2) or MHP; the normal yield in fact is only 20%. We present here a reaction scheme and kinetic model that adequately describes this behavior and should provide a path to substantially increase the sensitivity of this important assay method.     

Continuous collection of soluble atmospheric particles with a wetted hydrophilic filter

Approximately one-third of the area (14-mm diameter of a 25-mm diameter) of a 5-microm uniform pore size polycarbonate filter is continuously wetted by a 0.25 mL/min water mist. The water forms a continuous thin film on the filter and percolates through it. The flowing water substantially reduces the effective pore size of the filter. At the operational air sampling flow rate of 1.5 standard liters per minute, such a particle collector (PC) efficiently captures particles down to very small size. As determined by fluorescein-tagged NaCl aerosol generated by a vibrating orifice aerosol generator, the capture efficiency was 97.7+% for particle aerodynamic diameters ranging from 0.28 to 3.88 microm. Further, 55.3 and 80.3% of 25- and 100-nm (NH4)2SO4 particles generated by size classification with a differential mobility analyzer were respectively collected by the device. The PC is integrally coupled with a liquid collection reservoir. The liquid effluent from the wetted filter collector, bearing the soluble components of the aerosol, can be continuously collected or periodically withdrawn. The latter strategy permits the use of a robust syringe pump for the purpose. Coupled with a PM2.5 cyclone inlet and a membrane-based parallel plate denuder at the front end and an ion chromatograph at the back end, the PC readily operated for at least 4-week periods without filter replacement or any other maintenance.     

Dynamical Monte Carlo modelling of organic solar cells: the dependence of internal quantum efficiency on morphology

We present a dynamical Monte Carlo study of the dependence of the internal quantum efficiency (IQE) of an organic bulk heterojunction solar cell on the device morphology. The IQE is found to be strongly sensitive to the scale of phase separation in the morphology, with a peak at approximately 20 nm for the PFB/F8BT system studied. An ordered, checkered morphology exhibits a peak IQE 1.5 times higher than a disordered blend.     

根据洞室开挖引起的应力变化确定原岩应力

原岩应力状态是地下工程开挖的重要设计参数,它由主应力的大小和方向确定。通常的原岩应力测试方法,如套芯法,都只能得到小范围内的测量资料,且费用很大。本文介绍了一种大范围岩体的地下洞室应力测试方法,这是一种典型的区域应力测量方法。该法要求测出洞室开挖所引起的应力变化。通过把实测应力变化同理论预测的应力变化进行比较而拟合出原岩应力场。通过在两组应力变化值之间得出一个误差函数,使误差趋于极小而求解。本文通过一个具收敛解的圆形洞室的实例来阐述这种方法及其应用。工程实例研究表明,该法具有很大的潜在优势。所得反分析值与大量套芯法实测值相当一致。与常规方法相比,这种新方法有如下优点:(1)应力资料可在工程进展中随时得到校正;(2)测得的是大范围岩体而不是某个点的应力状态;(3)最重要的是费用相对较低。