Beam quality characterization of a radial laser array

Abstract

With the Hermite-Gaussian mode used to describe radial laser arrays and the M²-factor and power in the bucket (PIB) chosen as criteria for characterizing beam quality, a detailed study of beam quality of coherent and incoherent radial laser arrays is made. The closed-form expression for the M²-factor of incoherent radial arrays, which depends upon the Hermite-Gaussian order m, inverse radial fill factor r' and aspect ratio w _0x /w _0y , is derived. Numerical examples are given to illustrate and compare beam quality of coherent and incoherent radial arrays.     

小口径镀锌钢管井点降水技术在泵站深基坑开挖中的运用

结合多年来的工作实践与经验，分析了小口径镀锌钢管井点降水施工技术的重点和难点，通过多种基坑防水形式比选，以选取最优方案。     

Growth rates of ibuprofen crystals grown from ethanol and aqueous ethanol

To quantify the crystallization of racemic ibuprofen [2-(4-isobutyl-phenyl)-propionic acid] from aqueous ethanol it is necessary to know the growth rate kinetics. Growth rates were measured by adding SPG (size proportional growth) seed crystals to an isothermal non-nucleating batch crystallization and sampling during the batch. The supersaturation was measured by refractive index and the crystal size by laser light scattering (Malvern). To ensure the batch was non-nucleating the supersaturation was kept within the narrow secondary MZ (metastable zone). Measurements were made at three temperatures, 10, 25 and 40 °C. The growth rate was proportional (first order kinetics) to the solution supersaturation, expressed in mass ratio of ibuprofen to ethanol units. Despite the narrow MZ, the initial growth rates were substantial (up to 1 μm/min). Temperature has a large effect on growth rate with an activation energy of 13.7 kJ/mol. The water content affects the growth rate coefficient differently depending on the temperature.     

北京市地埋管地源热泵项目应用效果评价分析

通过对27个北京市地埋管地源热泵项目应用数据的监测调查，从系统性能、地温变化、节能效益、环保效益和节能成本等方面进行统计分析，并应用主成分分析法和数据包络分析法对项目的效率进行综合评价，得出效率相对有效的项目17个，相对无效的项目10个，并分析无效项目的参数改进方向。最后提出地埋管地源热泵发展的4点建议：1）增加财政补贴可有效提高项目的投入产出效率；2）项目参数设计的合理性和运维管理的科学性是决定项目效率的根本因素；3）加强长期监测才能对地源热泵技术对环境影响程度有更准确的判断；4）优化项目投入产出效率是地埋管地源热泵项目普遍应用需要解决的重要问题。     

Thermal behaviour of polyethylene‐block‐poly(methyl methacrylate) block copolymer: effect of multiple heating and cooling rates versus mathematical artefact

The melting and crystallization behaviours of a polyethylene‐block‐poly(methyl methacrylate) (PE‐b‐PMMA) diblock copolymer and a PE homopolymer were investigated using multiple heating and cooling rate differential scanning calorimetry (DSC) experiments, and modelling of the crystallization kinetics and lamellar thickness distribution. This new model was first validated applying literature and experimental data. The model‐predicted morphology (n = 3.2) closely matched the spherulitic morphology (n = 3), which was determined using polarized optical microscopy. For each experimental cooling rate, the model predicted diblock copolymer crystallinity that well matched the entire DSC crystallinity curve, notably for an Avrami–Erofeev index of n = 2; and apparent crystallization activation energy that hardly varied with the cooling rates used, relative crystallinity (α), and crystallization temperature or time. This disfavours the concept of variable activation energy. The use of the right crystallization model and parameter estimation algorithm is important for addressing the mathematical artefact. Under non‐isothermal cooling, the PE‐b‐PMMA diblock copolymer, as per the model prediction, crystallized without confinement (n ≠ 1), preserving the cylindrical structure. From the characteristic shapes of the crystallization function f(α(T)) versus 1/T and crystallization rate versus α plots, the resulting T_cmax and narrow α_max range can guide the search for an appropriate crystallization model. The overall treatment illustrated in this study is not restricted to a PE homopolymer and a PE‐b‐isotactic PMMA block copolymer. It can be generally applied to crystalline homopolymers and copolymers (alternating, random and block), as well as their blends. The block copolymers and blends can be crystalline–amorphous as well as crystalline–crystalline. © 2014 Society of Chemical Industry     

An exposure based study of crash and injury rates in a cohort of transport and recreational cyclists in New South Wales,Australia

This paper examines self-reported prospectively collected data from 2038 adult transport and recreational cyclists from New South Wales (Australia) to determine exposure-based incident crash and injury rates. During 25,971 days of cycling, 198 crashes were reported, comprising approximately equal numbers of falls and collisions. The overall crash rate was 0.290 (95% CI, 0.264–0.319) per 1000 km or 6.06 (95% CI, 5.52–6.65) per 1000 h of travel. The rate of crashes causing any injury (self-treated, or medically attended without overnight hospital stay) was 0.148 (95% CI, 0.133–0.164) per 1000 km or 3.09 (95% CI, 2.79-3.43) per 1000 h of travel. The rate of crashes causing a medically attended injury (without overnight hospital stay) was 0.023 (95% CI, 0.020–0.027) per 1000 km or 0.49 (95% CI, 0.43-0.56) per 1000 h of travel. No injuries requiring an overnight stay in hospital were reported on days meeting the inclusion criteria. After adjustment for exposure in hours, or for the risks associated with different infrastructure utilisation, the rates of crashes and medically attended injuries were found to be greater for females than males, less experienced than more experienced cyclists, and for those who rode mainly for transport rather than mainly for recreation. Comparison of estimated crash and injury rates on different infrastructure types were limited by the small number of events, however findings suggest that the separation of cyclists from motorised traffic is by itself not sufficient to ensure safe cycling.     

同向抽运光纤拉曼放大器功率转换效率的理论分析

为了对同向抽运光纤拉曼放大器的功率转换效率进行研究,由耦合方程出发,首先理论推导出功率转换效率的解析解,然后采用数值计算的方法详细分析不同物理因素对功率转换效率的影响。结果表明：功率转换效率先随着光纤长度和单位面积的拉曼增益系数增加而增加,当增加到最大值时保持数值不变;小信号时,初始信号光功率对功率转换效率的影响较小;大信号时,功率转换效率随着初始信号光功率增加而快速增加;功率转换效率和初始抽运光功率呈抛物线曲线关系;抽运光与信号光的频率比增加时,功率转换效率减小。