A simulation-based approach for fleet design in a technician dispatch problem with stochastic demand

We address the problem of developing policies for selecting the proper number of technicians to hire (fleet size) for an on-call repair service operating over a yearly planning horizon in an environment where the number of requests to be serviced each day can vary significantly from day to day and on a seasonal basis. We propose a new approach based on the simulation of a large number of sampled weekly instances and the application of a previously developed optimization procedure for the daily dispatch of technicians. The sampled instances are derived from an extensive statistical analysis of demand data with respect to several key parameters. The results of the simulations are utilized to adjust performance curves in function of fleet size that are then used in an economic analysis of the trade-offs between service quality and cost. Efficient policies for fleet design are then deducted from this analysis.     

Analytical determination of specific 4,4′-methylene diphenyl diisocyanate hemoglobin adducts in human blood

4,4′-Methylene diphenyl diisocyanate (MDI) is one of the most important isocyanates in the industrial production of polyurethane and other MDI-based synthetics. Because of its high reactivity, it is known as a sensitizing agent, caused by protein adducts. Analysis of MDI is routinely done by determination of the nonspecific 4,4′-methylenedianiline as a marker for MDI exposure in urine and blood. Since several publications have reported specific adducts of MDI and albumin or hemoglobin, more information about their existence in humans is necessary. Specific adducts of MDI and hemoglobin were only reported in rats after high-dose MDI inhalation. The aim of this investigation was to detect the hemoglobin adduct 5-isopropyl-3-[4-(4-aminobenzyl)phenyl]hydantoin (ABP-Val-Hyd) in human blood for the first time. We found values up to 5.2 ng ABP-Val-Hyd/g globin (16 pmol/g) in blood samples of workers exposed to MDI. Because there was no information available about possible amounts of this specific MDI marker, the analytical method focused on optimal sensitivity and selectivity. Using gas chromatography–high-resolution mass spectrometry with negative chemical ionization, we achieved a detection limit of 0.02 ng ABP-Val-Hyd/g globin (0.062 pmol/g). The robustness of the method was confirmed by relative standard deviations between 3.0 and 9.8 %. Combined with a linear detection range up to 10 ng ABP-Val-Hyd/g globin (31 pmol/g), the enhanced precision parameter demonstrates that the method described is optimized for screening studies of the human population.     

Single‐electron transfer‐living radical polymerization of oligo(ethylene oxide) methyl ether methacrylate in the absence and presence of air

The efficient Cu(0) wire‐catalyzed single‐electron transfer‐living radical polymerization (SET‐LRP) of oligo(ethylene oxide) methyl ether methacrylate (OEOMA) in DMSO and binary mixtures of DMSO with H₂O is reported. Addition of 10–80% H₂O to DMSO resulted in an increase in the apparent rate constant of propagation ( ), corresponding to an increase in the polarity and extent of disproportionation. At higher H₂O content, decreases, and in H₂O is slightly lower than that in DMSO. This unexpected behavior was attributed to the physical inaccessibility of Cu(0) wire catalyst to the hydrophobic reactive centers of OEOMA and initiator which self‐assemble in H₂O into micellar aggregates and vesicles. This hypothesis was confirmed by the faster polymerization in H₂O than in DMSO during catalysis with Cu(0) nanoparticles generated by disproportionation of CuBr. SET‐LRP of OEOMA can be performed in protic and dipolar aprotic solvents in air by the addition of hydrazine hydrate. The polymerization exhibited no induction period and identical as in the degassed experiment, and led to polymers with narrow molecular weigh distribution. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 3110–3122     

Gadolinium(III)‐Hydroxy Ladders Trapped in Succinate Frameworks with Optimized Magnetocaloric Effect

Two kinds of inorganic gadolinium(III)‐hydroxy “ladders”, [2×n] and [3×n], were successfully trapped in succinate (suc) coordination polymers, [Gd₂(OH)₂(suc)₂(H₂O)]_n ? 2n H₂O ( 1 ) and [Gd₆(OH)₈(suc)₅(H₂O)₂]_n ? 4n H₂O ( 2 ), respectively. Such coordination polymers could be regarded as alternating inorganic–organic hybrid materials with relatively high density. Magnetic and heat capacity studies reveal a large cryogenic magnetocaloric effect (MCE) in both compounds, namely (ΔH=70 kG) 42.8 J kg^?1 K^?1 for complex 1 and 48.0 J kg^?1 K^?1 for complex 2 . The effect of the high density is evident, which gives very large volumetric MCEs up to 120 and 144 mJ cm^?3 K^?1 for complexes 1 and 2 , respectively.     

Simulation of nuclide migration in a middle- and low-level radioactive waste repository based on GMS

Journal of Radioanalytical and Nuclear Chemistry - Groundwater is the most important factor contributing to the diffusion and migration of radionuclides in the repository. In this paper, the...     

Reversible Photoinduced Conversion of Unprecedented Norbornadiene-Based Photoswitches with Redox-Active Naphthalene Diimide Functionalities

An unprecedented compound class of functional organic hybrids consisting of a photoswitchable norbornadiene building block and a redoxactive chromophore, namely naphthalene diimide, were designed and synthesized. Within these structures the capability of rylene chromophores to function as a redox active catalyst upon their photoexcitation was utilized to initiate the oxidative back-conversion of the in situ formed quadricyclane unit to its norbornadiene analogue. In this way successive photoexcitation at two different wavelengths enabled a controlled photoswitching between the two isomerical states of the hybrids. Beyond this prove of concept, the dependency of the reaction rate to the intramolecular distance of the two functional molecular building blocks as well as the concentration of the photoexcited sample was monitored. The experimental findings and interpretations were furthermore supported by quantum chemical investigations.     

Enhanced Crystal Quality of Perovskite via Protonated Graphitic Carbon Nitride Added in Carbon-Based Perovskite Solar Cells

The quality of perovskite layers has a great impact on the performance of perovskite solar cells (PSCs). However, defects and related trap sites are generated inevitably in the solution-processed polycrystalline perovskite films. It is meaningful to reduce and passivate the defect states by incorporating additive into the perovskite layer to improve perovskite crystallization. Here an environmental friendly 2D nanomaterial protonated graphitic carbon nitride (p-g-C\begin{document}$_3$\end{document}N\begin{document}$_4$\end{document}) was successfully synthesized and doped into perovskite layer of carbon-based PSCs. The addition of p-g-C\begin{document}$_3$\end{document}N\begin{document}$_4$\end{document} into perovskite precursor solution not only adjusts nucleation and growth rate of methylammonium lead tri-iodide (MAPbI\begin{document}$_3$\end{document}) crystal for obtaining flat perovskite surface with larger grain size, but also reduces intrinsic defects of perovskite layer. It is found that the p-g-C\begin{document}$_3$\end{document}N\begin{document}$_4$\end{document} locates at the perovskite core, and the active groups -NH\begin{document}$_2$\end{document}/NH\begin{document}$_3$\end{document} and NH have a hydrogen bond strengthening, which effectively passivates electron traps and enhances the crystal quality of perovskite. As a result, a higher power conversion efficiency of 6.61% is achieved, compared with that doped with g-C\begin{document}$_3$\end{document}N\begin{document}$_4$\end{document} (5.93%) and undoped one (4.48%). This work demonstrates a simple method to modify the perovskite film by doping new modified additives and develops a low-cost preparation for carbon-based PSCs.     

Ultrahigh-intensity optical slow-wave structure

We report the development of corrugated "slow-wave" plasma guiding structures with application to quasiphase-matched direct laser acceleration of charged particles and generation of a wide spectrum of electromagnetic radiation. These structures support guided propagation at intensities up to 2 x 10(17) W/cm(2), limited by our current laser energy and side leakage. Hydrogen and argon plasma waveguides up to 1.5 cm in length with corrugation period as short as 35 microm are generated in a cryogenic cluster jet. Experimental data are consistent with simulations showing periodic modulations of the laser pulse intensity.     

优化金属磷化物电催化析氢性能的策略

日益严重的能源危机和环境污染问题使得探索清洁的可再生能源载体及减少对传统化石燃料的过度依赖成为人们面临的一项重要任务.因此,各种可持续能源如太阳能、风能、海洋能和生物质能等得到了广泛研究并取得了一定的进展.然而,这些能源因存在间歇性和不稳定性等缺点阻碍了其实际应用.近年,氢气作为一种能源载体,以其高能量密度和无碳排放的优点引起了人们的广泛关注,被认为是缓解日益严重的污染问题的最有前途的环保能源.对比目前采用的天然气热解和煤炭气化等传统制氢策略,电催化水裂解由于催化效率高,制氢纯度高和不产生温室气体,被认为是高效、环保、可持续的制氢策略.电催化水裂解由两个独立的半反应组成,分别是析氢反应和析氧反应.析氢反应作为水裂解的一个半反应,在降低制氢成本及提高产氢催化效率方面起着关键作用.然而,目前的核心问题之一是要开发高效的析氢电催化剂,以加快反应速度.目前,铂和铂基纳米材料被认为是高效的析氢电催化剂,但是其稀缺性和高成本阻碍了大规模实际应用.金属磷化物由于具有较高的本征活性并且在不同的电解质中都具有良好的电催化析氢性能,被证明是一种优良的析氢电催化剂.此外,与普通催化剂相比,金属磷化电催化剂还具有合成简便、效率高、成本低、省时等优点.本文详细介绍了近年人们在金属磷化物用于电催化析氢研究中取得的进展.首先,介绍了电催化析氢反应机理,金属磷化物的结构及作用,并对其优缺点进行了总结;随后,综述了金属磷化物的合成方法,包括后处理、原位生成和电沉积策略,并对不同方法进行了比较和讨论.此外,从元素掺杂、界面工程、空穴工程、修饰特定载体、构建特定纳米结构、设计双或多金属磷化物和其他发展的新方法等七个方面详细总结了促进金属磷化物电催化活性的多种策略,并进行了对比和讨论.最后,归纳了金属磷化物在电催化析氢应用中存在的问题和面临的挑战,并对未来的研究发展提出了展望.