Racemic dipeptide glycyl‐dl‐leucine at 120 K

The structure of glycyl‐dl ‐leucine, C₈H₁₆N₂O₃, has been determined at 120 K by single‐crystal X‐ray diffraction. In addition to three N—H?O‐type hydrogen bonds of the positively charged RNH₃⁺ group of the zwitterionic mol­ecule, an intermolecular N—H?O contact exists between the peptide bond and the carboxyl­ate group. Four hydrogen‐bond cycles were identified, giving a complex pattern.     

Hydrogen ADPs with Cu Kα data? Invariom and Hirshfeld atom modelling of fluconazole

For the structure of fluconazole [systematic name: 2‐(2,4‐difluorophenyl)‐1,3‐bis(1H‐1,2,4‐triazol‐1‐yl)propan‐2‐ol] monohydrate, C₁₃H₁₂F₂N₆O·H₂O, a case study on different model refinements is reported, based on single‐crystal X‐ray diffraction data measured at 100 K with Cu Kα radiation to a resolution of sin θ/λ of 0.6 Å⁻¹. The structure, anisotropic displacement parameters (ADPs) and figures of merit from the independent atom model are compared to `invariom' and `Hirshfeld atom' refinements. Changing from a spherical to an aspherical atom model lowers the figures of merit and improves both the accuracy and the precision of the geometrical parameters. Differences between results from the two aspherical‐atom refinements are small. However, a refinement of ADPs for H atoms is only possible with the Hirshfeld atom density model. It gives meaningful results even at a resolution of 0.6 Å⁻¹, but requires good low‐order data.     

Yields and recoil properties of products from the reaction between natural copper and 86 MeV/A12C ions

Absolute cross sections and thick target/thick catcher recoil properties have been determined for radionuclides produced in the reaction between copper and 86 MeV/A¹²C ions. Integration of the obtained mass yield curve gives a cross section of reactions leading to spallation products of 1,440 mb. TheF/B-ratios are found to increase with decreasing product mass, reaching a maximum of ～100 for products with masses 20–25 mass units lower than the target mass, followed by a decrease. The recoil data have been analyzed with the two-step vector model to deduce momentum transfer and product kinetic energies. The momentum transferred to an intermediate system is found to increase for reactions leading to decreasing product masses, reaching values of 1/3 of full momentum transfer. The derived mean kinetic energies are found to be higher than found in comparable proton induced reactions. Some possible explanations for this phenomenon have been discussed. The results have been compared with Monte Carlo cascade-evaporation calculations, and the agreement between the predictions and experiment is in general found to be good.     

Motion of positrons in metals

In this review we discuss the different aspects of positron annihilation in metals that involve the dynamics of positron motion before annihilation. The emphasis is on the theory, but also some experimental evidence is quoted. The topics covered are: slowing down and thermalization, effective mass, temperature dependence of positron vacancy trapping, positron channeling, and escape of low energy positrons from metal surfaces.     

Autocorrelations between pseudo-random numbers

In this paper some generating methods of the multiplicative and mixed congruential types for obtaining pseudo-random numbers are reviewed. Procedures to determine autocorrelations are demonstrated and a few numerical results are also given.     

Expanding the Landscape of Diterpene Structural Diversity through Stereochemically Controlled Combinatorial Biosynthesis

Plant‐derived diterpenoids serve as important pharmaceuticals, food additives, and fragrances, yet their low natural abundance and high structural complexity limits their broader industrial utilization. By mimicking the modularity of diterpene biosynthesis in plants, we constructed 51 functional combinations of class I and II diterpene synthases, 41 of which are “new‐to‐nature”. Stereoselective biosynthesis of over 50 diterpene skeletons was demonstrated, including natural variants and novel enantiomeric or diastereomeric counterparts. Scalable biotechnological production for four industrially relevant targets was accomplished in engineered strains of Saccharomyces cerevisiae.     

Managing inventory and service levels in a safety stock‐based inventory routing system with stochastic retailer demands

The inherent uncertainty in supply chain systems compels managers to be more perceptive to the stochastic nature of the systems' major parameters, such as suppliers' reliability, retailers' demands, and facility production capacities. To deal with the uncertainty inherent to the parameters of the stochastic supply chain optimization problems and to determine optimal or close to optimal policies, many approximate deterministic equivalent models are proposed. In this paper, we consider the stochastic periodic inventory routing problem modeled as chance‐constrained optimization problem. We then propose a safety stock‐based deterministic optimization model to determine near‐optimal solutions to this chance‐constrained optimization problem. We investigate the issue of adequately setting safety stocks at the supplier's warehouse and at the retailers so that the promised service levels to the retailers are guaranteed, while distribution costs as well as inventory throughout the system are optimized. The proposed deterministic models strive to optimize the safety stock levels in line with the planned service levels at the retailers. Different safety stock models are investigated and analyzed, and the results are illustrated on two comprehensively worked out cases. We conclude this analysis with some insights on how safety stocks are to be determined, allocated, and coordinated in stochastic periodic inventory routing problem. Copyright © 2017 John Wiley & Sons, Ltd.