Nanoporous Materials Can Tune the Critical Point of a Pure Substance

Molecular simulations and NMR relaxometry experiments demonstrate that pure benzene or xylene confined in isoreticular metal–organic frameworks (IRMOFs) exhibit true vapor–liquid phase equilibria where the effective critical point may be reduced by tuning the structure of the MOF. Our results are consistent with vapor and liquid phases extending over many MOF unit cells. These results are counterintuitive since the MOF pore diameters are approximately the same length scale as the adsorbate molecules. As applications of these materials in catalysis, separations, and gas storage rely on the ability to tune the properties of adsorbed molecules, we anticipate that the ability to systematically control the critical point, thereby preparing spatially inhomogeneous local adsorbate densities, could add a new design tool for MOF applications.     

Synthesis and characterization of dithienobenzothiadiazole-based donor–acceptor conjugated polymers for organic solar cell applications

New donor–acceptor conjugated polymers (P1 and P2) containing a fused-ring dithienobenzothiadiazole (DT-BTD building block) were synthesized by using the Stille copolymerization method. The synthesized polymers were characterized by ¹H NMR, GPC, and elemental analysis. The optical band gaps of the polymers were found to be 1.86 and 1.9 eV, respectively, as calculated from their film onset absorption edge. Upon annealing both produced a distinct shoulder peak in their film absorption spectra. The electrochemical studies of P1 and P2 revealed that the HOMO and LUMO energy levels of the polymer were −5.3, −5.1 eV, and −3.4, −3.2 eV, respectively. The polymers are thermally stable up to 250–350 °C.     

色散耦合道光学模型对28Si的核子散射数据分析

在光学势中引入色散关系, 相比于通常的耦合道光学模型, 极大地减少了光学势 参数的个数. 采用基于软旋转子模型的耦合道方法对较轻形变核²⁸Si核的中子和质子散射实验数据进行了计算分析, 拟合得到一组色散光学势参数. 计算的中子总截面、以及中子、质子的弹性与非弹性散射微分截面与实验数据有较好的符合.     

Three Saponins, a Steroid, and a Flavanol Glycoside from Achyrantes aspera

Summary.  Three bisdesmosidic saponins, 20-hydroxyecdysone, and quercetin-3-O-β-D-galactoside were isolated from the methanol extract of the aerial parts of Achyranthes aspera L. (Amaranthaceae). Their structures were established on the basis of NMR spectroscopic analysis; the complete ¹H and ¹³C assignments of the compounds were achieved by means of 2D NMR studies. Received July 21, 1999. Accepted August 26, 1999     

Potential of membrane distillation in seawater desalination: Thermal efficiency,sensitivity study and cost estimation

In this work, an extensive analysis on direct contact membrane distillation (DCMD) performance was developed to estimate the mass flux and the heat efficiency, considering transport phenomena, membrane structural properties and most sensitive process parameters, with the aim to provide optimization guidelines for materials and methods. The results showed that an increase of the temperature gradient resulted in the enhancement of both transmembrane flux and thermal efficiency. The investigation of the effects of membrane properties confirmed that better DCMD performance was achieved when using polymeric membranes characterized by low thermal conductivity (flux and thermal efficiency declined by 26% and 50%, respectively, when increasing thermal conductivity from 0.1 to 0.5 W/m K), and high porosity. An optimal thickness value (around 0.7 mm) was identified when operating at low temperature gradient (<5 °C). However, at higher temperature gradient (>10 °C), increasing the membrane thickness from 0.25 to 1.55 mm resulted in a flux decay of about 70% without a significant improvement in thermal efficiency.     

Low temperature magnetic structure of MnSe

In this paper we report low temperature neutron diffraction studies on MnSe in order to understand the anomalous behaviour of their magnetic and transport properties. Our study indicates that at low temperatures MnSe has two coexisting crystal structures, high temperature NaCl and hexagonal NiAs. NiAs phase appears below 266 K and is antiferromagnetically ordered at all temperatures while the NaCl phase orders antiferromagnetically at 130 K.     

Membrane distillation operated at high seawater concentration factors: Role of the membrane on CaCO3 scaling in presence of humic acid

This study aims at investigating the kinetics of calcium carbonate precipitation (scaling), that occurs in the form of vaterite, when treating seawater by direct contact membrane distillation (DCMD) operated at high concentration factors (from 4 to 6). Induction time measurements carried out by dynamic light scattering (DLS) allowed to identify the shifting between homogeneous and heterogeneous nucleation mechanisms as a function of supersaturation. CaCO₃ interfacial energy, evaluated for concentrated seawater solutions as 45 mJ/m², increased by 7% as a consequence of the inhibition effect of humic acid, and it was reduced to 32 mJ/m² in correspondence of heterogeneous nucleation occurring on microporous polypropylene membranes. Gibbs free energy barrier to the formation of critical nuclei was predicted with good accuracy as a function of physico-chemical properties of the membrane (porosity: 0.70, contact angle: 115 ± 2°).     

Simulation-based evolution of resupply and routing policies in rich vendor-managed inventory scenarios

Vendor managed inventory combines inventory management and transportation. Compared to classical inventory management approaches, this strategy offers various degrees of freedom for the vendor while providing a certain service quality level for the customers. To capture the characteristics of rich real-world scenarios, our problem formulation consists of multiple customers, many products and stochastic product usages. Additionally, we also consider mixed formulations, where only a certain part of the customers is switched to a vendor managed inventory to allow a stepwise transition. We show that resupply and routing policies can be evolved autonomously for those scenarios using a simulation-based optimization approach. By combining inventory management and routing, the resulting policies aim to minimize costs and to maximize resource usage while maintaining a given service level. In order to validate our approach, we perform case studies and apply the evolved rules on a large-scale vendor managed inventory scenario for supermarkets. Furthermore, we show that our methodology can be used to perform a sensitivity analysis by considering the influence of exogenous and endogenous factors on the decision process, if a customer base should be transitioned to a vendor managed inventory.