Chiral counteranion-directed silver-catalyzed asymmetric synthesis of 1,2-dihydroisoquinolines by Friedel–Crafts alkylation reactions

The reaction of ortho-alkynylaryl aldimines and indoles catalyzed by a silver binol-derived phosphate was realized to afford a series of enantioenriched 1,2-dihydroisoquinolines in moderate to good yields and ee. An interesting phenomenon that highly enantioenriched products could be obtained from their lower ee form by silica gel column chromatography was observed, providing an easy access to the enantiopure form of the product.     

Self-assembly of 1,4-benzenedithiolate/tetrahydrofuran on a gold surface: a Monte Carlo simulation study

We report a Monte Carlo simulation study of the self-assembly of 1,4-benzenedithiolate (BDT), tetrahydrofuran (THF), and their mixtures on a Au (111) surface. We use the grand canonical Monte Carlo method to obtain the equilibrium adsorption coverage. Canonical ensemble (NVT) simulation is then used to explore further the structural information of the equilibrated systems. Our results indicate that BDT molecules adsorb onto the Au (111) surface with one of the sulfur atoms bonded to Au atoms. THF molecules form clusters on the surface. For BDT-THF mixtures, BDT can selectively adsorb on Au (111) to form a monolayer, whereas the solvent THF molecules either float above BDT monolayer or occupy vacancies on the surface that are not covered by BDT molecules. BDT molecules adsorb on a Au (111) surface with an average tilt angle of about 18-35 degrees to the surface normal. The tilting angle decreases as the coverage increases. In addition, the BDT monolayer constitutes an ordered herringbone structure on the Au (111) surface, and the ordering pattern is insensitive to the BDT coverage. In comparison, the THF molecules exhibit amorphous structure on the Au surface. Interestingly, simulations indicate that the bonding behavior of BDT molecules on Au (111) is coverage-dependent. BDT bonds preferably on the Au top site when the surface coverage is low. As coverage increases, most BDT molecules bond on the bridge and fcc hollow sites.     

Hydrogen storage properties of Li-Mg-N-H systems with different ratios of LiH/Mg(NH2)2

In this work, the hydrogen desorption and structural properties of the Li-Mg-N-H systems with different LiH/Mg(NH2)2 ratios are systemically investigated. The results indicate that the system with the LiH/Mg(NH2)2 ratio of 6/3 transforms into Li2NH and MgNH, and then, the mixture forms an unknown phase by a solid-solid reaction, which presumably is the ternary imide Li2Mg(NH)2; the system with the LiH/Mg(NH2)2 ratio of 8/3 transforms into 4Li2NH and Mg3N2 after releasing H2 at T < 400 degrees C; the system with the LiH/Mg(NH2)2 ratio of 12/3 transforms into 4Li3N and Mg3N2 after releasing H2 at T > 400 degrees C, where the LiMgN phase is formed by the reaction between Li3N and Mg3N2. The characteristics of the phase transformations and the thermal gas desorption behaviors in these Li-Mg-N-H systems could be reasonably explained by the ammonia mediated reaction model, irrespective of the difference in the LiH/Mg(NH2)2 ratios.     

Experimental determination of a Viviparus contectus thermometry equation

Experimental measurements of the ¹⁸O/¹⁶O isotope fractionation between the biogenic aragonite of Viviparus contectus (Gastropoda) and its host freshwater were undertaken to generate a species‐specific thermometry equation. The temperature dependence of the fractionation factor and the relationship between Δδ¹⁸O (δ¹⁸O_carb. – δ¹⁸O_water) and temperature were calculated from specimens maintained under laboratory and field (collection and cage) conditions. The field specimens were grown (Somerset, UK) between August 2007 and August 2008, with water samples and temperature measurements taken monthly. Specimens grown in the laboratory experiment were maintained under constant temperatures (15°C, 20°C and 25°C) with water samples collected weekly. Application of a linear regression to the datasets indicated that the gradients of all three experiments were within experimental error of each other (±2 times the standard error); therefore, a combined (laboratory and field data) correlation could be applied. The relationship between Δδ¹⁸O (δ¹⁸O_carb. – δ¹⁸O_water) and temperature (T) for this combined dataset is given by: (T is in °C, δ¹⁸O_carb. is with respect to Vienna Pee Dee Belemnite (VPDB) and δ¹⁸O_water is with respect to Vienna Standard Mean Ocean Water (VSMOW). Quoted errors are 2 times standard error). Comparisons made with existing aragonitic thermometry equations reveal that the linear regression for the combined Viviparus contectus equation is within 2 times the standard error of previously reported aragonitic thermometry equations. This suggests there are no species‐specific vital effects for Viviparus contectus. Seasonal δ¹⁸O_carb. profiles from specimens retrieved from the field cage experiment indicate that during shell secretion the δ¹⁸O_carb. of the shell carbonate is not influenced by size, sex or whether females contained eggs or juveniles. Copyright © 2009 John Wiley & Sons, Ltd.     

Side-payment contracts in two-person nonzero-sum supply chain games: Review,discussion and applications

This paper investigates supply chain coordination with side-payment contracts. We first summarize specific side-payment contracts and present our review on the literature that developed general side-payment schemes to coordinate supply chains. Following our review, we discuss two criteria that a proper side-payment contract must satisfy, and accordingly introduce a decision-dependent transfer payment function and a constant transfer term. We present the condition that the transfer function must satisfy, and use Nash arbitration scheme and Shapley value to compute the constant transfer term and derive its closed-form solution. Next, we provide a five-step procedure for the development of side-payment contract, and apply it to four supply chain games: Cournot and Bertrand games, a two-retailer supply chain game with substitutable products and a one-supplier, one-retailer supply chain. More specifically, for the Cournot game, we construct a linear transfer function and a constant side-payment to coordinate two producers. For the Bertrand game, we build a nonlinear transfer function which is equivalent to a revenue-sharing contract, and show that the constant term is zero and two firms in the game equally share the system-wide profit. For a supply chain with substitutable products, we present a side-payment contract to coordinate two retailers. For a two-echelon supply chain, we develop a proper side-payment scheme that can coordinate the supply chain and also help reduce the impact of forward buying on supply chain performance.     

Extremal problems related to Gauss-John position

In this paper,we consider the extremal problem of the lp-norm:min {lp(TK),o∈TK■L,T∈GL(n)},where K,L are two convex bodies in Rn.Using the optimization theorem of John,we give necessary conditions for K to be in extremal position in terms of a decomposition of the identity.Furthermore,the weaker optimization problem,min{(lp(TK))p:TK■B2n,TK∩Sn-1≠,T∈GL(n)},is also considered.As an application,the geometric distance between the unit ball B2n and a centrally symmetric convex body K is obtained.     

Indications of an electronic phase transition in two-dimensional superconducting YBa2Cu3O(7-x) thin films induced by electrostatic doping

We successfully tuned an underdoped ultrathin YBa2Cu3O(7-x) film into the overdoped regime by means of electrostatic doping using an ionic liquid as a dielectric material. This process proved to be reversible. Transport measurements showed a series of anomalous features compared to chemically doped bulk samples and a different two-step doping mechanism for electrostatic doping was revealed. The normal resistance increased with carrier concentration on the overdoped side and the high temperature (180 K) Hall number peaked at a doping level of p～0.15. These anomalous behaviors suggest that there is an electronic phase transition in the Fermi surface around the optimal doping level.     

基于低密度奇偶校验码的MPPM比特符号映射及系统性能研究

建立了基于低密度奇偶校验(LDPC)码和多脉冲位置调制(MPPM)的无线光通信系统模型,给出了相应系统模型下的解码算法,研究了(m,2)MPPM的比特符号映射方式,提出了用改进的遗传算法(GA)搜索的优化映射方法,最后在大气湍流信道下进行了仿真。仿真结果表明基于LDPC码和MPPM的无线光通信系统性能明显优于未编码的MPPM系统,结合LDPC码和多光束发射技术可以提高系统抗强大气湍流影响的能力;通过GA优化的映射方法在不增加系统复杂性的情况下能进一步提高系统的纠错性能,可以获得更大的编码增益。     

Modeling and identification on nonlinear saturable and reverse-saturable absorptions of gold nanorods using femtosecond Z-scan technique

An improved Z-scan analysis approach is proposed by establishing and solving the saturable absorption (SA) and reverse-SA (RSA) models, respectively. Near-infrared femtosecond Z-scans are carried out on the synthesized gold nanorods (NRs) possessing the average length of 46 nm using a femtosecond laser operated at the wavelength of 800 nm, which is close to the peak position of longitudinal surface plasmon resonance (SPR) (710 nm) of gold NRs. At lower input intensity of less than 400 GW/cm2 , the normalized transmission exhibits only SA phenomenon; however, when it exceeds 400 GW/cm2 , both SA and RSA are observed. By using the presented Z-scan modeling and theory, the three-photon absorption (3PA) is identified in the material, and the 3PA cross-section is determined to be 1.58×1071 cm6s2 .