Applications of Danishefsky’s dienes in asymmetric Oxo-Diels-Alder reactions

Applications of Danishefsky’s dienes in catalytic asymmetric hetero-Diels-Alder (AHDA) reactions or specifically, their asymmetric Oxo-Diels-Alder (AOxo-DA) reactions with appropriate dienophiles are highlighted in detail, including the preparation of catalysts with discussion from a mechanistic points of view. Danishefsky’s dienes are effective and useful compounds for the synthesis of optically active six-membered rings such as dihydropyrones, dihydropyridones and dihydropyrans. Due to the broad range of the overall subject, we have limited ourselves, to the recent developments in the utility of Danishefsky’s dienes in the reaction with carbonyl compounds (aldehydes, ketones and 1,2-dicarbonyl compounds) in asymmetric Oxo-Diels-Alder (AOxo-DA) reactions.     

论译者主体性之受动性

随着译者主体性研究的盛行，译者主体性的受动性问题也开始受到关注。越来越多研究表明，翻译行为本身不可避免地受到种种制约与控制。在语言层面和非语言层面，受动性都是译者主体性不可或缺的组成部分。合格的译者应该既有创造性也有自我约束性，两者互相约束，互相补充。译者主体性的发挥应避免无限制的极度张扬与限制重重的过度压抑，只有这样译者主体性才能真正发挥作用，有效提高译本的质量与效用。     

王存生平考--兼论王存与苏轼的交游

王存是润州人，是北宋重臣、著名地理学家，但对其展开的研究是不充分的，甚至有混淆视听的现象。对其生平进行梳理，有助于匡正视听；对其与苏轼的交往进行梳理，有助于对其政治取向有更清楚的了解。这些对于深入挖掘镇江的历史文化资源、拓展镇江的旅游资源都是有益的。     

Rapid separation of polysaccharides using a novel spiral coil column by high‐speed countercurrent chromatography

The separation of polysaccharides is time consuming. We developed and optimized a type‐J counter‐current chromatography system with a novel tri‐rotor spiral coil column for the rapid separation of polysaccharides. The optimal composition of an aqueous PEG1000/K₂HPO₄/KH₂PO₄ system was found to be 14:16:14 w/w/w where the lower phase was the mobile phase. Optimal performance was achieved at a column rotational speed, temperature, and flow rate of 1200 rpm, 45°C, and 3.0 mL/min, respectively. The mobile phase was pumped from the inner terminal in a ‘‘head‐to‐tail’’ elution mode. Polysaccharide LCP‐1 (10.7 mg) was successfully obtained in high purity in one step from 50.0 mg of a crude polysaccharide extracted from the lychee fruit (Litchi chinensis) within 100 min. LCP‐1 possess a number‐average molecular weight and weight‐average molecular weight of 1.05 × 10⁵ and 1.59 × 10⁵ kDa, respectively. The monosaccharide composition consists of the molar ratio of glucose, galactose, and arabinose of 1.3:3.5:1.     

手性氨基醇衍生物催化苯基锂与亚胺的不对称加成反应研究

本文报道几种不同结构的手性氨基醇衍生物在亚胺与苯基锂不对称加成反应中的应用,并对配体结构与对映选择性的关系进行了初步探索,研究结果表明,在双手性配体中,具有反式(S,S)构型的配体催化效果优于顺式(S,R)。     

南水北调中线工程沿线文物分布特征及其受渠道工程影响的模糊评价

水资源开发利用必须与文物保护紧密结合。南水北调中线工程的设计和建设中必须考虑其对沿线数量多、分布广的文物的影响评价 ,以便通过调查和评价来保护这些文物。工作中我们从对水系分布、地层岩性、地貌类型划分 ,文物级别、保护状况及同引水渠道空间关系等调查入手 ,一方面在输水渠道两侧各 3km宽的影响范围内 ,对不同时代的文物地貌分布特征进行了统计 ,另一方面 ,用影响指数E对沿线文物受影响的程度及保护等级进行了模糊定量评价。     

Mixed-mode stress intensity factors and critical angles of cracks in bolted joints by weight function method

Summary   Mechanical joints, such as bolted or riveted joints, are widely used in structural components. Reliable determination of stress intensity factors for cracks in bolted joints is required to evaluate their safety and fatigue life. The weight function method is an efficient technique to calculate stress intensity factors for various loading conditions by the stress analysis of an uncracked model. In this paper, the mixed-mode stress intensity factors for cracks in bolted joints are analyzed by the weight function method, and coefficients included in the weight function are determined by finite element analysis for reference loadings. The critical angle at which mode I stress intensity factor becomes maximum is determined, and the effects of the amount of clearance and crack length on the critical angle are investigated. Received 28 February 2001; accepted for publication 22 June 2001 RID=" ID=" The authors are grateful for the support provided by a grant from the Korea Science & Engineering Foundation (KOSEF) and Safety and Structural Integrity Research Center at the Sungkyunkwan University.     

Extrudate swell through an orifice die

The extrudate swell of a viscoelastic fluid through an orifice die is investigated by using a mixed finite element and a streamline integration method (FESIM), using a version of the K-BKZ model. The free surface calculation is based on a local mass conservation scheme and an approximate numerical treatment for the contact point movement of the free surface. The numerical results show a vortex growth and an increasing swelling ratio with the Weissenberg number. Convergence with mesh refinement is demonstrated, even at a high Weissenberg number of O(587), where the swelling ratio reaches a value of about 360%. In addition, it is found that the effective flow channel at the entrance region next to the orifice die is reduced due to the enhanced vortex growth, which may be a source of flow instability.     

Hysteresis loops predicted by isoenergy density theory for polycrystals. Part I: fundamentals of non-equilibrium thermal–mechanical coupling effects

When a polycrystal is stressed or strained at fifty percent of the corresponding yield value, damage will be inflicted non-homogeneously in the material due to the fact that the stress and/or strain distribution is non-uniform even if isotropy and homogeneity are assumed for the initial microstructure. This effect will be cumulated for each cycle of the load if the applied stress or strain is repeated continuously. Nucleation of microcracks can eventually lead to the propagation of a macrocrack.The process of damage accumulation in fatigue is defined to be sufficiently slow such that inhomogeneity of material behavior created by loading is a significant factor that can not be arbitrarily dismissed without a good reason. What this means specifically is that the difference of the stress and strain behavior at each point in a fatigue specimen must be accounted for in the analytical model in order to predict the correct cumulative effect. Such a requirement translates into a non-equilibrium formulation where the constitutive relations for each point and loading cycle must be determined separately. In this sense, the true problem of fatigue cannot be completely treated by the classical continuum mechanics approach that is limited to equilibrium mechanics for a closed system. Having said this, the isoenergy density theory will be applied to estimate the hysteresis loops of a hour-glass profile cylindrical bar specimen as recommended by the American Society for Testing and Materials (ASTM) for low-cycle fatigue.The work will be divided into two parts. Part I will cover the fundamentals of a non-equilibrium theory where the continuum elements are finite in size; they do not vanish in the limit. Therefore, size effects are immediately encountered as a function of time. General expressions for the rate change of volume of these elements with surface area are derived such that they can be computed from the nine displacement gradients. These elements can differ in size and must fit together without discontinuities or gaps to form the continuum. The condition of isoenergy energy density is invoked such that the size of these individual elements under large and finite deformation and rotation can be determined without loss in generality. The existence of such a space having the property of the same isoenergy density in all directions is thus proved. This enables the establishment of the one dimensional energy state with that in three dimensions without restriction, the absence of which has prevented the development of a complete non-linear theory of mechanics that can be solved in a direct fashion in contrast to the inverse method of assuming the displacement field. Illustration is provided for deriving the constitutive relation incrementally for a given location for the hour-glass specimen made of 6061-T6 aluminum. Once the specimen is loaded, each material point will follow a different stress and strain curve according to the local displacement rate. Hence, the method applies to material with non-homogeneous microstructure if their individual expressions can be assessed and fed into the computer.Part II computes for the non-equilibrium temperature and an entropy-like quantity that can be positive and negative. This implies that the system can absorb or dissipate energy with reference to the surrounding. Additional data for hysteresis loops are given for 6061-T6 aluminum, SAE 4340 steel and Ti–8Al–1Mo–1V titanium. Accumulation of the local hysteresis energy per cycle is found to be the highest near the surface of the uniaxial specimen where load symmetry prevails. This is a consequence of the difference in accumulation of the energy density due to distortion in contrast to dilatation at the specimen center. This is why fatigue cracks tend to nucleate near the specimen surface, at a small distance towards the interior. Another distinct feature of fatigue is that the non-equilibrium temperature is found to oscillate about the ambient temperature while the local stress states fluctuate between tension and compression. This temperature reversal behavior is typical of non-equilibrium behavior and also occurs under monotonic loading. The space and time variations of the dissipated energy density for different materials are found to be related to the initial monotonic energy density or area under the true stress and true strain curve.What will be demonstrated is that no special consideration need to be made when applying the isoenergy density theory for analyzing the nucleation of micro and macrocracks in addition to failure of the specimen. Crack nucleation under fatigue is assumed to occur when the total hysteresis energy reaches a critical value. It is possible to establish a relation between the average hysteresis energy per cycle and the number of cycles to failure. The proposed method requires only a knowledge of the initial monotonic energy density curve for a given material. Predicted results for the fatigue of cylindrical bar specimens with hour-glass profile are given and they can be found in Part II of this work.     

Analytical calculation of DNB-superheating by a postulated thermo-mechanical effect of nucleate boiling

Observations of stationary subcooled nucleate boiling with forced convection in a glass-pipe at a pressure of 0.1 MPa lead to a new interpretation of the wall. This interpretation applied to the rules of linear non-equilibrium thermodynamics results in framework equations with non-linear heat transfer as indicated by several empirical correlations. Momentum balances at the singular surfaces of a bubble have been combined with a sonic limit for the mass transfer through the interfaces serving as a maximum condition with respect to heat transfer (DNB). The calculation predicts the corresponding wall temperature from properties of state without using empirical coefficients and therefore must be valid independent of coolants' geometries and surface conditions. Documented measurements at pool boiling, forced and free convection with cryogenic liquids, water and liquid metals emphasize this if data are properly selected corresponding to the precondition that void fraction remains low.