基于微段插补模型的数控刀具运动优化控制

针对直线段与圆弧连接处的过渡,采用微小线段插补进行处理;通过前瞻分析的方法,控制直线段与圆弧段过渡处的进给速度提前减速,有效地减少了直线与圆弧过渡处的加工误差,建立混合S型双向加减速曲线模型,实现了圆弧段拐角处速度的控制.为了更好地优化数控刀具的加工时间,改进S型加速曲线原来加速缓慢耗时的前半部分,建立非零启动S型曲线加减速模型,从而减少启动时间,这种改进极大地优化刀具在走圆弧时的时间及平稳性.     

From planes to cluster: The design of polynitrogen molecules

Polynitrogen compounds are a class of promising green high‐energy‐density materials. Using three‐membered to six‐memberd nitrogen rings, called all‐nitrogen building blocks, a series of two dimensional (planar) to three dimensional (cluster) polynitrogen molecules can be built. Small‐angle strain of small nitrogen rings and noncovalent interaction between neighboring nitrogen atoms leads to cage strain, and cage strain energy can be used to describe the stability of polynitrogen molecules theoretically. Density functional theory B3LYP/6‐31g(d,p) was used to optimize geometrical configurations and second‐order perturbation theory MP2/6‐311g(d,p) was applied to calculate single point energies of polynitrogen and other related compounds. Homodesmotic reactions were designed to compute cage strain energies of polynitrogen molecules and average bond energies of their N? N bonds. Some strategies were proposed to enhance the stability of polynitrogen molecules. This work provides theoretical evidence for the stability prediction of some nanomaterials (e.g., nanotube). © 2014 Wiley Periodicals, Inc.     

Synthesis of Novel,Chiral Bicyclo[3.1.0]hex‐2‐ene Amino Acid Derivatives as Useful Synthons in Medicinal Chemistry

A short and concise synthesis of novel, chiral bicyclo[3.1.0]hex‐2‐ene amino acid derivatives 13 and 14 has been developed. The key step is a stereo‐ and regioselective allylic amination of exo‐ and endo‐methyl bicyclo[3.1.0]hex‐2‐ene‐6‐carboxylates 8 and 9 , which were prepared from 7,7‐dichlorobicyclo[3.2.0]hept‐2‐en‐6‐one ( 1 ). These amino acid derivatives are useful building blocks in medicinal chemistry and can be prepared as chiral compounds by using either (+)‐ 1 or (?)‐ 1 as starting material.     

Formyl MIDA Boronate: C1 Building Block Enables Straightforward Access to α-Functionalized Organoboron Derivatives

Formyl MIDA boronate has been known to be an elusive type of acylboronate that has not been obtained to date. In this work, an approach to the one-pot preparation and chemical transformations of formyl MIDA boronate were developed to provide new types of α-functionalized organoboron compounds. Among them are acylboronate reagents which present boron-substituted analogues of ynones and β-dicarbonyl compounds. The developed synthetic procedures, utilizing formyl MIDA boronate, are tolerant to diverse functional groups, making this reagent an advantageous C₁ building block for extending the scope of organoboron chemistry.     

On AGT relations with surface operator insertion and a stationary limit of beta-ensembles

We present a summary of what is currently known about of the AGT relations for conformal blocks with the additional insertion of the simplest degenerate operator, and a special choice of the corresponding intermediate dimension, in which the conformal blocks satisfy hypergeometric-type differential equations in the position of the degenerate operator. Special attention is devoted to the representation of the conformal block through using the beta-ensemble resolvents and to its asymptotics in the limit of large dimensions (both external and intermediate) taken asymmetrically in terms of the deformation epsilon-parameters. The next-to-leading term in the asymptotics defines the generating differential in the Bohr–Sommerfeld representation of the one-parameter deformed Seiberg–Witten prepotentials, (whose full two-parameter deformation leads to Nekrasov functions). This generating differential is also shown to be the one-parameter version of the single-point resolvent for the corresponding beta-ensemble, and its periods in the perturbative limit of the gauge theory are expressed through the ratios of the Harish–Chandra function. The Schrödinger/Baxter equations, considered earlier in this context, directly follow from the differential equations for the degenerate conformal block. This approach provides a powerful method for the evaluation of the single-deformed prepotentials, and even for the Seiberg–Witten prepotentials themselves. We primarily concentrate on the representative case of the insertion into the four-point block on a sphere and the one-point block on a torus.     

Asymmetric syntheses of (8R,8aS)- and (8R,8aR)-8-hydroxy-5-indolizidinones:Two promising oxygenated indolizidine building blocks

Starting from the oxygenated piperidine building block 20,two synthetic approaches to new building blocks (8R,8aS)-and (8R,8aR)-8-hydroxy-5-indolizidinones 19a/19b and 15a/15b have been developed,respectively. The first one is based on the trans-diastereoselective reductive alkylation (dr = 93:7),followed by a four-step procedure; and the second one called for the RCM reaction on the N,O-acetal derived from a vinylation,which was followed by a pyrrole formation,and a stereocontrolled cis-selective (dr = 91:...     

Chiral building blocks from biomass: 2,5-diamino-2,5-dideoxy-1,4-3,6-dianhydroiditol

An efficient route towards the synthesis of 2,5-diamino-2,5-dideoxy-1,4-3,6-dianhydroiditol 4 has been developed resulting in significant improvements in both isolated yields and purity when compared to literature procedures. As a consequence, resin-grade 2,5-diamino-2,5-dideoxy-1,4-3,6-dianhydroiditol 4 has become available for laboratory scale step-growth polymer synthesis. Additionally, an interesting renewable chiral 2-amino-2-deoxy-1,4-3,6-dianhydroiditol 10, has been isolated.     

α-Functionally Substituted α,β-Unsaturated Aldehydes as Fine Chemicals Reagents: Synthesis and Application

α-Functionalized α,β-unsaturated aldehydes is an important class of compounds, which are widely used in fine organic synthesis, biology, medicine and pharmacology, chemical industry, and agriculture. Some of the 2-substituted 2-alkenals are found to be the key metabolites in plant and animal cells. Therefore, the development of efficient methods for their synthesis attracts the attention of organic chemists. This review focusses on the recent advances in the synthesis of 2-functionally substituted 2-alkenals. The approaches to the preparation of α-alkyl α,β-unsaturated aldehydes are not included in this review.     

Analysis of polystyrene-b-polyisoprene copolymers by coupling of liquid chromatography at critical conditions to NMR at critical conditions of polystyrene and polyisoprene

For the investigation of the molecular heterogeneity of polystyrene-b-polyisoprene block copolymers, a chromatographic separation method, namely liquid chromatography at critical conditions was developed. This method was coupled on-line with (1)H-NMR(where NMR stands for nuclear magnetic resonance) for the comprehensive analysis of the polystyrene-b-polyisoprene copolymers. The copolymers were synthesized by two different methods: sequential living anionic polymerization and coupling of living precursor blocks. While (1)H-NMR allows just for the analysis of the bulk chemical composition of the block copolymers, the coupling with liquid chromatography at critical conditions provides selective molar mass information on the polystyrene and polyisoprene blocks within the copolymers. The polyisoprene block molar mass is determined by operating at chromatographic conditions corresponding to the critical point of adsorption of polystyrene and size exclusion chromatography mode for polyisoprene. The molar mass of the polystyrene block is determined by operating at the critical conditions of polyisoprene. In addition to the molar mass of each block of the copolymers, the chemical composition distribution of the block copolymers was determined. By using the coupling of liquid chromatography at critical conditions to (1)H-NMR, one can also detect the homopolymers formed during synthesis. Finally the microstructure of the polyisoprene block in the copolymers was evaluated as a function of molar mass.     

疏水链段对两亲性三嵌段共聚物在水中聚集行为的影响

以结构明确的两端为短的聚苯乙烯(PS)或聚甲基丙烯酸甲酯(PMMA)链段,中间为长的聚乙二醇(PEG)链段的PS-b-PEG-b-PS和PMMA-b-PEG-b-PMMA两亲性三嵌段共聚物为对象,研究了PS和PMMA链段对其在水中形成胶束和凝胶的影响.两种三嵌段共聚物在水中形成以PS或PMMA链段为核、PEG链段为壳的球形胶束,流体力学半径Rh,app为15.3~24.3 nm,并随PEG链段长度增长而增大.临界胶束浓度CMC均小于0.01 mg/mL,随着PS和PMMA链段长度的增加而减小.PS-b-PEG-b-PS浓度高于4.5 wt%可形成较强的疏水缔合的物理凝胶,平衡模量Ge可达到103Pa;PMMA-b-PEG-b-PMMA浓度高于7.5 wt%可以形成弱的凝胶,Ge<10 Pa.凝胶的储存模量G′和损耗模量G″均随着PS或PMMA链段的增长而增大.