旋光性氰醇的酶催化合成

综述了酶催化立体选择性合成及动力学折分制备旋光性氰醇的几种方法。     

Dilatation Behavior of Two Differently Heat-Treated Commercial Magnesia-Partially-Stabilized Zirconias

The dilatation behavior of two grades of partially stabilized zirconia (PSZ) was determined. ZN 40 is a material which contains 40% to 50% t -ZrO₂ particles, and has a reproducible dilatometric behavior up to 900°C. ZN 50 is a Mg-PSZ containing 20% to 30% of the monoclinic phase. The cyclic dilatation curves show an unstable hysteresis effect which arises from the tetragonal-monoclinic phase transformation.     

Dissolution of particles in binary alloys: part I. computer simulations

A detailed numerical study has been made of the dissolution kinetics of particles in binary alloys during isothermal annealing. In earlier models, the assumption was made that the dissolution reaction could be described by the dissolution of only one particle in an infinite matrix or the dissolution of a regular array of particles of equal size. This assumption has been relaxed and a log-normal size distribution of particles has been introduced instead. The calculations have been done numerically by applying a finite difference technique to a spherical particle in a spherical cell of finite size. The presence of a size distribution of particles was found to have a great effect on the dissolution kinetics and, therefore, must be included in a reliable model for the dissolution of particles. The results have been presented in diagrams, giving the volume fraction as a function of the dimensionless annealing time with the geometrical standard deviation as a parameter, and thus should be useful in making accurate predictions of the dissolution kinetics of binary alloys. The curves can be used for all volume fractions provided that all of the particles can be dissolved completely at the temperature considered. Also, equations have been derived that can easily be used to give an estimate of the annealing time to dissolve 90 pct of the initial volume fraction.     

High-resolution compact X-ray microscopy

We demonstrate compact full‐field soft X‐ray transmission microscopy with sub 60‐nm resolution operating at λ= 2.48 nm. The microscope is based on a 100‐Hz regenerative liquid‐nitrogen‐jet laser‐plasma source in combination with a condenser zone plate and a micro‐zone plate objective for high‐resolution imaging onto a 2048 × 2048 pixel CCD detector. The sample holder is mounted in a helium atmosphere and allows imaging of both dry and wet specimens. The microscope design enables fast sample switching and the sample can be pre‐aligned using a visible‐light microscope. High‐quality images can be acquired with exposure times of less than 5 min. We demonstrate the performance of the microscope using both dry and wet samples.     

Cardiovascular conditions in hemodialysis patients may be worsened by extensive interdialytic weight gain

The risk of death is increased for hemodialysis (HD) patients compared with age-matched healthy subjects, the main reason for this being cardiovascular conditions. This prospective study investigated whether the burden of interdialytic weight gain (IDWG) was of importance for cardiovascular end points and survival. A total of 97 HD patients were studied. The end points included death (reasons given), acute myocardial infarction, or coronary vascular intervention. The extent of ultrafiltration was measured at predefined follow-up points. The IDWG was calculated as ultrafiltration/body weight given in weight%. The burden of IDWG was analyzed. End points occurred in 77 (79%) of the patients during the 5-year study period. The extent of IDWG was higher in those with end points due to cardiovascular reasons (3.77 weight% vs. 3.19 P<0.001), cardiac reasons (P<0.001), congestive heart failure (P<0.01), aortic aneurysm, and intracerebral bleeding (P<0.024). To reduce the risk for cardiovascular events, it is important to avoid too extensive IDWG in HD patients.     

Comment on ‘Precision tracking control of non-minimum phase systems with zero phase error’

This paper comments on a technical problem arising in the article ‘ Precision tracking control of non-minimum phase systems with zero phase error’ by Xia and Menq.     

Dissolution of particles in binary alloys: part II. experimental investigation on an Al-Si alloy

A detailed experimental study of the dissolution kinetics of Si particles in an Al-Si alloy has been carried out in order to test the validity of the two models presented in the accompanying article.[1] In these models, the dissolution kinetics are dependent on the particle size distribution of the alloy. An alloy with composition C_o = 0.77 at. pct Si was heat-treated in order to obtain rather coarse spherical particles (1 to 10 μn). The size distribution of the particles was found to be close to the log-normal distribution. At high temperatures, when the solvus concentration was well above C_o, the experimental values were very close to the values of the model which predicted the highest dissolution rates. At lower temperatures, when the solvus concentration was closer toC _o, the experimental values lay in between the values predicted by the two models. The results clearly demonstrate that a size distribution of particles must be included in the model if an accurate prediction of the dissolution kinetics is to be achieved.