Taming reactive phenol tautomers and o-quinone methides with transition metals: a structure-reactivity relationship

Quinone methides act as important intermediates in organic syntheses, as well as in chemical and biological processes; however, examples of such isolated species are scarce as a result of their high reactivity. Phenol tautomers (keto form of phenol) are also important intermediates in several organic and organometallic reactions; nevertheless, isolated complexes are rare. This Account reviews the recent progress on the synthesis and reactivity of iridium and rhodium o-quinone methide complexes as well as on iridium-mediated ortho functionalization of phenols. This reaction was at the origin of the discovery of a general synthetic procedure to prepare the first metal-stabilized o-quinone methide.     

B-spline image model for energy minimization-based optical flow estimation.

Robust estimation of the optical flow is addressed through a multiresolution energy minimization. It involves repeated evaluation of spatial and temporal gradients of image intensity which rely usually on bilinear interpolation and image filtering. We propose to base both computations on a single pyramidal cubic B-spline model of image intensity. We show empirically improvements in convergence speed and estimation error and validate the resulting algorithm on real test sequences.     

模糊控制节水洗衣机模型

洗衣机的最小用水量涉及洗衣量、肮脏度、衣料质地、洗涤剂、机械力等多种因素，难以建立精确的解析模型进行控制。而采用熟练洗衣者的经验知识构成的模糊推理规则进行控制，则能达到很好的节水效果。本文采用模糊数学的基本原理选择洗衣布量和浑浊度两个主要因素对洗衣机的用水量进行模糊控制，以达到尽可能节水的目的。本模型经过计算机仿真后，所得到的用水量与市场上的几种洗衣机的耗水量相比，具有明显的节水效果，节水量达到10％－20％。     

Isoplanatism in a multiconjugate adaptive optics system

Turbulence correction in a large field of view by use of an adaptive optics imaging system with several deformable mirrors (DM's) conjugated to various heights is considered. The residual phase variance is computed for an optimized linear algorithm in which a correction of each turbulent layer is achieved by applying a combination of suitably smoothed and scaled input phase screens to all DM's. Finite turbulence outer scale and finite spatial resolution of the DM's are taken into account. A general expression for the isoplanatic angle thetaM of a system with M mirrors is derived in the limiting case of infinitely large apertures and Kolmogorov turbulence. Like Fried's isoplanatic angle theta0,thetaM is a function only of the turbulence vertical profile, is scalable with wavelength, and is independent of the telescope diameter. Use of angle thetaM permits the gain in the field of view due to the increased number of DM's to be quantified and their optimal conjugate heights to be found. Calculations with real turbulence profiles show that with three DM's a gain of 7-10x is possible, giving the typical and best isoplanatic field-of-view radii of 16 and 30 arcseconds, respectively, at lambda = 0.5 microm. It is shown that in the actual systems the isoplanatic field will be somewhat larger than thetaM owing to the combined effects of finite aperture diameter, finite outer scale, and optimized wave-front spatial filtering. However, this additional gain is not dramatic; it is less than 1.5x for large-aperture telescopes.     

Optical Waveguides Fabricated from Oxidised Porous Silicon

Further results on the optical properties of oxidised porous silicon as a function of porosity and oxidation conditions are presented in this paper. The refractive index varies logarithmically with the oxidation time irrespective of the porosity of the sample and the oxidation temperature. Burried waveguides have been realised from as-prepared and oxidised porous silicon. Optical losses of 18 dB cm^–1 at = 1.3 m have been obtained after oxidation at 800°C for 35 min.     

Method for fabricating pixelated, multicolor polarizing films

Pixelated, multicolor polarizing filters-of potential use in full-color displays-were produced by what we believe to be a novel method, i.e., masked evaporation of silver and gold onto glass substrates partially covered with separated sub-micrometer-wide strips of oriented poly(tetrafluoroethylene) (PTFE), prepared by friction deposition. The evaporated metal films preferentially nucleated at the glass surface and, consequently, formed parallel arrays in between the PTFE strips. The structures thus produced feature a strong angle-dependent absorption of polarized visible light, allowing for optical switching between red and blue and between green and yellow.     

Evaluation of biohazards in dehydrated biofilms on foodstuff packaging

Plastic materials used for food packaging are clean but not sterile when the food is just packaged. Accidental wet contamination may occur at every moment between packaging and opening by the consumer: on polyethylene (PET), bacteria may adhere strongly and constitute a biofilm in less than 24 h. By rolling on themselves, PET sheets may contaminate food. We tried to show that contact with salted foodstuffs favoured microbial recovery. Four strains were chosen to perform biofilms on PET: Staphylococcus aureus, Staphylococcus epidermidis, Pseudomonas aeruginosa and Escherichia coli. Biofilms were dried up 24 h. Biofilm bacteria were stressed by adhesion, by starvation and by dehydration. However, they were capable of recovery in salted solutions or media, probably because one (or more) stress protected them against another stress. Stress was demonstrated by stress protein production, by mean of electrophoresis, and membrane lesions by mean of flow cytometry. Stress recovery was performed in aqueous salted solutions or salted brain-heart infusion with NaCl 9, 15, 20 and 30 g/l. Staphylococci were more sensitive to these stresses and recovery was a function of salt concentration. Gram-negative bacteria were little affected by stresses; salt effects were less important. If all these biofilms were capable of recovery from stresses in salted media, flexible PET could possibly lead to a health hazard when it is used for wet salt meats, e.g.     

小米淀粉特性的研究

选用推广品种冀谷一号小米,依据Greenwood,Adkins实验室法获得其淀粉。铁氰化钾法测得小米淀粉含量为58.61％(干基)。显微观察,小米淀粉为多角形,粒径为6.14～11.96μm,6.3×100镜下可见清析的编光十字。Juliano比色法测得其中直链淀粉含量为30. 8％。粘度法测得其直链淀粉平均分子量在235868左右。布拉班德粘度曲线显示小米淀粉的最高粘度高于大米淀粉,起始糊化温度略低于大米淀粉,小米淀粉的热稳定性差,长时间热搅拌中粘度下降很多,而在冷却过程中又上升较快,易回生。