Quantum-confined stark effect in single CdSe nanocrystallite quantum dots

The quantum-confined Stark effect in single cadmium selenide (CdSe) nanocrystallite quantum dots was studied. The electric field dependence of the single-dot spectrum is characterized by a highly polarizable excited state ( approximately 10(5) cubic angstroms, compared to typical molecular values of order 10 to 100 cubic angstroms), in the presence of randomly oriented local electric fields that change over time. These local fields result in spontaneous spectral diffusion and contribute to ensemble inhomogeneous broadening. Stark shifts of the lowest excited state more than two orders of magnitude larger than the linewidth were observed, suggesting the potential use of these dots in electro-optic modulation devices.     

METHOD FOR THE DETECTION OF INDOLE

A simple and sensitive method for the detection of indole in cultures, urine, sewage, etc., is presented. The indole is extracted with chloroform and is then treated with a modified Ehrlich reagent. The possibility of use for the detection of water pollution is indicated.     

A fossil snake with limbs

A 95-million-year-old fossil snake from the Middle East documents the most extreme hindlimb development of any known member of that group, as it preserves the tibia, fibula, tarsals, metatarsals, and phalanges. It is more complete than Pachyrhachis, a second fossil snake with hindlimbs that was recently portrayed to be basal to all other snakes. Phylogenetic analysis of the relationships of the new taxon, as well as reanalysis of Pachyrhachis, shows both to be related to macrostomatans, a group that includes relatively advanced snakes such as pythons, boas, and colubroids to the exclusion of more primitive snakes such as blindsnakes and pipesnakes.     

Selective chemical catalysis by an antibody

The immunoglobulin MOPC167, which binds the transition state analog p-nitrophenylphosphorylcholine with high affinity, catalyzed the hydrolysis of the corresponding carbonate 1. MOPC167 catalysis displayed saturation kinetics with catalytic constant (kcat) = 0.4 min-1 and Michaelis constant (Km) = 208 microM, showed substrate specificity, and was inhibited by p-nitrophenylphosphorylcholine. The rate of the reaction was first order in hydroxide ion concentration between pH 6.0 and 8.0. The lower limit for the rate of acceleration of hydrolysis by the antibody above the uncatalyzed reaction was 770. This study begins to define the rules for the generation of catalytic antibodies.     

基于EDA技术的自动立木整枝机无线遥控接收系统

在分析自动立木整枝机工作过程和控制要求的基础上,该文详细阐述了自动立木整枝机无线遥控接收系统的组成及工作原理,进而采用电子设计自动化(EDA)技术设计了自动立木整枝机无线遥控接收系统的数字控制逻辑.通过优化CPLD内部逻辑电路,有效消除了逻辑竞争冒险.仿真结果表明,该系统控制可靠性较高,能有效提高自动立木整枝机的功能安全性.      

Spectral tuning of pigments underlying red-green color vision

Variations in the absorption spectra of cone photopigments over the spectral range of about 530 to 562 nanometers are a principal cause of individual differences in human color vision and of differences in color vision within and across other primates. To study the molecular basis of these variations, nucleotide sequences were determined for eight primate photopigment genes. The spectral peaks of the pigments specified by these genes spanned the range from 530 to 562 nanometers. Comparisons of the deduced amino acid sequences of these eight pigments suggest that three amino acid substitutions produce the approximately 30-nanometer difference in spectral peaks of the pigments underlying human red-green color vision, and red shifts of specific magnitudes are produced by replacement of nonpolar with hydroxyl-bearing amino acids at each of the three critical positions.