我国单级单吸离心泵的现状及发展方向

指出了单级单吸离心泵的现状,分析其发展方向,并针对金融危机的影响,提出了一些建议。     

基于四参数的汽车发动机外特性模型

分析了传统发动机外特性模型建立的条件和现有模型的不足,在只有发动机最大功率、最大扭矩及其对应转速等四大参数的情况下,引入最大功率点的附件损失系数,建立了基于四参数的发动机使用外特性模型。结合具体实例分析了该计算模型与拟合模型及试验数据的偏差,运用Matlab程序分析了该理论模型的精确性和工程实用性,最后提出了该模型的使用条件。     

预冷却吸气式涡轮冲压膨胀循环发动机发展简介

分析了吸气式涡轮冲压膨胀循环( ATREX)发动机模型和工作原理,介绍了其主要害》件的研究和发展情况,与常规发动机相比说明了其发展的优势,总结归纳了这种发动机技术特点和发展的关键技术。研究认为ATREX发动机采用液态氢预冷却方式,大大扩展了常规涡轮发动机的工作范围,可满足高速飞行器或两级入轨航空航天飞机第一级动力装置的要求。     

Identification of Components of Male-Produced Pheromone of Coffee White Stemborer, Xylotrechus quadripes

The coffee white stem borer, Xylotrechus quadripes Chevrolat (Coleoptera: Cerambycidae), is the foremost pest of arabica coffee in India, Sri Lanka, China, Vietnam, and Thailand. Previous work showed that female beetles were attracted to traps baited with male beetles. Analyses of volatiles from male X. quadripes of Indian origin by gas chromatography (GC) linked to electroantennographic (EAG) recording from a female beetle antenna showed three male-specific components comprising more than 90% of the volatiles, two of which elicited EAG responses. The major EAG-active component was produced at up to 2 μg hr⁻¹ insect⁻¹ and was identified as (S)-2-hydroxy-3-decanone (I) by comparison of GC data, and mass (MS), infrared, and nuclear magnetic resonance (NMR) spectra with those of synthetic standards. The second component was identified as 3-hydroxy-2-decanone (II) produced in part by isomerization of I under the conditions of the GC analysis, although the NMR spectrum suggested it is naturally produced at up to 7% of I. The minor component that elicited an EAG response, present at 7% of the amount of I, was identified as (S,S)-2,3-dihydroxyoctane (III) from GC and MS data. 2-Hydroxy-3-octanone (0.2–0.5% of I), 2,3-decanedione (2% of I), 2-phenylethanol (3% of I), and octanoic acid (4% of I) were also identified in volatiles from male beetles. A general, stereospecific synthetic route to the enantiomers of 2-hydroxy-3-alkanones from the enantiomers of ethyl lactate was developed. The enantiomers of III were synthesized from (E)-2-octene by Sharpless asymmetric dihydroxylation. (S)-(I) was attractive to male X. quadripes in laboratory bioassays, but addition of (S,RS)-(III) at 10% of I reduced attractiveness. In field trials carried out in India with sticky, cross-vane traps, (S)- and (RS)-(I) attracted male X. quadripes and addition of (S,S)-(III) at 10% of I reduced attractiveness. Significant numbers of female Demonax balyi Pascoe (Coleoptera: Cerambycidae) were sometimes caught in traps baited with (S)-(I) alone.     

The potential of P1 site alterations in peptidomimetic protease inhibitors as suggested by virtual screening and explored by the use of C-C-coupling reagents

A synthetic concept is presented that allows the construction of peptide isostere libraries through polymer-supported C-acylation reactions. A phosphorane linker reagent is used as a carbanion equivalent; by employing MSNT as a coupling reagent, the C-acylation can be conducted without racemization. Diastereoselective reduction was effected with L-selectride. The reagent linker allows the preparation of a norstatine library with full variation of the isosteric positions including the P1 side chain that addresses the protease S1 pocket. Therefore, the concept was employed to investigate the P1 site specificity of peptide isostere inhibitors systematically. The S1 pocket of several aspartic proteases including plasmepsin II and cathepsin D was modeled and docked with approximately 500 amino acid side chains. Inspired by this virtual screen, a P1 site mutation library was designed, synthesized, and screened against three aspartic proteases (plasmepsin II, HIV protease, and cathepsin D). The potency of norstatine inhibitors was found to depend strongly on the P1 substituent. Large, hydrophobic residues such as biphenyl, 4-bromophenyl, and 4-nitrophenyl enhanced the inhibitory activity (IC50) by up to 70-fold against plasmepsin II. In addition, P1 variation introduced significant selectivity, as up to 9-fold greater activity was found against plasmepsin II relative to human cathepsin D. The active P1 site residues did not fit into the crystal structure; however, molecular dynamics simulation suggested a possible alternative binding mode.     

Dose build up correction for radiation monitors in high-energy bremsstrahlung photon radiation fields

Conventional radiation monitors have been found to underestimate the personal dose equivalent in the high-energy bremsstrahlung photon radiation fields encountered near electron storage rings. Depth-dose measurements in a water phantom were carried out with a radiation survey meter in the bremsstrahlung photon radiation fields from a 450 MeV electron storage ring to find out the magnitude of the underestimation. Dose equivalent indicated by the survey meter was found to build up with increase in thickness of water placed in front of the meter up to certain depth and then reduce with further increase in thickness. A dose equivalent build up factor was estimated from the measurements. An absorbed dose build up factor in a water phantom was also estimated from calculations performed using the Monte Carlo codes, EGS-4 and EGSnrc. The calculations are found to be in very good agreement with the measurements. The studies indicate inadequacy of commercially available radiation monitors for radiation monitoring within shielded enclosures and in streaming high-energy photon radiation fields from electron storage rings, and the need for proper correction for use in such radiation fields.     

Differential geometry of normalized Stokes vector trajectories in anisotropic media

Trajectory of the normalized Stokes vector on the Poincaré sphere corresponding to light propagation in anisotropic tissues with birefringence and biattenuance is derived. Analytic expressions are determined from the Serret-Frenet formulas and derivatives of arc length for five quantities including the tangent, normal, and binormal vectors with curvature and torsion. Depth variation of curvature and torsion of normalized Stokes vector trajectories corresponding to light propagating in rodent tail tendon are given. Use of analytic expressions for depth variation of curvature and torsion of the normalized Stokes vector trajectories on the Poincaré sphere is discussed for analysis of polarization-sensitive optical coherence tomography data recorded from anisotropic biological tissues with birefringence and biattenuance.     

Optically driven resonance of nanoscale flexural oscillators in liquid

We demonstrate the operation of radio frequency nanoscale flexural resonators in air and liquid. Doubly clamped string, as well as singly clamped cantilever resonators, with nanoscale cross-sectional dimensions and resonant frequencies as high as 145 MHz are driven in air as well as liquid with an amplitude modulated laser. We show that this laser drive technique can impart sufficient energy to a nanoscale resonator to overcome the strong viscous damping present in these media, resulting in a mechanical resonance that can be measured by optical interference techniques. Resonance in air, isopropyl alcohol, acetone, water, and phosphate-buffered saline is demonstrated for devices having cross-sectional dimensions close to 100 nm. For operation in air, quality factors as high as 400 at 145 MHz are demonstrated. In liquid, quality factors ranging from 3 to 10 and frequencies ranging from 20 to 100 MHz are observed. These devices, and an all-optical actuation and detection system, may provide insight into the physics of the interaction of nanoscale mechanical structures with their environments, greatly extending the viscosity range over which such small flexural resonant devices can be operated.     

Nanofiber frequency doublers

Nanoscaled, needle-shaped frequency doublers have been generated via self-assembled surface growth from functionalized quaterphenylene molecules with a designed large hyperpolarizability. The nanofiber frequency doublers exhibit very weak fluorescence centered around 430 nm but emit a strong, resonance-enhanced second-harmonic signal when excited with infrared 80 fs laser pulses. The frequency doublers are employed to correlate second-harmonic response and morphology via two-dimensional true second-harmonic images of individual nanoaggregates obtained with the help of a femtosecond laser scanning microscope.