Sequential proton transfer through water bridges in acid-base reactions

The proton transfer mechanism between aqueous Br?nsted acids and bases, forming an encounter pair, has been studied in real time with ultrafast infrared spectroscopy. The transient intermediacy of a hydrated proton, formed by ultrafast dissociation from an optically triggered photoacid proton donor ROH, is implicated by the appearance of an infrared absorption marker band before protonation of the base, B-. Thus, proton exchange between an acid and a base in aqueous solution is shown to proceed by a sequential, von Grotthuss-type, proton-hopping mechanism through water bridges. The spectra suggest a hydronium cation H3O+ structure for the intermediate, stabilized in the Eigen configuration in the ionic complex RO-...H3O+...B-.     

Real-time observation of bimodal proton transfer in acid-base pairs in water

The neutralization reaction between an acid and a base in water, triggered after optical excitation, was studied by femtosecond vibrational spectroscopy. Bimodal dynamics were observed. In hydrogen-bonded acid-base complexes, the proton transfer proceeds extremely fast (within 150 femtoseconds). In encounter pairs formed by diffusion of uncomplexed photoacid and base molecules, the reaction upon contact was an order of magnitude slower, in agreement with earlier reported values. These results call for a refinement of the traditional Eigen-Weller picture of acid-base reactions: A three-stage model is introduced to account for all observed dynamics.     

The effect of using passive hybrid muffler on a small generator set noise fuelled by natural gas

A detailed experimental study has been conducted to evaluate the effect of a hybrid muffler (HM) installation on sound emission of a small generator set fuelled by natural gas, which was covered by an acoustic enclosure. Specifications of a reactive muffler were calculated according to recommendation of ASHRAE 2.6 technical committee and based on an appropriate muffler was selected. The selected muffler was added to the muffler installed by manufacturer on generator (GM) and formed hybrid muffler (HM). The sound of generator set was measured for GM and HM setups on four sides of the generator at five different loading conditions (0, 25, 50, 75 and 100% load) using a sound level meter. The results showed that application of HM could reduce the sound of generator at firing frequency (31.5 Hz) and frequencies greater than 1000 Hz, with the maximum values of 11.7 and 26 dB, respectively. The overall A-weighted generator sound was in the range of 73.2–85.8 dB (A) at all the loading conditions and sides by using HM. The acoustical performance of HM on the side with the maximum generator sound (side 1) increased from 5.1 dB (A) at no load to 10.61 dB (A) at full load conditions. Therefore, the HM usage could be recommended as a useful approach to attenuate the generator sound.     

A high-brightness source of narrowband, identical-photon pairs

We generated narrowband pairs of nearly identical photons at a rate of 5 x 10(4) pairs per second from a laser-cooled atomic ensemble inside an optical cavity. A two-photon interference experiment demonstrated that the photons could be made 90% indistinguishable, a key requirement for quantum information-processing protocols. Used as a conditional single-photon source, the system operated near the fundamental limits on recovery efficiency (57%), Fourier transform-limited bandwidth, and pair-generation-rate-limited suppression of two-photon events (factor of 33 below the Poisson limit). Each photon had a spectral width of 1.1 megahertz, ideal for interacting with atomic ensembles that form the basis of proposed quantum memories and logic.     

Two-photon imaging of lymphocyte motility and antigen response in intact lymph node

Lymphocyte motility is vital for trafficking within lymphoid organs and for initiating contact with antigen-presenting cells. Visualization of these processes has previously been limited to in vitro systems. We describe the use of two-photon laser microscopy to image the dynamic behavior of individual living lymphocytes deep within intact lymph nodes. In their native environment, T cells achieved peak velocities of more than 25 micrometers per minute, displaying a motility coefficient that is five to six times that of B cells. Antigenic challenge changed T cell trajectories from random walks to "swarms" and stable clusters. Real-time two-photon imaging reveals lymphocyte behaviors that are fundamental to the initiation of the immune response.     

Optically defined multifunctional patterning of photosensitive thin-film silica mesophases

Photosensitive films incorporating molecular photoacid generators compartmentalized within a silica-surfactant mesophase were prepared by an evaporation-induced self-assembly process. Ultraviolet exposure promoted localized acid-catalyzed siloxane condensation, which can be used for selective etching of unexposed regions; for "gray-scale" patterning of refractive index, pore size, surface area, and wetting behavior; and for optically defining a mesophase transformation (from hexagonal to tetragonal) within the film. The ability to optically define and continuously control both structure and function on the macro- and mesoscales is of interest for sensor arrays, nanoreactors, photonic and fluidic devices, and low-dielectric-constant films.     

High-gain backward lasing in air

The compelling need for standoff detection of hazardous gases and vapor indicators of explosives has motivated the development of a remotely pumped, high-gain air laser that produces lasing in the backward direction and can sample the air as the beam returns. We demonstrate that high gain can be achieved in the near-infrared region by pumping with a focused ultraviolet laser. The pumping mechanism is simultaneous resonant two-photon dissociation of molecular oxygen and resonant two-photon pumping of the atomic oxygen fragments. The high gain from the millimeter-length focal zone leads to equally strong lasing in the forward and backward directions. Further backward amplification is achieved with the use of earlier laser spark dissociation. Low-divergence backward air lasing provides possibilities for remote detection.     

Three-dimensional optical storage memory

A novel three-dimensional (3-D) optical memory device is presented that allows fast random access of the information and extremely high bit densities. This device is based on two-photon writing, reading, and erasing of the information in a photochromic material embedded in a polymer matrix. Absorption and emission data show that two-photon writing and reading of information is feasible. The advantages and properties of such a 3-D optical memory are discussed.     

离子色谱法测定伊班膦酸钠注射液主成分的方法探讨

为建立一种药物伊班膦酸钠注射液主成分-伊班膦酸的离子色谱分析方法,采用Ion Pac AS18阴离子交换色谱柱,利用在线淋洗液发生器自动产生氢氧化钾梯度淋洗液(12~70 mmol·L~(-1),时间程序为17 min),并使用自动再生抑制型电导检测。结果表明,伊班膦酸浓度在0~75.25?g·m L~(-1)范围内,线性相关系数R2=0.9995,呈现显著的线性相关关系;供试液重复进样5次,峰面积RSD为0.21%,保留时间RSD为0.01%,理论板数均大于50 000,方法系统适用性良好;5份供试样品溶液伊班膦酸含量的RSD值为0.80%,小于等于2.0%,方法重复性良好;供试样品3个浓度水平的回收率均在99%~101%之间,加标回收率试验的RSD均小于1.00%,符合药品规定要求。该方法稳定、重复性好且回收率高,可满足伊班膦酸钠注射液中主成分含量的测定要求。     

串联磁路混合励磁爪极发电机的研究

针对电励磁爪极发电机效率低、永磁爪极发电机磁场调节困难的问题,提出了一种串联磁路混合励磁爪极同步发电机,利用磁路计算方法和三维有限元的分析研究了这种新型电机各部分的磁密大小,确定了合适的极对数和合理的磁钢厚度,探讨了这种新型电机的空载特性、外特性和调节特性.研究表明:串联磁路混合励磁爪极发电机合适的极对数为2,且磁钢厚度存在一个较为合理的优化值.相对于电励磁爪极发电机,它实现了励磁电流的双向控制;相对于永磁爪极发电机它使得输出电压可调,在更宽的负载范围内实现了输出电压的恒定.在参数相同的情况下,与电励磁爪极发电机相比,该电机具有更高的气隙磁密和功率密度.     

The spread of Ras activity triggered by activation of a single dendritic spine

In neurons, individual dendritic spines isolate N-methyl-d-aspartate (NMDA) receptor-mediated calcium ion (Ca2+) accumulations from the dendrite and other spines. However, the extent to which spines compartmentalize signaling events downstream of Ca2+ influx is not known. We combined two-photon fluorescence lifetime imaging with two-photon glutamate uncaging to image the activity of the small guanosine triphosphatase Ras after NMDA receptor activation at individual spines. Induction of long-term potentiation (LTP) triggered robust Ca2+-dependent Ras activation in single spines that decayed in approximately 5 minutes. Ras activity spread over approximately 10 micrometers of dendrite and invaded neighboring spines by diffusion. The spread of Ras-dependent signaling was necessary for the local regulation of the threshold for LTP induction. Thus, Ca2+-dependent synaptic signals can spread to couple multiple synapses on short stretches of dendrite.     

离子交换色谱法测定枇杷果实和叶片中的有机酸

用离子交换色谱法对枇杷有机酸进行有效分离与测定,EG40淋洗液在线发生器能降低背景电导,获得较好的重现性和平稳的基线.测定结果表明,枇杷果实和叶片中有机酸组分和含量有较大差别.果实中以苹果酸为主,其次为奎尼酸和酒石酸,而柠檬酸、草酸和顺乌头酸等含量较低.叶片中以奎尼酸为主,苹果酸、柠檬酸和草酸含量很低.     

Large first hyperpolarizabilities in push-pull polyenes by tuning of the bond length alternation and aromaticity

Conjugated organic compounds with 3-phenyl-5-isoxazolone or N,N'-diethylthiobarbituric acid acceptors have large first molecular hyperpolarizabilities (beta) in comparison with compounds with 4-nitrophenyl acceptors. For example, julolidinyl-(CH=CH)(3)-CH=N,N'- diethylthiobarbituric acid, which has 12 atoms between the donor and acceptor, has a beta(0) of 911 x 10(-30) electrostatic units, whereas (CH(3))(2)NC(6)H(4),-(CH=CH)(4)-C(6)H(4)NO(2), with 16 atoms between its donor and acceptor, has a beta(0) of 133 x 10(-30) electrostatic units. The design strategies demonstrated here have resulted in chromophores that when incorporated into poled-polymer electrooptic modulators exhibited significant enhancements in electrooptic coefficients relative to polymers containing the commonly used dye Disperse Red-1. Poled polymer devices based on these or related chromophores may ultimately lead to high-speed electrooptic switching elements with low drive-power requirements, suitable for telecommunications applications.     

Deep-ultraviolet quantum interference metrology with ultrashort laser pulses

Precision spectroscopy at ultraviolet and shorter wavelengths has been hindered by the poor access of narrow-band lasers to that spectral region. We demonstrate high-accuracy quantum interference metrology on atomic transitions with the use of an amplified train of phase-controlled pulses from a femtosecond frequency comb laser. The peak power of these pulses allows for efficient harmonic upconversion, paving the way for extension of frequency comb metrology in atoms and ions to the extreme ultraviolet and soft x-ray spectral regions. A proof-of-principle experiment was performed on a deep-ultraviolet (2 x 212.55 nanometers) two-photon transition in krypton; relative to measurement with single nanosecond laser pulses, the accuracy of the absolute transition frequency and isotope shifts was improved by more than an order of magnitude.     

利用FPGA实现DDS信号发生器的研究

采用直接数字频率合成技术(DDS),通过数字控制相位信号的增量在FPGA中实现了频率可调的信号发生器。所产生的信号不仅幅度频率灵活可调,而且具有频率分辨率高、频率切换速度快、相位噪声低等优点,因而在有关的科学试验中具有重要意义。     

RP-HPLC同时检测苹果汁中乳酸、富马酸、5-HMF和展青霉素

 【目的】同时定量检测苹果汁中乳酸、富马酸、5-HMF和展青霉素,建立一种基于多通道紫外检测器的反相高效液相色谱（RP-HPLC）分离方法。【方法】采用C18色谱柱（250 mm×4.6 mm ID,5.0 μm）,以pH为2.5的磷酸水溶液和乙腈按95:5混合为流动相,在流速1.00 ml•min-1,温度30℃下进行乳酸、富马酸、5-HMF和展青霉素的色谱分析。【结果】前10 min,两种有机酸在210 nm下被分离和检测;后10 min,5-HMF和展青霉素于276 nm下被分离和检测。检测限分别为: 乳酸0.1790 mg•L-1、富马酸0.0032 mg•L-1、5-HMF 0.0057 mg•L-1和展青霉素0.0089 mg•L-1,保留时间、峰高和峰面积的重现性（n=3）变异系数（CV）均小于1.0%。保留时间的日内重现性（n=3）和日间精密度（n=10）变异系数（CV）分别小于0.09%和0.5%。平均回收率为95.64%～99.17%。【结论】该方法可应用于同时定量检测苹果浓缩汁中乳酸、富马酸、5-HMF和展青霉素。     

毛细管区带电泳法测定中草药中的有机酸

阿魏酸、绿原酸、咖啡酸是三种结构相似的酚酸类化合物,本研究建立了毛细管区带电泳法测定中草药中的阿魏酸、绿原酸、咖啡酸的分析方法,以pH=8.7的150 mmol/L硼酸为缓冲溶液,在0.5 psi进样8 s,分离电压23 kV,检测波长320 nm,温度25℃的条件下进行测定。阿魏酸、绿原酸、咖啡酸的浓度在0.01~0.2 mg/mL范围内与峰面积呈良好的线性关系,线性相关系数分别为0.999,0.997和0.999,其检出限分别为0.2μg/mL、0.4μg/mL和0.2μg/mL(信噪比为3∶1)。该方法用于金银花、蒲公英、蜂胶、感冒止咳颗粒等药物中阿魏酸、绿原酸、咖啡酸含量的测定,其样品平均回收率在96.0%~100.4%之间,取得了满意的结果。     

Electron solvation in two dimensions

Ultrafast two-photon photoemission has been used to study electron solvation at two-dimensional metal/polar-adsorbate interfaces. The molecular motion that causes the excess electron solvation is manifested as a dynamic shift in the electronic energy. Although the initially excited electron is delocalized in the plane of the interface, interactions with the adsorbate can lead to its localization. A method for determining the spatial extent of the localized electron in the plane of the interface has been developed. This spatial extent was measured to be on the order of a single adsorbate molecule.     

基于直接积分最小二乘法的同步发电机的参数辨识

针对同步发电机模型参数中多个不可观测量的存在使得需要求解复杂的微分方程组对电机参数进行辨识,进而导致了辨识困难,提出了一种完全由可观测量表示的同步发电机辨识模型,即状态量均为由发电机出口电流、励磁电压、励磁电流以及功角,转速变量增量表示的可量测量,并基于该模型提出用直接积分最小二乘原理（DILS）来辨识发电机参数.这样既避免了复杂微分方程的求解过程,简化了参数辨识方法,又提高了辨识效率.辨识后,利用MATLAB进行算例仿真,通过实测曲线和辨识曲线的拟合表明了所采用的辨识模型与算法是正确、有效的.     

高效液相色谱法测定中药复方透皮软膏中绿原酸和咖啡酸的含量

建立了同时测定中药复方透皮软膏中绿原酸和咖啡酸含量的高效液相色谱方法.采用Shim-pack VP-ODS( 150 mm×4.6 mm,5 μm)色谱柱,以乙腈和0.1％磷酸溶液(体积比为9∶91)为流动相,等度洗脱,327 nm处检测,绿原酸和咖啡酸分别在0.078～0.786 μg/mL(R2=0.9997)和0.042～0.420 μg/mL (R2=0.999 5)范围内线性关系良好,平均回收率分别为98.95％和100.06％,RSD分别为0.42％和1.35％.结果表明,此方法灵敏度高、操作简便、结果准确、重复性好,可用于中药复方透皮软膏中绿原酸及咖啡酸含量测定.