Quasi-phase-matched second-harmonic generation by use of a total-internal-reflection phase shift in gallium arsenide and zinc selenide plates

We fabricated a novel quasi-phase-matched frequency converter, using a zigzag optical beam path in a thin, polished parallel plate. Second-harmonic generation experiments demonstrated angle-tuned output at 4.6 to 5.3mum in GaAs and 1.7 to 2.0mum in ZnSe crystals when pulsed infrared laser sources were used.     

Global Analysis of Dynamic Fluorescence Anisotropy by a Polarized Phasor Approach

Recently, the graphical analysis of the fluorescence lifetime imaging using the phasor approach has been highlight, and a series of the reports have made it on the way for the applications by the nonprofessionals. In this paper, we put forward a similar theory validated by the experiments for the dynamic fluorescence anisotropy imaging. By subtracting the perpendicular component from the parallel one in the frequency-domain polarization measurement, we deduce a new analytical expression about the fluorescence joint time, and find that as much as the fluorophore is a single exponential decay and $ {r_\infty } $ is equal to zero, ??I(t) is a single exponential decay with the time constant X as well, and the center of its histograms is located on the semicircle in the polarized phasor plot. In the end, we conclude that the fluorescence joint time is the best parameter to weigh the fluorescence dynamics for the macromolecules.     

The microwave spectrum of methyl chlorodifluoroacetate: Methyl internal rotation and chlorine nuclear electric quadrupole coupling

A chirped pulse microwave spectrometer has been used to record microwave spectra of the ³⁵Cl and ³⁷Cl isotopologues of methyl chlorodifluoroacetate, CClF₂C(O)OCH₃, between 8 GHz and 16 GHz. The target compound was spectroscopically examined as it participated in a supersonic expansion of argon. Only one conformer was observed. The rotational spectra were recorded with sufficient resolution to observe (i) splittings due to the internal rotation of the methyl group, and (ii) splittings from the coupling of the chlorine quadrupolar nucleus. A total of 785 transitions have had quantum numbers assigned. Analysis of the spectra observed has produced an experimental barrier to the methyl group internal rotation, V₃, of 370(2) cm⁻¹. It is noted that this barrier is a little lower than that determined for methyl acetate [V₃ = 425 cm⁻¹, J. Sheridan, W. Bossert and A. Bauder, J. Mol. Spectrosc., 80 (1980) 1-11], and this is rationalized through a comparison of molecular structures. Lastly, all components of both the ³⁵Cl and ³⁷Cl chlorine nuclear electric quadrupolar coupling tensor have been determined.     

Forward- and reverse-synthesis of piperazinopiperidine amide analogs: a general access to structurally diverse 4-piperazinopiperidine-based CCR5 antagonists

Piperazinopiperidine amide analogs are among the most promising CCR5 antagonists. As an effective extension of a previously-reported methodology to synthesize such compounds, forward- and reverse-syntheses were successfully developed in which the convergent synthesis of the piperazinopiperidine nucleus, with a building block of 4-substituent-4-aminopiperidine, served as a common key step. The two-way approach affords a comprehensive access to the piperazinopiperidine templated library with variation on the pharmacophore sites. Thus, a SAR study of our synthesized piperazinopiperidine-based CCR5 antagonists was conducted with respect to the structure and configuration of the substituent on the piperazine ring. The S-configuration of the benzylic-substituent is vital for the CCR5 binding, and the bulky or aryl substituent on the 2-position in the piperazine ring is detrimental to the activity. By using the forward-synthesis approach, the best compound in the chiral piperazine-based CCR5 antagonist series, Sch-D (Vicriviroc), was conveniently synthesized in an excellent yield.     

Direct experimental evidence for atomic tunneling of europium in crystalline Eu8Ga16Ge30

M?ssbauer-effect and microwave absorption experimental evidence unambiguously demonstrates the presence of slow, approximately 450 MHz, tunneling of magnetic europium between four equivalent sites in Eu8Ga16Ge30, a stoichiometric clathrate. Remarkably, six of the eight europium atoms, or 11% of the constituents in this solid, tunnel between these four sites separated by 0.55 A. The off centering of the atoms or ions in crystalline clathrates appears to be a promising route for producing Rabi oscillators in solid-state materials.     

A disk-pivot structure micro piezoelectric actuator using vibration mode B11

Micro piezoelectric actuator using vibration mode B(11) (B(mn), where m is the number of nodal circles, n is the nodal diameters) is designed. Different from conventional wobble-type ultrasonic motor using piezoelectric rod or cylinder, piezoelectric disc is used to excite wobble modes and metal cylinder stator is used to amplify the transverse displacement, metal rod rotor is actuated to rotate. The outer diameter of the actuator is 14mm. There are features such as low drive voltage, micromation, and convenient control of wobble state by modifying the structure of stator, etc. Finite element analysis (FEA) of the stator has been made. It is found that the resonant frequency of vibration mode B(11) is 49.03kHz, which is measured at 45.7kHz by the laser vibrometer and impedance analyzer. The rotation speed has been measured, which could be as high as 10,071rpm under an alternating current 100V. Such piezoelectric actuator can be optimized and adjusted to fit practical conditions. It can be applied in the fields of precise instrument, bioengineering and other micro actuator system.     

Do Reuss and Voigt bounds really bound in high-pressure rheology experiments?

Energy dispersive synchrotron x-ray diffraction is carried out to measure differential lattice strains in polycrystalline Fe(2)SiO(4) (fayalite) and MgO samples using a multi-element solid state detector during high-pressure deformation. The theory of elastic modelling with Reuss (iso-stress) and Voigt (iso-strain) bounds is used to evaluate the aggregate stress and weight parameter, α (0≤α≤1), of the two bounds. Results under the elastic assumption quantitatively demonstrate that a highly stressed sample in high-pressure experiments reasonably approximates to an iso-stress state. However, when the sample is plastically deformed, the Reuss and Voigt bounds are no longer valid (α becomes beyond 1). Instead, if plastic slip systems of the sample are known (e.g.?in the case of MgO), the aggregate property can be modelled using a visco-plastic self-consistent theory.     

Enantioselective construction of quaternary carbon centre catalysed by bifunctional organocatalyst

The bifunctional thiourea-tertiary amine derivatives of simple chiral diamines serve as highly enantioselective catalysts for the Michael addition of alpha-substituted cyanoacetates to vinyl sulfones, giving an efficient protocol for the construction of an all-carbon substituted quaternary stereocentre.     

Aligned porous materials by directional freezing of solutions in liquid CO2

We report here a method for generating structures with aligned macropores by templating solidified carbon dioxide. The CO2 template phase can be removed by direct sublimation to yield a dry, solvent-free porous material that may be useful in applications such as tissue engineering and aligned cell growth.     

纳米结构链的hopping电导实空间重正化群方法

基于Miller-Abrahams理论,发展了一种重正化群方法,研究了一维纳米结构体系的hopping电导.研究表明在纳米结构体系中晶粒种类、晶粒尺寸对hopping电导有显著的调制作用,界面结构及晶格畸变等对hopping电导也有不同程度的影响.