Time and temperature induced phase transformation in L‐isoleucine hydrochloride monohydrated crystal

Semi organic crystals have been intensively studied aiming applications in nonlinear optical (NLO). Such applicability requires crystals with both high quality and thermal stability, which make the full characterization of this material a topic issue. In this paper, single crystals of L‐isoleucine hydrochloride monohydrated (L‐Ile.H2O.HCl) was synthesized by slow evaporation technique and characterized by thermal analysis and X‐ray diffraction (XRD) measurements. XRD results at 298 K showed that the sample crystallize with the orthorhombic structure, and the lattice parameters obtained by Rietveld refinement were a = 5.873(3) Å, b = 24.814(4) Å, and c = 6.873(5) Å. Thermal analysis measurements shows four decomposition stages between 328 ‐480 K which were associated with loss of water by desolvation, loss crystallization water and decomposition of L‐Ile.HCl. XRD measurements as a function of temperature up to 428 K show an irreversible phase transformation. This transformation was obtained after 32 hours keeping the L‐Ile.HCl.H2O sample at 413 K. The analysis shows that phase transformation occurs due to water and chlorine losses without destroy the amino acid carbon chain and in the end of transformation only the precursor amino acid remains. L‐Ile.HCl.H2O present low thermal stability and the phase transformation is time and temperature dependent.     

Nonlinear analysis of the forced response of a beam with three mode interaction

An analysis is presented for the primary resonance of a clamped-hinged beam, which occurs when the frequency of excitation is near one of the natural frequencies,_n . Three mode interaction (₂ 3₁ and _{3 1} + 2₂) is considered and its influence on the response is studied. The case of two mode interaction (₂ 3₁) is also considered to compare it with the case of three mode interaction. The straight beam experiencing mid-plane stretching is governed by a nonlinear partial differential equation. By using Galerkin's method the governing equation is reduced to a system of nonautonomous ordinary differential equations. The method of multiple scales is applied to solve the system. Steady-state responses and their stability are examined. Results of numerical investigations show that there exists no significant difference between both modal interactions' influences on the responses.     

On some nearly viscometric flows of viscoelastic liquids

Superposition of oscillatory shear imposed from the boundary and through pressure gradient oscillations and simple shear is investigated. The integral fluid with fading memory shows flow enhancement effects due to the nonlinear structure. Closed-form expressions for the change in the mass transport rate are given at the lowest significant order in the perturbation algorithm. The elasticity of the liquid plays as important a role in determining the enhancement as does the shear dependent viscosity. Coupling of shear thinning and elasticity may produce sharp increases in the flow rate. The interaction of oscillatory shear components may generate a steady flow, either longitudinal or orthogonal, resulting in increases in flow rates akin to resonance, and due to frequency cancellation, even in the absence of a mean gradient. An algorithm to determine the constitutive functions of the integral fluid of order three is outlined.Nomenclature A _n Rivlin-Ericksen tensor of order . - A _k Non-oscillatory component of the first order linear viscoelastic oscillatory velocity field induced by the kth wave in the pressure gradient - d Half the gap between the plates - e _x, e _z Unit vectors in the longitudinal and orthogonal directions, respectively - G(s) Relaxation modulus - G History of the deformation - Stress response functional - I() Enhancement defined as the ratio of the frequency dependent part of the discharge to the frequencyindependent part of it at the third order - I ^*() Enhancement defined as the ratio of the increase in discharge due to oscillations to the total discharge without the oscillations - k Power index in the relaxation modulus G(s) - k _i ^–1 Relaxation times in the Maxwell representation of the quadratic shear relaxation modulus (s ₁, s ₂) - m _i ^–1, n _i ^–1 Relaxation times in the Maxwell representations of the constitutive functions ₁(s ₁,s ₂,s ₃) and ₄ (s ₁, s ₂,s ₃), respectively - P Constant longitudinal pressure gradient - p Pressure field - _mx ,⁽³⁾ _nz ,⁽³⁾ Mean volume transport rates at the third order in the longitudinal and orthogonal directions, respectively - ₀,⁽³⁾, ₁,⁽³⁾ Frequency independent and dependent volume transport rates, respectively, at the third order - s = t- Difference between present and past times t and      

Wavelength encoded analytical imaging and fiber optic sensing with pH sensitive CdTe quantum dots

CdTe quantum dots (QDs), capped with mercaptopropionic acid (MPA), were synthesized and the variation of their fluorescence properties (steady state and lifetime) with pH was assessed in solution and when immobilized in a sol-gel host. Three different sizes of CdTe QDs with excited state lifetimes ranging from 42 to 48 ns and with emission maximum at 540 nm (QD₅₄₀), 580 nm (QD₅₈₀) and 625 nm (QD₆₂₅) were selected. The solution pH affects the maximum emission wavelength (shifts to higher wavelengths of 23, 24 and 27 nm for QD₅₄₀, QD₅₈₀ and QD₆₂₅, respectively), the excited state lifetime and the fluorescence intensity in a reversible way. Linearization of the maximum emission wavelength variation with the pH allows the estimation of an apparent ionization constant (pK_a) for each QD: 6.5 ± 0.1 (QD₅₄₀), 6.1 ± 0.5 (QD₅₈₀) and 5.4 ± 0.3 (QD₆₂₅). The variation of the QDs fluorescence properties was further explored using confocal laser scanning microscopy allowing the implementation of a new calibration method for pH imaging in solution. QDs were successfully immobilized on the tip of an optical fiber by dip-coating using sol-gel procedure. The immobilized QDs showed a similar pH behaviour to the one observed in solution and an apparent lifetime of 80, 68 and 99 ns, respectively. The proposed QDs based methodology can be successfully used to monitor pH using wavelength encoded data in imaging and fiber optic sensing applications.     

Redox‐induced configuration conversion for thioacetamide dimer can function as a molecular switch

The electronic switching properties of thioacetamide dimer (TAD) were investigated using the nonequilibrium Green's function method combined with density functional theory for design of a novel molecular switch. The H‐bonded TAD can be converted upon hole‐trapping to a three‐electron (3e)‐bonded configuration with a S∴S linkage which could provide a more favorable channel for charge transfer than the before. The redox‐induced configuration conversion between the H‐bonded and the 3e‐bonded TADs could govern the charge migration through the molecular junction with a considerable difference in conduction currents. The calculated I–V characteristic curves of two configurations exhibit a switching behavior with an On‐Off ratio in a range of about 4.3–7.6 within the applied voltages. Clearly, this hypothetical scheme provides a potential way to explore the novel conformation‐dependent molecular switch. © 2010 Wiley Periodicals, Inc. J Comput Chem 2010     

Harmonic and intermodulation performance of optical-fiber Mach–Zehnder microphone

In this paper, closed-form mathematical expressions are obtained for the amplitudes of the harmonic and intermodulation products of the fiber optic Mach–Zehnder microphone excited by a multitone acoustical perturbation. The results show the strong dependence of the harmonic and intermodulation performance on the amplitude of the acoustical perturbation tones and the phase shift produced by the DC bias voltage applied to the reference fiber of the Mach–Zehnder interferometer. The results also show that depending on the phase shift produced by the DC bias voltage, either the third-order or the second-order intermodulation will be dominant. Compared to previously published results for other types of microphones, it appears that the phase shift produced by the DC bias voltage plays an important role in deciding the order of the dominant intermodulation product.     

60 GHz Radio over Fiber Technology for Wireless Access by employing Narrow-Angle PSK Modulation

This paper investigates two key techniques used in 60 GHz Radio over Fiber (RoF) technology for wireless access, namely, the generation of 60 GHz signals and the distribution of 60 GHz local oscillator (LO). In the proposed model, a 60 GHz PSK signal is generated by a heterodyne of two subcarriers with narrow-angle PSK (NA-PSK) modulation, whose phase shift is equal to one half that of a normal PSK signal. Then we use a 60 GHz mixer to frequency mix two PSK signals in two different bands, 60 GHz and baseband. By doing this, the modulation information can be fully eliminated, resulting in a 60 GHz LO. In the wireless terminal, coherent demodulation is realized by a self-mixing of the transmitted 60 GHz PSK signal and LO. Thus no millimeter-wave (mm-wave) band oscillator is needed in the wireless terminal.     

两轴光电跟踪仪高仰角跟踪盲区分析

 从轴准直误差、动态滞后误差两方面分析了采用俯仰轴叠加于方位轴光机座结构方式的光电跟踪仪在高俯仰角跟踪时的误差变化及由此导致的盲区问题,从轴准直误差和动态滞后误差两方面对高仰角跟踪盲区的形成及其空间分布进行分析,并用MATLAB进行了仿真,给出跟踪盲区随方位、俯仰角变化的的分布图形。从盲区分布图形可以看出：光电跟踪仪在性能一定的情况下,跟踪盲区随着仰角增大而增大,并结合直线航路给出这两种误差导致的跟踪盲区的计算方法。跟踪直线航路实验数据显示跟踪误差随着仰角增大而增大。     

车辆寻北车长镜的设计与实现

 描述了一种车辆寻北车长镜的设计,采用2个光纤陀螺和2个加速度计,解决了惯性测量组件力学编排结构设计与寻北、瞄准线稳定共享陀螺信息的问题,设计系统控制流程和组合算法,在保障车长镜瞄准线稳定精度的同时,增加了车体方位平台非调平状态下任意位置的寻北功能,寻北方法是：车长镜方位固定四位置转动,每个位置点停止、延迟、数据采样、存储,四位置转动完毕后,对存储数据组合、滤波、解算,输出寻北结果。对方案设计、实现途径和解算推导方法作了详细论述,性能测试验证设计实现达到预期效果。     

Investigation of morphology selection for CBr_4-C_2Cl_6 alloy in three dimensions with multi-phase field method

With the multi-phase field model, the unidirectional solidification with constant velocity growth and variable velocity growth of the CBr4-C2Cl6 eutectic alloy is simulated in three dimensions. The simulated results with constant velocity growth show that with the increase of pulling velocity, the morphology of the CBr4-C2Cl6 alloy evolves in the sequence of lamellar merging →lamellar-rod transition→stable lamellar growth→oscillating growth→lamellar branching. A morphology selection map is established with ...