Vibrational analysis of boldine hydrochloride using QM/MM approach

A complete vibrational analysis was performed on the molecular structure of boldine hydrochloride using QM/MM method. The equilibrium geometry, harmonic vibrational frequencies and infrared intensities were calculated by QM/MM method with B3LYP/6-31G(d) and universal force field (UFF) combination using ONIOM code. We found the geometry obtained by the QM/MM method to be very accurate, and we can use this rapid method in place of time consuming ab initio methods for large molecules. A detailed interpretation of the infrared spectra of boldine hydrochloride is reported. The scaled theoretical wave numbers are in perfect agreement with the experimental values. The FT-IR spectra of boldine hydrochloride in the region 4000-500 cm(-1) were recorded in CsI (solid phase) and in chloroform with concentration 5 and 10 mg/ml.

The Alfvén Wave Equation for Magnetospheric Plasmas

It is shown that besides the continuous spectrum which damps away as inverse power of time, the coupled Alfvén wave equation, which gives coupling between a shear Alfvén wave and a surface wave, can also admit a well behaved harmonic solution in the closed form for a set of initial conditions. This solution, though valid for finite time intervals, points out that the Alfvén surface waves can have a band of frequency (instead of a monochromatic frequency for a nonsheared magnetic field) within which the local field line resonance frequency can lie, and thus can excite magnetic pulsations with latitude-dependent frequency. By considering magnetic fields not only varying in magnitude but also in direction, it is shown that the time interval for the validity of the harmonic solution depend upon the angle between the magnetic field directions on either side of the magnetopause. For small values of the angle the time interval can become appreciably large.

The behaviour of excited plane jets

A plane subsonic jet can be excited to entrain more fluid from its surroundings by subjecting it to antisymmetric periodic disturbances. The essential feature in this phenomenon is the rolling-up motion of an initially flapping jet to form large vortices which are responsible for greater entrainment. Several methods developed to impart oscillations to the flow at the nozzle, such as the acoustic pressure oscillator, the vibration of a single vane in the potential core region, the reciprocating lip system and the twin vane exciter, are described in this article. A minimum threshold in amplitude is necessary for exciting the flow. However, the frequency of oscillation is much less than that predicted by stability considerations.

Correlation of helicopter rotor aeroelastic response with HART-II wind tunnel test data

Purpose - This paper aims to validate a comprehensive aeroelastic analysis for a helicopter rotor with the higher harmonic control aeroacoustic rotor test (HART-II) wind tunnel test data. Design/methodology/approach - Aeroelastic analysis of helicopter rotor with elastic blades based on finite element method in space and time and capable of considering higher harmonic control inputs is carried out. Moderate deflection and coriolis nonlinearities are included in the analysis. The rotor aerodynamics are represented using free wake and unsteady aerodynamic models. Findings - Good correlation between analysis and HART-II wind tunnel test data is obtained for blade natural frequencies across a range of rotating speeds. The basic physics of the blade mode shapes are also well captured. In particular, the fundamental flap, lag and torsion modes compare very well. The blade response compares well with HART-II result and other high-fidelity aeroelastic code predictions for flap and torsion mode. For the lead-lag response, the present analysis prediction is somewhat better than other aeroelastic analyses. Research limitations/implications - Predicted blade response trend with higher harmonic pitch control agreed well with the wind tunnel test data, but usually contained a constant offset in the mean values of lead-lag and elastic torsion response. Improvements in the modeling of the aerodynamic environment around the rotor can help reduce this gap between the experimental and numerical results. Practical implications - Correlation of predicted aeroelastic response with wind tunnel test data is a vital step towards validating any helicopter aeroelastic analysis. Such efforts lend confidence in using the numerical analysis to understand the actual physical behavior of the helicopter system. Also, validated numerical analyses can take the place of time-consuming and expensive wind tunnel tests during the initial stage of the design process. Originality/value - While the basic physics appears to be well captured by the aeroelastic analysis, there is need for improvement in the aerodynamic modeling which appears to be the source of the gap between numerical predictions and HART-II wind tunnel experiments.

Applications of reverse saturable absorbers in laser science

A variety of applications exist for reverse saturable absorbers (RSAs) in the area of optical pulse processing and computing. An RSA can be used as power limiter/pulse smoother and energy limiter/pulse shortner of laser pulses. A combination of RSA and saturable absorber (SA) can be used for mode locking and pulse shaping between high power laser amplifiers in oscillator amplifier chain. Also, an RSA can be used for the construction of a molecular spatial light modulator (SLM) which acts as an input/output device in optical computers. A detailed review of the theoretical studies of these processes is presented. Current efforts to find RSAs at desired wavelength for testing these theoretical predictions are also discussed.

Crystal Chemistry of the Noncentrosymmetric Eulytites: A(3)Bi(XO4)(3) (X = V, A = Pb; X = P, A = Ca, Cd, Sr, Pb)

Eulytite compounds, A(3)Bi(XO4)(3) (X = P, A = Ca, Cd, Sr, Pb), belong to the noncentrosymmetric space group l (4) over bar 3d (No. 220) as determined by single-crystal X-ray diffraction studies. The crystals were grown from the melt-cool technique with considerable difficulty as the compounds melt incongruently at their melting temperature, except for the compound Pb3Bi(PO4)(3). The unit cell parameter a is 9.984(5), 9.8611(3), 10.2035(3), and 10.3722(2) angstrom for Ca3Bi(PO4)(3), Cd3Bi(PO4)(3), Sr3Bi(PO4)(3), and Pb3Bi(PO4)(3) respectively, and there are four formula units in the unit cell. The structure of Pb3Bi(VO4)(3), a unique eulytite with vanadium substitution, is compared with all these phosphorus substituted eulytites. The A(2+) and Bi3+ cations occupy the special position (16c) while the O anions occupy the general Wyckoff position (48e) in the crystal structure. Only one O position has been identified for Pb3Bi(PO4)(3) and Pb3Bi(VO4)(3), whereas two O atom sites were identified for Ca3Bi(PO4)(3), Cd3Bi(PO4)(3), and Sr3Bi(PO4)(3). The UV-vis diffuse reflectance spectra indicate large band gaps for all the phosphate eulytites while a lower band gap is observed for the vanadate eulytite. The feasibility of the use of these compounds in optoelectronic devices has been tested by measuring the second-harmonic generation (SHG) values which have been found to be of a magnitude equivalent to the commercially used KDP (KH2PO4).

Narrowband random excitation of a limit cycle system

The response of the Van der Pol oscillator to stationary narrowband Gaussian excitation is considered. The central frequency of excitation is taken to be in the neighborhood of the system limit cycle frequency. The solution is obtained using a non-Gaussian closure approximation on the probability density function of the response. The validity of the solution is examined with the help of a stochastic stability analysis. Solution based on Stratonovich''s quasistatic averaging technique is also obtained. The comparison of the theoretical solutions with the digital simulations shows that the theoretical estimates are reasonably good.

Studies on nonlinear optical materials: structure of diphenylmethyl (Z)-1-(1-methylthio-2-nitrovinyl)tetrahydropyrrole-2-carboxylate

C21H22N2045, M r = 398.5, orthorhombic, P212~21, a = 9.799 (1), b = 11.853 (1), c = 17.316(2)/~, V=2011.4A 3, Z=4, Dm=l.320, Dx=1.314Mgm -3, CuKa, A=1.5418A, Iz= 1.63 ram-1, F(000) = 840.0, T = 293 K, R = 0.055 for 1735 significant reflections. In the 1-methylthio-2- nitrovinyl moiety the C--C bond, 1.368 (7)A, is significantly longer than in ethylene, 1.336 (2)/~. The second harmonic generation (SHG) efficiency of this compound is only 0.25 of the urea standard. The correlation between the molecular packing and SHG is discussed.

Principle of a Dual Current Source Converter for AC Motor Drives

The principle of operation of a dual current source converter is briefly explained. The combination of two single current source converters (SCSC) to form a ``dual (duplex) current source converter'' (DCSC) is proposed. The DCSC is shown to have the following merits: 1) it retains all the advantages of the SCSC; 2) it reduces the harmonic content of the current waveform considerably; and 3) since the load current is shared equally between two current source converters, ratings of the individual components employed in the circuit are considerably lowered. A DCSC can be an attractive choice for sophisticated large horsepower drives where a good performance of the drive rather than cost is a prime factor. An open-loop control scheme employing the DCSC for an ac motor drive has been successfully implemented in the laboratory. Oscillograms of the improved load current waveforms are shown.

Temperature and pressure dependence of 35Cl NQR in NaClO3 and Ba(ClO3)2·H2O

Pressure and temperature dependence of 35Cl nuclear quadrupole resonance (NQR) has been investigated in NaClO3 and Ba(ClO3)2·H2O. NQR frequencies are measured in the temperature range 77–300 K and up to 5 kbar pressure. The torsional frequency of the ClO3 pyramid and its variation with both pressure and temperature are evaluated from the NQR frequencies under the harmonic approximation. In general, the pressure effect on the internal motions is found to be less in Ba (ClO3)2·H2O compared to NaClO3. When the samples are cooled to 77 K the pressure coeffecient of NQR frequency becomes nearly zero in sodium chlorate, whereas it retains a value of 6 kHz kbar−1 in barium chlorate. This behaviour follows from the fact that at 77K, the torsional frequency in NaClO3 is unaffected by the application of pressure while it increases at the rate 12 cm−1 kbar−1 in Ba(ClO3)2·H2O.

A New Liquid Level Sensor for Process-Control Applications

Many process-control systems are air-operated. In such an environment, it would be desirable and economical to use pneumatic sensors. Bubble-back pressure sensors perform quite satisfactorily, but in case of viscous inflammable and slurry-like liquids with a tendency to froth, this level sensor is inadequate. The method suggested in this paper utilizes a pneumatic capacitor, one boundary of which is formed by the liquid level, to modulate a fluid amplifier feedback oscillator. The absence of moving parts and economy obtained makes this method attractive for process-control applications. The system has been mathematically modeled and simulated on an IBM 360/44 digital computer. Experimental values compare fairly well with the theoretical results. For the range tested, the sensor is found to have a linear frequency variation with the liquid level Extended running in the laboratory shows that the system is very reliable. This system has been found insensitive to temperature variations of up to 15ðC.

Diffraction of a cylindrical pulse by a half plane under mixed boundary conditions

The general time dependent source problem has been solved by the method of transforms (Laplace, Lebedev–Kontorovich in succession) and the solution is obtained in the form of an infinite series involving Legendre functions. The solutions in the case of harmonic time dependence and the incident plane wave have been derived from the above solution and are presented in the form of an infinite series. In the case of an incident plane wave, the series has been summed and the final solution involves an improper integral which behaves like a complementary error function for large values of the argument. Finally, the far field evaluation has been shown. The results are compared with those of Sommerfeld's half-plane diffraction problem with unmixed boundary conditions.

Filter Optimization for Grid Interactive Voltage Source Inverters

Higher order LCL filters are essential in meeting the interconnection standard requirement for grid-connected voltage source converters. LCL filters offer better harmonic attenuation and better efficiency at a smaller size when compared to the traditional L filters. The focus of this paper is to analyze the LCL filter design procedure from the point of view of power loss and efficiency. The IEEE 1547-2008 specifications for high-frequency current ripple are used as a major constraint early in the design to ensure that all subsequent optimizations are still compliant with the standards. Power loss in each individual filter component is calculated on a per-phase basis. The total inductance per unit of the LCL filter is varied, and LCL parameter values which give the highest efficiency while simultaneously meeting the stringent standard requirements are identified. The power loss and harmonic output spectrum of the grid-connected LCL filter is experimentally verified, and measurements confirm the predicted trends.

Frequency-comb-referenced molecular spectroscopy in the mid-infrared region

A simple method for absolute frequency measurements of molecular transitions in the mid-infrared region is reported. The method is based on a cw singly-resonant optical parametric oscillator (SRO), which is tunable from 3.2 to 3.45 µm. The mid- infrared frequency of the SRO is referenced to an optical frequency comb through its pump and signal beams. Sub-Doppler spectroscopy and absolute frequency measurement of the P(7) transition of the ν3 band of CH4 are demonstrated.

Diffraction of a cylindrical pulse by a metallic half plane

A direct transform technique is applied to the initial and boundary value problem involving diffraction of a cylindrical pulse by a half plane, on which impedance type of boundary conditions must be met by the total field. The solution to the time harmonic incident plane wave is deduced as a particular case of the general time-dependent problem considered here and we avoid the Wiener–Hopf technique which leads to very complicated factorization and which masks the role of the impedance factor Z′ (a small quantity) in the expression for the scattered field.