Solvent Effect on Characteristic Vibration of IR Spectrum of 4,4'-Dibromodiphenyl Ether

The optimal geometry, IR spectrum and vibration assignment of 4,4＇-dibromodiphenyl ether（BDE-15） in gas phase were calculated via the density functional theory（DFT） at the level of B3LYP/6-3 l＋G（d）. Based on the vi- bration assignment, the calculation of vibration frequencies and intensities of 5 main vibration types of BDE-15 in 25 kinds of solvents was carried out by means of a self-consistent reaction field（SCRF） theoretical model at the level of B3LYP/6-31＋G（d） to analyze the solvent effect on the vibration of IR spectrum of BDE-15. To study the solvent ef- fect further, C--O asymmetric stretching vibration fluctuating, which is relatively acute in both vibration frequency and intensity, was selected as the characteristic vibration to establish different linear solvation energy relation（LSER） models for solvent categoring. Solvent parameters（a, /3, ~r＊）, acceptable number（AN） and quantitative structure- activity relationship（QSAR） models were established via chemical quantum parameters of solvent moleculer, which were first been introduced to investigate different solvent-solute interaction mechanisms in alcoholic and non-alcoholic solvents on molecular level. At last, a single solvent molecule was embedded in the framework of po- larizable continuum model（PCM） to validate the effect of hydrogen bonding on solvent-solute interaction in alcohol solvents. The obtained results show that 5 main vibration types of BDE-15 in different solvents have small variation range in frequency and intensity and all the vibration frequencies in solvents are lower than those in gas phase, de- creasing along with the increasing of the dielectric Constant（e） of solvents exponentially. In contrast, all the vibration intensities in solvents are greater than those in gas phase and present positive exponential trend. Twenty-five solvents were divided into two categories（non-alcoholic solvents and alcoholic solvents） by LSER. The CmO asymmetric stretching vibration was mainly reg     

Properties of acoustic resonance in double-actuator ultra-sonic gas nozzle: numerical study

The ultra-sonic gas atomization(USGA) nozzle is an important apparatus in the metal liquid air-blast atomization process.It can generate oscillating supersonic gas efflux,which is proved to be effective to enforce the atomization and produce narrow-band particle distributions.A double-actuator ultra-sonic gas nozzle is proposed in the present paper by joining up two active signals at the ends of the resonance tubes.Numerical simulations are adopted to study the effects of the flow development on the acoustic resonant properties inside the Hartmann resonance cavity with/without actuators.Comparisons show that the strength and the onset process of oscillation are enhanced remarkably with the actuators.The multiple oscillating amplitude peaks are found on the response curves,and two kinds of typical behaviors,i.e.,the Hartmann mode and the global mode,are discussed for the corresponding frequencies.The results for two driving actuators are also investigated.When the amplitudes,the frequencies,or the phase difference of the input signals of the actuators are changed,the oscillating amplitudes of gas efflux can be altered effectively.     

Wind induced deformation and vibration of a Platanus acerifolia leaf

Deformation and vibration of twig-connected single leaf in wind is investigated experimentally.Results showthat the Reynolds number based on wind speed and lengthof leaf blade is a key parameter to the aerodynamic problem.In case the front surface facing the wind and with an increase of Reynolds number,the leaf experiences static deformation,large amplitude and low frequency sway,reconfiguration to delta wing shape,flapping of tips,high frequencyvibration of whole leaf blade,recovery of delta wing shape,and twig-leaf coupling vibration.Abrupt changes from onestate to another occur at critical Reynolds numbers.In casethe back surface facing the wind,the large amplitude andlow frequency sway does not occur,the recovered delta wingshape is replaced by a conic shape,and the critical Reynoldsnumbers of vibrations are higher than the ones corresponding to the case with the front surface facing the wind.Apair of ram-horn vortex is observed behind the delta wingshaped leaf.A single vortex is found downstream of theconic shaped leaf.A lift is induced by the vortex,and thislift helps leaf to adjust position and posture,stabilize bladedistortion and reduce drag and vibration.     

纵振驱动球面弯曲振动超声聚焦系统的聚焦特性*

为了将超声聚焦效应应用于工业加工中的冷却技术中,该文提出一种由夹心式换能器纵向振动驱动球面弯曲振动超声聚焦系统。基于基尔霍夫-亥姆霍兹声场理论分析了由换能器中心面纵向振动和球面弯曲振动组成的复合超声振动条件下的声场聚焦特性,并通过实验进行验证。研究结果表明,该聚焦系统具有显著的聚焦特性,球面弯曲振动将声能汇聚在声场焦区;当声场相位相同时,换能器中心面纵向振动和球面弯曲振动产生的声场在焦区发生叠加,可以进一步提高焦区声压;减小换能器中心面半径和球面曲率半径、增加球面开口半径可以增强复合超声振动的聚焦效果。     

Vibration control of nonlinear Absorber–Isolator-Combined structure with time-delayed coupling

A nonlinear combined structure consisted of isolator and absorber with time-delayed coupling active control is proposed in this study, whose vibration suppression effectiveness and control mechanism are investigated. The mathematical model of the combined structure is obtained and stability analysis for different structural parameters and time delay are firstly carried out, which provides a general guideline for the ranges of active control parameters. Then the combined effect of nonlinearity and time delay on vibration suppression and energy transfer is discussed in details based on the analysis of control mechanism by the method of multiple scales. Since the time-delayed nonlinear absorber can induce internal resonance between different modes, the vibration energy at low frequencies can be transferred to high frequency mode and the vibration of the fundamental frequency range is thus suppressed. This paper provides a novel application of internal resonance in vibration suppression of an Absorber–Isolator-Combined structure.     

Thermomechanical bending and free vibration of single-layered graphene sheets embedded in an elastic medium

In the present paper, the sinusoidal shear deformation plate theory (SDPT) is reformulated using the nonlocal differential constitutive relations of Eringen to analyze the bending and vibration of the nanoplates, such as single-layered graphene sheets, resting on two-parameter elastic foundations. The present SDPT is compared with other plate theories. The nanoplates are assumed to be subjected to mechanical and thermal loads. The equations of motion of the nonlocal model are derived including the plate foundation interaction and thermal effects. The governing equations are solved analytically for various boundary conditions. Nonlocal theory is employed to bring out the effect of the nonlocal parameter on the bending and natural frequencies of the nanoplates. The influences of nonlocal parameter, side-to-thickness ratio and elastic foundation moduli on the displacements and vibration frequencies are investigated.     

Ultrawide low frequency band gap of phononic crystal in nacreous composite material

The band structure of a nacreous composite material is studied by two proposed models, where an ultrawide low frequency band gap is observed. The first model (tension-shear chain model) with two phases including brick and mortar is investigated to describe the wave propagation in the nacreous composite material, and the dispersion relation is calculated by transfer matrix method and Bloch theorem. The results show that the frequency ranges of the pass bands are quite narrow, because a special tension-shear chain motion in the nacreous composite material is formed by some very slow modes. Furthermore, the second model (two-dimensional finite element model) is presented to investigate its band gap by a multi-level substructure scheme. Our findings will be of great value to the design and synthesis of vibration isolation materials in a wide and low frequency range. Finally, the transmission characteristics are calculated to verify the results.     

Correction strategy for diffusion-weighted images corrupted with motion: application to the DTI evaluation of infants' white matter

Objective

Diffusion imaging techniques such as DTI and HARDI are difficult to implement in infants because of their sensitivity to subject motion. A short acquisition time is generally preferred, at the expense of spatial resolution and signal-to-noise ratio. Before estimating the local diffusion model, most pre-processing techniques only register diffusion-weighted volumes, without correcting for intra-slice artifacts due to motion or technical problems. Here, we propose a fully automated strategy, which takes advantage of a high orientation number and is based on spherical-harmonics decomposition of the diffusion signal.

Material and methods

The correction strategy is based on two successive steps: 1) automated detection and resampling of corrupted slices; 2) correction for eddy current distortions and realignment of misregistered volumes. It was tested on DTI data from adults and non-sedated healthy infants.

Results

The methodology was validated through simulated motions applied to an uncorrupted dataset and through comparisons with an unmoved reference. Second, we showed that the correction applied to an infant group enabled to improve DTI maps and to increase the reliability of DTI quantification in the immature cortico-spinal tract.

Conclusion

This automated strategy performed reliably on DTI datasets and can be applied to spherical single- and multiple-shell diffusion imaging.     

Investigations on vibration characteristics of two-layered piezoceramic disks

This paper investigates the transverse and planar vibration characteristics of two-layered piezoceramic disks for traction-free boundary conditions by theoretical analysis, finite element numerical calculation, and experimental measurements. Amplitude-fluctuation electronic speckle pattern interferometry (AF-ESPI), laser Doppler vibrometer (LDV), and impedance analysis were used to perform measurements and verify the theoretical solutions for extensional, tangential, and transverse vibrations. The poling direction of piezoelectric elements determines whether they are denoted as either of series- or parallel-type. This study observed that the resonant frequencies and mode shapes of the series- and parallel-type piezoceramic disks present different dynamic characteristics in resonance. Planar and transverse vibrations are coupled in series-type piezoceramic disks and uncoupled in those of parallel-type. Good agreements of dynamic characteristics determined by theoretical analysis, experimental measurements, and numerical calculation are presented for series- and parallel-type piezoceramic disks.