Ragged oscillation death in coupled nonidentical oscillators

In this paper, the effect of spatial frequencies distributions on the oscillation death in a ring of coupled nonidentical oscillators is studied. We find that the rearrangement of the spatial frequencies may deform the domain of oscillation death and give rise to a ragged oscillation death in some parameter spaces. The usual critical curves with shape V in the parameter space of frequency-mismatch vs coupling-strength may become the shape W (or even shape WV). This phenomenon has been not only numerically observed in coupled nonidentical nonlinear systems, but also well supported by our theoretical analysis.     

A comparison of measured room acoustics metrics using a spherical microphone array and conventional methods

The traditional microphone configuration used to measure room impulse responses (IRs) according to ISO 3382:2009 is an omnidirectional and figure-8 microphone pair. IRs measurements were taken in a 2500-seat auditorium to determine how the results from a spherical microphone array (an mh acoustics Eigenmike-em32) compare to those from the traditional microphone setup (a Brüel & Kjær Type-4192 omnidirectional microphone and a Sennheiser MKH30 figure-8 microphone). Measurements were obtained at six receiver locations, with three repetitions each in order to first evaluate repeatability. The metrics considered in this study were: reverberation time (T30), early decay time (EDT), clarity index (C80), strength (G), lateral energy fraction (J_LF) and late lateral energy level (L_J). Before calculating these quantities, the IRs were filtered to equalize the frequency response of the microphones and sound source. For the spherical array measurements, the omnidirectional (monopole) and figure-8 (dipole) patterns were extracted using beamforming. In terms of repeatability, the average standard deviation of the three measurements at each receiver location averaged across all metrics, receivers, and octave bands was found to be 0.01 just noticeable differences (JNDs). The analysis comparing the measurements from the two microphone configurations yielded differences which were less than 1 JND for the majority of metrics, with a few exceptions of EDT and C80 slightly above 1 JND. Based on this case study, these results indicate that spherical microphone arrays can be used to obtain valid room IR measurements, which will allow for the development of new metrics utilizing the higher spatial resolution made possible with spherical arrays.     

Improving the sharpness of a non-uniformly illuminated image by an integral mask-filtering approach

We demonstrate an extended mask-filtering approach to improve the sharpness of an image with non-uniform illumination. The proposed method comprises two different masks which cope with higher and lower spatial frequencies respectively. By using this integral algorithm, the enhanced image has much better performance than that derived from the conventional technique.     

Evaluation of three interventions teaching area measurement as spatial structuring to young children

We evaluated the effects of three instructional interventions designed to support young children’s understanding of area measurement as a structuring process. Replicating microgenetic procedures we used in previous research with older children to ascertain whether we can build these competencies earlier, we also extended the previous focus on correctness to include analyses of children’s use of procedural and conceptual knowledge and examined individual differences in strategy shifts before and after transitions, enabling a more detailed examination of the hypothesized necessity of development through each level of a learning trajectory. The two experimental interventions focused on a dynamic conception of area measurement while also emphasizing unit concepts, such as unit identification, iteration, and composition. The findings confirm and extend earlier results that seeing a complete record of the structure of the 2D array—in the form of a drawing of organized rows and columns—supported children’s spatial structuring and performance.     

Effect of variation in signal amplitude and transit time on reliability analysis of ultrasonic time of flight diffraction characterization of vertical and inclined cracks

The variation of amplitude and transit time of the diffracted signal from the crack-tip in complex geometry components and their resulting effect on the probability of detection (POD) and probability of sizing (POS) was studied. The diffracted signal amplitude has been evaluated from the standard expressions for diffraction coefficient, spatial attenuation and the transit time from the respective mathematical models for both vertical and inclined cracks. The same parameters namely the signal amplitude and the transit time have been measured through experiments conducted on simulated test specimens. It has been observed that the analytical and experimental results compare well with each other. Based on this result the trend and shape (width of the transition zone) of the POD/POS curves can be predicted.     

The anisotropic effect of functional groups in H NMR spectra is the molecular response property of spatial NICS—the frozen conformational equilibria of 9-arylfluorenes

Rotation about the single bond adjoining the aryl and fluorene moieties in 9-arylfluorenes can be frozen out on the NMR timescale if methyl groups are located at either one or both of the ortho positions of the aryl substituent. In the ground-state of these rotamers, the planes of the aryl and fluorene moieties are perpendicular to each other and the methyl substituents are consequently positioned either above the fluorene moiety or in-plane with it; thus, the methyl protons are either shielded or deshielded, respectively, due to the ring current effect of the fluorene moiety. This anisotropic effect on the ¹H chemical shifts of the methyl protons has been quantified on the basis of through-space NMR shieldings (TSNMRS) and subsequently Δδ_calcd compared with the experimentally observed chemical shift differences, Δδ_exp. In this context, the experimental anisotropic effects of functional groups in the ¹H NMR have proven to quantitatively be the molecular response property of theoretical spatial nucleus independent chemical shieldings (NICS). Differences between Δδ_calcd and Δδ_exp were, for the first time, also quantified as arising from steric compression.     

基于空间光调制器的波面重建优化方法研究

针对不同非球面面形的实时检测需求,研究了基于空间光调制器的标准波面重建技术.基于空间光调制器波面重建的原理设计了干涉测量系统,依据空间光调制器的自身特点选取修正离轴计算全息编码方式实现对标准球波面的编码.针对实验中空间光调制器作为全息再现介质引起重建波面质量下降问题,提出了错位叠加优化方案,并将这一过程进行了模拟实验....     

DAC加载下材料高压声速的激光超声测量技术

 设计并建立了可测量金刚石压砧（DAC）加载下材料高压声速的激光超声系统。该系统采用脉宽为6.3 ns的调Q激光器作为超声波激发光源,使用光纤位移干涉仪和速度干涉仪混合系统进行超声位移探测,不需要借助其它任何参数即可直接测量样品的高压声速和原位厚度。利用该系统,测量了2.6 GPa压力下铜样品的高压纵波声速和原位厚度,并给出了测量结果。     

基于LabVIEW的驻波法测量声速的实验模拟

利用LabVIEW编写的测量声速的实验模拟软件不仅模拟了传统物理实验的操作过程,而且还加入了数据处理模块,实验数据采集完成后即可得出实验数据处理结果,可以用于学生实验前的预习与探究,或者实验教学中的演示。