Saturation mechanism in clarinet-like instruments, the effect of the localised non-linear losses

The question of what limits the amplitude of the oscillations of clarinet-like instruments is investigated. The study is based on numerical simulations in which two kind of losses are taken into account: linear losses and non-linear losses localised at the open end of the tube. The influence of the amount of losses on the saturation process and on the playing range of clarinet-like instruments is shown. Results are confirmed by experiments using an artificial mouth in which the non-linear losses are varied using several terminations with different geometries.     

Surface impedance models for high impedance surfaces

Different analytical and numerical methods for calculating the surface impedance of a high impedance surface (HIS) structure have been studied and compared. In this article, two new approaches are proposed for calculating the surface impedance for general 2D-spatial periodic HIS structures, which include both the symmetric and asymmetric planar structures. Different comparisons are made, among analytical, numerical and experimental results, to validate our numerical calculation.     

Outdoor ground impedance models

Many models for the acoustical properties of rigid-porous media require knowledge of parameter values that are not available for outdoor ground surfaces. The relationship used between tortuosity and porosity for stacked spheres results in five characteristic impedance models that require not more than two adjustable parameters. These models and hard-backed-layer versions are considered further through numerical fitting of 42 short range level difference spectra measured over various ground surfaces. For all but eight sites, slit-pore, phenomenological and variable porosity models yield lower fitting errors than those given by the widely used one-parameter semi-empirical model. Data for 12 of 26 grassland sites and for three beech wood sites are fitted better by hard-backed-layer models. Parameter values obtained by fitting slit-pore and phenomenological models to data for relatively low flow resistivity grounds, such as forest floors, porous asphalt, and gravel, are consistent with values that have been obtained non-acoustically. Three impedance models yield reasonable fits to a narrow band excess attenuation spectrum measured at short range over railway ballast but, if extended reaction is taken into account, the hard-backed-layer version of the slit-pore model gives the most reasonable parameter values.     

采用数字合成技术的三相正弦波信号发生器

采用数字合成技术制作了三相正弦波信号发生器 ,其波形采用 3个加权电阻网络和高速CMOS开关数字合成 ,精确保证 3个正弦波之间的相位差为 12 0° ,产生的信号具有极好的幅值、稳定的频率、小失真和高达 3.3MHz的宽频率范围     

Delayed models for simplified musical instruments

Most musical instruments contain, at their very basis, a continuous vibrating element (string or air column) which can be treated as a one-dimensional system. Its oscillation is obtained either through an initial condition or by means of a continuous energy input through a nonlinear device. In both cases and as a first approach, the excitation can be localized at one single point, and the continuous system can be considered as a linear one. The coupling between these two elements is often represented through a convolution integral. This convolution will be rewritten here in a way that different phenomena taking place in the continuous element (internal losses, radiation at the ends...) are separated. Different choices in the formulation of these processes and some mathematical manipulation will lead to either algebraic iterative or delayed differential equations. These equations are valid for any form of energy input. Once this energy input is defined, they can be used to simulate the behavior of different instruments in a more efficient way than that of traditional convolution. Moreover, these equations allow an analytical analysis of possible regimes using the tools of nonlinear dynamical systems (NLDS). The case of woodwinds will be emphasized throughout the paper, while that of strings will be presented briefly for the sake of completeness.     

Optimal instruments and models for noisy chaos

Analysis of finite, noisy time series data leads to modern statistical inference methods. Here we adapt Bayesian inference for applied symbolic dynamics. We show that reconciling Kolmogorov's maximum-entropy partition with the methods of Bayesian model selection requires the use of two separate optimizations. First, instrument design produces a maximum-entropy symbolic representation of time series data. Second, Bayesian model comparison with a uniform prior selects a minimum-entropy model, with respect to the considered Markov chain orders, of the symbolic data. We illustrate these steps using a binary partition of time series data from the logistic and Henon maps as well as the R?ssler and Lorenz attractors with dynamical noise. In each case we demonstrate the inference of effectively generating partitions and kth-order Markov chain models.     

Acoustical impedance models for outdoor ground surfaces

A theory which predicts the acoustical characteristics of rigid porous materials in terms of four physical parameters is used to provide impedance versus frequency models for various types of ground surface. It is found possible to obtain tolerable agreement with measurements of surface normal impedance for grass-covered ground, bare ground and layered forest floor when measured values of flow resistivity and porosity and estimated values of the other two parameters are used. The agreement with measured acoustical data is shown to be superior to that obtainable with the single-parameter, semi-empirical model that is widely used to predict ground effect even when the single parameter is adjusted for best-fit. A low frequency/high flow resistivity approximation is derived in a form that requires the adjustment of only a single parameter when fitting impedance versus frequency data. This model predicts that the real part of the surface normal impedance, or resistance, and imaginary part, or reactance, are equal and decrease as the inverse square root of frequency. The low frequency/high flow resistivity approximation makes possible the derivation of a two-parameter impedance versus frequency model for a medium with a porosity that decreases exponentially with depth. If the two parameters are considered to be adjustable for best-fit, then some measurements of surface impedance are found to be explicable by means of such a model. The low frequency/high flow resistivity approximation is used, together with the assumption of layer thickness small compared with internal wavelength, to derive another simple two-parameter model for grounds that behave acoustically as thin hard-backed porous layers. Examples of the validity of this model are provided. Both of the two-parameter models predict values of reactance which are greater than those of resistance over the audio-frequency range. Methods of adjusting the two parameters of each model in fitting short-range excess-attenuation data are suggested as alternatives to the single-parameter method, and as the basis for predicting ground effect at long range and low frequencies.     

基于数字全息干涉的实时微振动检测

基于数字全息理论的方法,构建了一套微振动实时测量的实验系统。通过运用基于全息干涉图像的振动快速解算算法,直接从记录的全息图中提取振动信息,实现对振动物体振幅值进行实时测量。该系统的接收光为散射光,使得测量角度不受被测物体结构的影响。通过测量由标准正弦波驱动的被测物微振动情况,对该实验系统进行了实验验证,实验结果表明,该系统能够实时测量微振动的振幅值（算法处理时间约为0.11 ms）,在550～2700 Hz频段内被测物的振幅较为稳定,系统稳定性误差为1.66%,真实地反映了其振动情况。     

Accuracy in the measurement of highway noise levels with digital instruments

The usual way of assessing a change of the L_eq due to a new construction along a highway is the before and after construction measurement of the noise. To avoid the influence of all variables other than those caused by the new construction, a measurement technique known as ‘controlled’ is used. It consists of a simultaneous measurement of sound levels at the site where the L_eq change is expected to occur and at a place near the highway, but far from the new construction.The accuracy of such a measurement was studied by using three instruments and by running four series of ten measurements each, at four different sites. The standard deviation was found to be within ±2 dB.     

Automated chemical synthesis: From resins to instruments

Summary Solid-phase organic synthesis is now a prevalent activity in drug discovery. In keeping with this keen interest is the need to develop reliable automated synthesis instrumentation as well as polymeric supports and linkers suitable for the full range of organic synthesis applications. In this paper, we review our activities in the development of new and enabling tools for automated chemical synthesis, including the following: (i) new solid supports such asArgoGel (PS-PEG-based) andArgo-X203 (PS-based); and (ii) theNautilus 2400 system, a fully closed and inert automated chemistry development workstation. Selected chemistry optimization and synthesis examples performed on the Nautilus and new solid supports will be described.     

Multi-wavelengths digital holography: reconstruction, synthesis and display of holograms using adaptive transformation

A method based on spatial transformations of multiwavelength digital holograms and the correlation matching of their numerical reconstructions is proposed, with the aim to improve superimposition of different color reconstructed images. This method is based on an adaptive affine transform of the hologram that permits management of the physical parameters of numerical reconstruction. In addition, we present a procedure to synthesize a single digital hologram in which three different colors are multiplexed. The optical reconstruction of the synthetic hologram by a spatial light modulator at one wavelength allows us to display all color features of the object, avoiding loss of details.     

Real-time dual-wavelength digital holographic microscopy based on polarizing separation

We report on a manifold advanced dual-wavelength digital holographic microscopy (DHM) configuration with a real-time measurement capability. The proposed configuration based on a polarizing separation scheme can be used for microscopic imaging polarimetry as well as dual wavelength digital holographic microscopy. In this paper, we show the feasibility of the proposed scheme by conducting the dual wavelength DHM experiments on a sample with a step height of 1.34 μm nominally. An averaging technique is treated and three-dimensional (3D) topographic measurements are presented. The results obtained by the proposed polarization separation based single shot DHM approach shows it can provide a real time solution for measuring 3D profile information of small objects with excellent accuracy.     

重离子加速器电源数字调节器的实时数据交互

为了解决兰州重离子加速器研究装置(HIRFL-CSR)磁铁电源数字调节器的通讯堵塞问题,采用了新的体系架构,并将P2P技术嵌入到数字调节器的核心控制器ARM中,运用UDP的打洞技术,使调节器之间的数据不再通过中心Oracle数据库转发,而是在调节器间直接建立通讯,这种方式分散了中心Oracle数据库的通讯量,减少了网路堵塞的风险,提高了通讯的效率、有效性和可靠性。     

数字全息图取样模型的简化研究

数字全息研究领域目前存在两种不同的数字全息图取样模型.按照这两种模型进行研究时, 不但涉及较复杂的数学运算, 在许多情况下还会导致不同的研究结果, 不便于理论分析及实际应用.基于对数字全息图记录的物理过程分析及电荷藕合器件(charge coupled device, CCD)几何结构的研究, 本文将这两种取样模型简化为相同的数学表达式. 利用数字全息图的余弦级数展开及取样定理对简化模型的研究表明, 简化模型不但具有清晰的物理意义, 而且可以方便地为应用研究服务. 基于简化模型对物光波通过光学系统到达CCD的数字全息记录系统进行了研究, 导出得到实验证实的波前重建表达式. 关键词： 数字全息 波前重建 相干光成像     

Real-time digital holographic microscopy of multiple and arbitrarily oriented planes

Digital holographic microscopy is used to numerically refocus a recorded hologram at an arbitrary axial distance. However, as a straightforward property of coherent light fields, image reconstruction on an arbitrary tilted plane could be directly obtained by a rotation in k-space. We demonstrate that this property allows the real-time microscopic inspection of particle distribution over three mutually orthogonal planes at the same time. As a straightforward application we use the proposed technique for real-time monitoring of fluid flow over the three cross sections of a microfluidic channel.     

Reduced models of multi-stage cyclic structures using cyclic symmetry reduction and component mode synthesis

Reduced models of multi-stage cyclic structures such as bladed-disk assemblies are developed by using the multi-stage cyclic symmetry reduction and/or component mode synthesis methods. The multi-stage cyclic symmetry reduction consists in writing the equations of the bladed disks, the inter-disk structures, the inter-disk constraints and the whole multi-stage coupled system in terms of the traveling wave coordinates for all the phase indexes of the reference sectors and for all the bladed disks. Several reduced coupled systems are then solved by selecting at each time only one or a few phase indexes for each bladed disk and by applying the cyclic symmetry boundary conditions. On the other hand, component mode synthesis methods are used either independently or in combination with the multi-stage cyclic symmetry reduction to obtain reduced models of the multi-stage structure. Two of them are particularly efficient, that are firstly component mode synthesis methods with interface modes applied on the bladed disks and secondly component mode synthesis methods with traveling wave coordinates applied on the reference sectors.     

Compact cavity resonators using high impedance surfaces

This paper presents a miniaturization concept for cavity resonators. The idea is to create a λ/4 long cavity resonator by using a combination of Perfect Electric Conductor (PEC) and Perfect Magnetic Conductor (PMC) boundary conditions. Reducing by half the length and width of a metallic cavity resonator and placing PMC boundary conditions on two adjacent side walls allows the resonance of a λ/4 mode inside the hybrid cavity resonator, at the same frequency as the λ/2 long metallic one. The practical implementation of the PMC boundary condition is realized by using High Impedance Surfaces (HIS). The design of the surfaces is realized at the element level and is implemented on standard microwave substrate. Measurements demonstrate a cavity resonator operating at 4 GHz with half the length and width of a metallic cavity resonator, meanwhile its volume is divided by four.     

Manipulation of superconducting qubit with direct digital synthesis

We investigate the XY control and manipulation of the superconducting qubit state using direct digital synthesis(DDS)for the microwave pulse signal generation.The decoherence time, gate fidelity, and other qubit properties are measured and carefully characterized, and compared with the results obtained by using the traditional mixing technique for the microwave pulse generation.In particular, the qubit performance in the state manipulation with respect to the sampling rate of DDS is studied.Our results demonstrate that the present technique provides a simple and effective method for the XY control and manipulation of the superconducting qubit state.Realistic applications of the technique for the possible future scalable superconducting quantum computation are discussed.     

巧用数码相机使运动定格

许多实验过程持续时间短,速度快,不便于观察. 用数码相机的摄像功能摄录运动的全过程,再逐帧播放,即可清晰再现实验结果,便于客观准确地得出结论.