Calibration and measurement issues for therapeutic ultrasound

This review paper examines some of the issues relating to calibration and measurement of therapeutic medical ultrasonic equipment (MUE). This is not intended to be an all-encompassing review of all aspects of characterising therapeutic ultrasound. Instead it concentrates on issues related to the acoustic output of two applications: physiotherapy and high intensity focused ultrasound surgery (HIFUS or HIFU; also referred to as high intensity therapeutic ultrasound, HITU). Physiotherapy has a well-established standards infrastructure for calibration: the requirements are small in number and well-defined. The issue for physiotherapy is not so much 'How to calibrate?' but rather, 'How to ensure that equipment IS calibrated?' The situation in the much newer area of HIFU is very different: the first steps towards writing standards are just starting and even the very basic questions of what to measure and with what type of sensor are open for debate. Readers whose main interest is in other ultrasound therapies will find ideas of relevance to their own specialty.     

DWDM System Components

The hottest word in telecommunications technology is dense wavelength division multiplexing (DWDM). In this paper, a review of the DWDM component market is presented together with a worldwide forecast over the next 5 years. The most dramatic changes in telecommunications have taken place in the last several years with the advent of DWDM to exploit the potential of unlimited bandwidth on a fiber pair. Originally installed to solve the problem of fiber exhaust in long-distance networks, DWDM is becoming the leading driver to an all-topical network. DWDM is insensitive to bit rate and format and permits a telecommunications network to increase capacity without installing new fiber, and at a decreased cost with much greater flexibility. DWDM places narrowly spaced channels onto the same fiber and increases capacity on existing fiber routes by factors of 16, 32, 40, or more. DWDM has also made it possible for new carriers to enter the market using IP-based rather than circuit-switched networks at considerably lower costs.     

地铁列车客室车门自动试验装置研制与应用

介绍了一种地铁车门自动试验装置,用于车辆组装完成后的车门调试试验。地铁车门试验是地铁电气静态调试试验的重要组成部分,而车门性能的优劣将直接影响到乘客的安全。针对地铁车门系统在车辆上的布置规律,综合各车门系统供货厂家的电气接口特点,制作车门自动试验装置,该试验装置可根据试验要求向地铁车门系统发送开门、关门、零速等指令,并实时采集各车门的开关、故障等总线信息,对车门状态进行显示、存储。通过使用该试验装置简易明了的展示了地铁各车门装置并对数据进行存储,最终证明车门自动试验装置可以缩短试验时间,提高试验效率的同时增加了试验数据的可追溯性。     

Study of Internal Wavelength Locker Integrated 10 Gbps Electro-Absorption Modulated Laser Modules in Metro DWDM Applications

Several different divergences are tested in the several internal wavelength locker schemes for 10 Gbps electro-absorption modulated laser (EML) module. A 10 Gbps EML module with a simple and robust internal wavelength locker for metro dense WDM application is successfully demonstrated. The wavelength aging over 2000 h is done at elevated temperature of 70°C. The average wavelength drift of 10 modules is measured to be ± 5 pm. These modules can be successfully applied to the 10 Gbps DWDM systems with 50 GHz channel spacing.     

全光纤密集型波分复用器

分析了全光纤Ｍａｃｈ－Ｚｅｈｎｄｅｒ结构的功率谱特性，并利用自行设计的耦合器拉锥设备，研制成功最小波长复用间隔为０．４５ｎｍ的密集型波分复用器。该类器件具有附加损耗低，偏振不灵敏和较好的温度及机械稳定性等特点。     

Diffusion configuration of water molecules in diffusion weighted imaging

In the studying of fibers microstructure of brain white matter, many reconstruction methods have been proposed to interpret the diffusion-weighted signal. Those methods can be categorized into model-based and model-free methods. In this paper, the diffusion configuration of water molecules are discussed, and two questions are put forward to analyze the performance of the current algorithms about diffusion configuration. The first question is what the diffusion profile looks like in voxel? The second question is what is the location of fibers in a voxel? As a result, firstly, most of model-based algorithms ignore much information coming from the isotropic diffusion, which will lead to an inaccurate estimation. Secondly, model-free algorithms just provide direction information of fibers, ignore or cannot provide location information of fibers. So unfortunately, neither model-based methods nor model-free methods can resolve those two questions very well. How to resolve those questions is still an open problem, and it may be an interesting direction in the future research.     

All-fiber Mach-Zehnder interferometer for DWDM filter direct group-delay measurement

The group delay of the dense wavelength division multiplexing (DWDM) filter is becoming more important in optical communication. This study proposes a Mach-Zehnder interferometer based on the direct group delay measurement of an optical thin film filter. The interferometer provides a simple, accurate and physically intuitive picture of what happens to broadband optical pulses on common optical materials. A 100 GHz DWDM filter was used as an example in the measurement and showed that the time of measurement and selection of Gaussian window were two important factors.     

The reconstruction of finite extent objects with the superlens

The imaging of three-dimensional source objects with the Veselago–Pendry superlens has not been extensively researched. In this paper, we attempt to answer two fundamental questions. Firstly, can the superlens image an object with non-zero dimension normal to the lens surfaces—at least in principle? Secondly, if the answer is yes, would it be possible to realize such a system, and what are the conditions that it would have to satisfy? To answer these questions, we develop an image reconstruction algorithm based on a spatial Fourier decomposition of the field functions and an optimal sampling technique employing Deslauriers–Dubuc interpolation wavelets. We conclude that it is theoretically possible to image 3-D objects with the superlens, but that real-world limitations impose stringent restrictions on the system.     

Objective Probability and Quantum Fuzziness

This paper offers a critique of the Bayesian interpretation of quantum mechanics with particular focus on a paper by Caves, Fuchs, and Schack containing a critique of the “objective preparations view” or OPV. It also aims to carry the discussion beyond the hardened positions of Bayesians and proponents of the OPV. Several claims made by Caves et al. are rebutted, including the claim that different pure states may legitimately be assigned to the same system at the same time, and the claim that the quantum nature of a preparation device cannot legitimately be ignored. Both Bayesians and proponents of the OPV regard the time dependence of a quantum state as the continuous dependence on time of an evolving state of some kind. This leads to a false dilemma: quantum states are either objective states of nature or subjective states of belief. In reality they are neither. The present paper views the aforesaid dependence as a dependence on the time of the measurement to whose possible outcomes the quantum state serves to assign probabilities. This makes it possible to recognize the full implications of the only testable feature of the theory, viz., the probabilities it assigns to measurement outcomes. Most important among these are the objective fuzziness of all relative positions and momenta and the consequent incomplete spatiotemporal differentiation of the physical world. The latter makes it possible to draw a clear distinction between the macroscopic and the microscopic. This in turn makes it possible to understand the special status of measurements in all standard formulations of the theory. Whereas Bayesians have written contemptuously about the “folly” of conjoining “objective” to “probability,” there are various reasons why quantum-mechanical probabilities can be considered objective, not least the fact that they are needed to quantify an objective fuzziness. But this cannot be appreciated without giving thought to the makeup of the world, which Bayesians refuse to do. Doing this on the basis of how quantum mechanics assigns probabilities, one finds that what constitutes the macroworld is a single Ultimate Reality, about which we know nothing, except that it manifests the macroworld or manifests itself as the macroworld. The so-called microworld is neither a world nor a part of any world but instead is instrumental in the manifestation of the macroworld. Quantum mechanics affords us a glimpse “behind” the manifested world, at stages in the process of manifestation, but it does not allow us to describe what lies “behind” the manifested world except in terms of the finished product—the manifested world, for without the manifested world there is nothing in whose terms we could describe its manifestation.     

Prediction of vibrations induced by underground railway traffic in Beijing

This paper examines the problem of subway induced vibrations on line 4 of Beijing metro, which is currently under construction and is planned to pass in close proximity of the Physics Laboratory of Beijing University. The laboratory has a lot of equipment that is very sensitive to traffic induced vibrations and future operation of metro line 4 is a matter of concern. Hence, it is important to study the influence of subway induced vibrations inside the laboratory and to propose a viable solution to mitigate the vibrations. In this paper, the tunnel north of Chengfulu station is modelled using a coupled periodic FE-BE model and the free-field response due to moving trains is predicted. In addition, vibration measurements have been performed on the site of the Physics Laboratory to estimate the existing vibration levels due to road traffic. The predicted and measured vibrations are superimposed to assess the vibrations due to the combined effect of road and railway traffic in the vicinity of the Physics Laboratory. Apart from the numerical investigations, vibration measurements have also been performed on a similar site at line 1 of Beijing metro to substantiate the estimated results on metro line 4. Finally, it is studied how the vibrations can be controlled using a floating slab track, which is widely used as an effective measure of vibration isolation in tunnels. The efficiency of a 7.9 Hz floating slab track as a vibration countermeasure is assessed in this paper. This study demonstrates the applicability of the numerical model for the relevant assessment of subway induced vibrations and its use to study the performance of different track structures in the tunnel.     

Tunable holographic components in WDM optical networks

This paper describes the applications of a multipurpose holographic device in optical networks with Coarse and Dense Wavelength Division Multiplexing (CWDM/ DWDM) technologies. In its basic structure, it can operate as a tunable wavelength filter, wavelength multiplexer or λ router. By using a more complex structure, the device works as OADM (Optical Add Drop Multiplexer) or OS (Optical Switch). Some simulations of the basic devices, from the optical transmission point of view, are made to match the transmission parameters for the application in optical networks. Performance parameters of the device, like switching time, losses, cross-talk or polarization insensitivity are analyzed and compared with other multiplexing or switching technologies. To complete the review of these components, a study of computer generated holograms (CGH) design is carried out. The results are used in the design of holographic devices to perform different applications: in Metro networks, where a design of a holographic device with wavelength conversion and routing is analyzed, or, in Access Networks like a tunable filter or demultiplexer in Fiber to the Home/Business (FTTH/FTTB) topologies.     

Mechanical grain growth in nanocrystalline copper

Nanograined materials have some unusual properties. To maintain the small size of the grains, grain growth should be avoided. But recently grain growth has been observed under an indenter at liquid-nitrogen temperatures. Such grain growth has never been reported before. How can this happen and how can it be prevented? These questions are answered here using a simple tilt boundary. It is found that high purity and nonequilibrium structure are necessary conditions for mechanical grain growth. The material must be pure enough so that free dislocations are available to move out of the boundary. But the boundary should not be in the lowest-energy state so that extra dislocations are available to be emitted by stress. Based on these conditions, methods can be devised to avoid low temperature grain growth.     

Metro Optical Networks for Homeland Security

Metro optical networks provide an enticing opportunity for strengthening homeland security. Many existing and emerging fiber-optic networks can be adapted for enhanced security applications. Applications include airports, theme parks, sports venues, and border surveillance systems. Here real-time high-quality video and captured images can be collected, transported, processed, and stored for security applications. Video and data collection are important also at correctional facilities, courts, infrastructure (e.g., dams, bridges, railroads, reservoirs, power stations), and at military and other government locations. The scaling of DWDM-based networks allows vast amounts of data to be collected and transported including biometric features of individuals at security check points. Here applications will be discussed along with potential solutions and challenges. Examples of solutions to these problems are given. This includes a discussion of metropolitan aggregation platforms for voice, video, and data that are SONET compliant for use in SONET networks and the use of DWDM technology for scaling and transporting a variety of protocols. Element management software allows not only network status monitoring, but also provides optimized allocation of network resources through the use of optical switches or electrical cross connects.     

Synchronization in simple network motifs with negligible correlation and mutual information measures

Can different or even identical coupled oscillators be completely uncorrelated and still be synchronized? What can be concluded from the absence of correlations or even mutual information in networks of dynamical elements about their connectivity? These are fundamental and far-reaching questions arising in many complex systems. In this Letter, we address these two questions and demonstrate in simple and generic network motifs that synchronized behavior in the generalized sense can be realized and constructed such that no correlations and even negligible mutual information remain. Our findings raise new questions, in particular, whether and to what extent indirect connections are being underestimated, since the related collective behavior and even synchronization are less likely to be detected.     

光电信息工程实验教学的思考与改革

面对急剧变化的世界,工程知识本身的有效期变得越来越短,社会对学生各种素质的要求越来越高。如何定位大学工程教育本身的角色?如何在光电工程实验教学中培养社会对学生所提出的各种要求?结合对这些问题的思考,讨论了光电信息工程专业实验教学所面临的挑战,以及为应对这些挑战所进行的教学改革实践。     

Investigation on the influence of intensity scintillation and beam wander in space optical uplink DWDM communication system

Abstract

Dense wavelength division multiplexing (DWDM) has been widely applied in ground optical communication. However, the technology of DWDM is still not mature enough in the space optical communication system. In order to further advance the use of DWDM into space optical communication, the probability density function (PDF) and the bit-error rate (BER) performance of DWDM is investigated in uplink communications under the influence of atmospheric turbulence, consisting of intensity scintillation and beam wander caused by atmospheric turbulence. Numerical results show that the atmospheric turbulence has a great impact on BER and PDF, and wavelength, divergence angel, and other relevant parameters should be carefully considered in this DWDM system. This work can be conducive for improving DWDM design of space optical uplink communication systems.     

The big problems in star formation: The star formation rate,stellar clustering,and the initial mass function

Star formation lies at the center of a web of processes that drive cosmic evolution: generation of radiant energy, synthesis of elements, formation of planets, and development of life. Decades of observations have yielded a variety of empirical rules about how it operates, but at present we have no comprehensive, quantitative theory. In this review I discuss the current state of the field of star formation, focusing on three central questions: What controls the rate at which gas in a galaxy converts to stars? What determines how those stars are clustered, and what fraction of the stellar population ends up in gravitationally-bound structures? What determines the stellar initial mass function, and does it vary with star-forming environment? I use these three questions as a lens to introduce the basics of star formation, beginning with a review of the observational phenomenology and the basic physical processes. I then review the status of current theories that attempt to solve each of the three problems, pointing out links between them and opportunities for theoretical and numerical work that crosses the scale between them. I conclude with a discussion of prospects for theoretical progress in the coming years.     

Quantum-realistic interpretation

1. Realism. Physicists claim rightly to speak about reality. But what does “reality” mean?2. The Copenhagen Interpretation (CI). We consider CI as a minimal semantics for quantum theory, leaving ways open for additional interpretation.3. The Measuring Process. Several interpretations of the process as given in the liteature are discussed.4. Realistic Interpretation. Discussion of the de Broglie-Bohm-Bell interpretation. If well formulated, it is not a necessary consequence of quantum theory but cannot be excluded.