Analysis of a strip in a waveguide

An analysis and an experimental study of a strip in a transverse plane of a rectangular waveguide below cutoff are presented. This work is a preliminary step in analyzing a stripline-fed slot antenna array in which each stripline feed is enclosed in a rectangular waveguide below cutoff. A numerical method is developed to solve a “pseudo” mixed-potential integral equation for the current on the strip excited by a delta-gap source at some point along the strip. The Green's function for dipole sources in the rectangular waveguide is used in the spectral and spatial representations and Shanks' transform is employed to speed up the convergence of the doubly infinite series. Numerical and experimental results are presented for a monopole fed at one wall of a rectangular waveguide and for a bottom-fed and bottom-loaded strip in a rectangular waveguide     

Computation availability of crossbar systems in a non-uniform traffic environment

Multiprocessor systems can provide higher performance, reliability, and availability than single processor systems. In order to properly assess the effectiveness of multiprocessor systems, measures that combine performance and reliability are needed. Most previous studies have considered the performance and reliability/availability separately. Only a limited number of studies have been carried out by considering the performance and reliability together in the presence of a uniform traffic in the network. Hot spots in a multiprocessor system result in a non uniform traffic in the network and results in a degradation in the performance of the network. The aim of this paper is to study the combined performance and reliability of a crossbar system in the presence of a hot spot in the system. Computation availability is taken as the criteria for measuring the combined performance and reliability. Markov chain models have been developed to compute the above measurement criteria.     

Some effects of localized stress on silicon planar transistors

When local compressive stress is applied to the emitter surface of a silicon planar transistor, increases in collector and base currents are observed. From the relationship between these currents and the base-to-emitter junction potential, it is inferred that changes in minority-carrier current occur in the stressed material. It is well known that the energy gap of a semiconductor is affected by mechanical stress, and the effects described here are consistent with a decrease in energy gap of a few tenths of an electron volt at compressive stresses of the order of 10¹¹dynes cm^-2. It is shown that the influence of stress on the current gain of a transistor depends on the strain distribution in the material. When the stress is applied over a relatively large area using a blunt stressing element, the increased minority-carrier current causes a rise in common-emitter current gain at low currents. In the case of the stress pattern produced by a sharper stressing element, a decrease in current gain is observed over a wide current range. It is proposed that this decrease results from a degradation in emitter efficiency caused by the stress concentration in the emitter region.     

Modeling the flow-level performance of hierarchical modulation in?OFDMA-based networks

Hierarchical Modulation (HM) is a means to enhance the spectral efficiency of a system by superposing, in terms of modulation, an additional stream for a given user with good radio conditions on a basic stream of a user with worse radio conditions. This, in turn, increases the throughput of the former user and hence the overall performance of the whole system. We consider, in this work, such a performance at the flow level, for a realistic dynamic setting where users come to the system and leave it after a finite duration corresponding, for instance, to the completion of a file transfer. We specifically model and quantify, both analytically and via simulations, the gain thus achieved and propose two extensions to the basic HM algorithm: a first one in which a user with bad radio conditions is also superposed on one with better radio conditions and a second one in which a user of one type is further superposed on a user of the same type as well.     

Perspectives on special issues [From the Editor]

The special issues of IEEE Signal Processing Magazine (SPM) provide a forum wherein a collection of tutorials, concentrated on a specific topic, span the entire field and expose a wide-ranging segment of readers in the signal processing community to a thorough overview of the topic. The presentation of complementary tutorials, focused on a particular area in signal processing and aimed at a broad technical audience, is a unique feature of this publication. The wide exposure of selected topics to a large audience makes the special issues in SPM a top venue to educate and raise the prominence of important disciplines in signal processing.     

Introduction to the special section: professional communication inRussia

There is a rising interest within the world community in what is occurring in professional communication in Russia, and in the social and market opportunities that will appear there in the future. We live in a world in which the pace of change is more rapid than at any time in our history. The most important aspect of this change is the fact that we are making a transition to a democratic society at the same time as we are in the process of establishing the principles of a market economy. Russia is a country with enormous reserves of raw materials, vast territories, and rich intellectual resources. And now, as Russia is experiencing a painful transition to a market economy, the nation's economic potential becomes more and more dependent on the sophistication of its infrastructure. That is the reason why the information technologies and professional communication have become key factors of social progress. The Russian centers of research and industry are widely dispersed geographically, in such cities as Vladivostok, Irkutsk, Novosibirsk, Tomsk, Ekaterinburg, Saint Petersburg and Moscow. The last three or four years have seen a sharp increase in the demands for business information, electronic mail and communications for far-flung business and financial operations     

Joint scheduling and routing using space–time graphs for TDM wireless mesh networks

This paper presents a novel algorithm for joint routing and scheduling in TDM wireless mesh networks. We introduce a new construct, called a “space–time graph,” which incorporates the spatial and temporal aspects of routing in one structure by replicating a spatial network connectivity graph in layers along the time dimension. The power of the space–time graph lies in the fact that a path from one node to another in it specifies both a physical route in space as well as a schedule in time for a message. Hence the complicated and intractable problem of routing and scheduling reduces to the relatively simpler problem of determining shortest paths in a graph. Through simulations we show that a simply greedy algorithm on the space–time graph outperforms two state-of-the-art methods in terms of time taken to successfully transmit a set of messages from their sources to their destinations.     

A Bio-Functional Wnt3a Gradient Microarray for Cell Niche Studies

The Wingless/Integrated (Wnt) signaling is a central player in regulating multiple cellular events ranging from developmental process, adult homeostasis to tumorigenesis. In native microenvironments, Wnt signals often function through the concentration gradients between the secreting site and the targeting site. Hence, presenting Wnt molecules in a concentration gradient in vitro in a controllable manner recapitulates the native Wnt niche. Nevertheless, most in vitro Wnt niche models, where the ligands are homogeneously immobilized on material surface, fail in reconstituting the concentration gradient of Wnt as that in vivo. Herein, using a previously established Multiphoton Microfabrication and Micropatterning (MMM) technology, a concentration gradient of Wnt3a is immobilized on a protein substrate via neutravidin-biotin interactions, in a quantitatively and spatially controllable manner. Such Wnt3a gradient is bioactive as it triggers a dose- and time-dependent upregulation of β-catenin and cell proliferation, in model mouse L cells. Most importantly, human hair dermal papilla cells (HHDPCs) cultured in a cell niche with Wnt3a gradient proliferate in a Wnt3a-gradient-dependent manner and exhibit a Wnt3a-gradient-dependent hair-inductive phenotype including Wnt/β-catenin signaling activation and alkaline phosphatase (ALP) expression. This work contributes to the future development of a hair follicle inductivity biochip for screening of drugs and therapeutics on hair regeneration.     

多频带数字滤波器的设计和FPGA实现

本文介绍了一种应用于FPGA芯片的多频带数字滤波器的快速高效的设计、验证和实现的方法,该方法不同于传统的FPGA滤波器设计而且十分实用能大大缩短开发周期。首先根据多频带数字滤波器的性能要求,介绍了在具体性能指标下的多频带数字滤波在FPGA中实现的思想和原理,接下来描述了FPGA数字滤波器的传统设计方法和MATLAB设计方法,解释了采用极小化极大准则对滤波器的频率响应进行逼近的原理,然后结合一个具体的多频带数字滤波器的设计,给出了利用MATLAB进行多频带滤波器设计的过程以及HDL代码的生成步骤,最后介绍了该多频带滤波器在Modelsim中的RTL级仿真和在FPGA芯片中的门级实现。     

Lumatron: A high-resolution storage and projection display device

The Lumatron is a high-resolution storage and projection display device that separates the functions of light generation and modulation that are combined in the normal CRT or DVST. The modulation function is achieved in a single vacuum chamber by the formation of a depth-modulated diffraction pattern in a deformable medium with a fine electrostatically focused and deflected electron beam. The illumination function is provided by a single-lens schlieren optical system external to the vacuum. The electron beam and light paths in the Lumatron are coaxial and the maximum voltage required by the device is 7.5 kV. Permanent storage and continuous readout without degradation for more than 24 h is possible, and yet the stored information can be intentionally erased in less than 1 s. Resolution in excess of 1800 TV lines/in at the storage surface has been measured and full 10-step grey scales have been stored and projected. Once an image is stored in a Lumatron, the only power required to generate the display is that required by the light source. In a demountable version of the projector, the storage surface can be easily removed and the stored pattern displayed in a remote schlieren projector without degradation.     

Performance Evaluation of Silence-Feature Normalization Model using Cepstrum Features of Noise Signals

Speech enhancement algorithms play an important role in speech signal processing. Over the past several decades, many algorithms have been studied for speech enhancement. A speech enhancement algorithm uses a noise removal method and a statistical model filter to analyze the speech signal in the frequency domain. Spectral subtraction and Wiener filters have been used as representative algorithms. These algorithms have excellent speech enhancement performance, but suffer from deterioration in performance due to specific noise or low signal-to-noise ratio (SNR) environments. In addition, according to estimations of erroneous noise, a noise existing in a voice signal is maintained so that a spectrum corresponding to a voice signal is distorted, or a frame corresponding to a voice signal cannot be retrieved, and voice recognition performance deteriorates. The problem of deterioration in speech recognition performance arises from the difference between speech recognition and training model. We use silence-feature normalization model as a methodology to improve the recognition rate resulting from the difference in the noisy environments. Conventional silence-feature normalization has a problem in that the silent part of the energy increases, which affects recognition performance due to unclear boundaries categorizing the voice. In this study, we use the cepstrum feature of the noise signals in the silence-feature normalization model to improve the performance of silence-feature normalization in a signal with a low SNR by setting a reference value for voiced and unvoiced classification. As a result of recognition rate confirmation, the recognition rates improve in performance, compared with other methods.     

Optical pulse sequence transmission through single-mode fibers:interference signal analysis

The transmission of a pulse sequence through a single-mode fiber is considered under first- and second-order dispersion. An expression is given for the output power signal envelope in terms of the Fourier transform of a spectral function. The output envelope is composed of two terms: a linear one which is a distorted replica of the information sequence, and a nonlinear interference term. The latter is expressed in a more meaningful way and analyzed. The results allow a characterization and a classification of the interference pulses in terms of physically intuitive parameters     

No Shades of Gray: The Binary Discourse of George W. Bush and an Echoing Press

Binary communications represent the world as a place of polar opposites. Such conceptions of reality, although not uncommon in Western thought, take on a heightened importance when political leaders employ them in a concerted, strategic discourse in a mass media environment. With this in mind, this research offers a conception of binary discourse and uses this as a foundation to examine (a) the use of binaries by U.S. President George W. Bush in 15 national addresses, from his inauguration in January 2001 to commencement of the Iraq War in March 2003, and (b) the responses of editorials in 20 leading U.S. newspapers to the president's communications.     

The Comparison Reflectometer

The comparison reflectometer is an instrument designed to locate and measure the characteristics of reflections in waveguide and transmission-line systems: it is particularly suitable for measuring small reflections in precise microwave measuring instruments up to one meter in length. It consists of a reflectometer in which the returning waves are combined with an accurately known reference wave and a measure of the total reflection coefficient is recorded automatically on punched paper tape at a number of preset frequencies covering a particular waveband. From sets of readings taken without, and with, the test component connected, a computer calculates and plots the distribution of reflections as a function of distance and prints out their magnitudes and phases. The reflection coefficients of individual discontinuities are also plotted by the computer as a function of frequency on Smith charts. Under suitable conditions point reflections may be Iocated in X-band waveguide within a few tenths of a millimeter and measured with an accuracy of /spl plusmn/3 percent in magnitude and /spl plusmn/ 5/spl deg/ in phase angle. The method compensates for imperfections in the reflectometer and so reduces the background level of spurious reflections to less than 0.00006.     

Mechatronics for a new robot generation

The paper outlines the DLR's mechatronic developments in the robotics area over the last five years. They aim at designing a new multisensory, modularly configurable lightweight robot generation in a unified and integral way. A first step in this direction has been the development of a complex multisensory gripper. It turned out to be a key element in ROTEX, the first real robot in space that flew with shuttle Columbia in early 1993. Sensors and actuators in DLR's new ultra-lightweight robot show up miniaturized integration of mechanics, electronics, and microprocessor control. Joint torque control based on inductive sensing is realized in the compact, highly reducing rotational gearings. With optimized carbon-fiber grid structures, optical high-speed information transfer between the joints and all power and signal electronics integrated into the arm, a new extremely lightweight type of robot arises. Joint control concepts are outlined and a 7 degree-of-freedom version of such a lightweight arm is described. The paper also outlines the concept of the artificial muscle and its use in the fingers of a new modular articulated robot hand. Sensor-based man-machine interfaces and automatic camera guidance by robots in minimal invasive surgery are other topics covered in the paper.     

A fast-settling CMOS op amp for SC circuits with 90-dB DC gain

A technique that combines the high-frequency behavior of a single-stage op amp with the high DC gain of a multistage design is presented. This technique is based on the concept that a very high DC gain can be achieved in combination with any unity-gain frequency achievable by a (folded-) cascode design. Bode-plot measurements for an op amp realized in a 1.6-μm process show a DC gain of 90 dB and a unity-gain frequency of 116 MHz (16-pF load). Settling measurements with a feedback factor of 1/3 show a fast single-pole settling behavior corresponding to a closed-loop bandwidth of 18 MHz (35-pF load) and a settling accuracy better than 0.03%. This technique does not cause any loss in output voltage swing. At a supply voltage of 5.0 V an output swing of about 4.2 V is achieved without loss in DC gain. The above advantages are achieved with a 30% increase in chip area and a 15% increase in power consumption     

Exploitation of the ambient noise for the structural health monitoring of bars and tubes

Image processing is a very vast field that includes both IT and applied mathematics. It is a discipline that studies the improvement and transformations of digital images hence permitting the improvement of the quality of these images and the extraction of information. The comparison of digital images is a paramount issue that has been discussed in several researches because of its various applications especially in the field of control and surveillance such as the Structural Health Monitoring using acoustic waves. In this study we will present an experimental study conducted on a bar and a tube in order to show the constant possibility of performing a structural health monitoring in a medium by studying the ambient noise present therein. Finally, a comparison algorithm described in a previous work (Hourany et al. in Leban Sci J 17(2):177–192, 2016) will be validated in order to show the influence of the presence of a defect in the structure on the cross-correlation.     

Assignment of Dynamically Perceived Tasks by Token Passing in Multirobot Systems

The problem of assigning tasks to a group of robots acting in a dynamic environment is a fundamental issue for a multirobot system (MRS) and several techniques have been studied to address this problem. Such techniques usually rely on the assumption that tasks to be assigned are inserted into the system in a coherent fashion. In this work we consider a scenario where tasks to be accomplished are perceived by the robots during mission execution. This issue has a significative impact on the task allocation process and, at the same time, makes it strictly dependent on perception capabilities of robots. More specifically, we present an asynchronous distributed mechanism based on Token Passing for allocating tasks in a team of robots. We tested and evaluated our approach by means of experiments both in a simulated environment and with real robots; our scenario comprises a set of robots that must cooperatively collect a set of objects scattered in the working environment. Each object collection task requires the cooperation of two robots. The experiments in the simulation environment allowed us to extract quantitative data from several missions and in different operative conditions and to characterize in a statistical way the results of our approach, especially when the team size increases.     

Connected sensor cover: self-organization of sensor networks for efficient query execution

Spatial query execution is an essential functionality of a sensor network, where a query gathers sensor data within a specific geographic region. Redundancy within a sensor network can be exploited to reduce the communication cost incurred in execution of such queries. Any reduction in communication cost would result in an efficient use of the battery energy, which is very limited in sensors. One approach to reduce the communication cost of a query is to self-organize the network, in response to a query, into a topology that involves only a small subset of the sensors sufficient to process the query. The query is then executed using only the sensors in the constructed topology. The self-organization technique is beneficial for queries that run sufficiently long to amortize the communication cost incurred in self-organization. In this paper, we design and analyze algorithms for suchself-organization of a sensor network to reduce energy consumption. In particular, we develop the notion of a connected sensor cover and design a centralized approximation algorithm that constructs a topology involving a near-optimal connected sensor cover. We prove that the size of the constructed topology is within an O(logn) factor of the optimal size, where n is the network size. We develop a distributed self-organization version of the approximation algorithm, and propose several optimizations to reduce the communication overhead of the algorithm. We also design another distributed algorithm based on node priorities that has a further lower communication overhead, but does not provide any guarantee on the size of the connected sensor cover constructed. Finally, we evaluate the distributed algorithms using simulations and show that our approaches results in significant communication cost reductions.