Empty pathways: faculty use of computer-mediated communication

The availability of computers to university faculty members and the capability of those computer systems have increased exponentially over the past several years; however, many faculty still do not use the technology. The extent of diffusion of the capabilities of computer-mediated communication (CMC) among faculty is a core issue. This paper surveys literature on CMC with regard to diffusion of the practice among faculty. Through interviews and case studies, the authors examine characteristics of faculty who are active users of CMC as well as those who do not use the communication technology. Possible barriers to a more widespread use are examined, and implications for further research are discussed     

Spread-spectrum code acquisition in the presence of Doppler shiftand data modulation

A spread-spectrum code acquisition technique for a direct-sequence (DS) system in the presence of Doppler effect and data modulation is investigated. Both the carrier-frequency offset and code-frequency offset due to severe Doppler effect are considered. The code-chip slipping during the correlation process caused by code-frequency offset can degrade the acquisition performance significantly. However, this issue can be alleviated by compensating code-frequency offset in an appropriate manner. Results are presented for the cases with and without data modulation. Coherent detection is considered when there is no data modulation. If data modulation is present, the authors partition the correlation time into subintervals and the integration results in these subintervals are square-law noncoherently combined for detection. The implementation of this code acquisition technique using the fast Fourier transform (FFT) algorithm is described. The use of theoretical results to estimate the hardware complexity of an actual system is illustrated step by step, showing that implementation is feasible with existing technology. The tradeoff between hardware complexity and acquisition performance is discussed     

Sampled-data modeling of the average-input current-mode-controlledbuck converter

Average-input current-mode control (AICMC) is a new control scheme for shaping the input current of a buck converter in a high-power-factor rectifier. AICMC is presented along with a continuous-time model that includes sampled-data effects. AICMC is found to be analogous to current mode control (CMC), so existing CMC models are reviewed with regard to the controversies over low-frequency modulator gain and the experimental measurement of loop gain. Two useful modeling approaches which include modulator gain and sampling effects in a continuous model are identified and reviewed. The “Ridley approach” is used to produce a continuous model which exhibits good experimental confirmation on a 100 W 24.5 kHz buck converter. Possible hazards in the implementation of the “digital” method of loop gain measurement are identified, along with the reason the “analog” method does not actually measure the desired quantity     

Design and analysis of general rotor-flux-oriented vector controlsystems

Reduced-order observers for rotor flux estimation of induction motors are considered. The “current” model and “voltage” model are obtained as special cases. It is shown that the flux dynamics form a nonlinear closed-loop system when the flux estimate is used for field orientation. The observer gain selection is extremely critical for good behavior of this system. A framework is developed, in which the properties of any gain selection can easily be assessed. Four candidate gain selections are considered, two of which yield schemes that do not use the rotor speed in their equations (inherently sensorless schemes). It is also shown that for any gain selection, an equivalent synchronous-frame implementation (i.e., indirect field orientation) always exists     

Significance of Force-Feedback in Controlling Artificial Locomotion?Manipulation Systems

In the paper two aspects of force-feedback implementation in controlling artificial locomotion-manipulation systems are considered: 1) as a global control, for reducing the influence of coupling among subsystems when decentralized control is applied, and (b) for solving dynamic control tasks often encountered when the aforementioned systems are considered. In order to illustrate the implementation of force-feedback, four examples are presented, two for a biped system and two for an anthropomorphic manipulator.     

Hybrid block-convolutional rate-½ coding strategy forconstant envelope (CE)Q2PSK

The authors address the problem of trellis coding on multidimensional signal space for incorporation into a 4D quadrature-quadrature phase-shift keying (Q²PSK) communication system. A low-complexity rate-½ hybrid block-convolutional coding scheme is proposed, to be utilised in a constant envelope (CE)Q²PSK system configuration. The encoder and decoder designs have been structured to facilitate simple implementation with standard components. The bit error rate performance of the proposed coding scheme is studied by means of simulation on a non-frequency selective Rician fading channel assuming coherent detection. The benefits of the use of channel state information (CSI) in conjunction with maximum-likelihood Viterbi decoding are also considered     

Adaptive equalization for TDMA digital mobile radio

Adaptive equalization for a TDMA (time-division multiple-access) digital cellular system is discussed. A survey of adaptive equalization techniques that includes their performance characteristics and limitations and their implementation complexity is presented. The design of adaptive equalization algorithms for a narrowband TDMA system is considered. It is concluded that, on the basis of implementation complexity and performance in the presence of multipath distortion and signal fading, MLSE (maximum-likelihood sequence estimation) and DFE (decision feedback equalization) are viable equalization methods for mobile radio     

Visual telephony as an ISDN application

The key factors deterring the use of visual telephony are identified, and an overview of a typical system architecture is given. The video signal formats and video and audio coding algorithms used are described. Video codec implementation is considered, and an implementation based on application-specific integrated circuits is presented. In particular, three key signal processing modules in the video codec are examined: a discrete cosine transform chip, a motion estimation chip, and a variable-length codec chip. Standardization activities in the video coding area are discussed     

Implementing OSI-based interfaces for network management

Experience acquired in the development of an interface between a fiber optic system and a prototype management system developed using an object-oriented approach is discussed. Open System Interconnection (OSI) implementation concerns, the use of an ASN.1 compiler, and the use of standard application programming interfaces (APIs) are described. The role of the seven-layer OSI stack in exchanging information between managing operating systems and managed network elements is reviewed. The implementation of an OSI stack on a SUN workstation using the UNIX operating system is also described. Methods for passive and active testing of the resulting programs are discussed     

NOMA Transceiver Design for Highway Transportation in Mobile Hotspot Networks

The mobile hotspot network (MHN), which is capable of providing a data rate of gigabits per second at high speed, is considered a potential use case of the future enhanced mobile broadband for 5G. Because a unidirectional network deployment has been considered for an MHN, non‐orthogonal multiple access (NOMA) can be employed to improve the system performance. For a practical implementation of NOMA under an MHN highway scenario where multiple pieces of MHN terminal equipment are served through the same beam simultaneously, a NOMA transceiver is proposed in this paper. For the NOMA transmitter, Gray‐coded QAM constellation mapping is extended to arbitrary modulation order q. For the NOMA receiver, successive interference cancellation (SIC) is no longer necessary, and instead, a parallel demodulation is proposed. The numerical and simulation results suggest that the proposed NOMA transceiver outperforms the conventional NOMA SIC receiver and can be flexibly used for an MHN highway scenario.     

Uplink power control for TDMA portable radio channels

Power control based on signal-to-interference ratio (SIR) has been proposed as a technique for managing co-channel interference in frequency reuse radio systems. Recently, new autonomous power control methods were introduced to achieve near-optimum performance without difficult centralized control proposed earlier. The achievable performance from preliminary studies appears promising for providing significant increase in spectrum efficiency. However, the implementation of the SIR-based power control algorithms remains challenging. In this paper, implementation of power control that indirectly depends on SIR is discussed. As an example, a simple closed-loop power control algorithm for the portable transmitter is introduced for TDMA portable radio systems. While it may appear specific for the system considered, the underlying principle and parameters required (i.e., error indicator, received power level, and signal quality indicator) are common to the implementation of digital demodulation circuitry. Computer simulations indicate that SIR level is maintained at a level suitable for sustaining desirable performance. Furthermore, when the power-control updating period is short, as in the specific system considered, moderate-rate short-term fading can be tracked and mitigated     

Queuing system with absolute priorities as a model of diversity radio-reception

A possible implementation of system for space-diversity radio-reception has been considered. The system under consideration makes use of digital control system operating in the mode of the queuing system with absolute priorities and interruption. The main parameters of such system were also determined.     

A coherent multichannel demonstrator

The authors describe an advanced coherent multichannel (CMC) communications demonstrator that has been designed by the RACE 1010 consortium. This fully engineered demonstrator examines the application of CMC techniques to broadband signal distribution (e.g. television and high-definition television) in the local loop. Ten 140 Mbit/s digitised video signals are transmitted on ten optical carriers 10 GHz apart. Up to 1000 receiver terminals can be served from a single central transmitter assembly. The authors explore the system operation, system specifications, and subsystem results that have been achieved     

Enhanced Physiochemical and Mechanical Performance of Chitosan‐Grafted Graphene Oxide for Superior Osteoinductivity

The regeneration of artificial bone substitutes is a potential strategy for repairing bone defects. However, the development of substitutes with appropriate osteoinductivity and physiochemical properties, such as water uptake and retention, mechanical properties, and biodegradation, remains challenging. Therefore, there is a motivation to develop new synthetic grafts that possess good biocompatibility, physiochemical properties, and osteoinductivity. Here, we fabricate a biocompatible scaffold through the covalent crosslinking of graphene oxide (GO) and carboxymethyl chitosan (CMC). The resulting GO‐CMC scaffold shows significant high water retention (44% water loss) compared with unmodified CMC scaffolds (120% water loss) due to a steric hindrance effect. The modulus and hardness of the GO‐CMC scaffold are 2.75‐ and 3.51‐fold higher, respectively, than those of the CMC scaffold. Furthermore, the osteoinductivity of the GO‐CMC scaffold is enhanced due to the π–π stacking interactions of the GO sheets, which result in striking upregulation of osteogenesis‐related genes, including osteopontin, bone sialoprotein, osterix, osteocalcin, and alkaline phosphatase. Finally, the GO‐CMC scaffold exhibits excellent reparative effects in repairing rat calvarial defects via the synergistic effects of GO and bone morphogenetic protein‐2. This study provides new insights for developing bone substitutes for tissue engineering and regenerative medicine.     

Distributed supervisory control for multiple robot autonomous navigation performing single-robot tasks

This paper proposes two new approaches based on the Supervisory Control Theory (SCT) of Discrete Event Systems (DES) for autonomous navigation of multiple robots with single-robot tasks being assigned by a centralized scheduler. The two planning strategies differ regarding their implementation, which can be centralized or distributed. Nevertheless, both approaches share the central objective of considering the scheduler and robots as DES, allowing the use of SCT to model and control the behavior of the whole multi-robotic system. Particularly, SCT is used to gather deliberative and reactive motion planning algorithms through a structured procedure, aiming to safely navigate in cluttered, dynamic, partially-known environments. The open-loop behavior of the autonomous navigation system is modeled for both approaches. Moreover, standard supervisors are obtained for the centralized planning approach. In addition, the supervisor localization method is considered to allow a distributed planning approach. Furthermore, as a case study, real experiments considering mobile robots are carried out to corroborate the proposed framework.     

太赫兹时域光谱仪在陶瓷涂层及低压气体检测中的应用

太赫兹时域光谱仪(Terahertz Time-Domain Spectrometer,THz--TDS)在光谱学、材料表征、安检、通信等众多领域具有广阔的应用前景。介绍了一种稳定的波长为1560 nm的光纤短脉冲激光器以及一种基于该激光器的THz--TDS系统。然后用该系统对几种陶瓷基复合材料(Ceramic Matrix Composites,CMC)进行了无损检测。特别是在对热障涂层(Thermal Barrier Coating,TBC)的厚度进行检测时,实现了微米量级的精度。相比于传统方法,太赫兹波对CMC具有较强的穿透性并且应用灵活,因此提供了更好的解决方案。最后使用太赫兹异步光学采样系统(Terahertz Asynchronous Optical Sampling,THz--ASOPS)对低压水蒸气进行了高分辨率光谱分析。结果表明,光谱分辨率达到10 MHz,比传统的THz--TDS提高了100倍以上。     

Baseband emulators for the protocol testing of multimediacommunication networks

The testing of protocols for survivable computer communications networks that use different propagation media, so that the vulnerability of any one medium is offset by the availability of another, is considered. The design and construction of a prototype testbed that can emulate the effects of a stressed medium at either a packet or bit level is discussed, with particular reference to the Multi-Media Link Emulation currently under development. The design incorporates emulation-service protocols that fit in below the user packet switch network protocol and replace the actual user physical link layer and makes use of a seven-event fault set. The components of the ultimate system and its present implementation status are described     

High-speed transport components

An overview of research of high-speed transport components is given. High-speed protocols as well as high-speed implementations are considered. The use of parallelism to increase the performance of communication nodes is considered. A parallel implementation of Open Systems Interconnection (OSI) protocols on transputer networks based on the parallel concepts discussed is described. Selected performance values of the implementations are presented. The outlook on the design of high-speed transport components for future communication systems is examined