解放前我国的无线电电子学

解放后我国出版的一些科学史著中,很少提及解放前一段时期国内无线电电子学的进展情况。为填补这块空白,本文作者阅了许多资料,概括地介给了当时这一学科的知识传播、人才培养以及科学研究方面的情况。

位相教学初探

凡是周期性变化的函数均可用位相描述,位相做为物理学的一个基本概念,应用十分广泛,同学们初次遇到“位相”名词,是在高中代数讲到二次函数图象时,位相作为描述周期性函数的变量出现的。数学没赋于位相以物理意义,当物理学科的教学进入理工科大学,电视大学,函授大学的有关专业时,如医学系、药学系、中医系(北京中医大学)、卫校、护校……才赋于位相以特定含义。位相的应用是多方面的,如声学,光学,交流电工学,无线电学,量子力学……位相的内容几乎涉及《医用物理学》的许多有关章节,是医用物理讲授的一个重点。全国科研院所每年招考研究生的物理试题中,有关位相及位相差,位相应用方面的内容很多,说明位相教学有一定难度,探讨位相讲解艺术,是件很有意义的工作。

论中专校名教师、学科带头人和骨干教师的培养

九十年代,中专教师队伍进入新老交替的重要时期.到本世纪末,“文革”前大学毕业的教师都将到退休年龄,名教师、学科带头人和骨干教师的培养迫在眉睫.目前,许多学校的青年教师已经挑起教学的重型担.但他们在事业心和责任感方面,在课堂教学、实习、实验和育人经验等方面,与老教师相比,还有一定差距.目前,学校面临改造老专业,创建新专业,培养目标多元化,多层次、多渠道办学,提高办学效益等一系列问题,需要知识新颖、思想敏捷、富于开拓进取、勇于改革实践的青年教师来承担.因此学校在抓教师队伍整体建设时,必须重视并努力做好名教师、学科带头人和骨干教师的培养.

清末民初近代传播设备和技术的引进及其对电化教育学发展的影响

清末民初传播设备和技术的引进是中国电化教育学发展的重要前提,其主要内容包括游艺场的引进、电影及其技术的引进与无线电技术和理论的引进。本文通过考察上述三个前提,旨在进一步揭示近代中国电化教育学发展的技术和理论背景。

江苏批准16所重点中专办高职班

经江苏省政府同意,省教委、省计委今年决定,在无锡商业学校、南通航运学校、苏州卫生学校、盐城卫生学校、连云港水产学校、常州轻工业学校、南京交通学校、南京无线电学校、南通纺织工业学校、常州纺织工业学校、淮阴电子工业学校、苏州农业学校、苏州工艺美术学校、南京机电学校、徐州工业学校、常州化工学校16所省部级以上重点中专的18个专业试办900人规模高等职业教育班.

Impacts of feedback delay and estimation error on secrecy performance of MISO single eavesdropper cognitive radio networks

Due to the broadcast nature of wireless transmission medium,security threats may hinder propagation of cognitive radio systems for commercial and military data application. This paper sets a channel error analytical framework and studies the joint impact of estimation errors and feedback delay on secrecy performance in cognitive radio networks. Under the assumption that system applies beamforming and jamming scheme,a multi-antenna cognitive base station( CBS) sends confidential signals to a secondary user( SU) in the presence of M primary users( PUs) and an eavesdropper. Assuming only imperfect channel state information( CSI) about the receivers is available,secrecy rate,outage probability,secrecy throughput are deduced to obtain a closed-form expression. It is shown that while the transmit power increases,secrecy throughput would reach to a constant. Simulation results show that feedback delay adversely impacts on secrecy rate,connection outage probability and secrecy throughput,while estimation error causes more impact on secrecy outage probability. Furthermore,the secrecy rate could increase progressively with the transmit power only if there exists no feedback delay.

Adaptive Spectr um Decision Method for Heterogeneous Cognitive Radio Networks

To improve spectrum utilization and minimize interference to Primary User (PU), an adaptive spectrum decision method is proposed for Secondary User (SU), while taking traffic load balancing and spectrum heterogeneity into consideration. Long-term statistics and current sensing results are integrated into the proposed decision method of spectrum access. Two decision methods, namely probability based and sensing based, are presented, compared and followed by performance analysis in terms of delay. For probability based spectrum decision, Short-Time-Job-First (STJF) priority queuing discipline is employed to minimize average residual time and theoretical conclusion is derived in a novel way. For sensing based decision we treat the interrupted service of SU as newly incoming and re-decision process is initialized to find available spectrum in a First-Available-First-Access (FAFA) fashion. Effect of sensing error in PHY layer is also analyzed in terms of extended average residual time. Simulation results show that, for relatively low arriving rate of SU traffic, the proposed spectrum decision method yields at least a delay reduction of 39.5% compared with non-adaptive method. The proposed spectrum decision can significantly improve delay performance even facing sensing errors, which cause performance degeneration to both PU and SU.

On the Backlog and Delay Distributions of Primary and Secondary Users in a Cognitive Radio Network

In a cognitive radio network, the secondary users can use the spectrum holes when the primary users do not utilize the spectrum, but they must vacant the spectrum when the primary users need to transmit data on the spectrum. In other words, the primary users have higher priority over the secondary users. In this paper, backlog and delay distribution bounds for both primary users and secondary users are obtained. The analysis is based on stochastic network calculus, for which, stochastic service curves are t-n-st derived for both primary users and secondary users, and the network calculus independent case analysis approach is used to find the distribution bounds. Numerical results and simulation results are also presented and discussed.

SPECTRAL CORRELATION METHOD IN THE IDENTIFICATION OF FREQUENCY-SELECTIVE FADING RADIO ENVIRONMENT

Many modulated communication signals exhibit a cyclostationarity （or periodic correlation） property. To exploit the underlying periodicity of the modulated signal in the real-time recognition schcme of radio eilvironments, this letter introduces a spectral correlation method to identify the number and the direction of multi-path in the environment of frequency-selective fading channel. By simulation, the graphs of spatial spectra corresponding to a certain cycle frequency is presented to show the accuracy of spectral correlation method in multi-path environment recognition.

Error analysis and distribution of the driving mechanism for large spherical radio telescope active reflector

In order to reduce the cost,3-PRS mechanism is introduced into the application of supporting theactive reflector unit of large radio telescope.The kinematic model of 3-PRS mechanism with rotationaljoint errors is derived to solve the error problem in actual engineering application.Then based on the errormodel,inverse and forward kinematics are analyzed.Because the solutions can not be analytically ex-pressed,a numerical method is applied.Afterwards,the parasitic motion errors are analyzed using searchmethod and empirical formulas of the maximum parasitic motion error are put forward.Finally,the toler-ance is distributed using empirical formulas to avoid interference between adjacent reflector units.Theanalyses provide a theoretical basis for the design and installation of large radio telescope active reflector.

Research and application on wireless remote measurement system of drill hydrology

The configuration, function, principle of operation and the main design of the wireless remote measurement system of drill hydrology based on GPRS were introduced in this paper. The current resources of GPIRS network was used by the system, and water level, water temperature and turbidity were measured by the intelligent sensors. Then the data were transmitted to the monitoring computer by the GPRS modem in wireless, which processed the data, forecasted and predicted water disaster. The monitoring computer software has the Chinese operation interface in the windows circumstance with simple and convenience using. The managers can operate every function by the Chinese cue. The data communications between the remote indicating instrument distributing in every drill and the monitoring computer is built only by one monitoring computer. The technology of data collection, GPRS wireless communication, computer, data processing, database were collected by the system, some functions such as real time supervising, early-warning, decision-making supporting, and so on had been achieved. The system has such merits as high precision, low cost, flexible distributing, credible transmitting and simple operation.

Predictive Spectrum Sensing Strategy Based on Reinforcement Learning

In this paper,we consider a cognitive radio(CR) system with a single secondary user(SU) and multiple licensed channels.The SU requests a fixed number of licensed channels and must sense the licensed channels one by one before transmission.By leveraging prediction based on correlation between the licensed channels,we propose a novel spectrum sensing strategy,to decide which channel is the best choice to sense in order to reduce the sensing time overhead and further improve the SU's achievable throughput.Since the correlation coefficients between the licensed channels cannot be exactly known in advance,the spectrum sensing strategy is designed based on the model-free reinforcement learning(RL).The experimental results show that the proposed spectrum sensing strategy based on reinforcement learning converges and outperforms random sensing strategy in terms of long-term statistics.

Wireless environmental monitoring system for transformer substation based on acoustic sensor

In this paper, an indoor environmental monitoring solution is proposed for the transformer sub- station system by using the ZigBee technology. It mainly analyzes the principle of sulfur hexafluoride sensor based on the acoustic method and puts forward a difference data processing method of single- channel and temperature compensation point at power consumption issues for sensor detection. The method not only reduces the sensor power consumption, but also ensures the accuracy and extends the lifetime of wireless sensor nodes effectively. This paper also analyzes the design of the base sta- tion mode, and demonstrates the running processes of routers and sensors. The feasibility of the pro- posed approach has been testified and proved.

Application of Controlled Hypothermia Radio-frequency Ablation Technique in Otolaryngology

Objective: To explore the application of controlled hypothermia radio-frequency ablation technique in otolaryngology. Methods: Germany Bipolar controlled hypothermia radio-frequency with varying tips was used for obstructive sleep apnea-hyponea syndrome, chronic hypertrophic rhinitis, allergic rhinitis, aural pseudocyst, phymatoid proliferation of tongue root, capillary hemangioma of nose and pharynx. Follow up was made up to six months. Results:All patients had curative effects. Conclusion: Hypothermia radio-frequency ablation technique was used effectively for many diseases in otolaryngology with features of accurate ablation, low complication, reliable effects as well as easyusing. It was a prospective method of micro invasive surgery.

江总书记的尊师情

江总书记的尊师情１９４７年，江泽民毕业于上海交通大学机电专业。九三学社西安交大支社的严睃、沈尚贤、钟光琳、赵富鑫蒋大宗等五位教授，当时曾做过江泽民同志的教师。而今，江泽民同志已成为中共中央总书记、中华人民共和国主席，但是在他内心深处却一直眷恋着哺育过...

A puzzle of the radio-quiet quasar PG 1407+265:Are optical and X-ray emissions produced from a relativistic jet?

PG 1407+265 is a radio quiet quasar that has a relativistic jet.In this report,we show some peculiar properties of its optical and X-ray emissions,which indicate possible non-thermal origins produced from the jet.We use a simple synchrotron + synchrotron self Compton (SSC) model to fit the emissions with different ratios of energy densities between the magnetic field and electrons (η≡U B/U e),which predicts a different γ-ray luminosity.The First LAT AGN Catalog (1LAC) did not include PG 1407+265,which indicates an upper limit of γ-ray luminosity.This upper limit constrains the ratio to be unreasonably large (η≥10 4-5).This inversely indicates that the optical and X-ray emissions may not be produced from the beaming jet.We discuss the physical implications of these results.

Functionalized CVD monolayer graphene for label-free impedimetric biosensing

Recent advances in large area graphene growth have led to many applications in different areas. In the present study, chemical vapor deposited （CVD） monolayer graphene supported on glass substrate electrochemical biosensing applications was examined as electrode material for We report a facile strategy for covalent functionalization of CVD monolayer graphene by electrochemical reduction of carboxyphenyl diazonium salt prepared in situ in acidic aqueous solution. The carboxyphenyl-modified graphene is characterized using Raman spectroscopy, X-ray photoelectron spectroscopy （XPS）, and atomic force microscopy （AFM）, as well as electrochemical impedance spectroscopy （hIS）. We also show that the number of grafted carboxyphenyl groups on the graphene surface can be controlled by the number of cyclic voltammetry （CV） scans used for electrografting. We further present the fabrication and characterization of an immunosensor based on immobilization of ovalbumin antibody on the graphene surface after the activation of the grafted carboxylic groups via EDC/NHS chemistry. The binding between the surface-immobilized antibodies and ovalbumin was then monitored using Faradaic EIS in [Fe（CN）6]^3-/4- solution. The percentage change of charge transfer resistance （Rct） after binding exhibited a linear dependence for ovalbumin concentrations ranging from 1.0 pg·mL^-1 to 100 ng·mL^-1, with a detection limit of 0.9 pg·mL^-1. Our results indicate good sensitivity of the developed functionalized CVD graphene platform, paving the way for using CVD monolayer graphene in a variety of electrochemical biosensing devices.