热敏电阻风速传感器的线性补偿

热敏电阻风速传感器的风速/电压曲线受到气体温度、湿度等的影响,呈现明显的非线性化.通过设计基于双恒流源的双臂电桥,与常用的惠斯登电桥进行比较.实验表明,双恒流源双臂电桥比惠斯登电桥能更好地补偿热敏电阻风速传感器的非线性关系,并获得较高的灵敏度.     

Buffering packetised data: an examination of the crossover effect

Buffer analysis has traditionally relied heavily on the use of traffic models with short range (exponentially decaying) autocorrelation, e.g. Poisson and Markov modulated Poisson processes. Recent literature has suggested the presence of traffic with slowly (hyperbolically) decaying autocorrelation functions; these sources collectively and individually seem to be exhibiting the phenomenon of long range dependence (LRD). Furthermore, it has been claimed that this sort of traffic may exhibit behaviour, when buffered, that is advantageous in that a smaller buffer may be required than would be the case with non-LRD traffic. This phenomenon has been named the crossover effect, and the authors quantify its relevance to ATM networking, using simulation studies of a homogenous mix of chaotic sources. These show that there is a crossover effect, but the key finding is that this effect is much nearer to a buffer length of zero than was predicted by previous theoretical studies, actually occurring at a value so low that it has no practical significance     

InP中皮秒快速现象

利用测量瞬态反射谱的方法，探索了掺硫、铁、锌以及非掺杂的ＩｎＰ中载流子寿命，观察到非掺杂ＩｎＰ中载流子寿命最长约６０ｐｓ，掺锌ＩｎＰ中载流子寿命３８ｐｓ居中，掺硫和掺铁的寿命最短约１ｐｓ掺硫、铁和锌的ＩｎＰ中载流子寿命下降，是由于掺杂引入了复合中心，这一结果已被喇曼光谱所证实。     

Heat-transfer phenomena in alloys

The phonon heat conductivity k _ph in Bi_{1 − x} Sb _x (x = 0.04–0.12) alloys is investigated in the temperature range of 6–60 K. The results are compared with the theory of solids at low temperatures, and the basic sources of phonon scattering are revealed. It is shown that phonon scattering at local mass changes dominates over other sources. The dependences of k _ph on composition are considered at temperatures of 60 and 90 K, and it is found that the normal N processes substantially affect the phonon scattering under these conditions. The donor-impurity effect on heat conductivity of Bi_0.88Sb_0.12 is considered, and the heat resistance caused by the phonon scattering at impurity centers is singled out.     

Transient phenomena and control of such phenomena in a generator with a delay

Results of the numerical analysis of transient processes in a mathematical model describing a generator with a time lag and delayed action are presented. Regular and chaotic oscillation modes under chaotically varying initial conditions are considered. The possibility of controlling a generator’s chaotic oscillations via a radio pulse is analyzed in the case when there are one or two attraction basins.     

Breakover phenomena in field-controlled thyristors

The occurrence of breakover in the forward-blocking anode current-voltage characteristics of field-controlled thyristors is analyzed. It is demonstrated that this breakover occurs due to gate current flow which causes a debiasing of the gate potential in the presence of any series gate resistance. Based upon this mechanism, analytical expressions have been derived which describe the anode current-voltage breakover characteristics. These theoretical expressions have been found to be in very good agreement with the measured data obtained from asymmetrical field-controlled thyristors fabricated with various device thicknesses. From the analysis presented in this paper, it can be concluded that the occurrence of breakover in the forward-blocking characteristics of field-controlled thyristors can be minimized by ensuring low series gate resistances which biasing the devices and by using gate bias voltages well in excess of the minimum value required to block any desired anode voltage.     

Fluctuation phenomena in nerve membrane

The fluctuations of the voltage across the resting membrane of myelinated nerve fibers have been analyzed. They show a 1/f spectrum and a Gaussian amplitude distribution and are related to the net flow of potassium through the membrane. When the average membrane voltage is made more negative by means of an external current, depolarizing deflections can be observed. They cause an asymmetry in the noise amplitude distribution and a marked increase in the subaudio spectral components of the noise. The depolarizing deflections can be attributed to batch-wise inflow of sodium ions. Possible mechanisms of both types of membrane voltage fluctuations are discussed.     

Intermittency phenomena in electrical connectors

Fretting is known to be a major cause of contact deterioration and failure, particularly in tin-plated contacts. During fretting the contact resistance generally increases slowly with time. Superimposed on this slow increase in contact resistance are rapid changes in contact resistance within fractions of a second, called intermittences or short duration discontinuities. Although intermittences have been reported by several authors, they are frequently overlooked in traditional fretting experiments and not much is known about their origin. The present study aims at filling this gap. A test apparatus has been built to measure the contact voltage-drop profile during an intermittence and fretting experiments on tin-plated copper contacts have been carried out. The results lead to a set of requirements for a model to explain intermittency phenomena     

Quantum phenomena in field-effect-controlled semiconductornanostructures

Quantum effects resulting from sub-100 nm features in planar, field-effect-controlled semiconductor structures or devices are discussed, and experimental results are compared with calculations. These devices are based on the GaAs-AlGaAs modulation-doped field-effect transistor (MODFET) and include grating-gate lateral surface superlattices. (LSSLs), grid-gate LSSLs, planar-resonant-tunneling field-effect transistors (PRESTFETs), multiple parallel quantum wires (MPQWs), and arrays of quantum dots (QDs). In contrast to conventional, epitaxially grown vertical quantum structures, planar structures offer the opportunity for electron confinement in three, two, and one dimensions and the flexibility of electrical tuning of quantum effects     

Creep phenomena in lead-free solders

A critical review of data on microstructure and creep process activation energy values for a number of lead-free solder alloys like Sn-Ag; Sn-Bi; Sn-In was conducted. The review revealed a scatter in experimental data, which could not be explained by the dislocation creep mechanism only, even after the published data was corrected for Young’s modulus temperature dependence. An analysis of the data implies that possible origin of such a scatter is nucleation, accumulation and further growth of such internal defects as pores and microcracks during creep. It is shown that these processes may affect the measured steady-state creep rates, and may be one of the major reasons for the observed scatter in experimental data, and, therefore, must be taken into consideration in lead-free solder alloys’ creep studies.     

Triggering phenomena in avalanche diodes

The operation of a small area p-n junction diode above the breakdown voltage is analyzed. A new formulation in terms of ionization probability is used to derive the rate of turn-on of current in such structures. Two differential equations are given which may be used to compute the probability that a carrier swept into or generated within the space-charge region triggers avalanche breakdown. For a 27-V n⁺-p diode biased 1 V above breakdown, this probability is close to 0.5 for an electron entering from the p side, or 0.1 for a hole entering from n side. Experimental measurements are in good agreement with the theoretical predictions.     

Microwave phenomena in bulk GaAs

CW microwave oscillations were generated at room temperature by usingn-GaAs with a carrier concentration 10¹³- 10¹⁴per cc. Fundamental frequencies between 1 - 10 kMc were excited, and harmonic signals up to 21 kMc were detected. The maximum power output and efficiency on CW basis were 56 mW and 5.2 percent, respectively, at 2 - 3 kMc. A study was made of harmonic content, linewidth, circuit and electronic tunability, as well as the effects of sample thickness, bias voltage, and temperature, on the observed signal frequency. For sample length × carrier concentration products between 2×10¹⁰- 2 × 10¹²cm^-2there was a wide diversity in behavior observed in different samples. This was tentatively attributed to the possibility of exciting not only traveling dipole domains but also growing space-charge waves. These growing space-charge waves were found to exist in samples where the condition nl < 2 × 10¹²cm^-2was satisfied, and are also suspected of being responsible for the observed microwave amplification in bulk GaAs. Three different contacts were used successfully: nickeltin, indium-nickel, and indium-gold. These contacts, and the general semiconductor preparation techniques, will be described in detail.     

Diagram of Gunn-effect phenomena

The phenomena observed with Gunn-effect semiconductors can be combined distinctly in a diagram; this is illustrated in detail. Subsequently, some experimental results are interpreted using the diagram.     

Full-wave analysis of a strip crossover

A full-wave analysis of a strip crossover above a conducting plane is carried out. Higher-order modes are excited in the form of evanescent waves in the vicinity of the discontinuity, while further away only the dominant (TEM) modes exist. The higher-order mode currents are modeled by triangle functions and the dominant modes by outgoing traveling waves. The method of moments is used to reduce the integral equations on the surface of each strip to matrix equations whose solution determines the currents on each strip. The impedance and scattering matrices of the four-port network and the equivalent circuit were determined. At low frequencies, the equivalent circuit agrees very well with that which was obtained previously using a quasi-static analysis. The two approaches begin to disagree when the cross-sectional dimensions of the crossover become comparable to a tenth of the wavelength. At that point the quasi-static analysis becomes inaccurate, while the full-wave analysis presented here remains valid     

A study of locking phenomena in oscillators

Impression of an external signal upon an oscillator of similar fundamental frequency affects both the instantaneous amplitude and instantaneous frequency. Using the assumption that time constants in the oscillator circuit are small compared to the length of one beat cycle, a differential equation is derived which gives the oscillator phase as a function of time. With the aid of this equation, the transient process of "pull-in" as well as the production of a distorted beat note are described in detail. It is shown that the same equation serves to describe the motion of a pendulum suspended in a viscous fluid inside a rotating container. The whole range of locking phenomena is illustrated with the aid of this simple mechanical model.     

Second-breakdown phenomena in avalanching silicon-on-sapphire diodes

A new experimental technique, based on local temperature-induced changes in optical absorption, is used to study second breakdown in avalanching reverse-biased silicon-on-sapphire diodes. The technique allows spatial resolution down to 1 µm and temperature resolution of a few degrees Celsius. Further, used stroboscopically, the technique allows time resolution on the order of nanoseconds. The technique, in conjunction with special constant-current bias circuits and light-emission studies, has been used to elucidate the physical mechanisms underlying second breakdown in avalanching diodes. It is found that second breakdown occurs when the thermally generated leakage current becomes large enough at some localized region of the junction to quench the avalanche there. Under pulse biases, the product of the average pulse power times the square root of the delay timeτDwas essentially constant forτDas short as 1½ ns. However, the junction temperature atτDincreased asτDdecreased, and for very shortτDthe heating was highly nonuniform.