ALBERT

Notes: The operating thermal power transfer mechanisms in a thermal-wave resonant cavity were explored theoretically and experimentally. Both steady-state ac (thermal-wave) and dc temperature rise were considered, and conduction and radiation heat transfer modes were found to co-exist in the cavity. By introducing controlled variable offset dc resistive heating superposed on the fixed-amplitude thermal-wave oscillation, it was also found that the thermal-diffusivity values of the intracavity gas can vary sensitively as a function of the dc temperature rise within a thin boundary layer adjacent to the cavity thermal source (a metallic Cr–Ni alloy strip). This resulted in the measurement of the temperature dependence of the thermal diffusivity of air. Furthermore, the observed dominance of thermal-wave radiation power transfer in the phase channel of the thermal-wave signal at large cavity lengths allowed the measurement of the absolute infrared emissivity of the thin Cr–Ni strip source material: cursive-epsilon=0.091±0.004. © 1998 American Institute of Physics.

Notes: It is predicted that thin quantum-well superlattices or spike superlattices of GaAs in ZnSe will produce band gaps in the yellow-green, and that (GaAs)1−x(ZnSe)x spikes will lead to green and blue-green gaps. These thin quantum-well structures should have better doping properties than ZnSe for x〈0.6.

Notes: The doping effect on the current–voltage characteristics of organic electroluminescent devices is studied based upon the double-carrier injection theory. The equations for the currents in the trap-charge-limited region are derived by assuming a doping-induced discrete trap level in the energy gap. Possible explanations of current experimental observations are proposed based on the equations. © 1998 American Institute of Physics.

Notes: Several possible doping effects in organic electroluminescent devices are studied within the framework of the trap-charge limited conduction models. A significant increase in the trapped charges in the doped layer can cause an overall trap charge redistribution and a shift of the location of the recombination zone. Some experimental data are analyzed and their possible relevance to our predictions is discussed. An experimental verification scheme is also proposed. © 1998 American Institute of Physics.

Notes: We have developed a numerical model to simulate the double-carrier injection trap-charge limited (TCL) transport processes in organic electroluminescent devices (OEDs). Current–voltage characteristics, energy and charge profiles are obtained and analyzed to understand the mechanisms governing the OED performance under TCL conditions. Good agreement with general experimental trends and previous analytical predictions are achieved. Dependencies on several important parameters (carrier injection level, device thickness, recombination constant, temperature, etc.) are also studied. © 1998 American Institute of Physics.

Notes: We have studied the effects of discrete trap levels on organic light emitting diodes under the space charge limited conditions. The interplay among the free, discrete, and exponential trap charges in single- and double-carrier devices is discussed. The sharp transitions in the current–voltage characteristics often associated with the discrete trap levels in single-carrier devices may disappear in double-carrier devices such as the organic light emitting diodes. The physics is elucidated using the energy and charge profiles. © 1999 American Institute of Physics.

Notes: Summary 1. The response characteristics of the cercus-to-giant interneuron system in the bushcricketTettigonia cantans to low-frequency airborne sound have been studied using intracellular or quasi-intracellular recording; the morphology of the giant interneurons has been investigated using Lucifer Yellow filling and axonal backfill with cobalt. 2. The giant interneurons excited by the cereal sensory afferents can be classified into four types based on their time courses of firing (Fig. 1): ‘quasi’-tonic, tonic burst, phasic and ‘sustained’ burst type, respectively. 3. The giant interneurons in the bushcricket are maximally sensitive to air particle displacement at 300 Hz and the lowest threshold is less than 0.1 μm (Fig. 2). 4. The intensity characteristics for three tpyes of the giant interneurons (Type I, II and IV) indicate that spike counts for these interneurons increase with increasing stimulus amplitude (Fig. 3). The phasic type of the interneuron (Type III) fired more frequently only one spike to each sound stimulus. 5. The cercus-to-giant interneuron system in the bushcricket is composed of seven bilateral pairs of the interneurons, each of which possesses a cell body, neurite and dendrites within the last abdominal ganglion and also has a giant axon which ascends the ventral nerve cord. Compared with other neurons, the axons of these neurons are giant and have diameters of 8–15 μm for GI1 and GI4 to 7, and about 5 μm for GI2 and GI3. The position of the cell body and the locations and orientations of the major processes are characteristic for each giant interneuron (Fig. 5). 6. The projections of single cereal afferents are made visible with Lucifer Yellow filling, which restricted within the ipsilateral half of the terminal ganglion. There is a great degree of the overlap between the cereal projections and the dendritic fields of the GIs (Fig. 4). 7. The branching details of the investigated giant interneurons within the thoracic ganglia and the brain are disclosed by Lucifer Yellow filling (Figs. 6, 7). The neurons Type I and III send two main collaterals medially directed within the prothoracic ganglion and the neuron Type IV sends three collaterals close to the midline of this ganglion. Within the metathoracic ganglion the neuron Type II sends three medially directed collaterals. At the ends of many branching terminals the buttonlike enlargements with stronger fluorescence can be seen and probably these terminals are the presynaptic endings. The projections of the axons of the GIs also can be found within the brain. The axons run through the tritocerebrum and deutocerebrum and terminate mainly in the mediolateral region of the lateral posterior protocerebrum.

Notes: M3:2 high speed steels with and without carbon addition were prepared by using powdermetallurgy at sintering temperature between 1210 and 1280 °C. Densification, microstructure andmechanical properties of M3:2 high speed steels were investigated. Experimental results show thatwith 0.4wt% carbon addition, full density high speed steels were obtained at temperatures in therange 1240-1260 °C which is 40 °C lower than that of the undoped counterparts, leading to a sinteringwindow expanded by 10 to 20 °C. By the addition of 0.4wt% carbon, the sintered steels showattractive combinations of bend strength and hardness over those of M3:2 steels without carbonaddition. The results reveal that the addition of carbon will not only lower the sintering temperatureand oxygen content, but also improve the mechanical properties of the sintered steels

Notes: A new approach for progressive failure and reliability analysis of carbon fiber reinforcedpolymeric (CFRP) composite pressure vessel with many base random variables is developed in thepaper. The elastic constants of CFRP lamina and geometric parameters of the vessel are selected asthe base design variables. CFRP lamina specimen and pressure vessel were manufactured and testedin order to obtain statistics of design variables. The limit state function for progressive failureanalysis was set up. Then the progressive failure and reliability analysis of the vessel wereperformed according to the stiffness degradation model based on Monte Carlo simulation procedureusing MATLAB. The distributions of failure loads and the probability of failure of the vessel wereobtained. The feasibility and accuracy of the proposed method is validated by good agreementbetween the simulation and experimental results. Further analysis indicates that the lamina tensilestrength in the fiber direction and hoop layer thickness of the vessel have significant influence onthe probability of failure of composite pressure vessel

Notes: To meet the high reliability of structural design and safety evaluation on carbon fiberwound reinforced polymeric (CFWRP) pressure vessel, the traditional safety factor design wassubstituted by reliability design based on the reliability theory and statistical principle. EightCFWRP pressure vessels were manufactured with the same material system by the same windingtechnique. And experiments were conducted to obtain the probabilistic distributions of designvariables. Results derived from reliability design (fiber thickness) agreed well with experimentalresults and were much lower than that from conventional design. Through comparison amongreliability design results with different statistics of fiber strength, significant effect of the variationof fiber strength on structural reliability of composite pressure vessel was demonstrated. Theconventional design was verified to be not reasonable since it considers only the mean value of fiberstrength without the effect of fiber strength distribution on structural resistance of pressure vessel