Frequency Variations of π-equivalent Circuit Parameters of a Junction Transistor †

One of the most useful small-signal equivalent circuit representations is based on a m-equivalent circuit representation of the transistor in a common-emitter connection. This m-equivalent circuit representation is more readily and commonly employed in circuit analysis or design in comparison with a ^'-equivalent circuit representation. The variation of equivalent circuit parameters at high frequencies in the π-equivalent circuit representation was determined by Giacoletto experimentally. Unfortunately, however, we have no example but the above, in spite of this problem being very common and important. The exact expression for π-equivalent circuit parameters is too complicated to be calculated. The result may be somewhat simplified by expanding the hyperbolic function into a Taylor series and retaining only the first few terms. Numerical values of these approximate expressions are calculated and then compared with values calculated from the corresponding exact expression. Furthermore, w-equivalent circuit parameters relative to low-frequency values are given as a function of frequency relative to f_T and f_α. The π-equivalent circuit parameters of a p-n-p germanium alloy-junction transistor of the diffusion (homogeneous base) type are obtained by measuring small-signal h parameters under the low-level injection conditions with an impedance bridge. Then, it is made clear that they are in reasonably good agreement with theoretical values. The approximate expression for α is proposed, where α is analysed in terms of magnitude and phase shift. It is shown that it is more exact and more useful than the expressions such as the Thomas-Moll expression, etc., as a result of discussing the errors in the approximations of the equations.     

Gelation of Bovine Serum Albumin by Glutathione

Bovine serum albumin (BSA) formed an opaque gel when incubated at 37°C with reduced glutathione (GSH). Gelation was highly dependent on concentration of GSH and pH, at 70 mM GSH and pH 8.2 BSA showed maximum gel hardness. Sodium dodecyl sulfate polyacrylamide gel electrophoresis and the number of protein sulfhydryls revealed that gelation involves reduction of intramolecular disulfides in BSA and subsequent cross-links through intermolecular protein disulfides. Gelation was strongly inhibited by high concentrations of salts; inhibitory effects were highly dependent on species of anions, but not cations.     

Growth of calcium phosphate on phosphorylated chitin fibres

Calcium phosphate growth on chitin phosphorylated fibres was studied using scanning electron microscopy and energy dispersive X-ray analysis (SEM, EDX), micro-Fourier transform infrared spectroscopy (FTIR), and solid state magic angle spinning nuclear magnetic resonance (MAS NMR) techniques. The C6 chemical shift positions of 13C MAS NMR in the chitin fibres phosphorylated using urea and H3PO4 are obvious indicating that phosphorylation takes place not in the C1 but in the C6 region. Micro-FTIR and 31P MAS NMR suggested that ammonium hydrogen phosphate formed during the phosphorylation procedure. Chitin fibres phosphorylated using urea and H3PO4 and then soaked in saturated Ca(OH)2 solution at ambient temperature, which lead to the formation of thin coatings formed by partial hydrolysis of the PO4 functionalities, were found to stimulate the growth of a calcium phosphate coating on their surfaces after soaking in 1.5×SBF solution for as little as one day. The thin layer after Ca(OH)2 treatment functioned as a nucleation layer for further calcium phosphate deposition after soaking in 1.5×SBF solution. EDX-measured Ca : P ratios of the coatings of Ca(OH)2-treated phosphorylated chitin in 1.5×SBF solution suggested that calcium-deficient apatite was formed.     

Complex Permittivity Spectra of Various Insulating Polymers at Ultrawide‐Band Frequencies

Nowadays, trials to use even higher frequencies are pursued to realize high‐speed wireless communications. In order to respond to such a trend, dielectric properties of insulating polymers at high frequencies have to be clarified, although the importance of clarifying low‐frequency properties is still very high, especially for use as high‐voltage insulators. In this regard, complex permittivity spectra from 10 mHz to 4.0 THz were obtained for various insulating polymers. The spectra obtained in the very wide frequency range are important, because they can be a valuable database and they provide various pieces of important information on dielectric characteristics.     

Crystallization and Transformation of Zirconia Under Hydrothermal Conditions

During constant-rate heating to 350°C in concentrated NaOH solutions, cubic ZrO₂ crystallized at ∼120°C from hydrated amorphous ZrO₂; these One cubic ZrO₂ particles abruptly changed into needlelike monoclinic ZrO₂ single crystals at 300°C. Crystallization and phase transformation were studied by XRD, TEM, and EPMA. Cubic ZrO₂ appears to crystallize via collapse of the ZrO₂−nH₂O structure and subsequent slight rearrangement of the lattice. The abrupt formation of mono-clinic ZrO₂ was considered to result when the very fine cubic ZrO₂ particles coagulated in a highly oriented fashion.     

Two-line neuristor with active element in series and in parallel†

A neuristor of a constant K two-line active circuit proposed by the authors was realised and the dependence of neuristor characteristics on the circuit parameters was obtained. It is known that the neuristor proposed as a micro-logic device has many advantages. However, no functional device which works as the neuristor has been completed. The proposed neuristor models have not been satisfactorily developed as a micro-electronic device because they cannot be integrated due to their structural difficulties, or even if the integration is realized, the relation between the structure and the neuristor characteristics was often obscure.

From the above point of view, a two-line circuit is proposed in this paper which is easily integrated because of its simple structure and is easy to explain theoretically. The neuristor is realized by a lumped-constant K active circuit to obtain the dependence of the neuristor characteristics on the circuit parameters. As a circuit, a series and a parallel type neuristor are used into which an S-shaped and an N-shaped negative resistive element are inserted, respectively.

First, by transmitting pulses the circuit shows that the neuristor characteristics are realized by the constant K circuit. Next the dependence of the neuristor characteristics on the circuit parameters is obtained as a function of the impedance of the circuit element, and finally, to explain theoretically the measured results, the circuit is analysed by Gauss-Seidels method which improves the conventional phase plane analysis.

As a result, it is demonstrated experimentally that the neuristor can be realized using the constant K two-line circuit. The relation between the neuristor characteristics and the circuit parameters is also obtained. Almost all the experimental results are proved theoretically. The difference of the neuristor characteristics between the S-shaped and the N-shaped negative resistance element is demonstrated. Thus now knowledge for the optimum circuit structure in order to realize the neuristor with new negative resistance elements is presented.     

Fabrication and Characterization of Ba(Ti,Zr)O3 Thin Films Through the Chemical Solution Deposition Process

Lead- and bismuth-free Ba(Ti_{1 ? x} Zr _x )O₃ (BTZ) thin films were fabricated on Pt(111)/Ti/SiO₂/Si(100) substrates by the chemical solution deposition (CSD) process. The single phase BTZ thin films were obtained at 650°C by conventional process and the control of lattice parameter a was possible by Zr substitution. As the D-E hysteresis loops and J-V characteristics depended on the precipitates on film surface, the fabrication process was reexamined by 2-step sintering process. Consequently the decreasing of first sintering time was able to prevent the precipitates, and the larger grain of about 40–50 nm were obtained by additional sintering for 2 hour.     

Zonal Flows and Geodesic Acoustic Mode Oscillations in Tokamaks and Helical Systems

This paper reviews the theoretical foundations of zonal flow, putting emphasis on the linear response function of plasma to the external flow drive. An extension of the theory is made in order to apply it to helical systems and to study the properties of the zonal flow in the low frequency range. Further refinement of the theory is made incorporating the orbital effects of particles more precisely, and the role of neoclassical polarization current is identified.