Connection‐Strength Estimation of Neuronal Networks by Fitting for Izhikevich Model

Recently, there has been abundant research using multineuron recording, but there are many problems with extracting the features from the obtained spike time series, which are huge in volume and complex. Here we introduce a new method of estimating synaptic connection strengths between neurons by fitting to the Izhikevich model by maximum likelihood estimation. We demonstrate that our method can estimate connection strengths from spike time series given by a simulated neural ensemble and can estimate nonconnectivity between two independent cultured neuronal networks. These results suggest that our method is applicable to network and plasticity analysis of neuronal networks.     

Frequency shift of a GaAlAs diode laser in a magnetic field

The oscillation frequency shift of a GaAlAs diode laser under a magnetic field at room temperature is reported. In this experiment the observed frequency shift is 500 MHz to the low-frequency side at the magnetic flux density of 1.4 T, and shows the quadratic dependence on the magnetic flux density.     

Frequency stabilization of a semiconductor laser under direct FSK modulation: The modulation method and evaluation of stability

The frequency stability of a semiconductor laser deteriorated under direct frequency shift keying (FSK) when stabilization depended entirely upon an external frequency reference. Therefore, the PEAK method was devised for the purpose of improving frequency stability. This method requires two distinct frequency components and, therefore, will not work effectively in a communications system that produces a succession of identical frequencies, as does the FSK method on occasion. This paper, then, explains the results of our comparative analysis of the two modulation methods. The evaluation of frequency stability requires us to use a beat note between two stabilized laser beams, referred to here, as “signal” and “reference,” lasers. The reference laser is stabilized by a method that takes advantage of the magneto-optical effect. This laser restrains the tendency of the beat note frequency to broaden in other stabilization methods, and even makes it possible to predetermine the beat frequency to be employed. The improvement in frequency stability obtained is about one order of magnitude. © 1998 Scripta Technica, Electr Eng Jpn, 125(2): 44–51, 1998     

Frequency stabilisation of semiconductor laser using atomicabsorption line under direct FSK

The oscillation frequency of an AlGaAs laser diode is stabilised using the Rb-D2 absorption line (780 nm) under the direct frequency shift keying (FSK) condition. Only one side (mark or space) frequency signal is used to obtain the feedback signal for stabilisation in this system. The stability obtained is almost the same as that of the case without FSK     

Enhancement of nucleoside phosphorylation activity in an acid phosphatase

Escherichia blattae non-specific acid phosphatase (EB-NSAP)possesses a pyrophosphate-nucleoside phosphotransferase activity,which is C-5'-position selective. Current mutational and structuraldata were used to generate a mutant EB-NSAP for a potentialindustrial application as an effective and economical proteincatalyst in synthesizing nucleotides from nucleosides. First,Gly74 and Ile153 were replaced by Asp and Thr, respectively,since the corresponding replacements in the homologous enzymefrom Morganella morganii reduced the K_m value for inosine andthus increased the productivity of 5'-IMP. We determined thecrystal structure of G74D/I153T, which has a reduced K_m valuefor inosine, as expected. The tertiary structure of G74D/I153Twas virtually identical to that of the wild-type. In addition,neither of the introduced side chains of Asp74 and Thr153 isdirectly involved in the interaction with inosine in a hypotheticalbinding mode of inosine to EB-NSAP, although both residues aresituated near a potential inosine-binding site. These findingssuggested that a slight structural change caused by an aminoacid replacement around the potential inosine-binding site couldsignificantly reduce the K_m value. Prompted by this hypothesis,we designed several mutations and introduced them to G74D/I153T,to decrease the K_m value further. This strategy produced a S72F/G74D/I153Tmutant with a 5.4-fold lower K_m value and a 2.7-fold higherV_max value as compared to the wild-type EB-NSAP.     

Radio propagation characteristics due to rain at 20-GHz band

Measurements of 20-GHz radio wave rainfall attenuation and cross-polarization discrimination due to rain have been conducted since July 1971 in Tokyo. There was a high correlation between rainfall attenuation and cross-polarization discrimination. Rainfall attenuation of 45 dB caused cross-polarization discrimination of 12 dB.     

Frequency stabilisation of semiconductor laser using Faraday effect

The oscillation frequency stabilisation of a semiconductor laser without direct modulation of the injection current is reported. The Rb-D/sub 2/ absorption line is used as a frequency reference and the Faraday effect is used to obtain the control signal for stabilisation.<>     

Signal level degradation due to snow accretion on a radome

The received signal level and antenna pattern variation due to snow accretion on a radome have been measured. Large signal level attenuation was observed when the snow accreted asymmetrically on the radome.     

Oscillation wavelength shift characters of a semiconductor laser in a magnetic field: Observation by using a beat note

In papers published previously, we discussed the oscillation wavelength shift of a semiconductor laser in a magnetic field at room temperature. Observations were carried out by means of a monochromator that was able to measure the oscillation wavelength shift in a steady state only and that was subject to a certain degree of measurement error. In this work, we used the beat note between two semiconductor lasers as a means of observing the wavelength shift. This method reduces the overall measurement error to about one tenth that obtained when using the monochromator and enables us to observe the time dependence of the wavelength shift, after establishing a magnetic field. The observed wavelength shift was delayed in comparison with the square of the magnetic flux density, which is proportional to the wavelength shift in a steady state. The delay was about 0.07 s, which is much longer than we actually expected, when changing the temperature in an active layer. © 1998 Scripta Technica. Electr Eng Jpn, 122(3): 46–54, 1998