Bifurcation analysis in a silicon neuron

In this paper, we describe an analysis of the nonlinear dynamical phenomenon associated with a silicon neuron. Our silicon neuron in Very Large Scale Integration (VLSI) integrates Hodgkin?CHuxley (HH) model formalism, including the membrane voltage dependency of temporal dynamics. Analysis of the bifurcation conditions allow us to identify different regimes in the parameter space that are desirable for biasing our silicon neuron. This approach of studying bifurcations is useful because it is believed that computational properties of neurons are based on the bifurcations exhibited by these dynamical systems in response to some changing stimulus. We describe numerical simulations of the Hopf bifurcation which is characteristic of class 2 excitability in the HH model. We also show experimental measurements of an observed phenomenon in biological neurons and termed excitation block, firing rate and effect of current impulses. Hence, by showing that this silicon neuron has similar bifurcations to a certain class of biological neurons, we can claim that the silicon neuron can also perform similar computations.     

A MOSFET-based model of a class 2 nerve membrane

We have constructed a nerve membrane using MOSFET circuitry, which can be a basic element of an FET-based neural system. Its mechanism of action potentials generation is designed to reproduce that of the Hodgkin-Huxley equations. The responses to singlet, doublet, repetitive pulse, and sustained stimuli are analyzed to show that it exhibits similar properties to the Hodgkin-Huxley equations; namely, 1) excitable dynamics with generation of action potentials, 2) the existence of a chaotic response to periodic stimuli, and 3) Class 2 excitability. It is known that Class 2 excitability is generated by an inverted Hopf bifurcation. We have applied Hopf bifurcation theory to our nerve membrane's system equations and have shown a routine for ascertaining whether a certain parameter set generates an inverted Hopf bifurcation.     

Ultra-sensitive high-speed density measurement of the “piston effect” in a critical fluid

In order to conduct a detailed investigation of the piston effect, the peculiar heat transportation phenomenon in critical fluids, an ultra-sensitive high-speed density measurement system was developed using a very thin heater, a sensitive interferometer and a large-capacity high-speed data acquisition system. As the first step of the investigation, an experiment was conducted to measure the velocity of sound in CO2 near its critical point. Short heat pulses suppressing the disturbance of natural convection were applied to a small cell filled with almost-critical CO2 fluid and were detected by the measurement system. Because the pulses propagated through the cell at the velocity of sound and were reflected several times between the cell walls, the velocity could be precisely determined by measuring the time intervals between successive reflections. The resulting velocity profile versus temperature showed good agreement with theoretical prediction and numerical simulations. This result validated the density measurement system, and it is considered that the measurement system will be a very effective tool for further studies on critical phenomena with the aid of numerical simulation.     

Mechanical-sensorless permanent-magnet motor drive using relative phase information of harmonic currents caused by frequency-modulated three-phase PWM carriers

This paper proposes a novel control strategy of a permanent-magnet motor drive without a rotor position sensor. The strategy is based on use of relative phase information of harmonic currents caused by frequency-modulated three-phase pulsewidth-modulation (PWM) carriers. In this system, the PWM carrier source is placed on an estimated rotor reference frame, and coordinate transformation is applied to the carrier source to generate the frequency-modulated three-phase PWM carriers on a stator reference frame. By modulating voltage references with the transformed carriers, a locus of the corresponding harmonic currents on the estimated rotor reference frame is observed as a stationary ellipse because of a rotor saliency. Since a long-diameter direction of the harmonic-current ellipse indicates a true d-axis direction, orienting the estimated d axis to the long-diameter direction makes the sensorless operation possible. The paper describes a theoretical aspect of the proposed method and, then, presents experimental results as well as computer simulation results. Consequently, not only excellent controllability over a wide speed range including zero speed has been verified, but also robustness to the motor parameter variations has been confirmed.     

Genomic Instability and Cancer Risk Associated with Erroneous DNA Repair

Many cancers develop as a consequence of genomic instability, which induces genomic rearrangements and nucleotide mutations. Failure to correct DNA damage in DNA repair defective cells, such as in BRCA1 and BRCA2 mutated backgrounds, is directly associated with increased cancer risk. Genomic rearrangement is generally a consequence of erroneous repair of DNA double-strand breaks (DSBs), though paradoxically, many cancers develop in the absence of DNA repair defects. DNA repair systems are essential for cell survival, and in cancers deficient in one repair pathway, other pathways can become upregulated. In this review, we examine the current literature on genomic alterations in cancer cells and the association between these alterations and DNA repair pathway inactivation and upregulation.     

Surface properties of perfluoroalkylethyl acrylate/n-alkyl acrylate copolymers

Wetting behavior of perfluoroalkylethyl acrylate (FA)/n-alkyl acrylate (AA) copolymers with the various length of side chains of the AAs is discussed from a standpoint of surface molecular mobility. The copolymerization reactivity ratio indicates that these polymers are random copolymers. The surface properties were studied by measuring dynamic contact angle, static contact angle and freeze-dried X-ray photoelectron spectroscopy, and the bulk properties by wide-angle X-ray diffraction and differential scanning calorimetry. The advancing contact angles for water were independent of side-chain length of AAs and were almost constant at 120°. We have attributed this phenomenon to the orientation of perfluoroalkyl groups (R_f groups, C_xF_2x+1) in air, which is independent of side-chain length of AAs. On the contrary, the receding contact angles showed small values of about 45° when n numbers below 8 and increased when n numbers above 12. This can be explained as follows. High wettability during the receding process at the n numbers below 8 results from regression of R_f groups at the water–solid interface caused by minimization of the interface free energy. The low wettability during the receding process at the n numbers above 12 shows that R_f groups cannot regress due to its crystallization. This mechanism is also supported by other measurements. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 1741–1749, 1999     

Power system damping enhancement using unified power flow controller (UPFC)

The Unified Power Flow Controller (UPFC) can inject voltage with controllable magnitude and phase angle in series with a transmission line. It can also generate or absorb controllable reactive power. UPFC is expected to be able to damp power system oscillations more effectively than power electronics devices such as SVG and TCSC. In this paper, a control system design of a UPFC for power system damping enhancement based on the eigenvalue control method is proposed. It is made clear that the best design method for the power system damping enhancement is to determine steady‐state values of the UPFC control variables and the control parameters of the UPFC such as gains and time constants simultaneously, because the controllability of UPFC depends on the steady‐state values of UPFC and the power flow condition. The effectiveness of the proposed control system taking into account UPFC inverter ratings is verified by digital time simulation. Furthermore the effects of the input signals to the UPFC controller on small‐signal stability and transient stability enhancement are studied, and it is made clear that UPFC controllers using global information are more effective for power system damping enhancement than those using local information because global information has stronger observability for power system oscillations than local information. © 2000 Scripta Technica, Electr Eng Jpn, 133(3): 35–47, 2000     

Coke powder heat-treated with boron oxide using an Acheson furnace for lithium battery anodes

Coal tar pitch-based coke power was heat-treated with B₂O₃ using an Acheson furnace. The heat-treated coke powder contained nitrogen and oxygen probably derived from BN and B₂O₃, respectively, and exhibited a large irreversible capacity in the first charge-discharge (lithium dope-undope) cycle. The large irreversible capacity was decreased not by the decomposition of BN or B₂O₃ but drastically by the increase of dissolved boron concentration. The discharge capacity also correlated well with the concentration of dissolved boron.     

Inhibition of male response of drugstore beetles to stegobinone by its isomer

Stegobinone, (2S, 3R, 1R)-2,3,-dihy dro-2,3,5-trimethyl-6-(1-methyl-2-oxobutyl)-4H-pyran-4-one, the sex pheromone of drugstore beetles (Stegobium paniceum L.), elicited the pheromonal response from the males of the species in our bioassay system; however, the synthesized diastereomeric mixture of this compound was actually inactive to the males. Although the stegobinone isolated from the beetles of this species had significant activity, its enantiomeric [(±)-2S,3R,1S-] and diatereomeric [(±)-2S,3S,1RS-] isomers were inactive. Adding the (±)-2S,3R,1S isomer to stegobinone significantly reduced the male response. Furthermore, the activity of Stegobinone vanished on keeping it at room temperature for two weeks. In such a stored stegobinone sample, the presence of 2S,3R,1S isomer, the inhibitory component, was confirmed. This isomer might be produced by C-1 epimerization during storage.     

Interaction between coal and liquefaction catalysts studied by high temperature electron spin resonance

The high temperature electron spin resonance technique has been used to obtain in situ information on the behaviour of liquefaction catalysts during coal pyrolysis. The spin concentration in coal was induced in the presence of a catalyst at the pyrolysis temperature. ZnCl₂ drastically increased the spin concentration of coal. The order of activity of the catalysts with respect to the increase in spin concentration was: ZnCl₂ (impregnated) ?ZnCl₂ (dispersed) >ZnCl₂/KCl>SnCl₂ > SbCl₃≈AlCl₃ ≈CaCl₂ > coal alone.