Recrystallization by annealing in SiC amorphized with Ne irradiation

Alpha-silicon carbide was irradiated with Ne+ ions at room temperature to various fluences up to 7.5 x 10(20) Ne+ m(-2) and then isochronally annealed under observation with a transmission electron microscope. In all cases, thin regions were completely amorphized by irradiation and epitaxial growth occurred from the residual crystalline region by subsequent annealing. Crystal nucleation occurred with annealing at 1000 degrees C in the cases of 3.8 x 10(20) and 7.5 x 10(20) Ne+ m(-2) irradiation, and at 1100 degrees C in the cases of 1.3 x 10(20) and 2.3 x 10(20) Ne+ m(-2) irradiation. Growth or formation of bubbles was observed with annealing at 1000 degrees C after 1.3 x 10(20), 2.3 x 10(20), and 3.8 x 10(20) Ne+ m(-2) irradiation.     

Ion and solvent diffusion and ion conduction of PC-DEC and PC-DME binary solvent electrolytes of LiN(SO2CF3)2

Two binary mixed solvent systems typically used for lithium batteries were studied by measuring the self-diffusion coefficients of the solvent, lithium ion and anion, independently by using the multi-nuclear pulsed field-gradient spin-echo (PGSE) , and NMR method. One system was propylene carbonate (PC) and diethyl carbonate (DEC) system and the other binary system was PC and 1,2-dimethoxyethane (DME), and the lithium salt used was LiN(SO₂CF₃)₂ (LiTFSI). The relative ratio of the PC was changed from zero (pure DME and DEC) to 100% (pure PC) in the DME-PC and the DEC-PC systems, respectively. The self-diffusion coefficients of the solvents were measured with and without the lithium salt, and the two solvents had almost the same diffusion coefficient in the DEC-PC system, while DME diffused faster than PC in the DME-PC system. In the electrolytes the solvents diffused the fastest, followed by the anion with the lithium ion diffusing the slowest. The degree of ion dissociation was estimated for each electrolyte by comparing the ionic conductivities estimated from the ion diffusion and those measured directly by the electrochemical method.     

Chaotic block ciphers: from theory to practical algorithms

Digital chaotic ciphers have been investigated for more than a decade. However, their overall performance in terms of the tradeoff between security and speed, as well as the connection between chaos and cryptography, has not been sufficiently addressed. We propose a chaotic Feistel cipher and a chaotic uniform cipher. Our plan is to examine crypto components from both dynamical-system and cryptographical points of view, thus to explore connection between these two fields. In the due course, we also apply dynamical system theory to create cryptographically secure transformations and evaluate cryptographical security measures.     

Radiation effects on MgAl2O4–yttria stabilized ZrO2 composite material irradiated with Ne ions at high temperatures

Spinel (MgAl₂O₄) and yttria stabilized ZrO₂ (YSZ) are candidates for fuel materials for use in nuclear reactors and the optical and insulating materials for fusion reactors. In our previous studies, the amorphization of spinel under 60 keV Xe ion irradiation at RT was observed. On the other hand, amorphization could not be confirmed in YSZ single crystals under the same irradiation conditions. In the present study, the damage evolution process of polycrystalline spinel–YSZ composite materials has been studied by in situ TEM observation during ion irradiation. The irradiation was performed with 30 keV Ne⁺ ions at a flux of 5 × 10¹³ ions cm⁻² s⁻¹ at 923 K and 1473 K, respectively. The observed results revealed a clear difference in morphology of damage depending on irradiation temperature and crystal grains. In the irradiation at 923 K, defect clusters and bubbles were formed homogeneously in YSZ grains. On the other hand, at 1473 K, only bubble formation was observed. The bubbles grew remarkably with increasing ion fluence in both grains. Even though the growth of the bubbles was observed in both grains, the average diameter of grown bubbles in spinel grains was larger than those in YSZ ones. The bubbles tended to form along the grain boundary at both temperatures.     

Combination of an actor/critic algorithm with goal-directed reasoning

In this paper, we propose an actor/critic algorithm combined with goal-directed reasoning. The actor/critic algorithm has been considered to be a model of the basal ganglia in the brain. However, the basal ganglia also appear to contribute to goal-directed reasoning. Thus, we study goal-directed reasoning in the framework of the actor/critic algorithm and discuss its neural substrates. First, since goal-directed reasoning is realized by repeatedly setting subgoals, we consider setting a subgoal to be anaction, and incorporated it into the actor/critic algorithm. Next, two additional mechanisms, the rejection of bad subgoals and double learning, are introduced to improve the performance of the new algorithm. As a consequence, goal-directed reasoning is successfully combined with the actor/critic algorithm, and the performance of the actor/critic algorithm is improved by this combination. It is also shown that a hierarchical control structure appears during the learning process and disappears after the learning has been repeated many times.     

Neuron-synapse IC chip-set for large-scale chaotic neural networks.

We propose a neuron-synapse integrated circuit (IC) chip-set for large-scale chaotic neural networks. We use switched-capacitor (SC) circuit techniques to implement a three-internal-state transiently-chaotic neural network model. The SC chaotic neuron chip faithfully reproduces complex chaotic dynamics in real numbers through continuous state variables of the analog circuitry. We can digitally control most of the model parameters by means of programmable capacitive arrays embedded in the SC chaotic neuron chip. Since the output of the neuron is transfered into a digital pulse according to the all-or-nothing property of an axon, we design a synapse chip with digital circuits. We propose a memory-based synapse circuit architecture to achieve a rapid calculation of a vast number of weighted summations. Both of the SC neuron and the digital synapse circuits have been fabricated as IC forms. We have tested these IC chips extensively, and confirmed the functions and performance of the chip-set. The proposed neuron-synapse IC chip-set makes it possible to construct a scalable and reconfigurable large-scale chaotic neural network with 10000 neurons and 10000/sup 2/ synaptic connections.     

Self-organization of orientation-selective and ocular-dominance maps through spike-timing-dependent plasticity

In the primary visual cortex, there are orientation-selective and ocular-dominance maps. These maps correlate with each other. Although many models have been proposed which explain the formation of the orientation-selective map and the ocular-dominance map, these models contain a physiologically implausible process. It is indicated that spike-timing-dependent plasticity (STDP) can yield a “topographic map” without any constraints. We show that large STDP time constants yield the orientation-selective map, and small STDP time constants yield the ocular-dominance map. This result suggests that the relationship between the orientation-selective and the ocular-dominance maps can be explained by the modulation of STDP time constants.