The dependence of the negative nonlinear absorption effect on the modulation degree and frequency of the incident laser was investigated in Er3+: LiYF4 crystals. With a decreasing modulation degree, a reverse-phased waveform was obtained in the transmitted waveform for modulation intensities of sinusoidal and rectangle waves. The transmitted waveform was observed symmetrically at modulation frequency of 0. 25 MHz. However, the transmitted waveform was asymmetrical at higher than 0. 5 MHz. In addition, the reverse-phased waveforms were obtained for sample lengths greater than 12 mm in the incident modulation degree of 10 to 56%. The NNA effect was observed at a temperature range of 20 to 500 K. It has been confirmed that a mechanism of the negative nonlinear absorption can be explained by considering an enhanced absorption model for a five-level system of the Er3+ ion.

This article presents an indoor positioning and communication platform, using fluorescent lights. We set up a practical implementation of a VLC (Visible Light Communication) system in a University building. To finalize this work, it is important that we analyze the properties of the reception signal, especially the length of the data string that can be received at different walking speed. In this paper, we present a model and a series of formulae for analyzing the relationship between positioning signal availability and other important parameters, such as sensor angle, walking speed, data transmission rate, etc. We report a series of real-life experiments using VLC system and compare the results with those generated by the formula. The outcome is an improved design for determination of the reception area with more than 97% accurate signals, and an optimal transmission data length, and transmission rate.

We proposed a hard-wired CPG hardware network to reproduce the gaits of four-legged animals. It should reproduce walking and bounding, and they should be switchable with each other by changing the value of only one voltage.

Reproducing quadruped locomotion from an engineering viewpoint is important not only to control robot locomotion but also to clarify the nonlinear mechanism for switching between locomotion patterns. In this paper, we reproduced a quadruped locomotion pattern, gallop, using a central pattern generator (CPG) hardware network based on the abelian group Z4×Z2, originally proposed by Golubitsky et al. We have already used the network to generate three locomotion patterns, walk, trot, and bound, by controlling the voltage, EMLR, inputted to all CPGs which acts as a signal from the midbrain locomotor region (MLR). In order to generate the gallop and canter patterns, we first analyzed the network symmetry using group theory. Based on the results of the group theory analysis, we desymmetrized the contralateral couplings of the CPG network using a new parameter in addition to EMLR, because, whereas the walk, trot, and bound patterns were able to be generated from the spatio-temporal symmetry of the product group Z4×Z2, the gallop and canter patterns were not. As a result, using a constant element $hat{kappa}$ on Z2, the gallop and canter locomotion patterns were generated by the network on ${f Z}_4+hat{kappa}{f Z}_4$, and actually in this paper, the gallop locomotion pattern was generated on the actual circuit.

In this paper we show that the performance workload of button-input interfaces do not monotonically increase with the number of buttons, but there is an optimal number of buttons in the sense that the performance workload is minimized. As the number of buttons increases, it becomes more difficult to search for the target button, and, as such, the user's cognitive workload is increased. As the number of buttons decreases, the user's cognitive workload decreases but his operational workload increases, i.e., the amount of operations becomes larger because one button has to be used for plural functions. The optimal number of buttons emerges by combining the cognitive and operational workloads. The experiments used to measure performance were such that we were able to describe a multiple regression equation using two observable variables related to the cognitive and operational workloads. As a result, our equation explained the data well and the optimal number of buttons was found to be about 8, similar to the number adopted by commercial cell phone manufacturers. It was clarified that an interface with a number of buttons close to the number of letters in the alphabet was not necessarily easy to use.

Bit error rate characteristic of negative feedback optical amplifier was investigated by manipulating the negative feedback signal intensity fed into the semiconductor optical amplifier together with the input signal. Consequently, bit error rate was reduced as negative feedback signal intensity increases. Suppression towards the unevenness at the power level `1' and overshoot during rising phase on the output signal eye-diagram was recorded. With negative feedback, through gain decrease of 2.4 dB, power penalty improved remarkably by 15 dB.

We present a hard-wired central patter generator (CPG) hardware network that reproduces the periodic oscillations of the typical gaits, namely, walk, trot, and bound. Notably, the three gaits are generated by a single parameter, i.e., the battery voltage EMLR, which acts like a signal from the midbrain's locomotor region. One CPG is composed of two types of hardware neuron models, reproducing neuronal bursting and beating (action potentials), and three types of hardware synapse models: a gap junction, excitatory and inhibitory synapses. When four hardware CPG models were coupled into a Z4 symmetry network in a previous study [22], two neuronal oscillation patterns corresponding to four-legged animal gaits (walk and bound) were generated by manipulating a single control parameter. However, no more than two neuronal oscillation patterns have been stably observed on a hard-wired four-CPG hardware network. In the current study, we indicate that three neuronal oscillation patterns (walk, trot, and bound) can be generated by manipulating a single control parameter on a hard-wired eight-CPG (Z4 × Z2 symmetry) hardware network.