Kenta Abe

Power-aware dynamic cache partitioning for CMPs

Cache partitioning and power-gating schemes are major research topics to achieve a high-performance and low-power shared cache for next generation chip multiprocessors(CMPs). We propose a power-aware cache partitioning mechanism, which is a scheme to realize both low power and high performance using power-gating and cache partitioning at the same time. The proposed cache mechanism is composed of a way-allocation function and power control function; each function works based on the cache locality assessment. The performance evaluation results show that the proposed cache mechanism with a performance-oriented parameter setting can reduce energy consumption by 20% while keeping the performance, and the mechanism with an energy-oriented parameter setting can reduce 54% energy consumption with a performance degradation of 13%. The hardware implementation results indicate that the delay and area overheads to control the proposed mechanism are negligible, and therefore hardly affect both the entire chip design and performance.

Ultrafast Hydrogen-Bonding Dynamics in the Electronic Excited State of Photoactive Yellow Protein Revealed by Femtosecond Stimulated Raman Spectroscopy

The ultrafast structural dynamics in the electronic excited state of photoactive yellow protein (PYP) is studied by femtosecond stimulated Raman spectroscopy. Stimulated Raman spectra in the electronic excited state, S(1), can be obtained by using a Raman pump pulse in resonance with the S(1)-S(0) transition. This is confirmed by comparing the experimental results with numerical calculations based on the density matrix treatment. We also investigate the hydrogen-bonding network surrounding the wild-type (WT)-PYP chromophore in the ground and excited states by comparing its stimulated Raman spectra with those of the E46Q-PYP mutant. We focus on the relative intensity of the Raman band at 1555 cm(-1), which includes both vinyl bond C═C stretching and ring vibrations and is sensitive to the hydrogen-bonding network around the phenolic oxygen of the chromophore. The relative intensity for the WT-PYP decreases after actinic excitation within the 150 fs time resolution and reaches a similar intensity to that for E46Q-PYP. These observations indicate that the WT-PYP hydrogen-bonding network is immediately rearranged in the electronic excited state to form a structure similar to that of E46Q-PYP.

Optogenetic conditioning of paradigm and pattern discrimination in the rat somatosensory system

The rodent whisker-barrel cortical system is a model for studying somatosensory discrimination at high spatiotemporal precision. Here, we applied optogenetics to produce somatosensory inputs in the whisker area using one of transgenic rat lines, W-TChR2V4, which expresses channelrhodopsin-2 (ChR2) in the mechanoreceptive nerve endings around whisker follicles. An awake W-TChR2V4 rat was head-fixed and irradiated by blue LED light on the whisker area with a paradigm conditioned with a reward. The Go task was designed so the rat is allowed to receive a reward, when it licked the nozzle within 5 s after photostimulation. The No-go task was designed so as the rat has to withhold licking for at least 5 s to obtain a reward after photostimulation. The Go-task conditioning was established within 1 hr of training with a reduction in the reaction time and increase of the success rate. To investigate the relationship between the spatiotemporal pattern of sensory inputs and the behavioral output, we designed a multi-optical fiber system that irradiates the whisker area at 9 spots in a 3×3 matrix. Although the Go-task conditioning was established using synchronous irradiation of 9 spots, the success rate was decreased with an increase of the reaction time for the asynchronous irradiation. After conditioning to the Go task, the rat responded to the blue LED flash irradiated on the barrel cortex, where many neurons also express ChR2, or photostimulation of the contralateral whisker area with a similar reaction time and success rate. Synchronous activation of the peripheral mechanoreceptive nerves is suggested to drive a neural circuit in the somatosensory cortex that efficiently couples with the decision. Our optogenetic system would enable the precise evaluation of the psychophysical values, such as the reaction time and success rate, to gain some insight into the brain mechanisms underlying conditioned behaviors.

Coherent Control of the Selected Excited State by Two-Color Multipulse Excitation

The selected excited state is controlled by combination of the first pump pulse generating the target state and the second shaped pump pulse. Coherent vibrations can be induced even in the optically forbidden state.

Ultrafast dynamics of light-harvesting function of β-carotene in carbon nanotube

Ultrafast dynamics of β-carotene encapsulated in single-walled carbon nanotubes (SWCNTs) was investigated by femtosecond absorption spectroscopy. Energy transfer from the excited states of β-carotene to SWCNTs (light-harvesting function) has been observed.