Kaoru Yamamoto

Chronic Optogenetic Activation Augments Aβ Pathology in a Mouse Model of Alzheimer Disease

In vivo experimental evidence indicates that acute neuronal activation increases Aβ release from presynaptic terminals, whereas long-term effects of chronic synaptic activation on Aβ pathology remain unclear. To address this issue, we adopted optogenetics and transduced stabilized step-function opsin, a channelrhodopsin engineered to elicit a long-lasting neuronal hyperexcitability, into the hippocampal perforant pathway of APP transgenic mice. In vivo microdialysis revealed a ∼24% increase in the hippocampal interstitial fluid Aβ42 levels immediately after acute light activation. Five months of chronic optogenetic stimulation increased Aβ burden specifically in the projection area of the perforant pathway (i.e., outer molecular layer of the dentate gyrus) of the stimulated side by ∼2.5-fold compared with that in the contralateral side. Epileptic seizures were observed during the course of chronic stimulation, which might have partly contributed to the Aβ pathology. These findings implicate functional abnormalities of specific neuronal circuitry in Aβ pathology and Alzheimer disease.

Hydrogen-Bond-Dynamics-Based Switching of Conductivity and Magnetism: A Phase Transition Caused by Deuterium and Electron Transfer in a Hydrogen-Bonded Purely Organic Conductor Crystal

A hydrogen bond (H-bond) is one of the most fundamental and important noncovalent interactions in chemistry, biology, physics, and all other molecular sciences. Especially, the dynamics of a proton or a hydrogen atom in the H-bond has attracted increasing attention, because it plays a crucial role in (bio)chemical reactions and some physical properties, such as dielectricity and proton conductivity. Here we report unprecedented H-bond-dynamics-based switching of electrical conductivity and magnetism in a H-bonded purely organic conductor crystal, κ-D3(Cat-EDT-TTF)2 (abbreviated as κ-D). This novel crystal κ-D, a deuterated analogue of κ-H3(Cat-EDT-TTF)2 (abbreviated as κ-H), is composed only of a H-bonded molecular unit, in which two crystallographically equivalent catechol-fused ethylenedithiotetrathiafulvalene (Cat-EDT-TTF) skeletons with a +0.5 charge are linked by a symmetric anionic [O···D···O](-1)-type strong H-bond. Although the deuterated and parent hydrogen systems, κ-D and κ-H, are isostructural paramagnetic semiconductors with a dimer-Mott-type electronic structure at room temperature (space group: C2/c), only κ-D undergoes a phase transition at 185 K, to change to a nonmagnetic insulator with a charge-ordered electronic structure (space group: P1). The X-ray crystal structure analysis demonstrates that this dramatic switching of the electronic structure and physical properties originates from deuterium transfer or displacement within the H-bond accompanied by electron transfer between the Cat-EDT-TTF π-systems, proving that the H-bonded deuterium dynamics and the conducting TTF π-electron are cooperatively coupled. Furthermore, the reason why this unique phase transition occurs only in κ-D is qualitatively discussed in terms of the H/D isotope effect on the H-bond geometry and potential energy curve.

New Equalizer to Improve Signal-to-Noise Ratio

Signal-to-noise ratio (SNR) of an optical memory disc deteriorates as the recording density increases. The authors have coped with this problem and developed a new equalizer which can improve the SNR by boosting higher frequency components on the readout signal without increasing the inter-symbol interference (ISI). The authors measured the jitter values on a prototype disc applying the new equalizer. The disc had a capacity of 15 Gbytes, a track pitch of 0.37 µm and a minimum pit length of 0.25 µm. An optical head with a second harmonic generation (SHG) blue laser with a wavelength of 430 nm and an objective lens with a NA of 0.6 was used. As a result, it was confirmed that the new equalizer could improve not only the SNR but also the tilt margins. Furthermore, the correlation between the jitter and the bit error rate observed on a conventional equalizer was found unchanged even with the new equalizer.

One-Dimensional Growth of Phenylene Oligomer Single Crystals on Friction-Transferred Poly(p-phenylene) Film

One-dimensionally oriented thin crystals of a phenylene oligomer, p-sexiphenylene (6P), are grown on the poly( p-phenylene) (PPP) film prepared by the friction-transfer method. The 6P molecules tend to grow epitaxially on the (001) planes of alkali halides and the molecular axis is parallel to the directions of alkali halides. The needle crystals orient along two directions. On the other hand, 6P stands on quartz plates with random orientations. The slender crystals of 6P formed on the friction-transferred PPP on alkali halides and quartz plates confirm that the uniaxial orientation has anisotropic optical properties.

The Path from a Digital Versatile Disc (DVD) using a Red Laser to a DVD using a Blue Laser

The next generation digital versatile disc(DVD) using a blue laser is required to have 15 Gbytes capacity so that it can reproduce motion picture expert group 2(MPEG2) video stream with a main profile at a high level format for a maximum of 133 min. To achieve this goal, further improvements are necessary in both the recording and the reproducing systems. For the recording system the authors developed a super resolution recording material and an electron beam recording system. For the reproducing system the authors devised four technologies: a Viterbi decoder, a liquid crystal tilt servo system, a cross talk cancel system and a tangential adaptive equalizer. By combining these with a pick up head of 430 nm vavelength/0.6 NA lens and a 0.6-mm-thick substrate, the authors confirmed sufficient tilt margins in the case of 12.7 Gbytes (radial tilt margin: ±1.61°, tangential tilt margin: ±0.48°). Our next target is to work on the 15 Gbytes capacity.

Benzothienobenzothiophene-Based Molecular Conductors: High Conductivity, Large Thermoelectric Power Factor, and One-Dimensional Instability

On the basis of an excellent transistor material, [1]benzothieno[3,2-b][1]benzothiophene (BTBT), a series of highly conductive organic metals with the composition of (BTBT)2XF6 (X = P, As, Sb, and Ta) are prepared and the structural and physical properties are investigated. The room-temperature conductivity amounts to 4100 S cm(-1) in the AsF6 salt, corresponding to the drift mobility of 16 cm(2) V(-1) s(-1). Owing to the high conductivity, this salt shows a thermoelectric power factor of 55-88 μW K(-2) m(-1), which is a large value when this compound is regarded as an organic thermoelectric material. The thermoelectric power and the reflectance spectrum indicate a large bandwidth of 1.4 eV. These salts exhibit an abrupt resistivity jump under 200 K, which turns to an insulating state below 60 K. The paramagnetic spin susceptibility, and the Raman and the IR spectra suggest 4kF charge-density waves as an origin of the low-temperature insulating state.

Optical freezing of charge motion in an organic conductor

Dynamical localization, that is, reduction of the intersite electronic transfer integral t by an alternating electric field, E(ω), is a promising strategy for controlling strongly correlated systems with a competing energy balance between t and the Coulomb repulsion energy. Here we describe a charge localization induced by the 9.3 MV cm(-1) instantaneous electric field of a 1.5 cycle (7 fs) infrared pulse in an organic conductor α-(bis[ethylenedithio]-tetrathiafulvalene)(2)I(3). A large reflectivity change of >25% and a coherent charge oscillation along the time axis reflect the opening of the charge ordering gap in the metallic phase. This optical freezing of charges, which is the reverse of the photoinduced melting of electronic orders, is attributed to the ~10% reduction of t driven by the strong, high-frequency (ω ≧ t/ħ) electric field.

25 GB Read-Only Disk System using the Two-Dimensional Equalizer

In order to achieve a higher density disk system, we applied a two-dimensional equalizer along with a limit equalizer to an optical disk drive system which has an objective lens with a numerical aperture of 0.85 and a thin transparent cover layer of 0.1 mm thickness. Consequently we realized the 25 GB read-only disk system with sufficient margins against disk tilt and defocus. The two-dimensional equalizer is composed of a cross-talk cancel system and a tangential adaptive equalizer, and could prevent deterioration due to inter-symbol interference and cross-talk from adjacent tracks. Using the limit equalizer could prevent deterioration due to disk noise. By measuring the jitter with the limit equalizer, which has an ability to expand the system margin almost equivalent to that of the Viterbi decoder, we could evaluate the disk quality for standardization and verification.

Signal Processing for 15/27 GB Read-Only Disk System

In order to realize 15/27 GB read-only disk systems using blue laser, new signal processing is required. The technology of large-scale integrated circuits has advanced considerably. Hence we can use a complicated circuit with a big gate size without increasing the system cost significantly when we fabricate the blue laser disk system. We have realized the 15/27 GB system using the two-dimensional equalizer and the limit equalizer. The two-dimensional equalizer was composed of the cross-talk cancel system and the asymmetry compensation type tangential adaptive equalizer. And could improve the deterioration due to the inter symbol interference and the cross-talk from the adjacent tracks. The limit equalizer could improve the deterioration due to the disk noise. Using these signal-processing systems, we could reduce the bottom jitter by more than 3% and expand the tilt margin.

Thermodynamics of the mesoscopic thermoelectric heat engine beyond the linear-response regime.

Mesoscopic thermoelectric heat engine is much anticipated as a device that allows us to utilize with high efficiency wasted heat inaccessible by conventional heat engines. However, the derivation of the heat current in this engine seems to be either not general or described too briefly, even inappropriately in some cases. In this paper, we give a clear-cut derivation of the heat current of the engine with suitable assumptions beyond the linear-response regime. It resolves the confusion in the definition of the heat current in the linear-response regime. After verifying that we can construct the same formalism as that of the cyclic engine, we find the following two interesting results within the Landauer-Büttiker formalism: the efficiency of the mesoscopic thermoelectric engine reaches the Carnot efficiency if and only if the transmission probability is finite at a specific energy and zero otherwise; the unitarity of the transmission probability guarantees the second law of thermodynamics, invalidating Benenti et al.s argument in the linear-response regime that one could obtain a finite power with the Carnot efficiency under a broken time-reversal symmetry [Phys. Rev. Lett. 106, 230602 (2011)]. These results demonstrate how quantum mechanics constrains thermodynamics.