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A strong demand is expected for high-sensitivity, high-resolution and low-cost brain positron emission tomography (PET) imaging for early diagnosis of dementia, as well as for general neuroscience studies. Therefore, we have proposed novel geometries of a hemisphere detector arrangement for high-sensitivity brain imaging, in which an add-on detector at the chin position or neck position helps in sensitivity uniformity improvement. In this study, we developed the first prototype system for proof-of-concept using four-layer depth-of-interaction detectors, each of which consisted of 16 × 16 × 4 Zr-doped GSO crystals with dimensions of 2.8 × 2.8 × 7.5 mm3 and a high-sensitivity 64-channel flat-panel photomultiplier tube. We used 47 detectors to form a hemisphere detector with a hemisphere shape of 25 cm inner diameter and 50 cm outer diameter, and we used seven detectors for each of the add-on detectors. The total detector number of 54 was about one-fourth that of a typical whole-body PET scanner. The hemisphere detector for the prototype system was realized by multiple rings having different numbers of detectors and a cross-shaped top detector unit covering the top. Performance evaluation showed uniform spatial resolutions of 3-4 mm by the filtered back-projection method. Imaging tests of a hot-rod phantom done with an iterative method were able to resolve 2.2 mm rods. Peak sensitivity was measured as more than 10% at a region near the top of the head, which was achieved with the help of the top detector unit. In addition, using the prototype system, we performed the first FDG clinical test with a healthy volunteer. The results showed that the proposed geometries had high potential for realizing high-sensitivity, high-resolution, and low-cost brain PET imaging. As for the add-on detector position, it was shown that the neck position resulted in higher sensitivity and wider field of view (FOV) than the chin position because the add-on detector at the neck position can be placed continuously to the hemisphere detector and close to the FOV.

We developed a low-detection-limit filter-free fluorescence sensor by a charge accumulation technique. For charge accumulation, a floating diffusion amplifier (FDA), which included a floating diffusion capacitor, a transfer gate, and a source follower circuit, was used. To integrate CMOS circuits with the filter-free fluorescence sensor, we adopted a triple-well process to isolate transistors from the sensor on a single chip. We detected 0.1 nW fluorescence under the illumination of excitation light by 1.5 ms accumulation, which was one order of magnitude greater than that of a previous current detection sensor.

The improvement of a filter-less fluorescence sensor, by suppressing forward scattering in silicon by surface planarization is presented. A fluorescence microscope has been widely used in biochemical fields. However, it is difficult to miniaturize because optical filters and other parts are necessary. We previously developed a filter-less fluorescence sensor. The separation ability of excitation light and fluorescence in the previous device was 550:1. It is necessary to improve the separation ability. This study focuses on the suppression of forward-scattered incident light in silicon, through the enhanced surface planarization of polysilicon, which is the gate electrode material. The separation ability of the filter-less fluorescence sensor was increased from 550:1 to 1250:1 by the suppression of forward-scattered light.

The dielectric constant, threshold voltage, and response time were measured for a nematic binary mixture of 4-cyano-4'-pentylbiphenyl (5CB) molecules and the doped electron acceptor tetracyanoethylene (TCNE). The doping of TCNE caused a large increase in the dielectric constant and dielectric anisotropy. However, no marked improvement was achieved for threshold voltage and response time. Considering that the large increase was due to mobile charges in the system, we proposed a theoretical model to discuss the singularity that appeared in experimental results obtained in an electric field.

We have measured molecular-frame photoelectron angular distributions from carbon 1s and oxygen 1s levels of CO molecules up to a photoelectron kinetic energy (KE) of ~150 eV. The backward-scattering intensities exhibited a strong modulation as a function of the kinetic energy of the photoelectrons, whereas the intensities for the forward-scattering gradually increased and then became nearly constant over KE ~100 eV. Multiple scattering calculations with a muffin-tin potential qualitatively reproduced the experimental results. The present results may be considered as the observation of low-energy photoelectron diffraction patterns for gaseous free CO molecules, which are involved in modulations in extended X-ray absorption fine structure (EXAFS) spectra.

The interparticle force between two colloidal particles in a nematic liquid crystal is directly measured as a function of the interparticle distance R by two different experimental methods: the free-release method and the optical tweezing method. The obtained force between an elastic 'dipole', which constitutes a colloidal particle and an accompanying hyperbolic hedgehog defect, confirms previous theoretical predictions that the force is attractive and proportional to R−4. We also observe that a repulsive component emerges at short distances to preclude direct contact of the particles. We find that the magnitudes of the forces obtained by the two methods are different. The origin of this discrepancy is discussed by a comparison between the static and the non-static measurements.

A new measurement method of complex electrophoretic mobility µ* of colloidal particles in suspension was developed using a heterodyne technique of quasi-elastic light scattering under a sinusoidal electric field. The influence of diffusion was removed by squaring the time-domain signal of scattered light and we succeeded in accurate and highly sensitive measurement of µ* in a wide frequency range for the first time. The frequency dependence of µ* of latex particles was measured up to 50 kHz by this method. The relaxation of mobility due to anomalous double-layer polarization was observed above 1 kHz in the obtained spectrum.

We have developed a new apparatus for measuring dielectric relaxation under shear flow, and applied it to a typical polymer electrolyte system, polypropylene oxide (PPO)-lithium perchloride, while changing the molecular weight of PPO. We observed a drastic increase in dielectric increment Δε and a drastic decrease in conductivity σ with increasing shear rate. The molecular weight dependence of σ and the relaxation time τ suggests that the conductivity is due to ion transport assisted by the conformational change of the entire polymer chain and the permittivity is ascribed to the ion fluctuation within a single chain assisted by the segmental motion of a polymer. On applying shear flow, the conformational change of a polymer chain is strongly suppressed, which would cause the decrease in conductivity.

The phase mode in a ferroelectric liquid crystal has been studied by photon correlation spectroscopy under a dc electric field applied perpendicular to the helical axis of the liquid crystal. The parabolic continuous dispersion of the inverse correlation time τ-1 against the scattering wave number splits into two branches with a gap at nearly half the wave number at which τ-1 takes a minimum value. The gap frequency is found to increase in proportion to the applied electric field below the critical field E c where the helical structure completely unwinds. Above E c, τ-1 increases continuously with the wave number and shows no minimum. The experimental findings are compared with the recent predictions based on the phenomenological theory.

The Smectic-A (SmA) phases of the antiferroelectric liquid crystals (R)-MHPOBC, (R)-MHPOCBC and slightly racemized MHPOBC (R:S=17:3) have been studied by means of simultaneous measurements of the electric displacement and the tilt angle induced by the electric field. The SmA–SmCα * phase transition was observed in (R)-MHPOBC and (R)-MHPOCBC, while a phase transition similar to the SmA–SmC* one was observed in slightly racemized MHPOBC. In both cases, the Landau-type phenomenological theory explains well the critical behavior in the SmA phase, and the coefficients related to the theory can be determined.

The Smectic- Cβ * (SmCβ *) phase, which appears between the SmA and SmC A * phases in an optically pure liquid crystal of MHPOBC, has been studied by means of simultaneous measurements of the dielectric constant ε and the electroclinic coefficient κ under a dc bias electric field. The result of electroclinic coefficient measurement shows that the SmCβ * phase is obviously different from the SmC* phase and can be considered as a ferrielectric phase. From the simultaneous measurement of ε and κ, we can observe the difference in the phase transition behaviors between pure and slightly racemized MHPOBC samples and confirm that the decrease of optical purity causes the change from the SmCβ * phase to the SmC* phase.

Nonlinear dielectric relaxation spectroscopy has recently been utilized to investigate the details of electrical dynamics in a variety of substances. The nonlinear spectra obtained have usually been analyzed in terms of a phenomenological nonlinear response theory proposed by Nakada. In this paper, to check the validity of the phenomenological theory, the dielectric relaxation spectra of first and third orders are calculated from the molecular theory based on a free rotation model of the dipole moment. The after-effect function of exponential decay type assumed in the phenomenological theory is not applicable to the free rotation model. The validity of phenomenological expressions for nonlinear spectra as approximate or semiempirical formulas is discussed in detail.