Shigetoshi Nakamura

Electrooptical Properties of Heterostructure (Pb, La)(Zr, Ti)O3 Waveguides on Nb–SrTiO3

The electrooptic behavior of (Pb, La)(Zr, Ti)O3 (PLZT) heterostructure waveguides, including PLZT/Pb(Zr0.95Ti0.05)O3 [PZT (95/5)] and Pb(Zr0.52Ti0.48)O3 [PZT (52/48)]/Pb(Zr0.85Ti0.15)O3 [PZT (85/15)] on Nb–ST substrates was examined. Electrooptic behavior was characterized by fabricating beam deflectors using these heterostructures. The heterostructure waveguides exhibited hysteresis-free electrooptic behavior after the application of initial voltage. The electrooptic behavior of PLZT/PZT (95/5) and PZT (52/48)/PZT (85/15) heterostructure waveguides presented a nonlinear dependence and a linear dependence, respectively. The apparent electrooptic coefficient of the PLZT/PZT (95/5) heterostructure obtained from the linear part of the V–θ characteristic above +7.5 V was 53 pm/V, and that of the PZT (52/48)/PZT (85/15) heterostructure was 37 pm/V. The electrooptic coefficient of the PZT (52/48) waveguide layer using an effective voltage was estimated to be 53 pm/V.

Apparent brain atrophy and subdural hematoma following ACTH therapy

A case of subdural hematoma following ACTH-Z therapy for infantile spasms was presented. A female baby of 5 months old showed little clinical evidence of cerebral dysfunction associated with subdural hematoma. There have been several reports about the relationship between steroid treatment and apparent brain atrophy on the CT brain scans. Then, we studied the CT brain scans before and after ACTH-Z therapy for infantile spasms, atonic seizure or Lennox syndrome and showed some relationship between apparent brain atrophy on the CT brain scans and ACTH-Z treatment. We also discussed the possible etiology of apparent brain atrophy and subdural hematoma, and stressed the necessity of extreme caution with long-term ACTH-Z administration.

Laryngeal stridor associated with the Chiari II malformation.

Twelve patients with Chiari II malformation developed laryngeal stridor and respiratory distress. This may develop when there is acute downward or upward displacement of the malformed brain stem secondary to increased or decreased intracranial pressure. Rapidly progressive hydrocephalus and compression of the lower portion of the IV ventricle are more important factors than the size of the head at birth. For the treatment of these symptoms relief of the increase in intracranial pressure, relief of the pressure difference between intracranial and intraspinal compartments, and selection of a shunt system with a proper flow rate are important. Posterior fossa decompression did not show a favorable effect.

The value of EEG and cerebral evoked potentials in the assessment of neonatal intracranial hemorrhage.

The EEG, visual and auditory evoked potentials (VEP, AEP) were evaluated in 16 full-term newborn infants who had intracranial hemorrhage documented by computerized tomography (CT). Three of them had supratentorial, three, supra- and infratentorial hemorrhage, while the other ten had infra- or peri-tentorial bleeding. Three died during the neonatal period. Eight of the 13 surviving infants were neurologically normal and five were abnormal at the time of the follow-up. Those who had normal or mildly abnormal background EEGs all developed normally, while those whose neonatal EEG was severely abnormal subsequently developed neurological sequelae irrespective of the extent of intracranial hemorrhage. The EEG, VEP or AEP is of little value in the diagnosis of intracranial bleeding but the EEG is valuable in assessing the degree of associated parenchymatous damage and is of great prognostic significance.

Potential fluctuation associated with the energetic-particle-induced geodesic acoustic mode in the Large Helical Device

Geodesic acoustic modes (GAM) driven by energetic particles are observed in the Large Helical Device (LHD) by a heavy ion beam probe. The GAM localizes near the magnetic axis. It is confirmed that the energetic-particle-induced GAM is accompanied by an electrostatic potential fluctuation and radial electric field fluctuation. The amplitude of the potential fluctuation is several hundred volts, and it is much larger than the potential fluctuation associated with turbulence-induced GAMs observed in the edge region in tokamak plasmas. The energetic-particle-induced GAM modulates the amplitude of the density fluctuation in a high-frequency range. The observed GAM frequency is constant at the predicted GAM frequency in plasmas with reversed magnetic shear. On the other hand, it shifts upwards from the predicted GAM frequency in plasmas with monotonic magnetic shear.

Neurophysiological evaluation of newborns with congenital hydrocephalus.

EEGs and visual and auditory evoked potentials (VEP and AEP) were studied in 27 newborns with congenital hydrocephalus. Asynchronous sleep patterns were the main EEG abnormality in the newborn as well as in the older infants and children. Asynchronous tracé alternant patterns, the most common finding, were more frequently encountered in infants with more severe hydrocephalus. Asynchrony of bifrontal humps was another finding observed in a few infants. Intermittent semirhythmic theta or delta waves were noted in some infants. Depression of the EEG background activity was an infrequent finding observed in more severe hydrocephalus. VEP showed prolonged latency in 60% of cases, but its wave form was normal in most cases, even sometimes in patients with highly abnormal EEGs. Therefore, it can serve as a tool to assess the maturity of such infants. In contrast, AEP was normal in 76% of the cases. The neonatal EEG findings were significantly correlated with the clinical outcome and can be an additional prognostic indicator in congenital hydrocephalus.

Experimental study of radial electric field and electrostatic potential fluctuation in the Large Helical Device

A heavy ion beam probe was installed on the Large Helical Device (LHD) to investigate the roles of radial electric fields (Er) in magnetically confined high-temperature plasmas. Two new observations are presented. One is the observation of electrostatic potential profiles during the formation of extremely hollow density profiles of impurities, called the impurity hole (Ida K et al 2009 Phys. Plasmas 16 056111), in the LHD plasmas. The measured Er is negative, and the Er determined by the ambipolarity condition of neoclassical particle fluxes is consistent with this observation. However, the transport analysis indicates that the formation of the extremely hollow profile is not attributable to the impurity fluxes driven by Er and the density and temperature gradients of the impurity. The other new observation is on the geodesic acoustic mode (GAM). The electrostatic potential fluctuation associated with the GAM, which is probably induced by energetic particles, in plasmas with the reversed or weak magnetic shear is identified. The GAM is localized in the core region of the plasma.

Cervical spinal deformity in craniometaphyseal dysplasia

A child with craniometaphyseal dysplasia had the presenting symptoms of progressive quadriparesis. She exhibited proportionate tall stature, peculiar face with craniomegaly, genu valgum, and 46,XX,t(12;18)(q13;q12) chromosome aberration. Delayed physical development and mild mental retardation were also present. Subluxation of C-2 on C-3 and kyphosis of the cervical spine, and myelographic blockage at this level were noted. Treatment consisted of fusion of the C-2 to C5-6 vertebra following laminectomies of C-3 and C-4 with satisfactory results. Early detection and surgery for cervical spine deformity and cord compression are necessary to prevent profound neurological deficits in this disorder.

DEVELOPMENT OF 6-MeV HEAVY ION BEAM PROBE ON LHD

Abstract A heavy-ion beam probe (HIBP) using a 3-MV tandem accelerator was installed in Large Helical Device (LHD). It is designed to measure the electrostatic potential in the core region directly. The electrostatic potential profiles can be measured successfully using the HIBP, and the radial electric field predicted by the neoclassical theory is consistent with that measured using the HIBP as long as the ambipolarity condition of the neoclassical particle flux has a single solution. Although the turbulent fluctuation is not detected because of low signal-to-noise ratio, several coherent fluctuations, which are inferred to be reversed-shear-induced Alfvén eigenmode and the geodesic acoustic mode, are observed directly in core plasmas, and the spatial distribution is revealed.

Potential measurements with heavy ion beam probe system on LHD

The heavy ion beam probe system in the Large Helical Device (LHD) was improved as follows. At first, the additional new sweeper was installed into the diagnostic port to extend the observable region. By using this sweeper, the potential profile was measured in a wider minor radius range than in previous experiments, in the case of outward shifted magnetic configuration of LHD. Next, the real time control system was installed to control the probe beam orbit for measuring the potential in plasma with large plasma current. In this system, a digital signal processor was used to control the probe beam in real time. The system worked well in the fixed position observation mode. In the sweeping mode for profile measurement, this control system became unstable. The details of this system and the experimental results are reported in this article.