Characteristics of constrained turbulent transport in flux-driven toroidal plasmas.

We study the dynamics of turbulence transport subject to a constraint on the profile formation and relaxation, dominated by the ion temperature gradient modes, within the framework of adiabatic electron response using a flux-driven global gyro-kinetic toroidal code, GKNET. We observe exponentially constrained profiles, with two different scale lengths, that are spatially constant in each region in higher input power regimes. The profiles are smoothly connected in the knee region located at [Formula: see text] of the minor radius, outside which the gradient is steepened and shows a weak confinement improvement. Based on the probability density function analysis of heat flux eddies, the power law demonstrates a dependence on the eddy size S, as [Formula: see text], which distinguishes events into diffusive and non-diffusive parts including the validation of quasi-linear hypotheses. Radially localized avalanches and global bursts, which exhibit different spatial scales, play central roles in giving rise to constrained profiles on an equal footing. It is also found that the [Formula: see text] shear layers are initiated by the global bursts, which evolve downward on a slow time scale across the knee region and play a role in adjusting the profile by increasing the gradient. This article is part of a discussion meeting issue 'H-mode transition and pedestal studies in fusion plasmas'.

Measurement of Paα line from pellet ablation cloud in Heliotron J.

The Paα line (1875.13 nm) in the near-infrared (NIR) region was evaluated to apply Stark broadening of the line spectrum to the electron density measurement of the small-pellet ablation cloud in Heliotron J, a medium-sized helical-axis heliotron device. Paα is three-to-four times broader than the visible Hß line (486.13 nm) for the same electron density. Using a portable NIR spectrometer, preliminary proof-of-concept experiments determined the marginal density, below which the broadening was undetectable. The lower detection density limit can be decreased using a narrower entrance slit or a denser grating.

Precise spectroscopy of 167Er:Y2SiO5 based on laser frequency stabilization using a fiber laser comb.

Precise spectroscopy of the hyperfine level system of 167Er-doped Y2SiO5 was achieved in the frequency domain. By using an optical frequency comb to stabilize the light source frequency to an accuracy on the order of hertz on a long-term scale, Allan deviation < 10 Hz was achieved for an integration time of 180 s. As a result, spectral hole-burning experiments yielded a more accurate hole spectrum with a narrow homogeneous linewidth. The method opens the way to the straightforward exploration of relaxation mechanisms in the frequency domain by simple steady-state measurements.

Persistence of Ion Temperature Gradient Turbulent Transport at Finite Normalized Pressure.

Plasma ß dependence of electromagnetic turbulent transport is investigated by means of gyrokinetic simulations with self-consistent change of the equilibrium magnetic field. It is found that energy transport due to ion-temperature-gradient (ITG) driven turbulence does not decrease with increasing ß; that is, the ion energy diffusivity does not decrease, and the electron energy diffusivity increases with ß. This is because magnetic fluctuations are significantly influenced by the background magnetic field structure change with ß by the Pfirsch-Schluter current. The magnetic field change weakens the suppression effect of magnetic perturbations on the growth of the ITG mode, and it also suppresses nonlinear zonal flow production. The influence of the magnetic field change is significant as the global magnetic shear increases.

Application of portable near-infrared spectrometer to Heliotron J plasma diagnostics.

A simple near-infrared (NIR) spectrometer with a wavelength range of 898-2130 nm has recently been applied to diagnose Heliotron J plasmas. It adopts a symmetrical crossed Czerny-Turner mount equipped with a thermoelectrically cooled 512 channel InGaAs linear sensor. Reciprocal linear dispersion was deduced to 96.37 nm/mm at the center of the detector. External filters can be inserted into the path of the collection optics to reject second-order spectra, as needed. Absolute intensity calibration was performed together with a visible spectrometer using a tungsten halogen lamp, and the effect of the transmittance fringe in the visible region of the applied long-pass filter on the NIR calibration was investigated. The intended application of the NIR spectrometer includes extending the wavelength region of a spectral monitor to less contaminated regions for Heliotron J plasma studies. In preliminary measurements, we observed the Paschen series for the hydrogen pellet injection plasma and two atomic helium lines, i.e., 2S-2P singlet and triplet lines, in helium gas puffing experiments. A continuum spectrum in this regime that is attributable to black-body radiation from hot spots on the plasma-facing components was identified. In addition, this may also be used to monitor background radiation in the YAG-Thomson scattering signals near 1064 nm.

Suppression of Ion-Scale Microtearing Modes by Electron-Scale Turbulence via Cross-Scale Nonlinear Interactions in Tokamak Plasmas.

Gyrokinetic turbulence simulations are applied for the first time to the cross-scale interactions of microtearing modes (MTMs) and electron-temperature-gradient (ETG) modes. The investigation of the fluctuation response in a multiscale simulation including both types of instabilities indicates that MTMs are suppressed by ETG turbulence. A detailed analysis of nonlinear mode coupling reveals that radially localized current-sheet structures of MTMs are strongly distorted by fine-scale E×B flows of ETG turbulence. Consequently, electron heat transport caused by the magnetic flutter of MTMs is significantly reduced and ETG turbulence dominates electron heat transport.

Development of beam emission spectroscopy for turbulence transport study in Heliotron J.

This paper describes the development study of the beam emission spectroscopy (BES) for the turbulent transport study in Heliotron J. Modification of the sightlines (10 × 4 for edge and 10 × 2 for edge) enables us to obtain 2-dimensional BES imaging. The cooling effect on the reduction in the electrical noise of avalanche photodiode (APD) assembly has been investigated using a refrigerant cooling system. When the temperature of the APD element has set to be -20 °C, the electrical noise can be reduced more than 50%. The measurement error of the phase difference in the case of low signal level has been tested by two light-emitting diode lamps. The APD cooling has an effect to improve the measurement error at the low signal level of APD.

Ultralow-phase-noise millimetre-wave signal generator assisted with an electro-optics-modulator-based optical frequency comb.

Low-noise millimetre-wave signals are valuable for digital sampling systems, arbitrary waveform generation for ultra-wideband communications, and coherent radar systems. However, the phase noise of widely used conventional signal generators (SGs) will increase as the millimetre-wave frequency increases. Our goal has been to improve commercially available SGs so that they provide a low-phase-noise millimetre-wave signal with assistance from an electro-optics-modulator-based optical frequency comb (EOM-OFC). Here, we show that the phase noise can be greatly reduced by bridging the vast frequency difference between the gigahertz and terahertz ranges with an EOM-OFC. The EOM-OFC serves as a liaison that magnifies the phase noise of the SG. With the EOM-OFC used as a phase noise "booster" for a millimetre-wave signal, the phase noise of widely used SGs can be reduced at an arbitrary frequency f (6 ≦ f ≦ 72 GHz).

Cross-Scale Interactions between Electron and Ion Scale Turbulence in a Tokamak Plasma.

Multiscale gyrokinetic turbulence simulations with the real ion-to-electron mass ratio and ß value are realized for the first time, where the ß value is given by the ratio of plasma pressure to magnetic pressure and characterizes electromagnetic effects on microinstabilities. Numerical analysis at both the electron scale and the ion scale is used to reveal the mechanism of their cross-scale interactions. Even with the real-mass scale separation, ion-scale turbulence eliminates electron-scale streamers and dominates heat transport, not only of ions but also of electrons. Suppression of electron-scale turbulence by ion-scale eddies, rather than by long-wavelength zonal flows, is also demonstrated by means of direct measurement of nonlinear mode-to-mode coupling. When the ion-scale modes are stabilized by finite-ß effects, the contribution of the electron-scale dynamics to the turbulent transport becomes non-negligible and turns out to enhance ion-scale turbulent transport. Damping of the ion-scale zonal flows by electron-scale turbulence is responsible for the enhancement of ion-scale transport.

An artery accompanying the sciatic nerve (arteria comitans nervi ischiadici) and the position of the hip joint: a comparative histological study using chick, mouse, and human foetal specimens.

Birds and reptiles always carry a long and thick artery accompanying the sciatic nerve (i.e., the sciatic artery), whereas mammals do not. We attempted to demonstrate a difference in courses of the nerve and artery in fetuses in relation with the hip joint posture. Eight mid-term human fetuses (15-18 weeks), five mouse fetuses (E18) and five chick embryos (11 days after incubation) were examined histologically. Thin feeding arteries in the sciatic nerve were consistently observed in human fetuses in spite of the long, inferiorly curved course of the nerve around the ischium. The tissue around the human sciatic nerve was not so tight because of the medial and inferior shift of the nerve away from the hip joint. The fetal hip joint position differed among the species, being highly flexed in humans and almost at right angle flexion in mice and chicks. Because of deep adduction of the hip joint in the mouse, the knee was located near the midline of the body. The mouse sciatic nerve ran through the tight tissue along the head of the femur, whereas the chick nerve ran through the loose space even in the gluteal region. In birds, evolution of the pelvis including the hip joint without adduction seemed to make the arterial development possible. In mammals, highly flexed or adducted hip joint seemed to be one of the disturbing factors against development of the long and thick artery. A slight change in posture may cause significant arterial variation.

Suppression of Hall-term effects by gyroviscous cancellation in steady collisionless magnetic reconnection.

The formation of an ion-dissipation region, in which motions of electrons and ions decouple and fast magnetic reconnection occurs, is demonstrated during a steady state of two-dimensional collisionless driven reconnection by means of full-particle simulations. The Hall-term effect is suppressed due to the gyroviscous cancellation at scales between the ion-skin depth and ion-meandering-orbit scale, and thus ions are tied to the magnetic field. The ion frozen-in constraint is strongly broken by nongyrotropic pressure tensor effects due to ion-meandering motion, and thus the ion-dissipation region is formed at scales below the ion-meandering-orbit scale. A similar process is observed in the formation of an electron-dissipation region. These two dissipation regions are clearly observed in an out-of-plane current density profile.

Shell model for rotating turbulence.

A modified shell model for rotating turbulence is proposed. The effect of rotation is introduced by a randomized linear term. Randomization is shown to be important in correctly modeling the rotation effect. Numerical simulation shows that the exponent of the energy spectrum in the inertial range changes from -5/3 to -2 as rotation rate increases. The mechanism behind this change is explained by weak turbulence theory and supported by numerical results.

Highly directive 18.9 nm nickel-like molybdenum x-ray laser operating at 150 mJ pump energy.

We experimentally demonstrate that by longitudinally pumping 2 mm long molybdenum preformed plasma with high-intensity 475 fs duration laser pulse, a highly directive soft-x-ray laser at 18.9 nm wavelength is generated. The divergence of the beam is evaluated to be of the submilliradian order, and only requires a pump laser energy of 150 mJ.

Measurements of blue shifts due to collisionless absorption in harmonic generation from subpicosecond laser-produced plasmas.

Harmonic generation from solid surface plasmas is studied using a subpicosecond Nd:glass laser system. For a 45 degrees angle of incidence, the speculars up to the fifth harmonics are blue shifted when the laser intensity exceeds 2 x 10(16) W cm(-2). The second harmonic is blueshifted by approximately 16 A, and the fifth harmonic is blue shifted by approximately 51 A for p polarization at the intensity of 1 x 10(17) W cm(-2). We observed the blue shift of the fifth harmonics and found that the magnitude of blue shift is higher compared with that for the second harmonics. The blue shift is interpreted as a collisionless absorption due to the anomalous skin effect. It is also found that the divergence of harmonics preserves a smaller divergence when using a shorter pulse length for the driving laser.

Variations observed during a 1999 dissection course--their sum and analysis.

A systematic study of anomalies in all body areas of 12 male and 12 female cadavers was attempted from data obtained during a 1999 dissection course. A total of 229 anomalies (132 in males, 97 in females) were observed, and they were comprised of 142 varieties. Classified by system, there were 71 (45 varieties) muscular, 118 (71) vascular, 29 (18) neural, 10 (7) visceral and 1 bone anomaly; by region, there were 50 in the head and trunk, 56 in the upper limbs, and 52 in the lower limbs. The other 71 anomalies were vascular ones confined to the viscera (61) and visceral (10). A maximum of 26 anomalies, including 10 muscular, 14 vascular and 2 neural anomalies, were ascertained to exist coincidentally in a single male. Among vascular anomalies, the visceral ones (61) were dominant. In all structures, 75% of the varieties of anomalies were single occurrences. In the text, the multiple occurrence of anomalies in an individual and their relationships are discussed.

Non-surgical closure of atrial septal defect.

BACKGROUND: Recently many devices for the transcatheter closure of atrial septal defect (ASD) were developed in the world. Several ASD closing devices, such as Clamshell device, buttoned device, ASD occluder system (ASDOS), Angel Wings, are not fully acceptable from a practical point of view. We reported the clinical trials of transcatheter closure of ASD for Clamshell double umbrella device and Amplatzer septal occluder (ASO) in Japan. METHODS: Clamshell devices were implanted in 11 patients. Clinical trials for ASO device were carried out in 34 patients in Japan. We reported the results of 17 patients in National Children's Hospital. RESULTS: Clamshell devices were implanted in all of the patients successfully. Minimal residual shunt was present in four patients (36%), 1 year after the procedure by Doppler color flow imaging. Nine of 11 umbrellas demonstrated fracture of the stainless steel arm. Arm fracture occurred between 1 week and 12 months after implantation. The implantations of ASO device were successful in all of the 17 patients. Sixteen out of 17 (94.1%) had complete closure in the average observation period of 5.5 months. Complications were minimal and transient. CONCLUSIONS: With respect to complete closure rate, easy manipulation, and complication rate, ASO is the best transcatheter ASD closure device among all the devices at the present time.

Direct closure of ostium primum defect in the repair of atrioventricular septal defect.

BACKGROUND: Patch closure is generally performed for atrial septation of an atrioventricular septal defect. We recently developed a new surgical technique for repairing atrioventricular septal defects that avoids the use of any patch material for closing the atrial septal defect. We report our experience with this procedure. METHODS: Seven patients (complete type: 5, partial type: 2) underwent this new operation. The diameters of the atrial septal defects were measured by transesophageal echocardiography. The preoperative electrocardiograms were compared with those taken after the operations. RESULTS: Diameters of the atrial defects ranged from 3 to 10 mm. Electrocardiograms before and after the operations did not change. No significant atrioventricular valve regurgitation and no residual shunts were detected by postoperative echocardiography. CONCLUSIONS: This method simplifies the repair of atrioventricular septal defects. In the short-term results, no arrhythmia and no valve regurgitation was seen.

Quantitative analysis of hypertrophy in cardiac chambers in cyanotic tetralogy of Fallot.

Although early total corrective repair for cyanotic tetralogy of Fallot is now safely performed at many institutions, long-term complications after surgical repair have been demonstrated. Therefore, the optimal procedure and timing for surgical treatment remain controxersial. In the present study, we conducted a quantitative analysis of the hypertrophy of all four chambers of 87 autopsied hearts of cyanotic tetralogy of Fallot and 71 normal control hearts utilizing the myocardial mass index, and evaluated the progression of lesions with advancing age. In cyanotic tetralogy of Fallot, hypertrophy of the right ventricle progresses immediately after birth, with that of the right atrium developing soon after. The left side of the heart is normal or slightly atrophied which could be corrected by sufficient palliative intervention or total corrective repair. The growth curves of both ventricles were parallel to those of normal hearts for the period studied. Pulmonary atresia, palliative operation, and total corrective repair have been shown to have some influence on the morphological characteristics of hearts of cyanotic tetralogy of Fallot.

[Middle fossa arachnoid cyst presenting an interesting clinical course: a case report].

The mechanism of the disappearance of arachnoid cysts is not fully understood. We report a case of arachnoid cyst which disappeared after head injury. A 28-year-old male was found to have an arachnoid cyst in the left middle fossa following head injury. We followed him up, because he had no symptoms. Two weeks later, he suffered from severe headache. CT image showed a dilatation of the subdural space, and his symptom deteriorated. We performed subdural-perifocal shunt, but one month after, he developed a subdural hematoma. The subdural hematoma was irrigated through a burr hole. His symptom disappeared post operatively. Two months later, CT image showed the disappearance of subdural hematoma and the arachnoid cyst. This case suggested one of the mechanisms involved in the disappearance of arachnoid cyst after head injury.