Collision of ion acoustic solitary waves in a magnetized plasma: Effect of dust grains and trapped electrons.

The head-on collision of two ion acoustic solitary waves is investigated in a magnetized plasma containing trapped electrons and dust grains. For completeness, the fluctuations in dust grain charge are taken into account. By using the extended Poincaré-Lighthill-Kuo (PLK) perturbation method, an analytical expression is obtained for the phase shift that takes place due to the collision of the waves. How the phase shift behaves under the combined effect of trapped electrons and dust grains along with the finite temperature of ions is examined. A focus is given to uncover the situations of fluctuating charge and fixed charge on the dust grains in the plasma. Interestingly, the solitary waves acquire a larger phase shift and are delayed more in the case of dust grains having a fluctuating charge.

Multichannel microwave interferometer with an antenna switching system for electron density measurement in a laboratory plasma experiment.

This study presents a simple and powerful technique for multichannel measurements of the density profile in laboratory plasmas by microwave interferometry. This technique uses electromechanical microwave switches to temporally switch the connection between multiple receiver antennas and one phase-detection circuit. Using this method, the phase information detected at different positions is rearranged into a time series that can be acquired from a minimum number of data acquisition channels (e.g., two channels in the case of quadrature detection). Our successfully developed multichannel microwave interferometer that uses the antenna switching method was applied to measure the radial electron density profiles in a magnetized plasma experiment. The advantage of the proposed method is its compactness and scalability to multidimensional measurement systems at low cost.

Pure ion current collection in ion sensitive probe measurement with a metal mesh guard electrode for evaluation of ion temperature in magnetized plasma.

This paper presents a new design of ion sensitive probe (ISP) that enables collection of pure ion current for accurate measurement of the perpendicular ion temperature in magnetized plasmas. The new type of ISP resolves a longstanding issue widely observed in ISP type measurements, namely, that the current-voltage characteristic is smeared by an unexpected electron current in the standard ISP model. The new ISP is equipped with a fine scale metal mesh on the sensor entrance to prevent electrons from flowing to the sensor, a phenomenon considered to be caused by the space-charge effect. The new ISP successfully measured the ion temperature of electron cyclotron resonance plasmas.

Short sleep duration and long spells of driving are associated with the occurrence of Japanese drivers' rear-end collisions and single-car accidents.

Sleepiness and fatigue are important risk factors for traffic accidents. However, the relation between the accident type and lack of sleep as well as spells of driving has not been examined sufficiently. This study aimed to clarify that short sleep duration and long spells of driving are more associated with rear-end collisions and single-car accidents as compared with accidents of other types in cases of people who cause accidents. After removing drunken driving as a cause of accidents, 1772 parties involved in accidents were questioned. The quantities of rear-end collisions and single-car accidents were, respectively, 240 and 293. Logistic regression analysis showed that short nocturnal sleep (<6 h) and 10-min increments of spells of driving were significantly associated not only with rear-end collisions but also with single-car accidents as compared with accidents of other types. Furthermore, younger age (

Elevated risk of motor vehicle accident for male drivers with obstructive sleep apnea syndrome in the Tokyo metropolitan area.

Previous studies have suggested that patients with obstructive sleep apnea syndrome (OSAS) are at an increased risk of motor vehicle accidents (MVAs). This study is the first systematic investigation of MVA risk among Japanese drivers with obstructive sleep apnea syndrome (OSAS). We investigated the rate of MVAs in the preceding 5 years and dozing off at the wheel in Japanese male OSAS drivers (n = 616, mean [S.D.] age: 46.3 [10.1] years old) and age-matched male controls (n = 600), and the characteristics of OSAS patients who experienced multiple MVAs as well as the effectiveness of continuous positive airway pressure (CPAP) treatment in reducing MVA risk. The odds ratio of MVA in the OSAS group compared to a general population was 2.36. Multivariate logistic regression analysis revealed that MVA was significantly associated with either subjective sleepiness beyond normal limits (Epworth sleepiness scale: ESS > or = 11) or serious respiratory disorders (apnea hypopnea index: AHI > or = 40). AHI scores were significantly higher in the group with multiple MVAs than in those with a single MVA, despite the ESS score in the former group being significantly lower. CPAP treatment was effective for reduction of MVA. The MVA rate among OSAS patients in the research area was significantly higher than that among the controls. Subjective excessive daytime sleepiness and severity of OSAS are independently associated with the occurrence of MVA. In conclusion, early diagnosis and treatment of OSAS drivers especially with serious respiratory disorder should be made to prevent multiple MVAs.

Effect of a small dose of alcohol on driving-related behavior of Japanese who self-reported facial flush and nonflushing.

About half of northeastern Asians lack ALDH2 (Acetaldehyde Dehydrogenase 2), an enzyme involved in alcohol metabolism. People with deficient ALDH2 often experience facial flushing after drinking a small dose of alcohol. The present study examined the effect of a small dose of alcohol on driving-related behavior of northeastern Asians (Japanese). Participants were 9 Japanese flushers and 12 Japanese nonflushers. They were evaluated using a driving simulator and self-report of intoxication after ingesting 0.6g/kg or 0.4g/kg of alcohol or a placebo. Facial flushers were more likely to experience subjective feelings of intoxication than were nonflushers. There were no significant differences between facial flushers and nonflushers in blood alcohol concentration and choice reaction time to visual stimuli. Despite having different subjective feelings of intoxication, facial flushers and nonflushers were equally impaired after having ingested equal amounts of alcohol per body weight.

Association of objective measures of trauma exposure from motor vehicle accidents and posttraumatic stress symptoms.

Associations of objective measures of trauma exposure with psychological sequelae following motor vehicle accidents (MVA) were examined in a Japanese population. Impact and injury severity of 93 MVA victims was assessed using on-the-scene in-depth investigations measured by the Injury Severity Score (ISS), barrier equivalent speed (BES), and change in velocity during the impact (Delta-v). Results showed that ISS, BES, and Delta-v were not related to posttraumatic stress symptoms (PTSS) or psychiatric symptoms at 5 and 14 months after the MVA. Subjective measures (e.g., perceived life risk, persistent medical problems) were significantly related to psychological sequelae. These findings suggest that the objective measures of trauma exposure are not associated directly with PTSS or psychiatric symptoms after an MVA.

Low-frequency sheath instability in a non-Maxwellian plasma with energetic ions.

Spontaneous low-frequency oscillations have been observed in the circuit of a positively biased electrode when the ambient nonuniform plasma is irradiated by a microwave pulse of short duration, which is approximately equal to the ion-plasma period. The instability with its characteristic frequency below the ion-plasma frequency is driven by an accelerated ion component interacting with the sheath of the electrode. A qualitative model of the instability is suggested.

Excitation of ion-wave wakefield by the resonant absorption of a short pulsed microwave with plasma.

Unmagnetized, inhomogeneous laboratory plasma irradiated by a high power (eta=E(2)(0)/4pin(e)kT(e) approximately 5.0x10(-2)) short pulsed microwave with pulse length of the order of ion-plasma period (tau(pi) less, similar 2pi/omega(pi)) is studied. Large density perturbation traveling through the underdense plasma with a velocity much greater than the ion sound speed produced by the resonant absorption of the microwave pulse has been observed. In the beginning the density perturbation has large amplitude (deltan/n(0) approximately 40%) and propagates with a velocity of the order of 10(6) cm/s. But later its amplitude as well as the velocity decrease rapidly, and finally the velocity arrives with twice the ion sound speed. The oscillating incident electromagnetic waves enhance highly localized electric field by the resonant absorption process and develop time-averaged force field which pushes plasma electrons from the resonant layer. As the electrons are accelerated to be ejected, they pull plasma ions as a bunch with them by means of self-consistent Coulomb force. This suprathermal ion bunch can excite an ion-wave wakefield.

Radiation from high-intensity ultrashort-laser-pulse and gas-jet magnetized plasma interaction.

Using a gas-jet flow, via the interaction between an ultrashort high-intensity laser pulse and plasma in the presence of a perpendicular external dc magnetic field, the short pulse radiation from a magnetized plasma wakefield has been observed. Different nozzles are used in order to generate different densities and gas profiles. The neutral density of the gas-jet flow measured with a Mach-Zehnder interferometer is found to be proportional to back pressure of the gas jet in the range of 1 to 8 atm. Strength of the applied dc magnetic field varies from 0 to 8 kG at the interaction region. The frequency of the emitted radiation with the pulse width of 200 ps (detection limit) is in the millimeter wave range. Polarization and spatial distributions of the experimental data are measured to be in good agreement with the theory based on the V(p)xB radiation scheme, where V(p) is the phase velocity of the electron plasma wave and B is the steady magnetic field intensity. Characteristics of the radiation are extensively studied as a function of plasma density and magnetic field strength. These experiments should contribute to the development of a new kind of millimeter wavelength radiation source that is tunable in frequency, pulse duration, and intensity.

Experimental observation of short-pulse upshifted frequency microwaves from a laser-created overdense plasma.

A short and frequency upshifted from a source microwave pulse is experimentally generated by the overdense plasma that is rapidly created by a laser. The source wave, whose frequency is 9 GHz, is propagating in the waveguide filled with tetrakis-dimethyl-amino-ethylene gas, which is to be converted to the overdense plasma by the laser. The detected frequency of the pulse is over 31.4 GHz and its duration is 10 ns. This technique has the potential for the generation of a tunable frequency source.

Observation of the second-harmonic generation from relativistically quivering electrons in exciting laser wakefield.

The second-harmonic emission generated by the spatially asymmetric quivering electrons caused by the ponderomotive force was studied. The intensity of the second harmonic was proportional to the focused intensity of the pump pulse with the power of 1.8. This intensity dependence can be explained by the relativistic effect of the quivering electrons.