Noriyuki Kawada

Initial validations for pursuing irradiation using a gimbals tracking system

Our newly designed image-guided radiotherapy (IGRT) system enables the dynamic tracking irradiation with a gimbaled X-ray head and a dual on-board kilovolt imaging subsystem for real-time target localization. Examinations using a computer-controlled three-dimensionally movable phantom demonstrated that our gimbals tracking system significantly reduced motion blurring effects in the dose distribution compared to the non-tracking state.

Development of a three-dimensionally movable phantom system for dosimetric verifications.

The authors developed a three-dimensionally movable phantom system (3D movable phantom system) which can reproduce three-dimensional movements to experimentally verify the impact of radiotherapy treatment-related movements on dose distribution. The phantom system consists of three integrated components: a three-dimensional driving mechanism (3D driving mechanism), computer control system, and phantoms for film dosimetry. The 3D driving mechanism is a quintessential part of this system. It is composed of three linear-motion tables (single-axis robots) which are joined orthogonally to each other. This mechanism has a motion range of 100 mm, with a maximum velocity of 200 mm/s in each dimension, and 3D motion ability of arbitrary patterns. These attributes are sufficient to reproduce almost all organ movements. The positional accuracy of this 3D movable phantom system in a state of geostationary is less than 0.1 mm. The maximum error in terms of the absolute position on movement was 0.56 mm. The positional reappearance error on movement was up to 0.23 mm. The observed fluctuation of time was 0.012 s in the cycle of 4.5 s of oscillation. These results suggested that the 3D movable phantom system exhibited a sufficient level of accuracy in terms of geometry and timing to reproduce interfractional organ movement or setup errors in order to assess the influence of these errors on high-precision radiotherapy such as stereotactic irradiation and intensity-modulated radiotherapy. In addition, the authors 3D movable phantom system will also be useful in evaluating the adequacy and efficacy of new treatment techniques such as gating or tracking radiotherapy.

Differential absorption lidar at 1.67 μm for remote sensing of methane leakage

A differential absorption lidar (DIAL) for field monitoring of methane (CH4) leakage at a wavelength of 1.67 µm was developed. Compared with traditional DIAL systems for environmental monitoring, this system has a higher distance resolution (~15 m) for determining the leak position and a shorter detection range up to 500 m. First, considering appropriate design parameters, a theoretical simulation was performed to evaluate the sensitivity and the detectable range of the system. Based on the analytical simulation, a prototype DIAL system was constructed and the detection of CH4 which had leaked into the atmosphere was demonstrated. The CH4 leakage of 6000 ppmm at a distance of 130 m was successfully detected. The detection limit was 1000 ppmm. With the improvements in the light source and the detector system, the detectable boundary can be increased in the range from 90 to 540 m for a concentration of 1500 ppmm.

Sensitive H 2 Detection Using a New Technique of Photoacoustic Raman Spectroscopy

A new technique of photoacoustic Raman spectroscopy (PARS) is proposed and demonstrated for the detection of trace gas molecules in the atmosphere. No tunable laser is required in the proposed method. Only a fixed-wavelength pulsed laser is used as a light source, and a Raman shifter, filled with the same gas as that to be detected, automatically generates the Raman-shifted radiation required for the detection by PARS. In the detection of trace H2 gas in the atmospheric pressure mixture with N2, the detection limit of 3 ppm (3×10-6 in partial pressure) was obtained using a Q-switched, frequency-doubled Nd:YAG laser.

An attempt at development of a magnetic levitation transport system in vacuum using the mechanism of induced repulsive force

Abstract It is now necessary to make dust-free and contactless transporting systems, for instance, in the field of manufacturing semiconductor memories which are becoming more and integrated. Due to these circumstances, we have developed a basic mechanism of non-contact transport system in vacuum which utilizes the induced repulsive levitation force by alternating magnetic field and the propulsion force of linear motors. In this system, the aluminum transport carrier can be isolated from electromagnets by a stainless steel vacuum tunnel. Levitation of carrier is self-stabilized due to the cross-shape. The system configuration is extremely simple as compared with a conventional active controlled type system. At the present stage of development, the load carrying capacity is about 100 g and the maximum transport velocity is 0.4 m s −1 for a levitation height of about 10 mm and a carrier weight of 300 g.

Nonlinear Raman spectroscopies with Raman shifter for sensitive gas detection

In recent years, measurements of the trace greenhouse gases such as CO/sub 2/, and CH/sub 4/ has become important due to environment problems. In chemical plants and gas pipe lines, continuous monitoring of the leak of inflammable gases is also very important from the safety point of view. We proposed a new scheme for nonlinear Raman spectroscopy, in which a fixed-frequency laser is combined with a Raman shifter. In the scheme, no IR tunable laser is required like absorption spectroscopy and photo-acoustic spectroscopy (PAS). We applied this scheme to different kinds of nonlinear Raman spectroscopy; photo-acoustic Raman spectroscopy (PARS), coherent anti-Stokes Raman spectroscopy (CARS) and stimulated Raman gain spectroscopy (SRGS).

Sensitive Trace Gas Detection By Photoacoustic Raman Spectroscopy Without Tunable Laser

Pulsed Nd:YAGlaser ( S W a pulsed laser transmitter and optical receiver on brief Space Shuttle flights to evaluate both the technology and data processes of laser remote sensing. Each flight instrument for the planned series of four flights contains a separate, modified set of instrumentation aimed at improving the flight mission data. All flight instruments use the Space-Shuttle Hitchhiker interface which provides electrical power, down-link data, up-link commands, thermal protection, and two sealed containers that are pressurized at one atmosphere of nitrogen. The laser sensor is mounted in a cylindrical container that is equipped with a large optical window (0.38 meter diameter) and a motorized door assembly. The door opens on orbit to permit laser operations. The first Shuttle Laser Altimeter (SLA-01) was flown on the STS-72 mission, January 11-20, 1996. It was based on a diode-pumped Nd:YAG laser transmitter that produced 40 mJoule, 10 nsec pulses at a rate of 10 pulses per sec at 1064 nm. Eighty hours of flight data were acquired in a segmented record of laser pulse echoes along the nadir track of the Space Shuttle. Individual sensor footprints were 100 meters in diameter. The instrument performed flawlessly throughout the mission and mission data sets were posted on the world wide web at www.denali.gsfc.nasa.gov/sla. The SLA-01 instrument was built from spare space flight laser, detector, and altimetry electronics that were first developed for the Mars Observer Laser Altimeter investigation and lidar electronics and a data system that were developed in airborne laser altimetry and lidar instruments. An important component of all Shuttle Laser Altimeter instruments is the surface lidar function which is implemented by a high-speed electronic pulse digitizer. Surface lidar is the principal technique that supplements the pulse time-of-flight data of laser altimetry, provides the correction of laser pulse ranges for the distorted pulse shapes reflected from the Earths surface, and provides new information on the vertical structure within each footprint. Typical pulse digitization rate is 200 megasamples per sec for 100 or more samples of the surface retum. For example, these surface lidar data can be used to assess vegetation height. A second flight of SLA is planned for STS-85 in July 1997 to take a modified instrument to a 57 degree inclination orbit for as many as 60 hours of Earth-viewing time. The instrumentation has been modified to include a 32 Mhz bandwidth optical receiver and a variable gain amplifier in the silicon-avalanche photo diode circuitry. These changes are intended to permit a higher resolution examination of Earth landform echoes. Planning for the third mission in 1998 or 1999 is now underway. Instrument modifications are centered on an order-ofmagnitude increase in laser pulse rate to 100 pulses per sec and the addition of an atmospheric lidar channel. Ramancell I-: * Thj2 1130

In-situ surface charge distribution measurement of alumina insulator surfaces after impulse voltage application in vacuum

This paper investigates the surface charge distribution of an alumina insulator surface after flashover tests by impulse voltage applications. The measurement of surface charge distribution and the voltage testing were both done in vacuum (in situ). The vacuum chamber for the voltage flashover testing experiments was maintained at the pressure of 1.3 X 10-8 Pa. Impulse voltage was applied with positive and negative polarity. The surface charge was measured for both positive (flashover and unflashover) and negative (flashover and unflashover) polarity. Applying the positive impulse polarity produces a positive charge on the alumina surface, when the impulse polarity is reversed both the positive and negative charges were detected in case of flashover, and only negative charge was detected in case of unflashover.