Induced radioactive nuclides of 10-MeV radiotherapy accelerators detected by using a portable HP-Ge survey meter

The radioactivation of linear accelerator components for radiation therapy is interest for radiation protection in general, and particularly, when decommissioning these structures. The energy spectra of gamma rays emitted from the heads of two accelerator models, EXL-15SP and Clinac iX, after 10-MeV X-ray irradiation, were measured using a high-purity germanium semiconductor survey meter. After spectrum analyses, activities of (24)Na, (28)Al, (54)Mn, (56)Mn, (57)Ni, (58)Co, (60)Co, (64)Cu, (65)Zn, (122)Sb, (124)Sb, (181)W, (187)W, (196)Au, and (198)Au were detected. One centimetre deep dose-equivalent rate of the heads of the linear accelerator was measured using the survey meter. The dose rate decreased to ～10 % of its initial rate after 1 week. Long-term activations were few, the radioactivity level was low, and a cooling time of several days was effective for reducing dose rate to an acceptable level for decommissioning.     

含铝PSBR复合橡胶的制备及其力学性能

利用铝的醇盐与PSBR季铵盐乳液反应,制成含铝有机－无机杂化弹性体胶片,再与天然橡胶进行并用,制得含铝PSBR复合硫化胶,这种复合硫化胶具有优良的力学性能和独特的抗震作用,用IR和NMR以及其它方法分析了其相关结构.     

Message encoding and decoding using an asynchronous chaotic laser diode transmitter-receiver array

We have numerically investigated a chaotic laser diode transmitter-receiver array scheme (CLDTRAS), which is a secure digital communication scheme using a difference between two types of transmitter-receiver array consisting of two self-pulsating laser diodes (LDs), i.e., a receiver LD and a transmitter LD. By analyzing the bit error rate, particularly its dependence on the parameter mismatches of the hardware and channel noise and on the correlation coefficient between a transmitter LD and receiver LD, we examined the problems of sensitivity to parameter mismatches and channel noise and a dependence on chaos synchronization between a transmitter LD and a receiver LD. The former makes communication difficult, and the latter makes it possible for an eavesdropper to estimate the receiver LD using chaos synchronization and to forge the hardware. Then we studied the effects of the bit error rate for various values of the threshold, which determines a binary message, and for various numbers of transmitters-receivers making up a LD transmitter-receiver array. It has been shown that a highly noise-tolerant and hardware-dependent communication scheme can be achieved with the LD transmitter-receiver array, whose transmitter and receiver LDs are asynchronous with respect to each other, by choosing the proper threshold and increasing the number of LD transmitters-receivers. Since it is possible to communicate without chaos synchronization, it becomes difficult to forge hardware and to eavesdrop with the forged hardware even if the key is stolen.     

Lattice dynamics of the Zn-Mg-Sc icosahedral quasicrystal and its Zn-Sc periodic 1/1 approximant

Quasicrystals are long-range-ordered materials that lack translational invariance, so the study of their physical properties remains a challenging problem. Here, we have carried out inelastic-X-ray- and neutron-scattering experiments on single-grain samples of the Zn-Mg-Sc icosahedral quasicrystal and of the Zn-Sc periodic cubic 1/1 approximant, with the aim of studying the respective influence of the local order and of the long-range order (periodic or quasiperiodic) on lattice dynamics. Besides the overall similarities and the existence of a pseudo-gap in the transverse dispersion relation, marked differences are observed, the pseudo-gap being larger and better defined in the approximant than in the quasicrystal. This can be qualitatively explained using the concept of a pseudo-Brillouin-zone in the quasicrystal. These results are compared with simulations on atomic models and using oscillating pair potentials, and the simulations reproduce in detail the experimental results. This paves the way for a detailed understanding of the physics of quasicrystals.     

Photoluminescence properties of a hollandite compound K2Ga2Sn6O16

A hollandite compound K₂Ga₂Sn₆O₁₆ (KGSO) has photocatalytic activity, although little is known about the optical properties of the compound. To design a higher quality photocatalyst, studies on its optical properties are required. In this study, a KGSO powder and a SnO₂ (rutile structure) powder were prepared by the sol—gel method. Photoluminescence (PL) and PL excitation spectra of the two powders were measured. To our knowledge, this is the first report of PL from a hollandite compound. It was found that the band gap energy of the KGSO powder is 3.6 eV, the value of which is identical with that of the band gap energy of SnO₂. This was confirmed by the result of the photoacoustic spectrum of the KGSO. The shapes of the PL excitation spectra of the two powders agreed. Moreover, the PL spectra of the two powders have one broad band around 600 nm. From these results, one can conclude that the mechanism of PL of KGSO is the same as that of SnO₂. In air with ethanol, however, the time-course of the KGSO powder was different from that of the SnO₂ powder. By adding ethanol vapor in air, the PL intensity of the SnO₂ powder increased, whereas the PL intensity of the KGSO powder remained unchanged. By comparing the PL time-courses of the two powders with those of a commercial rutile TiO₂ powder, it was concluded that the photodesorption of O₂ in air with ethanol occurs on the SnO₂ powder, not on the KGSO powder. This was supported by the results of the inorganic carbon concentrations on the two powders. These results indicate that the behavior of O₂ on the KGSO surface during a photocatalytic oxidation is different from that on the SnO₂ surface during the oxidation.

© 2003 Elsevier Ltd. All rights reserved.     

An approach to the automation of the assembly of flexible belt-shaped objects

A robot system was developed for the assembly of flexible belt-shaped objects, and the assembly procedures employed by workers in using it were analysed. A multi-fingered hand was developed to hold the objects at several points, and to move them into the proper position for attachment to a part. In addition, an image processing method that can recognize the gripping positions on source objects and conditions after the source objects are attached is proposed.     

Elastic Inflatable Actuators for Soft Robotic Applications

The 20th century's robotic systems have been made from stiff materials, and much of the developments have pursued ever more accurate and dynamic robots, which thrive in industrial automation, and will probably continue to do so for decades to come. However, the 21st century's robotic legacy may very well become that of soft robots. This emerging domain is characterized by continuous soft structures that simultaneously fulfill the role of robotic link and actuator, where prime focus is on design and fabrication of robotic hardware instead of software control. These robots are anticipated to take a prominent role in delicate tasks where classic robots fail, such as in minimally invasive surgery, active prosthetics, and automation tasks involving delicate irregular objects. Central to the development of these robots is the fabrication of soft actuators. This article reviews a particularly attractive type of soft actuators that are driven by pressurized fluids. These actuators have recently gained traction on the one hand due to the technology push from better simulation tools and new manufacturing technologies, and on the other hand by a market pull from applications. This paper provides an overview of the different advanced soft actuator configurations, their design, fabrication, and applications.     

Electrical breakdown of individual Si nanochains and silicide nanochains

Electron transport across individual Si nanochains and silicide nanochains is investigated using a micro-manipulator in a transmission electron microscope. The current increases nonlinearly with increasing the bias voltage. Electrical breakdowns occur with a current typically as large as 10(1)-10(2) nA. Furthermore, some FN plots exhibit a bend presumably due to the formation of a heavily distorted nanotube of carbon.     

Rising Tc in Bi and Cu co-doped BaTiO3

The solid solution (Ba_1−2xBi_2x)(Cu_xTi_1− x)O₃ (0.0 < x ≤ 0.10) was prepared by conventional high temperature reaction. In the region of x ≤ 0.040 single phases of tetragonal perovskite-type compounds were obtained and the c-axis increased up to x = 0.015 and the maximum of the a/c ratio was 1.0123 at x = 0.010. In x > 0.040 a small amount of an unknown impurity phase appeared in addition to a tetragonal perovskite-type phase. The Curie temperature Tc increased to 140 °C at x = 0.010. Rising Tc was confirmed by temperature dependence of the dielectric constants and the endothermic peaks observed in DTA curves. This is the first example for rising Tc in the solid solution based on BaTiO₃ except for doping of Pb²⁺ ion.