Phase transition at a temperature immediately below the melting point of poly(vinylidene fluoride) from I: A proposition for the ferroelectric Curie point

A phase transition at a temperature immediately below the melting point of poly(vinylidene fluoride) form I has been found by means of differential scanning calorimetry (d.s.c.) and infra-red (i.r.) vibrational spectroscopy. An endothermic d.s.c. shoulder has been observed at a temperature about 10°C below the melting point, in the vicinity of which the i.r. crystalline trans bands decrease in intensity steeply and the crystalline gauche bands increase in intensity, indicating the conformational change from all-trans to T₃GT₃G type. These observations have been found to be detectable more clearly for samples subjected to the poling treatment under a d.c. high voltage. The transition shows the characteristic behaviour essentially identical to those observed for ferroelectric copolymers of vinylidene fluoride and trifluoroethylene, except for the irreversibility of the structural change, suggesting that the phase transformation revealed here may be a ferroelectric-to-paraelectric phase transition of polar form I crystal and the the Curie point may be about 172°C. It is consistent with Micheron's measurement of the temperature dependence of the dielectric constant. Other structural changes in the form I sample occurring in the temperature range from 20° to 170°C have also been discussed based on the i.r. spectral measurements.     

Structural change of st-PMMA on drawing,absorption and desorption of solvents

Well-oriented crystalline samples of syndiotactic poly(methylmethacrylate) (st-PMMA) could be prepared from stretched non-crystalline samples on solvent-induced crystallization using chloroacetone, diethyl ketone, etc. as the solvent. X-ray fibre diagrams of these samples usually show period of 35.4Å and also suggest that the st-PMMA chains have a helical conformation of large radius and small axial pitch along the original stretched direction. Inversion of dichroism for most infra-red absorption bands during the crystallization, which is an indication of a wide variation in the orientation of the chains, again supports the large helical conformation. It was also confirmed that the solvents are necessary in maintaining the crystalinity as the samples lose crystallinity on desorption of the solvents. From these results, it is conceivable that st-PMMA forms a complex with the solvents similar to the well-known amylose-iodine complex.     

A motion base with 6-DOF by parallel cable drive architecture

This paper proposes a new type of motion base for virtual sensation of acceleration by applying a parallel cable drive architecture. It has outstanding advantages in comparison with conventional Stewart platforms. Especially, 1) rotational motion range is large; 2) the motion platform can be grounded on the floor; 3) scene projection to all the walls is possible; and 4) its redundancy of cables improves safety for cut of cables. Optimal fundamental mechanical design is performed from the viewpoint of kinematics. Simulation results show that a 3-3-2 cable configuration is one of the best designs as a motion base. The prototype developed has the maximum motion range of translation ±0.45 m × ±0.4 m × 1.1 m and that of rotation ±45° in roll angle, ±45° in pitch, and ±35° in yaw. It can produce acceleration 1 G for 0.8 s at its maximum, even if gravity is not used. A trajectory planning method for longer-term sensation utilizing gravity is proposed. Low-frequency component of acceleration is realized by rotational motion and high frequency is produced by translational motion. Experimental results to create virtual acceleration of a roller coaster demonstrated effectiveness of this new design     

High-resolution cardiac PET in rabbits: imaging and quantitation of myocardial blood flow

A high-resolution PET system for small animals was tested for its applicability to the investigation of regional myocardial blood flow (MBF) in rabbits. METHODS: Nineteen measurements were performed in 10 closed-chest anesthetized rabbits at baseline and during infusions of adenosine (0.2 mg/kg/min) and propranolol (0.20-1.20 mg slow infusion) to obtain a wide range of MBF. Myocardial blood flow was assessed both by dynamic 13N-ammonia PET and by colored microspheres. Blood was withdrawn directly from the femoral artery, and arterial 13N activity was measured by coincidence type gamma detection system for the input function. Nitrogen-13 myocardial uptake was calculated by dividing the myocardial 13N activity by the integral value of the input function. RESULTS: Three or four contiguous cross-sectional myocardial images were obtained after 13N-ammonia injection. The left ventricular wall and cardiac cavity were clearly visualized. Moreover, initial passage of the tracer through the heart was obtained with serial 10-sec PET images. Nitrogen-13 myocardial uptake correlated well with flow measured with microspheres (r = 0.88). CONCLUSION: Our cardiac PET system can be used for in vivo imaging and quantitation of MBF in small animals and may play an important role in the future study of animal models of cardiovascular diseases.     

A lattice model of fashion propagation with correlation analysis

Spatial and temporal changes in fashion are very complicated in an information-oriented society. In this article, we introduce a lattice model of fashion which is composed of two competing trends. Simulation is carried out by two methods: local and global interactions. In the former case interaction occurs between adjacent lattice sites, while in the latter it occurs between any pair of lattice sites. Computer simulations reveal that the fashion is more prevalent for global interaction than for local interaction. Various spatial patterns in fashion are analysed by both auto- and cross-correlations. We find universally a power law which leads to collective behaviours of fashion: if the number of people with a trend is extremely decreased, they are localised in scattered very small areas. For the producer/maker of fashion, global transmission is far more important than local dispersal.