a-SiC:H/SiO2 Laminated Polarization Splitter for the Wavelength Region Longer Than 1.3 μm Prepared by Plasma-Enhanced Chemical Vapor Deposition

A laminated polarization splitter for the wavelength region longer than 1.3 μm is fabricated for the first time. It is composed of a-SiC:H/SiO₂ alternative multilayers prepared by plasma-enhanced chemical vapor deposition. Splitting behavior is also verified experimentally. It has low absorption loss even for the wavelength region around λ = 1.3 μm because the band-gap energy of a-Sic is larger than that of a-Si. The measured splitting angle is 13.8°, which is 2.4 times larger than the 5.7° splitting angle of rutile. The absorption loss of the multilayer is reduced to 1 × 10^-3 dB/μm at λ = 1.3 μm. The magnitude of the residual stress is 9.45 × 10⁸ dyn/cm², which is about one-third of that prepared by the rf bias sputtering equipment which is used for another project of our group. The deposition rate of SiO₂, is increased to 135 nm/min, which is 27 times larger than that prepared by the sputtering equipment.     

The structure and mechanical properties of syndiotactic polypropylene

The drawing behaviour of several syndiotactic polypropylenes is examined as a function of molecular weight and initial morphology. It is found that these materials can be drawn to a much lesser extent than comparable isotactic polypropylene. This limited drawability is attributed to the absence of an effective crystallinec-slip process, a view supported by dynamic mechanical measurements. Highest draw ratios are achieved in gel spun high molecular weight material where the degree of molecular entanglement is low enough to suppress the undesirable increase in drawing stress with extension.     

Plasma polymerized membranes and gas permeability. II

Thin films were deposited onto porous substrates by plasma polymerization using three kinds of organosilicic compounds, tetramethylsilane (TMS), hexamethyldisiloxane (M₂), and octamethylcyclotetrasiloxane (D₄). Those composite membranes showed different characteristics of gas permeability. When D₄ was plasma-deposited onto a porous substrate, the composites membrane showed the highest oxygen permeability and the lowest oxygen-to-nitrogen permeability ratio. The composite membrane prepared from TMS showed the permeability characteristics opposite to the membrane obtained from D₄. Infrared spectrum of the polymer from D₄ resembles that of dimethylpolysiloxane. The plasma polymers from TMS and M₂ showed different profiles in Si? O absorption bands in the range 1100–1000 cm^-1 or in absorption bands of SiCH₃ groups in the range 850–750 cm^-1 from respective monomers. X-ray photoelectron spectroscopic observation indicated that all the plasma polymers contained more than two species of Si atom with different oxidation states. The greater part of Si atoms in plasma polymers took the same oxidation states in corresponding monomer. The gas permeability characteristics were closely related to the oxidation states of Si atom in the plasma polymers.     

Transmission Properties of Translucent Polycrystalline Alumina

Effects of residual pores and optical birefringence on transmission through translucent polycrystalline alumina have been studied with the Mie scattering theory. The in-line and total forward transmissions of the translucent polycrystalline alumina were simulated as a function of porosity, pore radius, and grain size. The model revealed that porosity has a significant effect on both the total forward scattering and the in-line transmission, whereas grain size affects only in-line transmission. The calculated transmittance is in good agreement with the experimental values. The in-line transmission gradually increased with a decrease in grain size, and the effect of birefringence on the total forward transmission is negligible in the visible spectrum. The total forward transmission in the visible spectrum is mainly governed by residual pores.     

A two-stage preparation of mesophase pitch from the vacuum residue of FCC decant oil

The preparation of mesophase pitch as a precursor for the high-performance carbon fiber from a vacuum residue of FCC-decant oil (FCC-DOVR) was studied, applying a two-stage heat treatment to improve the pitch yield as well as its liquid crystal properties. The present two-stage preparation consisted of the pressurized heat treatment (1–5 MP) of the first stage at 430–480°C and the successive heat treatment under 13–260 Pa at 430°C. Such a two-stage preparation increased the yield of the spinnable mesophase pitch of 100% domain texture with lower softening point to 45% from 22% by the single-stage one from the same feedstock. Spinning properties of the mesophase pitch were excellent to allow smooth spinning for longer than 15 min and random orientation of mesogen molecules in the tranverse section of the fiber perpendicular to the fiber axis. The chemistry of the two-stage preparation for the higher yield and better properties as the fiber precursor is briefly discussed.     

Radiation grafting of α,β,β-trifluorostyrene onto poly(ethylene–tetrafluoroethylene) film by preirradiation method. I. Effects of preirradiation dose,monomer concentration,reaction temperature,and film thickness

Preirradiation grafting of α,β,β-trifluorostyrene onto poly(ethylene–tetrafluoroethylene) film was studied. The trapped radicals formed upon irradiation were able to induce graft polymerization under appropriate conditions. The influences of the grafting conditions were analyzed kinetically. The grafting rate dependency on the preirradiation dose was found to be of order 0.3, and the monomer concentrations, 1.0. The overall activation energies for this grafting were calculated to be 6.2 × 10⁴ and 9.3 × 10³ J/mol below and above 50°C. The grafting rate was found to be independent of the film thickness, which ranged from 25 to 100 μm.     

Thermoplastic elastomer by radiation grafting. I. Evaluation of processability of natural rubber grafted methyl methacrylate

Processability of thermoplastic elastomer (TPE) prepared by radiation-induced grafting of methyl methacrylate (MMA) onto radiation vulcanized natural rubber latex (RVNRL) has been evaluated using a kneader and a hot roll mill at 150°C. It was found that mixing time and revolution rate (rpm) of the kneader have significantly affected the processability. The longer mixing time and the higher revolution rate result in better processability. In such processing conditions, however, the mechanical properties were found to be inferior because the molecular chain scissions occurred during the mixing. A considerable improvement of mechanical properties was obtained when the mixing was carried out without added process oils. Blends of the grafted vulcanized natural rubber latex (RVNRL-g-PMMA) and MMA grafted on unvulcanized natural rubber latex (NRL-g-PMMA) improved processability where the better processability could be achieved at a shorter mixing time and a lower revolution rate. In addition, a comparable value of mechanical properties was obtained.     

A Power-Efficient Distributed TDMA Scheduling Algorithm with Distance-Measurement for Wireless Sensor Networks

This paper describes a power-efficient distributed TDMA slot scheduling algorithm which the slot allocation priority is controlled by distance measurement information in details. In our former proposed scheme, L-DRAND+, an extension of Lamport’s bakery algorithm for prioritized slot allocation based on the distance measurement information between nodes and a packet-based transmission power control had been applied. In this paper, we propose its enhanced scheme with a weighted rule control and state machines refinements of L-DRAND+, named L-DRAND++. This aims at the achievement of media access control methods which can construct a local wireless network practically by limiting the scope, and eliminate the redundant power consumption in the network. The proposed scheme can be shown as a possible replacement of DRAND algorithm for Z-MAC scheme in a distance-measurement-oriented manner. In addition, to evaluate the ordered node sequence determined by the algorithm, node sequence metric is proposed. By using the metric, we can evaluate protocol behaviors according to the environmental situation around the node.     

Comparison of the radiation dose in a cardiac IVR X-ray system

In this study, the entrance surface dose rates received by a phantom during cineangiography and fluoroscopy were compared. The X-ray conditions used in the measurements were those normally used in facilities performing percutaneous coronary intervention. Although, today, the entrance surface doses (cineangiography and fluoroscopy) of X-ray equipment used for cardiac interventional radiology (IVR) tends to be lower than they were previously, some equipment produces a high radiation dose. Therefore, the X-ray equipment used for cardiac IVR procedures must be maintained in good repair and must be carefully calibrated. In addition, periodic measurement of the radiation dose from the X-ray equipment used for both cineangiography and fluoroscopy for cardiac IVR is necessary. If the radiation dose of the X-ray system in use is too high, the IVR staff should determine the reason and make an effort to reduce it. Hence, the IVR staff must be adequately trained in radiation protection.