Space charge behavior in polymer film based on increment of capacitance under AC high field

Polymer materials have excellent dielectric and insulation properties; however, those properties in AC high field region have not been known well. Recently we established an evaluation method of high‐field AC dissipation current waveform of polymer materials 1 . AC dissipation current waveforms of polyethylene and polypropylene films show nonlinear distortion in AC high‐field region. This nonlinearity was thought to be related to the behavior of AC space charge formation in the sample near electrodes. The properties of space charge formed under AC high field at power frequency seem to differ from those formed under DC high field. The measurement of AC space charge distribution is not so easy due to the resolution limit of the space charge measurement. We studied the dielectric properties of biaxially oriented polypropylene (BOPP) film under AC high field up to 120 °C. It was found that tan δ, AC dissipation current (Ixr), and unbalanced component of capacitive current (ΔIxc) increased when the temperature became higher. In particular, ΔIxc increased above some threshold field and was considered to be due to the AC space charge formation. This AC space charge layer near electrode is thought to be formed due to carrier injection under AC high‐field application. Usually, the carrier mobility becomes smaller on lowering the temperature. Most of the carriers injected from the electrode are trapped near the electrode in the sample film. But in the high‐temperature region, the carrier mobility becomes larger and the carrier injection starts to increase from lower field. Many more carriers are injected from the electrode. It is thought that some of the injected carriers are trapped inside the sample film; the others go through the sample to the opposite side. © 2002 Wiley Periodicals, Inc. Electr Eng Jpn, 141(2): 8–16, 2002; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10018     

The growth of carbon coating layers on iron particles and the effect of alloying the iron with silicon

Magnetic fine particles of metallic Fe coated with graphitic carbon layers were synthesized by annealing Fe₂O₃ particles with carbon powders at 1673 K in nitrogen atmosphere. For comparison, SiC was added to Fe₂O₃. X-ray diffraction measurement showed that the lattice constants of Fe changed depending on the Si contents. Mössbauer spectroscopy confirmed that Fe-Si alloys were formed by the Si addition and that the iron carbide disappeared. Electron microscope images revealed that the thickness of carbon coating layers increased from 24 nm to 36 nm as a result of the Si addition. Soaking tests showed that the corrosion resistance of the carbon-coated Fe particles was improved by the addition of Si. The results suggest that Si caused C to leave the Fe cores and move to the surface to form a carbon coating.     

High-field dielectric properties of polyethylene in the high-temperature region

Nonpolar polymers such as polyethylene or polypropylene are widely used as insulation materials, often under conditions involving strong electric fields and high temperatures. Under these conditions, the conduction loss due to DC-like carrier transport may give rise to a high-field AC dissipation factor (tan δ). This paper describes the high-field dielectric properties of polyethylene films at frequencies from 50 to 400 Hz and temperatures from room temperature to 100°C, as measured with a new type electrode design developed by the authors. In the high-temperature region, the AC dissipation current waveform at 50 Hz was also measured. At room temperature, the electric-field dependence of tan δ is almost unaffected by the frequency of the applied field. But at high temperatures and strong electric fields, tan δ tends to have a large field dependence and to be almost inversely proportional to the frequency. Thus the AC conductivity becomes independent of the frequency of the applied field in the region of strong fields and high temperatures. A theoretical analysis shows that the high-field dielectric loss is governed by two processes, namely, the dielectric relaxation loss inherent to the AC field and the DC-like carrier transport loss that becomes prominent in the high-temperature region, where AC dissipation current waveform becomes significantly nonsinusoidal.     

Functional competence of T cells in the absence of glycosylphosphatidylinositol-anchored proteins caused by T cell-specific disruption of the Pig-a gene

T lymphocytes express various glycosylphosphatidylinositol (GPI)-anchored surface proteins, such as Thy-1 and Ly-6A. However, functional contribution of GPI-anchored proteins in T cell activation is as yet poorly understood. Here we report the generation of mutant mice deficient in the expression of GPI-anchored molecules exclusively in their T cells. We established mice carrying three identically oriented lox-P sites within the Pig-a gene, which encodes a component essential for the initial step of GPI anchor biosynthesis. These mice were crossed with mice carrying the Cre recombinase gene driven by the T cell-specific p56lck proximal promoter. Offspring carrying both the lox-P-containing Pig-a gene and the Cre transgene exhibited almost complete loss of the surface expression of GPI-anchored molecules on peripheral T cells. Interestingly, those T cells deficient in GPI-anchored molecules were capable of responding to T cell receptor stimulation in vitro and in vivo. These results indicate that T cells lacking the expression of GPI-anchored molecules are functionally competent in exerting TCR-mediated immune responses.     

Synthesis and structures of iron nanoparticles coated with boron nitride nanomaterials

Iron (Fe) nanoparticles coated with boron nitride (BN) nanomaterials were synthesized by using Fe(4)N and B powders as raw materials. The Fe(4)N was reduced to alpha-Fe during annealing at 1000 degrees C for several hours with flowing 100 sccm N(2) gas. The reaction was predicted by Ellingham diagram. The atomic structure and magnetic properties were investigated by high-resolution electron microscopy and vibrating sample magnetometer system.     

Photoinduced Magnetization with a High Curie Temperature and a Large Coercive Field in a Co‐W Bimetallic Assembly

The crystal structure, magnetic properties, and temperature‐ and photoinduced phase transition of [{Co^II(4‐methylpyridine)(pyrimidine)}₂{Co^II(H₂O)₂}{W^V(CN)₈}₂]·4H₂O are described. In this compound, a temperature‐induced phase transition from the Co^II (S = 3/2)‐NC‐W^V(S = 1/2) [high‐temperature (HT)] phase to the Co^III(S = 0)‐NC‐W^IV(S = 0) [low temperature (LT)] phase is observed due to a charge‐transfer‐induced spin transition. When the LT phase is irradiated with 785 nm light, ferromagnetism with a high Curie temperature (T_C) of 48 K and a gigantic magnetic coercive field (H_c) of 27 000 Oe are observed. These T_C and H_c values are the highest in photoinduced magnetization systems. The LT phase is optically converted to the photoinduced phase, which has a similar valence state as the HT phase due to the optically induced charge‐transfer‐induced spin transition.     

Subretinal bleeding without choroidal neovascularization in pathologic myopia. A sign of new lacquer crack formation

PURPOSE: The clinical significance of subretinal bleeding without choroidal neovascularization in pathologic myopia is unclear. Only two reports in the ophthalmic literature have demonstrated the clinical course of subretinal bleeding and have indicated that it might be a precursor of lacquer cracks. In this study, the authors observed the clinical course of subretinal bleeding in highly myopic eyes and studied this condition in relation to new lacquer crack formation. METHODS: The authors examined consecutively and prospectively 22 highly myopic eyes (19 patients) with subretinal bleeding. Indirect ophthalmoscopy and fluorescein fundus angiography were performed in all patients. Indocyanine green (ICG) angiography could be performed in three patients. The follow-up period ranged from 6 to 198 months (mean, 61.3 months). RESULTS: In 17 of 22 eyes, lacquer cracks appeared at the site of previous subretinal bleeding. The period for the formation of new lacquer cracks after the onset of the bleeding ranged from 2 to 6 months (mean, 4.0 months). In one patient, ICG angiography revealed linear hypofluorescence, indicating a ruptured Bruch's membrane at the onset of subretinal bleeding. CONCLUSION: A rupture of Bruch's membrane and choriocapillaris complex results in subretinal bleeding, which is the first process of new lacquer crack formation. Atrophy of the overlying pigment epithelium and further scar formation results in the development of a lacquer crack.     

Friction characteristics of inorganic or organic thin coatings on solid surfaces under water lubrication

Water has been considered as an alternative working fluid for hydraulic power systems in order to minimize the consumption of fossil fuels and mineral oils. In spite of the many advantages to this use of water, difficult technical problems remain. The key technology for establishing a water hydraulic system is tribology, because water has a lack of lubricity, and thus some coating is needed to protect the metal surfaces from corrosion and frictional wear when using water as a lubricant. It has already been demonstrated that some Si-containing materials have good lubricity in a water environment. Recently, it has been shown that diamond-like carbon (DLC) coatings also have good lubricity with water. In order to clarify the mechanism by which such materials are lubricated with water, and to develop surface coatings that have good lubricity with water, the friction characteristic of several coated metals were investigated in this study. Coatings of CrN, CrSiN, and two types of DLC were applied on an SUS630 stainless steel flat disk substrate. Additive-free distilled water was used as a lubricating fluid. The friction characteristics of these coatings at different sliding speeds were evaluated using a tribometer with two contact configurations in which stainless steel balls and a flat ring without coatings were used as mating specimens.In addition, the lubrication characteristics of organic hydro-gels such as alginic acid or its metal salt were studied by immobilizing them on the surface, and their effects on the lubrication with water were discussed.