各种引气剂以及抑泡剂对混凝土经时变化状态等的影响

众所周知,采用粉煤灰制备混凝土,因粉煤灰成分中含有未燃炭等微粒子,容易造成阴离子型引气剂吸附在这些微粒子上,导致含气量经时损失.同时在混凝土的制备、运输过程中,因受采用的材料、拌和状态等物理因素影响,还会发生含气量经时增加的现象.所以在制备、管理混凝土时,如何保证出机初期一定的含气量、缓解含气量的经时损失或经时增加,是一项极其关键的技术.本文将就采用能改善上述状态的引气剂、抑泡剂拌和混凝土,对混凝土的经时变化以及抗冻融性等特征产生的影响进行论述.     

Characterization of microstructural damage due to low-cycle fatigue by EBSD observation

Electron backscatter diffraction (EBSD) in conjunction with scanning electron microscopy was used to assess the damage due to cyclic or uniform strain. Samples of Type 316 stainless steel after fatigue and tensile tests were prepared for EBSD observation and the misorientation angle between neighboring points (local misorientation) was evaluated. It was shown that the local misorientation developed due to the cyclic and uniform strain and that its spatial distribution was not uniform. In fatigue samples, the area of large local misorientation tended to form clusters, whereas it localized to the grain boundaries in the tensile samples, and the magnitude of local misorientation and the degree of the localization increased with the strain amplitude. The degree of localization was quantified via statistical processing of the measured data. It was also shown that the source of damage (cyclic or uniform strain) and the loading direction could be deduced from the EBSD observations of the damaged sample.     

Preliminary spectrum shifter design for intermediate energy nuclear data benchmark experiments with DT neutrons

Integral benchmark experiments with DT neutrons are not always sufficient for nuclear data benchmarking in the MeV region, below 10 MeV. A neutron spectrum shifter, which will be placed between a sample and a DT neutron source, is effective to moderate DT neutrons incident to the sample. In order to estimate effects of the spectrum shifter, the ratio of the contribution of 14 MeV neutrons in the leakage neutron and gamma-ray spectra was calculated with MCNP-4C for an experimental configuration at FNS of JAEA, Japan. The calculations were carried out for a Li₂TiO₃ sample with a Be, D₂O, or ⁷LiD spectrum shifter. It was found out that the Be shifter was superior to others and the Be shifter was effective to decrease the contribution of 14 MeV neutrons especially for secondary gamma-ray spectrum measurements.     

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     

Tan δ of ethylene-propylene rubber in cryogenic temperature region–effects of additives and sample thickness

The authors have been developing extruded polymer insulated superconducting power cables. Dielectric loss in electrical insulation cannot be ignored in superconducting cables since conductor loss in the cables is minimal. Studies so far show that ethylene-propylene rubber (EPR) is suitable as an electrical insulating material in the extruded polymer insulated superconducting cable design because it demonstrates excellent mechanical and relatively good electrical qualities at a cryogenic temperature. Widely used EPR includes some kinds of additives; however, their effect on tan δ of EPR at cryogenic temperature remains unknown. The effect of additives such as crosslinking agent and fillers on tan δ of EPR was examined at temperatures of between 4.2 K and 300 K. Thickness dependence of tan δ was also measured using EPR films of different thickness and an extruded EPR insulated cable sample. The results show that additives increase tan δ of relatively thin films of EPR even in the cryogenic temperature region; however, they do not have an intolerable dielectric loss in comparison with conductor loss and heat inflow of the superconducting cable. The remedy to tan δ increase due to the polymer contraction relative to shielding wires has been established.     

Development of Laser-Induced Capillary Wave Method for Viscosity Measurement Using Pulsed Carbon Dioxide Laser

A new experimental apparatus, based on the laser-induced capillary wave method involving the use of a pulsed carbon dioxide laser (wavelength 10.6 m, pulse width 50 ns, power 65 mJ) as a heating source has been developed. Since the present technique is applicable to a wide range of viscosity, this method is applicable to the process in which the viscosity drastically changes within a short period of time. In this method, interfering laser beams heat a liquid surface and generate a capillary wave (the wavelength can be adjusted from 20 to 200 m) caused by a spatially sinusoidal temperature distribution. The temporal behavior of the capillary wave is detected by a diffracted probe beam (He–Ne laser, 15 mW) at the heated area. The dynamics of the capillary wave provide information regarding thermophysical properties such as viscosity and surface tension. In the present study, several liquid samples spanning the viscosity range from 0.33 to 7080 MPa·s (e.g., acetone, toluene, 1-hexanol, ethylene glycol, JS1000, and JS14000) were investigated at room temperature. The detected signals for several liquid samples exhibiting a wide range of viscosity agree well with theoretical calculations, taking into account the influence of the distribution of surface tension.     

Applying secondary ion mass spectrometry to the analysis of elements in goblet cells of conjunctiva

We investigated the location of elements in the goblet cells of rat conjunctiva by analyzing ion images produced by secondary ion mass spectrometry (SIMS) and comparing them with those produced by energy dispersive X-ray analyser (EDX). Conjunctivas of normal Spraque-Dawley rats were quenched in propane prechilled liquid nitrogen. Semi-thin sections were made with a cryo-ultramicrotome, freeze-dried, carbon-coated and observed under a light microscope, SIMS and scanning electron microscope (SEM). In the element analysis by SIMS, images of positive ions were examined with an O2+ primary ion source and images of negative ions with a Ga+ ion source. The same sections were observed and analysed with SEM-EDX. Morphological features and images of elements with SIMS and EDX were compared. Na, Mg, K, and Ca were detected as positive ions and OH, CN, P, S, and Cl as negative ions with SIMS, but C, N, O, Na, Mg, P, S, Cl, K, and Ca were detected with EDX. The spatial resolution of SIMS in element location was higher than that of EDX. Many elements were clearly located in the goblet cells on ion images by SIMS. Element ion images were demonstrated more densely in goblet cells than in other parts within conjunctiva and by SIMS compared to EDX. SIMS is a useful method for the detection of elements and their locations in ocular tissues and cells.     

An ESR study of the film formation steps of vapor deposition polymerization of polyamic acid

A film of polyamic acid is formed by vapor deposition polymerization of pyromellitic dianhydride (PMDA) and 4,4′-diaminodiphenyl ether (ODA). We have taken ESR spectrum during the polymerization process and compared it with the ESR spectrum of films obtained from solution polymerization. In the intermediate polymers during vapor deposition polymerization, the amide bond (? CONH? ) is coplanar with the benzene ring and two protons in the PMDA molecule. This intermediate polymer has one unpaired electron that interacts with the two nitrogen nuclei equally. On the other hand, in the polymer obtained by solution polymerization, the amide bond and the benzene ring of PMDA are not coplanar. In this polymer, too, some of the molecules have an unpaired electron that seems to have almost no coupling with NH groups. These results imply that the polymer formation via vapor deposition proceeds through different intermediates and different molecular configurations from that via the solution process.