Measurement of stress profiles in the preform of a polarization-holding fiber with stress-applying parts

Stress difference distribution, principal stress trajectories, and surface stress profiles are measured for the preform of a polarization-holding fiber with stress-applying parts. Experimentally evaluated stresses are compared with stresses computed by a finite element method. Experimental results are well explained by the calculated ones. Contour maps for stress difference and principal stress are presented. Surface stress is found to be compressive for the entire boundary of the fiber. Tensile test is carried out for the fiber drawn from the same preform rod. The result reveals that the strength of the polarization-holding fiber is comparable with that of a usual fiber without a stress-producing structure.     

DLTS Studies of Neutron Camage in P-Type Silicon

Damage produced in p-type silicon by neutron irradiation at room temperature was studied by deep-level transient spectroscopy (DLTS). The production of three defects (Ev + 0.15, Ev + 0.34 and Ev + 0.45 eV) by neutron irradiation and the formation of two defects (Ev + 0.25 and Ev + 0.21 eV) during annealing were reported. It was found that many properties of the neutron damage were similar to those of the electron damage obtained by other works as far as the DLTS measurements are concerned. The DLTS measuements indicated no evidence for the production of defect clusters in the neutron damage. By comparing with the results previously obtained by the Hall effect measurements, it was found that the DLTS measurements mainly evaluated the properties of the point defects outside the clusters. The fact that the DLTS measurements did nto reflect the properties fo the defect clusters was ascribed to the reduction of majority carrier capture by defects inside the clusters due to the potential barrier formed by the cluster-space-charge regions.     

Numerical calculations for two-phase flow analyses in pin bundles

Two-phase flow equation systems, in which equations are defined for each phase, are discussed for use in analyzing coolant behaviors in LMFBR pin bundles. These equation systems have not yet consolidated, because of theoretical and experimental difficulties and complexities.One of the problems is the equation systems' stability. This paper shows the stability for the low Reynolds number (O(1)) system, using a one dimensional linear equation system. Based on this fact, a two-phase flow equation system is numerically solved by using the subchannel method for 19- and 37-pin bundles. The calculational examples are LOF and TOP conditions with/without the blockage, and fission gas release.     

Selective synthesis of carbon nanotubes and nanocapsules using naphthalene pyrolysis assisted with ferrocene

Selective synthesis of well aligned multi-walled carbon nanotubes (MW-CNT) and multi-shelled carbon nanocapsule (MS-CNC) using pyrolysis of naphthalene with the presence of ferrocene was experimentally examined. With higher mole fraction of naphthalene to ferrocene, more MW-CNTs could be synthesized due to higher concentration of carbonaceous precursors emerging from the decomposed naphthalene. Based on kinetic analysis, at lower temperature, MW-CNTs could preferably be synthesized due to the controlled supply of carbonaceous clusters to get onto the surface of Fe clusters. On the other hand, at temperature higher than 900 °C the Fe clusters become more active to catalyze carbonaceous precursors to undergo self assembling process of MS-CNCs. With cheaper cost of naphthalene compared with other high-value hydrocarbons, usage of naphthalene would provide an advantage of reasonably economical synthesis of MW-CNT or MS-CNC.     

A predictive model and mechanisms associated with hydrogen production via hydrothermal reactions of sulfide

Hydrogen generation and the concurrent formation of sulfur products from hydrothermal reactions of aqueous sulfide solutions at pH values between 9 and 13 and temperatures between 280 and 330 °C were studied. A hydrogen production model was developed by kinetic and statistical analysis of sulfide consumption rates and the ratio of hydrogen produced to sulfide consumed. Results showed that the amount of hydrogen generated in a given reaction may be predicted by a series of equations incorporating starting conditions such as the initial sulfide concentration, pH and temperature. The data from this study suggested that the overall hydrogen generation reaction mechanism consists of one or more elementary reactions which result in the formation of various sulfur products, such as polysulfides and sulfur oxyanions, depending on the reaction conditions. The possible specific sulfur compounds included pentasulfide (S₅²⁻), thiosulfate (S₂O₃²⁻), trithionate (S₃O₆²⁻) and sulfate (SO₄²⁻). The production rate constants of these products increased with temperature, but were independent of pH. Additionally, it was indicated that increasing the reaction temperature and/or pH resulted in the formation of sulfur products with higher oxidation numbers. This work suggests that the optimal mechanism for hydrogen generation via the sulfur redox cycle, taking into account the requirement for sulfide regeneration, is that which forms trithionate as the sole sulfur product.     

Microstructure of ion-implanted region in TiNi alloy

TiNi alloy samples implanted with various fluences of 3 MeV Cu²⁺ ions were characterized by transmission electron microscope (TEM) and X-ray diffractometer. Cross-sectional TEM images of the samples showed that amorphous region was seen at the fluence of 10¹⁴ ions cm^?2 in case of ion implantation at 300 K of the substrate temperature, but in case of ion implantation at 100 K it did not appear even at 10¹⁵ ions cm^?2. These results were also confirmed by X-ray diffraction profiles of the same samples. Consequently, the extent of microstructure change of TiNi alloy by ion implantation was different depending on the substrate temperature.     

Current distribution in a two-dimensional narrow gap cell composed of a gas evolving electrode with an open part

On the basis of the observation of gas bubbles evolved by electrolysis, a two-dimensional vertical model cell composed of electrodes with open parts for releasing gas bubbles to the back side is proposed. The model cell consists of two layers. One layer forms a bubble curtain with a maximum volume fraction of gas bubbles in the vicinity of the working electrode with open parts. The other. being located out of the bubble layer, is a convection layer with a small volume fraction distributed in the vertical direction under forced convection conditions. The cell resistance and the current distribution were computed by the finite element method when resistivity in the back side varied in the vertical direction along the cell. The following three cases for overpotential were considered: no overpotential, overpotential of the linear type and overpotential of the Butler-Volmer type. It was found that the cell resistance was determined not only by the interelectrode gap but also by the percentage of open area and in some cases by the superficial surface area. The cell resistance varied only slightly with the distribution of the bubble layer in the back side.Nomenclature b linear overpotential coefficient given byb=/i - C proportionality constant given by Equation 15 - d ₁ distance between front side of working electrode and separator - d ₂ thickness of separator - F Faraday constant - I total current per half pitch - i current density at working electrode - i ₀ exchange current density - L length of a real electrolysis cell - n number of electrons transferred in electrode reaction - O _p percentage of open area given by Equation 1 - p pitch, i.e. twice the length of the unit cell, defined by 2(BC) in Fig. 4 - q thickness of bubble curtain, defined by (AM) in Fig. 4 - R gas constant - r _t total cell resistance - r unit-cell resistance defined by (V – V _eq)/I - r _rs residue ofr from sum ofr ₀ andr - r ₀ ohmic resistance of solution when0 _p=0 - r resistance due to overpotential when0 _p=0 - s electrode surface ratio or superficial surface area given by Equation 2 for the present model - T absolute temperature - t thickness of working electrode defined by EF in Fig. 4 - V cell voltage - V _eq open circuit potential difference between working and counter electrodes - solution velocity in cell - ₀ solution velocity at bottom of cell - w width of working electrode, defined by 2(DE) in Fig. 4 - x abscissa located on cell model - y ordinate located on cell model - anodic transfer coefficient - linear overpotential kinetic parameter defined byb/[_bc(p/2)] - d infinitesimally small length on the boundary - volume fraction of gas bubbles in cell - dimensionless cell voltage defined bynF(V – V _eq)/RT - overpotential at working electrode - Butler-Volmer overpotential kinetic parameter defined by [nFi _0bc(p/2)]/RT - coordinate perpendicular to boundary of model cell - ₁ resistivity of bubble-free solution - ₂ resistivity of separator - _bc resistivity of bubble curtain - potential in cell