Electrical treeing phenomena in two-layer silicone gel with different crosslinking degrees and its dielectric strength

Silicone gel is widely used to encapsulate power modules, and improvement of its dielectric strength has been required. So, the purpose of our research is to improve dielectric strength of silicone gel encapsulant, and we focus on crosslinking degree of silicone gel. Previous studies have shown that growth mechanism of electrical tree changes with crosslinking degree of silicone gel. This suggests the possibility that the presence of the interface by different crosslinking degrees inhibits the tree growth. In this paper, we have investigated the tree growth and breakdown characteristics in silicone gel—crosslinking degrees graded layer materials. The interfaces in our study are arrange as being vertical to the line of electric force. Consequently, it was clarified that barrier effect of interface by different crosslinking degrees and the relaxation of electric field in low crosslinking degree region retards on tree growth, which improves the dielectric strength.     

Modification of the carbonization properties of coal-tar pitch by supercritical fluid extraction

The carbonization properties of coal-tar pitch were modified by supercritical fluid (SCF) extraction. Pitches extracted with supercritical toluene (SCFE pitch) contained none of the quinoline insoluble (QI) matter responsible for anisotropic structures with small unit sizes. The size of anisotropic structures from SCFE pitches was closely related to the β-resin (toluene insoluble and quinoline soluble fraction) content. Anisotropic structures from blended pitches prepared to have the same β-resin content as SCFE pitches (by blending toluene soluble (TS) and β-resin fractions obtained through a conventional liquid solvent extraction) were smaller. Extraction of the β-resin fraction with supercritical toluene could be interpreted by the co-solvent effects of the TS fraction dissolved in the extract phase. The high concentration of TS fraction in the extract phase enhanced the solubility of the β-resin fraction into this phase. In the raffinate phase, the heavier β-resin components, which are unsuitable for the development of mesophase structures, coagulated and formed unextractable QI matter through reduction in the concentration of the TS fraction. Since the TS concentration in both the phases depends on pressure and the ratio of the amounts of supercritical toluene and pitch, the control of the β-resin content in the SCFE pitches is possible through the adjustment of these two parameters.     

三次B样条插值曲面及其实现

目前在ＣＡＭ／ＣＡＭ的自由曲面构造方法中，较流行的有Ｂ样条曲面，Ｂｅｚｉｅｒ曲面、Ｂａｌｌ曲面等方法，但由这几种方法和成都是拟合曲面，而百插值曲面，常常不能满足一些工程实际中严格插值的要求，本文构造了一种自由插值曲面生成方法－Ｂ样条母线法，所生成曲面达到Ｃ＾２级光滑，适用机械，模具、汽车、造船等制造加工行业的复杂曲面设计。     

Synthesis of polyaniline/electrochemically exfoliated graphene composite as counter-electrode in dye-sensitized solar cell

ABSTRACT

Polyaniline (PANI)/graphene composite is a good candidate for the counter-electrode in a Pt-free DSSC. In this study, the electrochemically exfoliated graphene (EEG) from the used-battery graphite rod was produced. DC measurement reveals that EEG has a relatively low sheet resistance of 502.72 Ω/square. EEG suspension in DMF was used as synthesis media of PANI/EEG composite using the direct mixing method. Raman spectra show that the PANI/EEG composite was successfully synthesized as indicated by the presence of their characteristic peaks. Current density-voltage (J-V) measurements show that the power conversion efficiency of PANI/EEG composite better than the PANI-based counter-electrode.     

In Situ Time-Resolved Energy-Dispersive XAFS Study on Reduction Behavior of Pt Supported on TiO2 and Al2O3

The dynamic reduction behavior of a highly dispersed Pt⁴⁺ to Pt⁰ particles on TiO₂ and Al₂O₃ surfaces under the reductive atmosphere with an in situ time-resolved energy-dispersive X-ray absorption fine structure (DXAFS) analysis. A highly dispersed Pt⁴⁺ on TiO₂ was reduced to Pt⁰ even at room temperature. In contrast, a highly dispersed Pt⁴⁺ on Al₂O₃ was gradually reduced to Pt⁰ even at 473 K. This result may suggest that the semiconductive behavior of TiO₂ promotes the low temperature adsorption of hydrogen and supply of hydrogen atom to Pt⁴⁺ to be reduced and the activation of hydrogen on Al₂O₃ requires high temperature.     

Numerical simulation of natural convection heat transfer in the open space between two horizontal circular planes

Numerical simulations were conducted for natural convection heat transfer in a narrow gap between two horizontal plates in air. The lower plate is an infinite plate with a circular heating zone. The upper one is the bottom of a vertical cylinder, which is placed right above the circular heated plate and kept at room temperature. A set of Navier–Stokes equations and an energy equation are analyzed for a variety of combinations of gap clearance and Rayleigh number. The calculated average heat transfer values are shown to be in good agreement with the experimentally obtained ones reported in a previous paper. From the obtained isotherms, streamlines, and local Nusselt numbers, it is found that two types of convection appear in the gap space according to the conditions of Rayleigh number and gap clearance: one is a simple convection due to a single renewal flow which replaces heated air with ambient air and the other is a combined convection due to several vortex flows and a renewal flow. Furthermore, the flow rate of each flow controls the rate of heat transfer from the limited area which is covered by each flow. From this fact, the validity of the previously proposed heat transfer correlation is briefly discussed. © 2001 Scripta Technica, Heat Trans Asian Res, 30(6): 485–502, 2001     

Pore-Size Dependence of the Acidic Property of Mesoporous Silica FSM-16

The pore-size dependence of the acidic properties of mesoporous silica FSM-16 in the range from 1.8 to 3.8 nm was investigated with the catalysis of 2-butanol dehydration and using FTIR spectra of adsorbed pyridine. The activity was the highest for FSM-16 with a minimum pore diameter, and decreased with increasing pore size. Differences in the acid amounts of siliceous FSM-16 and the strength dependent on the pore diameter were not confirmed by FTIR characterization using pyridine as a probe molecule.     

Clinical review of 74 cases with miliary tuberculosis

Seventy-four cases of miliary tuberculosis were studied retrospectively. The mean age of the patients was 45.3 years. Twenty-two patients suffered from another underlying diseases. Six were infected with human immunodeficiency virus. Twelve had been treated with corticosteroids. Fever was present in 97.3 per cent of patients. Elevation of serum alkaline phosphatase was found in 67.6 per cent of cases. The skin reaction to tuberculin was positive in 61.2 per cent. Nodular shadows were found in the chest X-ray in 98.6 per cent of cases. The nodules were smaller than 2 mm in diameter in 52.7 per cent of cases. Other findings were enlargement of mediastinal lymph node (17.6%), cavities (23.0%), pleural effusion (27.0%), and consolidation (35.1%). Sputum cultures and urine cultures were positive for Mycobacterium tuberculosis in 76.8 per cent and 58.6 per cent of cases respectively. The diagnosis was confirmed by histopathological findings in some cases. The rate of positive biopsies was 61.5 per cent by bone marrow aspiration, 83.3 per cent by lymph node biopsy, 100 per cent by liver and lung biopsy. Antituberculosis therapy was successful in most of the patients. Seven patients died of miliary tuberculosis, 4 of them had adult respiratory distress syndrome.     

Development of a cashew nut shell liquid (CNSL)‐based polymer for antibacterial activity

A biobased polymer derived from cashew nut shell liquid (CNSL) as a renewable resource was investigated for use as an antibacterial material. CNSL is a mixture of aromatics containing cardanol as the main component and cardol and 2‐methylcardol as minor components. CNSL composition analyses showed that the minor components (i.e., cardol and 2‐methylcardol) in CNSL had higher contents of unsaturated structures than cardanol. These higher unsaturated contents promoted the thermal polymerization in the preparation of an epoxy CNSL prepolymer (ECNP). The biobased polymer film was fabricated by the reaction of amine compounds and ECNP without any organic solvent. The ECNP film took less than 2.0 h to reach a hardened dry condition at room temperature because of the crosslinking reaction between epoxy and amine groups. The antibacterial activities of the biobased polymer against Escherichia coli and Staphylococcus aureus were evaluated. CNSL showed antibacterial activity against S. aureus, whereas epoxy CNSL and ECNP alone showed no significant antibacterial activity against E. coli or S. aureus. This indicated that the antibacterial activity was based on the phenolic and catechol hydroxyl groups of CNSL. In addition, a biobased polymer film derived from CNSL and diamine showed antibacterial activity against both E. coli and S. aureus, even with alcohol conditioning. This suggested that the antibacterial activity was certainly fixed in the structure of the ECNP‐based polymers after the standard antisepsis treatment in medical facilities. Therefore, this biobased polymer could be useful in antibacterial materials as a coating and resin for health care applications. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42725.     

Marangoni convection in the LiCaAIF6 crystal growth by the Czochralski technique

Numerical simulation of the mixed convection induced by buoyancy, crystal rotation, and also unbalanced surface tension at the melt-gas interface is conducted by means of the finite volume method in the model of the Czochralski crystal growth. The role of Marangoni convection in the heat and mass transfer is investigated by the comparison of the models with and without surface tension included, and our results indicate that Marangoni convection plays an important role in the heat and mass transfer near the interface of melt and crystal, and also the convection structure.