连铸板坯偏离角纵裂纹成因分析及控制措施

通过对济钢第三炼钢厂1号连铸机连铸工艺环节的分析,并根据实际生产中所采取的相关措施及取得效果,认为板坯角部纵裂纹主要源于结晶器侧面足辊与样板的间隙、结晶器冷却和锥度、钢水成分和过热度、拉速等。对其采取有效措施后,使板坯的偏离角纵裂纹发生率由2.77%降低到0.09%。     

Isolation of some luteolin derivatives from Mentha longifolia (L.) Hudson subsp. longifolia and determination of their genotoxic potencies

This study was designed to evaluate the mutagenic and antimutagenic activities of luteolin derivatives (luteolin 7-O-glucoside, luteolin 7-O-rutinoside and luteolin 7-O-glucuronide) isolated from Mentha longifolia (L.) Huds. subsp. longifolia by using Ames Salmonella test (TA 1535 and TA1537 strains). In the antimutagenicity assays, luteolin 7-O-glucoside, luteolin 7-O-rutinoside and luteolin 7-O-glucuronide showed antimutagenic effects on TA1537 and TA1535 strains. The highest inhibition rates for luteolin 7-O-glucoside, luteolin 7-O-rutinoside and luteolin 7-O-glucuronide on TA1537 strain were 84.03%, 87.63% and 67.77%, respectively. Similarly, in the antimutagenicity assays performed with the TA1535 strain, the inhibition rates for luteolin 7-O-glucoside and luteolin 7-O-rutinoside were 23.86% and 23.76% respectively. Our findings showed that the antimutagenic properties of luteolin derivatives on TA1537 and TA1535 strains have been found to be structure dependent. The clarification of differences in antimutagenic potency of these luteolin derivatives based on their structures has been demonstrated in this study.     

The vendor location problem

The vendor location problem is the problem of locating a given number of vendors and determining the number of vehicles and the service zones necessary for each vendor to achieve at least a given profit. We consider two versions of the problem with different objectives: maximizing the total profit and maximizing the demand covered. The demand and profit generated by a demand point are functions of the distance to the vendor. We propose integer programming models for both versions of the vendor location problem. We then prove that both are strongly NP-hard and we derive several families of valid inequalities to strengthen our formulations. We report the outcomes of a computational study where we investigate the effect of valid inequalities in reducing the duality gaps and the solution times for the vendor location problem.     

Microdosimetry of inhomogeneous radon progeny distributions in bronchial airways

A Monte Carlo code, initially developed for the calculation of microdosimetric spectra for alpha particles in cylindrical airways, has been extended to allow the computation (i) of additional microdosimetric parameters and (ii) for realistic exposure conditions in human bronchial airways with respect to surface activity distribution and airway geometry. The objective of the present study was to investigate the effects of non-uniform distributions of radon progeny activities in bronchial airways on cellular energy deposition parameters. Significant variations of hit frequencies, doses and microscopic energy deposition patterns were observed for epithelial cell nuclei, depending strongly on the assumed activity distributions. Thus, epithelial cells located at different positions in a given bronchial airway may experience a wide range of biological responses. The results obtained suggest that the hit frequency may be the primary physical parameter for alpha particles, supplemented by microdosimetric single event spectra, to be related to biological effects for chronic low level exposures.     

Dosimetric comparison of Monte Carlo codes (EGS4, MCNP, MCNPX) considering external and internal exposures of the Zubal phantom to electron and photon sources

This paper aims at comparing dosimetric assessments performed with three Monte Carlo codes: EGS4, MCNP4c2 and MCNPX2.5e, using a realistic voxel phantom, namely the Zubal phantom, in two configurations of exposure. The first one deals with an external irradiation corresponding to the example of a radiological accident. The results are obtained using the EGS4 and the MCNP4c2 codes and expressed in terms of the mean absorbed dose (in Gy per source particle) for brain, lungs, liver and spleen. The second one deals with an internal exposure corresponding to the treatment of a medullary thyroid cancer by 131I-labelled radiopharmaceutical. The results are obtained by EGS4 and MCNPX2.5e and compared in terms of S-values (expressed in mGy per kBq and per hour) for liver, kidney, whole body and thyroid. The results of these two studies are presented and differences between the codes are analysed and discussed.     

Synthesis and characterization of new hydrogels on the basis of water‐soluble maleic anhydride copolymers with γ‐aminopropyltriethoxysilane

This work describes the synthesis and macromolecular reactions of maleic anhydride (MA)–acrylic acid (AA) binary reactive copolymers with γ‐aminopropyltriethoxysilane (APTS) as a polyfunctional crosslinker. Copolymers with a given composition of MA–AA (47.17–52.83 wt %) were synthesized by radical binary copolymerization with benzoyl peroxide as an initiator in p‐dioxane at 70°C in nitrogen atmosphere and initial monomer ratio of 1 : 1. It is shown that the network structure is formed in MA–AA/APTS in water by intermolecular reaction between the anhydride unit and the amine group, as well as between the etoxysilyl fragment and free carboxyl groups of the acrylic acid and maleic anhydride unit. Swelling parameters such as beginning time of hydrogel formation, initial rate of swelling, swelling rate constant, equilibrium swelling, and equilibrium water content were determined for copolymer/APTS/water systems with various copolymer/crosslinker ratios. Formation of a hyperbranched network structure through the fragmentation of side‐chain reactive groups in the studied systems was confirmed by FTIR, TGA, and DSC methods. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 4009–4015, 2003     

硅灰石与连续玻璃纤维毡组合增强聚丙烯的力学性能

采用硅灰石与连续玻璃纤维毡组合增强聚丙烯,研究了硅灰石的含量,玻璃纤维毡的面密度、基体树脂的性质及界面改性等对材料力学性能的影响。结果表明：采用硅灰石与连续玻璃纤维毡组合增强,可提高复合材料的拉伸、弯曲强度及模量,但过高的硅灰石含量,会导致拉伸及弯曲强度下降,材料的力学性能随着所用玻璃纤维毡面密度的增大而显著提高,采用偶联剂对硅灰石进行处理及在基体聚丙烯中添加功能化聚丙烯,可改善界面结合、提高材料性能,随着功能化聚丙烯含量的增加,材料的拉伸、弯曲强度及模量有所提高,但含量过高时,会引起材料冲击强度的下降;组合增强材料的性能与基体树脂本身的力学性能密切相关,同时还受基体树脂熔体流动性的影响。     

Separation of PET and PVC by Flotation Technique Without Using Alkaline Treatment

PET and PVC cannot be separated by gravity separation techniques due to their close density. For this reason, plastic recycling needs other separation techniques. Froth flotation, which is used in mineral processing, could be useful because of its low cost and simplicity. The main objective of this research is to investigate the flotation characteristic of PET and PVC and determine the effects of plasticizers on plastic separation without any alkali pre-treatment. In selective flotation experiments, water bottles and waste water pipes were used for this purpose, and Triton XL-100 N and diethylene glycol dibenzoate were used as plasticizers. Various parameters such as pH, plasticizer concentration, conditioning time, and flotation time were investigated. According to the results, PET particles were floated with 100% purity, and the product remaining in flotation cell (PVC particles) was obtained with 86.1% purity.     

Perturbation methods for moderately elliptical plates with a core

Fundamental frequencies of vibrating moderately elliptic plates with a concentric circular core have been determined analytically. A boundary perturbation method is developed to extract the fundamental eigenvalue of the governing biharmonic boundary value problem. The method is then applied to moderately elliptic plates with clamped and simply supported outer boundary conditions. Clamped, simply supported, and free circular cores are considered. Approximate analytical formulations of the fundamental frequency for such plates with core are obtained.