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91.
Fazal-ur-Rehman M.I. Al-Jarallah F. Abu-Jarad M.A. Qureshi 《Radiation measurements》2005,40(2-6):595-600
A set of five 241Am–Be neutron sources are utilized in research and teaching at King Fahd University of Petroleum and Minerals (KFUPM). Three of these sources have an activity of 16 Ci each and the other two are of 5 Ci each. A well-shielded storage area was designed for these sources. The aim of the study is to check the effectiveness of shielding of the KFUPM neutron source storage area. Poly allyl diglycol carbonate (PADC) Nuclear track detectors (NTDs) based fast and thermal neutron area passive dosimeters have been utilized side by side for 33 days to assess accumulated low ambient dose equivalents of fast and thermal neutrons at 30 different locations around the source storage area and adjacent rooms. Fast neutron measurements have been carried out using bare NTDs, which register fast neutrons through recoils of protons, in the detector material. NTDs were mounted with lithium tetra borate (Li2B4O7) converters on their surfaces for thermal neutron detection via and nuclear reactions. The calibration factors of NTD both for fast and thermal neutron area passive dosimeters were determined using thermoluminescent dosimeters (TLD) with and without a polyethylene moderator. The calibration factors for fast and thermal neutron area passive dosimeters were found to be 1.33 proton tracks and 31.5 alpha tracks , respectively. The results show variations of accumulated dose with the locations around the storage area. The fast neutron dose equivalents rates varied from as low as up to whereas those for thermal neutron ranged from as low as up to . The study indicates that the area passive neutron dosimeter was able to detect dose rates as low as 7 and from accumulated dose for thermal and fast neutrons, respectively, which were not possible to detect with the available active neutron dosimeters. 相似文献
92.
The structure of diaquo(1,2-dimethoxyethane)lithium tetraphenylborate, [Li(CH3OCH2-CH2OCH3)(H2O)2][BPh4], has been determined at 293 K. The compound crystallizes in the trigonal P3(1)21 space group (a = b = 9.9760(14), c = 23.662(5)). Both the lithium and the boron sit on a twofold rotation axis. The lithium is coordinated to two water oxygens and both ether oxygens of the 1,2-dimethoxyethane group. The coordination geometry is significantly distorted from a tetrahedron by the twisting of the plane containing the two water oxygens and the lithium relative to that containing the two 1,2-dimethoxyethane oxygens and the lithium. The five-membered chelate ring formed by chelation of the 1,2-dimethoxyethane to the lithium is a twist envelope consistent with the twofold rotation axis passing through the lithium and the center of the carbon–carbon bond of the 1,2-dimethoxyethane. Hydrogen bonding between each water hydrogen and a phenyl group of the tetraphenylborate is observed and results in a linear polymeric structure. 相似文献
93.
Ritu Agarwal Sunil D. Purohit Kritika 《Mathematical Methods in the Applied Sciences》2019,42(18):7160-7171
In calcium signalling, activation of receptor is a very significant aspect. To understand the mechanism of calcium signalling, receptors are the important components. The mobilization of intracellular calcium from intracellular stores depends upon binding of agonist to cell surface receptor. Thrombin is chosen as model ligand. In order to understand thrombin receptor activation, we analyze fractional model incorporating derivative of arbitrary order and nonsingular kernel which can precisely describe the effect of memory and can explain the model in better and more efficient manner as compared with fractional operators with singular kernels. The problem has been solved by perturbation iterative method. Using fixed‐point theorem, it is proved that solution of the system will exist and also it will be unique. 相似文献
94.
以硼酸三正丁酯、甲醇锂为主要原料,甲醇和四氢呋喃为溶剂,利用溶胶-凝胶法通过优化工艺制备了掺锂硼酸盐凝胶。分别采用粘度分析、热分析、X射线衍射、扫描电镜、透射电镜及红外光谱,对凝胶形成过程、物相、成分、微观形貌等进行表征。结果表明:对凝胶在150 ℃条件下处理4 h获得干凝胶,干凝胶在450 ℃左右产生结晶的倾向,492 ℃干凝胶已经完全从非晶态转变为晶态,在808 ℃左右晶体熔解;干凝胶是多孔网络结构材料;干凝胶网络结构的基本组成单元是以≡B—O—B=键的方式连接的,其中一个硼原子是四配位,另一个是三配位的。 相似文献
95.
《中国化学会会志》2018,65(9):1053-1059
The effect of boric acid on the properties of high‐alumina phosphate‐bonded plastic refractory materials at medium temperature is investigated in this work. Powder X‐ray diffraction (XRD), thermogravimetric analysis/differential thermal analysis (TG/DTA), and scanning electron microscopy (SEM) techniques are used to investigate the compositions and microstructures of the Al2O3–H3BO3 sintering products, in order to study the influence of the generated aluminum borate on the high‐aluminum refractories. Additionally, the effect of the addition of H3BO3 on the densification and mechanical strength of high‐aluminum phosphate‐bonded plastic refractories is studied by the permanent linear change, apparent porosity, cold compressive strength, flexural strength, and scanning electron microscopy pattern. The densification and mechanical strength of the refractories can be improved significantly by the optimal addition of H3BO3. However, excess H3BO3 will bring about a large amount of bound water into the refractories, and superabundant aluminum borate whiskers will be generated by the excess addition of H3BO3, both of them resulting in the reduction of the densification and mechanical strength of the refractory. In conclusion, the optimum dosages of H3BO3 in the powder system of high‐alumina phosphate‐bonded plastic refractories are 5, 4, and 3 wt%, sintered at 700, 900, and 1100 °C, respectively. 相似文献
96.
Moloy Sarkar Raghavendra Yellampalli Bhaswati Bhattacharya Ravi Kumar Kanaparthi Anunay Samanta 《Journal of Chemical Sciences》2007,119(2):91-97
Fluorescence behaviour of 4-benzoylamido-N-methylphthalimide (1), designed and developed for selective detection of fluoride ions, is reported. 1 displays F−-induced colour change that allows its detection with the naked eye. The F− specificity of the sensor system is evident from the fact that unlike F−, other halides do not affect the absorption characteristics of 1. Apart from the colorimetric response, the fluorescence output of 1 is also modulated by F− in a manner that permits ratiometric fluorescence signalling of F− as well. It is found that the system can detect F− in the concentration range of 10–60 μM. The results of the experiments and theoretical calculations unambiguously suggest that the changes of the electronic absorption
and fluorescence behaviour of 1, which have been exploited for signalling purpose, are due to F−-induced deprotonation of the 4-amido moiety of the sensor system. 相似文献
97.
Quasi-CW diode-pumped Yb3+∶borate glass and Yb3+∶phosphate glass microchip lasers have been reported. From Yb3+∶phosphate glass laser, the maximum average output power was 31 mW and the optical-optical conversion efficiency was 5%.The maximum average output power was 18 mW, and optical-optical conversion efficiency was 3% for Yb3+∶borate glass laser. 相似文献
98.
本文在以前工作的基础上,用电子计算机计算了Li_2O-B_2O_3-SiO_2,CdO-B_2O_3-GeO_2和Li_2O一B_2O_3-TeO_2三元玻璃系统的NMR数据(N_(BO_4)),和实验结果相比较,根据相图原理,提出了一种新的玻璃结构模型,即相图模型.作者认为:玻璃和晶体具有相似的结构,多成分玻璃则是由相图中最邻近的同成分熔融化合物组成的混合物,且各化合物的量可按“杠杆原理”计算,即相图模型.对于未知相图的三元系统,在相图模型的基础上,作者作了一些简单的假设并进行修正. 相似文献
99.
100.