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排序方式: 共有984条查询结果,搜索用时 15 毫秒
1.
周冰毅 《有色金属(冶炼部分)》1996,(6):14-17
亚铜离子氨浸法作为大洋多金属结核处理方法之一,一直被认为是一个很有前途的冶金处理工艺,是催化化学还原技术在冶金生产中的具体应用,具有流程简单,能耗低,浸出选择性好,产品结构灵活,市场适应能力强,浸出试剂腐蚀性与毒性小,环境污染小等优点。 相似文献
2.
The oxidation of a quasicrystal with the nominal compositionAl63Cu25Fe12 was studied around 800°Cin environmental and synthetic air by means of thermogravimetric analysis,electron microscopy, and analytical electron spectroscopy. In an earlyoxidation stage, -Al2O3 formed with an orientational relationship tothe quasicrystal. At the oxide–metal interface, -Al2O3transformed into large hexagonal shaped -Al2O3grains. The change in surface morphology indicated that at theoxide–gas interface -Al2O3 continued togrow as -Al2O3. Locally the metastable aluminalayer was transformed thoroughly into -Al2O3,which then continued to grow with a nodular morphology. On top of the oxidenodules, several at.% of Cu2+ were detected. 相似文献
3.
The present paper deals with the extraction of cobalt from a solution containing cobalt and nickel in a sulphate medium similar
to the leach liquor obtained by the dilute sulphuric acid pressure leaching of the Pacific Ocean nodules matte followed by
copper extraction. The commercial extractant Cyanex 272 (bis (2, 4, 4-trimethylpentyl) phosphinic acid) is used for this purpose.
The leach liquor used for the present study contains Co =1.78 g/L and Ni=16.78 g/L. Before cobalt extraction, impurities,
such as copper and iron, are removed from the leach liquor by the precipitation method. Increasing the concentration of Cyanex
272 increased the extraction percentage of cobalt due to the increase of equilibrium pH. Cobalt extraction efficiency of >99.9
% is achieved with 0.20 M Cyanex 272 in two counter-current stages at an aqueous: organic (A:O) phase ratio of 1.5∶1. Complete
stripping of cobalt from the loaded organic containing 2.73 g/L Co was carried out at pH 1.4 by a synthetic cobalt spent electrolyte
in two stages at an A:O ratio of 1∶2. The enrichment of cobalt during extraction and stripping operations was about 3.5 times.
A complete process flowsheet for the separation and recovery of cobalt is presented. 相似文献
4.
Assessment of biological nitrogen fixation 总被引:3,自引:0,他引:3
S. K. A. Danso 《Nutrient Cycling in Agroecosystems》1995,42(1-3):33-41
The four commonly used methods for measuring biological nitrogen fixation (BNF) in plants are: the total nitrogen difference (TND) method, acetylene reduction assay (ARA) technique, xylem-solute (or ureide production) method and the use of15N labelled compounds.The TND method relies on a control non-N2-fixing plant to estimate the amount of N absorbed by the fixing plant from soil. It is one of the simplest and least expensive methods, but works best under low soil N conditions. The ARA technique measures the rate of acetylene conversion to ethylene by the N2-fixing enzyme, nitrogenase. The ethylene produced can then be converted into N2 fixed, using a conversion ratio, originally recommended as 3. Although the method is inexpensive and highly sensitive, its major disadvantages are, the short-term nature of the assays, the doubtful validity of always using a conversion ratio of 3 and the auto-inhibition of acetylene conversion to ethylene. The ARA technique is therefore not a method of choice for measuring BNF.The xylem-solute technique can be used to measure BNF for those species that produce significant quantities of ureide as product of BNF. Although simple and relatively inexpensive, it is an instantaneous assay and also needs to be calibrated against a known method. The most serious limitation is, that only a small proportion of N2-fixing plants examined are ureide exporters, and the method is therefore not widely applicable.The15N methods, classified into the isotope dilution and A-value methods, appear to be the most accurate, but also the most expensive. They involve labelling soil with15N fertilizer and using a non-N2-fixing reference plant to measure the15N/14N ratio in the soil. The15N isotope dilution approach is both operationally and mathematically simpler than the A-value approach. To limit potential errors in the selection of reference crops, it is recommended to use15N labelled compounds or soil labelling methods that result in the slow release of15N or the slow decline of15N/14N ratio in the soil. Additionally, the use of several reference plants rather than a single one can improve the accuracy of the results. 相似文献
5.
针对磨玻璃肺结节(Ground Glass Opacity,GGO)边界对比度低、大小各异和灰度不均匀等造成分割准确率低的问题,提出一种基于边缘敏感的SLIC和二次密度聚类相结合的分割算法。将图像边缘检测结果与SLIC超像素算法相结合,并将其中含有边缘的超像素块用区域质心代替其原始聚类中心,改善SLIC边界黏连性较差的问题;针对密度聚类不能完整分割GGO的问题,提出二次密度聚类的方法,对密度聚类定位到的簇及其邻域簇进行二次密度聚类。实验结果表明,该算法分割GGO的平均准确率达90.17%,灵敏度达84%。 相似文献
6.
针对肺结节良恶性分类模型中特征选择过程无法避免特征多样性不受破坏的问题,提出一种将肺结节特征矢量化处理的特征选择方法。首先,假设每个肺结节特征都是由数据、类型构成的一个矢量。然后,按照特征类型添加特征到相应的特征子集,并分别利用Relief算法评价特征、特征子集的分类重要性。最后,通过动态阈值的方式筛选得到优化后的特征子集。在150个肺结节样本的分类实验中,采用本文算法所取得的敏感性为94.7%、特异性为93.7%、虚警率为5.2%、受试者工作特性曲线下面积为97.3%。分析表明,本文算法几乎不破坏肺结节特征的多样性,能够显著提高肺结节良恶性分类的准确性。 相似文献
7.
Yuanjin Zhan Peng Yu Xiaohan Wang Yang Xie Hongxin Zhang Fan Zhang 《Advanced functional materials》2023,33(36):2301683
Chemotherapy-induced enteritis is one of the side effects associated with cancer therapy, which significantly affects the treatment effect, but there is no effective clinical detection method that can early diagnose its occurrence and progression. Here, a series of second near-infrared window (NIR-II) hybrid nanosensors are designed that consisted of lanthanide nanoparticles and β-Mo2C-derived polymetallic oxomolybdate nanoclusters (Ln@POM). Based on the high sensitivity of POM to reactive oxygen species (ROS) closely related to chemotherapy-induced enteritis, the NIR-II luminescence intensity and lifetime of Ln@POM (Ln: Yb3+, Nd3+, Ho3+, Tm3+, Er3+) show excellent responsiveness to H2O2 and HClO with the detection limit down to 0.15 and 0.14 µm , respectively. Utilizing Nd@POM as a ROS-activated NIR-II nanosensor, the chemotherapeutic enteritis is successfully detected within 7 h after induction of chemotherapy drugs, which is significantly earlier than the gold standard method (immunohistochemistry, 24 h). These results demonstrate that the designed hybrid nanosensors are promising optical tools for the early diagnosis of ROS-related diseases. 相似文献
8.
Michalis Savelonas Dimitris Maroulis Manolis Sangriotis 《Computer methods and programs in biomedicine》2009,96(1):25-32
In this paper, a novel computer-based approach is proposed for malignancy risk assessment of thyroid nodules in ultrasound images. The proposed approach is based on boundary features and is motivated by the correlation which has been addressed in medical literature between nodule boundary irregularity and malignancy risk. In addition, local echogenicity variance is utilized so as to incorporate information associated with local echogenicity distribution within nodule boundary neighborhood. Such information is valuable for the discrimination of high-risk nodules with blurred boundaries from medium-risk nodules with regular boundaries. Analysis of variance is performed, indicating that each boundary feature under study provides statistically significant information for the discrimination of thyroid nodules in ultrasound images, in terms of malignancy risk. k-nearest neighbor and support vector machine classifiers are employed for the classification tasks, utilizing feature vectors derived from all combinations of features under study. The classification results are evaluated with the use of the receiver operating characteristic. It is derived that the proposed approach is capable of discriminating between medium-risk and high-risk nodules, obtaining an area under curve, which reaches 0.95. 相似文献
9.
Scanning electron microscopic observations were made on the micro-organisms of root nodules of Tribulus terrestris L. The results showed that nodules of T. terrestris contained dual infection consisting of Rhizobium sp. and Newmania karachiensis. Based on these observations, T. terrestris should be grouped with nonlegume Parasponia-type bacterial nodules. 相似文献
10.