Search Results

You are looking at 61 - 70 of 405 items for :

  • All content x
Clear All

Abstract  

The adsorption behavior of Eu(III) from aqueous solution to mesoporous molecular sieves (Al-MCM-41) is investigated as a function of contact time, solid content, ionic strength, pH, foreign ions and temperature by using batch technique. The experimental results show that Eu(III) adsorption is strongly dependent on pH values, but independent of ionic strength and foreign cations under our experimental conditions. The kinetic process is described by a pseudo-second-order rate model very well. The adsorption isotherms are simulated by Langmuir model very well. The thermodynamic parameters (∆G°, ∆S°, ∆H°) are calculated from the temperature dependent adsorption isotherms at 293, 313 and 333 K, respectively, and the results suggest that the adsorption of Eu(III) on Al-MCM-41 is a spontaneous and endothermic process. Desorption studies indicate that the adsorbed Eu(III) is very difficult to be desorbed from the solid surface. Al-MCM-41 is a suitable material for the preconcentration and solidification of Eu(III) from large volumes of aqueous solutions.

Restricted access

Abstract  

The objective of this study is to use a clustering algorithm based on journal cross-citation to validate and to improve the journal-based subject classification schemes. The cognitive structure based on the clustering is visualized by the journal cross-citation network and three kinds of representative journals in each cluster among the communication network have been detected and analyzed. As an existing reference system the 15-field subject classification by Glänzel and Schubert (Scientometrics 56:55–73, <cite>2003</cite>) has been compared with the clustering structure.

Restricted access

Abstract  

In this study, a local bentonite from Gaomiaozi county (Inner Mongolia, China) was converted to Na-bentonite and was characterized by FTIR and XRD to determine its chemical constituents and micro-structure. The removal of cobalt from aqueous solutions by Na-bentonite was investigated as a function of contact time, pH, ionic strength, foreign ions and temperature by batch technique under ambient conditions. The results indicated that the sorption of Co(II) was strongly dependent on pH. At low pH, the sorption of Co(II) was dominated by outer-sphere surface complexation or ion exchange whereas inner-sphere surface complexation was the main sorption mechanism at high pH. The Langmuir, Freundlich, and D-R models were used to simulate the sorption isotherms of Co(II) at the temperatures of 293.15, 313.15 and 333.15 K, respectively. The thermodynamic parameters (∆, ∆, ∆) of Co(II) sorption on GMZ bentonite calculated from the temperature-dependent sorption isotherms indicated that the sorption of Co(II) on GMZ bentonite was an exothermic and spontaneous process. The Na-bentonite is a suitable material for the preconcentration and solidification of Co(II) from aqueous solutions.

Restricted access
Scientometrics
Authors: Liming Liang, Hildrun Kretschmer, Yongzheng Guo, and Donald deB. Beaver

Abstract  

This paper is a scientometric study of the age structure of scientific collaboration in Chinese computer science. Analysis reveals some special age structures in scientific collaboration in Chinese computer science. Most collaborations are composed of scientists younger than thirty-six (Younger) or older than fifty (Elder). For two-dimensional collaboration formed by first and second authors, Younger-Elder and Younger-Younger are the predominant age structures. For three-dimensional collaboration formed by first, second and third authors, Younger-Younger-Elder and Younger-Younger-Younger are the most important age structures. Collaboration between two authors older than 38 amounts to only 6.4 percent of all two-person collaborations. Collaboration between two middle-aged scientists is seldom seen. Why do such types of age structure in Chinese computer science exist? We suggest a tentative explanation based on analyses of the age composition of all authors, the age distributions of the authors in different ranks, and the name-ordering of authors in articles written by professors and their students.

Restricted access

Abstract  

A β-cyclodextrin (β-CD) based monomer (MAH-β-CD) containing vinyl and carboxyl functional groups was synthesized by reaction of β-CD with maleic anhydride (MAH). A novel hydrogel, poly(AAc-co-MAH-β-CD) with pH and ionic strength sensitivities, was prepared by irradiating the aqueous solution mixture of acrylic acid (AAc) and MAH-β-CD with electron beam. The effect of the feed ratio of the components and irradiation dose on the swelling and deswelling properties of the hydrogel was studied, respectively, the effect of pH and ionic strength on the swelling ratio was determined. Experimental results showed that these copolymer hydrogels did not show any noticeable change in swelling ratio at lower pH range (pH 1–3). However they showed an abrupt increase in swelling ratio at the range of pH 3–6, due to the ionization of carboxyl groups. Fourier transform infrared (FT-IR) spectrometer was applied in the attenuated total reflectance (ATR) mode for analyzing the structure change of the hydrogels after the treatment of different pH buffer solutions.

Restricted access

Abstract  

The mesoporous molecular sieves (Al-MCM-41) are synthesized with montmorillonite as silica–alumina source by hydrothermal method. The application of Al-MCM-41 for the adsorption of Th(IV) from aqueous solution is studied by batch technique. The effects of contact time, solid content, pH, ionic strength, foreign ions, and temperature are determined, and the results indicate that the adsorption of Th(IV) to Al-MCM-41 is strongly dependent on pH values but independent of ionic strength. The adsorption isotherms are simulated by D–R and Freundlich models well. The thermodynamic parameters (ΔH 0, ΔS 0, ΔG 0) are calculated from the temperature dependent adsorption isotherms at 293, 313 and 333 K, respectively, and the results suggest that the adsorption of Th(IV) on Al-MCM-41 is a spontaneous and endothermic process. Al-MCM-41 is a suitable material for the preconcentration of Th(IV) from large volumes of aqueous solutions.

Restricted access

Summary  

To compare science growth of different countries is both, of theoretical and of pragmatic interest. Using methods for the analysis of complex growth processes introduced by H. E. Stanley and others, we exhibit quantitative features of Chinese science growth from 1986 to 1999 and compare them with corresponding features of western countries. Patterns of growth dynamics of Chinese universities publication output do not differ significantly from those found in the case of western countries. The same is valid for Chinese journals when compared to international journals. In nearly all cases the size distribution of output over universities or journals is near to a lognormal one, the growth rate distribution is Laplace-like, and the standard deviations of the corresponding conditional distributions with regard to size decay according to a power law. This means that regarding some structural-dynamical properties China's recent science system cannot be distinguished from a western one - despite different prehistory and different political and economic environment.

Restricted access

Abstract

In this paper the role of Chinese universities in enterprise–university research collaboration is investigated. This study focuses on a special aspect of the collaboration—co-authored articles. The two cases are analyzed: (1) research collaboration between Baosteel Group Corporation and Chinese universities; (2) research collaboration between China Petroleum & Chemical Corporation and Chinese universities. The co-authorship data over the period 1998–2007 were searched from CNKI database, the largest Chinese publication and citation database. The main findings are as follows: the number of articles co-authored by enterprise and university scientists has been increasing rapidly; the share of co-authored articles has been growing; the authors from universities are more possible to be the first authors; as a whole, enterprise–university co-authored articles tend to receive more citations and get downloaded more frequently; a mathematical orientation emerges in the enterprise–university articles. To reveal and describe such a trend the methods of keywords analysis and co-occurrence analysis are applied. The Chinese government's policy instruments and substantial supports for pushing and improving enterprise–university research collaboration are introduced and analyzed.

Restricted access

Abstract  

A statistical analysis is made of two data sets and it is found that the distribution of major scientific and technological achievements in terms of the age of those achievement makers is Weibull distribution. Pearson'sx 2 test results are satisfactory. This finding holds for different centuries, different nations and different disciplines.

Restricted access