scholarly journals Immigrants' spatial concentration: Region or locality attractiveness?

2021 ◽  
Author(s):  
Ana Viñuela
Keyword(s):  
Spatial Concentration ◽  
Concentration Region

Determination of alcohols in mixtures by 19F NMR spectroscopy using hexefluoroacetone reagent

1982 ◽  
Vol 47 (7) ◽  
pp. 1973-1978 ◽  
Author(s):  
Jiří Karhan ◽  
Zbyněk Ksandr ◽  
Jiřina Vlková ◽  
Věra Špatná
Keyword(s):  
Standard Deviation ◽  
Nmr Spectroscopy ◽  
Standard Method ◽  
Internal Standard ◽  
Internal Standard Method ◽  
Concentration Region ◽  
Experimental Conditions ◽  
Curve Method ◽  
Sample Preparation Procedure

The determination of alcohols by 19F NMR spectroscopy making use of their reaction with hexafluoroacetone giving rise to hemiacetals was studied on butanols. The calibration curve method and the internal standard method were used and the results were mutually compared. The effects of some experimental conditions, viz. the sample preparation procedure, concentration, spectrometer setting, and electronic integration, were investigated; the conditions, particularly the concentrations, proved to have a statistically significant effect on the results of determination. For the internal standard method, the standard deviation was 0.061 in the concentration region 0.032-0.74 mol l-1. The method was applied to a determination of alcohols in the distillation residue from an oxo synthesis.

Induction period of the crystallization of silver nitrate solutions in ethylene glycol

1991 ◽  
Vol 56 (10) ◽  
pp. 2142-2147
Author(s):  
Ivo Sláma
Keyword(s):  
Ethylene Glycol ◽  
Silver Nitrate ◽  
Induction Period ◽  
Glass Forming Ability ◽  
Transformation Theory ◽  
Concentration Region ◽  
Glass Forming ◽  
Temperature Transformation ◽  
Silver Nitrate Solutions ◽  
Nitrate Solutions

The dependence of the induction period of crystallization on supercooling was examined for the silver nitrate-ethylene glycol system over the concentration region of silver nitrate lome fraction of 0 to 0.12. Addition of AgNO3 to ethylene glycol was found to increase considerably the critical induction period of crystallization, although to a lesser extent than Ca(NO3)2, CaCl2, ZnCl2, LiCl and LiNO3 do. The effect of these salts on the critical induction period of crystallization in dimethylsulfoxide, dimethylformamide, dimethylacetamide and methanol was compared in terms of the solvent-rich composition limit of the glass-forming ability. By using the TTT(Time-Temperature-Transformation) theory, it has been deduced that the effect of the salts on the critical induction period of crystallization of ethylene glycol is probably due to the different dependences of viscosity on their concentration in ethylene glyco in the supercooling region.

Polarographic and voltammetric determination of N,N’-dinitrosopiperazine

1991 ◽  
Vol 56 (7) ◽  
pp. 1434-1445 ◽  
Author(s):  
Jiří Barek ◽  
Ivana Švagrová ◽  
Jiří Zima
Keyword(s):  
Mercury Electrode ◽  
Linear Sweep Voltammetry ◽  
Differential Pulse ◽  
Differential Pulse Polarography ◽  
Polarographic Reduction ◽  
Concentration Region ◽  
Pulse Polarography ◽  
Chemical Efficiency ◽  
Dropping Mercury Electrode

Polarographic reduction of the genotoxic N,N’-dinitrosopiperazine was studied and its mechanism was suggested. Optimum conditions were established for the determination of this substance by tast polarography over the concentration region of 1 . 10-3 to 1 . 10-6 mol l-1 and by differential pulse polarography on the conventional dropping mercury electrode or by fast scan differential pulse voltammetry and linear sweep voltammetry on a hanging mercury drop electrode over the concentration region of 1 . 10-3 to 1 . 10-7 mol l-1. Attempts at increasing further the sensitivity via adsorptive accumulation of the analyte on the surface of the hanging mercury drop failed. The methods are applicable to the testing of the chemical efficiency of destruction of the title chemical carcinogen based on its oxidation with potassium permanganate in acid solution.

Numerical evaluation of contaminants mixing uniformity in a full-scale test chamber with mixing fan

2020 ◽  
pp. 1420326X2097902
Author(s):  
Hai-Xia Xu ◽  
Yu-Tong Mu ◽  
Yin-Ping Zhang ◽  
Wen-Quan Tao
Keyword(s):  
Concentration Distribution ◽  
Test Chamber ◽  
Full Scale ◽  
Numerical Results ◽  
Test Method ◽  
Test Accuracy ◽  
Full Scale Test ◽  
Concentration Region ◽  
Airflow Field ◽  
Scale Test

Most existing models and standards for volatile organic compounds emission assume that contaminants are uniform in the testing devices. In this study, a three-dimensional transient numerical model was proposed to simulate the mass transport process based on a full-scale test chamber with a mixing fan, and the airflow field and contaminants concentration distribution were obtained within the chamber under airtight and ventilated conditions. The model was validated by comparing the numerical results with experimental data. The numerical results show that the contaminant source position and the airflow field characteristics have significant impact on the contaminant mixing, and the fan rotation has an important role in accelerating mixing. In the initial mixing stage, the concentration distribution is obviously uneven; as the mixing progresses, it gradually reaches acceptable uniformity except for some sensitive regions, such as high concentration region at the injection point of the contaminants and low concentration region at the air inlet. To ensure test accuracy, the monitor should avoid above sensitive regions; and some special regions are recommended where contaminant concentration uniformity can be reached sooner. The ventilated chamber results indicate that the mixture of contaminants in the chamber is actually better than the results shown by conventional test method.

Trade and Spatial Growth

2017 ◽  
Vol 18 (1) ◽  
pp. 94-111
Author(s):  
Sirimal Abeyratne ◽  
N. S. Cooray
Keyword(s):  
International Trade ◽  
Comparative Advantage ◽  
Global Economy ◽  
Spatial Concentration ◽  
Trade Theory ◽  
Missing Link ◽  
Spatial Growth

Comparative advantage is based on ‘locational factors’ so that trade leads to growth and its spatial concentration. Until recently, the nexus between trade and spatial growth received little space within trade analyses though it did not appear to be a missing link in initial contributions to trade theory. The reshaping of the global economy with greater integration has called for analyses of trade and spatial growth. This article examines theoretical premises of the link between international trade and spatial growth, and the implications of reshaping of the global economy for the study of spatial growth within trade theory.

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