680 research outputs found
Особенности подхода к вопросу собственности в Приднестровской Молдавской Республике
The aim of the study is to evaluate the peculiarities of the right to property in the Republic of Moldova. The author focus on the property rights law system of the Republic of Moldova with a special emphasis on the fragility of state institutions and the significant role of businesses environment
Das Programm "Forschung zur Humanisierung des Arbeitslebens". Stand und Möglichkeiten der Evaluierung eines staatlichen Forschungsprogramms
"In diesem Beitrag sollen Möglichkeiten und Schwierigkeiten von Bilanzierung - Bestandsaufnahme und Evaluierung - am Beispiel des Programms "Forschung zur Humanisierung des Arbeitslebens" aufzgezeigt werden. ... Es wird ein erster Versuch unternommen, einige Aspekte der Durchführbarkeit von Evaluierung innerhalb eines instabilen Politikfeldes zu benennen und zu systematisieren. Nach einer kurzen Beschreibung des Programms, seiner Ziele und Instrumente, sollen zunächst einige Probleme der Evaluierung von Programmen mit quasiexperimentellem Charakter dargelegt werden. Im Mittelpunkt dieses Überblickes stehen Probleme der Wirkungsanalyse, vor allem die Nutzung von Programmvollzugsdaten für eine programmbegleitende Evaluierung und die Nutzung von Fallstudien zur Teilbilanzierung. Hierbei werden auch die Verfahren und Ergebnisse des Projektes "Wirkungsanalyse zu ausgewählten Zielaspekten des HdA-Programms" geschildert.."Humanisierung der Arbeit, Wirkungsforschung
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Simple model of adsorption on external surface of carbon nanotubes: a new analytical approach basing on molecular simulation data
Nitrogen adsorption on carbon nanotubes is wide- ly studied because nitrogen adsorption isotherm measurement is a standard method applied for porosity characterization. A further reason is that carbon nanotubes are potential adsorbents for separation of nitrogen from oxygen in air. The study presented here describes the results of GCMC simulations of nitrogen (three site model) adsorption on single and multi walled closed nanotubes. The results obtained are described by a new adsorption isotherm model proposed in this study. The model can be treated as the tube analogue of the GAB isotherm taking into account the lateral adsorbate-adsorbate interactions. We show that the model describes the simulated data satisfactorily. Next this new approach is applied for a description of experimental data measured on different commercially available (and characterized using HRTEM) carbon nanotubes. We show that generally a quite good fit is observed and therefore it is suggested that the observed mechanism of adsorption in the studied materials is mainly determined by adsorption on tubes separated at large distances, so the tubes behave almost independently
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Folding of graphene slit like pore walls—a simple method of improving CO2 separation from mixtures with CH4 or N2
We report for the first time a detailed procedure for creating a simulation model of energetically stable, folded graphene-like pores and simulation results of CO2/CH4 and CO2/N2 separation using these structures. We show that folding of graphene structures is a very promising method to improve the separation of CO2 from mixtures with CH4 and N2. The separation properties of the analyzed materials are compared with carbon nanotubes having similar diameters or S/V ratio. The presented results have potential importance in the field of CO2 capture and sequestration
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Synergetic effect of carbon nanopore size and surface oxidation on CO2 capture from CO2/CH4 mixtures
We have studied the synergetic effect of confinement (carbon nanopore size) and surface chemistry (the number of carbonyl groups) on CO2 capture from its mixtures with CH4 at typical operating conditions for industrial adsorptive separation (298 K and compressed CO2CH4 mixtures). Although both confinement and surface oxidation have an impact on the efficiency of CO2/CH4 adsorptive separation at thermodynamics equilibrium, we show that surface functionalization is the most important factor in designing an efficient adsorbent for CO2 capture. Systematic Monte Carlo simulations revealed that adsorption of CH4 either pure or mixed with CO2 on oxidized nanoporous carbons is only slightly increased by the presence of functional groups (surface dipoles). In contrast, adsorption of CO2 is very sensitive to the number of carbonyl groups, which can be examined by a strong electric quadrupolar moment of CO2. Interestingly, the adsorbed amount of CH4 is strongly affected by the presence of the co-adsorbed CO2. In contrast, the CO2 uptake does not depend on the molar ratio of CH4 in the bulk mixture. The optimal carbonaceous porous adsorbent used for CO2 capture near ambient conditions should consist of narrow carbon nanopores with oxidized pore walls. Furthermore, the equilibrium separation factor was the greatest for CO2/CH4 mixtures with a low CO2 concentration. The maximum equilibrium separation factor of CO2 over CH4 of ∼18–20 is theoretically predicted for strongly oxidized nanoporous carbons. Our findings call for a review of the standard uncharged model of carbonaceous materials used for the modeling of the adsorption separation processes of gas mixtures containing CO2 (and other molecules with strong electric quadrupolar moment or dipole moment)
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Applicability of molecular simulations for modelling the adsorption of the greenhouse gas CF4 on carbons
Tetrafluoromethane, CF4, is powerful greenhouse gas, and the possibility of storing it in microporous carbon has been widely studied. In this paper we show, for the first time, that the results of molecular simulations can be very helpful in the study of CF4 adsorption. Moreover, experimental data fit to the results collected from simulations. We explain the meaning of the empirical parameters of the supercritical Dubinin–Astakhov model proposed by Ozawa and finally the meaning of the parameter k of the empirical relation proposed by Amankwah and Schwarz
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The influence of the carbon surface chemical composition on Dubinin-Astakhov equation parameters calculated from SF(6) adsorption data-grand canonical Monte Carlo simulation
Using grand canonical Monte Carlo simulation we show, for the first time, the influence of the carbon porosity and surface oxidation on the parameters of the Dubinin-Astakhov (DA) adsorption isotherm equation. We conclude that upon carbon surface oxidation, the adsorption decreases for all carbons studied. Moreover, the parameters of the DA model depend on the number of surface oxygen groups. That is why in the case of carbons containing surface polar groups, SF(6) adsorption isotherm data cannot be used for characterization of the porosity
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To what extent can mutual shifting of folded carbonaceous walls in slit-like pores affect their adsorption properties?
We have performed systematic Monte Carlo studies on the influence of shifting the walls in slit-like systems constructed from folded graphene sheets on their adsorption properties. Specifically, we have analysed the effect on the mechanism of argon adsorption (T = 87 K) and on adsorption and separation of three binary gas mixtures: CO2/N2, CO2/CH4 and CH4/N2 (T = 298 K). The effects of the changes in interlayer distance were also determined. We show that folding of the walls significantly improves the adsorption and separation properties in comparison to ideal slit-like systems. Moreover, we demonstrate that mutual shift of sheets (for small interlayer distances) causes the appearance of small pores between opposite bulges. This causes an increase in vapour adsorption at low pressures. Due to overlapping of interactions with opposite walls causing an increase in adsorption energy, the mutual shift of sheets is also connected with the rise in efficiency of mixtures separation. The effects connected with sheet orientation vanish as the interlayer distance increases
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