9 research outputs found
Uncertainty in pore size distribution derived from adsorption isotherms: I. classical methods
Procedures for propagation of uncertainty in pore size distribution calculation based on classical methods for both micro and mesoporous materials are described. Uncertainty in experimental adsorption isotherm data and uncertainty in temperature are introduced as the main sources for uncertainty in height and position of peaks of PSD determined via classical mesopore size distribution determination method. Uncertainty in PSD derived from classical micropore size distribution methods mainly arises from uncertainty in experimental isotherm data. Calculation step size is shown to have some effects on magnitude of uncertainty in micropore calculation. Micropore size distribution calculations are also highly sensitive to the adsorptive molecular diameter
Uncertainty in pore size distribution derived from adsorption isotherms: II. adsorption integral approach
Uncertainty in the amount adsorbed in manometric adsorption isotherm measurements is well established. Here, we extend uncertainty methodologies from adsorption isotherm data uncertainty and apply them to calculate pore size distributions based on adsorption integral methods. The analyses consider as variables: uncertainty in adsorption isotherm data, regularization parameter, molecular potential model, and the number of single pore isotherms calculated with an associated quadrature interval. We demonstrate how the calculated pore size distribution is quite insensitive to the uncertainty in experimental data, but in contrast, the uncertainty in the experimental data affects the calculated value of the optimized regularization parameter which, in turn, leads to considerable variation in the calculated pore size distribution. The calculated pore size distribution is also shown to be highly dependent on the potential model selected and on the number of single pore isotherms applied to the inversion process. We conclude and suggest a quantitative comparison between calculated pore size distributions should be discouraged unless the uncertainty in the experimental data is relatively small and, default values for regularization parameters, potential models, the number of single pore isotherms and their distribution are exactly the same for each pore size distribution evaluation
Analysis of adsorbate-adsorbate and adsorbate-adsorbent interactions to decode isosteric heats of gas adsorption
A qualitative interpretation is proposed to interpret isosteric heats of adsorption by considering contributions from three general classes of interaction energy: fluid–fluid heat, fluid–solid heat, and fluid—high-energy site (HES) heat. Multiple temperature adsorption isotherms are defined for nitrogen, T=(75, 77, 79) K, argon at T=(85, 87, 89) K, and for water and methanol at T=(278, 288, 298) K on a well-characterized polymer-based, activated carbon. Nitrogen and argon are subjected to isosteric heat analyses; their zero filling isosteric heats of adsorption are consistent with slit-pore, adsorption energy enhancement modelling. Water adsorbs entirely via specific interactions, offering decreasing isosteric heat at low pore filling followed by a constant heat slightly in excess of water condensation enthalpy, demonstrating the effects of micropores. Methanol offers both specific adsorption via the alcohol group and non-specific interactions via its methyl group; the isosteric heat increases at low pore filling, indicating the predominance of non-specific interactions
Isosteric Heats of Adsorption of Gases and Vapors on a Microporous Carbonaceous Material
High-resolution,
multiple temperature adsorption isotherms of ten
adsorptives classified into highly polar (1.7 ± 0.1 D) and nonpolar
(0 D) probes with increasing kinetic diameters were measured on a
well-characterized poly(furfuryl alcohol)-based microporous carbon.
The Clausius–Clapeyron equation was applied to each, resulting
in isosteric heats of adsorption. Fluid–fluid interactions,
nonspecific fluid–solid interactions, and specific fluid–high
energy site interactions were identified and discussed as variables
contributing to the total isosteric heat of adsorption. Each isosteric
heat was compared against its position relative to adsorption heat
by a flat surface, twice this heat, and adsorptive latent heat of
condensation. The shape of each curve was analyzed via the contribution
of each interaction to the total across the fractional filing range,
leading to identification of fillings as Zero Coverage, Low Coverage,
and High Coverage. This systematic investigation provided a detailed
analysis of the influences of adsorptive size, its conformation, and
polarity effects on micropore filling, and tabulation of the analyses
gave a clear and comprehensive insight into the adsorption mechanisms
Immersion calorimetry: molecular packing effects in micropores
Repeated and controlled immersion calorimetry experiments were performed to determine the specific surface area and pore-size distribution (PSD) of a well-characterized, microporous poly(furfuryl alcohol)-based activated carbon. The PSD derived from nitrogen gas adsorption indicated a narrow distribution centered at 0.57±0.05 nm. Immersion into liquids of increasing molecular sizes ranging from 0.33 nm (dichloromethane) to 0.70 nm (α-pinene) showed a decreasing enthalpy of immersion at a critical probe size (0.43–0.48 nm), followed by an increase at 0.48–0.56 nm, and a second decrease at 0.56–0.60 nm. This maximum has not been reported previously. After consideration of possible reasons for this new observation, it is concluded that the effect arises from molecular packing inside the micropores, interpreted in terms of 2D packing. The immersion enthalpy PSD was consistent with that from quenched solid density functional theory (QSDFT) analysis of the nitrogen adsorption isotherm
Factors Affecting Skin Tannin Extractability in Ripening Grapes
The
acetone-extractable (70% v/v) skin tannin content of Vitis vinifera L. cv. Cabernet Sauvignon grapes was
found to increase during late-stage ripening. Conversely, skin tannin
content determined following ethanol extraction (10, 20, and 50% v/v)
did not consistently reflect this trend. The results indicated that
a fraction of tannin became less extractable in aqueous ethanol during
ripening. Skin cell walls were observed to become more porous during
ripening, which may facilitate the sequestering of tannin as an adsorbed
fraction within cell walls. For ethanol extracts, tannin molecular
mass increased with advancing ripeness, even when extractable tannin
content was constant, but this effect was negligible in acetone extracts.
Reconstitution experiments with isolated skin tannin and cell wall
material indicated that the selectivity of tannin adsorption by cell
walls changed as tannin concentration increased. Tannin concentration,
tannin molecular mass, and cell wall porosity are discussed as factors
that may influence skin tannin extractability
Pore size distributions derived from adsorption isotherms, immersion calorimetry, and isosteric heats: a comparative study
We compare the pore size distribution of a well-characterized activated carbon derived from model-dependent, adsorption integral equation (AIE) methods with those from model-independent, immersion calorimetry and isosteric heat analyses. The AIE approach applied to nitrogen gave a mean pore width of 0.57 nm; the CO2 distribution exhibited wider dispersion. Spherical model application to CO2 and diffusion limitations for nitrogen and argon were proposed as primary reasons for inconsistency. Immersion enthalpy revealed a sharp decrease in available area equivalent to a cut-off due to molecular exclusion when the accessible surface was assessed against probe kinetic diameter. Mean pore width was identified as 0.58 ± 0.02 nm, endorsing the underlying assumptions for the nitrogen-based AIE approach. A comparison of the zero-coverage isosteric heat of adsorption for various non-polar adsorptives by the porous test sample was compared with the same adsorptives in contact with a non-porous reference adsorbent, leading to an energy ratio or adsorption enhancement factor. A linear relationship between the energy ratio and probe kinetic diameter indicated a primary pore size at 0.59 nm. The advantage of this enthalpy, model-independent methods over AIE were due to no assumptions regarding probe molecular shape, and no assumptions for pore shape and/or connectivity
Financial Analysis of Company
Import 29/09/2010Bakalářská práce „Finanční analýza podniku“ se zabývá obecnou charakteristikou finanční analýzy, vymezením její základní problematiky, jejími přístupy a metodami. Teoretická část zdůrazňuje pojetí finančního zdraví podniku, z metod poukazuje především na analýzu poměrových ukazatelů a soustavy ukazatelů. Praktická část se věnuje aplikaci vybraných metod na konkrétních příkladech a zároveň interpretuje jejich vypovídací schopnost.The thesis „Financial Analysis of Company“ deals with the general characteristics
of the financial analysis, and determinates its fundamental problems, its approaches
and methods. The theoretical section highlights the concept of the financial health
of company; among the available methods, it highlights the analysis of financial ratios
and system indicators. The practical part deals with the application of selected methods
to specific examples, while interpreting their explanatory power.Prezenční634 - Katedra ekonomiky a managementu v metalurgiivelmi dobř
Формирование навыков здорового образа жизни и психомоторных качеств у учащихся младшего школьного возраста / Healthy lifestyle and psychomotor skills building in elementary school students
выполнить оценку уровня знаний, умений и сформированности навыков ведения здорового образа жизни у учащихся младшего школьного возраста по результатам преподавания физической культуры в начальной школе. Проведённое исследование после проведения трёхлетнего педагогического эксперимента показало суще-ственное (р < 0,001) превосходство учащихся экспериментальной группы над сверстниками из контрольной группы по уровню знаний, умений и сформирован-ности навыков ведения здорового образа жизни младшими школьниками