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11.
Pinto ML Pires J Carvalho AP de Carvalho MB 《The journal of physical chemistry. B》2006,110(1):250-257
Adsorption isotherms of toluene and ethyl benzene, at 25 degrees C and 40 degrees C, were determined in two microporous activated carbons and one zeolite. Significant differences were found in the adsorption behavior, at low pressures, between the two vapors on the same adsorbent material. The quantities of adsorbed ethyl benzene at 25 degrees C, in the low-pressure region, were lower than what was observed at 40 degrees C in all the studied adsorbents, contrary to what was found for toluene. This fact was not related to kinetic effects at the two temperatures nor to vapor swelling of the adsorbents structure. Also, there was no molecular sieving since at high pressures the toluene and ethyl benzene occupied the same adsorption space. The differences found in the ethyl benzene adsorption at the two temperatures pose difficulties in the analysis of the adsorption data and, therefore, in the prediction of results. This is discussed in the analysis of the results with the application of the Dubinin-Astakhov equation and in the estimation of the isosteric heats of adsorption. The adsorption potentials of two possible ethyl benzene conformations were estimated for the adsorption in the pores of activated carbon from the Horvath and Kawazoe model, and the values compared with those found experimentally. The results were interpreted in terms of the ethyl benzene conformation effects when the molecule is confined in pores that are about the same size of one of the conformations. 相似文献
12.
Given a collection of test functions, one defines the associated Schur–Agler class as the intersection of the contractive multipliers over the collection of all positive kernels for which each test function is a contractive multiplier. We indicate extensions of this framework to the case where the test functions, kernel functions, and Schur–Agler-class functions are allowed to be matrix- or operator-valued. We illustrate the general theory with two examples: (1) the matrix-valued Schur class over a finitely-connected planar domain and (2) the matrix-valued version of the constrained Hardy algebra (bounded analytic functions on the unit disk with derivative at the origin constrained to have zero value). Emphasis is on examples where the matrix-valued version is not obtained as a simple tensoring with ${{\mathbb C}^{N}}$ of the scalar-valued version. 相似文献
13.
Mihaela Dochia Dorina Chambre Simona Gavrilaş Cristian Moisă 《Journal of Thermal Analysis and Calorimetry》2018,132(3):1489-1498
The nature of the complexing agents used in the bioscouring process of cotton fabrics aiming to eliminate the non-cellulosic compounds (pectin, waxes, etc.) and to improve the hydrophilic and wetting properties influences the thermal behaviour and the FT-IR spectra of the textile materials. In this paper, we study the influence of the experimental conditions and complexing agent nature (sodium citrate or disodium EDTA salt) on the pectin elimination in bioscouring treatment of cotton fabric by FT-IR and TG/DTG/DTA analysis. The changes from FT-IR spectra of the specific bands (absorbance intensity at 2916, 2852, 1732 and 1640/1642 cm?1) were evaluated. The thermal behaviour of the investigated samples’ fabric by using TG/DTG/DTA analysis was studied at 30–600 °C temperature range, in air atmosphere. All samples showed three mass-loss steps due to the elimination of humidity, decomposition of the non-cellulosic and cellulosic components (main degradation stage of the samples) and thermo-oxidative decomposition of the formed degradation products. The Tonset values corresponding to the main decomposition step, the mass-loss values (%Δm) and the % residual mass (at 600 °C) were influenced by the complexing agent nature as well as the concentration and the action time of the commercial enzyme product. In addition, the calcium content of some samples treated with and without ultrasound was determined using atomic absorption spectroscopy method (AAS) in order to correlate the results with TG/DTG/DTA analysis. The obtained results have shown that the synergistic action of experimental conditions (enzyme concentration, pH, enzyme product action time, ultrasound) and the presence of sodium citrate as a biodegradable complexing agent led to the elimination of a higher amount of pectin from the cotton samples than that eliminated when using EDTA. 相似文献
14.
Let X be a compact metric space and let Lip(X) be the Banach algebra of all scalar- valued Lipschitz functions on X, endowed with a natural norm. For each f ∈ Lip(X), σπ(f) denotes the peripheral spectrum of f. We state that any map Φ from Lip(X) onto Lip(Y) which preserves multiplicatively the peripheral spectrum:
σπ(Φ(f)Φ(g)) = σπ(fg), A↓f, g ∈ Lip(X)
is a weighted composition operator of the form Φ(f) = τ· (f °φ) for all f ∈ Lip(X), where τ : Y → {-1, 1} is a Lipschitz function and φ : Y→ X is a Lipschitz homeomorphism. As a consequence of this result, any multiplicatively spectrum-preserving surjective map between Lip(X)-algebras is of the form above. 相似文献
σπ(Φ(f)Φ(g)) = σπ(fg), A↓f, g ∈ Lip(X)
is a weighted composition operator of the form Φ(f) = τ· (f °φ) for all f ∈ Lip(X), where τ : Y → {-1, 1} is a Lipschitz function and φ : Y→ X is a Lipschitz homeomorphism. As a consequence of this result, any multiplicatively spectrum-preserving surjective map between Lip(X)-algebras is of the form above. 相似文献
15.
Avido?Yuliestyan Antonio?A.?Cuadri Moisés?García-Morales Pedro?PartalEmail author 《Rheologica Acta》2018,57(1):71-82
Bitumen modification with ethylene-vinyl acetate (EVA), in a wide range temperatures (between ??30 and 100 °C), has been studied as a function of polymer concentration and EVA characteristics (vinyl acetate (VA) content and melt flow index (MFI)). Viscous flow, dynamic shear (DSR) temperature sweep, and technological tests were conducted to assess binder performance at medium-to-high in-service temperatures. Evaluation of binder low-temperature viscoelastic behavior has been performed using a solid rectangular fixture (SRF) in torsional mode, either in the linear viscoelastic region or under non-linear conditions (by strain breakage tests between ??30 and 0 °C). Further microstructural analysis based on modulated differential scanning calorimetry (MDSC) and optical microscopy was conducted to support rheological and technological results. Hence, total crystalline fraction (related to the VA content and polymer concentration) turned out to be a key parameter to achieve a suitable binder modification at medium-high temperatures. In addition, MFI appears to be an important EVA parameter at low temperatures, as it was found that lower MFI values enhanced resistance to low-temperature cracking. 相似文献
16.
Martín-Garrido Moisés Martínez-Ramírez Sagrario 《Journal of Thermal Analysis and Calorimetry》2021,143(6):4331-4339
Journal of Thermal Analysis and Calorimetry - The calcium silicate hydrate gel (C–S–H) was synthesized by the double decomposition method because of the simplicity and the quickness of... 相似文献
17.
Mihaela Dochia Monica Pustianu Cristian Moisă Dorina Chambre Simona Gavrilaş 《Chemical Papers》2018,72(8):1881-1888
A 50% of cotton–50% of flax fabric was subjected to an enzymatic treatment (bioscouring) in ultrasound for removing the compounds which could negatively affect the further specific technological processes as whitening and dyeing. During the scouring process, some parameters of the fabrics are improved. Even EDTA is usually used as a chelating agent in the pretreatments of the fabrics, recent studies aimed to identify new biodegradable complexing agents. In this study, we present the results obtained for bioscouring treatment of the cellulosic/lignocellulosic fabrics in the presence of sodium citrate as a complexing agent. The treatments were made in 0.1 M phosphate buffer of pH 8 and ultrasound media. The samples were immersed in an aliquot containing the commercial pectinolytic product BEISOL PRO, Denimcol Wash-RGN as a surfactant and sodium citrate or EDTA (ethylenediaminetetraacetic acid). The reactions were conducted by varying the enzyme concentration and action time using a central, rotatable second-order compound program. All the parameters determined after bioscouring [weight loss, hydrophilicity, whiteness index, yellowness index, tensile strength, elongation at break, the relative absorbance (A1731) from FT-IR spectra, color strength (K/S) and color difference (ΔE*ab)] of the investigated samples showed in the case of sodium citrate (an eco-friendly biodegradable compound) treatments better or comparable values to treatments conducted using EDTA (non-biodegradable compound). 相似文献
18.
Summary The [Ni(S2PR2)2] complexes (R=i-PrO, PhO, or Et) can be conveniently prepared by reaction of [Ni{P(OPh)3}4] with [R2P(S)S]2 (R=i-PrO, PhO, or Et) in refluxing CHCl3. The electrochemical behaviour of the complexes in CH2Cl2 and MeCN has been studied by cyclic voltammetry and coulometry. The oxidation of complexes at a glassy carbon reveals an e.c. mechanism. The [Ni(S2PR2)2] complexes undergo a one-electron irreversible reduction. 相似文献
19.
Moisés Morán 《Transition Metal Chemistry》1981,6(1):42-44
Summary Reactions between -Cp2V and PX3 (X=Cl, Br or I) yield the corresponding dihalogenated derivatives -Cp2VX2 (X=Cl, Br or I). The oxidative addition of ICl and IBr to -Cp2V gives mixed halogenated derivatives -Cp2VIX (X=Cl or Br). All the compounds have been characterized by elemental analyses, magnetic moment measurements and i.r. and e.p.r. spectra. 相似文献
20.
The characterization of the hydrophobic-hydrophilic properties of different types of microporous materials, namely activated carbons, pillared clays and zeolites, was made by the determination of water adsorption isotherms. The data were analysed by the Dubinin and Astakhov (D-A) equation. The use of the E parameter of the D-A equation as a measure of the hydrophobic-hydrophilic character is proposed. When the information obtained from the E parameter is compared with the information that can be obtained from other parameters used in the literature to characterize the hydrophobicity of materials, it is found that the former is more sensitive and is more directly related with the shape of the adsorption isotherms which, ultimately, is the more direct manifestation of the hydrophobic-hydrophilic properties of a given material. 相似文献