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Moisture sorption isotherm characteristics of freeze-dried D-limonene emulsions in modified chitosan and maltodextrin

BORGOGNONI, Camila Figueiredo; POLAKIEWICZ, Bronislaw; PITOMBO, Ronaldo Nogueira de Moraes
Fonte: TAYLOR & FRANCIS INC Publicador: TAYLOR & FRANCIS INC
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
56.84%
This article reports on modified chitosan as an alternative substance for protecting loss of volatile compounds during freeze drying. Moisture sorption isotherms of freeze-dried D-limonene emulsions in modified chitosan were determined at 15, 25, and 35 degrees C. The data were adjusted to the GAB model. Maltodextrin was used in a parallel experiment. Flavor released from microcapsules was measured. The monolayer humidity, the sorption heat, the diffusivity coefficients, and the surface area of freeze-dried D-limonene emulsions were determined.

Estudo da sorção do antibiótico oxitetraciclina a solos e ácidos húmicos e avaliação dos mecanismos de interação envolvidos; Study of sorption of antibiotic oxytetracycline to the soils and humic acids and evaluation of interaction mechanisms involved

Vaz Júnior, Silvio
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 16/04/2010 PT
Relevância na Pesquisa
36.81%
Na atualidade estudos direcionados para a avaliação do risco químico e do impacto ambiental produzidos por compostos químicos de uso intensivo, como agrotóxicos, petroquímicos e fármacos, vêm ganhando importância por elucidarem as implicações ao meio ambiente e à saúde pública decorrentes deste uso pela sociedade moderna de forma a estabelecer parâmetros restritivos para suas aplicações, evitando-se danos posteriores. Este Estudo compreendeu as observações de sorção e de interação do antibiótico de uso animal e agrícola oxitetraciclina (OTC) com solos brasileiros e ácidos húmicos (AH) extraídos de solos, tendo-se como objetivos gerais comprovar a sorção aos solos e aos AH e verificar a influência da matéria orgânica (MO) e do pH sobre a sorção, definindo quais os mecanismos moleculares de interação envolvidos, cabendo destacar que as tetraciclinas são uma das principais classes de antibióticos utilizadas na pecuária brasileira, tanto para tratamento de enfermidades quanto como Antibióticos Promotores de Crescimento (APC), além de serem freqüentemente aplicados na agricultura para controle de fungos e bactérias. Utilizou-se a Cromatografia Líquida de Alta Eficiência (CLAE) para a coleta de dados quantitativos que permitiram a construção de isotermas de sorção solo-OTC em pH 4...

Role of enthalpy and entropy in moisture sorption behavior of pineapple pulp powder produced by different drying methods

Vigano, Juliane; Azuara, Ebner; Telis, Vania R. N.; Beristain, Cesar I.; Jimenez, Maribel; Telis-Romero, Javier
Fonte: Elsevier B.V. Publicador: Elsevier B.V.
Tipo: Artigo de Revista Científica Formato: 63-71
ENG
Relevância na Pesquisa
46.54%
Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP); Processo FAPESP: 09/11675-3; Sorption mechanisms of pineapple powders produced by vibro-fluidized drying (VFD), spray drying (SD), freeze drying (FD) or vacuum drying (VD) were interpreted through enthalpy/entropy variations with respect to equilibrium moisture content (EMC) at 20, 30, 40 and 50 degrees C and water activity (a(w)) between 0.059 and 0.907. Powders from SD and VFD were more hygroscopic and integral properties indicated higher stability at changing a, compared to powders from VD and FD. Powders showed an enthalpy driven zone with equal isokinetic temperature (T-BI = 499.0 +/- 4.8 K) due to their same composition, and an entropy controlled zone with different isokinetic temperature, T-B2 (VD: 116.0 +/- 40.6 K; FD: 118.3 +/- 24.1 K; SD: 95.8 +/- 23.4 K; VFD: 81.8 +/- 6.3 K), caused by different microstructures resulting from different drying methods. Powders from SD and VFD presented larger entropic zones that shifted the minimum integral entropy to higher a(w), improving storage stability. (C) 2011 Elsevier B.V. All rights reserved.

Study of the enthalpy-entropy mechanism from water sorption of orange seeds (C. sinensis cv. Brazilian) for the use of agro-industrial residues as a possible source of vegetable oil production

Rosa, Daniele Penteado; Villa-Vélez, Harvey Alexander; Telis-Romero, Javier
Fonte: Sociedade Brasileira de Ciência e Tecnologia de Alimentos Publicador: Sociedade Brasileira de Ciência e Tecnologia de Alimentos
Tipo: Artigo de Revista Científica Formato: 95-101
ENG
Relevância na Pesquisa
46.61%
Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP); Processo FAPESP: 11/05094-8; As sementes de laranja são resíduos promissores da agroindústria com um alto potencial de aplicação na produção de óleo vegetal. A relação entre o conteúdo de umidade de equilíbrio e a atividade de água fornece informações úteis para seu processamento e armazenamento. O objetivo deste trabalho foi determinar o mecanismo entalpia-entropia de sorção da água de sementes de laranja (C. sinensis cv. Brasileiros) em função do teor de umidade. Para isso, isotermas de dessorção das sementes de laranja foram determinados em cinco níveis de temperaturas (30, 40, 50, 60 e 70 ºC) em um intervalo de umidade de equilíbrio (0.005-0.057 kg kg-1 d.b.) e atividade de água de 0,02-0,756. Modelos teóricos e empíricos foram usados para a modelagem das isotermas de dessorção. A solução analítica da equação de Clausius-Clapeyron foi proposta para calcular o calor isostérico de sorção, a entropia diferencial e a energia livre de Gibbs através do modelo de Oswin quando o efeito da temperatura sobre o equilíbrio higroscópico foi considerado.; Orange seeds are a promising agroindustry-waste which can be implemented in the extraction and production of vegetable oil. The relationship between moisture content and water activity provides useful information for the processing and storage of this waste item. The aim of this study was to determine the mechanism of water sorption enthalpy-entropy of orange seeds (C. sinensis cv. Brazilians) according to the moisture content. Therefore...

Sorption isotherm, glass transitions and state diagram for freeze-dried plum skin and pulp

Telis, V. R. Nicoletti; Sobral, P. J. Do Amaral; Telis-Romero, J.
Fonte: Universidade Estadual Paulista Publicador: Universidade Estadual Paulista
Tipo: Artigo de Revista Científica Formato: 181-187
ENG
Relevância na Pesquisa
67.09%
Differential scanning calorimetry (DSC) was used to determine phase transitions of freeze-dried plums. Samples at low and intermediate moisture contents, were conditioned by adsorption at various water activities (0.11≤a w≤0.90) at 25°C, whereas in the high moisture content region (a w>0.90) samples were obtained by direct water addition, with the resulting sorption isotherm being well described by the Guggenheim-Anderson-deBoer (GAB) model. Freeze-dried samples of separated plum skin and pulp were also analysed. At a w≤0.75, two glass transitions were visible, with the glass transition temperature (T g) decreasing with increasing a w due to the water plasticising effect. The first T g was attributed to the matrix formed by sugars and water. The second one, less visible and less plasticised by water, was probably due to macromolecules of the fruit pulp. The Gordon-Taylor model represented satisfactorily the matrix glass transition curve for a w≤0.90. In the higher moisture content range T g remained practically constant around T g′ (-57.5°C). Analysis of the glass transition curve and the sorption isotherm indicated that stability at a temperature of 25°C, would be attained by freeze dried plum at a water activity of 0.04...

A potencialidade do reagente metacrilato de glicidila imobilizado no biopolímerio quitosana para a remoção de cátions; The possibilities of the reagent glycidylmethacrylate immobilized on biopolymer chitosan for cations removal

Adnan Khan
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 17/11/2011 PT
Relevância na Pesquisa
37.1%
O biopolímero quitosana foi quimicamente modificado com a finalidade de inserir diferentes grupos funcionais nas cadeias pendentes, as quais contêm os centros básicos enxofre, nitrogênio e oxigênio, visando o desenvolvimento de novos materiais para a remoção de metais de solução aquosa. Em um procedimento típico, a quitosana reagiu com metacrilato de glicidila através da abertura do anel epóxido de três membros, dispondo da dupla ligação livre. Assim, esse precursor reagiu com aminas: etilenodiamina, dietilenotriamina, trietilenotetramina, 1,4-(3- aminopropil)piperazina, acetilhidrazina e com tióis: 1,2-etanoditiol e 2-aminoetanotiol. A quitosana foi também modificada com o tiocarbamato e diotiocarbamato por meio da reação de adição de Michael, em uma reação de etapa única de três componentes, empregando-se acriloilmorfolina, acrilonitrila e acrilamida como receptores. Os novos derivados modificados obtidos foram caracterizados por meio de análise elementar, espectroscopia na região do infravermelho, ressonância magnética nuclear no estado sólido para o núcleo de carbono, termogravimetria e microscopia eletrônica de varredura. Os novos materiais sintetizados foram empregados para a sorção dos cátions divalentes cobre...

Role of Sorption Isotherms in the Analysis of Coupled Heat and Mass Fluxes in Porous Media

Reis, A. Heitor; Rosa, Rui
Fonte: Begell House Publicador: Begell House
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
36.89%
The aim of this work is to show the importance of the sorption isotherms in the study of the heat and mass fluxes in unsaturated porous media. General forms of the heat and mass fluxes are presented in terms of experimentally accessible quantities. The role of the isotherm slope in the coupling of heat and mass fluxes and its influence on the effective permeability are shown. Separate relations for vapor and liquid fluxes through the porous medium are presented as functions of the temperature and the isotherm slopes. Nonstationary isothermal mass flux is also analyzed, a relaxation time for this process is identifled, and its relation to the isotherm slope is also discussed.

Modelling the Desorption Isotherms of Chestnuts

Barroca, Maria João; Guiné, Raquel; Correia, Paula; Andrade, Sónia; Pina, Andreia
Fonte: Instituto Politécnico de Viseu Publicador: Instituto Politécnico de Viseu
Tipo: Conferência ou Objeto de Conferência
Publicado em //2013 ENG
Relevância na Pesquisa
36.77%
The sorption isotherm of food material is pertinent in the processing and storage of food products. Desorption isotherms for peeled and unpeeled chestnuts were investigated using the hygrometric technique at 60 ºC and water activity (aw) ranged between 0.989 and 0.23. The experimental data were compared with four widely recommended models in the literature for food sorption isotherms (GAB, Freundlich, Henderson, and Smith). A non-linear least square regression program was used to evaluate the models constants. The four models were found to be acceptable for predicting the moisture sorption isotherms for chestnut cultivars. However, the empirical Smith model followed by the kinetic GAB was found to better represent the experimental data in the water activity range. Overall, the Smith model appears to be most suitable for fitting the desorption moisture isotherms data for the chestnut.

Effect of Solution Ionic Strength and Iron Coatings on Mineral Grains on the Sorption of Bacterial Cells to Quartz Sand

Mills, Aaron L.; Herman, Janet S.; Hornberger, George M.; DeJesús, Todd H.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /09/1994 EN
Relevância na Pesquisa
36.93%
Understanding the interaction between bacterial cells and solid surfaces is essential to our attempts to quantify and predict the transport of microbes in groundwater aquifers, whether from the point of view of contamination or from that of bioremediation. The sorption of bacterial cells suspended in groundwater to porous medium grains was examined in batch studies. Bacterial sorption to clean quartz sand yielded equilibrium, linear, adsorption isotherms that varied with the bacterial strain used and the ionic strength of the aqueous solution. Values of Kd (the slope of the linear sorption isotherm) ranged from 0.55 to 6.11 ml g-1, with the greatest sorption observed for the highest groundwater ionic strength. These findings are consistent with the interpretation that an increasingly compressed electrical double layer results in stronger adsorption between the like-charged mineral surface and the bacterial cells. When iron-oxyhydroxide-coated sand was used, however, all of the added bacteria were adsorbed up to a threshold of 6.93 × 108 cells g of coated sand-1, beyond which no further adsorption occurred. The irreversible, threshold adsorption is the result of a strong electrostatic attraction between the sesquioxide coating and the bacterial cells. Experimental results of adsorption in mixtures of quartz and Fe(III)-coated sand were successfully predicted by a simple additive model for sorption by the two substrate phases. Even small amounts of Fe(III)-coated sand in a mixture influenced the extent of adsorption of bacterial cells. A quantitative description of adsorption in the mixtures can be realized by using a linear isotherm for reversible adsorption to the quartz grains with a y intercept that represents the number of cells irreversibly adsorbed to the Fe(III)-coated sand.

Estudos de sorção de um corante aniônico modelo em partículas de quitosana reticulada

Morais, Waldenice de Alencar
Fonte: Universidade Federal do Rio Grande do Norte; BR; UFRN; Programa de Pós-Graduação em Química; Físico-Química; Química Publicador: Universidade Federal do Rio Grande do Norte; BR; UFRN; Programa de Pós-Graduação em Química; Físico-Química; Química
Tipo: Dissertação Formato: application/pdf
POR
Relevância na Pesquisa
36.95%
Textile activity results in effluents with a variety of dyes. Among the several processes for dye-uptaking from these wastewaters, sorption is one of the most effective methods, chitosan being a very promising alternative for this end. The sorption of Methyl Orange by chitosan crosslinked particles was approached using equilibrium and kinetic analyses at different pH s. Besides the standard pseudo-order analysis normally effectuated (i.e. pseudo-first-order and pseudo-second-order), a novel approach involving a pseudo-nth-order kinetics was used, nbeing determined via non-linear regression, using the Levenberg-Marquardt method. Zeta potential measurements indicated that electrostatic interactions were important for the sorption process. Regarding equilibrium experiments, data were well fitted to a hybrid Langmuir-Freundlich isotherm, and estimated Gibbs free energy of adsorption as a function of mass of dye per area of chitosan showed that the process of adsorption becomes more homogeneous as the pH of the continuous phase decreased. Considering the kinetics of sorption, although a pseudo-nth-order description yielded good fits, a kinetic equation involving diffusion adsorption phenomena was found to be more consistent in terms of a physicochemical description of the sorption process; Coordenação de Aperfeiçoamento de Pessoal de Nível Superior; A atividade têxtil resulta em efluentes com uma variedade de corantes. Dentre os vários processos para a remoção de corantes destes efluentes...

Retenção de metais pesados em solos agricultáveis do Estado de Goiás; Retention of heavy metals in agricultural soils of the State of Goiás

CASTRO, Mara Lucia Lemke de
Fonte: Universidade Federal de Goiás; BR; UFG; Mestrado em Agronomia; Ciências Agrárias Publicador: Universidade Federal de Goiás; BR; UFG; Mestrado em Agronomia; Ciências Agrárias
Tipo: Dissertação Formato: application/pdf
POR
Relevância na Pesquisa
37.04%
The intensification of the use of land for farming has caused great concern, mainly due to the impacts that these activities are causing the environment, particularly with regard to it s contamination by chemicals. The application of chemicals and waste ground and in several, or in plants in order to take agronomically solid waste, improve productivity and increase agricultural production has been growing in the practices of cultivation. The form of improper disposal of waste in the soil, without any control of dose and form of application, and without knowledge of their ability to assimilate the different soil types, possibly predisposing the occurrence of contamination and pollution along the profile these soils and may reach the water table and contaminate groundwater. This work aimed the analysis of the retention of some heavy metals in Ultisol, Oxisol Typic Acrustox, Quartzipsamment and Kandic Oxisol found in savannah soil of the Goiás. Heavy metals in tests were Cadmium (Cd+2), lead (Pb+2), copper (Cu+2), chromium (Cr+3 and Cr+6), nickel (Ni+2) and zinc (Zn+2). The sorption of the heavy metals in soil was evaluated by batch method and described by potential and linear models of the Freundlich isotherm. For the establishment of sorption isotherm were added in 5...

Phosphorus sorption capacity of alkaline Manitoba soils and its relationship to soil properties

Ige, D.; Akinremi, O.; Flaten, D.; Ajiboye, A.; Kashem, M.
Fonte: Agricultural Inst Canada Publicador: Agricultural Inst Canada
Tipo: Artigo de Revista Científica
Publicado em //2005 EN
Relevância na Pesquisa
36.78%
The establishment of the P retention capacity of soil in Manitoba is essential for effective management of P in the region. However, the methods for determining the P retention capacity for neutral to calcareous soils in the Eastern Prairies are not well developed. The objectives of this study were to determine the P retention capacity of Manitoba soils and to generate equations that relate these capacities to other soil properties. One hundred and fifteen archived surface soils were selected and their physico-chemical properties were measured. These soils were used to generate a single-point P adsorption index by equilibrating 2 g of soil in 20 mL of 0.01 M KCl solution containing either 150 (P150) or 400 (P400) mg P L-1. A subset of 26 of these soils was used for multipoint isotherms with P concentrations in the range of 0–1000 mg P L-1. The data obtained were fitted to the Langmuir isotherm and the adsorption indices were correlated with the various soil properties that were then used to developed predictive equations of the P retention capacity of the soil. The values of the adsorption index, P150, obtained from the single point adsorption study using 150 mg P L-1, ranged between 88 and 891 mg P kg-1, while that of P400 ranged between 100 and 1250 mg P kg-1. A better correlation was obtained between P150 and soil properties compared with P400. For the 26 soil subset...

Influence of biosolids on phosphorus sorption characteristics of a Vertisol in comparison with manures and fertilizer

Ajiboye, A.; Akinremi, O.; Flaten, D.; Racz, G.
Fonte: Agricultural Institute of Canada Publicador: Agricultural Institute of Canada
Tipo: Artigo de Revista Científica
Publicado em //2007 EN
Relevância na Pesquisa
56.97%
Regulation of manure application in Manitoba has raised the question of whether or not biosolids application should be regulated in the same way. This study examined the effects of biosolids (BIO) applications on P sorption characteristics of a Vertisol in comparison with dairy cattle (DAIRY) and hog (HOG) manures, and monoammonium phosphate (MAP) fertilizer using the classical sorption isotherm and single point sorption index. Pertinent chemical properties and degree of P saturation (DPS) were also determined. The sorption maximum (Smax) in the control was reduced from 655 mg kg⁻¹, to a range of 536–655 mg kg⁻¹ with BIO, 559–650 mg kg⁻¹ with MAP, 402–568 mg kg⁻¹ with DAIRY, and 350–587 mg kg⁻¹ with HOG depending upon the rate of P added. The lower DPS in the soil amended with BIO suggests a lower risk of P loss with biosolids compared with manures. The higher P sorption capacity of biosolids-amended soils compared with soils amended with manures suggest that Ca added with BIO increased the number of P sorption sites by a similar proportion to the amount of P added.; Babasola Ajiboye, Olalekan O. Akinremi, Donald N. Flaten, and Geza J. Racz

Determination of phosphorous sorption - desorption characteristics of Manitoba soils

Akinremi, Olalekan O.; Ige, D. V.; Flaten, Donald N.; Ajiboye, Abraham Babasola; Kashem, Mohammad Abul; Eilers, R. G.; Haluschack, P.
Fonte: Manitoba Livestock Manure Management Initiative Publicador: Manitoba Livestock Manure Management Initiative
Tipo: Relatório
Publicado em //2004 EN
Relevância na Pesquisa
36.89%
Develop a relationship between routinely measured soil properties and sorption maxima and degree of P saturation of Manitoba soils; http://www.manure.mb.ca/projects/viewproject.php?id=24; Project: MLMMI 03-01-15

Sorption and Transport Behaviour of Hydrophobic Organic Compounds in Soils and Sediments of Bangladesh and Their Impact on Groundwater Pollution : Laboratory Investigations and Model Simulations

Rahman, Mohammed Mokhlesur
Fonte: Universität Tübingen Publicador: Universität Tübingen
Tipo: Buch (Monographie)
EN
Relevância na Pesquisa
46.76%
*** Zugleich als Dissertation an der Univ. Tübingen erschienen, 2002 *** This thesis focuses on the elucidation of the sorption and related transport processes controlling the fate of hydrophobic organic compounds (HOCs) (contaminants and pesticide) in the subsurface environment. For a variety of organic compounds (phenanthrene, 1,2-DCB, TCE and carbofuran) batch and column experiments were carried out with different geosorbents (deltaic, floodplain and residuum soils, aquifer sediments and peat) to simulate the effect in Bangladesh top soils and sediments and the ultimate impact on groundwater. Overall, the results reported here so far indicate that sorption in these samples for the chemicals investigated is dominated by the partitioning processes. A nonlinear type sorption isotherm is described by the combination of the partitioning and pore-filling mechanisms. The solubility normalized Freundlich model predicts an inverse linear relationship between the sorption coefficient measured at a given relative concentration vs. S which facilitate the prediction of sorption of a variety of pollutants based on measured data of one probe compound. An effect of preferential solute transport coupled with diffusion into the surrounding matrix region has been examined by conducting macropore flow column experiments. A new analytical solution was developed to model the breakthrough curves. The model accounts for advection in the macropore region...

Adsorption isotherm studies of BOD, TSS and colour reduction from palm oil mill effluent (POME) using boiler fly ash

Igwe,J.C; Onyegbado,C.O; Abia,A.A
Fonte: Fundação Editora da Universidade Estadual Paulista Júlio de Mesquita Filho - UNESP Publicador: Fundação Editora da Universidade Estadual Paulista Júlio de Mesquita Filho - UNESP
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/09/2010 EN
Relevância na Pesquisa
36.85%
Palm oil is one of the two most important vegetable oils in the world's oil and fats market. The extraction and purification processes generate different kinds of waste generally known as palm oil mill effluent (POME). Earlier studies had indicated the possibility of using boiler fly ash to adsorb impurities and colour in POME treatment. The adsorption treatment of POME using boiler fly ash was further investigated in detail in this work with regards to the reduction of BOD, colour and TSS from palm oil mill effluent. The amount of BOD, colour and TSS adsorbed increased as the weight of the boiler fly ash used was increased. Also, the smaller particle size of 425µm adsorbed more than the 850µm size. Attempts were made to fit the experimental data with the Freundlich, Langmuir and Dubinin-Radushkevich isotherms. The R² values, which ranged from 0.8974-0.9898, 0.8848-0.9824 and 0.6235-0.9101 for Freundlich, Langmuir and Dubinin-Radushkevich isotherms respectively, showed that Freundlich isotherm gave a better fit followed by Langmuir and then Dubinin-Radushkevich isotherm. The sorption trend could be put as BOD > Colour > TSS. The apparent energy of adsorption was found to be 1.25, 0.58 and 0.97 (KJ/mol) for BOD, colour and TSS respectively...

Determinação do coeficiente de distribuição (Kd) de benzo(a)pireno em solo por isotermas de sorção

D'Agostinho,Adriana; Flues,Marlene
Fonte: Sociedade Brasileira de Química Publicador: Sociedade Brasileira de Química
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/07/2006 PT
Relevância na Pesquisa
46.84%
Leaking of diesel oil from gas stations is frequent in Brazil. The presence of polycyclic aromatic hydrocarbons (PAHs), which are highly toxic is an indication of contamination by heavy hydrocarbons from diesel oil. Here were present the determination of the distribution coefficient (Kd) of benzo(a)pyrene (the most carcinogenic of the PAHs) in tropical soils using the sorption isotherm model. The sorption curves acquired for benzo(a)pyrene were of the S-type, probably due to the water/methanol experimental conditions. The sorption curves allowed calculation of the distribution coefficient (Kd). The experimental Kd values were lower than those calculated from literature Koc values (partition coefficient normalized by organic carbon), due mainly to the cosolvency effect and the percentage of organic matter and clay in soil.

Capillary Condensation, Freezing, and Melting in Silica Nanopores: A Sorption Isotherm and Scanning Calorimetry Study on Nitrogen in Mesoporous SBA-15

Moerz, Sebastian T.; Knorr, Klaus; Huber, Patrick
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 08/02/2012
Relevância na Pesquisa
46.89%
Condensation, melting and freezing of nitrogen in a powder of mesoporous silica grains (SBA-15) has been studied by combined volumetric sorption isotherm and scanning calorimetry measurements. Within the mean field model of Saam and Cole for vapor condensation in cylindrical pores a liquid nitrogen sorption isotherm is well described by a bimodal pore radius distribution. It encompasses a narrow peak centered at 3.3 nm, typical of tubular mesopores, and a significantly broader peak characteristic of micropores, located at 1 nm. The material condensed in the micropores as well as the first two adsorbed monolayers in the mesopores do not exhibit any caloric anomaly. The solidification and melting transformation affects only the pore condensate beyond approx. the second monolayer of the mesopores. Here, interfacial melting leads to a single peak in the specific heat measurements. Homogeneous and heterogeneous freezing along with a delayering transition for partial fillings of the mesopores result in a caloric freezing anomaly similarly complex and dependent on the thermal history as has been observed for argon in SBA-15. The axial propagation of the crystallization in pore space is more effective in the case of nitrogen than previously observed for argon...

Equipamento experimental para determinação de isotermas de adsorção pelo método dinâmico; Experimental apparatus for the determination of sorption isotherms by the dynamic method

Padro Filho, L.G.; Sabbagh, M.
Fonte: Universidade de São Paulo. Escola Superior de Agricultura Luiz de Queiroz Publicador: Universidade de São Paulo. Escola Superior de Agricultura Luiz de Queiroz
Tipo: info:eu-repo/semantics/article; info:eu-repo/semantics/publishedVersion; ; ; ; ; Formato: application/pdf
Publicado em 01/12/1993 POR
Relevância na Pesquisa
56.84%
Foi realizada a avaliação do desempenho de equipamento experimental para a determinação de curvas de umidade de equilíbrio - isoterma de adsorção - de farinhas pelo método dinâmico. Para o ajuste dos valores definidos (0,51; 0,57; 0,67; 0,75; 0,79 e 0,81) de atividade de água - Aa - na corrente de ar, foram usadas soluções saturadas de sais. A comparação da eficiência do equipamento, com e sem recirculação de ar, foi feita determinando-se a isoterma de adsorção de farinha de soja a 35°C. A versão com recirculação de ar permite a obtenção de dados de equilíbrio em elevados níveis de Aa, nos quais há perda das amostras por crescimento microbiano quando se emprega a versão sem recirculação. Os tempos necessários para a obtenção do equilíbrio da farinha com as umidades relativas das correntes de ar são cerca de 50% menores na versão com recirculação de ar.; The evaluation of the performance of an experimental apparatus for the determination of flour sorption isotherms was carried out. To adjust the water activity - Aa - values (0.51; 0.57; 0.67; 0.75; 0.79 and 0.81) of the air stream, saturated salt solutions were used. The comparison of the apparatus with and without air recycling, was done by determining the sorption isotherm of soybean flour at 35°C. The air recycling model enables to obtain reliable data in a high Aa range...

AN EXPERIMENTAL EVALUATION OF SUSTAINABLE DRAINAGE SYSTEMS

Tsavdaris, Alexandros; Williams, John B.; Mitchell, Steve
Fonte: JUEE Press Publicador: JUEE Press
Tipo: info:eu-repo/semantics/article; info:eu-repo/semantics/publishedVersion; Formato: application/pdf
Publicado em 08/12/2013 ENG
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This paper investigates the behaviour of certain water and sediment quality indicators of a vegetated detention pond system located at Waterlooville, Hampshire, UK. The period of study was 2 years (March 2011-March 2013) with sampling carried out once a month. Statistical analysis was performed using Minitab™. The aim of the study was to examine the changes in quality of various constituents with time and possible linear associations between them. Pond sediments and pond water quality were monitored for a range of variables at each monthly visit. Results indicate that the system demonstrates low levels of pollution while not having a direct impact on the oxygen balance of the receiving water-body. Oxygen demanding substances along with suspended matter and certain metals/elements were found to accumulate in the system with time. Significant linear associations were observed for road salts (containing Na, Cl, Mg) and certain pollutants, suggesting that road salts have a major impact on SuDS water/sediment quality. Sorption characteristics of specific metals were also evaluated by means of adsorption isotherm equations. Three widely used sorption isotherms were employed in this study. It was found that the sorption behaviour of metals is highly variable. This study highlights the dynamic nature of vegetated ponds and the importance of understanding the behaviour of different pollutants for SuDS design.