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Biosorption of zinc ions from aqueous solution by the microalga Scenedesmus obliquus

Monteiro, Cristina M.; Castro, Paula M. L.; Malcata, F. Xavier
Fonte: Universidade Católica Portuguesa Publicador: Universidade Católica Portuguesa
Tipo: Artigo de Revista Científica
Publicado em //2011 ENG
Relevância na Pesquisa
281.76908%
Aquatic environments are often exposed to toxic heavy metals, which gain access to the food chain via microalgae and may cause severe problems at higher trophic levels. However, such a metabolic specificity can be taken advantage of in bioremediation strategies. The potential of a novel wild strain of Scenedesmus obliquus, previously isolated from a heavy metal-contaminated site in northern Portugal, to remove Zn from aqueous solutions was thus studied, using several initial concentrations. The removal extent reached its maximum by 1 day: 836.5 mg Zn/g biomass, at the initial concentration of 75 mg/L, mainly by adsorption onto the cell surface. Comparative studies encompassing a commercially available strain of the same microalgal species led to a maximum removal extent of only 429.6 mg Zn/g biomass, under identical conditions. Heat-inactivated cells permitted a maximum removal of 209.6 mg Zn/g biomass, at an initial concentration of 50 mg Zn/L. The maximum adsorption capacity of Zn, estimated via Langmuir’s isotherm, was 330 mg Zn/g biomass. Finally, Zn removal was highest at pH 6.0–7.0. It was proven, for the first time, that such a wild microalga can uptake and adsorb Zn very efficiently, which unfolds a particularly good potential for bioremediation. Its performance is far better than similar (reference) species...

Adsorption of n-Pentane on Mesoporous Silica and Adsorbent Deformation

Gor, G.Y.; Paris, O.; Prass, J.; Russo, P.A.; Ribeiro Carrott, M.M.L.; Neimark, A.V.
Fonte: ACS Publications Publicador: ACS Publications
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
401.4564%
Development of quantitative theory of adsorption-induced deformation is important, e.g., for enhanced coalbed methane recovery by CO2 injection. It is also promising for the interpretation of experimental measurements of elastic properties of porous solids. We study deformation of mesoporous silica by n-pentane adsorption. The shape of experimental strain isotherms for this system differs from the shape predicted by thermodynamic theory of adsorption-induced deformation. We show that this difference can be attributed to the difference of disjoining pressure isotherm, responsible for the solid−fluid interactions. We suggest the disjoining pressure isotherm suitable for n-pentane adsorption on silica and derive the parameters for this isotherm from experimental data of n-pentane adsorption on nonporous silica. We use this isotherm in the formalism of macroscopic theory of adsorption-induced deformation of mesoporous materials, thus extending this theory for the case of weak solid−fluid interactions. We employ the extended theory to calculate solvation pressure and strain isotherms for SBA-15 and MCM-41 silica and compare it with experimental data obtained from small-angle X-ray scattering. Theoretical predictions for MCM-41 are in good agreement with the experiment...

Strained In1-xGaxAsyP1-y/InP quantum well heterostructures grown by low-pressure metalorganic vapor phase epitaxy

Carvalho Jr,Wilson de; Bernussi,Ayrton André; Furtado,Mário Tosi; Gobbi,Ângelo Luiz; Cotta,Mônica A.
Fonte: ABM, ABC, ABPol Publicador: ABM, ABC, ABPol
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/04/1999 EN
Relevância na Pesquisa
270.88799%
We have investigated the optical and the structural properties of strained In1-xGaxAsyP1-y/InP and strain compensated In1-xGaxAsyP1-y/In1-zGazAsqP1-q/InP multi-quantum well heterostructures grown by low-pressure metalorganic vapor phase epitaxy at different growth conditions. Our results indicate an increase of the compositional fluctuation of quaternary materials as the alloy composition moves from the outer spinodal isotherm into the miscibility gap region. In1-xGaxAsyP1-y layers grown at high tensile strained values exhibit a three-dimensional-like growth mode. Strain compensated structures revealed the presence of a broad photoluminescence emission band below the fundamental quantum well transition, well defined elongated features along the [011] direction and interface undulations. All these effects were found to be strongly dependent on the growth temperature and the number of wells.

Assessment of Bioavailability of Soil-Sorbed Atrazine

Park, Jeong-Hun; Feng, Yucheng; Ji, Pingsheng; Voice, Thomas C.; Boyd, Stephen A.
Fonte: American Society for Microbiology Publicador: American Society for Microbiology
Tipo: Artigo de Revista Científica
Publicado em /06/2003 EN
Relevância na Pesquisa
170.88799%
Bioavailability of pesticides sorbed to soils is an important determinant of their environmental fate and impact. Mineralization of sorbed atrazine was studied in soil and clay slurries, and a desorption-biodegradation-mineralization (DBM) model was developed to quantitatively evaluate the bioavailability of sorbed atrazine. Three atrazine-degrading bacteria that utilized atrazine as a sole N source (Pseudomonas sp. strain ADP, Agrobacterium radiobacter strain J14a, and Ralstonia sp. strain M91-3) were used in the bioavailability assays. Assays involved establishing sorption equilibrium in sterile soil slurries, inoculating the system with organisms, and measuring the CO2 production over time. Sorption and desorption isotherm analyses were performed to evaluate distribution coefficients and desorption parameters, which consisted of three desorption site fractions and desorption rate coefficients. Atrazine sorption isotherms were linear for mineral and organic soils but displayed some nonlinearity for K-saturated montmorillonite. The desorption profiles were well described by the three-site desorption model. In many instances, the mineralization of atrazine was accurately predicted by the DBM model, which accounts for the extents and rates of sorption/desorption processes and assumes biodegradation of liquid-phase...

Adsorption characteristics of cellulolytic enzymes from the anaerobic fungus Piromyces sp. strain E2 on microcrystalline cellulose.

Dijkerman, R; Vervuren, M B; Op Den Camp, H J; van der Drift, C
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /01/1996 EN
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266.96252%
Characteristics of the cellulolytic system of the anaerobic fungus Piromyces sp. strain E2 with respect to adsorption onto microcrystalline cellulose were examined. Cellulolytic enzymes were separated by gel filtration chromatography into a high-molecular-mass complex with an apparent mass of approximately 1,200 to 1,400 kDa and proteins of lower molecular weights. Adsorption of cellulolytic enzymes was not only very fast (within 2 min, equilibrium was attained) but also very effective: Avicelase, endoglucanase, and beta-glucosidase activities from the high-molecular-mass complex were almost completely removed by Avicel. Adsorption of these enzyme activities was proportional and appeared to obey the Langmuir isotherm. For Avicelase, endoglucanase, and beta-glucosidase activities, the maximum amounts adsorbed (Amax) and apparent adsorption constants (Kad) were 16.8, 600, and 33.5 IU/g and 284, 6.93 and 126 ml/IU, respectively. The results of this study strongly support the existence of a multiprotein enzyme complex. This complex was found not to be specifically associated with cell wall fragments as judged by chitin determination.

Sorption of Heavy Metals to the Filamentous Bacterium Thiothrix Strain A1

Shuttleworth, Kay L.; Unz, Richard F.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /05/1993 EN
Relevância na Pesquisa
273.30367%
A study was undertaken to determine the ability of the filamentous bacterium Thiothrix strain A1 to sorb heavy metals from solution. Cells of Thiothrix strain A1 were harvested, washed, and suspended in solutions of metals. After an equilibration period, biomass was separated from solution and the metal content in acid-digested cells and/or filtrates was determined by atomic absorption spectrophotometry. Sorption of nickel and zinc was very rapid; most of the sorbed metal was bound in less than 10 min. The sorption data for copper fit the Freundlich isotherm, and nickel and zinc data fit biphasic Freundlich isotherms. Sorption of both nickel and zinc was dependent on cell age. Cells harvested 24 h after inoculation sorbed approximately one-half of the amount of metal per gram cell protein than did cells harvested after 48, 72, or 96 h. Calcium and magnesium effectively competed with zinc for binding sites, whereas potassium had only a slight effect on the capacity of cells to sorb zinc. The primary mechanism of metal sorption apparently was ion exchange, because 66 to 75% of nickel or zinc could be desorbed by placing metal-laden cells in a solution of 5 mM CaCl2. A competition experiment with nickel and zinc indicated that both metals occupied the same sorption sites. The strong chelating agents EDTA and NTA effectively prevented metal uptake...

Potential of Agrobacterium tumefaciens and Octopine-Utilizing Fluorescent Pseudomonas Strains To Attach to Susceptible Potato Tissues

Chan, James W. Y. F.; Ramey, William D.; Moore, Larry W.; Bell, Colin R.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /09/1990 EN
Relevância na Pesquisa
185.69457%
The binding characteristics of two octopine-catabolizing pseudomonads, Pseudomonas fluorescens B99A and E175D, which were isolated from crown galls, have been examined. The binding of strain B99A to potato disks was very weak, followed a Freundlich isotherm, and was temperature and pH independent. Strain E175D displayed strong attachment and followed a Langmuir isotherm. Despite these fundamental differences in binding characteristics, when each strain was placed in competitive binding assays with either Agrobacterium tumefaciens B6 or A. tumefaciens ATCC 15955, the number of bound pseudomonad cells decreased compared with those obtained in independent trials. Furthermore, the binding of A. tumefaciens cells was increased. In prebinding experiments, in which the potato disks were bound with the pseudomonads before exposure to the agrobacteria, the number of bound pseudomonad cells again decreased. This implies that increased desorption was occurring. In these prebinding studies, the numbers of bound A. tumefaciens ATCC 15955 increased, but the number of bound A. tumefaciens B6 remained the same. The mechanism for this observed synergism on the binding of agrobacterial cells and the depression in bound pseudomonad cells is believed to be alterations in the electrostatic or ionic charges on the plant and bacterial cell surfaces. The synergistic effect on A. tumefaciens undermines the use of these pseudomonads as potential biocontrol agents for crown gall.

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
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174.27498%
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.

Isotherm for Adsorption of Agrobacterium tumefaciens to Susceptible Potato (Solanum tuberosum L.) Tissues †

Kluepfel, Daniel A.; Pueppke, Steven G.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /06/1985 EN
Relevância na Pesquisa
274.27498%
Potato tuber disks were submerged in suspensions containing 101 to 109 cells of Agrobacterium tumefaciens B6 per ml. After 60 min, the disks were rinsed and homogenized, and portions of the homogenates were plated to measure the number of adsorbed bacteria. At low initial bacterial concentrations (105/ml), 5 to 23% of the bacteria adsorbed. At higher bacterial concentrations, the corresponding value was approximately 1.2%. Adsorption was a reversible equilibrium process. Binding saturation was not achieved, and adsorbed bacteria were confined to monolayers on the surfaces of tissue prepared for scanning electron microscopy. Adsorption of strain B6 to potato tuber tissues is described accurately by the Freundlich adsorption isotherm and may be a nonspecific phenomenon.

Binding Characteristics of N2-Fixing Bacteria to Cereal Roots †

Shimshick, Edward J.; Hebert, Richard R.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /09/1979 EN
Relevância na Pesquisa
170.88799%
The attachment of Rhizobium japonicum 61A89 and Rhizobium spp. 32H1 to the roots of wheat and rice seedlings is analyzed in terms of an equilibrium model. A Langmuir adsorption isotherm describes the binding. Strain 61A89 binds to a greater extent than does strain 32H1, and the equilibrium constants for each strain binding to wheat are strongly temperature dependent. Both time-dependent dissociation and association, predicted by an equilibrium model, have been found. The dissociation rate constant for 32H1 is approximately twice that of 61A89, and each is weakly temperature dependent. The rate equation for the binding of exponentially growing 61A89 to wheat roots has been solved as a function of time. Theory and experiment both indicate that the binding at very short times is much less than the equilibrium values. The binding of Azotobacter vinelandii 12837 to wheat roots has also been measured. Root-associated Azotobacter fixes nitrogen, whereas under aerobic growth conditions, root-associated 61A89 and 32H1 do not. The effect of metabolic inhibitors and antibiotics on the binding of Rhizobia and Azotobacter was examined.

Concentration-Dependent Multiple Binding Sites on Saliva-Treated Hydroxyapatite for Streptococcus sanguis

Gibbons, R. J.; Moreno, E. C.; Etherden, I.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /01/1983 EN
Relevância na Pesquisa
182.03082%
The influence of bacterial cell concentration on estimates of the number of binding sites and the affinity for the adsorption of a strain of Streptococcus sanguis to saliva-treated hydroxyapatite was determined, and the possible presence of multiple binding sites for this organism was tested. The range of concentrations of available bacteria varied from 4.7 × 106 to 5,960 × 106 cells per ml. The numbers of adsorbed bacteria increased over the entire range tested, but a suggestion of a break in an otherwise smooth adsorption isotherm was evident. Values for the number of binding sites and the affinity varied considerably depending upon the range of available bacterial concentrations used to estimate them; high correlation coefficients were obtained in all cases. The use of low bacterial cell concentrations yielded lower values for the number of sites and much higher values for the affinity constant than did the use of high bacterial cell concentrations. When data covering the entire range of bacterial concentrations were employed, values for the number of sites and the affinity were similar to those obtained by using only high bacterial cell concentrations. The simplest explanation for these results is that there are multiple binding sites for S. sanguis on saliva-treated hydroxyapatite surfaces. When present in low concentration...

In vitro studies of dental plaque formation: adsorption of oral streptococci to hydroxyaptite.

Appelbaum, B; Golub, E; Holt, S C; Rosan, B
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /08/1979 EN
Relevância na Pesquisa
166.96252%
A mixture of saliva-coated hydroxyapatite beads and radioactively labeled bacteria has been employed as an in vitro model for the initial phase of dental plaque formation. Adsorption in this model can be expressed by the Langmuir adsorption isotherm, and the adherence of oral streptococci can be expressed as the product of the affinity constant (Ka) and the number of binding sites (N), KaN. With this approach, Streptococcus sanguis serotype 1 strains adhered better (KaN = [187 +/- 72] X 10(-2)) than serotype 2 strains (KaN = [97 +/- 84] X 10(-2)); a t test showed this difference to be statistically significant to the 99.99% confidence level. Strains of S. mitis, S. mutans, and S. salivarius did not appear to adhere as well. To analyze the bacterial receptors involved in adherence, competition studies in which increasing quantities of unlabeled bacteria were added to a fixed quantity (4 X 10(9) cells per ml) of 3H-labeled serotype 1, reference strain S. sanguis G9B, were performed. These studies indicated that the type 1 strains competed for the same, or closely related, binding sites. Competition studies using serotype 2 S. sanguis strains resulted in an increased binding of reference strain G9B to hydroxyapatite. Scanning electron microscopy indicated this effect was due to the formation of localized aggregations of bacteria...

Adherence of Actinomyces viscosus T14V and T14AV to Hydroxyapatite Surfaces In Vitro and Human Teeth In Vivo

Wheeler, Timothy T.; Clark, William B.; Birdsell, Dale C.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /09/1979 EN
Relevância na Pesquisa
178.27713%
Adsorption of Actinomyces viscosus strains T14V and T14AV to hydroxyapatite (HA) surfaces was studied, using an adsorption model based on the Langmuir adsorption isotherm. Data generally followed the adsorption model as judged by high correlation coefficients obtained for both strains to most of the treated surfaces studied. The number of binding sites for strains T14V and T14AV cells to human saliva-treated HA was similar to that for untreated HA. The affinity of strain T14V for saliva-treated HA was tenfold greater than the affinity of strain T14AV for that surface. To approximate the pellicle of the gingival crevice and margin and to determine whether adherence by strain T14V was to specific saliva or serum receptors, experimental pellicles were formed on HA by saliva/serum mixtures. The number of binding sites on the saliva/serum-treated HA remained the same as for the saliva-treated surface. Although the affinity of strain T14V cells for the saliva/serum HA surface remained generally the same as the affinity for the HA treated with saliva alone, the affinity of strain T14AV cells decreased further as the serum content increased. Strain T14V cell numbers adsorbed to serum-treated HA, and albumin-treated HA were less than those adsorbed to saliva-treated HA...

Comparative Estimates of Bacterial Affinities and Adsorption Sites on Hydroxyapatite Surfaces

Clark, W. B.; Bammann, L. L.; Gibbons, R. J.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /03/1978 EN
Relevância na Pesquisa
166.96252%
The adsorption of strains of prominent oral bacteria to hydroxyapatite (HA) surfaces was studied by use of an adsorption model based on the Langmuir adsorption isotherm; this permitted comparative estimates of the number of adsorption sites and the strength of the adsorption bonds on untreated and salivatreated HA surfaces for strain of Streptococcus mutans, S. salivarius, S. sanguis, S. mitis, Actinomyces viscosus, and A. naeslundii. The experimental data closely followed the adsorption model as judged by the high correlation coefficients obtained for all strains studied. Adsorption to untreated HA was similar for strains of the six species studied, suggesting that a common adsorption mechanism, possibly Ca2+ bridging, may exist for attachment to HA. More complex interactions appeared to be involved in bacterial adsorption to saliva-treated HA since adsorption of the strains tested at unsaturating cell concentrations varied more than 30-fold. This indicates that adsorbed salivary components on HA surfaces impart a higher order of specificity for subsequent bacterial adsorption. Fewer cells of strains of S. mutans, S. salivarius, and A. naeslundii adsorbed to saliva-treated HA than to untreated HA because adsorbed salivary components presented fewer adsorption sites. Substantially higher numbers of cells of strains of S. sanguis...

Biosorption of Cr(VI) by Ceratocystis paradoxa MSR2 Using Isotherm Modelling, Kinetic Study and Optimization of Batch Parameters Using Response Surface Methodology

Samuel, Melvin S.; E.A. Abigail, M.; Ramalingam, Chidambaram
Fonte: Public Library of Science Publicador: Public Library of Science
Tipo: Artigo de Revista Científica
Publicado em 30/03/2015 EN
Relevância na Pesquisa
274.27498%
This study is focused on the possible use of Ceratocystis paradoxa MSR2 native biomass for Cr(VI) biosorption. The influence of experimental parameters such as initial pH, temperature, biomass dosage, initial Cr(VI) concentration and contact time were optimized using batch systems as well as response surface methodology (RSM). Maximum Cr(VI) removal of 68.72% was achieved, at an optimal condition of biomass dosage 2g L−1, initial Cr(VI) concentration of 62.5 mg L−1 and contact time of 60 min. The closeness of the experimental and the predicted values exhibit the success of RSM. The biosorption mechanism of MSR2 biosorbent was well described by Langmuir isotherm and a pseudo second order kinetic model, with a high regression coefficient. The thermodynamic study also revealed the spontaneity and exothermic nature of the process. The surface characterization using FT-IR analysis revealed the involvement of amine, carbonyl and carboxyl groups in the biosorption process. Additionally, desorption efficiency of 92% was found with 0.1 M HNO3. The Cr(VI) removal efficiency, increased with increase in metal ion concentration, biomass concentration, temperature but with a decrease in pH. The size of the MSR2 biosorbent material was found to be 80 μm using particle size analyzer. Atomic force microscopy (AFM) visualizes the distribution of Cr(VI) on the biosorbent binding sites with alterations in the MSR2 surface structure. The SEM-EDAX analysis was also used to evaluate the binding characteristics of MSR2 strain with Cr(VI) metals. The mechanism of Cr(VI) removal of MSR2 biomass has also been proposed.

Understanding the Role of the Bacteria, Isolated from the Hanford Site Soil, on the Fate and Transport of Uranium

Carvajal, Denny A
Fonte: FIU Digital Commons Publicador: FIU Digital Commons
Tipo: Artigo de Revista Científica Formato: application/pdf
Relevância na Pesquisa
166.96252%
Bacteria are known for their abilities to influence the geochemical processes and affect the mobility of contaminants in the subsurface. Arthrobacter strain G975 was studied to improve our understanding of their effect on uranium’s fate and transport. The research experimentally identified and compared several parameters, including cell growth rate, cell viability, and the bacteria partition coefficient, Kd, under various uranium and bicarbonate concentrations mimicking Hanford Site subsurface environmental conditions, as well as the microbes ability to interact with uranyl phosphate minerals. The results show that the G975 strain can uptake up to 90% of the U(VI) concentrations tested, following linear isotherm models whose uptake capacity was measured up to 150.2 ± 71.4 mg/g and decreased with increasing bicarbonate concentrations. AFM and SEM/EDS analysis confirmed surface membrane uranium precipitates. The research presented here is part of a large effort to advance the understanding of the biogeochemistry processes and plausible remediation strategies concerning uranium contamination.

Monolayer Adsorption of a “Bald” Mutant of the Highly Adhesive and Hydrophobic Bacterium Acinetobacter sp. Strain Tol 5 to a Hydrocarbon Surface▿

Hori, Katsutoshi; Watanabe, Hisami; Ishii, Shun'ichi; Tanji, Yasunori; Unno, Hajime
Fonte: American Society for Microbiology (ASM) Publicador: American Society for Microbiology (ASM)
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
270.88799%
The affinity of microbial cells for hydrophobic interfaces is important because it directly affects the efficiency of various bioprocesses, including green biotechnologies. The toluene-degrading bacterium Acinetobacter sp. strain Tol 5 has filamentous appendages and a hydrophobic cell surface, shows high adhesiveness to solid surfaces, and self-agglutinates. A “bald” mutant of this bacterium, strain T1, lacks the filamentous appendages and has decreased adhesiveness but retains a hydrophobic cell surface. We investigated the interaction between T1 cells and an organic solvent dispersed in an aqueous matrix. During a microbial-adhesion-to-hydrocarbon (MATH) test, which is frequently used to measure cell surface hydrophobicity, T1 cells adhered to hexadecane droplet surfaces in a monolayer, whereas wild-type cells aggregated on the droplet surfaces. The adsorbed T1 cells on the hexadecane surfaces hindered the coalescence of the droplets formed by vortexing, stabilizing the emulsion phase. Following the replacement of the aqueous phase with fresh pure water after the MATH test, a proportion of the T1 cells that had adsorbed to the hydrocarbon surface detached during further vortexing, suggesting a reversible adsorption of T1 cells. The final ratio of the adhering cells to the total cells in the detachment test coincided with that in the MATH test. The adhesion of T1 cells to the hydrocarbon surface conformed to the Langmuir adsorption isotherm...

The effect of strain on the adsorption of CO on Pd(100)

Wu, M. W.; Metiu, H.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 25/02/2000
Relevância na Pesquisa
274.9401%
We study how the binding energy, the vibrational frequencies and the adsorption isotherm of CO on Pd(100) are modified when the solid is subject to uniform strain. The parameters controlling the thermodynamics of adsorption (the adsorption energy, the vibrational frequencies of the adsorbed molecules and the interaction energy between the molecules) have been calculated by using density functional theory. These parameters are then used in a grand canonical Monte Carlo simulation that determines the CO coverage when the surface is in thermodynamic equilibrium with a CO gas, at a specified pressure and temperature. We find that this is substantially affected by the strain. Our results, along with those obtained by others, suggest that the development of "elastochemistry", a study of the change in the chemical properties of a surface when subjected to strain, will lead to interesting and measurable results. It also suggests that differences in chemical activity between clusters on a support and clusters in gas phase may be partly due to the strain induced when a cluster is placed on the support.; Comment: 8 pages, 5 figures, Submitted to J. Chem. Phys

Crustal geophysics and seismicity in southern California

Hauksson, Egill
Fonte: Royal Astronomical Society Publicador: Royal Astronomical Society
Tipo: Article; PeerReviewed Formato: application/pdf
Publicado em /07/2011
Relevância na Pesquisa
188.11023%
The geographical distribution of the (1981–2005) seismicity in southern California forms a ±150 km broad zone adjacent to the Pacific–North America plate boundary, ranging from depths of ∼1–~30 km, with the bulk of the focal depths in the range of 2–12 km. The distribution of the seismicity that includes both mainshock–aftershock sequences and background events is affected by both static and kinematic geophysical parameters of the crust. The static parameters include heat flow, topography, crustal density, V_(p)/V_(s) ratio, hypocentral fault-distance and crustal thickness from receiver functions. The tectonic loading is represented by kinematic parameters such as the crustal shear strain rate field, and the dilatational strain rate field. In our analysis, we normalize the seismicity relative to the areal density of the range of values of each of the parameters. Most of the seismicity occurs in areas of average heat flow, low to intermediate topography, average Vp/Vs and high late Quaternary fault density, and forms seismogenic zones that extend through the brittle crust. The location of late Quaternary faults, often described as zones of weakness, influences the geographical distribution of seismicity more than any other parameter. Although above or below average crustal properties such as high heat flow...

Shock compression of liquid silicates to 125 GPa: The anorthite‐diopside join

Ahrens, Thomas J.; Asimow, Paul D.
Fonte: American Geophysical Union Publicador: American Geophysical Union
Tipo: Article; PeerReviewed Formato: application/pdf
Publicado em 26/10/2010
Relevância na Pesquisa
166.96252%
We determined the equation of state (EOS) of three silicate liquid compositions by shock compression of preheated samples up to 127 GPa. Diopside (Di; Ca_2Mg_2SiO_6) at 1773 K, anorthite (An; CaAl_2Si_2O_8) at 1923 K and the eutectic composition Di_(64)An_(36) at 1673 K were previously studied by shock compression to 38 GPa. The new data extend the EOS of each composition nearly to the Earth’s core-mantle boundary. The previously reported anomaly at 25 GPa for Di_(64)An_(36) eutectic was not reproduced; rather all data for this composition fit within error a straight line Hugoniot in particle velocity vs. shock velocity. Di also displays a linear Hugoniot consistent with ultrasonic data and a third-order finite strain EOS. The full anorthite data set is complex; we examine a model with a transition between two structural states and a fourth‐order finite strain model excluding two points that may not display relaxed behavior. We also report an experiment on room-temperature solid Di_(64)An_(36) aggregate that clearly demonstrates increase upon compression of the Grüneisen parameter of this liquid, much as experiment and theory have shown for forsterite and enstatite liquids. We construct isentropes and isotherms from our Hugoniots using Mie-Grüneisen thermal pressure and evaluate the model of ideal mixing of volumes. Volume may mix almost linearly at high temperature...