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Experimental Measurement of Water Diffusion through Fine Aggregate Mixtures

VASCONCELOS, Kamilla L.; BHASIN, Amit; LITTLE, Dallas N.; LYTTON, Robert L.
Fonte: ASCE-AMER SOC CIVIL ENGINEERS Publicador: ASCE-AMER SOC CIVIL ENGINEERS
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
56.23%
The water diffusion attributable to concentration gradients is among the main mechanisms of water transport into the asphalt mixture. The transport of small molecules through polymeric materials is a very complex process, and no single model provides a complete explanation because of the small molecule`s complex internal structure. The objective of this study was to experimentally determine the diffusion of water in different fine aggregate mixtures (FAM) using simple gravimetric sorption measurements. For the purposes of measuring the diffusivity of water, FAMs were regarded as a representative homogenous volume of the hot-mix asphalt (HMA). Fick`s second law is generally used to model diffusion driven by concentration gradients in different materials. The concept of the dual mode diffusion was investigated for FAM cylindrical samples. Although FAM samples have three components (asphalt binder, aggregates, and air voids), the dual mode was an attempt to represent the diffusion process by only two stages that occur simultaneously: (1) the water molecules are completely mobile, and (2) the water molecules are partially mobile. The combination of three asphalt binders and two aggregates selected from the Strategic Highway Research Program`s (SHRP) Materials Reference Library (MRL) were evaluated at room temperature [23.9 degrees C (75 degrees F)] and at 37.8 degrees C (100 degrees F). The results show that moisture uptake and diffusivity of water through FAM is dependent on the type of aggregate and asphalt binder. At room temperature...

Pulsed field gradient-spin echo NMR studies of water diffusion in a phospholipid model membrane.

Wassall, S R
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /11/1996 EN
Relevância na Pesquisa
46.27%
Water diffusion in the lamellar phase of egg phosphatidylcholine (egg PC)-water was studied by 1H NMR using the pulsed field gradient-spin echo method. The curvature of diffusion plots obtained with egg PC-water mixtures indicates that water diffusion is highly anisotropic with respect to lipid lamellae. This was confirmed by measurements made on macroscopically aligned egg PC-water as a function of orientation that categorically establish DII/DI >> .1, where the respective subscripts refer to parallel and perpendicular to the lipid bilayer. A smooth, monotonic dependence on water concentration was observed for water diffusion in aligned egg PC-water, varying at 25 degrees C from DII = 1.2 x 10(-10) m2 s 1 at n = 4.9 mol water/lipid to DII = 4.0 x 10(-10) m2 s-1 at n = 18.6 mol water/lipid. The diffusion is approximately a factor of 10 slower than in pure water because of water binding and restriction to translational motion within the aqueous layer. No evidence for a sudden drop in water diffusion coefficient at a specific water content, as previously reported with egg PC-water mixtures (Lange and Gary Bobo. 1974. J. Gen. Physiol 63:690-706), was detected. A morphological reorganization of lamellar domains, which in random orientational distribution comprise lipid-water mixtures...

Lipid and water diffusion in bicontinuous cubic phases measured by NMR.

Eriksson, P O; Lindblom, G
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /01/1993 EN
Relevância na Pesquisa
46.23%
Lipid and water diffusion coefficients in bicontinuous cubic liquid crystalline phases have been determined with the NMR pulsed magnetic field gradient technique. In the monoolein-water system, a discontinuity in the variation of the water diffusion coefficient with water content is observed, which coincides with the two-phase region between the two cubic phases in this system. The degree of water association to the lipid has been determined, considering the obstruction factor for diffusion in the cubic phases. The lipid diffusion coefficient increases with increased unsaturation of the lipid, and decreases when larger amphiphile molecules like cholesterol, gramicidin-A, and lyso-oleoyl-phosphatidylcholine are solubilized in the cubic phase. In a cubic liquid crystal of monoolein (MO), dioleoylphosphatidylcholine (DOPC), and water, the individual lipid diffusion coefficients have been determined simultaneously in the same sample. The diffusion coefficients of MO and DOPC differ by a factor of two, and both decrease with increasing DOPC content. The results are discussed in relation to probe techniques for measurements of lipid diffusion.

Biexponential Characterization of Prostate Tissue Water Diffusion Decay Curves Over an Extended b-factor Range

Mulkern, Robert V.; Barnes, Agnieszka Szot; Haker, Steven J.; Hung, Yin P.; Rybicki, Frank J.; Maier, Stephan E.; Tempany, Clare M.C.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
46.19%
Detailed measurements of water diffusion within the prostate over an extended b-factor range were performed to assess whether the standard assumption of monoexponential signal decay is appropriate in this organ. From nine men undergoing prostate MR staging exams at 1.5 T, a single 10 mm thick axial slice was scanned with a line scan diffusion imaging (LSDI) sequence in which 14 equally spaced b- factors from 5 to 3500 s/mm2 were sampled along three orthogonal diffusion sensitization directions in 6 minutes. Due to the combination of long scan time and limited volume coverage associated with the multi-b- factor, multi-directional sampling, the slice was chosen online from the available T2-weighted axial images with the specific goal of enabling the sampling of presumed non-cancerous regions of interest (ROI’s) within the central gland (CG) and peripheral zone (PZ). Histology from pre-scan biopsy (N = 9) and post-surgical resection (N = 4) was subsequently employed to help confirm that the ROIs sampled were non-cancerous. The CG ROIs were characterized from the T2-weighted images as primarily mixtures of glandular and stromal benign prostatic hyperplasia (BPH) which is prevalent in this population. The water signal decays with b- factor from all ROI’s were clearly non-monoexponential and better served with bi- vs monoexponential fits...

Water diffusion-exchange effect on the paramagnetic relaxation enhancement in off-resonance rotating frame

Zhang, Huiming; Xie, Yang; Ji, Tongyu
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
46.28%
The off-resonance rotating frame technique based on the spin relaxation properties of off-resonance T1ρ can significantly increase the sensitivity of detecting paramagnetic labeling at high magnetic fields. However, the in vivo detectable dimension for labeled cell clusters/tissues in T1ρ -weighted images is limited by the water diffusion-exchange between mesoscopic scale compartments. An experimental investigation of the effect of water diffusion-exchange between compartments on the paramagnetic relaxation enhancement of paramagnetic agent compartment is presented for in vitro/in vivo models. In these models, the size of paramagnetic agent compartment is comparable to the mean diffusion displacement of water molecules during the long RF pulses that are used to generate the off-resonance rotating frame. The three main objectives of this study were: (1) to qualitatively correlate the effect of water diffusion-exchange with the RF parameters of the long pulse and the rates of water diffusion, (2) to explore the effect of water diffusion-exchange on the paramagnetic relaxation enhancement in vitro, and (3) to demonstrate the paramagnetic relaxation enhancement in vivo. The in vitro models include the water permeable dialysis tubes or water permeable hollow fibers embedded in cross-linked proteins gels. The MWCO of the dialysis tubes was chosen from 0.1 to 15 kDa to control the water diffusion rate. Thin hollow fibers were chosen to provide sub-millimeter scale compartments for the paramagnetic agents. The in vivo model utilized the rat cerebral vasculatures as a paramagnetic agent compartment...

Intracellular Water Specific MR of Microbead-adherent Cells: HeLa Cell Intracellular Water Diffusion

Zhao, L.; Sukstanskii, A. L.; Kroenke, C. D.; Song, J.; Piwnica-Worms, D.; Ackerman, J. J. H.; Neil, J. J.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /01/2008 EN
Relevância na Pesquisa
46.27%
The 1H MR signal arising from flowing extracellular media in a perfused, microbead-adherent cultured cell system can be suppressed with a slice-selective, spin-echo pulse sequence. The signal from intracellular water can, thus, be selectively monitored. Herein, this technique was combined with pulsed field gradients to quantify intracellular water diffusion in HeLa cells. The intracellular water MR diffusion-signal attenuation at various diffusion times was well described by a biophysical model that characterizes the incoherent displacement of intracellular water as a truncated Gaussian distribution of apparent diffusion coefficients. At short diffusion times, the water “free” diffusion coefficient and the surface-to-volume ratio of HeLa cells were estimated and were, respectively, 2.0 ± 0.3 μm2/ms and 0.48 ± 0.1 μm-1 (mean ± standard deviation). At long diffusion times, the cell radius of 10.1 ± 0.4 μm was inferred and was consistent with that measured by optical microscopy. In summary: (i) intracellular water “free” diffusion in HeLa cells was rapid, two thirds that of pure water; (ii) the cell radius inferred from modeling the incoherent displacement of intracellular water by a truncated Gaussian distribution of apparent diffusion coefficients was confirmed by independent optical microscopy measures.

Focal Reversible Deactivation of Cerebral Metabolism Affects Water Diffusion

Khachaturian, Mark H.; Arsenault, John; Ekstrom, Leeland B.; Tuch, David S.; Vanduffel, Wim
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /11/2008 EN
Relevância na Pesquisa
46.11%
The underlying biophysical mechanisms which affect cerebral diffusion contrast remain poorly understood. We hypothesized that cerebral metabolism may affect cerebral diffusion contrast. The purpose of this study was to develop the methodology to reversibly deactivate cerebral metabolism and measure the effect on the diffusion MRI signal. We developed an MRI-compatible cortical cooling system to reversibly deactivate cortical metabolism in rhesus monkey area V1 and used MR thermometry to calculate three-dimensional temperature maps of the brain to define the extent of deactivated brain in vivo. Significant changes in the apparent diffusion coefficient (ADC) were only observed during those experiments in which the cortex was cooled below the metabolic cutoff temperature of 20°C. ADC decreases (12–20%) were observed during cortical cooling in regions where the temperature did not change. The normalized in vivo ADC as function of temperature was measured and found to be equivalent to the normalized ADC of free water at temperatures above 20°C, but was significantly decreased below 20°C (20–25% decrease). No changes in fractional anisotropy were observed. In future experiments, we will apply this methodology to quantify the effect of reversible deactivation on neural activity as measured by the hemodynamic response and compare water diffusion changes with hemodynamic changes.

Assessment of the Effects of Cellular Tissue Properties on ADC Measurements by Numerical Simulation of Water Diffusion

Harkins, Kevin D.; Galons, Jean-Philippe; Secomb, Timothy W.; Trouard, Theodore P.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /12/2009 EN
Relevância na Pesquisa
46.14%
The apparent diffusion coefficient (ADC), as measured by diffusion-weighted MRI has proven useful in the diagnosis and evaluation of ischemic stroke. The ADC of tissue water is reduced by 30-50% following ischemia and provides excellent contrast between normal and affected tissue. Despite its clinical utility, there is no consensus on the biophysical mechanism underlying the reduction in ADC. In this work, a numerical simulation of water diffusion is used to predict the effects of cellular tissue properties on experimentally measured ADC. The model shows that the biophysical mechanisms responsible for changes in ADC post-ischemia depend upon the time over which diffusion is measured. At short diffusion times, the ADC is dependent upon the intrinsic diffusivity, while at longer, clinically relevant diffusion times, the ADC is highly dependent upon the cell volume fraction. The model also predicts that at clinically relevant diffusion times, the 30-50% drop in ADC after ischemia can be accounted for by cell swelling alone when intracellular T2 is allowed to be shorter than extracellular T2.

Active-Site Hydration and Water Diffusion in Cytochrome P450cam: A Highly Dynamic Process

Miao, Yinglong; Baudry, Jerome
Fonte: The Biophysical Society Publicador: The Biophysical Society
Tipo: Artigo de Revista Científica
Publicado em 21/09/2011 EN
Relevância na Pesquisa
46.18%
Long-timescale molecular dynamics simulations (300 ns) are performed on both the apo- (i.e., camphor-free) and camphor-bound cytochrome P450cam (CYP101). Water diffusion into and out of the protein active site is observed without biased sampling methods. During the course of the molecular dynamics simulation, an average of 6.4 water molecules is observed in the camphor-binding site of the apo form, compared to zero water molecules in the binding site of the substrate-bound form, in agreement with the number of water molecules observed in crystal structures of the same species. However, as many as 12 water molecules can be present at a given time in the camphor-binding region of the active site in the case of apo-P450cam, revealing a highly dynamic process for hydration of the protein active site, with water molecules exchanging rapidly with the bulk solvent. Water molecules are also found to exchange locations frequently inside the active site, preferentially clustering in regions surrounding the water molecules observed in the crystal structure. Potential-of-mean-force calculations identify thermodynamically favored trans-protein pathways for the diffusion of water molecules between the protein active site and the bulk solvent. Binding of camphor in the active site modifies the free-energy landscape of P450cam channels toward favoring the diffusion of water molecules out of the protein active site.

Water Diffusion In And Out Of The β-Barrel Of GFP and The Fast Maturing Fluorescent Protein, TurboGFP

Li, Binsen; Shahid, Ramza; Peshkepija, Paola; Zimmer, Marc
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
46.12%
The chromophore of fluorescent proteins is formed by an internal cyclization of the tripeptide 65SYG67 fragment and a subsequent oxidation. The oxidation is slow - the kinetics of this step is presumably improved in fast maturing GFPs. Water molecules can aid in the chromophore formation. We have used 50ns molecular dynamics simulations of the mature and immature forms of avGFP and TurboGFP to examine the diffusion of water molecules in-and-out of the protein β-barrel. Most crystal structures of GFPs have well-structured waters within hydrogen-bonding distance of Glu222 and Arg96. It has been proposed that they have an important role in chromophore formation. Stable waters are found in similar positions in all simulations conducted. The simulations confirm the existence of a pore that leads to the chromophore in the rapidly maturing TurboGFP; decreased water diffusion upon chromophore formation; and increased water diffusion due to the pore formation.

Evaluation of Moisture-Related Attenuation Coefficient and Water Diffusion Velocity in Human Skin Using Optical Coherence Tomography

Lee, Cheng-Kuang; Tsai, Meng-Tsan; Chang, Feng-Yu; Yang, Chih-Hsun; Shen, Su-Chin; Yuan, Ouyang; Yang, Chih-He
Fonte: Molecular Diversity Preservation International (MDPI) Publicador: Molecular Diversity Preservation International (MDPI)
Tipo: Artigo de Revista Científica
Publicado em 25/03/2013 EN
Relevância na Pesquisa
46.15%
In this study, time-resolved optical coherence tomography (OCT) scanning images of the process of water diffusion in the skin that illustrate the enhancement in the backscattered intensities due to the increased water concentration are presented. In our experiments, the water concentration in the skin was increased by soaking the hand in water, and the same region of the skin was scanned and measured with the OCT system and a commercial moisture monitor every three minutes. To quantitatively analyze the moisture-related optical properties and the velocity of water diffusion in human skin, the attenuation coefficients of the skin, including the epidermis and dermis layers, were evaluated. Furthermore, the evaluated attenuation coefficients were compared with the measurements made using the commercial moisture monitor. The results demonstrate that the attenuation coefficient increases as the water concentration increases. Furthermore, by evaluating the positions of center-of mass of the backscattered intensities from OCT images, the diffusion velocity can be estimated. In contrast to the commercial moisture monitor, OCT can provide three-dimensional structural images of the skin and characterize its optical property, which together can be used to observe morphological changes and quantitatively evaluate the moisture-related attenuation coefficients in different skin layers.

White matter in temporal lobe epilepsy: clinico-pathological correlates of water diffusion abnormalities

Rodríguez-Cruces, Raúl; Concha, Luis
Fonte: AME Publishing Company Publicador: AME Publishing Company
Tipo: Artigo de Revista Científica
Publicado em /04/2015 EN
Relevância na Pesquisa
46.13%
Using magnetic resonance imaging, it is possible to measure the behavior of diffusing water molecules, and the metrics derived can be used as indirect markers of tissue micro-architectural properties. Numerous reports have demonstrated that patients with temporal lobe epilepsy (TLE) have water diffusion abnormalities in several white matter structures located within and beyond the epileptogenic temporal lobe, showing that TLE is not a focal disorder, but rather a brain network disease. Differences in severity and spatial extent between patients with or without mesial temporal sclerosis (MTS), as well as differences related to hemispheric seizure onset, are suggestive of different pathophysiological mechanisms behind different forms of TLE, which in turn result in specific cognitive disabilities. The biological interpretation of diffusion abnormalities is based on a wealth of information from animal models of white matter damage, and is supported by recent reports that directly correlate diffusion metrics with histological characteristics of surgical specimens of TLE patients. Thus, there is now more evidence showing that the increased mean diffusivity (MD) and concomitant reductions of diffusion anisotropy that are frequently observed in several white matter bundles in TLE patients reflect reduced axonal density (increased extra-axonal space) due to smaller-caliber axons...

Water Diffusion and Fracture Behavior in Nano-Porous Low-K Dielectric Film Stacks

Vlassak, Joost; Tsui, Ting T.; Li, Han
Fonte: American Institute of Physics Publicador: American Institute of Physics
Tipo: Artigo de Revista Científica
EN_US
Relevância na Pesquisa
66.12%
Among various low-dielectric constant (‘low-k’) materials under development, organosilicate glasses (OSG) containing nanometer-size pores are leading candidates for use as intra-metal dielectrics in future microelectronics technologies. In this paper, we investigate the direct impact of water diffusion on the fracture behavior of film stacks that contain porous OSG coatings. We demonstrate that exposure of the film stacks to water causes significant degradation of the interfacial adhesion energy, but that it has negligible effect on the cohesive fracture energy of the nanoporous OSG layer. Isotope tracer diffusion experiments combined with dynamic secondary ion mass spectroscopy (SIMS) show that water diffuses predominantly along the interfaces, and not through the porous films. This unexpected result is attributed to the hydrophilic character of the interfaces.; Engineering and Applied Sciences

Multi-directional diffusion weighted imaging: Implementation, verification and clinical application; Multidirektionale dissusionsgewichtete MR-Bildgebung: Implementierung, Verifizierung und klinische Anwendung

Gorczewski, Kamil Marek
Fonte: Universidade de Tubinga Publicador: Universidade de Tubinga
Tipo: Dissertação
EN
Relevância na Pesquisa
46.23%
A water diffusion in a human brain can be used to analyze fibers within the white matter. The basis of the method is a measurement of a MR signal attenuation due to the water particles motion in a presence of a magnetic field gradient. The signal loss is related to the free path that a particle can travel. The obstacles keep the signal from the water spins coherent. Therefore, the attenuation of MR signal is stronger in the directions of the axons. The information about the directional structure of the white matter can be extracted from the data with various methods. Those approaches can be divided into two groups: a model-based and direct measurements. Both groups have their own advantages and disadvantages. The model-based approach like for example a diffusion tensor imaging (DTI) or a spherical harmonics deconvolution (SHD) can shorten the acquisition time and give high resolution images. However, the additional information from the acquisition have to be provided by some prior knowledge (response function in SHD) or assumptions (diffusion function can be described by a tensor). The results from those methods are biased by the first choice of the input functions. At the other hand, a direct measurement is free from the mentioned above defects...

Kinetic of water diffusion and color stability of a resin composite as a function of the curing tip distance

Svizero, Nádia da Rocha; Alonso, Roberta Caroline Bruschi; Wang, Linda; Palma-Dibb, Regina Guenka; Atta, Maria Teresa; D'Alpino, Paulo Henrique Perlatti
Fonte: ABM, ABC, ABPol Publicador: ABM, ABC, ABPol
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
46.13%
The influence of curing tip distance and storage time in the kinetics of water diffusion (water sorption-W SP, solubility-W SB, and net water uptake) and color stability of a composite were evaluated. Composite samples were polymerized at different distances (5, 10, and 15 mm) and compared to a control group (0 mm). After desiccation, the specimens were stored in distilled water to evaluate the water diffusion over a 120-day period. Net water uptake was calculated (sum of WSP and WSB). The color stability after immersion in a grape juice was compared to distilled water. Data were submitted to three-way ANOVA/Tukey's test (α = 5%). The higher distances caused higher net water uptake (p < 0.05). The immersion in the juice caused significantly higher color change as a function of curing tip distance and the time (p < 0.05). The distance of photoactivation and storage time provide the color alteration and increased net water uptake of the resin composite tested.

Coarse-grained molecular dynamics simulation of water diffusion in the presence of carbon nanotubes

Lado Touriño, María Isabel; Cerpa Naranjo, Arisbel; Negri, Viviana; Cerdán, Sebastián; Ballesteros, Paloma
Fonte: Universidade Européia Publicador: Universidade Européia
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
46.24%
Computational modeling of the translational diffusion of water molecules in anisotropic environments entails vital relevance to understand correctly the information contained in the magnetic resonance images weighted in diffusion (DWI) and of the diffusion tensor images (DTI). In the present work we investigated the validity, strengths and weaknesses of a coarse-grained (CG) model based on the MARTINI force field to simulate water diffusion in a medium containing carbon nanotubes (CNTs) as models of anisotropic water diffusion behavior. We show that water diffusion outside the nanotubes follows Ficḱs law, while water diffusion inside the nanotubes is not described by a Ficḱs behavior. We report on the influence on water diffusion of various parameters such as length and concentration of CNTs, comparing the CG results with those obtained from the more accurate classic force field calculation, like the all-atom approach.

Magnetic resonance microimaging of intraaxonal water diffusion in live excised lamprey spinal cord

Takahashi, Masaya; Hackney, David B.; Zhang, Guixin; Wehrli, Suzanne L.; Wright, Alex C.; O'Brien, William T.; Uematsu, Hidemasa; Wehrli, Felix W.; Selzer, Michael E.
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
46.21%
Anisotropy of water diffusion in axon tracts, as determined by diffusion-weighted MRI, has been assumed to reflect the restriction of water diffusion across axon membranes. Reduction in this anisotropy has been interpreted as degeneration of axons. These interpretations are based primarily on a priori reasoning that has had little empirical validation. We used the experimental advantages of the sea lamprey spinal cord, which contains several very large axons, to determine whether intraaxonal diffusion is isotropic and whether anisotropy is attributable to restriction of water mobility by axon surface membranes. Through the application of magnetic resonance microimaging, we were able to measure the purely intraaxonal diffusion characteristics of the giant reticulospinal axons (20–40 μm in diameter). The intraaxonal apparent diffusion coefficients of water parallel (longitudinal ADC, l-ADC) and perpendicular (transverse ADC, t-ADC) to the long axis were 0.98 ± 0.06 (10−3 mm2/sec) and 0.97 ± 0.11 (10−3 mm2/sec), respectively. In white matter regions that included multiple axons, l-ADCs were almost identical regardless of axon density in the sampled axon tract. By comparison, t-ADCs were reduced and varied inversely with the number of axons (and thus axolemmas) in a fixed cross-sectional area. Thus...

Kinetic of water diffusion and color stability of a resin composite as a function of the curing tip distance

Svizero,Nádia da Rocha; Alonso,Roberta Caroline Bruschi; Wang,Linda; Palma-Dibb,Regina Guenka; Atta,Maria Teresa; D'Alpino,Paulo Henrique Perlatti
Fonte: ABM, ABC, ABPol Publicador: ABM, ABC, ABPol
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/08/2012 EN
Relevância na Pesquisa
46.13%
The influence of curing tip distance and storage time in the kinetics of water diffusion (water sorption-W SP, solubility-W SB, and net water uptake) and color stability of a composite were evaluated. Composite samples were polymerized at different distances (5, 10, and 15 mm) and compared to a control group (0 mm). After desiccation, the specimens were stored in distilled water to evaluate the water diffusion over a 120-day period. Net water uptake was calculated (sum of WSP and WSB). The color stability after immersion in a grape juice was compared to distilled water. Data were submitted to three-way ANOVA/Tukey's test (α = 5%). The higher distances caused higher net water uptake (p < 0.05). The immersion in the juice caused significantly higher color change as a function of curing tip distance and the time (p < 0.05). The distance of photoactivation and storage time provide the color alteration and increased net water uptake of the resin composite tested.

A Lattice Boltzmann model for diffusion of binary gas mixtures

Bennett, Sam
Fonte: University of Cambridge; Department of Engineering Publicador: University of Cambridge; Department of Engineering
Tipo: Thesis; doctoral; PhD
EN
Relevância na Pesquisa
46.14%
This thesis describes the development of a Lattice Boltzmann (LB) model for a binary gas mixture. Specifically, channel flow driven by a density gradient with diffusion slip occurring at the wall is studied in depth. The first part of this thesis sets the foundation for the multi-component model used in the subsequent chapters. Commonly used single component LB methods use a non-physical equation of state, in which the relationship between pressure and density varies according to the scaling used. This is fundamentally unsuitable for extension to multi-component systems containing gases of differing molecular masses that are modelled with the ideal gas equation of state. Also, existing methods for implementing boundary conditions are unsuitable for extending to novel boundary conditions, such as diffusion slip. Therefore, a new single component LB derivation and a new method for implementing boundary conditions are developed, and validated against Poiseuille flow. However, including a physical equation of state reduces stability and time accuracy, leading to longer computational times, compared with 'incompressible' LB methods. The new method of analysing LB boundary conditions successfully explains observations from other commonly used schemes...

Experimental study of water diffusion in haplobasaltic and haploandesitic melts

Persikov, Eduard S.; Newman, Sally; Bukhtiyarov, Pavel G.; Nekrasov, Alexey N.; Stolper, Edward M.
Fonte: Elsevier Publicador: Elsevier
Tipo: Article; PeerReviewed Formato: application/pdf
Publicado em /09/2010
Relevância na Pesquisa
46.23%
The diffusion of water in polymerized silicate melts has been studied extensively, but only limited data are available for water diffusion in depolymerized melts such as andesite and basalt. We report here results of eight experiments to determine the diffusivity of water (D_(H_(2)O), defined to be the diffusivity of total H_(2)O; i.e., regardless of speciation) in haplobasalt and haploandesite melts at 1300 °C and P_(H_(2)O)=0.3–100 MPa using hydration and diffusion-couple methods. Water contents of the melts ranged from < 0.1 to ~4 wt.%. Our results contribute to understanding the dependence of water diffusivity on melt composition, especially the concentration of water itself. Diffusion experiments were conducted for 420–1500 s using an internally heated pressure vessel. Water concentration vs. distance profiles in quenched glasses was determined using Fourier transform infrared (FTIR) spectroscopy. D_(H_(2)O) values were determined by fitting these profiles using either Boltzmann–Matano methods, simple functional forms for the relationship between water content and D_(H_(2)O), or the D_(H_(2)O) vs. water content function implied by a simple water speciation model. For both of the compositions studied, D_(H_(2)O) increases with increasing water content. The increase in D_(H_(2)O) with water content can be modeled as exponential over the range investigated...