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Sample records for pore size distributions

  1. Pore-size-distribution of cationic polyacrylamide hydrogels

    SciTech Connect

    Kremer, M.; Prausnitz, J.M.

    1992-06-01

    The pore size distribution of a AAm/MAPTAC (acrylamide copolymerized with (3-methacrylamidopropyl)trimethylammonium chloride) hydrogel was investigated using Kuga's mixed-solute-exclusion method, taking into account the wall effect. A Brownian-motion model is also used. Results show the feasibility of determining pore-size distribution of porous materials using the mixed-solute-exclusion method in conjunction with solution of the Fredholm equation; good agreement was obtained with experiment, even for bimodal pore structures. However, different pore size distributions were calculated for the two different probe-solutes (Dextran and poly(ethylene glycol/oxide)). Future work is outlined. 32 figs, 25 refs.

  2. Pore-size-distribution of cationic polyacrylamide hydrogels. Progress report

    SciTech Connect

    Kremer, M.; Prausnitz, J.M.

    1992-06-01

    The pore size distribution of a AAm/MAPTAC (acrylamide copolymerized with (3-methacrylamidopropyl)trimethylammonium chloride) hydrogel was investigated using Kuga`s mixed-solute-exclusion method, taking into account the wall effect. A Brownian-motion model is also used. Results show the feasibility of determining pore-size distribution of porous materials using the mixed-solute-exclusion method in conjunction with solution of the Fredholm equation; good agreement was obtained with experiment, even for bimodal pore structures. However, different pore size distributions were calculated for the two different probe-solutes (Dextran and poly(ethylene glycol/oxide)). Future work is outlined. 32 figs, 25 refs.

  3. Effects of pore-size and shape distributions on diffusion pore imaging by nuclear magnetic resonance

    NASA Astrophysics Data System (ADS)

    Kuder, Tristan Anselm; Laun, Frederik Bernd

    2015-08-01

    In medical imaging and porous media research, NMR diffusion measurements are extensively used to investigate the structure of diffusion restrictions such as cell membranes. Recently, several methods have been proposed to unambiguously determine the shape of arbitrary closed pores or cells filled with an NMR-visible medium by diffusion experiments. The first approach uses a combination of a long and a short diffusion-weighting gradient pulse, while the other techniques employ short gradient pulses only. While the eventual aim of these methods is to determine pore-size and shape distributions, the focus has been so far on identical pores. Thus, the aim of this work is to investigate the ability of these different methods to resolve pore-size and orientation distributions. Simulations were performed comparing the various pore imaging techniques employing different distributions of pore size and orientation and varying timing parameters. The long-narrow gradient profile is most advantageous to investigate pore distributions, because average pore images can be directly obtained. The short-gradient methods suppress larger pores or induce a considerable blurring. Moreover, pore-shape-specific artifacts occur; for example, the central part of a distribution of cylinders may be largely underestimated. Depending on the actual pore distribution, short-gradient methods may nonetheless yield good approximations of the average pore shape. Furthermore, the application of short-gradient methods can be advantageous to differentiate whether pore-size distributions or intensity distributions, e.g., due to surface relaxation, are predominant.

  4. Mechanical properties, pore size distribution, and pore solution of fly ash-belite cement mortars

    SciTech Connect

    Guerrero, A.; Goni, S.; Macias, A.; Luxan, M.P.

    1999-11-01

    The mechanical properties, pore size distribution, and extracted pore solution of fly ash-belite cement (FABC) mortars were studied for a period of 200 days. The influence of the calcination temperature, which ranged from 700 to 900 C, of the fly ash-belite cement was discussed. The evolution with hydration time of the pore size distribution was followed by mercury intrusion porosimetry, and the results correlated with those of flexural and compressive strength. The pore solution was expressed and analyzed at different times of hydration.

  5. Pore-size distributions of N-isopropylacrylamide (NIPA) hydrogels

    SciTech Connect

    Walther, D.H.; Blanch, H.W.; Prausnitz, J.M. |

    1993-11-01

    Pore-size distributions have been measured for N-isopropylacrylamide (NIPA) hydrogels at 25 and 32{degrees}C with swelling capacities 11.3 and 6.0 g swollen gel per g dry gel. The mixed-solute-exclusion method (introduced by Kuga) was used to obtain the experimental solute-exclusion curve which represents the amount of imbibed liquid inside the gel inaccessible for a solute of radius r. The pore-size distributions were obtained by using Casassa`s Brownian-motion model and numerically solving the Fredholm integral equation. The pore-size distributions of temperature-sensitive NIPA hydrogels are strongly dependent on temperature which determines swelling capacity. With increasing swelling capacity (from 6.0 to 11.3), the pore-size distribution shifts to higher mode values (27.3 to 50.6 {angstrom}) and to higher variance (1.07{center_dot}10{sup 3} to 3.58{center_dot}10{sup 3} {angstrom}{sup 2}).

  6. Using radial NMR profiles to characterize pore size distributions

    NASA Astrophysics Data System (ADS)

    Deriche, Rachid; Treilhard, John

    2012-02-01

    Extracting information about axon diameter distributions in the brain is a challenging task which provides useful information for medical purposes; for example, the ability to characterize and monitor axon diameters would be useful in diagnosing and investigating diseases like amyotrophic lateral sclerosis (ALS)1 or autism.2 Three families of operators are defined by Ozarslan,3 whose action upon an NMR attenuation signal extracts the moments of the pore size distribution of the ensemble under consideration; also a numerical method is proposed to continuously reconstruct a discretely sampled attenuation profile using the eigenfunctions of the simple harmonic oscillator Hamiltonian: the SHORE basis. The work presented here extends Ozarlan's method to other bases that can offer a better description of attenuation signal behaviour; in particular, we propose the use of the radial Spherical Polar Fourier (SPF) basis. Testing is performed to contrast the efficacy of the radial SPF basis and SHORE basis in practical attenuation signal reconstruction. The robustness of the method to additive noise is tested and analysed. We demonstrate that a low-order attenuation signal reconstruction outperforms a higher-order reconstruction in subsequent moment estimation under noisy conditions. We propose the simulated annealing algorithm for basis function scale parameter estimation. Finally, analytic expressions are derived and presented for the action of the operators on the radial SPF basis (obviating the need for numerical integration, thus avoiding a spectrum of possible sources of error).

  7. Computer program calculates and plots surface area and pore size distribution data

    NASA Technical Reports Server (NTRS)

    Halpert, G.

    1968-01-01

    Computer program calculates surface area and pore size distribution of powders, metals, ceramics, and catalysts, and prints and plots the desired data directly. Surface area calculations are based on the gas adsorption technique of Brunauer, Emmett, and Teller, and pore size distribution calculations are based on the gas adsorption technique of Pierce.

  8. Prediction of Hydraulic Conductivity as Related to Pore Size Distribution in Unsaturated Soils

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Soil pore volume as well as pore size, shape, type (i.e. biopore versus crack), continuity, and distribution in soil affect soil water and gas exchange. Vertical and lateral drainage of water by gravitational forces occurs through large, non-capillary soil pores, but redistribution and upward moveme...

  9. Modelling mass transport through a porous partition: Effect of pore size distribution

    NASA Astrophysics Data System (ADS)

    Khayet, Mohamed; Velázquez, Armando; Mengual, Juan I.

    2004-09-01

    Direct contact membrane distillation process has been studied using microporous polytetrafluoroethylene and polyvinylidene fluoride membranes. The membranes were characterized in terms of their non-wettability, pore size distribution and porosity. The mean pore sizes and pore size distributions were obtained by means of wet/dry flow method. The mean pore size and the effective porosity of the membranes were also determined from the gas permeation test. A theoretical model that considers the pore size distribution together with the gas transport mechanisms through the membrane pores was developed for this process. The contribution of each mass transport mechanism was analyzed. It was found that both membranes have pore size distributions in the Knudsen region and in the transition between Knudsen and ordinary diffusion region. The transition region was the major contribution to mass transport. The predicted water vapor permeability of the membranes were compared with the experimental ones. The effect of considering pore size distribution instead of mean pore size to predict the water vapor permeability of the membranes was investigated.

  10. Pore size distribution of shaley rock by small angle neutron scattering

    NASA Astrophysics Data System (ADS)

    Hall, P. L.; Mildner, D. F. R.; Borst, R. L.

    1983-08-01

    Information concerning pore microstructure of shaly rocks is of considerable relevance to petroleum exploration and production. Pore sizes and distributions within shaly samples have been determined by small angle neutron scattering. The data are indicative of a considerable spread of pore dimension, showing inhomogeneities with a range from 20 Å and greater. The cumulative pore volumes are compared with those derived from mercury intrusion porosimetry and nitrogen adsorption and desorption isotherms.

  11. Pore size distribution of shaly rock by small angle neutron scattering

    SciTech Connect

    Hall, P.L.; Mildner, D.F.R.; Borst, R.L.

    1983-08-01

    Information concerning pore microstructure of shaly rocks is of considerable relevance to petroleum exploration and production. Pore sizes and distributions within shaly samples have been determined by small angle neutron scattering. The data are indicative of a considerable spread of pore dimension, showing inhomogeneities with a range from 20 A and greater. The cumulative pore volumes are compared with those derived from mercury intrusion porosimetry and nitrogen adsorption and desorption isotherms.

  12. Unified method for the total pore volume and pore size distribution of hierarchical zeolites from argon adsorption and mercury intrusion.

    PubMed

    Kenvin, Jeffrey; Jagiello, Jacek; Mitchell, Sharon; Pérez-Ramírez, Javier

    2015-02-01

    A generalized approach to determine the complete distribution of macropores, mesopores, and micropores from argon adsorption and mercury porosimetry is developed and validated for advanced zeolite catalysts with hierarchically structured pore systems in powder and shaped forms. Rather than using a fragmented approach of simple overlays from individual techniques, a unified approach that utilizes a kernel constructed from model isotherms and model intrusion curves is used to calculate the complete pore size distribution and the total pore volume of the material. An added benefit of a single full-range pore size distribution is that the cumulative pore area and the area distribution are also obtained without the need for additional modeling. The resulting complete pore size distribution and the kernel accurately model both the adsorption isotherm and the mercury porosimetry. By bridging the data analysis of two primary characterization tools, this methodology fills an existing gap in the library of familiar methods for porosity assessment in the design of materials with multilevel porosity for novel technological applications.

  13. Idealized Shale Sorption Isotherm Measurements to Determine Pore Volume, Pore Size Distribution, and Surface Area

    NASA Astrophysics Data System (ADS)

    Holmes, R.; Wang, B.; Aljama, H.; Rupp, E.; Wilcox, J.

    2014-12-01

    One method for mitigating the impacts of anthropogenic CO2-related climate change is the sequestration of CO2 in depleted gas and oil reservoirs, including shale. The accurate characterization of the heterogeneous material properties of shale, including pore volume, surface area, pore size distributions (PSDs) and composition is needed to understand the interaction of CO2 with shale. Idealized powdered shale sorption isotherms were created by varying incremental amounts of four essential components by weight. The first two components, organic carbon and clay, have been shown to be the most important components for CO2 uptake in shales. Organic carbon was represented by kerogen isolated from a Silurian shale, and clay groups were represented by illite from the Green River shale formation. The rest of the idealized shale was composed of equal parts by weight of SiO2 to represent quartz and CaCO3 to represent carbonate components. Baltic, Eagle Ford, and Barnett shale sorption measurements were used to validate the idealized samples. The idealized and validation shale sorption isotherms were measured volumetrically using low pressure N2 (77K) and CO2 (273K) adsorbates on a Quantachrome Autosorb IQ2. Gravimetric isotherms were also produced for a subset of these samples using CO2 and CH4adsorbates under subsurface temperature and pressure conditions using a Rubotherm magnetic suspension balance. Preliminary analyses were inconclusive in validating the idealized samples. This could be a result of conflicting reports of total organic carbon (TOC) content in each sample, a problem stemming from the heterogeneity of the samples and different techniques used for measuring TOC content. The TOC content of the validation samples (Eagle Ford and Barnett) was measured by Rock-Eval pyrolysis at Weatherford Laboratories, while the TOC content in the Baltic validation samples was determined by LECO TOC. Development of a uniform process for measuring TOC in the validation samples is

  14. Pore-size distribution in loamy soils: A comparison between microtomographic and capillarimetric determination methods

    NASA Astrophysics Data System (ADS)

    Shein, E. V.; Skvortsova, E. B.; Dembovetskii, A. V.; Abrosimov, K. N.; Il'in, L. I.; Shnyrev, N. A.

    2016-03-01

    Pore-size distribution in a soddy-podzolic silt loamy soil developing from mantle loesslike loam (Eutric Albic Retisol (Loamic, Cutanic)) was calculated from the water retention curve according to Jurin's equation and directly determined in microtomographic experiments. Rounded macropores with the diameter of their sections from 75 to 1000 μm predominate in horizontal sections if the studied soil samples. A larger part of the soil pores (>30-35%) belongs to micro- and nanopores, and they cannot be quantitatively determined by the tomographic method, because their sizes are smaller than the detection limit of the applied X-ray microtomography (8.75 μm per pixel). This leads to a significantly larger pore volume determined from the water retention curve in comparison with the "tomographic" pore volume. A comparative analysis of pore-size distribution curves obtained by these methods shows that the major regularities of the pore-size distribution in the range from 30 to 5000 μm are similar in both cases. Fine macropores and, partly, mesopores predominate. Common characteristics of the pore-size distribution curves obtained by these methods, including the coincidence of the peaks, attest to the validity of classical approaches, according to which the hydrology of soil pore space can be perceived as a physical model of cylindrical capillaries of different sizes with capillary-sorbed water.

  15. Determination of the pore size distribution and hydraulic properties from Nuclear Magnetic Resonance relaxometry

    NASA Astrophysics Data System (ADS)

    Stingaciu, Laura R.; Weihermüller, Lutz; Haber-Pohlmeier, Sabina; Stapf, Siegfried; Vereecken, Harry; Pohlmeier, Andreas

    2010-05-01

    Known pore size distributions can be directly linked to the water retention characteristic which is essential for the prognosis of water and solute movement through the material. In our study, we evaluated the feasibility to use Nuclear Magnetic Resonance (NMR) relaxometry measurements for the characterization of pore size distribution in four porous samples with different texture and composition. Therefore, NMR T2 and T1 relaxation measurements at 6.47 MHz were carried out for three model samples (medium sand; fine sand; and a homogenous sand / kaolin clay mixture) and a natural soil. To quantify the goodness of the approach, the NMR measurements were compared in terms of cumulated pore size distribution functions and mean pore diameter with the two classical techniques based on water retention and mercury porosimetry measurements. The results showed that T1 and T2 derived mean pore size diameters are in good agreement with each other but deviate from retention curve derived ones. This is especially the case for well sorted sands with n values > 2.7. For finer materials differences are less pronounced. A short study was performed to evaluate the influence of the variations observed in the pore diameter distributions on the hydraulic properties of the samples: θS, α, and n. In conclusion, NMR T1 and T2 relaxation measurements can be used to estimate pore size distribution, mean pore diameter, as well as the retention function and corresponding hydraulic properties.

  16. Estimation of pore size distribution using concentric double pulsed-field gradient NMR.

    PubMed

    Benjamini, Dan; Nevo, Uri

    2013-05-01

    Estimation of pore size distribution of well calibrated phantoms using NMR is demonstrated here for the first time. Porous materials are a central constituent in fields as diverse as biology, geology, and oil drilling. Noninvasive characterization of monodisperse porous samples using conventional pulsed-field gradient (PFG) NMR is a well-established method. However, estimation of pore size distribution of heterogeneous polydisperse systems, which comprise most of the materials found in nature, remains extremely challenging. Concentric double pulsed-field gradient (CDPFG) is a 2-D technique where both q (the amplitude of the diffusion gradient) and φ (the relative angle between the gradient pairs) are varied. A recent prediction indicates this method should produce a more accurate and robust estimation of pore size distribution than its conventional 1-D versions. Five well defined size distribution phantoms, consisting of 1-5 different pore sizes in the range of 5-25 μm were used. The estimated pore size distributions were all in good agreement with the known theoretical size distributions, and were obtained without any a priori assumption on the size distribution model. These findings support that in addition to its theoretical benefits, the CDPFG method is experimentally reliable. Furthermore, by adding the angle parameter, sensitivity to small compartment sizes is increased without the use of strong gradients, thus making CDPFG safe for biological applications. PMID:23548563

  17. Estimation of pore size distribution using concentric double pulsed-field gradient NMR.

    PubMed

    Benjamini, Dan; Nevo, Uri

    2013-05-01

    Estimation of pore size distribution of well calibrated phantoms using NMR is demonstrated here for the first time. Porous materials are a central constituent in fields as diverse as biology, geology, and oil drilling. Noninvasive characterization of monodisperse porous samples using conventional pulsed-field gradient (PFG) NMR is a well-established method. However, estimation of pore size distribution of heterogeneous polydisperse systems, which comprise most of the materials found in nature, remains extremely challenging. Concentric double pulsed-field gradient (CDPFG) is a 2-D technique where both q (the amplitude of the diffusion gradient) and φ (the relative angle between the gradient pairs) are varied. A recent prediction indicates this method should produce a more accurate and robust estimation of pore size distribution than its conventional 1-D versions. Five well defined size distribution phantoms, consisting of 1-5 different pore sizes in the range of 5-25 μm were used. The estimated pore size distributions were all in good agreement with the known theoretical size distributions, and were obtained without any a priori assumption on the size distribution model. These findings support that in addition to its theoretical benefits, the CDPFG method is experimentally reliable. Furthermore, by adding the angle parameter, sensitivity to small compartment sizes is increased without the use of strong gradients, thus making CDPFG safe for biological applications.

  18. Pore size distribution, strength, and microstructure of portland cement paste containing metal hydroxide waste

    SciTech Connect

    Majid, Z.A.; Mahmud, H.; Shaaban, M.G.

    1996-12-31

    Stabilization/solidification of hazardous wastes is used to convert hazardous metal hydroxide waste sludge into a solid mass with better handling properties. This study investigated the pore size development of ordinary portland cement pastes containing metal hydroxide waste sludge and rice husk ash using mercury intrusion porosimetry. The effects of acre and the addition of rice husk ash on pore size development and strength were studied. It was found that the pore structures of mixes changed significantly with curing acre. The pore size shifted from 1,204 to 324 {angstrom} for 3-day old cement paste, and from 956 to 263 {angstrom} for a 7-day old sample. A reduction in pore size distribution for different curing ages was also observed in the other mixtures. From this limited study, no conclusion could be made as to any correlation between strength development and porosity. 10 refs., 6 figs., 3 tabs.

  19. Direct correlation of internal gradients and pore size distributions with low field NMR.

    PubMed

    Zhang, Yan; Xiao, Lizhi; Liao, Guangzhi; Blümich, Bernhard

    2016-06-01

    Internal magnetic field gradients Gint, which arise from the magnetic susceptibility difference Δχ between solid matrix and fluid in porous media relate to the pore geometry. However, this relationship is complex and not well understood. Here we correlate internal-gradient distributions to pore-size distributions directly to examine internal gradients in detail at low field NMR. The pore-size distributions were obtained by the method of Decay due to Diffusion in the Internal Field (DDIF), and the internal-gradient distributions were measured with the Carr-Purcell-Meiboom-Gill (CPMG) method. The internal-gradient-pore-size distributions correlation maps were obtained for water in packs of glass beads with different diameter and in a sandstone sample. The relationship between internal gradients and pore structure is analyzed in detail by considering the restricted diffusion of fluids in porous samples. For each case diffusion regimes are assigned by plotting normalized CPMG data and comparing the diffusion lengths, the dephasing lengths and pore diameters. In the free-diffusion limit, the correlation maps reveal the true relationship between pore structure and internal gradients so that Δχ can be approximated from the correlation maps. This limit is met most easily at low field. It provides information about porous media, which is expected to benefit the oil industry, in particular NMR well logging.

  20. Direct correlation of internal gradients and pore size distributions with low field NMR

    NASA Astrophysics Data System (ADS)

    Zhang, Yan; Xiao, Lizhi; Liao, Guangzhi; Blümich, Bernhard

    2016-06-01

    Internal magnetic field gradients Gint, which arise from the magnetic susceptibility difference Δχ between solid matrix and fluid in porous media relate to the pore geometry. However, this relationship is complex and not well understood. Here we correlate internal-gradient distributions to pore-size distributions directly to examine internal gradients in detail at low field NMR. The pore-size distributions were obtained by the method of Decay due to Diffusion in the Internal Field (DDIF), and the internal-gradient distributions were measured with the Carr-Purcell-Meiboom-Gill (CPMG) method. The internal-gradient-pore-size distributions correlation maps were obtained for water in packs of glass beads with different diameter and in a sandstone sample. The relationship between internal gradients and pore structure is analyzed in detail by considering the restricted diffusion of fluids in porous samples. For each case diffusion regimes are assigned by plotting normalized CPMG data and comparing the diffusion lengths, the dephasing lengths and pore diameters. In the free-diffusion limit, the correlation maps reveal the true relationship between pore structure and internal gradients so that Δχ can be approximated from the correlation maps. This limit is met most easily at low field. It provides information about porous media, which is expected to benefit the oil industry, in particular NMR well logging.

  1. Direct correlation of internal gradients and pore size distributions with low field NMR.

    PubMed

    Zhang, Yan; Xiao, Lizhi; Liao, Guangzhi; Blümich, Bernhard

    2016-06-01

    Internal magnetic field gradients Gint, which arise from the magnetic susceptibility difference Δχ between solid matrix and fluid in porous media relate to the pore geometry. However, this relationship is complex and not well understood. Here we correlate internal-gradient distributions to pore-size distributions directly to examine internal gradients in detail at low field NMR. The pore-size distributions were obtained by the method of Decay due to Diffusion in the Internal Field (DDIF), and the internal-gradient distributions were measured with the Carr-Purcell-Meiboom-Gill (CPMG) method. The internal-gradient-pore-size distributions correlation maps were obtained for water in packs of glass beads with different diameter and in a sandstone sample. The relationship between internal gradients and pore structure is analyzed in detail by considering the restricted diffusion of fluids in porous samples. For each case diffusion regimes are assigned by plotting normalized CPMG data and comparing the diffusion lengths, the dephasing lengths and pore diameters. In the free-diffusion limit, the correlation maps reveal the true relationship between pore structure and internal gradients so that Δχ can be approximated from the correlation maps. This limit is met most easily at low field. It provides information about porous media, which is expected to benefit the oil industry, in particular NMR well logging. PMID:27111138

  2. Estimating the 3D pore size distribution of biopolymer networks from directionally biased data.

    PubMed

    Lang, Nadine R; Münster, Stefan; Metzner, Claus; Krauss, Patrick; Schürmann, Sebastian; Lange, Janina; Aifantis, Katerina E; Friedrich, Oliver; Fabry, Ben

    2013-11-01

    The pore size of biopolymer networks governs their mechanical properties and strongly impacts the behavior of embedded cells. Confocal reflection microscopy and second harmonic generation microscopy are widely used to image biopolymer networks; however, both techniques fail to resolve vertically oriented fibers. Here, we describe how such directionally biased data can be used to estimate the network pore size. We first determine the distribution of distances from random points in the fluid phase to the nearest fiber. This distribution follows a Rayleigh distribution, regardless of isotropy and data bias, and is fully described by a single parameter--the characteristic pore size of the network. The bias of the pore size estimate due to the missing fibers can be corrected by multiplication with the square root of the visible network fraction. We experimentally verify the validity of this approach by comparing our estimates with data obtained using confocal fluorescence microscopy, which represents the full structure of the network. As an important application, we investigate the pore size dependence of collagen and fibrin networks on protein concentration. We find that the pore size decreases with the square root of the concentration, consistent with a total fiber length that scales linearly with concentration. PMID:24209841

  3. Influence of pore size distribution on the adsorption of phenol on PET-based activated carbons.

    PubMed

    Lorenc-Grabowska, Ewa; Diez, María A; Gryglewicz, Grazyna

    2016-05-01

    The role of pore size distribution in the adsorption of phenol in aqueous solutions on polyethylene terephthalate (PET)-based activated carbons (ACs) has been analyzed. The ACs were prepared from PET and mixtures of PET with coal-tar pitch (CTP) by means of carbonization and subsequent steam and carbon dioxide activation at 850 and 950 °C, respectively. The resultant ACs were characterized on the basis of similarities in their surface chemical features and differences in their micropore size distributions. The adsorption of phenol was carried out in static conditions at ambient temperature. The pseudo-second order kinetic model and Langmuir model were found to fit the experimental data very well. The different adsorption capacities of the ACs towards phenol were attributed to differences in their micropore size distributions. Adsorption capacity was favoured by the volume of pores with a size smaller than 1.4 nm; but restricted by pores smaller than 0.8 nm. PMID:26890386

  4. Synthesis and characterization of mesoporous ZnS with narrow size distribution of small pores

    NASA Astrophysics Data System (ADS)

    Nistor, L. C.; Mateescu, C. D.; Birjega, R.; Nistor, S. V.

    2008-08-01

    Pure, nanocrystalline cubic ZnS forming a stable mesoporous structure was synthesized at room temperature by a non-toxic surfactant-assisted liquid liquid reaction, in the 9.5 10.5 pH range of values. The appearance of an X-ray diffraction (XRD) peak in the region of very small angles (˜ 2°) reveals the presence of a porous material with a narrow pore size distribution, but with an irregular arrangement of the pores, a so-called worm hole or sponge-like material. The analysis of the wide angle XRD diffractograms shows the building blocks to be ZnS nanocrystals with cubic structure and average diameter of 2 nm. Transmission electron microscopy (TEM) investigations confirm the XRD results; ZnS crystallites of 2.5 nm with cubic (blende) structure are the building blocks of the pore walls with pore sizes from 1.9 to 2.5 nm, and a broader size distribution for samples with smaller pores. Textural measurements (N2 adsorption desorption isotherms) confirm the presence of mesoporous ZnS with a narrow range of small pore sizes. The relatively lower surface area of around 100 m2/g is attributed to some remaining organic molecules, which are filling the smallest pores. Their presence, confirmed by IR spectroscopy, seems to be responsible for the high stability of the resulting mesoporous ZnS as well.

  5. A thermal porosimetry method to estimate pore size distribution in highly porous insulating materials.

    PubMed

    Félix, V; Jannot, Y; Degiovanni, A

    2012-05-01

    Standard pore size determination methods such as mercury porosimetry, nitrogen sorption, microscopy, or x-ray tomography are not always applicable to highly porous, low density, and thus very fragile materials. For this kind of materials, a method based on thermal characterization is proposed. Indeed, the thermal conductivity of a highly porous and insulating medium is significantly dependent on the thermal conductivity of the interstitial gas that depends on both gas pressure and size of the considered pore (Knudsen effect). It is also possible to link the pore size with the thermal conductivity of the medium. Thermal conductivity measurements are realized on specimens placed in an enclosure where the air pressure is successively set to different values varying from 10(-1) to 10(5) Pa. Knowing the global porosity ratio, an effective thermal conductivity model for a two-phase air-solid material based on a combined serial-parallel model is established. Pore size distribution can be identified by minimizing the sum of the quadratic differences between measured values and modeled ones. The results of the estimation process are the volume fractions of the chosen ranges of pore size. In order to validate the method, measurements done on insulating materials are presented. The results are discussed and show that pore size distribution estimated by the proposed method is coherent. PMID:22667640

  6. A thermal porosimetry method to estimate pore size distribution in highly porous insulating materials

    NASA Astrophysics Data System (ADS)

    Félix, V.; Jannot, Y.; Degiovanni, A.

    2012-05-01

    Standard pore size determination methods such as mercury porosimetry, nitrogen sorption, microscopy, or x-ray tomography are not always applicable to highly porous, low density, and thus very fragile materials. For this kind of materials, a method based on thermal characterization is proposed. Indeed, the thermal conductivity of a highly porous and insulating medium is significantly dependent on the thermal conductivity of the interstitial gas that depends on both gas pressure and size of the considered pore (Knudsen effect). It is also possible to link the pore size with the thermal conductivity of the medium. Thermal conductivity measurements are realized on specimens placed in an enclosure where the air pressure is successively set to different values varying from 10-1 to 105 Pa. Knowing the global porosity ratio, an effective thermal conductivity model for a two-phase air-solid material based on a combined serial-parallel model is established. Pore size distribution can be identified by minimizing the sum of the quadratic differences between measured values and modeled ones. The results of the estimation process are the volume fractions of the chosen ranges of pore size. In order to validate the method, measurements done on insulating materials are presented. The results are discussed and show that pore size distribution estimated by the proposed method is coherent.

  7. A thermal porosimetry method to estimate pore size distribution in highly porous insulating materials

    SciTech Connect

    Felix, V.; Jannot, Y.; Degiovanni, A.

    2012-05-15

    Standard pore size determination methods such as mercury porosimetry, nitrogen sorption, microscopy, or x-ray tomography are not always applicable to highly porous, low density, and thus very fragile materials. For this kind of materials, a method based on thermal characterization is proposed. Indeed, the thermal conductivity of a highly porous and insulating medium is significantly dependent on the thermal conductivity of the interstitial gas that depends on both gas pressure and size of the considered pore (Knudsen effect). It is also possible to link the pore size with the thermal conductivity of the medium. Thermal conductivity measurements are realized on specimens placed in an enclosure where the air pressure is successively set to different values varying from 10{sup -1} to 10{sup 5} Pa. Knowing the global porosity ratio, an effective thermal conductivity model for a two-phase air-solid material based on a combined serial-parallel model is established. Pore size distribution can be identified by minimizing the sum of the quadratic differences between measured values and modeled ones. The results of the estimation process are the volume fractions of the chosen ranges of pore size. In order to validate the method, measurements done on insulating materials are presented. The results are discussed and show that pore size distribution estimated by the proposed method is coherent.

  8. New general pore size distribution model by classical thermodynamics application: Activated carbon

    USGS Publications Warehouse

    Lordgooei, M.; Rood, M.J.; Rostam-Abadi, M.

    2001-01-01

    A model is developed using classical thermodynamics to characterize pore size distributions (PSDs) of materials containing micropores and mesopores. The thermal equation of equilibrium adsorption (TEEA) is used to provide thermodynamic properties and relate the relative pore filling pressure of vapors to the characteristic pore energies of the adsorbent/adsorbate system for micropore sizes. Pore characteristic energies are calculated by averaging of interaction energies between adsorbate molecules and adsorbent pore walls as well as considering adsorbate-adsorbate interactions. A modified Kelvin equation is used to characterize mesopore sizes by considering variation of the adsorbate surface tension and by excluding the adsorbed film layer for the pore size. The modified-Kelvin equation provides similar pore filling pressures as predicted by density functional theory. Combination of these models provides a complete PSD of the adsorbent for the micropores and mesopores. The resulting PSD is compared with the PSDs from Jaroniec and Choma and Horvath and Kawazoe models as well as a first-order approximation model using Polanyi theory. The major importance of this model is its basis on classical thermodynamic properties, less simplifying assumptions in its derivation compared to other methods, and ease of use.

  9. The effect of magnetic particles on pore size distribution in soft polyurethane foams

    NASA Astrophysics Data System (ADS)

    Schümann, M.; Günther, S.; Odenbach, S.

    2014-07-01

    The combination of elastomeric matrices with magnetic particles to obtain magnetically controllable hybrid materials is an actual field of intense research. An important aspect in this context is the stiffness of the matrix, which determines the effectiveness of the magnetically driven changes in the material properties. In this paper an approach has been undertaken to use soft polyurethane foams as matrix material. By means of x-ray computed microtomography and digital image processing the pore size distribution has been determined to get information on how this distribution is affected by the introduction of magnetic microparticles. To do so, 20 000 to 40 000 pores per foam sample were evaluated. As a result, it could be proven that the pore sizes of the analysed foams clearly obey the Weibull distribution. Increasing the carbonyl iron particle concentrations leads to a decrement of the shape parameter of the distribution. Based on known particle stabilization mechanisms, an approach to explain the experimental results is proposed.

  10. Direct correlation of diffusion and pore size distributions with low field NMR

    NASA Astrophysics Data System (ADS)

    Zhang, Yan; Xiao, Lizhi; Liao, Guangzhi; Song, Yi-Qiao

    2016-08-01

    The time-dependent diffusion coefficient (D) is a powerful tool to probe microstructure in porous media, and can be obtained by the NMR method. In a real porous sample, molecular diffusion is very complex. Here we present a new method which directly measures the relationship between effective diffusion coefficients and pore size distributions without knowing surface relaxivity. This method is used to extract structural information and explore the relationship between D and a in porous media having broad pore size distributions. The diffusion information is encoded by the Pulsed Field Gradient (PFG) method and the pore size distributions are acquired by the Decay due to Diffusion in the Internal Field (DDIF) method. Two model samples were measured to verify this method. Restricted diffusion was analyzed, and shows that most fluid molecules experience pore wall. The D(a) curves obtained from correlation maps were fitted to the Padé approximant equation and a good agreement was found between the fitting lines and the measured data. Then a sandstone sample with unknown structure was measured. The state of confined fluids was analyzed and structural information, such as pore size distributions, were extracted. The D - T1 correlation maps were also obtained using the same method, which yielded surface relaxivities for different samples. All the experiments were conducted on 2 MHz NMR equipment to obtain accurate diffusion information, where internal gradients can be neglected. This method is expected to have useful applications in the oil industry, particularly for NMR logging in the future.

  11. Direct correlation of diffusion and pore size distributions with low field NMR.

    PubMed

    Zhang, Yan; Xiao, Lizhi; Liao, Guangzhi; Song, Yi-Qiao

    2016-08-01

    The time-dependent diffusion coefficient (D) is a powerful tool to probe microstructure in porous media, and can be obtained by the NMR method. In a real porous sample, molecular diffusion is very complex. Here we present a new method which directly measures the relationship between effective diffusion coefficients and pore size distributions without knowing surface relaxivity. This method is used to extract structural information and explore the relationship between D and a in porous media having broad pore size distributions. The diffusion information is encoded by the Pulsed Field Gradient (PFG) method and the pore size distributions are acquired by the Decay due to Diffusion in the Internal Field (DDIF) method. Two model samples were measured to verify this method. Restricted diffusion was analyzed, and shows that most fluid molecules experience pore wall. The D(a) curves obtained from correlation maps were fitted to the Padé approximant equation and a good agreement was found between the fitting lines and the measured data. Then a sandstone sample with unknown structure was measured. The state of confined fluids was analyzed and structural information, such as pore size distributions, were extracted. The D - T1 correlation maps were also obtained using the same method, which yielded surface relaxivities for different samples. All the experiments were conducted on 2MHz NMR equipment to obtain accurate diffusion information, where internal gradients can be neglected. This method is expected to have useful applications in the oil industry, particularly for NMR logging in the future. PMID:27371788

  12. Modeling of the lithium-air battery cathodes with broad pore size distribution

    NASA Astrophysics Data System (ADS)

    Sergeev, Artem V.; Chertovich, Alexander V.; Itkis, Daniil M.

    2016-09-01

    Achieving theoretical promises of 1000 W h/kg specific energy for lithium-air batteries is quite challenging due to limited transport in the cathode along with electrode passivation. Transport can be enhanced in the electrodes with complex hierarchical pore architecture. Here, using computer simulations we analyze the effects of cathode pore size distribution (PSD) on capacity and discharge curve shape. Calculations considering a broad PSD revealed that even small discharge product resistivity prevents larger pores from accumulating the discharge product and thus turning them into non-clogging oxygen supply channels. Thus optimization of cathode architecture by adding of large-scale cavities enables cell capacity enhancement.

  13. Strategies for Tailoring the Pore-Size Distribution of Virus Retention Filter Papers.

    PubMed

    Gustafsson, Simon; Mihranyan, Albert

    2016-06-01

    The goal of this work is to demonstrate how the pore-size distribution of the nanocellulose-based virus-retentive filter can be tailored. The filter paper was produced using cellulose nanofibers derived from Cladophora sp. green algae using the hot-press drying at varying drying temperatures. The produced filters were characterized using scanning electron microscopy, atomic force microscopy, and N2 gas sorption analysis. Further, hydraulic permeability and retention efficiency toward surrogate 20 nm model particles (fluorescent carboxylate-modified polystyrene spheres) were assessed. It was shown that by controlling the rate of water evaporation during hot-press drying the pore-size distribution can be precisely tailored in the region between 10 and 25 nm. The mechanism of pore formation and critical parameters are discussed in detail. The results are highly valuable for development of advanced separation media, especially for virus-retentive size-exclusion filtration. PMID:27144657

  14. Strategies for Tailoring the Pore-Size Distribution of Virus Retention Filter Papers.

    PubMed

    Gustafsson, Simon; Mihranyan, Albert

    2016-06-01

    The goal of this work is to demonstrate how the pore-size distribution of the nanocellulose-based virus-retentive filter can be tailored. The filter paper was produced using cellulose nanofibers derived from Cladophora sp. green algae using the hot-press drying at varying drying temperatures. The produced filters were characterized using scanning electron microscopy, atomic force microscopy, and N2 gas sorption analysis. Further, hydraulic permeability and retention efficiency toward surrogate 20 nm model particles (fluorescent carboxylate-modified polystyrene spheres) were assessed. It was shown that by controlling the rate of water evaporation during hot-press drying the pore-size distribution can be precisely tailored in the region between 10 and 25 nm. The mechanism of pore formation and critical parameters are discussed in detail. The results are highly valuable for development of advanced separation media, especially for virus-retentive size-exclusion filtration.

  15. Xenon porometry: a novel method for the derivation of pore size distributions.

    PubMed

    Telkki, Ville-Veikko; Lounila, Juhani; Jokisaari, Jukka

    2007-05-01

    Xenon porometry is a novel method used for characterizing porous materials by the (129)Xe nuclear magnetic resonance of xenon gas. With the method, the diffusion of gas is slowed down by immersing the material in a medium, which can be in liquid or solid state during measurements. Because of slow diffusion, the signal of a xenon atom is characteristic of the properties of only one pore, and the composite signal of all atoms represents the distribution of properties. The method is especially applicable for determining pore size distribution because the chemical shifts of two different xenon signals (one from liquid and the other from gas pockets in solid) are dependent on pore size. Therefore, the shapes of these signals represent pore size distribution function. In addition, the porosity of the material can be determined by comparing the intensities of two signals. This article focuses on describing xenon signals observed from gas pockets in a solid medium, which has turned out to be most convenient for pore size determination. PMID:17466763

  16. Pore size distribution and supercritical hydrogen adsorption in activated carbon fibers.

    PubMed

    Purewal, J J; Kabbour, H; Vajo, J J; Ahn, C C; Fultz, B

    2009-05-20

    Pore size distributions (PSD) and supercritical H2 isotherms have been measured for two activated carbon fiber (ACF) samples. The surface area and the PSD both depend on the degree of activation to which the ACF has been exposed. The low-surface-area ACF has a narrow PSD centered at 0.5 nm, while the high-surface-area ACF has a broad distribution of pore widths between 0.5 and 2 nm. The H2 adsorption enthalpy in the zero-coverage limit depends on the relative abundance of the smallest pores relative to the larger pores. Measurements of the H2 isosteric adsorption enthalpy indicate the presence of energy heterogeneity in both ACF samples. Additional measurements on a microporous, coconut-derived activated carbon are presented for reference.

  17. A Model for Hydraulic Properties Based on Angular Pores with Lognormal Size Distribution

    NASA Astrophysics Data System (ADS)

    Durner, W.; Diamantopoulos, E.

    2014-12-01

    Soil water retention and unsaturated hydraulic conductivity curves are mandatory for modeling water flow in soils. It is a common approach to measure few points of the water retention curve and to calculate the hydraulic conductivity curve by assuming that the soil can be represented as a bundle of capillary tubes. Both curves are then used to predict water flow at larger spatial scales. However, the predictive power of these curves is often very limited. This can be very easily illustrated if we measure the soil hydraulic properties (SHPs) for a drainage experiment and then use these properties to predict the water flow in the case of imbibition. Further complications arise from the incomplete wetting of water at the solid matrix which results in finite values of the contact angles between the solid-water-air interfaces. To address these problems we present a physically-based model for hysteretic SHPs. This model is based on bundles of angular pores. Hysteresis for individual pores is caused by (i) different snap-off pressures during filling and emptying of single angular pores and (ii) by different advancing and receding contact angles for fluids that are not perfectly wettable. We derive a model of hydraulic conductivity as a function of contact angle by assuming flow perpendicular to pore cross sections and present closed-form expressions for both the sample scale water retention and hydraulic conductivity function by assuming a log-normal statistical distribution of pore size. We tested the new model against drainage and imbibition experiments for various sandy materials which were conducted with various liquids of differing wettability. The model described both imbibition and drainage experiments very well by assuming a unique pore size distribution of the sample and a zero contact angle for the perfectly wetting liquid. Eventually, we see the possibility to relate the particle size distribution with a model which describes the SHPs.

  18. A facile method to determine pore size distribution in porous scaffold by using image processing.

    PubMed

    Lo Re, G; Lopresti, F; Petrucci, G; Scaffaro, R

    2015-09-01

    Image processing permits scientists to investigate morphological properties of three-dimensional structures starting from their bi-dimensional gray-scale representation. In many cases porous structure with complex architecture has to be designed in order to attempt specific properties such in the case of scaffold for tissue engineering. Traditional morphological characterization, like scanning electron microscopy, should be coupled with quantitative information such as pore size distribution (PSD) in order to get a deeper understanding of the influence of the porous structure on tissue regeneration processes and on other related applications, it is remarkable to study a quantitative analysis of porosity and of pores dimension. In this work it was developed as a software able to accomplish the segmentation of images containing pores of any geometry in a semi-automatic way with the aim to measure the PSD. Case study constituted by PLA porous scaffolds with different pore size was adopted. Results indicate that image processing methods well fit the pore size features of PLA scaffolds, overcoming the limits of the more invasive porosimetry techniques. PMID:26026425

  19. A solid with a hierarchical tetramodal micro-meso-macro pore size distribution

    PubMed Central

    Ren, Yu; Ma, Zhen; Morris, Russell E.; Liu, Zheng; Jiao, Feng; Dai, Sheng; Bruce, Peter G.

    2013-01-01

    Porous solids have an important role in addressing some of the major energy-related problems facing society. Here we describe a porous solid, α-MnO2, with a hierarchical tetramodal pore size distribution spanning the micro-, meso- and macro pore range, centred at 0.48, 4.0, 18 and 70 nm. The hierarchical tetramodal structure is generated by the presence of potassium ions in the precursor solution within the channels of the porous silica template; the size of the potassium ion templates the microporosity of α-MnO2, whereas their reactivity with silica leads to larger mesopores and macroporosity, without destroying the mesostructure of the template. The hierarchical tetramodal pore size distribution influences the properties of α-MnO2 as a cathode in lithium batteries and as a catalyst, changing the behaviour, compared with its counterparts with only micropores or bimodal micro/mesopores. The approach has been extended to the preparation of LiMn2O4 with a hierarchical pore structure. PMID:23764887

  20. Nondestructive technique for the characterization of the pore size distribution of soft porous constructs for tissue engineering.

    PubMed

    Safinia, Laleh; Mantalaris, Athanasios; Bismarck, Alexander

    2006-03-28

    Polymer scaffolds tailored for tissue engineering applications possessing the desired pore structure require reproducible fabrication techniques. Nondestructive, quantitative methods for pore characterization are required to determine the pore size and its distribution. In this study, a promising alternative to traditional pore size characterization techniques is presented. We introduce a quantitative, nondestructive and inexpensive method to determine the pore size distribution of large soft porous solids based on the on the displacement of a liquid, that spreads without limits though a porous medium, by nitrogen. The capillary pressure is measured and related to the pore sizes as well as the pore size distribution of the narrowest bottlenecks of the largest interconnected pores in a porous medium. The measured pore diameters correspond to the narrowest bottleneck of the largest pores connecting the bottom with the top surface of a given porous solid. The applicability and reproducibility of the breakthrough technique is demonstrated on two polyurethane foams, manufactured using the thermally induced phase separation (TIPS) process, with almost identical overall porosity (60-70%) but very different pore morphology. By selecting different quenching temperatures to induce polymer phase separation, the pore structure could be regulated while maintaining the overall porosity. Depending on the quenching temperature, the foams exhibited either longitudinally oriented tubular macropores interconnected with micropores or independent macropores connected to adjacent pores via openings in the pore walls. The pore size and its distribution obtained by the breakthrough test were in excellent agreement to conventional characterization techniques, such as scanning electron microscopy combined with image analysis, BET technique, and mercury intrusion porosimetry. This technique is suitable for the characterization of the micro- and macropore structure of soft porous solids

  1. Design of nanoporous metals with bimodal pore size distributions for enhanced biosensing

    NASA Astrophysics Data System (ADS)

    Qiu, Huajun; Dong, Xiaochen; Huang, Xirong

    2012-07-01

    Nanoporous gold (np-Au) has shown great potential in catalysis, plasmonics, sensing, etc. In this work, by two-step dealloying a well-designed AuAgAl ternary precursor alloy, np-Au with bimodal ligament/pore size distributions is successfully fabricated. The first dealloying in HCl solution removes Al and generates a nanoporous AuAg alloy which would be mildly annealed at 200 °C for 30 min to homogenize the alloy ligament and enlarge the ligament/pore size. Next, the nanoporous AuAg alloy is further dealloyed in a HNO3 solution to etch Ag and fabricate np-Au with a hierarchical microstructure. This novel bimodal np-Au is demonstrated to exhibit enhanced electrocatalytic activity towards H2O2 reduction and be a better support for the fabrication of an oxidase-based biosensor compared with normal np-Au, with a uniform pore/ligament size of 30-40 nm. In a proof-of-concept study, a sensitive glucose biosensor with a linear range up to 21 mM is fabricated by immobilization of glucose oxidase on the bimodal np-Au.Nanoporous gold (np-Au) has shown great potential in catalysis, plasmonics, sensing, etc. In this work, by two-step dealloying a well-designed AuAgAl ternary precursor alloy, np-Au with bimodal ligament/pore size distributions is successfully fabricated. The first dealloying in HCl solution removes Al and generates a nanoporous AuAg alloy which would be mildly annealed at 200 °C for 30 min to homogenize the alloy ligament and enlarge the ligament/pore size. Next, the nanoporous AuAg alloy is further dealloyed in a HNO3 solution to etch Ag and fabricate np-Au with a hierarchical microstructure. This novel bimodal np-Au is demonstrated to exhibit enhanced electrocatalytic activity towards H2O2 reduction and be a better support for the fabrication of an oxidase-based biosensor compared with normal np-Au, with a uniform pore/ligament size of 30-40 nm. In a proof-of-concept study, a sensitive glucose biosensor with a linear range up to 21 mM is fabricated by

  2. Importance of Pore Size Distribution of Fine-grained Sediments on Gas Hydrate Equilibrium

    NASA Astrophysics Data System (ADS)

    Kwon, T. H.; Kim, H. S.; Cho, G. C.; Park, T. H.

    2015-12-01

    Gas hydrates have been considered as a new source of natural gases. For the gas hydrate production, the gas hydrate reservoir should be depressurized below the equilibrium pressure of gas hydrates. Therefore, it is important to predict the equilibrium of gas hydrates in the reservoir conditions because it can be affected by the pore size of the host sediments due to the capillary effect. In this study, gas hydrates were synthesized in fine-grained sediment samples including a pure silt sample and a natural clayey silt sample cored from a hydrate occurrence region in Ulleung Basin, East Sea, offshore Korea. Pore size distributions of the samples were obtained by the nitrogen adsorption and desorption test and the mercury intrusion porosimetry. The equilibrium curve of gas hydrates in the fine-grained sediments were found to be significantly influenced by the clay fraction and the corresponding small pores (>50 nm in diameter). For the clayey silt sample, the equilibrium pressure was higher by ~1.4 MPa than the bulk equilibrium pressure. In most cases of oceanic gas hydrate reservoirs, sandy layers are found interbedded with fine-grained sediment layers while gas hydrates are intensively accumulated in the sandy layers. Our experiment results reveal the inhibition effect of fine-grained sediments against gas hydrate formation, in which greater driving forces (e.g., higher pressure or lower temperature) are required during natural gas migration. Therefore, gas hydrate distribution in interbedded layers of sandy and fine-grained sediments can be explained by such capillary effect induced by the pore size distribution of host sediments.

  3. Permeability-Selectivity Analysis of Microfiltration and Ultrafiltration Membranes: Effect of Pore Size and Shape Distribution and Membrane Stretching.

    PubMed

    Siddiqui, Muhammad Usama; Arif, Abul Fazal Muhammad; Bashmal, Salem

    2016-01-01

    We present a modeling approach to determine the permeability-selectivity tradeoff for microfiltration and ultrafiltration membranes with a distribution of pore sizes and pore shapes. Using the formulated permeability-selectivity model, the effect of pore aspect ratio and pore size distribution on the permeability-selectivity tradeoff of the membrane is analyzed. A finite element model is developed to study the effect of membrane stretching on the distribution of pore sizes and shapes in the stretched membrane. The effect of membrane stretching on the permeability-selectivity tradeoff of membranes is also analyzed. The results show that increasing pore aspect ratio improves membrane performance while increasing the width of pore size distribution deteriorates the performance. It was also found that the effect of membrane stretching on the permeability-selectivity tradeoff is greatly affected by the uniformity of pore distribution in the membrane. Stretching showed a positive shift in the permeability-selectivity tradeoff curve of membranes with well-dispersed pores while in the case of pore clustering, a negative shift in the permeability-selectivity tradeoff curve was observed. PMID:27509528

  4. Permeability-Selectivity Analysis of Microfiltration and Ultrafiltration Membranes: Effect of Pore Size and Shape Distribution and Membrane Stretching

    PubMed Central

    Siddiqui, Muhammad Usama; Arif, Abul Fazal Muhammad; Bashmal, Salem

    2016-01-01

    We present a modeling approach to determine the permeability-selectivity tradeoff for microfiltration and ultrafiltration membranes with a distribution of pore sizes and pore shapes. Using the formulated permeability-selectivity model, the effect of pore aspect ratio and pore size distribution on the permeability-selectivity tradeoff of the membrane is analyzed. A finite element model is developed to study the effect of membrane stretching on the distribution of pore sizes and shapes in the stretched membrane. The effect of membrane stretching on the permeability-selectivity tradeoff of membranes is also analyzed. The results show that increasing pore aspect ratio improves membrane performance while increasing the width of pore size distribution deteriorates the performance. It was also found that the effect of membrane stretching on the permeability-selectivity tradeoff is greatly affected by the uniformity of pore distribution in the membrane. Stretching showed a positive shift in the permeability-selectivity tradeoff curve of membranes with well-dispersed pores while in the case of pore clustering, a negative shift in the permeability-selectivity tradeoff curve was observed. PMID:27509528

  5. Multiscale characterization of pore size distributions using mercury porosimetry and nitrogen adsorption

    NASA Astrophysics Data System (ADS)

    Paz-Ferreiro, J.; Tarquis, A. M.; Miranda, J. G. V.; Vidal Vázquez, E.

    2009-04-01

    The soil pore space is a continuum extremely variable in size, including structures smaller than nanometres and as large as macropores or cracks with millimetres or even centimetres size. Pore size distributions (PSDs) affects important soil functions, such as those related with transmission and storage of water, and root growth. Direct and indirect measurements of PSDs are becoming increasingly used to characterize soil structure. Mercury injection porosimetry and nitrogen adsorption isotherms are techniques commonly employed for assessing equivalent pore size diameters in the range from about 50 nm to 100 m and 2 to 500 nm, respectively. The multifractal formalism was used to describe Hg injection curves and N2 adsorption isotherms from two series of a Mollisol cultivated under no tillage and minimum tillage. Soil samples were taken from 0-10, 10-20 and 20-30 cm depths in two experimental fields located in the north of Buenos Aires and South of Santa Fe provinces, Argentina. All the data sets analyzed from the two studied soil attributes showed remarkably good scaling trends as assessed by singularity spectrum and generalized dimension spectrum. Both, experimental Hg injection curves and N2 adsorption isotherms could be fitted reasonably well with multifractal models. A wide variety of singularity and generalized dimension spectra was found for the variables. The capacity dimensions, D0, for both Hg injection and N2 adsorption data were not significantly different from the Euclidean dimension. However, the entropy dimension, D1, and correlation dimension, D2, obtained from mercury injection and nitrogen adsorption data showed significant differences. So, D1 values were on average 0.868 and varied from 0.787 to 0.925 for Hg intrusion curves. Entropy dimension, D1, values for N2 adsorption isotherms were on average 0.582 significantly lower than those obtained when using the former technique. Twenty-three out of twenty-four N2 isotherms had D1 values in a

  6. Pore-size distributions of cationic polyacrylamide hydrogels varying in initial monomer concentration and cross-linker/monomer ratio

    SciTech Connect

    Kremer, M.; Pothmann, E.; Roessler, T.; Baker, J.; Yee, A.; Blanch, H.; Prausnitz, J.M. )

    1994-05-23

    Pore-size distributions have been measured for cationic acrylamide-based hydrogels. The authors use the experimental mixed-solute-exclusion method, MSE (introduced by Kuga), to obtain the solute-exclusion curve representing the amount of imbibed liquid inside the gel inaccessible for a solute of radius r. The authors use the Brownian motion model (developed by Cassasa) to convert the size-exclusion curve into the pore-size distribution, which gives the frequency of pore radius R as a function of R. This theoretically-based interpretation of MSE data leads to the Fredholm integral equation that they solve numerically. Results are reported for a series of hydrogels containing acrylamide and 3% MAPTAC; the hydrogels differed in extent of cross-linking and/or initial concentration of monomer. Pore-size distributions shift to lower pore sizes with rising initial monomer concentration and with rising cross-linker-to-monomer ratio.

  7. Pore Size Distributions Inferred from Modified Inversion Percolation Modeling of Drainage Curves

    NASA Astrophysics Data System (ADS)

    Dralus, D. E.; Wang, H. F.; Strand, T. E.; Glass, R. J.; Detwiler, R. L.

    2005-12-01

    Experiments have been conducted of drainage in sand packs. At equilibrium, the interface between the fluids forms a saturation transition fringe where the saturation decreases monotonically with height. This behavior was observed in a 1-inch thick pack of 20-30 sand contained front and back within two thin, 12-inch-by-24-inch glass plates. The translucent chamber was illuminated from behind by a bank of fluorescent bulbs. Acquired data were in the form of images captured by a CCD camera with resolution on the grain scale. The measured intensity of the transmitted light was used to calculate the average saturation at each point in the chamber. This study used a modified invasion percolation (MIP) model to simulate the drainage experiments to evaluate the relationship between the saturation-versus-height curve at equilibrium and the pore size distribution associated with the granular medium. The simplest interpretation of a drainage curve is in terms of a distribution of capillary tubes whose radii reproduce the the observed distribution of rise heights. However, this apparent radius distribution obtained from direct inversion of the saturation profile did not yield the assumed radius distribution. Further investigation demonstrated that the equilibrium height distribution is controlled primarily by the Bond number (ratio of gravity to capillary forces) with some influence from the width of the pore radius distribution. The width of the equilibrium fringe is quantified in terms of the ratio of Bond number to the standard deviation of the pore throat distribution. The normalized saturation-vs-height curves exhibit a power-law scaling behavior consistent with both Brooks-Corey and Van Genuchten type curves. Fundamental tenets of percolation theory were used to quantify the relationship between the apparent and actual radius distributions as a function of the mean coordination number and of the ratio of Bond number to standard deviation, which was supported by both MIP

  8. Pore size distribution and methane equilibrium conditions at Walker Ridge Block 313, northern Gulf of Mexico

    SciTech Connect

    Bihani, Abhishek; Daigle, Hugh; Cook, Ann; Glosser, Deborah; Shushtarian, Arash

    2015-12-15

    Coexistence of three methane phases (liquid (L), gas (G), hydrate (H)) in marine gas hydrate systems may occur according to in-situ pressure, temperature, salinity and pore size. In sediments with salinity close to seawater, a discrete zone of three-phase (3P) equilibrium may occur near the base of the regional hydrate stability zone (RHSZ) due to capillary effects. The existence of a 3P zone influences the location of the bottom-simulating reflection (BSR) and has implications for methane fluxes at the base of the RHSZ. We studied hydrate stability conditions in two wells, WR313-G and WR313-H, at Walker Ridge Block 313 in the northern Gulf of Mexico. We determined pore size distributions (PSD) by constructing a synthetic nuclear magnetic resonance (NMR) relaxation time distribution. Correlations were obtained by non-linear regression on NMR, gamma ray, and bulk density logs from well KC-151 at Keathley Canyon. The correlations enabled construction of relaxation time distributions for WR313-G and WR313-H, which were used to predict PSD through comparison with mercury injection capillary pressure measurements. With the computed PSD, L+H and L+G methane solubility was determined from in-situ pressure and temperature. The intersection of the L+G and L+H curves for various pore sizes allowed calculation of the depth range of the 3P equilibrium zone. As in previous studies at Blake Ridge and Hydrate Ridge, the top of the 3P zone moves upwards with increasing water depth and overlies the bulk 3P equilibrium depth. In clays at Walker Ridge, the predicted thickness of the 3P zone is approximately 35 m, but in coarse sands it is only a few meters due to the difference in absolute pore sizes and the width of the PSD. The thick 3P zone in the clays may explain in part why the BSR is only observed in the sand layers at Walker Ridge, although other factors may influence the presence or absence of a BSR.

  9. Pore Size Distribution and Methane Equilibrium Conditions at Walker Ridge Block 313, Northern Gulf of Mexico

    NASA Astrophysics Data System (ADS)

    Bihani, A. D.; Daigle, H.; Cook, A.; Glosser, D.; Shushtarian, A.

    2015-12-01

    Coexistence of three methane phases (liquid (L), gas (G), hydrate (H)) in marine gas hydrate systems may occur according to in-situ pressure, temperature, salinity and pore size. In sediments with salinity close to seawater, a discrete zone of three-phase (3P) equilibrium may occur near the base of the regional hydrate stability zone (RHSZ) due to capillary effects. The existence of a 3P zone influences the location of the bottom-simulating reflection (BSR) and has implications for methane fluxes at the base of the RHSZ. We studied hydrate stability conditions in two wells, WR313-G and WR313-H, at Walker Ridge Block 313 in the northern Gulf of Mexico. We determined pore size distributions (PSD) by constructing a synthetic nuclear magnetic resonance (NMR) relaxation time distribution. Correlations were obtained by non-linear regression on NMR, gamma ray, and bulk density logs from well KC-151 at Keathley Canyon. The correlations enabled construction of relaxation time distributions for WR313-G and WR313-H, which were used to predict PSD through comparison with mercury injection capillary pressure measurements. With the computed PSD, L+H and L+G methane solubility was determined from in-situ pressure and temperature. The intersection of the L+G and L+H curves for various pore sizes allowed calculation of the depth range of the 3P equilibrium zone. As in previous studies at Blake Ridge and Hydrate Ridge, the top of the 3P zone moves upwards with increasing water depth and overlies the bulk 3P equilibrium depth. In clays at Walker Ridge, the predicted thickness of the 3P zone is approximately 35 m, but in coarse sands it is only a few meters due to the difference in absolute pore sizes and the width of the PSD. The thick 3P zone in the clays may explain in part why the BSR is only observed in the sand layers at Walker Ridge, although other factors may influence the presence or absence of a BSR.

  10. The investigation of gadolinium oxide porous structure and refinement of the pore size distribution based on the NLDFT-models

    NASA Astrophysics Data System (ADS)

    Mashkovtsev, Maxim A.; Botalov, Maxim S.; Smyshlyaev, Denis V.; Kasimova, Renata E.; Bereskina, Polina A.; Vereshchagin, Artem O.

    2016-09-01

    The study focuses on the characterization of gadolinium oxide surface by the method of low-temperature adsorption/desorption of nitrogen. The specific surface area of gadolinium oxide, the average pore diameter and fractal dimensions were determined. The refinement of the pore distribution was performed on the basis of the NLDFT model. It was shown that there were three kinds of pores with average sizes of 150, 300 and 600 Å.

  11. Pore size distribution of a deeply excavated Oxisol after 19 years reclamation

    NASA Astrophysics Data System (ADS)

    dos Santos Batista Bonini, Carolina; de Cássia Marchini, Débora; Alves, Marlene Cristina; García de Arruda, Otton; Paz-Ferreiro, Jorge

    2013-04-01

    Digging of the local soil and using it as a raw material for construction purposes has been identified as a non-negligible source of land degradation. Techniques aimed at soil profile reconstruction and ecological restoration of soils truncated by mechanical excavation using heavy machinery have been investigated Both, total soil porosity and pore size distribution are important properties for soil management as well as for assessing the recovery of soil function after land degradation. In this way, macropores are responsible for aeration, whereas water storage depends on soil meso- and micropores in the soil and the optimal pore-size distribution is also an indicator of soil quality. We investigated the changes in the pore size distribution of a soil that was beheaded to extract raw materials after a 19 year period of reclamation, which involved the use of green manures, gypsum and pasture for the purpose of profile recovery. The studied area is located in Mato Grosso do Sul State, Brzil. A field trial was performed following a completely randomized experimental design with seven treatments and four replications. Starting 1992, the initial treatments were: 1) control (tilled bare soil), 2)Stizolobium aterrium, 3)Cajanus cajan, 4)lime+S. aterrimum, 5) lime+C. cajan, 6) lime + gypsum + S. aterrimum, 7) lime + gypsum+C. cajan. In 1994, all treatments with C. cajan were replaced by Canavalia ensiformis and in 1999, Brachiaria decumbens was implanted in all the experimental plots. Data from vegetated treatments were compared with bare soil (control) and native vegetation (Savannah). Soil samples were collected in 2011 at the 0.00-0.10, 0.10-0.20, and 0.20-0.40 m depths. Treatment differences were assessed by analysis of variance, following the Scott-Knott test (5%) of probability to compare averages. Macroporosity of the 0.00-0.10 m top layer was above the 0.10 m3m-3 threshold considered as critical for plant growth. On the 0.10-0.20 m layer only treatments with C

  12. Pore size distribution analysis of activated carbons prepared from coconut shell using methane adsorption data

    NASA Astrophysics Data System (ADS)

    Ahmadpour, A.; Okhovat, A.; Darabi Mahboub, M. J.

    2013-06-01

    The application of Stoeckli theory to determine pore size distribution (PSD) of activated carbons using high pressure methane adsorption data is explored. Coconut shell was used as a raw material for the preparation of 16 different activated carbon samples. Four samples with higher methane adsorption were selected and nitrogen adsorption on these adsorbents was also investigated. Some differences are found between the PSD obtained from the analysis of nitrogen adsorption isotherms and their PSD resulting from the same analysis using methane adsorption data. It is suggested that these differences may arise from the specific interactions between nitrogen molecules and activated carbon surfaces; therefore caution is required in the interpretation of PSD obtained from the nitrogen isotherm data.

  13. Computer Simulation of Random Packings for Self-Similar Particle Size Distributions in Soil and Granular Materials: Porosity and Pore Size Distribution

    NASA Astrophysics Data System (ADS)

    Martín, Miguel Angel; Muñoz, Francisco J.; Reyes, Miguel; Taguas, F. Javier

    2014-09-01

    A 2D computer simulation method of random packings is applied to sets of particles generated by a self-similar uniparametric model for particle size distributions (PSDs) in granular media. The parameter p which controls the model is the proportion of mass of particles corresponding to the left half of the normalized size interval [0,1]. First the influence on the total porosity of the parameter p is analyzed and interpreted. It is shown that such parameter, and the fractal exponent of the associated power scaling, are efficient packing parameters, but this last one is not in the way predicted in a former published work addressing an analogous research in artificial granular materials. The total porosity reaches the minimum value for p = 0.6. Limited information on the pore size distribution is obtained from the packing simulations and by means of morphological analysis methods. Results show that the range of pore sizes increases for decreasing values of p showing also different shape in the volume pore size distribution. Further research including simulations with a greater number of particles and image resolution are required to obtain finer results on the hierarchical structure of pore space.

  14. Critical assessment of the pore size distribution in the rim region of high burnup UO2 fuels

    NASA Astrophysics Data System (ADS)

    Cappia, F.; Pizzocri, D.; Schubert, A.; Van Uffelen, P.; Paperini, G.; Pellottiero, D.; Macián-Juan, R.; Rondinella, V. V.

    2016-11-01

    A new methodology is introduced to analyse porosity data in the high burnup structure. Image analysis is coupled with the adaptive kernel density estimator to obtain a detailed characterisation of the pore size distribution, without a-priori assumption on the functional form of the distribution. Subsequently, stereological analysis is carried out. The method shows advantages compared to the classical approach based on the histogram in terms of detail in the description and accuracy within the experimental limits. Results are compared to the approximation of a log-normal distribution. In the investigated local burnup range (80-200 GWd/tHM), the agreement of the two approaches is satisfactory. From the obtained total pore density and mean pore diameter as a function of local burnup, pore coarsening is observed starting from ≈100 GWd/tHM, in agreement with a previous investigation.

  15. Application of SAXS and SANS in evaluation of porosity, pore size distribution and surface area of coal

    USGS Publications Warehouse

    Radlinski, A.P.; Mastalerz, Maria; Hinde, A.L.; Hainbuchner, M.; Rauch, H.; Baron, M.; Lin, J.S.; Fan, L.; Thiyagarajan, P.

    2004-01-01

    This paper discusses the applicability of small angle X-ray scattering (SAXS) and small angle neutron scattering (SANS) techniques for determining the porosity, pore size distribution and internal specific surface area in coals. The method is noninvasive, fast, inexpensive and does not require complex sample preparation. It uses coal grains of about 0.8 mm size mounted in standard pellets as used for petrographic studies. Assuming spherical pore geometry, the scattering data are converted into the pore size distribution in the size range 1 nm (10 A??) to 20 ??m (200,000 A??) in diameter, accounting for both open and closed pores. FTIR as well as SAXS and SANS data for seven samples of oriented whole coals and corresponding pellets with vitrinite reflectance (Ro) values in the range 0.55% to 5.15% are presented and analyzed. Our results demonstrate that pellets adequately represent the average microstructure of coal samples. The scattering data have been used to calculate the maximum surface area available for methane adsorption. Total porosity as percentage of sample volume is calculated and compared with worldwide trends. By demonstrating the applicability of SAXS and SANS techniques to determine the porosity, pore size distribution and surface area in coals, we provide a new and efficient tool, which can be used for any type of coal sample, from a thin slice to a representative sample of a thick seam. ?? 2004 Elsevier B.V. All rights reserved.

  16. Linking Intra-Aggregate Pore Size Distribution with Organic Matter Decomposition Status, Evidence from FTIR and X-Ray Tomography

    NASA Astrophysics Data System (ADS)

    Toosi, E. R.; Quigley, M.; Kravchenko, A. N.

    2014-12-01

    It has been reported that conversion of intensively cultivated lands to less disturbed systems enhances soil OM storage capacity, primarily through OM stabilization in macroaggregates. We hypothesized that the potential for OM stabilization inside macro-aggregates is influenced by presence and abundance of intra-aggregate pores. Pores determine microbial access to OM and regulate diffusion of solution/gases within aggregates which drives microbial functioning. We investigated the influence of longterm disturbance intensity on soil OM composition and its relation to pore size distribution within macroaggregates. We used quantitative FTIR to determine OM decomposition status and X-ray micro-tomography to assess pore size distribution in macroaggregates as affected by management and landuse. Macroaggregates 4-6 mm in size where selected from topsoil under long term conventional tillage (CT), cover-crop (CC), and native succession vegetation (NS) treatments at Kellogg Biological Station, Michigan. Comparison of main soil OM functional groups suggested that with increasing disturbance intensity, the proportion of aromatic and carboxylic/carbohydrates associated compounds increased and it was concomitant with a decrease in the proportion of aliphatic associated compounds and lignin derivatives. Further, FTIR-based decomposition indices revealed that overall decomposition status of macroaggregates followed the pattern of CT > CC ≈ NS. X-ray micro-tomography findings suggested that greater OM decomposition within the macroaggregates was associated with i) greater percent of pores >13 micron in size within the aggregates, as well as ii) greater proportion of small to medium pores (13-110 micron). The results develop previous findings, suggesting that shift in landuse or management indirectly affects soil OM stabilization through alteration of pore size distribution within macroaggregates that itself, is coupled with OM decomposition status.

  17. Statistical physics studies of multilayer adsorption isotherm in food materials and pore size distribution

    NASA Astrophysics Data System (ADS)

    Aouaini, F.; Knani, S.; Ben Yahia, M.; Ben Lamine, A.

    2015-08-01

    Water sorption isotherms of foodstuffs are very important in different areas of food science engineering such as for design, modeling and optimization of many processes. The equilibrium moisture content is an important parameter in models used to predict changes in the moisture content of a product during storage. A formulation of multilayer model with two energy levels was based on statistical physics and theoretical considerations. Thanks to the grand canonical ensemble in statistical physics. Some physicochemical parameters related to the adsorption process were introduced in the analytical model expression. The data tabulated in literature of water adsorption at different temperatures on: chickpea seeds, lentil seeds, potato and on green peppers were described applying the most popular models applied in food science. We also extend the study to the newest proposed model. It is concluded that among studied models the proposed model seems to be the best for description of data in the whole range of relative humidity. By using our model, we were able to determine the thermodynamic functions. The measurement of desorption isotherms, in particular a gas over a solid porous, allows access to the distribution of pore size PSD.

  18. Sulfur infiltrated activated carbon cathodes for lithium sulfur cells: The combined effects of pore size distribution and electrolyte molarity

    NASA Astrophysics Data System (ADS)

    Lee, Jung Tae; Zhao, Youyang; Kim, Hyea; Cho, Won Il; Yushin, Gleb

    2014-02-01

    In this paper, we adopted three different commercial activated carbon samples (ACs) having different particle size, specific surface area and pore size to make sulfur-carbon (S-AC) nanocomposites for rechargeable lithium sulfur batteries. The effect of the physical parameters of ACs and the combined effect of electrolyte molarity were investigated. The performance of the cells at two different temperatures of 25 and 70 °C were compared. For room temperature operation of the cells, the capacities of S infiltrated into microporous AC having smaller pore size and stronger interactions with sulfur and sulfides were lower than those of the S infiltrated into micro- and mesoporous ACs containing larger pores. In contrast, the microporous AC demonstrated higher capacity at the elevated temperature due to the improved ion transport rate. The effect of electrolyte molarity on the performance of Li/S cells was found to depend on the AC pore size and particle size distributions. Increasing electrolyte molarity from 1 to 3 M demonstrated improved cell performance and reduced polysulfide dissolution in all the studied S-AC samples. However, further increasing electrolyte salt concentration resulted in a high polarization and reduced cell performance in S-ACs having large particle size or smaller pores.

  19. In-situ method for determining pore size distribution, capillary pressure and permeability

    SciTech Connect

    Vinegar, H.J.; Waxman, M.H.

    1987-02-17

    A method is described for determining the pore sizes entered by the oil phase in an oil-bearing formation, comprising: logging the formation of interest with an induced polarization logging tool having at least one source electrode; computing from the induced polarization measurements obtained by the logging tool a normalized induced polarization response function; obtaining core material from the formation of interest; extracting the water and hydrocarbons from the core material; resaturating the core material with formation brine; measuring the normalized induced polarization response function for the core material; and determining the pore sizes containing oil in the formation by comparing the normalized induced polarization response function from the formation with the normalized induced polarization response function of the core.

  20. Impact of Matric Potential and Pore Size Distribution on Growth Dynamics of Filamentous and Non-Filamentous Soil Bacteria

    PubMed Central

    Wolf, Alexandra B.; Vos, Michiel; de Boer, Wietse; Kowalchuk, George A.

    2013-01-01

    The filamentous growth form is an important strategy for soil microbes to bridge air-filled pores in unsaturated soils. In particular, fungi perform better than bacteria in soils during drought, a property that has been ascribed to the hyphal growth form of fungi. However, it is unknown if, and to what extent, filamentous bacteria may also display similar advantages over non-filamentous bacteria in soils with low hydraulic connectivity. In addition to allowing for microbial interactions and competition across connected micro-sites, water films also facilitate the motility of non-filamentous bacteria. To examine these issues, we constructed and characterized a series of quartz sand microcosms differing in matric potential and pore size distribution and, consequently, in connection of micro-habitats via water films. Our sand microcosms were used to examine the individual and competitive responses of a filamentous bacterium (Streptomyces atratus) and a motile rod-shaped bacterium (Bacillus weihenstephanensis) to differences in pore sizes and matric potential. The Bacillus strain had an initial advantage in all sand microcosms, which could be attributed to its faster growth rate. At later stages of the incubation, Streptomyces became dominant in microcosms with low connectivity (coarse pores and dry conditions). These data, combined with information on bacterial motility (expansion potential) across a range of pore-size and moisture conditions, suggest that, like their much larger fungal counterparts, filamentous bacteria also use this growth form to facilitate growth and expansion under conditions of low hydraulic conductivity. The sand microcosm system developed and used in this study allowed for precise manipulation of hydraulic properties and pore size distribution, thereby providing a useful approach for future examinations of how these properties influence the composition, diversity and function of soil-borne microbial communities. PMID:24391805

  1. Effect of hypercrosslinking conditions on pore size distribution and efficiency of monolithic stationary phases.

    PubMed

    Urban, Jiří; Škeříková, Veronika

    2014-11-01

    Three dihalogenic solvents differing in the length of alkyl chain (1,2-dichloroethane, 1,4-dichlorobutane, and 1,6-dichlorohexane) with three Friedel-Crafts alkylation catalysts varying in reactivity (AlCl3 , FeCl3 , and SnCl4 ) have been used to prepare hypercrosslinked poly(styrene-co-vinylbenzyl chloride-co-divinylbenzene) columns. Hydrodynamic characteristics as well as column efficiency and mass transfer resistance were tuned by the combination of swelling solvent and alkylation reaction catalyst in the modification mixture. The column swelled in 1,6-dichlorohexane and hypercrosslinked in the presence of AlCl3 provided the highest column efficiency and enabled fast isocratic separations of small molecules in a RP mode. To uncover factors controlling the efficiency of hypercrosslinked monolithic columns, we have studied pore volume distribution of prepared columns. We found that column efficiency increases with the higher pore volume of pores smaller than 2 nm. PMID:25113521

  2. Determination of pore size distributions in capillary-channeled polymer fiber stationary phases by inverse size-exclusion chromatography and implications for fast protein separations.

    PubMed

    Wang, Zhengxin; Marcus, R Kenneth

    2014-07-18

    Capillary-channeled polymer (C-CP) fibers have been utilized as liquid chromatography stationary phases, primarily for biomacromolecule separations on the analytical and preparative scales. The collinear packing of the eight-channeled C-CP fibers provides for very efficient flow, allowing operation at high linear velocity (u>100mm s(-1)) and low backpressure (<2000psi) in analytical-scale separations. To take advantage of these fluid transport properties, there must not be mass transfer limitations as would be imposed by having an appreciably porous phase, wherein solute diffusion limits the overall mass transport rates. To better understand the physical nano-/micro- structure of C-CP fibers, inverse size exclusion chromatography (iSEC) has been employed to determine the pore size distribution (PSD) within C-CP fibers. A diversity of test species (from metal ions to large proteins) was used as probes under non-retaining conditions to obtain a response curve reflecting the apparent partition coefficient (Kd) versus hydrodynamic radii (rm). A mean pore radius (rp) of 4.2nm with standard deviation (sp) of ±1.1nm was calculated by fitting the Kd versus rm data to model equations with a Gaussian pore size distribution, and a pore radius of 4.0±0.1nm was calculated based on a log-normal distribution. The derived mean pore radius is much smaller than traditional support materials, with the standard deviation showing a relatively uniform pore distribution. van Deemter plots were analyzed to provide practical confirmation of the structural implications. Large molecules (e.g., proteins) that are fully excluded from pores have no significant C-terms in the van Deemter plots whereas small molecules that can access the pore volumes display appreciable C-terms, as expected. Fitting of retention data to the Knox equation suggests that the columns operate with a characteristic particle diameter (dp) of ∼53μm. PMID:24877979

  3. Determination by Small-angle X-ray Scattering of Pore Size Distribution in Nanoporous Track-etched Polycarbonate Membranes

    NASA Astrophysics Data System (ADS)

    Jonas, A. M.; Legras, R.; Ferain, E.

    1998-03-01

    Nanoporous track-etched membranes with narrow pore size distributions and average pore size diameters tunable from 100 to 1000 Åare produced by the chemical etching of latent tracks in polymer films after irradiation by a beam of accelerated heavy ions. Nanoporous membranes are used for highly demanding filtration purposes, or as templates to obtain metallic or polymeric nanowires (L. Piraux et al., Nucl. Instr. Meth. Phys. Res. 1997, B131, 357). Such applications call for developments in nanopore size characterization techniques. In this respect, we report on the characterization by small-angle X-ray scattering (SAXS) of nanopore size distribution (nPSD) in polycarbonate track-etched membranes. The obtention of nPSD requires inverting an ill-conditioned inhomogeneous equation. We present different numerical routes to overcome the amplification of experimental errors in the resulting solutions, including a regularization technique allowing to obtain the nPSD without a priori knowledge of its shape. The effect of deviations from cylindrical pore shape on the resulting distributions are analyzed. Finally, SAXS results are compared to results obtained by electron microscopy and conductometry.

  4. Isolating the effect of pore size distribution on electrochemical double-layer capacitance using activated fluid coke

    NASA Astrophysics Data System (ADS)

    Zuliani, Jocelyn E.; Tong, Shitang; Kirk, Donald W.; Jia, Charles Q.

    2015-12-01

    Electrochemical double-layer capacitors (EDLCs) use physical ion adsorption in the capacitive electrical double layer of high specific surface area (SSA) materials to store electrical energy. Previous work shows that the SSA-normalized capacitance increases when pore diameters are less than 1 nm. However, there still remains uncertainty about the charge storage mechanism since the enhanced SSA-normalized capacitance is not observed in all microporous materials. In previous studies, the total specific surface area and the chemical composition of the electrode materials were not controlled. The current work is the first reported study that systematically compares the performance of activated carbon prepared from the same raw material, with similar chemical composition and specific surface area, but different pore size distributions. Preparing samples with similar SSAs, but different pores sizes is not straightforward since increasing pore diameters results in decreasing the SSA. This study observes that the microporous activated carbon has a higher SSA-normalized capacitance, 14.1 μF cm-2, compared to the mesoporous material, 12.4 μF cm-2. However, this enhanced SSA-normalized capacitance is only observed above a threshold operating voltage. Therefore, it can be concluded that a minimum applied voltage is required to induce ion adsorption in these sub-nanometer micropores, which increases the capacitance.

  5. Pore size distribution of OPC and SRPC mortars in presence of chlorides

    SciTech Connect

    Suryavanshi, A.K.; Scantlebury, J.D.; Lyon, S.B.

    1995-07-01

    The pore structure of chloride-free ordinary portland cement (OPC) and sulphate resistant portland cement (SRPC) mortars are compared with the corresponding mortars with NaCl and CaCl{sub 2} added during mixing. In both OPC and SRPC mortars the addition of chlorides reduced the total accessible pore volumes compared to the corresponding chloride-free mortars. Also, in the presence of chlorides, the number of coarse pores were increased. These changes in the pore structure are believed to be due to dense calcium silicate hydrate (C-S-H) gel morphology formed in the presence of chlorides. The SRPC showed greater changes in pore structures than the OPC with equivalent amounts of chlorides added. This may be due to the lower chloride binding capacity of the SRPC and hence the higher availability of free chlorides to modify the gel morphology.

  6. Influence of pore size distributions on decomposition of maize leaf residue: evidence from X-ray computed micro-tomography

    NASA Astrophysics Data System (ADS)

    Negassa, Wakene; Guber, Andrey; Kravchenko, Alexandra; Rivers, Mark

    2014-05-01

    Soil's potential to sequester carbon (C) depends not only on quality and quantity of organic inputs to soil but also on the residence time of the applied organic inputs within the soil. Soil pore structure is one of the main factors that influence residence time of soil organic matter by controlling gas exchange, soil moisture and microbial activities, thereby soil C sequestration capacity. Previous attempts to investigate the fate of organic inputs added to soil did not allow examining their decomposition in situ; the drawback that can now be remediated by application of X-ray computed micro-tomography (µ-CT). The non-destructive and non-invasive nature of µ-CT gives an opportunity to investigate the effect of soil pore size distributions on decomposition of plant residues at a new quantitative level. The objective of this study is to examine the influence of pore size distributions on the decomposition of plant residue added to soil. Samples with contrasting pore size distributions were created using aggregate fractions of five different sizes (<0.05, 0.05-0.1, 0.10-05, 0.5-1.0 and 1.0-2.0 mm). Weighted average pore diameters ranged from 10 µm (<0.05 mm fraction) to 104 µm (1-2 mm fraction), while maximum pore diameter were in a range from 29 µm (<0.05 mm fraction) to 568 µm (1-2 mm fraction) in the created soil samples. Dried pieces of maize leaves 2.5 mg in size (equivalent to 1.71 mg C g-1 soil) were added to half of the studied samples. Samples with and without maize leaves were incubated for 120 days. CO2 emission from the samples was measured at regular time intervals. In order to ensure that the observed differences are due to differences in pore structure and not due to differences in inherent properties of the studied aggregate fractions, we repeated the whole experiment using soil from the same aggregate size fractions but ground to <0.05 mm size. Five to six replicated samples were used for intact and ground samples of all sizes with and without

  7. Control of pore size in epoxy systems.

    SciTech Connect

    Sawyer, Patricia Sue; Lenhart, Joseph Ludlow; Lee, Elizabeth; Kallam, Alekhya; Majumdar, Partha; Dirk, Shawn M.; Gubbins, Nathan; Chisholm, Bret J.; Celina, Mathias Christopher; Bahr, James; Klein, Robert J.

    2009-01-01

    Both conventional and combinatorial approaches were used to study the pore formation process in epoxy based polymer systems. Sandia National Laboratories conducted the initial work and collaborated with North Dakota State University (NDSU) using a combinatorial research approach to produce a library of novel monomers and crosslinkers capable of forming porous polymers. The library was screened to determine the physical factors that control porosity, such as porogen loading, polymer-porogen interactions, and polymer crosslink density. We have identified the physical and chemical factors that control the average porosity, pore size, and pore size distribution within epoxy based systems.

  8. Experimental Study of Porosity Changes in Shale Caprocks Exposed to CO2-Saturated Brines I: Evolution of Mineralogy, Pore Connectivity, Pore Size Distribution, and Surface Area

    DOE PAGESBeta

    Mouzakis, Katherine M.; Navarre-Sitchler, Alexis K.; Rother, Gernot; Bañuelos, José Leobardo; Wang, Xiuyu; Kaszuba, John P.; Heath, Jason E.; Miller, Quin R. S.; Alvarado, Vladimir; McCray, John E.

    2016-07-18

    Carbon capture, utilization, and storage, one proposed method of reducing anthropogenic emissions of CO2, relies on low permeability formations, such as shales, above injection formations to prevent upward migration of the injected CO2. Porosity in caprocks evaluated for sealing capacity before injection can be altered by geochemical reactions induced by dissolution of injected CO2 into pore fluids, impacting long-term sealing capacity. Therefore, long-term performance of CO2 sequestration sites may be dependent on both initial distribution and connectivity of pores in caprocks, and on changes induced by geochemical reaction after injection of CO2, which are currently poorly understood. This paper presentsmore » results from an experimental study of changes to caprock porosity and pore network geometry in two caprock formations under conditions relevant to CO2 sequestration. Pore connectivity and total porosity increased in the Gothic Shale; while total porosity increased but pore connectivity decreased in the Marine Tuscaloosa. Gothic Shale is a carbonate mudstone that contains volumetrically more carbonate minerals than Marine Tuscaloosa. Carbonate minerals dissolved to a greater extent than silicate minerals in Gothic Shale under high CO2 conditions, leading to increased porosity at length scales <~200 nm that contributed to increased pore connectivity. In contrast, silicate minerals dissolved to a greater extent than carbonate minerals in Marine Tuscaloosa leading to increased porosity at all length scales, and specifically an increase in the number of pores >~1 μm. Mineral reactions also contributed to a decrease in pore connectivity, possibly as a result of precipitation in pore throats or hydration of the high percentage of clays. Finally, this study highlights the role that mineralogy of the caprock can play in geochemical response to CO2 injection and resulting changes in sealing capacity in long-term CO2 storage projects.« less

  9. Estimation of near-saturated hydraulic conductivity by minidisk infiltrometers for soils with wide pore-size distribution

    NASA Astrophysics Data System (ADS)

    Dohnal, Michal; Dusek, Jaromir; Vogel, Tomas

    2010-05-01

    Disk infiltrometers are widely used devices for quick and convenient measurement of soil surface hydraulic properties. In the present study, several estimation procedures, commonly used for the determination of near-saturated hydraulic conductivity from disk infiltration data, are evaluated using numerical modeling of three-dimensional axisymmetric flow below infiltrometer disk. The analysis is performed for a set of soils representing a wide spectrum of textural classes. Special attention is paid to the sandy loam soils typical for the mountain regions of Central Europe (classified as Cambisols). Improved conductivity estimates, specifically for the soils with low value of van Genuchten's parameter n (characterized by wide pore-size distribution), are obtained by extending the semi-empirical estimation procedure of Zhang (1997).

  10. Non-linear behaviour of electrical parameters in porous, water-saturated rocks: a model to predict pore size distribution

    NASA Astrophysics Data System (ADS)

    Hallbauer-Zadorozhnaya, Valeriya; Santarato, Giovanni; Abu Zeid, Nasser

    2015-08-01

    In this paper, two separate but related goals are tackled. The first one is to demonstrate that in some saturated rock textures the non-linear behaviour of induced polarization (IP) and the violation of Ohm's law not only are real phenomena, but they can also be satisfactorily predicted by a suitable physical-mathematical model, which is our second goal. This model is based on Fick's second law. As the model links the specific dependence of resistivity and chargeability of a laboratory sample to the injected current and this in turn to its pore size distribution, it is able to predict pore size distribution from laboratory measurements, in good agreement with mercury injection capillary pressure test results. This fact opens up the possibility for hydrogeophysical applications on a macro scale. Mathematical modelling shows that the chargeability acquired in the field under normal conditions, that is at low current, will always be very small and approximately proportional to the applied current. A suitable field test site for demonstrating the possible reliance of both resistivity and chargeability on current was selected and a specific measuring strategy was established. Two data sets were acquired using different injected current strengths, while keeping the charging time constant. Observed variations of resistivity and chargeability are in agreement with those predicted by the mathematical model. These field test data should however be considered preliminary. If confirmed by further evidence, these facts may lead to changing the procedure of acquiring field measurements in future, and perhaps may encourage the design and building of a new specific geo-resistivity meter. This paper also shows that the well-known Marshall and Madden's equations based on Fick's law cannot be solved without specific boundary conditions.

  11. Effect of rock composition and texture on pore size distributions in shales: Applications in low field nuclear magnetic resonance

    NASA Astrophysics Data System (ADS)

    Saidian, Milad

    There are various methods to assess the pore size distribution (PSD) of porous materials; amongst all, NMR is the only technique that can be utilized for subsurface applications. The key parameter to transform NMR time domain response to PSD size domain data is surface relaxivity. The common practice is to consider a constant surface relaxivity throughout a well, formation or rock type regardless of the variations in rock compositions; this results in inaccurate PSD estimation using NMR log data. In this thesis I established a methodology to calculate the surface relaxivity in shales considering the rock composition and texture. I present the steps to achieve this goal in three steps: (a) Understanding the challenges of NMR acquisition, analysis and interpretation in shales, (b) Measuring the porosity, PSD and surface area and providing a practice to check the reliability of these measurements in shales, (c) Developing a methodology to calculate the surface relaxivity honoring the variations paramagnetic mineral content, susceptibility, distribution and texture. Application of NMR in unconventional rocks requires adjustment of NMR data acquisition and analysis to the unique properties of these rocks such as high level of heterogeneity, complex pore structure, fine grains, and presence of nano-scale pores. Identifying these challenges improves our understanding of NMR response in shales and increases the quality of the acquired and analyzed data. Calculation of surface relaxivity, as a measure of how fluids and rock surfaces react, requires reliable measurement of different petrophysical properties of the rock such as porosity, total specific surface area, and PSD using other techniques. I studied the reliability of different techniques to measure these petrophysical properties for shales by performing a thorough comparative study of porosity and PSD for different shale formations. The result of my study showed that clay type and content, total organic carbon (TOC

  12. Nonparametric pore size distribution using d-PFG: comparison to s-PFG and migration to MRI.

    PubMed

    Benjamini, Dan; Komlosh, Michal E; Basser, Peter J; Nevo, Uri

    2014-09-01

    Here we present the successful translation of a pore size distribution (PSD) estimation method from NMR to MRI. This approach is validated using a well-characterized MRI phantom consisting of stacked glass capillary arrays (GCA) having different diameters. By employing a double pulsed-field gradient (d-PFG) MRI sequence, this method overcomes several important theoretical and experimental limitations of previous single-PFG (s-PFG) based MRI methods by allowing the relative diffusion gradients' direction to vary. This feature adds an essential second dimension in the parameters space, which can potentially improve the reliability and stability of the PSD estimation. To infer PSDs from the MRI data in each voxel an inverse linear problem is solved in conjunction with the multiple correlation function (MCF) framework, which can account for arbitrary experimental parameters (e.g., long diffusion pulses). This scheme makes no a priori assumptions about the functional form of the underlying PSD. Creative use of region of interest (ROI) analysis allows us to create different underlying PSDs using the same GCA MRI phantom. We show that an s-PFG experiment on the GCA phantom fails to accurately reconstruct the size distribution, thus demonstrating the superiority of the d-PFG experiment. In addition, signal simulations corrupted by different noise levels were used to generate continuous and complex PSDs, which were then successfully reconstructed. Finally, owing to the reduced q- or b- values required to measure microscopic PSDs via d-PFG MRI, this method will be better suited to biomedical and clinical applications, in which gradient strength of scanners is limited. PMID:25064269

  13. Nonlinear Effect of Moisture Content on Effective Thermal Conductivity of Building Materials with Different Pore Size Distributions

    NASA Astrophysics Data System (ADS)

    Liu, Yanfeng; Ma, Chao; Wang, Dengjia; Wang, Yingying; Liu, Jiaping

    2016-06-01

    Understanding the quantitative relationship between the effective thermal conductivity and the moisture content of a material is required to accurately calculate the envelope heat and mass transfer and, subsequently, the building energy consumption. We experimentally analyzed the pore size distributions and porosities of common building materials and the influence of the moisture content on the effective thermal conductivity of building materials. We determined the quantitative relationship between the effective thermal conductivity and moisture content of building materials. The results showed that a larger porosity led to a more significant effect of the moisture content on the effective thermal conductivity. When the volumetric moisture content reached 10 %, the thermal conductivities of foam concrete and aerated concrete increased by approximately 200 % and 100 %, respectively. The effective thermal conductivity increased rapidly in the low moisture content range and increased slowly in the high moisture content range. The effective thermal conductivity is related to the moisture content of the materials through an approximate power function. As the moisture content in the walls of a new building stabilizes, the effective thermal conductivity of normal concrete varies only slightly, whereas that of aerated concrete varies more significantly. The effective thermal conductivity of the material is proportional to the relative humidity of the environment. This trend is most noticeable when the wall material is aerated concrete.

  14. Size of seismic events during borehole injections: the effects of source mechanisms, stress and pore pressure distribution

    NASA Astrophysics Data System (ADS)

    Fischer, T.; Ondovcin, T.; Zhao, P.

    2012-12-01

    and space-time distributions, source mechanisms and stress analyses on the available data to shed light on these questions. Our inversion for moment tensors of the Basel injection-induced seismicity shows that the microearthquakes had higher non-DC components during injection than after shut-in. This could be related to the higher stress drops found during injection. We model the pore pressure distribution and out-flow from the well the numerically solving the diffusion equation for the shut-in and open-well conditions. We compare the results of seismicity analysis with the models of pore pressure distribution during and after the injection to test the relevancy of several hypotheses of the occurrence of large events. We find that their anomalous occurrence during the shut-in phase is most-likely caused by the transient effects during the stop of injection. The anomalous space occurrence of large events is probably also related to the unequal distribution of faults in the vicinity of the injection well.

  15. Deriving NMR surface relaxivities, pore size distributions and water retention curves by NMR relaxation experiments on partially de-saturated rocks

    NASA Astrophysics Data System (ADS)

    Mohnke, O.; Nordlund, C. L.; Klitzsch, N.

    2013-12-01

    Nuclear magnetic resonance (NMR) is a method used over a wide field of geophysical applications to non-destructively determine transport and storage properties of rocks and soils. In NMR relaxometry signal amplitudes correspond directly to the rock's fluid (water, oil) content. On the other hand the NMR relaxation behavior, i.e. the longitudinal (T1) and transverse (T2) NMR relaxation times, can be used to derive pore sizes and permeability as it is linearly linked to the pore's surface-to-volume-ratio and physiochemical properties of the rock-fluid interface by the surface relaxivity ρ_s This parameter, however, is dependent on the type and mineral constituents of the investigated rock sample and thus has to be determined and calibrated prior to estimating pore sizes from NMR relaxometry measurements. Frequently used methods to derive surface relaxivity to calibrate NMR pore sizes comprise mercury injection, pulsed field gradients (PFG-NMR) or grain size analysis. This study introduces an alternative approach to jointly estimate NMR surface relaxivity and pore radii distributions using NMR relaxation data obtained from partially de-saturated rocks. In this, inverse modeling is carried on a linked Young Laplace equation for capillary bundles and the Brownstein and Tarr equations. Subsequently, this approach is used to predict water retention curves of the investigated rocks. The method was tested and validated on simulated and laboratory transverse NMR data. Calculated inverse models are generally in a good agreement with results obtained from mercury injection and drainage measurements. Left: Measured and predicted water retention (pF) curves. Center: NMR relaxometry data, fit and error. Right: Mercury injection data (HgPor, dashed line) and jointly derived pore radii distributions and surface relaxivity by joint inverse modelling

  16. Ovariectomized rats' femur treated with fibrates and statins. Assessment of pore-size distribution by ¹H-NMR relaxometry.

    PubMed

    Şipoş, Remus Sebastian; Fechete, Radu; Chelcea, Ramona Ioana; Moldovan, Dumitriţa; Pap, Zsuzsánna; Pávai, Zoltán; Demco, Dan Eugen

    2015-01-01

    The effects of two wonder drugs, simvastatins and fenofibrates on the proximal part of the femoris of a series of ovariectomized and non-ovariectomized Wistar albino rats was estimated qualitatively and semi-quantitatively by the modern method of 1D 1H-NMR T2-distribution. The 72 rats subjected to this study were divided in six groups and were sacrificed at two, four, six and eight weeks after ovariectomy and the proximal part of femoris was harvested. The CPMG (Carr-Purcell-Meiboom-Gill) echoes train curves were measured for the bones fully saturated with water during two months after two months of natural drying. These decays were analyzed by Laplace inversion and an average of normalized T2-distributions was considered for all rat's groups. The 1D averaged T2-distributions present four peaks, which were associated with protons in four major environments, from which the free water protons are used as spy molecules to explore the boundaries of cavities. In the approximation of spherical pores, the averaged T2-distributions were transformed in distributions of pores diameters. These were found in the range from 2 μm up to 2 mm. The relative amplitudes, widths and position of deconvoluted distributions of small, medium and large cavities are used for a qualitatively analysis of the effect of our lipid-lowering drugs. For a semi-quantitatively analysis, we chose the diameter d of proximal part of femoris' trabecular cavities. We show that the positive or negative effects of treatments with simvastatins and fenofibrates are strongly dependent on the duration of treatment. Moreover, the treatment of healthy bone is generally counter-indicated. PMID:26429167

  17. Pore size engineering applied to starved electrochemical cells and batteries

    NASA Technical Reports Server (NTRS)

    Abbey, K. M.; Thaller, L. H.

    1982-01-01

    To maximize performance in starved, multiplate cells, the cell design should rely on techniques which widen the volume tolerance characteristics. These involve engineering capillary pressure differences between the components of an electrochemical cell and using these forces to promote redistribution of electrolyte to the desired optimum values. This can be implemented in practice by prescribing pore size distributions for porous back-up plates, reservoirs, and electrodes. In addition, electrolyte volume management can be controlled by incorporating different pore size distributions into the separator. In a nickel/hydrogen cell, the separator must contain pores similar in size to the small pores of both the nickel and hydrogen electrodes in order to maintain an optimum conductive path for the electrolyte. The pore size distributions of all components should overlap in such a way as to prevent drying of the separator and/or flooding of the hydrogen electrode.

  18. Effects of coarse grain size distribution and fine particle content on pore fluid pressure and shear behavior in experimental debris flows

    NASA Astrophysics Data System (ADS)

    Kaitna, Roland; Palucis, Marisa C.; Yohannes, Bereket; Hill, Kimberly M.; Dietrich, William E.

    2016-02-01

    Debris flows are typically a saturated mixture of poorly sorted particles and interstitial fluid, whose density and flow properties depend strongly on the presence of suspended fine sediment. Recent research suggests that grain size distribution (GSD) influences excess pore pressures (i.e., pressure in excess of predicted hydrostatic pressure), which in turn plays a governing role in debris flow behaviors. We report a series of controlled laboratory experiments in a 4 m diameter vertically rotating drum where the coarse particle size distribution and the content of fine particles were varied independently. We measured basal pore fluid pressures, pore fluid pressure profiles (using novel sensor probes), velocity profiles, and longitudinal profiles of the flow height. Excess pore fluid pressure was significant for mixtures with high fines fraction. Such flows exhibited lower values for their bulk flow resistance (as measured by surface slope of the flow), had damped fluctuations of normalized fluid pressure and normal stress, and had velocity profiles where the shear was concentrated at the base of the flow. These effects were most pronounced in flows with a wide coarse GSD distribution. Sustained excess fluid pressure occurred during flow and after cessation of motion. Various mechanisms may cause dilation and contraction of the flows, and we propose that the sustained excess fluid pressures during flow and once the flow has stopped may arise from hindered particle settling and yield strength of the fluid, resulting in transfer of particle weight to the fluid. Thus, debris flow behavior may be strongly influenced by sustained excess fluid pressures controlled by particle settling rates.

  19. Can carbon surface oxidation shift the pore size distribution curve calculated from Ar, N2 and CO2 adsorption isotherms? Simulation results for a realistic carbon model

    NASA Astrophysics Data System (ADS)

    Furmaniak, Sylwester; Terzyk, Artur P.; Gauden, Piotr A.; Harris, Peter J. F.; Kowalczyk, Piotr

    2009-08-01

    Using the virtual porous carbon model proposed by Harris et al, we study the effect of carbon surface oxidation on the pore size distribution (PSD) curve determined from simulated Ar, N2 and CO2 isotherms. It is assumed that surface oxidation is not destructive for the carbon skeleton, and that all pores are accessible for studied molecules (i.e., only the effect of the change of surface chemical composition is studied). The results obtained show two important things, i.e., oxidation of the carbon surface very slightly changes the absolute porosity (calculated from the geometric method of Bhattacharya and Gubbins (BG)); however, PSD curves calculated from simulated isotherms are to a greater or lesser extent affected by the presence of surface oxides. The most reliable results are obtained from Ar adsorption data. Not only is adsorption of this adsorbate practically independent from the presence of surface oxides, but, more importantly, for this molecule one can apply the slit-like model of pores as the first approach to recover the average pore diameter of a real carbon structure. For nitrogen, the effect of carbon surface chemical composition is observed due to the quadrupole moment of this molecule, and this effect shifts the PSD curves compared to Ar. The largest differences are seen for CO2, and it is clearly demonstrated that the PSD curves obtained from adsorption isotherms of this molecule contain artificial peaks and the average pore diameter is strongly influenced by the presence of electrostatic adsorbate-adsorbate as well as adsorbate-adsorbent interactions.

  20. Can carbon surface oxidation shift the pore size distribution curve calculated from Ar, N(2) and CO(2) adsorption isotherms? Simulation results for a realistic carbon model.

    PubMed

    Furmaniak, Sylwester; Terzyk, Artur P; Gauden, Piotr A; Harris, Peter J F; Kowalczyk, Piotr

    2009-08-01

    Using the virtual porous carbon model proposed by Harris et al, we study the effect of carbon surface oxidation on the pore size distribution (PSD) curve determined from simulated Ar, N(2) and CO(2) isotherms. It is assumed that surface oxidation is not destructive for the carbon skeleton, and that all pores are accessible for studied molecules (i.e., only the effect of the change of surface chemical composition is studied). The results obtained show two important things, i.e., oxidation of the carbon surface very slightly changes the absolute porosity (calculated from the geometric method of Bhattacharya and Gubbins (BG)); however, PSD curves calculated from simulated isotherms are to a greater or lesser extent affected by the presence of surface oxides. The most reliable results are obtained from Ar adsorption data. Not only is adsorption of this adsorbate practically independent from the presence of surface oxides, but, more importantly, for this molecule one can apply the slit-like model of pores as the first approach to recover the average pore diameter of a real carbon structure. For nitrogen, the effect of carbon surface chemical composition is observed due to the quadrupole moment of this molecule, and this effect shifts the PSD curves compared to Ar. The largest differences are seen for CO(2), and it is clearly demonstrated that the PSD curves obtained from adsorption isotherms of this molecule contain artificial peaks and the average pore diameter is strongly influenced by the presence of electrostatic adsorbate-adsorbate as well as adsorbate-adsorbent interactions. PMID:21828590

  1. How realistic is the pore size distribution calculated from adsorption isotherms if activated carbon is composed of fullerene-like fragments?

    PubMed

    Terzyk, Artur P; Furmaniak, Sylwester; Harris, Peter J F; Gauden, Piotr A; Włoch, Jerzy; Kowalczyk, Piotr; Rychlicki, Gerhard

    2007-11-28

    A plausible model for the structure of non-graphitizing carbon is one which consists of curved, fullerene-like fragments grouped together in a random arrangement. Although this model was proposed several years ago, there have been no attempts to calculate the properties of such a structure. Here, we determine the density, pore size distribution and adsorption properties of a model porous carbon constructed from fullerene-like elements. Using the method proposed recently by Bhattacharya and Gubbins (BG), which was tested in this study for ideal and defective carbon slits, the pore size distributions (PSDs) of the initial model and two related carbon models are calculated. The obtained PSD curves show that two structures are micro-mesoporous (with different ratio of micro/mesopores) and the third is strictly microporous. Using the grand canonical Monte Carlo (GCMC) method, adsorption isotherms of Ar (87 K) are simulated for all the structures. Finally PSD curves are calculated using the Horvath-Kawazoe, non-local density functional theory (NLDFT), Nguyen and Do, and Barrett-Joyner-Halenda (BJH) approaches, and compared with those predicted by the BG method. This is the first study in which different methods of calculation of PSDs for carbons from adsorption data can be really verified, since absolute (i.e. true) PSDs are obtained using the BG method. This is also the first study reporting the results of computer simulations of adsorption on fullerene-like carbon models.

  2. Pore size analysis of activated carbons from argon and nitrogen porosimetry using density functional theory

    SciTech Connect

    Dombrowski, R.J.; Hyduke, D.R.; Lastoskie, C.M.

    2000-05-30

    The authors present isotherms calculated from density functional theory for the adsorption of argon in model slit-shaped carbon pores at 77 K. The model isotherms are used to interpret experimental argon uptake measurements and to obtain the pore size distributions of several porous carbons. A similar set of density measurements and to obtain the pore size distributions of several porous carbons. A similar set of density functional theory isotherms, previously reported for nitrogen adsorption on carbon slit pores at 77 K, are used to determine pore size distributions for the same set of carbons. The pore size distribution maxima, mean pore widths, and specific pore volumes measured using the two different probe gases are all found to agree to within approximately 8% on average. Some of the differences in the pore size distributions obtained from argon and nitrogen porosimetry may be attributable to quadrupolar interactions of the nitrogen molecules with functional groups on the carbon surface.

  3. Effect of seawater salinity on pore-size distribution on a poly(styrene)-based HP20 resin and its adsorption of diarrhetic shellfish toxins.

    PubMed

    Fan, Lin; Sun, Geng; Qiu, Jiangbing; Ma, Qimin; Hess, Philipp; Li, Aifeng

    2014-12-19

    In the present study, okadaic acid (OA) and dinophysistoxin-1 (DTX1) were spiked into artificial seawater at low, medium and high estuarine salinities (9‰, 13.5‰ and 27‰). Passive samplers (HP20 resin) used for solid phase adsorption toxin tracking (SPATT) technology were exposed in these seawaters for 12-h periods. Adsorption curves well fitted a pseudo-secondary kinetics model. The highest initial sorption rates of both toxins occurred in the seawater of medium salinity, followed by seawater of low and high estuarine salinity. Pore volumes of micropores (<2 nm) and small mesopores (2 nmsize) in seawaters of high and low salinity. More toxin or other matrix agglomerates were displayed on the surface of resin deployed in the seawater of medium salinity. Taking into consideration the pore-size distribution and surface images, it appears that intra-particle diffusion governs toxin adsorption in seawater at high salinity while film diffusion mainly controls the adsorption process in seawater at medium salinity. This is the first study to confirm that molecules of OA and DTX1 are able to enter into micropores (<2nm) and small mesopores (2-10nm) of HP20 resin in estuarine seawater with high salinity (∼27‰).

  4. Pore size effect of collagen scaffolds on cartilage regeneration.

    PubMed

    Zhang, Qin; Lu, Hongxu; Kawazoe, Naoki; Chen, Guoping

    2014-05-01

    Scaffold pore size is an important factor affecting tissue regeneration efficiency. The effect of pore size on cartilage tissue regeneration was compared by using four types of collagen porous scaffolds with different pore sizes. The collagen porous scaffolds were prepared by using pre-prepared ice particulates that had diameters of 150-250, 250-355, 355-425 and 425-500μm. All the scaffolds had spherical large pores with good interconnectivity and high porosity that facilitated cell seeding and spatial cell distribution. Chondrocytes adhered to the walls of the spherical pores and showed a homogeneous distribution throughout the scaffolds. The in vivo implantation results indicated that the pore size did not exhibit any obvious effect on cell proliferation but exhibited different effects on cartilage regeneration. The collagen porous scaffolds prepared with ice particulates 150-250μm in size best promoted the expression and production of type II collagen and aggrecan, increasing the formation and the mechanical properties of the cartilage.

  5. Pore sizes and filtration rates from two alumina slips

    SciTech Connect

    Smith, P.A. . Materials Science Dept.); Kerch, H.; Krueger, S.; Long, G.G. . Ceramics Div.); Keller, J.; Haber, R.A. . Dept. of Ceramics)

    1994-07-01

    The relationship between filtration rate and the resultant green body microstructure was examined for aqueous alumina slips cast at two different deflocculation states. The volume loading of both slips was 40%. Slip viscosities of 500 and 60 mPa[center dot]s were produced by different tetrasodium pyrophosphate additions. The filtration rate of these slips varied by a factor of 2; however, mercury porosimetry results showed the same average pore size for both samples. Single and multiple small-angle neutron scattering results showed the specimen cast with the higher-viscosity slip to possess a bimodal pore size distribution. The body cast with the low-viscosity slip showed unimodal porosity and, consequently, the filtration is attributed to the toroidal region between the packed particles. These results showed that mercury porosimetry does not provide a pore size that predicts filtration behavior of slips with different degrees of dispersion.

  6. Relation between the ion size and pore size for an electric double-layer capacitor.

    PubMed

    Largeot, Celine; Portet, Cristelle; Chmiola, John; Taberna, Pierre-Louis; Gogotsi, Yury; Simon, Patrice

    2008-03-01

    The research on electrochemical double layer capacitors (EDLC), also known as supercapacitors or ultracapacitors, is quickly expanding because their power delivery performance fills the gap between dielectric capacitors and traditional batteries. However, many fundamental questions, such as the relations between the pore size of carbon electrodes, ion size of the electrolyte, and the capacitance have not yet been fully answered. We show that the pore size leading to the maximum double-layer capacitance of a TiC-derived carbon electrode in a solvent-free ethyl-methylimmidazolium-bis(trifluoro-methane-sulfonyl)imide (EMI-TFSI) ionic liquid is roughly equal to the ion size (approximately 0.7 nm). The capacitance values of TiC-CDC produced at 500 degrees C are more than 160 F/g and 85 F/cm(3) at 60 degrees C, while standard activated carbons with larger pores and a broader pore size distribution present capacitance values lower than 100 F/g and 50 F/cm(3) in ionic liquids. A significant drop in capacitance has been observed in pores that were larger or smaller than the ion size by just an angstrom, suggesting that the pore size must be tuned with sub-angstrom accuracy when selecting a carbon/ion couple. This work suggests a general approach to EDLC design leading to the maximum energy density, which has been now proved for both solvated organic salts and solvent-free liquid electrolytes. PMID:18257568

  7. Relation between the ion size and pore size for an electric double-layer capacitor.

    PubMed

    Largeot, Celine; Portet, Cristelle; Chmiola, John; Taberna, Pierre-Louis; Gogotsi, Yury; Simon, Patrice

    2008-03-01

    The research on electrochemical double layer capacitors (EDLC), also known as supercapacitors or ultracapacitors, is quickly expanding because their power delivery performance fills the gap between dielectric capacitors and traditional batteries. However, many fundamental questions, such as the relations between the pore size of carbon electrodes, ion size of the electrolyte, and the capacitance have not yet been fully answered. We show that the pore size leading to the maximum double-layer capacitance of a TiC-derived carbon electrode in a solvent-free ethyl-methylimmidazolium-bis(trifluoro-methane-sulfonyl)imide (EMI-TFSI) ionic liquid is roughly equal to the ion size (approximately 0.7 nm). The capacitance values of TiC-CDC produced at 500 degrees C are more than 160 F/g and 85 F/cm(3) at 60 degrees C, while standard activated carbons with larger pores and a broader pore size distribution present capacitance values lower than 100 F/g and 50 F/cm(3) in ionic liquids. A significant drop in capacitance has been observed in pores that were larger or smaller than the ion size by just an angstrom, suggesting that the pore size must be tuned with sub-angstrom accuracy when selecting a carbon/ion couple. This work suggests a general approach to EDLC design leading to the maximum energy density, which has been now proved for both solvated organic salts and solvent-free liquid electrolytes.

  8. Preparation of mesoporous cadmium sulfide nanoparticles with moderate pore size

    SciTech Connect

    Han Zhaohui Zhu, Huaiyong; Shi, Jeffrey; Parkinson, Gordon; Lu, G.Q.

    2007-03-15

    The preparation of cadmium sulfide nanoparticles that have a moderate pore size is reported. This preparation method involves a hydrothermal process that produces a precursor mixture and a following acid treatment of the precursor to get the porous material. The majority of the particles have a pore size close to 20nm, which complements and fills in the gap between the existing cadmium sulfide materials, which usually have a pore size either less than 10nm or are well above 100nm.

  9. Decreasing transmembrane segment length greatly decreases perfringolysin O pore size

    SciTech Connect

    Lin, Qingqing; Li, Huilin; Wang, Tong; London, Erwin

    2015-04-08

    Perfringolysin O (PFO) is a transmembrane (TM) β-barrel protein that inserts into mammalian cell membranes. Once inserted into membranes, PFO assembles into pore-forming oligomers containing 30–50 PFO monomers. These form a pore of up to 300 Å, far exceeding the size of most other proteinaceous pores. In this study, we found that altering PFO TM segment length can alter the size of PFO pores. A PFO mutant with lengthened TM segments oligomerized to a similar extent as wild-type PFO, and exhibited pore-forming activity and a pore size very similar to wild-type PFO as measured by electron microscopy and a leakage assay. In contrast, PFO with shortened TM segments exhibited a large reduction in pore-forming activity and pore size. This suggests that the interaction between TM segments can greatly affect the size of pores formed by TM β-barrel proteins. PFO may be a promising candidate for engineering pore size for various applications.

  10. Decreasing transmembrane segment length greatly decreases perfringolysin O pore size

    DOE PAGESBeta

    Lin, Qingqing; Li, Huilin; Wang, Tong; London, Erwin

    2015-04-08

    Perfringolysin O (PFO) is a transmembrane (TM) β-barrel protein that inserts into mammalian cell membranes. Once inserted into membranes, PFO assembles into pore-forming oligomers containing 30–50 PFO monomers. These form a pore of up to 300 Å, far exceeding the size of most other proteinaceous pores. In this study, we found that altering PFO TM segment length can alter the size of PFO pores. A PFO mutant with lengthened TM segments oligomerized to a similar extent as wild-type PFO, and exhibited pore-forming activity and a pore size very similar to wild-type PFO as measured by electron microscopy and a leakagemore » assay. In contrast, PFO with shortened TM segments exhibited a large reduction in pore-forming activity and pore size. This suggests that the interaction between TM segments can greatly affect the size of pores formed by TM β-barrel proteins. PFO may be a promising candidate for engineering pore size for various applications.« less

  11. THE SIZE OF SONOPORATION PORES ON THE CELL MEMBRANE

    PubMed Central

    Zhou, Yun; Kumon, Ronald E.; Cui, Jianmin; Deng, Cheri X.

    2009-01-01

    Sonoporation uses ultrasound (US) to generate transient non-selective pores on the cell membrane and has been exploited as a non-viral intracellular drug and gene delivery strategy. The pore size determines the size of agents that can be delivered into the cytoplasm using the technique. However, measurements of the dynamic, submicron-scale pores have not been readily available. Electron microscopy or atomic force microscopy has been used to gauge pore size but such techniques are intrinsically limited to post US measurements that may not accurately reveal the relevant information. As previously demonstrated, changes of the transmembrane current (TMC) of a single cell under voltage clamp can be used for monitoring sonoporation in real time. Because the TMC is related to the diffusion of ions through the pores on the membrane, it can potentially provide information of the pore size generated in sonoporation. Using Xenopus laevis oocytes as the model system, the TMC of single cells under voltage clamp was measured in real time to assess formation of pores on the membrane in sonoporation. The cells were exposed to US (0.2 s, 0.3 MPa, 1.075 MHz) in the presence of Definity™ microbubbles. Experiments were designed to obtain the TMC corresponding to a single pore on the membrane. The size of the pores was estimated from an electro-diffusion model that relates the TMC with pore size from the ion transport through the pores on the membrane. The mean radius of single pores was determined to be 110 nm with standard deviation of 40 nm. This study reports the first results of pore size from the TMC measured using the voltage clamp technique. PMID:19647924

  12. Construction of Nuclear Envelope Shape by a High-Genus Vesicle with Pore-Size Constraint

    NASA Astrophysics Data System (ADS)

    Noguchi, Hiroshi

    2016-08-01

    Nuclear pores have an approximately uniform distribution in the nuclear envelope of most living cells. Hence, the morphology of the nuclear envelope is a spherical stomatocyte with a high genus. We have investigated the morphology of high-genus vesicles under pore-size constraint using dynamically triangulated membrane simulations. Bending-energy minimization without volume or other constraints produces a circular-cage stomatocyte, where the pores are aligned in a circular line on an oblate bud. As the pore radius is reduced, the circular-pore alignment is more stabilized than a random pore distribution on a spherical bud. However, we have clarified the conditions for the formation of a spherical stomatocyte: a small perinuclear volume, osmotic pressure within nucleoplasm, and repulsion between the pores. When area-difference elasticity is taken into account, the formation of cylindrical or budded tubules from the stomatocyte and discoidal stomatocyte is found.

  13. Construction of Nuclear Envelope Shape by a High-Genus Vesicle with Pore-Size Constraint.

    PubMed

    Noguchi, Hiroshi

    2016-08-23

    Nuclear pores have an approximately uniform distribution in the nuclear envelope of most living cells. Hence, the morphology of the nuclear envelope is a spherical stomatocyte with a high genus. We have investigated the morphology of high-genus vesicles under pore-size constraint using dynamically triangulated membrane simulations. Bending-energy minimization without volume or other constraints produces a circular-cage stomatocyte, where the pores are aligned in a circular line on an oblate bud. As the pore radius is reduced, the circular-pore alignment is more stabilized than a random pore distribution on a spherical bud. However, we have clarified the conditions for the formation of a spherical stomatocyte: a small perinuclear volume, osmotic pressure within nucleoplasm, and repulsion between the pores. When area-difference elasticity is taken into account, the formation of cylindrical or budded tubules from the stomatocyte and discoidal stomatocyte is found. PMID:27558725

  14. Anomalous cyclic voltammetric response from pores smaller than ion size by voltage-induced force.

    PubMed

    Yang, Cheol-Min; Jung, Hwan Jung; Kim, Yong Jung

    2015-05-15

    Nanoporous carbons, with different micropore size distributions, were prepared based on waste coffee grounds by a chemical activation process in order to elucidate the correlation between desolvated ions and pores smaller than the sizes of ions using an organic electrolyte. The pore structure of the coffee-based nanoporous carbon was strongly dependent on the heat-treatment temperature prior to the activation process. Cyclic voltammograms of the nanoporous carbons mainly dominated by the smaller pore relative to that of the bare ion size clearly showed deviation from an ideal feature of the current response. It was clearly envisaged that even a bare ion of a size larger than the pore size can penetrate into the pore by voltage-induced force. PMID:25668782

  15. Immobilization of nanobeads on a surface to control the size, shape and distribution of pores in electrochemically generated sol-gel films

    PubMed Central

    Ciabocco, Michela; Berrettoni, Mario; Zamponi, Silvia

    2015-01-01

    Electrochemically assisted deposition of an ormosil film at a potential where hydrogen ion is generated as the catalyst yields insulating films on electrodes. When the base electrode is modified with 20-nm poly(styrene sulfonate), PSS, beads bound to the surface with 3-aminopropyltriethoxysilane (APTES) and using (CH3)3SiOCH3 as the precursor, the resulting film of organically modified silica (ormosil) has cylindrical channels that reflect both the diameter of the PSS and the distribution of the APTES-PSS on the electrode. At an electrode modified by a 20-min immersion in 0.5 mmol dm-3 APTES followed by a 30-s immersion in PSS, a 20-min electrolysis at 1.5 V in acidified (CH3)3SiOCH3 resulted in an ormosil film with 20-nm pores separated by 100 nm. Cyclic voltammetry of Ru(CN)64- at scan rates above 5 mVs-1 yielded currents controlled primarily by linear diffusion. Below 5 mVs-1, convection rather than the expected factor, radial diffusion, apparently limited the current. PMID:26167128

  16. Size of diffusion pore of Alcaligenes faecalis.

    PubMed Central

    Ishii, J; Nakae, T

    1988-01-01

    The diffusion pore of the outer membrane of Alcaligenes faecalis was shown to be substantially smaller than the Escherichia coli porin pore. In experiments with intact cells, pentoses and hexoses penetrated into the NaCl-expanded periplasm, whereas saccharides of Mr greater than 342 did not. Cells treated with 0.5 M saccharides of Mr greater than 342 weighed 33 to 38% less than cells treated with isotonic solution, suggesting that these saccharides do not permeate through the outer membrane. The diffusion rates of various solutes through the liposome membranes reconstituted from the Mr-43,000 outer membrane protein showed the following characteristics. (i) The relative diffusion rates of pentoses, hexoses, and methylhexoses appeared to be about 1.0, 0.6, and negligibly small, respectively. (ii) The diffusion rate of glucose appeared to be about 1/10th that with the E. coli B porin. (iii) The diffusion rate of gluconic acid was five to seven times higher than that of glucose. (iv) The diffusion rates of beta-lactam antibiotics appeared to be 40 to less than 10% of those with the E. coli B porin. Images PMID:2835003

  17. Pore size matters for potassium channel conductance.

    PubMed

    Naranjo, David; Moldenhauer, Hans; Pincuntureo, Matías; Díaz-Franulic, Ignacio

    2016-10-01

    Ion channels are membrane proteins that mediate efficient ion transport across the hydrophobic core of cell membranes, an unlikely process in their absence. K(+) channels discriminate K(+) over cations with similar radii with extraordinary selectivity and display a wide diversity of ion transport rates, covering differences of two orders of magnitude in unitary conductance. The pore domains of large- and small-conductance K(+) channels share a general architectural design comprising a conserved narrow selectivity filter, which forms intimate interactions with permeant ions, flanked by two wider vestibules toward the internal and external openings. In large-conductance K(+) channels, the inner vestibule is wide, whereas in small-conductance channels it is narrow. Here we raise the idea that the physical dimensions of the hydrophobic internal vestibule limit ion transport in K(+) channels, accounting for their diversity in unitary conductance.

  18. Porous Boron Nitride with Tunable Pore Size.

    PubMed

    Dai, Jun; Wu, Xiaojun; Yang, Jinlong; Zeng, Xiao Cheng

    2014-01-16

    On the basis of a global structural search and first-principles calculations, we predict two types of porous boron-nitride (BN) networks that can be built up with zigzag BN nanoribbons (BNNRs). The BNNRs are either directly connected with puckered B (N) atoms at the edge (type I) or connected with sp(3)-bonded BN chains (type II). Besides mechanical stability, these materials are predicted to be thermally stable at 1000 K. The porous BN materials entail large surface areas, ranging from 2800 to 4800 m(2)/g. In particular, type-II BN material with relatively large pores is highly favorable for hydrogen storage because the computed hydrogen adsorption energy (-0.18 eV) is very close to the optimal adsorption energy (-0.15 eV) suggested for reversible hydrogen storage at room temperature. Moreover, the type-II materials are semiconductors with width-dependent direct bandgaps, rendering the type-II BN materials promising not only for hydrogen storage but also for optoelectronic and photonic applications. PMID:26270717

  19. Laser damage dependence on the size and concentration of precursor defects in KDP crystals: view through differently sized filter pores.

    PubMed

    Wang, Yueliang; Zhao, Yuanan; Xie, Xiaoyi; Hu, Guohang; Yang, Liujiang; Xu, Ziyuan; Shao, Jianda

    2016-04-01

    We investigate the laser-induced damage performance at 1064 nm of potassium dihydrogen phosphate (KDP) crystals grown using filters of different pore sizes. The aim is to explore a novel method for understanding laser-matter interactions with regard to physical parameters affecting the ability of damage precursors to initiate damage. By reducing the pore size of filters in continuous filtration growth, we can improve laser damage resistance. Furthermore, we develop a model based on a Gaussian distribution of precursor thresholds and heat transfer to obtain a size distribution of the precursor defects. Smaller size and/or lower concentration of precursor defects could lead to better damage resistance. PMID:27192280

  20. Facile fabrication of BiVO4 nanofilms with controlled pore size and their photoelectrochemical performances.

    PubMed

    Feng, Chenchen; Jiao, Zhengbo; Li, Shaopeng; Zhang, Yan; Bi, Yingpu

    2015-12-28

    We demonstrate a facile method for the rational fabrication of pore-size controlled nanoporous BiVO(4) photoanodes, and confirmed that the optimum pore-size distributions could effectively absorb visible light through light diffraction and confinement functions. Furthermore, in situ X-ray photoelectron spectroscopy (XPS) reveals more efficient photoexcited electron-hole separation than conventional particle films, induced by light confinement and rapid charge transfer in the inter-crossed worm-like structures.

  1. EFFECT OF PORE SIZE ON TRAPPING ZINC VAPORS

    SciTech Connect

    Korinko, P.

    2010-12-17

    A series of experiments were conducted to determine the effect of pore size on pumping efficiency and zinc vapor trapping efficiency. A simple pumping efficiency test was conducted for all five pore diameters where it was observed that evacuation times were adversely affected by reducing the pore size below 5 {micro}m. Common test conditions for the zinc trapping efficiency experiments were used. These conditions resulted in some variability, to ascribe different efficiencies to the filter media. However, the data suggest that there is no significant difference in trapping efficiency for filter media with pores from 0.2 to 20 {micro}m with a thickness of 0.065-inch. Consequently, the 20 {micro}m pore filter media that is currently used at SRS is a suitable filter material for to utilize for future extractions. There is evidence that smaller pore filter will adversely affect the pumping times for the TEF and little evidence to suggest that a smaller pore diameters have significant impact on the trapping efficiency.

  2. Distributed Pore Chemistry in Porous Organic Polymers

    NASA Technical Reports Server (NTRS)

    Koontz, Steven L. (Inventor)

    1998-01-01

    A method for making a biocompatible polymer article using a uniform atomic oxygen treatment is disclosed. The sub-strate may be subsequently optionally grated with a compatibilizing compound. Compatibilizing compounds may include proteins, phosphorylcholine groups, platelet adhesion preventing polymers, albumin adhesion promoters, and the like. The compatibilized substrate may also have a living cell layer adhered thereto. The atomic oxygen is preferably produced by a flowing afterglow microwave discharge, wherein the substrate resides in a sidearm out of the plasma. Also, methods for culturing cells for various purposes using the various membranes are disclosed as well. Also disclosed are porous organic polymers having a distributed pore chemistry (DPC) comprising hydrophilic and hydrophobic region, and a method for making the DPC by exposing the polymer to atomic oxygen wherein the rate of hydrophilization is greater than the rate of mass loss.

  3. Distributed Pore Chemistry in Porous Organic Polymers

    NASA Technical Reports Server (NTRS)

    Koontz, Steven L. (Inventor)

    1999-01-01

    A method for making a biocompatible polymer article using a uniform atomic oxygen treatment is disclosed. The substrate may be subsequently optionally grated with a compatibilizing compound. Compatibilizing compounds may include proteins, phosphorylcholine groups, platelet adhesion preventing polymers, albumin adhesion promoters, and the like. The compatibilized substrate may also have a living cell layer adhered thereto. The atomic oxygen is preferably produced by a flowing afterglow microwave discharge. wherein the substrate resides in a sidearm out of the plasma. Also, methods for culturing cells for various purposes using the various membranes are disclosed as well. Also disclosed are porous organic polymers having a distributed pore chemistry (DPC) comprising hydrophilic and hydrophobic regions. and a method for making the DPC by exposing the polymer to atomic oxygen wherein the rate of hydrophilization is greater than the rate of mass loss.

  4. Pore-throat sizes in sandstones, tight sandstones, and shales

    USGS Publications Warehouse

    Nelson, Philip H.

    2009-01-01

    Pore-throat sizes in silidclastic rocks form a continuum from the submillimeter to the nanometer scale. That continuum is documented in this article using previously published data on the pore and pore-throat sizes of conventional reservoir rocks, tight-gas sandstones, and shales. For measures of central tendency (mean, mode, median), pore-throat sizes (diameters) are generally greater than 2 μm in conventional reservoir rocks, range from about 2 to 0.03 μm in tight-gas sandstones, and range from 0.1 to 0.005 μm in shales. Hydrocarbon molecules, asphaltenes, ring structures, paraffins, and methane, form another continuum, ranging from 100 Å (0.01 μm for asphaltenes to 3.8 A (0.00038 μm) for methane. The pore-throat size continuum provides a useful perspective for considering (1) the emplacement of petroleum in consolidated siliciclastics and (2) fluid flow through fine-grained source rocks now being exploited as reservoirs.

  5. Neutrons measure phase behavior in pores at Angstrom size

    SciTech Connect

    Bardoel, Agatha A; Melnichenko, Yuri B

    2012-01-01

    Researchers have measured the phase behavior of green house gases in pores at the Angstrom-level, using small angle neutron scattering (SANS) at the Oak Ridge National Laboratory's High Flux Isotope Reactor. Yuri Melnichenko, an instrument scientist on the General Purpose Small Angle Neutron Scattering (GP SANS) Diffractometer at ORNL's High Flux Isotope Reactor, his postdoctoral associate Lilin He and collaborators Nidia Gallego and Cristian Contescu from the Material Sciences Division (ORNL) were engaged in the work. They were studying nanoporous carbons to assess their attractiveness as storage media for hydrogen, with a view to potential use for on-board hydrogen storage for transportation applications. Nanoporous carbons can also serve as electrode material for supercapacitors and batteries. The researchers successfully determined that the most efficiently condensing pore size in a carbon nanoporous material for hydrogen storage is less than one nanometer. In a paper recently published by the Journal of the American Chemical Society, the collaborators used small angle neutron scattering to study how hydrogen condenses in small pores at ambient temperature. They discovered that the surface-molecule interactions create internal pressures in pores that may exceed the external gas pressure by a factor of up to 50. 'This is an exciting result,' Melnichenko said, 'as you achieve extreme densification in pores 'for free', i.e. without spending any energy. These results can be used to guide the development of new carbon adsorbents tailored to maximize hydrogen storage capacities.' Another important factor that defines the adsorption capacity of sub-nanometer pores is their shape. In order to get accurate structural information and maximize sorption capacity, it is important that pores are small and of approximately uniform size. In collaboration with Drexel University's Yury Gogotsi who supplied the samples, Melnichenko and his collaborators used the GP SANS

  6. Size effects of pore density and solute size on water osmosis through nanoporous membrane.

    PubMed

    Zhao, Kuiwen; Wu, Huiying

    2012-11-15

    Understanding the behavior of osmotic transport across nanoporous membranes at molecular level is critical to their design and applications, and it is also beneficial to the comprehension of the mechanism of biological transmembrane transport processes. Pore density is an important parameter for nanoporous membranes. To better understand the influence of pore density on osmotic transport, we have performed systematic molecular dynamics simulations on water osmosis across nanoporous membranes with different pore densities (i.e., number of pores per unit area of membrane). The simulation results reveal that significant size effects occur when the pore density is so high that the center-to-center distance between neighboring nanopores is comparable to the solute size. The size effects are independent of the pore diameter and solute concentration. A simple quantitative correlation between pore density, solute size, and osmotic flux has been established. The results are excellently consistent with the theoretical predictions. It is also shown that solute hydration plays an important role in real osmotic processes. Solute hydration strengthens the size effects of pore density on osmotic processes due to the enlarged effective solute size induced by hydration. The influence of pore density, solute size, and solute hydration on water osmosis through nanoporous membranes can be introduced to eliminate the deviations of real osmotic processes from ideal behavior.

  7. Size effects of pore density and solute size on water osmosis through nanoporous membrane.

    PubMed

    Zhao, Kuiwen; Wu, Huiying

    2012-11-15

    Understanding the behavior of osmotic transport across nanoporous membranes at molecular level is critical to their design and applications, and it is also beneficial to the comprehension of the mechanism of biological transmembrane transport processes. Pore density is an important parameter for nanoporous membranes. To better understand the influence of pore density on osmotic transport, we have performed systematic molecular dynamics simulations on water osmosis across nanoporous membranes with different pore densities (i.e., number of pores per unit area of membrane). The simulation results reveal that significant size effects occur when the pore density is so high that the center-to-center distance between neighboring nanopores is comparable to the solute size. The size effects are independent of the pore diameter and solute concentration. A simple quantitative correlation between pore density, solute size, and osmotic flux has been established. The results are excellently consistent with the theoretical predictions. It is also shown that solute hydration plays an important role in real osmotic processes. Solute hydration strengthens the size effects of pore density on osmotic processes due to the enlarged effective solute size induced by hydration. The influence of pore density, solute size, and solute hydration on water osmosis through nanoporous membranes can be introduced to eliminate the deviations of real osmotic processes from ideal behavior. PMID:23116121

  8. Grainsize and pore size changes due to the flow of granular materials

    NASA Astrophysics Data System (ADS)

    Marks, Benjy; Einav, Itai

    2014-05-01

    Granular materials exhibit behaviour which can cause spatial or local changes in their grainsize distribution, such as crushing, mixing and segregation. These mechanisms are modelled simultaneously using a cellular automaton, and the complex phenomena that emerge as they interact are explored. We find that either power law or log-normal grainsize distributions can develop. Finally, detailed information about the evolution of the local grainsize distribution is used to describe the evolution of the pore size distribution.

  9. Aromatization of Ethanol Over Desilicated ZSM-5 Zeolites: Effect of Pore Size in the Mesoporous Region.

    PubMed

    Jun, Jong Won; Hasan, Zubair; Kim, Chul-Ung; Jeong, Soon-Yong; Jhung, Sung Hwa

    2016-05-01

    Mesoporous ZSM-5 zeolites were obtained from microporous ZSM-5 by desilication using aqueous NaOH solutions, and their catalytic activity in the aromatization of ethanol was investigated in order to understand the effects of pore size, in the mesoporous region, on the product distribution and stability of the catalysts. Mesopores generally enhanced the selectivities towards aromatics and stability for aromatization. Mesopores with a maximum pore diameter of around 13 nm were the most effective in the aromatization process (especially for benzene and toluene), suggesting that pore-diameter optimization is necessary for efficient catalysis such as aromatization.

  10. Unraveling the potential and pore-size dependent capacitance of slit-shaped graphitic carbon pores in aqueous electrolytes.

    PubMed

    Kalluri, R K; Biener, M M; Suss, M E; Merrill, M D; Stadermann, M; Santiago, J G; Baumann, T F; Biener, J; Striolo, A

    2013-02-21

    Understanding and leveraging physicochemical processes at the pore scale are believed to be essential to future performance improvements of supercapacitors and capacitive desalination (CD) cells. Here, we report on a combination of electrochemical experiments and fully atomistic simulations to study the effect of pore size and surface charge density on the capacitance of graphitic nanoporous carbon electrodes. Specifically, we used cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) to study the effect of potential and pore size on the capacitance of nanoporous carbon foams. Molecular dynamics simulations were performed to study the pore-size dependent accumulation of aqueous electrolytes in slit-shaped graphitic carbon pores of different widths (0.65 to 1.6 nm). Experimentally, we observe a pronounced increase of the capacitance of sub-nm pores as the applied potential window gets wider, from a few F g(-1) for narrow potential ranges (-0.3 to 0.3 V vs. Ag/AgCl) to ~40 F g(-1) for wider potential windows (-0.9 V to 0.9 V vs. Ag/AgCl). By contrast, the capacitance of wider pores does not depend significantly on the applied potential window. Molecular dynamics simulations confirm that the penetration of ions into pores becomes more difficult with decreasing pore width and increasing strength of the hydration shell. Consistent with our experimental results, we observe a pore- and ion-size dependent threshold-like charging behavior when the pore width becomes comparable to the size of the hydrated ion (0.65 nm pores for Na(+) and 0.79 nm pores for Cl(-) ions). The observed pore-size and potential dependent accumulation of ions in slit-shaped carbon pores can be explained by the hydration structure of the ions entering the charged pores. The results are discussed in view of their effect on energy-storage and desalination efficiency.

  11. Pore distributions in nanocrystalline metals from small-angle neutron scattering

    SciTech Connect

    Sanders, P.G.; Weertman, J.R.; Eastman, J.A.

    1998-07-24

    Recent upgrades in inert-gas condensation processing equipment have produced nanocrystalline metal samples with high densities and low-impurity levels. Typical Cu and Pd samples have densities {ge}98% of theoretical and oxygen and hydrogen impurity concentrations {le}0.5 at. %. Lower porosity and impurity levels may make it difficult to produce and maintain samples with the smallest nanocrystalline grain sizes. These improved samples were studied by small-angle neutron scattering (SANS) to determine the volume fraction and size distribution of pores. Excellent correlation was obtained between the total volume fraction of pores and the Archimedes density for Pd, signifying that most of the pores were relatively small and in the detectability range of SANS ({approx}1--100 nm). Nanocrystalline Cu is shown to exhibit a wider pore size distribution. For Pd, the average pore sizes were slightly smaller than the average grain size, while for Cu the pore size and grain size were about the same. Both materials exhibited a trend of increasing pore size with increasing grain size. In terms of processing prerequisites, the principal condition for the production of high-density nanocrystalline Cu is an exceptionally clean synthesis environment, while nanocrystalline Pd requires compaction at elevated temperatures. These differences are the result of Cu having both a lower melting point and a greater susceptibility to contamination by gaseous impurities such as oxygen.

  12. Anomalous or regular capacitance? The influence of pore size dispersity on double-layer formation

    NASA Astrophysics Data System (ADS)

    Jäckel, N.; Rodner, M.; Schreiber, A.; Jeongwook, J.; Zeiger, M.; Aslan, M.; Weingarth, D.; Presser, V.

    2016-09-01

    The energy storage mechanism of electric double-layer capacitors is governed by ion electrosorption at the electrode surface. This process requires high surface area electrodes, typically highly porous carbons. In common organic electrolytes, bare ion sizes are below one nanometer but they are larger when we consider their solvation shell. In contrast, ionic liquid electrolytes are free of solvent molecules, but cation-anion coordination requires special consideration. By matching pore size and ion size, two seemingly conflicting views have emerged: either an increase in specific capacitance with smaller pore size or a constant capacitance contribution of all micro- and mesopores. In our work, we revisit this issue by using a comprehensive set of electrochemical data and a pore size incremental analysis to identify the influence of certain ranges in the pore size distribution to the ion electrosorption capacity. We see a difference in solvation of ions in organic electrolytes depending on the applied voltage and a cation-anion interaction of ionic liquids in nanometer sized pores.

  13. Distribution over pore radii in random and isotropic systems of polydisperse rods with finite aspect ratios

    NASA Astrophysics Data System (ADS)

    Chatterjee, Avik P.

    2016-06-01

    Excluded-volume arguments are applied toward modeling the pore-size distribution in systems of randomly arranged cylindrical rods with finite and nonuniform aspect ratios. An explicit expression for the pore-size distribution is obtained by way of an analogy to a hypothetical system of fully penetrable objects, through a mapping that is designed to preserve the volume fraction occupied by the particle cores and the specific surface area. Results are presented for the mean value and standard deviation of the pore radius as functions of the rod aspect ratio, volume fraction, and polydispersity (degree of nonuniformity in the aspect ratios of the particles).

  14. Effects of Pore Distributions on Ductility of Thin-Walled High Pressure Die-Cast Magnesium

    SciTech Connect

    Choi, Kyoo Sil; Li, Dongsheng; Sun, Xin; Li, Mei; Allison, John

    2013-06-01

    In this paper, a microstructure-based three-dimensional (3D) finite element modeling method is adopted to investigate the effects of porosity in thin-walled high pressure die-cast (HPDC) Magnesium alloys on their ductility. For this purpose, the cross-sections of AM60 casting samples are first examined using optical microscope and X-ray tomography to obtain the general information on the pore distribution features. The experimentally observed pore distribution features are then used to generate a series of synthetic microstructure-based 3D finite element models with different pore volume fractions and pore distribution features. Shear and ductile damage models are adopted in the finite element analyses to induce the fracture by element removal, leading to the prediction of ductility. The results in this study show that the ductility monotonically decreases as the pore volume fraction increases and that the effect of ‘skin region’ on the ductility is noticeable under the condition of same local pore volume fraction in the center region of the sample and its existence can be beneficial for the improvement of ductility. The further synthetic microstructure-based 3D finite element analyses are planned to investigate the effects of pore size and pore size distribution.

  15. Adsorption of phenolics on activated carbon--impact of pore size and molecular oxygen.

    PubMed

    Lu, Qiuli; Sorial, George A

    2004-05-01

    The impact of pore size of activated carbon fibers (ACFs) on adsorption capacity and on the potential for oligomerization of phenolic compounds on the surface of ACFs in the presence of molecular oxygen has been investigated in this study. Compared with granular activated carbon (GAC), ACFs have unique pore size distributions, suitable to be used to elucidate the effect of pore structure on adsorption. Adsorption isotherm data were collected for o-cresol and 2-ethylphenol on four ACFs (ACC-10, ACC-15, ACC-20, and ACC-25) with different micropore volumes and BET surface area and on one type of GAC bituminous base. These isotherms were collected under anoxic (absence of molecular oxygen) and oxic (presence of molecular oxygen) conditions. No significant impact of the presence of molecular oxygen on adsorption capacity was noted for ACC-10. ACC-10 has an average pore width of 19.2 A and total pore volume of 0.43 cm3g(-1). On the other hand, for the remaining ACFs, which have larger average pore width and larger pore volume, significant increase in the adsorptive capacity had been observed when molecular oxygen was present. The GAC gave the greatest difference between anoxic and oxic conditions when compared to all the ACFs studied. Binary adsorption of o-cresol and 2-ethylphenol on ACFs with the least pore size (ACC-10) also showed no significant differences between oxic and anoxic environment. The binary system under both anoxic and oxic conditions was well predicted by the ideal adsorbed solution theory (IAST).

  16. Facile fabrication of BiVO4 nanofilms with controlled pore size and their photoelectrochemical performances

    NASA Astrophysics Data System (ADS)

    Feng, Chenchen; Jiao, Zhengbo; Li, Shaopeng; Zhang, Yan; Bi, Yingpu

    2015-12-01

    We demonstrate a facile method for the rational fabrication of pore-size controlled nanoporous BiVO4 photoanodes, and confirmed that the optimum pore-size distributions could effectively absorb visible light through light diffraction and confinement functions. Furthermore, in situ X-ray photoelectron spectroscopy (XPS) reveals more efficient photoexcited electron-hole separation than conventional particle films, induced by light confinement and rapid charge transfer in the inter-crossed worm-like structures.We demonstrate a facile method for the rational fabrication of pore-size controlled nanoporous BiVO4 photoanodes, and confirmed that the optimum pore-size distributions could effectively absorb visible light through light diffraction and confinement functions. Furthermore, in situ X-ray photoelectron spectroscopy (XPS) reveals more efficient photoexcited electron-hole separation than conventional particle films, induced by light confinement and rapid charge transfer in the inter-crossed worm-like structures. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr06584d

  17. Effect of pretreatments and fermentation on pore size in cellulosic materials

    SciTech Connect

    Lin, K.W.; Ladisch, M.R.; Voloch, M.; Patterson, J.A.; Noller, C.H.

    1985-10-01

    Surface area has been proposed as a major factor determining the extent of enzymatic hydrolysis of cellulose. We used cornstalk residues (CR) and Solka Floc BW-300 (SF) as substrates and NaOH and iron sodium tartrate (FeTNa), as pretreatments to study the effect of surface area on extent of fermentation. Micropore sizes (8-130 A) were determined using glucose, cellobiose, and polyethylene glycols as molecular probes. The pore size distributions follow the logistic model function: l = a/(1 + exp(b-cX)) where l is pore volume; X = log D; D is the molecular probe diameter; and a, b, and c are constants. The pore volumes of CR (1.9 ml/g) and SF (1.6 ml/g) are increased to 2.1 ml/g by pretreatment with NaOH. Pretreatment of SF with NaOH and cornstalk residue with FeTNa caused an upward shift in the pore size distribution. Fermentation of untreated CR by rumen microbes resulted in a 46% loss of dry matter while increasing the internal pore size and decreasing the pore volume to 0.9 ml/g. Fermentation of NaOH pretreated CR resulted in a 73% loss of dry matter with little change in pore size, total pore volume, or fiber composition. Fiber analysis indicated that selective utilization of hemicellulose over cellulose in both fermentations was small. The data show that: 1) removal of hemicellulose and lignin increases dry matter disappearance upon fermentation of the remaining material; 2) relative to the size of bacterial cellulases (40-160A) the pretreatments have little effect on increasing accessibility of surface internal to the cellulose particles; and 3) the micropore changes caused by NaOH or FeTNa treatment do not explain the enhanced fermentation obtained for treated cr. These observations infer that external or macropore surface properties may be a significant factor in determining the extent of utilization of the solid substrates by cellulolytic microorganisms. 29 references.

  18. Hail Size Distribution Mapping

    NASA Technical Reports Server (NTRS)

    2008-01-01

    A 3-D weather radar visualization software program was developed and implemented as part of an experimental Launch Pad 39 Hail Monitor System. 3DRadPlot, a radar plotting program, is one of several software modules that form building blocks of the hail data processing and analysis system (the complete software processing system under development). The spatial and temporal mapping algorithms were originally developed through research at the University of Central Florida, funded by NASA s Tropical Rainfall Measurement Mission (TRMM), where the goal was to merge National Weather Service (NWS) Next-Generation Weather Radar (NEXRAD) volume reflectivity data with drop size distribution data acquired from a cluster of raindrop disdrometers. In this current work, we adapted these algorithms to process data from a cluster of hail disdrometers positioned around Launch Pads 39A or 39B, along with the corresponding NWS radar data. Radar data from all NWS NEXRAD sites is archived at the National Climatic Data Center (NCDC). That data can be readily accessed at . 3DRadPlot plots Level III reflectivity data at four scan elevations (this software is available at Open Channel Software, ). By using spatial and temporal interpolation/extrapolation based on hydrometeor fall dynamics, we can merge the hail disdrometer array data coupled with local Weather Surveillance Radar-1988, Doppler (WSR-88D) radial velocity and reflectivity data into a 4-D (3-D space and time) picture of hail size distributions. Hail flux maps can then be generated and used for damage prediction and assessment over specific surfaces corresponding to structures within the disdrometer array volume. Immediately following a hail storm, specific damage areas and degree of damage can be identified for inspection crews.

  19. Pore size engineering applied to the design of separators for nickel-hydrogen cells and batteries

    NASA Technical Reports Server (NTRS)

    Abbey, K. M.; Britton, D. L.

    1983-01-01

    Pore size engineering in starved alkaline multiplate cells involves adopting techniques to widen the volume tolerance of individual cells. Separators with appropriate pore size distributions and wettability characteristics (capillary pressure considerations) to have wider volume tolerances and an ability to resist dimensional changes in the electrodes were designed. The separators studied for potential use in nickel-hydrogen cells consist of polymeric membranes as well as inorganic microporous mats. In addition to standard measurements, the resistance and distribution of electrolyte as a function of total cell electrolyte content were determined. New composite separators consisting of fibers, particles and/or binders deposited on Zircar cloth were developed in order to engineer the proper capillary pressure characteristics in the separator. These asymmetric separators were prepared from a variety of fibers, particles and binders. Previously announced in STAR as N83-24571

  20. Pore size engineering applied to the design of separators for nickel-hydrogen cells and batteries

    NASA Technical Reports Server (NTRS)

    Abbey, K. M.; Britton, D. L.

    1983-01-01

    Pore size engineering in starved alkaline multiplate cells involves adopting techniques to widen the volume tolerance of individual cells. Separators with appropriate pore size distributions and wettability characteristics (capillary pressure considerations) to have wider volume tolerances and an ability to resist dimensional changes in the electrodes were designed. The separators studied for potential use in nickel-hydrogen cells consist of polymeric membranes as well as inorganic microporous mats. In addition to standard measurements, the resistance and distribution of electrolyte as a function of total cell electrolyte content were determined. New composite separators consisting of fibers, particles and/or binders deposited on Zircar cloth were developed in order to engineer the proper capillary pressure characteristics in the separator. These asymmetric separators were prepared from a variety of fibers, particles and binders.

  1. First Synthesis of Continuous Mesoporous Copper Films with Uniformly Sized Pores by Electrochemical Soft Templating.

    PubMed

    Li, Cuiling; Jiang, Bo; Wang, Zhongli; Li, Yunqi; Hossain, Md Shahriar A; Kim, Jung Ho; Takei, Toshiaki; Henzie, Joel; Dag, Ömer; Bando, Yoshio; Yamauchi, Yusuke

    2016-10-01

    Although mesoporous metals have been synthesized by electrochemical methods, the possible compositions have been limited to noble metals (e.g., palladium, platinum, gold) and their alloys. Herein we describe the first fabrication of continuously mesoporous Cu films using polymeric micelles as soft templates to control the growth of Cu under sophisticated electrochemical conditions. Uniformly sized mesopores are evenly distributed over the entire film, and the pore walls are composed of highly crystalized Cu. PMID:27554196

  2. Pore-throat sizes in sandstones, siltstones, and shales: Reply

    USGS Publications Warehouse

    Nelson, Philip H.

    2011-01-01

    In his discussion of my article (Nelson, 2009), W. K. Camp takes issue with the concept that buoyancy is not the dominant force in forming and maintaining the distribution of gas in tight-gas accumulations (Camp, 2011). I will restrict my response to the issues he raised regarding buoyant versus nonbuoyant drive and to a few comments regarding water saturation and production. I claim that the pressure generated in petroleum source rocks (Pg), instead of the buoyancy pressure (Pb), provides the energy to charge most tight sandstones with gas. The arguments are fourfold: (1) buoyant columns of sufficient height seldom exist in low-permeability sand-shale sequences, (2) tight-gas systems display a pressure profile that declines instead of increases upward, (3) gas is pervasive in overpressured systems, and (4) source rocks can generate pore pressures sufficiently high to charge tight sandstones.

  3. Improving prediction of hydraulic conductivity by constraining capillary bundle models to a maximum pore size

    NASA Astrophysics Data System (ADS)

    Iden, Sascha C.; Peters, Andre; Durner, Wolfgang

    2015-11-01

    The prediction of unsaturated hydraulic conductivity from the soil water retention curve by pore-bundle models is a cost-effective and widely applied technique. One problem for conductivity predictions from retention functions with continuous derivatives, i.e. continuous water capacity functions, is that the hydraulic conductivity curve exhibits a sharp drop close to water saturation if the pore-size distribution is wide. So far this artifact has been ignored or removed by introducing an explicit air-entry value into the capillary saturation function. However, this correction leads to a retention function which is not continuously differentiable. We present a new parameterization of the hydraulic properties which uses the original saturation function (e.g. of van Genuchten) and introduces a maximum pore radius only in the pore-bundle model. In contrast to models using an explicit air entry, the resulting conductivity function is smooth and increases monotonically close to saturation. The model concept can easily be applied to any combination of retention curve and pore-bundle model. We derive closed-form expressions for the unimodal and multimodal van Genuchten-Mualem models and apply the model concept to curve fitting and inverse modeling of a transient outflow experiment. Since the new model retains the smoothness and continuous differentiability of the retention model and eliminates the sharp drop in conductivity close to saturation, the resulting hydraulic functions are physically more reasonable and ideal for numerical simulations with the Richards equation or multiphase flow models.

  4. Silicon nanofilter with absolute pore size and high mechanical strength

    NASA Astrophysics Data System (ADS)

    Chu, Wen Hwa; Ferrari, Mauro

    1995-12-01

    Microfabricated silicon filters with a nominal pore size of 20 nm have been successfully fabricated and characterized. The filter consists of a filtration membrane on top of a silicon surface and a mechanical support on the silicon substrate. Two polysilicon layers together with a low temperature oxide layer are used to generate the filtration membrane on the front side of silicon wafers. The filtration function is accomplished by the flow channel generated from a sandwiched thin silicon dioxide layer. The thickness of the sandwiched oxide determines the particle size that can pass through the filter. Both distilled water and cell culture medium have been used to test the flow rate for this nanofilter. We have found that the flow rate of the nanofilter is highest at the beginning of the test, and then slowly decreases to its asymptotic values for both water and the cell culture medium. The observed flow rate is linearly proportional to the applied pressure in the ranges tested. The typical flow rate of distilled water for 20 nm filter with 1.19 cm2 effective filtration area is about 0.07 ml/min for applied pressure of 8 PSI. The filter successfully sustained pressure of up to 20 PSI.

  5. Potts model simulation of grain size distributions during final stage sintering

    SciTech Connect

    Zeng, P.; Tikare, V.

    1998-09-01

    The Potts Monte Carlo model was used to simulate microstructural evolution and characterize grain size distribution during the final stages of sintering. Simultaneous grain growth, pore migration and pore shrinkage were simulated in a system with an initial porosity of 10% with varying ratios of grain boundary mobility to pore shrinkage rates. This investigation shows that the presence of pores changes the grain size distribution and the topological characteristics due to pinning of grains by pores. As pores shrink away, their pinning effect decreases. Once pore shrinkage is complete, normal grain growth is achieved.

  6. Pore size and pore throat types in a heterogeneous dolostone reservoir, Devonian Grosmont formation, western Canada sedimentary basin

    SciTech Connect

    Luo, P.; Machel, H. G.

    1995-11-01

    The Devonian Grosmont Formation in northeastern Alberta, Canada, is a giant heavy-oil reservoir. The main reservoir rocks are dolomitized and karstified platform and ramp carbonates, and the best reservoir facies occur in the upper Grosmont (UGM) units 3 and 2. In these units, reservoir properties are highly heterogeneous. Hand specimen, thin section, UV, and SEM petrography, as well as grading scales, mercury capillary pressure curve analysis, and statistics, have been used to characterize reservoir heterogeneity. Our investigation led to a new pore size classification for carbonate reservoirs; this new classification has four pore sizes: microporosity (pore diameters <1 {mu}m), mesoporosity (pore diameters 1-1000 {mu}m), macroporosity (pore diameters 1-256 mm), and megaporosity (pore diameters >256 mm). A combination of microscopic observations and capillary pressure curve characteristics led to the recognition of four pore throat texture types on the microporosity scale, and to five types on the mesoporosity scale. Microporosity pore types include (1) intracrystal dissolution porosity, (2) pervasive intercrystal and intracrystal dissolution porosity, (3) intergranular and/or intercrystal porosity in grainstones, and (4) primary or solution microporosity in mud matrix (only in limestones). Mesoporosity pore types include (1) intercrystal porosity, (2) solution-enhanced intercrystal porosity, (3) oversized porosity, (4) intragranular solution porosity, and (5) intergranular solution porosity. Some of these types are homogeneous (e.g., non-fabric selective dissolution porosity and intercrystal primary porosity), whereas others are heterogeneous. Generally, hydrocarbon recovery efficiency is good in the homogeneous pore throat types, but poor in the heterogeneous types.

  7. Determining the dynamic range of MCPs based on pore size and strip current

    NASA Astrophysics Data System (ADS)

    Hunt, C.; Adrian, M. L.; Herrero, F.; James, P.; Jones, H. H.; Rodriguez, M.; Roman, P.; Shappirio, M.

    2010-12-01

    Micro-Channel Plates (MCPs) are used as detectors for almost all detectors measuring particles (both ions, electrons and neutrals) below 30 keV. Recent advances in the manufacturing technology of the MCPs have increased the number of options one has when selecting plates for an instrument. But it is not clear how many of these options affect the performance of the MCPs. In particular the dynamic range is not a clear cut calculation to make from the strip current. There is also some evidence that pore size and coating play a role. We measured the dynamic range and pulse height distribution of MCPs detector chevron stacks with a wide variety of strip currents from the low “normal” range in the EDR range. We also looked at the effects of varying the pore size from 25 microns to 10 microns, partial plating of the MCP surface and coating one surface on each MCP with gold rather than the standard zinc chromium. We will show how the dynamic range and pulse height distributions vary vs. strip current, pore size, and surface plating configurations.

  8. Nuclear magnetic resonance pore size determination for unconsolidated sediments with strong internal gradients

    NASA Astrophysics Data System (ADS)

    Duschl, M.; Pohlmeier, A. J.; Galvosas, P.; Vereecken, H.

    2014-12-01

    Water distribution and flow within porous media are mainly controlled by the pore space structure. Well established methods for the determination of pore sizes like multistep outflow and gas adsorption isotherms (BET) are often time consuming, expensive, or produce toxic waste. As an alternative fast and non-destructive technique, nuclear magnetic resonance (NMR) is used because it probes hydrogen and therefore the dynamics and interactions of water. Pore space is most easily characterized by NMR relaxometry where the total relaxation rate is controlled by the surface relaxivity ρ of the porous medium in combination with the surface-to-volume ratio (S/V) [1]. Furthermore, there are contributions of molecular diffusion through local magnetic field gradients which are created by susceptibility differences between solid and liquid phases [2] as well as by paramagnetic impurities [3]. Hence, surface to volume ratios and surface relaxivities of porous media cannot be measured individually with NMR relaxometry. Therefore, NMR diffusion measurements are applied to probe the S/V of pores without other contributions. In this study, we demonstrate that NMR diffusion measurements are feasible to determine the S/V ratio of the pore space of quartz sand coated with goethite (α-FeOOH) as paramagnetic impurity. Our findings were compared to BET measurements and we found no dependence of the S/V on the coating density with NMR diffusion and a clear dependence between coating density and S/V with krypton BET measurements. Possible explanations are the different characteristic length scales on which the pore space is probed, and the intrinsic fractal nature of porous media [4] together with the roughness of the pore surface on a nm-scale due to the coating process. After isolating the additional contribution of the paramagnetic impurities to the NMR relaxation and the calibration of the NMR relaxation signal for each coating density it was possible to use fast relaxometry

  9. Controlling the pore sizes and related properties of inverse opal scaffolds for tissue engineering applications.

    PubMed

    Zhang, Yu Shrike; Regan, Kevin P; Xia, Younan

    2013-03-25

    Inverse opal scaffolds are finding widespread use in tissue engineering and regenerative medicine. Herein, the way in which the pore sizes and related physical properties of poly(D,L-lactide-co-glycolide) inverse opal scaffolds are affected by the fabrication conditions is systematically investigated. It is found that the window size of an inverse opal scaffold is mainly determined by the annealing temperature rather than the duration of time, and the surface pore size is largely determined by the concentration of the infiltration solution. Although scaffolds with larger pore or window sizes facilitate faster migration of cells, they show slightly lower compressive moduli than scaffolds with smaller pore or window sizes.

  10. Pore space analysis of NAPL distribution in sand-clay media

    USGS Publications Warehouse

    Matmon, D.; Hayden, N.J.

    2003-01-01

    This paper introduces a conceptual model of clays and non-aqueous phase liquids (NAPLs) at the pore scale that has been developed from a mathematical unit cell model, and direct micromodel observation and measurement of clay-containing porous media. The mathematical model uses a unit cell concept with uniform spherical grains for simulating the sand in the sand-clay matrix (???10% clay). Micromodels made with glass slides and including different clay-containing porous media were used to investigate the two clays (kaolinite and montmorillonite) and NAPL distribution within the pore space. The results were used to understand the distribution of NAPL advancing into initially saturated sand and sand-clay media, and provided a detailed analysis of the pore-scale geometry, pore size distribution, NAPL entry pressures, and the effect of clay on this geometry. Interesting NAPL saturation profiles were observed as a result of the complexity of the pore space geometry with the different packing angles and the presence of clays. The unit cell approach has applications for enhancing the mechanistic understanding and conceptualization, both visually and mathematically, of pore-scale processes such as NAPL and clay distribution. ?? 2003 Elsevier Science Ltd. All rights reserved.

  11. The failure of hydrodynamic analysis to define pore size in cell membranes.

    PubMed

    Galey, W R; Brahm, J

    1985-09-10

    The equivalent pore theory predicts that the size of water transporting pores can be calculated from the ratio of osmotic (Pf, cm . s-1) to diffusive (Pd, cm . s-1) water permeability. Determinations of Pf and Pd in human red cells within the last thirty years have increased the ratio of Pf to Pd. According to the equivalent pore theory the pore diameter has increased from 9 A to 25 A. A pore diameter of 25 A is not compatible with the permeability characteristics of the red cell membrane. We conclude that the equivalent pore theory fails to determine pore size in red blood cells. We suggest that water transporting pores in human red cells transport water molecules in a single file fashion. PMID:2994730

  12. Characterization of pore scale NAPL morphology in homogeneous sands as a function of grain size and NAPL dissolution.

    PubMed

    Cho, Jaehyun; Annable, Michael D

    2005-11-01

    In this study, we investigate pore scale morphology of nonaqueous phase liquids (NAPLs) trapped in different pore sizes using tracer techniques. Specific interfacial area and saturation of NAPL trapped in homogeneous sands were measured using the interfacial and partitioning tracer techniques. The observed NAPL-water interfacial areas increased in a log-linear fashion with decreasing sand grain size, but showed no clear trend with residual NAPL saturation formed in the various grain sizes. The measured values were used to calculate the NAPL morphology index, which characterizes the spatial NAPL distribution within the pore space. The NAPL morphology indices, increased exponentially with decreasing grain size, indicating that the NAPL becomes smaller, but more blobs. For a fixed grain size, the specific interfacial area and saturation of the NAPL were measured following changes caused by dissolution using alcohol. The observed interfacial areas showed a decrease linearly as a function of the NAPL saturation.

  13. Two micron pore size MCP-based image intensifiers

    NASA Astrophysics Data System (ADS)

    Glesener, John; Estrera, Joseph

    2010-02-01

    Image intensifiers (I2) have many advantages as detectors. They offer single photon sensitivity in an imaging format, they're light in weight and analog I2 systems can operate for hours on a single AA battery. Their light output is such as to exploit the peak in color sensitivity of the human eye. Until recent developments in CMOS sensors, they also were one of the highest resolution sensors available. The closest all solid state solution, the Texas Instruments Impactron chip, comes in a 1 megapixel format. Depending on the level of integration, an Impactron based system can consume 20 to 40 watts in a system configuration. In further investing in I2 technology, L-3 EOS determined that increasing I2 resolution merited a high priority. Increased I2 resolution offers the system user two desirable options: 1) increased detection and identification ranges while maintaining field-of-view (FOV) or 2) increasing FOV while maintaining the original system resolution. One of the areas where an investment in resolution is being made is in the microchannel plate (MCP). Incorporation of a 2 micron MCP into an image tube has the potential of increasing the system resolution of currently fielded systems. Both inverting and non-inverting configurations are being evaluated. Inverting tubes are being characterized in night vision goggle (NVG) and sights. The non-inverting 2 micron tube is being characterized for high resolution I2CMOS camera applications. Preliminary measurements show an increase in the MTF over a standard 5 micron pore size, 6 micron pitch plate. Current results will be presented.

  14. Laser scanning confocal microscopy characterization of water repellent distribution in a sandstone pore network.

    PubMed

    Zoghlami, Karima; Gómez-Gras, David; Corbella, Mercè; Darragi, Fadila

    2008-11-01

    In the present work, we propose the use of the Laser Scanning Confocal Microscopy (LSCM) to determine the effect of water repellents on rock's pore-network configuration and interconnection. The rocks studied are sandstones of Miocene age, a building material that is commonly found in the architectural heritage of Tunisia. The porosity quantitative data of treated and untreated samples, obtained by mercury porosimetry tests, were compared. The results show a slight decrease in total porosity with the water repellent treatment, which reduced both microporosity and macroporosity. This reduction produced a modification in pore size distribution and a shift of the pore access size mode interval toward smaller pore diameters (from the 30-40 microm to the 20-30 microm intervals). The water repellent was observed in SEM images as a continuous film coating grain surfaces; moreover, it was easily visualized in LSCM, by staining the water repellent with Epodye fluorochrome, and the coating thickness was straightforwardly measured (1.5-2 microm). In fact, the combination of mercury intrusion porosimetry data and LSCM observations suggests that the porosity reduction and the shift of the pore diameter mode were mainly due to the general reduction of pore diameters, but also to the plugging of the smallest pores (less than 3-4 microm in diameter) by the water repellent film. Finally, the LSCM technique enabled the reconstruction of 3D views of the water repellent coating film in the pore network, indicating that its distribution was uniform and continuous over the 100 microm thick sample. The LSCM imaging facilitates the integration and interpretation of mercury porosimetry and SEM data. PMID:18767050

  15. A general diagram for estimating pore size of ultrafiltration and reverse osmosis membranes

    NASA Technical Reports Server (NTRS)

    Sarbolouki, M. N.

    1982-01-01

    A slit sieve model has been used to develop a general correlation between the average pore size of the upstream surface of a membrane and the molecular weight of the solute which it retains by better than 80%. The pore size is determined by means of the correlation using the high retention data from an ultrafiltration (UF) or a reverse osmosis (RO) experiment. The pore population density can also be calculated from the flux data via appropriate equations.

  16. Discontinuous pore fluid distribution under microgravity--KC-135 flight investigations.

    PubMed

    Reddi, Lakshmi N; Xiao, Ming; Steinberg, Susan L

    2005-01-01

    Designing a reliable plant growth system for crop production in space requires the understanding of pore fluid distribution in porous media under microgravity. The objective of this experimental investigation, which was conducted aboard NASA KC-135 reduced gravity flight, is to study possible particle separation and the distribution of discontinuous wetting fluid in porous media under microgravity. KC-135 aircraft provided gravity conditions of 1, 1.8, and 10(-2) g. Glass beads of a known size distribution were used as porous media; and Hexadecane, a petroleum compound immiscible with and lighter than water, was used as wetting fluid at residual saturation. Nitrogen freezer was used to solidify the discontinuous Hexadecane ganglia in glass beads to preserve the ganglia size changes during different gravity conditions, so that the blob-size distributions (BSDs) could be measured after flight. It was concluded from this study that microgravity has little effect on the size distribution of pore fluid blobs corresponding to residual saturation of wetting fluids in porous media. The blobs showed no noticeable breakup or coalescence during microgravity. However, based on the increase in bulk volume of samples due to particle separation under microgravity, groups of particles, within which pore fluid blobs were encapsulated, appeared to have rearranged themselves under microgravity.

  17. Discontinuous pore fluid distribution under microgravity--KC-135 flight investigations

    NASA Technical Reports Server (NTRS)

    Reddi, Lakshmi N.; Xiao, Ming; Steinberg, Susan L.

    2005-01-01

    Designing a reliable plant growth system for crop production in space requires the understanding of pore fluid distribution in porous media under microgravity. The objective of this experimental investigation, which was conducted aboard NASA KC-135 reduced gravity flight, is to study possible particle separation and the distribution of discontinuous wetting fluid in porous media under microgravity. KC-135 aircraft provided gravity conditions of 1, 1.8, and 10(-2) g. Glass beads of a known size distribution were used as porous media; and Hexadecane, a petroleum compound immiscible with and lighter than water, was used as wetting fluid at residual saturation. Nitrogen freezer was used to solidify the discontinuous Hexadecane ganglia in glass beads to preserve the ganglia size changes during different gravity conditions, so that the blob-size distributions (BSDs) could be measured after flight. It was concluded from this study that microgravity has little effect on the size distribution of pore fluid blobs corresponding to residual saturation of wetting fluids in porous media. The blobs showed no noticeable breakup or coalescence during microgravity. However, based on the increase in bulk volume of samples due to particle separation under microgravity, groups of particles, within which pore fluid blobs were encapsulated, appeared to have rearranged themselves under microgravity.

  18. Effect of pore size and interpore distance on endothelial cell growth on polymers.

    PubMed

    Narayan, D; Venkatraman, S S

    2008-12-01

    The endothelization of polymers using surface modification has received great attention. In particular, creation of physical surface features such as craters or pores has been an active area of research. However, there have been no reported studies of the effects of pore sizes (wide range) and interpore distance on endothelial cell growth. This report details the study done on endothelial cell attachment on the surfaces of polymers modified by porogen leaching. The polymeric system studied includes PLLA and PLGA (80/20). Factors such as porogen type, pore size, and interpore distance were varied, and the surface was evaluated for its influence on endothelial cell growth. Three groups of pore sizes were evaluated: small (5-20 mum), medium (20-45 mum), and large pores (45-90 mum). Two porogens were evaluated: sugar and gelatin. In addition to counting the attached endothelial cells, their proliferation was also quantified. Pore size and interpore distances were evaluated using scanning electron microscopy (SEM), and cell morphology was studied by staining with crystal violet. Analysis of variance demonstrated that the main parameters, pore size and interpore distance were significant in endothelial cell growth. In PLGA (80/20), it was found that endothelial cell growth was enhanced by smaller pore size and lower interpore distance, whereas the growth was poor on PLLA regardless of pore features. PMID:18200559

  19. Kinetic narrowing of size distribution

    NASA Astrophysics Data System (ADS)

    Dubrovskii, V. G.

    2016-05-01

    We present a model that reveals an interesting possibility for narrowing the size distribution of nanostructures when the deterministic growth rate changes its sign from positive to negative at a certain stationary size. Such a behavior occurs in self-catalyzed one-dimensional III-V nanowires and more generally whenever a negative "adsorption-desorption" term in the growth rate is compensated by a positive "diffusion flux." By asymptotically solving the Fokker-Planck equation, we derive an explicit representation for the size distribution that describes either Poissonian broadening or self-regulated narrowing depending on the parameters. We show how the fluctuation-induced spreading of the size distribution can be completely suppressed in systems with size self-stabilization. These results can be used for obtaining size-uniform ensembles of different nanostructures.

  20. Effect on the Pore-Size Dependence of an Organic Electrolyte Supercapacitor

    SciTech Connect

    Jiang, Deen; Jin, Zhehui; Henderson, Douglous; Wu, Jianzhong

    2012-01-01

    Organic electrolytes such as tetraethylammonium tetrafluoroborate dissolved in acetonitrile (TEA-BF{sub 4}/ACN) are widely used in commercial supercapacitors and academic research, but conflicting experimental results have been reported regarding the dependence of surface-area-normalized capacitance on the pore size. Here we show from a classical density functional theory the dependence of capacitance on the pore size from 0.5 to 3.0 nm for a model TEA-BF{sub 4}/ACN electrolyte. We find that the capacitance-pore size curve becomes roughly flat after the first peak around the ion diameter, and the peak capacitance is not significantly higher than the large-pore average. We attribute the invariance of capacitance with the pore size to the formation of an electric double-layer structure that consists of counterions and highly organized solvent molecules. This work highlights the role of the solvent molecules in modulating the capacitance and reconciles apparently conflicting experimental reports.

  1. A direct and quantitative three-dimensional reconstruction of the internal structure of disordered mesoporous carbon with tailored pore size.

    PubMed

    Balach, Juan; Soldera, Flavio; Acevedo, Diego F; Mücklich, Frank; Barbero, César A

    2013-06-01

    A new technique that allows direct three-dimensional (3D) investigations of mesopores in carbon materials and quantitative characterization of their physical properties is reported. Focused ion beam nanotomography (FIB-nt) is performed by a serial sectioning procedure with a dual beam FIB-scanning electron microscopy instrument. Mesoporous carbons (MPCs) with tailored mesopore size are produced by carbonization of resorcinol-formaldehyde gels in the presence of a cationic surfactant as a pore stabilizer. A visual 3D morphology representation of disordered porous carbon is shown. Pore size distribution of MPCs is determined by the FIB-nt technique and nitrogen sorption isotherm methods to compare both results. The obtained MPCs exhibit pore sizes of 4.7, 7.2, and 18.3 nm, and a specific surface area of ca. 560 m(2)/g.

  2. Magnetic relaxation - coal swelling, extraction, pore size. Final technical report

    SciTech Connect

    Doetschman, D.C.

    1994-10-26

    The aim of the contract was to employ electron and nuclear magnetic relaxation techniques to investigate solvent swelling of coals, solvent extraction of coals and molecular interaction with solvent coal pores. Many of these investigations have appeared in four major publications and a conference proceedings. Another manuscript has been submitted for publication. The set of Argonne Premium Coals was chosen as extensively characterized and representative samples for this project.

  3. Pore-size-dependent calcium carbonate precipitation controlled by surface chemistry.

    PubMed

    Stack, Andrew G; Fernandez-Martinez, Alejandro; Allard, Lawrence F; Bañuelos, José L; Rother, Gernot; Anovitz, Lawrence M; Cole, David R; Waychunas, Glenn A

    2014-06-01

    Induced mineral precipitation is potentially important for the remediation of contaminants, such as during mineral trapping during carbon or toxic metal sequestration. The prediction of precipitation reactions is complicated by the porous nature of rocks and soils and their interaction with the precipitate, introducing transport and confinement effects. Here X-ray scattering measurements, modeling, and electron microscopies were used to measure the kinetics of calcium carbonate precipitation in a porous amorphous silica (CPG) that contained two discrete distributions of pore sizes: nanopores and macropores. To examine the role of the favorability of interaction between the substrate and precipitate, some of the CPG was functionalized with a self-assembled monolayer (SAM) similar to those known to enhance nucleation densities on planar substrates. Precipitation was found to occur exclusively in macropores in the native CPG, while simultaneous precipitation in nanopores and macropores was observed in the functionalized CPG. The rate of precipitation in the nanopores estimated from the model of the X-ray scattering matched that measured on calcite single crystals. These results suggest that the pore-size distribution in which a precipitation reaction preferentially occurs depends on the favorability of interaction between substrate and precipitate, something not considered in most studies of precipitation in porous media.

  4. Exploring possible relationships between plate pore size character and cell performance

    NASA Technical Reports Server (NTRS)

    Thaller, Lawrence H.; Hill, Melvin; Tinker, Lawrence A.; Dell, R. Dan

    1991-01-01

    The pore size character and plate manufacturing information for selected samples of older plate material were reviewed. When compared to certain cell performance parameters, certain correlations were found between plate pore character and cell performance. This technique may be useful for screening out certain types of plate material prior to assembly into cells.

  5. Analysis and Visualization of 2D and 3D Grain and Pore Size ofFontainebleau Sandstone Using Digital Rock Physics

    NASA Astrophysics Data System (ADS)

    Latief, FDE

    2016-08-01

    Fontainebleau sandstone is sandstone found in one of the cities in France. This sandstone has unique characteristics, which is a clean-fme sandstone, composed of 99% quartz, virtually devoid of clay, with the grain size of about 200 μm. Fontainebleau sandstone is widely used as a reference in the study of rock microstructure analysis and modelling. In this work analysis regarding the grain and pore size of Fontainebleau is presented. Calculation of 2D pore size and grain size distribution were done on the 299 slice of digital image of the Fontainebleau sandstone using Feret's diameters, equivalent diameters (d = 4A/P), and by means of local thickness/separation using plate model. For the 3D grain and pore size distribution, calculation of local thickness and local separation of the structure were used. Two dimensional analysis by means of Feret's diameter and equivalent diameter reveal that both grain and pore size distributions are in the form of reverse-J shaped (right skewed) while the local thickness/separation approach produces almost similar to symmetric Gaussian distribution. Three dimensional analysis produces fairly symmetric Gaussian distribution for both the grain and pore size. Further image processing were conducted and were succeed in producing three dimensional visual of the colour coded structure thickness (grain related) and structure separation (pore related).

  6. Heat of adsorption and density distribution in slit pores with defective walls: GCMC simulation studies and comparison with experimental data

    NASA Astrophysics Data System (ADS)

    Do, D. D.; Nicholson, D.; Do, H. D.

    2007-04-01

    The adsorption behavior (capacity, density distribution and packing density) and the isosteric heat versus loading in a slit pore whose walls contain defective graphene layers are investigated in this paper. The defective wall is characterized by the extent and size of the defect. Simulation results obtained with the Grand Canonical Monte Carlo method reveal complex patterns of isosteric heat, and this complex behavior is a result of the interplay between three factors: (i) the surface heterogeneity (solid-fluid interaction, sites with varying degree of affinity), (ii) fluid-fluid interaction and (iii) the overlapping of potentials exerted by the two defective walls. We illustrate this with argon adsorption in pores of various sizes, and results obtained from the simulation agree qualitatively with the experimental data at 77 K on Saran microporous S600H and micro-mesoporous S84 charcoals of Beebe et al. [R.A. Beebe, B. Millard, J. Cynarski, J. Am. Chem. Soc. 75 (1953) 839]. The S600H was found to contain pores predominantly in the neighborhood of 7 Å with 30% of defect and a defective size of 2.84 Å. This is consistent with the argument made by Beebe et al. that this sample is a microporous solid and most pores can accommodate only one layer. The other sample, S84, has larger pores than S600H, and it is found that it has a wider pore size distribution and the pore width is centered at about 12 Å.

  7. Pore Scale Heterogeneity in the Mineral Distribution and Surface Area of Porous Rocks

    NASA Astrophysics Data System (ADS)

    Lai, Peter; Krevor, Sam

    2015-04-01

    An important control on rate of interfacial processes between minerals and aqueous solutions such as nucleation of solids, and mineral dissolution and growth is reactive surface area. In geochemical modelling, the continuum hypothesis is based on the assumption that the system can be represented by a sufficiently large number of representative elemental volumes. There has been recent interest in studying the impact of this assumption on reaction-transport coupled systems. In this study, the impact of pore-scale heterogeneity on the distribution of reactive surface area is discussed. 3D images obtained using x-ray micro-tomography were used to characterise the distribution of reactive surface area. The results were compared to independent observations. Mineral identification using x- ray diffraction and fluorescence suggested general agreement with CT analysis. Nitrogen BET surface areas were one to two orders of magnitude higher than measurements from x-ray imagery. Co- registered images of Berea sandstone from x-ray and energy dispersive spectroscopy imagery suggested that quartz, K-feldspar and most clays could be identified. However, minor minerals such as albite and illite did not exhibit enough contrast. In Berea sandstone, mineral surface area fraction was poorly correlated to the mineral volumetric fraction. Clay and feldspar minerals exhibited higher surface area fractions than bulk mineralogy suggested. In contrast, in the Edwards carbonate samples, modal mineral composition correlated with mineral-specific surface area. Berea sandstone revealed a characteristic pore size at which a surface area distribution may be used to quantify heterogeneity. Conversely, the carbonate samples suggested a continuous range of pore sizes across length scales. A comparison with pore network model simulations from the literature was made. First order estimates of mineral specific correlations between geometric area measured in the x-ray images were used to convert the CT

  8. Pore Distribution and Water Uptake in a Cenosphere-Cement Paste Composite Material

    NASA Astrophysics Data System (ADS)

    Baronins, J.; Setina, J.; Sahmenko, G.; Lagzdina, S.; Shishkin, A.

    2015-11-01

    Alumina silicate cenospheres (CS) is a significant waste material from power plants that use a coal. Use CS as Portland cement replacement material gives opportunity to control physical and mechanical properties and makes a product lighter and more cost-effective. In the frame of this study, Portland cement paste samples were produced by adding CS in the concentration range from 0 to 40 volume %. Water uptake of hardened samples was checked and pore size distribution by using the mercury porosimetry was determined. In a cold climate where the temperature often falls below 0 °C, it is important to avoid the amount of micrometer sized pores in the final structure and to decrease water absorption capacity of material. In winter conditions, water fills such pores and causes additional stresses to their walls by expansion while freezing. It was found that generally water uptake capacity for cement paste samples decreased up to 20% by increasing the concentration of CS up to 40 volume %, at the same time, the volume of micrometer sized opened pores increases.

  9. Controlling internal pore sizes in bicontinuous polymeric nanospheres.

    PubMed

    McKenzie, Beulah E; Friedrich, Heiner; Wirix, Maarten J M; de Visser, Joël F; Monaghan, Olivia R; Bomans, Paul H H; Nudelman, Fabio; Holder, Simon J; Sommerdijk, Nico A J M

    2015-02-16

    Complex polymeric nanospheres were formed in water from comb-like amphiphilic block copolymers. Their internal morphology was determined by three-dimensional cryo-electron tomographic analysis. Varying the polymer molecular weight (MW) and the hydrophilic block weight content allowed for fine control over the internal structure. Construction of a partial phase diagram allowed us to determine the criteria for the formation of bicontinuous polymer nanosphere (BPN), namely for copolymers with MW of up to 17 kDa and hydrophilic weight fractions of ≤0.25; and varying the organic solvent to water ratio used in their preparation allowed for control over nanosphere diameters from 70 to 460 nm. Significantly, altering the block copolymer hydrophilic-hydrophobic balance enabled control of the internal pore diameter of the BPNs from 10 to 19 nm. PMID:25640026

  10. Anomalous increase in carbon capacitance at pore sizes less than 1 nanometer.

    PubMed

    Chmiola, J; Yushin, G; Gogotsi, Y; Portet, C; Simon, P; Taberna, P L

    2006-09-22

    Carbon supercapacitors, which are energy storage devices that use ion adsorption on the surface of highly porous materials to store charge, have numerous advantages over other power-source technologies, but could realize further gains if their electrodes were properly optimized. Studying the effect of the pore size on capacitance could potentially improve performance by maximizing the electrode surface area accessible to electrolyte ions, but until recently, no studies had addressed the lower size limit of accessible pores. Using carbide-derived carbon, we generated pores with average sizes from 0.6 to 2.25 nanometer and studied double-layer capacitance in an organic electrolyte. The results challenge the long-held axiom that pores smaller than the size of solvated electrolyte ions are incapable of contributing to charge storage.

  11. Pore scale heterogeneity in the mineral distribution and reactive surface area of rocks

    NASA Astrophysics Data System (ADS)

    Lai, P. E.; Krevor, S. C.

    2013-12-01

    There are long-standing challenges in characterizing reactive transport in porous media at scales larger than individual pores. This hampers the prediction of the field-scale impact of geochemical processes on fluid flow [1]. This is a source of uncertainty for CO2 injection, which results in a reactive fluid-rock system, particularly in carbonate rock reservoirs. A potential cause is the inability of the continuum approach to incorporate the impact of heterogeneity in pore-scale reaction rates. This results in part from pore-scale heterogeneities in surface area of reactive minerals [2,3]. In this study we have created μm resolution 3D images of 3 sandstone and 4 carbonate rocks using x-ray microtomography. Using in-house image processing techniques and auxiliary characterisation with thin section, electron microscope and spectroscopic techniques we quantified the surface area of each mineral phase in the x-ray CT images. This quantification was validated against N2 BET surface area and He porosity measurements of the imaged samples. Distributions in reactive surface area for each mineral phase were constructed by calculating surface areas in thousands of randomly selected subvolume images of the total sample, each normalized to the pore volume in that image. In all samples, there is little correlation between the reactive surface area fraction and the volumetric fraction of a mineral in a bulk rock. Berea sandstone was far less heterogeneous and has a characteristic pore size at which a surface area distribution may be used to quantify heterogeneity. In carbonates, heterogeneity is more complex and surface area must be characterized at multiple length scales for an accurate description of reactive transport. [1] Maher, Steefel, Depaolo and Vianni (2006) Geochimica et Cosmochimica Acta, 70, 337-363 [2] Landrot, Ajo-Franklin, Yang, Cabrini and Steefel (2012) Chemical Geology 318-319, 113-125 [3] Li, Peters and Celia (2007) American Journal of Science 307, 1146

  12. Pore formation of phospholipid membranes by the action of two hemolytic arachnid peptides of different size.

    PubMed

    Belokoneva, Olga S; Satake, Honoo; Mal'tseva, Elena L; Pal'mina, Nadezhda P; Villegas, Elba; Nakajima, Terumi; Corzo, Gerardo

    2004-08-30

    Pin2 and Oxki1 are cationic amphipathic peptides that permeate lipid membranes through formation of pores. Their mechanism of binding to phosphocholine (PC) membranes differs. Spin-probe experiments showed that both Pin2 and Oxki1 penetrate the lipid membrane of small unilamellar vesicles (SUVs). Moreover, the leakage of calcein and dextrans from PC vesicles showed that Pin2 agrees with the accumulation of peptides on lipid membranes and form pores of different size. On the other hand, Oxki1 did not act strictly cooperatively and form pores of limited size.

  13. IMPACT OF COMPOSITION AND HEAT TREATMENT ON PORE SIZE IN POROUS WALLED HOLLOW GLASS MICROSPHERES

    SciTech Connect

    Raszewski, F; Erich Hansen, E; Ray Schumacher, R; David Peeler, D

    2007-12-04

    The Savannah River National Laboratory (SRNL) developed a new geometric form: hollow glass microspheres (HGMs), with unique porous walls. The new geometric form combines the existing technology of HGMs with basic glass science knowledge in the realm of glass-in-glass phase separation. Conceptually, the development of a HGM with porous walls (referred to as a PWHGM) provides a unique system in which various media or filling agents can be incorporated into the PWHGM (via transport through the porous walls) and ultimately has the capacity to serve as a functional delivery system in various industrial applications. Applications of these types of systems could range from hydrogen storage, molecular sieves, drug and bioactive delivery systems, to environmental, chemical and biological indicators, relevant to Energy, Environmental Processing and Homeland Security fields. As a specific example, previous studies at SRNL have introduced materials capable of hydrogen storage (as well as other materials) into the interior of the PWHGMs. The goal of this project was to determine if the microstructure (i.e., pore size and pore size distribution) of a PWHGM could be altered or tailored by varying composition and/or heat treatment (time and/or temperature) conditions. The ability to tailor the microstructure through composition or heat treatments could provide the opportunity to design the PWHGM system to accommodate different additives or fill agents. To meet this objective, HGMs of various alkali borosilicate compositions were fabricated using a flame forming apparatus installed at the Aiken County Technical Laboratory (ACTL). HGMs were treated under various heat treatment conditions to induce and/or enhance glass in glass phase separation. Heat treatment temperatures ranged from 580 C to 620 C, while heat treatment times were either 8 or 24 hours. Of the two primary variables assessed in this study, heat treatment temperature was determined to be most effective in changing the

  14. Determination of an equivalent pore size from acoustic flow measurements

    NASA Astrophysics Data System (ADS)

    Clark, Linde; Liu, Jin; Garrett, Steven

    2005-09-01

    The hydraulic radius, rh, is defined as the ratio of a channel's cross-sectional area to its perimeter. This parameter is important for specification of the performance of a porous medium that can be used as a regenerator in a Stirling engine or refrigerator. It is easy to calculate rh for pores of regular geometry, but difficult in more complex media. Two techniques which use oscillating flow to determine this parameter will be presented and compared. One technique extracts rh by finding the low velocity limit of the standard expression for viscous pressure drop in the Poiseuille flow regime. The other involves a plot of the nondimensional viscous flow resistance, Δpvis/Δxωρu, versus the reciprocal of the viscous penetration depth, 1/δν, in the laminar flow regime. When rh<δν, the flow behavior is frequency independent and the dynamics is characterized by rh only. When rh>δν, the flow resistance is frequency dependent and the dynamics is characterized by both rh and δν. It is possible to identify an effective hydraulic radius by equating it to the value of δν where that transition occurs. [Work supported by ONR.

  15. Size Distribution of Bacterial Cells

    PubMed Central

    Stull, V. R.

    1972-01-01

    By using differential light-scattering measurements of single cells suspended in a laser beam, an effective cell radius has been determined for 141 individual bacteria from suspensions of Staphylococcus epidermidis. The accumulation of these measurements has provided the size distribution for the sampling. PMID:4551753

  16. Size distribution of ring polymers

    NASA Astrophysics Data System (ADS)

    Medalion, Shlomi; Aghion, Erez; Meirovitch, Hagai; Barkai, Eli; Kessler, David A.

    2016-06-01

    We present an exact solution for the distribution of sample averaged monomer to monomer distance of ring polymers. For non-interacting and local-interaction models these distributions correspond to the distribution of the area under the reflected Bessel bridge and the Bessel excursion respectively, and are shown to be identical in dimension d ≥ 2, albeit with pronounced finite size effects at the critical dimension, d = 2. A symmetry of the problem reveals that dimension d and 4 - d are equivalent, thus the celebrated Airy distribution describing the areal distribution of the d = 1 Brownian excursion describes also a polymer in three dimensions. For a self-avoiding polymer in dimension d we find numerically that the fluctuations of the scaled averaged distance are nearly identical in dimension d = 2, 3 and are well described to a first approximation by the non-interacting excursion model in dimension 5.

  17. Relation between pore size and the compressibility of a confined fluid

    SciTech Connect

    Gor, Gennady Y.; Siderius, Daniel W.; Krekelberg, William P.; Shen, Vincent K.; Rasmussen, Christopher J.; Bernstein, Noam

    2015-11-21

    When a fluid is confined to a nanopore, its thermodynamic properties differ from the properties of a bulk fluid, so measuring such properties of the confined fluid can provide information about the pore sizes. Here, we report a simple relation between the pore size and isothermal compressibility of argon confined in such pores. Compressibility is calculated from the fluctuations of the number of particles in the grand canonical ensemble using two different simulation techniques: conventional grand-canonical Monte Carlo and grand-canonical ensemble transition-matrix Monte Carlo. Our results provide a theoretical framework for extracting the information on the pore sizes of fluid-saturated samples by measuring the compressibility from ultrasonic experiments.

  18. Relation between pore size and the compressibility of a confined fluid

    NASA Astrophysics Data System (ADS)

    Gor, Gennady Y.; Siderius, Daniel W.; Rasmussen, Christopher J.; Krekelberg, William P.; Shen, Vincent K.; Bernstein, Noam

    2015-11-01

    When a fluid is confined to a nanopore, its thermodynamic properties differ from the properties of a bulk fluid, so measuring such properties of the confined fluid can provide information about the pore sizes. Here, we report a simple relation between the pore size and isothermal compressibility of argon confined in such pores. Compressibility is calculated from the fluctuations of the number of particles in the grand canonical ensemble using two different simulation techniques: conventional grand-canonical Monte Carlo and grand-canonical ensemble transition-matrix Monte Carlo. Our results provide a theoretical framework for extracting the information on the pore sizes of fluid-saturated samples by measuring the compressibility from ultrasonic experiments.

  19. Pore size effects on the sorption of supercritical carbon dioxide in mesoporous CPG-10 silica

    SciTech Connect

    Rother, Gernot; Krukowski, Elizabeth G; Wallacher, Dirk; Grimm, Nico; Bodnar, Robert J; Cole, David

    2012-01-01

    Excess sorption isotherms of supercritical carbon dioxide in mesoporous CPG-10 silica glasses with nominal pore sizes of 75 (7.5 nm) and 350 (35 nm) were measured gravimetrically at 35 C and 50 C and pressures of 0-200 bar. Formation of broad maxima in the excess sorption was observed at fluid densities below the bulk critical density. Positive values of excess sorption were measured at bulk densities below about 0.65-0.7 g/cm3, whereas zero and negative values were obtained at higher densities, indicating that the interfacial fluid becomes less dense than the corresponding bulk fluid at high fluid densities. A shift of the excess sorption peak position to higher fluid density is found with increasing pore width. The excess sorption of CO2 normalized to the specific surface area is higher for the 35 nm pore size material, suggesting pore confinement effects. Conversely, the pore volume normalized excess sorption is higher for the 7.5 nm pore size material. Assessment of mean pore density reveals regions of constant pore fluid density, located between the excess sorption peak and the adsorption/depletion transition. Both materials exhibit such regions of constant mean pore fluid density as a function of bulk CO2 density at the lower temperature of 35 C, but not at 50 C. The results of this study suggest that the CO2 storage capacity in quartz-rich reservoirs is higher for sites with low temperature and rock textures characterized by narrow pores with high surface to volume ratios.

  20. Protein adsorption on DEAE ion-exchange resins with different ligand densities and pore sizes.

    PubMed

    Lu, Hui-Li; Lin, Dong-Qiang; Zhu, Mi-Mi; Yao, Shan-Jing

    2012-11-01

    Ion exchange chromatography (IEC) is a common and powerful technique for the purification of proteins. The ligand density and pore properties of ion-exchange resins have significant effects on the separation behaviors of protein, however, the understandings are quite limited. In the present work, the adsorption isotherms of bovine serum albumin (BSA) and human serum albumin (HSA) were investigated systematically with series of diethylaminoethyl (DEAE) ion-exchange resins, which have different ligand densities and pore sizes. The Langmuir equation was used to fit the experimental data and the influences of ligand density and pore size on the saturated adsorption capacity and the dissociation constant were discussed. The zeta potentials and hydrodynamic diameters of proteins at different pHs were also measured, and the surface charge characteristics of proteins and the adsorption mechanism were discussed. The results demonstrated that the ligand density, pore size, and protein properties affect the protein adsorption capacities in an integrative way. An integrative parameter was introduced to describe the complicated effects of ligand density and pore size on the protein adsorption. For a given protein, the ligand density and pore size should be optimized for improving the protein adsorption.

  1. Improved capacitance characteristics of electrospun ACFs by pore size control and vanadium catalyst.

    PubMed

    Im, Ji Sun; Woo, Sang-Wook; Jung, Min-Jung; Lee, Young-Seak

    2008-11-01

    Nano-sized carbon fibers were prepared by using electrospinning, and their electrochemical properties were investigated as a possible electrode material for use as an electric double-layer capacitor (EDLC). To improve the electrode capacitance of EDLC, we implemented a three-step optimization. First, metal catalyst was introduced into the carbon fibers due to the excellent conductivity of metal. Vanadium pentoxide was used because it could be converted to vanadium for improved conductivity as the pore structure develops during the carbonization step. Vanadium catalyst was well dispersed in the carbon fibers, improving the capacitance of the electrode. Second, pore-size development was manipulated to obtain small mesopore sizes ranging from 2 to 5 nm. Through chemical activation, carbon fibers with controlled pore sizes were prepared with a high specific surface and pore volume, and their pore structure was investigated by using a BET apparatus. Finally, polyacrylonitrile was used as a carbon precursor to enrich for nitrogen content in the final product because nitrogen is known to improve electrode capacitance. Ultimately, the electrospun activated carbon fibers containing vanadium show improved functionality in charge/discharge, cyclic voltammetry, and specific capacitance compared with other samples because of an optimal combination of vanadium, nitrogen, and fixed pore structures. PMID:18771778

  2. New and conventional pore size tests in virus-removing membranes.

    PubMed

    Duek, Aviv; Arkhangelsky, Elizabeth; Krush, Ronit; Brenner, Asher; Gitis, Vitaly

    2012-05-15

    Microorganisms are retained by ultrafiltration (UF) membranes mainly due to size exclusion. The sizes of viruses and membrane pores are close to each other and retention of viruses can be guaranteed only if the precise pore diameter is known. Unfortunately and rather surprisingly, there is no direct method to determine the membrane pore size. As a result, the UF membranes are not trusted to remove the viruses, and the treatment plants are required to enhance viral disinfection. Here we propose a new, simple and effective method for UF pore size determination using aquasols of gold and silver nanoparticles. We synthesized highly monodispersed suspensions ranging in diameter from 3 to 50 nm, which were later transferred through polymer and ceramic UF membranes. The retention percentage was plotted against the particle diameter to determine the pore size for which a membrane has a retention capability of 50, 90 and 100%. The d(50), d(90) and d(100) values were compared with data obtained from conventional transmembrane flux, polyethylene glycol, and dextran tests, and with the retention of phi X 174 and MS2 bacteriophages. The absolute pore size, d(100), for the majority of tested UF membranes is within 40-50 nm, and can only be detected with the new tests. The average 1.2 log retention of hydrophilic phi X 174 was predicted accurately by models based on the virus hydrodynamic radii and d(100) pore size. The 2.5 log MS2 retention suggests hydrophobic interactions in addition to simple ball-through-cylinder geometry. PMID:22265254

  3. Parameterizing the Raindrop Size Distribution

    NASA Technical Reports Server (NTRS)

    Haddad, Ziad S.; Durden, Stephen L.; Im, Eastwood

    1996-01-01

    This paper addresses the problem of finding a parametric form for the raindrop size distribution (DSD) that(1) is an appropriate model for tropical rainfall, and (2) involves statistically independent parameters. Such a parameterization is derived in this paper. One of the resulting three "canonical" parameters turns out to vary relatively little, thus making the parameterization particularly useful for remote sensing applications. In fact, a new set of r drop-size-distribution-based Z-R and k-R relations is obtained. Only slightly more complex than power laws, they are very good approximations to the exact radar relations one would obtain using Mie scattering. The coefficients of the new relations are directly related to the shape parameters of the particular DSD that one starts with. Perhaps most important, since the coefficients are independent of the rain rate itself, the relations are ideally suited for rain retrieval algorithms.

  4. Passive permeability and effective pore size of HeLa cell nuclear membranes.

    PubMed

    Samudram, Arunkarthick; Mangalassery, Bijeesh M; Kowshik, Meenal; Patincharath, Nandakumar; Varier, Geetha K

    2016-09-01

    Nuclear pore complexes in the nuclear membrane act as the sole gateway of transport of molecules from the cytoplasm to the nucleus and vice versa. Studies on biomolecular transport through nuclear membranes provide vital data on the nuclear pore complexes. In this work, we use fluorescein isothiocyanate-labeled dextran molecules as a model system and study the passive nuclear import of biomolecules through nuclear pore complexes in digitonin-permeabilized HeLa cells. Experiments are carried out under transient conditions in the time lapse imaging scheme using an in-house constructed confocal laser scanning microscope. Transport rates of dextran molecules having molecular weights of 4-70 kDa corresponding to Stokes radius of 1.4-6 nm are determined. Analyzing the permeability of the nuclear membrane for different sizes the effective pore radius of HeLa cell nuclear membrane is determined to be 5.3 nm, much larger than the value reported earlier using proteins as probe molecules. The range of values reported for the nuclear pore radius suggest that they may not be rigid structures and it is quite probable that the effective pore size of nuclear pore complexes is critically dependent on the probe molecules and on the environmental factors.

  5. Size distribution of ring polymers

    PubMed Central

    Medalion, Shlomi; Aghion, Erez; Meirovitch, Hagai; Barkai, Eli; Kessler, David A.

    2016-01-01

    We present an exact solution for the distribution of sample averaged monomer to monomer distance of ring polymers. For non-interacting and local-interaction models these distributions correspond to the distribution of the area under the reflected Bessel bridge and the Bessel excursion respectively, and are shown to be identical in dimension d ≥ 2, albeit with pronounced finite size effects at the critical dimension, d = 2. A symmetry of the problem reveals that dimension d and 4 − d are equivalent, thus the celebrated Airy distribution describing the areal distribution of the d = 1 Brownian excursion describes also a polymer in three dimensions. For a self-avoiding polymer in dimension d we find numerically that the fluctuations of the scaled averaged distance are nearly identical in dimension d = 2, 3 and are well described to a first approximation by the non-interacting excursion model in dimension 5. PMID:27302596

  6. Pore size assessment during corneal endothelial cells permeabilization by femtosecond laser activated carbon nanoparticles

    NASA Astrophysics Data System (ADS)

    Jumelle, C.; Mauclair, C.; Houzet, J.; Bernard, A.; He, Z.; Piselli, S.; Perrache, C.; Egaud, G.; Baubeau, E.; Gain, P.; Thuret, G.

    2015-07-01

    Corneal therapeutic molecules delivery represents a promising solution to maintain human corneal endothelial cells (HCECs) viability, but the difficulty is transport across cell membrane. A new delivery method published recently consists in ephemerally permeabilizing cell membranes using a photo-acoustic reaction produced by carbon nanoparticles (CNPs) and femtosecond laser (FsL). The aim of this work is to investigate the size of pores formed at cell membrane by this technique. To induce cell permeabilization, HCECs were put in contact with CNPs and irradiated with a 500 μm diameter Ti:Sa FsL focalized spot. Four sizes of marker molecules were delivered into HCECs to investigate pore sizes: calcein (1.2 nm), FITC-Dextran 4kDa (2.8 nm) and FITC-Dextran 70kDa (12 nm) and FITC-Dextran 2MDa (50 nm). Delivery of each molecule was assessed by flow cytometry, a technique able to measure their presence into cells. We showed that the delivery rate was dependent of their size. Calcein was delivered in 56.1±8.2% of HCECs, FITC-Dextran 4kDa in 42.2±3.5%, FITC-Dextran 70 kDa in 21.5±2.7% and finally FITC-Dextran 2MDa in 12.9±2.0%. It means that a large number of pores in the size ranging from 1.2 to 2.8 nm were formed. However, 12 nm and larger pores were almost half more infrequent. Pore sizes formed at cell membrane by the technique of cell permeabilization by FsL activated CNPs was investigated. The results indicated that the pore sizes are large enough for the efficient delivery of small, medium and big therapeutics molecules on HCECs by this technique.

  7. Relating pore size variation of poly (ɛ-caprolactone) scaffolds to molecular weight of porogen and evaluation of scaffold properties after degradation.

    PubMed

    Columbus, Soumya; Krishnan, Lissy K; Kalliyana Krishnan, V

    2014-05-01

    The major challenge in designing a scaffold for fabricating tissue engineered blood vessels is optimization of its microstructure for supporting uniform cellular in-growth with good mechanical integrity and degradation kinetics suitable for long-term implantation. In this study, we have investigated the feasibility of varying the pore size of poly(ɛ-caprolactone) (PCL) scaffold by altering the molecular weight of porogen and studied the effect of degradation on morphological characteristics and mechanical properties of scaffolds by correlating to the extent of degradation. Scaffolds with two different pore sizes were prepared by solvent casting and particulate leaching where poly(ethylene glycol) (PEG) porogens having two molecular weights (3400 and 8000) were used and subjected to in vitro degradation in phosphate buffered saline (PBS) upto six months. Microcomputed tomography studies of scaffolds revealed narrower pore size distribution when PEG-3400 was used as porogen and had 78% pores in the 12-24 µ range, whereas incorporation of PEG-8000 resulted in broader distribution with only 65% pores in the same range. Degradation resulted in scaffolds with narrower pore size distribution to have better retention of morphological and mechanical characteristics compared to scaffolds with broader distribution. Gravimetric and molecular weight studies also showed that scaffold degradation in both cases was only in initial stages after 6 months and PCL scaffolds had potential to be recommended for vascular tissue engineering applications.

  8. Tricontinuous Cubic Nanostructure and Pore Size Patterning in Mesostructured Silica Films Templated with Glycerol Monooleate.

    PubMed

    Dunphy, Darren R; Garcia, Fred L; Kaehr, Bryan; Khripin, Constantine Y; Collord, Andrew D; Baca, Helen K; Tate, Michael P; Hillhouse, Hugh W; Strzalka, Joseph W; Jiang, Zhang; Wang, Jin; Brinker, C Jeffrey

    2011-04-26

    The fabrication of nanostructured films possessing tricontinuous minimal surface mesophases with well-defined framework and pore connectivity remains a difficult task. As a new route to these structures, we introduce glycerol monooleate (GMO) as a template for evaporation-induced self-assembly. As deposited, a nanostructured double gyroid phase is formed, as indicated by analysis of grazing-incidence small-angle x-ray scattering data. Removal of GMO by UV/O(3) treatment or acid extraction induces a phase change to a nanoporous body-centered structure which we tentatively identify as based on the IW-P surface. To improve film quality, we add a co-surfactant to the GMO in a mass ratio of 1:10; when this co-surfactant is cetyltrimethylammonium bromide, we find an unusually large pore size (8-12 nm) in acid extracted films, while UV/O(3) treated films yield pores of only ca. 4 nm. Using this pore size dependence on film processing procedure, we create a simple method for patterning pore size in nanoporous films, demonstrating spatially-defined size-selective molecular adsorption.

  9. Investigation of the effect of pore size on gas uptake in two metal-organic frameworks.

    PubMed

    Wang, Rongming; Meng, Qingguo; Zhang, Liangliang; Wang, Haifeng; Dai, Fangna; Guo, Wenyue; Zhao, Lianming; Sun, Daofeng

    2014-05-18

    Two porous metal–organic frameworks (1 and 2) with a fsc topology based on mixed ligands have been assembled and characterized. The different pillared ligands (pyrazine for 1 and 4,4′-bipyridine for 2) significantly influence the pore size of the frameworks. Gas uptake measurements reveal that complex 1 possesses higher H2, CO2, and CH4 uptake capacities than 2, although the surface area of 1 is lower than that of complex 2. These results further experimentally prove that the pore size plays an important role in gas uptake in porous MOFs, and the slit pore with a size of ~6 Å exhibits stronger interactions with gas molecules.

  10. Kinetics of pore size during irreversible electrical breakdown of lipid bilayer membranes.

    PubMed Central

    Wilhelm, C; Winterhalter, M; Zimmermann, U; Benz, R

    1993-01-01

    The kinetics of pore formation followed by mechanical rupture of lipid bilayer membranes were investigated in detail by using the charge-pulse method. Membranes of various compositions were charged to a sufficiently high voltage to induce mechanical breakdown. The subsequent decrease of membrane voltage was used to calculate the conductance. During mechanical breakdown, which was probably caused by the widening of one single pore, the membrane conductance was a linear and not exponential function of time after the initial starting process. In a large number of experiments using various lipids and electrolytes, the characteristic opening process of the pore turned out to be independent of the actual membrane potential and electrolyte concentration. Our theoretical analysis of the pore formation suggested that the voltage-induced irreversible breakdown is due to a decrease in edge energy when the pore had formed. After initiation of the pore, the electrical contribution to surface tension is negligible. The time course of the increase of pore size shows that our model of the irreversible breakdown is in good agreement with mechanical properties of membranes reported elsewhere. PMID:8431536

  11. Characterizing pore sizes and water structure in stimuli-responsive hydrogels

    SciTech Connect

    Hoffman, A.S.; Antonsen, K.P.; Ashida, T.; Bohnert, J.L.; Dong, L.C.; Nabeshima, Y.; Nagamatsu, S.; Park, T.G.; Sheu, M.S.; Wu, X.S.; Yan, Q.

    1993-12-31

    Hydrogels have been extensively investigated as potential matrices for drug delivery. In particular, hydrogels responsive to pH and temperature changes have been of greatest interest most recently. Proteins and peptide drugs are especially relevant for delivery from such hydrogel matrices due to the relatively {open_quotes}passive{close_quotes} and biocompatible microenvironment which should exist within the hydrogel aqueous pores. The large molecular size of many proteins requires an interconnected large pore structure. Furthermore, the gel pore {open_quotes}walls{close_quotes} should not provide hydrophobic sites for strong interactions with proteins. In the special case of ion exchange release the protein would be attracted by opposite charges on the polymer backbones. Therefore, it is important both to control and to characterize the pore structure and the water character within a hydrogel to be used or protein or peptide drug delivery. This talk will critically review techniques for estimating these two key parameters in hydrogels.

  12. Pore Size Control of Ultra-thin Silicon Membranes by Rapid Thermal Carbonization

    PubMed Central

    Fang, David Z.; Striemer, Christopher C.; Gaborski, Thomas R.; McGrath, James L.; Fauchet, Philippe M.

    2010-01-01

    Rapid thermal carbonization in a dilute acetylene (C2H2) atmosphere has been used to chemically modify and precisely tune the pore size of ultrathin porous nanocrystalline silicon (pnc-Si). The magnitude of size reduction was controlled by varying the process temperature and time. Under certain conditions, the carbon coating displayed atomic ordering indicative of graphene layer formation conformal to the pore walls. Initial experiments show that carbonized membranes follow theoretical predictions for hydraulic permeability and retain the precise separation capabilities of untreated membranes. PMID:20839831

  13. A Novel Approach to Estimate Iron Distribution Within Different Pore Domains of Structured Media.

    SciTech Connect

    Kamolpornwijit, Wiwat; Brooks, Scott C.; Kim, Y.; Scheibe, Timothy D.

    2007-11-25

    The success and long-term performance of bioremediation processes employing iron-reducing bacteria depends on several factors. A crucial factor is the availability of Fe(III) as an electron acceptor which may be dictated by both chemical (e.g., oxide mineralogy) and physical (distribution of Fe(III) in space) effects. The iron content of subsurface media usually is obtained through different extraction techniques performed in a well-mixed batch experiment. For structured media where preferential flow prevails over the matrix flow, however, the iron content determined from homogenized samples may not well represent the iron content available for microbial activity. Metal reducing bacteria may be physically excluded from a significant fraction of pores due to their sizes. In this study we performed Fe(III) oxide extraction on an intact core of saprolite where intact structure was preserved. An unsaturated flow setup was modified to allow the extraction of oxalate-extractable Fe(III) oxides under two pore tensions, 15 and 0 cm of water. The result suggested the existence of Fe(III) oxide distribution with its mass mainly contained within the finer pore domain of matrix potential larger than 15 cm. Less than 15.5% mass (an upper bound) of oxalate-extractable Fe (III) oxides were present in domains of pore tension less than 15 cm. Hence the use of extraction results from well mixed batch extraction techniques can overestimate the quantity of Fe(III) oxides accessible to bacteria in structured media. To the extent that Fe (III) oxide minerals play an important role in contaminant biogeochemistry and solute transport, the distribution of Fe(III) oxides in structured subsurface media are critical to our understanding of these processes.

  14. Pore-size dependence and characteristics of water diffusion in slitlike micropores

    SciTech Connect

    Diallo, S. O.

    2015-07-16

    The temperature dependence of the dynamics of water inside microporous activated carbon fibers (ACF) is investigated by means of incoherent elastic and quasielastic neutron-scattering techniques. The aim is to evaluate the effect of increasing pore size on the water dynamics in these primarily hydrophobic slit-shaped channels. Using two different micropore sizes (similar to 12 and 18 angstrom, denoted, respectively, ACF-10 and ACF-20), a clear suppression of the mobility of the water molecules is observed as the pore gap or temperature decreases. Suppression, we found, is accompanied by a systematic dependence of the average translational diffusion coefficient D-r and relaxation time [tau(0)] of the restricted water on pore size and temperature. We observed D-r values and tested against a proposed scaling law, in which the translational diffusion coefficient D-r of water within a porous matrix was found to depend solely on two single parameters, a temperature-independent translational diffusion coefficient D-c associated with the water bound to the pore walls and the ratio theta of this strictly confined water to the total water inside the pore, yielding unique characteristic parameters for water transport in these carbon channels across the investigated temperature range.

  15. Pore-size dependence and characteristics of water diffusion in slitlike micropores

    DOE PAGESBeta

    Diallo, S. O.

    2015-07-16

    The temperature dependence of the dynamics of water inside microporous activated carbon fibers (ACF) is investigated by means of incoherent elastic and quasielastic neutron-scattering techniques. The aim is to evaluate the effect of increasing pore size on the water dynamics in these primarily hydrophobic slit-shaped channels. Using two different micropore sizes (similar to 12 and 18 angstrom, denoted, respectively, ACF-10 and ACF-20), a clear suppression of the mobility of the water molecules is observed as the pore gap or temperature decreases. Suppression, we found, is accompanied by a systematic dependence of the average translational diffusion coefficient D-r and relaxation timemore » [tau(0)] of the restricted water on pore size and temperature. We observed D-r values and tested against a proposed scaling law, in which the translational diffusion coefficient D-r of water within a porous matrix was found to depend solely on two single parameters, a temperature-independent translational diffusion coefficient D-c associated with the water bound to the pore walls and the ratio theta of this strictly confined water to the total water inside the pore, yielding unique characteristic parameters for water transport in these carbon channels across the investigated temperature range.« less

  16. Neovascularization in Biodegradable Inverse Opal Scaffolds with Uniform and Precisely Controlled Pore Sizes**

    PubMed Central

    Choi, Sung-Wook; Zhang, Yu; MacEwan, Matthew R.; Xia, Younan

    2012-01-01

    The formation of a stable vascular network in a scaffold is one of the most challenging tasks in tissue engineering and regenerative medicine. Despite the common use of porous scaffolds in these applications, little is known about the effect of pore size on the neovascularization in these scaffolds. Here we fabricated poly(D, L-lactide-co-glycolide) inverse opal scaffolds with uniform pore sizes of 79, 147, 224, and 312 μm in diameter and then used them to systematically study neovascularization in vivo. Histology analyses revealed that scaffolds with small pores (<200 μm) favored the formation of vascular networks with small vessels at high densities and poor penetration depth. By contrast, scaffolds with large pores (>200 μm) favored the formation of vascular networks with large blood vessels at low densities and deep penetration depth. Based on the different patterns of vessel ingrowth as regulated by the pore size, we proposed a model to describe vascularization in a three-dimensional porous scaffold, which can potentially serve as a guideline for future design of porous scaffolds. PMID:23184495

  17. Pore-size dependence and characteristics of water diffusion in slitlike micropores

    NASA Astrophysics Data System (ADS)

    Diallo, S. O.

    2015-07-01

    The temperature dependence of the dynamics of water inside microporous activated carbon fibers (ACF) is investigated by means of incoherent elastic and quasielastic neutron-scattering techniques. The aim is to evaluate the effect of increasing pore size on the water dynamics in these primarily hydrophobic slit-shaped channels. Using two different micropore sizes (˜12 and 18 Å, denoted, respectively, ACF-10 and ACF-20), a clear suppression of the mobility of the water molecules is observed as the pore gap or temperature decreases. This suppression is accompanied by a systematic dependence of the average translational diffusion coefficient Dr and relaxation time <τ0> of the restricted water on pore size and temperature. The observed Dr values are tested against a proposed scaling law, in which the translational diffusion coefficient Dr of water within a porous matrix was found to depend solely on two single parameters, a temperature-independent translational diffusion coefficient Dc associated with the water bound to the pore walls and the ratio θ of this strictly confined water to the total water inside the pore, yielding unique characteristic parameters for water transport in these carbon channels across the investigated temperature range.

  18. Simple thermal treatment for the size control of pore arrays in a polystyrene colloidal crystal films

    NASA Astrophysics Data System (ADS)

    Jamiolkowski, Ryan M.; Fiorenza, Shane A.; Chen, Kevin; Tate, Alyssa M.; Pfeil, Shawn H.; Goldman, Yale E.

    Nanosphere Lithography (NSL) offers an attractive route to fabricating periodic structures with nanoscale features, without e-beam or deep UV lithography. In particular, it is uniquely suited to the low cost fabrication of large repeated arrays pores or pillars created by taking advantage of the interstitial spaces in close-packed monolayers of nano to micro-scale beads. However pore size, shape, and spacing cannot be controlled independently. We present both a robust method for producing large, approximately 1 cm2, hexagonally close packed monolayer films of 1 micron diameter polystyrene beads on glass substrates, and thermal treatment of these films near the glass temperature, Tg, of polystyrene to modify the pore size. This builds on earlier work showing that pore size can be modified for colloidal crystals formed at a liquid gas interface [2]. These processes promise a simple, reproducible, and low cost route to periodic pore arrays for nano-photonic applications such as zero mode waveguides (ZMWs) Funding: F30 AI114187 (RMJ), R01-GM080376 (YEG).

  19. Development of gelatin-chitosan-hydroxyapatite based bioactive bone scaffold with controlled pore size and mechanical strength.

    PubMed

    Maji, Kanchan; Dasgupta, Sudip; Kundu, Biswanath; Bissoyi, Akalabya

    2015-01-01

    Hydroxyapatite-chitosan/gelatin (HA:Chi:Gel) nanocomposite scaffold has potential to serve as a template matrix to regenerate extra cellular matrix of human bone. Scaffolds with varying composition of hydroxyapatite, chitosan, and gelatin were prepared using lyophilization technique where glutaraldehyde (GTA) acted as a cross-linking agent for biopolymers. First, phase pure hydroxyapatite-chitosan nanocrystals were in situ synthesized by coprecipitation method using a solution of 2% acetic acid dissolved chitosan and aqueous solution of calcium nitrate tetrahydrate [Ca(NO3)2,4H2O] and diammonium hydrogen phosphate [(NH4)2H PO4]. Keeping solid loading constant at 30 wt% and changing the composition of the original slurry of gelatin, HA-chitosan allowed control of the pore size, its distribution, and mechanical properties of the scaffolds. Microstructural investigation by scanning electron microscopy revealed the formation of a well interconnected porous scaffold with a pore size in the range of 35-150 μm. The HA granules were uniformly dispersed in the gelatin-chitosan network. An optimal composition in terms of pore size and mechanical properties was obtained from the scaffold with an HA:Chi:Gel ratio of 21:49:30. The composite scaffold having 70% porosity with pore size distribution of 35-150 μm exhibited a compressive strength of 3.3-3.5 MPa, which is within the range of that exhibited by cancellous bone. The bioactivity of the scaffold was evaluated after conducting mesenchymal stem cell (MSC) - materials interaction and MTT (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide) assay using MSCs. The scaffold found to be conducive to MSC's adhesion as evident from lamellipodia, filopodia extensions from cell cytoskeleton, proliferation, and differentiation up to 14 days of cell culture.

  20. Pore size regulates operating stomatal conductance, while stomatal densities drive the partitioning of conductance between leaf sides

    PubMed Central

    Fanourakis, Dimitrios; Giday, Habtamu; Milla, Rubén; Pieruschka, Roland; Kjaer, Katrine H.; Bolger, Marie; Vasilevski, Aleksandar; Nunes-Nesi, Adriano; Fiorani, Fabio; Ottosen, Carl-Otto

    2015-01-01

    Background and Aims Leaf gas exchange is influenced by stomatal size, density, distribution between the leaf adaxial and abaxial sides, as well as by pore dimensions. This study aims to quantify which of these traits mainly underlie genetic differences in operating stomatal conductance (gs) and addresses possible links between anatomical traits and regulation of pore width. Methods Stomatal responsiveness to desiccation, gs-related anatomical traits of each leaf side and estimated gs (based on these traits) were determined for 54 introgression lines (ILs) generated by introgressing segments of Solanum pennelli into the S. lycopersicum ‘M82’. A quantitative trait locus (QTL) analysis for stomatal traits was also performed. Key Results A wide genetic variation in stomatal responsiveness to desiccation was observed, a large part of which was explained by stomatal length. Operating gs ranged over a factor of five between ILs. The pore area per stomatal area varied 8-fold among ILs (2–16 %), and was the main determinant of differences in operating gs between ILs. Operating gs was primarily positioned on the abaxial surface (60–83 %), due to higher abaxial stomatal density and, secondarily, to larger abaxial pore area. An analysis revealed 64 QTLs for stomatal traits in the ILs, most of which were in the direction of S. pennellii. Conclusions The data indicate that operating and maximum gs of non-stressed leaves maintained under stable conditions deviate considerably (by 45–91 %), because stomatal size inadequately reflects operating pore area (R2 = 0·46). Furthermore, it was found that variation between ILs in both stomatal sensitivity to desiccation and operating gs is associated with features of individual stoma. In contrast, genotypic variation in gs partitioning depends on the distribution of stomata between the leaf adaxial and abaxial epidermis. PMID:25538116

  1. Effect of hydrofluoric acid (HF) concentration to pores size diameter of silicon membrane.

    PubMed

    Burham, Norhafizah; Hamzah, Azrul Azlan; Majlis, Burhanuddin Yeop

    2014-01-01

    This paper studies parameters which affect the pore size diameter of a silicon membrane. Electrochemical etching is performed in characterise the parameter involved in this process. The parameter has been studied is volume ratio of hydrofluoric acid (HF) and ethanol as an electrolyte aqueous for electrochemical etch. This electrolyte aqueous solution has been mixed between HF and ethanol with volume ratio 3:7, 5:5, 7:3 and 9:1. As a result, the higher volume of HF in this electrolyte gives the smallest pore size diameter compared to the lower volume of HF. These samples have been dipped into HF and ethanol electrolyte aqueous with supplied 25 mA/cm2 current density for 20, 30, 40, and 50 minutes. The samples will inspect under Scanning Electron Microscope (SEM) to execute the pore formations on silicon membrane surface.

  2. The effect of fiber size and pore size on cell proliferation and infiltration in PLLA scaffolds on bone tissue engineering.

    PubMed

    Wang, Xuejun; Lou, Tao; Zhao, Wenhua; Song, Guojun; Li, Chunyao; Cui, Guangpeng

    2016-05-01

    The scaffold microstructure has a great impact on cell functions in tissue engineering. Herein, the PLLA scaffolds with hierarchical fiber size and pore size were successfully fabricated by thermal-induced phase separation or combined thermal-induced phase separation and salt leaching methods. The PLLA scaffolds were fabricated as microfibrous scaffolds, microfibrous scaffolds with macropores (50-350 µm), nanofibrous scaffolds with micropores (100 nm to 10 µm), and nanofibrous scaffolds with both macropores and micropores by tailoring selective solvents for forming different fiber size and pre-sieved salts for creating controlled pore size. Among the four kinds of PLLA scaffolds, the nanofibrous scaffolds with both macropores and micropores provided a favorable microenvironment for protein adsorption, cell proliferation, and cell infiltration. The results further confirmed the significance of fiber size and pore size on the biological properties, and a scaffold with both micropores and macropores, and a nanofibrous matrix might have promising applications in bone tissue engineering.

  3. Size Control of Porous Silicon-Based Nanoparticles via Pore-Wall Thinning.

    PubMed

    Secret, Emilie; Leonard, Camille; Kelly, Stefan J; Uhl, Amanda; Cozzan, Clayton; Andrew, Jennifer S

    2016-02-01

    Photoluminescent silicon nanocrystals are very attractive for biomedical and electronic applications. Here a new process is presented to synthesize photoluminescent silicon nanocrystals with diameters smaller than 6 nm from a porous silicon template. These nanoparticles are formed using a pore-wall thinning approach, where the as-etched porous silicon layer is partially oxidized to silica, which is dissolved by a hydrofluoric acid solution, decreasing the pore-wall thickness. This decrease in pore-wall thickness leads to a corresponding decrease in the size of the nanocrystals that make up the pore walls, resulting in the formation of smaller nanoparticles during sonication of the porous silicon. Particle diameters were measured using dynamic light scattering, and these values were compared with the nanocrystallite size within the pore wall as determined from X-ray diffraction. Additionally, an increase in the quantum confinement effect is observed for these particles through an increase in the photoluminescence intensity of the nanoparticles compared with the as-etched nanoparticles, without the need for a further activation step by oxidation after synthesis.

  4. Vesicular release of neurotransmitters: converting amperometric measurements into size, dynamics and energetics of initial fusion pores.

    PubMed

    Oleinick, Alexander; Lemaître, Frédéric; Collignon, Manon Guille; Svir, Irina; Amatore, Christian

    2013-01-01

    Amperometric currents displaying a pre-spike feature (PSF) may be treated so as to lead to precise information about initial fusion pores, viz., about the crucial event initiating neurotransmitter vesicular release in neurons and medullary glands. However, amperometric data alone are not self-sufficient, so their full exploitation requires external calibration to solve the inverse problem. For this purpose we resorted to patch-clamp measurements published in the literature on chromaffin cells. Reported pore radii were thus used to evaluate the diffusion rate of neurotransmitter cations in the partially altered matrix located near the fusion pore entrance. This allowed an independent determination of each initial fusion pore radius giving rise to a single PSF event. The statistical distribution of the radii thus obtained provided for the first time an experimental access to the potential energy well governing the thermodynamics of such systems. The shape of the corresponding potential energy well strongly suggested that, after their creation, initial fusion pores are essentially controlled by the usual physicochemical laws describing pores formed in bilayer lipidic biological membranes, i.e., they have an essentially lipidic nature. PMID:24466657

  5. Metal electrode integration on macroporous silicon: pore distribution and morphology

    PubMed Central

    2012-01-01

    In this work, a new approach for the one-step integration of interdigitated electrodes on macroporous silicon substrates is presented. Titanium/gold interdigitated electrodes are used to pattern p-type silicon substrates prior the anodization in an organic electrolyte. The electrolyte characteristics, conductivity, and pH have been found to affect the adherence of the metal layer on the silicon surface during the electrochemical etching. The impact of the metal pattern on size distribution and morphology of the resulting macroporous silicon layer is analyzed. A formation mechanism supported by finite element simulation is proposed. PMID:22799456

  6. Reduction in glomerular pore size is not restricted to pregnant women. Evidence for a new syndrome: 'Shrunken pore syndrome'.

    PubMed

    Grubb, Anders; Lindström, Veronica; Jonsson, Magnus; Bäck, Sten-Erik; Åhlund, Tomas; Rippe, Bengt; Christensson, Anders

    2015-07-01

    The plasma levels of cystatin C, β2-microglobulin, beta-trace protein, retinol binding protein (RBP) and creatinine were determined in plasma samples from 111 randomly selected patients with eGFRcystatin C ≤ 60% of eGFRcreatinine and from 55 control patients with 0.9eGFRcreatinine ≤ eGFRcystatin C ≤ 1.1eGFRcreatinine (eGFRcystatin C ≈ eGFRcreatinine). The concentration ratios of cystatin C/creatinine, β2-microglobulin/creatinine, beta-trace protein/creatinine and RBP/creatinine were significantly higher in patients with eGFRcystatin C ≤ 60% of eGFRcreatinine than in patients with eGFRcystatin C ≈ eGFRcreatinine. When the patients were divided into three groups with different estimated GFR intervals (≤ 40, 40-60 and ≥ 60 mL/min/1.73m(2)) the concentration ratios of cystatin C/creatinine, β2-microglobulin/creatinine, and beta-trace protein/creatinine were significantly higher in patients with eGFRcystatin C ≤ 60% of eGFRcreatinine than in patients with eGFRcystatin C ≈ eGFRcreatinine for all GFR intervals. Similar results were obtained when the population without pregnant women was studied as well as the subpopulations of men or of non-pregnant women. Populations of pre-eclamptic women and pregnant women in the third trimester display similar results. Since the production of these four proteins with sizes similar to that of cystatin C is not co-regulated, the most likely explanation for the simultaneous increase of their creatinine-ratios in patients with eGFRcystatin C ≤ 60% of eGFRcreatinine is that their elimination by glomerular filtration is decreased. We suggest that this is due to a reduction in pore diameter of the glomerular membrane and propose the designation 'Shrunken pore syndrome' for this pathophysiological state.

  7. Pore scale heterogeneity in the mineral distribution and surface area of porous rocks

    NASA Astrophysics Data System (ADS)

    Lai, Peter; Moulton, Kevin; Krevor, Samuel

    2014-05-01

    There are long-standing challenges in characterizing reactive transport in porous media at scales larger than individual pores. This hampers the prediction of the field-scale impact of geochemical processes on fluid flow [1]. This is a source of uncertainty for carbon dioxide injection, which results in a reactive fluid-rock system, particularly in carbonate rock reservoirs. A potential cause is the inability of the continuum approach to incorporate the impact of heterogeneity in pore-scale reaction rates. This results in part from pore-scale heterogeneities in surface area of reactive minerals [2,3]. The objective of this study was to quantify heterogeneity in reactive surface and observe the extent of its non-normal character. In this study we describe our work in using micron-scale x-ray imaging and other spectroscopic techniques for the purpose of describing the statistical distribution of reactive surface area within a porous medium, and identifying specific mineral phases and their distribution in 3-dimensions. Using in-house image processing techniques and auxilary charactersation with thin section, electron microscope and spectroscopic techniques we quantified the surface area of each mineral phase in the x-ray CT images. This quantification was validated against nitrogen BET surface area and backscattered electron imaging measurements of the CT-imaged samples. Distributions in reactive surface area for each mineral phase were constructed by calculating surface areas in thousands of randomly selected subvolume images of the total sample, each normalized to the pore volume in that image. In all samples, there is little correlation between the reactive surface area fraction and the volumetric fraction of a mineral in a bulk rock. Berea sandstone was far less heterogeneous and has a characteristic pore size at which a surface area distribution may be used to quantify heterogeneity. In carbonates, heterogeneity is more complex and surface area must be

  8. Three-Dimensional Scaffolds for Tissue Engineering Applications: Role of Porosity and Pore Size

    PubMed Central

    Loh, Qiu Li

    2013-01-01

    Tissue engineering applications commonly encompass the use of three-dimensional (3D) scaffolds to provide a suitable microenvironment for the incorporation of cells or growth factors to regenerate damaged tissues or organs. These scaffolds serve to mimic the actual in vivo microenvironment where cells interact and behave according to the mechanical cues obtained from the surrounding 3D environment. Hence, the material properties of the scaffolds are vital in determining cellular response and fate. These 3D scaffolds are generally highly porous with interconnected pore networks to facilitate nutrient and oxygen diffusion and waste removal. This review focuses on the various fabrication techniques (e.g., conventional and rapid prototyping methods) that have been employed to fabricate 3D scaffolds of different pore sizes and porosity. The different pore size and porosity measurement methods will also be discussed. Scaffolds with graded porosity have also been studied for their ability to better represent the actual in vivo situation where cells are exposed to layers of different tissues with varying properties. In addition, the ability of pore size and porosity of scaffolds to direct cellular responses and alter the mechanical properties of scaffolds will be reviewed, followed by a look at nature's own scaffold, the extracellular matrix. Overall, the limitations of current scaffold fabrication approaches for tissue engineering applications and some novel and promising alternatives will be highlighted. PMID:23672709

  9. Virus-sized colloid transport in a single pore: model development and sensitivity analysis.

    PubMed

    Seetha, N; Mohan Kumar, M S; Majid Hassanizadeh, S; Raoof, Amir

    2014-08-01

    A mathematical model is developed to simulate the transport and deposition of virus-sized colloids in a cylindrical pore throat considering various processes such as advection, diffusion, colloid-collector surface interactions and hydrodynamic wall effects. The pore space is divided into three different regions, namely, bulk, diffusion and potential regions, based on the dominant processes acting in each of these regions. In the bulk region, colloid transport is governed by advection and diffusion whereas in the diffusion region, colloid mobility due to diffusion is retarded by hydrodynamic wall effects. Colloid-collector interaction forces dominate the transport in the potential region where colloid deposition occurs. The governing equations are non-dimensionalized and solved numerically. A sensitivity analysis indicates that the virus-sized colloid transport and deposition is significantly affected by various pore-scale parameters such as the surface potentials on colloid and collector, ionic strength of the solution, flow velocity, pore size and colloid size. The adsorbed concentration and hence, the favorability of the surface for adsorption increases with: (i) decreasing magnitude and ratio of surface potentials on colloid and collector, (ii) increasing ionic strength and (iii) increasing pore radius. The adsorbed concentration increases with increasing Pe, reaching a maximum value at Pe=0.1 and then decreases thereafter. Also, the colloid size significantly affects particle deposition with the adsorbed concentration increasing with increasing particle radius, reaching a maximum value at a particle radius of 100nm and then decreasing with increasing radius. System hydrodynamics is found to have a greater effect on larger particles than on smaller ones. The secondary minimum contribution to particle deposition has been found to increase as the favorability of the surface for adsorption decreases. The sensitivity of the model to a given parameter will be high if

  10. Virus-sized colloid transport in a single pore: Model development and sensitivity analysis

    NASA Astrophysics Data System (ADS)

    Seetha, N.; Mohan Kumar, M. S.; Majid Hassanizadeh, S.; Raoof, Amir

    2014-08-01

    A mathematical model is developed to simulate the transport and deposition of virus-sized colloids in a cylindrical pore throat considering various processes such as advection, diffusion, colloid-collector surface interactions and hydrodynamic wall effects. The pore space is divided into three different regions, namely, bulk, diffusion and potential regions, based on the dominant processes acting in each of these regions. In the bulk region, colloid transport is governed by advection and diffusion whereas in the diffusion region, colloid mobility due to diffusion is retarded by hydrodynamic wall effects. Colloid-collector interaction forces dominate the transport in the potential region where colloid deposition occurs. The governing equations are non-dimensionalized and solved numerically. A sensitivity analysis indicates that the virus-sized colloid transport and deposition is significantly affected by various pore-scale parameters such as the surface potentials on colloid and collector, ionic strength of the solution, flow velocity, pore size and colloid size. The adsorbed concentration and hence, the favorability of the surface for adsorption increases with: (i) decreasing magnitude and ratio of surface potentials on colloid and collector, (ii) increasing ionic strength and (iii) increasing pore radius. The adsorbed concentration increases with increasing Pe, reaching a maximum value at Pe = 0.1 and then decreases thereafter. Also, the colloid size significantly affects particle deposition with the adsorbed concentration increasing with increasing particle radius, reaching a maximum value at a particle radius of 100 nm and then decreasing with increasing radius. System hydrodynamics is found to have a greater effect on larger particles than on smaller ones. The secondary minimum contribution to particle deposition has been found to increase as the favorability of the surface for adsorption decreases. The sensitivity of the model to a given parameter will be high

  11. A general approach to crystalline and monomodal pore size mesoporous materials.

    PubMed

    Poyraz, Altug S; Kuo, Chung-Hao; Biswas, Sourav; King'ondu, Cecil K; Suib, Steven L

    2013-01-01

    Mesoporous oxides attract a great deal of interest in many fields, including energy, catalysis and separation, because of their tunable structural properties such as surface area, pore volume and size, and nanocrystalline walls. Here we report thermally stable, crystalline, thermally controlled monomodal pore size mesoporous materials. Generation of such materials involves the use of inverse micelles, elimination of solvent effects, minimizing the effect of water content and controlling the condensation of inorganic frameworks by NO(x) decomposition. Nanosize particles are formed in inverse micelles and are randomly packed to a mesoporous structure. The mesopores are created by interconnected intraparticle voids and can be tuned from 1.2 to 25 nm by controlling the nanoparticle size. Such phenomena allow the preparation of multiple phases of the same metal oxide and syntheses of materials having compositions throughout much of the periodic table, with different structures and thermal stabilities as high as 800 °C. PMID:24335918

  12. Fabrication of Cell-Laden Macroporous Biodegradable Hydrogels with Tunable Porosities and Pore Sizes

    PubMed Central

    Wang, Limin; Lu, Steven; Lam, Johnny; Kasper, F. Kurtis

    2015-01-01

    In this work, we investigated a cytocompatible particulate leaching method for the fabrication of cell-laden macroporous hydrogels. We used dehydrated and uncrosslinked gelatin microspheres as leachable porogens to create macroporous oligo(poly(ethylene glycol) fumarate) hydrogels. Varying gelatin content and size resulted in a wide range of porosities and pore sizes, respectively. Encapsulated mesenchymal stem cells (MSCs) exhibited high viability immediately following the fabrication process, and culture of cell-laden hydrogels revealed improved cell viability with increasing porosity. Additionally, the osteogenic potential of the encapsulated MSCs was evaluated over 16 days. Overall, this study presents a robust method for the preparation of cell-laden macroporous hydrogels with desired porosity and pore size for tissue engineering applications. PMID:25156274

  13. The influence of pore size and surface area of activated carbons on the performance of ionic liquid based supercapacitors.

    PubMed

    Pohlmann, Sebastian; Lobato, Belén; Centeno, Teresa A; Balducci, Andrea

    2013-10-28

    This study analyses and compares the behaviour of 5 commercial porous carbons in the ionic liquid N-butyl-N-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (PYR14TFSI) and its mixture with propylene carbonate (PC) as electrolytes. The results of this investigation show that the existence of a distribution of pore sizes and/or constrictions at the entrance of the pores leads to significant changes in the specific capacitance of the investigated materials. The use of PYR14TFSI as an electrolyte has a positive effect on the EDLC energy storage, but its high viscosity limits the power density. The mixture 50 : 50 wt% propylene carbonate-PYR14TFSI provides high operative voltage as well as low viscosity and thus notably enhances EDLC operation. PMID:24019082

  14. Effective porosity and pore-throat sizes of Conasauga Group mudrock: Application, test and evaluation of petrophysical techniques

    SciTech Connect

    Dorsch, J.; Katsube, T.J.; Sanford, W.E. |; Dugan, B.E.; Tourkow, L.M.

    1996-04-01

    Effective porosity (specifically referring to the interconnected pore space) was recently recognized as being essential in determining the effectiveness and extent of matrix diffusion as a transport mechanism within fractured low-permeability rock formations. The research presented in this report was performed to test the applicability of several petrophysical techniques for the determination of effective porosity of fine-grained siliciclastic rocks. In addition, the aim was to gather quantitative data on the effective porosity of Conasauga Group mudrock from the Oak Ridge Reservation (ORR). The quantitative data reported here include not only effective porosities based on diverse measurement techniques, but also data on the sizes of pore throats and their distribution, and specimen bulk and grain densities. The petrophysical techniques employed include the immersion-saturation method, mercury and helium porosimetry, and the radial diffusion-cell method.

  15. Pore Size Effect on Methane Adsorption in Mesoporous Silica Materials Studied by Small-Angle Neutron Scattering.

    PubMed

    Chiang, Wei-Shan; Fratini, Emiliano; Baglioni, Piero; Chen, Jin-Hong; Liu, Yun

    2016-09-01

    Methane adsorption in model mesoporous silica materials with the size range characteristic of shale is studied by small-angle neutron scattering (SANS). Size effect on the temperature-dependent gas adsorption at methane pressure about 100 kPa is investigated by SANS using MCM-41 and SBA-15 as adsorbents. Above the gas-liquid condensation temperature, the thickness of the adsorption layer is found to be roughly constant as a function of the temperature. Moreover, the gas adsorption properties, such as the adsorbed layer thickness and the specific amount of adsorbed gas, have little dependence on the pore size being studied, i.e., pore radius of 16.5 and 34.1 Å, but are mainly affected by the roughness of the pore surfaces. Hence, the surface properties of the pore wall are more dominant than the pore size in determining the methane gas adsorption of pores at the nanometer size range. Not surprisingly, the gas-liquid condensation temperature is observed to be sensitive to pore size and shifts to higher temperature when the pore size is smaller. Below the gas-liquid condensation temperature, even though the majority of gas adsorption experiments/simulations have assumed the density of confined liquid to be the same as the bulk density, the measured methane mass density in our samples is found to be appreciably smaller than the bulk methane density regardless of the pore sizes studied here. The mass density of liquid/solid methane in pores with different sizes shows different temperature dependence below the condensation temperature. With decreasing temperature, the methane density in larger pores (SBA-15) abruptly increases at approximately 65 K and then plateaus. In contrast, the density in smaller pores (MCM-41) monotonically increases with decreasing temperature before reaching a plateau at approximately 30 K.

  16. Pore Size Effect on Methane Adsorption in Mesoporous Silica Materials Studied by Small-Angle Neutron Scattering.

    PubMed

    Chiang, Wei-Shan; Fratini, Emiliano; Baglioni, Piero; Chen, Jin-Hong; Liu, Yun

    2016-09-01

    Methane adsorption in model mesoporous silica materials with the size range characteristic of shale is studied by small-angle neutron scattering (SANS). Size effect on the temperature-dependent gas adsorption at methane pressure about 100 kPa is investigated by SANS using MCM-41 and SBA-15 as adsorbents. Above the gas-liquid condensation temperature, the thickness of the adsorption layer is found to be roughly constant as a function of the temperature. Moreover, the gas adsorption properties, such as the adsorbed layer thickness and the specific amount of adsorbed gas, have little dependence on the pore size being studied, i.e., pore radius of 16.5 and 34.1 Å, but are mainly affected by the roughness of the pore surfaces. Hence, the surface properties of the pore wall are more dominant than the pore size in determining the methane gas adsorption of pores at the nanometer size range. Not surprisingly, the gas-liquid condensation temperature is observed to be sensitive to pore size and shifts to higher temperature when the pore size is smaller. Below the gas-liquid condensation temperature, even though the majority of gas adsorption experiments/simulations have assumed the density of confined liquid to be the same as the bulk density, the measured methane mass density in our samples is found to be appreciably smaller than the bulk methane density regardless of the pore sizes studied here. The mass density of liquid/solid methane in pores with different sizes shows different temperature dependence below the condensation temperature. With decreasing temperature, the methane density in larger pores (SBA-15) abruptly increases at approximately 65 K and then plateaus. In contrast, the density in smaller pores (MCM-41) monotonically increases with decreasing temperature before reaching a plateau at approximately 30 K. PMID:27512895

  17. Tuning Pore Size in Square-Lattice Coordination Networks for Size-Selective Sieving of CO2.

    PubMed

    Chen, Kai-Jie; Madden, David G; Pham, Tony; Forrest, Katherine A; Kumar, Amrit; Yang, Qing-Yuan; Xue, Wei; Space, Brian; Perry, John J; Zhang, Jie-Peng; Chen, Xiao-Ming; Zaworotko, Michael J

    2016-08-22

    Porous materials capable of selectively capturing CO2 from flue-gases or natural gas are of interest in terms of rising atmospheric CO2 levels and methane purification. Size-exclusive sieving of CO2 over CH4 and N2 has rarely been achieved. Herein we show that a crystal engineering approach to tuning of pore-size in a coordination network, [Cu(quinoline-5-carboxyate)2 ]n (Qc-5-Cu) ena+bles ultra-high selectivity for CO2 over N2 (SCN ≈40 000) and CH4 (SCM ≈3300). Qc-5-Cu-sql-β, a narrow pore polymorph of the square lattice (sql) coordination network Qc-5-Cu-sql-α, adsorbs CO2 while excluding both CH4 and N2 . Experimental measurements and molecular modeling validate and explain the performance. Qc-5-Cu-sql-β is stable to moisture and its separation performance is unaffected by humidity.

  18. Tuning Pore Size in Square-Lattice Coordination Networks for Size-Selective Sieving of CO2.

    PubMed

    Chen, Kai-Jie; Madden, David G; Pham, Tony; Forrest, Katherine A; Kumar, Amrit; Yang, Qing-Yuan; Xue, Wei; Space, Brian; Perry, John J; Zhang, Jie-Peng; Chen, Xiao-Ming; Zaworotko, Michael J

    2016-08-22

    Porous materials capable of selectively capturing CO2 from flue-gases or natural gas are of interest in terms of rising atmospheric CO2 levels and methane purification. Size-exclusive sieving of CO2 over CH4 and N2 has rarely been achieved. Herein we show that a crystal engineering approach to tuning of pore-size in a coordination network, [Cu(quinoline-5-carboxyate)2 ]n (Qc-5-Cu) ena+bles ultra-high selectivity for CO2 over N2 (SCN ≈40 000) and CH4 (SCM ≈3300). Qc-5-Cu-sql-β, a narrow pore polymorph of the square lattice (sql) coordination network Qc-5-Cu-sql-α, adsorbs CO2 while excluding both CH4 and N2 . Experimental measurements and molecular modeling validate and explain the performance. Qc-5-Cu-sql-β is stable to moisture and its separation performance is unaffected by humidity. PMID:27439315

  19. Imaging calcium carbonate distribution in human sweat pore in vivo using nonlinear microscopy

    NASA Astrophysics Data System (ADS)

    Chen, Xueqin; Gasecka, Alicja; Formanek, Florian; Galey, Jean-Baptiste; Rigneault, Hervé

    2015-03-01

    Nonlinear microscopies, including two-photon excited autofluorescence (TPEF) and coherent anti-Stokes Raman scattering (CARS), were used to study individual human sweat pore morphology and topically applied antiperspirant salt penetration inside sweat pore, in vivo on human palms. Sweat pore inner morphology in vivo was imaged up to the depth of 100 μm by TPEF microscopy. The 3D penetration and distribution of "in situ calcium carbonate" (isCC), an antiperspirant salt model, was investigated using CARS microscopy.

  20. Strain-based in-situ study of anion and cation insertion into porous carbon electrodes with different pore sizes

    SciTech Connect

    Black, Jennifer M; Feng, Guang; Fulvio, Pasquale F; Hillesheim, Patrick C; Dai, Sheng; Gogotsi, Yury G.; Cummings, Peter T; Kalinin, Sergei V; Balke, Nina

    2013-01-01

    The expansion of porous carbon electrodes in a room temperature ionic liquid (RTIL) is studied using in-situ atomic force microscopy (AFM). The effect of carbon surface area and pore size/pore size distribution on the observed strain profile and ion kinetics is examined. Also, the influence of potential scan rate on the strain response is investigated. By analyzing the strain data at various potential scan rates information on ion kinetics in the different carbon materials is obtained. Molecular dynamics (MD) simulations are performed to compare with and provide molecular insights into experimental results, which is the first MD work investigating the pressure exerted on porous electrodes under applied potential in a RTIL electrolyte. Using MD, the pressure exerted on the pore wall is calculated as a function of potential/charge for both a micropore (1.2 nm) and a mesopore (7.0 nm). The shape of the calculated pressure profile matches closely with the strain profiles observed experimentally.

  1. Scaffolds and cells for tissue regeneration: different scaffold pore sizes-different cell effects.

    PubMed

    Bružauskaitė, Ieva; Bironaitė, Daiva; Bagdonas, Edvardas; Bernotienė, Eiva

    2016-05-01

    During the last decade biomaterial sciences and tissue engineering have become new scientific fields supplying rising demand of regenerative therapy. Tissue engineering requires consolidation of a broad knowledge of cell biology and modern biotechnology investigating biocompatibility of materials and their application for the reconstruction of damaged organs and tissues. Stem cell-based tissue regeneration started from the direct cell transplantation into damaged tissues or blood vessels. However, it is difficult to track transplanted cells and keep them in one particular place of diseased organ. Recently, new technologies such as cultivation of stem cell on the scaffolds and subsequently their implantation into injured tissue have been extensively developed. Successful tissue regeneration requires scaffolds with particular mechanical stability or biodegradability, appropriate size, surface roughness and porosity to provide a suitable microenvironment for the sufficient cell-cell interaction, cell migration, proliferation and differentiation. Further functioning of implanted cells highly depends on the scaffold pore sizes that play an essential role in nutrient and oxygen diffusion and waste removal. In addition, pore sizes strongly influence cell adhesion, cell-cell interaction and cell transmigration across the membrane depending on the various purposes of tissue regeneration. Therefore, this review will highlight contemporary tendencies in application of non-degradable scaffolds and stem cells in regenerative medicine with a particular focus on the pore sizes significantly affecting final recover of diseased organs.

  2. Control of both particle and pore size in nanoporous palladium alloy powders

    SciTech Connect

    Jones, Christopher G.; Cappillino, Patrick J.; Stavila, Vitalie; Robinson, David B.

    2014-07-15

    Energy storage materials often involve chemical reactions with bulk solids. Porosity within the solids can enhance reaction rates. The porosity can be either within or between individual particles of the material. Greater control of the size and uniformity of both types of pore should lead to enhancements of charging and discharging rates in energy storage systems. Furthermore, to control both particle and pore size in nanoporous palladium (Pd)-based hydrogen storage materials, first we created uniformly sized copper particles of about 1 μm diameter by the reduction of copper sulfate with ascorbic acid. In turn, these were used as reducing agents for tetrachloropalladate in the presence of a block copolymer surfactant. The copper reductant particles are geometrically self-limiting, so the resulting Pd particles are of similar size. The surfactant induces formation of 10 nm-scale pores within the particles. Some residual copper is alloyed with the Pd, reducing hydrogen storage capacity; use of a more reactive Pd salt can mitigate this. The reaction is conveniently performed in gram-scale batches.

  3. Control of both particle and pore size in nanoporous palladium alloy powders

    DOE PAGESBeta

    Jones, Christopher G.; Cappillino, Patrick J.; Stavila, Vitalie; Robinson, David B.

    2014-07-15

    Energy storage materials often involve chemical reactions with bulk solids. Porosity within the solids can enhance reaction rates. The porosity can be either within or between individual particles of the material. Greater control of the size and uniformity of both types of pore should lead to enhancements of charging and discharging rates in energy storage systems. Furthermore, to control both particle and pore size in nanoporous palladium (Pd)-based hydrogen storage materials, first we created uniformly sized copper particles of about 1 μm diameter by the reduction of copper sulfate with ascorbic acid. In turn, these were used as reducing agentsmore » for tetrachloropalladate in the presence of a block copolymer surfactant. The copper reductant particles are geometrically self-limiting, so the resulting Pd particles are of similar size. The surfactant induces formation of 10 nm-scale pores within the particles. Some residual copper is alloyed with the Pd, reducing hydrogen storage capacity; use of a more reactive Pd salt can mitigate this. The reaction is conveniently performed in gram-scale batches.« less

  4. Pore Pressure Distribution and Flank Instability in Hydrothermally Altered Stratovolcanoes

    NASA Astrophysics Data System (ADS)

    Ball, J. L.; Taron, J.; Hurwitz, S.; Reid, M. E.

    2015-12-01

    Field and geophysical investigations of stratovolcanoes with long-lived hydrothermal systems commonly reveal that initially permeable regions (such as brecciated layers of pyroclastic material) can become both altered and water-bearing. Hydrothermal alteration in these regions, including clay formation, can turn them into low-permeability barriers to fluid flow, which could increase pore fluid pressures resulting in flank slope instability. We examined elevated pore pressure conditions using numerical models of hydrothermal flow in stratovolcanoes, informed by geophysical data about internal structures and deposits. Idealized radially symmetric meshes were developed based on cross-sectional profiles and alteration/permeability structures of Cascade Range stratovolcanoes. We used the OpenGeoSys model to simulate variably saturated conditions in volcanoes heated only by regional heat fluxes, as well as 650°C intrusions at two km depth below the surface. Meteoric recharge was estimated from precipitation rates in the Cascade Range. Preliminary results indicate zones of elevated pore pressures form: 1) where slopes are underlain by continuous low-permeability altered layers, or 2) when the edifice has an altered core with saturated, less permeable limbs. The first scenario might control shallow collapses on the slopes above the altered layers. The second could promote deeper flank collapses that are initially limited to the summit and upper slopes, but could progress to the core of an edifice. In both scenarios, pore pressures can be further elevated by shallow intrusions, or evolve over longer time scales under forcing from regional heat flux. Geometries without confining low-permeability layers do not show these pressure effects. Our initial scenarios use radially symmetric models, but we are also simulating hydrothermal flow under real 3D geometries with asymmetric subsurface structures (Mount Adams). Simulation results will be used to inform 3D slope

  5. Porous silicon structures with high surface area/specific pore size

    DOEpatents

    Northrup, M.A.; Yu, C.M.; Raley, N.F.

    1999-03-16

    Fabrication and use of porous silicon structures to increase surface area of heated reaction chambers, electrophoresis devices, and thermopneumatic sensor-actuators, chemical preconcentrates, and filtering or control flow devices. In particular, such high surface area or specific pore size porous silicon structures will be useful in significantly augmenting the adsorption, vaporization, desorption, condensation and flow of liquids and gases in applications that use such processes on a miniature scale. Examples that will benefit from a high surface area, porous silicon structure include sample preconcentrators that are designed to adsorb and subsequently desorb specific chemical species from a sample background; chemical reaction chambers with enhanced surface reaction rates; and sensor-actuator chamber devices with increased pressure for thermopneumatic actuation of integrated membranes. Examples that benefit from specific pore sized porous silicon are chemical/biological filters and thermally-activated flow devices with active or adjacent surfaces such as electrodes or heaters. 9 figs.

  6. Porous silicon structures with high surface area/specific pore size

    DOEpatents

    Northrup, M. Allen; Yu, Conrad M.; Raley, Norman F.

    1999-01-01

    Fabrication and use of porous silicon structures to increase surface area of heated reaction chambers, electrophoresis devices, and thermopneumatic sensor-actuators, chemical preconcentrates, and filtering or control flow devices. In particular, such high surface area or specific pore size porous silicon structures will be useful in significantly augmenting the adsorption, vaporization, desorption, condensation and flow of liquids and gasses in applications that use such processes on a miniature scale. Examples that will benefit from a high surface area, porous silicon structure include sample preconcentrators that are designed to adsorb and subsequently desorb specific chemical species from a sample background; chemical reaction chambers with enhanced surface reaction rates; and sensor-actuator chamber devices with increased pressure for thermopneumatic actuation of integrated membranes. Examples that benefit from specific pore sized porous silicon are chemical/biological filters and thermally-activated flow devices with active or adjacent surfaces such as electrodes or heaters.

  7. Water Desalination Using Nanoporous Single-Layer Graphene with Tunable Pore Size

    SciTech Connect

    Surwade, Sumedh P.; Smirnov, Sergei N.; Vlassiouk, Ivan V.; Unocic, Raymond R.; Veith, Gabriel M.; Dai, Sheng; Mahurin, Shannon Mark

    2015-03-23

    Graphene has great potential to serve as a separation membrane due to its unique properties such as chemical and mechanical stability, flexibility and most importantly its one-atom thickness. In this study, we demonstrate first experimental evidence of the use of single-layer porous graphene as a desalination membrane. Nanometer-sized pores are introduced into single layer graphene using a convenient oxygen plasma etching process that permits tuning of the pore size. The resulting porous graphene membrane exhibited high rejection of salt ions and rapid water transport, thus functioning as an efficient water desalination membrane. Salt rejection selectivity of nearly 100% and exceptionally high water fluxes exceeding 105 g m-2 s-1 at 40 C were measured using saturated water vapor as a driving force.

  8. Water Desalination Using Nanoporous Single-Layer Graphene with Tunable Pore Size

    DOE PAGESBeta

    Surwade, Sumedh P.; Smirnov, Sergei N.; Vlassiouk, Ivan V.; Unocic, Raymond R.; Veith, Gabriel M.; Dai, Sheng; Mahurin, Shannon Mark

    2015-03-23

    Graphene has great potential to serve as a separation membrane due to its unique properties such as chemical and mechanical stability, flexibility and most importantly its one-atom thickness. In this study, we demonstrate first experimental evidence of the use of single-layer porous graphene as a desalination membrane. Nanometer-sized pores are introduced into single layer graphene using a convenient oxygen plasma etching process that permits tuning of the pore size. The resulting porous graphene membrane exhibited high rejection of salt ions and rapid water transport, thus functioning as an efficient water desalination membrane. Salt rejection selectivity of nearly 100% and exceptionallymore » high water fluxes exceeding 105 g m-2 s-1 at 40 C were measured using saturated water vapor as a driving force.« less

  9. Charge Distribution and Imperfect Amphipathicity Affect Pore Formation by Antimicrobial Peptides

    PubMed Central

    Mihajlovic, Maja

    2012-01-01

    Antimicrobial peptides often permeabilize biological membranes via a pore mechanism. Two pore types have been proposed: toroidal, where the pore is partly lined by lipid, and barrel-stave, where a cylindrical pore is completely lined by peptides. What drives the preference of antimicrobial peptides for a certain pore type is not yet fully understood. According to neutron scattering and oriented circular dichroism, melittin and MG-H2 induce toroidal pores whereas alamethicin forms barrel-stave pores. In previous work we found that indeed melittin seems to favor toroidal pores whereas alamethicin favors cylindrical pores. Here we designed mutants of these two peptides and the magainin analogue MG-H2, aimed to probe how the distribution of charges along the helix and its imperfectly amphipathic structure influence pore formation. Molecular dynamics (MD) simulations of the peptides in a pre-formed cylindrical pore have been performed. The duration of the simulations was 136 ns to 216 ns. We found that a melittin mutant with lysine 7 neutralized favors cylindrical pores whereas a MG-H2 mutant with lysines in the N-terminal half of these peptides neutralized and an alamethicin mutant with a positive charge at the position 7 form semitoroidal pores. These results suggest that charged residues within the N-terminal half are important for the toroidal pore formation. Toroidal pores produced by MG-H2 are more disordered than the melittin pores, likely because of the charged residues located in the middle of the MG-H2 helix (K11 and K14). Imperfect amphipathicity of melitin seems to play a role in its preference for toroidal pores since the substitutions of charged residues located within the nonpolar face by hydrophobic residues suppress evolution of a toroidal pore. The mutations change the position of lysine 7 near the N-terminus, relative to the lower leaflet headgroups. The MD simulations also show that the melittin P14A mutant forms a toroidal pore, but its

  10. Microfluidic Directed Synthesis of Alginate Nanogels with Tunable Pore Size for Efficient Protein Delivery.

    PubMed

    Bazban-Shotorbani, Salime; Dashtimoghadam, Erfan; Karkhaneh, Akbar; Hasani-Sadrabadi, Mohammad Mahdi; Jacob, Karl I

    2016-05-17

    Alginate is a biopolymer with favorable pH-sensitive properties for oral delivery of peptides and proteins. However, conventional alginate nanogels have limitations such as low encapsulation efficiency because of drug leaching during bead preparation and burst release in high pH values. These shortcomings originate from large pore size of the nanogels. In this work, we proposed an on-chip hydrodynamic flow focusing approach for synthesis of alginate nanogels with adjustable pore size to achieve fine-tunable release profile of the encapsulated bioactive agents. It is demonstrated that the microstructure of nanogels can be controlled through adjusting flow ratio and mixing time directed on microfluidic platforms consisting of cross-junction microchannels. In this study, the average pore size of alginate nanogels (i.e., average molecular weight between cross-links, Mc) was related to synthesis parameters. Mc was calculated from equations based on equilibrium swelling theory and proposed methods to modify the theory for pH-sensitive nanogels. In the equations we derived, size and compactness of nanogels are key factors, which can be adjusted by controlling the flow ratio. It was found that increase in flow ratio increases the size of nanogels and decreases their compactness. The size of on-chip generated nanogels for flow ratio of 0.02-0.2 was measured to be in the range of 68-138 nm. Moreover, a method based on the Mie theory was implemented to estimate the aggregation number (Nagg) of polymer chains inside the nanogels as an indicator of compactness. According to the size and compactness results along with equations of modified swelling theory, Mc obtained to be in the range of 0.5-0.8 kDa. The proposed method could be considered as a promising approach for efficient polypeptides encapsulation and their sustained release. PMID:26938744

  11. Controlling drug delivery kinetics from mesoporous titania thin films by pore size and surface energy.

    PubMed

    Karlsson, Johan; Atefyekta, Saba; Andersson, Martin

    2015-01-01

    The osseointegration capacity of bone-anchoring implants can be improved by the use of drugs that are administrated by an inbuilt drug delivery system. However, to attain superior control of drug delivery and to have the ability to administer drugs of varying size, including proteins, further material development of drug carriers is needed. Mesoporous materials have shown great potential in drug delivery applications to provide and maintain a drug concentration within the therapeutic window for the desired period of time. Moreover, drug delivery from coatings consisting of mesoporous titania has shown to be promising to improve healing of bone-anchoring implants. Here we report on how the delivery of an osteoporosis drug, alendronate, can be controlled by altering pore size and surface energy of mesoporous titania thin films. The pore size was varied from 3.4 nm to 7.2 nm by the use of different structure-directing templates and addition of a swelling agent. The surface energy was also altered by grafting dimethylsilane to the pore walls. The drug uptake and release profiles were monitored in situ using quartz crystal microbalance with dissipation (QCM-D) and it was shown that both pore size and surface energy had a profound effect on both the adsorption and release kinetics of alendronate. The QCM-D data provided evidence that the drug delivery from mesoporous titania films is controlled by a binding-diffusion mechanism. The yielded knowledge of release kinetics is crucial in order to improve the in vivo tissue response associated to therapeutic treatments.

  12. Controlling drug delivery kinetics from mesoporous titania thin films by pore size and surface energy.

    PubMed

    Karlsson, Johan; Atefyekta, Saba; Andersson, Martin

    2015-01-01

    The osseointegration capacity of bone-anchoring implants can be improved by the use of drugs that are administrated by an inbuilt drug delivery system. However, to attain superior control of drug delivery and to have the ability to administer drugs of varying size, including proteins, further material development of drug carriers is needed. Mesoporous materials have shown great potential in drug delivery applications to provide and maintain a drug concentration within the therapeutic window for the desired period of time. Moreover, drug delivery from coatings consisting of mesoporous titania has shown to be promising to improve healing of bone-anchoring implants. Here we report on how the delivery of an osteoporosis drug, alendronate, can be controlled by altering pore size and surface energy of mesoporous titania thin films. The pore size was varied from 3.4 nm to 7.2 nm by the use of different structure-directing templates and addition of a swelling agent. The surface energy was also altered by grafting dimethylsilane to the pore walls. The drug uptake and release profiles were monitored in situ using quartz crystal microbalance with dissipation (QCM-D) and it was shown that both pore size and surface energy had a profound effect on both the adsorption and release kinetics of alendronate. The QCM-D data provided evidence that the drug delivery from mesoporous titania films is controlled by a binding-diffusion mechanism. The yielded knowledge of release kinetics is crucial in order to improve the in vivo tissue response associated to therapeutic treatments. PMID:26185444

  13. Controlling drug delivery kinetics from mesoporous titania thin films by pore size and surface energy

    PubMed Central

    Karlsson, Johan; Atefyekta, Saba; Andersson, Martin

    2015-01-01

    The osseointegration capacity of bone-anchoring implants can be improved by the use of drugs that are administrated by an inbuilt drug delivery system. However, to attain superior control of drug delivery and to have the ability to administer drugs of varying size, including proteins, further material development of drug carriers is needed. Mesoporous materials have shown great potential in drug delivery applications to provide and maintain a drug concentration within the therapeutic window for the desired period of time. Moreover, drug delivery from coatings consisting of mesoporous titania has shown to be promising to improve healing of bone-anchoring implants. Here we report on how the delivery of an osteoporosis drug, alendronate, can be controlled by altering pore size and surface energy of mesoporous titania thin films. The pore size was varied from 3.4 nm to 7.2 nm by the use of different structure-directing templates and addition of a swelling agent. The surface energy was also altered by grafting dimethylsilane to the pore walls. The drug uptake and release profiles were monitored in situ using quartz crystal microbalance with dissipation (QCM-D) and it was shown that both pore size and surface energy had a profound effect on both the adsorption and release kinetics of alendronate. The QCM-D data provided evidence that the drug delivery from mesoporous titania films is controlled by a binding–diffusion mechanism. The yielded knowledge of release kinetics is crucial in order to improve the in vivo tissue response associated to therapeutic treatments. PMID:26185444

  14. Control of Porosity and Pore Size of Metal Reinforced Carbon Nanotube Membranes

    PubMed Central

    Dumee, Ludovic; Velleman, Leonora; Sears, Kallista; Hill, Matthew; Schutz, Jurg; Finn, Niall; Duke, Mikel; Gray, Stephen

    2011-01-01

    Membranes are crucial in modern industry and both new technologies and materials need to be designed to achieve higher selectivity and performance. Exotic materials such as nanoparticles offer promising perspectives, and combining both their very high specific surface area and the possibility to incorporate them into macrostructures have already shown to substantially increase the membrane performance. In this paper we report on the fabrication and engineering of metal-reinforced carbon nanotube (CNT) Bucky-Paper (BP) composites with tuneable porosity and surface pore size. A BP is an entangled mesh non-woven like structure of nanotubes. Pure CNT BPs present both very high porosity (>90%) and specific surface area (>400 m2/g). Furthermore, their pore size is generally between 20–50 nm making them promising candidates for various membrane and separation applications. Both electro-plating and electroless plating techniques were used to plate different series of BPs and offered various degrees of success. Here we will report mainly on electroless plated gold/CNT composites. The benefit of this method resides in the versatility of the plating and the opportunity to tune both average pore size and porosity of the structure with a high degree of reproducibility. The CNT BPs were first oxidized by short UV/O3 treatment, followed by successive immersion in different plating solutions. The morphology and properties of these samples has been investigated and their performance in air permeation and gas adsorption will be reported. PMID:24957493

  15. Impact of pore size on the sorption of uranyl under seawater conditions

    DOE PAGESBeta

    Mayes, Richard T.; Gorka, Joanna; Dai, Sheng

    2016-04-05

    The extraction of uranium from seawater has received significant interest recently, because of the possibility of a near-limitless supply of uranium to fuel the nuclear power industry. While sorbent development has focused primarily on polymeric sorbents, nanomaterials represent a new area that has the potential to surpass the current polymeric sorbents, because of the high surface areas that are possible. Mesoporous carbon materials are a stable, high-surface-area material capable of extracting various chemical species from a variety of environments. Herein, we report the use of a dual templating process to understand the effect of pore size on the adsorption ofmore » uranyl ions from a uranyl brine consisting of seawater-relevant sodium, chloride, and bicarbonate ions. It was found that pore size played a more significant role in the effective use of the grafted polymer, leading to higher uranium capacities than the surface area. Furthermore, the pore size must be tailored to meet the demands of the extraction medium and analyte metal to achieve efficacy as an adsorbent.« less

  16. Microtomography and pore-scale modeling of two-phase Fluid Distribution

    SciTech Connect

    Silin, D.; Tomutsa, L.; Benson, S.; Patzek, T.

    2010-10-19

    Synchrotron-based X-ray microtomography (micro CT) at the Advanced Light Source (ALS) line 8.3.2 at the Lawrence Berkeley National Laboratory produces three-dimensional micron-scale-resolution digital images of the pore space of the reservoir rock along with the spacial distribution of the fluids. Pore-scale visualization of carbon dioxide flooding experiments performed at a reservoir pressure demonstrates that the injected gas fills some pores and pore clusters, and entirely bypasses the others. Using 3D digital images of the pore space as input data, the method of maximal inscribed spheres (MIS) predicts two-phase fluid distribution in capillary equilibrium. Verification against the tomography images shows a good agreement between the computed fluid distribution in the pores and the experimental data. The model-predicted capillary pressure curves and tomography-based porosimetry distributions compared favorably with the mercury injection data. Thus, micro CT in combination with modeling based on the MIS is a viable approach to study the pore-scale mechanisms of CO{sub 2} injection into an aquifer, as well as more general multi-phase flows.

  17. Systematic Design of Pore Size and Functionality in Isoreticular MOFs and Their Application in Methane Storage

    NASA Astrophysics Data System (ADS)

    Eddaoudi, Mohamed; Kim, Jaheon; Rosi, Nathaniel; Vodak, David; Wachter, Joseph; O'Keeffe, Michael; Yaghi, Omar M.

    2002-01-01

    A strategy based on reticulating metal ions and organic carboxylate links into extended networks has been advanced to a point that allowed the design of porous structures in which pore size and functionality could be varied systematically. Metal-organic framework (MOF-5), a prototype of a new class of porous materials and one that is constructed from octahedral Zn-O-C clusters and benzene links, was used to demonstrate that its three-dimensional porous system can be functionalized with the organic groups -Br, -NH2, -OC3H7, -OC5H11, -C2H4, and -C4H4 and that its pore size can be expanded with the long molecular struts biphenyl, tetrahydropyrene, pyrene, and terphenyl. We synthesized an isoreticular series (one that has the same framework topology) of 16 highly crystalline materials whose open space represented up to 91.1% of the crystal volume, as well as homogeneous periodic pores that can be incrementally varied from 3.8 to 28.8 angstroms. One member of this series exhibited a high capacity for methane storage (240 cubic centimeters at standard temperature and pressure per gram at 36 atmospheres and ambient temperature), and others the lowest densities (0.41 to 0.21 gram per cubic centimeter) for a crystalline material at room temperature.

  18. Porous carbon with defined pore size as anode of microbial fuel cell.

    PubMed

    Chen, Xiaofen; Cui, Dan; Wang, Xiaojun; Wang, Xianshu; Li, Weishan

    2015-07-15

    This paper reported a novel anode material, porous carbon with a defined pore size (DPC) matching bacteria, for microbial fuel cell (MFC). The DPC was prepared by using silica spheres as templates and sucrose as carbon precursor. The structure and morphology of the as-prepared DPC were characterized with X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM), and its performance as anode of MFC based on Escherichia coli (E. coli) was evaluated with chronoamperometry, cyclic voltammetry (CV) and polarization curve measurement. The result from SEM demonstrates that pores in the as-prepared DPC are well defined with an average diameter of 400nm, which is a little larger than that of E. coli, and the polarization curve measurement shows that the as-prepared DPC exhibits superior performance as anode material loaded on carbon felt, delivering a power output of 1606mWm(-2), compared to the 402mWm(-2) of naked carbon felt anode, in the solution containing 2g/L glucose. The excellent performance of the as-prepared DPC is attributed to its suitable pore size for accommodating E. coli strain, which facilitates the formation of bacterial biofilm and the electron transfer between bacteria and anode.

  19. Influence of the pore size in multi-walled carbon nanotubes on the hydrogen storage behaviors

    SciTech Connect

    Lee, Seul-Yi; Park, Soo-Jin

    2012-10-15

    Activated multi-walled carbon nanotubes (A-MWCNTs) were prepared using a chemical activation method to obtain well-developed pore structures for use as hydrogen storage materials. The microstructure and crystallinity of the A-MWCNTs were evaluated by X-ray diffraction and Fourier transform Raman spectroscopy. The textural properties of the A-MWCNTs were investigated by nitrogen gas sorption analysis at 77 K. The hydrogen storage capacity of the A-MWCNTs was evaluated at 77 K and 1 bar. The results showed that the specific surface area of the MWCNTs increased from 327 to 495 m{sup 2}/g as the activation temperature was increased. The highest hydrogen storage capacity was observed in the A-MWCNTs sample activated at 900 Degree-Sign C (0.54 wt%). This was attributed to it having the narrowest microporosity, which is a factor closely related to the hydrogen storage capacity. This shows that the hydrogen storage behaviors depend on the pore volume. Although a high pore volume is desirable for hydrogen storage, it is also severely affected if the pore size in the A-MWCNTs for the hydrogen molecules is suitable for creating the activation process. Highlights: Black-Right-Pointing-Pointer The AT-800 and AT-900 samples were prepared by a chemical activation method at activation temperature of 800 and 900 Degree-Sign C, respectively. Black-Right-Pointing-Pointer The AT-900 sample has the narrowest peak in comparison with the AT-800 sample, resulting from the overlap of the two peaks (Peak I and Peak II). Black-Right-Pointing-Pointer This overlapping effect is due to the newly created micropores or shrinkages of pores in Peak II. So, these determining characteristics are essential for designing materials that are suitable for molecular hydrogen storage.

  20. Controlled porosity and pore size substrates for nickel-cadmium cells

    NASA Technical Reports Server (NTRS)

    Gordy, D. J.; Luksha, E.; Menard, C. J.

    1973-01-01

    A novel process for the preparation of improved cadmium electrode plaques with precisely controlled pore size and porosity is described. The requirements for these plaques include far better uniformity, reproducibility, and life than is currently available with conventional materials. The key features of the work were preparation of plaques via a powder metallurgical technique which consisted of isostatically compacting a blend of a nickel powder with a fugitive pore-former and subsequently sintering the 'green' compact. Cadmium electrodes were prepared from these materials and were cycle tested in negative-limited cells using an accelerated, torturous test regime. Results were obtained which showed the new structures yielded electrodes that were superior to the conventional structures in mechanical properties and performance.

  1. Reversible control of pore size and surface chemistry of mesoporous silica through dynamic covalent chemistry: philicity mediated catalysis

    NASA Astrophysics Data System (ADS)

    Singh, Dheeraj Kumar; Pavan Kumar, B. V. V. S.; Eswaramoorthy, M.

    2015-08-01

    Here, we report the synthesis of adaptive hybrid mesoporous silica having the ability to reconfigure its pore properties such as pore size and philicity in response to the external environment. Decyl chains were reversibly appended to the pore walls of silica through imine motifs as dynamic covalent modules to switch the pore size and philicity in response to pH. This switching of pore properties was used to gate the access of reactants to the gold nanoparticles immobilized inside the nanopores, thus enabling us to turn-on/turn-off the catalytic reaction. The use of such dynamic covalent modules to govern pore properties would enable the realization of intelligent hybrids capable of controlling many such chemical processes in response to stimuli.Here, we report the synthesis of adaptive hybrid mesoporous silica having the ability to reconfigure its pore properties such as pore size and philicity in response to the external environment. Decyl chains were reversibly appended to the pore walls of silica through imine motifs as dynamic covalent modules to switch the pore size and philicity in response to pH. This switching of pore properties was used to gate the access of reactants to the gold nanoparticles immobilized inside the nanopores, thus enabling us to turn-on/turn-off the catalytic reaction. The use of such dynamic covalent modules to govern pore properties would enable the realization of intelligent hybrids capable of controlling many such chemical processes in response to stimuli. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr02959g

  2. Novel magnetic Fe onion-like fullerene micrometer-sized particles of narrow size distribution

    NASA Astrophysics Data System (ADS)

    Snovski, Ron; Grinblat, Judith; Margel, Shlomo

    2012-01-01

    Magnetic polydivinylbenzene (PDVB)/magnetite micrometer-sized particles of narrow size distribution were prepared by entrapping Fe(CO)5 within the pores of uniform porous PDVB particles, followed by the thermal decomposition of the encapsulated Fe(CO)5 at 300 °C in a sealed cell under inert atmosphere. Magnetic Fe onion-like fullerene micrometer-sized particles of narrow size distribution have been prepared by the thermal decomposition of the PDVB/magnetite magnetic microspheres at 1100 °C under inert atmosphere. The graphitic coating protects the elemental iron particles from oxidation and thereby preserves their very high magnetic moment for at least a year. Characterization of these unique magnetic carbon graphitic particles was also performed.

  3. Pore Scale Heterogeneity in the Mineral Distribution, Surface Area and Adsorption in Porous Rocks

    NASA Astrophysics Data System (ADS)

    Lai, P. E. P.; Krevor, S. C.

    2014-12-01

    The impact of heterogeneity in chemical transport and reaction is not understood in continuum (Darcy/Fickian) models of reactive transport. This is manifested in well-known problems such as scale dependent dispersion and discrepancies in reaction rate observations made at laboratory and field scales [1]. Additionally, this is a source of uncertainty for carbon dioxide injection, which produces a reactive fluid-rock system particularly in carbonate rock reservoirs. A potential cause is the inability of the continuum approach to incorporate the impact of heterogeneity in pore-scale reaction rates. This results in part from pore-scale heterogeneities in surface area of reactive minerals [2, 3]. We use x-ray micro tomography to describe the non-normal 3-dimensional distribution of reactive surface area within a porous medium according to distinct mineral groups. Using in-house image processing techniques, thin sections, nitrogen BET surface area, backscattered electron imaging and energy dispersive spectroscopy, we compare the surface area of each mineral phase to those obtained from x-ray CT imagery. In all samples, there is little correlation between the reactive surface area fraction and the volumetric fraction of a mineral in a bulk rock. Berea sandstone was far less heterogeneous and has a characteristic pore size at which a surface area distribution may be used to quantify heterogeneity. In carbonates, heterogeneity is more complex and surface area must be characterized at multiple length scales for an accurate description of reactive transport. We combine the mineral specific surface area characterisation to dynamic tomography, imaging the flow of water and solutes, to observe flow dependent and mineral specific adsorption. The observations may contribute to the incorporation of experimentally based statistical descriptions of pore scale heterogeneity in reactive transport into upscaled models, moving it closer to predictive capabilities for field scale

  4. Experimental measurement and thermodynamic modeling of the mixed CH4 + C3H8 clathrate hydrate equilibria in silica gel pores: effects of pore size and salinity.

    PubMed

    Lee, Seungmin; Seo, Yongwon

    2010-06-15

    We measured hydrate phase equilibria for the ternary CH(4) (90%) + C(3)H(8) (10%) + water mixtures in silica gel pores with nominal diameters of 6.0, 15.0, 30.0, and 100.0 nm and for the quaternary CH(4) (90%) + C(3)H(8) (10%) + NaCl + water mixtures of two different NaCl concentrations (3 and 10 wt %) in silica gel pores with nominal diameters of 6.0, 15.0, and 30.0 nm. The CH(4) (90%) + C(3)H(8) (10%) hydrate-water interfacial tension (sigma(HW)) of 42 +/- 3 mJ/m(2) was obtained through the Gibbs-Thomson equation for dissociation within cylindrical pores. With this value, the experimental results were in good agreement with the calculated ones based on the van der Waals and Platteeuw model. A correction term for the capillary effect and a Pitzer model for electrolyte solutions were adopted to calculate the activity of water in the aqueous electrolyte solutions within silica gel pores. At a specified temperature, three-phase H-L(W)-V equilibrium curves of pore hydrates were shifted to higher-pressure regions depending on pore sizes and NaCl concentrations. From the cage-dependent (13)C NMR chemical shifts of enclathrated guest molecules, the mixed CH(4) (90%) + C(3)H(8) (10%) gas hydrate was confirmed to be structure II.

  5. An integrated approach for determination of pore-type distribution in carbonate-siliciclastic Asmari Reservoir, Cheshmeh-Khosh Oilfield, SW Iran

    NASA Astrophysics Data System (ADS)

    Gharechelou, Sajjad; Amini, Abdolhossein; Kadkhodaie-Ilkhchi, Ali; Moradi, Babak

    2015-10-01

    This paper presents an integrated pore type study at microscopic (core data), mesoscopic (well logs) and megascopic scales (3D seismic data) in the mixed carbonate-siliciclastic Asmari Reservoir of the Cheshmeh-Khosh Oilfield, SW Iran. Firstly, pore types are determined in a microscopic scale based on petrographic studies of thin sections. Well logs and nuclear magnetic resonance (NMR) log data are employed for pore type determination based on a velocity deviation log (mesoscopic scale). For each pore type subclass, a suite of physical rock properties including average poroperm values, T2 distribution, capillary pressure, pore size distribution and depositional texture are calculated. For this purpose, the NMR log, mercury injection capillary pressure data and core descriptions are interpreted in an integrated approach. Capillary pressure and pore size distribution in each pore type class are determined by mercury injection capillary pressure tests and synthesis of a continuous capillary pressure log from the NMR log (pseudo Pc curves). For dynamic behavior examination of the reservoir, the pore types are analysed in the framework of hydraulic flow units. Finally, 3D post-stacked seismic data are converted to a cube of pore types based on acoustic impedance inversion and seismic attributes. The methodology of this study is accomplished by using core and log data from three key wells and a 3D post-stack seismic data from the studied field. Lastly, a map of pore type distribution is established to provide a clue on the high and low permeable zones of the field. The presented methodology signifies reservoir anatomy on micro to mega scales.

  6. Cell Contraction Forces in Scaffolds with Varying Pore Size and Cell Density

    PubMed Central

    Corin, K. A.

    2010-01-01

    The contractile behavior of cells is relevant in understanding wound healing and scar formation. In tissue engineering, inhibition of the cell contractile response is critical for the regeneration of physiologically normal tissue rather than scar tissue. Previous studies have measured the contractile response of cells in a variety of conditions (e.g. on two-dimensional solid substrates, on free-floating tissue engineering scaffolds and on scaffolds under some constraint in a cell force monitor). Tissue engineering scaffolds behave mechanically like open-cell elastomeric foams: between strains of about 10 and 90%, cells progressively buckle struts in the scaffold. The contractile force required for an individual cell to buckle a strut within a scaffold has been estimated based on the strut dimensions (radius, r, and length, ℓ) and the strut modulus, Es. Since the buckling force varies, according to Euler's law, with r4∕ℓ2, and the relative density of the scaffold varies as (r∕ℓ)2, the cell contractile force associated with strut buckling is expected to vary with the square of the pore size for scaffolds of constant relative density. As the cell density increases, the force per cell to achieve a given strain in the scaffold is expected to decrease. Here we model the contractile response of fibroblasts by analyzing the response of a single tetrakaidecahedron to forces applied to individual struts (simulating cell contractile forces) using finite element analysis. We model tetrakaidecahedra of different strut lengths, corresponding to different scaffold pore sizes, and of varying numbers of loaded struts, corresponding to varying cell densities. We compare our numerical model with the results of free floating contraction experiments of normal human dermal fibroblasts (NHDF) in collagen-GAG scaffolds of varying pore size and with varying cell densities. PMID:20362329

  7. Body size distribution of the dinosaurs.

    PubMed

    O'Gorman, Eoin J; Hone, David W E

    2012-01-01

    The distribution of species body size is critically important for determining resource use within a group or clade. It is widely known that non-avian dinosaurs were the largest creatures to roam the Earth. There is, however, little understanding of how maximum species body size was distributed among the dinosaurs. Do they share a similar distribution to modern day vertebrate groups in spite of their large size, or did they exhibit fundamentally different distributions due to unique evolutionary pressures and adaptations? Here, we address this question by comparing the distribution of maximum species body size for dinosaurs to an extensive set of extant and extinct vertebrate groups. We also examine the body size distribution of dinosaurs by various sub-groups, time periods and formations. We find that dinosaurs exhibit a strong skew towards larger species, in direct contrast to modern day vertebrates. This pattern is not solely an artefact of bias in the fossil record, as demonstrated by contrasting distributions in two major extinct groups and supports the hypothesis that dinosaurs exhibited a fundamentally different life history strategy to other terrestrial vertebrates. A disparity in the size distribution of the herbivorous Ornithischia and Sauropodomorpha and the largely carnivorous Theropoda suggests that this pattern may have been a product of a divergence in evolutionary strategies: herbivorous dinosaurs rapidly evolved large size to escape predation by carnivores and maximise digestive efficiency; carnivores had sufficient resources among juvenile dinosaurs and non-dinosaurian prey to achieve optimal success at smaller body size.

  8. Body Size Distribution of the Dinosaurs

    PubMed Central

    O’Gorman, Eoin J.; Hone, David W. E.

    2012-01-01

    The distribution of species body size is critically important for determining resource use within a group or clade. It is widely known that non-avian dinosaurs were the largest creatures to roam the Earth. There is, however, little understanding of how maximum species body size was distributed among the dinosaurs. Do they share a similar distribution to modern day vertebrate groups in spite of their large size, or did they exhibit fundamentally different distributions due to unique evolutionary pressures and adaptations? Here, we address this question by comparing the distribution of maximum species body size for dinosaurs to an extensive set of extant and extinct vertebrate groups. We also examine the body size distribution of dinosaurs by various sub-groups, time periods and formations. We find that dinosaurs exhibit a strong skew towards larger species, in direct contrast to modern day vertebrates. This pattern is not solely an artefact of bias in the fossil record, as demonstrated by contrasting distributions in two major extinct groups and supports the hypothesis that dinosaurs exhibited a fundamentally different life history strategy to other terrestrial vertebrates. A disparity in the size distribution of the herbivorous Ornithischia and Sauropodomorpha and the largely carnivorous Theropoda suggests that this pattern may have been a product of a divergence in evolutionary strategies: herbivorous dinosaurs rapidly evolved large size to escape predation by carnivores and maximise digestive efficiency; carnivores had sufficient resources among juvenile dinosaurs and non-dinosaurian prey to achieve optimal success at smaller body size. PMID:23284818

  9. Optimization of protein fractionation by skim milk microfiltration: Choice of ceramic membrane pore size and filtration temperature.

    PubMed

    Jørgensen, Camilla Elise; Abrahamsen, Roger K; Rukke, Elling-Olav; Johansen, Anne-Grethe; Schüller, Reidar B; Skeie, Siv B

    2016-08-01

    The objective of this study was to investigate how ceramic membrane pore size and filtration temperature influence the protein fractionation of skim milk by cross flow microfiltration (MF). Microfiltration was performed at a uniform transmembrane pressure with constant permeate flux to a volume concentration factor of 2.5. Three different membrane pore sizes, 0.05, 0.10, and 0.20µm, were used at a filtration temperature of 50°C. Furthermore, at pore size 0.10µm, 2 different filtration temperatures were investigated: 50 and 60°C. The transmission of proteins increased with increasing pore size, giving the permeate from MF with the 0.20-µm membrane a significantly higher concentration of native whey proteins compared with the permeates from the 0.05- and 0.10-µm membranes (0.50, 0.24, and 0.39%, respectively). Significant amounts of caseins permeated the 0.20-µm membrane (1.4%), giving a permeate with a whitish appearance and a casein distribution (αS2-CN: αS1-CN: κ-CN: β-CN) similar to that of skim milk. The 0.05- and 0.10-µm membranes were able to retain all caseins (only negligible amounts were detected). A permeate free from casein is beneficial in the production of native whey protein concentrates and in applications where transparency is an important functional characteristic. Microfiltration of skim milk at 50°C with the 0.10-µm membrane resulted in a permeate containing significantly more native whey proteins than the permeate from MF at 60°C. The more rapid increase in transmembrane pressure and the significantly lower concentration of caseins in the retentate at 60°C indicated that a higher concentration of caseins deposited on the membrane, and consequently reduced the native whey protein transmission. Optimal protein fractionation of skim milk into a casein-rich retentate and a permeate with native whey proteins were obtained by 0.10-µm MF at 50°C. PMID:27265169

  10. Optimization of protein fractionation by skim milk microfiltration: Choice of ceramic membrane pore size and filtration temperature.

    PubMed

    Jørgensen, Camilla Elise; Abrahamsen, Roger K; Rukke, Elling-Olav; Johansen, Anne-Grethe; Schüller, Reidar B; Skeie, Siv B

    2016-08-01

    The objective of this study was to investigate how ceramic membrane pore size and filtration temperature influence the protein fractionation of skim milk by cross flow microfiltration (MF). Microfiltration was performed at a uniform transmembrane pressure with constant permeate flux to a volume concentration factor of 2.5. Three different membrane pore sizes, 0.05, 0.10, and 0.20µm, were used at a filtration temperature of 50°C. Furthermore, at pore size 0.10µm, 2 different filtration temperatures were investigated: 50 and 60°C. The transmission of proteins increased with increasing pore size, giving the permeate from MF with the 0.20-µm membrane a significantly higher concentration of native whey proteins compared with the permeates from the 0.05- and 0.10-µm membranes (0.50, 0.24, and 0.39%, respectively). Significant amounts of caseins permeated the 0.20-µm membrane (1.4%), giving a permeate with a whitish appearance and a casein distribution (αS2-CN: αS1-CN: κ-CN: β-CN) similar to that of skim milk. The 0.05- and 0.10-µm membranes were able to retain all caseins (only negligible amounts were detected). A permeate free from casein is beneficial in the production of native whey protein concentrates and in applications where transparency is an important functional characteristic. Microfiltration of skim milk at 50°C with the 0.10-µm membrane resulted in a permeate containing significantly more native whey proteins than the permeate from MF at 60°C. The more rapid increase in transmembrane pressure and the significantly lower concentration of caseins in the retentate at 60°C indicated that a higher concentration of caseins deposited on the membrane, and consequently reduced the native whey protein transmission. Optimal protein fractionation of skim milk into a casein-rich retentate and a permeate with native whey proteins were obtained by 0.10-µm MF at 50°C.

  11. Choice of pore size can introduce artefacts when filtering picoeukaryotes for molecular biodiversity studies.

    PubMed

    Sørensen, Nikolaj; Daugbjerg, Niels; Richardson, Katherine

    2013-05-01

    Published results of studies based on samples size fractionated by sequential filtration (e.g. 0.2-3 μm) indicate that many ciliate, dinoflagellate and rhizarian phylotypes are found among marine picoeukaryotes. This is somewhat surprising as these protists are typically known as being large organisms (often >10 μm) and no picoplanktonic species have so far been identified. Here, the abundances of ciliate and dinoflagellate phylotypes in published molecular studies of picoeukaryotes are shown to correlate negatively with the pore size chosen for the end filter in the sequential filtrations (i.e. the filter used to collect the microbial biomass). This suggests that extracellular DNA adhering to small particles may be the source of ciliate and dinoflagellate phylotypes in picoplanktonic size fractions. This hypothesis was confirmed using real-time qPCR, which revealed significantly less dinoflagellate 18S rDNA in a 0.8-3-μm size fraction compared to 0.2-3 μm. On average, the abundance of putative extracellular phylotypes decreased by 84-89 % when a 0.8- μm end filter was used rather than a 0.2-μm end filter. A 0.8-μm filter is, however, not sufficient to retain all picoeukaryotic cells. Thus, selection of filter pore size involves a trade-off between avoiding artefacts generated by extracellular DNA and sampling the entire picoeukaryotic community. In contrast to ciliate and dinoflagellate phylotypes, rhizarian phylotypes in the picoplankton size range do not display a pattern consistent with an extracellular origin. This is likely due to the documented existence of picoplanktonic swarmer cells within this group.

  12. Glycidol-modified gels for molecular-sieve chromatography. Surface hydrophilization and pore size reduction.

    PubMed

    Eriksson, K O

    1987-11-01

    Divinyl sulfone-crosslinked agarose gels were made hydrophilic by coupling glycidol to the agarose chains. The concentration of glycidol in the reaction mixture determines the pore size of the gels (the glycidol molecules probably form polymers, the degree of polymerization increasing with the glycidol concentration). Gels prepared with moderate glycidol concentrations are still porous enough to be used for separation of proteins and peptides. Gels with a high degree of glycidol polymerization are suited for desalting of low-molecular-weight compounds, for instance peptides.

  13. Effect of collagen-glycosaminoglycan scaffold pore size on matrix mineralization and cellular behavior in different cell types.

    PubMed

    Murphy, Ciara M; Duffy, Garry P; Schindeler, Aaron; O'brien, Fergal J

    2016-01-01

    We have previously examined osteoblast behavior on porous collagen-glycosaminoglycan (CG) scaffolds with a range of mean pore sizes demonstrating superior cell attachment and migration in scaffolds with the largest pores (325 μm). Scaffolds provide a framework for construct development; therefore, it is crucial to identify the optimal pore size for augmented tissue formation. Utilizing the same range of scaffolds (85 μm - 325 μm), this study aimed to examine the effects of mean pore size on subsequent osteoblast differentiation and matrix mineralization, and to understand the mechanism by which pore size influences behavior of different cell types. Consequently, primary mesenchymal stem cells (MSCs) were assessed and their behavior compared to osteoblasts. Results demonstrated that scaffolds with the largest pore size (325 μm) facilitated improved osteoblast infiltration, earlier expression of mature bone markers osteopontin (OPN) and osteocalcin (OCN), and increased mineralization. MSCs responded similarly to osteoblasts whereby cell attachment and scaffold infiltration improved with increasing pore size. However, MSCs showed reduced cell motility, proliferation, and scaffold infiltration compared to osteoblasts. This was associated with differences in the profile of integrin subunits (α2) and collagen receptors (CD44), indicating that osteoblasts have a stronger affinity for CG scaffolds compared to MSCs. In summary, these results reveal how larger pores promote improved cell infiltration, essential for construct development, however the optimal scaffold pore size can be cell type specific. As such, this study highlights a necessity to tailor both scaffold micro-architecture and cell-type when designing constructs for successful bone tissue engineering applications.

  14. Micro and nano-size pores of clay minerals in shale reservoirs: Implication for the accumulation of shale gas

    NASA Astrophysics Data System (ADS)

    Chen, Shangbin; Han, Yufu; Fu, Changqin; Zhang, han; Zhu, Yanming; Zuo, Zhaoxi

    2016-08-01

    A pore is an essential component of shale gas reservoirs. Clay minerals are the adsorption carrier second only to organic matter. This paper uses the organic maturity test, Field-Emission Scanning Electron Microscopy (FE-SEM), and X-ray Diffraction (XRD) to study the structure and effect of clay minerals on storing gas in shales. Results show the depositional environment and organic maturity influence the content and types of clay minerals as well as their structure in the three types of sedimentary facies in China. Clay minerals develop multi-size pores which shrink to micro- and nano-size by close compaction during diagenesis. Micro- and nano-pores can be divided into six types: 1) interlayer, 2) intergranular, 3) pore and fracture in contact with organic matter, 4) pore and fracture in contact with other types of minerals, 5) dissolved and, 6) micro-cracks. The contribution of clay minerals to the presence of pores in shale is evident and the clay plane porosity can even reach 16%, close to the contribution of organic matter. The amount of clay minerals and pores displays a positive correlation. Clay minerals possess a strong adsorption which is affected by moisture and reservoir maturity. Different pore levels of clay minerals are mutually arranged, thus essentially producing distinct reservoir adsorption effects. Understanding the structural characteristics of micro- and nano-pores in clay minerals can provide a tool for the exploration and development of shale gas reservoirs.

  15. Effective pore size and radius of capture for K(+) ions in K-channels.

    PubMed

    Moldenhauer, Hans; Díaz-Franulic, Ignacio; González-Nilo, Fernando; Naranjo, David

    2016-01-01

    Reconciling protein functional data with crystal structure is arduous because rare conformations or crystallization artifacts occur. Here we present a tool to validate the dimensions of open pore structures of potassium-selective ion channels. We used freely available algorithms to calculate the molecular contour of the pore to determine the effective internal pore radius (r(E)) in several K-channel crystal structures. r(E) was operationally defined as the radius of the biggest sphere able to enter the pore from the cytosolic side. We obtained consistent r(E) estimates for MthK and Kv1.2/2.1 structures, with r(E) = 5.3-5.9 Å and r(E) = 4.5-5.2 Å, respectively. We compared these structural estimates with functional assessments of the internal mouth radii of capture (r(C)) for two electrophysiological counterparts, the large conductance calcium activated K-channel (r(C) = 2.2 Å) and the Shaker Kv-channel (r(C) = 0.8 Å), for MthK and Kv1.2/2.1 structures, respectively. Calculating the difference between r(E) and r(C), produced consistent size radii of 3.1-3.7 Å and 3.6-4.4 Å for hydrated K(+) ions. These hydrated K(+) estimates harmonize with others obtained with diverse experimental and theoretical methods. Thus, these findings validate MthK and the Kv1.2/2.1 structures as templates for open BK and Kv-channels, respectively. PMID:26831782

  16. Effective pore size and radius of capture for K+ ions in K-channels

    PubMed Central

    Moldenhauer, Hans; Díaz-Franulic, Ignacio; González-Nilo, Fernando; Naranjo, David

    2016-01-01

    Reconciling protein functional data with crystal structure is arduous because rare conformations or crystallization artifacts occur. Here we present a tool to validate the dimensions of open pore structures of potassium-selective ion channels. We used freely available algorithms to calculate the molecular contour of the pore to determine the effective internal pore radius (rE) in several K-channel crystal structures. rE was operationally defined as the radius of the biggest sphere able to enter the pore from the cytosolic side. We obtained consistent rE estimates for MthK and Kv1.2/2.1 structures, with rE = 5.3–5.9 Å and rE = 4.5–5.2 Å, respectively. We compared these structural estimates with functional assessments of the internal mouth radii of capture (rC) for two electrophysiological counterparts, the large conductance calcium activated K-channel (rC = 2.2 Å) and the Shaker Kv-channel (rC = 0.8 Å), for MthK and Kv1.2/2.1 structures, respectively. Calculating the difference between rE and rC, produced consistent size radii of 3.1–3.7 Å and 3.6–4.4 Å for hydrated K+ ions. These hydrated K+ estimates harmonize with others obtained with diverse experimental and theoretical methods. Thus, these findings validate MthK and the Kv1.2/2.1 structures as templates for open BK and Kv-channels, respectively. PMID:26831782

  17. Experimental determination of size distributions: analyzing proper sample sizes

    NASA Astrophysics Data System (ADS)

    Buffo, A.; Alopaeus, V.

    2016-04-01

    The measurement of various particle size distributions is a crucial aspect for many applications in the process industry. Size distribution is often related to the final product quality, as in crystallization or polymerization. In other cases it is related to the correct evaluation of heat and mass transfer, as well as reaction rates, depending on the interfacial area between the different phases or to the assessment of yield stresses of polycrystalline metals/alloys samples. The experimental determination of such distributions often involves laborious sampling procedures and the statistical significance of the outcome is rarely investigated. In this work, we propose a novel rigorous tool, based on inferential statistics, to determine the number of samples needed to obtain reliable measurements of size distribution, according to specific requirements defined a priori. Such methodology can be adopted regardless of the measurement technique used.

  18. 1.9 μm superficially porous packing material with radially oriented pores and tailored pore size for ultra-fast separation of small molecules and biomolecules.

    PubMed

    Min, Yi; Jiang, Bo; Wu, Ci; Xia, Simin; Zhang, Xiaodan; Liang, Zhen; Zhang, Lihua; Zhang, Yukui

    2014-08-22

    In this work, 1.9 μm reversed-phase packing materials with superficially porous structure were prepared to achieve the rapid and high efficient separation of peptides and proteins. The silica particles were synthesized via three steps, nonporous silica particle preparation by a modified seeded growth method, mesoporous shell formation by a one pot templated dissolution and redeposition strategy, and pore size expansion via acid-refluxing. By such a method, 1.9 μm superficially porous materials with 0.18 μm shell thickness and tailored pore diameter (10 nm, 15 nm) were obtained. After pore enlargement, the formerly dense arrays of mesoporous structure changed, the radially oriented pores dominated the superficially porous structure. The chromatographic performance of such particles was investigated after C18 derivatization. For packing materials with 1.9 μm diameter and 10 nm pore size, the column efficiency could reach 211,300 plates per m for naphthalene. To achieve the high resolution separation of peptides and proteins, particles with pore diameter of 15 nm were tailored, by which the baseline separation of 5 peptides and 5 intact proteins could be respectively achieved within 1 min, demonstrating the superiority in the high efficiency and high throughput analysis of biomolecules. Furthermore, BSA digests were well separated with peak capacity of 120 in 30 min on a 15 cm-long column. Finally, we compared our columns with a 1.7 μm Kinetex C18 column under the same conditions, our particles with 10nm pore size demonstrated similar performance for separation of the large intact proteins. Moreover, the particles with 15 nm pore size showed more symmetrical peaks for the separation of large proteins (BSA, OVA and IgG) and provided rapid separation of protein extracts from Escherichia coli in 5 min. All these results indicated that the synthesized 1.9 μm superficially porous silica packing materials would be promising in the ultra-fast and high

  19. Asteroid Size-Frequency Distribution

    NASA Technical Reports Server (NTRS)

    Tedesco, Edward F.

    2001-01-01

    A total of six deep exposures (using AOT CAM01 with a 6 inch PFOV) through the ISOCAM LW10 filter (IRAS Band 1, i.e. 12 micron) were obtained on an approximately 15 arcminute square field centered on the ecliptic plane. Point sources were extracted using the technique described. Two known asteroids appear in these frames and 20 sources moving with velocities appropriate for main belt asteroids are present. Most of the asteroids detected have flux densities less than 1 mJy, i,e., between 150 and 350 times fainter than any of the asteroids observed by IRAS. These data provide the first direct measurement of the 12 pm sky-plane density for asteroids on the ecliptic equator. The median zodiacal foreground, as measured by ISOCAM during this survey, is found to be 22.1 +/- 1.5 mJy per pixel, i.e., 26.2 +/- 1.7 MJy/sr. The results presented here imply that the actual number of kilometer-sized asteroids is significantly greater than previously believed and in reasonable agreement with the Statistical Asteroid Model.

  20. Characterization and structural investigation of fractal porous-silica over an extremely wide scale range of pore size.

    PubMed

    Ono, Yusuke; Mayama, Hiroyuki; Furó, István; Sagidullin, Alexander I; Matsushima, Keiichiro; Ura, Haruo; Uchiyama, Tomoyuki; Tsujii, Kaoru

    2009-08-01

    We have succeeded in creating Menger sponge-like fractal body, i.e., porous-silica samples with Menger sponge-like fractal geometries, by a novel template method utilizing template particles of alkylketene dimer (AKD) and a sol-gel synthesis of tetramethyl orthosilicate (TMOS). We report here the first experimental results on characterization and structural investigations of the fractal porous-silica samples prepared with various conditions such as calcination temperature and packing condition of the template particles. In order to characterize the fractal porous-silica samples, pore volume distribution, porosity and specific surface area were measured over an extremely wide scale from 1 nm to 100 microm by means of mercury porosimetry, (1)H NMR cryoporometry, nitrogen gas adsorption experiments together with direct evaluations of cross-sectional fractal dimension D(cs), and size limits of D(cs). We have found that the pore volume distribution and specific surface area of the fractal porous-silica samples can be discussed in terms of different fractal porous structures at different scale regions. PMID:19406424

  1. Anodic aluminum oxide with fine pore size control for selective and effective particulate matter filtering

    NASA Astrophysics Data System (ADS)

    Zhang, Su; Wang, Yang; Tan, Yingling; Zhu, Jianfeng; Liu, Kai; Zhu, Jia

    2016-07-01

    Air pollution is widely considered as one of the most pressing environmental health issues. Particularly, atmospheric particulate matters (PM), a complex mixture of solid or liquid matter suspended in the atmosphere, are a harmful form of air pollution due to its ability to penetrate deep into the lungs and blood streams, causing permanent damages such as DNA mutations and premature death. Therefore, porous materials which can effectively filter out particulate matters are highly desirable. Here, for the first time, we demonstrate that anodic aluminum oxide with fine pore size control fabricated through a scalable process can serve as effective and selective filtering materials for different types of particulate matters (such as PM2.5, PM10). Combining selective and dramatic filtering effect, fine pore size control and a scalable process, this type of anodic aluminum oxide templates can potentially serve as a novel selective filter for different kinds of particulate matters, and a promising and complementary solution to tackle this serious environmental issue.

  2. Particle size distribution instrument. Topical report 13

    SciTech Connect

    Okhuysen, W.; Gassaway, J.D.

    1995-04-01

    The development of an instrument to measure the concentration of particles in gas is described in this report. An in situ instrument was designed and constructed which sizes individual particles and counts the number of occurrences for several size classes. Although this instrument was designed to detect the size distribution of slag and seed particles generated at an experimental coal-fired magnetohydrodynamic power facility, it can be used as a nonintrusive diagnostic tool for other hostile industrial processes involving the formation and growth of particulates. Two of the techniques developed are extensions of the widely used crossed beam velocimeter, providing simultaneous measurement of the size distribution and velocity of articles.

  3. Domain Size Distribution in Segregating Binary Superfluids

    NASA Astrophysics Data System (ADS)

    Takeuchi, Hiromitsu

    2016-05-01

    Domain size distribution in phase separating binary Bose-Einstein condensates is studied theoretically by numerically solving the Gross-Pitaevskii equations at zero temperature. We show that the size distribution in the domain patterns arising from the dynamic instability obeys a power law in a scaling regime according to the dynamic scaling analysis based on the percolation theory. The scaling behavior is kept during the relaxation dynamics until the characteristic domain size becomes comparable to the linear size of the system, consistent with the dynamic scaling hypothesis of the phase-ordering kinetics. Our numerical experiments indicate the existence of a different scaling regime in the size distribution function, which can be caused by the so-called coreless vortices.

  4. Micron-pore-sized metallic filter tube membranes for filtration of particulates and water purification.

    PubMed

    Phelps, T J; Palumbo, A V; Bischoff, B L; Miller, C J; Fagan, L A; McNeilly, M S; Judkins, R R

    2008-07-01

    Robust filtering techniques capable of efficiently removing particulates and biological agents from water or air suffer from plugging, poor rejuvenation, low permeance, and high backpressure. Operational characteristics of pressure-driven separations are in part controlled by the membrane pore size, charge of particulates, transmembrane pressure and the requirement for sufficient water flux to overcome fouling. With long term use filters decline in permeance due to filter-cake plugging of pores, fouling, or filter deterioration. Though metallic filter tube development at ORNL has focused almost exclusively on gas separations, a small study examined the applicability of these membranes for tangential filtering of aqueous suspensions of bacterial-sized particles. A mixture of fluorescent polystyrene microspheres ranging in size from 0.5 to 6 microm in diameter simulated microorganisms in filtration studies. Compared to a commercial filter, the ORNL 0.6 microm filter averaged approximately 10-fold greater filtration efficiency of the small particles, several-fold greater permeance after considerable use and it returned to approximately 85% of the initial flow upon backflushing versus 30% for the commercial filter. After filtering several liters of the particle-containing suspension, the ORNL composite filter still exhibited greater than 50% of its initial permeance while the commercial filter had decreased to less than 20%. When considering a greater filtration efficiency, greater permeance per unit mass, greater percentage of rejuvenation upon backflushing (up to 3-fold), and likely greater performance with extended use, the ORNL 0.6 microm filters can potentially outperform the commercial filter by factors of 100-1,000 fold. PMID:17884208

  5. Micron-pore-sized metallic filter tube membranes for filtration of particulates and water purification

    SciTech Connect

    Phelps, Tommy Joe; Palumbo, Anthony Vito; Fagan, Lisa Anne; Bischoff, Brian L; Miller, Curtis Jack; Drake, Meghan M; Judkins, Roddie Reagan

    2008-01-01

    Robust filtering techniques capable of efficiently removing particulates and biological agents from water or air suffer from plugging, poor rejuvenation, low permeance, and high backpressure. Operational characteristics of pressure-driven separations are in part controlled by the membrane pore size, charge of particulates, transmembrane pressure and the requirement for sufficient water flux to overcome fouling. With long term use filters decline in permeance due to filter-cake plugging of pores, fouling, or filter deterioration. Though metallic filter tube development at ORNL has focused almost exclusively on gas separations, a small study examined the applicability of these membranes for tangential filtering of aqueous suspensions of bacterial-sized particles. A mixture of fluorescent polystyrene microspheres ranging in size from 0.5 to 6 {micro}m in diameter simulated microorganisms in filtration studies. Compared to a commercial filter, the ORNL 0.6 {micro}m filter averaged approximately 10-fold greater filtration efficiency of the small particles, several-fold greater permeance after considerable use and it returned to approximately 85% of the initial flow upon backflushing versus 30% for the commercial filter. After filtering several liters of the particle-containing suspension, the ORNL composite filter still exhibited greater than 50% of its initial permeance while the commercial filter had decreased to less than 20%. When considering a greater filtration efficiency, greater permeance per unit mass, greater percentage of rejuvenation upon backflushing (up to 3-fold), and likely greater performance with extended use, the ORNL 0.6 {micro}m filters can potentially outperform the commercial filter by factors of 100-1000 fold.

  6. Analytic modeling of aerosol size distributions

    NASA Technical Reports Server (NTRS)

    Deepack, A.; Box, G. P.

    1979-01-01

    Mathematical functions commonly used for representing aerosol size distributions are studied parametrically. Methods for obtaining best fit estimates of the parameters are described. A catalog of graphical plots depicting the parametric behavior of the functions is presented along with procedures for obtaining analytical representations of size distribution data by visual matching of the data with one of the plots. Examples of fitting the same data with equal accuracy by more than one analytic model are also given.

  7. Adjustable virtual pore-size filter for automated sample preparation using acoustic radiation force

    SciTech Connect

    Jung, B; Fisher, K; Ness, K; Rose, K; Mariella, R

    2008-05-22

    We present a rapid and robust size-based separation method for high throughput microfluidic devices using acoustic radiation force. We developed a finite element modeling tool to predict the two-dimensional acoustic radiation force field perpendicular to the flow direction in microfluidic devices. Here we compare the results from this model with experimental parametric studies including variations of the PZT driving frequencies and voltages as well as various particle sizes and compressidensities. These experimental parametric studies also provide insight into the development of an adjustable 'virtual' pore-size filter as well as optimal operating conditions for various microparticle sizes. We demonstrated the separation of Saccharomyces cerevisiae and MS2 bacteriophage using acoustic focusing. The acoustic radiation force did not affect the MS2 viruses, and their concentration profile remained unchanged. With optimized design of our microfluidic flow system we were able to achieve yields of > 90% for the MS2 with > 80% of the S. cerevisiae being removed in this continuous-flow sample preparation device.

  8. Evaluation of borate bioactive glass scaffolds with different pore sizes in a rat subcutaneous implantation model.

    PubMed

    Deliormanli, Aylin M; Liu, Xin; Rahaman, Mohamed N

    2014-01-01

    Borate bioactive glass has been shown to convert faster and more completely to hydroxyapatite and enhance new bone formation in vivo when compared to silicate bioactive glass (such as 45S5 and 13-93 bioactive glass). In this work, the effects of the borate glass microstructure on its conversion to hydroxyapatite (HA) in vitro and its ability to support tissue ingrowth in a rat subcutaneous implantation model were investigated. Bioactive borate glass scaffolds, designated 13-93B3, with a grid-like microstructure and pore widths of 300, 600, and 900 µm were prepared by a robocasting technique. The scaffolds were implanted subcutaneously for 4 weeks in Sprague Dawley rats. Silicate 13-93 glass scaffolds with the same microstructure were used as the control. The conversion of the scaffolds to HA was studied as a function of immersion time in a simulated body fluid. Histology and scanning electron microscopy were used to evaluate conversion of the bioactive glass implants to hydroxyapatite, as well as tissue ingrowth and blood vessel formation in the implants. The pore size of the scaffolds was found to have little effect on tissue infiltration and angiogenesis after the 4-week implantation.

  9. Quantitative multi-scale analysis of mineral distributions and fractal pore structures for a heterogeneous Junger Basin shale

    NASA Astrophysics Data System (ADS)

    Wang, Y. D.; Liu, K. Y.; Yang, Y. S.; Ren, Y. Q.; Hu, T.; Deng, B.; Xiao, T. Q.

    2016-04-01

    Three dimensional (3D) characterization of shales has recently attracted wide attentions in relation to the growing importance of shale oil and gas. Obtaining a complete 3D compositional distribution of shale has proven to be challenging due to its multi-scale characteristics. A combined multi-energy X-ray micro-CT technique and data-constrained modelling (DCM) approach has been used to quantitatively investigate the multi-scale mineral and porosity distributions of a heterogeneous shale from the Junger Basin, northwestern China by sub-sampling. The 3D sub-resolution structures of minerals and pores in the samples are quantitatively obtained as the partial volume fraction distributions, with colours representing compositions. The shale sub-samples from two areas have different physical structures for minerals and pores, with the dominant minerals being feldspar and dolomite, respectively. Significant heterogeneities have been observed in the analysis. The sub-voxel sized pores form large interconnected clusters with fractal structures. The fractal dimensions of the largest clusters for both sub-samples were quantitatively calculated and found to be 2.34 and 2.86, respectively. The results are relevant in quantitative modelling of gas transport in shale reservoirs.

  10. Population size, distribution and growth in Iran.

    PubMed

    Kamiar, M

    1985-01-01

    The author examines population size, distribution, and growth in Iran using data for 1966, 1976 census data, and some historical data for the nineteenth century. "This paper discusses changes in the size of population through time, population distribution, and regional patterns of population growth of the 23 provinces. It has been argued in this paper that because of a large family size norm as a religious duty to increase the numbers of the Islamic faith, early age at marriage, especially among females, common practice of polygamy, and the war with Iraq, population will grow even faster. It is concluded that population policy must be integrated into the national development plans."

  11. Particle Size Distributions in Atmospheric Clouds

    NASA Technical Reports Server (NTRS)

    Paoli, Roberto; Shariff, Karim

    2003-01-01

    In this note, we derive a transport equation for a spatially integrated distribution function of particles size that is suitable for sparse particle systems, such as in atmospheric clouds. This is done by integrating a Boltzmann equation for a (local) distribution function over an arbitrary but finite volume. A methodology for evolving the moments of the integrated distribution is presented. These moments can be either tracked for a finite number of discrete populations ('clusters') or treated as continuum variables.

  12. Exponential Size Distribution of von Willebrand Factor

    PubMed Central

    Lippok, Svenja; Obser, Tobias; Müller, Jochen P.; Stierle, Valentin K.; Benoit, Martin; Budde, Ulrich; Schneppenheim, Reinhard; Rädler, Joachim O.

    2013-01-01

    Von Willebrand Factor (VWF) is a multimeric protein crucial for hemostasis. Under shear flow, it acts as a mechanosensor responding with a size-dependent globule-stretch transition to increasing shear rates. Here, we quantify for the first time, to our knowledge, the size distribution of recombinant VWF and VWF-eGFP using a multilateral approach that involves quantitative gel analysis, fluorescence correlation spectroscopy, and total internal reflection fluorescence microscopy. We find an exponentially decaying size distribution of multimers for recombinant VWF as well as for VWF derived from blood samples in accordance with the notion of a step-growth polymerization process during VWF biosynthesis. The distribution is solely described by the extent of polymerization, which was found to be reduced in the case of the pathologically relevant mutant VWF-IIC. The VWF-specific protease ADAMTS13 systematically shifts the VWF size distribution toward smaller sizes. This dynamic evolution is monitored using fluorescence correlation spectroscopy and compared to a computer simulation of a random cleavage process relating ADAMTS13 concentration to the degree of VWF breakdown. Quantitative assessment of VWF size distribution in terms of an exponential might prove to be useful both as a valuable biophysical characterization and as a possible disease indicator for clinical applications. PMID:24010664

  13. Size distributions of chemically synthesized Ag nanocrystals

    NASA Astrophysics Data System (ADS)

    Thøgersen, Annett; Bonsak, Jack; Fosli, Carl Huseby; Muntingh, Georg

    2011-08-01

    Silver nanocrystals made by a chemical reduction of silver salts (AgNO3) by sodium borohydride (NaBH4) were studied using transmission electron microscopy and light scattering simulations. For various AgNO3/NaBH4 molar ratios, the size distributions of the nanocrystals were found to be approximately log-normal. In addition, a linear relation was found between the mean nanocrystal size and the molar ratio. In order to relate the size distribution of Ag nanocrystals of the various molar ratios to the scattering properties of Ag nanocrystals in solar cell devices, light scattering simulations of Ag nanocrystals in Si, SiO2, SiN, and Al2O3 matrices were carried out using MiePlot. These light scattering spectra for the individual nanocrystal sizes were combined into light scattering spectra for the fitted size distributions. The evolution of these scattering spectra with respect to an increasing mean nanocrystal size was then studied. From these findings, it is possible to find the molar ratio for which the corresponding nanocrystal size distribution has maximum scattering at a particular wavelength in the desired matrix.

  14. Modeling the controllable pH-responsive swelling and pore size of networked alginate based biomaterials.

    PubMed

    Chan, Ariel W; Neufeld, Ronald J

    2009-10-01

    Semisynthetic network alginate polymer (SNAP), synthesized by acetalization of linear alginate with di-aldehyde, is a pH-responsive tetrafunctionally linked 3D gel network, and has potential application in oral delivery of protein therapeutics and active biologicals, and as tissue bioscaffold for regenerative medicine. A constitutive polyelectrolyte gel model based on non-Gaussian polymer elasticity, Flory-Huggins liquid lattice theory, and non-ideal Donnan membrane equilibria was derived, to describe SNAP gel swelling in dilute and ionic solutions containing uni-univalent, uni-bivalent, bi-univalent or bi-bi-valent electrolyte solutions. Flory-Huggins interaction parameters as a function of ionic strength and characteristic ratio of alginates of various molecular weights were determined experimentally to numerically predict SNAP hydrogel swelling. SNAP hydrogel swells pronouncedly to 1000 times in dilute solution, compared to its compact polymer volume, while behaving as a neutral polymer with limited swelling in high ionic strength or low pH solutions. The derived model accurately describes the pH-responsive swelling of SNAP hydrogel in acid and alkaline solutions of wide range of ionic strength. The pore sizes of the synthesized SNAP hydrogels of various crosslink densities were estimated from the derived model to be in the range of 30-450 nm which were comparable to that measured by thermoporometry, and diffusion of bovine serum albumin. The derived equilibrium swelling model can characterize hydrogel structure such as molecular weight between crosslinks and crosslinking density, or can be used as predictive model for swelling, pore size and mechanical properties if gel structural information is known, and can potentially be applied to other point-link network polyelectrolytes such as hyaluronic acid gel.

  15. Can flow velocity distribution at a pore-scale be quantified by a celerity-saturation curve?

    NASA Astrophysics Data System (ADS)

    Shao, Wei; Su, Ye; Bogaard, Thom; Bakker, Mark; Savenije, Huub

    2015-04-01

    -Corey constitutive relationships were used to describe the non-linear hydraulic conductivity of the soils. The analysis manifests that under full saturated conditions, a small fraction of the pores (with larger size and lower tortuosity) can conduct a large amount of volumetric water flow, while, under near-saturated condition, the celerity can be significantly larger than the Darcian velocity or average pore water velocity. If the soil saturation is below a certain threshold, pore water velocity and its variability are rather small. Solute transport in a variable saturated soil is controlled by both process of diffusion (driven by concentration gradient) and convection (related with distribution of flow velocities). Therefore, a variable pore water velocity induces a bimodal behaviour of the mass transport that is often observed in tracer experiments. We will present the results of our analysis and focus on pore water velocities derived from celerity - effective saturation plots and discuss whether this could be considered as a universal phenomenon in the subsurface flow system.

  16. Clouds of venus: particle size distribution measurements.

    PubMed

    Knollenberg, R G; Hunten, D M

    1979-02-23

    Data from the Pioneer Venus cloud particle size spectrometer experiment has revealed the Venus cloud system to be a complicated mixture of particles of various chemical composition distinguishable by their multimodal size distributions. The appearance, disappearance, growth, and decay of certain size modes has aided the preliminary identification of both sulfuric acid and free sulfur cloud regions. The discovery of large particles > 30 micrometers, significant particle mass loading, and size spectral features suggest that precipitation is likely produced; a peculiar aerosol structure beneath the lowest cloud layer could be residue from a recent shower.

  17. Atomic layer deposition of SIO2 on porous alumina membranes: controlling the pore size and transport properties

    NASA Astrophysics Data System (ADS)

    Velleman, Leonora; Traini, Gerry; Evans, Peter J.; Atanacio, Armand; Shapter, Joe G.; Losic, Dusan

    2008-12-01

    Atomic layer deposition (ALD) of SiO2 onto nanoporous alumina (PA) membranes was investigated with the aim of adjusting the pore size and transport properties. PA membranes from commercial sources with a range of pore diameters (20 nm, 100 nm and 200 nm) were used and modified by atomic layer deposition using tris(tert-butoxy)silanol and water as the precursor couple. By adjusting the number of deposition cycles, the thickness of the conformal silica coating was controlled, reducing the effective pore diameter, and subsequently changing the transport properties of the PA membrane. Silica coated PA membranes with desired pore diameters from <5 nm to 100 nm were fabricated. In addition to the pore size, the transport properties and selectivity of fabricated silica coated PA membranes were controlled by chemical functionalisation using a silane with hydrophobic properties. Structural and chemical properties of modified membranes were studied by dynamic secondary ion mass spectrometry (DSIMS) and scanning electron microscopy (SEM). Spectrophotometric methods were used to evaluate the transport properties and selectivity of silica coated membranes by permeation studies of hydrophobic and hydrophilic organic molecules. The resultant silica/PA membranes with specific surface chemistry and controlled pore size are applicable for molecular separation, cell culture, bioreactors, biosensing and drug delivery.

  18. Recommendation for Using Smaller (0.1 micro sign) Pore-Size Media for Filtration in Salt Waste Processing Project

    SciTech Connect

    Poirier, M.R.

    2003-05-02

    Based on experimental studies with simulated and actual wastes, we recommend adopting the use of 0.1-micron pore-size, sintered stainless-steel filter elements within the design of the Salt Waste Processing Facility. Furthermore, adopting the smaller pore size elements for the Actinide Removal Process would result in a significant risk to the start-up schedule due to delays for buying, installing, and testing new equipment. The existing 0.5-micron pore-size filters will provide nearly equivalent service with no additional capital investment. Unless the planned filter test at Building 512-S fails to meet specifications, the project should proceed with the existing equipment, including spares. When the existing equipment reaches the end of the service life, management can consider replacement with the smaller pore-size elements. The laboratory studies indicate that use of the smaller pore size equipment will result in greater protection against particulate fines passing to downstream facilities while giving equivalent or superior processing rates than provided by the 0.5-micron elements.

  19. Temperature and pore pressure distribution in a concrete slab during the microwave decontamination process

    SciTech Connect

    Li, W.; Ebadian, M.A.; White, T.L.; Grubb, R.G.; Foster, D. Jr.

    1994-10-01

    As an application of microwave engineering, the new technology of concrete decontamination and decommissioning using microwave energy has been recently developed. The temperature and pore pressure within the concrete are studied theoretically in this paper. The heat and mass transfer within the porous concrete, coupled with temperature dependent dielectric property are investigated. The effects of microwave frequency (f), microwave power intensity (Q{sub 0,ave}), concrete porosity ({phi}) on the temperature and pore pressure distributions and their variations are fully discussed. The effects of the variation of complex dielectric permittivity ({epsilon}) and presentation of different steel reinforcements are also illustrated.

  20. A macromolecular crowding study of RNA folding and activity: polymer pore size matters! (Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Börner, Richard; Fiorini, Erica; Paudel, Bishnu; Rueda, David; Sigel, Roland K. O.

    2016-03-01

    Catalytic RNAs, like the group IIB intron ribozyme of S. cerevesiae, require a high magnesium(II) concentration to show folding and function in vitro [1]. In contrast, in vivo conditions are characterized by a highly crowded cellular environment and much lower ion concentration. Molecular crowding agents are a widespread tool to mimic cellular crowding [2]. However, particular physical/chemical properties explaining the crowders influence are mostly not understood. In this study, we gain new insights on how polymer properties like viscosity, pore size etc. influence the activity and folding of a large RNA. We combined bulk activity assays and single-molecule Förster Resonance Energy Transfer experiments, screening the PEG volume fraction (%) and molecular weight (MW). Our results revealed that upon the influence of crowding agents, a compaction of the underlying structure depends on the PEG % and the presence of different PEG MW and % unveiled an optimal pore size in terms of catalytic activity. In summary, an increasing density of the crowding environment shifts the RNA towards the most compact state, but the ribozyme is only active if the crowders network matches its size [4]. We interpret the most compact state as necessary, but not sufficient, to keep the ribozyme active. Financial support from the European Research Council (MIRNA N° 259092, to RKOS), the Swiss National Fund (SNF), and the Forschungskredit Grant of the University of Zürich (FK-14-096 and 15-092 to RB) are gratefully acknowledged. [1] Swisher J.F., Su L.J., Brenowitz M., Anderson V.E., Pyle A.M., J. Mol. Bio., 315, 297-310 (2002). [2] Kilburn D., Roh J.H., Guo L., Briber R.M., Woodson S.A., JACS, 132, 8690-6 (2010). [3] Steiner M., Karunatilaka K.S., Sigel R.K.O., Rueda D., Proc. Natl. Acad. Sci. U.S.A.,105, 13853-8 (2008). [4] aBörner R, Fiorini E, Sigel R.K.O., Chimia, 69, 207-212 (2015).; bFiorini E., Paudel B., Börner R., Rueda D., Sigel R.K.O., submitted. [5] König S.L.B., Hadzic M

  1. Effect of membrane polymeric materials on relationship between surface pore size and membrane fouling in membrane bioreactors

    NASA Astrophysics Data System (ADS)

    Miyoshi, Taro; Yuasa, Kotaku; Ishigami, Toru; Rajabzadeh, Saeid; Kamio, Eiji; Ohmukai, Yoshikage; Saeki, Daisuke; Ni, Jinren; Matsuyama, Hideto

    2015-03-01

    We investigated the effect of different membrane polymeric materials on the relationship between membrane pore size and development of membrane fouling in a membrane bioreactor (MBR). Membranes with different pore sizes were prepared using three different polymeric materials, cellulose acetate butyrate (CAB), polyvinyl butyral (PVB), and polyvinylidene fluoride (PVDF), and the development of membrane fouling in each membrane was evaluated by batch filtration tests using a mixed liquor suspension obtained from a laboratory-scale MBR. The results revealed that the optimal membrane pore size to mitigate membrane fouling differed depending on membrane polymeric material. For PVDF membranes, the degree of membrane fouling decreased as membrane pore size increased. In contrast, CAB membranes with smaller pores had less fouling propensity than those with larger ones. Such difference can be attributed to the difference in major membrane foulants in each membrane; in PVDF, they were small colloids or dissolved organics in which proteins are abundant, and in CAB, microbial flocs. The results obtained in this study strongly suggested that optimum operating conditions of MBRs differ depending on the characteristics of the used membrane.

  2. Quantitative Control of Pore Size of Mesoporous Carbon Nanospheres through the Self-Assembly of Diblock Copolymer Micelles in Solution.

    PubMed

    Tian, Hao; Lin, Zhixing; Xu, Fugui; Zheng, Jingxu; Zhuang, Xiaodong; Mai, Yiyong; Feng, Xinliang

    2016-06-01

    This paper reports facile synthesis of nitrogen-doped mesoporous carbon nanospheres (MCNSs) with average diameters of around 300 nm and well-controlled pore sizes ranging from 8 to 38 nm, by employing polystyrene-b-poly(ethylene oxide) (PS-b-PEO) diblocks with different PS block lengths as the soft templates and dopamine as the carbon-rich precursor. For the first time, a linear equation is achieved for the quantitative control of the average pore size of MCNSs by simply adjusting a block length of diblock copolymer. The resultant MCNSs possess high surface areas of up to 450 m(2) g(-1) and nitrogen doping contents of up to ≈3 wt%. As electrode materials of supercapacitors, the MCNSs exhibit excellent electrochemical performance with high specific capacitances of up to 350 F g(-1) at 0.1 A g(-1) , superior rate capability, and cycling stability. Interestingly, the specific capacitance of the MCNSs reduces linearly with increasing pore size, whereas the normalized capacitance by specific surface area remains invariable. This represents a new spectrum of the relationship between electrochemical capacitance and pore size (>5 nm) for porous carbons, which makes a complement to the existing spectra focusing on pore diameters of <5 nm. PMID:27120340

  3. Comparison of drop size distributions from two droplet sizing systems

    NASA Technical Reports Server (NTRS)

    Oldenburg, John R.; Ide, Robert F.

    1990-01-01

    A comparison between the Phase Doppler Particle Analyzer and the combined measurements from Particle Measuring Systems' Forward Scattering Spectrometer Probe and the Optical Array Probe was conducted in an icing wind tunnel using NASA Icing Research Tunnel spray nozzles to produce the supercooled water droplet cloud. Clouds having a range of volume median diameters from 10 to greater than 50 microns were used for the instrument comparisons. A volume median diameter was calculated from combining the droplet distributions of the Optical Array Probe and the Forward Scattering Spectrometer Probe. A comparison of the combined volume median diameters and the Phase Doppler Particle Analyzer volume median diameters showed agreement from 10 microns up to 30 microns. Typical drop size distributions from the Phase Doppler Particle Analyzer, the Forward Scattering Spectrometer Probe, and Optical Array Probe are presented for several median volume diameters. A comparison of the distributions illustrates regions of the distributions where there is good agreement and other regions where there are discrepancies between the Phase Doppler Particle Analyzer and the Particle Measuring Systems' droplet size instruments.

  4. Formation factor and the microscopic distribution of wetting phase in pore space of Berea sandstone

    SciTech Connect

    Schlueter, E.M.; Myer, L.R.; Cook, N.G.W.; Witherspoon, P.A.

    1992-11-01

    Experimental studies have been accomplished aimed at studying the formation factor of a partially saturated rock. The effective formation factors to an electrolyte solution of the pore spaces not occupied by a wetting raid (paraffin wax) have been measured at various saturations, after solidifying the wetting fluid in place. The experimental data is studied in light of the role of the pore structure on the wetting fluid invasion process with the aid of fluid distributions at each saturation regime, a complete rock pore cast, and its associated rock section. The effect of clay minerals on formation factor is studied. The surface conductance contribution of day minerals to overall electrical conductivity is assessed. The effect of partial hydrocarbon saturation on overall rock conductivity and on the Archei saturation exponent is discussed.

  5. Simulations of Pore Formation in Lipid Membranes: Reaction Coordinates, Convergence, Hysteresis, and Finite-Size Effects.

    PubMed

    Awasthi, Neha; Hub, Jochen S

    2016-07-12

    Transmembrane pores play an important role in various biophysical processes such as membrane permeation, membrane fusion, and antimicrobial peptide activity. In principal, all-atom molecular dynamics (MD) simulations provide an accurate model of pore formation in lipid membranes. However, the free energy landscape of transmembrane pore formation remains poorly understood, partly because potential of mean force (PMF) calculations of pore formation strongly depend on the choice of the reaction coordinate. In this study, we used umbrella sampling to compute PMFs for pore formation using three different reaction coordinates, namely, (i) a coordinate that steers the lipids in the lateral direction away from the pore center, (ii) the distance of a single lipid phosphate group from the membrane center, and (iii) the average water density inside a membrane-spanning cylinder. Our results show that while the three reaction coordinates efficiently form pores in membranes, they suffer from strong hysteresis between pore-opening and pore-closing simulations, suggesting that they do not restrain the systems close to the transition state for pore formation. The two reaction coordinates that act via restraining the lipids lead to more pronounced hysteresis compared with the coordinate acting on the water molecules. By comparing PMFs computed from membranes with different numbers of lipids, we observed significant artifacts from the periodic boundary conditions in small simulation systems. Further analysis suggests that the formation and disruption of a continuous hydrogen-bonding network across the membrane corresponds to the transition state for pore formation. Our study provides molecular insights into the critical steps of transmembrane pore formation, and it may guide the development of efficient reaction coordinates for pore formation.

  6. Simulations of Pore Formation in Lipid Membranes: Reaction Coordinates, Convergence, Hysteresis, and Finite-Size Effects.

    PubMed

    Awasthi, Neha; Hub, Jochen S

    2016-07-12

    Transmembrane pores play an important role in various biophysical processes such as membrane permeation, membrane fusion, and antimicrobial peptide activity. In principal, all-atom molecular dynamics (MD) simulations provide an accurate model of pore formation in lipid membranes. However, the free energy landscape of transmembrane pore formation remains poorly understood, partly because potential of mean force (PMF) calculations of pore formation strongly depend on the choice of the reaction coordinate. In this study, we used umbrella sampling to compute PMFs for pore formation using three different reaction coordinates, namely, (i) a coordinate that steers the lipids in the lateral direction away from the pore center, (ii) the distance of a single lipid phosphate group from the membrane center, and (iii) the average water density inside a membrane-spanning cylinder. Our results show that while the three reaction coordinates efficiently form pores in membranes, they suffer from strong hysteresis between pore-opening and pore-closing simulations, suggesting that they do not restrain the systems close to the transition state for pore formation. The two reaction coordinates that act via restraining the lipids lead to more pronounced hysteresis compared with the coordinate acting on the water molecules. By comparing PMFs computed from membranes with different numbers of lipids, we observed significant artifacts from the periodic boundary conditions in small simulation systems. Further analysis suggests that the formation and disruption of a continuous hydrogen-bonding network across the membrane corresponds to the transition state for pore formation. Our study provides molecular insights into the critical steps of transmembrane pore formation, and it may guide the development of efficient reaction coordinates for pore formation. PMID:27254744

  7. Acoustical properties of air-saturated porous material with periodically distributed dead-end pores.

    PubMed

    Leclaire, P; Umnova, O; Dupont, T; Panneton, R

    2015-04-01

    A theoretical and numerical study of the sound propagation in air-saturated porous media with straight main pores bearing lateral cavities (dead-ends) is presented. The lateral cavities are located at "nodes" periodically spaced along each main pore. The effect of periodicity in the distribution of the lateral cavities is studied, and the low frequency limit valid for the closely spaced dead-ends is considered separately. It is shown that the absorption coefficient and transmission loss are influenced by the viscous and thermal losses in the main pores as well as their perforation rate. The presence of long or short dead-ends significantly alters the acoustical properties of the material and can increase significantly the absorption at low frequencies (a few hundred hertz). These depend strongly on the geometry (diameter and length) of the dead-ends, on their number per node, and on the periodicity along the propagation axis. These effects are primarily due to low sound speed in the main pores and to thermal losses in the dead-end pores. The model predictions are compared with experimental results. Possible designs of materials of a few cm thicknesses displaying enhanced low frequency absorption at a few hundred hertz are proposed. PMID:25920830

  8. Acoustical properties of air-saturated porous material with periodically distributed dead-end pores.

    PubMed

    Leclaire, P; Umnova, O; Dupont, T; Panneton, R

    2015-04-01

    A theoretical and numerical study of the sound propagation in air-saturated porous media with straight main pores bearing lateral cavities (dead-ends) is presented. The lateral cavities are located at "nodes" periodically spaced along each main pore. The effect of periodicity in the distribution of the lateral cavities is studied, and the low frequency limit valid for the closely spaced dead-ends is considered separately. It is shown that the absorption coefficient and transmission loss are influenced by the viscous and thermal losses in the main pores as well as their perforation rate. The presence of long or short dead-ends significantly alters the acoustical properties of the material and can increase significantly the absorption at low frequencies (a few hundred hertz). These depend strongly on the geometry (diameter and length) of the dead-ends, on their number per node, and on the periodicity along the propagation axis. These effects are primarily due to low sound speed in the main pores and to thermal losses in the dead-end pores. The model predictions are compared with experimental results. Possible designs of materials of a few cm thicknesses displaying enhanced low frequency absorption at a few hundred hertz are proposed.

  9. The size-distribution of Earth's lakes.

    PubMed

    Cael, B B; Seekell, D A

    2016-01-01

    Globally, there are millions of small lakes, but a small number of large lakes. Most key ecosystem patterns and processes scale with lake size, thus this asymmetry between area and abundance is a fundamental constraint on broad-scale patterns in lake ecology. Nonetheless, descriptions of lake size-distributions are scarce and empirical distributions are rarely evaluated relative to theoretical predictions. Here we develop expectations for Earth's lake area-distribution based on percolation theory and evaluate these expectations with data from a global lake census. Lake surface areas ≥8.5 km(2) are power-law distributed with a tail exponent (τ = 1.97) and fractal dimension (d = 1.38), similar to theoretical expectations (τ = 2.05; d = 4/3). Lakes <8.5 km(2) are not power-law distributed. An independently developed regional lake census exhibits a similar transition and consistency with theoretical predictions. Small lakes deviate from the power-law distribution because smaller lakes are more susceptible to dynamical change and topographic behavior at sub-kilometer scales is not self-similar. Our results provide a robust characterization and theoretical explanation for the lake size-abundance relationship, and form a fundamental basis for understanding and predicting patterns in lake ecology at broad scales. PMID:27388607

  10. Bulk stress distributions in the pore space of sphere-packed beds under Darcy flow conditions.

    PubMed

    Pham, Ngoc H; Voronov, Roman S; Tummala, Naga Rajesh; Papavassiliou, Dimitrios V

    2014-03-01

    In this paper, bulk stress distributions in the pore space of columns packed with spheres are numerically computed with lattice Boltzmann simulations. Three different ideally packed and one randomly packed configuration of the columns are considered under Darcy flow conditions. The stress distributions change when the packing type changes. In the Darcy regime, the normalized stress distribution for a particular packing type is independent of the pressure difference that drives the flow and presents a common pattern. The three parameter (3P) log-normal distribution is found to describe the stress distributions in the randomly packed beds within statistical accuracy. In addition, the 3P log-normal distribution is still valid when highly porous scaffold geometries rather than sphere beds are examined. It is also shown that the 3P log-normal distribution can describe the bulk stress distribution in consolidated reservoir rocks like Berea sandstone.

  11. Bulk stress distributions in the pore space of sphere-packed beds under Darcy flow conditions

    NASA Astrophysics Data System (ADS)

    Pham, Ngoc H.; Voronov, Roman S.; Tummala, Naga Rajesh; Papavassiliou, Dimitrios V.

    2014-03-01

    In this paper, bulk stress distributions in the pore space of columns packed with spheres are numerically computed with lattice Boltzmann simulations. Three different ideally packed and one randomly packed configuration of the columns are considered under Darcy flow conditions. The stress distributions change when the packing type changes. In the Darcy regime, the normalized stress distribution for a particular packing type is independent of the pressure difference that drives the flow and presents a common pattern. The three parameter (3P) log-normal distribution is found to describe the stress distributions in the randomly packed beds within statistical accuracy. In addition, the 3P log-normal distribution is still valid when highly porous scaffold geometries rather than sphere beds are examined. It is also shown that the 3P log-normal distribution can describe the bulk stress distribution in consolidated reservoir rocks like Berea sandstone.

  12. Acoustical concept for measuring particle size distributions

    SciTech Connect

    Mahler, D.S.; Kaufman, M.

    1981-02-01

    A new concept is investigated for measuring particle size and distribution for air pollution control applications. This study illustrates that the proposed device--the Acoustic Particulate Monitor (APM)--can measure total mass loading, mean particle diameter, and width of particle size distributions on an in-situ basis. The concept for such an instrument is based upon experimental and theoretical observations that the presence of dust in air causes a reduction in the speed of sound as a function of the transmitted frequency. These percentage reductions in the speed of sound are small and the research results illustrate how the accompanying shift in the acoustical phase is a highly sensitive method for detecting such effects. The magnitudes of the phase shift are related to mass loading. The frequency associated with the maximum phase shift is defined as the acoustic frequency, fA. Experimentally determining fA provides a measure of the mean particle size of the distribution. The detailed shape of the phase shift as a function of frequency is a measure of the spread in the size distribution of the entrained particulate. Experiments were performed using several configurations. Results were verified using direct mass measurements and microphotographs.

  13. PARTICLE SIZE DISTRIBUTIONS FOR AN OFFICE AEROSOL

    EPA Science Inventory

    The article discusses an evaluation of the effect of percent outdoor air supplied and occupation level on the particle size distributions and mass concentrations for a typical office building. (NOTE: As attention has become focused on indoor air pollution control, it has become i...

  14. Pore size is a critical parameter for obtaining sustained protein release from electrochemically synthesized mesoporous silicon microparticles

    PubMed Central

    Pastor, Ester L.; Reguera-Nuñez, Elaine; Matveeva, Eugenia

    2015-01-01

    Mesoporous silicon has become a material of high interest for drug delivery due to its outstanding internal surface area and inherent biodegradability. We have previously reported the preparation of mesoporous silicon microparticles (MS-MPs) synthesized by an advantageous electrochemical method, and showed that due to their inner structure they can adsorb proteins in amounts exceeding the mass of the carrier itself. Protein release from these MS-MPs showed low burst effect and fast delivery kinetics with complete release in a few hours. In this work, we explored if tailoring the size of the inner pores of the particles would retard the protein release process. To address this hypothesis, three new MS-MPs prototypes were prepared by electrochemical synthesis, and the resulting carriers were characterized for morphology, particle size, and pore structure. All MS-MP prototypes had 90 µm mean particle size, but depending on the current density applied for synthesis, pore size changed between 5 and 13 nm. The model protein α-chymotrypsinogen was loaded into MS-MPs by adsorption and solvent evaporation. In the subsequent release experiments, no burst release of the protein was detected for any prototype. However, prototypes with larger pores (>10 nm) reached 100% release in 24–48 h, whereas prototypes with small mesopores (<6 nm) still retained most of their cargo after 96 h. MS-MPs with ∼6 nm pores were loaded with the osteogenic factor BMP7, and sustained release of this protein for up to two weeks was achieved. In conclusion, our results confirm that tailoring pore size can modify protein release from MS-MPs, and that prototypes with potential therapeutic utility for regional delivery of osteogenic factors can be prepared by convenient techniques. PMID:26557423

  15. Raindrop Size Distribution Measurements in Tropical Cyclones

    NASA Technical Reports Server (NTRS)

    Tokay, Ali; Bashor, Paul G.; Habib, Emad; Kasparis, Takis

    2008-01-01

    Characteristics of the raindrop size distribution in seven tropical cyclones have been studied through impact-type disdrometer measurements at three different sites during the 2004-06 Atlantic hurricane seasons. One of the cyclones has been observed at two different sites. High concentrations of small and/or midsize drops were observed in the presence or absence of large drops. Even in the presence of large drops, the maximum drop diameter rarely exceeded 4 mm. These characteristics of raindrop size distribution were observed in all stages of tropical cyclones, unless the storm was in the extratropical stage where the tropical cyclone and a midlatitude frontal system had merged. The presence of relatively high concentrations of large drops in extratropical cyclones resembled the size distribution in continental thunderstorms. The integral rain parameters of drop concentration, liquid water content, and rain rate at fixed reflectivity were therefore lower in extratropical cyclones than in tropical cyclones. In tropical cyclones, at a disdrometercalculated reflectivity of 40 dBZ, the number concentration was 700 plus or minus 100 drops m(sup -3), while the liquid water content and rain rate were 0.90 plus or minus 0.05 g m(sup -3) and 18.5 plus or minus 0.5 mm h(sup -1), respectively. The mean mass diameter, on the other hand, was 1.67 plus or minus 0.3 mm. The comparison of raindrop size distributions between Atlantic tropical cyclones and storms that occurred in the central tropical Pacific island of Roi-Namur revealed that the number density is slightly shifted toward smaller drops, resulting in higher-integral rain parameters and lower mean mass and maximum drop diameters at the latter site. Considering parameterization of the raindrop size distribution in tropical cyclones, characteristics of the normalized gamma distribution parameters were examined with respect to reflectivity. The mean mass diameter increased rapidly with reflectivity, while the normalized

  16. Size from Specular Highlights for Analyzing Droplet Size Distributions

    NASA Astrophysics Data System (ADS)

    Jalba, Andrei C.; Westenberg, Michel A.; Grooten, Mart H. M.

    In mechanical engineering, heat-transfer models by dropwise condensation are under development. The condensation process is captured by taking many pictures, which show the formation of droplets, of which the size distribution and area coverage are of interest for model improvement. The current analysis method relies on manual measurements, which is time consuming. In this paper, we propose an approach to automatically extract the positions and radii of the droplets from an image. Our method relies on specular highlights that are visible on the surfaces of the droplets. We show that these highlights can be reliably extracted, and that they provide sufficient information to infer the droplet size. The results obtained by our method compare favorably with those obtained by laborious and careful manual measurements. The processing time per image is reduced by two orders of magnitude.

  17. Bimodal spatial distribution of pores in anodically oxidized aluminum thin films

    NASA Astrophysics Data System (ADS)

    Behnke, J. F.; Sands, T.

    2000-12-01

    Though porous anodic aluminum oxide has been the subject of considerable research since the 1950s, little attention has been devoted to the characterization of the self-organization of the pore structures, and fewer of these studies have focused on anodization of thin films. The degree to which these structures self-organize, however, could play a vital role in future applications of porous anodic aluminum oxide. In this study a model is developed to describe pore ordering in thin anodized aluminum films. The model is based on a radial distribution function approach to describe the interpore spacings. Idealized one-dimensional and two-dimensional (2D) radial distribution functions are combined by linear superposition to approximate experimental radial distribution functions. Using these radial distribution functions, an order parameter is developed and an improved definition of pore spacing is constructed. This method confirms that the oxide initially forms with a highly frustrated porous structure and reorganizes toward greater 2D order as the oxide grows into the film.

  18. New Pulp Biobleaching System Involving Manganese Peroxidase Immobilized in a Silica Support with Controlled Pore Sizes

    PubMed Central

    Sasaki, Toshiya; Kajino, Tsutomu; Li, Bo; Sugiyama, Hidehiko; Takahashi, Haruo

    2001-01-01

    Attempts have been made to use manganese peroxidase (MnP) for chlorine-free pulp biobleaching, but they have not been commercially viable because of the enzyme's low stability. We developed a new pulp biobleaching method involving mesoporous material-immobilized manganese peroxidase from Phanerochaete chrysosporium. MnP immobilized in FSM-16, a folded-sheet mesoporous material whose pore size is nearly the same as the diameter of the enzyme, had the highest thermal stability and tolerance to H2O2. MnP immobilized in FSM-16 retained more than 80% of its initial activity even after 10 days of continuous reaction. We constructed a thermally discontinuous two-stage reactor system, in which the enzyme (39°C) and pulp-bleaching (70°C) reactions were performed separately. When the treatment of pulp with MnP by means of the two-stage reactor system and alkaline extraction was repeated seven times, the brightness of the pulp increased to about 88% within 7 h after completion of the last treatment. PMID:11319102

  19. Facile synthesis of diverse graphene nanomeshes based on simultaneous regulation of pore size and surface structure

    NASA Astrophysics Data System (ADS)

    Zhang, Jia; Song, Huaibing; Zeng, Dawen; Wang, Hao; Qin, Ziyu; Xu, Keng; Pang, Aimin; Xie, Changsheng

    2016-08-01

    Recently, graphene nanomesh (GNM) has attracted great attentions due to its unique porous structure, abundant active sites, finite band gap and possesses potential applications in the fields of electronics, gas sensor/storage, catalysis, etc. Therefore, diverse GNMs with different physical and chemical properties are required urgently to meet different applications. Herein we demonstrate a facile synthetic method based on the famous Fenton reaction to prepare GNM, by using economically fabricated graphene oxide (GO) as a starting material. By precisely controlling the reaction time, simultaneous regulation of pore size from 2.9 to 11.1 nm and surface structure can be realized. Ultimately, diverse GNMs with tunable band gap and work function can be obtained. Specially, the band gap decreases from 4.5–2.3 eV for GO, which is an insulator, to 3.9–1.24 eV for GNM-5 h, which approaches to a semiconductor. The dual nature of electrophilic addition and oxidizability of HO• is responsible for this controllable synthesis. This efficient, low-cost, inherently scalable synthetic method is suitable for provide diverse and optional GNMs, and may be generalized to a universal technique.

  20. Facile synthesis of diverse graphene nanomeshes based on simultaneous regulation of pore size and surface structure

    PubMed Central

    Zhang, Jia; Song, Huaibing; Zeng, Dawen; Wang, Hao; Qin, Ziyu; Xu, Keng; Pang, Aimin; Xie, Changsheng

    2016-01-01

    Recently, graphene nanomesh (GNM) has attracted great attentions due to its unique porous structure, abundant active sites, finite band gap and possesses potential applications in the fields of electronics, gas sensor/storage, catalysis, etc. Therefore, diverse GNMs with different physical and chemical properties are required urgently to meet different applications. Herein we demonstrate a facile synthetic method based on the famous Fenton reaction to prepare GNM, by using economically fabricated graphene oxide (GO) as a starting material. By precisely controlling the reaction time, simultaneous regulation of pore size from 2.9 to 11.1 nm and surface structure can be realized. Ultimately, diverse GNMs with tunable band gap and work function can be obtained. Specially, the band gap decreases from 4.5–2.3 eV for GO, which is an insulator, to 3.9–1.24 eV for GNM-5 h, which approaches to a semiconductor. The dual nature of electrophilic addition and oxidizability of HO• is responsible for this controllable synthesis. This efficient, low-cost, inherently scalable synthetic method is suitable for provide diverse and optional GNMs, and may be generalized to a universal technique. PMID:27561350

  1. Metal and Metalloid Size-Fractionation Strategies in Spatial High-Resolution Sediment Pore Water Profiles.

    PubMed

    Fabricius, Anne-Lena; Duester, Lars; Ecker, Dennis; Ternes, Thomas A

    2016-09-01

    Sediment water interfaces (SWIs) are often characterized by steep biogeochemical gradients determining the fate of inorganic and organic substances. Important transport processes at the SWI are sedimentation and resuspension of particulate matter and fluxes of dissolved materials. A microprofiling and micro sampling system (missy), enabling high resolution measurements of sediment parameters in parallel to a direct sampling of sediment pore waters (SPWs), was combined with two fractionation approaches (ultrafiltration (UF) and cloud point extraction (CPE)) to differentiate between colloidal and dissolved fractions at a millimeter scale. An inductively coupled plasma-quadrupole mass spectrometry method established for volumes of 300 μL enabled the combination of the high resolution fractionation with multi-element analyzes. UF and CPE comparably indicated that manganese is predominantly present in dissolved fractions of SPW profiles. Differences found for cobalt and iron showed that the results obtained by size-dependent UF and micelle-mediated CPE do not necessarily coincide, probably due to different fractionation mechanisms. Both methods were identified as suitable for investigating fraction-related element concentrations in SPW along sediment depth profiles at a millimeter scale. The two approaches are discussed with regard to their advantages, limitations, potential sources of errors, further improvements, and potential future applications. PMID:27504804

  2. Facile synthesis of diverse graphene nanomeshes based on simultaneous regulation of pore size and surface structure.

    PubMed

    Zhang, Jia; Song, Huaibing; Zeng, Dawen; Wang, Hao; Qin, Ziyu; Xu, Keng; Pang, Aimin; Xie, Changsheng

    2016-01-01

    Recently, graphene nanomesh (GNM) has attracted great attentions due to its unique porous structure, abundant active sites, finite band gap and possesses potential applications in the fields of electronics, gas sensor/storage, catalysis, etc. Therefore, diverse GNMs with different physical and chemical properties are required urgently to meet different applications. Herein we demonstrate a facile synthetic method based on the famous Fenton reaction to prepare GNM, by using economically fabricated graphene oxide (GO) as a starting material. By precisely controlling the reaction time, simultaneous regulation of pore size from 2.9 to 11.1 nm and surface structure can be realized. Ultimately, diverse GNMs with tunable band gap and work function can be obtained. Specially, the band gap decreases from 4.5-2.3 eV for GO, which is an insulator, to 3.9-1.24 eV for GNM-5 h, which approaches to a semiconductor. The dual nature of electrophilic addition and oxidizability of HO(•) is responsible for this controllable synthesis. This efficient, low-cost, inherently scalable synthetic method is suitable for provide diverse and optional GNMs, and may be generalized to a universal technique. PMID:27561350

  3. Surfactant-Free Assembly of Mesoporous Carbon Hollow Spheres with Large Tunable Pore Sizes.

    PubMed

    Zhang, Hongwei; Noonan, Owen; Huang, Xiaodan; Yang, Yannan; Xu, Chun; Zhou, Liang; Yu, Chengzhong

    2016-04-26

    Mesoporous carbon hollow spheres (MCHS) have wide applications, including catalysis, absorption, and energy storage/conversion. Herein, we report a one-pot, surfactant-free synthesis of MCHS using three molecules: resorcinol, formaldehyde, and tetrapropyl orthosilicate. The co-condensation process between the in situ generated silica primary particles and the polymer oligomers is regulated, leading to monodispersed MCHS with adjustable pore sizes from micropores to 13.9 nm. The resultant MCHS shows excellent performance for electrochemical double-layer capacitors with high capacitance (310 F g(-1) at 1 A g(-1)), excellent rate capability (157 F g(-1) at 50 A g(-1)), and outstanding cycling stability (98.6% capacity retention after 10 000 cycles at 10 A g(-1)). Our one-pot synthesis strategy is versatile and can be extended to fabricate metal oxide@mesoporous carbon yolk-shell structures in the absence of surfactant, paving the way toward designed synthesis of nanostructured mesoporous carbon composites for various applications. PMID:27050771

  4. Pore size dynamics in interpenetrated metal organic frameworks for selective sensing of aromatic compounds.

    PubMed

    Myers, Matthew; Podolska, Anna; Heath, Charles; Baker, Murray V; Pejcic, Bobby

    2014-03-28

    The two-fold interpenetrated metal-organic framework, [Zn2(bdc)2(dpNDI)]n (bdc=1,4-benzenedicarboxylate, dpNDI=N'N'-di(4-pyridyl)-1,4,5,8-naphthalenediimide) can undergo structural re-arrangement upon adsorption of chemical species changing its pore structure. For a competitive binding process with multiple analytes of different sizes and geometries, the interpenetrated framework will adopt a conformation to maximize the overall binding interactions. In this study, we show for binary mixtures that there is a high selectivity for the larger methylated aromatic compounds, toluene and p-xylene, over the small non-methylated benzene. The dpNDI moiety within [Zn2(bdc)2(dpNDI)]n forms an exciplex with these aromatic compounds. The emission wavelength is dependent on the strength of the host-guest CT interaction allowing these compounds to be distinguished. We show that the sorption selectivity characteristics can have a significant impact on the fluorescence sensor response of [Zn2(bdc)2(dpNDI)]n towards environmentally important hydrocarbons based contaminants (i.e., BTEX, PAH). PMID:24636414

  5. Effect of pore size on bone ingrowth into porous titanium implants fabricated by additive manufacturing: An in vivo experiment.

    PubMed

    Taniguchi, Naoya; Fujibayashi, Shunsuke; Takemoto, Mitsuru; Sasaki, Kiyoyuki; Otsuki, Bungo; Nakamura, Takashi; Matsushita, Tomiharu; Kokubo, Tadashi; Matsuda, Shuichi

    2016-02-01

    Selective laser melting (SLM) is an additive manufacturing technique with the ability to produce metallic scaffolds with accurately controlled pore size, porosity, and interconnectivity for orthopedic applications. However, the optimal pore structure of porous titanium manufactured by SLM remains unclear. In this study, we evaluated the effect of pore size with constant porosity on in vivo bone ingrowth in rabbits into porous titanium implants manufactured by SLM. Three porous titanium implants (with an intended porosity of 65% and pore sizes of 300, 600, and 900μm, designated the P300, P600, and P900 implants, respectively) were manufactured by SLM. A diamond lattice was adapted as the basic structure. Their porous structures were evaluated and verified using microfocus X-ray computed tomography. Their bone-implant fixation ability was evaluated by their implantation as porous-surfaced titanium plates into the cortical bone of the rabbit tibia. Bone ingrowth was evaluated by their implantation as cylindrical porous titanium implants into the cancellous bone of the rabbit femur for 2, 4, and 8weeks. The average pore sizes of the P300, P600, and P900 implants were 309, 632, and 956μm, respectively. The P600 implant demonstrated a significantly higher fixation ability at 2weeks than the other implants. After 4weeks, all models had sufficiently high fixation ability in a detaching test. Bone ingrowth into the P300 implant was lower than into the other implants at 4weeks. Because of its appropriate mechanical strength, high fixation ability, and rapid bone ingrowth, our results indicate that the pore structure of the P600 implant is a suitable porous structure for orthopedic implants manufactured by SLM. PMID:26652423

  6. Effect of pore size on bone ingrowth into porous titanium implants fabricated by additive manufacturing: An in vivo experiment.

    PubMed

    Taniguchi, Naoya; Fujibayashi, Shunsuke; Takemoto, Mitsuru; Sasaki, Kiyoyuki; Otsuki, Bungo; Nakamura, Takashi; Matsushita, Tomiharu; Kokubo, Tadashi; Matsuda, Shuichi

    2016-02-01

    Selective laser melting (SLM) is an additive manufacturing technique with the ability to produce metallic scaffolds with accurately controlled pore size, porosity, and interconnectivity for orthopedic applications. However, the optimal pore structure of porous titanium manufactured by SLM remains unclear. In this study, we evaluated the effect of pore size with constant porosity on in vivo bone ingrowth in rabbits into porous titanium implants manufactured by SLM. Three porous titanium implants (with an intended porosity of 65% and pore sizes of 300, 600, and 900μm, designated the P300, P600, and P900 implants, respectively) were manufactured by SLM. A diamond lattice was adapted as the basic structure. Their porous structures were evaluated and verified using microfocus X-ray computed tomography. Their bone-implant fixation ability was evaluated by their implantation as porous-surfaced titanium plates into the cortical bone of the rabbit tibia. Bone ingrowth was evaluated by their implantation as cylindrical porous titanium implants into the cancellous bone of the rabbit femur for 2, 4, and 8weeks. The average pore sizes of the P300, P600, and P900 implants were 309, 632, and 956μm, respectively. The P600 implant demonstrated a significantly higher fixation ability at 2weeks than the other implants. After 4weeks, all models had sufficiently high fixation ability in a detaching test. Bone ingrowth into the P300 implant was lower than into the other implants at 4weeks. Because of its appropriate mechanical strength, high fixation ability, and rapid bone ingrowth, our results indicate that the pore structure of the P600 implant is a suitable porous structure for orthopedic implants manufactured by SLM.

  7. Pore-scale investigation of micron-size polyacrylamide elastic microspheres (MPEMs) transport and retention in saturated porous media.

    PubMed

    Yao, Chuanjin; Lei, Guanglun; Cathles, Lawrence M; Steenhuis, Tammo S

    2014-05-01

    Knowledge of micrometer-size polyacrylamide elastic microsphere (MPEM) transport and retention mechanisms in porous media is essential for the application of MPEMs as a smart sweep improvement and profile modification agent in improving oil recovery. A transparent micromodel packed with translucent quartz sand was constructed and used to investigate the pore-scale transport, surface deposition-release, and plugging deposition-remigration mechanisms of MPEMs in porous media. The results indicate that the combination of colloidal and hydrodynamic forces controls the deposition and release of MPEMs on pore-surfaces; the reduction of fluid salinity and the increase of Darcy velocity are beneficial to the MPEM release from pore-surfaces; the hydrodynamic forces also influence the remigration of MPEMs in pore-throats. MPEMs can plug pore-throats through the mechanisms of capture-plugging, superposition-plugging, and bridge-plugging, which produces resistance to water flow; the interception with MPEM particulate filters occurring in the interior of porous media can enhance the plugging effect of MPEMs; while the interception with MPEM particulate filters occurring at the surface of low-permeability layer can prevent the low-permeability layer from being damaged by MPEMs. MPEMs can remigrate in pore-throats depending on their elasticity through four steps of capture-plugging, elastic deformation, steady migration, and deformation recovery.

  8. Pore-scale investigation of micron-size polyacrylamide elastic microspheres (MPEMs) transport and retention in saturated porous media.

    PubMed

    Yao, Chuanjin; Lei, Guanglun; Cathles, Lawrence M; Steenhuis, Tammo S

    2014-05-01

    Knowledge of micrometer-size polyacrylamide elastic microsphere (MPEM) transport and retention mechanisms in porous media is essential for the application of MPEMs as a smart sweep improvement and profile modification agent in improving oil recovery. A transparent micromodel packed with translucent quartz sand was constructed and used to investigate the pore-scale transport, surface deposition-release, and plugging deposition-remigration mechanisms of MPEMs in porous media. The results indicate that the combination of colloidal and hydrodynamic forces controls the deposition and release of MPEMs on pore-surfaces; the reduction of fluid salinity and the increase of Darcy velocity are beneficial to the MPEM release from pore-surfaces; the hydrodynamic forces also influence the remigration of MPEMs in pore-throats. MPEMs can plug pore-throats through the mechanisms of capture-plugging, superposition-plugging, and bridge-plugging, which produces resistance to water flow; the interception with MPEM particulate filters occurring in the interior of porous media can enhance the plugging effect of MPEMs; while the interception with MPEM particulate filters occurring at the surface of low-permeability layer can prevent the low-permeability layer from being damaged by MPEMs. MPEMs can remigrate in pore-throats depending on their elasticity through four steps of capture-plugging, elastic deformation, steady migration, and deformation recovery. PMID:24749927

  9. Size distributions of submicrometer aerosols from cooking

    SciTech Connect

    Li, C.S.; Lin, W.H.; Jeng, F.T. )

    1993-01-01

    Although gas stove usage varies from country to country, it is still one of the major indoor combustion sources. In order to assess the health effects of using gas stoves, the physical characteristics of the particle emissions from cooking were conducted in a first-floor apartment in the Taipei area. The particle size distributions from scrambling eggs, frying chicken, and cooking soup were measured in the kitchen by a high resolution particle sizer, which could measure the particles in the size range of 0.01 [mu]m to 1 [mu]m. The concentrations of the submicrometer particles increased significantly from 15,000 cm[sup [minus]3] to 150,000 cm[sup [minus]3] during cooking. Additionally, the ultrafine particles constituted 60%--70% of the total submicron aerosols. The changes in the size distributions and the concentrations of the submicrometer aerosols before, during, and after the aerosol generations were compared. On the average, the median diameters of scrambling eggs, frying chicken, cooking soup, and of the background conditions were 40 nm, 50 nm, 30 nm, and 70 nm, respectively. Regarding the surface area-weighted size distributions, the surface median diameters of the four situations were 180 nm, 300 nm, 150 nm, and 220 nm, respectively. Furthermore, the volume median diameters in the conditions mentioned above were almost similar, namely 300--350 nm. 10 refs., 6 figs., 2 tabs.

  10. The size distribution of 'gold standard' nanoparticles.

    PubMed

    Bienert, Ralf; Emmerling, Franziska; Thünemann, Andreas F

    2009-11-01

    The spherical gold nanoparticle reference materials RM 8011, RM 8012, and RM 8013, with a nominal radius of 5, 15, and 30 nm, respectively, have been available since 2008 from NIST. These materials are recommended as standards for nanoparticle size measurements and for the study of the biological effects of nanoparticles, e.g., in pre-clinical biomedical research. We report on determination of the size distributions of these gold nanoparticles using different small-angle X-ray scattering (SAXS) instruments. Measurements with a classical Kratky type SAXS instrument are compared with a synchrotron SAXS technique. Samples were investigated in situ, positioned in capillaries and in levitated droplets. The number-weighted size distributions were determined applying model scattering functions based on (a) Gaussian, (b) log-normal, and (c) Schulz distributions. The mean radii are 4.36 +/- 0.04 nm (RM 8011), 12.20 +/- 0.03 nm (RM 8012), and 25.74 +/- 0.27 nm (RM 8013). Low polydispersities, defined as relative width of the distributions, were detected with values of 0.067 +/- 0.006 (RM 8011), 0.103 +/- 0.003, (RM 8012), and 0.10 +/- 0.01 (RM 8013). The results are in agreement with integral values determined from classical evaluation procedures, such as the radius of gyration (Guinier) and particle volume (Kratky). No indications of particle aggregation and particle interactions--repulsive or attractive--were found. We recommend SAXS as a standard method for a fast and precise determination of size distributions of nanoparticles.

  11. Pore-scale dynamics of salt transport and distribution in drying porous media

    NASA Astrophysics Data System (ADS)

    Shokri, Nima

    2014-01-01

    Understanding the physics of water evaporation from saline porous media is important in many natural and engineering applications such as durability of building materials and preservation of monuments, water quality, and mineral-fluid interactions. We applied synchrotron x-ray micro-tomography to investigate the pore-scale dynamics of dissolved salt distribution in a three dimensional drying saline porous media using a cylindrical plastic column (15 mm in height and 8 mm in diameter) packed with sand particles saturated with CaI2 solution (5% concentration by mass) with a spatial and temporal resolution of 12 μm and 30 min, respectively. Every time the drying sand column was set to be imaged, two different images were recorded using distinct synchrotron x-rays energies immediately above and below the K-edge value of Iodine. Taking the difference between pixel gray values enabled us to delineate the spatial and temporal distribution of CaI2 concentration at pore scale. Results indicate that during early stages of evaporation, air preferentially invades large pores at the surface while finer pores remain saturated and connected to the wet zone at bottom via capillary-induced liquid flow acting as evaporating spots. Consequently, the salt concentration increases preferentially in finer pores where evaporation occurs. Higher salt concentration was observed close to the evaporating surface indicating a convection-driven process. The obtained salt profiles were used to evaluate the numerical solution of the convection-diffusion equation (CDE). Results show that the macro-scale CDE could capture the overall trend of the measured salt profiles but fail to produce the exact slope of the profiles. Our results shed new insight on the physics of salt transport and its complex dynamics in drying porous media and establish synchrotron x-ray tomography as an effective tool to investigate the dynamics of salt transport in porous media at high spatial and temporal resolution.

  12. Pore-scale dynamics of salt transport and distribution in drying porous media

    SciTech Connect

    Shokri, Nima

    2014-01-15

    Understanding the physics of water evaporation from saline porous media is important in many natural and engineering applications such as durability of building materials and preservation of monuments, water quality, and mineral-fluid interactions. We applied synchrotron x-ray micro-tomography to investigate the pore-scale dynamics of dissolved salt distribution in a three dimensional drying saline porous media using a cylindrical plastic column (15 mm in height and 8 mm in diameter) packed with sand particles saturated with CaI{sub 2} solution (5% concentration by mass) with a spatial and temporal resolution of 12 μm and 30 min, respectively. Every time the drying sand column was set to be imaged, two different images were recorded using distinct synchrotron x-rays energies immediately above and below the K-edge value of Iodine. Taking the difference between pixel gray values enabled us to delineate the spatial and temporal distribution of CaI{sub 2} concentration at pore scale. Results indicate that during early stages of evaporation, air preferentially invades large pores at the surface while finer pores remain saturated and connected to the wet zone at bottom via capillary-induced liquid flow acting as evaporating spots. Consequently, the salt concentration increases preferentially in finer pores where evaporation occurs. Higher salt concentration was observed close to the evaporating surface indicating a convection-driven process. The obtained salt profiles were used to evaluate the numerical solution of the convection-diffusion equation (CDE). Results show that the macro-scale CDE could capture the overall trend of the measured salt profiles but fail to produce the exact slope of the profiles. Our results shed new insight on the physics of salt transport and its complex dynamics in drying porous media and establish synchrotron x-ray tomography as an effective tool to investigate the dynamics of salt transport in porous media at high spatial and temporal

  13. Experimental study on the influence of foam porosity and pore size on the melting of phase change materials

    NASA Astrophysics Data System (ADS)

    Lafdi, K.; Mesalhy, O.; Shaikh, S.

    2007-10-01

    Experimental study was carried out to study the phase change heat transfer within a composite of phase change material (PCM) infiltrated high thermal conductivity foam. An experimental setup was built to measure the temperature profiles and capture the melting evolution of the PCM inside aluminum foams. Aluminum foams were used as the porous material, and low melting temperature paraffin wax was used as the PCM. It was observed from the results that the system parameters of the wax/foam composite had a significant influence on its heat transfer behavior. By using higher porosity aluminum foam, the steady-state temperature was reached faster as compared to the foams with lower porosity. Similarly for the bigger pore size foams the steady state was attained faster as compared to the smaller pore size foams. This was due to the greater effect of convection in both the higher porosity and bigger pore size foams. However, for the lower porosity foams the heater temperature was comparatively lower than the higher porosity foams due to greater heat conduction through the foam material. Therefore, an optimal value should be selected for the foam porosity and pore size such that the effects of both conduction and convection heat transfers can be completely utilized to have a greater and improved thermal performance for the wax/aluminum foam composite.

  14. Tailoring Pore Size of Nitrogen-Doped Hollow Carbon Nanospheres for Confi ning Sulfur in Lithium–Sulfur Batteries

    SciTech Connect

    Zhou, Weidong; Wang, Chong M.; Zhang, Quiglin; Abruna, Hector D.; He, Yang; Wang, Jiangwei; Mao, Scott X.; Xiao, Xingcheng

    2015-08-19

    Three types of nitrogen-doped hollow carbon spheres with different pore sized porous shells are prepared to investigate the performance of sulfur confinement. The reason that why no sulfur is observed in previous research is determined and it is successfully demonstrated that the sulfur/polysulfide will overflow the porous carbon during the lithiation process.

  15. Company size distribution in different countries

    NASA Astrophysics Data System (ADS)

    Ramsden, J. J.; Kiss-Haypál, Gy.

    2000-03-01

    The distribution of companies in a country, ranked in order of size (annual net revenue) s, follows the simplified canonical law s r∼(r+ρ) -1/θ remarkably well, where r is the rank, and θ and ρ are the parameters of the distribution. These parameters have been determined for 20 countries in America, Asia and Europe. Significant differences between countries are found. Neither θ nor ρ appears to correlate well with traditional economic indicators; indeed some countries often thought to be economically and politically, but not necessarily socially, similar show surprising differences, suggesting that wealth and prosperity are influenced by hidden layers hitherto inaccessible through standard economic theory.

  16. Oriented bioactive glass (13-93) scaffolds with controllable pore size by unidirectional freezing of camphene-based suspensions: microstructure and mechanical response

    PubMed Central

    Liu, Xin; Rahaman, Mohamed N.; Fu, Qiang

    2010-01-01

    Scaffolds of 13-93 bioactive glass (composition 6Na2O, 8K2O, 8MgO, 22CaO, 2P2O5, 54SiO2; mol %), containing oriented pores with controllable diameter, were prepared by unidirectional freezing of camphene-based suspensions (10 vol% particles) on a cold substrate (−196°C or 3°C). By varying the annealing time (0–72 h) to coarsen the camphene phase, constructs with the same porosity (86 ± 1%) but with controllable pore diameters (15–160 μm) were obtained after sublimation of the camphene. The pore diameters had a self-similar distribution that could be fitted by a diffusion-controlled coalescence model. Sintering (1 h at 690°C) was accompanied by a decrease in the porosity and pore diameter, the magnitude of which depended on the pore size of the green constructs, giving scaffolds with a porosity of 20–60% and average pore diameter of 6–120 μm. The compressive stress vs. deformation response of the sintered scaffolds in the orientation direction was linear, followed by failure. The compressive strength and elastic modulus in the orientation direction varied from 180 MPa and 25 GPa, respectively, (porosity = 20%) to 16 MPa and 4 GPa, respectively, (porosity = 60%), which were 2–3 times larger than the values in the direction perpendicular to the orientation. The potential use of these 13-93 bioactive glass scaffolds for the repair of large defects in load-bearing bones, such as segmental defects in long bones, is discussed. PMID:20807594

  17. Effect of TiO2 microbead pore size on the performance of DSSCs with a cobalt based electrolyte

    NASA Astrophysics Data System (ADS)

    Chen, Yang; Huang, Fuzhi; Xiang, Wanchun; Chen, Dehong; Cao, Lu; Spiccia, Leone; Caruso, Rachel A.; Cheng, Yi-Bing

    2014-10-01

    Mesoporous TiO2 microbeads with well-defined intra-bead pore sizes (14 nm, 23 nm or 33 nm) were employed to investigate the effect of pore size on the performance of dye-sensitized solar cells constructed with an organic dye (MK2) and a [Co(bpy)3]2+/3+ (bpy = 2,2'-bipyridine)-based electrolyte. The TiCl4 post treatment and film thickness were optimized for the TiO2 electrodes made from beads with 33 nm intra-bead pores, and an overall energy conversion efficiency of 8.5% was achieved for a device with a 6.5 μm thick TiO2 film treated with a 20 mM TiCl4 solution. Although beads with larger pores had a smaller specific surface area, devices derived from these beads produced better photovoltaic performance. This is attributed to the improved diffusion of cobalt species inside the working electrode, as evidenced by a higher electron lifetime and dye regeneration rate recorded on these solar cells.Mesoporous TiO2 microbeads with well-defined intra-bead pore sizes (14 nm, 23 nm or 33 nm) were employed to investigate the effect of pore size on the performance of dye-sensitized solar cells constructed with an organic dye (MK2) and a [Co(bpy)3]2+/3+ (bpy = 2,2'-bipyridine)-based electrolyte. The TiCl4 post treatment and film thickness were optimized for the TiO2 electrodes made from beads with 33 nm intra-bead pores, and an overall energy conversion efficiency of 8.5% was achieved for a device with a 6.5 μm thick TiO2 film treated with a 20 mM TiCl4 solution. Although beads with larger pores had a smaller specific surface area, devices derived from these beads produced better photovoltaic performance. This is attributed to the improved diffusion of cobalt species inside the working electrode, as evidenced by a higher electron lifetime and dye regeneration rate recorded on these solar cells. Electronic supplementary information (ESI) available: Photocurrent transient plots of the devices treated with different concentrations of TiCl4 and UV-vis spectra of dye desorption

  18. Hydrogel Pore-Size Modulation for Enhanced Single-Cell Western Blotting.

    PubMed

    Duncombe, Todd A; Kang, Chi-Chih; Maity, Santanu; Ward, Toby M; Pegram, Mark D; Murthy, Niren; Herr, Amy E

    2016-01-13

    Pore-gradient microgel arrays enable thousands of parallel high-resolution single-cell protein electrophoresis separations for targets accross a wide molecular mass (25-289 kDa), yet within 1 mm separation distances. Dual crosslinked hydrogels facilitate gel-pore expansion after electrophoresis for efficient and uniform immunoprobing. The photopatterned, light-activated, and acid-expandable hydrogel underpins single-cell protein analysis, here for oncoprotein-related signaling in human breast biopsy.

  19. The Nature of Tensile Ductility as Controlled by Extreme-Sized Pores in Powder Metallurgy Ti-6Al-4V Alloy

    NASA Astrophysics Data System (ADS)

    Kumar, P.; Ravi Chandran, K. S.; Cao, F.; Koopman, M.; Fang, Z. Zak

    2016-05-01

    Tensile properties of Ti-6Al-4V titanium alloy, sintered by a new process (sintering, phase transformation, and dehydrogenation of titanium hydride compacts, termed HSPT process), were investigated to determine how the sintering pores influence the tensile strength and ductility. It was found that the ductility in the sintered alloy is severely affected by the size of the largest pore, referred here as extreme-sized pore, even when the average volume fraction of porosity is nearly constant between a large number of samples. It is shown that the rapid decrease in ductility, with an increase in the extreme pore size, is caused by strain localization around the extreme-sized pore and early crack initiation. This crack initiation leads to fracture of the plane containing the pore thereby limiting the extent of uniform plastic strain that can be attained before fracture. Interestingly, the strength properties are, however, found to be independent of the size of the extreme-sized pore. The results are explained on the basis of stress concentration and strain localization around the extreme-sized pores. The work also reveals that if the extreme-sized pores are eliminated, PM Ti-6Al-4V alloy with high strength (~1100 MPa) and good ductility (~12 pct), which is easily comparable to a wrought Ti-6Al-4V alloy, can be achieved even at oxygen levels up to 0.4 wt pct.

  20. Pore-scale simulations of drainage in granular materials: Finite size effects and the representative elementary volume

    NASA Astrophysics Data System (ADS)

    Yuan, Chao; Chareyre, Bruno; Darve, Félix

    2016-09-01

    A pore-scale model is introduced for two-phase flow in dense packings of polydisperse spheres. The model is developed as a component of a more general hydromechanical coupling framework based on the discrete element method, which will be elaborated in future papers and will apply to various processes of interest in soil science, in geomechanics and in oil and gas production. Here the emphasis is on the generation of a network of pores mapping the void space between spherical grains, and the definition of local criteria governing the primary drainage process. The pore space is decomposed by Regular Triangulation, from which a set of pores connected by throats are identified. A local entry capillary pressure is evaluated for each throat, based on the balance of capillary pressure and surface tension at equilibrium. The model reflects the possible entrapment of disconnected patches of the receding wetting phase. It is validated by a comparison with drainage experiments. In the last part of the paper, a series of simulations are reported to illustrate size and boundary effects, key questions when studying small samples made of spherical particles be it in simulations or experiments. Repeated tests on samples of different sizes give evolution of water content which are not only scattered but also strongly biased for small sample sizes. More than 20,000 spheres are needed to reduce the bias on saturation below 0.02. Additional statistics are generated by subsampling a large sample of 64,000 spheres. They suggest that the minimal sampling volume for evaluating saturation is one hundred times greater that the sampling volume needed for measuring porosity with the same accuracy. This requirement in terms of sample size induces a need for efficient computer codes. The method described herein has a low algorithmic complexity in order to satisfy this requirement. It will be well suited to further developments toward coupled flow-deformation problems in which evolution of the

  1. Remote Laser Diffraction Particle Size Distribution Analyzer

    SciTech Connect

    Batcheller, Thomas Aquinas; Huestis, Gary Michael; Bolton, Steven Michael

    2001-03-01

    In support of a radioactive slurry sampling and physical characterization task, an “off-the-shelf” laser diffraction (classical light scattering) particle size analyzer was utilized for remote particle size distribution (PSD) analysis. Spent nuclear fuel was previously reprocessed at the Idaho Nuclear Technology and Engineering Center (INTEC—formerly recognized as the Idaho Chemical Processing Plant) which is on DOE’s INEEL site. The acidic, radioactive aqueous raffinate streams from these processes were transferred to 300,000 gallon stainless steel storage vessels located in the INTEC Tank Farm area. Due to the transfer piping configuration in these vessels, complete removal of the liquid can not be achieved. Consequently, a “heel” slurry remains at the bottom of an “emptied” vessel. Particle size distribution characterization of the settled solids in this remaining heel slurry, as well as suspended solids in the tank liquid, is the goal of this remote PSD analyzer task. A Horiba Instruments Inc. Model LA-300 PSD analyzer, which has a 0.1 to 600 micron measurement range, was modified for remote application in a “hot cell” (gamma radiation) environment. This technology provides rapid and simple PSD analysis, especially down in the fine and microscopic particle size regime. Particle size analysis of these radioactive slurries down in this smaller range was not previously achievable—making this technology far superior than the traditional methods used. Successful acquisition of this data, in conjunction with other characterization analyses, provides important information that can be used in the myriad of potential radioactive waste management alternatives.

  2. Magnetic-resonance pore imaging of nonsymmetric microscopic pore shapes

    NASA Astrophysics Data System (ADS)

    Hertel, Stefan Andreas; Wang, Xindi; Hosking, Peter; Simpson, M. Cather; Hunter, Mark; Galvosas, Petrik

    2015-07-01

    Imaging of the microstructure of porous media such as biological tissue or porous solids is of high interest in health science and technology, engineering and material science. Magnetic resonance pore imaging (MRPI) is a recent technique based on nuclear magnetic resonance (NMR) which allows us to acquire images of the average pore shape in a given sample. Here we provide details on the experimental design, challenges, and requirements of MRPI, including its calibration procedures. Utilizing a laser-machined phantom sample, we present images of microscopic pores with a hemiequilateral triangular shape even in the presence of NMR relaxation effects at the pore walls. We therefore show that MRPI is applicable to porous samples without a priori knowledge about their pore shape and symmetry. Furthermore, we introduce "MRPI mapping," which combines MRPI with conventional magnetic resonance imaging (MRI). This enables one to resolve microscopic pore sizes and shapes spatially, thus expanding the application of MRPI to samples with heterogeneous distributions of pores.

  3. Pore-Scale Heterogeneity in the Mineral Distribution and Reactive Surface Area of Porous Rocks

    NASA Astrophysics Data System (ADS)

    Lai, P. E. P.; Krevor, S. C.

    2015-12-01

    The reactive surface area is an important control on interfacial processes between minerals and aqueous fluids in porous rocks. Spatial heterogeneity in the surface area can lead to complications in modelling reactive transport processes, but quantitative characterisation of this property has been limited. In this paper 3D images obtained using x-ray micro-tomography were used to characterise heterogeneity in surface area in one sandstone and five carbonate rocks. Measurements of average surface area from x-ray imagery were 1-2 orders of magnitude lower than measurements from nitrogen BET. A roughness factor, defined as the ratio of BET surface area to x-ray based surface area, was correlated to the presence of clay or microporosity. Coregistered images of Berea sandstone from x-ray and energy dispersive spectroscopy imagery were used to guide the identification of quartz, K-feldspar, dolomite, calcite and clays in x-ray images. In Berea sandstone, clay and K-feldspar had higher average surface area fractions than their volumetric fractions in the rock. In the Edwards carbonate, however, modal mineral composition correlated with surface area. By sub-sampling digital images, statistical distributions of the surface area were generated at various length scales of subsampling. Comparing these to distributions used in published modelling studies showed that the common practice of leaving surface area and pore volume uncorrelated in a pore leads to unrealistic combinations of surface area and pore volume in the models. We suggest these models adopt a moderate correlation based on observations. In Berea sandstone, constraining ratios of surface area to pore volume to a range of values between that of quartz-lined and five times that of clay-lined spheres appeared sufficient.

  4. Particle size distribution of indoor aerosol sources

    SciTech Connect

    Shah, K.B.

    1990-10-24

    As concern about Indoor Air Quality (IAQ) has grown in recent years, it has become necessary to determine the nature of particles produced by different indoor aerosol sources and the typical concentration that these sources tend to produce. These data are important in predicting the dose of particles to people exposed to these sources and it will also enable us to take effective mitigation procedures. Further, it will also help in designing appropriate air cleaners. A new state of the art technique, DMPS (Differential Mobility Particle Sizer) System is used to determine the particle size distributions of a number of sources. This system employs the electrical mobility characteristics of these particles and is very effective in the 0.01--1.0 {mu}m size range. A modified system that can measure particle sizes in the lower size range down to 3 nm was also used. Experimental results for various aerosol sources is presented in the ensuing chapters. 37 refs., 20 figs., 2 tabs.

  5. Effect of TiO₂ microbead pore size on the performance of DSSCs with a cobalt based electrolyte.

    PubMed

    Chen, Yang; Huang, Fuzhi; Xiang, Wanchun; Chen, Dehong; Cao, Lu; Spiccia, Leone; Caruso, Rachel A; Cheng, Yi-Bing

    2014-11-21

    Mesoporous TiO2 microbeads with well-defined intra-bead pore sizes (14 nm, 23 nm or 33 nm) were employed to investigate the effect of pore size on the performance of dye-sensitized solar cells constructed with an organic dye (MK2) and a [Co(bpy)3](2+/3+) (bpy = 2,2'-bipyridine)-based electrolyte. The TiCl4 post treatment and film thickness were optimized for the TiO2 electrodes made from beads with 33 nm intra-bead pores, and an overall energy conversion efficiency of 8.5% was achieved for a device with a 6.5 μm thick TiO2 film treated with a 20 mM TiCl4 solution. Although beads with larger pores had a smaller specific surface area, devices derived from these beads produced better photovoltaic performance. This is attributed to the improved diffusion of cobalt species inside the working electrode, as evidenced by a higher electron lifetime and dye regeneration rate recorded on these solar cells. PMID:25287230

  6. Measurement of nonvolatile particle number size distribution

    NASA Astrophysics Data System (ADS)

    Gkatzelis, G. I.; Papanastasiou, D. K.; Florou, K.; Kaltsonoudis, C.; Louvaris, E.; Pandis, S. N.

    2016-01-01

    An experimental methodology was developed to measure the nonvolatile particle number concentration using a thermodenuder (TD). The TD was coupled with a high-resolution time-of-flight aerosol mass spectrometer, measuring the chemical composition and mass size distribution of the submicrometer aerosol and a scanning mobility particle sizer (SMPS) that provided the number size distribution of the aerosol in the range from 10 to 500 nm. The method was evaluated with a set of smog chamber experiments and achieved almost complete evaporation (> 98 %) of secondary organic as well as freshly nucleated particles, using a TD temperature of 400 °C and a centerline residence time of 15 s. This experimental approach was applied in a winter field campaign in Athens and provided a direct measurement of number concentration and size distribution for particles emitted from major pollution sources. During periods in which the contribution of biomass burning sources was dominant, more than 80 % of particle number concentration remained after passing through the thermodenuder, suggesting that nearly all biomass burning particles had a nonvolatile core. These remaining particles consisted mostly of black carbon (60 % mass contribution) and organic aerosol (OA; 40 %). Organics that had not evaporated through the TD were mostly biomass burning OA (BBOA) and oxygenated OA (OOA) as determined from AMS source apportionment analysis. For periods during which traffic contribution was dominant 50-60 % of the particles had a nonvolatile core while the rest evaporated at 400 °C. The remaining particle mass consisted mostly of black carbon with an 80 % contribution, while OA was responsible for another 15-20 %. Organics were mostly hydrocarbon-like OA (HOA) and OOA. These results suggest that even at 400 °C some fraction of the OA does not evaporate from particles emitted from common combustion processes, such as biomass burning and car engines, indicating that a fraction of this type of OA

  7. Particle Size Distribution in Aluminum Manufacturing Facilities

    PubMed Central

    Liu, Sa; Noth, Elizabeth M.; Dixon-Ernst, Christine; Eisen, Ellen A.; Cullen, Mark R.; Hammond, S. Katharine

    2015-01-01

    As part of exposure assessment for an ongoing epidemiologic study of heart disease and fine particle exposures in aluminum industry, area particle samples were collected in production facilities to assess instrument reliability and particle size distribution at different process areas. Personal modular impactors (PMI) and Minimicro-orifice uniform deposition impactors (MiniMOUDI) were used. The coefficient of variation (CV) of co-located samples was used to evaluate the reproducibility of the samplers. PM2.5 measured by PMI was compared to PM2.5 calculated from MiniMOUDI data. Mass median aerodynamic diameter (MMAD) and concentrations of sub-micrometer (PM1.0) and quasi-ultrafine (PM0.56) particles were evaluated to characterize particle size distribution. Most of CVs were less than 30%. The slope of the linear regression of PMI_PM2.5 versus MiniMOUDI_PM2.5 was 1.03 mg/m3 per mg/m3 (± 0.05), with correlation coefficient of 0.97 (± 0.01). Particle size distribution varied substantively in smelters, whereas it was less variable in fabrication units with significantly smaller MMADs (arithmetic mean of MMADs: 2.59 μm in smelters vs. 1.31 μm in fabrication units, p = 0.001). Although the total particle concentration was more than two times higher in the smelters than in the fabrication units, the fraction of PM10 which was PM1.0 or PM0.56 was significantly lower in the smelters than in the fabrication units (p < 0.001). Consequently, the concentrations of sub-micrometer and quasi-ultrafine particles were similar in these two types of facilities. It would appear, studies evaluating ultrafine particle exposure in aluminum industry should focus on not only the smelters, but also the fabrication facilities. PMID:26478760

  8. The size distribution of interstellar grains

    NASA Technical Reports Server (NTRS)

    Witt, Adolf N.

    1987-01-01

    Three major areas involving interstellar grains were investigated. First, studies were performed of scattering in reflection nebulae with the goal of deriving scattering characteristics of dust grains such as the albedo and the phase function asymmetry throughout the visible and the ultraviolet. Secondly, studies were performed of the wavelength dependence of interstellar extinction designed to demonstrate the wide range of grain size distributions naturally occurring in individual clouds in different parts of the galaxy. And thirdly, studies were also performed of the ultraviolet powered emission of dust grains in the 0.5 to 1.0 micron wavelength range in reflection nebulae. Findings considered of major importance are highlighted.

  9. Aerosol Size Distribution in the marine regions

    NASA Astrophysics Data System (ADS)

    Markuszewski, Piotr; Petelski, Tomasz; Zielinski, Tymon; Pakszys, Paulina; Strzalkowska, Agata; Makuch, Przemyslaw; Kowalczyk, Jakub

    2014-05-01

    We would like to present the data obtained during the regular research cruises of the S/Y Oceania over a period of time between 2009 - 2012. The Baltic Sea is a very interesting polygon for aerosol measurements, however, also difficult due to the fact that mostly cases of a mixture of continental and marine aerosols are observed. It is possible to measure clear marine aerosol, but also advections of dust from southern Europe or even Africa. This variability of data allows to compare different conditions. The data is also compared with our measurements from the Arctic Seas, which have been made during the ARctic EXperiment (AREX). The Arctic Seas are very suitable for marine aerosol investigations since continental advections of aerosols are far less frequent than in other European sea regions. The aerosol size distribution was measured using the TSI Laser Aerosol Spectrometer model 3340 (99 channels, measurement range 0.09 μm to 7 μm), condensation particle counter (range 0.01 μm to 3 μm) and laser particle counter PMS CSASP-100-HV-SP (range 0.5 μm to 47 μm in 45 channels). Studies of marine aerosol production and transport are important for many Earth sciences such as cloud physics, atmospheric optics, environmental pollution studies and interaction between ocean and atmosphere. All equipment was placed on one of the masts of S/Y Oceania. Measurements using the laser aerosol spectrometer and condensation particle counter were made on one level (8 meters above sea level). Measurements with the laser particle counter were performed at five different levels above the sea level (8, 11, 14, 17 and 20 m). Based on aerosol size distribution the parameterizations with a Log-Normal and a Power-Law distributions were made. The aerosol source functions, characteristic for the region were also determined. Additionally, poor precision of the sea spray emission determination was confirmed while using only the aerosol concentration data. The emission of sea spray depends

  10. Importance of small pores in microcrystalline cellulose for controlling water distribution during extrusion-spheronization.

    PubMed

    Soh, Josephine L P; Yang, Lei; Liew, Celine V; Cui, Fu D; Heng, Paul W S

    2008-01-01

    The purpose of this research was to investigate the effects of particle size on the wet massing behavior of microcrystalline cellulose (MCC). In this study, a series of six fractionated MCC grades were customized and specially classified to yield different particle size varieties of the standard grade, Comprecel M101. All seven MCC grades were extensively characterized for the physical properties and wet massing behavior using mixer torque rheometry. Effects of MCC physical properties on the maximum torque (Torque(max)) were determined using partial least squares (PLS) analysis. Most physical properties varied systematically with particle size and morphological changes. Marked differences were observed in the small pore volumes (V (highP)) and BET surface areas of the MCC grades. Variables that exerted dominant influences on Torque(max) were identified. In particular, the significance of V (highP) in governing wet mass consistency was established. The role of V (highP) has not been reported in any study because this small but significant variation is likely to be obliterated or compensated by variation in other physical properties from MCC grades from different suppliers. The findings demonstrated the role of small pores in governing the wet mass consistency of MCC and provide a better understanding of MCC's superior performance as a spheronization aid by the ability to fulfill the function as a molecular sponge to facilitate pellet formation during wet granulation processes. PMID:18720015

  11. Charge and Size Distributions of Electrospray Drops

    PubMed

    de Juan L; de la Mora JF

    1997-02-15

    The distributions of charge q and diameter d of drops emitted from electrified liquid cones in the cone-jet mode are investigated with two aerosol instruments. A differential mobility analyzer (DMA, Vienna type) first samples the spray drops, selects those with electrical mobilities within a narrow band, and either measures the associated current or passes them to a second instrument. The drops may also be individually counted optically and sized by sampling them into an aerodynamic size spectrometer (API's Aerosizer). For a given cone-jet, the distribution of charge q for the main electrospray drops is some 2.5 times broader than their distribution of diameters d, with qmax/qmin approximately 4. But mobility-selected drops have relative standard deviations of only 5% for both d and q, showing that the support of the (q, d) distribution is a narrow band centered around a curve q(d). The approximate one-dimensionality of this support region is explained through the mechanism of jet breakup, which is a random process with only one degree of freedom: the wavelength of axial modulation of the jet. The observed near constancy of the charge over volume ratio (q approximately d3) shows that the charge is frozen in the liquid surface at the time scale of the breakup process. The charge over volume ratio of the primary drops varies between 98 and 55% of the ratio of spray current I over liquid flow rate Q, and decreases at increasing Q. I/Q is therefore an unreliable measure of the charge density of these drops.

  12. Molecularly imprinted macroporous monoliths for solid-phase extraction: Effect of pore size and column length on recognition properties.

    PubMed

    Vlakh, E G; Stepanova, M A; Korneeva, Yu M; Tennikova, T B

    2016-09-01

    The series of macroporous monolithic molecularly imprinted monoliths differed by pore size, column length (volume) and amount of template used for imprinting was synthesized using methacrylic acid and glycerol dimethacrylate as co-monomers and antibiotic ciprofloxacin as a template. The prepared monoliths were characterized regarding to their permeability, pore size, porosity, and resistance to the flow of a mobile phase. The surface morphology was also analyzed. The slight dependence of imprinting factor on flow rate, as well as its independence on pore size of macroporous molecularly imprinted monolithic media was observed. The column obtained at different conditions exhibited different affinity of ciprofloxacin to the imprinted sites that was characterized with Kdiss values in the range of 10(-5)-10(-4)M. The solid-phase extraction of ciprofloxacin from such biological liquids as human blood serum, human urine and cow milk serum was performed using the developed monolithic columns. In all cases, the extraction was found to be 95.0-98.6%. Additionally, the comparison of extraction of three fluoroqinolone analogues, e.g. ciprofloxacin, levofloxacin and moxifloxacin, from human blood plasma was carried out. Contrary to ciprofloxacin extracted with more than 95%, this parameter did not exceed 40% for its analogues. PMID:27433985

  13. Effect of Pore Size and Porosity on the Biomechanical Properties and Cytocompatibility of Porous NiTi Alloys

    PubMed Central

    Jian, Yu-Tao; Yang, Yue; Tian, Tian; Stanford, Clark; Zhang, Xin-Ping; Zhao, Ke

    2015-01-01

    Five types of porous Nickel-Titanium (NiTi) alloy samples of different porosities and pore sizes were fabricated. According to compressive and fracture strengths, three groups of porous NiTi alloy samples underwent further cytocompatibility experiments. Porous NiTi alloys exhibited a lower Young’s modulus (2.0 GPa ~ 0.8 GPa). Both compressive strength (108.8 MPa ~ 56.2 MPa) and fracture strength (64.6 MPa ~ 41.6 MPa) decreased gradually with increasing mean pore size (MPS). Cells grew and spread well on all porous NiTi alloy samples. Cells attached more strongly on control group and blank group than on all porous NiTi alloy samples (p < 0.05). Cell adhesion on porous NiTi alloys was correlated negatively to MPS (277.2 μm ~ 566.5 μm; p < 0.05). More cells proliferated on control group and blank group than on all porous NiTi alloy samples (p < 0.05). Cellular ALP activity on all porous NiTi alloy samples was higher than on control group and blank group (p < 0.05). The porous NiTi alloys with optimized pore size could be a potential orthopedic material. PMID:26047515

  14. Effect of Pore Size and Porosity on the Biomechanical Properties and Cytocompatibility of Porous NiTi Alloys.

    PubMed

    Jian, Yu-Tao; Yang, Yue; Tian, Tian; Stanford, Clark; Zhang, Xin-Ping; Zhao, Ke

    2015-01-01

    Five types of porous Nickel-Titanium (NiTi) alloy samples of different porosities and pore sizes were fabricated. According to compressive and fracture strengths, three groups of porous NiTi alloy samples underwent further cytocompatibility experiments. Porous NiTi alloys exhibited a lower Young's modulus (2.0 GPa ~ 0.8 GPa). Both compressive strength (108.8 MPa ~ 56.2 MPa) and fracture strength (64.6 MPa ~ 41.6 MPa) decreased gradually with increasing mean pore size (MPS). Cells grew and spread well on all porous NiTi alloy samples. Cells attached more strongly on control group and blank group than on all porous NiTi alloy samples (p < 0.05). Cell adhesion on porous NiTi alloys was correlated negatively to MPS (277.2 μm ~ 566.5 μm; p < 0.05). More cells proliferated on control group and blank group than on all porous NiTi alloy samples (p < 0.05). Cellular ALP activity on all porous NiTi alloy samples was higher than on control group and blank group (p < 0.05). The porous NiTi alloys with optimized pore size could be a potential orthopedic material.

  15. Aggregate size distribution of the soil loss

    NASA Astrophysics Data System (ADS)

    Szabó, Judit Alexandra; Jakab, Gergely; Szabó, Boglárka; Józsa, Sándor; Szalai, Zoltán; Centeri, Csaba

    2016-04-01

    aggregate size distribution which is led to nutrient and organic matter redistribution is one of a key questions to improve erosion estimation. G. Jakab was supported by the János Bolyai fellowship of the HAS.

  16. Estimation of the pore pressure distribution from three dimensional groundwater flow model at mine sites in Korea

    NASA Astrophysics Data System (ADS)

    Kang, Sangsoo; Jang, Myounghwan; Kim, Gyoungman; Kim, Donghui; Kim, Daehoon; Baek, Hwanjo

    2016-04-01

    Mining activities continually change the groundwater flow and associated pore pressure distributions within the rockmass around the mine openings or the open-pit bench during the operational periods. As the pore pressure distributions may substantially affect the mechanical behaviour or stability of the rockmass, it is important to monitor the variation of pore pressure incurred by mining operation. The pore pressure distributions within the rockmass can be derived using a two- or three-dimensional finite element groundwater flow model, adopted to simulate the groundwater flow. While the groundwater inflow at mines has generally been dealt with respect to the working environment, detailed case studies on the distribution of pore water pressure related to the stability analysis of mine openings have been relatively rare in Korea. Recently, however, as the health and safety problems are emerged for sustainable mining practice, these issues are of the major concerns for the mining industries. This study aims to establish a three dimensional groundwater flow model to estimate the pore pressure distributions in order to employ as an input parameter for numerical codes such as the FLAC 3D. Also, the groundwater flow simulated can be used for de-watering design at a mine site. The MINEDW code, a groundwater flow model code specifically developed to simulate the complicated hydro-geologic conditions related to mining, has mainly been used in this study. Based on the data collected from field surveys and literature reviews, a conceptual model was established and sensitivity analysis was performed.

  17. Power laws, discontinuities and regional city size distributions

    USGS Publications Warehouse

    Garmestani, A.S.; Allen, C.R.; Gallagher, C.M.

    2008-01-01

    Urban systems are manifestations of human adaptation to the natural environment. City size distributions are the expression of hierarchical processes acting upon urban systems. In this paper, we test the entire city size distributions for the southeastern and southwestern United States (1990), as well as the size classes in these regions for power law behavior. We interpret the differences in the size of the regional city size distributions as the manifestation of variable growth dynamics dependent upon city size. Size classes in the city size distributions are snapshots of stable states within urban systems in flux. ?? 2008.

  18. Pore-scale investigation on stress-dependent characteristics of granular packs and the impact of pore deformation on fluid distribution

    DOE PAGESBeta

    Yoon, Hongkyu; Klise, Katherine A.; Torrealba, Victor A.; Karpyn, Zuleima T.; Crandall, D.

    2015-05-25

    Understanding the effect of changing stress conditions on multiphase flow in porous media is of fundamental importance for many subsurface activities including enhanced oil recovery, water drawdown from aquifers, soil confinement, and geologic carbon storage. Geomechanical properties of complex porous systems are dynamically linked to flow conditions, but their feedback relationship is often oversimplified due to the difficulty of representing pore-scale stress deformation and multiphase flow characteristics in high fidelity. In this work, we performed pore-scale experiments of single- and multiphase flow through bead packs at different confining pressure conditions to elucidate compaction-dependent characteristics of granular packs and their impactmore » on fluid flow. A series of drainage and imbibition cycles were conducted on a water-wet, soda-lime glass bead pack under varying confining stress conditions. Simultaneously, X-ray micro-CT was used to visualize and quantify the degree of deformation and fluid distribution corresponding with each stress condition and injection cycle. Micro-CT images were segmented using a gradient-based method to identify fluids (e.g., oil and water), and solid phase redistribution throughout the different experimental stages. Changes in porosity, tortuosity, and specific surface area were quantified as a function of applied confining pressure. Results demonstrate varying degrees of sensitivity of these properties to confining pressure, which suggests that caution must be taken when considering scalability of these properties for practical modeling purposes. Changes in capillary number with confining pressure are attributed to the increase in pore velocity as a result of pore contraction. Furthermore, this increase in pore velocity was found to have a marginal impact on average phase trapping at different confining pressures.« less

  19. Pore-scale investigation on stress-dependent characteristics of granular packs and the impact of pore deformation on fluid distribution

    SciTech Connect

    Yoon, Hongkyu; Klise, Katherine A.; Torrealba, Victor A.; Karpyn, Zuleima T.; Crandall, D.

    2015-05-25

    Understanding the effect of changing stress conditions on multiphase flow in porous media is of fundamental importance for many subsurface activities including enhanced oil recovery, water drawdown from aquifers, soil confinement, and geologic carbon storage. Geomechanical properties of complex porous systems are dynamically linked to flow conditions, but their feedback relationship is often oversimplified due to the difficulty of representing pore-scale stress deformation and multiphase flow characteristics in high fidelity. In this work, we performed pore-scale experiments of single- and multiphase flow through bead packs at different confining pressure conditions to elucidate compaction-dependent characteristics of granular packs and their impact on fluid flow. A series of drainage and imbibition cycles were conducted on a water-wet, soda-lime glass bead pack under varying confining stress conditions. Simultaneously, X-ray micro-CT was used to visualize and quantify the degree of deformation and fluid distribution corresponding with each stress condition and injection cycle. Micro-CT images were segmented using a gradient-based method to identify fluids (e.g., oil and water), and solid phase redistribution throughout the different experimental stages. Changes in porosity, tortuosity, and specific surface area were quantified as a function of applied confining pressure. Results demonstrate varying degrees of sensitivity of these properties to confining pressure, which suggests that caution must be taken when considering scalability of these properties for practical modeling purposes. Changes in capillary number with confining pressure are attributed to the increase in pore velocity as a result of pore contraction. Furthermore, this increase in pore velocity was found to have a marginal impact on average phase trapping at different confining pressures.

  20. Size and spacial distribution of micropores in SBA-15 using CM-SANS

    SciTech Connect

    Pollock, Rachel A; Walsh, Brenna R; Fry, Jason A; Ghampson, Tyrone; Centikol, Ozgul; Melnichenko, Yuri B; Kaiser, Helmut; Pynn, Roger; Frederick, Brian G

    2011-01-01

    Diffraction intensity analysis of small-angle neutron scattering measurements of dry SBA-15 have been combined with nonlocal density functional theory (NLDFT) analysis of nitrogen desorption isotherms to characterize the micropore, secondary mesopore, and primary mesopore structure. The radial dependence of the scattering length density, which is sensitive to isolated surface hydroxyls, can only be modeled if the NLDFT pore size distribution is distributed relatively uniformly throughout the silica framework, not localized in a 'corona' around the primary mesopores. Contrast matching-small angle neutron scattering (CM-SANS) measurements, using water, decane, tributylamine, cyclohexane, and isooctane as direct probes of the size of micropores indicate that the smallest pores in SBA-15 have diameter between 5.7 and 6.2 {angstrom}. Correlation of the minimum pore size with the onset of the micropore size distribution provides direct evidence that the shape of the smallest micropores is cylinderlike, which is consistent with their being due to unraveling of the polymer template.

  1. Parameterizing Size Distribution in Ice Clouds

    SciTech Connect

    DeSlover, Daniel; Mitchell, David L.

    2009-09-25

    PARAMETERIZING SIZE DISTRIBUTIONS IN ICE CLOUDS David L. Mitchell and Daniel H. DeSlover ABSTRACT An outstanding problem that contributes considerable uncertainty to Global Climate Model (GCM) predictions of future climate is the characterization of ice particle sizes in cirrus clouds. Recent parameterizations of ice cloud effective diameter differ by a factor of three, which, for overcast conditions, often translate to changes in outgoing longwave radiation (OLR) of 55 W m-2 or more. Much of this uncertainty in cirrus particle sizes is related to the problem of ice particle shattering during in situ sampling of the ice particle size distribution (PSD). Ice particles often shatter into many smaller ice fragments upon collision with the rim of the probe inlet tube. These small ice artifacts are counted as real ice crystals, resulting in anomalously high concentrations of small ice crystals (D < 100 µm) and underestimates of the mean and effective size of the PSD. Half of the cirrus cloud optical depth calculated from these in situ measurements can be due to this shattering phenomenon. Another challenge is the determination of ice and liquid water amounts in mixed phase clouds. Mixed phase clouds in the Arctic contain mostly liquid water, and the presence of ice is important for determining their lifecycle. Colder high clouds between -20 and -36 oC may also be mixed phase but in this case their condensate is mostly ice with low levels of liquid water. Rather than affecting their lifecycle, the presence of liquid dramatically affects the cloud optical properties, which affects cloud-climate feedback processes in GCMs. This project has made advancements in solving both of these problems. Regarding the first problem, PSD in ice clouds are uncertain due to the inability to reliably measure the concentrations of the smallest crystals (D < 100 µm), known as the “small mode”. Rather than using in situ probe measurements aboard aircraft, we employed a treatment of ice

  2. Filter-extruded liposomes revisited: a study into size distributions and morphologies in relation to lipid-composition and process parameters.

    PubMed

    Hinna, Askell; Steiniger, Frank; Hupfeld, Stefan; Stein, Paul; Kuntsche, Judith; Brandl, Martin

    2016-01-01

    Filter-extrusion is a widely used technique for down-sizing of phospholipid vesicles. In order to gain a detailed insight into size and size distributions of filter-extruded vesicles composed of egg phosphatidyl-choline (with varying fractions of cholesterol)--in relation to extrusion-parameters (pore-size, number of filter passages, and flow-rate), flow field-flow fractionation in conjunction with multi-angle laser light scattering (AF4-MALLS, Wyatt Technology Corp., Santa Barbara, CA) was employed. Liposome size-distributions determined by AF4-MALLS were compared with those of dynamic light scattering and correlated with cryo-transmission electron microscopy and (31)P-NMR-analysis of lamellarity. Both the mean size of liposome and the width of size distribution were found to decrease with sequential extrusion through smaller pore size filters, starting at a size range of ≈70-415 nm upon repeated extrusion through 400 nm pore-filters, eventually ending with a size range from ≈30 to 85 nm upon extrusion through 30 nm pore size filters. While for small pores sizes (50 nm), increased flow rates resulted in smaller vesicles, no significant influence of flow rate on mean vesicle size was seen with larger pores. Cholesterol at increasing mol fractions up to 0.45 yielded bigger vesicles (at identical process conditions). For a cholesterol mol fraction of 0.5 in combination with small filter pore size, a bimodal size distribution was seen indicating cholesterol micro-crystallites. Finally, a protocol is suggested to prepare large (∼ 300 nm) liposomes with rather narrow size distribution, based on the filter extrusion at defined flow-rates in combination with freeze-/thaw-cycling and bench-top centrifugation. PMID:25826203

  3. The effect of particle shape and size distribution on the acoustical properties of mixtures of hemp particles.

    PubMed

    Glé, Philippe; Gourdon, Emmanuel; Arnaud, Laurent; Horoshenkov, Kirill-V; Khan, Amir

    2013-12-01

    Hemp concrete is an attractive alternative to traditional materials used in building construction. It has a very low environmental impact, and it is characterized by high thermal insulation. Hemp aggregate particles are parallelepiped in shape and can be organized in a plurality of ways to create a considerable proportion of open pores with a complex connectivity pattern, the acoustical properties of which have never been examined systematically. Therefore this paper is focused on the fundamental understanding of the relations between the particle shape and size distribution, pore size distribution, and the acoustical properties of the resultant porous material mixture. The sound absorption and the transmission loss of various hemp aggregates is characterized using laboratory experiments and three theoretical models. These models are used to relate the particle size distribution to the pore size distribution. It is shown that the shape of particles and particle size control the pore size distribution and tortuosity in shiv. These properties in turn relate directly to the observed acoustical behavior. PMID:25669282

  4. Transport of biocolloids in water saturated columns packed with sand: Effect of grain size and pore water velocity.

    PubMed

    Syngouna, Vasiliki I; Chrysikopoulos, Constantinos V

    2011-11-01

    The main objective of this study was to evaluate the combined effects of grain size and pore water velocity on the transport in water saturated porous media of three waterborne fecal indicator organisms (Escherichia coli, MS2, and ΦX174) in laboratory-scale columns packed with clean quartz sand. Three different grain sizes and three pore water velocities were examined and the attachment behavior of Escherichia coli, MS2, and ΦX174 onto quartz sand was evaluated. The mass recoveries of the biocolloids examined were shown to be highest for Escherichia coli and lowest for MS2. However, no obvious relationships between mass recoveries and water velocity or grain size could be established from the experimental results. The observed mean dispersivity values for each sand grain size were smaller for bacteria than coliphages, but higher for MS2 than ΦX174. The single collector removal and collision efficiencies were quantified using the classical colloid filtration theory. Furthermore, theoretical collision efficiencies were estimated only for E. coli by the Interaction-Force-Boundary-Layer, and Maxwell approximations. Better agreement between the experimental and Maxwell theoretical collision efficiencies were observed.

  5. Correlation between structure and mass distribution of the nuclear pore complex and of distinct pore complex components

    PubMed Central

    1990-01-01

    Nuclear pore complexes (NPCs) prepared from Xenopus laevis oocyte nuclear envelopes were studied in "intact" form (i.e., unexposed to detergent) and after detergent treatment by a combination of conventional transmission electron microscopy (CTEM) and quantitative scanning transmission electron microscopy (STEM). In correlation- averaged CTEM pictures of negatively stained intact NPCs and of distinct NPC components (i.e., "rings," "spoke" complexes, and "plug- spoke" complexes), several fine structural features arranged with octagonal symmetry about a central axis could reproducibly be identified. STEM micrographs of unstained/freeze-dried intact NPCs as well as of their components yielded comparable but less distinct features. Mass determination by STEM revealed the following molecular masses: intact NPC with plug, 124 +/- 11 MD; intact NPC without plug, 112 +/- 11 MD; heavy ring, 32 +/- 5 MD; light ring, 21 +/- 4 MD; plug- spoke complex, 66 +/- 8 MD; and spoke complex, 52 +/- 3 MD. Based on these combined CTEM and STEM data, a three-dimensional model of the NPC exhibiting eightfold centrosymmetry about an axis perpendicular to the plane of the nuclear envelope but asymmetric along this axis is proposed. This structural polarity of the NPC across the nuclear envelope is in accord with its well-documented functional polarity facilitating mediated nucleocytoplasmic exchange of molecules and particles. PMID:2324201

  6. Thermal analysis of porous medium with ellipsoidal pores using a homogenization method

    NASA Astrophysics Data System (ADS)

    Asakuma, Yusuke; Yamamoto, Tsuyoshi

    2016-10-01

    Effective thermal conductivity including radiation is analyzed using a homogenization method. This method can precisely represent the microstructure of a porous medium with ellipsoidal pores. Here, the effects of parameters such as porosity, pore shape, pore distribution, and temperature of the porous medium on the conductivity are estimated to clarify the mechanisms in complex pore structures. For example, heat transfer by radiation does not dominate if the medium has pores of less than 1 mm in size. Moreover, the anisotropy of the effective thermal conductivity is found to depend on temperature, pore shape, pore size, and pore distribution.

  7. Phylogenetic characterization of 16S rRNA gene clones from deep-groundwater microorganisms that pass through 0.2-micrometer-pore-size filters.

    PubMed

    Miyoshi, Tatsuo; Iwatsuki, Teruki; Naganuma, Takeshi

    2005-02-01

    A total of 247 clones of 16S rRNA genes from microorganisms captured by 0.2- and 0.1-microm-pore-size filters from sedimentary and granite rock aquifers were amplified and yielded 37 operational taxonomic units (OTUs). Fifteen OTUs captured by 0.1-microm-pore-size filters were affiliated with the candidate divisions OD1 and OP11, representing novel lineages. On the other hand, OTUs captured by 0.2-microm-pore-size filters were largely affiliated with Betaproteobacteria.

  8. Distribution of 1-Butyl-3-methylimidazolium Bistrifluoromethylsulfonimide in Mesoporous Silica as a Function of Pore Filling

    SciTech Connect

    Han, Kee Sung; Wang, Xiqing; Hagaman, Edward {Ed} W; Dai, Sheng

    2013-01-01

    Rotational dynamics of the ionic liquid (IL) 1-butyl-3-methlyimidazolium bistrifluoromethylsulfonimide, [C4mim][Tf2N], 1, as a neat liquid and confined in mesoporous silica were investigated by 1H spin-spin (T2) and spin-lattice (T1) relaxation measurements and 13C NMR spectroscopy. Translational dynamics (self-diffusion) were monitored via the diffusion coefficient, D, obtained with 1H pulsed field gradient NMR measurements. These data were used to determine the distribution of 1 in the pores of KIT-6, a mesoporous silica with a bicontinuous gyroid pore structure, as a function of filling fraction. Relaxation studies performed as a function of filling factor and temperature, reveal a dynamic heterogeneity in both translational and rotational motions for 1 at filling factors, f, = 0.2-1.0 (f = 1 corresponds to fully filled pores). Spin-lattice and spin-spin relaxation times reveal the motion of 1 in silica mesopores conform to that expected for a two-dimensional relaxation model. The relaxation dynamics are interpreted using a two-state, fast exchange model for all motions; a slow rotation (and translation) of molecules in contact with the surface and a faster motion approximated by the values for bulk relaxation and diffusion. 1 retains liquid like behavior at all filling factors and temperatures that extend to ca. 50 degrees below the bulk melting point. Translational motion in these systems, interpreted with MD-simulated diffusivity limits, confirms the high propensity of 1 to form a monolayer film on the silica surface at low filling factors.. The attractive interaction of 1 with the surface is greater than that for self-association of 1. The trends in diffusion data at short and long diffusion time suggest that the population of surface-bound 1 is in intimate contact with 1 in the pores. This condition is most easily met at higher filling fractions with successive additions of 1 increasing the layer thickness built up on the surface layer.

  9. Antimicrobial performance of mesoporous titania thin films: role of pore size, hydrophobicity, and antibiotic release

    PubMed Central

    Atefyekta, Saba; Ercan, Batur; Karlsson, Johan; Taylor, Erik; Chung, Stanley; Webster, Thomas J; Andersson, Martin

    2016-01-01

    Implant-associated infections are undesirable complications that might arise after implant surgery. If the infection is not prevented, it can lead to tremendous cost, trauma, and even life threatening conditions for the patient. Development of an implant coating loaded with antimicrobial substances would be an effective way to improve the success rate of implants. In this study, the in vitro efficacy of mesoporous titania thin films used as a novel antimicrobial release coating was evaluated. Mesoporous titania thin films with pore diameters of 4, 6, and 7 nm were synthesized using the evaporation-induced self-assembly method. The films were characterized and loaded with antimicrobial agents, including vancomycin, gentamicin, and daptomycin. Staphylococcus aureus and Pseudomonas aeruginosa were used to evaluate their effectiveness toward inhibiting bacterial colonization. Drug loading and delivery were studied using a quartz crystal microbalance with dissipation monitoring, which showed successful loading and release of the antibiotics from the surfaces. Results from counting bacterial colony-forming units showed reduced bacterial adhesion on the drug-loaded films. Interestingly, the presence of the pores alone had a desired effect on bacterial colonization, which can be attributed to the documented nanotopographical effect. In summary, this study provides significant promise for the use of mesoporous titania thin films for reducing implant infections. PMID:27022263

  10. A Novel Approach to Estimate the Distribution of Reducible Iron Within Different Pore Fractions of Structured Media.

    NASA Astrophysics Data System (ADS)

    Kamolpornwijit, W.; Brooks, S. C.; Kim, Y.; Scheibe, T. D.

    2005-12-01

    The success of bioremediation processes employing iron reducing bacteria depends on several factors; one of the crucial factors is the availability of Fe(III) as an electron acceptor. The iron content of subsurface media usually is obtained through different extraction techniques performed in a well-mixed batch experiment. For structured media where preferential flow prevails over the matrix flow, however, the iron content from homogenized samples may not well represent the iron content available for microbial activity. Results from the batch experiments may overestimate the availability of reducible iron. As microbes remain within the macro- and mesopores due to their cellular size restriction, the iron content within micropores may play an insignificant role during the biostimulation process. In this new approach, we extract Fe from different pore classes of intact cores of structured saprolite. The extracting solution (0.2 M ammonium oxalate) is introduced to an unsaturated column at specific tension. Unit gradient across the cores is maintained with a Marriotte device and vacuum chamber at the column inlet and outlet, respectively. Nonreactive tracers are included in the extractant solution to quantify transport properties. When the iron content in the effluent falls below detection limit, the tension is decreased (higher degree of saturation). The process is repeated until the column is operated at saturated conditions. The distribution of extractable iron within different pore fractions will be obtained directly from the experiment. In this study we will estimate the flow distribution, affected area, and mass concentration of iron using transport parameters obtained from non reactive tracer tests under both saturated and unsaturated conditions. The study will provide a novel approach supplementing the bulk extraction procedures which is critical to the success of bioremediation processes especially in structured media.

  11. Impact of the carbon pore size and topology on the equilibrium quantum sieving of hydrogen isotopes at zero coverage and finite pressures.

    PubMed

    Kowalczyk, Piotr; Gauden, Piotr A; Terzyk, Artur P; Furmaniak, Sylwester

    2009-04-01

    Carbonaceous slit-shaped and square-shaped pores efficiently differentiate adsorbed hydrogen isotopes at 77 and 33 K. Extensive path integral Monte Carlo simulations revealed that the square-shaped carbon pores enhanced the selectivity of deuterium over hydrogen in comparison to equivalent slit-shaped carbon pores at zero coverage as well as at finite pressures (i.e. quantum sieving of hydrogen isotopes is pore-topology-dependent). We show that this enhancement of the D(2)/H(2) equilibrium selectivity results from larger localization of hydrogen isotopes in square-shaped pores. The operating pressures for efficient quantum sieving of hydrogen isotopes are strongly dependent on the topology as well as on the size of the carbon pores. However, for both considered carbon pore topologies the highest D(2)/H(2) separation factor is observed at zero-coverage limit. Depending on carbon pore size and topology we predicted monotonic decreasing and non-monotonic shape of the D(2)/H(2) equilibrium selectivity at finite pressures. For both kinds of carbonaceous pores of molecular sizes we predict high compression of hydrogen isotopes at 77 and 33 K (for example, the pore density of compressed hydrogen isotopes at 77 K and 0.25 MPa in a square-shaped carbon pore of size 2.6 Å exceeds 60 mmol cm(-3); for comparison, the liquid density of para-H(2) at 30 K and 30 MPa is 42 mmol cm(-3)). Finally, by direct comparison of simulation results with experimental data it is explained why 'ordinary' carbonaceous materials are not efficient quantum sieves.

  12. Gradients in pore size enhance the osteogenic differentiation of human mesenchymal stromal cells in three-dimensional scaffolds

    NASA Astrophysics Data System (ADS)

    di Luca, Andrea; Ostrowska, Barbara; Lorenzo-Moldero, Ivan; Lepedda, Antonio; Swieszkowski, Wojcech; van Blitterswijk, Clemens; Moroni, Lorenzo

    2016-03-01

    Small fractures in bone tissue can heal by themselves, but in case of larger defects current therapies are not completely successful due to several drawbacks. A possible strategy relies on the combination of additive manufactured polymeric scaffolds and human mesenchymal stromal cells (hMSCs). The architecture of bone tissue is characterized by a structural gradient. Long bones display a structural gradient in the radial direction, while flat bones in the axial direction. Such gradient presents a variation in bone density from the cancellous bone to the cortical bone. Therefore, scaffolds presenting a gradient in porosity could be ideal candidates to improve bone tissue regeneration. In this study, we present a construct with a discrete gradient in pore size and characterize its ability to further support the osteogenic differentiation of hMSCs. Furthermore, we studied the behaviour of hMSCs within the different compartments of the gradient scaffolds, showing a correlation between osteogenic differentiation and ECM mineralization, and pore dimensions. Alkaline phosphatase activity and calcium content increased with increasing pore dimensions. Our results indicate that designing structural porosity gradients may be an appealing strategy to support gradual osteogenic differentiation of adult stem cells.

  13. Gradients in pore size enhance the osteogenic differentiation of human mesenchymal stromal cells in three-dimensional scaffolds

    PubMed Central

    Di Luca, Andrea; Ostrowska, Barbara; Lorenzo-Moldero, Ivan; Lepedda, Antonio; Swieszkowski, Wojcech; Van Blitterswijk, Clemens; Moroni, Lorenzo

    2016-01-01

    Small fractures in bone tissue can heal by themselves, but in case of larger defects current therapies are not completely successful due to several drawbacks. A possible strategy relies on the combination of additive manufactured polymeric scaffolds and human mesenchymal stromal cells (hMSCs). The architecture of bone tissue is characterized by a structural gradient. Long bones display a structural gradient in the radial direction, while flat bones in the axial direction. Such gradient presents a variation in bone density from the cancellous bone to the cortical bone. Therefore, scaffolds presenting a gradient in porosity could be ideal candidates to improve bone tissue regeneration. In this study, we present a construct with a discrete gradient in pore size and characterize its ability to further support the osteogenic differentiation of hMSCs. Furthermore, we studied the behaviour of hMSCs within the different compartments of the gradient scaffolds, showing a correlation between osteogenic differentiation and ECM mineralization, and pore dimensions. Alkaline phosphatase activity and calcium content increased with increasing pore dimensions. Our results indicate that designing structural porosity gradients may be an appealing strategy to support gradual osteogenic differentiation of adult stem cells. PMID:26961859

  14. Thermal Investigations of Periodically Nanoporous Si Films -- The Impact of Structure Sizes and Pore-Edge Amorphization

    NASA Astrophysics Data System (ADS)

    Xu, Dongchao; Zhao, Hongbo; Hao, Qing

    In recent years, nanoporous Si films have been intensively studied as promising thermoelectric materials, which mainly benefits from their dramatically reduced lattice thermal conductivity kL and bulk-like electrical properties.1,2 Despite many encouraging results, challenges still exist in the theoretical explanation of the observed low kL.3 Existing studies mainly attribute the low kL to 1) phonon bandstructure modification by coherent phonon processes in a periodic structure (phononic effects), and/or 2) pore-edge defects. In this work, temperature-dependent kL is measured for nanoporous Si films with different pore sizes and spacing to compare with model predictions. For systematic studies, two fabrication techniques are used to drill the nanopores: 1) reactive ion etching, and 2) a focus ion beam to introduce more pore-edge defects. The results from this work will provide guidance for phonon engineering in general materials with periodic interfaces or boundaries. References: 1. Tang et al., Nano Letters 10, 4279-4283 (2010). 2. Yu et al., Nature Nanotechnology 5, 718-721 (2010). 3. Cahill et al., Applied Physics Reviews 1, 011305/1-45 (2014) Nanoscale thermal transport. II. 2003-2012.

  15. Distributed Pore Chemistry in Porous Organic Polymers in Tissue Culture Flasks

    NASA Technical Reports Server (NTRS)

    Koontz, Steven L. (Inventor)

    1999-01-01

    A method for making a biocompatible polymer article using a uniform atomic oxygen treatment is disclose. The substrate may be subsequently optionally grated with a compatibilizing compound. Compatibilizing compounds may include proteins, phosphorylcholine groups, platelet adhesion preventing polymers, albumin adhesion promoters, and the like. The compatibilized substrate may also have a living cell layer adhered thereto. The atomic oxygen is preferably produced by a flowing afterglow microwave discharge, wherein the substrate resides in a sidearm out of the plasma. Also, methods for culturing cells for various purposes using the various membranes are disclosed as well. Also disclosed are porous organic polymers having a distributed pore chemistry (DPC) comprising hydrophilic and hydrophobic regions, and a method for making the DPC by exposing the polymer to atomic oxygen wherein the rate of hydrophilization is greater than the rate of mass loss.

  16. Significant effect of grain size distribution on compaction rates in granular aggregates

    NASA Astrophysics Data System (ADS)

    Niemeijer, André; Elsworth, Derek; Marone, Chris

    2009-07-01

    We investigate the role of pressure solution in deformation of upper- to mid-crustal rocks using aggregates of halite as a room temperature analog for fluid-assisted deformation processes in the Earth's crust. Experiments evaluate the effects of initial grain size distribution on macroscopic pressure solution rate of the aggregate and compare the results to theoretical models for pressure solution. We find that the grain size exponent deviates significantly from the theoretical value of 3 for diffusion-controlled pressure solution. Models typically assume mono-dispersed spherical particles in pseudo-regular packing. We infer that the discrepancy between experimentally determined grain size exponents and the theoretical values are a result of deviation of experimental (and natural) samples from regular packs of mono-dispersed spherical particles. Moreover, we find that compaction rates can vary by up to one order of magnitude as a function of the width of the grain size distribution for a given mean grain size. Wider size distributions allow for higher initial compaction rates, increasing the macroscopic compaction rate with respect to more narrow grain size distributions. Grain sizes in rocks, fault gouges, and hydrocarbon reservoirs are typically log-normal or power law distributed and therefore pressure solution rates may significantly exceed theoretical predictions. Spatiotemporal variations in pressure solution rates due to variations in grain size may cause the formation of low porosity zones, which could potentially focus deformation in these zones and produce pockets of high pore pressures, promoting nucleation of frictional instability and earthquake rupture.

  17. Nanometer scale pores similar in size to the entrance of the ribosomal exit cavity are a common feature of large RNAs

    PubMed Central

    Rivas, Mario; Tran, Quyen; Fox, George E.

    2013-01-01

    The highly conserved peptidyl transferase center (PTC) of the ribosome contains an RNA pore that serves as the entrance to the exit tunnel. Analysis of available ribosome crystal structures has revealed the presence of multiple additional well-defined pores of comparable size in the ribosomal (rRNA) RNAs. These typically have dimensions of 1–2 nm, with a total area of ∼100 Å2 or more, and most are associated with one or more ribosomal proteins. The PTC example and the other rRNA pores result from the packing of helices. However, in the non-PTC cases the nitrogenous bases do not protrude into the pore, thereby limiting the potential for hydrogen bonding within the pore. Instead, it is the RNA backbone that largely defines the pore likely resulting in a negatively charged environment. In many but not all cases, ribosomal proteins are associated with the pores to a greater or lesser extent. With the exception of the PTC case, the large subunit pores are not found in what are thought to be the evolutionarily oldest regions of the 23S rRNA. The unusual nature of the PTC pore may reflect a history of being created by hybridization between two or more RNAs early in evolution rather than simple folding of a single RNA. An initial survey of nonribosomal RNA crystal structures revealed additional pores, thereby showing that they are likely a general feature of RNA tertiary structure. PMID:23940386

  18. Relationships between specific surface area and pore size in electrospun polymer fibre networks

    PubMed Central

    Eichhorn, S. J.; Sampson, W. W.

    2010-01-01

    From consideration of the extent of contact between fibres in electrospun polymer networks, we provide theory relating the specific surface area of the network to the characteristic dimensions of interfibre voids. We show that these properties are strongly influenced by the cross-sectional morphologies of fibres. Whereas porosity has a strong influence on pore dimensions, in the range of porosities typically obtained in real networks, its influence on specific surface area is weak. By considering reference geometries of collapsed ribbons and fibres with circular cross sections, we demonstrate that at a given network porosity, fibre parameters that increase the specific surface area reduce the characteristic dimensions of voids. The implications of the theory, mainly in the context of cell proliferation on electrospun polymer scaffolds, are discussed; the theory has relevance also to future applications of these materials in composites. PMID:19812071

  19. Porous Carbon Fibers Containing Pores with Sizes Controlled at the Ångstrom Level by the Cavity Size of Pillar[6]arene.

    PubMed

    Ogoshi, Tomoki; Yoshikoshi, Kumiko; Sueto, Ryuta; Nishihara, Hirotomo; Yamagishi, Tada-Aki

    2015-05-26

    We report a new synthesis method of fibrous carbon material with pores sizes that are precisely controlled at the Ångstrom level, by carbonization of two dimensional (2D) porous sheets of pillar[6]arenes. The 2D porous sheets were prepared by 2D supramolecular polymerization induced by oxidation of hydroquinone units of pillar[6]arenes. Owing to the hexagonal structure of pillar[6]arene, the assembly induced by 2D supramolecular polymerization gave hexagonal 2D porous sheets, and the highly ordered structure of the 2D porous sheets formed regular fibrous structures. Then, carbonization of the 2D porous sheets afforded fibrous carbon materials with micropores. The micropore size of the fibrous porous carbon prepared from pillar[6]arene was the same size as that of the starting material pillar[6]arene assembly.

  20. An Interface Coassembly in Biliquid Phase: Toward Core-Shell Magnetic Mesoporous Silica Microspheres with Tunable Pore Size.

    PubMed

    Yue, Qin; Li, Jialuo; Luo, Wei; Zhang, Yu; Elzatahry, Ahmed A; Wang, Xiqing; Wang, Chun; Li, Wei; Cheng, Xiaowei; Alghamdi, Abdulaziz; Abdullah, Aboubakr M; Deng, Yonghui; Zhao, Dongyuan

    2015-10-21

    Core-shell magnetic mesoporous silica microspheres (Magn-MSMs) with tunable large mesopores in the shell are highly desired in biocatalysis, magnetic bioseparation, and enrichment. In this study, a shearing assisted interface coassembly in n-hexane/water biliquid systems is developed to synthesize uniform Magn-MSMs with magnetic core and mesoporous silica shell for an efficient size-selective biocatalysis. The synthesis features the rational control over the electrostatic interaction among cationic surfactant molecules, silicate oligomers, and Fe3O4@RF microspheres (RF: resorcinol formaldehyde) in the presence of shearing-regulated solubilization of n-hexane in surfactant micelles. Through this multicomponent interface coassembly, surfactant-silica mesostructured composite has been uniformly deposited on the Fe3O4@RF microspheres, and core-shell Magn-MSMs are obtained after removing the surfactant and n-hexane. The obtained Magn-MSMs possess excellent water dispersibility, uniform diameter (600 nm), large and tunable perpendicular mesopores (5.0-9.0 nm), high surface area (498-623 m(2)/g), large pore volume (0.91-0.98 cm(3)/g), and high magnetization (34.5-37.1 emu/g). By utilization of their large and open mesopores, Magn-MSMs with a pore size of about 9.0 nm have been demonstrated to be able to immobilize a large bioenzyme (trypsin with size of 4.0 nm) with a high loading capacity of ∼97 μg/mg via chemically binding. Magn-MSMs with immobilized trypsin exhibit an excellent convenient and size selective enzymolysis of low molecular proteins in the mixture of proteins of different sizes and a good recycling performance by using the magnetic separability of the microspheres.

  1. An Interface Coassembly in Biliquid Phase: Toward Core-Shell Magnetic Mesoporous Silica Microspheres with Tunable Pore Size.

    PubMed

    Yue, Qin; Li, Jialuo; Luo, Wei; Zhang, Yu; Elzatahry, Ahmed A; Wang, Xiqing; Wang, Chun; Li, Wei; Cheng, Xiaowei; Alghamdi, Abdulaziz; Abdullah, Aboubakr M; Deng, Yonghui; Zhao, Dongyuan

    2015-10-21

    Core-shell magnetic mesoporous silica microspheres (Magn-MSMs) with tunable large mesopores in the shell are highly desired in biocatalysis, magnetic bioseparation, and enrichment. In this study, a shearing assisted interface coassembly in n-hexane/water biliquid systems is developed to synthesize uniform Magn-MSMs with magnetic core and mesoporous silica shell for an efficient size-selective biocatalysis. The synthesis features the rational control over the electrostatic interaction among cationic surfactant molecules, silicate oligomers, and Fe3O4@RF microspheres (RF: resorcinol formaldehyde) in the presence of shearing-regulated solubilization of n-hexane in surfactant micelles. Through this multicomponent interface coassembly, surfactant-silica mesostructured composite has been uniformly deposited on the Fe3O4@RF microspheres, and core-shell Magn-MSMs are obtained after removing the surfactant and n-hexane. The obtained Magn-MSMs possess excellent water dispersibility, uniform diameter (600 nm), large and tunable perpendicular mesopores (5.0-9.0 nm), high surface area (498-623 m(2)/g), large pore volume (0.91-0.98 cm(3)/g), and high magnetization (34.5-37.1 emu/g). By utilization of their large and open mesopores, Magn-MSMs with a pore size of about 9.0 nm have been demonstrated to be able to immobilize a large bioenzyme (trypsin with size of 4.0 nm) with a high loading capacity of ∼97 μg/mg via chemically binding. Magn-MSMs with immobilized trypsin exhibit an excellent convenient and size selective enzymolysis of low molecular proteins in the mixture of proteins of different sizes and a good recycling performance by using the magnetic separability of the microspheres. PMID:26186087

  2. Topical application of a cleanser containing extracts of Diospyros kaki folium, Polygonum cuspidatum and Castanea crenata var. dulcis reduces skin oil content and pore size in human skin

    PubMed Central

    LEE, BO MI; AN, SUNGKWAN; KIM, SOO-YEON; HAN, HYUN JOO; JEONG, YU-JIN; LEE, KYOUNG-ROK; ROH, NAM KYUNG; AHN, KYU JOONG; AN, IN-SOOK; CHA, HWA JUN

    2015-01-01

    The effects of skin pores on skin topographic features can be reduced by decreasing excessive production and accumulation of sebum and elimination of comedones. Therefore, a cosmetic cleanser that regulates sebum homeostasis is required. In the present study, the effects of a cosmetic cleanser that contained Diospyros kaki folium, Polygonum cuspidatum and Castanea crenata var. dulcis (DPC) was examined on the removal of sebum and on skin pore size. Healthy volunteers (n=23) aged 20–50 years were asked to apply the test materials to the face. Skin oil content, pore size, pore number and extracted sebum surface area were measured using various measurement methods. All the measurements were performed at pre- and post-application of the test materials. When the cosmetic cleanser containing DPC was applied to the skin, the oil content decreased by 77.3%, from 6.19 to 1.40. The number of skin pores decreased by 24.83%, from 125.39 to 94.23. Skin pore size decreased from 0.07 to 0.02 µm3 (71.43% decrease). The amount of extracted sebum increased by 335% when the DPC cleanser was used. Compared to the control cleanser, skin oil content was significantly decreased when the cleanser that contained DPC was used. The cleanser containing DPC also decreased pore size and number. Finally, the DPC cleanser easily removed solidified sebum from the skin. PMID:26137233

  3. Effects of particle size distribution in thick film conductors

    NASA Technical Reports Server (NTRS)

    Vest, R. W.

    1983-01-01

    Studies of particle size distribution in thick film conductors are discussed. The distribution of particle sizes does have an effect on fired film density but the effect is not always positive. A proper distribution of sizes is necessary, and while the theoretical models can serve as guides to selecting this proper distribution, improved densities can be achieved by empirical variations from the predictions of the models.

  4. A combinatorial variation in surface chemistry and pore size of three-dimensional porous poly(ε-caprolactone) scaffolds modulates the behaviors of mesenchymal stem cells.

    PubMed

    Zhao, Yingdi; Tan, Ke; Zhou, Yan; Ye, Zhaoyang; Tan, Wen-Song

    2016-02-01

    Biomaterial properties play significant roles in controlling cellular behaviors. The objective of the present study was to investigate how pore size and surface chemistry of three-dimensional (3D) porous scaffolds regulate the fate of mesenchymal stem cells (MSCs) in vitro in combination. First, on poly(ε-caprolactone) (PCL) films, the hydrolytic treatment was found to stimulate the adhesion, spreading and proliferation of human MSCs (hMSCs) in comparison with pristine films, while the aminolysis showed mixed effects. Then, 3D porous PCL scaffolds with varying pore sizes (100-200μm, 200-300μm and 300-450μm) were fabricated and subjected to either hydrolysis or aminolysis. It was found that a pore size of 200-300μm with hydrolysis in 3D scaffolds was the most favorable condition for growth of hMSCs. Importantly, while a pore size of 200-300μm with hydrolysis for 1h supported the best osteogenic differentiation of hMSCs, the chondrogenic differentiation was greatest in scaffolds with a pore size of 300-450μm and treated with aminolysis for 1h. Taken together, these results suggest that surface chemistry and pore size of 3D porous scaffolds may potentially have a synergistic impact on the behaviors of MSCs.

  5. Pore-Scale Investigation on Stress-Dependent Characteristics of Granular Packs and Their Impact on Multiphase Fluid Distribution

    NASA Astrophysics Data System (ADS)

    Torrealba, V.; Karpyn, Z.; Yoon, H.; Hart, D. B.; Klise, K. A.

    2013-12-01

    The pore-scale dynamics that govern multiphase flow under variable stress conditions are not well understood. This lack of fundamental understanding limits our ability to quantitatively predict multiphase flow and fluid distributions in natural geologic systems. In this research, we focus on pore-scale, single and multiphase flow properties that impact displacement mechanisms and residual trapping of non-wetting phase under varying stress conditions. X-ray micro-tomography is used to image pore structures and distribution of wetting and non-wetting fluids in water-wet synthetic granular packs, under dynamic load. Micro-tomography images are also used to determine structural features such as medial axis, surface area, and pore body and throat distribution; while the corresponding transport properties are determined from Lattice-Boltzmann simulations performed on lattice replicas of the imaged specimens. Results are used to investigate how inter-granular deformation mechanisms affect fluid displacement and residual trapping at the pore-scale. This will improve our understanding of the dynamic interaction of mechanical deformation and fluid flow during enhanced oil recovery and geologic CO2 sequestration. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.

  6. The determination and optimization of (rutile) pigment particle size distributions

    NASA Technical Reports Server (NTRS)

    Richards, L. W.

    1972-01-01

    A light scattering particle size test which can be used with materials having a broad particle size distribution is described. This test is useful for pigments. The relation between the particle size distribution of a rutile pigment and its optical performance in a gray tint test at low pigment concentration is calculated and compared with experimental data.

  7. Effects of pore sizes and oxygen-containing functional groups on desulfurization activity of Fe/NAC prepared by ultrasonic-assisted impregnation

    NASA Astrophysics Data System (ADS)

    Shu, Song; Guo, Jia-Xiu; Liu, Xiao-Li; Wang, Xue-Jiao; Yin, Hua-Qiang; Luo, De-Ming

    2016-01-01

    A series of Fe-loaded activated carbons treated by HNO3 (Fe/NAC) were prepared by incipient impregnation method with or without ultrasonic assistance and characterized using X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy with energy disperse spectroscope (SEM-EDS), transmission electron microscopy (TEM) and N2 adsorption/desorption. The desulfurization activities were evaluated at a fixed bed reactor under a mixed gas simulated from flue gas. The results showed that desulfurization activity from excellent to poor is as follows: Fe/NAC-60 > Fe/NAC-80 > Fe/NAC-30 > Fe/NAC-15 > Fe/NAC-0 > Fe/NAC-100 > NAC. Fe/NAC-60 exhibits the best desulfurization activity and has breakthrough sulfur capacity of 319 mg/g and breakthrough time of 540 min. The introduction of ultrasonic oscillation does not change the form of Fe oxides on activated carbon but can change the dispersion and relative contents of Fe3O4. The types of oxygen-containing functional groups have no obvious change for all samples but the texture properties show some differences when they are oscillated for different times. The fresh Fe/NAC-60 has a surface area of 1045 m2/g and total pore volume of 0.961 cm3/g with micropore volume of 0.437 cm3/g and is larger than Fe/NAC-0 (823 m2/g, 0.733 and 0.342 cm3/g). After desulfurization, surface area and pore volume of all samples decrease significantly, and those of the exhausted Fe/NAC-60 decrease to 233 m2/g and 0.481 cm3/g, indicating that some byproducts deposit on surface to cover pores. Pore size distribution influences SO2 adsorption, and fresh Fe/NAC-60 has more pore widths centralized at about 0.7 nm and 1.0-2.0 nm and corresponds to an excellent desulfurization activity, showing that micropore is conducive to the removal of SO2.

  8. Thorium adsorption in the ocean: reversibility and distribution amongst particle sizes

    NASA Astrophysics Data System (ADS)

    Moore, Robert M.; Hunter, Keith A.

    1985-11-01

    Experiments have been carried out to determine whether the adsorption of Th by marine suspended particles is a reversible process. The results indicate reversibility on a time scale of hours. The distribution of Th between the 'dissolved' state (<0.22 μm particle size) and various particle size fractions has been compared with predictions based on a hyperbolic size distribution of marine particles assuming spherical geometry and surface adsorption. Thorium is present in small particles to a much smaller degree than such a model would predict, so that the use of 1 μm pore size filters to separate 'dissolved' and 'particulate' Th does not introduce serious errors. The implications of these results on the reversible exchange model of BACON and ANDERSON (1982) and on the settling model of TSUNOGAI and MINAGAWA (1978) are discussed.

  9. Soil-pore water distribution of silver and gold engineered nanoparticles in undisturbed soils under unsaturated conditions.

    PubMed

    Tavares, D S; Rodrigues, S M; Cruz, N; Carvalho, C; Teixeira, T; Carvalho, L; Duarte, A C; Trindade, T; Pereira, E; Römkens, P F A M

    2015-10-01

    Release of engineered nanoparticles (ENPs) to soil is well documented but little is known on the subsequent soil-pore water distribution of ENPs once present in soil. In this study, the availability and mobility of silver (Ag) and gold (Au) ENPs added to agricultural soils were assessed in two separate pot experiments. Pore water samples collected from pots from day 1 to 45 using porous (<0.17 μm) membrane samplers suggest that both Ag and Au are retained almost completely within 24 h with less than 13% of the total added amount present in pore water on day 1. UV-Vis and TEM results showed that AuENPs in pore water were present as both homoaggregates and heteroaggregates until day 3 after which the concentration in pore water was too low to detect the presence of aggregates. A close relation between the concentration of Au and Fe in pore water suggests that the short term solubility of Au is partly controlled by natural soil colloids. Results suggest that under normal aerated soil conditions the actual availability of Ag and AuENPs is low which is relevant in view of risk assessment even though the impact of environmental conditions and soil properties on the reactivity of ENPs (and/or large ENPs aggregates) retained in the solid matrix need to be addressed further. PMID:25965160

  10. Soil-pore water distribution of silver and gold engineered nanoparticles in undisturbed soils under unsaturated conditions.

    PubMed

    Tavares, D S; Rodrigues, S M; Cruz, N; Carvalho, C; Teixeira, T; Carvalho, L; Duarte, A C; Trindade, T; Pereira, E; Römkens, P F A M

    2015-10-01

    Release of engineered nanoparticles (ENPs) to soil is well documented but little is known on the subsequent soil-pore water distribution of ENPs once present in soil. In this study, the availability and mobility of silver (Ag) and gold (Au) ENPs added to agricultural soils were assessed in two separate pot experiments. Pore water samples collected from pots from day 1 to 45 using porous (<0.17 μm) membrane samplers suggest that both Ag and Au are retained almost completely within 24 h with less than 13% of the total added amount present in pore water on day 1. UV-Vis and TEM results showed that AuENPs in pore water were present as both homoaggregates and heteroaggregates until day 3 after which the concentration in pore water was too low to detect the presence of aggregates. A close relation between the concentration of Au and Fe in pore water suggests that the short term solubility of Au is partly controlled by natural soil colloids. Results suggest that under normal aerated soil conditions the actual availability of Ag and AuENPs is low which is relevant in view of risk assessment even though the impact of environmental conditions and soil properties on the reactivity of ENPs (and/or large ENPs aggregates) retained in the solid matrix need to be addressed further.

  11. Slip-weakening zone sizes at nucleation of catastrophic subaerial and submarine landslides by gradually increasing pore pressure

    NASA Astrophysics Data System (ADS)

    Viesca, R. C.; Rice, J. R.

    2011-12-01

    We address the nucleation of dynamic landslide rupture in response to gradual pore pressure increases. Nucleation marks the onset of acceleration of the overlying slope mass due to the suddenly rapid enlargement of a sub-surface zone of shear failure, previously deforming quasi-statically. We model that zone as a planar surface undergoing initially linear slip-weakening frictional failure within a bordering linear-elastic medium. The results are also relevant to earthquake nucleation. The sub-surface rupture zone considered runs parallel to the free surface of a uniform slope, under a 2D plane-strain deformation state. We show results for ruptures with friction coefficients following linear slip weakening (i.e., the residual friction is not yet reached). For spatially broad increases in pore pressure, the nucleation length depends on a ratio of depth to a cohesive zone length scale. In the very broad-increase limit, a direct numerical solution for nucleation lengths compares well with solutions to a corresponding eigenvalue problem (similar to Uenishi and Rice [JGR '03]), in which spatial variations in normal stress are neglected. We estimate nucleation lengths for subaerial and submarine conditions using data [e.g., Bishop et al., Géotech. '71; Stark et al., JGGE '05] from ring-shear tests on sediments (peak friction fp = 0.5, frictional slip-weakening rate within the range w = -df/d(slip) = 0.1/cm-1/cm). We assume that only pre-stresses, and not material properties, vary with depth. With such fp and w, we find for a range of subsurface depths and shear moduli μ that nucleation lengths are typically several hundred meters long for shallow undersea slopes, and up to an order of magnitude less for steeper slopes on the Earth's surface. In the submarine case, this puts nucleation lengths in a size range comparable to observed pore-pressure-generated seafloor disturbances as pockmarks [e.g., Gay et al., MG '06].

  12. Unimodal tree size distributions possibly result from relatively strong conservatism in intermediate size classes.

    PubMed

    Bin, Yue; Ye, Wanhui; Muller-Landau, Helene C; Wu, Linfang; Lian, Juyu; Cao, Honglin

    2012-01-01

    Tree size distributions have long been of interest to ecologists and foresters because they reflect fundamental demographic processes. Previous studies have assumed that size distributions are often associated with population trends or with the degree of shade tolerance. We tested these associations for 31 tree species in a 20 ha plot in a Dinghushan south subtropical forest in China. These species varied widely in growth form and shade-tolerance. We used 2005 and 2010 census data from that plot. We found that 23 species had reversed J shaped size distributions, and eight species had unimodal size distributions in 2005. On average, modal species had lower recruitment rates than reversed J species, while showing no significant difference in mortality rates, per capita population growth rates or shade-tolerance. We compared the observed size distributions with the equilibrium distributions projected from observed size-dependent growth and mortality. We found that observed distributions generally had the same shape as predicted equilibrium distributions in both unimodal and reversed J species, but there were statistically significant, important quantitative differences between observed and projected equilibrium size distributions in most species, suggesting that these populations are not at equilibrium and that this forest is changing over time. Almost all modal species had U-shaped size-dependent mortality and/or growth functions, with turning points of both mortality and growth at intermediate size classes close to the peak in the size distribution. These results show that modal size distributions do not necessarily indicate either population decline or shade-intolerance. Instead, the modal species in our study were characterized by a life history strategy of relatively strong conservatism in an intermediate size class, leading to very low growth and mortality in that size class, and thus to a peak in the size distribution at intermediate sizes. PMID:23300714

  13. Characterisation of pore structures in nanoporous materials for advanced bionanotechnology.

    PubMed

    Heo, K; Yoon, J; Jin, K S; Jin, S; Ree, M

    2006-08-01

    Porous materials are potential candidates for applications in various fields, such as bionanotechnology, gas separation, catalysts and micro-electronics. In particular, their applications in bionanotechnology include biosensors, biomedical implants and microdevices, biosupporters, bio-encapsules, biomolecule separations and biomedical therapy. All these bionanotechnology applications utilise the shape, size and size distribution of pores in porous materials. Therefore the controlled creation of pores with desired shape, size and size distribution is most important in the development of nanoporous materials. Accordingly, the accurate evaluation of pore structure is necessary in the development of nanoporous materials and their applications. This article reviews recent developments in analytical techniques to characterise the pore structures of nanoporous materials.

  14. Determination of the cumulus size distribution from LANDSAT pictures

    NASA Technical Reports Server (NTRS)

    Karg, E.; Mueller, H.; Quenzel, H.

    1983-01-01

    Varying insolation causes undesirable thermic stress to the receiver of a solar power plant. The rapid change of insolation depends on the size distribution of the clouds; in order to measure these changes, it is suitable to determine typical cumulus size distributions. For this purpose, LANDSAT-images are adequate. Several examples of cumulus size distributions will be presented and their effects on the operation of a solar power plant are discussed.

  15. Dip TIPS as a Facile and Versatile Method for Fabrication of Polymer Foams with Controlled Shape, Size and Pore Architecture for Bioengineering Applications

    PubMed Central

    Kasoju, Naresh; Kubies, Dana; Kumorek, Marta M.; Kříž, Jan; Fábryová, Eva; Machová, Lud'ka; Kovářová, Jana; Rypáček, František

    2014-01-01

    The porous polymer foams act as a template for neotissuegenesis in tissue engineering, and, as a reservoir for cell transplants such as pancreatic islets while simultaneously providing a functional interface with the host body. The fabrication of foams with the controlled shape, size and pore structure is of prime importance in various bioengineering applications. To this end, here we demonstrate a thermally induced phase separation (TIPS) based facile process for the fabrication of polymer foams with a controlled architecture. The setup comprises of a metallic template bar (T), a metallic conducting block (C) and a non-metallic reservoir tube (R), connected in sequence T-C-R. The process hereinafter termed as Dip TIPS, involves the dipping of the T-bar into a polymer solution, followed by filling of the R-tube with a freezing mixture to induce the phase separation of a polymer solution in the immediate vicinity of T-bar; Subsequent free-drying or freeze-extraction steps produced the polymer foams. An easy exchange of the T-bar of a spherical or rectangular shape allowed the fabrication of tubular, open- capsular and flat-sheet shaped foams. A mere change in the quenching time produced the foams with a thickness ranging from hundreds of microns to several millimeters. And, the pore size was conveniently controlled by varying either the polymer concentration or the quenching temperature. Subsequent in vivo studies in brown Norway rats for 4-weeks demonstrated the guided cell infiltration and homogenous cell distribution through the polymer matrix, without any fibrous capsule and necrotic core. In conclusion, the results show the “Dip TIPS” as a facile and adaptable process for the fabrication of anisotropic channeled porous polymer foams of various shapes and sizes for potential applications in tissue engineering, cell transplantation and other related fields. PMID:25275373

  16. Zipf Distribution of U.S. Firm Sizes

    NASA Astrophysics Data System (ADS)

    Axtell, Robert L.

    2001-09-01

    Analyses of firm sizes have historically used data that included limited samples of small firms, data typically described by lognormal distributions. Using data on the entire population of tax-paying firms in the United States, I show here that the Zipf distribution characterizes firm sizes: the probability a firm is larger than size s is inversely proportional to s. These results hold for data from multiple years and for various definitions of firm size.

  17. Joint radius-length distribution as a measure of anisotropic pore eccentricity: An experimental and analytical framework

    NASA Astrophysics Data System (ADS)

    Benjamini, Dan; Basser, Peter J.

    2014-12-01

    In this work, we present an experimental design and analytical framework to measure the nonparametric joint radius-length (R-L) distribution of an ensemble of parallel, finite cylindrical pores, and more generally, the eccentricity distribution of anisotropic pores. Employing a novel 3D double pulsed-field gradient acquisition scheme, we first obtain both the marginal radius and length distributions of a population of cylindrical pores and then use these to constrain and stabilize the estimate of the joint radius-length distribution. Using the marginal distributions as constraints allows the joint R-L distribution to be reconstructed from an underdetermined system (i.e., more variables than equations), which requires a relatively small and feasible number of MR acquisitions. Three simulated representative joint R-L distribution phantoms corrupted by different noise levels were reconstructed to demonstrate the process, using this new framework. As expected, the broader the peaks in the joint distribution, the less stable and more sensitive to noise the estimation of the marginal distributions. Nevertheless, the reconstruction of the joint distribution is remarkably robust to increases in noise level; we attribute this characteristic to the use of the marginal distributions as constraints. Axons are known to exhibit local compartment eccentricity variations upon injury; the extent of the variations depends on the severity of the injury. Nonparametric estimation of the eccentricity distribution of injured axonal tissue is of particular interest since generally one cannot assume a parametric distribution a priori. Reconstructing the eccentricity distribution may provide vital information about changes resulting from injury or that occurred during development.

  18. Modulation of pore sizes of titanium dioxide photocatalysts by a facile template free hydrothermal synthesis method: implications for photocatalytic degradation of rhodamine B.

    PubMed

    Rasalingam, Shivatharsiny; Wu, Chia-Ming; Koodali, Ranjit T

    2015-02-25

    Mesoporous TiO2 photocatalysts were prepared in ethanol media by using relatively green, template free sol-gel technique. A mild hydrothermal treatment procedure was employed to tune the pore sizes of the materials. Comprehensive techniques that include powder X-ray diffraction, diffuse reflectance spectroscopy, specific surface area analysis, electron microscopy, FT-IR, TGA, and ζ-potential measurements were used to characterize the titania materials. Porosity (pore size and pore volume) of the materials were found to be key factors for the variation in the rate of photocatalytic degradation of rhodamine B; in addition to specific surface area, and surface hydroxyl groups. An increase in porosity permits effective transport of the dye molecules resulting in an increase in the rate of the degradation in materials having larger pores. A detailed electrospray ionization-mass spectrometric (ESI-MS) study was carried out for selected materials to identify photodegraded intermediates and products formed during the degradation of rhodamine B. In addition, experiments were also carried out to understand the role of reactive oxygen species (ROS). In summary, this work provides a simple way to tune pore sizes without the use of any template and an insight into the influence of pore size for the photocatalytic degradation of rhodamine B. PMID:25633643

  19. Modulation of pore sizes of titanium dioxide photocatalysts by a facile template free hydrothermal synthesis method: implications for photocatalytic degradation of rhodamine B.

    PubMed

    Rasalingam, Shivatharsiny; Wu, Chia-Ming; Koodali, Ranjit T

    2015-02-25

    Mesoporous TiO2 photocatalysts were prepared in ethanol media by using relatively green, template free sol-gel technique. A mild hydrothermal treatment procedure was employed to tune the pore sizes of the materials. Comprehensive techniques that include powder X-ray diffraction, diffuse reflectance spectroscopy, specific surface area analysis, electron microscopy, FT-IR, TGA, and ζ-potential measurements were used to characterize the titania materials. Porosity (pore size and pore volume) of the materials were found to be key factors for the variation in the rate of photocatalytic degradation of rhodamine B; in addition to specific surface area, and surface hydroxyl groups. An increase in porosity permits effective transport of the dye molecules resulting in an increase in the rate of the degradation in materials having larger pores. A detailed electrospray ionization-mass spectrometric (ESI-MS) study was carried out for selected materials to identify photodegraded intermediates and products formed during the degradation of rhodamine B. In addition, experiments were also carried out to understand the role of reactive oxygen species (ROS). In summary, this work provides a simple way to tune pore sizes without the use of any template and an insight into the influence of pore size for the photocatalytic degradation of rhodamine B.

  20. Synthesis of microtubes with a surface of "house of cards" structure via needlelike particles and control of their pore size.

    PubMed

    Mitsuhashi, Kohei; Tagami, Naoki; Tanabe, Katsuyuki; Ohkubo, Takahiro; Sakai, Hideki; Koishi, Masumi; Abe, Masahiko

    2005-04-12

    The conditions for synthesizing microtubes with a surface of "house of cards" structure via needlelike particles were examined in detail. Magnesium carbonate trihydrate was formed as a metastable phase in the reaction process using magnesium hydroxide and carbon dioxide as starting materials. Subsequently, in the formation of basic magnesium carbonate from magnesium carbonate trihydrate, microtubes with a surface of house of cards structure were obtained via needlelike particles of magnesium carbonate trihydrate under certain conditions where the temperature and added amount of sodium hydroxide were properly controlled. The pore size of the microtubes could be controlled within a range of 0.5-6 microm by adjusting the condition of needlelike particle formation. In addition, the sustainability of naphthalene release from the microtube was found to be about 6 times higher than that from naphthalene crystal. PMID:15807617

  1. Cluster size distribution in Gaussian glasses

    NASA Astrophysics Data System (ADS)

    Novikov, S. V.

    2011-03-01

    A simple method for the estimation of the asymptotics of the cluster numbers in Gaussian glasses is described. Validity of the method was tested by the comparison with the exact analytic result for the non-correlated field and simulation data for the distribution of random energies in strongly spatially correlated dipolar glass model.

  2. The distribution of bubble sizes during reionization

    NASA Astrophysics Data System (ADS)

    Lin, Yin; Oh, S. Peng; Furlanetto, Steven R.; Sutter, P. M.

    2016-09-01

    A key physical quantity during reionization is the size of H II regions. Previous studies found a characteristic bubble size which increases rapidly during reionization, with apparent agreement between simulations and analytic excursion set theory. Using four different methods, we critically examine this claim. In particular, we introduce the use of the watershed algorithm - widely used for void finding in galaxy surveys - which we show to be an unbiased method with the lowest dispersion and best performance on Monte Carlo realizations of a known bubble size probability density function (PDF). We find that a friends-of-friends algorithm declares most of the ionized volume to be occupied by a network of volume-filling regions connected by narrow tunnels. For methods tuned to detect the volume-filling regions, previous apparent agreement between simulations and theory is spurious, and due to a failure to correctly account for the window function of measurement schemes. The discrepancy is already obvious from visual inspection. Instead, H II regions in simulations are significantly larger (by factors of 10-1000 in volume) than analytic predictions. The size PDF is narrower, and evolves more slowly with time, than predicted. It becomes more sharply peaked as reionization progresses. These effects are likely caused by bubble mergers, which are inadequately modelled by analytic theory. Our results have important consequences for high-redshift 21 cm observations, the mean free path of ionizing photons, and the visibility of Lyα emitters, and point to a fundamental failure in our understanding of the characteristic scales of the reionization process.

  3. Particle size distribution of airborne Aspergillus fumigatus spores emitted from compost using membrane filtration

    NASA Astrophysics Data System (ADS)

    Deacon, L. J.; Pankhurst, L. J.; Drew, G. H.; Hayes, E. T.; Jackson, S.; Longhurst, P. J.; Longhurst, J. W. S.; Liu, J.; Pollard, S. J. T.; Tyrrel, S. F.

    Information on the particle size distribution of bioaerosols emitted from open air composting operations is valuable in evaluating potential health impacts and is a requirement for improved dispersion simulation modelling. The membrane filter method was used to study the particle size distribution of Aspergillus fumigatus spores in air 50 m downwind of a green waste compost screening operation at a commercial facility. The highest concentrations (approximately 8 × 10 4 CFU m -3) of culturable spores were found on filters with pore diameters in the range 1-2 μm which suggests that the majority of spores are emitted as single cells. The findings were compared to published data collected using an Andersen sampler. Results were significantly correlated ( p < 0.01) indicating that the two methods are directly comparable across all particles sizes for Aspergillus spores.

  4. The first systematic analysis of 3D rapid prototyped poly(ε-caprolactone) scaffolds manufactured through BioCell printing: the effect of pore size and geometry on compressive mechanical behaviour and in vitro hMSC viability.

    PubMed

    Domingos, M; Intranuovo, F; Russo, T; De Santis, R; Gloria, A; Ambrosio, L; Ciurana, J; Bartolo, P

    2013-12-01

    Novel additive manufacturing processes are increasingly recognized as ideal techniques to produce 3D biodegradable structures with optimal pore size and spatial distribution, providing an adequate mechanical support for tissue regeneration while shaping in-growing tissues. With regard to the mechanical and biological performances of 3D scaffolds, pore size and geometry play a crucial role. In this study, a novel integrated automated system for the production and in vitro culture of 3D constructs, known as BioCell Printing, was used only to manufacture poly(ε-caprolactone) scaffolds for tissue engineering; the influence of pore size and shape on their mechanical and biological performances was investigated. Imposing a single lay-down pattern of 0°/90° and varying the filament distance, it was possible to produce scaffolds with square interconnected pores with channel sizes falling in the range of 245-433 µm, porosity 49-57% and a constant road width. Three different lay-down patterns were also adopted (0°/90°, 0°/60/120° and 0°/45°/90°/135°), thus resulting in scaffolds with quadrangular, triangular and complex internal geometries, respectively. Mechanical compression tests revealed a decrease of scaffold stiffness with the increasing porosity and number of deposition angles (from 0°/90° to 0°/45°/90°/135°). Results from biological analysis, carried out using human mesenchymal stem cells, suggest a strong influence of pore size and geometry on cell viability. On the other hand, after 21 days of in vitro static culture, it was not possible to detect any significant variation in terms of cell morphology promoted by scaffold topology. As a first systematic analysis, the obtained results clearly demonstrate the potential of the BioCell Printing process to produce 3D scaffolds with reproducible well organized architectures and tailored mechanical properties.

  5. Lunar soil: Size distribution and mineralogical constituents

    USGS Publications Warehouse

    Duke, M.B.; Woo, C.C.; Bird, M.L.; Sellers, G.A.; Finkelman, R.B.

    1970-01-01

    The lunar soil collected by Apollo 11 consists primarily of submillimeter material and is finer in grain size than soil previously recorded photographically by Surveyor experiments. The main constituents are fine-grained to glassy rocks of basaltic affinity and coherent breccia of undetermined origin. Dark glass, containing abundant nickel-iron spheres, coats many rocks, mineral, and breccia fragments. Several types of homogeneous glass occur as fragments and spheres. Colorless spheres, probably an exotic component, are abundant in the fraction finer than 20 microns.

  6. The size distribution of inhabited planets

    NASA Astrophysics Data System (ADS)

    Simpson, Fergus

    2016-02-01

    Earth-like planets are expected to provide the greatest opportunity for the detection of life beyond the Solar system. However, our planet cannot be considered a fair sample, especially if intelligent life exists elsewhere. Just as a person's country of origin is a biased sample among countries, so too their planet of origin may be a biased sample among planets. The magnitude of this effect can be substantial: over 98 per cent of the world's population live in a country larger than the median. In the context of a simple model where the mean population density is invariant to planet size, we infer that a given inhabited planet (such as our nearest neighbour) has a radius r < 1.2r⊕ (95 per cent confidence bound). We show that this result is likely to hold not only for planets hosting advanced life, but also for those which harbour primitive life forms. Further, inferences may be drawn for any variable which influences population size. For example, since population density is widely observed to decline with increasing body mass, we conclude that most intelligent species are expected to exceed 300 kg.

  7. Resonance-induced multimodal body-size distributions in ecosystems

    PubMed Central

    Lampert, Adam; Tlusty, Tsvi

    2013-01-01

    The size of an organism reflects its metabolic rate, growth rate, mortality, and other important characteristics; therefore, the distribution of body size is a major determinant of ecosystem structure and function. Body-size distributions often are multimodal, with several peaks of abundant sizes, and previous studies suggest that this is the outcome of niche separation: species from distinct peaks avoid competition by consuming different resources, which results in selection of different sizes in each niche. However, this cannot explain many ecosystems with several peaks competing over the same niche. Here, we suggest an alternative, generic mechanism underlying multimodal size distributions, by showing that the size-dependent tradeoff between reproduction and resource utilization entails an inherent resonance that may induce multiple peaks, all competing over the same niche. Our theory is well fitted to empirical data in various ecosystems, in which both model and measurements show a multimodal, periodically peaked distribution at larger sizes, followed by a smooth tail at smaller sizes. Moreover, we show a universal pattern of size distributions, manifested in the collapse of data from ecosystems of different scales: phytoplankton in a lake, metazoans in a stream, and arthropods in forests. The demonstrated resonance mechanism is generic, suggesting that multimodal distributions of numerous ecological characters emerge from the interplay between local competition and global migration. PMID:23248320

  8. Knife mill operating factors effect on switchgrass particle size distributions

    SciTech Connect

    Bitra, V.S.P.; Womac, A.R.; Yang, Y.T.; Igathinathane, C.; Miu, P.I; Chevanan, Nehru; Sokhansanj, Shahabaddine

    2009-06-01

    Biomass particle size impacts handling, storage, conversion, and dust control systems. Switchgrass (Panicum virgatum L.) particle size distributions created by a knife mill were determined for integral classifying screen sizes from 12.7 to 50.8 mm, operating speeds from 250 to 500 rpm, and mass input rates from 2 to 11 kg/min. Particle distributions were classified with standardized sieves for forage analysis that included horizontal sieving motion with machined-aluminum sieves of thickness proportional to sieve opening dimensions. Then, a wide range of analytical descriptors were examined to mathematically represent the range of particle sizes in the distributions. Correlation coefficient of geometric mean length with knife mill screen size, feed rate, and speed were 0.872, 0.349, and 0.037, respectively. Hence, knife mill screen size largely determined particle size of switchgrass chop. Feed rate had an unexpected influence on particle size, though to a lesser degree than screen size. The Rosin Rammler function fit the chopped switchgrass size distribution data with an R2 > 0.982. Mass relative span was greater than 1, which indicated a wide distribution of particle sizes. Uniformity coefficient was more than 4.0, which indicated a large assortment of particles and also represented a well-graded particle size distribution. Knife mill chopping of switchgrass produced strongly fine skewed mesokurtic particles with 12.7 25.4 mm screens and fine skewed mesokurtic particles with 50.8 mm screen. Results of this extensive analysis of particle sizes can be applied to selection of knife mill operating parameters to produce a particular size of switchgrass chop, and will serve as a guide for relations among the various analytic descriptors of biomass particle distributions.

  9. Knife mill operating factors effect on switchgrass particle size distributions.

    PubMed

    Bitra, Venkata S P; Womac, Alvin R; Yang, Yuechuan T; Igathinathane, C; Miu, Petre I; Chevanan, Nehru; Sokhansanj, Shahab

    2009-11-01

    Biomass particle size impacts handling, storage, conversion, and dust control systems. Switchgrass (Panicum virgatum L.) particle size distributions created by a knife mill were determined for integral classifying screen sizes from 12.7 to 50.8 mm, operating speeds from 250 to 500 rpm, and mass input rates from 2 to 11 kg/min. Particle distributions were classified with standardized sieves for forage analysis that included horizontal sieving motion with machined-aluminum sieves of thickness proportional to sieve opening dimensions. Then, a wide range of analytical descriptors were examined to mathematically represent the range of particle sizes in the distributions. Correlation coefficient of geometric mean length with knife mill screen size, feed rate, and speed were 0.872, 0.349, and 0.037, respectively. Hence, knife mill screen size largely determined particle size of switchgrass chop. Feed rate had an unexpected influence on particle size, though to a lesser degree than screen size. The Rosin-Rammler function fit the chopped switchgrass size distribution data with an R(2)>0.982. Mass relative span was greater than 1, which indicated a wide distribution of particle sizes. Uniformity coefficient was more than 4.0, which indicated a large assortment of particles and also represented a well-graded particle size distribution. Knife mill chopping of switchgrass produced 'strongly fine skewed mesokurtic' particles with 12.7-25.4 mm screens and 'fine skewed mesokurtic' particles with 50.8 mm screen. Results of this extensive analysis of particle sizes can be applied to selection of knife mill operating parameters to produce a particular size of switchgrass chop, and will serve as a guide for relations among the various analytic descriptors of biomass particle distributions.

  10. Interpretation of size-exclusion chromatography for the determination of molecular-size distribution of human immunoglobulins.

    PubMed

    Christians, S; Schluender, S; van Treel, N D; Behr-Gross, M-E

    2016-01-01

    Molecular-size distribution by size-exclusion chromatography (SEC) [1] is used for the quantification of unwanted aggregated forms in therapeutic polyclonal antibodies, referred to as human immunoglobulins (Ig) in the European Pharmacopoeia. Considering not only the requirements of the monographs for human normal Ig (0338, 0918 and 2788) [2-4], but also the general chapter on chromatographic techniques (2.2.46) [5], several chromatographic column types are allowed for performing this test. Although the EDQM knowledge database gives only 2 examples of suitable columns as a guide for the user, these monographs permit the use of columns with different lengths and diameters, and do not prescribe either particle size or pore size, which are considered key characteristics of SEC columns. Therefore, the columns used may differ significantly from each other with regard to peak resolution, potentially resulting in ambiguous peak identity assignment. In some cases, this may even lead to situations where the manufacturer and the Official Medicines Control Laboratory (OMCL) in charge of Official Control Authority Batch Release (OCABR) have differing molecular-size distribution profiles for aggregates of the same batch of Ig, even though both laboratories follow the requirements of the relevant monograph. In the present study, several formally acceptable columns and the peak integration results obtained therewith were compared. A standard size-exclusion column with a length of 60 cm and a particle size of 10 µm typically detects only 3 Ig fractions, namely monomers, dimers and polymers. This column type was among the first reliable HPLC columns on the market for this test and very rapidly became the standard for many pharmaceutical manufacturers and OMCLs for batch release testing. Consequently, the distribution of monomers, dimers and polymers was established as the basis for the interpretation of the results of the molecular-size distribution test in the relevant monographs

  11. Interpretation of size-exclusion chromatography for the determination of molecular-size distribution of human immunoglobulins.

    PubMed

    Christians, S; Schluender, S; van Treel, N D; Behr-Gross, M-E

    2016-01-01

    Molecular-size distribution by size-exclusion chromatography (SEC) [1] is used for the quantification of unwanted aggregated forms in therapeutic polyclonal antibodies, referred to as human immunoglobulins (Ig) in the European Pharmacopoeia. Considering not only the requirements of the monographs for human normal Ig (0338, 0918 and 2788) [2-4], but also the general chapter on chromatographic techniques (2.2.46) [5], several chromatographic column types are allowed for performing this test. Although the EDQM knowledge database gives only 2 examples of suitable columns as a guide for the user, these monographs permit the use of columns with different lengths and diameters, and do not prescribe either particle size or pore size, which are considered key characteristics of SEC columns. Therefore, the columns used may differ significantly from each other with regard to peak resolution, potentially resulting in ambiguous peak identity assignment. In some cases, this may even lead to situations where the manufacturer and the Official Medicines Control Laboratory (OMCL) in charge of Official Control Authority Batch Release (OCABR) have differing molecular-size distribution profiles for aggregates of the same batch of Ig, even though both laboratories follow the requirements of the relevant monograph. In the present study, several formally acceptable columns and the peak integration results obtained therewith were compared. A standard size-exclusion column with a length of 60 cm and a particle size of 10 µm typically detects only 3 Ig fractions, namely monomers, dimers and polymers. This column type was among the first reliable HPLC columns on the market for this test and very rapidly became the standard for many pharmaceutical manufacturers and OMCLs for batch release testing. Consequently, the distribution of monomers, dimers and polymers was established as the basis for the interpretation of the results of the molecular-size distribution test in the relevant monographs

  12. A multifunctional role of trialkylbenzenes for the preparation of aqueous colloidal mesostructured/mesoporous silica nanoparticles with controlled pore size, particle diameter, and morphology

    NASA Astrophysics Data System (ADS)

    Yamada, Hironori; Ujiie, Hiroto; Urata, Chihiro; Yamamoto, Eisuke; Yamauchi, Yusuke; Kuroda, Kazuyuki

    2015-11-01

    Both the pore size and particle diameter of aqueous colloidal mesostructured/mesoporous silica nanoparticles (CMSS/CMPS) derived from tetrapropoxysilane were effectively and easily controlled by the addition of trialkylbenzenes (TAB). Aqueous highly dispersed CMPS with large pores were successfully obtained through removal of surfactants and TAB by a dialysis process. The pore size (from 4 nm to 8 nm) and particle diameter (from 50 nm to 380 nm) were more effectively enlarged by the addition of 1,3,5-triisopropylbenzene (TIPB) than 1,3,5-trimethylbenzene (TMB), and the enlargement did not cause the variation of the mesostructure and particle morphology. The larger molecular size and higher hydrophobicity of TIPB than TMB induce the incorporation of TIPB into micelles without the structural change. When TMB was used as TAB, the pore size of CMSS was also enlarged while the mesostructure and particle morphology were varied. Interestingly, when tetramethoxysilane and TIPB were used, CMSS with a very small particle diameter (20 nm) with concave surfaces and large mesopores were obtained, which may strongly be related to the initial nucleation of CMSS. A judicious choice of TAB and Si sources is quite important to control the mesostructure, size of mesopores, particle diameter, and morphology.Both the pore size and particle diameter of aqueous colloidal mesostructured/mesoporous silica nanoparticles (CMSS/CMPS) derived from tetrapropoxysilane were effectively and easily controlled by the addition of trialkylbenzenes (TAB). Aqueous highly dispersed CMPS with large pores were successfully obtained through removal of surfactants and TAB by a dialysis process. The pore size (from 4 nm to 8 nm) and particle diameter (from 50 nm to 380 nm) were more effectively enlarged by the addition of 1,3,5-triisopropylbenzene (TIPB) than 1,3,5-trimethylbenzene (TMB), and the enlargement did not cause the variation of the mesostructure and particle morphology. The larger molecular size

  13. Optical heterodyne measurement of cloud droplet size distributions.

    PubMed

    Gollub, J P; Chabay, L; Flygare, W H

    1973-12-01

    Optical heterodyne spectra of laser light quasi-elastically scattered by falling water droplets (1-10-micro radius) in a diffusion cloud chamber were used to determine the droplet size distribution. The rate of fall depends on radius in a known way, thus yielding a heterodyne spectrum manifesting a distribution of Doppler shifts. This spectrum, in conjunction with the calculated Mie scattering intensity as a function of droplet radius, provides a direct measure of the droplet size distribution for droplets large enough that Brownian motion is negligible. The experiments described in this paper demonstrate the technique and establish the potential for further more quantitative studies of size distributions.

  14. Calculating Confidence Intervals for Effect Sizes Using Noncentral Distributions.

    ERIC Educational Resources Information Center

    Norris, Deborah

    This paper provides a brief review of the concepts of confidence intervals, effect sizes, and central and noncentral distributions. The use of confidence intervals around effect sizes is discussed. A demonstration of the Exploratory Software for Confidence Intervals (G. Cuming and S. Finch, 2001; ESCI) is given to illustrate effect size confidence…

  15. Effects of hydrophobic treatments of stone on pore water studied by continuous distribution analysis of NMR relaxation times.

    PubMed

    Appolonia, L; Borgia, G C; Bortolotti, V; Brown, R J; Fantazzini, P; Rezzaro, G

    2001-01-01

    The effects of protective hydrophobic products applied to porous media such as stone or mortar vary greatly with the product, the porous medium, and the mode of application. Nuclear Magnetic Resonance (NMR) measurements on fluids in the pore spaces of both treated and untreated samples can give information on the contact of the fluid with the internal surfaces, which is affected by all the above factors. Continuous distributions of relaxation times T(1) and T(2) of water in the pores of both synthetic and natural porous media were obtained before and after hydrophobic treatment. The synthetic porous media are ceramic filter materials characterized by narrow distributions of pore dimensions and show that the treatment does not produce large changes in the relaxation times of the water. For three travertine samples most of a long relaxation time component, presumably from the largest pores, remains after treatment, while the amplitude of an intermediate component is greatly reduced. For three pudding-stone samples, treatment leads to a substantial loss from the long component and an even greater loss from the intermediate component. PMID:11445343

  16. Magnetic relaxation -- coal swelling, extraction, pore size. Quarterly technical progress report, October 1, 1993--December 31, 1993

    SciTech Connect

    Doetschman, D.C.

    1993-12-31

    During this quarter, the CW (continuous wave) and pulsed EPR (electron paramagnetic resonance) have been examined of the swelled Argonne Premium whole coals and the swelled residues of these coals. The CW EPR spectra will not be of high quality due to the unexpectedly microwave-lossy character of the pyridine used for swelling. Being relatively unaffected by this characteristic, the pulsed EPR measurements of the spin relaxation times of the broad (non-inertinite) and narrow (inertinite) macerals have been completed. Although detailed analyses of these results have not yet been done, marked differences have been found between the relaxation times of the swelled and unswelled coals and residues. The most startling are the less than 200 nsec times T{sub 1} of the spin-lattice relaxation of the inertinite radicals in the swelled samples. The T{sub 1} of this maceral in the unswelled coal were approaching 1 millisecond. The T{sub 1} contrast was much less pronounced between the swelled and non-swelled non-inertinite macerals. The prospects of significant progress in coal pore size measurements with xenon and NMR (nuclear magnetic resonance) have dimmed since the beginning of this project. This assessment is based on the dearth of these types of studies, a paper at a contractors` meeting on this subject that did not materialize, and discussions with colleagues with experience with the technique in coals. Instead, the authors have been developing a pulsed EPR technique for the spin probing of molecular motion to be applied to pores in carbonaceous materials. This report contains a copy of a nearly final draft of a paper being prepared on the development of this technique, entitled {open_quotes}Physical Characterization of the State of Motion of the Phenalenyl Spin Probe in Cation-Exchanged Faujasite Zeolite Supercages with Pulsed EPR.{close_quotes}

  17. Mesoporous Silica Gel–Based Mixed Matrix Membranes for Improving Mass Transfer in Forward Osmosis: Effect of Pore Size of Filler

    PubMed Central

    Lee, Jian-Yuan; Wang, Yining; Tang, Chuyang Y.; Huo, Fengwei

    2015-01-01

    The efficiency of forward osmosis (FO) process is generally limited by the internal concentration polarization (ICP) of solutes inside its porous substrate. In this study, mesoporous silica gel (SG) with nominal pore size ranging from 4–30 nm was used as fillers to prepare SG-based mixed matrix substrates. The resulting mixed matrix membranes had significantly reduced structural parameter and enhanced membrane water permeability as a result of the improved surface porosity of the substrates. An optimal filler pore size of ~9 nm was observed. This is in direct contrast to the case of thin film nanocomposite membranes, where microporous nanoparticle fillers are loaded to the membrane rejection layer and are designed in such a way that these fillers are able to retain solutes while allowing water to permeate through them. In the current study, the mesoporous fillers are designed as channels to both water and solute molecules. FO performance was enhanced at increasing filler pore size up to 9 nm due to the lower hydraulic resistance of the fillers. Nevertheless, further increasing filler pore size to 30 nm was accompanied with reduced FO efficiency, which can be attributed to the intrusion of polymer dope into the filler pores. PMID:26592565

  18. Mesoporous Silica Gel-Based Mixed Matrix Membranes for Improving Mass Transfer in Forward Osmosis: Effect of Pore Size of Filler

    NASA Astrophysics Data System (ADS)

    Lee, Jian-Yuan; Wang, Yining; Tang, Chuyang Y.; Huo, Fengwei

    2015-11-01

    The efficiency of forward osmosis (FO) process is generally limited by the internal concentration polarization (ICP) of solutes inside its porous substrate. In this study, mesoporous silica gel (SG) with nominal pore size ranging from 4-30 nm was used as fillers to prepare SG-based mixed matrix substrates. The resulting mixed matrix membranes had significantly reduced structural parameter and enhanced membrane water permeability as a result of the improved surface porosity of the substrates. An optimal filler pore size of ~9 nm was observed. This is in direct contrast to the case of thin film nanocomposite membranes, where microporous nanoparticle fillers are loaded to the membrane rejection layer and are designed in such a way that these fillers are able to retain solutes while allowing water to permeate through them. In the current study, the mesoporous fillers are designed as channels to both water and solute molecules. FO performance was enhanced at increasing filler pore size up to 9 nm due to the lower hydraulic resistance of the fillers. Nevertheless, further increasing filler pore size to 30 nm was accompanied with reduced FO efficiency, which can be attributed to the intrusion of polymer dope into the filler pores.

  19. Mesoporous Silica Gel-Based Mixed Matrix Membranes for Improving Mass Transfer in Forward Osmosis: Effect of Pore Size of Filler.

    PubMed

    Lee, Jian-Yuan; Wang, Yining; Tang, Chuyang Y; Huo, Fengwei

    2015-11-23

    The efficiency of forward osmosis (FO) process is generally limited by the internal concentration polarization (ICP) of solutes inside its porous substrate. In this study, mesoporous silica gel (SG) with nominal pore size ranging from 4-30 nm was used as fillers to prepare SG-based mixed matrix substrates. The resulting mixed matrix membranes had significantly reduced structural parameter and enhanced membrane water permeability as a result of the improved surface porosity of the substrates. An optimal filler pore size of ~9 nm was observed. This is in direct contrast to the case of thin film nanocomposite membranes, where microporous nanoparticle fillers are loaded to the membrane rejection layer and are designed in such a way that these fillers are able to retain solutes while allowing water to permeate through them. In the current study, the mesoporous fillers are designed as channels to both water and solute molecules. FO performance was enhanced at increasing filler pore size up to 9 nm due to the lower hydraulic resistance of the fillers. Nevertheless, further increasing filler pore size to 30 nm was accompanied with reduced FO efficiency, which can be attributed to the intrusion of polymer dope into the filler pores.

  20. Size distribution of Amazon River bed sediment

    USGS Publications Warehouse

    Nordin, C.F.; Meade, R.H.; Curtis, W.F.; Bosio, N.J.; Landim, P.M.B.

    1980-01-01

    The first recorded observations of bed material of the Amazon River were made in 1843 by Lt William Lewis Herndon of the US Navy, when he travelled the river from its headwaters to its mouth, sounding its depths, and noting the nature of particles caught in a heavy grease smeared to the bottom of his sounding weight1. He reported the bed material of the river to be mostly sand and fine gravel. Oltman and Ames took samples at a few locations in 1963 and 1964, and reported the bed material at O??bidos, Brazil, to be fine sands, with median diameters ranging from 0.15 to 0.25 mm (ref. 2). We present here a summary of particle-size analyses of samples of streambed material collected from the Amazon River and its major tributaries along a reach of the river from Iquitos in Peru, ???3,500 km above Macapa?? Brazil, to a point 220 km above Macapa??3. ?? 1980 Nature Publishing Group.

  1. Mesoporous calcium-silicon xerogels with mesopore size and pore volume influence hMSC behaviors by load and sustained release of rhBMP-2.

    PubMed

    Song, Wenhua; Li, Xiangde; Qian, Jun; Lv, Guoyu; Yan, Yonggang; Su, Jiacan; Wei, Jie

    2015-01-01

    Mesoporous calcium-silicon xerogels with a pore size of 15 nm (MCS-15) and pore volume of 1.43 cm(3)/g were synthesized by using 1,3,5-mesitylene (TMB) as the pore-expanding agent. The MCS-15 exhibited good degradability with the weight loss of 50 wt% after soaking in Tris-HCl solution for 56 days, which was higher than the 30 wt% loss shown by mesoporous calcium-silicon xerogels with a pore size of 4 nm (MCS-4). The pore size and pore volume of MCS-15 had significant influences on load and release of recombinant human bone morphogenetic protein-2 (rhBMP-2). The MCS-15 had a higher capacity to encapsulate a large amount of rhBMP-2; it could adsorb 45 mg/g of rhBMP-2 in phosphate-buffered saline after 24 hours, which was more than twice that with MCS-4 (20 mg/g). Moreover, the MCS-15 system exhibited sustained release of rhBMP-2 as compared with MCS-4 system (showing a burst release). The MCS-15/rhBMP-2 system could promote the proliferation and differentiation of human mesenchymal stem cells, showing good cytocompatibility and bioactivity. The results indicated that MCS-15, with larger mesopore size and higher pore volume, might be a promising carrier for loading and sustained release of rhBMP-2, which could be used as bone repair material with built-in osteoinduction function in bone reconstruction.

  2. Mesoporous calcium–silicon xerogels with mesopore size and pore volume influence hMSC behaviors by load and sustained release of rhBMP-2

    PubMed Central

    Song, Wenhua; Li, Xiangde; Qian, Jun; Lv, Guoyu; Yan, Yonggang; Su, Jiacan; Wei, Jie

    2015-01-01

    Mesoporous calcium–silicon xerogels with a pore size of 15 nm (MCS-15) and pore volume of 1.43 cm3/g were synthesized by using 1,3,5-mesitylene (TMB) as the pore-expanding agent. The MCS-15 exhibited good degradability with the weight loss of 50 wt% after soaking in Tris-HCl solution for 56 days, which was higher than the 30 wt% loss shown by mesoporous calcium–silicon xerogels with a pore size of 4 nm (MCS-4). The pore size and pore volume of MCS-15 had significant influences on load and release of recombinant human bone morphogenetic protein-2 (rhBMP-2). The MCS-15 had a higher capacity to encapsulate a large amount of rhBMP-2; it could adsorb 45 mg/g of rhBMP-2 in phosphate-buffered saline after 24 hours, which was more than twice that with MCS-4 (20 mg/g). Moreover, the MCS-15 system exhibited sustained release of rhBMP-2 as compared with MCS-4 system (showing a burst release). The MCS-15/rhBMP-2 system could promote the proliferation and differentiation of human mesenchymal stem cells, showing good cytocompatibility and bioactivity. The results indicated that MCS-15, with larger mesopore size and higher pore volume, might be a promising carrier for loading and sustained release of rhBMP-2, which could be used as bone repair material with built-in osteoinduction function in bone reconstruction. PMID:25784801

  3. Analytic scaling function for island-size distributions.

    PubMed

    Dubrovskii, V G; Sibirev, N V

    2015-04-01

    We obtain an explicit solution for the island-size distribution described by the rate equations for irreversible growth with the simplified capture rates of the form σ(s)(Θ)∝Θ(p)(a+s-1) for all s≥1, where s is the size and Θ is the time-dependent coverage. The intrinsic property of this solution is its scaling form in the continuum limit. The analytic scaling function depends on the two parameters a and p and is capable of describing very dissimilar distribution shapes, both monomodal and monotonically decreasing. The obtained results suggest that the scaling features of the size distributions are closely related to the size linearity of the capture rates. A simple analytic scaling is obtained rigorously here and helps to gain a better theoretical understanding of possible origins of the scaling behavior of the island-size distributions. PMID:25974509

  4. Size distributions of quantum islands on stepped substrates.

    PubMed

    Liang, S; Zhu, H L; Wang, W

    2009-10-21

    The size distributions of self-assembled quantum islands on stepped substrates are studied using kinetic Monte Carlo simulations. It is found that the energy barrier E(SW) between the step and the terrace region is the key factor in affecting the size distribution of islands. With small E(SW) (< or = 0.1 eV), lines of uniform islands can be obtained at relative low surface coverage. As the surface coverage is increased, wirelike islands can be obtained. Scaling behavior is obeyed for the size distributions of the wirelike islands. When the size distributions are separated into their width and length components, however, scaling is only observed in the length distribution of the wirelike islands. With larger E(SW), the size distribution of islands shows a clear bimodal size distribution and anomalous growth temperature dependent island size evolutions are observed. The simulation results reproduce qualitatively the phenomena observed in the cases of InAs islands grown on stepped GaAs substrates.

  5. Intercomparison of 15 aerodynamic particle size spectrometers (APS 3321): uncertainties in particle sizing and number size distribution

    NASA Astrophysics Data System (ADS)

    Pfeifer, Sascha; Müller, Thomas; Weinhold, Kay; Zikova, Nadezda; Martins dos Santos, Sebastiao; Marinoni, Angela; Bischof, Oliver F.; Kykal, Carsten; Ries, Ludwig; Meinhardt, Frank; Aalto, Pasi; Mihalopoulos, Nikolaos; Wiedensohler, Alfred

    2016-04-01

    Aerodynamic particle size spectrometers are a well-established method to measure number size distributions of coarse mode particles in the atmosphere. Quality assurance is essential for atmospheric observational aerosol networks to obtain comparable results with known uncertainties. In a laboratory study within the framework of ACTRIS (Aerosols, Clouds, and Trace gases Research Infrastructure Network), 15 aerodynamic particle size spectrometers (APS model 3321, TSI Inc., St. Paul, MN, USA) were compared with a focus on flow rates, particle sizing, and the unit-to-unit variability of the particle number size distribution. Flow rate deviations were relatively small (within a few percent), while the sizing accuracy was found to be within 10 % compared to polystyrene latex (PSL) reference particles. The unit-to-unit variability in terms of the particle number size distribution during this study was within 10 % to 20 % for particles in the range of 0.9 up to 3 µm, which is acceptable for atmospheric measurements. For particles smaller than that, the variability increased up to 60 %, probably caused by differences in the counting efficiencies of individual units. Number size distribution data for particles smaller than 0.9 µm in aerodynamic diameter should only be used with caution. For particles larger than 3 µm, the unit-to-unit variability increased as well. A possible reason is an insufficient sizing accuracy in combination with a steeply sloping particle number size distribution and the increasing uncertainty due to decreasing counting. Particularly this uncertainty of the particle number size distribution must be considered if higher moments of the size distribution such as the particle volume or mass are calculated, which require the conversion of the aerodynamic diameter measured to a volume equivalent diameter. In order to perform a quantitative quality assurance, a traceable reference method for the particle number concentration in the size range 0.5-3 µm

  6. Scale invariance of incident size distributions in response to sizes of their causes.

    PubMed

    Englehardt, James D

    2002-04-01

    Incidents can be defined as low-probability, high-consequence events and lesser events of the same type. Lack of data on extremely large incidents makes it difficult to determine distributions of incident size that reflect such disasters, even though they represent the great majority of total losses. If the form of the incident size distribution can be determined, then predictive Bayesian methods can be used to assess incident risks from limited available information. Moreover, incident size distributions have generally been observed to have scale invariant, or power law, distributions over broad ranges. Scale invariance in the distributions of sizes of outcomes of complex dynamical systems has been explained based on mechanistic models of natural and built systems, such as models of self-organized criticality. In this article, scale invariance is shown to result also as the maximum Shannon entropy distribution of incident sizes arising as the product of arbitrary functions of cause sizes. Entropy is shown by simulation and derivation to be maximized as a result of dependence, diversity, abundance, and entropy of multiplicative cause sizes. The result represents an information-theoretic explanation of invariance, parallel to those of mechanistic models. For example, distributions of incident size resulting from 30 partially dependent causes are shown to be scale invariant over several orders of magnitude. Empirical validation of power law distributions of incident size is reviewed, and the Pareto (power law) distribution is validated against oil spill, hurricane, and insurance data. The applicability of the Pareto distribution, in particular, for assessment of total losses over a planning period is discussed. Results justify the use of an analytical, predictive Bayesian version of the Pareto distribution, derived previously, to assess incident risk from available data.

  7. The Size Distribution of Jupiter-Family Cometary Nuclei

    NASA Technical Reports Server (NTRS)

    Weissman, Paul R.; Lowry, Stephen C.

    2003-01-01

    Introduction: We are continuing our program to determine the size distribution of cometary nuclei. We have compiled a catalog of 105 measurements of 57 cometary nuclei, drawn from the general literature, from our own program of CCD photometry of distant cometary nuclei (Lowry and Weissman), and from unpublished observations by colleagues. We model the cumulative size distribution of the nuclei as a power law. Previous determinations of the size distribution slope do not agree. Fernandez et al. found a slope of alpha = 2.65+/-0.25 whereas Lowry et al. and Weissman and Lowry each found a slope of alpha = 1.60+/-0.10.

  8. (99m)Tc-human serum albumin nanocolloids: particle sizing and radioactivity distribution.

    PubMed

    Persico, Marco G; Lodola, Lorenzo; Buroni, Federica E; Morandotti, Marco; Pallavicini, Piersandro; Aprile, Carlo

    2015-07-01

    Several parameters affect the biodistribution of administered nanocolloids (NC) for Sentinel Lymph Node (SLN) detection: particle size distribution, number of Tc atoms per particle and specific activity (SA). Relatively few data are available with frequently conflicting results. (99m)Tc-NC-human serum albumin (HSA) Nanocoll®, Nanoalbumon® and Nanotop® were analysed for particles' dimensional and radioactivity distribution, and a mathematical model was elaborated to estimate the number of particles involved. Commercially available kits were reconstituted at maximal SA of 11 MBq/µg HSA. Particles size distribution was evaluated by Dynamic Light Scattering. These data were related to the radioactivity distribution analysis passing labelled NC through three polycarbonate filters (15-30-50-nm pore size) under vacuum. Highest radioactivity was carried by 30-50 nm particles. The smallest ones, even though most numerous, carried only the 10% of (99m)Tc atoms. Nanocoll and Nanotop are not significantly different, while Nanoalbumon is characterized by largest particles (>30 nm) that carried the most of radioactivity (80%). Smallest particles could saturate the clearing capacity of macrophages; therefore, if the tracer is used for SLN detection, more node tiers could be visualized, reducing accuracy of SLN mapping. Manufacturers could implement technical leaflets with particle size distribution and could improve the labelling protocol to provide clinicians useful information.

  9. Scaling of spin-echo amplitudes with frequency, diffusion coefficient, pore size, and susceptibility difference for the NMR of fluids in porous media and biological tissues

    NASA Astrophysics Data System (ADS)

    Borgia, Giulio C.; Brown, Robert J. S.; Fantazzini, Paola

    1995-03-01

    Both Carr-Purcell-Meiboom-Gill (CPMG) measurements and single-spin-echo measurements have been made at frequencies of ν=10, 20, and 50 MHz for two relatively homogeneous porous porcelain materials with different pore sizes, both saturated separately with three liquids of different diffusion coefficients. The CPMG transverse relaxation rate is increased by an amount R by diffusion in the inhomogeneous fields caused by susceptibility differences χ R shows the dependence on τ (half the echo spacing) given by the model of Brown and Fantazzini [Phys. Rev. B 47, 14 823 (1993)] if relaxation is slow enough that there are several CPMG echoes in a transverse relaxation time. For τ values over a range of a factor of about 40, the increase of R with τ is nearly linear, with a slope that is independent of pore dimension a and diffusion coefficient D. For this nearly linear region and a short initial region quadratic in τ, we find R~(χν)2. In these regions we can scale and compare measurements of R taken for different values of χ ν, a, and D by plotting RD/(1/3χνa)2 vs Dτ/a2. The asymptotic values of R for large τ for CPMG data can be inferred from the asymptotic slope, -Rs, of lnM (magnetization) for single spin echoes as a function of echo time t=2τ. It is shown from the Bloch-Torrey equations for NMR with diffusion that, for any combination of parameters χ, ν, a, or D, the magnetization M is a function of both a dimensionless time (either tu=Dt/a2 or tv=1/3χνt) and a dimensionless parameter ξ=1/3χνa2/D. If ξ<2 (for our particular porous media and definition of the distance a), the asymptotic slope of -lnM is approximately Rs=1/3χν, that is, it is proportional to only the first power of χν and does not depend on either a or D. These results are compatible with the existence of a long-tailed distribution of phases, such as a truncated Cauchy distribution, at echo time. Diffusion does not lead to a reduction of Rs because averages of choices from a

  10. Pore water distributions of dissolved copper and copper-complexing ligands in estuarine and coastal marine sediments

    SciTech Connect

    Skrabal, S.A.; Donat, J.R.; Burdige, D.J.

    2000-06-01

    The distributions and seasonal variability of total dissolved Cu (TDCu) and Cu-complexing ligands in sediment pore waters have been investigated at two contrasting sites in the Chesapeake Bay. Two ligand classes, which differ on the basis of the conditional stability constants (K{prime}{sub cond}) of their Cu complexes, were detected at all depths at both sites. For comparison, one pore water profile from a slope station off of the Chesapeake Bay also showed the presence of two ligand classes. Virtually all TDCu fluxing from these sediments is complexed during sediment-water exchange. A relatively small fraction of the TDCu is exchanged as inorganic species, which are widely regarded as the most bioavailable form of Cu. Total ligand concentrations are 15 to >100 times higher in the upper intervals of the pore waters relative to ligand concentrations in the bottom waters of the Chesapeake Bay (30--60 nM), consistent with previous observations of fluxes of these ligands from the sediments to overlying waters. These results suggest that sediments are potentially significant sources of Cu-complexing ligands to the overlying waters of the Chesapeake Bay, and perhaps, other shallow water estuarine and coastal environments. Copper-complexing ligands released from sediment pore waters may play an important role in influencing Cu speciation in overlying waters.

  11. The pore size of non-graminaceous plant cell walls is rapidly decreased by borate ester cross-linking of the pectic polysaccharide rhamnogalacturonan II

    SciTech Connect

    Fleischer, A.; O'Neill, M.A.; Ehwald, R.

    1999-11-01

    The walls of suspension-cultured Chenopodium album L. cells grown continually for more than 1 year on B-deficient medium contained monomeric rhamnogalacturonan (mRG-II) but not the borate ester cross-linked RG II dimer (dRG-II-B). The walls of these cells had an increased size limit for dextran permeation, which is a measure of wall pore size. Adding boric acid to growing B-deficient cells resulted in B binding to the wall, the formation of dRG-II-B from mRG-II, and a reduction in wall pore size within 10 min. The wall pore size of denatured B-grown cells was increased by treatment at pH {le} 2.0 or by treatment with Ca{sup 2+}-chelating agents. The acid-mediated increase in wall pore size was prevented by boric acid alone at pH 2.0 and by boric acid together with Ca{sup 2+}, but not by Na{sup +} or Mg{sup 2+} ions at pH 1.5. The Ca{sup 2+}-chelator-mediated increase in pore size was partially reduced by boric acid. Their results suggest that B-mediated cross-linking of RG-II in the walls of living plant cells generates a pectin network with a decreased size exclusion limit for polymers. The formation, stability, and possible functions of a borate ester cross-linked pectic network in the primary walls of nongraminaceous plant cells are discussed.

  12. The Pore Size of Non-Graminaceous Plant Cell Walls Is Rapidly Decreased by Borate Ester Cross-Linking of the Pectic Polysaccharide Rhamnogalacturonan II1

    PubMed Central

    Fleischer, Axel; O'Neill, Malcolm A.; Ehwald, Rudolf

    1999-01-01

    The walls of suspension-cultured Chenopodium album L. cells grown continually for more than 1 year on B-deficient medium contained monomeric rhamnogalacturonan II (mRG-II) but not the borate ester cross-linked RG II dimer (dRG-II-B). The walls of these cells had an increased size limit for dextran permeation, which is a measure of wall pore size. Adding boric acid to growing B-deficient cells resulted in B binding to the wall, the formation of dRG-II-B from mRG-II, and a reduction in wall pore size within 10 min. The wall pore size of denatured B-grown cells was increased by treatment at pH ≤ 2.0 or by treatment with Ca2+-chelating agents. The acid-mediated increase in wall pore size was prevented by boric acid alone at pH 2.0 and by boric acid together with Ca2+, but not by Na+ or Mg2+ ions at pH 1.5. The Ca2+-chelator-mediated increase in pore size was partially reduced by boric acid. Our results suggest that B-mediated cross-linking of RG-II in the walls of living plant cells generates a pectin network with a decreased size exclusion limit for polymers. The formation, stability, and possible functions of a borate ester cross-linked pectic network in the primary walls of nongraminaceous plant cells are discussed. PMID:10557231

  13. What We Can Learn From Supernova Remnant Size Distributions

    NASA Astrophysics Data System (ADS)

    Elwood, Benjamin; Murphy, Jeremiah; Diaz, Mariangelly

    2016-01-01

    Previous literature regarding size distributions of supernova remnants generally discuss a uniform distribution for the radius, occasionally considering a Gaussian alternative. We indeed show that these distributions are consistent with log-normal, which can be considered a natural consequence of the Central Limit Theorem and Sedov expansion. Modeling explosion energy, remnant age, and ambient density as independent, random distributions, we show, using simple Monte Carlo simulations, that the size distribution is indistinguishable from log-normal when the SNR sample size is of order three hundred. This implies that these SNR distributions provide only information on the mean and variance, yielding additional information only when the sample size grows large. We then proceed to Bayesian statistical inference to characterize the information provided by the size distributions. In particular, we use the mean and variance of sizes and explosion energies to subsequently estimate the mean and variance of the ambient medium surrounding SNR progenitors. This in turn allows us to characterize potential bias in studies involving samples of supernova remnants.

  14. Determination of aerosol size distributions from spectral attenuation measurements.

    PubMed

    Grassl, H

    1971-11-01

    An iteration method for the determination of size distributions of aerosols from spectral attenuation data, similar to the one previously published for clouds, is presented. The basis for this iteration is to consider the extinction efficiency factor of particles as a set of weighting functions covering the entire radius region of a distribution. The weighting functions were calculated exactly from the Mie theory. Aerosol distributions are shown derived from tests with analytical size distributions and also generated from measured aerosol extinction data in seven spectral channels from 0.4-microto 10-micro wavelength in continental aerosols. The influence of relative humidity on the complex index of refraction is also discussed.

  15. Applicability of colloid filtration theory in size-distributed, reduced porosity, granular media in the absence of energy barriers.

    PubMed

    Pazmino, Eddy F; Ma, Huilian; Johnson, William P

    2011-12-15

    The vast majority of colloid transport experiments use granular porous media with narrow size distribution to facilitate comparison with colloid filtration theory, which represents porous media with a single collector size. In this work we examine retention of colloids ranging in size from 0.21 to 9.1 μm in diameter, in columns packed with uniform and size-distributed borosilicate glass bead porous media with porosity ranging from 0.38 to 0.28. Conditions were favorable to attachment (absent a significant energy barrier). The goal was to determine the applicability of colloid filtration theory to colloid retention in these media. We also directly observed deposition at the pore scale in packed flow cells. The pore domain was characterized via high resolution computerized X-ray micro tomography (HRXMT). The flow field was examined using Lattice-Boltzmann flow simulation methods (LBM). The influence of preferential flow paths on colloid retention in the lowest porosity media was accounted for by correcting the fluid velocity. Straining in pore throats too small to pass was not a significant contributor to colloid retention despite colloid-to-collector size ratios up to 0.05. Mechanistic simulations via the Ma-Pedel-Fife-Johnson correlation equation (MPFJ) for colloid filtration predicted the experimentally observed trends in deposition with porosity when a number-based mean grain size was used.

  16. SELF-CONSISTENT SIZE AND VELOCITY DISTRIBUTIONS OF COLLISIONAL CASCADES

    SciTech Connect

    Pan, Margaret; Schlichting, Hilke E. E-mail: hilke@ucla.edu

    2012-03-10

    The standard theoretical treatment of collisional cascades derives a steady-state size distribution assuming a single constant velocity dispersion for all bodies regardless of size. Here we relax this assumption and solve self-consistently for the bodies' steady-state size and size-dependent velocity distributions. Specifically, we account for viscous stirring, dynamical friction, and collisional damping of the bodies' random velocities in addition to the mass conservation requirement typically applied to find the size distribution in a steady-state cascade. The resulting size distributions are significantly steeper than those derived without velocity evolution. For example, accounting self-consistently for the velocities can change the standard q = 3.5 power-law index of the Dohnanyi differential size spectrum to an index as large as q = 4. Similarly, for bodies held together by their own gravity, the corresponding power-law index range 2.88 < q < 3.14 of Pan and Sari can steepen to values as large as q = 3.26. Our velocity results allow quantitative predictions of the bodies' scale heights as a function of size. Together with our predictions, observations of the scale heights for different-sized bodies for the Kuiper belt, the asteroid belt, and extrasolar debris disks may constrain the mass and number of large bodies stirring the cascade as well as the colliding bodies' internal strengths.

  17. 4D Imaging of Salt Precipitation during Evaporation from Saline Porous Media Influenced by the Particle Size Distribution

    NASA Astrophysics Data System (ADS)

    Norouzi Rad, M.; Shokri, N.

    2014-12-01

    Understanding the physics of water evaporation from saline porous media is important in many processes such as evaporation from porous media, vegetation, plant growth, biodiversity in soil, and durability of building materials. To investigate the effect of particle size distribution on the dynamics of salt precipitation in saline porous media during evaporation, we applied X-ray micro-tomography technique. Six samples of quartz sand with different grain size distributions were used in the present study enabling us to constrain the effects of particle and pore sizes on salt precipitation patterns and dynamics. The pore size distributions were computed using the pore-scale X-ray images. The packed beds were saturated with NaCl solution of 3 Molal and the X-ray imaging was continued for one day with temporal resolution of 30 min resulting in pore scale information about the evaporation and precipitation dynamics. Our results show more precipitation at the early stage of the evaporation in the case of sand with the larger particle size due to the presence of fewer evaporation sites at the surface. The presence of more preferential evaporation sites at the surface of finer sands significantly modified the patterns and thickness of the salt crust deposited on the surface such that a thinner salt crust was formed in the case of sand with smaller particle size covering larger area at the surface as opposed to the thicker patchy crusts in samples with larger particle sizes. Our results provide new insights regarding the physics of salt precipitation in porous media during evaporation.

  18. Temporal and Spatial Pore Water Pressure Distribution Surrounding a Vertical Landfill Leachate Recirculation Well

    PubMed Central

    Kadambala, Ravi; Townsend, Timothy G.; Jain, Pradeep; Singh, Karamjit

    2011-01-01

    Addition of liquids into landfilled waste can result in an increase in pore water pressure, and this in turn may increase concerns with respect to geotechnical stability of the landfilled waste mass. While the impact of vertical well leachate recirculation on landfill pore water pressures has been mathematically modeled, measurements of these systems in operating landfills have not been reported. Pressure readings from vibrating wire piezometers placed in the waste surrounding a liquids addition well at a full-scale operating landfill in Florida were recorded over a 2-year period. Prior to the addition of liquids, measured pore pressures were found to increase with landfill depth, an indication of gas pressure increase and decreasing waste permeability with depth. When liquid addition commenced, piezometers located closer to either the leachate injection well or the landfill surface responded more rapidly to leachate addition relative to those far from the well and those at deeper locations. After liquid addition stopped, measured pore pressures did not immediately drop, but slowly decreased with time. Despite the large pressures present at the bottom of the liquid addition well, much smaller pressures were measured in the surrounding waste. The spatial variation of the pressures recorded in this study suggests that waste permeability is anisotropic and decreases with depth. PMID:21655145

  19. Temporal and spatial pore water pressure distribution surrounding a vertical landfill leachate recirculation well.

    PubMed

    Kadambala, Ravi; Townsend, Timothy G; Jain, Pradeep; Singh, Karamjit

    2011-05-01

    Addition of liquids into landfilled waste can result in an increase in pore water pressure, and this in turn may increase concerns with respect to geotechnical stability of the landfilled waste mass. While the impact of vertical well leachate recirculation on landfill pore water pressures has been mathematically modeled, measurements of these systems in operating landfills have not been reported. Pressure readings from vibrating wire piezometers placed in the waste surrounding a liquids addition well at a full-scale operating landfill in Florida were recorded over a 2-year period. Prior to the addition of liquids, measured pore pressures were found to increase with landfill depth, an indication of gas pressure increase and decreasing waste permeability with depth. When liquid addition commenced, piezometers located closer to either the leachate injection well or the landfill surface responded more rapidly to leachate addition relative to those far from the well and those at deeper locations. After liquid addition stopped, measured pore pressures did not immediately drop, but slowly decreased with time. Despite the large pressures present at the bottom of the liquid addition well, much smaller pressures were measured in the surrounding waste. The spatial variation of the pressures recorded in this study suggests that waste permeability is anisotropic and decreases with depth. PMID:21655145

  20. INITIAL PLANETESIMAL SIZES AND THE SIZE DISTRIBUTION OF SMALL KUIPER BELT OBJECTS

    SciTech Connect

    Schlichting, Hilke E.; Fuentes, Cesar I.; Trilling, David E.

    2013-08-01

    The Kuiper Belt is a remnant from the early solar system and its size distribution contains many important constraints that can be used to test models of planet formation and collisional evolution. We show, by comparing observations with theoretical models, that the observed Kuiper Belt size distribution is well matched by coagulation models, which start with an initial planetesimal population with radii of about 1 km, and subsequent collisional evolution. We find that the observed size distribution above R {approx} 30 km is primordial, i.e., it has not been modified by collisional evolution over the age of the solar system, and that the size distribution below R {approx} 30 km has been modified by collisions and that its slope is well matched by collisional evolution models that use published strength laws. We investigate in detail the resulting size distribution of bodies ranging from 0.01 km to 30 km and find that its slope changes several times as a function of radius before approaching the expected value for an equilibrium collisional cascade of material strength dominated bodies for R {approx}< 0.1 km. Compared to a single power-law size distribution that would span the whole range from 0.01 km to 30 km, we find in general a strong deficit of bodies around R {approx} 10 km and a strong excess of bodies around 2 km in radius. This deficit and excess of bodies are caused by the planetesimal size distribution left over from the runaway growth phase, which left most of the initial mass in small planetesimals while only a small fraction of the total mass is converted into large protoplanets. This excess mass in small planetesimals leaves a permanent signature in the size distribution of small bodies that is not erased after 4.5 Gyr of collisional evolution. Observations of the small Kuiper Belt Object (KBO) size distribution can therefore test if large KBOs grew as a result of runaway growth and constrained the initial planetesimal sizes. We find that results from

  1. A statistical approach to estimate the 3D size distribution of spheres from 2D size distributions

    USGS Publications Warehouse

    Kong, M.; Bhattacharya, R.N.; James, C.; Basu, A.

    2005-01-01

    Size distribution of rigidly embedded spheres in a groundmass is usually determined from measurements of the radii of the two-dimensional (2D) circular cross sections of the spheres in random flat planes of a sample, such as in thin sections or polished slabs. Several methods have been devised to find a simple factor to convert the mean of such 2D size distributions to the actual 3D mean size of the spheres without a consensus. We derive an entirely theoretical solution based on well-established probability laws and not constrained by limitations of absolute size, which indicates that the ratio of the means of measured 2D and estimated 3D grain size distribution should be r/4 (=.785). Actual 2D size distribution of the radii of submicron sized, pure Fe0 globules in lunar agglutinitic glass, determined from backscattered electron images, is tested to fit the gamma size distribution model better than the log-normal model. Numerical analysis of 2D size distributions of Fe0 globules in 9 lunar soils shows that the average mean of 2D/3D ratio is 0.84, which is very close to the theoretical value. These results converge with the ratio 0.8 that Hughes (1978) determined for millimeter-sized chondrules from empirical measurements. We recommend that a factor of 1.273 (reciprocal of 0.785) be used to convert the determined 2D mean size (radius or diameter) of a population of spheres to estimate their actual 3D size. ?? 2005 Geological Society of America.

  2. Nanocrystal size distribution analysis from transmission electron microscopy images

    NASA Astrophysics Data System (ADS)

    van Sebille, Martijn; van der Maaten, Laurens J. P.; Xie, Ling; Jarolimek, Karol; Santbergen, Rudi; van Swaaij, René A. C. M. M.; Leifer, Klaus; Zeman, Miro

    2015-12-01

    We propose a method, with minimal bias caused by user input, to quickly detect and measure the nanocrystal size distribution from transmission electron microscopy (TEM) images using a combination of Laplacian of Gaussian filters and non-maximum suppression. We demonstrate the proposed method on bright-field TEM images of an a-SiC:H sample containing embedded silicon nanocrystals with varying magnifications and we compare the accuracy and speed with size distributions obtained by manual measurements, a thresholding method and PEBBLES. Finally, we analytically consider the error induced by slicing nanocrystals during TEM sample preparation on the measured nanocrystal size distribution and formulate an equation to correct this effect.We propose a method, with minimal bias caused by user input, to quickly detect and measure the nanocrystal size distribution from transmission electron microscopy (TEM) images using a combination of Laplacian of Gaussian filters and non-maximum suppression. We demonstrate the proposed method on bright-field TEM images of an a-SiC:H sample containing embedded silicon nanocrystals with varying magnifications and we compare the accuracy and speed with size distributions obtained by manual measurements, a thresholding method and PEBBLES. Finally, we analytically consider the error induced by slicing nanocrystals during TEM sample preparation on the measured nanocrystal size distribution and formulate an equation to correct this effect. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr06292f

  3. Mass transfer kinetic mechanism in monolithic columns and application to the characterization of new research monolithic samples with different average pore sizes.

    PubMed

    Gritti, Fabrice; Guiochon, Georges

    2009-06-01

    A general reduced HETP (height equivalent to a theoretical plate) equation is proposed that accounts for the mass transfer of a wide range of molecular weight compounds in monolithic columns. The detailed derivatization of each one of the individual and independent mass transfer contributions (longitudinal diffusion, eddy dispersion, film mass transfer resistance, and trans-skeleton mass transfer resistance) is discussed. The reduced HETPs of a series of small molecules (phenol, toluene, acenaphthene, and amylbenzene) and of a larger molecule, insulin, were measured on three research grade monolithic columns (M150, M225, M350) having different average pore size (approximately 150, 225, and 350 A, respectively) but the same dimension (100 mm x 4.6 mm). The first and second central moments of 2 muL samples were measured and corrected for the extra-column contributions. The h data were fitted to the new HETP equation in order to identify which contribution controls the band broadening in monolithic columns. The contribution of the B-term was found to be negligible compared to that of the A-term, even at very low reduced velocities (nu<1). At moderate velocities (1size and molecular diffusivity of the compound studied due to faster mass transfer across the column. Experimental chromatograms exhibited variable degrees of systematic peak fronting, depending on the column studied. The heterogeneity of the distribution of eluent velocities from the column center to its wall (average 5%) is the source of this peak fronting. At high reduced velocities (nu>5), the C-term of the monolithic columns is controlled by film mass transfer resistance between the eluent circulating in the large throughpores and the eluent stagnant inside the thin porous skeleton. The experimental Sherwood number measured on the monolith columns increases from 0.05 to 0.22 while the adsorption energy increases by nearly 6 k

  4. Dissolved sulfide distributions in the water column and sediment pore waters of the Santa Barbara Basin

    USGS Publications Warehouse

    Kuwabara, J.S.; VanGeen, A.; McCorkle, D.C.; Bernhard, J.M.

    1999-01-01

    Dissolved sulfide concentrations in the water column and in sediment pore waters were measured by square-wave voltammetry (nanomolar detection limit) during three cruises to the Santa Barbara Basin in February 1995, November-December 1995, and April 1997. In the water column, sulfide concentrations measured outside the basin averaged 3 ?? 1 nM (n = 28) in the 0 to 600 m depth range. Inside the basin, dissolved sulfides increased to reach values of up to 15 nM at depths >400 m. A suite of box cores and multicores collected at four sites along the northeastern flank of the basin showed considerable range in surficial (400 ??M at 10 cm. Decreases in water-column nitrate below the sill depth indicate nitrate consumption (-55 to -137 ??mole m-2 h-1) similar to nearby Santa Monica Basin. Peaks in pore-water iron concentrations were generally observed between 2 and 5 cm depth with shallowest peaks at the 590 m site. These observations, including observations of the benthic microfauna, suggest that the extent to which the sulfide flux, sustained by elevated pore-water concentrations, reaches the water column may be modulated by the abundance of sulfide-oxidizing bacteria in addition to iron redox and precipitation reactions.

  5. Airborne Particle Size Distribution Measurements at USDOE Fernald

    SciTech Connect

    Harley, N.H.; Chittaporn, P.; Heikkinen, M.; Medora, R.; Merrill, R.

    2003-03-27

    There are no long term measurements of the particle size distribution and concentration of airborne radionuclides at any USDOE facility except Fernald. Yet the determinant of lung dose is the particle size, determining the airway and lower lung deposition. Beginning in 2000, continuous (6 to 8 weeks) measurements of the aerosol particle size distribution have been made with a miniature sampler developed under EMSP. Radon gas decays to a chain of four short lived solid radionuclides that attach immediately to the resident atmospheric aerosol. These in turn decay to long lived polonium 210. Alpha emitting polonium is a tracer for any atmospheric aerosol. Six samplers at Fernald and four at QC sites in New Jersey show a difference in both polonium concentration and size distribution with the winter measurements being higher/larger than summer by almost a factor of two at all locations. EMSP USDOE Contract DE FG07 97ER62522.

  6. Characterization of events by aerosol mass size distributions.

    PubMed

    Nicolás, José; Yubero, Eduardo; Galindo, Nuria; Giménez, Joaquín; Castañer, Ramón; Carratalá, Adoración; Crespo, Javier; Pastor, Carlos

    2009-02-01

    Continuous measurements of particle mass size distributions were carried out in summer 2004 at an urban location in the western Mediterranean using an optical particle counter. In this work we propose a simple methodology to identify PM episodes and determine their influence on mass size distributions. During the study period three types of event produced a significant increase in TSP daily levels: Saharan dust intrusions, firework displays and strong winds, modifying size distributions in different ways. As well, a traffic-related mass size spectrum was obtained showing road dust particles injected into the atmosphere by vehicle-induced resuspension having mainly aerodynamic diameters between 5 and 15 microm. This was confirmed by principal component and conditional probability function analyses.

  7. Particle size and shape distributions of hammer milled pine

    SciTech Connect

    Westover, Tyler Lott; Matthews, Austin Colter; Williams, Christopher Luke; Ryan, John Chadron Benjamin

    2015-04-01

    Particle size and shape distributions impact particle heating rates and diffusion of volatized gases out of particles during fast pyrolysis conversion, and consequently must be modeled accurately in order for computational pyrolysis models to produce reliable results for bulk solid materials. For this milestone, lodge pole pine chips were ground using a Thomas-Wiley #4 mill using two screen sizes in order to produce two representative materials that are suitable for fast pyrolysis. For the first material, a 6 mm screen was employed in the mill and for the second material, a 3 mm screen was employed in the mill. Both materials were subjected to RoTap sieve analysis, and the distributions of the particle sizes and shapes were determined using digital image analysis. The results of the physical analysis will be fed into computational pyrolysis simulations to create models of materials with realistic particle size and shape distributions. This milestone was met on schedule.

  8. Size distribution of microbubbles as a function of shell composition.

    PubMed

    Dicker, Stephen; Mleczko, Michał; Schmitz, Georg; Wrenn, Steven P

    2013-09-01

    The effect of modifying the shell composition of a population of microbubbles on their size demonstrated through experiment. Specifically, these variations include altering both the mole fraction and molecular weight of functionalized polymer, polyethylene glycol (PEG) in the microbubble phospholipid monolayer shell (1-15 mol% PEG, and 1000-5000 g/mole, respectively). The size distribution is measured with an unbiased image segmentation program written in MATLAB which identifies and sizes bubbles from micrographs. For a population of microbubbles with a shell composition of 5 mol% PEG2000, the mean diameter is 1.42 μm with a variance of 0.244 μm. For the remainder of the shell compositions studied herein, we find that the size distributions do not show a statistically significant correlation to either PEG molecular weight or mole fraction. All the measured distributions are nearly Gaussian in shape and have a monomodal peak.

  9. Inferring Volcanic Degassing Processes From Vesicle Size Distributions

    NASA Astrophysics Data System (ADS)

    Blower, J. D.; Keating, J. P.; Mader, H. M.; Phillips, J. C.

    2001-12-01

    Both power law and exponential vesicle size distributions (VSDs) have been observed in many different types of volcanic rocks. We present results of laboratory analogue experiments, of the type pioneered by Brad Sturtevant, which reproduce these observations, and use experimental results and computer simulations to show that the distributions can be interpreted as the product of continuous bubble nucleation resulting from non-equilibrium degassing. This ongoing nucleation causes the bubbles to evolve through an exponential size distribution into a power law size distribution as nucleation and growth progress. The process of continuous nucleation is a mechanism whereby the volcanic system maintains near-equilibrium in the case of rapid depressurisation and slow volatile diffusion.

  10. Packing fraction of particles with lognormal size distribution.

    PubMed

    Brouwers, H J H

    2014-05-01

    This paper addresses the packing and void fraction of polydisperse particles with a lognormal size distribution. It is demonstrated that a binomial particle size distribution can be transformed into a continuous particle-size distribution of the lognormal type. Furthermore, an original and exact expression is derived that predicts the packing fraction of mixtures of particles with a lognormal distribution, which is governed by the standard deviation, mode of packing, and particle shape only. For a number of particle shapes and their packing modes (close, loose) the applicable values are given. This closed-form analytical expression governing the packing fraction is thoroughly compared with empirical and computational data reported in the literature, and good agreement is found.

  11. Density, chemistry, and size distribution of interplanetary dust

    NASA Technical Reports Server (NTRS)

    Brownlee, D. E.; Horz, F.; Hartung, J. B.; Gault, D. E.

    1975-01-01

    Depth/diameter ratios measured for 98 craters in lunar glass targets reveal a broad distribution with a single strong peaking between 0.55 and 0.8. The measured values indicate a mean meteoroid density greater than 1 g/cu cm and probably less than 4 g/cu cm. Microprobe analyses show that typical glass pit liners on silicate targets contain only approximately 0.1% or less of meteoritic material. The size-frequency distribution of meteoroids was analyzed for a fractured glass surface of 60095, and a very steep size distribution of submicron meteoroids is indicated. As in the case of 15205, a dip at approximately 5 micron in the size-frequency distribution is detected.

  12. Pore scale distribution of gas hydrates in sediments by micro X-ray Computed Tomography (X-CT)

    NASA Astrophysics Data System (ADS)

    Hu, G.; Li, C.; Ye, Y.; Liu, C.; Best, A. I.

    2013-12-01

    A dedicated apparatus was developed to observe in-situ pore scale distribution of gas hydrate directly during hydrate formation in artificial cores. The high-resolution X-ray Computed Tomography (type: GE Sensing & Inspection Technologies GmbH Phoenix x-ray V/tomex/s) was used and the effective resolution for observing gas hydrate bearing sediments can up to about 18μm. Methane gas hydrate was formed in 0.425-0.85mm sands under a pressure of 6MPa and a temperature of 3°C. During the process, CT scanning was conducted if there's a pressure drop (the scanning time is 66 minutes each time), so that the hydrate morphology could be detected. As a result, five scanning CT images of the same section during gas hydrate formation (i.e. hydrate saturation at 3.9%, 24.6%, 35.0%, 51.4% and 97.0%) were obtained. The result shows that at each hydrate saturation level, hydrate morphology models are complicated. The occurrence of 'floating model' (i.e. hydrate floats in pore fluid), 'contact model' (i.e. hydrate contact with the sediment particle), and the 'cementing model' (i.e. hydrates cement the sediment particles) can be found at the same time (Fig. 1). However, it shows that at different hydrate formation stages, the dominant hydrate morphology are not the same. For instance, at the first stage of hydrate formation, although there are some hydrates floating in the pore fluid, most hydrates connect the sediment particles. Consequently, the hydrate morphology at this moment can be described as a cementing model. With this method, it can be obtained that at the higher level of saturation (e.g., hydrate saturation at 24.6% and 35.0%), hydrates are mainly grow as a floating model. As hydrate saturation is much higher (e.g. after hydrate saturation is more than 51.4%), however, the floating hydrates coalesce with each other and the hydrates cement the sediment particle again. The direct observed hydrate morphology presented here may have significant impact on investigating

  13. Crater size distributions on Ganymede and Callisto: fundamental issues

    NASA Astrophysics Data System (ADS)

    Wagner, Roland; Schmedemann, Nico; Werner, Stefanie; Ivanov, Boris; Stephan, Katrin; Jaumann, Ralf

    2015-04-01

    Crater size distributions on the two largest Jovian satellites Ganymede and Callisto and the origin of impactors are subject of intense and controversial debates. In this paper, we reinvestigate crater size distributions measured in surface units derived from a recently published global geologic map, based on Voyager and Galileo SSI images at a scale of 1 km/pxl (Collins G. C. et al. (2013), U. S. Geol. Surv., Sci. Inv. Map 3237). These units are used as a context to units mapped in more detail at higher resolution in Galileo SSI images. We focus on the following fundamental issues: (1) Similarity between shapes of crater distributions on the Galilean satellites and on inner solar system bodies; (2) production versus equilibrium distributions; (3) apex/antapex variations in crater distributions. First, our results show a strong similarity in shape between the crater distributions on the most densely cratered regions on Ganymede and Callisto with those in the lunar highlands. We conclude that the shape of the crater distributions on these two Jovian satellites implies the craters were preferentially formed from members of a collisionally evolved projectile family, derived either from Main Belt asteroids as candidates of impactors on the Jovian satellites, or from projectiles stemming from the outer solar system which have undergone collisional evolution, resulting in a size distribution similar to those of Main Belt asteroids. Second, the complex shape of the crater distributions on Ganymede and Callisto indicates they are mostly production distributions and can be used to infer the underlying shape of the projectile size distribution. Locally, equilibrium distributions occur, especially at smaller sub-kilometer diameters. Third, the most densely cratered regions on both satellites do not show apex-antapex variations in crater frequency, as inferred for bodies from heliocentric orbits (e.g., Zahnle K. et al. (2003), Icarus 163, 263-289). This indicates that these

  14. Size Distributions of Solar Proton Events: Methodological and Physical Restrictions

    NASA Astrophysics Data System (ADS)

    Miroshnichenko, L. I.; Yanke, V. G.

    2016-10-01

    Based on the new catalogue of solar proton events (SPEs) for the period of 1997 - 2009 (Solar Cycle 23) we revisit the long-studied problem of the event-size distributions in the context of those constructed for other solar-flare parameters. Recent results on the problem of size distributions of solar flares and proton events are briefly reviewed. Even a cursory acquaintance with this research field reveals a rather mixed and controversial picture. We concentrate on three main issues: i) SPE size distribution for > 10 MeV protons in Solar Cycle 23; ii) size distribution of > 1 GV proton events in 1942 - 2014; iii) variations of annual numbers for > 10 MeV proton events on long time scales (1955 - 2015). Different results are critically compared; most of the studies in this field are shown to suffer from vastly different input datasets as well as from insufficient knowledge of underlying physical processes in the SPEs under consideration. New studies in this field should be made on more distinct physical and methodological bases. It is important to note the evident similarity in size distributions of solar flares and superflares in Sun-like stars.

  15. Thresholded Power law Size Distributions of Instabilities in Astrophysics

    NASA Astrophysics Data System (ADS)

    Aschwanden, Markus J.

    2015-11-01

    Power-law-like size distributions are ubiquitous in astrophysical instabilities. There are at least four natural effects that cause deviations from ideal power law size distributions, which we model here in a generalized way: (1) a physical threshold of an instability; (2) incomplete sampling of the smallest events below a threshold x0; (3) contamination by an event-unrelated background xb; and (4) truncation effects at the largest events due to a finite system size. These effects can be modeled in the simplest terms with a “thresholded power law” distribution function (also called generalized Pareto [type II] or Lomax distribution), N(x){dx}\\propto {(x+{x}0)}-a{dx}, where x0 > 0 is positive for a threshold effect, while x0 < 0 is negative for background contamination. We analytically derive the functional shape of this thresholded power law distribution function from an exponential growth evolution model, which produces avalanches only when a disturbance exceeds a critical threshold x0. We apply the thresholded power law distribution function to terrestrial, solar (HXRBS, BATSE, RHESSI), and stellar flare (Kepler) data sets. We find that the thresholded power law model provides an adequate fit to most of the observed data. Major advantages of this model are the automated choice of the power law fitting range, diagnostics of background contamination, physical instability thresholds, instrumental detection thresholds, and finite system size limits. When testing self-organized criticality models that predict ideal power laws, we suggest including these natural truncation effects.

  16. On the Challenge of Fitting Tree Size Distributions in Ecology

    PubMed Central

    Taubert, Franziska; Hartig, Florian; Dobner, Hans-Jürgen; Huth, Andreas

    2013-01-01

    Patterns that resemble strongly skewed size distributions are frequently observed in ecology. A typical example represents tree size distributions of stem diameters. Empirical tests of ecological theories predicting their parameters have been conducted, but the results are difficult to interpret because the statistical methods that are applied to fit such decaying size distributions vary. In addition, binning of field data as well as measurement errors might potentially bias parameter estimates. Here, we compare three different methods for parameter estimation – the common maximum likelihood estimation (MLE) and two modified types of MLE correcting for binning of observations or random measurement errors. We test whether three typical frequency distributions, namely the power-law, negative exponential and Weibull distribution can be precisely identified, and how parameter estimates are biased when observations are additionally either binned or contain measurement error. We show that uncorrected MLE already loses the ability to discern functional form and parameters at relatively small levels of uncertainties. The modified MLE methods that consider such uncertainties (either binning or measurement error) are comparatively much more robust. We conclude that it is important to reduce binning of observations, if possible, and to quantify observation accuracy in empirical studies for fitting strongly skewed size distributions. In general, modified MLE methods that correct binning or measurement errors can be applied to ensure reliable results. PMID:23469137

  17. Bayesian analysis of size-dependent overwinter mortality from size-frequency distributions.

    PubMed

    Carlson, Stephanie M; Kottas, Athanasios; Mangel, Marc

    2010-04-01

    Understanding the relationship between body size and mortality is an important problem in ecology. We introduce a novel Bayesian method that can be used to quantify this relationship when the only data available are size-frequency distributions of unmarked individuals measured at two successive time periods. The inverse Gaussian distribution provides a parametric form for the statistical model development, and we use Markov chain Monte Carlo methods to evaluate posterior distributions. We illustrate the method using data on threespine stickleback (Gasterosteus aculeatus) collected before and after the winter season in an Alaskan lake. Our method allows us to compare the intensity of size-biased mortality in different years. We discuss generalizations that include more complicated relationships between size and survival as well as time-series modeling.

  18. Isometric size-scaling of metabolic rate and the size abundance distribution of phytoplankton

    PubMed Central

    Huete-Ortega, María; Cermeño, Pedro; Calvo-Díaz, Alejandra; Marañón, Emilio

    2012-01-01

    The relationship between phytoplankton cell size and abundance has long been known to follow regular, predictable patterns in near steady-state ecosystems, but its origin has remained elusive. To explore the linkage between the size-scaling of metabolic rate and the size abundance distribution of natural phytoplankton communities, we determined simultaneously phytoplankton carbon fixation rates and cell abundance across a cell volume range of over six orders of magnitude in tropical and subtropical waters of the Atlantic Ocean. We found an approximately isometric relationship between carbon fixation rate and cell size (mean slope value: 1.16; range: 1.03–1.32), negating the idea that Kleiber's law is applicable to unicellular autotrophic protists. On the basis of the scaling of individual resource use with cell size, we predicted a reciprocal relationship between the size-scalings of phytoplankton metabolic rate and abundance. This prediction was confirmed by the observed slopes of the relationship between phytoplankton abundance and cell size, which have a mean value of −1.15 (range: −1.29 to −0.97), indicating that the size abundance distribution largely results from the size-scaling of metabolic rate. Our results imply that the total energy processed by carbon fixation is constant along the phytoplankton size spectrum in near steady-state marine ecosystems. PMID:22171079

  19. Isometric size-scaling of metabolic rate and the size abundance distribution of phytoplankton.

    PubMed

    Huete-Ortega, María; Cermeño, Pedro; Calvo-Díaz, Alejandra; Marañón, Emilio

    2012-05-01

    The relationship between phytoplankton cell size and abundance has long been known to follow regular, predictable patterns in near steady-state ecosystems, but its origin has remained elusive. To explore the linkage between the size-scaling of metabolic rate and the size abundance distribution of natural phytoplankton communities, we determined simultaneously phytoplankton carbon fixation rates and cell abundance across a cell volume range of over six orders of magnitude in tropical and subtropical waters of the Atlantic Ocean. We found an approximately isometric relationship between carbon fixation rate and cell size (mean slope value: 1.16; range: 1.03-1.32), negating the idea that Kleiber's law is applicable to unicellular autotrophic protists. On the basis of the scaling of individual resource use with cell size, we predicted a reciprocal relationship between the size-scalings of phytoplankton metabolic rate and abundance. This prediction was confirmed by the observed slopes of the relationship between phytoplankton abundance and cell size, which have a mean value of -1.15 (range: -1.29 to -0.97), indicating that the size abundance distribution largely results from the size-scaling of metabolic rate. Our results imply that the total energy processed by carbon fixation is constant along the phytoplankton size spectrum in near steady-state marine ecosystems.

  20. Initial drop size and velocity distributions for airblast coaxial atomizers

    NASA Technical Reports Server (NTRS)

    Eroglu, H.; Chigier, N.

    1991-01-01

    Phase Doppler measurements were used to determine initial drop size and velocity distributions after a complete disintegration of coaxial liquid jets. The Sauter mean diameter (SMD) distribution was found to be strongly affected by the structure and behavior of the preceding liquid intact jet. The axial measurement stations were determined from the photographs of the coaxial liquid jet at very short distances (1-2 mm) downstream of the observed break-up locations. Minimum droplet mean velocities were found at the center, and maximum velocities were near the spray boundary. Size-velocity correlations show that the velocity of larger drops did not change with drop size. Drop rms velocity distributions have double peaks whose radial positions coincide with the maximum mean velocity gradients.

  1. Production, depreciation and the size distribution of firms

    NASA Astrophysics Data System (ADS)

    Ma, Qi; Chen, Yongwang; Tong, Hui; Di, Zengru

    2008-05-01

    Many empirical researches indicate that firm size distributions in different industries or countries exhibit some similar characters. Among them the fact that many firm size distributions obey power-law especially for the upper end has been mostly discussed. Here we present an agent-based model to describe the evolution of manufacturing firms. Some basic economic behaviors are taken into account, which are production with decreasing marginal returns, preferential allocation of investments, and stochastic depreciation. The model gives a steady size distribution of firms which obey power-law. The effect of parameters on the power exponent is analyzed. The theoretical results are given based on both the Fokker-Planck equation and the Kesten process. They are well consistent with the numerical results.

  2. The Size Frequency Distribution of Small Main-Belt Asteroids

    NASA Technical Reports Server (NTRS)

    Burt, Brian J.; Trilling, David E.; Hines, Dean C.; Stapelfeldt, Karl R.; Rebull, Luisa M.; Fuentes, Cesar I.; Hulsebus, Alan

    2012-01-01

    The asteroid size distribution informs us about the formation and composition of the Solar System. We build on our previous work in which we harvest serendipitously observed data of the Taurus region and measure the brightness and size distributions of Main-belt asteroids. This is accomplished with the highly sensitive MIPS 24 micron channel. We expect to catalog 104 asteroids, giving us a statistically significant data set. Results from this investigation will allow us to characterize the total population of small, Main-belt asteroids. Here we will present new results on the completeness of our study; on the presence of size distribution variations with inclination and radial distance in the belt; and early result on other archival fields.

  3. Dependence of hydrogen permeabilities of isotropic graphites on the pore structure

    NASA Astrophysics Data System (ADS)

    Yamawaki, M.; Yamaguchi, K.; Suzuki, Y.; Tanaka, S.

    1991-03-01

    The permeation behavior of molecular hydrogen through isotropic graphites is investigated. The observed dependences of the permeation rate on pressure, specimen thickness, temperature and molecular weight suggest that hydrogen permeates by molecular flow, probably through open pores. A simple pore structure model is developed and is compared with the experimental results. It is revealed that hydrogen permeation through isotropic graphites depends not only on the pore size or the porosity, but also on the pore size distribution and tortuosity.

  4. Particle size distribution and particle size-related crystalline silica content in granite quarry dust.

    PubMed

    Sirianni, Greg; Hosgood, Howard Dean; Slade, Martin D; Borak, Jonathan

    2008-05-01

    Previous studies indicate that the relationship between empirically derived particle counts, particle mass determinations, and particle size-related silica content are not constant within mines or across mine work tasks. To better understand the variability of particle size distributions and variations in silica content by particle size in a granite quarry, exposure surveys were conducted with side-by-side arrays of four closed face cassettes, four cyclones, four personal environmental monitors, and a real-time particle counter. In general, the proportion of silica increased as collected particulate size increased, but samples varied in an inconstant way. Significant differences in particle size distributions were seen depending on the extent of ventilation and the nature and activity of work performed. Such variability raises concerns about the adequacy of silica exposure assessments based on only limited numbers of samples or short-term samples.

  5. Theory of Nanocluster Size Distributions from Ion Beam Synthesis

    SciTech Connect

    Yuan, C.W.; Yi, D.O.; Sharp, I.D.; Shin, S.J.; Liao, C.Y.; Guzman, J.; Ager III, J.W.; Haller, E.E.; Chrzan, D.C.

    2008-06-13

    Ion beam synthesis of nanoclusters is studied via both kinetic Monte Carlo simulations and the self-consistent mean-field solution to a set of coupled rate equations. Both approaches predict the existence of a steady state shape for the cluster size distribution that depends only on a characteristic length determined by the ratio of the effective diffusion coefficient to the ion flux. The average cluster size in the steady state regime is determined by the implanted species/matrix interface energy.

  6. Synthesis and characterization of high-surface-area millimeter-sized silica beads with hierarchical multi-modal pore structure by the addition of agar

    SciTech Connect

    Han, Yosep; Choi, Junhyun; Tong, Meiping; Kim, Hyunjung

    2014-04-01

    Millimeter-sized spherical silica foams (SSFs) with hierarchical multi-modal pore structure featuring high specific surface area and ordered mesoporous frameworks were successfully prepared using aqueous agar addition, foaming and drop-in-oil processes. The pore-related properties of the prepared spherical silica (SSs) and SSFs were systematically characterized by field emission-scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), small-angle X-ray diffraction (SAXRD), Hg intrusion porosimetry, and N{sub 2} adsorption–desorption isotherm measurements. Improvements in the BET surface area and total pore volume were observed at 504 m{sup 2} g{sup −1} and 5.45 cm{sup 3} g{sup −1}, respectively, after an agar addition and foaming process. Despite the increase in the BET surface area, the mesopore wall thickness and the pore size of the mesopores generated from the block copolymer with agar addition were unchanged based on the SAXRD, TEM, and BJH methods. The SSFs prepared in the present study were confirmed to have improved BET surface area and micropore volume through the agar loading, and to exhibit interconnected 3-dimensional network macropore structure leading to the enhancement of total porosity and BET surface area via the foaming process. - Highlights: • Millimeter-sized spherical silica foams (SSFs) are successfully prepared. • SSFs exhibit high BET surface area and ordered hierarchical pore structure. • Agar addition improves BET surface area and micropore volume of SSFs. • Foaming process generates interconnected 3-D network macropore structure of SSFs.

  7. Three optical methods for remotely measuring aerosol size distributions.

    NASA Technical Reports Server (NTRS)

    Reagan, J. A.; Herman, B. M.

    1971-01-01

    Three optical probing methods for remotely measuring atmospheric aerosol size distributions are discussed and contrasted. The particular detection methods which are considered make use of monostatic lidar (laser radar), bistatic lidar, and solar radiometer sensing techniques. The theory of each of these measurement techniques is discussed briefly, and the necessary constraints which must be applied to obtain aerosol size distribution information from such measurements are pointed out. Theoretical and/or experimental results are also presented which demonstrate the utility of the three proposed probing methods.

  8. Modal character of atmospheric black carbon size distributions

    NASA Astrophysics Data System (ADS)

    Berner, A.; Sidla, S.; Galambos, Z.; Kruisz, C.; Hitzenberger, R.; ten Brink, H. M.; Kos, G. P. A.

    1996-08-01

    Samples of atmospheric aerosols, collected with cascade impactors in the urban area of Vienna (Austria) and at a coastal site on the North Sea, were investigated for black carbon (BC) as the main component of absorbing material and for mass. The size distributions are structured. The BC distributions of these samples show a predominant mode, the accumulation aerosol, in the upper submicron size range, a less distinct finer mode attributable to fresh emissions from combustion sources, and a distinct coarse mode of unclear origin. It is important to note that some parameters of the accumulation aerosol are related statistically, indicating the evolution of the atmospheric accumulation aerosol.

  9. Space Shuttle exhausted aluminum oxide - A measured particle size distribution

    NASA Technical Reports Server (NTRS)

    Cofer, W. R., III; Purgold, G. C.; Edahl, R. A.; Winstead, E. L.

    1991-01-01

    Aluminum oxide (A2O3) particles were collected from the Space Shuttle exhaust plume immediately following the launch of STS-34 on October 18, 1989. A2O3 samples were obtained at 2.4, 3.0, 3.2, and 7.4 km in altitude. The samples were analyzed using SEM to develope particle size distributions. There were no indications that the particle size distribution changed as a function of altitude. The particle number concentrations per cubic meter of air sampled for the four collections was found to fit an exponential expression.

  10. Saturn's rings - Particle size distributions for thin layer model

    NASA Technical Reports Server (NTRS)

    Zebker, H. A.; Marouf, E. A.; Tyler, G. L.

    1985-01-01

    A model incorporating limited interaction between the incident energy and particles in the ring is considered which appears to be consistent with the multiple scattering process in Saturn's rings. The model allows for the small physical thickness of the rings and can be used to relate Voyager 1 observations of 3.6- and 13-cm wavelength microwave scatter from the rings to the ring particle size distribution function for particles with radii ranging from 0.001 to 20 m. This limited-scatter model yields solutions for particle size distribution functions for eight regions in the rings, which exhibit approximately inverse-cubic power-law behavior.

  11. Size distribution of Portuguese firms between 2006 and 2012

    NASA Astrophysics Data System (ADS)

    Pascoal, Rui; Augusto, Mário; Monteiro, A. M.

    2016-09-01

    This study aims to describe the size distribution of Portuguese firms, as measured by annual sales and total assets, between 2006 and 2012, giving an economic interpretation for the evolution of the distribution along the time. Three distributions are fitted to data: the lognormal, the Pareto (and as a particular case Zipf) and the Simplified Canonical Law (SCL). We present the main arguments found in literature to justify the use of distributions and emphasize the interpretation of SCL coefficients. Methods of estimation include Maximum Likelihood, modified Ordinary Least Squares in log-log scale and Nonlinear Least Squares considering the Levenberg-Marquardt algorithm. When applying these approaches to Portuguese's firms data, we analyze if the evolution of estimated parameters in both lognormal power and SCL is in accordance with the known existence of a recession period after 2008. This is confirmed for sales but not for assets, leading to the conclusion that the first variable is a best proxy for firm size.

  12. Time evolution of cell size distributions in dense cell cultures

    NASA Astrophysics Data System (ADS)

    Khain, Evgeniy

    2015-03-01

    Living cells in a dense system are all in contact with each other. The common assumption is that such cells stop dividing due to a lack of space. Recent experimental observations have shown, however, that cells continue dividing for a while, but other cells in the system must shrink, to allow the newborn cells to grow to a normal size. Due to these ``pressure'' effects, the average cell size dramatically decreases with time, and the dispersion in cell sizes decreases, too. The collective cell behavior becomes even more complex when the system is expanding: cells near the edges are larger and migrate faster, while cells deep inside the colony are smaller and move slower. This exciting experimental data still needs to be described theoretically, incorporating the distribution of cell sizes in the system. We propose a mathematical model for time evolution of cell size distribution both in a closed and open system. The model incorporates cell proliferation, cell growth after division, cell shrinking due to ``pressure'' from other cells, and possible cell detachment from the interface of a growing colony. This research sheds light on physical and biological mechanisms of cell response to a dense environment and on the role of mechanical stresses in determining the distribution of cell sizes in the system.

  13. Particle size distributions of several commonly used seeding aerosols

    NASA Technical Reports Server (NTRS)

    Crosswy, F. L.

    1985-01-01

    During the course of experimentation, no solid particle powder could be found which produced an aerosol with a narrow particle size distribution when fluidization was the only flow process used in producing the aerosol. The complication of adding particle size fractionation processes to the aerosol generation effort appears to be avoidable. In this regard, a simple sonic orifice is found to be effective in reducing the percentage of agglomerates in the several metal oxide powders tested. Marginally beneficial results are obtained for a 0.5/99.5 percent by weight mixture of the flow agent and metal oxide powder. However, agglomeration is observed to be enhanced when the flow agent percentage is increased to 5 percent. Liquid atomization using the Collison nebulizer as well as a version of the Laskin nozzle resulted in polydispersed aerosols with particle size distributions heavily weighted by the small particle end of the size spectrum. The aerosol particle size distributions produced by the vaporization/condensation seeder are closer to the ideal monodispersed aerosol than any of the other aerosols tested. In addition, this seeding approach affords a measure of control over particle size and particle production rate.

  14. Size Evolution and Stochastic Models: Explaining Ostracod Size through Probabilistic Distributions

    NASA Astrophysics Data System (ADS)

    Krawczyk, M.; Decker, S.; Heim, N. A.; Payne, J.

    2014-12-01

    The biovolume of animals has functioned as an important benchmark for measuring evolution throughout geologic time. In our project, we examined the observed average body size of ostracods over time in order to understand the mechanism of size evolution in these marine organisms. The body size of ostracods has varied since the beginning of the Ordovician, where the first true ostracods appeared. We created a stochastic branching model to create possible evolutionary trees of ostracod size. Using stratigraphic ranges for ostracods compiled from over 750 genera in the Treatise on Invertebrate Paleontology, we calculated overall speciation and extinction rates for our model. At each timestep in our model, new lineages can evolve or existing lineages can become extinct. Newly evolved lineages are assigned sizes based on their parent genera. We parameterized our model to generate neutral and directional changes in ostracod size to compare with the observed data. New sizes were chosen via a normal distribution, and the neutral model selected new sizes differentials centered on zero, allowing for an equal chance of larger or smaller ostracods at each speciation. Conversely, the directional model centered the distribution on a negative value, giving a larger chance of smaller ostracods. Our data strongly suggests that the overall direction of ostracod evolution has been following a model that directionally pushes mean ostracod size down, shying away from a neutral model. Our model was able to match the magnitude of size decrease. Our models had a constant linear decrease while the actual data had a much more rapid initial rate followed by a constant size. The nuance of the observed trends ultimately suggests a more complex method of size evolution. In conclusion, probabilistic methods can provide valuable insight into possible evolutionary mechanisms determining size evolution in ostracods.

  15. Cell Wall-Degrading Enzymes Enlarge the Pore Size of Intervessel Pit Membranes in Healthy and Xylella fastidiosa-Infected Grapevines1[C][W][OA

    PubMed Central

    Pérez-Donoso, Alonso G.; Sun, Qiang; Roper, M. Caroline; Greve, L. Carl; Kirkpatrick, Bruce; Labavitch, John M.

    2010-01-01

    The pit membrane (PM) is a primary cell wall barrier that separates adjacent xylem water conduits, limiting the spread of xylem-localized pathogens and air embolisms from one conduit to the next. This paper provides a characterization of the size of the pores in the PMs of grapevine (Vitis vinifera). The PM porosity (PMP) of stems infected with the bacterium Xylella fastidiosa was compared with the PMP of healthy stems. Stems were infused with pressurized water and flow rates were determined; gold particles of known size were introduced with the water to assist in determining the size of PM pores. The effect of introducing trans-1,2-diaminocyclohexane-N,N,N′,N′-tetraacetic acid (CDTA), oligogalacturonides, and polygalacturonic acid into stems on water flux via the xylem was also measured. The possibility that cell wall-degrading enzymes could alter the pore sizes, thus facilitating the ability of X. fastidiosa to cross the PMs, was tested. Two cell wall-degrading enzymes likely to be produced by X. fastidiosa (polygalactuoronase and endo-1,4- β -glucanase) were infused into stems, and particle passage tests were performed to check for changes in PMP. Scanning electron microscopy of control and enzyme-infused stem segments revealed that the combination of enzymes opened holes in PMs, probably explaining enzyme impacts on PMP and how a small X. fastidiosa population, introduced into grapevines by insect vectors, can multiply and spread throughout the vine and cause Pierce's disease. PMID:20107028

  16. Fine Tuning of Nanocrystal and Pore Sizes of TiO2 Submicrospheres toward High Performance Dye-Sensitized Solar Cells.

    PubMed

    Li, Zhao-Qian; Ding, Yong; Mo, Li-E; Hu, Lin-Hua; Wu, Ji-Huai; Dai, Song-Yuan

    2015-10-14

    In general, the properties and performance of mesoporous TiO2 are greatly dependent on its crystal size, crystallinity, porosity, surface area, and morphology; in this regard, design and fine-tuning the crystal and pore sizes of the TiO2 submicrospheres and investigating the effect of these factors on the properties and photoelectric performance of dye-sensitized solar cells (DSSCs) is essential. In this work, uniform TiO2 submicrospheres were synthesized by a two-step procedure containing hydrolysis and solvothermal process. The crystal and pore sizes of the TiO2 submicrospheres were fine-tuned and controlled in a narrow range by adjusting the quantity of NH4OH during the solvothermal process. The effect of crystal and pore size of TiO2 submicrosphere on the performance of the DSSCs and their properties including dye-loading capacity, light scattering effect, power conversion efficiency (PCE), incident photon-to-electron conversion efficiencies (IPCEs), and electron recombination were compared and analyzed. The results show that increasing pore size plays a more significant role in improving the dye-loading capacity and PCE than increasing surface area, and an overall PCE value of 8.62% was obtained for the device with a 7.0 μm film thickness based on the TiO2 submicrospheres treated with 0.6 mL of NH4OH. Finally, the best TiO2 submicrosphere based photoanode film was optimized by TiCl4 treatment, and increasing film thickness and a remarkable PCE up to 11.11% were achieved.

  17. Fine Tuning of Nanocrystal and Pore Sizes of TiO2 Submicrospheres toward High Performance Dye-Sensitized Solar Cells.

    PubMed

    Li, Zhao-Qian; Ding, Yong; Mo, Li-E; Hu, Lin-Hua; Wu, Ji-Huai; Dai, Song-Yuan

    2015-10-14

    In general, the properties and performance of mesoporous TiO2 are greatly dependent on its crystal size, crystallinity, porosity, surface area, and morphology; in this regard, design and fine-tuning the crystal and pore sizes of the TiO2 submicrospheres and investigating the effect of these factors on the properties and photoelectric performance of dye-sensitized solar cells (DSSCs) is essential. In this work, uniform TiO2 submicrospheres were synthesized by a two-step procedure containing hydrolysis and solvothermal process. The crystal and pore sizes of the TiO2 submicrospheres were fine-tuned and controlled in a narrow range by adjusting the quantity of NH4OH during the solvothermal process. The effect of crystal and pore size of TiO2 submicrosphere on the performance of the DSSCs and their properties including dye-loading capacity, light scattering effect, power conversion efficiency (PCE), incident photon-to-electron conversion efficiencies (IPCEs), and electron recombination were compared and analyzed. The results show that increasing pore size plays a more significant role in improving the dye-loading capacity and PCE than increasing surface area, and an overall PCE value of 8.62% was obtained for the device with a 7.0 μm film thickness based on the TiO2 submicrospheres treated with 0.6 mL of NH4OH. Finally, the best TiO2 submicrosphere based photoanode film was optimized by TiCl4 treatment, and increasing film thickness and a remarkable PCE up to 11.11% were achieved. PMID:26393366

  18. Improving stability of virus-like particles by ion-exchange chromatographic supports with large pore size: advantages of gigaporous media beyond enhanced binding capacity.

    PubMed

    Yu, Mengran; Li, Yan; Zhang, Songping; Li, Xiunan; Yang, Yanli; Chen, Yi; Ma, Guanghui; Su, Zhiguo

    2014-02-28

    Limited binding capacity and low recovery of large size multi-subunits virus-like particles (VLPs) in conventional agarose-gel based chromatographic supports with small pores have long been a bottleneck limiting the large scale purification and application of VLPs. In this study, four anion exchange media including DEAE-Sepharose FF (DEAE-FF), DEAE-Capto, gigaporous DEAE-AP-120nm and DEAE-AP-280nm with average pore diameters of 32nm, 20nm, 120nm and 280nm, respectively, were applied for purification of hepatitis B virus surface antigen (HBsAg) VLPs. Pore size effects of media on the VLPs adsorption equilibrium, adsorption kinetics, dynamic binding capacity (DBC), and recovery were investigated in detail. According to the confocal laser scanning microscopy observation, adsorption of the VLPs in DEAE-FF and DEAE-Capto was mostly confined to a thin shell on the outer surface of the beads, leaving the underlying pore space and the binding sites inaccessibly, while the large pores in gigaporous media enabled the VLPs to access to the interior pore spaces by diffusion transport efficiently. Compared to the most widely used DEAE-FF, gigaporous media DEAE-AP-280nm gained about 12.9 times increase in static adsorption capacity, 8.0 times increase in DBC, and 11.4 times increase in effective pore diffusivity. Beyond increasing the binding capacity and enhancing the mass transfer, the gigaporous structure also significantly improved the stability of the VLPs during intensive adsorption-desorption process by lowing the multi-point interaction between the VLPs and binding sites in the pores. At 2.0mg/mL-media loading quantity, about 85.5% VLPs were correctly self-assembled after the chromatography with DEAE-AP-280nm media; oppositely about 85.2% VLPs lost their normal assembly with DEAE-FF due to irreversible disassembly. Comparative investigation was made to study the purifying performance of these four chromatographic media for actual VLPs purification from recombinant

  19. Improving stability of virus-like particles by ion-exchange chromatographic supports with large pore size: advantages of gigaporous media beyond enhanced binding capacity.

    PubMed

    Yu, Mengran; Li, Yan; Zhang, Songping; Li, Xiunan; Yang, Yanli; Chen, Yi; Ma, Guanghui; Su, Zhiguo

    2014-02-28

    Limited binding capacity and low recovery of large size multi-subunits virus-like particles (VLPs) in conventional agarose-gel based chromatographic supports with small pores have long been a bottleneck limiting the large scale purification and application of VLPs. In this study, four anion exchange media including DEAE-Sepharose FF (DEAE-FF), DEAE-Capto, gigaporous DEAE-AP-120nm and DEAE-AP-280nm with average pore diameters of 32nm, 20nm, 120nm and 280nm, respectively, were applied for purification of hepatitis B virus surface antigen (HBsAg) VLPs. Pore size effects of media on the VLPs adsorption equilibrium, adsorption kinetics, dynamic binding capacity (DBC), and recovery were investigated in detail. According to the confocal laser scanning microscopy observation, adsorption of the VLPs in DEAE-FF and DEAE-Capto was mostly confined to a thin shell on the outer surface of the beads, leaving the underlying pore space and the binding sites inaccessibly, while the large pores in gigaporous media enabled the VLPs to access to the interior pore spaces by diffusion transport efficiently. Compared to the most widely used DEAE-FF, gigaporous media DEAE-AP-280nm gained about 12.9 times increase in static adsorption capacity, 8.0 times increase in DBC, and 11.4 times increase in effective pore diffusivity. Beyond increasing the binding capacity and enhancing the mass transfer, the gigaporous structure also significantly improved the stability of the VLPs during intensive adsorption-desorption process by lowing the multi-point interaction between the VLPs and binding sites in the pores. At 2.0mg/mL-media loading quantity, about 85.5% VLPs were correctly self-assembled after the chromatography with DEAE-AP-280nm media; oppositely about 85.2% VLPs lost their normal assembly with DEAE-FF due to irreversible disassembly. Comparative investigation was made to study the purifying performance of these four chromatographic media for actual VLPs purification from recombinant

  20. Effective porosity and pore-throat sizes of mudrock saprolite from the Nolichucky Shale within Bear Creek Valley on the Oak Ridge Reservation: Implications for contaminant transport and retardation through matrix diffusion

    SciTech Connect

    Dorsch, J.; Katsube, T.J.

    1996-05-01

    Specimens of saprolite developed from mudrock of the Nolichucky Shale (Upper Cambrian, Conasauga Group) from the Whiteoak Mountain thrust sheet on the Oak Ridge Reservation (ORR) were analyzed. Petrophysical techniques include helium porosimetry and mercury porosimetry. Petrophysical data obtained from the laboratory experiments include effective porosity, pore-throat sizes and their distribution, specimen bulk-density, and specimen grain-density. It is expected that the data from this study will significantly contribute to constraining the modeling of the hydrologic behavior of saprolite developed from mudrock of the Conasauga Group in general and from the Nolichucky Shale specifically.

  1. Size distribution of native cytosolic proteins of Thermoplasma acidophilum.

    PubMed

    Sun, Na; Tamura, Noriko; Tamura, Tomohiro; Knispel, Roland Wilhelm; Hrabe, Thomas; Kofler, Christine; Nickell, Stephan; Nagy, István

    2009-07-01

    We used molecular sieve chromatography in combination with LC-MS/MS to identify protein complexes that can serve as templates in the template matching procedures of visual proteomics approaches. By this method the sample complexity was lowered sufficiently to identify 464 proteins and - on the basis of size distribution and bioinformatics analysis - 189 of them could be assigned as subunits of macromolecular complexes over the size of 300 kDa. From these we purified six stable complexes of Thermoplasma acidophilum whose size and subunit composition - analyzed by electron microscopy and MALDI-TOF-MS, respectively - verified the accuracy of our method.

  2. Size distributions of gold nanoclusters studied by liquid chromatography

    SciTech Connect

    WILCOXON,JESS P.; MARTIN,JAMES E.; PROVENCIO,PAULA P.

    2000-05-23

    The authors report high pressure liquid chromatography, (HPLC), and transmission electron microscopy, (TEM), studies of the size distributions of nanosize gold clusters dispersed in organic solvents. These metal clusters are synthesized in inverse micelles at room temperature and those investigated range in diameter from 1--10 nm. HPLC is sensitive enough to discern changes in hydrodynamic volume corresponding to only 2 carbon atoms of the passivating agent or metal core size changes of less than 4 {angstrom}. The authors have determined for the first time how the total cluster volume (metal core + passivating organic shell) changes with the size of the passivating agent.

  3. The size-distribution of Earth’s lakes

    PubMed Central

    Cael, B. B.; Seekell, D. A.

    2016-01-01

    Globally, there are millions of small lakes, but a small number of large lakes. Most key ecosystem patterns and processes scale with lake size, thus this asymmetry between area and abundance is a fundamental constraint on broad-scale patterns in lake ecology. Nonetheless, descriptions of lake size-distributions are scarce and empirical distributions are rarely evaluated relative to theoretical predictions. Here we develop expectations for Earth’s lake area-distribution based on percolation theory and evaluate these expectations with data from a global lake census. Lake surface areas ≥8.5 km2 are power-law distributed with a tail exponent (τ = 1.97) and fractal dimension (d = 1.38), similar to theoretical expectations (τ = 2.05; d = 4/3). Lakes <8.5 km2 are not power-law distributed. An independently developed regional lake census exhibits a similar transition and consistency with theoretical predictions. Small lakes deviate from the power-law distribution because smaller lakes are more susceptible to dynamical change and topographic behavior at sub-kilometer scales is not self-similar. Our results provide a robust characterization and theoretical explanation for the lake size-abundance relationship, and form a fundamental basis for understanding and predicting patterns in lake ecology at broad scales. PMID:27388607

  4. The size-distribution of Earth’s lakes

    NASA Astrophysics Data System (ADS)

    Cael, B. B.; Seekell, D. A.

    2016-07-01

    Globally, there are millions of small lakes, but a small number of large lakes. Most key ecosystem patterns and processes scale with lake size, thus this asymmetry between area and abundance is a fundamental constraint on broad-scale patterns in lake ecology. Nonetheless, descriptions of lake size-distributions are scarce and empirical distributions are rarely evaluated relative to theoretical predictions. Here we develop expectations for Earth’s lake area-distribution based on percolation theory and evaluate these expectations with data from a global lake census. Lake surface areas ≥8.5 km2 are power-law distributed with a tail exponent (τ = 1.97) and fractal dimension (d = 1.38), similar to theoretical expectations (τ = 2.05 d = 4/3). Lakes <8.5 km2 are not power-law distributed. An independently developed regional lake census exhibits a similar transition and consistency with theoretical predictions. Small lakes deviate from the power-law distribution because smaller lakes are more susceptible to dynamical change and topographic behavior at sub-kilometer scales is not self-similar. Our results provide a robust characterization and theoretical explanation for the lake size-abundance relationship, and form a fundamental basis for understanding and predicting patterns in lake ecology at broad scales.

  5. Aggregation dynamics explain vegetation patch-size distributions.

    PubMed

    Irvine, M A; Bull, J C; Keeling, M J

    2016-04-01

    Vegetation patch-size distributions have been an intense area of study for theoreticians and applied ecologists alike in recent years. Of particular interest is the seemingly ubiquitous nature of power-law patch-size distributions emerging in a number of diverse ecosystems. The leading explanation of the emergence of these power-laws is due to local facilitative mechanisms. There is also a common transition from power law to exponential distribution when a system is under global pressure, such as grazing or lack of rainfall. These phenomena require a simple mechanistic explanation. Here, we study vegetation patches from a spatially implicit, patch dynamic viewpoint. We show that under minimal assumptions a power-law patch-size distribution appears as a natural consequence of aggregation. A linear death term also leads to an exponential term in the distribution for any non-zero death rate. This work shows the origin of the breakdown of the power-law under increasing pressure and shows that in general, we expect to observe a power law with an exponential cutoff (rather than pure power laws). The estimated parameters of this distribution also provide insight into the underlying ecological mechanisms of aggregation and death.

  6. Aerosol mobility imaging for rapid size distribution measurements

    DOEpatents

    Wang, Jian; Hering, Susanne Vera; Spielman, Steven Russel; Kuang, Chongai

    2016-07-19

    A parallel plate dimensional electrical mobility separator and laminar flow water condensation provide rapid, mobility-based particle sizing at concentrations typical of the remote atmosphere. Particles are separated spatially within the electrical mobility separator, enlarged through water condensation, and imaged onto a CCD array. The mobility separation distributes particles in accordance with their size. The condensation enlarges size-separated particles by water condensation while they are still within the gap of the mobility drift tube. Once enlarged the particles are illuminated by a laser. At a pre-selected frequency, typically 10 Hz, the position of all of the individual particles illuminated by the laser are captured by CCD camera. This instantly records the particle number concentration at each position. Because the position is directly related to the particle size (or mobility), the particle size spectra is derived from the images recorded by the CCD.

  7. Size distributions of metal nanoparticles in polyelectrolyte gels

    NASA Astrophysics Data System (ADS)

    Svergun, D. I.; Shtykova, E. V.; Dembo, A. T.; Bronstein, L. M.; Platonova, O. A.; Yakunin, A. N.; Valetsky, P. M.; Khokhlov, A. R.

    1998-12-01

    Small-angle x-ray scattering is used to study size distributions of noble metal nanoparticles embedded in polyelectrolyte hydrogels with oppositely charged surfactants. A procedure is proposed to subtract matrix scattering and to extract pure scattering due to the nanoparticles allowing to evaluate their size distribution functions by means of a regularization technique. Two kinds of collapsed gel-surfactant complexes were studied: a complex of a cationic gel of poly(diallyldimethylammonium chloride) with an anionic surfactant sodium dodecyl sulfate (PDADMACl/SDS), and that of an anionic gel of poly(methacrylic acid) with a cationic surfactant cetylpyridinium chloride (PMA/CPC). Addition of a gold compound (HAuCl4ṡ3H2O) to the PDADMACl/SDS system forms the metal compound clusters and leads to a partial distortion of the gel structure. After subsequent reduction of the gold compound with sodium borohydride (NaBH4) ordering in the gel disappears and gold nanoparticles are formed. Their size distribution includes a fraction of small particles with approximately the same size as the compound clusters before reduction and a fraction of larger particles with the radii up to 40 nm. For the collapsed PDADMACl/SDS gels, aging does not change the size distribution profile; for the noncollapsed PDADMACl gels without surfactant, metal particles are found to grow with time. This suggests that the aggregation of metal colloids is prevented by the ordering in the collapsed gel-surfactant complex. The addition of HAuCl4ṡ3H2O and the subsequent reduction of the metal ions in the PMA/CPC system does not distort the gel structure as the degree of incorporation of AuCl4- ions is very low. Particle sizes in the PMA/CPC system are found to be somewhat larger than those in the PDADMACl/SDS system. The PDADMACl/SDS gels loaded with the PtCl4 compound were also studied to analyze the influence of the reducing agent type on the particle size distribution distributions. Fast reduction

  8. Particle Size Distribution in Saturn’s Ring C

    NASA Astrophysics Data System (ADS)

    Marouf, Essam A.; Wong, K.; French, R.; Rappaport, N.

    2012-10-01

    Information about particle sizes in Saturn’s rings is provided by two complementary types of Cassini radio occultation measurements. The first is differential extinction of three coherent sinusoidal signals transmitted by Cassini through the rings back to Earth (wavelength = 0.94, 3.6, and 13 cm, respectively). The differential measurements strongly constraint three parameters of an assumed power-law size distribution n(a) = n0 (a/a0)q, amin ≤ a ≤ amax: namely, the power law index q, the minimum radius amin, and reference abundance n0 at reference radius a0. The differential measurements are particularly sensitive to radii in the range 0.1 mm < a < 1 m. Complementing this capability, is a second type of measurements that is particularly sensitive to the larger radii 1 m < a < 20 m and their abundance. Signature of the collective near-forward scattering by these particles is captured in power spectrum measurements as broadened component of width, shape, and strength that depend on ring particle sizes, their spatial distribution, and observation geometry. Contributions of ring features of width as small several hundred kilometers can be identified and isolated in the measured spectra for a small subset of Cassini orbits of favorable geometry. We use three inverse scattering algorithms (Bayes, constrained linear inversion, generalized singular-value-decomposition) to recover the size distribution of particles of resolved ring features over the size range 1 m < a < 20 m without assuming an explicit size distribution model. We also investigate consistency of the results with a single power-law model extending over 0.1 mm < a < 20 m and implications to the spatial distribution of ring particles normal to the ring plane (vertical ring thickness). We present example results for selected features across Saturn’s Ring C where little evidence for gravitational wakes is present, hence the approaches above are applicable.

  9. EFFECTS OF LEACHING ON PORE SIZE DISTRIBUTION OF SOLIDIFIED/STABILIZED WASTES

    EPA Science Inventory

    Chemical solidification/stabilization processes are commonly used to immobilize metals in fly ash and flue gas desulfurization (FGD) sludges and to convert these wastes into monolithic or granular materials with better handling properties and reduced permeabilities. his study eva...

  10. Embedded NMR Sensor to Monitor Compressive Strength Development and Pore Size Distribution in Hydrating Concrete

    PubMed Central

    Díaz-Díaz, Floriberto; de J. Cano-Barrita, Prisciliano F.; Balcom, Bruce J.; Solís-Nájera, Sergio E.; Rodríguez, Alfredo O.

    2013-01-01

    In cement-based materials porosity plays an important role in determining their mechanical and transport properties. This paper describes an improved low–cost embeddable miniature NMR sensor capable of non-destructively measuring evaporable water loss and porosity refinement in low and high water-to-cement ratio cement-based materials. The sensor consists of two NdFeB magnets having their North and South poles facing each other, separated by 7 mm to allow space for a Faraday cage containing a Teflon tube and an ellipsoidal RF coil. To account for magnetic field changes due to temperature variations, and/or the presence of steel rebars, or frequency variation due to sample impedance, an external tuning circuit was employed. The sensor performance was evaluated by analyzing the transverse magnetization decay obtained with a CPMG measurement from different materials, such as a polymer phantom, fresh white and grey cement pastes with different w/c ratios and concrete with low (0.30) and high (0.6) w/c ratios. The results indicated that the sensor is capable of detecting changes in water content in fresh cement pastes and porosity refinement caused by cement hydration in hardened materials, even if they are prepared with a low w/c ratio (w/c = 0.30). The short lifetime component of the transverse relaxation rate is directly proportional to the compressive strength of concrete determined by destructive testing. The r2 (0.97) from the linear relationship observed is similar to that obtained using T2 data from a commercial Oxford Instruments 12.9 MHz spectrometer.

  11. Distributional shifts in size structure of phytoplankton community

    NASA Astrophysics Data System (ADS)

    Waga, H.; Hirawake, T.; Fujiwara, A.; Nishino, S.; Kikuchi, T.; Suzuki, K.; Takao, S.

    2015-12-01

    Increased understanding on how marine species shift their distribution is required for effective conservation of fishery resources under climate change. Previous studies have often predicted distributional shifts of fish using satellite derived sea surface temperature (SST). However, SST may not fully represent the changes in species distribution through food web structure and as such this remains an open issue due to lack of ecological perspective on energy transfer process in the earlier studies. One of the most important factors in ecosystem is composition of phytoplankton community, and its size structure determines energy flow efficiency from base to higher trophic levels. To elucidate spatiotemporal variation in phytoplankton size structure, chlorophyll-a size distribution (CSD) algorithm was developed using spectral variance of phytoplankton absorption coefficient through principal component analysis. Slope of CSD (CSD slope) indicates size structure of phytoplankton community where, strong and weak magnitudes of CSD slope indicate smaller and larger phytoplankton structure, respectively. Shifts in CSD slope and SST were derived as the ratio of temporal trend over the 12-year period (2003-2014) to 2-dimensional spatial gradient and the resulting global median velocity of CSD slope and SST were 0.361 and 0.733 km year-1, respectively. In addition, the velocity of CSD slope monotonically increases with increasing latitude, while relatively complex latitudinal pattern for SST emerged. Moreover, angle of shifts suggest that species are required to shift their distribution toward not limited to simple pole-ward migration, and some regions exhibit opposite direction between the velocity of CSD slope and SST. These findings further imply that combined phytoplankton size structure and SST may contribute for more accurate prediction of species distribution shifts relative to existing studies which only considering variations in thermal niches.

  12. Pore water pressure assessment in a forest watershed: Simulations and distributed field measurements related to forest practices

    NASA Astrophysics Data System (ADS)

    Dhakal, Amod S.; Sidle, Roy C.

    2004-02-01

    A distributed shallow groundwater model related to slope stability is described to assess the spatial distribution of pore water pressure in steep forested terrain in British Columbia. Additionally, effects of timber harvesting and roads on measured changes in pressure head during rainstorms were evaluated for the first time to assess the need for incorporating different hydrological components in the event-driven distributed model. Although explicit spatial quantification of pore water pressure requires many measurements for accurate prediction, model performance using average parameter values was reasonable when compared with pressure heads measured at nine spatially distributed sites. Increases in maximum pressure head (varying from 9 to 28 cm) between preharvesting (after road construction) and postharvesting rainstorm events were observed in seven of nine sites. The remaining two sites showed either a small decrease (≈5 cm) or similar peak pressure heads following harvesting. Peak pressure head evaluated at one piezometer located 46 m downslope of the road decreased substantially (≈50 cm) after road construction during moderate rainstorms and then recovered following harvesting. Piezometric responses in sites upslope of the road were not affected by road construction but did increase after harvesting. Moderate storms caused the largest relative increases in pressure head between preharvesting (after roads) and postharvesting conditions; such increases were small during large storms, lending support to the idea that timber harvesting in temperate forests enhances hydrologic response only during small and moderate storms. Since landslides in coastal Pacific Northwest are typically caused by large winter rainstorms, it appears more justified to include better spatial representation of soil physical and engineering parameters in the distributed shallow groundwater model compared to specifying evapotranspiration; road hydrology may, however, need to be included.

  13. Fabrication of Controllable Pore and Particle Size of Mesoporous Silica Nanoparticles via a Liquid-phase Synthesis Method and Its Absorption Characteristics

    NASA Astrophysics Data System (ADS)

    Nandiyanto, Asep Bayu Dani; Iskandar, Ferry; Okuyama, Kikuo

    2011-12-01

    Monodisperse spherical mesoporous silica nanoparticles were successfully synthesized using a liquid-phase synthesis method. The result showed particles with controllable pore size from several to tens nanometers with outer diameter of several tens nanometers. The ability in the control of pore size and outer diameter was altered by adjusting the precursor solution ratios. In addition, we have conducted the adsorption ability of the prepared particles. The result showed that large organic molecules were well-absorbed to the prepared silica porous particles, in which this result was not obtained when using commercial dense silica particle and/or hollow silica particle. With this result, the prepared mesoporous silica particles may be used efficiently in various applications, such as sensors, pharmaceuticals, environmentally sensitive pursuits, etc.

  14. Elemental composition and size distribution of particulates in Cleveland, Ohio

    NASA Technical Reports Server (NTRS)

    King, R. B.; Fordyce, J. S.; Neustadter, H. E.; Leibecki, H. F.

    1975-01-01

    Measurements were made of the elemental particle size distribution at five contrasting urban environments with different source-type distributions in Cleveland, Ohio. Air quality conditions ranged from normal to air pollution alert levels. A parallel network of high-volume cascade impactors (5-state) were used for simultaneous sampling on glass fiber surfaces for mass determinations and on Whatman-41 surfaces for elemental analysis by neutron activation for 25 elements. The elemental data are assessed in terms of distribution functions and interrelationships and are compared between locations as a function of resultant wind direction in an attempt to relate the findings to sources.

  15. Optical Sizing of Ultrafine Metallic Particles: Retrieval of Particle Size Distribution from Spectral Extinction Measurements.

    PubMed

    Oshchepkov; Sinyuk

    1998-12-01

    The inverse problem of optical sizing of ultrafine metallic particles from the spectral extinction measurements in the visible range is investigated. Solving the inverse problem becomes possible due to the strong size effect which in the framework of classical electrodynamics can be described by the dependence of complex refractive index on the particle size. It is shown that the size effect leads to the considerable increase of information content of spectral extinction data with respect to desired size composition of the particles. This makes it possible to retrieve the size distribution of ultrafine metallic particles with reasonably high accuracy, including the Rayleigh size region. The analysis is performed mainly within the framework of numerical tests by the typical example of ultrafine silver particles in a gelatin matrix. The results in retrieving of size distribution from experimentally measured extinction spectra are also presented. Calculations of spectral extinction coefficient are made by means of Mie theory. In so doing, the dielectric function of particles is modified by using the electron's mean free path limitation model. Copyright 1998 Academic Press.

  16. Distribution of arsenic and copper in sediment pore water: an ecological risk assessment case study for offshore drilling waste discharges.

    PubMed

    Sadiq, Rehan; Husain, Tahir; Veitch, Brian; Bose, Neil

    2003-12-01

    Due to the hydrophobic nature of synthetic based fluids (SBFs), drilling cuttings are not very dispersive in the water column and settle down close to the disposal site. Arsenic and copper are two important toxic heavy metals, among others, found in the drilling waste. In this article, the concentrations of heavy metals are determined using a steady state "aquivalence-based" fate model in a probabilistic mode. Monte Carlo simulations are employed to determine pore water concentrations. A hypothetical case study is used to determine the water quality impacts for two discharge options: 4% and 10% attached SBFs, which correspond to the best available technology option and the current discharge practice in the U.S. offshore. The exposure concentration (CE) is a predicted environmental concentration, which is adjusted for exposure probability and bioavailable fraction of heavy metals. The response of the ecosystem (RE) is defined by developing an empirical distribution function of predicted no-effect concentration. The pollutants' pore water concentrations within the radius of 750 m are estimated and cumulative distributions of risk quotient (RQ=CE/RE) are developed to determine the probability of RQ greater than 1.

  17. Distribution of arsenic and copper in sediment pore water: an ecological risk assessment case study for offshore drilling waste discharges.

    PubMed

    Sadiq, Rehan; Husain, Tahir; Veitch, Brian; Bose, Neil

    2003-12-01

    Due to the hydrophobic nature of synthetic based fluids (SBFs), drilling cuttings are not very dispersive in the water column and settle down close to the disposal site. Arsenic and copper are two important toxic heavy metals, among others, found in the drilling waste. In this article, the concentrations of heavy metals are determined using a steady state "aquivalence-based" fate model in a probabilistic mode. Monte Carlo simulations are employed to determine pore water concentrations. A hypothetical case study is used to determine the water quality impacts for two discharge options: 4% and 10% attached SBFs, which correspond to the best available technology option and the current discharge practice in the U.S. offshore. The exposure concentration (CE) is a predicted environmental concentration, which is adjusted for exposure probability and bioavailable fraction of heavy metals. The response of the ecosystem (RE) is defined by developing an empirical distribution function of predicted no-effect concentration. The pollutants' pore water concentrations within the radius of 750 m are estimated and cumulative distributions of risk quotient (RQ=CE/RE) are developed to determine the probability of RQ greater than 1. PMID:14641903

  18. Tracing Particle Size Distribution Curves Using an Analogue Circuit.

    ERIC Educational Resources Information Center

    Bisschop, F. De; Segaert, O.

    1986-01-01

    Proposes an analog circuit for use in sedimentation analysis of finely divided solid materials. Discusses a method of particle size distribution analysis and provides schematics of the circuit with list of components as well as a discussion about the operation of the circuit. (JM)

  19. Factors influencing the effect size distribution of adaptive substitutions.

    PubMed

    Dittmar, Emily L; Oakley, Christopher G; Conner, Jeffrey K; Gould, Billie A; Schemske, Douglas W

    2016-04-13

    The distribution of effect sizes of adaptive substitutions has been central to evolutionary biology since the modern synthesis. Early theory proposed that because large-effect mutations have negative pleiotropic consequences, only small-effect mutations contribute to adaptation. More recent theory suggested instead that large-effect mutations could be favoured when populations are far from their adaptive peak. Here we suggest that the distributions of effect sizes are expected to differ among study systems, reflecting the wide variation in evolutionary forces and ecological conditions experienced in nature. These include selection, mutation, genetic drift, gene flow, and other factors such as the degree of pleiotropy, the distance to the phenotypic optimum, whether the optimum is stable or moving, and whether new mutation or standing genetic variation provides the source of adaptive alleles. Our goal is to review how these factors might affect the distribution of effect sizes and to identify new research directions. Until more theory and empirical work is available, we feel that it is premature to make broad generalizations about the effect size distribution of adaptive substitutions important in nature.

  20. Asymmetric competition causes multimodal size distributions in spatially structured populations.

    PubMed

    Velázquez, Jorge; Allen, Robert B; Coomes, David A; Eichhorn, Markus P

    2016-01-27

    Plant sizes within populations often exhibit multimodal distributions, even when all individuals are the same age and have experienced identical conditions. To establish the causes of this, we created an individual-based model simulating the growth of trees in a spatially explicit framework, which was parametrized using data from a long-term study of forest stands in New Zealand. First, we demonstrate that asymmetric resource competition is a necessary condition for the formation of multimodal size distributions within cohorts. By contrast, the legacy of small-scale clustering during recruitment is transient and quickly overwhelmed by density-dependent mortality. Complex multi-layered size distributions are generated when established individuals are restricted in the spatial domain within which they can capture resources. The number of modes reveals the effective number of direct competitors, while the separation and spread of modes are influenced by distances among established individuals. Asymmetric competition within local neighbourhoods can therefore generate a range of complex size distributions within even-aged cohorts.

  1. Factors influencing the effect size distribution of adaptive substitutions

    PubMed Central

    Oakley, Christopher G.; Gould, Billie A.; Schemske, Douglas W.

    2016-01-01

    The distribution of effect sizes of adaptive substitutions has been central to evolutionary biology since the modern synthesis. Early theory proposed that because large-effect mutations have negative pleiotropic consequences, only small-effect mutations contribute to adaptation. More recent theory suggested instead that large-effect mutations could be favoured when populations are far from their adaptive peak. Here we suggest that the distributions of effect sizes are expected to differ among study systems, reflecting the wide variation in evolutionary forces and ecological conditions experienced in nature. These include selection, mutation, genetic drift, gene flow, and other factors such as the degree of pleiotropy, the distance to the phenotypic optimum, whether the optimum is stable or moving, and whether new mutation or standing genetic variation provides the source of adaptive alleles. Our goal is to review how these factors might affect the distribution of effect sizes and to identify new research directions. Until more theory and empirical work is available, we feel that it is premature to make broad generalizations about the effect size distribution of adaptive substitutions important in nature. PMID:27053750

  2. Sample Size Tables, "t" Test, and a Prevalent Psychometric Distribution.

    ERIC Educational Resources Information Center

    Sawilowsky, Shlomo S.; Hillman, Stephen B.

    Psychology studies often have low statistical power. Sample size tables, as given by J. Cohen (1988), may be used to increase power, but they are based on Monte Carlo studies of relatively "tame" mathematical distributions, as compared to psychology data sets. In this study, Monte Carlo methods were used to investigate Type I and Type II error…

  3. Isoreticular metal-organic frameworks, process for forming the same, and systematic design of pore size and functionality therein, with application for gas storage

    DOEpatents

    Yaghi, Omar M.; Eddaoudi, Mohamed; Li, Hailian; Kim, Jaheon; Rosi, Nathaniel

    2005-08-16

    An isoreticular metal-organic framework (IRMOF) and method for systematically forming the same. The method comprises the steps of dissolving at least one source of metal cations and at least one organic linking compound in a solvent to form a solution; and crystallizing the solution under predetermined conditions to form a predetermined IRMOF. At least one of functionality, dimension, pore size and free volume of the IRMOF is substantially determined by the organic linking compound.

  4. Relationship between pore size and reversible and irreversible immobilization of ionic liquid electrolytes in porous carbon under applied electric potential

    NASA Astrophysics Data System (ADS)

    Mahurin, Shannon M.; Mamontov, Eugene; Thompson, Matthew W.; Zhang, Pengfei; Turner, C. Heath; Cummings, Peter T.; Dai, Sheng

    2016-10-01

    Transport of electrolytes in nanoporous carbon-based electrodes largely defines the function and performance of energy storage devices. Using molecular dynamics simulation and quasielastic neutron scattering, we investigate the microscopic dynamics of a prototypical ionic liquid electrolyte, [emim][Tf2N], under applied electric potential in carbon materials with 6.7 nm and 1.5 nm pores. The simulations demonstrate the formation of dense layers of counter-ions near the charged surfaces, which is reversible when the polarity is reversed. In the experiment, the ions immobilized near the surface manifest themselves in the elastic scattering signal. The experimentally observed ion immobilization near the wall is fully reversible as a function of the applied electric potential in the 6.7 nm, but not in the 1.5 nm nanopores. In the latter case, remarkably, the first application of the electric potential leads to apparently irreversible immobilization of cations or anions, depending on the polarity, near the carbon pore walls. This unexpectedly demonstrates that in carbon electrode materials with the small pores, which are optimal for energy storage applications, the polarity of the electrical potential applied for the first time after the introduction of an ionic liquid electrolyte may define the decoration of the small pore walls with ions for prolonged periods of time and possibly for the lifetime of the electrode.

  5. Relationship between pore size and reversible and irreversible immobilization of ionic liquid electrolytes in porous carbon under applied electric potential

    DOE PAGESBeta

    Mahurin, Shannon M.; Mamontov, Eugene; Thompson, Matthew W.; Zhang, Pengfei; Turner, C. Heath; Cummings, Peter T.; Dai, Sheng

    2016-10-04

    Transport of electrolytes in nanoporous carbon-based electrodes largely defines the function and performance of energy storage devices. Here, using molecular dynamics simulation and quasielastic neutron scattering, we investigate the microscopic dynamics of a prototypical ionic liquid electrolyte, [emim][Tf2N], under applied electric potential in carbon materials with 6.7 nm and 1.5 nm pores. The simulations demonstrate the formation of dense layers of counter-ions near the charged surfaces, which is reversible when the polarity is reversed. In the experiment, the ions immobilized near the surface manifest themselves in the elastic scattering signal. The experimentally observed ion immobilization near the wall is fullymore » reversible as a function of the applied electric potential in the 6.7 nm, but not in the 1.5 nm nanopores. In the latter case, remarkably, the first application of the electric potential leads to apparently irreversible immobilization of cations or anions, depending on the polarity, near the carbon pore walls. This unexpectedly demonstrates that in carbon electrode materials with the small pores, which are optimal for energy storage applications, the polarity of the electrical potential applied for the first time after the introduction of an ionic liquid electrolyte may define the decoration of the small pore walls with ions for prolonged periods of time and possibly for the lifetime of the electrode.« less

  6. Turbulent Concentration of Chondrules: Size Distribution and Multifractal Scaling

    NASA Technical Reports Server (NTRS)

    Cuzzi, Jeffrey N.; Hogan, Robert C.; Paque, Julie M.; Dobrovolskis, Anthony R.

    1999-01-01

    Size-selective concentration of particles in 3D turbulence may be related to collection of chondrules and other constituents into primitive bodies in a weakly turbulent protoplanetary nebula. In the terrestrial planet region, both the characteristic size and narrow size distribution of chondrules are explained, whereas "fluffier" particles would be concentrated in lower density, or more intensely turbulent, regions of the nebula. The spatial distribution of concentrated particle density obeys multifractal scaling, suggesting a dose tie to the turbulent cascade process. This scaling behavior allows predictions of the concentration probabilities to be made in the protoplanetary nebula, which are so large (> 10(exp 3) - 10(exp 4)) that further studies must be made of the role of mass loading.

  7. Lognormal field size distributions as a consequence of economic truncation

    USGS Publications Warehouse

    Attanasi, E.D.; Drew, L.J.

    1985-01-01

    The assumption of lognormal (parent) field size distributions has for a long time been applied to resource appraisal and evaluation of exploration strategy by the petroleum industry. However, frequency distributions estimated with observed data and used to justify this hypotheses are conditional. Examination of various observed field size distributions across basins and over time shows that such distributions should be regarded as the end result of an economic filtering process. Commercial discoveries depend on oil and gas prices and field development costs. Some new fields are eliminated due to location, depths, or water depths. This filtering process is called economic truncation. Economic truncation may occur when predictions of a discovery process are passed through an economic appraisal model. We demonstrate that (1) economic resource appraisals, (2) forecasts of levels of petroleum industry activity, and (3) expected benefits of developing and implementing cost reducing technology are sensitive to assumptions made about the nature of that portion of (parent) field size distribution subject to economic truncation. ?? 1985 Plenum Publishing Corporation.

  8. Size distributions and failure initiation of submarine and subaerial landslides

    USGS Publications Warehouse

    ten Brink, U.S.; Barkan, R.; Andrews, B.D.; Chaytor, J.D.

    2009-01-01

    Landslides are often viewed together with other natural hazards, such as earthquakes and fires, as phenomena whose size distribution obeys an inverse power law. Inverse power law distributions are the result of additive avalanche processes, in which the final size cannot be predicted at the onset of the disturbance. Volume and area distributions of submarine landslides along the U.S. Atlantic continental slope follow a lognormal distribution and not an inverse power law. Using Monte Carlo simulations, we generated area distributions of submarine landslides that show a characteristic size and with few smaller and larger areas, which can be described well by a lognormal distribution. To generate these distributions we assumed that the area of slope failure depends on earthquake magnitude, i.e., that failure occurs simultaneously over the area affected by horizontal ground shaking, and does not cascade from nucleating points. Furthermore, the downslope movement of displaced sediments does not entrain significant amounts of additional material. Our simulations fit well the area distribution of landslide sources along the Atlantic continental margin, if we assume that the slope has been subjected to earthquakes of magnitude ??? 6.3. Regions of submarine landslides, whose area distributions obey inverse power laws, may be controlled by different generation mechanisms, such as the gradual development of fractures in the headwalls of cliffs. The observation of a large number of small subaerial landslides being triggered by a single earthquake is also compatible with the hypothesis that failure occurs simultaneously in many locations within the area affected by ground shaking. Unlike submarine landslides, which are found on large uniformly-dipping slopes, a single large landslide scarp cannot form on land because of the heterogeneous morphology and short slope distances of tectonically-active subaerial regions. However, for a given earthquake magnitude, the total area

  9. Relative permeability and the microscopic distribution of wetting and nonwetting phases in the pore space of Berea sandstone

    SciTech Connect

    Schlueter, E.M.; Cook, N.G.W. |; Witherspoon, P.A.; Myer, L.R.

    1994-04-01

    Experiments to study relative permeabilities of a partially saturated rock have been carried out in Berea sandstone using fluids that can be solidified in place. The effective permeability of the spaces not occupied by the wetting fluid (paraffin wax) or the nonwetting fluid (Wood`s metal), have been measured at various saturations after solidifying each of the phases. The tests were conducted on Berea sandstone samples that had an absolute permeability of about 600 md. The shape of the laboratory-derived relative permeability vs. saturation curves measured with the other phase solidified conforms well with typical curves obtained using conventional experimental methods. The corresponding wetting and nonwetting fluid distributions at different saturations are presented and analyzed in light of the role of the pore structure in the invasion process, and their impact on relative permeability and capillary pressure. Irreducible wetting and nonwetting phase fluid distributions are studied. The effect of clay minerals on permeability is also assessed.

  10. Comparison of residual oil cluster size distribution, morphology and saturation in oil-wet and water-wet sandstone.

    PubMed

    Iglauer, S; Fernø, M A; Shearing, P; Blunt, M J

    2012-06-01

    We imaged an oil-wet sandstone at residual oil saturation (S(or)) conditions using X-ray micro-tomography with a nominal voxel size of (9 μm)(3) and monochromatic light from a synchrotron source. The sandstone was rendered oil-wet by ageing with a North Sea crude oil to represent a typical wettability encountered in hydrocarbon reservoirs. We measured a significantly lower S(or) for the oil-wet core (18.8%) than for an analogue water-wet core (35%). We analysed the residual oil cluster size distribution and find consistency with percolation theory that predicts a power-law cluster size distribution. We measure a power-law exponent τ=2.12 for the oil-wet core which is higher than τ for the water-wet system (τ=2.05), indicating fewer large clusters in the oil-wet case. The clusters are rough and sheet-like consistent with connectivity established through layers in the pore space and occupancy of the smaller pores; in contrast the clusters for water-wet media occupy the centres of the larger pores. These results imply less trapping of oil, but with a greater surface area for dissolution. In carbon storage applications, this suggests that in CO(2)-wet systems, capillary trapping is less significant, but that there is a large surface area for dissolution and reaction.

  11. Size distribution of iron and manganese species in freshwaters

    NASA Astrophysics Data System (ADS)

    Laxen, Duncan P. H.; Chandler, I. Michael

    1983-04-01

    A recently established technique for size fractionation of particulate matter in freshwaters, based on low volume filtration through Nuclepore filters in the field, has been applied to the study of Fe and Mn species in 3 freshwater lakes and a stream feeding one of the lakes. The technique has also been used in a series of laboratory experiments to provide further insight into the process of particle formation. The results are complemented with scanning electron microscope examination of the particles. The raw data are transformed into mass size distributions, which are generally unimodal, with the major part of the mass confined to a single log unit size range. These size distributions are compared and contrasted with a theoretical model of particle behaviour in a lake. The results suggest that particulate Fe and Mn behave according to particle theory. The observed size distributions represent a