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Sample records for diffuse attenuation coefficient

  1. Remote sensing of normalized diffuse attenuation coefficient of downwelling irradiance

    NASA Astrophysics Data System (ADS)

    Lin, Junfang; Lee, Zhongping; Ondrusek, Michael; Du, Keping

    2016-09-01

    The diffuse attenuation of downwelling irradiance, Kd (m-1), is an important property related to light penetration and availability in aquatic ecosystems. The standard Kd(490) product (the diffuse attenuation coefficient at 490 nm) of the global oceans from satellite remote sensing has been produced with an empirical algorithm, which limits its reliability and applicability in coastal regions. More importantly, as an apparent optical property (AOP), Kd is a function of the angular distribution of the light field (e.g., solar zenith angle). The empirically derived product thus contains ambiguities when compared with in situ measurements as there is no specification regarding the corresponding solar zenith angle associated with this Kd(490) product. To overcome these shortcomings, we refined the Kd product with a product termed as the normalized diffuse attenuation coefficient (nKd, m-1), that is equivalent to the Kd in the absence of the atmosphere and with the sun at zenith. Models were developed to get nKd from both in situ measurements and ocean color remote sensing. Evaluations using field measurements indicated that the semianalytically derived nKd product will not only remove the ambiguities when comparing Kd values of different light fields but will also improve the quality of such a product, therefore maximizing the value offered by satellite ocean color remote sensing.

  2. A model for the diffuse attenuation coefficient of downwelling irradiance

    NASA Astrophysics Data System (ADS)

    Lee, Zhong-Ping; Du, Ke-Ping; Arnone, Robert

    2005-02-01

    The diffuse attenuation coefficient for downwelling irradiance (Kd) is an important parameter for ocean studies. For the vast ocean the only feasible means to get fine-scale measurements of Kd is by ocean color remote sensing. At present, values of Kd from remote sensing are estimated using empirical algorithms. Such an approach is insufficient to provide an understanding regarding the variation of Kd and contains large uncertainties in the derived values. In this study a semianalytical model for Kd is developed based on the radiative transfer equation, with values of the model parameters derived from Hydrolight simulations using the averaged particle phase function. The model is further tested with data simulated using significantly different particle phase functions, and the modeled Kd are found matching Hydrolight Kd very well (˜2% average error and ˜12% maximum error). Such a model provides an improved interpretation about the variation of Kd and a basis to more accurately determine Kd (especially using data from remote sensing).

  3. The remote sensing algorithm of spectral diffuse attenuation coefficient of ocean

    NASA Astrophysics Data System (ADS)

    Zhu, Qiankun; He, Xianqiang; Mao, Zhihua; Gong, Fang

    2008-10-01

    Diffuse attenuation coefficient is an apparent optical property (AOP) which directly links to the inherent optical properties in ocean color remote sensing. So far, the study on the satellite retrieve algorithm of water diffuse attenuation coefficient has not been deeply-going, which is mainly discussed using the bands-ratio methods based on the in situ data. Only a few scientists apply the remote sensing data (such as SeaWiFS and MODIS) to retrieve the diffuse attenuation coefficient based on the model developed by Mueller (2002). In this paper, a quasi-analytical algorithm of spectral diffuse attenuation coefficients were developed based on the QAA algorithm of the inherent optical properties (IOPs) developed by Lee (2002). The model could retrieve multi-bands of the diffuse attenuation coefficients at 412 nm, 443 nm, 490 nm, 510 nm and 555nm wavelength. The in-situ optical dataset of South China Sea in 1999 was used to validate the model, and the results showed that the model had a good performance in the case I water in South China Sea, and the relative errors were 15.4%, 12.6%, 13.3%, 10.2%, 11.9%, 9.8% and 10.3% for the 412 nm, 443 nm, 490 nm, 510 nm, 520 nm, 555nm and 565 nm bands respectively. For the complex case II water, the model should be further localized and tested.

  4. Evaluation of downwelling diffuse attenuation coefficient algorithms in the Red Sea

    NASA Astrophysics Data System (ADS)

    Tiwari, Surya Prakash; Sarma, Y. V. B.; Jones, Burton H.

    2016-05-01

    Despite the importance of the optical properties such as the downwelling diffuse attenuation coefficient for characterizing the upper water column, until recently no in situ optical measurements were published for the Red Sea. Kirby et al. used observations from the Coastal Zone Color Scanner to characterize the spatial and temporal variability of the diffuse attenuation coefficient (Kd(490)) in the Red Sea. To better understand optical variability and its utility in the Red Sea, it is imperative to comprehend the diffuse attenuation coefficient and its relationship with in situ properties. Two apparent optical properties, spectral remote sensing reflectance (Rrs) and the downwelling diffuse attenuation coefficient (Kd), are calculated from vertical profile measurements of downwelling irradiance (Ed) and upwelling radiance (Lu). Kd characterizes light penetration into water column that is important for understanding both the physical and biogeochemical environment, including water quality and the health of ocean environment. Our study tests the performance of the existing Kd(490) algorithms in the Red Sea and compares them against direct in situ measurements within various subdivisions of the Red Sea. Most standard algorithms either overestimated or underestimated with the measured in situ values of Kd. Consequently, these algorithms provided poor retrieval of Kd(490) for the Red Sea. Random errors were high for all algorithms and the correlation coefficients (r2) with in situ measurements were quite low. Hence, these algorithms may not be suitable for the Red Sea. Overall, statistical analyses of the various algorithms indicated that the existing algorithms are inadequate for the Red Sea. The present study suggests that reparameterizing existing algorithms or developing new regional algorithms is required to improve retrieval of Kd(490) for the Red Sea.

  5. Comparison between the spectral diffuse attenuation coefficients and the IOP parameters

    NASA Astrophysics Data System (ADS)

    Mao, Zhihua; Zhou, Yan; Huang, Haiqing; Bai, Yan

    2009-01-01

    The spectral diffuse attenuation coefficients of downward irradiance (Kd) and upward radiance (Ku) are calculated from a profiler spectrometer measured data. Both Kd and Ku are the parameters of apparent optical properties (AOP) and need to be normalized according to the position of the Sun and sky conditions. Three kinds of sky indices are used to indicate the atmospheric conditions of clear, overcast and partly cloudy at the time of measurements. The values of normalized Kd can be compared with the sums of total absorption and backscattering coefficients. The total values from both measured data and the models fit the normalized Kd with the correlation coefficients of 0.85 and 0.81, respectively. The accuracy of Kd is also evaluated by the spectral root mean square error (RMSE) less than 0.15 m-1 in the spectral range from 450 to 700 nm.

  6. Remote estimation of the diffuse attenuation coefficient in a moderately turbid estuary

    USGS Publications Warehouse

    Stumpf, R.P.; Pennock, J.R.

    1991-01-01

    Solutions of the radiative transfer equation are used to derive relationships of water reflectance to the diffuse attenuation coefficient (K) in moderately turbid water (K > 0.5 m-1). Data sets collected from the NOAA AVHRR and in situ observations from five different dates confirm the appropriateness of these relationships, in particular the logistic equation. Values of K calculated from the reflectance data agree to within 60% of the observed values, although the reflectance derived using a more comprehensive aerosol correction is sensitive to chlorophyll concentrations greater than 50 ??g L-1. Agreement between in situ and remote observations improves as the time interval between samples is narrowed. ?? 1991.

  7. [Characteristics of diffuse attenuation coefficient of underwater irradiance in the lakes in the middle and lower reaches of Yangtze river ].

    PubMed

    Shi, Zhi-Qiang; Zhang, Yun-Lin; Wang, Ming-Zhu; Liu, Xiao-Han

    2013-02-01

    Based on the underwater irradiance profile measurement and water samples collection in September, October 2007 in Lake Donghu, Lake Liangzi and Lake Honghu, and in April in 2010 in Lake Kuileihu, the diffuse attenuation coefficient and the dominant attenuation factors were analyzed. The ranges of diffuse attenuation coefficient and total suspended solid (TSS), organic suspended solid (OSS), inorganic suspended solid (ISS), chlorophyll a (Chla), and dissolved organic carbon (DOC) concentration varied less in Lake Donghu and Lake Kuileihu than in Lake liangzi and Lake Honghu. The regression analysis showed that ISS was the dominant affecting factor of transparency in Lake Donghu and Lake Kuileihu, but ISS and OSS jointly controlled the transparency in Lake Liangzi and Lake Honghu. The diffuse attenuation coefficient minimum occurred near 580 nm. At around 675 nm, the diffuse attenuation coefficient peak was due to phytoplankton absorption, especially at sites with high pigment concentration. The euphotic depth was less than the mean water depth in Lake Donghu, suggesting that the submerged aquatic vegetation (SAV) can not grow in the present underwater light climate. However, the euphotic depth was larger than the mean water depth in other three lakes showing that the underwater light climate can meet the light requirements for the growth of SAV. The regression analysis showed that ISS was the dominant affecting factor of PAR attenuation in Lake Donghu and Lake Kuileihu, but ISS, OSS and Chla jointly controlled PAR attenuation in lake Liangzi and lake Honghu. The significant correlation between the beam attenuatin coefficient at 750 nm and PAR difffuse attenuation coefficient showed that the particles scattering significantly contributed to underwater irradiance attenuation.

  8. Diffuse attenuation coefficient of downwelling irradiance: An evaluation of remote sensing methods

    NASA Astrophysics Data System (ADS)

    Lee, Zhong-Ping; Darecki, Miroslaw; Carder, Kendall L.; Davis, Curtiss O.; Stramski, Dariusz; Rhea, W. Joseph

    2005-02-01

    The propagation of downwelling irradiance at wavelength λ from surface to a depth (z) in the ocean is governed by the diffuse attenuation coefficient, ?(λ). There are two standard methods for the derivation of ?(λ) in remote sensing, which both are based on empirical relationships involving the blue-to-green ratio of ocean color. Recently, a semianalytical method to derive ?(λ) from reflectance has also been developed. In this study, using ?(490) and ?(443) as examples, we compare the ?(λ) values derived from the three methods using data collected in three different regions that cover oceanic and coastal waters, with ?(490) ranging from ˜0.04 to 4.0 m-1. The derived values are compared with the data calculated from in situ measurements of the vertical profiles of downwelling irradiance. The comparisons show that the two standard methods produced satisfactory estimates of ?(λ) in oceanic waters where attenuation is relatively low but resulted in significant errors in coastal waters. The newly developed semianalytical method appears to have no such limitation as it performed well for both oceanic and coastal waters. For all data in this study the average of absolute percentage difference between the in situ measured and the semianalytically derived ? is ˜14% for λ = 490 nm and ˜11% for λ = 443 nm.

  9. A method for estimating the diffuse attenuation coefficient (KdPAR)from paired temperature sensors

    USGS Publications Warehouse

    Read, Jordan S.; Rose, Kevin C.; Winslow, Luke A.; Read, Emily K.

    2015-01-01

    A new method for estimating the diffuse attenuation coefficient for photosynthetically active radiation (KdPAR) from paired temperature sensors was derived. We show that during cases where the attenuation of penetrating shortwave solar radiation is the dominant source of temperature changes, time series measurements of water temperatures at multiple depths (z1 and z2) are related to one another by a linear scaling factor (a). KdPAR can then be estimated by the simple equation KdPAR ln(a)/(z2/z1). A suggested workflow is presented that outlines procedures for calculating KdPAR according to this paired temperature sensor (PTS) method. This method is best suited for conditions when radiative temperature gains are large relative to physical noise. These conditions occur frequently on water bodies with low wind and/or high KdPARs but can be used for other types of lakes during time periods of low wind and/or where spatially redundant measurements of temperatures are available. The optimal vertical placement of temperature sensors according to a priori knowledge of KdPAR is also described. This information can be used to inform the design of future sensor deployments using the PTS method or for campaigns where characterizing sub-daily changes in temperatures is important. The PTS method provides a novel method to characterize light attenuation in aquatic ecosystems without expensive radiometric equipment or the user subjectivity inherent in Secchi depth measurements. This method also can enable the estimation of KdPAR at higher frequencies than many manual monitoring programs allow.

  10. Diffuse Attenuation Coefficient of Downwelling Irradiance: An Evaluation of Remote Sensing Methods

    NASA Technical Reports Server (NTRS)

    Lee, Zhong-Ping; Darecki, Miroslaw; Carder, Kendall L.; Davis, Curtiss O.; Stramski, Dariusz; Rhea, W. Joseph

    2005-01-01

    The propagation of downwelling irradiance at wavelength lambda from surface to a depth (z) in the ocean is governed by the diffuse attenuation coefficient, K(sup -)(sub d)(lambda). There are two standard methods for the derivation of K(sup -)(sub d)(lambda) in remote sensing, which both are based on empirical relationships involving the blue-to-green ratio of ocean color. Recently, a semianalytical method to derive K(sup -)(sub d)(lambda) from reflectance has also been developed. In this study, using K(sup -)(sub d)(490) and K(sup -)(sub d)(443) as examples, we compare the K(sup -)(sub d)(lambda) values derived from the three methods using data collected in three different regions that cover oceanic and coastal waters, with K(sup -)(sub d)(490) ranging from approximately 0.04 to 4.0 per meter. The derived values are compared with the data calculated from in situ measurements of the vertical profiles of downwelling irradiance. The comparisons show that the two standard methods produced satisfactory estimates of K(sup -)(sub d)(lambda) in oceanic waters where attenuation is relatively low but resulted in significant errors in coastal waters. The newly developed semianalytical method appears to have no such limitation as it performed well for both oceanic and coastal waters. For all data in this study the average of absolute percentage difference between the in situ measured and the semianalytically derived K(sup -)(sub d) is approximately 14% for lambda = 490 nm and approximately 11% for lambda = 443 nm.

  11. Improved Algorithms for Accurate Retrieval of UV - Visible Diffuse Attenuation Coefficients in Optically Complex, Inshore Waters

    NASA Technical Reports Server (NTRS)

    Cao, Fang; Fichot, Cedric G.; Hooker, Stanford B.; Miller, William L.

    2014-01-01

    Photochemical processes driven by high-energy ultraviolet radiation (UVR) in inshore, estuarine, and coastal waters play an important role in global bio geochemical cycles and biological systems. A key to modeling photochemical processes in these optically complex waters is an accurate description of the vertical distribution of UVR in the water column which can be obtained using the diffuse attenuation coefficients of down welling irradiance (Kd()). The Sea UV Sea UVc algorithms (Fichot et al., 2008) can accurately retrieve Kd ( 320, 340, 380,412, 443 and 490 nm) in oceanic and coastal waters using multispectral remote sensing reflectances (Rrs(), Sea WiFS bands). However, SeaUVSeaUVc algorithms are currently not optimized for use in optically complex, inshore waters, where they tend to severely underestimate Kd(). Here, a new training data set of optical properties collected in optically complex, inshore waters was used to re-parameterize the published SeaUVSeaUVc algorithms, resulting in improved Kd() retrievals for turbid, estuarine waters. Although the updated SeaUVSeaUVc algorithms perform best in optically complex waters, the published SeaUVSeaUVc models still perform well in most coastal and oceanic waters. Therefore, we propose a composite set of SeaUVSeaUVc algorithms, optimized for Kd() retrieval in almost all marine systems, ranging from oceanic to inshore waters. The composite algorithm set can retrieve Kd from ocean color with good accuracy across this wide range of water types (e.g., within 13 mean relative error for Kd(340)). A validation step using three independent, in situ data sets indicates that the composite SeaUVSeaUVc can generate accurate Kd values from 320 490 nm using satellite imagery on a global scale. Taking advantage of the inherent benefits of our statistical methods, we pooled the validation data with the training set, obtaining an optimized composite model for estimating Kd() in UV wavelengths for almost all marine waters. This

  12. Estimating the Underwater Diffuse Attenuation Coefficient with a Low-Cost Instrument: The KdUINO DIY Buoy

    PubMed Central

    Bardaji, Raul; Sánchez, Albert-Miquel; Simon, Carine; Wernand, Marcel R.; Piera, Jaume

    2016-01-01

    A critical parameter to assess the environmental status of water bodies is the transparency of the water, as it is strongly affected by different water quality related components (such as the presence of phytoplankton, organic matter and sediment concentrations). One parameter to assess the water transparency is the diffuse attenuation coefficient. However, the number of subsurface irradiance measurements obtained with conventional instrumentation is relatively low, due to instrument costs and the logistic requirements to provide regular and autonomous observations. In recent years, the citizen science concept has increased the number of environmental observations, both in time and space. The recent technological advances in embedded systems and sensors also enable volunteers (citizens) to create their own devices (known as Do-It-Yourself or DIY technologies). In this paper, a DIY instrument to measure irradiance at different depths and automatically calculate the diffuse attenuation Kd coefficient is presented. The instrument, named KdUINO, is based on an encapsulated low-cost photonic sensor and Arduino (an open-hardware platform for the data acquisition). The whole instrument has been successfully operated and the data validated comparing the KdUINO measurements with the commercial instruments. Workshops have been organized with high school students to validate its feasibility. PMID:26999132

  13. Estimation of the Diffuse Attenuation Coefficient KdPAR Using MERIS Satellite Reflections for European Coastal Waters

    NASA Astrophysics Data System (ADS)

    Saulquin, Bertand; Hamdi, Anouar; Populus, Jacques; Loutier, Romain; Demaria, Julien; Mangin, Antoine; D'Andon, Odile Fanton

    2010-12-01

    Accurate estimations of the diffuse attenuation coefficient is critical to understand physical processes such as the heat transfer in the upper layer of the ocean and also biological processes such as phytoplankton photosynthesis in the ocean euphotic zone. Light availability in the water column and the seabed determine the euphotic zone and constraints the type and distribution of the algae species. The EuSeaMap project's aim is to characterize at a resolution of 250m the European infralitoral benthic zone, according to biology, physic and geology criteriums and using observations and models. Satellite observations of the diffuse attenuation coefficient of the downwelling spectral irradiance at wavelength 490 nm (Kd490) or the diffuse attenuation coefficient for the downwelling photosynthetically available radiation (KdPAR) is an effective method to provide large scale maps of these parameters at high spatial and temporal resolution. Several empirical and semi-analytical models are commonly used to derive the Kd490 and KdPAR maps from ocean colour satellite sensors such as the Medium Resolution Imaging Spectrometer Instrument (MERIS), the Sea- viewing Wide Field-of-view Sensor (SeaWiFS), and the Moderate Resolution Imaging Spectroradiometer (MODIS). Most of these existing empirical or semi- analytical models have been calibrated on open ocean waters and provide good results in these areas, but tend to underestimate the attenuation of light in coastal waters, our area of interest. We propose here a new estimation of the euphotic depth and the KdPAR for coastal European waters using MERIS reflectances at the resolution of 1km and 250 m. First, a semi-analytical model is used to estimate the Kd490, and in a second step, two relationships have been developed between the KdPAR and the Kd490 for respectively clear and turbid waters. Satellite-derived fields of Kd490 and the deduced KdPAR are validated using matchups collected over the world. Distribution maps of seabed

  14. Multi-Mission Remote Sensing of Suspended Particulate Matter and Diffuse Attenuation Coefficient in the Yangtze Estuarine and Coastal Waters

    NASA Astrophysics Data System (ADS)

    Yu, X.; Salama, S.; Shen, F.

    2016-08-01

    During the Dragon-3 project (ID: 10555) period, we developed and improved the atmospheric correction algorithms (AC) and retrieval models of suspended sediment concentration ( ) and diffuse attenuation coefficient ( ) for the Yangtze estuarine and coastal waters. The developed models were validated by measurements with consistently stable and fairly accurate estimations, reproducing reasonable distribution maps of and over the study area. Spatial-temporal variations of were presented and the mechanisms of the sediment transport were discussed. We further examined the compatibility of the developed AC algorithms and retrieval model and the consistency of satellite products for multi-sensor such as MODIS/Terra/Aqua, MERIS/Envisat, MERSI/ FY-3 and GOCI. The inter-comparison of multi- sensor suggested that different satellite products can be combined to increase revisit frequency and complement a temporal gap of time series satellites that may exist between on-orbit and off- orbit, facilitating a better monitor on the spatial- temporal dynamics of .

  15. MODIS-based retrieval of suspended sediment concentration and diffuse attenuation coefficient in Chinese estuarine and coastal waters

    NASA Astrophysics Data System (ADS)

    Sokoletsky, Leonid; Yang, Xianping; Shen, Fang

    2014-11-01

    Radiative transfer modelling in atmosphere, water, and on the air-water surface was used to create an algorithm and computer code for satellite monitoring Chinese estuarine and coastal waters. The atmospheric part of the algorithm is based on the Reference Evaluation of Solar Transmittance (REST) model for calculation of optical properties of the atmosphere from the top of the atmosphere to the target; for modelling optical properties from target towards satellite's sensor, an optical reciprocity principle has been used. An algorithm uses estimates derived from three different sources: 1) the MODIS-based software; 2) radiative transfer equations, and 3) well-known empirical relationships between measured parameters and optical depths and transmittances for such atmospheric components as molecules, aerosols, ozone, nitrogen dioxide, precipitable water vapor and uniformly mixed gases. Using this model allowed us to derive a reliable relationship relating an important parameter, the diffuse-to-global solar incoming irradiance ratio, to the aerosol optical thickness, solar zenith angle and wavelength. The surface and underwater parts of the algorithm contained theoretical and semi-empirical relationships between inherent (such as absorption, scattering and backscattering coefficients) and apparent (remote-sensing reflectance and diffuse attenuation coefficient, Kd) optical properties, and suspended sediment concentration (SSC) measured in the Yangtze River Estuary and its adjacent coastal area. The first false colour maps of SSC and Kd demonstrated a well accordance with the multi-year field observations in the region, and suggest promise for use of this algorithm for the regular monitoring of Chinese and worldwide natural waters.

  16. A simple optical model to estimate diffuse attenuation coefficient of photosynthetically active radiation in an extremely turbid lake from surface reflectance.

    PubMed

    Zhang, Yunlin; Liu, Xiaohan; Yin, Yan; Wang, Mingzhu; Qin, Boqiang

    2012-08-27

    Accurate estimation of the diffuse attenuation coefficient is critical for our understanding and modelling of key physical, chemical, and biological processes in water bodies. For extremely turbid, shallow, Lake Taihu in China, we synchronously monitored the diffuse attenuation coefficient of photosynthetically active radiation (Kd(PAR)) and the remote sensing reflectance at 134 sites. Kd(PAR)) varied greatly among different sites from 1.62 to 14.68 m(-1) with a mean value of 5.62 ± 2.99 m(-1). A simple optical model from near-infrared remote sensing reflectance of MODIS channels 2 (859 nm) and 15 (748 nm) was calibrated, and validated, to estimate Kd(PAR). With the simple optical model, the root mean square error and mean relative error were 0.95 m(-1) and 17.0% respectively at 748 nm, and 0.98 m(-1) and 17.6% at 859 nm, based on an independent validation data set. Our results showed a good precision of estimation for Kd(PAR) using the new simple optical model, contrasting with the poor estimations derived from existing empirical and semi-analytical models developed in clear, open ocean waters or slightly turbid coastal waters. Although at 748 nm the model had slightly higher precision than at 859 nm, the spatial resolution at 859 nm was four times that at 748 nm. Therefore, we propose a new model based on the MODIS-derived normalized water-leaving radiances at a wavelength of 859 nm, for accurate retrieval of Kd(PAR) in extremely turbid, shallow lakes with Kd(PAR) larger than 1.5 m(-1).

  17. Cytoplasmic hydrogen ion diffusion coefficient.

    PubMed Central

    al-Baldawi, N F; Abercrombie, R F

    1992-01-01

    The apparent cytoplasmic proton diffusion coefficient was measured using pH electrodes and samples of cytoplasm extracted from the giant neuron of a marine invertebrate. By suddenly changing the pH at one surface of the sample and recording the relaxation of pH within the sample, an apparent diffusion coefficient of 1.4 +/- 0.5 x 10(-6) cm2/s (N = 7) was measured in the acidic or neutral range of pH (6.0-7.2). This value is approximately 5x lower than the diffusion coefficient of the mobile pH buffers (approximately 8 x 10(-6) cm2/s) and approximately 68x lower than the diffusion coefficient of the hydronium ion (93 x 10(-6) cm2/s). A mobile pH buffer (approximately 15% of the buffering power) and an immobile buffer (approximately 85% of the buffering power) could quantitatively account for the results at acidic or neutral pH. At alkaline pH (8.2-8.6), the apparent proton diffusion coefficient increased to 4.1 +/- 0.8 x 10(-6) cm2/s (N = 7). This larger diffusion coefficient at alkaline pH could be explained quantitatively by the enhanced buffering power of the mobile amino acids. Under the conditions of these experiments, it is unlikely that hydroxide movement influences the apparent hydrogen ion diffusion coefficient. PMID:1617134

  18. Portable vapor diffusion coefficient meter

    DOEpatents

    Ho, Clifford K.

    2007-06-12

    An apparatus for measuring the effective vapor diffusion coefficient of a test vapor diffusing through a sample of porous media contained within a test chamber. A chemical sensor measures the time-varying concentration of vapor that has diffused a known distance through the porous media. A data processor contained within the apparatus compares the measured sensor data with analytical predictions of the response curve based on the transient diffusion equation using Fick's Law, iterating on the choice of an effective vapor diffusion coefficient until the difference between the predicted and measured curves is minimized. Optionally, a purge fluid can forced through the porous media, permitting the apparatus to also measure a gas-phase permeability. The apparatus can be made lightweight, self-powered, and portable for use in the field.

  19. Diffusion coefficients in leaflets of bilayer membranes.

    PubMed

    Seki, Kazuhiko; Mogre, Saurabh; Komura, Shigeyuki

    2014-02-01

    We study diffusion coefficients of liquid domains by explicitly taking into account the two-layered structure called leaflets of the bilayer membrane. In general, the velocity fields associated with each leaflet are different and the layers sliding past each other cause frictional coupling. We obtain analytical results of diffusion coefficients for a circular liquid domain in a leaflet, and quantitatively study their dependence on the interleaflet friction. We also show that the diffusion coefficients diverge in the absence of coupling between the bilayer and solvents, even when the interleaflet friction is taken into account. In order to corroborate our theory, the effect of the interleaflet friction on the correlated diffusion is examined.

  20. Diffusion and transport coefficients in synthetic opals

    SciTech Connect

    Sofo, J. O.; Mahan, G. D.

    2000-07-15

    Opals are structures composed of close-packed spheres in the size range of nano to micrometers. They are sintered to create small necks at the points of contact. We have solved the diffusion problem in such structures. The relation between the diffusion coefficient and the thermal and electrical conductivity is used to estimate the transport coefficients of opal structures as a function of the neck size and the mean free path of the carriers. The theory presented is also applicable to the diffusion problem in other periodic structures. (c) 2000 The American Physical Society.

  1. Attenuation coefficient of usable solar radiation of the global oceans

    NASA Astrophysics Data System (ADS)

    Lin, Junfang; Lee, Zhongping; Ondrusek, Michael; Kahru, Mati

    2016-05-01

    Usable solar radiation (USR) represents spectrally integrated solar energy in the spectral range of 400-560 nm, a domain where photons penetrate the most in oceanic waters and thus contribute to photosynthesis and heating at deeper depths. Through purely numerical simulations, it was found that the diffuse attenuation coefficient of downwelling USR (Kd(USR), m-1) is nearly a constant vertically in the upper water column for clear waters and most turbid waters. Subsequently an empirical model was developed to estimate Kd(USR) based on the diffuse attenuation coefficient at 490 nm (Kd(490), m-1). We here evaluate this relationship using data collected from a wide range of oceanic and coastal environments and found that the relationship between Kd(490) and Kd(USR) developed via the numerical simulation is quite robust. We further refined this relationship to extend the applicability to "clearest" natural waters. This refined relationship was then used to produce sample distribution of Kd(USR) of global oceans. As expected, extremely low Kd(USR) (˜0.02 m-1) was observed in ocean gyres, while significantly higher Kd(USR) (˜5.2 m-1) was found in very turbid coastal regions. A useful application of Kd(USR) is to easily and accurately propagate surface USR to deeper depths, potentially to significantly improve the estimation of basin scale primary production and heat fluxes in the upper water column.

  2. MODIS Solar Diffuser Attenuation Screen Modeling Results

    NASA Technical Reports Server (NTRS)

    Waluschka, Eugene; Xuong, Xiaoxiong; Guenther, Bruce; Barnes, William

    2004-01-01

    On-orbit calibration of the reflected solar bands on the EOS Moderate Resolution Imaging Spectroradiometer (MODIS) is accomplished by have the instrument view a high reflectance diffuse surface illuminated by the sun. For some of the spectral bands this proves to be much too bright a signal that results in the saturation of detectors designed for measuring low reflectance (ocean) surfaces signals. A mechanical attenuation device in the form of a pin hole screen is used to reduce the signals to calibrate these bands. The sensor response to solar illumination of the SD with and without the attenuation screen in place will be presented. The MODIS detector response to the solar diffuser is smooth when the attenuation screen is absent, but has structures up to a few percent when the attenuation screen is present. This structure corresponds to non-uniform illumination from the solar diffuser. Each pin hole produces a pin-hole image of the sun on the solar diffuser, and there are very many pin hole images of the sun on the solar diffuser for each MODIS detector. Even though there are very many pin-hole images of the sun on the solar diffuser, it is no longer perfectly uniformly illuminated. This non-uniformly illuminated solar diffuser produces intensity variation on the focal planes. The results of a very detailed simulation will be discussed which show how the illumination of the focal plane changes as a result of the attenuation, and the impacts on the calibration will be discussed.

  3. Correlation and prediction of gaseous diffusion coefficients.

    NASA Technical Reports Server (NTRS)

    Marrero, T. R.; Mason, E. A.

    1973-01-01

    A new correlation method for binary gaseous diffusion coefficients from very low temperatures to 10,000 K is proposed based on an extended principle of corresponding states, and having greater range and accuracy than previous correlations. There are two correlation parameters that are related to other physical quantities and that are predictable in the absence of diffusion measurements. Quantum effects and composition dependence are included, but high-pressure effects are not. The results are directly applicable to multicomponent mixtures.

  4. Diffusion coefficients in gravel under unsaturated conditions

    SciTech Connect

    Conca, J.L.; Wright, J. )

    1990-05-01

    Diffusion coefficients were experimentally determined in unsaturated gravel to evaluate the effectiveness of gravel as a diffusion barrier to ionic transport in the vadose zone. Water contents were fixed by use of an ultracentrifuge with an ultralow constant rate flow pump supplying solution to the sample via a rotating seal. Once the gravel was at hydraulic steady state, the electrical conductivity was measured, and the diffusion coefficient calculated using the Nernst-Einstein equation. Diffusion coefficient values for potassium ion (D{sub e}) in four types of angular gravel ranged from 1.7 {times} 10{sup {minus}11} m{sup 2}/s (1.7 {times} 10{sup {minus}7} cm{sup 2}/s) for a 6.3-9.5 mm angular granitic gravel at a volumetric water content of 5.5% to 2.2 {times} 10{sup {minus}14} m{sup 2}/s (2.2 {times} 10{sup {minus}10} cm{sup 2}/s) in a 4.0-6.3 mm quartzite gravel at a volumetric water content of 0.47%. Variations in D{sub e} values resulted primarily from differences in water content which depends on gravel type and particle size.

  5. Attenuation Coefficient Estimation of the Healthy Human Thyroid In Vivo

    NASA Astrophysics Data System (ADS)

    Rouyer, J.; Cueva, T.; Portal, A.; Yamamoto, T.; Lavarello, R.

    Previous studies have demonstrated that attenuation coefficients can be useful towards characterizing thyroid tissues. In this work, ultrasonic attenuation coefficients were estimated from healthy human thyroids in vivo using a clinical scanner. The selected subjects were five young, healthy volunteers (age: 26 ± 6 years old, gender: three females, two males) with no reported history of thyroid diseases, no palpable thyroid nodules, no smoking habits, and body mass index less than 30 kg/m2. Echographic examinations were conducted by a trained sonographer using a SonixTouch system (Ultrasonix Medical Corporation, Richmond, BC) equipped with an L14-5 linear transducer array (nominal center frequency of 10 MHz, transducer footprint of 3.8 cm). Radiofrequency data corresponding to the collected echographic images in both transverse and longitudinal views were digitized at a sampling rate of 40 MHz and processed with Matlab codes (MathWorks, Natick, MA) to estimate attenuation coefficients using the spectral log difference method. The estimation was performed using an analysis bandwidth spanning from 4.0 to 9.0 MHz. The average value of the estimated ultrasonic attenuation coefficients was equal to 1.34 ± 0.15 dB/(cm.MHz). The standard deviation of the estimated average attenuation coefficient across different volunteers suggests a non-negligible inter-subject variability in the ultrasonic attenuation coefficient of the human thyroid.

  6. Determination of Dimensionless Attenuation Coefficient in Shaped Resonators

    NASA Technical Reports Server (NTRS)

    Daniels, C.; Steinetz, B.; Finkbeiner, J.; Raman, G.; Li, X.

    2003-01-01

    The value of dimensionless attenuation coefficient is an important factor when numerically predicting high-amplitude acoustic waves in shaped resonators. Both the magnitude of the pressure waveform and the quality factor rely heavily on this dimensionless parameter. Previous authors have stated the values used, but have not completely explained their methods. This work fully describes the methodology used to determine this important parameter. Over a range of frequencies encompassing the fundamental resonance, the pressure waves were experimentally measured at each end of the shaped resonators. At the corresponding dimensionless acceleration, the numerical code modeled the acoustic waveforms generated in the resonator using various dimensionless attenuation coefficients. The dimensionless attenuation coefficient that most closely matched the pressure amplitudes and quality factors of the experimental and numerical results was determined to be the value to be used in subsequent studies.

  7. Apparent diffusion coefficient of normal adrenal glands*

    PubMed Central

    Teixeira, Sara Reis; Elias, Paula Condé Lamparelli; Leite, Andrea Farias de Melo; de Oliveira, Tatiane Mendes Gonçalves; Muglia, Valdair Francisco; Elias Junior, Jorge

    2016-01-01

    Objective To assess the feasibility and reliability of apparent diffusion coefficient (ADC) measurements of normal adrenal glands. Materials and methods This was a retrospective study involving 32 healthy subjects, divided into two groups: prepubertal (PreP, n = 12), aged from 2 months to 12.5 years (4 males; 8 females); and postpubertal (PostP, n = 20), aged from 11.9 to 61 years (5 males; 15 females). Diffusion-weighted magnetic resonance imaging (DW-MRI) sequences were acquired at a 1.5 T scanner using b values of 0, 20, 500, and 1000 s/mm2. Two radiologists evaluated the images. ADC values were measured pixel-by-pixel on DW-MRI scans, and automatic co-registration with the ADC map was obtained. Results Mean ADC values for the right adrenal glands were 1.44 × 10-3 mm2/s for the PreP group and 1.23 × 10-3 mm2/s for the PostP group, whereas they were 1.58 × 10-3 mm2/s and 1.32 × 10-3 mm2/s, respectively, for the left glands. ADC values were higher in the PreP group than in the PostP group (p < 0.05). Agreement between readers was almost perfect (intraclass correlation coefficient, 0.84-0.94; p < 0.05). Conclusion Our results demonstrate the feasibility and reliability of performing DW-MRI measurements of normal adrenal glands. They could also support the feasibility of ADC measurements of small structures. PMID:28057963

  8. Apparent diffusion coefficient normalization of normal liver

    PubMed Central

    Zhu, Jie; Zhang, Jie; Gao, Jia-Yin; Li, Jin-Ning; Yang, Da-Wei; Chen, Min; Zhou, Cheng; Yang, Zheng-Han

    2017-01-01

    Abstract Apparent diffusion coefficient (ADC) measurement in diffusion-weighted imaging (DWI) has been reported to be a helpful biomarker for detection and characterization of lesion. In view of the importance of ADC measurement reproducibility, the aim of this study was to probe the variability of the healthy hepatic ADC values measured at 3 MR scanners from different vendors and with different field strengths, and to investigate the reproducibility of normalized ADC (nADC) value with the spleen as the reference organ. Thirty enrolled healthy volunteers received DWI with GE 1.5T, Siemens 1.5T, and Philips 3.0T magnetic resonance (MR) systems on liver and spleen (session 1) and were imaged again after 10 to 14 days using only GE 1.5T MR and Philips 3.0T MR systems (session 2). Interscan agreement and reproducibility of ADC measurements of liver and the calculated nADC values (ADCliver/ADCspleen) were statistically evaluated between 2 sessions. In session 1, ADC and nADC values of liver were evaluated for the scanner-related variability by 2-way analysis of variance and intraclass correlation coefficients (ICCs). Coefficients of variation (CVs) of ADCs and nADCs of liver were calculated for both 1.5 and 3.0-T MR system. Interscan agreement and reproducibility of ADC measurements of liver and related nADCs between 2 sessions were found to be satisfactory with ICC values of 0.773 to 0.905. In session 1, the liver nADCs obtained from different scanners were consistent (P = 0.112) without any significant difference in multiple comparison (P = 0.117 to >0.99) by using 2-way analysis of variance with post-hoc analysis of Bonferroni method, although the liver ADCs varied significantly (P < 0.001). nADCs measured by 3 scanners were in good interscanner agreements with ICCs of 0.685 to 0.776. The mean CV of nADCs of both 1.5T MR scanners (9.6%) was similar to that of 3.0T MR scanner (8.9%). ADCs measured at 3 MR scanners with different field strengths and vendors

  9. Calculation and application of combined diffusion coefficients in thermal plasmas

    NASA Astrophysics Data System (ADS)

    Murphy, Anthony B.

    2014-03-01

    The combined diffusion coefficient method is widely used to treat the mixing and demixing of different plasma gases and vapours in thermal plasmas, such as welding arcs and plasma jets. It greatly simplifies the treatment of diffusion for many gas mixtures without sacrificing accuracy. Here, three subjects that are important in the implementation of the combined diffusion coefficient method are considered. First, it is shown that different expressions for the combined diffusion coefficients, arising from different definitions for the stoichiometric coefficients that assign the electrons to the two gases, are equivalent. Second, an approach is presented for calculating certain partial differential terms in the combined temperature and pressure diffusion coefficients that can cause difficulties. Finally, a method for applying the combined diffusion coefficients in computational models, which typically require diffusion to be expressed in terms of mass fraction gradients, is given.

  10. ANALYTIC FORMS OF THE PERPENDICULAR DIFFUSION COEFFICIENT IN NRMHD TURBULENCE

    SciTech Connect

    Shalchi, A.

    2015-02-01

    In the past different analytic limits for the perpendicular diffusion coefficient of energetic particles interacting with magnetic turbulence were discussed. These different limits or cases correspond to different transport modes describing how the particles are diffusing across the large-scale magnetic field. In the current paper we describe a new transport regime by considering the model of noisy reduced magnetohydrodynamic turbulence. We derive different analytic forms of the perpendicular diffusion coefficient, and while we do this, we focus on the aforementioned new transport mode. We show that for this turbulence model a small perpendicular diffusion coefficient can be obtained so that the latter diffusion coefficient is more than hundred times smaller than the parallel diffusion coefficient. This result is relevant to explain observations in the solar system where such small perpendicular diffusion coefficients have been reported.

  11. Diffusion coefficient of three-dimensional Yukawa liquids

    SciTech Connect

    Dzhumagulova, K. N.; Ramazanov, T. S.; Masheeva, R. U.

    2013-11-15

    The purpose of this work is an investigation of the diffusion coefficient of the dust component in complex plasma. The computer simulation of the Yukawa liquids was made on the basis of the Langevin equation, which takes into account the influence of buffer plasma on the dust particles dynamics. The Green–Kubo relation was used to calculate the diffusion coefficient. Calculations of the diffusion coefficient for a wide range of the system parameters were performed. Using obtained numerical data, we constructed the interpolation formula for the diffusion coefficient. We also show that the interpolation formula correctly describes experimental data obtained under microgravity conditions.

  12. Temperature dependence of the diffusion coefficient of nanoparticles

    NASA Astrophysics Data System (ADS)

    Rudyak, V. Ya.; Dubtsov, S. N.; Baklanov, A. M.

    2008-06-01

    The temperature dependence of the diffusion coefficient of nanoparticles in gases has been experimentally studied. It is established that this dependence significantly differs from that predicted by various correlations, in particular, by the Cunningham-Millikan-Davies correlation that is used as an instrumental basis for virtually all methods of measurement of the diffusion coefficient in aerosols.

  13. Analytic expressions for ULF wave radiation belt radial diffusion coefficients

    PubMed Central

    Ozeke, Louis G; Mann, Ian R; Murphy, Kyle R; Jonathan Rae, I; Milling, David K

    2014-01-01

    We present analytic expressions for ULF wave-derived radiation belt radial diffusion coefficients, as a function of L and Kp, which can easily be incorporated into global radiation belt transport models. The diffusion coefficients are derived from statistical representations of ULF wave power, electric field power mapped from ground magnetometer data, and compressional magnetic field power from in situ measurements. We show that the overall electric and magnetic diffusion coefficients are to a good approximation both independent of energy. We present example 1-D radial diffusion results from simulations driven by CRRES-observed time-dependent energy spectra at the outer boundary, under the action of radial diffusion driven by the new ULF wave radial diffusion coefficients and with empirical chorus wave loss terms (as a function of energy, Kp and L). There is excellent agreement between the differential flux produced by the 1-D, Kp-driven, radial diffusion model and CRRES observations of differential electron flux at 0.976 MeV—even though the model does not include the effects of local internal acceleration sources. Our results highlight not only the importance of correct specification of radial diffusion coefficients for developing accurate models but also show significant promise for belt specification based on relatively simple models driven by solar wind parameters such as solar wind speed or geomagnetic indices such as Kp. Key Points Analytic expressions for the radial diffusion coefficients are presented The coefficients do not dependent on energy or wave m value The electric field diffusion coefficient dominates over the magnetic PMID:26167440

  14. Improved diffusion coefficients generated from Monte Carlo codes

    SciTech Connect

    Herman, B. R.; Forget, B.; Smith, K.; Aviles, B. N.

    2013-07-01

    Monte Carlo codes are becoming more widely used for reactor analysis. Some of these applications involve the generation of diffusion theory parameters including macroscopic cross sections and diffusion coefficients. Two approximations used to generate diffusion coefficients are assessed using the Monte Carlo code MC21. The first is the method of homogenization; whether to weight either fine-group transport cross sections or fine-group diffusion coefficients when collapsing to few-group diffusion coefficients. The second is a fundamental approximation made to the energy-dependent P1 equations to derive the energy-dependent diffusion equations. Standard Monte Carlo codes usually generate a flux-weighted transport cross section with no correction to the diffusion approximation. Results indicate that this causes noticeable tilting in reconstructed pin powers in simple test lattices with L2 norm error of 3.6%. This error is reduced significantly to 0.27% when weighting fine-group diffusion coefficients by the flux and applying a correction to the diffusion approximation. Noticeable tilting in reconstructed fluxes and pin powers was reduced when applying these corrections. (authors)

  15. Measurement of Acoustic Attenuation and Absorption Coefficients using Thermometry

    NASA Astrophysics Data System (ADS)

    Morris, Hugh; Rivens, Ian; Shaw, Adam; ter Haar, Gail

    2007-05-01

    Accurate knowledge of both the attenuation and the absorption coefficient of tissue are required when planning an optimal high intensity focused ultrasound treatment. A novel technique for simple measurement of this parameters has been developed in which a thin-film thermocouple (TFT) is placed between two layers of tissue of different thicknesses. The sample can be rotated about an axis through the junction of the TFT so that it can be insonated from either side leaving the tissue adjacent to the junction unchanged, but changing the overlying thickness. The attenuation and absorption coefficients can be calculated from the heating curves measured in the two orientations. Experiments have been carried out in both tissue mimicking material (TMM) and in ex vivo liver tissue. Weakly focused transducers, resonant at 1.05 MHz, 2.4 MHz and 3.55 MHz were used at free-field spatial peak intensities of 9-14 W/cm2. The temperature rise was measured as a function of time using a TFT. These thermocouples are not subject to the viscous heating artefact that is common to other thermocouple devices and so are advantageous for this purpose. Alignment was achieved with a 3D automated gantry system, which was controlled with specialised software. Timing and data acquisition were also controlled with this software. All experiments were carried out in degassed water. Results for TMM and degassed excised bovine liver are presented.

  16. An inequality for longitudinal and transverse wave attenuation coefficients.

    PubMed

    Norris, Andrew N

    2017-01-01

    Total absorption, defined as the net flux of energy out of a bounded region averaged over one cycle for time harmonic motion, must be non-negative when there are no sources of energy within the region. This passivity condition places constraints on the non-dimensional absorption coefficients of longitudinal and transverse waves, γL and γT, in isotropic linearly viscoelastic materials. Typically, γL, γT are small, in which case the constraints imply that coefficients of attenuation per unit length, αL, αT, must satisfy the inequality αL/αT≥4cT(3)/3cL(3) where cL, cT are the wave speeds. This inequality, which as far as the author is aware, has not been presented before, provides a relative bound on wave speed in terms of attenuation, or vice versa. It also serves as a check on the consistency of ultrasonic measurements from the literature, with most but not all of the data considered passing the positive absorption test.

  17. Analytic expressions for ULF wave radiation belt radial diffusion coefficients.

    PubMed

    Ozeke, Louis G; Mann, Ian R; Murphy, Kyle R; Jonathan Rae, I; Milling, David K

    2014-03-01

    We present analytic expressions for ULF wave-derived radiation belt radial diffusion coefficients, as a function of L and Kp, which can easily be incorporated into global radiation belt transport models. The diffusion coefficients are derived from statistical representations of ULF wave power, electric field power mapped from ground magnetometer data, and compressional magnetic field power from in situ measurements. We show that the overall electric and magnetic diffusion coefficients are to a good approximation both independent of energy. We present example 1-D radial diffusion results from simulations driven by CRRES-observed time-dependent energy spectra at the outer boundary, under the action of radial diffusion driven by the new ULF wave radial diffusion coefficients and with empirical chorus wave loss terms (as a function of energy, Kp and L). There is excellent agreement between the differential flux produced by the 1-D, Kp-driven, radial diffusion model and CRRES observations of differential electron flux at 0.976 MeV-even though the model does not include the effects of local internal acceleration sources. Our results highlight not only the importance of correct specification of radial diffusion coefficients for developing accurate models but also show significant promise for belt specification based on relatively simple models driven by solar wind parameters such as solar wind speed or geomagnetic indices such as Kp.

  18. Numerical Integral of Resistance Coefficients in Diffusion

    NASA Astrophysics Data System (ADS)

    Zhang, Q. S.

    2017-01-01

    The resistance coefficients in the screened Coulomb potential of stellar plasma are evaluated to high accuracy. I have analyzed the possible singularities in the integral of scattering angle. There are possible singularities in the case of an attractive potential. This may result in a problem for the numerical integral. In order to avoid the problem, I have used a proper scheme, e.g., splitting into many subintervals where the width of each subinterval is determined by the variation of the integrand, to calculate the scattering angle. The collision integrals are calculated by using Romberg’s method, therefore the accuracy is high (i.e., ∼10‑12). The results of collision integrals and their derivatives for ‑7 ≤ ψ ≤ 5 are listed. By using Hermite polynomial interpolation from those data, the collision integrals can be obtained with an accuracy of 10‑10. For very weakly coupled plasma (ψ ≥ 4.5), analytical fittings for collision integrals are available with an accuracy of 10‑11. I have compared the final results of resistance coefficients with other works and found that, for a repulsive potential, the results are basically the same as others’ for an attractive potential, the results in cases of intermediate and strong coupling show significant differences. The resulting resistance coefficients are tested in the solar model. Comparing with the widely used models of Cox et al. and Thoul et al., the resistance coefficients in the screened Coulomb potential lead to a slightly weaker effect in the solar model, which is contrary to the expectation of attempts to solve the solar abundance problem.

  19. The temperature variation of hydrogen diffusion coefficients in metal alloys

    NASA Technical Reports Server (NTRS)

    Danford, M. D.

    1990-01-01

    Hydrogen diffusion coefficients were measured as a function of temperature for a few metal alloys using an electrochemical evolution technique. Results from these measurements are compared to those obtained by the time-lag method. In all cases, diffusion coefficients obtained by the electrochemical method are larger than those by the time-lag method by an order of magnitude or more. These differences are attributed mainly to hydrogen trapping.

  20. Calculation of Diffusion Coefficients from Bounce Resonance with Magnetosonic Waves

    NASA Astrophysics Data System (ADS)

    Tao, X.; Li, X.; Lu, Q.; Dai, L.

    2015-12-01

    Theoretical bounce resonance diffusion coefficients for interactions between electrons and magnetosonic waves are calculated and validated using guiding-center test particle simulations. First, we compare the theoretical diffusion coefficients of Roberts and Schulz with test particle simulations and find perfect agreement. However, the theoretical diffusion coefficients of Roberts and Schulz assume waves to be present on the whole trajectories of particles; therefore, they are not directly applicable to magnetosonic waves, which are found to be confined to equatorial regions from observations. Second, we derive a new set of bounce-resonance diffusion coefficients, taking into consideration the equatorial confinement of magnetosonic waves. These new diffusion coefficients are also validated by test particle simulations. Using a previously published magnetosonic wave model, our results demonstrate that bounce-resonance diffusion mainly results in strong pitch angle scattering of energetic electrons even with a moderate wave amplitude of 50 pT. We conclude that bounce-resonance diffusion plays an important role in relativistic electron dynamics and should be incorporated into global radiation belt modeling.

  1. Attenuation coefficient of single-mode periodic waveguides.

    PubMed

    Baron, A; Mazoyer, S; Smigaj, W; Lalanne, P

    2011-10-07

    It is widely accepted that, on ensemble average, the transmission T of guided modes decays exponentially with the waveguide length L due to small imperfections, leading to the important figure of merit defined as the attenuation-rate coefficient α=-⟨ln(T)⟩/L. In this Letter, we evidence that the exponential-damping law is not valid in general for periodic monomode waveguides, especially as the group velocity decreases. This result, that contradicts common beliefs and experimental practices aiming at measuring α, is supported by a theoretical study of light transport in the limit of very small imperfections, and by numerical results obtained for two waveguide geometries that offer contrasted damping behaviors.

  2. Uranium soft x-ray total attenuation coefficients

    SciTech Connect

    Del Grande, N.K.; Oliver, A.J.

    1981-01-01

    Uranium total attenuation coefficients were measured continuously from 0.84 to 6.0 keV and at selected higher energies using a vacuum single crystal diffractometer and flow-proportional counter. Statistical fluctuations ranged from 0.5% to 2%. The overall accuracy was 3%. Prominent structure was measured within 20 eV of the M/sub 5/ (3.552 keV) and M/sub 4/ (3.728 keV) edges. Jump ratios were determined from log-log polynomial fits to data at energies apart from the near-edge regions. These data were compared with calculations based on a relativistic HFS central potential model and with previously tabulated data.

  3. Attenuation Coefficient of Single-Mode Periodic Waveguides

    NASA Astrophysics Data System (ADS)

    Baron, A.; Mazoyer, S.; Smigaj, W.; Lalanne, P.

    2011-10-01

    It is widely accepted that, on ensemble average, the transmission T of guided modes decays exponentially with the waveguide length L due to small imperfections, leading to the important figure of merit defined as the attenuation-rate coefficient α=-⟨ln⁡(T)⟩/L. In this Letter, we evidence that the exponential-damping law is not valid in general for periodic monomode waveguides, especially as the group velocity decreases. This result, that contradicts common beliefs and experimental practices aiming at measuring α, is supported by a theoretical study of light transport in the limit of very small imperfections, and by numerical results obtained for two waveguide geometries that offer contrasted damping behaviors.

  4. Variational calculation of transport coefficients in diffusive lattice gases

    NASA Astrophysics Data System (ADS)

    Arita, Chikashi; Krapivsky, P. L.; Mallick, Kirone

    2017-03-01

    A diffusive lattice gas is characterized by the diffusion coefficient depending only on the density. The Green-Kubo formula for diffusivity can be represented as a variational formula, but even when the equilibrium properties of a lattice gas are analytically known, the diffusion coefficient can be computed only in the exceptional situation when the lattice gas is gradient. In the general case, minimization over an infinite-dimensional space is required. We propose an approximation scheme based on minimizing over finite-dimensional subspaces of functions. The procedure is demonstrated for one-dimensional generalized exclusion processes in which each site can accommodate at most two particles. Our analytical predictions provide upper bounds for the diffusivity that are very close to simulation results throughout the entire density range. We also analyze nonequilibrium density profiles for finite chains coupled to reservoirs. The predictions for the profiles are in excellent agreement with simulations.

  5. Effects of Diffusive Property Heterogeneity on Effective MatrixDiffusion Coefficient for Fractured Rock

    SciTech Connect

    Zhang, Yingqi; Liu, Hui-hai; Zhou, Quanlin; Finsterle, Stefan

    2005-08-16

    Heterogeneities of diffusion properties are likely toinfluence the effective matrix diffusion coefficient determined fromtracer breakthrough curves. The objectives of this study are (1) toexamine if it is appropriate to use a single, effective matrix diffusioncoefficient to predict breakthrough curves in a fractured formation, (2)to examine if a postulated scale dependence of the effective matrixdiffusion coefficient is caused by heterogeneity in diffusion properties,and (3) to examine whether multirate diffusion results in the previouslyobserved time dependence of the effective matrix diffusion coefficient.The results show that the use of a single effective matrix diffusioncoefficient is appropriate only if the interchannel and intrachannelvariability of diffusion properties is small. The scale dependence of theeffective matrix diffusion coefficient is not caused by the studied typesof heterogeneity. Finally, the multirate diffusion process does notresult in the time dependence of the effective matrix diffusioncoefficient. oefficient is appropriate only if the inter- andintrachannel variability of diffusion properties is small. The scaledependence of the effective matrix diffusion coefficient is not caused byeither type of the studied heterogeneity. Finally, the multi-ratediffusion process does not result in the time dependence of the effectivematrix diffusion coefficient.

  6. Quantitative photoacoustic microscopy of optical absorption coefficients from acoustic spectra in the optical diffusive regime.

    PubMed

    Guo, Zijian; Favazza, Christopher; Garcia-Uribe, Alejandro; Wang, Lihong V

    2012-06-01

    Photoacoustic (PA) microscopy (PAM) can image optical absorption contrast with ultrasonic spatial resolution in the optical diffusive regime. Conventionally, accurate quantification in PAM requires knowledge of the optical fluence attenuation, acoustic pressure attenuation, and detection bandwidth. We circumvent this requirement by quantifying the optical absorption coefficients from the acoustic spectra of PA signals acquired at multiple optical wavelengths. With the acoustic spectral method, the absorption coefficients of an oxygenated bovine blood phantom at 560, 565, 570, and 575 nm were quantified with errors of <3%. We also quantified the total hemoglobin concentration and hemoglobin oxygen saturation in a live mouse. Compared with the conventional amplitude method, the acoustic spectral method provides greater quantification accuracy in the optical diffusive regime. The limitations of the acoustic spectral method was also discussed.

  7. Determining Pitch-angle Diffusion Coefficients from Test Particle Simulations

    NASA Astrophysics Data System (ADS)

    Ivascenko, Alex; Lange, Sebastian; Spanier, Felix; Vainio, Rami

    2016-12-01

    The transport and acceleration of charged particles in turbulent media are topics of great interest in space physics and interstellar astrophysics. These processes are dominated by the scattering of particles off magnetic irregularities. The scattering process itself is usually described by small-angle scattering, with the pitch-angle coefficient {D}μ μ playing a major role. Since the diffusion coefficient {D}μ μ can be determined analytically only for the approximation of quasilinear theory, the determination of this coefficient from numerical simulations has become more important. So far these simulations have yielded particle tracks for small-scale scattering, which can then be interpreted using the running diffusion coefficients. This method has a limited range of validity. This paper presents two new methods that allow for the calculation of the pitch-angle diffusion coefficient from numerical simulations. These methods no longer analyze particle trajectories and instead examine the change of particle distribution functions. It is shown that these methods provide better resolved results and allow for the analysis of strong turbulence. The application of these methods to Monte Carlo simulations of particle scattering and hybrid MHD-particle simulations is presented. Both analysis methods are able to recover the diffusion coefficients used as input for the Monte Carlo simulations and provide better results in MHD simulations, especially for stronger turbulence.

  8. Diffusion coefficient in hydrogel under high-frequency ultrasound

    NASA Astrophysics Data System (ADS)

    Tsukamoto, Akira; Tanaka, Kei; Kumata, Tatsuya; Watanabe, Yoshiaki; Miyata, Shogo; Furukawa, Katsuko; Ushida, Takashi

    2007-03-01

    Modulating hydrogel properties by external stimuli can be applied for drug delivery system. For example, ultrasound can enhance drug release from hydrogel by the mechanism which is not fully understood. We measured diffusion coefficient in hydrogel under high-frequency ultrasound to understand mass transport property. To estimate diffusion coefficient, FRAP (fluorescence recovery after photobleaching) technique was applied with time-lapse fluorescence microscopy and we analyzed fluorescence recovery after photobleaching of FITC-dextran (4˜40 kDa) which was fully fused in agarose gel (1˜3 %). As a result, diffusion coefficient was altered when agarose gel was sonicated by 1MHz ultrasound with 400kPa (peak-peak). We discussed several possible underlying mechanisms such as cavitation, heat and phase transition with extended experimental data.

  9. Spatial Mapping of Translational Diffusion Coefficients Using Diffusion Tensor Imaging: A Mathematical Description

    PubMed Central

    SHETTY, ANIL N.; CHIANG, SHARON; MALETIC-SAVATIC, MIRJANA; KASPRIAN, GREGOR; VANNUCCI, MARINA; LEE, WESLEY

    2016-01-01

    In this article, we discuss the theoretical background for diffusion weighted imaging and diffusion tensor imaging. Molecular diffusion is a random process involving thermal Brownian motion. In biological tissues, the underlying microstructures restrict the diffusion of water molecules, making diffusion directionally dependent. Water diffusion in tissue is mathematically characterized by the diffusion tensor, the elements of which contain information about the magnitude and direction of diffusion and is a function of the coordinate system. Thus, it is possible to generate contrast in tissue based primarily on diffusion effects. Expressing diffusion in terms of the measured diffusion coefficient (eigenvalue) in any one direction can lead to errors. Nowhere is this more evident than in white matter, due to the preferential orientation of myelin fibers. The directional dependency is removed by diagonalization of the diffusion tensor, which then yields a set of three eigenvalues and eigenvectors, representing the magnitude and direction of the three orthogonal axes of the diffusion ellipsoid, respectively. For example, the eigenvalue corresponding to the eigenvector along the long axis of the fiber corresponds qualitatively to diffusion with least restriction. Determination of the principal values of the diffusion tensor and various anisotropic indices provides structural information. We review the use of diffusion measurements using the modified Stejskal–Tanner diffusion equation. The anisotropy is analyzed by decomposing the diffusion tensor based on symmetrical properties describing the geometry of diffusion tensor. We further describe diffusion tensor properties in visualizing fiber tract organization of the human brain. PMID:27441031

  10. THE DETERMINATION OF DIFFUSION COEFFICIENT OF INVERT MATERIALS

    SciTech Connect

    P. Heller and J. Wright

    2000-01-11

    The Engineered Barrier System (EBS) Testing Department is performing tests in the Department of Energy's Atlas Facility to evaluate the performance of various means for increasing the time for breakthrough of radionuclides from the waste package to the base of the invert. This includes testing various barriers in the invert as a means of increasing breakthrough time through the process of diffusion. A diffusion barrier may serve as an invert material for the emplacement drifts. The invert material may consist of crushed tuff from the repository excavation at Yucca Mountain or silica sand. The objective of this report is to determine the diffusion coefficient of the crushed tuff and silica sand invert materials specified by the EBS Testing Department. The laboratory derived information from the testing was used in the Nernst-Einstein equation (Jurinak et al. 1987, p. 626) to determine the diffusion coefficient of the invert material. This report transmits the results and describes the methodology and interpretation. The scope of this report is to determine the diffusion coefficients of the invert materials mentioned above using the centrifuge at UFA Ventures. Standard laboratory procedures, described in Section 2 of this report, were used. The diffusion coefficients are to be determined over a range of moisture contents. The report contains the diffusion coefficients calculated by the Nernst-Einstein equation (Jurinak et al. 1987, p. 626) that become a part of the Technical Database. Raw data is also included in the report, however this data does not become part of the Technical Database as per Section 3.23 of AP-SIII.3Q ''Submittal and Incorporation of Data to the Technical Data Management System''. A sieve analysis of the samples was not conducted as part of this report, but sieve analysis may be accomplished as part of other reports. Two samples of crushed tuff and two samples of silica sand were tested.

  11. Scale dependency of the effective matrix diffusion coefficient

    SciTech Connect

    Liu, H.H.; Bodvarsson, G.S.; Zhang, G.

    2003-05-30

    It has been recognized that matrix diffusion is an important process for retarding solute transport in fractured rock. Based on analyses of tracer transport data from a number of field tests, we demonstrate for the first time that the effective matrix-diffusion coefficient may be scale dependent and generally increases with test scale. A preliminary theoretical explanation of this scale dependency is also presented, based on the hypothesis that solute travel paths within a fracture network are fractals.

  12. Exact curvilinear diffusion coefficients in the repton model.

    PubMed

    Buhot, A

    2005-10-01

    The Rubinstein-Duke or repton model is one of the simplest lattice model of reptation for the diffusion of a polymer in a gel or a melt. Recently, a slightly modified model with hardcore interactions between the reptons has been introduced. The curvilinear diffusion coefficients of both models are exactly determined for all chain lengths. The case of periodic boundary conditions is also considered.

  13. Signal attenuation of PFG restricted anomalous diffusions in plate, sphere, and cylinder

    NASA Astrophysics Data System (ADS)

    Lin, Guoxing; Zheng, Shaokuan; Liao, Xinli

    2016-11-01

    Pulsed field gradient (PFG) NMR is a noninvasive tool to study anomalous diffusion, which exists widely in many systems such as in polymer or biological systems, in porous material, in single file structures and in fractal geometries. In a real system, the diffusion could be a restricted or a tortuous anomalous diffusion, rather than a free diffusion as the domains for fast and slow transport could coexist. Though there are signal attenuation expressions for free anomalous diffusion in literature, the signal attenuation formalisms for restricted anomalous diffusion is very limited, except for a restricted time-fractional diffusion within a plate reported recently. To better understand the PFG restricted fractional diffusion, in this paper, the PFG signal attenuation expressions were derived for three typical structures (plate, sphere, and cylinder) based on two models: fractal derivative model and fractional derivative model. These signal attenuation expressions include two parts, the time part Tn(t) and the space part Xn(r). Unlike normal diffusion, the time part Tn(t) in time-fractional diffusion can be either a Mittag-Leffler function from the fractional derivative model or a stretched exponential function from the fractal derivative model. However, provided the restricted normal diffusion and the restricted time-fractional diffusion are in an identical structure, they will have the same space part Xn(r) as both diffusions have the same space derivative parameter β equaling 2, therefore, they should have similar diffractive patterns. The restricted general fractional diffusion within a plate is also investigated, which indicates that at a long time limit, the diffusion type is insignificant to the diffractive pattern that depends only on the structure and the gradient pulses. The expressions describing the time-dependent behaviors of apparent diffusion coefficient Df,app for restricted anomalous diffusion are also proposed in this paper. Both the short and long

  14. Scaling law for diffusion coefficients in simple melts

    NASA Astrophysics Data System (ADS)

    Li, G. X.; Liu, C. S.; Zhu, Z. G.

    2005-03-01

    Employing realistic many-body potentials for a series of simple melts, including Ag, Al, Au, Co, Cu, Mg, Ni, Pb, Pd, Pt, Rh, and Si, we tested by molecular-dynamics simulation the scaling laws of diffusion coefficients with different expressions of the reduction parameters. Our simulation results give sound support to the universal excess entropy scaling laws proposed by Rosenfeld [Phys. Rev. A 15, 2545 (1977)] and Dzugutov [Nature (London) 381, 137 (1996)] for transport coefficients in liquid metals. In particular, we find that excess entropy (Sex) universally scales with temperature as Sex=-ES/T . When the diffusion coefficient is scaled as Dzugutov suggested, ES is essentially identical to the Arrhenius activation energy, indicating that the entropic component in the Arrhenius activation energy is solely responsible for controlling the diffusion rate. Thus, there exists a link between the scaling law and the Arrhenius law, i.e., the excess entropy scaling law for the diffusion coefficient can be interpreted as a straightforward extension of the Arrhenius law.

  15. Optimal estimation of diffusion coefficients from single-particle trajectories

    NASA Astrophysics Data System (ADS)

    Vestergaard, Christian L.; Blainey, Paul C.; Flyvbjerg, Henrik

    2014-02-01

    How does one optimally determine the diffusion coefficient of a diffusing particle from a single-time-lapse recorded trajectory of the particle? We answer this question with an explicit, unbiased, and practically optimal covariance-based estimator (CVE). This estimator is regression-free and is far superior to commonly used methods based on measured mean squared displacements. In experimentally relevant parameter ranges, it also outperforms the analytically intractable and computationally more demanding maximum likelihood estimator (MLE). For the case of diffusion on a flexible and fluctuating substrate, the CVE is biased by substrate motion. However, given some long time series and a substrate under some tension, an extended MLE can separate particle diffusion on the substrate from substrate motion in the laboratory frame. This provides benchmarks that allow removal of bias caused by substrate fluctuations in CVE. The resulting unbiased CVE is optimal also for short time series on a fluctuating substrate. We have applied our estimators to human 8-oxoguanine DNA glycolase proteins diffusing on flow-stretched DNA, a fluctuating substrate, and found that diffusion coefficients are severely overestimated if substrate fluctuations are not accounted for.

  16. Optimal estimation of diffusion coefficients from single-particle trajectories.

    PubMed

    Vestergaard, Christian L; Blainey, Paul C; Flyvbjerg, Henrik

    2014-02-01

    How does one optimally determine the diffusion coefficient of a diffusing particle from a single-time-lapse recorded trajectory of the particle? We answer this question with an explicit, unbiased, and practically optimal covariance-based estimator (CVE). This estimator is regression-free and is far superior to commonly used methods based on measured mean squared displacements. In experimentally relevant parameter ranges, it also outperforms the analytically intractable and computationally more demanding maximum likelihood estimator (MLE). For the case of diffusion on a flexible and fluctuating substrate, the CVE is biased by substrate motion. However, given some long time series and a substrate under some tension, an extended MLE can separate particle diffusion on the substrate from substrate motion in the laboratory frame. This provides benchmarks that allow removal of bias caused by substrate fluctuations in CVE. The resulting unbiased CVE is optimal also for short time series on a fluctuating substrate. We have applied our estimators to human 8-oxoguanine DNA glycolase proteins diffusing on flow-stretched DNA, a fluctuating substrate, and found that diffusion coefficients are severely overestimated if substrate fluctuations are not accounted for.

  17. An approximation to the reflection coefficient of plane longitudinal waves based on the diffusive-viscous wave equation

    NASA Astrophysics Data System (ADS)

    Zhao, Haixia; Gao, Jinghuai; Peng, Jigen

    2017-01-01

    The frequency-dependent seismic anomalies related to hydrocarbon reservoirs have lately attracted wide interest. The diffusive-viscous model was proposed to explain these anomalies. When an incident diffusive-viscous wave strikes a boundary between two different media, it is reflected and transmitted. The equation for the reflection coefficient is quite complex and laborious, so it does not provide an intuitive understanding of how different amplitude relates to the parameters of the media and how variation of a particular parameter affects the reflection coefficient. In this paper, we firstly derive a two-term (intercept-gradient) and three-term (intercept-gradient-curvature) approximation to the reflection coefficient of the plane diffusive-viscous wave without any assumptions. Then, we study the limitations of the obtained approximations by comparing the approximate value of the reflection coefficient with its exact value. Our results show that the two approximations match well with the exact solutions within the incident angle of 35°. Finally, we analyze the effects of diffusive and viscous attenuation parameters, velocity and density in the diffusive-viscous wave equation on the intercept, gradient and curvature terms in the approximations. The results show that the diffusive attenuation parameter has a big impact on them, while the viscous attenuation parameter is insensitive to them; the velocity and density have a significant influence on the normal reflections and they distinctly affect the intercept, gradient and curvature term at lower acoustic impedance.

  18. Determination of diffusion coefficient in disordered organic semiconductors

    NASA Astrophysics Data System (ADS)

    Rani, Varsha; Sharma, Akanksha; Ghosh, Subhasis

    2016-05-01

    Charge carrier transport in organic semiconductors is dominated by positional and energetic disorder in Gaussian density of states (GDOS) and is characterized by hopping through localized states. Due to the immobilization of charge carriers in these localized states, significant non-uniform carrier distribution exists, resulting diffusive transport. A simple, nevertheless powerful technique to determine diffusion coefficient D in disordered organic semiconductors has been presented. Diffusion coefficients of charge carriers in two technologically important organic molecular semiconductors, Pentacene and copper phthalocyanine (CuPc) have been measured from current-voltage (J-V) characteristics of Al/Pentacene/Au and Al/CuPc/Au based Schottky diodes. Ideality factor g and carrier mobility μ have been calculated from the exponential and space charge limited region respectively of J-V characteristics. Classical Einstein relation is not valid in organic semiconductors due to energetic disorders in DOS. Using generalized Einstein relation, diffusion coefficients have been obtained to be 1.31×10-6 and 1.73×10-7 cm2/s for Pentacene and CuPc respectively.

  19. Role of the Molar Volume on Estimated Diffusion Coefficients

    NASA Astrophysics Data System (ADS)

    Santra, Sangeeta; Paul, Aloke

    2015-09-01

    The role of the molar volume on the estimated diffusion parameters has been speculated for decades. The Matano-Boltzmann method was the first to be developed for the estimation of the variation of the interdiffusion coefficients with composition. However, this could be used only when the molar volume varies ideally or remains constant. Although there are no such systems, this method is still being used to consider the ideal variation. More efficient methods were developed by Sauer-Freise, Den Broeder, and Wagner to tackle this problem. However, there is a lack of research indicating the most efficient method. We have shown that Wagner's method is the most suitable one when the molar volume deviates from the ideal value. Similarly, there are two methods for the estimation of the ratio of intrinsic diffusion coefficients at the Kirkendall marker plane proposed by Heumann and van Loo. The Heumann method, like the Matano-Boltzmann method, is suitable to use only when the molar volume varies more or less ideally or remains constant. In most of the real systems, where molar volume deviates from the ideality, it is safe to use the van Loo method. We have shown that the Heumann method introduces large errors even for a very small deviation of the molar volume from the ideal value. On the other hand, the van Loo method is relatively less sensitive to it. Overall, the estimation of the intrinsic diffusion coefficient is more sensitive than the interdiffusion coefficient.

  20. Intercomparison of diffusion coefficient derived from the through-diffusion experiment using different numerical methods.

    PubMed

    Chen, Chih-Lung; Wang, Tsing-Hai; Lee, Ching-Hor; Teng, Shi-Ping

    Diffusion is a dominant mechanism regulating the transport of released nuclides. The through-diffusion method is typically applied to determine the diffusion coefficients (D). Depending on the design of the experiment, the concentrations in the source term [i.e., inlet reservoir (IR)] or the end term [i.e., outlet reservoir (OR)] can be fixed or vary. The combinations involve four distinct models (i.e., the CC-CC model, CC-VC model, VC-CC model, and the VC-VC model). Studies discussing the VC-CC model are scant. An analytical method considering the decay effect is required to accurately interpret the radioactive nuclide diffusion experiment results. Therefore, we developed a CC-CC model and a CC-VC model with a decay effect and the simplified formulas of these two models to determine the diffusion coefficient (i.e., the CC-CC method and CC-VC method). We also proposed two simplified methods using the VC-VC model to determine the diffusion coefficient straightforwardly based upon the concentration variation in IR and OR. More importantly, the best advantage of proposed method over others is that one can derive three diffusion coefficients based on one run of experiment. In addition, applying our CC-VC method to those data reported from Radiochemica Acta 96:111-117, 2008; and J Contam Hydrol 35:55-65, 1998, derived comparable diffusion coefficient lying in the identical order of magnitude. Furthermore, we proposed a formula to determine the conceptual critical time (Tc), which is particularly beneficial for the selection of using CC-VC or VC-VC method. Based on our proposed method, it becomes possible to calculate diffusion coefficient from a through-diffusion experiment in a shorter period of time.

  1. Vertical eddy diffusion coefficient from the LANDSAT imagery

    NASA Technical Reports Server (NTRS)

    Viswanadham, Y. (Principal Investigator); Torsani, J. A.

    1982-01-01

    Analysis of five stable cases of the smoke plumes that originated in eastern Cabo Frio (22 deg 59'S; 42 deg 02'W), Brazil using LANDSAT imagery is presented for different months and years. From these images the lateral standard deviation (sigma sub y) and the lateral eddy diffusion coefficient (K sub y) are obtained from the formula based on Taylor's theory of diffusion by continuous moment. The rate of kinetic energy dissipation (e) is evaluated from the diffusion parameters sigma sub y and K sub y. Then, the vertical diffusion coefficient (K sub z) is estimated using Weinstock's formulation. These results agree well with the previous experimental values obtained over water surfaces by various workers. Values of e and K sub z show the weaker mixing processes in the marine stable boundary layer. The data sample is apparently to small to include representative active turbulent regions because such regions are so intermittent in time and in space. These results form a data base for use in the development and validation of mesoscale atmospheric diffusion models.

  2. The Attenuation of Correlation Coefficients: A Statistical Literacy Issue

    ERIC Educational Resources Information Center

    Trafimow, David

    2016-01-01

    Much of the science reported in the media depends on correlation coefficients. But the size of correlation coefficients depends, in part, on the reliability with which the correlated variables are measured. Understanding this is a statistical literacy issue.

  3. Measurement of cesium diffusion coefficients in graphite IG-110

    NASA Astrophysics Data System (ADS)

    Carter, L. M.; Brockman, J. D.; Loyalka, S. K.; Robertson, J. D.

    2015-05-01

    An understanding of the transport of fission products in High Temperature Gas-Cooled Reactors (HTGRs) is needed for operational safety as well as source term estimations. We have measured diffusion coefficients of Cs in IG-110 by using the release method, wherein we infused small graphite spheres with Cs and measured the release rates using ICP-MS. Diffusion behavior was investigated in the temperature range of 1100-1300 K. We have obtained: DCs = (1.0 ×10-7m2 /s) exp(-1.1 ×105J /mol/RT) and, compared our results with those available in the literature.

  4. Measurement of diffusion coefficients from solution rates of bubbles

    NASA Technical Reports Server (NTRS)

    Krieger, I. M.

    1979-01-01

    The rate of solution of a stationary bubble is limited by the diffusion of dissolved gas molecules away from the bubble surface. Diffusion coefficients computed from measured rates of solution give mean values higher than accepted literature values, with standard errors as high as 10% for a single observation. Better accuracy is achieved with sparingly soluble gases, small bubbles, and highly viscous liquids. Accuracy correlates with the Grashof number, indicating that free convection is the major source of error. Accuracy should, therefore, be greatly increased in a gravity-free environment. The fact that the bubble will need no support is an additional important advantage of Spacelab for this measurement.

  5. An asixymmetric diffusion experiment for the determination of diffusion and sorption coefficients of rock samples

    SciTech Connect

    Takeda, M.; Hiratsuka, T.; Ito, K.; Finsterle, S.

    2011-02-01

    Diffusion anisotropy is a critical property in predicting migration of substances in sedimentary formations with very low permeability. The diffusion anisotropy of sedimentary rocks has been evaluated mainly from laboratory diffusion experiments, in which the directional diffusivities are separately estimated by through-diffusion experiments using different rock samples, or concurrently by in-diffusion experiments in which only the tracer profile in a rock block is measured. To estimate the diffusion anisotropy from a single rock sample, this study proposes an axisymmetric diffusion test, in which tracer diffuses between a cylindrical rock sample and a surrounding solution reservoir. The tracer diffusion between the sample and reservoir can be monitored from the reservoir tracer concentrations, and the tracer profile could also be obtained after dismantling the sample. Semi-analytical solutions are derived for tracer concentrations in both the reservoir and sample, accounting for an anisotropic diffusion tensor of rank two as well as the dilution effects from sampling and replacement of reservoir solution. The transient and steady-state analyses were examined experimentally and numerically for different experimental configurations, but without the need for tracer profiling. These experimental configurations are tested for in- and out-diffusion experiments using Koetoi and Wakkanai mudstones and Shirahama sandstone, and are scrutinized by a numerical approach to identify favorable conditions for parameter estimation. The analysis reveals the difficulty in estimating diffusion anisotropy; test configurations are proposed for enhanced identifiability of diffusion anisotropy. Moreover, it is demonstrated that the axisymmetric diffusion test is efficient in obtaining the sorption parameter from both steady-state and transient data, and in determining the effective diffusion coefficient if isotropic diffusion is assumed. Moreover, measuring reservoir concentrations in an

  6. Measurement of attenuation coefficients of the fundamental and second harmonic waves in water

    NASA Astrophysics Data System (ADS)

    Zhang, Shuzeng; Jeong, Hyunjo; Cho, Sungjong; Li, Xiongbing

    2016-02-01

    Attenuation corrections in nonlinear acoustics play an important role in the study of nonlinear fluids, biomedical imaging, or solid material characterization. The measurement of attenuation coefficients in a nonlinear regime is not easy because they depend on the source pressure and requires accurate diffraction corrections. In this work, the attenuation coefficients of the fundamental and second harmonic waves which come from the absorption of water are measured in nonlinear ultrasonic experiments. Based on the quasilinear theory of the KZK equation, the nonlinear sound field equations are derived and the diffraction correction terms are extracted. The measured sound pressure amplitudes are adjusted first for diffraction corrections in order to reduce the impact on the measurement of attenuation coefficients from diffractions. The attenuation coefficients of the fundamental and second harmonics are calculated precisely from a nonlinear least squares curve-fitting process of the experiment data. The results show that attenuation coefficients in a nonlinear condition depend on both frequency and source pressure, which are much different from a linear regime. In a relatively lower drive pressure, the attenuation coefficients increase linearly with frequency. However, they present the characteristic of nonlinear growth in a high drive pressure. As the diffraction corrections are obtained based on the quasilinear theory, it is important to use an appropriate source pressure for accurate attenuation measurements.

  7. Predicting diffusion coefficients of chemicals in and through packaging materials.

    PubMed

    Fang, Xiaoyi; Vitrac, Olivier

    2017-01-22

    Most of the physicochemical properties in polymers such as activity and partition coefficients, diffusion coefficients, and their activation with temperature are accessible to direct calculations from first principles. Such predictions are particularly relevant for food packaging as they can be used (1) to demonstrate the compliance or safety of numerous polymer materials and of their constitutive substances (e.g. additives, residues…), when they are used: as containers, coatings, sealants, gaskets, printing inks, etc. (2) or to predict the indirect contamination of food by pollutants (e.g. from recycled polymers, storage ambiance…) (3) or to assess the plasticization of materials in contact by food constituents (e.g. fat matter, aroma…). This review article summarizes the classical and last mechanistic descriptions of diffusion in polymers and discusses the reliability of semi-empirical approaches used for compliance testing both in EU and US. It is concluded that simulation of diffusion in or through polymers is not limited to worst-case assumptions but could also be applied to real cases for risk assessment, designing packaging with low leaching risk or to synthesize plastic additives with low diffusion rates.

  8. Response of radiation belt simulations to different radial diffusion coefficients

    NASA Astrophysics Data System (ADS)

    Drozdov, A.; Shprits, Y.; Subbotin, D.; Kellerman, A. C.

    2013-12-01

    Resonant interactions between Ultra Low Frequency (ULF) waves and relativistic electrons may violate the third adiabatic invariant of motion, which produces radial diffusion in the electron radiation belts. This process plays an important role in the formation and structure of the outer electron radiation belt and is important for electron acceleration and losses in that region. Two parameterizations of the resonant wave-particle interaction of electrons with ULF waves in the magnetosphere by Brautigam and Albert [2000] and Ozeke et al. [2012] are evaluated using the Versatile Electron Radiation Belt (VERB) diffusion code to estimate their relative effect on the radiation belt simulation. The period of investigation includes quiet time and storm time geomagnetic activity and is compared to data based on satellite observations. Our calculations take into account wave-particle interactions represented by radial diffusion transport, local acceleration, losses due to pitch-angle diffusion, and mixed diffusion. We show that the results of the 3D diffusion simulations depend on the assumed parametrization of waves. The differences between the simulations and potential missing physical mechanisms are discussed. References Brautigam, D. H., and J. M. Albert (2000), Radial diffusion analysis of outer radiation belt electrons during the October 9, 1990, magnetic storm, J. Geophys. Res., 105(A1), 291-309, doi:10.1029/1999JA900344 Ozeke, L. G., I. R. Mann, K. R. Murphy, I. J. Rae, D. K. Milling, S. R. Elkington, A. A. Chan, and H. J. Singer (2012), ULF wave derived radiation belt radial diffusion coefficients, J. Geophys. Res., 117, A04222, doi:10.1029/2011JA017463.

  9. Attenuation coefficient determination of printed ABS and PLA samples in diagnostic radiology standard beams

    NASA Astrophysics Data System (ADS)

    Veneziani, G. R.; Corrêa, E. L.; Potiens, M. P. A.; Campos, L. L.

    2016-07-01

    IAEA code of practice TRS-457 states that standard phantoms should offer the same primary attenuation and scatter production as relevant body section of a representative patient. Material cost, availability and dimensional stability must also be considered. The goal of this study is to determine the attenuation coefficient of printed ABS and PLA samples in standard X-ray beams, verifying if phantoms printed with these materials could be an easier-handle substitute for PMMA, enabling the creation of different designs in an easier and cheaper way. Results show that PMMA presents higher attenuation coefficient, followed by PLA and ABS, which means that thinner PMMA layer creates higher radiation attenuation.

  10. Material grain size characterization method based on energy attenuation coefficient spectrum and support vector regression.

    PubMed

    Li, Min; Zhou, Tong; Song, Yanan

    2016-07-01

    A grain size characterization method based on energy attenuation coefficient spectrum and support vector regression (SVR) is proposed. First, the spectra of the first and second back-wall echoes are cut into several frequency bands to calculate the energy attenuation coefficient spectrum. Second, the frequency band that is sensitive to grain size variation is determined. Finally, a statistical model between the energy attenuation coefficient in the sensitive frequency band and average grain size is established through SVR. Experimental verification is conducted on austenitic stainless steel. The average relative error of the predicted grain size is 5.65%, which is better than that of conventional methods.

  11. Two media method for gamma ray attenuation coefficient measurement of archaeological ceramic samples

    PubMed

    Cunha e Silva RM; Appoloni; Parreira; Espinoza-Quinones; Coimbra; Aragao

    2000-12-01

    This work reports the application of an alternative methodology for the linear attenuation coefficient determination of irregular shape samples, in such a way that it is not necessary to know the sample thickness. Based on this method, indigenous archaeological ceramic fragments from the region of Londrina, north of Parana State in Brazil, were studied. On the other hand, theoretical mass attenuation coefficient values were determined with the XCOM computer code. With the results obtained, it was concluded that the two media method works very well for the linear attenuation coefficient measurement of irregular-shaped ceramic samples, which makes it suitable, especially, for archaeometric studies.

  12. Determination of electrolyte friction from measurements of the tracer diffusion coefficients, mutual diffusion coefficients, and electrophoretic mobilities of charged spheres

    NASA Astrophysics Data System (ADS)

    Gorti, Sridhar; Plank, Lindsay; Ware, B. R.

    1984-07-01

    The technique of fluorescence recovery after photobleaching has been used to measure the tracer diffusion coefficient of fluorescein-labeled charged polystyrene spheres in dilute solutions as a function of solution ionic strength. As the ratio of the particle radius (a) to the Debye-Hückel screening length (κ-1) was varied from 13 to 0.6, a 20% reduction in tracer diffusion coefficient was observed. The mutual diffusion coefficient, measured by quasielastic light scattering, increased as κa was reduced, demonstrating the dominant effect of thermodynamic factors on this parameter. The tracer data have been compared with theoretical predictions of other workers describing the influence of small-ion interactions with a charge sphere on its translational friction. The theoretical results of Schurr, and Booth, involve an explicit dependence on the electrokinetic charge of the sphere and yield estimates of this parameter (by least squares) which are significantly smaller than those obtained from laser Doppler electrophoretic light scattering results for the electrophoretic mobility of the labeled spheres. Approximations in the theoretical analyses are expected to account for these discrepancies.

  13. Effect of concentration dependence of the diffusion coefficient on homogenization kinetics in multiphase binary alloy systems

    NASA Technical Reports Server (NTRS)

    Tenney, D. R.; Unnam, J.

    1978-01-01

    Diffusion calculations were performed to establish the conditions under which concentration dependence of the diffusion coefficient was important in single, two, and three phase binary alloy systems. Finite-difference solutions were obtained for each type of system using diffusion coefficient variations typical of those observed in real alloy systems. Solutions were also obtained using average diffusion coefficients determined by taking a logarithmic average of each diffusion coefficient variation considered. The constant diffusion coefficient solutions were used as reference in assessing diffusion coefficient variation effects. Calculations were performed for planar, cylindrical, and spherical geometries in order to compare the effect of diffusion coefficient variations with the effect of interface geometries. In most of the cases considered, the diffusion coefficient of the major-alloy phase was the key parameter that controlled the kinetics of interdiffusion.

  14. Radon diffusion coefficients in soils of varying moisture content

    NASA Astrophysics Data System (ADS)

    Papachristodoulou, C.; Ioannides, K.; Pavlides, S.

    2009-04-01

    Radon is a naturally occurring radioactive gas that is generated in the Earth's crust and is free to migrate through soil and be released to the atmosphere. Due to its unique properties, soil gas radon has been established as a powerful tracer used for a variety of purposes, such as exploring uranium ores, locating geothermal resources and hydrocarbon deposits, mapping geological faults, predicting seismic activity or volcanic eruptions and testing atmospheric transport models. Much attention has also been given to the radiological health hazard posed by increased radon concentrations in the living and working environment. In order to exploit radon profiles for geophysical purposes and also to predict its entry indoors, it is necessary to study its transport through soils. Among other factors, the importance of soil moisture in such studies has been largely highlighted and it is widely accepted that any measurement of radon transport parameters should be accompanied by a measurement of the soil moisture content. In principle, validation of transport models in the field is encountered by a large number of uncontrollable and varying parameters; laboratory methods are therefore preferred, allowing for experiments to be conducted under well-specified and uniform conditions. In this work, a laboratory technique has been applied for studying the effect of soil moisture content on radon diffusion. A vertical diffusion chamber was employed, in which radon was produced from a 226Ra source, was allowed to diffuse through a soil column and was finally monitored using a silicon surface barrier detector. By solving the steady-state radon diffusion equation, diffusion coefficients (D) were determined for soil samples of varying moisture content (m), from null (m=0) to saturation (m=1). For dry soil, a D value of 4.1×10-7 m2s-1 was determined, which increased moderately by a factor of ~3 for soil with low moisture content, i.e. up to m ~0.2. At higher water fractions, a decrease

  15. Monitoring changes of optical attenuation coefficients of acupuncture points during laser acupuncture by optical coherence tomography

    NASA Astrophysics Data System (ADS)

    Huang, Yimei; Yang, Hongqin; Wang, Yuhua; Zheng, Liqin; Xie, Shusen

    2010-11-01

    The physical properties of acupuncture point were important to discover the mechanism of acupuncture meridian. In this paper, we used an optical coherence tomography to monitor in vivo the changes of optical attenuation coefficients of Hegu acupuncture point and non-acupuncture point during laser irradiation on Yangxi acupuncture point. The optical attenuation coefficients of Hegu acupuncture point and non-acupuncture point were obtained by fitting the raw data according to the Beer-Lambert's law. The experimental results showed that the optical attenuation coefficient of Hegu acupuncture point decreased during the laser acupuncture, in contrast to a barely changed result in that of non-acupuncture point. The significant change of optical attenuation coefficient of Hegu acupuncture point indicated that there was a correlation between Hegu and Yangxi acupuncture points to some extent.

  16. Characterizations of the mirror attenuator mosaic - Solar diffuser plate

    NASA Technical Reports Server (NTRS)

    Lee, Robert B., III; Avis, Lee M.; Gibson, M. A.; Kopia, Leonard P.

    1992-01-01

    The mirror attenuator mosaic (MAM), a solar diffuser plate, was used for the flight calibration of the broadband shortwave (0.2-5-microns) and total (0.2 to greater than 200-microns) Earth Radiation Budget Experiment scanning thermistor bolometer radiometers. The MAM solar-reflecting surface consisted of a tightly packed array of vacuum-deposited aluminum, concave spherical mirrors, while its solar-absorbing surface consisted of black chrome. The effective reflectance of the MAM was constant to within +/- 2 percent after almost 2 years in orbit, a marked improvement over earlier solar diffusers.

  17. M558 radioactive tracer diffusion. [diffusion coefficients of Zn-65 in liquid zinc under weightlessness conditions

    NASA Technical Reports Server (NTRS)

    Ukanwa, A. O.

    1974-01-01

    This experiment was performed in Skylab 3 with two objectives in mind. First, the experimental self-diffusion coefficients for liquid zinc were to be determined in a convection-free environment. Secondly the reduction in convective mixing in earth gravity by going into the zero-gravity environment of space was to be estimated. The experiment was designed to utilize high temperatures and linear thermal gradients provided by the M518 Multipurpose Electric Furnace, and the radioactivity of zinc-65 of 245-day half-life to investigate self-diffusion in liquid zinc. The distribution of zinc-65 tracer, after melting, maintaining at soak temperature for 1 hour of soak time and then resolidifying, was obtained by sample sectioning. The concentration of activity of each section (microcurie-gram) was plotted against positions along the sample axial and radial position. Experimental data and theoretical results from solution of Fick's law of diffusion in one dimensional were compared. Samples tested on earth showed very rapid diffusion. Diffusion coefficient in unit gravity was 50 times the zero-gravity diffusion coefficient of Skylab.

  18. Comparison of RNFL thickness and RPE-normalized RNFL attenuation coefficient for glaucoma diagnosis

    NASA Astrophysics Data System (ADS)

    Vermeer, K. A.; van der Schoot, J.; Lemij, H. G.; de Boer, J. F.

    2013-03-01

    Recently, a method to determine the retinal nerve fiber layer (RNFL) attenuation coefficient, based on normalization on the retinal pigment epithelium, was introduced. In contrast to conventional RNFL thickness measures, this novel measure represents a scattering property of the RNFL tissue. In this paper, we compare the RNFL thickness and the RNFL attenuation coefficient on 10 normal and 8 glaucomatous eyes by analyzing the correlation coefficient and the receiver operator curves (ROCs). The thickness and attenuation coefficient showed moderate correlation (r=0.82). Smaller correlation coefficients were found within normal (r=0.55) and glaucomatous (r=0.48) eyes. The full separation between normal and glaucomatous eyes based on the RNFL attenuation coefficient yielded an area under the ROC (AROC) of 1.0. The AROC for the RNFL thickness was 0.9875. No statistically significant difference between the two measures was found by comparing the AROC. RNFL attenuation coefficients may thus replace current RNFL thickness measurements or be combined with it to improve glaucoma diagnosis.

  19. Direct measurement of effective diffusion coefficients in nanochannels using steady-state dispersion effects

    NASA Astrophysics Data System (ADS)

    Durand, Nicolas F. Y.; Bertsch, Arnaud; Todorova, Mina; Renaud, Philippe

    2007-11-01

    We present a method to measure effective diffusion coefficients of fluorescently labeled molecules inside a nanofluidic system. Molecules with small diffusion coefficients show a larger lateral dispersion than highly diffusive species, which is counterintuitive. We performed measurements with wheat germ agglutinin proteins and obtained an effective diffusion coefficient which is four orders of magnitude lower than its free diffusion coefficient. Our technique which is a direct and relatively simple measurement of the effective diffusion coefficients inside nanochannels of well controlled dimensions could help fundamental studies in membranes and separation sciences.

  20. Comparison Actin- and Glass-Supported Phospholipid Bilayer Diffusion Coefficients

    PubMed Central

    Sterling, Sarah M.; Dawes, Ryan; Allgeyer, Edward S.; Ashworth, Sharon L.; Neivandt, David J.

    2015-01-01

    The formation of biomimetic lipid membranes has the potential to provide insights into cellular lipid membrane dynamics. The construction of such membranes necessitates not only the utilization of appropriate lipids, but also physiologically relevant substrate/support materials. The substrate materials employed have been shown to have demonstrable effects on the behavior of the overlying lipid membrane, and thus must be studied before use as a model cushion support. To our knowledge, we report the formation and investigation of a novel actin protein-supported lipid membrane. Specifically, inner leaflet lateral mobility of globular actin-supported DMPC (1,2-dimyristoyl-sn-glycero-3-phosphocholine) bilayers, deposited via the Langmuir-Blodgett/Langmuir Schaefer methodology, was investigated by z-scan fluorescence correlation spectroscopy across a temperature range of 20–44°C. The actin substrate was found to decrease the diffusion coefficient when compared to an identical membrane supported on glass. The depression of the diffusion coefficient occurred across all measured temperatures. These results indicated that the actin substrate exerted a direct effect on the fluidity of the lipid membrane and highlighted the fact that the choice of substrate/support is critical in studies of model lipid membranes. PMID:25902434

  1. Calculation of combined diffusion coefficients in SF{sub 6}-Cu mixtures

    SciTech Connect

    Zhong, Linlin; Wang, Xiaohua Rong, Mingzhe Wu, Yi; Murphy, Anthony B.

    2014-10-15

    Diffusion coefficients play an important role in the description of the transport of metal vapours in gas mixtures. This paper is devoted to the calculation of four combined diffusion coefficients, namely, the combined ordinary diffusion coefficient, combined electric field diffusion coefficient, combined temperature diffusion coefficient, and combined pressure diffusion coefficient in SF{sub 6}-Cu mixtures at temperatures up to 30 000 K. These four coefficients describe diffusion due to composition gradients, applied electric fields, temperature gradients, and pressure gradients, respectively. The influence of copper fluoride and sulfide species on the diffusion coefficients is shown to be negligible. The effect of copper proportion and gas pressures on these diffusion coefficients is investigated. It is shown that increasing the proportion of copper generally increases the magnitude of the four diffusion coefficients, except for copper mole fractions of 90% or more. It is further found that increasing the pressure reduces the magnitude of the coefficients, except for the combined temperature diffusion coefficient, and shifts the maximum of all four coefficients towards higher temperatures. The results presented in this paper can be applied to the simulation of high-voltage circuit breaker arcs.

  2. X-Ray Attenuation Coefficients from 10 Kev to 100 Mev,

    DTIC Science & Technology

    1957-04-30

    fig. 1). A well- shielded detector measures the shells account for most of the absorption by this intensity of the trinsmitted beam, and any photon...narrow-beam measurements ----------------- 2 1.4. Combination of attenuation coefficients -------------------- 2 1.5. Energy absorption...thickness is increased measures the unlikely to be absorbed. Consequently, the ab- total probability of the interaction processes. sorption coefficient

  3. Attenuation of the Squared Canonical Correlation Coefficient under Varying Estimates of Score Reliability

    ERIC Educational Resources Information Center

    Wilson, Celia M.

    2010-01-01

    Research pertaining to the distortion of the squared canonical correlation coefficient has traditionally been limited to the effects of sampling error and associated correction formulas. The purpose of this study was to compare the degree of attenuation of the squared canonical correlation coefficient under varying conditions of score reliability.…

  4. The role of the reflection coefficient in precision measurement of ultrasonic attenuation

    NASA Technical Reports Server (NTRS)

    Generazio, E. R.

    1984-01-01

    Ultrasonic attenuation measurements using contact, pulse-echo techniques are sensitive to surface roughness and couplant thickness variations. This can reduce considerable inaccuracies in the measurement of the attenuation coefficient for broadband pulses. Inaccuracies arise from variations in the reflection coefficient at the buffer-couplant-sample interface. The reflection coefficient is examined as a function of the surface roughness and corresponding couplant thickness variations. Interrelations with ultrasonic frequency are illustrated. Reliable attenuation measurements are obtained only when the frequency dependence of the reflection coefficient is incorporated in signal analysis. Data are given for nickel 200 samples and a silicon nitride ceramic bar having surface roughness variations in the 0.3 to 3.0 microns range for signal bandwidths in the 50 to 100 MHz range.

  5. C-Depth Method to Determine Diffusion Coefficient and Partition Coefficient of PCB in Building Materials.

    PubMed

    Liu, Cong; Kolarik, Barbara; Gunnarsen, Lars; Zhang, Yinping

    2015-10-20

    Polychlorinated biphenyls (PCBs) have been found to be persistent in the environment and possibly harmful. Many buildings are characterized with high PCB concentrations. Knowledge about partitioning between primary sources and building materials is critical for exposure assessment and practical remediation of PCB contamination. This study develops a C-depth method to determine diffusion coefficient (D) and partition coefficient (K), two key parameters governing the partitioning process. For concrete, a primary material studied here, relative standard deviations of results among five data sets are 5%-22% for K and 42-66% for D. Compared with existing methods, C-depth method overcomes the inability to obtain unique estimation for nonlinear regression and does not require assumed correlations for D and K among congeners. Comparison with a more sophisticated two-term approach implies significant uncertainty for D, and smaller uncertainty for K. However, considering uncertainties associated with sampling and chemical analysis, and impact of environmental factors, the results are acceptable for engineering applications. This was supported by good agreement between model prediction and measurement. Sensitivity analysis indicated that effective diffusion distance, contacting time of materials with primary sources, and depth of measured concentrations are critical for determining D, and PCB concentration in primary sources is critical for K.

  6. Messages Do Diffuse Faster than Messengers: Reconciling Disparate Estimates of the Morphogen Bicoid Diffusion Coefficient

    PubMed Central

    Sigaut, Lorena; Pearson, John E.; Colman-Lerner, Alejandro; Ponce Dawson, Silvina

    2014-01-01

    The gradient of Bicoid (Bcd) is key for the establishment of the anterior-posterior axis in Drosophila embryos. The gradient properties are compatible with the SDD model in which Bcd is synthesized at the anterior pole and then diffuses into the embryo and is degraded with a characteristic time. Within this model, the Bcd diffusion coefficient is critical to set the timescale of gradient formation. This coefficient has been measured using two optical techniques, Fluorescence Recovery After Photobleaching (FRAP) and Fluorescence Correlation Spectroscopy (FCS), obtaining estimates in which the FCS value is an order of magnitude larger than the FRAP one. This discrepancy raises the following questions: which estimate is "correct''; what is the reason for the disparity; and can the SDD model explain Bcd gradient formation within the experimentally observed times? In this paper, we use a simple biophysical model in which Bcd diffuses and interacts with binding sites to show that both the FRAP and the FCS estimates may be correct and compatible with the observed timescale of gradient formation. The discrepancy arises from the fact that FCS and FRAP report on different effective (concentration dependent) diffusion coefficients, one of which describes the spreading rate of the individual Bcd molecules (the messengers) and the other one that of their concentration (the message). The latter is the one that is more relevant for the gradient establishment and is compatible with its formation within the experimentally observed times. PMID:24901638

  7. Diffusion coefficient of hydrogen in a cast gamma titanium aluminide

    SciTech Connect

    Sundaram, P.A.; Wessel, E.; Ennis, P.J.; Quadakkers, W.J.; Singheiser, L.

    1999-06-04

    Gamma titanium aluminides have the potential for high temperature applications because of their high specific strength and specific modulus. Their oxidation resistance is good, especially at intermediate temperatures and with suitable alloying additions, good oxidation resistance can be obtained up to 800 C. One critical area of application is in combustion engines in aero-space vehicles such as hypersonic airplanes and high speed civil transport airplanes. This entails the use of hydrogen as a fuel component and hence the effect of hydrogen on the mechanical properties of gamma titanium aluminides is of significant scientific and technological utility. The purpose of this short investigation is to use an electrochemical method under galvanostatic conditions to determine the diffusion coefficient of hydrogen in a cast gamma titanium aluminide, a typical technical alloy with potential application in gas turbines under creep conditions. This result will be then compared with that obtained by microhardness profiling of electrolytically hydrogen precharged material.

  8. Measurement of diffusion coefficient of propylene glycol in skin tissue

    NASA Astrophysics Data System (ADS)

    Genin, Vadim D.; Bashkatov, Alexey N.; Genina, Elina A.; Tuchin, Valery V.

    2015-03-01

    Optical clearing of the rat skin under the action of propylene glycol was studied ex vivo. It was found that collimated transmittance of skin samples increased, whereas weight and thickness of the samples decreased during propylene glycol penetration in skin tissue. A mechanism of the optical clearing under the action of propylene glycol is discussed. Diffusion coefficient of propylene glycol in skin tissue ex vivo has been estimated as (1.35±0.95)×10-7 cm2/s with the taking into account of kinetics of both weight and thickness of skin samples. The presented results can be useful for enhancement of many methods of laser therapy and optical diagnostics of skin diseases and localization of subcutaneous neoplasms.

  9. Benchmarking PET for geoscientific applications: 3D quantitative diffusion coefficient determination in clay rock

    NASA Astrophysics Data System (ADS)

    Lippmann-Pipke, J.; Gerasch, R.; Schikora, J.; Kulenkampff, J.

    2017-04-01

    The 3D diagonal anisotropic effective diffusion coefficient of Na+, Deff=(Dxx, Dyy, Dzz), was quantified in a clay material in one single experiment/simulation. That is possible due to the combination of the non-invasive observation of Na+ diffusion in Opalinus clay by means of GeoPET method (PET: positron emission tomography) followed by quantitative 3D+t data evaluation by means of the finite element numerical modelling (FEM). The extracted anisotropic effective diffusion coefficient parallel (||) and normal (⊥) to the bedding of the clay rock, Deff=(D||, D⊥, D||) are comparable to those obtained on earlier experimental studies in the same clay material but with different methods. We consider this study as benchmark for the long-standing development of our GeoPET method, that explicitly includes a resolute and physics based attenuation and Compton scatter correction algorithm (Kulenkampff, J., M. Gründig, A. Zakhnini and J. Lippmann-Pipke (2016). "Geoscientific process monitoring with positron emission tomography (GeoPET)." Solid Earth 7: 1217-1231). We suggest GeoPET based fluid flow transport visualization combined with computer based process simulation henceforth as a qualified way for the quantification of three-dimensional, effective transport parameters in geosciences.

  10. Estimation and Inference of Diffusion Coefficients in Complex Biomolecular Environments.

    PubMed

    Calderon, Christopher P

    2011-02-08

    The 1-D diffusion coefficient associated with a charged atom fluctuating in an ion-channel binding pocket is statistically analyzed. More specifically, unconstrained and constrained molecular dynamics simulations of potassium in gramicidin A are studied. Time domain transition density based inference methods are used to fit simple stochastic differential equations and also to carry out frequentist goodness of fit tests. Particular attention is paid to varying the time between adjacent time series observations due to the well-known "non-Markovian noise" that can appear in this system due to inertia and other unresolved coordinates influencing the dynamics. Different types of non-Markovian noise are shown by the goodness of fit tests to be statistically significant on vastly different time scales. On intermediate scales, a Markovian model is not rejected by the tests; models calibrated at these intermediate scales demonstrate a predictive capability for some physical quantities. However, in this intermediate regime, ergodic sampling does not occur over the length of a time series, but a local diffusion coefficient is deemed statistically acceptable for the observed raw data. It is demonstrated that a linear mixed effects model can be used to summarize the variation induced by slow unresolved degrees of freedom acting as a non-Markovian noise source. The utility of quantitative criteria for assessing low-dimensional stochastic models calibrated from time series generated by high-dimensional biomolecular systems is briefly discussed. Less coarse-grained data summaries of this type show promise for better understanding the kinetic signature of unresolved degrees of freedom in time series coming from simulations and single-molecule experiments.

  11. Consolidation with diffuse or focal high attenuation: computed tomography findings.

    PubMed

    Marchiori, Edson; Franquet, Tomás; Gasparetto, Taísa Davaus; Gonçalves, Letícia Pereira; Escuissato, Dante L

    2008-11-01

    This pictorial essay aims to present various lesions that could present as consolidations with diffuse of focal high attenuation on computed tomography, helping to make the diagnosis more confident and specific. The radiologic literature has limited information about such findings and the role of computed tomography in the differential diagnosis. The following diseases are presented: metastatic pulmonary calcification, pulmonary alveolar microlithiasis, amiodarone lung, talcosis, iodinated oil embolism, tuberculosis, silicoproteinosis, and amyloidosis. In conclusion, air-space consolidations can be seen in a wide variety of diseases affecting the lungs. The identification of the different patterns of consolidation with focal high attenuation narrows the differential diagnosis. We present a diagnostic approach based on appearance and distribution of these lesions.

  12. Beam hardening: analytical considerations of the effective attenuation coefficient of X-ray tomography.

    PubMed

    Alles, J; Mudde, R F

    2007-07-01

    Polychromatic x-ray beams traveling though material are prone to beam hardening, i.e., the high energy part of the incident spectrum gets over represented when traveling farther into the material. This study discusses the concept of a mean attenuation coefficient in a formal way. The total energy fluence is one-to-one related to the traveled distance in case of a polychromatic beam moving through a given, inhomogeneous material. On the basis of this one-to-one relation, it is useful to define a mean attenuation coefficient and study its decrease with depth. Our results are based on a novel parametrization of the energy dependence of the attenuation coefficient that allows for closed form evaluation of certain spectral integrals. This approach underpins the ad hoc semianalytical expressions given in the literature. An analytical model for the average attenuation coefficient is proposed that uses a simple fit of the attenuation coefficient as a function of the photon energy as input. It is shown that a simple extension of this model gives a rather good description of beam hardening for x-rays traveling through water.

  13. Beam hardening: Analytical considerations of the effective attenuation coefficient of x-ray tomography

    SciTech Connect

    Alles, J.; Mudde, R. F.

    2007-07-15

    Polychromatic x-ray beams traveling though material are prone to beam hardening, i.e., the high energy part of the incident spectrum gets over represented when traveling farther into the material. This study discusses the concept of a mean attenuation coefficient in a formal way. The total energy fluence is one-to-one related to the traveled distance in case of a polychromatic beam moving through a given, inhomogeneous material. On the basis of this one-to-one relation, it is useful to define a mean attenuation coefficient and study its decrease with depth. Our results are based on a novel parametrization of the energy dependence of the attenuation coefficient that allows for closed form evaluation of certain spectral integrals. This approach underpins the ad hoc semianalytical expressions given in the literature. An analytical model for the average attenuation coefficient is proposed that uses a simple fit of the attenuation coefficient as a function of the photon energy as input. It is shown that a simple extension of this model gives a rather good description of beam hardening for x-rays traveling through water.

  14. Measurement of the diffusion coefficient of sulfur hexafluoride in water

    NASA Astrophysics Data System (ADS)

    King, D. B.; Saltzman, E. S.

    1995-04-01

    Sulfur hexafluoride has been widely used in field studies and laboratory experiments to develop a relationship between gas transfer and wind speed. The interpretation of the data from such studies requires the diffusion coefficient of SF6 (DSF6), which has not previously been measured. In this study, DSF6 has been determined in pure water and in 35‰ NaCl over a temperature range of 5-25°C. The measurements were made using a continuous-flow diffusion cell where SF6 flows beneath an agar gel membrane while helium flows above the gel. The experimental data for pure water yielded the following equation: DSF6=0.029 exp (-19.3/RT, where R is the gas constant and T is temperature in kelvins). Measurements of DSF6 in 35‰ NaCl were not significantly different from the pure water values. On the basis of our data, we estimate the Schmidt numbers for seawater over the temperature range 5-25° C to be Sc=3016.1-172.00t+4.4996t2-0.047965t3, where t is temperature in degrees Celsius.

  15. Studies on effective atomic numbers, electron densities and mass attenuation coefficients in Au alloys.

    PubMed

    Han, I; Demir, L

    2010-01-01

    The total mass attenuation coefficients (mu/rho) for pure Au and Au99Be1, Au88Ge12, Au95Zn5 alloys were measured at 59.5 and 88.0 keV photon energies. The samples were irradiated with 241Am and 109Cd radioactive point source using transmission arrangement. The gamma- rays were counted by a Si(Li) detector with resolution of 160 eV at 5.9 keV. Total atomic and electronic cross-sections (sigmat and sigmae), effective atomic and electron densities (Zeff and Nel) were determined using the obtained mass attenuation coefficients for investigated Au alloys. The theoretical mass attenuation coefficients of each alloy were estimated using mixture rule.

  16. Investigation of photon attenuation coefficient of some building materials used in Turkey

    SciTech Connect

    Dogan, B.; Altinsoy, N.

    2015-03-30

    In this study, some building materials regularly used in Turkey, such as concrete, gas concrete, pumice and brick have been investigated in terms of mass attenuation coefficient at different gamma-ray energies. Measurements were carried out by gamma spectrometry containing NaI(Tl) detector. Narrow beam gamma-ray transmission geometry was used for the attenuation measurements. The results are in good agreement with the theoretical calculation of XCOM code.

  17. Effect of external magnetic field on attenuation coefficient for magnetic substances.

    PubMed

    Kumar Gupta, Manoj; Dhaliwal, A S; Kahlon, K S

    2014-10-29

    The measurement of attenuation coefficient of some magnetic substances, to include diamagnetic: Cu, Zn, Ag, Te, Au, Pb, and Perspex; paramagnetic: Al, Ti, Mo, Dy, Ho, and Pt and ferromagnetic substances: Fe, Co, Ni, Gd, FeO, NiO, FeS, and Fe2O3, both in the presence and absence of an external magnetic field has been carried out using narrow beam transmission geometry by using gamma ray photons of incident energy 59.54keV from 100mCi, (241)Am point source. It was observed very keenly that the value of linear attenuation coefficient of various substances mentioned above decreased remarkably. It varied in the range of 1-2%, 2-6% and 6-9% for diamagnetic, paramagnetic and ferromagnetic substances respectively in the presence of an external magnetic field. Measured results elucidated it very clearly that linear attenuation coefficient at H=0T, 0.6T and 1.2T continued to decrease with a regular increase of magnetic field. It is also manifested that measurements of linear attenuation coefficient is not affected with the change in thickness of the given substance. Within error limits (1-3%) variations are observed with increases of thickness along with magnetic field. Further to it the obtained results of linear attenuation coefficient without magnetic field (H=0T) were compared with theoretical data tables of FFAST and WinXCOM. It was established that values obtained are well within the experimental errors. To the best of our knowledge no other study in relation to the effect of linear attenuation coefficient in the presence of magnetic field available as precedence.

  18. Measurement of the linear attenuation coefficients of breast tissues by synchrotron radiation computed tomography

    NASA Astrophysics Data System (ADS)

    Chen, R. C.; Longo, R.; Rigon, L.; Zanconati, F.; De Pellegrin, A.; Arfelli, F.; Dreossi, D.; Menk, R.-H.; Vallazza, E.; Xiao, T. Q.; Castelli, E.

    2010-09-01

    The measurement of the linear attenuation coefficients of breast tissues is of fundamental importance in the field of breast x-ray diagnostic imaging. Different groups have evaluated the linear attenuation coefficients of breast tissues by carrying out direct attenuation measurements in which the specimens were thin and selected as homogeneous as possible. Here, we use monochromatic and high-intensity synchrotron radiation computed tomography (SR CT) to evaluate the linear attenuation coefficients of surgical breast tissues in the energy range from 15 to 26.5 keV. X-ray detection is performed by a custom digital silicon micro-strip device, developed in the framework of the PICASSO INFN experiment. Twenty-three human surgical breast samples were selected for SR CT and histological study. Six of them underwent CT, both as fresh tissue and after formalin fixation, while the remaining 17 were imaged only as formalin-fixed tissues. Our results for fat and fibrous tissues are in good agreement with the published values. However, in contrast to the published data, our measurements show no significant differences between fibrous and tumor tissues. Moreover, our results for fresh and formalin-fixed tissues demonstrate a reduction of the linear attenuation coefficient for fibrous and tumor tissues after fixation.

  19. Determination of the Absorption Coefficient and Cloudiness Multiplicity Attenuation During the Gamma-Radiation Passage

    NASA Astrophysics Data System (ADS)

    Orlova, K. N.; Borovikov, I. F.; Gaidamak, M. A.

    2016-08-01

    The paper presents background value equivalent dose of gamma-radiation investigation in different weather: clear cloudy and overcast. The change of the dose rate of gamma radiation, depending on the weather and the ability cloudiness to shield gamma rays is shown. A new method for eliminating the consequences of accidents at nuclear power plants or plants using radioactive elements is proposed. A calculation method of cloudiness coefficient absorption and cloudiness gamma-radiation multiplicity attenuation is developed. The gamma- radiation multiplicity attenuation and the absorption coefficient of gamma radiation were calculated.

  20. Weibull approximation of LiDAR waveforms for estimating the beam attenuation coefficient.

    PubMed

    Montes-Hugo, Martin A; Vuorenkoski, Anni K; Dalgleish, Fraser R; Ouyang, Bing

    2016-10-03

    Tank experiments were performed at different water turbidities to examine relationships between the beam attenuation coefficient (c) and Weibull shape parameters derived from LiDAR waveforms measured with the Fine Structure Underwater LiDAR (FSUIL). Optical inversions were made at 532 nm, within a c range of 0.045-1.52 m-1, and based on a LiDAR system having two field-of-view (15 and 75.7 mrad) and two linear polarizations. Consistently, the Weibull scale parameter or P2 showed the strongest covariation with c and was a more accurate proxy with respect to the LiDAR attenuation coefficient.

  1. Normative Apparent Diffusion Coefficient Values in the Developing Fetal Brain

    PubMed Central

    Schneider, M.M.; Berman, J.I.; Baumer, F.M.; Glass, H.C.; Jeng, S.; Jeremy, R.J.; Esch, M.; Biran, V.; Barkovich, A.J.; Studholme, C.; Xu, D.; Glenn, O.A.

    2013-01-01

    BACKGROUND AND PURPOSE Previous studies of diffusion-weighted imaging (DWI) in fetuses are limited. Because of the need for normative data for comparison with young fetuses and preterm neonates with suspected brain abnormalities, we studied apparent diffusion coefficient (ADC) values in a population of singleton, nonsedated, healthy fetuses. MATERIALS AND METHODS DWI was performed in 28 singleton nonsedated fetuses with normal or questionably abnormal results on sonography and normal fetal MR imaging results; 10 fetuses also had a second fetal MR imaging, which included DWI. ADC values in the periatrial white matter (WM), frontal WM, thalamus, basal ganglia, cerebellum, and pons were plotted against gestational age and analyzed with linear regression. We compared mean ADC in different regions using the Tukey Honestly Significant Difference test. We also compared rates of decline in ADC with increasing gestational age across different areas by using the t test with multiple comparisons correction. Neurodevelopmental outcome was assessed. RESULTS Median gestational age was 24.28 weeks (range, 21–33.43 weeks). Results of all fetal MR imaging examinations were normal, including 1 fetus with a normal variant of a cavum velum interpositum. ADC values were highest in the frontal and periatrial WM and lowest in the thalamus and pons. ADC declined with increasing gestational age in periatrial WM (P = .0003), thalamus (P < .0001), basal ganglia (P = .0035), cerebellum (P < .0001), and pons (P = .024). Frontal WM ADC did not significantly change with gestational age. ADC declined fastest in the cerebellum, followed by the thalamus. CONCLUSIONS Regional differences in nonsedated fetal ADC values and their evolution with gestational age likely reflect differences in brain maturation and are similar to published data in premature neonates. PMID:19556350

  2. High silicon self-diffusion coefficient in dry forsterite

    NASA Astrophysics Data System (ADS)

    Katsura, T.; Fei, H.; Hegoda, C.; Yamazaki, D.; Wiedenbeck, M.; Yurimoto, H.; Shcheka, S.

    2012-12-01

    Plastic deformation of mantle minerals is believed to be controlled by self-diffusion of the slowest species, which is silicon in silicate minerals. Olivine is the main constituent of upper mantle. Therefore, silicon self-diffusion coefficient (DSi) in olivine provides the basic information of upper mantle rheology. Dohmen et al. [1] and Jaoul et al. [2] measured the DSi at ambient pressure under dry conditions in natural olivine and iron-free forsterite, respectively. However, their results were ~2-3 orders of magnitude lower than that estimated from deformation experiments [3]. In this study, we revisited DSi in forsterite and resolved this discrepancy [4]. Forsterite single crystals were polished in colloidal silica solution, deposited with 300-500 nm of 29Si enriched Mg2SiO4 films, covered by 100 nm of ZrO2 films, and annealed at 1600-1800 K from ambient pressure up to 13 GPa using an ambient pressure furnace and multi-anvil apparatus. The surface roughness after diffusion were reduced to <50 nm by polishing again in colloidal silica solution. Diffusion profiles were obtained by SIMS. Water contents in the samples were <1 μg/g by FT-IR [4]. logDSi were determined to be -19.7±0.4 and -18.1±0.3 log[m2/s] under ambient pressure at 1600 and 1800 K, respectively. These values were 2.4 orders of magnitude higher than that determined by Jaoul et al. [2] in forsterite, as well as that reprted by Dohmen et al. [1] in natural olivine. Their low DSi could be obtained due to the bad contact of the coated films with the substrate. Our results well explain the high dislocation climb rates in deformation experiments [4]. We also determined a small negative pressure dependence of DSi with an activation volume of 1.7±0.4 cm3/mol, and an activation energy of ~410 kJ/mol. Calibratied to the same temperature, the nearly linear relationship of DSi against pressure in dry forsterite in this study, iron and water bearing wadsleyite and ringwoodite by Shimojuku et al. [5

  3. Experimental Method Development for Estimating Solid-phase Diffusion Coefficients and Material/Air Partition Coefficients of SVOCs

    EPA Science Inventory

    The solid-phase diffusion coefficient (Dm) and material-air partition coefficient (Kma) are key parameters for characterizing the sources and transport of semivolatile organic compounds (SVOCs) in the indoor environment. In this work, a new experimental method was developed to es...

  4. On the Origin of Quantum Diffusion Coefficient and Quantum Potential

    NASA Astrophysics Data System (ADS)

    Gupta, Aseem

    2016-03-01

    Synchronizability of space and time experiences between different inhabitants of a spacetime is abstracted as a fundamental premise of Classical physics. Absence thereof i.e. desynchronization between space and time experiences of a system under study and the observer is then studied for a single dimension single particle system. Desynchronization fundamentally makes probability concepts enter physics ab-initio and not as secondary tools to deal with situations wherein incomplete information in situation following perfectly deterministic dynamics demands its introduction. Desynchronization model based on Poisson distribution of events vis-à-vis an observer, leads to expectation of particle's motion as a Brownian motion deriving Nelson's quantum diffusion coefficient naturally, without needing to postulate it. This model also incorporates physical effects akin to those of Bohm's Quantum Potential, again without needing any sub-quantum medium. Schrodinger's equation is shown to be derivable incorporating desynchronization only of space while Quantum Field Theory is shown to model desynchronization of time as well. Fundamental suggestion of the study is that it is desynchronization that is at the root of quantum phenomena rather than sub-micro scales of spacetime. Absence of possibility of synchronization between system's space and time and those of observer is studied. Mathematical modeling of desynchronized evolution explains some intriguing aspects of Quantum Mechanical theory.

  5. Instantaneous signal attenuation method for analysis of PFG fractional diffusions

    NASA Astrophysics Data System (ADS)

    Lin, Guoxing

    2016-08-01

    An instantaneous signal attenuation (ISA) method for analyzing pulsed field gradient (PFG) fractional diffusion (FD) has been developed, which is modified from the propagator approach developed in 2001 by Lin et al. for analyzing PFG normal diffusion. Both, the current ISA method and the propagator method have the same fundamental basis that the total signal attenuation (SA) is the accumulation of all the ISA, and the ISA is the average SA of the whole diffusion system at each moment. However, the manner of calculating ISA is different. Unlike the use of the instantaneous propagator in the propagator method, the current method directly calculates ISA as A(K(t‧), t‧ + dt‧)/A(K(t‧), t‧), where A(K(t‧), t‧ + dt‧) and A(K(t‧), t‧) are the SA. This modification makes the current method applicable to PFG FD as the instantaneous propagator may not be obtainable in FD. The ISA method was applied to study PFG SA including the effect of finite gradient pulse widths (FGPW) for free FD, restricted FD and the FD affected by a non-homogeneous gradient field. The SA expressions were successfully obtained for all three types of free FDs while other current methods still have difficulty in obtaining all of them. The results from this method agree with reported results such as that obtained by the effective phase shift diffusion equation (EPSDE) method. The M-Wright phase distribution approximation was also used to derive an SA expression for time FD as a comparison, which agrees with ISA method. Additionally, the continuous-time random walk (CTRW) simulation was performed to simulate the SA of PFG FD, and the simulation results agree with the analytical results. Particularly, the CTRW simulation results give good support to the analytical results including FGPW effect for free FD and restricted time FD based on a fractional derivative model where there have been no corresponding theoretical reports to date. The theoretical SA expressions including FGPW obtained

  6. Instantaneous signal attenuation method for analysis of PFG fractional diffusions.

    PubMed

    Lin, Guoxing

    2016-08-01

    An instantaneous signal attenuation (ISA) method for analyzing pulsed field gradient (PFG) fractional diffusion (FD) has been developed, which is modified from the propagator approach developed in 2001 by Lin et al. for analyzing PFG normal diffusion. Both, the current ISA method and the propagator method have the same fundamental basis that the total signal attenuation (SA) is the accumulation of all the ISA, and the ISA is the average SA of the whole diffusion system at each moment. However, the manner of calculating ISA is different. Unlike the use of the instantaneous propagator in the propagator method, the current method directly calculates ISA as A(K(t'),t'+dt')/A(K(t'),t'), where A(K(t'),t'+dt') and A(K(t'),t') are the SA. This modification makes the current method applicable to PFG FD as the instantaneous propagator may not be obtainable in FD. The ISA method was applied to study PFG SA including the effect of finite gradient pulse widths (FGPW) for free FD, restricted FD and the FD affected by a non-homogeneous gradient field. The SA expressions were successfully obtained for all three types of free FDs while other current methods still have difficulty in obtaining all of them. The results from this method agree with reported results such as that obtained by the effective phase shift diffusion equation (EPSDE) method. The M-Wright phase distribution approximation was also used to derive an SA expression for time FD as a comparison, which agrees with ISA method. Additionally, the continuous-time random walk (CTRW) simulation was performed to simulate the SA of PFG FD, and the simulation results agree with the analytical results. Particularly, the CTRW simulation results give good support to the analytical results including FGPW effect for free FD and restricted time FD based on a fractional derivative model where there have been no corresponding theoretical reports to date. The theoretical SA expressions including FGPW obtained here such as [Formula: see

  7. Graded functional diffusion map-defined characteristics of apparent diffusion coefficients predict overall survival in recurrent glioblastoma treated with bevacizumab.

    PubMed

    Ellingson, Benjamin M; Cloughesy, Timothy F; Lai, Albert; Mischel, Paul S; Nghiemphu, Phioanh L; Lalezari, Shadi; Schmainda, Kathleen M; Pope, Whitney B

    2011-10-01

    Diffusion imaging has shown promise as a predictive and prognostic biomarker in glioma. We assessed the ability of graded functional diffusion maps (fDMs) and apparent diffusion coefficient (ADC) characteristics to predict overall survival (OS) in recurrent glioblastoma multiforme (GBM) patients treated with bevacizumab. Seventy-seven patients with recurrent GBMs were retrospectively examined. MRI scans were obtained before and approximately 6 weeks after treatment with bevacizumab. Graded fDMs were created by registering datasets to each patient's pretreatment scan and then performing voxel-wise subtraction between post- and pretreatment ADC maps. Voxels were categorized according to the degree of change in ADC within pretreatment fluid-attenuated inversion recovery (FLAIR) and contrast-enhancing regions of interest (ROIs). We found that the volume of tissue showing decreased ADC within both FLAIR and contrast-enhancing regions stratified OS (log-rank, P < .05). fDMs applied to contrast-enhancing ROIs more accurately predicted OS compared with fDMs applied to FLAIR ROIs. Graded fDMs (showing voxels with decreased ADC between 0.25 and 0.4 µm(2)/ms) were more predictive of OS than traditional (single threshold) fDMs, and the predictive ability of graded fDMs could be enhanced even further by adding the ADC characteristics from the fDM-classified voxels to the analysis (log-rank, P < .001). These results demonstrate that spatially resolved diffusion-based tumor metrics are a powerful imaging biomarker of survival in patients with recurrent GBM treated with bevacizumab.

  8. Coordinate-dependent diffusion coefficients: Decay rate in open quantum systems

    SciTech Connect

    Sargsyan, V. V.; Palchikov, Yu. V.; Antonenko, N. V.; Kanokov, Z.; Adamian, G. G.

    2007-06-15

    Based on a master equation for the reduced density matrix of an open quantum collective system, the influence of coordinate-dependent microscopical diffusion coefficients on the decay rate from a metastable state is treated. For various frictions and temperatures larger than a crossover temperature, the quasistationary decay rates obtained with the coordinate-dependent microscopical set of diffusion coefficients are compared with those obtained with the coordinate-independent microscopical set of diffusion coefficients and coordinate-independent and -dependent phenomenological sets of diffusion coefficients. Neglecting the coordinate dependence of diffusion coefficients, one can strongly overestimate or underestimate the decay rate at low temperature. The coordinate-dependent phenomenological diffusion coefficient in momentum are shown to be suitable for applications.

  9. Automated, Depth-resolved Estimation of the Attenuation Coefficient From Optical Coherence Tomography Data

    PubMed Central

    Smith, Gennifer T.; Dwork, Nicholas; O’Connor, Daniel; Sikora, Uzair; Lurie, Kristen L.; Pauly, John M.; Ellerbee, Audrey K.

    2015-01-01

    We present a method for automated, depth-resolved extraction of the attenuation coefficient from Optical Coherence Tomography (OCT) data. In contrast to previous automated, depth-resolved methods, the Depth-Resolved Confocal (DRC) technique derives an invertible mapping between the measured OCT intensity data and the attenuation coefficient while considering the confocal function and sensitivity fall-off, which are critical to ensure accurate measurements of the attenuation coefficient in practical settings (e.g., clinical endoscopy). We also show that further improvement of the estimated attenuation coefficient is possible by formulating image denoising as a convex optimization problem that we term Intensity Weighted Horizontal Total Variation (iwhTV). The performance and accuracy of DRC alone and DRC+iwhTV are validated with simulated data, optical phantoms, and ex-vivo porcine tissue. Our results suggest that implementation of DRC+iwhTV represents a novel way to improve OCT contrast for better tissue characterization through quantitative imaging. PMID:26126286

  10. Effect of ilmenite on the attenuation coefficient of gamma ray shielding cementious matrix

    NASA Astrophysics Data System (ADS)

    El-Faramawy, Nabil; Ramadan, Wageeh; El-Zakla, Tarek; Sayed, Magda; El-Dessouky, Mohamed; Sakr, Khaled

    2015-11-01

    The current work investigated the effect of the Portland cement mixed with different percentages of water and ilmenite ore on the attenuation of gamma radiation as shielding blocks. Different concentrations of ilmenite from 5% up to 20% with different grain size were mixed with cement. The properties of the investigated blocks, as compressive strength, wet and dry density, absorption and porosity percentages, were studied. The thermal stability of the studied samples and their X-ray diffraction (XRD) patterns were examined through thermogravimetric analysis and XRD respectively. In addition, the attenuation coefficients of the considered samples for gamma radiation were performed using gamma ray spectrometer. The results revealed that, the maximum linear attenuation coefficient (µ) and minimum transmission fraction were performed for cement mixed with 10% of ilmenite and with the size range 106-250 µm.

  11. Quantification of numerical aperture-dependence of the OCT attenuation coefficient (Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Peinado, Liliana M.; Bloemen, Paul R.; Almasian, Mitra; van Leeuwen, Ton G.; Faber, Dirk J.

    2016-03-01

    Despite the improvements in early cancer diagnosis, adequate diagnostic tools for early staging of bladder cancer tumors are lacking [1]. MEMS-probes based on optical coherence tomography (OCT) provide cross-sectional imaging with a high-spatial resolution at a high-imaging speed, improving visualization of cancerous tissue [2-3]. Additionally, studies show that the measurement of localized attenuation coefficient allows discrimination between healthy and cancerous tissue [4]. We have designed a new miniaturized MEMS-probe based on OCT that will optimize early diagnosis by improving functional visualization of suspicious lesions in bladder. During the optical design phase of the probe, we have studied the effect of the numerical aperture (NA) on the OCT signal attenuation. For this study, we have employed an InnerVision Santec OCT system with several numerical apertures (25mm, 40mm, 60mm, 100mm, 150mm and 200mm using achromatic lenses). The change in attenuation coefficient was studied using 15 dilutions of intralipid ranging between 6*10-5 volume% and 20 volume%. We obtained the attenuation coefficient from the OCT images at several fixed positions of the focuses using established OCT models (e.g. single scattering with known confocal point spread function (PSF) [5] and multiple scattering using the Extended Huygens Fresnel model [6]). As a result, a non-linear increase of the scattering coefficient as a function of intralipid concentration (due to dependent scattering) was obtained for all numerical apertures. For all intralipid samples, the measured attenuation coefficient decreased with a decrease in NA. Our results suggest a non-negligible influence of the NA on the measured attenuation coefficient. [1] Khochikar MV. Rationale for an early detection program for bladder cancer. Indian J Urol 2011 Apr-Jun; 27(2): 218-225. [2] Sun J and Xie H. Review Article MEMS-Based Endoscopic Optical Coherence Tomography. IJO 2011, Article ID 825629, 12 pages. doi:10

  12. Estimation of near-surface quality factors by constrained inversion of Rayleigh-wave attenuation coefficients

    NASA Astrophysics Data System (ADS)

    Xia, Jianghai; Xu, Yixian; Miller, Richard D.; Ivanov, Julian

    2012-07-01

    Quality factors (Q) of near-surface materials are as important as velocities of the materials in many applications. Only phase information of surface-wave data is utilized when high-frequency (≥ 2 Hz) surface-wave data are routinely inverted to determine near-surface shear (S)-wave velocities. Amplitude information of high-frequency surface-wave data can be used to determine quality factors of near-surface materials. Given S-wave velocity, compressional (P)-wave velocity, and Rayleigh-wave phase velocities, it is feasible to solve for S-wave quality factor QS and P-wave quality factor QP (for some specific velocity models) down to 30 m below the ground surface in many settings by inverting high-frequency Rayleigh-wave attenuation coefficients in a layered earth model. Amplitude of seismic data is an exponential function of attenuation coefficients. When calculating attenuation coefficients from changes in amplitude, this nonlinear nature would result in that small variations in amplitude cause huge changes in attenuation coefficients. This result suggests data (attenuation coefficients) that normally possess large errors could eventually transfer to a model (quality factors); therefore, constraints (or a priori information) on models are necessary. Because an inversion system to solve this problem is unstable, a regularization parameter must be introduced into an inversion algorithm to stabilize the inversion. These characteristics of the inversion problem allow us to solve the problem as a constrained and regularized linear system. Usually, a set of models that meet the defined constraints can be obtained by solving the system. Based on the linear nature of the inversion system, a smooth model can be selected from the set of models as a solution of the inversion using the L-curve method. This approach is a trade-off solution between data misfit and model length. Several real-world examples demonstrate the importance of constraints in finding acceptable realistic

  13. [The effect of the surroundings to the apparent diffusion coefficient on diffusion weighted imaging].

    PubMed

    Yamatani, Yuya; Doi, Tsukasa; Shimizu, Kozo; Nogi, Akihiro

    2010-10-20

    Diffusion weighted imaging (DWI) is now widely used in magnetic resonance (MR) imaging of the head and body. Moreover, the Apparent diffusion coefficient (ADC) value is often used for the differential diagnosis of the tumor. However, the effect of the surroundings on the ADC value has not been reported. In this study, we used the phantom completely sealed up to measure the change in the ADC value depending on the surroundings material. The results showed that the ADC value decreased according to the density of superparamagnetic iron oxide (SPIO) in the surroundings. Clinically, hemorrhage or iron deposit around the tumor may affect the ADC value of the tumor and result in under-estimation.

  14. SIMPLE ANALYTICAL FORMS OF THE PERPENDICULAR DIFFUSION COEFFICIENT FOR TWO-COMPONENT TURBULENCE. I. MAGNETOSTATIC TURBULENCE

    SciTech Connect

    Shalchi, A.

    2013-09-01

    We explore perpendicular diffusion based on the unified nonlinear transport theory. We derive simple analytical forms for the perpendicular mean free path and investigate the influence of different model spectra. We show that for cases where the field line random walk is normal diffusive, the perpendicular diffusion coefficient consists of only two transport regimes. Details of the spectral shape are less important, especially those of the inertial range. Only the macroscopic properties of the turbulence spectrum control the perpendicular diffusion coefficient. Simple formulae for the perpendicular diffusion coefficient are derived which can easily be implemented in solar modulation or shock acceleration codes.

  15. Study of diffusion coefficients of glasses under zero-G

    NASA Technical Reports Server (NTRS)

    Kinser, D. L.

    1975-01-01

    Diffusion studies of the glass forming ion are examined in zero-g environments and diffusion data obtained from these experiments are unique because of earth based experimental problems. The choice of system for diffusion studies is discussed along with the lab processing. The space processing is described consisting of a heating cycle designed to maximize time exposed to the diffusion temperature without exposing the low viscosity melt to gravitational forces.

  16. Emission-based estimation of lung attenuation coefficients for attenuation correction in time-of-flight PET/MR

    NASA Astrophysics Data System (ADS)

    Mehranian, Abolfazl; Zaidi, Habib

    2015-06-01

    In standard segmentation-based MRI-guided attenuation correction (MRAC) of PET data on hybrid PET/MRI systems, the inter/intra-patient variability of linear attenuation coefficients (LACs) is ignored owing to the assignment of a constant LAC to each tissue class. This can lead to PET quantification errors, especially in the lung regions. In this work, we aim to derive continuous and patient-specific lung LACs from time-of-flight (TOF) PET emission data using the maximum likelihood reconstruction of activity and attenuation (MLAA) algorithm. The MLAA algorithm was constrained for estimation of lung LACs only in the standard 4-class MR attenuation map using Gaussian lung tissue preference and Markov random field smoothness priors. MRAC maps were derived from segmentation of CT images of 19 TOF-PET/CT clinical studies into background air, lung, soft tissue and fat tissue classes, followed by assignment of predefined LACs of 0, 0.0224, 0.0864 and 0.0975 cm-1, respectively. The lung LACs of the resulting attenuation maps were then estimated from emission data using the proposed MLAA algorithm. PET quantification accuracy of MRAC and MLAA methods was evaluated against the reference CT-based AC method in the lungs, lesions located in/near the lungs and neighbouring tissues. The results show that the proposed MLAA algorithm is capable of retrieving lung density gradients and compensate fairly for respiratory-phase mismatch between PET and corresponding attenuation maps. It was found that the mean of the estimated lung LACs generally follow the trend of the reference CT-based attenuation correction (CTAC) method. Quantitative analysis revealed that the MRAC method resulted in average relative errors of  -5.2   ±   7.1% and  -6.1   ±   6.7% in the lungs and lesions, respectively. These were reduced by the MLAA algorithm to  -0.8   ±   6.3% and  -3.3   ±   4.7%, respectively. In conclusion, we demonstrated

  17. Turbulent eddy diffusion models in exposure assessment - Determination of the eddy diffusion coefficient.

    PubMed

    Shao, Yuan; Ramachandran, Sandhya; Arnold, Susan; Ramachandran, Gurumurthy

    2017-03-01

    The use of the turbulent eddy diffusion model and its variants in exposure assessment is limited due to the lack of knowledge regarding the isotropic eddy diffusion coefficient, DT. But some studies have suggested a possible relationship between DT and the air changes per hour (ACH) through a room. The main goal of this study was to accurately estimate DT for a range of ACH values by minimizing the difference between the concentrations measured and predicted by eddy diffusion model. We constructed an experimental chamber with a spatial concentration gradient away from the contaminant source, and conducted 27 3-hr long experiments using toluene and acetone under different air flow conditions (0.43-2.89 ACHs). An eddy diffusion model accounting for chamber boundary, general ventilation, and advection was developed. A mathematical expression for the slope based on the geometrical parameters of the ventilation system was also derived. There is a strong linear relationship between DT and ACH, providing a surrogate parameter for estimating DT in real-life settings. For the first time, a mathematical expression for the relationship between DT and ACH has been derived that also corrects for non-ideal conditions, and the calculated value of the slope between these two parameters is very close to the experimentally determined value. The values of DT obtained from the experiments are generally consistent with values reported in the literature. They are also independent of averaging time of measurements, allowing for comparison of values obtained from different measurement settings. These findings make the use of turbulent eddy diffusion models for exposure assessment in workplace/indoor environments more practical.

  18. Simultaneous evaluation of acoustic nonlinearity parameter and attenuation coefficients using the finite amplitude method

    SciTech Connect

    Zhang, Shuzeng; Li, Xiongbing; Jeong, Hyunjo Cho, Sungjong

    2015-07-15

    A novel method to determine acoustic parameters involved in measuring the nonlinearity parameter of fluids or solids is proposed. The approach is based on the measurement of fundamental and second harmonic pressures with a calibrated receiver, and on a nonlinear least squares data-fitting to multi-Gaussian beam (MGB) equations which explicitly define the attenuation and diffraction effects in the quasilinear regime. Results obtained in water validate the proposed method. The choice of suitable source pressure is discussed with regard to the quasilinear approximation involved. The attenuation coefficients are also acquired in nonlinear regime and their relations are discussed.

  19. Quantitative RNFL attenuation coefficient measurements by RPE-normalized OCT data

    NASA Astrophysics Data System (ADS)

    Vermeer, K. A.; van der Schoot, J.; Lemij, H. G.; de Boer, J. F.

    2012-03-01

    We demonstrate significantly different scattering coefficients of the retinal nerve fiber layer (RNFL) between normal and glaucoma subjects. In clinical care, SD-OCT is routinely used to assess the RNFL thickness for glaucoma management. In this way, the full OCT data set is conveniently reduced to an easy to interpret output, matching results from older (non- OCT) instruments. However, OCT provides more data, such as the signal strength itself, which is due to backscattering in the retinal layers. For quantitative analysis, this signal should be normalized to adjust for local differences in the intensity of the beam that reaches the retina. In this paper, we introduce a model that relates the OCT signal to the attenuation coefficient of the tissue. The average RNFL signal (within an A-line) was then normalized based on the observed RPE signal, resulting in normalized RNFL attenuation coefficient maps. These maps showed local defects matching those found in thickness data. The average (normalized) RNFL attenuation coefficient of a fixed band around the optic nerve head was significantly lower in glaucomatous eyes than in normal eyes (3.0mm-1 vs. 4.9mm-1, P<0.01, Mann-Whitney test).

  20. Study of diffusion coefficients of glasses under Zero-G

    NASA Technical Reports Server (NTRS)

    Kinser, D. L.

    1977-01-01

    A diffusion experiment for glasses was formulated, such theoretical and earth bound results as were available were outlined, and the preliminary earth based experimental work in preparation for a weightless experiment was done. The fundamental premise of the work was that diffusion studies of the glass forming ion can be conducted in zero-g environments, and diffusion data obtained from these experiments are unique and valuable because of earth based experimental difficulties.

  1. Electrostatic coupling between DNA and its counterions modulates the observed translational diffusion coefficients.

    PubMed

    Stellwagen, Earle; Stellwagen, Nancy C

    2015-09-01

    Free solution capillary electrophoresis (CE) is a useful technique for measuring the translational diffusion coefficients of charged analytes. The measurements are relatively fast if the polarity of the electric field is reversed to drive the analyte back and forth past the detection window during each run. We have tested the validity of the resulting diffusion coefficients using double-stranded DNA molecules ranging in size from 20 to 960 base pairs as the model system. The diffusion coefficients of small DNAs are equal to values in the literature measured by other techniques. However, the diffusion coefficients of DNA molecules larger than ∼30 base pairs are anomalously high and deviate increasingly from the literature values with increasing DNA molar mass. The anomalously high diffusion coefficients are due to electrostatic coupling between the DNA and its counterions. As a result, the measured diffusion coefficients vary with the diffusion coefficient of the counterion, as well as with cation concentration and electric field strength. These effects can be reduced or eliminated by measuring apparent diffusion coefficients of the DNA at several different electric field strengths and extrapolating the results to zero electric field.

  2. MEASUREMENT OF EFFECTIVE AIR DIFFUSION COEFFICIENTS FOR TRICHLOROETHENE IN UNDISTURBED SOIL CORES. (R826162)

    EPA Science Inventory

    Abstract

    In this study, we measure effective diffusion coefficients for trichloroethene in undisturbed soil samples taken from Picatinny Arsenal, New Jersey. The measured effective diffusion coefficients ranged from 0.0053 to 0.0609 cm2/s over a range of air...

  3. Temperature effects on diffusion coefficient for 6-gingerol and 6-shogaol in subcritical water extraction

    NASA Astrophysics Data System (ADS)

    Ilia Anisa, Nor; Azian, Noor; Sharizan, Mohd; Iwai, Yoshio

    2014-04-01

    6-gingerol and 6-shogaol are the main constituents as anti-inflammatory or bioactive compounds from zingiber officinale Roscoe. These bioactive compounds have been proven for inflammatory disease, antioxidatives and anticancer. The effect of temperature on diffusion coefficient for 6-gingerol and 6-shogaol were studied in subcritical water extraction. The diffusion coefficient was determined by Fick's second law. By neglecting external mass transfer and solid particle in spherical form, a linear portion of Ln (1-(Ct/Co)) versus time was plotted in determining the diffusion coefficient. 6-gingerol obtained the higher yield at 130°C with diffusion coefficient of 8.582x10-11 m2/s whilst for 6-shogaol, the higher yield and diffusion coefficient at 170°C and 19.417 × 10-11 m2/s.

  4. Diffusion coefficient of an inclusion in a liquid membrane supported by a solvent of arbitrary thickness.

    PubMed

    Seki, Kazuhiko; Ramachandran, Sanoop; Komura, Shigeyuki

    2011-08-01

    The diffusion coefficient of an inclusion in a liquid membrane is investigated by taking into account the interaction between membranes and bulk solvents of arbitrary thickness. As illustrative examples, the diffusion coefficients of two types of inclusions, a circular domain composed of fluid with the same viscosity as the host membrane and that of a polymer chain embedded in the membrane, are studied. The diffusion coefficients are expressed in terms of the hydrodynamic screening lengths, which vary according to the solvent thickness. When the membrane fluid is dragged by the solvent of finite thickness, via stick boundary conditions, multiple hydrodynamic screening lengths together with the weight factors to the diffusion coefficients are obtained from the characteristic equation. The conditions for which the diffusion coefficients can be approximated by the expression including only a single hydrodynamic screening length are also shown.

  5. Total attenuation coefficient of intralipid dilutions for discrete laser wavelengths between 405 and 1315 nm

    NASA Astrophysics Data System (ADS)

    Dreischuh, Tanja N.; Gurdev, Ljuan L.; Vankov, Orlin I.; Avramov, Lachezar A.; Stoyanov, Dimitar V.

    2015-01-01

    The experimental investigations on different aspects of optical tomography require the knowledge of the optical parameters of tissues and tissue-like phantoms in order to unambiguously interpret the experimental data and specify characteristic inhomogeneities in tissue diagnostics. The main optical parameters of interest are the absorption coefficient, the scattering, backscattering, and reduced-scattering coefficients, the total attenuation (extinction) coefficient and the anisotropy factor. In this work, we extend our investigations of the optical properties of tissuemimicking phantoms, such as Intralipid-20% fat emulsion, using an approach we have developed recently based on the peculiarities of laser radiation beams propagating through semi-infinite turbid media. The dependence of the total attenuation coefficient on the Intralipid concentration, for laser radiation wavelengths λ=405, 672, 850, and 1314 nm, is studied, by using a set of phantoms consisting of different dilutions of Intralipid in distilled water. The experimental results for the extinction are in agreement with our previous results and with empiric formulae found by other authors concerning the wavelength dependence of the scattering coefficient of Intralipid -10% and Intralipid - 20%. They are also in agreement with known data of the water absorptance. As a whole, the results obtained in this work confirm the consideration of the experimental phantoms as semi-infinite media. They also confirm and extend theoretical and experimental results obtained previously, and reveal advantages of using longer wavelengths for deeper diagnostics of tissues and mimic turbid media.

  6. Multiple irradiation sensing of the optical effective attenuation coefficient for spectral correction in handheld OA imaging.

    PubMed

    Held, K Gerrit; Jaeger, Michael; Rička, Jaro; Frenz, Martin; Akarçay, H Günhan

    2016-06-01

    Spectral optoacoustic (OA) imaging enables spatially-resolved measurement of blood oxygenation levels, based on the distinct optical absorption spectra of oxygenated and de-oxygenated blood. Wavelength-dependent optical attenuation in the bulk tissue, however, distorts the acquired OA spectrum and thus makes quantitative oxygenation measurements challenging. We demonstrate a correction for this spectral distortion without requiring a priori knowledge of the tissue optical properties, using the concept of multiple irradiation sensing: recording the OA signal amplitude of an absorbing structure (e.g. blood vessel), which serves as an intrinsic fluence detector, as function of irradiation position. This permits the reconstruction of the bulk effective optical attenuation coefficient μeff,λ . If performed at various irradiation wavelengths, a correction for the wavelength-dependent fluence attenuation is achieved, revealing accurate spectral information on the absorbing structures. Phantom studies were performed to show the potential of this technique for handheld clinical combined OA and ultrasound imaging.

  7. Acoustic speed and attenuation coefficient in sheep aorta measured at 5-9 MHz.

    PubMed

    Fraser, Katharine H; Poepping, Tamie L; McNeilly, Alan; Megson, Ian L; Hoskins, Peter R

    2006-06-01

    B-mode ultrasound (US) images from blood vessels in vivo differ significantly from vascular flow phantom images. Phantoms with acoustic properties more closely matched to those of in vivo arteries may give better images. A method was developed for measuring the speed and attenuation coefficient of US over the range 5 to 9 MHz in samples of sheep aorta using a pulse-echo technique. The times-of-flight method was used with envelope functions to identify the reference points. The method was tested with samples of tissue-mimicking material of known acoustic properties. The tissue samples were stored in Krebs physiologic buffer solution and measured over a range of temperatures. At 37 degrees C, the acoustic speed and attenuation coefficient as a function of frequency in MHz were 1600 +/- 50 ms(-1) and 1.5 +/- 4f(0.94 +/- 1.3) dB cm(-1), respectively.

  8. An improved profiling method for the measurement of hyperspectral diffuse attenuation coefficents in shallow turbid waters

    NASA Astrophysics Data System (ADS)

    Ma, Li; Tao, Bangyi; Shi, Liangliang; Zhu, Qiankun

    2016-10-01

    The measurement of hyperspectral diffuse attenuation coefficients (Kd(λ)) in shallow turbid waters cannot be successfully achieved by the original Satlantic profiling system, because of less data available in the near-surface waters due to the rapid decrease of light intensity. In this paper, an improved profiling system and processing method are proposed. Firstly, a convenient buoyancy device is designed and mounted on the Satlantic Profiler II to allow the profiler to loiter close to the sea surface, thereby significantly improving the vertical sampling resolution to 1cm/s in near-surface waters, particularly in the depth between 0 and 1 meter. In addition, customized processing software CProSoft is developed to subjectively select the depths for various wavelengths that meet their different requirement for regression analysis. Comparison with original system results shows that our novel method can significantly improve the accuracy of Kd(λ) measurements especially in the short blue and red spectral range, and can even effectively derive near-surface Kd values in the extremely turbid waters with attenuation coefficients greater than 30 m-1, which dramatically enlarge the Kd(λ) measuring range

  9. Diffusion coefficients of water in biobased hydrogel polymer matrices by nuclear magnetic resonance imaging

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The diffusion coefficient of water in biobased hydrogels were measured utilizing a simple NMR method. This method tracks the migration of deuterium oxide through imaging data that is fit to a diffusion equation. The results show that a 5 wt% soybean oil based hydrogel gives aqueous diffusion of 1.37...

  10. Impurity Diffusion Coefficients of Al and Zn in Mg Determined from Solid-to-Solid Diffusion Couples

    SciTech Connect

    Kammerer, Catherine; Kulkarni, Nagraj S; Warmack, Robert J Bruce; Perry, Kelly A; Belova, Irina; Murch, Prof. Graeme; Sohn, Yong Ho

    2013-08-01

    Increasing use and development of lightweight Mgalloys have led to the desire for more fundamental research in and understanding of Mg-based systems. As property enhancing components, Al and Zn are two of the most important and common alloying elements for Mg-alloys. We have investigated the concentration dependent interdiffusion of Al and Zn in Mg using diffusion couples of pure polycrystalline Mg mated to Mg solid solutions containing either <9 at.% Al or <3 at.% Zn. Concentration profiles were determined by electron micro-probe microanalysis of the diffusion zone. The interdiffusion coefficients were determined by the classical Boltzmann-Matano method within the Mg solid solution. As the concentration of Al or Zn approaches the dilute ends, we employ an analytical approach based on the Hall method to estimate the impurity diffusion coefficients. Results of Al and Zn impurity diffusion in Mg are reported and compared to published impurity diffusion coefficients typically determined by thin film techniques.

  11. Determination of diffusion coefficients and diffusion characteristics for chlorferon and diethylthiophosphate in Ca-alginate gel beads.

    PubMed

    Ha, Jiyeon; Engler, Cady R; Lee, Seung Jae

    2008-07-01

    Diffusion characteristics of chlorferon and diethylthiophosphate (DETP) in Ca-alginate gel beads were studied to assist in designing and operating bioreactor systems. Diffusion coefficients for chlorferon and DETP in Ca-alginate gel beads determined at conditions suitable for biodegradation studies were 2.70 x 10(-11) m(2)/s and 4.28 x 10(-11) m(2)/s, respectively. Diffusivities of chlorferon and DETP were influenced by several factors, including viscosity of the bulk solution, agitation speed, and the concentrations of diffusing substrate and immobilized cells. Diffusion coefficients increased with increasing agitation speed, probably due to poor mixing at low speed and some attrition of beads at high speeds. Diffusion coefficients also increased with decreasing substrate concentration. Increased cell concentration in the gel beads caused lower diffusivity. Theoretical models to predict diffusivities as a function of cell weight fraction overestimated the effective diffusivities for both chlorferon and DETP, but linear relations between effective diffusivity and cell weight fraction were derived from experimental data. Calcium-alginate gel beads with radii of 1.65-1.70 mm used in this study were not subject to diffusional limitations: external mass transfer resistances were negligible based on Biot number calculations and effectiveness factors indicated that internal mass transfer resistance was negligible. Therefore, the degradation rates of chlorferon and DETP inside Ca-alginate gel beads were reaction-limited.

  12. Excitation and temperature dependent exciton-carrier transport in CVD diamond: Diffusion coefficient, recombination lifetime and diffusion length

    NASA Astrophysics Data System (ADS)

    Ščajev, Patrik

    2017-04-01

    Time-resolved induced absorption (IA) and light induced transient grating (LITG) techniques were applied for the investigation of nonequilibrium exciton-carrier diffusion and recombination processes in a high-purity CVD diamond. Injection range from 1015 to 1020 cm-3 carrier density was achieved by combining one photon and two photon excitations. The measurements were performed in the 10-750 K temperature range. The LITG diffusion coefficient peaked at 44 cm2/s value at room temperature under low injection conditions. At lower temperatures it transferred to much lower exciton diffusion coefficient. A strong decrease of diffusion coefficient under higher injection conditions was explained by exciton formation with a low diffusion coefficient and many body effects, as polyexciton and electron-hole droplet formation. High temperature phonon-limited diffusion coefficient was weakly injection dependent. Low excitation carrier lifetime was about 700 ns above 200 K. At lower temperatures, the decay time reduced by two orders of magnitude, which was explained by the formation of biexcitons. At lowest temperatures, an increase of the carrier recombination rate at high injection was attributed to Auger recombinations of polyexcitons and electron-hole droplets. While at high temperatures, the increase of the recombination rate with 490 meV activation energy was observed. The combination of IA and LITG measurements provided effective diffusion lengths in a 0.3-50 μm range, being strongly dependent on the excess carrier density and temperature.

  13. Derivation of diffusion coefficient of a Brownian particle in tilted periodic potential from the coordinate moments

    NASA Astrophysics Data System (ADS)

    Zhang, Yunxin

    2009-07-01

    In this research, diffusion of an overdamped Brownian particle in the tilted periodic potential is investigated. Using the one-dimensional hopping model, the formulations of the mean velocity V and effective diffusion coefficient D of the Brownian particle have been obtained [B. Derrida, J. Stat. Phys. 31 (1983) 433]. Based on the relation between the effective diffusion coefficient and the moments of the mean first passage time, the formulation of effective diffusion coefficient D of the Brownian particle also has been obtained [P. Reimann, et al., Phys. Rev. E 65 (2002) 031104]. In this research, we'll give another analytical expression of the effective diffusion coefficient D from the moments of the particle's coordinate.

  14. Nonlinearity Effects of Lateral Density Diffusion Coefficient on Gain-Guided VCSEL Performance

    NASA Technical Reports Server (NTRS)

    Li, Jian-Zhong; Cheung, Samson H.; Ning, C. Z.; Biegel, Bryan (Technical Monitor)

    2001-01-01

    Electron and hole diffusions in the plane of semiconductor quantum wells play an important part in the static and dynamic operations of semiconductor lasers. In this paper, we apply a hydrodynamic model developed from the semiconductor Bloch equations to numerically study the effects of nonlinearity in the diffusion coefficient on single mode operation and direct modulation of a gain-guided InGaAs/GaAs multiple quantum well laser, operating not too far from threshold. We found that a small diffusion coefficient is advantageous for lowering the threshold current and increasing the modulation bandwidth. Most importantly, the effects of nonlinearity in the coefficient can be approximately reproduced by replacing the coefficient with an effective constant diffusion coefficient, which corresponds roughly to the half height density of the density distribution.

  15. Measurement of effective air diffusion coefficients for trichloroethene in undisturbed soil cores.

    PubMed

    Bartelt-Hunt, Shannon L; Smith, James A

    2002-06-01

    In this study, we measure effective diffusion coefficients for trichloroethene in undisturbed soil samples taken from Picatinny Arsenal, New Jersey. The measured effective diffusion coefficients ranged from 0.0053 to 0.0609 cm2/s over a range of air-filled porosity of 0.23-0.49. The experimental data were compared to several previously published relations that predict diffusion coefficients as a function of air-filled porosity and porosity. A multiple linear regression analysis was developed to determine if a modification of the exponents in Millington's [Science 130 (1959) 100] relation would better fit the experimental data. The literature relations appeared to generally underpredict the effective diffusion coefficient for the soil cores studied in this work. Inclusion of a particle-size distribution parameter, d10, did not significantly improve the fit of the linear regression equation. The effective diffusion coefficient and porosity data were used to recalculate estimates of diffusive flux through the subsurface made in a previous study performed at the field site. It was determined that the method of calculation used in the previous study resulted in an underprediction of diffusive flux from the subsurface. We conclude that although Millington's [Science 130 (1959) 100] relation works well to predict effective diffusion coefficients in homogeneous soils with relatively uniform particle-size distributions, it may be inaccurate for many natural soils with heterogeneous structure and/or non-uniform particle-size distributions.

  16. Measurement of effective air diffusion coefficients for trichloroethene in undisturbed soil cores

    NASA Astrophysics Data System (ADS)

    Bartelt-Hunt, Shannon L.; Smith, James A.

    2002-06-01

    In this study, we measure effective diffusion coefficients for trichloroethene in undisturbed soil samples taken from Picatinny Arsenal, New Jersey. The measured effective diffusion coefficients ranged from 0.0053 to 0.0609 cm 2/s over a range of air-filled porosity of 0.23-0.49. The experimental data were compared to several previously published relations that predict diffusion coefficients as a function of air-filled porosity and porosity. A multiple linear regression analysis was developed to determine if a modification of the exponents in Millington's [Science 130 (1959) 100] relation would better fit the experimental data. The literature relations appeared to generally underpredict the effective diffusion coefficient for the soil cores studied in this work. Inclusion of a particle-size distribution parameter, d10, did not significantly improve the fit of the linear regression equation. The effective diffusion coefficient and porosity data were used to recalculate estimates of diffusive flux through the subsurface made in a previous study performed at the field site. It was determined that the method of calculation used in the previous study resulted in an underprediction of diffusive flux from the subsurface. We conclude that although Millington's [Science 130 (1959) 100] relation works well to predict effective diffusion coefficients in homogeneous soils with relatively uniform particle-size distributions, it may be inaccurate for many natural soils with heterogeneous structure and/or non-uniform particle-size distributions.

  17. Using molecular dynamics to obtain Maxwell-Stefan diffusion coefficients in liquid systems

    NASA Astrophysics Data System (ADS)

    van de Ven-Lucassen Thijs, Irma M. J. J.; Vlugt Antonius, J. H.; van der Zanden Piet, J. J.; Kerkhof, J. A. M.

    Two methods are compared for the calculation of Maxwell-Stefan diffusion coefficients. The first method is a non-equilibrium molecular dynamics (NEMD) algorithm, in which the system is driven away from equilibrium and the system response is monitored. The second method is the equilibrium molecular dynamics (EMD) calculation of the appropriate GreenKubo equation. Simulations were performed for systems of 250 and 300 Lennard-Jones particles at various densities and temperatures. The systems were divided into two or three components by attaching a colour label to the particles. Since a colour label plays no role in the dynamics, the Maxwell-Stefan diffusion coefficients of the binary and ternary systems are equal to the self-diffusion coefficient. In dense fluids, the system response to an external perturbation is not a first-order process, and the diffusion coefficients cannot be determined from the short term response in the NEMD method. Only the long term response can be used, after a steady state has been reached. In binary systems the Maxwell-Stefan diffusion coefficients, determined by the Green-Kubo (EMD) method, are more accurate than the NEMD coefficients. Since in the NEMD method only the long term response can be used, the GreenKubo method is also less time consuming and is therefore preferred for the calculation of the Maxwell-Stefan diffusion coefficients. In ternary systems the Green-Kubo method is tested for the 250 particle system. The Maxwell-Stefan diffusion coefficients agree well with the selfdiffusion coefficient. For low mole fractions of the coloured components the diffusion coefficients were less accurate.

  18. Scale Dependence of Effective Matrix Diffusion Coefficient Evidence and Preliminary Interpertation

    SciTech Connect

    H.H. Liu; Y. Zhang

    2006-06-20

    The exchange of solute mass (through molecular diffusion) between fluid in fractures and fluid in the rock matrix is called matrix diffusion. Owing to the orders-of-magnitude slower flow velocity in the matrix compared to fractures, matrix diffusion can significantly retard solute transport in fractured rock, and therefore is an important process for a variety of problems, including remediation of subsurface contamination and geological disposal of nuclear waste. The effective matrix diffusion coefficient (molecular diffusion coefficient in free water multiplied by matrix tortuosity) is an important parameter for describing matrix diffusion, and in many cases largely determines overall solute transport behavior. While matrix diffusion coefficient values measured from small rock samples in the laboratory are generally used for modeling field-scale solute transport in fractured rock (Boving and Grathwohl, 2001), several research groups recently have independently found that effective matrix diffusion coefficients much larger than laboratory measurements are needed to match field-scale tracer-test data (Neretnieks, 2002; Becker and Shapiro, 2000; Shapiro, 2001; Liu et al., 2003,2004a). In addition to the observed enhancement, Liu et al. (2004b), based on a relatively small number of field-test results, reported that the effective matrix diffusion coefficient might be scale dependent, and, like permeability and dispersivity, it seems to increases with test scale. This scale-dependence has important implications for large-scale solute transport in fractured rock. Although a number of mechanisms have been proposed to explain the enhancement of the effective matrix diffusion coefficient, the potential scale dependence and its mechanisms are not fully investigated at this stage. The major objective of this study is to again demonstrate (based on more data published in the literature than those used in Liu et al. [2004b]) the potential scale dependence of the effective

  19. Scale dependence of the effective matrix diffusion coefficient:Evidence and preliminary interpretation

    SciTech Connect

    Liu, Hui-Hai; Zhang, Yingqi; Molz, Fred J.

    2006-04-30

    The exchange of solute mass (through molecular diffusion) between fluid in fractures and fluid in the rock matrix is called matrix diffusion. Owing to the orders-of-magnitude slower flow velocity in the matrix compared to fractures, matrix diffusion can significantly retard solute transport in fractured rock, and therefore is an important process for a variety of problems, including remediation of subsurface contamination and geological disposal of nuclear waste. The effective matrix diffusion coefficient (molecular diffusion coefficient in free water multiplied by matrix tortuosity) is an important parameter for describing matrix diffusion, and in many cases largely determines overall solute transport behavior. While matrix diffusion coefficient values measured from small rock samples in the laboratory are generally used for modeling field-scale solute transport in fractured rock (Boving and Grathwohl, 2001), several research groups recently have independently found that effective matrix diffusion coefficients much larger than laboratory measurements are needed to match field-scale tracer-test data (Neretnieks, 2002; Becker and Shapiro, 2000; Shapiro, 2001; Liu et al., 2003, 2004a). In addition to the observed enhancement, Liu et al. (2004b), based on a relatively small number of field-test results, reported that the effective matrix diffusion coefficient might be scale dependent, and, like permeability and dispersivity, it seems to increases with test scale. This scale-dependence has important implications for large-scale solute transport in fractured rock. Although a number of mechanisms have been proposed to explain the enhancement of the effective matrix diffusion coefficient, the potential scale dependence and its mechanisms are not fully investigated at this stage. The major objective of this study is to again demonstrate (based on more data published in the literature than those used in Liu et al. [2004b]) the potential scale dependence of the effective

  20. Chromatographic determination of the diffusion coefficients of light hydrocarbons in polymers

    NASA Astrophysics Data System (ADS)

    Yakubenko, E. E.; Korolev, A. A.; Chapala, P. P.; Bermeshev, M. V.; Kanat'eva, A. Yu.; Kurganov, A. A.

    2017-01-01

    Gas-chromatographic determination of the diffusion coefficients that allows for the compressibility of the mobile phase has been suggested. The diffusion coefficients were determined for light hydrocarbons C1-C4 in four polymers with a high free volume, which are candidates for use as gas-separating membranes. The diffusion coefficients calculated from chromatographic data were shown to be one or two orders of magnitude smaller than the values obtained by the membrane method. This may be due to the presence of an additional flow through the membrane caused by the pressure gradient across the membrane in membrane methods.

  1. Analyzing the special PFG signal attenuation behavior of intermolecular MQC via the effective phase shift diffusion equation method.

    PubMed

    Lin, Guoxing

    2015-10-28

    Inter-molecular multiple quantum coherence (iMQC) has important applications in NMR and MRI. However, the current theoretical methods still have some difficulties in analyzing the behavior of iMQC signal attenuation of pulsed field gradient diffusion experiments. In this paper, the iMQC diffusion experiments were analyzed by an effective phase shift diffusion equation (EPSDE) method, which is based on the idea that the accumulating phase shift (APS) can be viewed as the result of a diffusion process in virtual phase space (VPS) with effective diffusion coefficient K(2)(t) D (rad(2)/s) where K(t)=∫0 (t)γg(t')dt' is a wavenumber and D is the physical diffusion coefficient of the spin carrier in the real space. The term K(t(tot)) z1 needs to be added to the APS when K(t(tot)) is not zero. Most of the time, K(t(tot)) equals zero. However, in iMQC experiments, the condition K(t(tot)) equaling zero or being non-zero for each spin depends on the gradient pulse setting. The signal attenuations of these two types of iMQC, zero or non-zero K(t(tot)), were analyzed in detail for free and restricted diffusions, which shows that there are significant differences between these two types of iMQC. Particularly, if an apparent diffusion coefficient D(app) is used to analyze the signal attenuation, it equals nD for zero K(t(tot)) which agrees with current theoretical and experimental reports, while for non-zero K(t(tot)), it equals (2n - 1) D which agrees with experimental results from the literature; there are no similar theoretical results reported for comparison. The result that D(app) equals (2n - 1) D is important because the higher value of D(app) means that non-zero K(t(tot)) iMQC can potentially provide more contrast and measure slower diffusion rates than zero K(t(tot)) iMQC. The EPSDE method provides a new way to analyze iMQC diffusion experiments.

  2. Banded Structures in Electron Pitch Angle Diffusion Coefficients from Resonant Wave Particle Interactions

    NASA Technical Reports Server (NTRS)

    Tripathi, A. K.; Singhal, R. P.; Khazanov, G. V.; Avanov, L. A.

    2016-01-01

    Electron pitch angle (D (alpha)) and momentum (D(pp)) diffusion coefficients have been calculated due to resonant interactions with electrostatic electron cyclotron harmonic (ECH) and whistler mode chorus waves. Calculations have been performed at two spatial locations L = 4.6 and 6.8 for electron energies 10 keV. Landau (n = 0) resonance and cyclotron harmonic resonances n = +/-1, +/-2,...+/-5 have been included in the calculations. It is found that diffusion coefficient versus pitch angle (alpha) profiles show large dips and oscillations or banded structures. The structures are more pronounced for ECH and lower band chorus (LBC) and particularly at location 4.6. Calculations of diffusion coefficients have also been performed for individual resonances. It is noticed that the main contribution of ECH waves in pitch angle diffusion coefficient is due to resonances n = +1 and n = +2. A major contribution to momentum diffusion coefficients appears from n = +2. However, the banded structures in D alpha and Dpp coefficients appear only in the profile of diffusion coefficients for n = +2. The contribution of other resonances to diffusion coefficients is found to be, in general, quite small or even negligible. For LBC and upper band chorus waves, the banded structures appear only in Landau resonance. The Dpp diffusion coefficient for ECH waves is one to two orders smaller than D alpha coefficients. For chorus waves, Dpp coefficients are about an order of magnitude smaller than D alpha coefficients for the case n does not = 0. In case of Landau resonance, the values of Dpp coefficient are generally larger than the values of D alpha coefficients particularly at lower energies. As an aid to the interpretation of results, we have also determined the resonant frequencies. For ECH waves, resonant frequencies have been estimated for wave normal angle 89 deg and harmonic resonances n = +1, +2, and +3, whereas for whistler mode waves, the frequencies have been calculated for angle

  3. Determination of the diffusion coefficient between corn syrup and distilled water using a digital camera

    NASA Astrophysics Data System (ADS)

    Ray, E.; Bunton, P.; Pojman, J. A.

    2007-10-01

    A simple technique for determining the diffusion coefficient between two miscible liquids is presented based on observing concentration-dependent ultraviolet-excited fluorescence using a digital camera. The ultraviolet-excited visible fluorescence of corn syrup is proportional to the concentration of the syrup. The variation of fluorescence with distance from the transition zone between the fluids is fit by the Fick's law solution to the diffusion equation. By monitoring the concentration at successive times, the diffusion coefficient can be determined in otherwise transparent materials. The technique is quantitative and makes measurement of diffusion accessible in the advanced undergraduate physics laboratory.

  4. Molecular modeling of diffusion coefficient and ionic conductivity of CO2 in aqueous ionic solutions.

    PubMed

    Garcia-Ratés, Miquel; de Hemptinne, Jean-Charles; Bonet Avalos, Josep; Nieto-Draghi, Carlos

    2012-03-08

    Mass diffusion coefficients of CO(2)/brine mixtures under thermodynamic conditions of deep saline aquifers have been investigated by molecular simulation. The objective of this work is to provide estimates of the diffusion coefficient of CO(2) in salty water to compensate the lack of experimental data on this property. We analyzed the influence of temperature, CO(2) concentration,and salinity on the diffusion coefficient, the rotational diffusion, as well as the electrical conductivity. We observe an increase of the mass diffusion coefficient with the temperature, but no clear dependence is identified with the salinity or with the CO(2) mole fraction, if the system is overall dilute. In this case, we notice an important dispersion on the values of the diffusion coefficient which impairs any conclusive statement about the effect of the gas concentration on the mobility of CO(2) molecules. Rotational relaxation times for water and CO(2) increase by decreasing temperature or increasing the salt concentration. We propose a correlation for the self-diffusion coefficient of CO(2) in terms of the rotational relaxation time which can ultimately be used to estimate the mutual diffusion coefficient of CO(2) in brine. The electrical conductivity of the CO(2)-brine mixtures was also calculated under different thermodynamic conditions. Electrical conductivity tends to increase with the temperature and salt concentration. However, we do not observe any influence of this property with the CO(2) concentration at the studied regimes. Our results give a first evaluation of the variation of the CO(2)-brine mass diffusion coefficient, rotational relaxation times, and electrical conductivity under the thermodynamic conditions typically encountered in deep saline aquifers.

  5. Diffusion Coefficients of Water and Leachables in Methacrylate-based Crosslinked Polymers using Absorption Experiments

    PubMed Central

    Parthasarathy, Ranganathan; Misra, Anil; Park, Jonggu; Ye, Qiang; Spencer, Paulette

    2012-01-01

    The diffusion of water into dentin adhesive polymers and leaching of unpolymerized monomer from the adhesive are linked to their mechanical softening and hydrolytic degradation. Therefore, diffusion coefficient data are critical for the mechanical design of these polymeric adhesives. In this study, diffusion coefficients of water and leachables were obtained for sixteen methacrylate-based crosslinked polymers using absorption experiments. The experimental mass change data was interpreted using numerical solution of the two-dimensional diffusion equations. The calculated diffusion coefficients varied from 1.05 × 10−8 cm2/sec (co-monomer TMTMA) to 3.15 × 10−8 cm2/sec (co-monomer T4EGDMA). Correlation of the diffusion coefficients with crosslink density and hydrophilicity showed an inverse trend (R2 = 0.41). The correlation of diffusion coefficient with crosslink density and hydrophilicity are closer for molecules differing by simple repeat units (R2 = 0.95). These differences in the trends reveal mechanisms of interaction of the diffusing water with the polymer structure. PMID:22430592

  6. Diffusive limits of nonlinear hyperbolic systems with variable coefficients

    NASA Astrophysics Data System (ADS)

    Miyoshi, Hironari; Tsutsumi, Masayoshi

    2016-09-01

    We consider the initial-boundary value problem for a 2-speed system of first-order nonhomogeneous semilinear hyperbolic equations whose leading terms have a small positive parameter. Using energy estimates and a compactness lemma, we show that the diffusion limit of the sum of the solutions of the hyperbolic system, as the parameter tends to zero, verifies the nonlinear parabolic equation of the p-Laplacian type.

  7. An analysis of diffuse light attenuation in the northern Gulf of Mexico hypoxic zone using the SeaWiFS satellite data record

    EPA Science Inventory

    The water column diffuse attenuation coefficient (Kd) of the Louisiana Continental Shelf (LCS) was examined during ten years to characterize the spatial and temporal variations on monthly scales from 1998 to 2007. This region is well-known for summer hypoxia (dissolved oxygen < 2...

  8. Simultaneous reconstruction of emission activity and attenuation coefficient distribution from TOF data, acquired with external transmission source.

    PubMed

    Panin, V Y; Aykac, M; Casey, M E

    2013-06-07

    The simultaneous PET data reconstruction of emission activity and attenuation coefficient distribution is presented, where the attenuation image is constrained by exploiting an external transmission source. Data are acquired in time-of-flight (TOF) mode, allowing in principle for separation of emission and transmission data. Nevertheless, here all data are reconstructed at once, eliminating the need to trace the position of the transmission source in sinogram space. Contamination of emission data by the transmission source and vice versa is naturally modeled. Attenuated emission activity data also provide additional information about object attenuation coefficient values. The algorithm alternates between attenuation and emission activity image updates. We also proposed a method of estimation of spatial scatter distribution from the transmission source by incorporating knowledge about the expected range of attenuation map values. The reconstruction of experimental data from the Siemens mCT scanner suggests that simultaneous reconstruction improves attenuation map image quality, as compared to when data are separated. In the presented example, the attenuation map image noise was reduced and non-uniformity artifacts that occurred due to scatter estimation were suppressed. On the other hand, the use of transmission data stabilizes attenuation coefficient distribution reconstruction from TOF emission data alone. The example of improving emission images by refining a CT-based patient attenuation map is presented, revealing potential benefits of simultaneous CT and PET data reconstruction.

  9. A new procedure to measure effective molecular diffusion coefficients of salts solutions in building materials

    NASA Astrophysics Data System (ADS)

    Delgado, J. M. P. Q.

    2013-06-01

    The aim of this work is to present a mathematical and experimental formulation of a new simple procedure for the measurement of effective molecular diffusion coefficients of a salt solution in a water-saturated building material. This innovate experimental procedure and mathematical formulation is presented in detail and experimental values of "effective" molecular diffusion coefficient of sodium chloride in a concrete sample ( w/ c = 0.45), at five different temperatures (between 10 and 30 °C) and four different initial NaCl concentrations (between 0.1 and 0.5 M), are reported. The experimental results obtained are in good agreement with the theoretical and experimental values of molecular diffusion coefficient presented in literature. An empirical correlation is presented for the prediction of "effective" molecular diffusion coefficient over the entire range of temperatures and initial salt concentrations studied.

  10. Numerical results using the conforming VEM for the convection-diffusion-reaction equation with variable coefficients.

    SciTech Connect

    Manzini, Gianmarco; Cangiani, Andrea; Sutton, Oliver

    2014-10-02

    This document presents the results of a set of preliminary numerical experiments using several possible conforming virtual element approximations of the convection-reaction-diffusion equation with variable coefficients.

  11. On the determinatino of high-pressure mass-diffusion coefficients for binary mixtures

    NASA Technical Reports Server (NTRS)

    Bellan, J.; Harstad, K.

    2003-01-01

    A model for high-pressure binary diffusion coefficient calculation is proposed based on considerations originating from recasting both the low pressure kinetic theory and the Stokes-Einstein infinite dilution expressions into forms consistent with corresponding states theory.

  12. Measurement of molecular diffusion coefficients in supercritical carbon dioxide using a coated capillary column

    SciTech Connect

    Lai, C.C.; Tan, C.S. . Dept. of Chemical Engineering)

    1995-02-01

    Molecular diffusion coefficients of ethyl acetate, toluene, phenol, and caffeine in supercritical carbon dioxide were measured by a chromatographic peak broadening technique in a coated capillary column at temperatures of 308, 318, and 328 K and pressures up to 145 bar. A linear adsorption in the polymer layer coated on the inner wall of the capillary column was observed. The experimentally determined diffusion coefficients showed substantial agreement with those reported in the literature. The diffusion coefficients were in the order of 10[sup [minus]4] cm[sup 2]/s and decreased with increasing carbon dioxide density. Based on the molecular diffusion coefficient data reported here and those published elsewhere, an empirically modified Wilke-Chang equation was proposed which was found to be more quantitative than some existing equations such as the Stokes-Einstein and Wilke-Chang equations.

  13. Calculated diffusion coefficients and the growth rate of olivine in a basalt magma

    NASA Technical Reports Server (NTRS)

    Donaldson, C. H.

    1975-01-01

    Concentration gradients in glass adjacent to skeletal olivines in a basalt have been examined by electron probe. The glass is depleted in Mg, Fe, and Cr and enriched in Si, Al, Na, and Ca relative to that far from olivine. Ionic diffusion coefficients for the glass compositions are calculated from temperature, ionic radius and melt viscosity, using the Stokes-Einstein relation. At 1170 C, the diffusion coefficient of Mg(2+) ions in the basalt is 4.5 billionths sq cm per sec. Comparison with measured diffusion coefficients in a mugearite suggests this value may be 16 times too small. The concentration gradient data and the diffusion coefficients are used to calculate instantaneous olivine growth rates. Growth necessarily preceded emplacement such that the composition of the crystals plus the enclosing glass need not be that of a melt. The computed olivine growth rates are compatible with the rate of crystallization deduced for the Skaegaard intrusion.

  14. Determination of the zincate diffusion coefficient and its application to alkaline battery problems

    NASA Technical Reports Server (NTRS)

    May, C. E.; Kautz, Harold E.

    1978-01-01

    The diffusion coefficient for the zincate ion at 24 C was found to be 9.9 X 10 to the minus 7th power squared cm per sec + or - 30 percent in 45 percent potassium hydroxide and 1.4 x 10 to the minus 7 squared cm per sec + or - 25 percent in 40 percent sodium hydroxide. Comparison of these values with literature values at different potassium hydroxide concentrations show that the Stokes-Einstein equation is obeyed. The diffusion coefficient is characteristic of the zincate ion (not the cation) and independent of its concentration. Calculations with the measured value of the diffusion coefficient show that the zinc concentration in an alkaline zincate half cell becomes uniform throughout in tens of hours by diffusion alone. Diffusion equations are derived which are applicable to finite size chambers. Details and discussion of the experimental method are also given.

  15. Diffusion coefficients for nanoparticles under flow and stop-flow conditions.

    PubMed

    Katayama, Kenji; Nomura, Hiroko; Ogata, Hiroki; Eitoku, Takeshi

    2009-11-28

    Dynamic light scattering (DLS) is a well-known technique for measuring the size of nanoparticles from the diffusion coefficient. We developed a new DLS technique with high sensitivity and used it as a detection tool in microchemical applications. We found a step-like downward change in the diffusion coefficient of nanoparticles just by starting a slight flow in the fluid channel. Because the diffusion coefficient is defined by the ratio of the force due to the chemical potential gradient to the frictional coefficient for the particle by a solvent, we propose that the frictional coefficient increased significantly. This result suggests that nanoscale friction under liquid motion differs from that under a steady state.

  16. Thin-film absorption coefficients by attenuated-total-reflection spectroscopy.

    PubMed

    Holm, R T; Palik, E D

    1978-02-01

    The application of attenuated-total-reflection spectroscopy to the measurement of the absorption coefficient of thin films is presented. For low absorption the sensitivity of ATR is discussed in terms of the concept of an effective thickness. Both the case in which the refractive index of the film is higher and the case in which it is lower than that of the ATR trapezoid are considered. Experimental ATR data for antireflection-coating materials for laser windows is analyzed and compared with calorimetric data.

  17. FITTING OF THE DATA FOR DIFFUSION COEFFICIENTS IN UNSATURATED POROUS MEDIA

    SciTech Connect

    B. Bullard

    1999-05-01

    The purpose of this calculation is to evaluate diffusion coefficients in unsaturated porous media for use in the TSPA-VA analyses. Using experimental data, regression techniques were used to curve fit the diffusion coefficient in unsaturated porous media as a function of volumetric water content. This calculation substantiates the model fit used in Total System Performance Assessment-1995 An Evaluation of the Potential Yucca Mountain Repository (TSPA-1995), Section 6.5.4.

  18. Response of radiation belt simulations to different radial diffusion coefficients models

    NASA Astrophysics Data System (ADS)

    Drozdov, Alexander; Baker, Daniel N.; Shprits, Yuri; Kellerman, Adam

    2016-07-01

    Two parameterizations of the resonant wave-particle interactions of electrons with ultra-low frequency waves in the magnetosphere by Brautigam and Albert [2000] and Ozeke et al. [2014] are evaluated using the Versatile Electron Radiation Belt (VERB) diffusion code to estimate the effect of changing a diffusion coefficient on the radiation belt simulation. The period of investigation includes geomagnetically quiet and active time. The simulations take into account wave-particle interactions represented by radial diffusion transport, local acceleration, losses due to pitch-angle diffusion, and mixed diffusion.

  19. An alternative model for estimating liquid diffusion coefficients requiring no viscosity data

    NASA Technical Reports Server (NTRS)

    Morales, Wilfredo

    1993-01-01

    An equation, based on the free volume of a liquid solvent, was derived via dimensional analysis, to predict binary diffusion coefficients. The equation assumed that interaction between the solute and liquid solvent molecules followed a Lennard-Jones potential. The equation was compared to other diffusivity equations and was found to give good results over the temperature range examined.

  20. Connection between diffusion coefficient and thermal conductivity of a metal matrix composite

    NASA Astrophysics Data System (ADS)

    Anisimova, M. A.; Knyazeva, A. G.; Sevostianov, I.

    2017-02-01

    The paper discusses the calculation of the effective thermal and diffusion properties of metal matrix composites containing diamond particles. The effective properties are calculated using Maxwell homogenization scheme. We also establish cross-property connection between overall thermal conductivity and diffusion coefficient and illustrate it on example of Al\\diamond composites.

  1. A new symmetric form of the bounce-averaged quasilinear diffusion coefficient in toroidal geometry

    NASA Astrophysics Data System (ADS)

    Lee, Jungpyo; Smithe, David; Berry, Lee; Jaeger, Erwin; Wright, John; Bonoli, Paul

    2016-10-01

    Kennel-Engelmann (K-E) quasilinear diffusion coefficients are used in many RF wave codes to couple the Maxwell equation solver with a Fokker-Plank calculation. The diagonal component of the coefficient tensor in the speed direction should be positive in the quasi-linear assumption for the H-theorem. However, in the application to toroidal geometry, the bounce-average of the K-E coefficients does not guarantee positive values for an arbitrary wave spectrum due to the interference between the spectral modes. The negative bounce-averaged diffusion coefficients unexpectedly occur because the K-E coefficient is derived in a cylindrical limit, in which the resonance kernel (gyrofrequency, wave vector and parallel velocity) in the phase integral do not vary along the phase trajectory, while the bounce-average is computed in a toroidal geometry. To guarantee the positiveness, we derive a new form of the diffusion coefficient that keeps the symmetric form between the bounce-integral and the trajectory integral. The new coefficients are implemented in a code for ion cyclotron waves in a tokamak (TORIC). Using the new form, the error of quasilinear diffusion coefficients due to the negative values is reduced significantly, and the toroidal effects are well captured. Work supported by US Department of Energy Contract No. DE-FC02-01ER54648.

  2. Eliminating illumination effects by discrete cosine transform (DCT) coefficients' attenuation and accentuation

    NASA Astrophysics Data System (ADS)

    Du, Shan; Shehata, Mohamed; Badawy, Wael; Rahman, Choudhury A.

    2013-03-01

    In this paper, we proposed a discrete cosine transform (DCT)-based attnuation and accentuation method to remove lighting effects on face images for faciliating face recognition task under varying lighting conditions. In the proposed method, logorithm transform is first used to convert a face image into logarithm domain. Then discrete cosine transform is applied to obtain DCT coefficients. The low-frequency DCT coefficients are attenuated since illumination variations mainly concentrate on the low-frequency band. The high-frequency coefficients are accentuated since when under poor illuminations, the high-frequency features become more important in recognition. The reconstructed log image by inverse DCT of the modified coefficients is used for the final recognition. Experiments are conducted on the Yale B database, the combination of Yale B and Extended Yale B databases and the CMU-PIE database. The proposed method does not require modeling and model fitting steps. It can be directly applied to single face image, without any prior information of 3D shape or light sources.

  3. Lateral diffusion coefficients in membranes measured by resonance energy transfer and a new algorithm for diffusion in two dimensions.

    PubMed Central

    Kuśba, Jósef; Li, Li; Gryczynski, Ignacy; Piszczek, Grzegorz; Johnson, Michael; Lakowicz, Joseph R

    2002-01-01

    We describe measurements of lateral diffusion in membranes using resonance energy transfer. The donor was a rhenium (Re) metal-ligand complex lipid, which displays a donor decay time near 3 micros. The long donor lifetime resulted in an ability to measure lateral diffusion coefficient below 10(-8) cm(2)/s. The donor decay data were analyzed using a new numerical algorithm for calculation of resonance energy transfer for donors and acceptors randomly distributed in two dimensions. An analytical solution to the diffusion equation in two dimensions is not known, so the equation was solved by the relaxation method in Laplace space. This algorithm allows the donor decay in the absence of energy transfer to be multiexponential. The simulations show that mutual lateral diffusion coefficients of the donor and acceptor on the order of 10(-8) cm(2)/s are readily recovered from the frequency-domain data with donor decay times on the microsecond timescale. Importantly, the lateral diffusion coefficients and acceptor concentrations can be recovered independently despite correlation between these parameters. This algorithm was tested and verified using the donor decays of a long lifetime rhenium lipid donor and a Texas red-lipid acceptor. Lateral diffusion coefficients ranged from 4.4 x 10(-9) cm(2)/s in 1,2-dimyristoyl-sn-glycero-3-[phospho-rac-(1-glycerol)] (DMPG) at 10 degrees C to 1.7 x 10(-7) cm(2)/s in 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) at 35 degrees C. These results demonstrated the possibility of direct measurements of lateral diffusion coefficients using microsecond decay time luminophores. PMID:11867452

  4. Linear attenuation coefficients of tissues from 1 keV to 150 keV

    NASA Astrophysics Data System (ADS)

    Böke, Aysun

    2014-09-01

    The linear attenuation coefficients and three interaction processes have been computed for liver, kidney, muscle, fat and for a range of x-ray energies from 1 keV to 150 keV. Molecular photoelectric absorption cross sections were calculated from atomic cross section data. Total coherent (Rayleigh) and incoherent (Compton) scattering cross sections were obtained by numerical integration over combinations of F2m(x) with the Thomson formula and Sm(x) with the Klein-Nishina formula, respectively. For the coherent (Rayleigh) scattering cross section calculations, molecular form factors were obtained from recent experimental data in the literature for values of x<1 Å-1 and from the relativistic modified atomic form factors for values of x≥1 Å-1. With the inclusion of molecular interference effects in the coherent (Rayleigh) scattering, more accurate knowledge of the scatter from these tissues will be provided. The number of elements involved in tissue composition is 5 for liver, 47 for kidney, 44 for muscle and 3 for fat. The results are compared with previously published experimental and theoretical linear attenuation coefficients. In general, good agreement is obtained. The molecular form factors and scattering functions and cross sections are incorporated into a Monte Carlo program. The energy distributions of x-ray photons scattered from tissues have been simulated and the results are presented.

  5. Measurements of mass attenuation coefficient, effective atomic number and electron density of some amino acids

    NASA Astrophysics Data System (ADS)

    Kore, Prashant S.; Pawar, Pravina P.

    2014-05-01

    The mass attenuation coefficients of some amino acids, such as DL-aspartic acid-LR(C4H7NO4), L-glutamine (C4H10N2O3), creatine monohydrate LR(C4H9N3O2H2O), creatinine hydrochloride (C4H7N3O·HCl) L-asparagine monohydrate(C4H9N3O2H2O), L-methionine LR(C5H11NO2S), were measured at 122, 356, 511, 662, 1170, 1275 and 1330 keV photon energies using a well-collimated narrow beam good geometry set-up. The gamma-rays were detected using NaI (Tl) scintillation detection system with a resolution of 0.101785 at 662 keV. The attenuation coefficient data were then used to obtain the effective atomic numbers (Zeff), and effective electron densities (Neff) of amino acids. It was observed that the effective atomic number (Zeff) and effective electron densities (Neff) initially decrease and tend to be almost constant as a function of gamma-ray energy. Zeff and Neff experimental values showed good agreement with the theoretical values with less than 1% error for amino acids.

  6. Lithium-doped hydroxyapatite nano-composites: Synthesis, characterization, gamma attenuation coefficient and dielectric properties

    NASA Astrophysics Data System (ADS)

    Badran, H.; Yahia, I. S.; Hamdy, Mohamed S.; Awwad, N. S.

    2017-01-01

    Lithium-hydroxyapatite (0, 1, 5, 10, 20, 30 and 40 wt% Li-HAp) nano-composites were synthesized by sol-gel technique followed by microwave-hydrothermal treatment. The composites were characterized by X-ray diffraction (XRD), Field emission scanning electron microscope (FE-SEM), energy dispersive spectroscopy (EDS), Fourier transform infrared (FTIR) and Raman techniques. Gamma attenuation coefficient and the dielectric properties for all composites were investigated. The crystallinity degree of Li-doped HAp was higher than that of un-doped HAp. Gamma attenuation coefficient values increased from 0.562 cm-1 for 0 wt% Li-HAp to 2.190 cm-1 for 40 wt% Li-HAp. The alternating current conductivity increased with increasing frequency. The concentration of Li affect the values of dielectric constant where Li doped HAp of low dielectric constant can have an advantage for healing in bone fractures. The calcium to phosphorus ratio decreased from 1.43 to 1.37 with the addition of lithium indicating the Ca deficiency in the studied composites. Our findings lead to the conclusion that Li-HAp is a new nano-composite useful for medical applications and could be doped with gamma shield materials.

  7. Note: On the relation between Lifson-Jackson and Derrida formulas for effective diffusion coefficient

    PubMed Central

    Kalnin, Juris R.; Berezhkovskii, Alexander M.

    2013-01-01

    The Lifson-Jackson formula provides the effective free diffusion coefficient for a particle diffusing in an arbitrary one-dimensional periodic potential. Its counterpart, when the underlying dynamics is described in terms of an unbiased nearest-neighbor Markovian random walk on a one-dimensional periodic lattice is given by the formula obtained by Derrida. It is shown that the latter formula can be considered as a discretized version of the Lifson-Jackson formula with correctly chosen position-dependent diffusion coefficient. PMID:24320354

  8. Note: On the relation between Lifson-Jackson and Derrida formulas for effective diffusion coefficient

    NASA Astrophysics Data System (ADS)

    Kalnin, Juris R.; Berezhkovskii, Alexander M.

    2013-11-01

    The Lifson-Jackson formula provides the effective free diffusion coefficient for a particle diffusing in an arbitrary one-dimensional periodic potential. Its counterpart, when the underlying dynamics is described in terms of an unbiased nearest-neighbor Markovian random walk on a one-dimensional periodic lattice is given by the formula obtained by Derrida. It is shown that the latter formula can be considered as a discretized version of the Lifson-Jackson formula with correctly chosen position-dependent diffusion coefficient.

  9. Diffusion Coefficient of Tin(II) Methanesulfonate in Ionic Liquid and Methane Sulfonic Acid (MSA) Solvent

    NASA Astrophysics Data System (ADS)

    Yang, Kok Kee; Mahmoudian, M. R.; Ebadi, Mehdi; Koay, Hun Lee; Basirun, Wan Jeffrey

    2011-12-01

    Voltammetry and chronoamperometry for the electrodeposition of tin from Tin(II) methane sulfonate mixed with ionic liquid and methane sulfonate acid at room temperature was studied. Cyclic voltammetry shows redox waves of Tin(II), which proves that the electrodeposition of tin from Tin(II) methane sulfonate is a diffusion-controlled process. The diffusion coefficient of Tin(II) ions in the solvent mixture showed good agreement from both voltammetry and chronoamperometry results. The diffusion coefficient of Tin(II) in the mixture was much smaller than in aqueous solution, and it depends on the anion of the ionic liquid.

  10. Anisotropic parallel self-diffusion coefficients near the calcite surface: A molecular dynamics study

    NASA Astrophysics Data System (ADS)

    Franco, Luís F. M.; Castier, Marcelo; Economou, Ioannis G.

    2016-08-01

    Applying classical molecular dynamics simulations, we calculate the parallel self-diffusion coefficients of different fluids (methane, nitrogen, and carbon dioxide) confined between two { 10 1 ¯ 4 } calcite crystal planes. We have observed that the molecules close to the calcite surface diffuse differently in distinct directions. This anisotropic behavior of the self-diffusion coefficient is investigated for different temperatures and pore sizes. The ion arrangement in the calcite crystal and the strong interactions between the fluid particles and the calcite surface may explain the anisotropy in this transport property.

  11. Anisotropic parallel self-diffusion coefficients near the calcite surface: A molecular dynamics study.

    PubMed

    Franco, Luís F M; Castier, Marcelo; Economou, Ioannis G

    2016-08-28

    Applying classical molecular dynamics simulations, we calculate the parallel self-diffusion coefficients of different fluids (methane, nitrogen, and carbon dioxide) confined between two {101̄4} calcite crystal planes. We have observed that the molecules close to the calcite surface diffuse differently in distinct directions. This anisotropic behavior of the self-diffusion coefficient is investigated for different temperatures and pore sizes. The ion arrangement in the calcite crystal and the strong interactions between the fluid particles and the calcite surface may explain the anisotropy in this transport property.

  12. Effective diffusion coefficient of biological liquids in porous calcium phosphate coatings

    NASA Astrophysics Data System (ADS)

    Nazarenko, N. N.; Knyazeva, A. G.

    2016-11-01

    The study offers a method to estimate effective diffusion coefficients for transfer of biological liquids in porous materials. The method is based on the analysis of areas occupied by pores and solid materials on slice images. The possibility is shown for ascertaining a correlation between the effective coefficient and technological conditions because different structure and porosity are observed experimentally. The correlations of effective diffusion coefficients with the production voltage for different coating-base compositions, on which the coating was grown, have been built.

  13. Entropy-scaling laws for diffusion coefficients in liquid metals under high pressures

    SciTech Connect

    Cao, Qi-Long Shao, Ju-Xiang; Wang, Fan-Hou; Wang, Pan-Pan

    2015-04-07

    Molecular dynamic simulations on the liquid copper and tungsten are used to investigate the empirical entropy-scaling laws D{sup *}=A exp(BS{sub ex}), proposed independently by Rosenfeld and Dzugutov for diffusion coefficient, under high pressure conditions. We show that the scaling laws hold rather well for them under high pressure conditions. Furthermore, both the original diffusion coefficients and the reduced diffusion coefficients exhibit an Arrhenius relationship D{sub M}=D{sub M}{sup 0} exp(−E{sub M}/K{sub B}T), (M=un,R,D) and the activation energy E{sub M} increases with increasing pressure, the diffusion pre-exponential factors (D{sub R}{sup 0} and D{sub D}{sup 0}) are nearly independent of the pressure and element. The pair correlation entropy, S{sub 2}, depends linearly on the reciprocal temperature S{sub 2}=−E{sub S}/T, and the activation energy, E{sub S}, increases with increasing pressure. In particular, the ratios of the activation energies (E{sub un}, E{sub R}, and E{sub D}) obtained from diffusion coefficients to the activation energy, E{sub S}, obtained from the entropy keep constants in the whole pressure range. Therefore, the entropy-scaling laws for the diffusion coefficients and the Arrhenius law are linked via the temperature dependence of entropy.

  14. Implications of observed PBDE diffusion coefficients in low density polyethylene and silicone rubber.

    PubMed

    Narváez Valderrama, Jhon F; Baek, Kine; Molina, Francisco J; Allan, Ian J

    2016-01-01

    A film-stacking technique was used to estimate diffusion coefficients of polybrominated diphenyl ethers (PBDEs) in low density polyethylene (LDPE) and silicone rubber. Substantially higher PBDE diffusion coefficients were observed for silicone rubber (AlteSil™) than for LDPE. A much steeper decrease in LDPE diffusion coefficients was found with increasing PBDE molecular weight than that for silicone rubber. From a passive sampling point-of-view, this means that for equivalent polymer-water partition coefficients for these two materials, the mass transfer resistance for these substances in the LDPE will be significantly higher than that for silicone rubber. Boundary layer control of the uptake process for silicone rubber can be expected for PBDEs. With a microplastic perspective, the low diffusion coefficients of PBDEs and in particular of decabromo diphenyl ether (BDE 209) in LDPE imply that the polymer diffusion coefficients for these plastic additives used as flame retardants need to be taken into account when considering the risk posed by microplastic particle ingestion by marine organisms.

  15. The calculation of mass attenuation coefficients of well-known thermoluminescent dosimetric compounds at wide energy range

    NASA Astrophysics Data System (ADS)

    Ermis, Elif Ebru

    2017-02-01

    The photon mass attenuation coefficients of LiF, BaSO4, CaCO3 and CaSO4 thermoluminescent dosimetric compounds at 100; 300; 500; 600; 800; 1,000; 1,500; 2,000; 3,000 and 5,000 keV gamma-ray energies were calculated. For this purpose, FLUKA Monte Carlo (MC) program which is one of the well-known MC codes was used in this study. Furthermore, obtained results were analyzed by means of ROOT program. National Institute of Standards and Technology (NIST) values were also used to compare the obtained theoretical values because the mass attenuation values of the used compounds could not found in the literature. Calculated mass attenuation coefficients were highly in accordance with the NIST values. As a consequence, FLUKA was successful in calculating the mass attenuation coefficients of the most used thermoluminescent compound.

  16. Effects of molecular weight on the diffusion coefficient of aquatic dissolved organic matter and humic substances.

    PubMed

    Balch, J; Guéguen, C

    2015-01-01

    In situ measurements of labile metal species using diffusive gradients in thin films (DGT) passive samplers are based on the diffusion rates of individual species. Although most studies have dealt with chemically isolated humic substances, the diffusion of dissolved organic matter (DOM) across the hydrogel is not well understood. In this study, the diffusion coefficient (D) and molecular weight (MW) of 11 aquatic DOM and 4 humic substances (HS) were determined. Natural, unaltered aquatic DOM was capable of diffusing across the diffusive gel membrane with D values ranging from 2.48×10(-6) to 5.31×10(-6) cm(2) s(-1). Humic substances had diffusion coefficient values ranging from 3.48×10(-6) to 6.05×10(-6) cm(2) s(-1), congruent with previous studies. Molecular weight of aquatic DOM and HS samples (∼500-1750 Da) measured using asymmetrical flow field-flow fractionation (AF4) strongly influenced D, with larger molecular weight DOM having lower D values. No noticeable changes in DOM size properties were observed during the diffusion process, suggesting that DOM remains intact following diffusion across the diffusive gel. The influence of molecular weight on DOM mobility will assist in further understanding and development of the DGT technique and the uptake and mobility of contaminants associated with DOM in aquatic environments.

  17. Clinical applications and characteristics of apparent diffusion coefficient maps for the brain of two dogs

    PubMed Central

    Kim, Boeun; Yi, Kangjae; Jung, Sunyoung; Ji, Seoyeon; Choi, Mincheol

    2014-01-01

    Diffusion-weighted imaging (DWI) and apparent diffusion coefficient (ADC) mapping are functional magnetic resonance imaging techniques for detecting water diffusion. DWI and the ADC map were performed for intracranial lesions in two dogs. In necrotizing leukoencephalitis, cavitated lesions contained a hypointense center with a hyperintense periphery on DWI, and hyperintense signals on the ADC maps. In metastatic sarcoma, masses including a necrotic region were hypointense with DWI, and hyperintense on the ADC map with hyperintense perilesional edema on DWI and ADC map. Since DWI and ADC data reflect the altered water diffusion, they can provide additional information at the molecular level. PMID:24675836

  18. Clinical applications and characteristics of apparent diffusion coefficient maps for the brain of two dogs.

    PubMed

    Kim, Boeun; Yi, Kangjae; Jung, Sunyoung; Ji, Seoyeon; Choi, Mincheol; Yoon, Junghee

    2014-01-01

    Diffusion-weighted imaging (DWI) and apparent diffusion coefficient (ADC) mapping are functional magnetic resonance imaging techniques for detecting water diffusion. DWI and the ADC map were performed for intracranial lesions in two dogs. In necrotizing leukoencephalitis, cavitated lesions contained a hypointense center with a hyperintense periphery on DWI, and hyperintense signals on the ADC maps. In metastatic sarcoma, masses including a necrotic region were hypointense with DWI, and hyperintense on the ADC map with hyperintense perilesional edema on DWI and ADC map. Since DWI and ADC data reflect the altered water diffusion, they can provide additional information at the molecular level.

  19. A technique for estimating one-dimensional diffusion coefficients in low-permeability sedimentary rock using X-ray radiography: comparison with through-diffusion measurements.

    PubMed

    Cavé, Lisa; Al, Tom; Xiang, Yan; Vilks, Peter

    2009-01-07

    The measurement of diffusive properties of low-permeability rocks is of interest to the nuclear power industry, which is considering the option of deep geologic repositories for management of radioactive waste. We present a simple, non-destructive, constant source in-diffusion method for estimating one-dimensional pore diffusion coefficients (D(p)) in geologic materials based on X-ray radiography. Changes in X-ray absorption coefficient (Deltamicro) are used to quantify changes in relative concentration (C/C(0)) of an X-ray attenuating iodide tracer as the tracer solution diffuses through the rock pores. Estimated values of D(p) are then obtained by fitting an analytical solution to the measured concentration profiles over time. Measurements on samples before and after saturation with iodide can also be used to determine iodide-accessible porosity (phi(I)). To evaluate the radiography method, results were compared with traditional steady-state through-diffusion measurements on two rock types: shale and limestone. Values of D(p) of (4.8+/-2.5)x10(-11) m(2).s(-1) (mean+/-standard deviation) were measured for samples of Queenston Formation shale and (2.6+/-1.0)x10(-11) m(2).s(-1) for samples of Cobourg Formation limestone using the radiography method. The range of results for each rock type agree well with D(p) values of (4.6+/-2.0)x10(-11) m(2).s(-1) for shale and (3.5+/-1.8)x10(-11) m(2).s(-1) for limestone, calculated from through-diffusion experiments on adjacent rock samples. Low porosity (0.01 to 0.03) and heterogeneous distribution of porosity in the Cobourg Formation may be responsible for the slightly poorer agreement between radiography and through-diffusion results for limestones. Mean values of phi(I) for shales (0.060) and limestones (0.028) were close to mean porosity measurements made on bulk samples by the independent water loss technique (0.062 and 0.020 for shales and limestones, respectively). Radiography measurements offer the advantage of time

  20. A first-principles methodology for diffusion coefficients in metals and dilute alloys

    NASA Astrophysics Data System (ADS)

    Mantina, Manjeera

    This work is a study exploring the extent of suitability of static first-principles calculations for studying diffusion in metallic systems. Specifically, vacancy-mediated volume diffusion in pure elements and alloys with dilute concentration of impurities is studied. A novel procedure is discovered for predicting diffusion coefficients that overcomes the shortcomings of the well-known transition state theory, by Vineyard. The procedure that evolves from Eyring's reaction rate theory yields accurate diffusivity results that include anharmonic effects within the quasi-harmonic approximation. Alongside, the procedure is straightforward in its application within the conventional harmonic approximation, from the results of static first-principles calculations. To prove the extensibility of the procedure, diffusivities have been computed for a variety of systems. Over a wide temperature range, the calculated self-diffusion and impurity diffusion coefficients using local density approximation (LDA) of density functional theory (DFT) are seen to be in excellent match with experimental data. Self-diffusion coefficients have been calculated for: (i) fcc Al, Cu, Ni and Ag (ii) bcc W and Mo (v) hcp Mg, Ti and Zn. Impurity diffusion coefficients have been computed for: (i) Mg, Si, Cu, Li, Ag, Mo and 3d transition elements in fcc Al (ii) Mo, Ta in bcc W and Nb, Ta and W in bcc Mo (iii) Sn and Cd in hcp Mg and Al in hcp Ti. It is also an observation from this work, that LDA does not require surface correction for yielding energetics of vacancy-containing system in good comparison with experiments, unlike generalized gradient approximation (GGA). It is known that first-principles' energy minimization procedures based on electronic interactions are suited for metallic systems wherein the valence electrons are freely moving. In this thesis, research has been extended to study suitability of first-principles calculations within LDA/GGA including the localization parameter U, for Al

  1. Sublimation kinetics and diffusion coefficients of TNT, PETN, and RDX in air by thermogravimetry.

    PubMed

    Hikal, Walid M; Weeks, Brandon L

    2014-07-01

    The diffusion coefficients of explosives are crucial in their trace detection and lifetime estimation. We report on the experimental values of diffusion coefficients of three of the most important explosives in both military and industry: TNT, PETN, and RDX. Thermogravimetric analysis (TGA) was used to determine the sublimation rates of TNT, PETN, and RDX powders in the form of cylindrical billets. The TGA was calibrated using ferrocene as a standard material of well-characterized sublimation rates and vapor pressures to determine the vapor pressures of TNT, PETN, and RDX. The determined sublimation rates and vapor pressures were used to indirectly determine the diffusion coefficients of TNT, PETN, and RDX for the first time. A linear log-log dependence of the diffusion coefficients on temperature is observed for the three materials. The diffusion coefficients of TNT, PETN, and RDX at 273 K were determined to be 5.76×10(-6)m(2)/sec, 4.94×10(-6)m(2)/s, and 5.89×10(-6)m(2)/s, respectively. Values are in excellent agreement with the theoretical values in literature.

  2. Distributional behavior of diffusion coefficients obtained by single trajectories in annealed transit time model

    NASA Astrophysics Data System (ADS)

    Akimoto, Takuma; Yamamoto, Eiji

    2016-12-01

    Local diffusion coefficients in disordered systems such as spin glass systems and living cells are highly heterogeneous and may change over time. Such a time-dependent and spatially heterogeneous environment results in irreproducibility of single-particle-tracking measurements. Irreproducibility of time-averaged observables has been theoretically studied in the context of weak ergodicity breaking in stochastic processes. Here, we provide rigorous descriptions of equilibrium and non-equilibrium diffusion processes for the annealed transit time model, which is a heterogeneous diffusion model in living cells. We give analytical solutions for the mean square displacement (MSD) and the relative standard deviation of the time-averaged MSD for equilibrium and non-equilibrium situations. We find that the time-averaged MSD grows linearly with time and that the time-averaged diffusion coefficients are intrinsically random (irreproducible) even in the long-time measurements in non-equilibrium situations. Furthermore, the distribution of the time-averaged diffusion coefficients converges to a universal distribution in the sense that it does not depend on initial conditions. Our findings pave the way for a theoretical understanding of distributional behavior of the time-averaged diffusion coefficients in disordered systems.

  3. Time of Flight Electrochemistry: Diffusion Coefficient Measurements Using Interdigitated Array (IDA) Electrodes

    SciTech Connect

    Liu, Fei; Kolesov, Grigory; Parkinson, Bruce A.

    2014-09-26

    A simple and straightforward method for measuring diffusion coefficients using interdigitated array (IDA) electrodes is reported. The method does not require that the exact electrode area be known but depends only the size of the gap between the IDA electrode pairs. Electroactive molecules produced at the generator electrode of the IDA by a voltage step or scan can diffuse to the collector electrode and the time delay before the current for the reverse electrochemical reaction is detected at the collector is used to calculate the diffusion coefficient. The measurement of the diffusion rate of Ru(NH3)6+2 in aqueous solution has been used as an example measuring diffusion coefficients using this method. Additionally, a digital simulation of the electrochemical response of the IDA electrodes was used to simulate the entire current/voltage/time behavior of the system and verify the experimentally measured diffusion coefficients. This work was supported as part of the Center for Molecular Electrocatalysis, an Energy Frontier Research Center funded by the Department of Energy, Office of Science, Office of Basic Energy Sciences.

  4. Estimation of radon diffusion coefficients in soil using an updated experimental system.

    PubMed

    Prasad, Ganesh; Ishikawa, Tetsuo; Hosoda, Masahiro; Sorimachi, Atsuyuki; Janik, Miroslaw; Sahoo, Sarata Kumar; Tokonami, Shinji; Uchida, Shigeo

    2012-09-01

    Radon diffusion through soil is strongly affected by the degree of water saturation of the soil pores. Methods have been developed by many researchers to measure radon diffusion coefficient. We developed an updated experimental system to estimate radon diffusion coefficients for typical types of soil in Japan and applied it to a typical loam with different water saturation levels (0-0.82). The system consists of a passive-type scintillation cell, soil column, accumulation tank, and radon source. The radon concentration in the accumulation tank is kept stable, and radon diffused through the soil column is continuously measured with the passive-type scintillation cell. We found the radon diffusion coefficients vary from 9.60 × 10(-6) m(2) s(-1) to 1.27 × 10(-7) m(2) s(-1) for the loam samples. Generally, the diffusion coefficients are almost constant for a water saturation range of 0-0.4 and decrease with increasing water saturation from 0.4 to 0.82.

  5. Combined measurement of surface, grain boundary and lattice diffusion coefficients on olivine bi-crystals

    NASA Astrophysics Data System (ADS)

    Marquardt, Katharina; Dohmen, Ralf; Wagner, Johannes

    2014-05-01

    Diffusion along interface and grain boundaries provides an efficient pathway and may control chemical transport in rocks as well as their mechanical strength. Besides the significant relevance of these diffusion processes for various geologic processes, experimental data are still very limited (e.g., Dohmen & Milke, 2010). Most of these data were measured using polycrystalline materials and the formalism of LeClaire (1951) to fit integrated concentration depth profiles. To correctly apply this formalism, certain boundary conditions of the diffusion problem need to be fulfilled, e.g., surface diffusion is ignored, and furthermore the lattice diffusion coefficient has to be known from other studies or is an additional fitting parameter, which produces some ambiguity in the derived grain boundary diffusion coefficients. We developed an experimental setup where we can measure the lattice and grain boundary diffusion coefficients simultaneously but independent and demonstrate the relevance of surface diffusion for typical grain boundary diffusion experiments. We performed Mg2SiO4 bicrystal diffusion experiments, where a single grain boundary is covered by a thin-film of pure Ni2SiO4 acting as diffusant source, produced by pulsed laser deposition. The investigated grain boundary is a 60° (011)/[100]. This specific grain boundary configuration was modeled using molecular dynamics for comparison with the experimental observations in the transmission electron microscope (TEM). Both, experiment and model are in good agreement regarding the misorientation, whereas there are still some disagreements regarding the strain fields along the grain boundary that are of outmost importance for the strengths of the material. The subsequent diffusion experiments were carried out in the temperature range between 800° and 1450° C. The inter diffusion profiles were measured using the TEMs energy dispersive x-ray spectrometer standardized using the Cliff-Lorimer equation and EMPA

  6. Electrical Conductivity and Chemical Diffusion Coefficient of Strontium-Doped Lanthanum Manganites

    NASA Astrophysics Data System (ADS)

    Yasuda, Isamu; Hishinuma, Masakazu

    1996-05-01

    Electrical conductivity and chemical diffusion coefficient of Sr-doped lanthanum manganites, La 1- xSr xMnO 3±δ( x= 0.05 - 0.20), were measured by the dc four-probe technique and relaxation type experiments where a sudden change of oxygen chemical potential was imposed on the pre-equilibrated sample and the change of electrical conductivity was followed as a function of elapsed time. A defect model is proposed to elucidate the oxygen partial pressure dependence of the measured conductivity and the reported oxygen nonstoichiometry. The transient conductivity behavior after an abrupt change of oxygen partial pressure was successfully described by a diffusion model with consideration of partial control by surface reaction. The determined chemical diffusion coefficients, of the order of 10 -5to 10 -4cm 2s -1at 1000°C, increased with decreased oxygen partial pressure due to the thermodynamic enhancement effect. Using the enhancement factor estimated by combination of the proposed defect model and the ambipolar diffusion theory, the oxygen vacancy diffusion coefficients were derived. High vacancy diffusivity comparable to that of Fe- or Co-based perovskites predicts fast oxide ion diffusion under conditions where the manganites show oxygen deficient type non-stoichiometry.

  7. Tracer diffusion coefficients in sedimentary rocks: correlation to porosity and hydraulic conductivity.

    PubMed

    Boving, T B; Grathwohl, P

    2001-12-01

    Matrix diffusion is an important transport process in geologic materials of low hydraulic conductivity. For predicting the fate and transport of contaminants, a detailed understanding of the diffusion processes in natural porous media is essential. In this study, diffusive tracer transport (iodide) was investigated in a variety of geologically different limestone and sandstone rocks. Porosity, structural and mineralogical composition, hydraulic conductivity, and other rock properties were determined. The effective diffusion coefficients were measured using the time-lag method. The results of the diffusion experiments indicate that there is a close relationship between total porosity and the effective diffusion coefficient of a rock (analogous to Archie's Law). Consequently, the tortousity factor can be expressed as a function of total porosity. The relationship fits best for thicker samples (> 1.0 cm) with high porosities (> 20%), because of the reduced influence of heterogeneity in larger samples. In general, these correlations appear to be a simple way to determine tortuosity and the effective diffusion coefficient from easy to determine rock porosity values.

  8. Relationships between atomic diffusion mechanisms and ensemble transport coefficients in crystalline polymorphs.

    PubMed

    Morgan, Benjamin J; Madden, Paul A

    2014-04-11

    Ionic transport in conventional ionic solids is generally considered to proceed via independent diffusion events or "hops." This assumption leads to well-known Arrhenius expressions for transport coefficients, and is equivalent to assuming diffusion is a Poisson process. Using molecular dynamics simulations of the low-temperature B1, B3, and B4 AgI polymorphs, we have compared rates of ion hopping with corresponding Poisson distributions to test the assumption of independent hopping in these common structure types. In all cases diffusion is a non-Poisson process, and hopping is strongly correlated in time. In B1 the diffusion coefficient can be approximated by an Arrhenius expression, though the physical significance of the parameters differs from that commonly assumed. In low temperature B3 and B4, diffusion is characterized by concerted motion of multiple ions in short closed loops. Diffusion coefficients cannot be expressed in a simple Arrhenius form dependent on single-ion free energies, and intrinsic diffusion must be considered a many-body process.

  9. Effective atomic numbers and mass attenuation coefficients of some thermoluminescent dosimetric compounds for total photon interaction

    SciTech Connect

    Shivaramu; Amutha, R.; Ramprasath, V.

    1999-05-01

    Effective atomic numbers for total gamma-ray interaction with some selected thermoluminescent dosimetric compounds such as barium acetate, barium sulfate, calcium carbonate, calcium sulfate, calcium sulfate dihydrate, cadmium sulfate (anhydrous), cadmium sulfate, strontium sulfate, and lithium fluoride have been calculated in the 1-keV to 20-MeV energy region. Experimental mass attenuation coefficients and effective atomic numbers for these compounds at selected photon energies of 26.3, 33.2, 59.54, and 661.6 keV have been obtained from good geometry transmission measurements and compared with theoretical values. The effect of absorption edge on effective atomic numbers and its variation with energy, and nonvalidity of the Bragg`s mixture rule at incident photon energies closer to the absorption edges of constituent elements of compounds are discussed.

  10. Regulation of nuclear NF-κB oscillation by a diffusion coefficient and its biological implications.

    PubMed

    Ohshima, Daisuke; Ichikawa, Kazuhisa

    2014-01-01

    The transcription factor NF-κB shuttles between the cytoplasm and the nucleus, and nuclear NF-κB is known to oscillate with a cycle of 1.5-2.5 h following the application of external stimuli. Oscillation pattern of NF-κB is implicated in regulation of the gene expression profile. In a previous report, we found that the oscillation pattern of nuclear NF-κB in a computational 3D spherical cell was regulated by spatial parameters such as nuclear to cytoplasmic volume ratio, nuclear transport, locus of protein synthesis, and diffusion coefficient. Here we report analyses and a biological implication for the regulation of oscillation pattern by diffusion coefficient. Our analyses show that the "reset" of nuclear NF-κB, defined as the return of nuclear NF-κB to the initial level or lower, was crucial for the oscillation; this was confirmed by the flux analysis. In addition, we found that the distant cytoplasmic location from the nucleus acted as a "reservoir" for storing newly synthesized IκBα. When the diffusion coefficient of proteins was large (≥ 10-11 m2/s), a larger amount of IκBα was stored in the "reservoir" with a large flux by diffusion. Subsequently, stored IκBα diffused back to the nucleus, where nuclear NF-κB was "reset" to the initial state. This initiated the next oscillation cycle. When the diffusion coefficient was small (≤ 10-13 m2/s), oscillation of nuclear NF-κB was not observed because a smaller amount of IκBα was stored in the "reservoir" and there was incomplete "reset" of nuclear NF-κB. If the diffusion coefficient for IκBα was increased to 10-11 m2/s keeping other proteins at 10-13 m2/s, the oscillation was rescued confirming the "reset" and "reservoir" hypothesis. Finally, we showed altered effective value of diffusion coefficient by diffusion obstacles. Thus, organelle crowding seen in stressed cells possibly changes the oscillation pattern by controlling the effective diffusion coefficient.

  11. Determination of mass attenuation coefficients for threshold contrast evaluation in digital mammography

    NASA Astrophysics Data System (ADS)

    Hummel, Johann; Semturs, Friedrich; Menhart, Susanne; Figl, Michael

    2010-04-01

    According to the 'European protocol for the quality control of the physical and technical aspects of mammography screening' (EPQC) image quality digital mammography units has to be evaluated at different breast thicknesses. At the standard thickness of 50 mm polymethyl methacrylate (PMMA) image quality is determined by the analysis of CDMAM contrast detail phantom images where threshold contrasts are calculated for different gold disc diameters. To extend these results to other breast thicknesses contrast-to-noise ratios (CNR) and threshold contrast (TC) visibilities have to be calculated for all required thicknesses. To calculate the latter the mass attenuation coefficient (MAC) of gold has to be known for all possible beam qualities in the tube voltage range between 26 and 32 kV. In this paper we first determined the threshold contrast visibility using the CDMAM phantom with the same beam quality at different current-time products (mAs). We can derive from Rose theory that CNR • CT • α = const, where α is the diameter of the gold cylinder. From this the corresponding attenuation coefficients can be calculated. This procedure was repeated for four different beam qualities (Mo/Mo 27kV, Rh/Rh 29kV, Rh/Rh 31 kV, and W/Rh 29 kV)). Next, we measured the aluminium half value layer (HVL) of all x-ray spectra relevant for mammography. Using a first order Taylor expansion of MAC as a function of HVL, all other desired MAC can be calculated. The MAC as a function of the HVL was derived to MAChvl = -286.97 * hvl+186.03 with R2 = 0.997, where MAChvl indicates the MAC for all specific x-ray spectrum defined by its aluminium half value layer. Based on this function all necessary MACs needed for quality assurance (QA) were calculated. The results were in good agreement with the data found in the protocol.

  12. Imaging the attenuation coefficients of magnetically constrained positron beams in matter

    NASA Astrophysics Data System (ADS)

    Watson, Charles C.

    2016-09-01

    This paper describes a method for tomographically imaging the linear attenuation coefficients (LACs) of positron beams in heterogeneous materials. A β+ ray emitter such as 68Ga, placed in a uniform 3T static magnetic field, generates a well-defined positron beam that maintains its spatial coherence over an attenuation of more than 10-3 while signaling its intensity via the annihilation radiation it generates. A positron emission tomography (PET) system embedded in the magnetic field measures the positron-electron annihilation distribution within objects illuminated by the beam. It's shown that this image can be decomposed into maps of the positron beam's flux and its material-dependent LACs without need for auxiliary measurements or transmission of the beam completely through the object. The initial implementation employs a hybrid PET/magnetic resonance imaging (MRI) scanner developed for medical applications. Mass thicknesses up to 0.55 g/cm2 at a spatial resolution of a few millimeters have been imaged.

  13. Ion diffusion coefficients model and molar conductivities of ionic salts in aprotic solvents.

    PubMed

    Garrido, Leoncio; Mejía, Alberto; García, Nuria; Tiemblo, Pilar; Guzmán, Julio

    2015-02-19

    In the study of the electric properties of electrolytes, the determination of the diffusion coefficients of the species that intervene in the charge transport process is of great importance, particularly that of the free ions (D(+) and D(-)), the only species that contribute to the conductivity. In this work we propose a model that allows, with reasonable assumptions, determination of D(+) and D(-), and the degree of dissociation of the salt, α, at different concentrations, using the diffusion coefficients experimentally obtained with NMR. Also, it is shown that the NMR data suffice to estimate the conductivity of the electrolytes. The model was checked by means of experimental results of conductivity and NMR diffusion coefficients obtained with solutions of lithium triflate in ethylene and propylene carbonates, as well as with other results taken from the literature.

  14. The Measurement of Polymer Swelling Processes by an Interferometric Method and Evaluation of Diffusion Coefficients

    PubMed Central

    Mráček, Aleš

    2010-01-01

    The amorphous polymer film swelling in a liquid solvent below the glass transition temperature was characterized by a few kinetic parameters (especially the mutual diffusion coefficient of swelling and its mean value) obtained by interference of monochromatic light in the wedge arrangement. This interferometric method allows one to determine the concentration field in the swollen surface layer and consequently to compute the concentration-dependent diffusion coefficient. A software system developed at the Department of Physics and Material Engineering at TBU in Zlin has been used for the evaluation of the main kinetic parameters of the swelling process. The software can be used for the on-line analyses of interferograms during the swelling process. The main application outputs are the computation of the concentration profile, the concentration gradient, the mutual diffusion coefficient of the swelling by the solvent and its mean value. PMID:20386653

  15. Stokes-flow computation of the diffusion coefficient and rotational diffusion tensor of lysozyme, a globular protein

    NASA Astrophysics Data System (ADS)

    Zhao, Hong; Pearlstein, Arne J.

    2002-07-01

    Based on a closed surface of triangles fitted to atomic coordinates determined crystallographically, Brune and Kim [Proc. Natl. Acad. Sci. USA 90, 3835-3839 (1993)] proposed a boundary-element Stokes-flow technique for ab initio computation of a translational diffusion coefficient and the rotational diffusion tensor Dr of globular proteins. They applied their approach to atomic coordinates for a tetragonal structure of hen egg-white lysozyme, and reported that computed values of a translational diffusion coefficient and Dr=tr(Dr)/3 agreed well with experiment. After establishing the identity between the infinite-dilution tracer diffusion coefficient of the protein macroion (D+ for lysozyme cation) and the "translational diffusion coefficient" computed by Brune and Kim, we adopt a somewhat different computational approach and show how convergence of D+ and Dr for tetragonal lysozyme depends on two computational parameters characterizing the fidelity of the geometric approximation to the protein surface and two others characterizing the accuracy of the Stokes-flow computations. We then compute D+ and Dr for lysozyme using atomic coordinates for the triclinic crystal structure, three structures determined by nuclear magnetic resonance spectroscopy in the liquid phase (presumably corresponding more closely to in vivo structures), the solvated tetragonal structure (with 108 water molecules) considered by Brune and Kim, and a "dry" version of the same structure. These computations show that D+ and Dr computed for all of the dry crystal structures are in excellent agreement with those for the liquid-phase conformations. Values of D+ and Dr computed for the solvated structure are lower, consistent with the larger volume and area of the corresponding polyhedral surface. We also show that several choices of the origin of the force system [discussed by Brenner, J. Colloid Interface Sci. 23, 407-436 (1967)] give rise to nearly identical translational diffusion coefficients

  16. Field-Scale Effective Matrix Diffusion Coefficient for FracturedRock: Results From Literature Survey

    SciTech Connect

    Zhou, Quanlin; Liu, Hui Hai; Molz, Fred J.; Zhang, Yingqi; Bodvarsson, Gudmundur S.

    2005-03-28

    Matrix diffusion is an important mechanism for solutetransport in fractured rock. We recently conducted a literature survey onthe effective matrix diffusion coefficient, Dem, a key parameter fordescribing matrix diffusion processes at the field scale. Forty fieldtracer tests at 15 fractured geologic sites were surveyed and selectedfor study, based on data availability and quality. Field-scale Dem valueswere calculated, either directly using data reported in the literature orby reanalyzing the corresponding field tracer tests. Surveyed dataindicate that the effective-matrix-diffusion-coefficient factor FD(defined as the ratio of Dem to the lab-scale matrix diffusioncoefficient [Dem]of the same tracer) is generally larger than one,indicating that the effective matrix diffusion coefficient in the fieldis comparatively larger than the matrix diffusion coefficient at therock-core scale. This larger value could be attributed to the manymass-transfer processes at different scales in naturally heterogeneous,fractured rock systems. Furthermore, we observed a moderate trend towardsystematic increase in the emDFmDDF value with observation scale,indicating that the effective matrix diffusion coefficient is likely tobe statistically scale dependent. The FD value ranges from 1 to 10,000for observation scales from 5 to 2,000 m. At a given scale, the FD valuevaries by two orders of magnitude, reflecting the influence of differingdegrees of fractured rock heterogeneity at different sites. In addition,the surveyed data indicate that field-scale longitudinal dispersivitygenerally increases with observation scale, which is consistent withprevious studies. The scale-dependent field-scale matrix diffusioncoefficient (and dispersivity) may have significant implications forassessing long-term, large-scale radionuclide and contaminant transportevents in fractured rock, both for nuclear waste disposal and contaminantremediation.

  17. Measurement of the local particle diffusion coefficient in a magnetized plasma

    SciTech Connect

    Meyerhofer, D.D.; Levinton, F.M.

    1987-02-01

    Local impurity particle diffusion coefficients have been measured in a low temperature plasma by the injection of test particles at the center of the plasma. The injection is accomplished by a high voltage discharge between two small graphite electrodes on a probe. The probe can be located anywhere in the plasma. The diffusion is observed spectroscopically. An analysis of the spatial and temporal evolution of the CII radiation from the carbon discharge can determine the parallel and perpendicular diffusion of the impurity ions. Results with the diagnostic have been obtained in the Proto S-1/C spheromak. The measured value of the diffusion coefficient in the afterglow plasma is in good agreement with classical predictions.

  18. Interferometric measurement of a diffusion coefficient: comparison of two methods and uncertainty analysis

    NASA Astrophysics Data System (ADS)

    Riquelme, Rodrigo; Lira, Ignacio; Pérez-López, Carlos; Rayas, Juan A.; Rodríguez-Vera, Ramón

    2007-05-01

    Two methods to measure the diffusion coefficient of a species in a liquid by optical interferometry were compared. The methods were tested on a 1.75 M NaCl aqueous solution diffusing into water at 26 °C. Results were D = 1.587 × 10-9 m2 s-1 with the first method and D = 1.602 × 10-9 m2 s-1 with the second method. Monte Carlo simulation was used to assess the possible dispersion of these results. The standard uncertainties were found to be of the order of 0.05 × 10-9 m2 s-1 with both methods. We found that the value of the diffusion coefficient obtained by either method is very sensitive to the magnification of the optical system, and that if diffusion is slow the measurement of time does not need to be very accurate.

  19. Modeling the role of diffusion coefficients on Turing instability in a reaction-diffusion prey-predator system.

    PubMed

    Mukhopadhyay, B; Bhattacharyya, R

    2006-02-01

    The paper is concerned with the effect of variable dispersal rates on Turing instability of a non-Lotka-Volterra reaction-diffusion system. In ecological applications, the dispersal rates of different species tends to oscillate in time. This oscillation is modeled by temporal variation in the diffusion coefficient with large as well as small periodicity. The case of large periodicity is analyzed using the theory of Floquet multipliers and that of the small periodicity by using Hill's equation. The effect of such variation on the resulting Turing space is studied. A comparative analysis of the Turing spaces with constant diffusivity and variable diffusivities is performed. Numerical simulations are carried out to support analytical findings.

  20. Diffusion coefficient of the protein in various crystallization solutions: The key to growing high-quality crystals in space

    NASA Astrophysics Data System (ADS)

    Tanaka, Hiroaki; Takahashi, Sachiko; Yamanaka, Mari; Yoshizaki, Izumi; Sato, Masaru; Sano, Satoshi; Motohara, Moritoshi; Kobayashi, Tomoyuki; Yoshitomi, Susumu; Tanaka, Tetsuo; Fukuyama, Seijiro

    2006-09-01

    The diffusion coefficients of lysozyme and alpha-amylase were measured in the various polyethylene glycol (PEG) solutions. Obtained diffusion coefficients were studied with the viscosity coefficient of the solution. It was found that the diffusion process of the protein was suppressed with a factor of vγ, where ν is a relative viscosity coefficient of the PEG solution. The value of γ is -0.64 at PEG1500 for both proteins. The value increased to -0.48 at PEG8000 for lysozyme, while decreased to -0.72 for alpha-amylase. The equation of an approximate diffusion coefficient at certain PEG molecular weight and concentration was roughly obtained.

  1. Correlation of high-pressure diffusion and viscosity coefficients for n-alkanes

    SciTech Connect

    Dymond, J.H.; Awan, M.A. )

    1989-09-01

    Self-diffusion coefficient and viscosity coefficient data for liquid n-alkanes over the whole pressure range at different temperatures are satisfactorily correlated simultaneously by a method which is just an extension of that previously used to apply the smooth hard-sphere theory of transport properties to individual transport coefficients. Universal curves are developed for reduced quantities D* and {eta}* as a function of reduced volume. A consistent set of values is derived for the characteristic volume V{sub 0} and for parameters R{sub D} and R{sub {eta}}, introduced to account for effects of nonspherical molecular shape and molecular roughness. On this basis, accurate calculation can be made of self-diffusion and viscosity coefficients for other members of the n-alkane series, for which data are at present limited.

  2. Determination of self-diffusion coefficients by quasielastic neutron scattering measurements of levitated Ni droplets

    NASA Astrophysics Data System (ADS)

    Meyer, A.; Stüber, S.; Holland-Moritz, D.; Heinen, O.; Unruh, T.

    2008-03-01

    Conventional techniques to measure diffusion coefficients in liquid metals and alloys are hampered by buoyancy-driven convective fluid flow and chemical reactions of the liquids with container material. To overcome these obstacles we combined containerless processing via electromagnetic levitation with quasielastic neutron scattering. This combination allowed us to study the atomic self-motion in liquid nickel within a broad temperature range from 200K above to more than 200K below the melting point, in the metastable regime of an undercooled melt. Other than in liquid Sn the temperature dependence of the Ni self-diffusion coefficient is well described with an Arrhenius law.

  3. Quantum statistics of classical particles derived from the condition of a free diffusion coefficient

    NASA Astrophysics Data System (ADS)

    Hoyuelos, M.; Sisterna, P.

    2016-12-01

    We derive an equation for the current of particles in energy space; particles are subject to a mean-field effective potential that may represent quantum effects. From the assumption that noninteracting particles imply a free diffusion coefficient in energy space, we derive Maxwell-Boltzmann, Fermi-Dirac, and Bose-Einstein statistics. Other new statistics are associated to a free diffusion coefficient; their thermodynamic properties are analyzed using the grand partition function. A negative relation between pressure and energy density for low temperatures can be derived, suggesting a possible connection with cosmological dark energy models.

  4. A New Method for the Calculation of Diffusion Coefficients with Monte Carlo

    NASA Astrophysics Data System (ADS)

    Dorval, Eric

    2014-06-01

    This paper presents a new Monte Carlo-based method for the calculation of diffusion coefficients. One distinctive feature of this method is that it does not resort to the computation of transport cross sections directly, although their functional form is retained. Instead, a special type of tally derived from a deterministic estimate of Fick's Law is used for tallying the total cross section, which is then combined with a set of other standard Monte Carlo tallies. Some properties of this method are presented by means of numerical examples for a multi-group 1-D implementation. Calculated diffusion coefficients are in general good agreement with values obtained by other methods.

  5. ICP-MS measurement of diffusion coefficients of Cs in NBG-18 graphite

    NASA Astrophysics Data System (ADS)

    Carter, L. M.; Brockman, J. D.; Robertson, J. D.; Loyalka, S. K.

    2015-11-01

    Graphite is used in the HGTR/VHTR as moderator and it also functions as a barrier to fission product release. Therefore, an elucidation of transport of fission products in reactor-grade graphite is required. We have measured diffusion coefficients of Cs in graphite NBG-18 using the release method, wherein we infused spheres of NBG-18 with Cs and measured the release rates in the temperature range of 1090-1395 K. We have obtained: These seem to be the first reported values of Cs diffusion coefficients in NBG-18. The values are lower than those reported for other graphites in the literature.

  6. LETTER TO THE EDITOR: Fractal diffusion coefficient from dynamical zeta functions

    NASA Astrophysics Data System (ADS)

    Cristadoro, Giampaolo

    2006-03-01

    Dynamical zeta functions provide a powerful method to analyse low-dimensional dynamical systems when the underlying symbolic dynamics is under control. On the other hand, even simple one-dimensional maps can show an intricate structure of the grammar rules that may lead to a non-smooth dependence of global observables on parameters changes. A paradigmatic example is the fractal diffusion coefficient arising in a simple piecewise linear one-dimensional map of the real line. Using the Baladi-Ruelle generalization of the Milnor-Thurnston kneading determinant, we provide the exact dynamical zeta function for such a map and compute the diffusion coefficient from its smallest zero.

  7. Determination of diffusion coefficients in polypyrrole thin films using a current pulse relaxation method

    NASA Technical Reports Server (NTRS)

    Penner, Reginald M.; Vandyke, Leon S.; Martin, Charles R.

    1987-01-01

    The current pulse E sub oc relaxation method and its application to the determination of diffusion coefficients in electrochemically synthesized polypyrrole thin films is described. Diffusion coefficients for such films in Et4NBF4 and MeCN are determined for a series of submicron film thicknesses. Measurement of the double-layer capacitance, C sub dl, and the resistance, R sub u, of polypyrrole thin films as a function of potential obtained with the galvanostatic pulse method is reported. Measurements of the electrolyte concentration in reduced polypyrrole films are also presented to aid in the interpretation of the data.

  8. Simultaneous inversion for the space-dependent diffusion coefficient and the fractional order in the time-fractional diffusion equation

    NASA Astrophysics Data System (ADS)

    Li, Gongsheng; Zhang, Dali; Jia, Xianzheng; Yamamoto, Masahiro

    2013-06-01

    This paper deals with an inverse problem of simultaneously identifying the space-dependent diffusion coefficient and the fractional order in the 1D time-fractional diffusion equation with smooth initial functions by using boundary measurements. The uniqueness results for the inverse problem are proved on the basis of the inverse eigenvalue problem, and the Lipschitz continuity of the solution operator is established. A modified optimal perturbation algorithm with a regularization parameter chosen by a sigmoid-type function is put forward for the discretization of the minimization problem. Numerical inversions are performed for the diffusion coefficient taking on different functional forms and the additional data having random noise. Several factors which have important influences on the realization of the algorithm are discussed, including the approximate space of the diffusion coefficient, the regularization parameter and the initial iteration. The inversion solutions are good approximations to the exact solutions with stability and adaptivity demonstrating that the optimal perturbation algorithm with the sigmoid-type regularization parameter is efficient for the simultaneous inversion.

  9. Broadening of polymer chromatographic signals: Analysis, quantification and correction through effective diffusion coefficients.

    PubMed

    Suárez, Inmaculada; Coto, Baudilio

    2015-08-14

    Average molecular weights and polydispersity indexes are some of the most important parameters considered in the polymer characterization. Usually, gel permeation chromatography (GPC) and multi angle light scattering (MALS) are used for this determination, but GPC values are overestimated due to the dispersion introduced by the column separation. Several procedures were proposed to correct such effect usually involving more complex calibration processes. In this work, a new method of calculation has been considered including diffusion effects. An equation for the concentration profile due to diffusion effects along the GPC column was considered to be a Fickian function and polystyrene narrow standards were used to determine effective diffusion coefficients. The molecular weight distribution function of mono and poly disperse polymers was interpreted as a sum of several Fickian functions representing a sample formed by only few kind of polymer chains with specific molecular weight and diffusion coefficient. Proposed model accurately fit the concentration profile along the whole elution time range as checked by the computed standard deviation. Molecular weights obtained by this new method are similar to those obtained by MALS or traditional GPC while polydispersity index values are intermediate between those obtained by the traditional GPC combined to Universal Calibration method and the MALS method. Values for Pearson and Lin coefficients shows improvement in the correlation of polydispersity index values determined by GPC and MALS methods when diffusion coefficients and new methods are used.

  10. Determining diffusion coefficients of ionic liquids by means of field cycling nuclear magnetic resonance relaxometry.

    PubMed

    Kruk, D; Meier, R; Rachocki, A; Korpała, A; Singh, R K; Rössler, E A

    2014-06-28

    Field Cycling Nuclear Magnetic Resonance (FC NMR) relaxation studies are reported for three ionic liquids: 1-ethyl-3- methylimidazolium thiocyanate (EMIM-SCN, 220-258 K), 1-butyl-3-methylimidazolium tetrafluoroborate (BMIM-BF4, 243-318 K), and 1-butyl-3-methylimidazolium hexafluorophosphate (BMIM-PF6, 258-323 K). The dispersion of (1)H spin-lattice relaxation rate R1(ω) is measured in the frequency range of 10 kHz-20 MHz, and the studies are complemented by (19)F spin-lattice relaxation measurements on BMIM-PF6 in the corresponding frequency range. From the (1)H relaxation results self-diffusion coefficients for the cation in EMIM-SCN, BMIM-BF4, and BMIM-PF6 are determined. This is done by performing an analysis considering all relevant intra- and intermolecular relaxation contributions to the (1)H spin-lattice relaxation as well as by benefiting from the universal low-frequency dispersion law characteristic of Fickian diffusion which yields, at low frequencies, a linear dependence of R1 on square root of frequency. From the (19)F relaxation both anion and cation diffusion coefficients are determined for BMIM-PF6. The diffusion coefficients obtained from FC NMR relaxometry are in good agreement with results reported from pulsed- field-gradient NMR. This shows that NMR relaxometry can be considered as an alternative route of determining diffusion coefficients of both cations and anions in ionic liquids.

  11. Field-scale effective matrix diffusion coefficient for fractured rock: results from literature survey.

    PubMed

    Zhou, Quanlin; Liu, Hui-Hai; Molz, Fred J; Zhang, Yingqi; Bodvarsson, Gudmundur S

    2007-08-15

    Matrix diffusion is an important mechanism for solute transport in fractured rock. We recently conducted a literature survey on the effective matrix diffusion coefficient, D(m)(e), a key parameter for describing matrix diffusion processes at the field scale. Forty field tracer tests at 15 fractured geologic sites were surveyed and selected for the study, based on data availability and quality. Field-scale D(m)(e) values were calculated, either directly using data reported in the literature, or by reanalyzing the corresponding field tracer tests. The reanalysis was conducted for the selected tracer tests using analytic or semi-analytic solutions for tracer transport in linear, radial, or interwell flow fields. Surveyed data show that the scale factor of the effective matrix diffusion coefficient (defined as the ratio of D(m)(e) to the lab-scale matrix diffusion coefficient, D(m), of the same tracer) is generally larger than one, indicating that the effective matrix diffusion coefficient in the field is comparatively larger than the matrix diffusion coefficient at the rock-core scale. This larger value can be attributed to the many mass-transfer processes at different scales in naturally heterogeneous, fractured rock systems. Furthermore, we observed a moderate, on average trend toward systematic increase in the scale factor with observation scale. This trend suggests that the effective matrix diffusion coefficient is likely to be statistically scale-dependent. The scale-factor value ranges from 0.5 to 884 for observation scales from 5 to 2000 m. At a given scale, the scale factor varies by two orders of magnitude, reflecting the influence of differing degrees of fractured rock heterogeneity at different geologic sites. In addition, the surveyed data indicate that field-scale longitudinal dispersivity generally increases with observation scale, which is consistent with previous studies. The scale-dependent field-scale matrix diffusion coefficient (and dispersivity

  12. The temperature and concentration dependencies of diffusion coefficients of seven helium-fluoroethane systems

    NASA Astrophysics Data System (ADS)

    Dunlop, Peter J.; Bignell, C. M.

    1992-10-01

    Binary diffusion coefficients are reported as functions of concentration and temperature for seven helium-fluoroethane systems. An empirical correlation is made between the temperature-dependent effective cross sections for diffusion and the number of electrons in the heavy species interacting with the light helium atoms. Some of the experiments suggest a possible ``isomer effect'' due to the differences in molecular configuration of the fluoroethane species.

  13. Non-Fermi liquid behavior of the drag and diffusion coefficients in QED plasma

    SciTech Connect

    Sarkar, Sreemoyee; Dutt-Mazumder, Abhee K.

    2011-11-01

    We calculate the drag and diffusion coefficients in low temperature QED plasma and go beyond the leading order approximation. The non-Fermi-liquid behavior of these coefficients are clearly revealed. We observe that the subleading contributions due to the exchange of soft transverse photon in both cases are larger than the leading order terms coming from the longitudinal sector. The results are presented in closed form at zero and low temperature.

  14. Noninvasive monitoring of photodynamic therapy on skin neoplastic lesions using the optical attenuation coefficient measured by optical coherence tomography

    NASA Astrophysics Data System (ADS)

    Goulart, Viviane P.; dos Santos, Moisés O.; Latrive, Anne; Freitas, Anderson Z.; Correa, Luciana; Zezell, Denise M.

    2015-05-01

    Photodynamic therapy (PDT) has become a promising alternative for treatment of skin lesions such as squamous cell carcinoma. We propose a method to monitor the effects of PDT in a noninvasive way by using the optical attenuation coefficient (OAC) calculated from optical coherence tomography (OCT) images. We conducted a study on mice with chemically induced neoplastic lesions and performed PDT on these lesions using homemade photosensitizers. The response of neoplastic lesions to therapy was monitored using, at the same time, macroscopic clinical visualization, histopathological analysis, OCT imaging, and OCT-based attenuation coefficient measurement. Results with all four modalities demonstrated a positive response to treatment. The attenuation coefficient was found to be 1.4 higher in skin lesions than in healthy tissue and it decreased after therapy. This study shows that the OAC is a potential tool to noninvasively assess the evolution of skin neoplastic lesions with time after treatment.

  15. Regional and directional anisotropy of apparent diffusion coefficient in rat brain.

    PubMed

    Hoehn-Berlage, M; Eis, M; Schmitz, B

    1999-02-01

    Quantitative diffusion maps were recorded in normal rat brain. In multi-slice sections covering the whole brain, strong variation of the apparent diffusion coefficient (ADC) was observed depending on slice position at constant gradient direction. Furthermore, a varying difference between apparent diffusion coefficients depending on gradient direction was found, reaching 32% in the cortex of the ventral-most horizontal sections while showing equal ADC on the dorsal cortex side. The regional variation and directional anisotropy of the ADC was not restricted to white matter but was described for both cortical and subcortical brain tissue. From diffusion coefficients along the three major field gradient directions (ADCx, ADCy, ADCz), the average ADC (ADCaverage) was determined from the trace of the diffusion tensor (D) as 653+/-28 microm2/s for parietal cortex and 671+/-32 microm2/s for lateral cortex, independent of position along the sagittal direction. From these observations about the regional diffusion anisotropy, a more stringent protocol for the description of ischemic ADC changes is proposed.

  16. Effect of surface modification, microstructure, and trapping on hydrogen diffusion coefficients in high strength alloys

    NASA Astrophysics Data System (ADS)

    Jebaraj Johnley Muthuraj, Josiah

    Cathodic protection is widely used for corrosion prevention. However, this process generates hydrogen at the protected metal surface, and diffusion of hydrogen through the metal may cause hydrogen embrittlement or hydrogen induced stress corrosion cracking. Thus the choice of a metal for use as fasteners depends upon its hydrogen uptake, permeation, diffusivity and trapping. The diffusivity of hydrogen through four high strength alloys (AISI 4340, alloy 718, alloy 686, and alloy 59) was analyzed by an electrochemical method developed by Devanathan and Stachurski. The effect of plasma nitriding and microstructure on hydrogen permeation through AISI 4340 was studied on six different specimens: as-received (AR) AISI 4340, nitrided samples with and without compound layer, samples quenched and tempered (Q&T) at 320° and 520°C, and nitrided samples Q&T 520°C. Studies on various nitrided specimens demonstrate that both the gamma'-Fe 4N rich compound surface layer and the deeper N diffusion layer that forms during plasma nitriding reduce the effective hydrogen diffusion coefficient, although the gamma'-Fe4N rich compound layer has a larger effect. Multiple permeation transients yield evidence for the presence of only reversible trap sites in as-received, Q&T 320 and 520 AISI 4340 specimens, and the presence of both reversible and irreversible trap sites in nitrided specimens. Moreover, the changes in microstructure during the quenching and tempering process result in a significant decrease in the diffusion coefficient of hydrogen compared to as-received specimens. In addition, density functional theory-based molecular dynamics simulations yield hydrogen diffusion coefficients through gamma'- Fe4N one order of magnitude lower than through α-Fe, which supports the experimental measurements of hydrogen permeation. The effect of microstructure and trapping was also studied in cold rolled, solutionized, and precipitation hardened Inconel 718 foils. The effective hydrogen

  17. Diffusion-weighted imaging of normal fibroglandular breast tissue: influence of microperfusion and fat suppression technique on the apparent diffusion coefficient.

    PubMed

    Baron, Paul; Dorrius, Monique D; Kappert, Peter; Oudkerk, Matthijs; Sijens, Paul E

    2010-05-01

    The influence of microperfusion and fat suppression technique on the apparent diffusion coefficient (ADC) values obtained with diffusion weighted imaging (DWI) of normal fibroglandular breast tissue was investigated. Seven volunteers (14 breasts) were scanned using diffusion weighting factors (b values) up to 1600 s/mm(2) and the four different fat suppression techniques: STIR, fat saturation, SPAIR, and Water Excitation. The relationship between the logarithmic DW attenuation curves and b was linear for b values up to 600 s/mm(2) (R(2) > 0.999). Small differences were noted between the ADC values obtained with the various fat suppression methods, especially at the higher b values. Water Excitation had the highest mean SNR, exceeding STIR (p = 0.03) though not significantly different from fat saturation and SPAIR. In conclusion, the ADC of fibroglandular breast tissue is not influenced by microperfusion and Water Excitation is recommended because it yielded the best SNR values. These factors may be crucial in the differentiation between benign and malignant lesions.

  18. Thermodiffusion, molecular diffusion and Soret coefficients of aromatic+n-alkane binary mixtures

    NASA Astrophysics Data System (ADS)

    Larrañaga, Miren; Bou-Ali, M. Mounir; Lapeira, Estela; Lizarraga, Ion; Santamaría, Carlos

    2016-10-01

    In the present work, we have measured the thermodiffusion coefficient of 51 binary liquid mixtures at 25 oC. These mixtures correspond to the series of the aromatics toluene and 1-methylnaphthalene with n-alkanes nCi (i = 6, 8, 10, 12, and 14) at different mass fractions in the whole range. For that, we have used the thermogravitational technique. It is shown that the thermodiffusion coefficient is a linear function of the mass fraction in all the mixtures. Extrapolating the lines, we obtain the thermodiffusion coefficient in dilute solutions of n-alkanes for both toluene and 1-methylnaphthalene. These limiting values show a linear dependence with the inverse of the product of the molecular weights. In addition, we have measured the molecular diffusion coefficient of all the mixtures at 0.5 of mass fraction and at 25 oC, by the sliding symmetric tubes technique. It is observed that the product of this coefficient with the viscosity at the same concentrations takes a constant value for each of the series considered. Finally, we have also determined the Soret coefficient of the equimass mixtures by the combination of the measurements of thermodiffusion and molecular diffusion coefficients.

  19. Extending the Diffuse Layer Model of Surface Acidity Behavior: III. Estimating Bound Site Activity Coefficients

    EPA Science Inventory

    Although detailed thermodynamic analyses of the 2-pK diffuse layer surface complexation model generally specify bound site activity coefficients for the purpose of accounting for those non-ideal excess free energies contributing to bound site electrochemical potentials, in applic...

  20. Effective diffusion coefficients of gas mixture in heavy oil under constant-pressure conditions

    NASA Astrophysics Data System (ADS)

    Li, Huazhou Andy; Sun, Huijuan; Yang, Daoyong

    2016-09-01

    We develop a method to determine the effective diffusion coefficient for each individual component of a gas mixture in a non-volatile liquid (e.g., heavy oil) at high pressures with compositional analysis. Theoretically, a multi-component one-way diffusion model is coupled with the volume-translated Peng-Robinson equation of state to quantify the mass transfer between gas and liquid (e.g., heavy oil). Experimentally, the diffusion tests have been conducted with a PVT setup for one pure CO2-heavy oil system and one C3H8-CO2-heavy oil system under constant temperature and pressure, respectively. Both the gas-phase volume and liquid-phase swelling effect are simultaneously recorded during the measurement. As for the C3H8-CO2-heavy oil system, the gas chromatography method is employed to measure compositions of the gas phase at the beginning and end of the diffusion measurement, respectively. The effective diffusion coefficients are then determined by minimizing the discrepancy between the measured and calculated gas-phase composition at the end of diffusion measurement. The newly developed technique can quantify the contributions of each component of mixture to the bulk mass transfer from gas into liquid. The effective diffusion coefficient of C3H8 in the C3H8-CO2 mixture at 3945 ± 20 kPa and 293.85 K, i.e., 18.19 × 10^{ - 10} m^{ 2} / s, is found to be much higher than CO2 at 3950 ± 18 kPa and 293.85 K, i.e., 8.68 × 10^{ - 10} m^{ 2} / s. In comparison with pure CO2, the presence of C3H8 in the C3H8-CO2 mixture contributes to a faster diffusion of CO2 from the gas phase into heavy oil and consequently a larger swelling factor of heavy oil.

  1. Spin Echo Attenuation of Restricted Diffusion as a Discord of Spin Phase Structure

    NASA Astrophysics Data System (ADS)

    Stepišnik, Janez

    1998-04-01

    By using the particle probability density we analyze the spin echo attenuation of particles, diffusing in a bounded region. It provides a means to expand a nonuniform spin phase distribution into a series of waves that characterize the geometry and boundary conditions of confinement. Random motion disrupts the initial phase structure created by applied gradients and consequently discords its structure waves. By assuming the spin phase fluctuation and/or the randomness of spin phase distribution in the subensemble as a Gaussian stochastic process, we derive a new analytical expression for the echo attenuation related to the particle velocity correlation. For a diffusion in porous structure we get the expression featuring the same "diffusive diffraction" patterns as those being found and explained by P. T. Callaghan and A. Coy ("Principles of Nuclear Magnetic Resonance Microscopy," Oxford Univ. Press, Oxford (1991);J. Chem. Phys.101, 4599-4609 (1994)) with the use of propagator theory. With the new approach we cast a new light on the phenomena and derive analitically how the diffusive diffractions appear when the sequence of finite or even modulated gradients are applied. The method takes into account the non-Markovian character of restricted diffusion, and therefore the echo dependence on the diffusion lengths and on the strength of applied gradient differs from the results of authors assuming the Markovian diffusion either by dealing with the diffusion propagators or by the computer simulation of Fick's diffusion.

  2. Accurate determination of the diffusion coefficient of proteins by Fourier analysis with whole column imaging detection.

    PubMed

    Zarabadi, Atefeh S; Pawliszyn, Janusz

    2015-02-17

    Analysis in the frequency domain is considered a powerful tool to elicit precise information from spectroscopic signals. In this study, the Fourier transformation technique is employed to determine the diffusion coefficient (D) of a number of proteins in the frequency domain. Analytical approaches are investigated for determination of D from both experimental and data treatment viewpoints. The diffusion process is modeled to calculate diffusion coefficients based on the Fourier transformation solution to Fick's law equation, and its results are compared to time domain results. The simulations characterize optimum spatial and temporal conditions and demonstrate the noise tolerance of the method. The proposed model is validated by its application for the electropherograms from the diffusion path of a set of proteins. Real-time dynamic scanning is conducted to monitor dispersion by employing whole column imaging detection technology in combination with capillary isoelectric focusing (CIEF) and the imaging plug flow (iPF) experiment. These experimental techniques provide different peak shapes, which are utilized to demonstrate the Fourier transformation ability in extracting diffusion coefficients out of irregular shape signals. Experimental results confirmed that the Fourier transformation procedure substantially enhanced the accuracy of the determined values compared to those obtained in the time domain.

  3. Temperature dependence of ion diffusion coefficients in NaCl electrolyte confined within graphene nanochannels.

    PubMed

    Kong, Jing; Bo, Zheng; Yang, Huachao; Yang, Jinyuan; Shuai, Xiaorui; Yan, Jianhua; Cen, Kefa

    2017-03-15

    The behavior of ion diffusion in nano-confined spaces and its temperature dependence provide important fundamental information about electric double-layer capacitors (EDLCs) employing nano-sized active materials. In this work, the ion diffusion coefficients of NaCl electrolyte confined within neutral and charged graphene nanochannels at different temperatures are investigated using molecular dynamics simulations. The results show that ions confined in neutral nanochannels diffuse faster (along the graphene surfaces) than those in bulk solution, which could be attributed to the relatively smaller concentration in confined spaces and the solvophobic nature of graphene surfaces. In charged nanochannels where the electrostatic interactions between counter-ions and charged channel surfaces govern the motion of ions, the diffusion coefficients are found to be lower than those in the neutral counterparts. The increase of temperature will lead to enhanced vibrant thermal motion of ions. Due to the significant role of ion-surface interactions, ion diffusion coefficients in nano-confined spaces are more stable, that is, insensitive to the temperature variation, than those in bulk solution. The electrical conductivity is further estimated using the Nernst-Einstein equation. The findings of the current work could provide basic data and information for research studies on the thermal effects of graphene-based EDLCs.

  4. Single-relaxation-time lattice Boltzmann scheme for advection-diffusion problems with large diffusion-coefficient heterogeneities and high-advection transport.

    PubMed

    Perko, Janez; Patel, Ravi A

    2014-05-01

    The paper presents an approach that extends the flexibility of the standard lattice Boltzmann single relaxation time scheme in terms of spatial variation of dissipative terms (e.g., diffusion coefficient) and stability for high Péclet mass transfer problems. Spatial variability of diffusion coefficient in SRT is typically accommodated through the variation of relaxation time during the collision step. This method is effective but cannot deal with large diffusion coefficient variations, which can span over several orders of magnitude in some natural systems. The approach explores an alternative way of dealing with large diffusion coefficient variations in advection-diffusion transport systems by introducing so-called diffusion velocity. The diffusion velocity is essentially an additional convective term that replaces variations in diffusion coefficients vis-à-vis a chosen reference diffusion coefficient which defines the simulation time step. Special attention is paid to the main idea behind the diffusion velocity formulation and its implementation into the lattice Boltzmann framework. Finally, the performance, stability, and accuracy of the diffusion velocity formulation are discussed via several advection-diffusion transport benchmark examples. These examples demonstrate improved stability and flexibility of the proposed scheme with marginal consequences on the numerical performance.

  5. Survey of Key Parameters of Impurities in Aluminum: Diffusion Coefficients, Solubility, and Liquidus Slopes

    NASA Astrophysics Data System (ADS)

    Pearce, Jonathan V.

    2016-12-01

    Impurities represent in many cases the largest contribution to the uncertainty associated with fixed points of the International Temperature Scale of 1990 (ITS-90). The effect of impurities on the solidification temperature of ITS-90 metals can be characterized by the liquidus slope, the values of which have recently been characterized for a large number of systems. Two other key parameters are the diffusion coefficient, which provides information on how rapidly diffusion, and hence mixing, proceeds, as well as on the validity of the Scheil model of solidification; and the solubility, which provides information on how much impurity is actually dissolved and hence participates in affecting the solidification temperature. In this study, a comprehensive survey is presented of liquidus slopes, together with a survey of 237 diffusion coefficients and 274 values for the solubility of impurities in both liquid and solid aluminum.

  6. Simultaneous Measurement of Tracer and Interdiffusion Coefficients: An Isotopic Phenomenological Diffusion Formalism for the Binary Alloy

    SciTech Connect

    Belova, Irina; Kulkarni, Nagraj S; Sohn, Yong Ho; Murch, Prof. Graeme

    2013-01-01

    In this paper, a new development of the classic Onsager phenomenological formalism is derived using relations based on linear response theory. The development concerns the correct description of the fluxes of the atomic isotopes. The resulting expressions in the laboratory frame are surprisingly simple and consist of terms coming from the standard interdiffusion expressions and from Fick s first law where the tracer diffusion coefficient is involved thus providing a better understanding of the relationship between the two approaches - Fick s first law and the Onsager phenomenological formalism. From an experimental application perspective, the new development is applied to the binary alloy case. The formalism provides the means to obtain the interdiffusion coefficient and tracer diffusion coefficients simultaneously from analysis of the interdiffusion concentration profiles in a single experiment.

  7. Space, energy and anisotropy effects on effective cross sections and diffusion coefficients in the resonance region

    SciTech Connect

    Meftah, B.

    1982-01-01

    Present methods used in reactor analysis do not include adequately the effect of anisotropic scattering in the calculation of resonance effective cross sections. Also the assumption that the streaming term ..cap omega...del Phi is conserved when the total, absorption and transfer cross sections are conserved, is bad because the leakage from a heterogeneous cell will not be conserved and is strongly anisotropic. A third major consideration is the coupling between different regions in a multiregion reactor; currently this effect is being completely ignored. To assess the magnitude of these effects, a code based on integral transport formalism with linear anisotropic scattering was developed. Also, a more adequate formulation of the diffusion coefficient in a heterogeneous cell was derived. Two reactors, one fast, ZPR-6/5, and one thermal, TRX-3, were selected for the study. The study showed that, in general, the inclusion of linear scattering anisotropy increases the cell effective capture cross section of U-238. The increase was up to 2% in TRX-3 and 0.5% in ZPR-6/5. The effect on the multiplication factor was -0.003% ..delta..k/k for ZPR-6/5 and -0.05% ..delta..k/k for TRX-3. For the case of the diffusion coefficient, the combined effect of heterogeneity and linear anisotropy gave an increase of up to 29% in the parallel diffusion coefficient of TRX-3 and 5% in the parallel diffusion coefficient of ZPR-6/5. In contrast, the change in the perpendicular diffusion coefficient did not exceed 2% in both systems.

  8. Linear attenuation coefficient and buildup factor of MCP-96 alloy for dose accuracy, beam collimation, and radiation protection.

    PubMed

    Hopkins, Deidre N; Maqbool, Muhammad; Islam, Mohammed S

    2012-07-01

    The linear attenuation coefficients and buildup factor of MCP-96 alloy were determined for (60)Co, (54)Mn, and (137)Cs gamma emitters and a NaI detector. The thickness of the MCP-96 attenuator was varied from 1 to 4 cm. A collimated beam of gamma rays was allowed to pass through various thicknesses of the MCP-96 alloy. The attenuated beam was detected by a NaI detector, and data were recorded by a multichannel analyzer. The run was repeated without the collimator for broad-beam geometry. For each run, the attenuated beam intensity was normalized by the intensity of the unattenuated incident beam obtained by removing the attenuators. Linear attenuation coefficients were determined by plotting of the intensity of the collimated beam against the attenuator thickness. For every thickness of the alloy, the ratio of the attenuated to the unattenuated beam was found to be higher in broad-beam geometry as compared to the same ratio in narrow-beam geometry. We used the difference in these ratios in broad and narrow-beam geometries to calculate the buildup factor. The buildup factor was found to increase with beam energy and attenuator thickness. Variation in the source-to-detector distance gave a lower value of the buildup factor for a small and a large distance and a higher value for an intermediate distance. The buildup factor was found to be greater than 1 in all cases. We conclude that the buildup factor must be calculated and incorporated for dose correction and precision when the MCP-96 alloy is used for tissue compensation or radiation shielding and protection purposes.

  9. Attenuation coefficient of the light in skin of BALB/c and C57BL/6 mice

    NASA Astrophysics Data System (ADS)

    Silva, C. R.; Camargo, C. F. M.; Aureliano, D. P.; De Pretto, L. R.; Freitas, A. Z.; Ribeiro, M. S.

    2015-06-01

    Optical properties of the biological tissue play an important role to a correct use of optical techniques for therapy and diagnosis. The mice skin presents morphological differences due to characteristics such as gender, body mass and age. Murine models are frequently used in pre-clinical trials in optical therapy and diagnosis. Therefore, the assessment of the skin tissue in animal models is needed for a proper understanding of how light interacts with skin. Noninvasive techniques such as optical coherence tomography (OCT) have been used to obtain optical information of the tissue, as the attenuation coefficient, with the advantage of obtaining sectional images in real time. In this study, eight female BALB/c albino mice (twenty-four weeks old) and eight male C57BL/6 black mice (eight weeks old) were used to measure the attenuation coefficient of the light in the skin, utilizing the OCT technique, aiming to check for influence of the aging process. Two moments were assessed twenty-two weeks apart from each other. Our data show that the aging process significantly affects the light attenuation coefficient in mice skin. Twenty-two weeks after, statistical significant differences were observed between groups within a same strain. We conclude that light attenuation coefficient of mice skin may be influenced by factors such as disorganization of the dermis. Morphological aspects of skin should be taken into account in studies that involve optical strategies in murine models.

  10. Apparent diffusion coefficients and chemical species of neptunium (V) in compacted Na-montmorillonite.

    PubMed

    Kozai, N; Inada, K; Kozaki, T; Sato, S; Ohashi, H; Banba, T

    2001-02-01

    Diffusion of neptunium (V) in compacted Na-montmorillonite was studied through the non-steady state diffusion method. In this study, two experimental attempts were carried out to understand the diffusion mechanism of neptunium. One was to establish the diffusion activation energy, which was then used to determine the diffusion process in the montmorillonite. The other was the measurement of the distribution of neptunium in the montmorillonite by a sequential batch extraction. The apparent diffusion coefficients of neptunium in the montmorillonite at a dry density of 1.0 Mg m-3 were from 3.7 x 10(-12) m2 s-1 at 288 K to 9.2 x 10(-12) m2 s-1 at 323 K. At a dry density of 1.6 Mg m-3, the apparent diffusion coefficients ranged between 1.5 x 10(-13) m2 s-1 at 288 K and 8.7 x 10(-13) m2 s-1 at 323 K. The activation energy for the diffusion of neptunium at a dry density of 1.0 Mg m-3 was 17.5 +/- 1.9 kJ mol-1. This value is similar to those reported for diffusion of other ions in free water, e.g., 18.4 and 17.4 kJ mol-1 for Na+ and Cl-, respectively. At a dry density of 1.6 Mg.m-3, the activation energy was 39.8 +/- 1.9 kJ mol-1. The change in the activation energy suggests that the diffusion process changes depending on the dry density of the compacted montmorillonite. A characteristic distribution profile was obtained by the sequential extraction procedure for neptunium diffused in compacted montmorillonite. The estimated fraction of neptunium in the pore water was between 3% and 11% at a dry density of 1.6 Mg m-3 and at a temperature of 313 K. The major fraction of the neptunium in the montmorillonite was identified as neptunyl ions sorbed on the outer surface of the montmorillonite. These findings suggested that the activation energy for diffusion and the distribution profile of the involved nuclides could become powerful parameters in understanding the diffusion mechanism.

  11. Diffusion coefficients from resonant interactions with electrostatic electron cyclotron harmonic waves

    SciTech Connect

    Tripathi, A. K.; Singhal, R. P.

    2009-11-15

    Pitch-angle diffusion coefficients have been calculated for resonant interaction with electrostatic electron cyclotron harmonic (ECH) waves using quasilinear diffusion theory. Unlike previous calculations, the parallel group velocity has been included in this study. Further, ECH wave intensity is expressed as a function of wave frequency and wave normal angle with respect to ambient magnetic field. It is found that observed wave electric field amplitudes in Earth's magnetosphere are sufficient to set electrons on strong diffusion in the energy ranges of a few hundred eV. However, the required amplitudes are larger than the observed values for keV electrons and higher by about a factor of 3 compared to past calculations. Required electric field amplitudes are smaller at larger radial distances. It is concluded that ECH waves are responsible for diffuse auroral precipitation of electrons with energies less than about 500 eV.

  12. Estimation of diffuse attenuation of ultraviolet light in optically shallow Florida Keys waters from MODIS measurements

    EPA Science Inventory

    Diffuse attenuation of solar light (Kd, m−1) determines the percentage of light penetrating the water column and available for benthic organisms. Therefore, Kd can be used as an index of water quality for coastal ecosystems that are dependent on photosynthesis, such as the coral ...

  13. Spectrophotometric Method for Differentiation of Human Skin Melanoma. I. Optical Diffuse Reflection Coefficient

    NASA Astrophysics Data System (ADS)

    Petruk, V. G.; Ivanov, A. P.; Kvaternyuk, S. M.; Barun, V. V.

    2016-03-01

    We have designed an experimental setup, based on two integrating spheres, that lets us measure the optical diffuse reflectance spectra (diffuse reflection coefficient vs. wavelength) of human skin quickly under clinical conditions in vivo. For the wavelength interval 520-1100 nm, we give the values of the diffuse reflection coefficient for healthy tissue, skin with a benign nevus, and skin with a malignant melanoma for a large group of test subjects. We experimentally established a number of wavelengths in the red-near IR region of the spectrum which can be used for early differential diagnosis of nevi and melanoma in patient cancer screening. According to the Kramer-Welch test, the probability of the diffuse reflection coefficient for skin with melanoma and a nevus having different distributions is >0.94, and at many wavelengths it is >0.999. By solving the inverse problem, we estimated the changes in a number of structural and biophysical parameters of the tissue on going from healthy skin to nevus and melanoma. The results obtained can provide a basis for developing a clinical approach to identifying the risk of malignant transformation of the skin before surgery and histological analysis of the tissue.

  14. Determination of the diffusion coefficient of hydrogen in gamma titanium aluminides during electrolytic charging

    SciTech Connect

    Sundaram, P.A.; Wessel, E.; Clemens, H.; Kestler, H.; Ennis, P.J.; Quadakkers, W.J.; Singheiser, L.

    2000-03-14

    The diffusion coefficient of hydrogen in some gamma based titanium aluminide alloys was determined at room temperature using an electrochemical techniques. A cast Ti-48Al-2Cr alloy as well as Ti-46.5Al-4(Cr,Nb,Ta,B) sheet material with primary annealed and designed fully lamellar microstructures were subjected to cathodic hydrogen charging at room temperature in the galvanostatic mode. The potential variation with time was monitored form which data the values of the diffusion coefficient of hydrogen, D were calculated form well known error function/infinite series solutions to Fick's second law. Very good correlation was obtained with respect to theoretical calculations. The diffusion coefficients appear to be in close agreement with those for the cast alloy calculated from microhardness measurements. The value of D can be overestimated for thick specimens. Results show that neither the microstructure in terms of grain/lamellar colony size, nor the charging current density, appear to have a significant effect on the value of D. Lattice diffusion appears to be rate controlling.

  15. An interpretation of potential scale dependence of the effectivematrix diffusion coefficient

    SciTech Connect

    Liu, H.H.; Zhang, Y.Q.; Zhou, Q.; Molz, F.J.

    2005-11-30

    Matrix diffusion is an important process for solutetransport in fractured rock, and the matrix diffusion coefficient is akey parameter for describing this process. Previous studies indicatedthat the effective matrix diffusion coefficient values, obtained from alarge number of field tracer tests, are enhanced in comparison with localvalues and may increase with test scale. In this study, we have performednumerical experiments to investigate potential mechanisms behind possiblescale-dependent behavior. The focus of the experiments is on solutetransport in flow paths having geometries consistent with percolationtheories and characterized by local flow loops formed mainly bysmall-scale fractures. The water velocity distribution through a flowpath was determined using discrete fracture network flow simulations, andsolute transport was calculated using a previously derivedimpulse-response function and a particle-tracking scheme. Values foreffective (or up-scaled) transport parameters were obtained by matchingbreakthrough curves from numerical experiments with an analyticalsolution for solute transport along a single fracture. Results indicatethat a combination of local flow loops and the associated matrixdiffusion process, together with scaling properties in flow pathgeometry, seems to be the dominant mechanism causing the observed scaledependence of theeffective matrix diffusion coefficient (at a range ofscales).

  16. Measuring precise diffusion coefficients with two-focus fluorescence correlation spectroscopy

    NASA Astrophysics Data System (ADS)

    Dertinger, Thomas; Gregor, Ingo; von der Hocht, Iris; Erdmann, Rainer; Krämer, Benedikt; Koberling, Felix; Hartmann, Rudolf; Enderlein, Jörg

    2006-02-01

    We present a new method for precisely measuring diffusion coefficients of fluorescent molecules at nanomolar concentrations. The method is based on a modified Fluorescence Correlation Spectroscopy (FCS)-setup which is robust against many artifacts that are inherent to standard FCS 1, 2. The core idea of the new method is the introduction of an external ruler by generating two laterally shifted and overlapping laser foci at a fixed and known distance. Data fitting is facilitated by ab initio calculations of resulting correlation curves and subsequent affine transformation of these curves to match the measured auto- and cross-correlation functions. The affine transformation coefficient along the time axis then directly yields the correct diffusion coefficient. This method is not relying on the rather inexact assumption of a 3D Gaussian shaped detection volume. We measured the diffusion coefficient of the red fluorescent dye Atto-655 (Atto-Tec GmbH) in water and compared the obtained value with results from Gradient Pulsed Field NMR (GPF-NMR).

  17. Determination of diffusion coefficient in gel and in aqueous solutions using scanning electrochemical microscopy.

    PubMed

    Csóka, Balázs; Nagy, Géza

    2004-10-29

    Diffusion coefficient of different species in different media is an important property needed in scientific research and practice. A method taking advantage on the special capability of scanning electrochemical microscopy (SECM) is described for the easy and accurate measurement of diffusion coefficient. The method is based on detecting the concentration-time transients with appropriate electrochemical microsensor positioned at the close vicinity of a miniature dose-source device. At a given time (ti), a small dose of the investigated species is introduced. The Deltatmax=(tcmax-ti) value and the distance (d=x+Deltaxn) between the source and the detector microelectrode are used for the calculation of D. While the original set distance (x) cannot be accurately measured in the micrometer scale, the tip travel distance (Deltaxn) of the microscope is well defined. Collecting a few Deltatmax-(x+Deltaxn) data pairs, a reliable value of the diffusion coefficient can be obtained. The procedure is simple, and no exact knowledge of the introduced dose is needed. Two ways of sample dose delivery were used: on the one hand, coulometric generation with current-controlled electric pulse using micro-disc electrode, and on the other one, pressure ejection of a nano-droplet from a glass micropipette. Diffusion coefficient of I2, H2O2, [Ru(NH3)6]Cl3 and K3[Fe(CN)6] were measured in solution and in agarose gel phases of different composition. The effect of polyelectrolyte ion exchangers on the diffusion of the investigated species was checked.

  18. New Hydrogen Self Diffusion Coefficients in Olivine Using NanoSIMS

    NASA Astrophysics Data System (ADS)

    Du Frane, W. L.; Novella, D.; Jacobsen, B.; Weber, P. K.; Ryerson, F. J.; Tyburczy, J. A.

    2015-12-01

    We have previously reported hydrogen self-diffusion coefficients for olivine in deuterium-hydrogen exchange experiments, but were only able to resolve diffusion profiles reliably in the 'fast' [100] orientation due to the limited spatial resolution of the Cameca 6f Secondary Ion Mass Spectrometry (SIMS) instrument. Samples were reanalyzed using the Cameca nanoSIMS, which enabled simultaneous measurements of diffusion coefficients in the 'fast' [100] orientation and the additional 'slow' [010] and [001] orientations to gain a complete 3D view of hydrogen self-diffusion. Measurement precision of deuterium (16O2H with a Cs+beam) is also improved by higher vacuum, better environmental control, and lower background. Deuterium-hydrogen exchange experiments were conducted at 2 GPa between 750-900 °C by first saturating olivine with homogenous distribution of hydrogen (1H) and then exchanging some of this with deuterium (2H) in a subsequent experiment. The diffusion coefficents in the [100] orientation that were measured using the nanoSIMS are in good agreement with the previous measurements on the 6f. Diffusion coefficients in the [010] and [001] orientations are very similar in magnitude to one another, ranging between 10-13 to 10-14 m2/s, which is over an order of magnitude lower than the [100] orientation. Hydrogen self-diffusion is highly anisotropic in this temperature range, although the activation enthalpies for diffusion in the [010] and [001] orientations are significantly higher than that of the [100] orientation, such that there will be less anisotropy at higher temperatures relevant to the upper mantle. Comparisons between chemical and self-diffusion measurements allow us to evaluate the various stoichiometric relationships that have been proposed for accommodating hydrogen into the nominally anhydrous structure of olivine. Based on these relationships, we estimate diffusivities of other point defects, small polarons and metal vacancies, as a function of

  19. The influence of ionic forces on the effective diffusion coefficient in fractured, porous chalk.

    NASA Astrophysics Data System (ADS)

    Kremer, K.; Reichert, B.

    2005-12-01

    Solute transport in fractured, highly porous chalk significantly depends on the diffusive mass transfer of substances between the mobile water in the fracture and the immobile water of the rock matrix. Matrix diffusion is an important transport mechanism and a central factor for the retardation of solutes. Until now, simple estimation methods for the diffusive behavior of substances such as Archie's law can only be applied to single substances. Multi-tracer experiments proved a mutual influence on the diffusion of ionic solutes thus leading to significant deviations in respect to the theoretically estimated effective diffusion coefficient D_e. An increase of ionic forces in the aqueous phase is often accompanied by a decrease of D_e for cations and an increase for anions. However, groundwater contamination usually consists of several pollutants in different mixtures. Besides ionic forces, effects of channeling and transport of colloids can result in incorrectly estimated D_e values and, hence, high inaccuracy in the modeling of contaminant transport in fractured porous media. In the context of a current DFG-project, the impact of ionic forces on D_e as well as the interaction of the diffusion of ionic ground water solutes in fractured chalk of Denmark (Cretaceous, Sigerslev) and Israel (Eocene, Negev desert) will be quantified to develop a procedure for an improved estimation of D_e in dependence of the ionic activity. Consequently, the well established Archie's law for the prediction of diffusivities on the basis of the total porosities will be modified by an extension term a. So far series of single-tracer through-diffusion experiments have been performed with potassium bromide in six different concentrations to quantify the concentration dependence on the matrix diffusion as well as to examine the influence of the ionic strength on the effective diffusion coefficients of ionic solutes. The simultaneously injected neutral deuterium serves as a reference tracer

  20. Diffusion coefficients for two-dimensional narrow asymmetric channels embedded on flat and curved surfaces

    NASA Astrophysics Data System (ADS)

    Pineda, I.; Chacón-Acosta, G.; Dagdug, L.

    2014-12-01

    This paper focuses on the derivation of a general position-dependent diffusion coefficient to describe the two-dimensional (2D) diffusion in a narrow and smoothly asymmetric channel of varying cross section and non-straight midline embedded in a flat or on a curved surface. We consider the diffusion of non-interacting point-like Brownian particles under no external field. In order to project the 2D diffusion equation into an effective one-dimensional generalized Fick-Jacobs equation in both, flat and curved manifolds using the generalization of the mapping procedure introduced by Kalinay and Percus. The expression obtained is the more general position-dependent diffusion coefficient for 2D narrow channels that lies in a plane, which contains all the well-known previous results both symmetric and asymmetric channels as special cases. In a straightforward manner, previously defining the corresponding Fick-Jacobs equation on a curved surface, this result can be generalized to the case of a narrow 2D channel embedded on a no-flat smooth surface where the full position-dependent diffusion coefficient is modified according to the metric elements that accounts for the curvature of the surface. In addition, the equations for the mean first-passage time are obtained for asymmetrical channels on curved surfaces. As an example we shall solve this equation for the case of an asymmetric channel defined by straight walls embedded on a cylindrical surface having a reflecting wall at the origin and an absorbent one at distance θL.

  1. A new in-situ method to determine the apparent gas diffusion coefficient of soils

    NASA Astrophysics Data System (ADS)

    Laemmel, Thomas; Paulus, Sinikka; Schack-Kirchner, Helmer; Maier, Martin

    2015-04-01

    Soil aeration is an important factor for the biological activity in the soil and soil respiration. Generally, gas exchange between soil and atmosphere is assumed to be governed by diffusion and Fick's Law is used to describe the fluxes in the soil. The "apparent soil gas diffusion coefficient" represents the proportional factor between the flux and the gas concentration gradient in the soil and reflects the ability of the soil to "transport passively" gases through the soil. One common way to determine this coefficient is to take core samples in the field and determine it in the lab. Unfortunately this method is destructive and needs laborious field work and can only reflect a small fraction of the whole soil. As a consequence insecurity about the resulting effective diffusivity on the profile scale must remain. We developed a new in-situ method using new gas sampling device, tracer gas and inverse soil gas modelling. The gas sampling device contains several sampling depths and can be easily installed into vertical holes of an auger, which allows for fast installation of the system. At the lower end of the device inert tracer gas is injected continuously. The tracer gas diffuses into the surrounding soil. The resulting distribution of the tracer gas concentrations is used to deduce the diffusivity profile of the soil. For Finite Element Modeling of the gas sampling device/soil system the program COMSOL is used. We will present the results of a field campaign comparing the new in-situ method with lab measurements on soil cores. The new sampling pole has several interesting advantages: it can be used in-situ and over a long time; so it allows following modifications of diffusion coefficients in interaction with rain but also vegetation cycle and wind.

  2. Determination of time-dependent partition coefficients for several pesticides using diffusion theory.

    PubMed

    Renaud, Fabrice G; Leeds-Harrison, Peter B; Brown, Colin D; van Beinum, Wendy

    2004-12-01

    Diffusion-retarded partitioning of pesticides with aggregated soils results in a time-dependent partition coefficient (Kd') which is different at equilibrium from the partition coefficient derived from conventional 24-h batch studies (Kd) measured on dispersed soil. An experiment was undertaken to determine the importance of Kd' for the prediction of pesticide concentrations in solutions bathing artificial soil aggregates and to determine whether diffusion theory could accurately predict the concentrations. Two clay soils were mixed with polyacrylamide to create artificial aggregates of 0.8, 1.4 and 1.7 cm diameter when dry. After saturation, the aggregates were immersed in solutions containing isoproturon or a mixture of isoproturon, chlorotoluron and triasulfuron. The decline with time of the pesticide concentrations in the bathing solution was monitored and the results were compared with predictions from a diffusion-based model. The effective diffusion coefficients of the compounds were obtained by either fitting the non-linear diffusion model to the data (D(ef)) or by independent calculations based on the properties of the compounds and of the aggregates (D(ec)). The diffusion model was able to predict the temporal variation in pesticide concentrations in the bathing solution reasonably well whether D(ef) or D(ec) values were used. However, equilibrium concentrations in solution were sometimes overestimated due to increased sorption with time at the particle scale. Overall, the ratio between D(ef) and D(ec) ranged from 0.23 to 0.95 which was a reasonable variation when compared to the range of aggregate sizes used in the experiments and of the Kd values of the compounds.

  3. Integral formula for the effective diffusion coefficient in two-dimensional channels

    NASA Astrophysics Data System (ADS)

    Kalinay, Pavol

    2016-07-01

    The effective one-dimensional description of diffusion in two-dimensional channels of varying cross section is revisited. The effective diffusion coefficient D (x ) , extending Fick-Jacobs equation, depending on the longitudinal coordinate x , is derived here without use of scaling of the transverse coordinates. The result of the presented method is an integral formula for D (x ) , calculating its value at x as an integral of contributions from the neighboring positions x' depending on h (x') , a function shaping the channel. Unlike the standard formulas based on the scaling, the new proposed formula also describes D (x ) correctly near the cusps, or in wider channels.

  4. Thermal Expansion and Diffusion Coefficients of Carbon Nanotube-Polymer Composites

    NASA Technical Reports Server (NTRS)

    Wei, Chengyu; Srivastava, Deepak; Cho, Kyeongjae; Biegel, Bryan (Technical Monitor)

    2001-01-01

    Classical molecular dynamics (MD) simulations employing Brenner potential for intra-nanotube interactions and van der Waals forces for polymer-nanotube interface have been used to investigate thermal expansion and diffusion characteristics of carbon nanotube-polyethylene composites. Addition of carbon nanotubes to polymer matrix is found to significantly increase the glass transition temperature Tg, and thermal expansion and diffusion coefficients in the composite above Tg. The increase has been attributed to the temperature dependent increase of the excluded volume for the polymer chains, and the findings could have implications in the composite processing, coating and painting applications.

  5. Diffusion coefficients of Fokker-Planck equation for rotating dust grains in a fusion plasma

    SciTech Connect

    Bakhtiyari-Ramezani, M. Alinejad, N.; Mahmoodi, J.

    2015-11-15

    In the fusion devices, ions, H atoms, and H{sub 2} molecules collide with dust grains and exert stochastic torques which lead to small variations in angular momentum of the grain. By considering adsorption of the colliding particles, thermal desorption of H atoms and normal H{sub 2} molecules, and desorption of the recombined H{sub 2} molecules from the surface of an oblate spheroidal grain, we obtain diffusion coefficients of the Fokker-Planck equation for the distribution function of fluctuating angular momentum. Torque coefficients corresponding to the recombination mechanism show that the nonspherical dust grains may rotate with a suprathermal angular velocity.

  6. A MATLAB program to calculate translational and rotational diffusion coefficients of a single particle

    NASA Astrophysics Data System (ADS)

    Charsooghi, Mohammad A.; Akhlaghi, Ehsan A.; Tavaddod, Sharareh; Khalesifard, H. R.

    2011-02-01

    We developed a graphical user interface, MATLAB based program to calculate the translational diffusion coefficients in three dimensions for a single diffusing particle, suspended inside a fluid. When the particles are not spherical, in addition to their translational motion also a rotational freedom is considered for them and in addition to the previous translational diffusion coefficients a planar rotational diffusion coefficient can be calculated in this program. Time averaging and ensemble averaging over the particle displacements are taken to calculate the mean square displacement variations in time and so the diffusion coefficients. To monitor the random motion of non-spherical particles a reference frame is used that the particle just have translational motion in it. We call it the body frame that is just like the particle rotates about the z-axis of the lab frame. Some statistical analysis, such as velocity autocorrelation function and histogram of displacements for the particle either in the lab or body frames, are available in the program. Program also calculates theoretical values of the diffusion coefficients for particles of some basic geometrical shapes; sphere, spheroid and cylinder, when other diffusion parameters like temperature and fluid viscosity coefficient can be adjusted. Program summaryProgram title: KOJA Catalogue identifier: AEHK_v1_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AEHK_v1_0.html Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.html No. of lines in distributed program, including test data, etc.: 48 021 No. of bytes in distributed program, including test data, etc.: 1 310 320 Distribution format: tar.gz Programming language: MatLab (MathWorks Inc.) version 7.6 or higher. Statistics Toolbox and Curve Fitting Toolbox required. Computer: Tested on windows and linux, but generally it would work on any

  7. An explicit formula for the coherent SH waves' attenuation coefficient in random porous materials with low porosities.

    PubMed

    Zhang, Jun; Ye, Wenjing

    2015-09-01

    In this paper, the attenuation coefficient of coherent SH waves in random porous material with uniformly randomly distributed elliptical cavities of different aspect ratios is studied. Based on an analysis of the mechanism for attenuation, a simple macro model for the attenuation coefficient is proposed. The macro model says that the attenuation coefficient can be expressed as a function of the mean scattering cross section and the number density of cavities at low porosities. Then, large-scale numerical simulations using the pre-corrected Fast Fourier Transform (pFFT) algorithm accelerated Boundary Element Method (BEM) are conducted to specify this macro model. Finally, this macro model is compared with four theoretical models derived for composite/porous materials with circular inclusions at the porosity p=3.17% and 5%. Results show this macro model agree well with three of them. Compared to the existing theoretical models, the form of this macro model is simple and has a clear physical meaning. In addition, it is applicable to cases with relatively complex cavities.

  8. A Monte Carlo model for determination of binary diffusion coefficients in gases

    SciTech Connect

    Panarese, A.; Bruno, D.; Colonna, G.; Diomede, P.; Laricchiuta, A.; Longo, S.; Capitelli, M.

    2011-06-20

    A Monte Carlo method has been developed for the calculation of binary diffusion coefficients in gas mixtures. The method is based on the stochastic solution of the linear Boltzmann equation obtained for the transport of one component in a thermal bath of the second one. Anisotropic scattering is included by calculating the classical deflection angle in binary collisions under isotropic potential. Model results are compared to accurate solutions of the Chapman-Enskog equation in the first and higher orders. We have selected two different cases, H{sub 2} in H{sub 2} and O in O{sub 2}, assuming rigid spheres or using a model phenomenological potential. Diffusion coefficients, calculated in the proposed approach, are found in close agreement with Chapman-Enskog results in all the cases considered, the deviations being reduced using higher order approximations.

  9. Correlation between Kolmogorov-Sinai entropy and self-diffusion coefficient in simple fluids

    NASA Astrophysics Data System (ADS)

    Ihm, Dongchul; Shin, Young-Han; Lee, Jae-Weon; Lee, Eok Kyun

    2003-02-01

    The relationship between the Kolmogorov-Sinai entropy, hKS and the self-diffusion coefficient D is studied for two classical simple fluid systems with purely repulsive potentials (one system with a Wayne-Chandler-Anderson potential and the other with a hard-sphere potential). Numerical simulation data for hKS and D, normalized by the average collision frequency ν and the diameter of the particle σ as natural units of time and distance, reveal that, in the region spanning from normal liquid up to near solidification (0.50⩽ρ⩽0.93), the Kolmogorov-Sinai entropy has a power law dependeney on the self-diffusion coefficient of the form hKS/ν∝(D/σ2ν)η, in which η is independent of density and temperature.

  10. Correlation between the Kolmogorov-Sinai entropy and the self-diffusion coefficient in simple liquids

    NASA Astrophysics Data System (ADS)

    Pang, Hyunsoo; Shin, Young-Han; Ihm, Dongchul; Lee, Eok Kyun; Kum, Oyeon

    2000-11-01

    Molecular dynamics simulations were performed for soft- and hard-sphere systems, for number densities ranging from 0.5 to 1.0, and the Kolmogorov-Sinai entropy (KS entropy) and self-diffusion coefficients were calculated. It is found that the KS entropy, when expressed in terms of average collision frequency, is uniquely related to the self-diffusion coefficient by a simple scaling law. The dependence of the KS entropy on average collision frequency and number density was also explored. Numerical results show that the scaling laws proposed by Dzugutov, and by Beijeren, Dorfman, Posch, and Dellago, can be applied to both soft- and hard-sphere systems by changing to more generalized forms.

  11. Correlation between Kolmogorov-Sinai entropy and self-diffusion coefficient in simple fluids.

    PubMed

    Ihm, Dongchul; Shin, Young-Han; Lee, Jae-Weon; Lee, Eok Kyun

    2003-02-01

    The relationship between the Kolmogorov-Sinai entropy, h(KS) and the self-diffusion coefficient D is studied for two classical simple fluid systems with purely repulsive potentials (one system with a Wayne-Chandler-Anderson potential and the other with a hard-sphere potential). Numerical simulation data for h(KS) and D, normalized by the average collision frequency nu and the diameter of the particle sigma as natural units of time and distance, reveal that, in the region spanning from normal liquid up to near solidification (0.50< or =rho< or =0.93), the Kolmogorov-Sinai entropy has a power law dependeney on the self-diffusion coefficient of the form h(KS)/nu proportional, variant (D/sigma(2)nu)(eta), in which eta is independent of density and temperature.

  12. Correlation between the kolmogorov-sinai entropy and the self-diffusion coefficient in simple liquids

    PubMed

    Pang; Shin; Ihm; Lee; Kum

    2000-11-01

    Molecular dynamics simulations were performed for soft- and hard-sphere systems, for number densities ranging from 0.5 to 1.0, and the Kolmogorov-Sinai entropy (KS entropy) and self-diffusion coefficients were calculated. It is found that the KS entropy, when expressed in terms of average collision frequency, is uniquely related to the self-diffusion coefficient by a simple scaling law. The dependence of the KS entropy on average collision frequency and number density was also explored. Numerical results show that the scaling laws proposed by Dzugutov, and by Beijeren, Dorfman, Posch, and Dellago, can be applied to both soft- and hard-sphere systems by changing to more generalized forms.

  13. Diffusion coefficients of energetic water group ions near Comet Giacobini-Zinner

    NASA Astrophysics Data System (ADS)

    Tan, L. C.; Mason, G. M.; Richardson, I. G.; Ipavich, F. M.

    1993-03-01

    Data from the ultralow-energy charge analyzer and energetic particle anisotropy spectrometer sensors, acquired when the ICE spacecraft flew past Comet Giacobini-Zinner on September 11, 1985, are combined, and a single, self-consistent analysis technique is applied to derive a single-particle spectrum from about 200 to 1600 km/s. This information, together with the deduced bulk flow speed of the ions, is used to calculate a parallel diffusion coefficient in the transition region downstream of the bow wave (2.3 +/- 0.5) x 10 exp 17 sq cm/s; the corresponding scattering mean free path is (6 +/- 1) x 10 exp 4 km. The parallel diffusion coefficient is found to depend on the collision frequency of water group ions with Alfven waves, which are assumed to be propagating parallel (antiparallel) to the magnetic field.

  14. Determination of the diffusion coefficient and solubility of radon in plastics.

    PubMed

    Pressyanov, D; Georgiev, S; Dimitrova, I; Mitev, K; Boshkova, T

    2011-05-01

    This paper describes a method for determination of the diffusion coefficient and the solubility of radon in plastics. The method is based on the absorption and desorption of radon in plastics. Firstly, plastic specimens are exposed for controlled time to referent (222)Rn concentrations. After exposure, the activity of the specimens is followed by HPGe gamma spectrometry. Using the mathematical algorithm described in this report and the decrease of activity as a function of time, the diffusion coefficient can be determined. In addition, if the referent (222)Rn concentration during the exposure is known, the solubility of radon can be determined. The algorithm has been experimentally applied for different plastics. The results show that this approach allows the specified quantities to be determined with a rather high accuracy-depending on the quality of the counting equipment, it can be better than 10 %.

  15. Iterative solutions for one-dimensional diffusion with time varying surface composition and composition-dependent diffusion coefficient

    NASA Technical Reports Server (NTRS)

    Chow, M.; Houska, C. R.

    1980-01-01

    Solutions are given for one-dimensional diffusion problems with a time varying surface composition and also a composition dependent diffusion coefficient. The most general solution does not require special mathematical functions to fit the variation in surface composition or D(C). In another solution, a series expansion may be used to fit the time dependent surface concentration. These solutions make use of iterative calculations that converge rapidly and are highly stable. Computer times are much shorter than that required for finite difference calculations and can efficiently make use of interactive graphics terminals. Existing gas carburization data were used to provide an illustration of an iterative approach with a time varying carbon composition at the free surface.

  16. Sorption kinetics of polycyclic aromatic hydrocarbons removal using granular activated carbon: intraparticle diffusion coefficients.

    PubMed

    Valderrama, C; Gamisans, X; de las Heras, X; Farrán, A; Cortina, J L

    2008-09-15

    Granular activated carbon (GAC) was evaluated as a suitable sorbent for polycyclic aromatic hydrocarbons (PAHs) removal from aqueous solutions. For this purpose, kinetic measurements on the extraction of a family of six PAHs were taken. A morphology study was performed by means of a scanning electron microscopy (SEM) analysis of GAC samples. Analyses of the batch rate data for each PAH were carried out using two kinetic models: the homogenous particle diffusion model (HPDM) and the shell progressive model (SPM). The process was controlled by diffusion rate the solutes (PAHs) that penetrated the reacted layer at PAH concentrations in the range of 0.2-10 mg L(-1). The effective particle diffusion coefficients (D(eff)) derived from the two models were determined from the batch rate data. The Weber and Morris intraparticle diffusion model made a double contribution to the surface and pore diffusivities in the sorption process. The D(eff) values derived from both the HPMD and SPM equations varied from 1.1 x 10(-13) to 6.0 x 10(-14) m(2) s(-1). The simplest model, the pore diffusion model, was applied first for data analysis. The model of the next level of complexity, the surface diffusion model, was applied in order to gain a deeper understanding of the diffusion process. This model is able to explain the data, and the apparent surface diffusivities are in the same order of magnitude as the values for the sorption of functionalized aromatic hydrocarbons (phenols and sulphonates) that are described in the literature.

  17. Computer-aided identification of the water diffusion coefficient for maize kernels dried in a thin layer

    NASA Astrophysics Data System (ADS)

    Kujawa, Sebastian; Weres, Jerzy; Olek, Wiesław

    2016-07-01

    Uncertainties in mathematical modelling of water transport in cereal grain kernels during drying and storage are mainly due to implementing unreliable values of the water diffusion coefficient and simplifying the geometry of kernels. In the present study an attempt was made to reduce the uncertainties by developing a method for computer-aided identification of the water diffusion coefficient and more accurate 3D geometry modelling for individual kernels using original inverse finite element algorithms. The approach was exemplified by identifying the water diffusion coefficient for maize kernels subjected to drying. On the basis of the developed method, values of the water diffusion coefficient were estimated, 3D geometry of a maize kernel was represented by isoparametric finite elements, and the moisture content inside maize kernels dried in a thin layer was predicted. Validation of the results against experimental data showed significantly lower error values than in the case of results obtained for the water diffusion coefficient values available in the literature.

  18. Measurement of the diffusion coefficient of acetone in succinonitrile at its melting point

    NASA Technical Reports Server (NTRS)

    Chopra, M. A.; Glicksman, M. E.; Singh, N. B.

    1988-01-01

    The diffusion coefficient of acetone in liquid succinonitrile at 331.1 K was determined using the method of McBain and Dawson (1935). Only dilute mixtures of SCN-acetone were studied. The interdiffusion constant was determined to be 0.0000127 sq cm/s and was essentially independent of the acetone concentration over the range investigated (0.5 to 18 mol pct acetone).

  19. Interpretation of electron diffusion coefficient in organic and inorganic semiconductors with broad distributions of states.

    PubMed

    Bisquert, Juan

    2008-06-14

    The carrier transport properties in nanocrystalline semiconductors and organic materials play a key role for modern organic/inorganic devices such as dye-sensitized (DSC) and organic solar cells, organic and hybrid light-emitting diodes (OLEDs), organic field-effect transistors, and electrochemical sensors and displays. Carrier transport in these materials usually occurs by transitions in a broad distribution of localized states. As a result the transport is dominated by thermal activation to a band of extended states (multiple trapping), or if these do not exist, by hopping via localized states. We provide a general view of the physical interpretation of the variations of carrier transport coefficients (diffusion coefficient and mobility) with respect to the carrier concentration, or Fermi level, examining in detail models for carrier transport in nanocrystalline semiconductors and organic materials with the following distributions: single and two-level systems, exponential and Gaussian density of states. We treat both the multiple trapping models and the hopping model in the transport energy approximation. The analysis is simplified by thermodynamic properties: the chemical capacitance, C(mu), and the thermodynamic factor, chi(n), that allow us to derive many properties of the chemical diffusion coefficient, D(n), used in Fick's law. The formulation of the generalized Einstein relation for the mobility to diffusion ratio shows that the carrier mobility is proportional to the jump diffusion coefficient, D(J), that is derived from single particle random walk. Characteristic experimental data for nanocrystalline TiO(2) in DSC and electrochemically doped conducting polymers are discussed in the light of these models.

  20. Method for Calculating the Optical Diffuse Reflection Coefficient for the Ocular Fundus

    NASA Astrophysics Data System (ADS)

    Lisenko, S. A.; Kugeiko, M. M.

    2016-07-01

    We have developed a method for calculating the optical diffuse reflection coefficient for the ocular fundus, taking into account multiple scattering of light in its layers (retina, epithelium, choroid) and multiple refl ection of light between layers. The method is based on the formulas for optical "combination" of the layers of the medium, in which the optical parameters of the layers (absorption and scattering coefficients) are replaced by some effective values, different for cases of directional and diffuse illumination of the layer. Coefficients relating the effective optical parameters of the layers and the actual values were established based on the results of a Monte Carlo numerical simulation of radiation transport in the medium. We estimate the uncertainties in retrieval of the structural and morphological parameters for the fundus from its diffuse reflectance spectrum using our method. We show that the simulated spectra correspond to the experimental data and that the estimates of the fundus parameters obtained as a result of solving the inverse problem are reasonable.

  1. Diffuse reflectance spectroscopy as a tool to measure the absorption coefficient in skin: system calibration.

    PubMed

    Karsten, A E; Singh, A; Karsten, P A; Braun, M W H

    2013-02-01

    An individualised laser skin treatment may enhance the treatment and reduces risks and side-effects. The optical properties (absorption and scattering coefficients) are important parameters in the propagation of laser light in skin tissue. The differences in the melanin content of different skin phototypes influence the absorption of the light. The absorption coefficient at the treatment wavelength for an individual can be determined by diffuse reflectance spectroscopy, using a probe containing seven fibres. Six of the fibres deliver the light to the measurement site and the central fibre collects the diffused reflected light. This is an in vivo technique, offering benefits for near-real-time results. Such a probe, with an effective wavelength band from 450 to 800 nm, was used to calibrate skin-simulating phantoms consisting of intralipid and ink. The calibration constants were used to calculate the absorption coefficients from the diffuse reflectance measurements of three volunteers (skin phototypes, II, IV and V) for sun-exposed and non-exposed areas on the arm.

  2. The effect of diffuser angle on the discharge coefficient of a miniature critical nozzle

    NASA Astrophysics Data System (ADS)

    Kim, Jae Hyung; Kim, Heuy Dong; Setoguchi, Toshiaki

    2010-06-01

    Many researches on critical nozzles have been performed to accurately measure the mass flow rate of gas flow, and to standardize the performance as a flow meter. Recently, much interest is being paid on the measurement of very small mass flow rate in industry fields such as MEMS applications. However, the design and performance data of the critical nozzles obtained so far have been applied mainly to the critical nozzles with comparatively large diameters, and the works available on miniature critical nozzles are lacking. In the present study, a computational fluid dynamics method has been applied to investigate the influence of the diffuser angle on discharge coefficient of the miniature critical nozzles. In computations, the throat diameter of critical nozzle is varied from 0.2 mm to 5.0 mm and the diffuser angle is changed from 2 deg to 8 deg. The computational results are validated with some experimental data available. The results show that the present computational results predict appropriately the discharge coefficient of the gas flows through miniature critical nozzles. It is known that the discharge coefficient is considerably influenced by the diffuser angle, as the throat diameter of nozzle becomes small below a certain value. This implies that the miniature critical nozzles should be carefully designed.

  3. Empirical correlations between the arrhenius' parameters of impurities' diffusion coefficients in CdTe crystals

    SciTech Connect

    Shcherbak, L.; Kopach, O.; Fochuk, P.; James, R. B.; Bolotnikov, A. E.

    2015-01-21

    Understanding of self- and dopant-diffusion in semiconductor devices is essential to our being able to assure the formation of well-defined doped regions. In this paper, we compare obtained in the literature up to date the Arrhenius’ parameters (D=D0exp(–ΔEa/kT)) of point-defect diffusion coefficients and the I-VII groups impurities in CdTe crystals and films. We found that in the diffusion process there was a linear dependence between the pre-exponential factor, D0, and the activation energy, ΔEa, of different species: This was evident in the self-diffusivity and isovalent impurity Hg diffusivity as well as for the dominant IIIA and IVA groups impurities and Chlorine, except for the fast diffusing elements (e.g., Cu and Ag), chalcogens O, S, and Se, halogens I and Br as well as the transit impurities Mn, Co, Fe. As a result, reasons of the lack of correspondence of the data to compensative dependence are discussed.

  4. Empirical correlations between the arrhenius' parameters of impurities' diffusion coefficients in CdTe crystals

    DOE PAGES

    Shcherbak, L.; Kopach, O.; Fochuk, P.; ...

    2015-01-21

    Understanding of self- and dopant-diffusion in semiconductor devices is essential to our being able to assure the formation of well-defined doped regions. In this paper, we compare obtained in the literature up to date the Arrhenius’ parameters (D=D0exp(–ΔEa/kT)) of point-defect diffusion coefficients and the I-VII groups impurities in CdTe crystals and films. We found that in the diffusion process there was a linear dependence between the pre-exponential factor, D0, and the activation energy, ΔEa, of different species: This was evident in the self-diffusivity and isovalent impurity Hg diffusivity as well as for the dominant IIIA and IVA groups impurities andmore » Chlorine, except for the fast diffusing elements (e.g., Cu and Ag), chalcogens O, S, and Se, halogens I and Br as well as the transit impurities Mn, Co, Fe. As a result, reasons of the lack of correspondence of the data to compensative dependence are discussed.« less

  5. Analyzing signal attenuation in PFG anomalous diffusion via a modified Gaussian phase distribution approximation based on fractal derivative model

    NASA Astrophysics Data System (ADS)

    Lin, Guoxing

    2017-02-01

    Pulsed field gradient (PFG) technique is a noninvasive tool, and has been increasingly employed to study anomalous diffusions in Nuclear Magnetic Resonance (NMR) and Magnetic Resonance Imaging (MRI). However, the analysis of PFG anomalous diffusion is much more complicated than normal diffusion. In this paper, a fractal derivative model based modified Gaussian phase distribution method is proposed to describe PFG anomalous diffusion. By using the phase distribution obtained from the effective phase shift diffusion method based on fractal derivatives, and employing some of the traditional Gaussian phase distribution approximation techniques, a general signal attenuation expression for free fractional diffusion is derived. This expression describes a stretched exponential function based attenuation, which is distinct from both the exponential attenuation for normal diffusion obtained from conventional Gaussian phase distribution approximation, and the Mittag-Leffler function based attenuation for anomalous diffusion obtained from fractional derivative. The obtained signal attenuation expression can analyze the finite gradient pulse width (FGPW) effect. Additionally, it can generally be applied to all three types of PFG fractional diffusions classified based on time derivative order α and space derivative order β. These three types of fractional diffusions include time-fractional diffusion with { 0 < α ≤ 2 , β = 2 } , space-fractional diffusion with { α = 1 , 0 < β ≤ 2 } , and general fractional diffusion with { 0 < α , β ≤ 2 } . The results in this paper are consistent with reported results based on effective phase shift diffusion equation method and instantaneous signal attenuation method. This method provides a new, convenient approximation formalism for analyzing PFG anomalous diffusion experiments. The expression that can simultaneously interpret general fractional diffusion and FGPW effect could be especially important in PFG MRI, where the narrow

  6. In Situ Effective Diffusion Coefficient Profiles in Live Biofilms Using Pulsed-Field Gradient Nuclear Magnetic Resonance

    SciTech Connect

    Renslow, Ryan S.; Majors, Paul D.; McLean, Jeffrey S.; Fredrickson, Jim K.; Ahmed, B.; Beyenal, Haluk

    2010-08-15

    Diffusive mass transfer in biofilms is characterized by the effective diffusion coefficient. It is well-documented that the effective diffusion coefficient can vary by location in a biofilm. The current literature is dominated by effective diffusion coefficient measurements for distinct cell clusters and stratified biofilms showing this spatial variation. Regardless of whether distinct cell clusters or surface-averaging methods are used, position-dependent measurements of the effective diffusion coefficient are currently: 1) invasive to the biofilm, 2) performed under unnatural conditions, 3) lethal to cells, and/or 4) spatially restricted to only certain regions of the biofilm. Invasive measurements can lead to inaccurate results and prohibit further (time dependent) measurements which are important for the mathematical modeling of biofilms. In this study our goals were to: 1) measure the effective diffusion coefficient for water in live biofilms, 2) monitor how the effective diffusion coefficient changes over time under growth conditions, and 3) correlate the effective diffusion coefficient with depth in the biofilm. We measured in situ two-dimensional effective diffusion coefficient maps within Shewanella oneidensis MR-1biofilms using pulsed-field gradient nuclear magnetic resonance methods, and used them to calculate surface-averaged relative effective diffusion coefficient (Drs) profiles. We found that 1) Drs decreased from the top of the biofilm to the bottom, 2) Drs profiles differed for biofilms of different ages, 3) Drs profiles changed over time and generally decreased with time, 4) all the biofilms showed very similar Drs profiles near the top of the biofilm, and 5) the Drs profile near the bottom of the biofilm was different for each biofilm. Practically, our results demonstrate that advanced biofilm models should use a variable effective diffusivity which changes with time and location in the biofilm.

  7. Mass dependence of the Soret coefficient for atomic diffusion in condensed matter.

    PubMed

    Yu, Wei-Feng; Lin, Zheng-Zhe; Ning, Xi-Jing

    2013-06-01

    Particle diffusion in condensed matters driven by thermal gradient, the so-called Ludwig-Soret effect, has been investigated for about 160 years, but up to the present, seldom do theories on atomic level understand a series of puzzles in relevant experiments. In this work, we derived an expression of Soret coefficient for atomic diffusion in condensed matter from a single atom statistic model with relevant parameters expressed in terms of atomic mass and the potential profile felt by the guest atom without empirical parameters. The reality of the model was strictly tested by molecular dynamics simulations, especially the result for He atom diffusing on graphene sheet, which suggests the Soret effect may be used to separate (3)He from (4)He.

  8. Molecular dynamics calculation of rotational diffusion coefficient of a carbon nanotube in fluid

    NASA Astrophysics Data System (ADS)

    Cao, Bing-Yang; Dong, Ruo-Yu

    2014-01-01

    Rotational diffusion processes are correlated with nanoparticle visualization and manipulation techniques, widely used in nanocomposites, nanofluids, bioscience, and so on. However, a systematical methodology of deriving this diffusivity is still lacking. In the current work, three molecular dynamics (MD) schemes, including equilibrium (Green-Kubo formula and Einstein relation) and nonequilibrium (Einstein-Smoluchowski relation) methods, are developed to calculate the rotational diffusion coefficient, taking a single rigid carbon nanotube in fluid argon as a case. We can conclude that the three methods produce same results on the basis of plenty of data with variation of the calculation parameters (tube length, diameter, fluid temperature, density, and viscosity), indicative of the validity and accuracy of the MD simulations. However, these results have a non-negligible deviation from the theoretical predictions of Tirado et al. [J. Chem. Phys. 81, 2047 (1984)], which may come from several unrevealed factors of the theory. The three MD methods proposed in this paper can also be applied to other situations of calculating rotational diffusion coefficient.

  9. Sandwich mixer-reactor: influence of the diffusion coefficient and flow rate ratios.

    PubMed

    Abonnenc, Mélanie; Josserand, Jacques; Girault, Hubert H

    2009-02-07

    A sandwich mixer consists of mixing two solutions in a channel, one central laminar flow being sandwiched between two outer flow solutions. The present numerical study considers the convection-diffusion of two reacting species A and B, provided respectively by the two incoming solutions. The simulations show how the diffusion coefficient, flow rate and species concentration ratios influence, via the transversal diffusion length and reaction kinetics, the reaction extent at the end of the sandwich mixer. First, this extent can be enhanced up to 60% if the species with the lowest diffusion coefficient is located in the outer solutions where the flow velocity is small compared to that of the central part (higher residence time). Secondly, decreasing the outer flow rates (to confine the reaction close to the walls) and increasing the local concentration to keep the same flux ratio improve the extent by 300%. Comparison with a bi-lamination passive mixer, with an ideal mixer and an electro-osmotic driven flow mixer is presented. These conclusions are also demonstrated for consecutive reactions, showing an amplification of the effects described above. The results are also presented versus the residence time in the mixer-reactor to show the time window for which the gain is appreciable.

  10. Minority carrier diffusion lengths and absorption coefficients in silicon sheet material

    NASA Technical Reports Server (NTRS)

    Dumas, K. A.; Swimm, R. T.

    1980-01-01

    Most of the methods which have been developed for the measurement of the minority carrier diffusion length of silicon wafers require that the material have either a Schottky or an ohmic contact. The surface photovoltage (SPV) technique is an exception. The SPV technique could, therefore, become a valuable diagnostic tool in connection with current efforts to develop low-cost processes for the production of solar cells. The technique depends on a knowledge of the optical absorption coefficient. The considered investigation is concerned with a reevaluation of the absorption coefficient as a function of silicon processing. A comparison of absorption coefficient values showed these values to be relatively consistent from sample to sample, and independent of the sample growth method.

  11. Applicable apparent diffusion coefficient of an orthotopic mouse model of gastric cancer by improved clinical MRI diffusion weighted imaging

    PubMed Central

    Sun, Jia; Zhang, Xiao-Peng; Li, Xiao-Ting; Tang, Lei; Cui, Yong; Zhang, Xiao-Yan; Sun, Ying-Shi

    2014-01-01

    In vivo imaging studies in animal models are hindered by variables that contribute to poor image quality and measurement reliability. As such we sought to improve the diffusion coefficient (ADC) of an orthotopic mouse model of gastric cancer in diffusion-weighted images (DWI) using alginate moulding and Ultrasonic coupling medium. BGC-823 human gastric cancer cells were subcutaneously injected into the abdomen of nude mice and 1 mm3 primary tumour was orthotopically transplanted. Alginate and coupling medium were applied to the mice and MRI (T2 and DWI) was performed for 6 weeks. Regions of interest (ROI) were drawn and liver and tumour ADC were evaluated. Using alginate moulding, the mean quality total score of DW imaging was 8.53; however, in control animals this value was 5.20 (p < 0.001). The coefficient of variation of ADC of liver in experimental and control groups were 0.071 and 0.270 (p < 0.001), respectively, suggesting this method may be helpful for DWI studies of important human diseases such as gastric cancer. PMID:25123166

  12. Calibration of a turbidity meter for making estimates of total suspended solids concentrations and beam attenuation coefficients in field experiments

    NASA Technical Reports Server (NTRS)

    Usry, J. W.; Whitlock, C. H.

    1981-01-01

    Management of water resources such as a reservoir requires using analytical models which describe such parameters as the suspended sediment field. To select or develop an appropriate model requires making many measurements to describe the distribution of this parameter in the water column. One potential method for making those measurements expeditiously is to measure light transmission or turbidity and relate that parameter to total suspended solids concentrations. An instrument which may be used for this purpose was calibrated by generating curves of transmission measurements plotted against measured values of total suspended solids concentrations and beam attenuation coefficients. Results of these experiments indicate that field measurements made with this instrument using curves generated in this study should correlate with total suspended solids concentrations and beam attenuation coefficients in the water column within 20 percent.

  13. Development of a cryogenic FTIR system for measuring very small attenuation coefficients of infrared materials

    NASA Astrophysics Data System (ADS)

    Kaji, Sayumi; Sarugaku, Yuki; Ikeda, Yuji; Nakanishi, Kenshi; Kobayashi, Naoto; Kondo, Sohei; Arasaki, Takayuki; Kawakita, Hideyo

    2016-07-01

    We have been working on a long-term project for developing a variety of infrared immersion gratings for near- to mid-infrared wavelengths. The transmittance of material is essential to realize high-efficiency immersion gratings for astronomical applications. For a typical grating, the attenuation coefficient αatt must be <0.01 cm-1 for the absolute diffraction efficiency of >70%. However, as there are few reports of αatt < 0.01 cm-1 for infrared optical materials in the literatures, we performed high-accuracy measurements of αatt for a variety of infrared materials applicable to immersion gratings. We have already reported αatt at room temperature for single-crystal Si, single-crystal Ge, CVD-ZnS, CVDZnSe, and high-resistivity single-crystal CdZnTe (Ikeda et al. 2009[7], Kaji et al. 2014[10], and Sarugaku et al. 2016[9]). Next, we proceeded with the measurements of αatt at cryogenic temperatures of 20-80 K range, which is the typical operational temperatures of infrared instruments, and for which the shifts of the band gap and/or the sharpness of the lattice absorption lines from the corresponding room temperature values are expected. Thus, we developed a new cryogenic FTIR system that enables high-accuracy measurements at cryogenic temperatures. The system has a mechanism with which two sample cells and a reference cell can be easily and quickly switched without any vacuum leak or temperature change. Our preliminary measurement of Ge using this cryogenic FTIR system found that both the cut-on and cut-off wavelengths shift to the shorter (from 2.0 to 1.7 μm) and longer (from 10.6 to 10.9 μm) wavelengths, respectively, when the temperature is decreased from room temperature to the cryogenic temperature (<28 K). We plan to complete cryogenic measurements for a variety of infrared materials by the end of 2016.

  14. Characterization of dopant diffusion within semiconducting polymer and small-molecule films using infrared-active vibrational modes and attenuated total reflectance infrared spectroscopy.

    PubMed

    Maliakal, Ashok J

    2013-09-11

    Understanding dopant diffusion within organic and polymeric semiconductors is of great importance toward the development of organic photovoltaic and electronic devices, many of which require layered structures with controlled doping profiles (e.g., p-n and p-i-n structures). The current paper demonstrates a new method to determine the diffusion and permeability coefficients for dopant diffusion within polymeric and small-molecule organic semiconductors using attenuated total reflectance infrared (ATR-IR) spectroscopy and taking advantage of the intense IR-active vibrational bands created when dopants such as iodine accept charge from a semiconducting polymer to generate polaronic species. The diffusion and permeability coefficients for iodine within poly(3-hexylthiophene) (P3HT) are determined to be 2.5×10(-11)±1.2×10(-11) cm2/s and 2.4×10(-8)±1.2×10(-8) cm2/s·atm, respectively. The approach is applied to P3HT/PCBM (1:1 mass ratio) films, and the diffusion and permeability coefficients through these composite films are determined to be 7.8×10(-11)±2.8×10(-11) cm2/s and 4.8×10(-8)±1.3×10(-8) cm2/s·atm, respectively. Finally, the approach is extended to determining iodine diffusion within the polycrystalline semiconductor tetraphenylporphyrin (TPP) in a bilayer film with P3HT, and the diffusion coefficient of iodine through TPP is determined to be 7.1×10(-14)±1.1×10(-14) cm2/s. Although the current paper determines diffusion and permeability for the dopant iodine, this approach should be applicable to a wide array of dopants and polymeric and small-molecule semiconductors of interest in photovoltaic and electronic applications.

  15. Determination of Diffusion Coefficients in Cement-Based Materials: An Inverse Problem for the Nernst-Planck and Poisson Models

    NASA Astrophysics Data System (ADS)

    Szyszkiewicz-Warzecha, Krzysztof; Jasielec, Jerzy J.; Fausek, Janusz; Filipek, Robert

    2016-08-01

    Transport properties of ions have significant impact on the possibility of rebars corrosion thus the knowledge of a diffusion coefficient is important for reinforced concrete durability. Numerous tests for the determination of diffusion coefficients have been proposed but analysis of some of these tests show that they are too simplistic or even not valid. Hence, more rigorous models to calculate the coefficients should be employed. Here we propose the Nernst-Planck and Poisson equations, which take into account the concentration and electric potential field. Based on this model a special inverse method is presented for determination of a chloride diffusion coefficient. It requires the measurement of concentration profiles or flux on the boundary and solution of the NPP model to define the goal function. Finding the global minimum is equivalent to the determination of diffusion coefficients. Typical examples of the application of the presented method are given.

  16. Anisotropie des coefficients de diffusion dans des cristaux liquides discotiques hexagonaux

    NASA Astrophysics Data System (ADS)

    Daoud, M.; Gharbia, M.; Gharbi, A.

    1994-06-01

    The diffusion constants of dyes in several hexagonal discotic liquid crystals are measured and discussed. For all the liquid crystals studied, these constants are anisotropic : the diffusion in the direction parallel to the columns is faster than that in the perpendicular plane (frac{D_allel}{D_perp}>1). The effects of the length and shape of the chains bound to the triphenylene discs are shown. The effect of the dye molecular size is also described. The study of the diffusion coefficients of hexapentoxytriphenylene (C5HET) as a function of temperature has shown that the activation energies along the columns and perpendicular to the columns are comparable. The main features of dye diffusion in the hexagonal columnar liquid crystals studied are similar to those reported in nematic phases. Les mesures des constantes de diffusion de colorants dans plusieurs cristaux liquides discotiques hexagonaux sont présentées et discutées. Pour tous les cristaux liquides étudiés, ces constantes présentent une anisotropie, avec une diffusion plus rapide parallèlement aux colonnes que perpendiculairement à celles-ci (frac{D_allel}{D_perp}>1). Des effets de longueur et de forme des chaînes branchées sur les disques de triphénylène sont mis en évidence. Il en est de même pour la taille des molécules de colorants. L'étude en fonction de la température a montré que dans le cas de l'hexapentoxytriphénylène (C5HET), les énergies d'activation dans les directions parallèle et perpendiculaire aux colonnes sont comparables. Les caractéristiques de la diffusion de colorants dans les cristaux liquides colonnaires hexagonaux étudiés sont semblables à celles des nématiques.

  17. Electrochemical methods for the determination of the diffusion coefficient of ionophores and ionophore-ion complexes in plasticized PVC membranes.

    PubMed

    Bodor, Sándor; Zook, Justin M; Lindner, Erno; Tóth, Klára; Gyurcsányi, Róbert E

    2008-05-01

    The diffusion coefficients of active components in ion-selective membranes have a decisive influence on the life-time and detection limit of the respective ion-selective electrodes, as well as influencing the rate of polarization and relaxation processes of electrically perturbed ion sensors. Therefore, the rational design of mass transport controlled ion-selective electrodes with sub-nanomolar detection limits requires reliable data on the diffusion coefficients. We have implemented electrochemical methods for the quantitative assessment of both the diffusion coefficients of free ionophores and ion-ionophore complexes. The diffusion coefficients of the pH-sensitive chromoionophore ETH 5294 and the calcium-selective ionophore ETH 5234 were determined in plasticized PVC membranes with different PVC to plasticizer ratios. The diffusion coefficient of the free chromoionophore determined by a chronoamperometric method was validated with optical methods for a variety of membrane compositions. The calcium-selective ionophore ETH 5234 was used as a model compound to assess the diffusion coefficient of the ion-ionophore complex calculated from the time required for the complexes to cross a freshly prepared membrane during potentiometric ion-breakthrough experiments. The difference between the diffusion coefficients of the free ionophore ETH 5234 and the ion-ionophore complex was found to be significant and correlated well with the geometry of the respective species.

  18. Determination of Krypton Diffusion Coefficients in Uranium Dioxide Using Atomic Scale Calculations.

    PubMed

    Vathonne, Emerson; Andersson, David A; Freyss, Michel; Perriot, Romain; Cooper, Michael W D; Stanek, Christopher R; Bertolus, Marjorie

    2017-01-03

    We present a study of the diffusion of krypton in UO2 using atomic scale calculations combined with diffusion models adapted to the system studied. The migration barriers of the elementary mechanisms for interstitial or vacancy assisted migration are calculated in the DFT+U framework using the nudged elastic band method. The attempt frequencies are obtained from the phonon modes of the defect at the initial and saddle points using empirical potential methods. The diffusion coefficients of Kr in UO2 are then calculated by combining this data with diffusion models accounting for the concentration of vacancies and the interaction of vacancies with Kr atoms. We determined the preferred mechanism for Kr migration and the corresponding diffusion coefficient as a function of the oxygen chemical potential μO or nonstoichiometry. For very hypostoichiometric (or U-rich) conditions, the most favorable mechanism is interstitial migration. For hypostoichiometric UO2, migration is assisted by the bound Schottky defect and the charged uranium vacancy, VU(4-). Around stoichiometry, migration assisted by the charged uranium-oxygen divacancy (VUO(2-)) and VU(4-) is the favored mechanism. Finally, for hyperstoichiometric or O-rich conditions, the migration assisted by two VU(4-) dominates. Kr migration is enhanced at higher μO, and in this regime, the activation energy will be between 4.09 and 0.73 eV depending on nonstoichiometry. The experimental values available are in the latter interval. Since it is very probable that these values were obtained for at least slightly hyperstoichiometric samples, our activation energies are consistent with the experimental data, even if further experiments with precisely controlled stoichiometry are needed to confirm these results. The mechanisms and trends with nonstoichiometry established for Kr are similar to those found in previous studies of Xe.

  19. Evolution of the Magnetic Field Line Diffusion Coefficient and Non-Gaussian Statistics

    NASA Astrophysics Data System (ADS)

    Snodin, A. P.; Ruffolo, D.; Matthaeus, W. H.

    2016-08-01

    The magnetic field line random walk (FLRW) plays an important role in the transport of energy and particles in turbulent plasmas. For magnetic fluctuations that are transverse or almost transverse to a large-scale mean magnetic field, theories describing the FLRW usually predict asymptotic diffusion of magnetic field lines perpendicular to the mean field. Such theories often depend on the assumption that one can relate the Lagrangian and Eulerian statistics of the magnetic field via Corrsin’s hypothesis, and additionally take the distribution of magnetic field line displacements to be Gaussian. Here we take an ordinary differential equation (ODE) model with these underlying assumptions and test how well it describes the evolution of the magnetic field line diffusion coefficient in 2D+slab magnetic turbulence, by comparisons to computer simulations that do not involve such assumptions. In addition, we directly test the accuracy of the Corrsin approximation to the Lagrangian correlation. Over much of the studied parameter space we find that the ODE model is in fairly good agreement with computer simulations, in terms of both the evolution and asymptotic values of the diffusion coefficient. When there is poor agreement, we show that this can be largely attributed to the failure of Corrsin’s hypothesis rather than the assumption of Gaussian statistics of field line displacements. The degree of non-Gaussianity, which we measure in terms of the kurtosis, appears to be an indicator of how well Corrsin’s approximation works.

  20. Study on the diffusion coefficients for ammonia nitrogen and nitrite and nitrate in PVA gels.

    PubMed

    Yang, Hong; Guan, Qingkun

    2016-10-01

    In order to quantify the proliferation of polyvinyl alcohol (PVA) gels in a matrix and optimize the performance of mass transfer, activated carbon (AC) and CaCO3 were selected as adding materials in this experiment. For the performance of mass transfer, the optimal conditions were analyzed using response surface method (RSM) considering the inter-correlated effects of the amount of AC and CaCO3. For RSM, 13 trials resulted in a partial cubic polynomial equation, which best predicted the amount of residual debris after homogenization. The results of the study show that the effective diffusion coefficient test device can analysis the diffusion rate nitrogen, nitrite and nitrate within the PVA gels quantitatively; adding appropriate amounts of AC and CaCO3 in the biological active filter can improve the performance of mass transfer effectively; the maximum effective diffusion coefficient of nitrogen and nitrite and nitrate in the packing were 1.3637 × 10(-9) and 1.0850 × 10(-9) and 1.0199 × 10(-9) m(2)/s, respectively, at optimal addition amount.

  1. Measurement of Retinalamin diffusion coefficient in human sclera by optical spectroscopy

    NASA Astrophysics Data System (ADS)

    Genina, Elina A.; Bashkatov, Alexey N.; Zubkova, Elena A.; Kamenskikh, Tatiana G.; Tuchin, Valery V.

    2008-12-01

    The use of cytomedines (such as Retinalamin) in clinical practice has shown high effectiveness of the medicaments in ophthalmology. The study of diffusion of Retinalamin in scleral tissue is important for estimation of a drug dose delivered into inner tissue of eye, time of drug action, etc. In vitro measurements of spectral reflectance of sclera interacting with aqueous solution of Retinalamin have been carried out. Ten human sclera samples were included in the study. The results of the experiments have shown that penetration of Retinalamin into scleral tissue leads to the decrease of scleral reflectance due to optical immersion. Estimation of diffusion coefficient of studied solution has been made on the basis of analysis of optical reflectance dynamics of the sclera samples. The diffusion coefficient of Retinalamin in human scleral tissue was evaluated as (1.82±0.14)×10 -6 cm 2/s. The results are important for treatment of partial optic atrophy observed at primary open-angle glaucoma and others eye diseases.

  2. Electric and magnetic radial diffusion coefficients using the Van Allen probes data

    NASA Astrophysics Data System (ADS)

    Ali, Ashar F.; Malaspina, David M.; Elkington, Scot R.; Jaynes, Allison N.; Chan, Anthony A.; Wygant, John; Kletzing, Craig A.

    2016-10-01

    ULF waves are a common occurrence in the inner magnetosphere and they contribute to particle motion, significantly, at times. We used the magnetic and the electric field data from the Electric and Magnetic Field Instrument Suite and Integrated Sciences (EMFISIS) and the Electric Field and Waves instruments (EFW) on board the Van Allen Probes to estimate the ULF wave power in the compressional component of the magnetic field and the azimuthal component of the electric field, respectively. Using L∗, Kp, and magnetic local time (MLT) as parameters, we conclude that the noon sector contains higher ULF Pc-5 wave power compared with the other MLT sectors. The dawn, dusk, and midnight sectors have no statistically significant difference between them. The drift-averaged power spectral densities are used to derive the magnetic and the electric component of the radial diffusion coefficient. Both components exhibit little to no energy dependence, resulting in simple analytic models for both components. More importantly, the electric component is larger than the magnetic component by one to two orders of magnitude for almost all L∗ and Kp; thus, the electric field perturbations are more effective in driving radial diffusion of charged particles in the inner magnetosphere. We also present a comparison of the Van Allen Probes radial diffusion coefficients, including the error estimates, with some of the previous published results. This allows us to gauge the large amount of uncertainty present in such estimates.

  3. Three FORTRAN programs for finite-difference solutions to binary diffusion in one and two phases with composition-and time-dependent diffusion coefficients

    USGS Publications Warehouse

    Sanford, R.F.

    1982-01-01

    Geological examples of binary diffusion are numerous. They are potential indicators of the duration and rates of geological processes. Analytical solutions to the diffusion equations generally do not allow for variable diffusion coefficients, changing boundary conditions, and impingement of diffusion fields. The three programs presented here are based on Crank-Nicholson finite-difference approximations, which can take into account these complicating factors. Program 1 describes the diffusion of a component into an initially homogeneous phase that has a constant surface composition. Specifically it is written for Fe-Mg exchange in olivine at oxygen fugacities appropriate for the lunar crust, but other components, phases, or fugacities may be substituted by changing the values of the diffusion coefficient. Program 2 simulates the growth of exsolution lamellae. Program 3 describes the growth of reaction rims. These two programs are written for pseudobinary Ca-(Mg, Fe) exchange in pyroxenes. In all three programs, the diffusion coefficients and boundary conditions can be varied systematically with time. To enable users to employ widely different numerical values for diffusion coefficients and diffusion distance, the grid spacing in the space dimension and the increment by which the grid spacing in the time dimension is increased at each time step are input constants that can be varied each time the programs are run to yield a solution of the desired accuracy. ?? 1982.

  4. Consequences of using nonlinear particle trajectories to compute spatial diffusion coefficients. [for cosmic ray propagation in interstellar and interplanetary space

    NASA Technical Reports Server (NTRS)

    Goldstein, M. L.

    1977-01-01

    In a study of cosmic ray propagation in interstellar and interplanetary space, a perturbed orbit resonant scattering theory for pitch angle diffusion in a slab model of magnetostatic turbulence is slightly generalized and used to compute the diffusion coefficient for spatial propagation parallel to the mean magnetic field. This diffusion coefficient has been useful for describing the solar modulation of the galactic cosmic rays, and for explaining the diffusive phase in solar flares in which the initial anisotropy of the particle distribution decays to isotropy.

  5. Influence of the scattering and absorption coefficients on homogeneous room simulations that use a diffusion equation model.

    PubMed

    Navarro, Juan M; Escolano, José; Cobos, Maximo; López, José J

    2013-03-01

    The diffusion equation model was used for room acoustic simulations to predict the sound pressure level and the reverberation time. The technical literature states that the diffusion equation method accurately models the late portion of the room impulse response if the energy is sufficiently scattered. This work provides conclusions on the validity of the diffusion equation model for rooms with homogeneous dimensions in relation to the scattering coefficients of the boundaries. A systematic evaluation was conducted out to determine the ranges of the absorption and scattering coefficient values that result in low noticeable differences between the predictions from a geometrical acoustic model and those from the diffusion equation model.

  6. Donnan dialysis with ion-exchange membranes. 3: Diffusion coefficients using ions of different valence

    SciTech Connect

    Miyoshi, Hirofumi

    1999-01-01

    Donnan dialysis with ion-exchange membranes was studied under various kinds of experimental conditions using ions of different valences. The diffusion coefficients (D{sub d}) of various kinds of ions in the ion-exchange membrane were obtained by curve fitting an equation derived from the mass balance to three kinds of Donnan dialytic experiments. It was found that the value of D{sub d}/D{sub s} using D{sub d} of monovalent ions in Donnan dialysis with a set of monovalent feed ions and bivalent driving ions was 1/175, where D{sub s} represents a diffusion coefficient in solution. D{sub s} was calculated from the Nernst-Einstein equation substituted by the ionic conductance of ions at infinite dilution in water. Using D{sub d} of bivalent ions in Donnan dialysis with the same set led to a D{sub d}/D{sub s} value of 1/438. Moreover, using D{sub d} in Donnan dialysis with the same set, the value of D{sub d}/D{sub e} was kept constant at 0.4 (D{sub e} expresses the diffusion coefficient in the membrane when the valences of the feed and driving ions are equal). On the other hand, both D{sub d}/D{sub s} and D{sub d}/D{sub e} using D{sub d} in Donnan dialysis with a set of bivalent feed ions and monovalent driving ions were not constant.

  7. Collisional relaxation in the inhomogeneous Hamiltonian mean-field model: Diffusion coefficients

    NASA Astrophysics Data System (ADS)

    Benetti, F. P. C.; Marcos, B.

    2017-02-01

    Systems of particles with long-range interactions present two important processes: first, the formation of out-of-equilibrium quasistationary states (QSS) and, second, the collisional relaxation towards Maxwell-Boltzmann equilibrium in a much longer time scale. In this paper, we study the collisional relaxation in the Hamiltonian mean-field model using the appropriate kinetic equations for a system of N particles at order 1 /N : the Landau equation when collective effects are neglected and the Lenard-Balescu equation when they are taken into account. We derive explicit expressions for the diffusion coefficients using both equations for any magnetization, and we obtain analytic expressions for highly clustered configurations. An important conclusion is that in this system collective effects are crucial in order to describe the relaxation dynamics. We compare the diffusion calculated with the kinetic equations with simulations set up to simulate the system with or without collective effects, obtaining a very good agreement between theory and simulations.

  8. A fast collocation method for a variable-coefficient nonlocal diffusion model

    NASA Astrophysics Data System (ADS)

    Wang, Che; Wang, Hong

    2017-02-01

    We develop a fast collocation scheme for a variable-coefficient nonlocal diffusion model, for which a numerical discretization would yield a dense stiffness matrix. The development of the fast method is achieved by carefully handling the variable coefficients appearing inside the singular integral operator and exploiting the structure of the dense stiffness matrix. The resulting fast method reduces the computational work from O (N3) required by a commonly used direct solver to O (Nlog ⁡ N) per iteration and the memory requirement from O (N2) to O (N). Furthermore, the fast method reduces the computational work of assembling the stiffness matrix from O (N2) to O (N). Numerical results are presented to show the utility of the fast method.

  9. Interdiffusion in Ni-rich, Ni-Cr-Al alloys at 1100 and 1200 C. I - Diffusion paths and microstructures. II - Diffusion coefficients and predicted concentration profiles

    NASA Technical Reports Server (NTRS)

    Nesbitt, J. A.; Heckel, R. W.

    1987-01-01

    Interdiffusion in Ni-rich Ni-Cr-Al alloys is investigated experimentally after annealing at 1100 and 1200 C using gamma/gamma, gamma/gamma+beta, gamma/gamma+gamma prime, and gamma/gamma+alpha diffusion couples. The amount and location of Kirkendall porosity suggests that Al diffuses more rapidly than Cr which diffuses more rapidly than Ni in the gamma phase of Ni-Cr-Al alloys. The location and extent of maxima and minima in the concentration profiles of the diffusion couples indicate that both cross-term diffusion coefficients are positive. Measurements are also presented of the ternary interdiffusion coefficients of the gamma phase in the Ni-Cr-Al system. It is shown that the interdiffusion coefficients can be accurately predicted by using a ternary finite-difference interdiffusion model.

  10. Phospholipid Diffusion Coefficients of Cushioned Model Membranes determined via Z-Scan Fluorescence Correlation Spectroscopy

    PubMed Central

    Sterling, Sarah M.; Allgeyer, Edward S.; Fick, Jörg; Prudovsky, Igor; Mason, Michael D.; Neivandt, David J.

    2013-01-01

    Model cellular membranes enable the study of biological processes in a controlled environment and reduce the traditional challenges associated with live or fixed cell studies. However, model membrane systems based on the air/water or oil/solution interface do not allow for incorporation of transmembrane proteins, or for the study of protein transport mechanisms. Conversely, a phospholipid bilayer deposited via the Langmuir-Blodgett/Langmuir Schaefer method on a hydrogel layer is potentially an effective mimic of the cross-section of a biological membrane, and facilitates both protein incorporation and transport studies. Prior to application, however, such membranes must be fully characterized, particularly with respect to the phospholipid bilayer phase transition temperature. Here we present a detailed characterization of the phase transition temperature of the inner and outer leaflets of a chitosan supported model membrane system. Specifically, the lateral diffusion coefficient of each individual leaflet has been determined as a function of temperature. Measurements were performed utilizing z-scan fluorescence correlation spectroscopy (FCS), a technique that yields calibration-free diffusion information. Analysis via the method of Wawrezinieck and coworkers, revealed that phospholipid diffusion changes from raft-like to free diffusion as the temperature is increased; an insight into the dynamic behavior of hydrogel supported membranes not previously reported. PMID:23705855

  11. Effects of magnetic field intensity on carbon diffusion coefficient in pure iron in γ-Fe temperature region

    NASA Astrophysics Data System (ADS)

    Wu, Yan; Duan, Guosheng; Zhao, Xiang

    2015-03-01

    Effects of magnetic field intensity on carbon diffusion coefficient in pure iron in the γ-Fe temperature region were investigated using carburizing technology. The carbon penetration profiles from the iron surface to interior were measured by field emission electron probe microanalyzer. The carbon diffusion coefficient in pure iron carburized with different magnetic field intensities was calculated according to the Fick's second law. It was found that the magnetic field intensity could obviously affect the carbon diffusion coefficient in pure iron in the γ-Fe temperature region, and the carbon diffusion coefficient decreased obviously with the enhancement of magnetic field intensity, when the magnetic field intensity was higher than 1 T, the carbon diffusion coefficient in field annealed specimen was less than half of that of the nonfield annealed specimen, further enhancing the magnetic field intensity, the carbon diffusion coefficient basically remains unchanged. The stiffening of lattice due to field-induced magnetic ordering was responsible for an increase in activation barrier for jumping carbon atoms. The greater the magnetic field intensity, the stronger the inhibiting effect of magnetic field on carbon diffusion.

  12. Determination of the bulk moisture diffusion coefficient for corn starch using an automated water sorption instrument.

    PubMed

    Yu, Xin; Schmidt, Arthur R; Bello-Perez, Luis A; Schmidt, Shelly J

    2008-01-09

    The bulk moisture diffusion coefficient (Db) is an important physical parameter of food ingredients and systems. However, the traditional method of measuring Db using saturated salt solutions is very time-consuming and cumbersome. New automated water sorption instruments, which can be used to conveniently and precisely control both relative humidity and temperature, provide a faster, more robust method for collecting the data needed for determining Db. Thus, the objectives of this study were to (1) investigate the use of the DVS instrument for collecting the data needed for determining the adsorption (Dba) and desorption (Dbd) bulk moisture diffusion coefficients for dent corn starch as a function of relative humidity and (2) determine the effect of temperature on Dba for dent corn starch at a constant relative humidity. Kinetic water sorption profiles of dent corn starch were obtained at eight relative humidity values ranging from 10 to 80% at 10% intervals at 25 degrees C and at five temperatures, 15, 20, 25, 30, and 35 degrees C, at 50% relative humidity using a DVS instrument. Db was calculated from the kinetic water sorption profiles using the full solution of Fick's second law for the thin slab model, as well as the slope method, a simplification of the full model. The Dba of dent corn starch at 25 degrees C reached a maximum at intermediate relative humidity values, after which Dba decreased due to a change in the moisture diffusion mechanism from vapor to liquid diffusion. The Dbd of dent corn starch at 25 degrees C remained nearly constant as a function of relative humidity. The Dba for dent corn starch increased as temperature increased from 15 to 35 degrees C, with an activation energy of 38.85 +/- 0.433 kJ/mol.

  13. Lateral diffusivity coefficients from the dynamics of a SF6 patch in a coastal environment

    NASA Astrophysics Data System (ADS)

    Kersalé, M.; Petrenko, A. A.; Doglioli, A. M.; Nencioli, F.; Bouffard, J.; Blain, S.; Diaz, F.; Labasque, T.; Quéguiner, B.; Dekeyser, I.

    2016-01-01

    The dispersion of a patch of the tracer sulfur hexafluoride (SF6) is used to assess the lateral diffusivity in the coastal waters of the western part of the Gulf of Lion (GoL), northwestern Mediterranean Sea, during the Latex10 experiment (September 2010). Immediately after the release, the spreading of the patch is associated with a strong decrease of the SF6 concentrations due to the gas exchange from the ocean to the atmosphere. This has been accurately quantified, evidencing the impact of the strong wind conditions during the first days of this campaign. Few days after the release, as the atmospheric loss of SF6 decreased, lateral diffusivity coefficient at spatial scales of 10 km has been computed using two approaches. First, the evolution of the patch with time was combined with a diffusion-strain model to obtain estimates of the strain rate (γ = 2.5 10- 6 s- 1) and of the lateral diffusivity coefficient (Kh = 23.2 m2 s- 1). Second, a steady state model was applied, showing Kh values similar to the previous method after a period of adjustment between 2 and 4.5 days. This implies that after such period, our computation of Kh becomes insensitive to the inclusion of further straining of the patch. Analysis of sea surface temperature satellite imagery shows the presence of a strong front in the study area. The front clearly affected the dynamics within the region and thus the temporal evolution of the patch. Our results are consistent with previous studies in open ocean and demonstrate the success and feasibility of those methods also under small-scale, rapidly-evolving dynamics typical of coastal environments.

  14. Self-diffusion coefficient of water in tofu determined by pulsed field gradient nuclear magnetic resonance.

    PubMed

    Hong, Young Shick; Lee, Cherl Ho

    2006-01-11

    The self-diffusion coefficient of water in soybean protein dispersion and tofu was measured by pulsed field gradient (PFG) NMR. A soy protein isolate (SPI) dispersion (6 and 12%, w/w) in water, calcium cross-linked precipitate, and tofu were used for comparison. The self-diffusion coefficient of water (D) in the SPI dispersion, 2.23 x 10(-9) m2/s, was estimated lower than that of free water, 2.6 x 10(-9) m2/s at 25 degrees C, and decreased as the SPI concentration increased. It further decreased by the addition of calcium chloride, reflecting the obstruction effect induced by the precipitates in addition to the hydration and hydrodynamic interaction in the protein dispersion. The two water regions in tofu were interpreted by the two-site Kärger model: D1 and D2 of soft tofu were 2.26 (+/-0.11) x 10(-9) and 6.84 (+/-0.34) x 10(-11) m2/s, respectively. The relative amount of proton (water) was p1 = 0.98 and p2 = 0.02 at 100 ms of diffusion time. The self-diffusion coefficients of water decreased in pressed tofu, and their relative amounts of water changed to p1 = 0.93 and p2 = 0.07. It was suggested that D1 corresponded to obstructed water in the network structure and D2 corresponded to hydrated water on the surface layer of pores formed in the protein network of tofu. The pore sizes estimated from the diffusion length of obstructed water were 21.3 microm in soft tofu and 20.8 microm in pressed tofu. The removal of fat from pressed tofu led to a decrease in D2 from 6.26 (+/-0.31) x 10(-11) to 3.53 (+/-0.18) x 10(-11) m2/s, and the relative amount of hydrated water increased from 0.07 to 0.14, which indicated hydrophobic hydration.

  15. Compilation and evaluation of gas phase diffusion coefficients of reactive trace gases in the atmosphere: volume 1. Inorganic compounds

    NASA Astrophysics Data System (ADS)

    Tang, M. J.; Cox, R. A.; Kalberer, M.

    2014-09-01

    Diffusion of gas molecules to the surface is the first step for all gas-surface reactions. Gas phase diffusion can influence and sometimes even limit the overall rates of these reactions; however, there is no database of the gas phase diffusion coefficients of atmospheric reactive trace gases. Here we compile and evaluate, for the first time, the diffusivities (pressure-independent diffusion coefficients) of atmospheric inorganic reactive trace gases reported in the literature. The measured diffusivities are then compared with estimated values using a semi-empirical method developed by Fuller et al. (1966). The diffusivities estimated using Fuller's method are typically found to be in good agreement with the measured values within ±30%, and therefore Fuller's method can be used to estimate the diffusivities of trace gases for which experimental data are not available. The two experimental methods used in the atmospheric chemistry community to measure the gas phase diffusion coefficients are also discussed. A different version of this compilation/evaluation, which will be updated when new data become available, is uploaded online (diffusion"target="_blank">https://sites.google.com/site/mingjintang/home/diffusion).

  16. Determination of partition and diffusion coefficients of formaldehyde in selected building materials and impact of relative humidity.

    PubMed

    Xu, Jing; Zhang, Jianshun S; Liu, Xiaoyu; Gao, Zhi

    2012-06-01

    The partition and effective diffusion coefficients of formaldehyde were measured for three materials (conventional gypsum wallboard, "green" gypsum wallboard, and "green" carpet) under three relative humidity (RH) conditions (20%, 50%, and 70% RH). The "green" materials contained recycled materials and were friendly to environment. A dynamic dual-chamber test method was used. Results showed that a higher relative humidity led to a larger effective diffusion coefficient for two kinds of wallboards and carpet. The carpet was also found to be very permeable resulting in an effective diffusion coefficient at the same order of magnitude with the formaldehyde diffusion coefficient in air. The partition coefficient (K(ma)) of formaldehyde in conventional wallboard was 1.52 times larger at 50% RH than at 20% RH, whereas it decreased slightly from 50% to 70% RH, presumably due to the combined effects of water solubility of formaldehyde and micro-pore blocking by condensed moisture at the high RH level. The partition coefficient of formaldehyde increased slightly with the increase of relative humidity in "green" wallboard and "green" carpet. At the same relative humidity level, the "green" wallboard had larger partition coefficient and effective diffusion coefficient than the conventional wallboard, presumably due to the micro-pore structure differences between the two materials. The data generated could be used to assess the sorption effects of formaldehyde on building materials and to evaluate its impact on the formaldehyde concentration in buildings.

  17. The effect of isotopic substitution on diffusion coefficients in silicate liquids

    NASA Astrophysics Data System (ADS)

    Watkins, J. M.; Depaolo, D. J.; Ryerson, F. J.

    2009-12-01

    We are using diffusion couple experiments to measure the relative diffusion coefficients of Ca isotopes in silicate liquids, and any dependence on silicate liquid composition. Isotopic signatures due to kinetic effects are increasingly recognized as being important in geological processes; however, there is no general theory for the mass dependence of diffusion coefficients in liquids. Chemical diffusion of major elements (Fe, Mg, Ca, and Li) in basalt-rhyolite and ugandite-rhyolite diffusion couple experiments produces isotopic fractionations in which the mass discrimination during diffusion (i.e., the isotope effect) is much greater for Li than it is for Fe, Mg, and Ca. In these natural liquids, the diffusivity of Fe, Mg, and Ca is similar to that of Si (Dcation/DSi≈1) whereas that of Li is much greater (DLi/DSi≈500). These experiments also show that the isotope effect, at least for Ca, is sensitive to slight changes in composition and therefore difficult to predict or generalize beyond the experimental conditions. However, the few experiments that have been conducted on silicate liquids provide an indication that the mobility of the cation relative to the liquid matrix (Dcation/DSi) correlates with the strength of the isotope effect. To further test this hypothesis, we conducted experiments using synthetic, simplified compositions in which Ca diffuses rapidly with respect to Si. Our diffusion couples consist of starting liquids that lie along the joins of albite-anorthite (ABAN) and albite-diopside (ABDI). In both experiments, albite is the main component of the liquid. In the ABAN experiment, DCa/DSi≈20 and the strength of the isotope effect for Ca is much greater than in the natural liquid experiments where DCa/DSi≈1. In the ABDI experiment, DCa/DSi≈6 and the strength of the isotope effect is between that of the natural liquid experiments and the ABAN experiment. For the ABDI experiment, we will present additional isotopic results for Mg, a cation

  18. Global ULF wave analysis of radial diffusion coefficients using a global MHD model for the 17 March 2015 storm

    NASA Astrophysics Data System (ADS)

    Li, Zhao; Hudson, Mary; Paral, Jan; Wiltberger, Michael; Turner, Drew

    2016-07-01

    The 17-18 March 2015 storm is the largest geomagnetic storm in the Van Allen Probes era to date. The Lyon-Fedder-Mobarry global MHD model has been run for this event using ARTEMIS data as solar wind input. The ULF wave power spectral density of the azimuthal electric field and compressional magnetic field is analyzed in the 0.5-8.3 mHz range. The lowest three azimuthal modes account for 70% of the total power during quiet times. However, during high activity, they are not exclusively dominant. The calculation of the radial diffusion coefficient is presented. We conclude that the electric field radial diffusion coefficient is dominant over the magnetic field coefficient by one to two orders of magnitude. This result contrasts with the dominant magnetic field diffusion coefficient used in most 3-D diffusion models.

  19. Determination of partition and diffusion coefficients of formaldehyde in selected building materials and impact of relative humidity (journal)

    EPA Science Inventory

    The partition and effective diffusion coefficients of formaldehyde were measured for three materials (conventional gypsum wallboard, "green" gypsum wallboard, and "green" carpet) under three relative humidity (RH) conditions (20%, 50% and 70% RH). A dynamic dual-chamber test meth...

  20. Determination of partition and diffusion coefficient of formaldehyde in selected building materials and impact of relative humidity

    EPA Science Inventory

    The partition and effective diffusion coefficients of formaldehyde were measured for three materials (conventional gypsum wallboard, "green" gypsum wallboard, and "green" carpet) under three relative humidity (RH) conditions (20%, 50% and 70% RH). A dynamic dual-chamber test meth...

  1. Thermodiffusion, molecular diffusion and Soret coefficient of binary and ternary mixtures of n-hexane, n-dodecane and toluene.

    PubMed

    Alonso de Mezquia, David; Wang, Zilin; Lapeira, Estela; Klein, Michael; Wiegand, Simone; Mounir Bou-Ali, M

    2014-11-01

    In this study, the thermodiffusion, molecular diffusion, and Soret coefficients of 12 binary mixtures composed of toluene, n-hexane and n-dodecane in the whole range of concentrations at atmospheric pressure and temperatures of 298.15 K and 308.15 K have been determined. The experimental measurements have been carried out using the Thermogravitational Column, the Sliding Symmetric Tubes and the Thermal Diffusion Forced Rayleigh Scattering techniques. The results obtained using the different techniques show a maximum deviation of 9% for the thermodiffusion coefficient, 8% for the molecular diffusion coefficient and 2% for the Soret coefficient. For the first time we report a decrease of the thermodiffusion coefficient with increasing ratio of the thermal expansion coefficient and viscosity for a binary mixture of an organic ring compound with a short n-alkane. This observation is discussed in terms of interactions between the different components. Additionally, the thermogravitational technique has been used to measure the thermodiffusion coefficients of four ternary mixtures consisting of toluene, n-hexane and n-dodecane at 298.15 K. In order to complete the study, the values obtained for the molecular diffusion coefficient in binary mixtures, and the thermodiffusion coefficient of binary and ternary mixtures have been compared with recently derived correlations.

  2. Broadband measurements of the frequency dependence of attenuation coefficient and velocity in amniotic fluid, urine and human serum albumin solutions.

    PubMed

    Verma, Prashant K; Humphrey, Victor F; Duck, Francis A

    2005-10-01

    The frequency dependence of attenuation coefficient in amniotic fluid, urine and 4.5% and 20% human serum albumin solutions over the frequency range 5 MHz to 25 MHz was measured at both room temperature and physiological temperature using a variable path length technique. A 15 MHz (13 mm diameter) transducer was used to produce a broadband single-cycle pulse and a 4 mm diameter bilaminar polyvinylidene difluoride membrane hydrophone was used to detect the attenuated pulse. Standard time-of-flight measurement techniques were used to measure the acoustic velocity in the same fluid samples. At physiological temperature, the attenuation coefficients in amniotic fluid, urine and 4.5% and 20% human albumin solution were found to be 0.0053 f(1.65), 0.0047 f(1.67), 0.019 f(1.57) and 0.167 f(1.27) dB cm(-1), respectively, where f is in MHz. The velocities in amniotic fluid, urine and 4.5% human albumin solution at physiological temperature were found to be 1541.1 m s(-1) +/- 1.3 m s(-1), 1551.3 m s(-1) +/- 1.3 ms(-1) and 1547.3 m s(-1) +/- 1.0 m s(-1), respectively. The results provide unique data over the diagnostic and therapeutic ultrasonic frequency range that can be used as input data for theoretical models that attempt to simulate nonlinear pressure fields and temperature rises from medical ultrasonic transducers.

  3. Analyzing signal attenuation in PFG anomalous diffusion via a non-Gaussian phase distribution approximation approach by fractional derivatives

    NASA Astrophysics Data System (ADS)

    Lin, Guoxing

    2016-11-01

    Anomalous diffusion exists widely in polymer and biological systems. Pulsed-field gradient (PFG) techniques have been increasingly used to study anomalous diffusion in nuclear magnetic resonance and magnetic resonance imaging. However, the interpretation of PFG anomalous diffusion is complicated. Moreover, the exact signal attenuation expression including the finite gradient pulse width effect has not been obtained based on fractional derivatives for PFG anomalous diffusion. In this paper, a new method, a Mainardi-Luchko-Pagnini (MLP) phase distribution approximation, is proposed to describe PFG fractional diffusion. MLP phase distribution is a non-Gaussian phase distribution. From the fractional derivative model, both the probability density function (PDF) of a spin in real space and the PDF of the spin's accumulating phase shift in virtual phase space are MLP distributions. The MLP phase distribution leads to a Mittag-Leffler function based PFG signal attenuation, which differs significantly from the exponential attenuation for normal diffusion and from the stretched exponential attenuation for fractional diffusion based on the fractal derivative model. A complete signal attenuation expression Eα(-Dfbα,β * ) including the finite gradient pulse width effect was obtained and it can handle all three types of PFG fractional diffusions. The result was also extended in a straightforward way to give a signal attenuation expression of fractional diffusion in PFG intramolecular multiple quantum coherence experiments, which has an nβ dependence upon the order of coherence which is different from the familiar n2 dependence in normal diffusion. The results obtained in this study are in agreement with the results from the literature. The results in this paper provide a set of new, convenient approximation formalisms to interpret complex PFG fractional diffusion experiments.

  4. Analyzing signal attenuation in PFG anomalous diffusion via a non-Gaussian phase distribution approximation approach by fractional derivatives.

    PubMed

    Lin, Guoxing

    2016-11-21

    Anomalous diffusion exists widely in polymer and biological systems. Pulsed-field gradient (PFG) techniques have been increasingly used to study anomalous diffusion in nuclear magnetic resonance and magnetic resonance imaging. However, the interpretation of PFG anomalous diffusion is complicated. Moreover, the exact signal attenuation expression including the finite gradient pulse width effect has not been obtained based on fractional derivatives for PFG anomalous diffusion. In this paper, a new method, a Mainardi-Luchko-Pagnini (MLP) phase distribution approximation, is proposed to describe PFG fractional diffusion. MLP phase distribution is a non-Gaussian phase distribution. From the fractional derivative model, both the probability density function (PDF) of a spin in real space and the PDF of the spin's accumulating phase shift in virtual phase space are MLP distributions. The MLP phase distribution leads to a Mittag-Leffler function based PFG signal attenuation, which differs significantly from the exponential attenuation for normal diffusion and from the stretched exponential attenuation for fractional diffusion based on the fractal derivative model. A complete signal attenuation expression Eα(-Dfbα,β(*)) including the finite gradient pulse width effect was obtained and it can handle all three types of PFG fractional diffusions. The result was also extended in a straightforward way to give a signal attenuation expression of fractional diffusion in PFG intramolecular multiple quantum coherence experiments, which has an n(β) dependence upon the order of coherence which is different from the familiar n(2) dependence in normal diffusion. The results obtained in this study are in agreement with the results from the literature. The results in this paper provide a set of new, convenient approximation formalisms to interpret complex PFG fractional diffusion experiments.

  5. Apparent diffusion coefficient in glioblastoma with PNET-like components, a GBM variant.

    PubMed

    Ali, Saad; Joseph, Nancy M; Perry, Arie; Barajas, Ramon F; Cha, Soonmee

    2014-09-01

    Glioblastoma (GBM) with primitive neuroectodermal tumor (PNET)-like (GBM-PNET) components is a rare variant of GBM. Recent studies describe PNET-like clinical behavior in these patients-with significantly increased propensity for CSF dissemination and a benefit of "PNET-like" chemotherapy. The imaging appearance of GBM-PNET is not well-described and given areas of marked cellularity in the PNET components one might expect significantly reduced diffusion on MRI. The purpose of this study is to quantitatively evaluate the diffusion characteristics in GBM-PNET and compare them with conventional GBMs. Nine patients with surgical specimens yielding GBM-PNET were identified from the UCSF Pathology files. MR images of these patients were reviewed retrospectively. DWI (diffusion-weighted imaging) sequences were analyzed with multiple regions of interests placed within the tumor, and ADC (apparent diffusion coefficient) values were measured. Results were compared to previously published ADC values in pathology-proven conventional GBM cases from our institution. Reduced ADC was seen in GBM-PNET (mean 581 × 10(-6) mm(2)/s, range 338-817) compared to previously published mean of 1,030 × 10(-6) mm(2)/s in the enhancing components of conventional GBMs. We report substantially reduced ADC values in GBM-PNETs compared to conventional GBMs. If demonstrated in a larger sample, when areas of marked reduced diffusion are seen in a suspected GBM, MRI may appropriately direct tissue sampling and can advocate a thorough search for PNET-like components on histopathology. These patients may have a higher chance of developing CSF dissemination and may benefit from "PNET-like" platinum-based chemotherapy.

  6. A comparison study of linear reconstruction techniques for diffuse optical tomographic imaging of absorption coefficient

    NASA Astrophysics Data System (ADS)

    Gaudette, Richard J.; Brooks, Dana H.; Di Marzio, Charles A.; Kilmer, Misha E.; Miller, Eric L.; Gaudette, Thomas; Boas, David A.

    2000-04-01

    We compare, through simulations, the performance of four linear algorithms for diffuse optical tomographic reconstruction of the three-dimensional distribution of absorption coefficient within a highly scattering medium using the diffuse photon density wave approximation. The simulation geometry consisted of a coplanar array of sources and detectors at the boundary of a half-space medium. The forward solution matrix is both underdetermined, because we estimate many more absorption coefficient voxels than we have measurements, and ill-conditioned, due to the ill-posedness of the inverse problem. We compare two algebraic techniques, ART and SIRT, and two subspace techniques, the truncated SVD and CG algorithms. We compare three-dimensional reconstructions with two-dimensional reconstructions which assume all inhomogeneities are confined to a known horizontal slab, and we consider two `object-based' error metrics in addition to mean square reconstruction error. We include a comparison using simulated data generated using a different FDFD method with the same inversion algorithms to indicate how our conclusions are affected in a somewhat more realistic scenario. Our results show that the subspace techniques are superior to the algebraic techniques in localization of inhomogeneities and estimation of their amplitude, that two-dimensional reconstructions are sensitive to underestimation of the object depth, and that an error measure based on a location parameter can be a useful complement to mean squared error.

  7. Modeling ion exchange in glass with concentration-dependent diffusion coefficients and mobilities

    NASA Astrophysics Data System (ADS)

    Lupascu, Alexandru I.; Kevorkian, Antoine P.; Boudet, Thierry; Saint-Andre, Francoise; Persegol, Dominique; Levy, Michel

    1996-06-01

    Multimode buried waveguides made in silicate glass by field-assisted ion exchange present very asymmetric profiles. We show how this phenomenon originates in the large dependence of the kinetics on the local ion concentrations. For this purpose, we derive an interdiffusion equation that includes the effects of concentration-dependent diffusion coefficients and mobilities. We show how to deduce this dependence from measurements on ion- diffused samples. The maximum concentration of the incoming ions is computed from surface equilibrium conditions and is used in the interdiffusion equation as a limiting parameter for coefficient variations. To control the model accuracy for surface as well as buried waveguides, we measure ion profiles with three independent methods: M-lines, scanning electron microscopy, and near-field refractometry. When applied to Ag+-Na+ exchange in silicate glass, the model yields theoretical estimations in good agreement with experiments. This approach underlines the fundamentally nonlinear process that takes place during ion exchange and is also valuable to properly model singlemode waveguide fabrication.

  8. Comparison of [corrected] actin- and glass-supported phospholipid bilayer diffusion coefficients.

    PubMed

    Sterling, Sarah M; Dawes, Ryan; Allgeyer, Edward S; Ashworth, Sharon L; Neivandt, David J

    2015-04-21

    The formation of biomimetic lipid membranes has the potential to provide insights into cellular lipid membrane dynamics. The construction of such membranes necessitates not only the utilization of appropriate lipids, but also physiologically relevant substrate/support materials. The substrate materials employed have been shown to have demonstrable effects on the behavior of the overlying lipid membrane, and thus must be studied before use as a model cushion support. To our knowledge, we report the formation and investigation of a novel actin protein-supported lipid membrane. Specifically, inner leaflet lateral mobility of globular actin-supported DMPC (1,2-dimyristoyl-sn-glycero-3-phosphocholine) bilayers, deposited via the Langmuir-Blodgett/Langmuir Schaefer methodology, was investigated by z-scan fluorescence correlation spectroscopy across a temperature range of 20-44°C. The actin substrate was found to decrease the diffusion coefficient when compared to an identical membrane supported on glass. The depression of the diffusion coefficient occurred across all measured temperatures. These results indicated that the actin substrate exerted a direct effect on the fluidity of the lipid membrane and highlighted the fact that the choice of substrate/support is critical in studies of model lipid membranes.

  9. Kubo number and magnetic field line diffusion coefficient for anisotropic magnetic turbulence.

    PubMed

    Pommois, P; Veltri, P; Zimbardo, G

    2001-06-01

    The magnetic field line diffusion coefficients Dx and D(y) are obtained by numerical simulations in the case that all the magnetic turbulence correlation lengths l(x), l(y), and l(z) are different. We find that the variety of numerical results can be organized in terms of the Kubo number, the definition of which is extended from R=(deltaB/B(0))(l(parallel)/l(perpendicular)) to R=(deltaB/B(0))(l(z)/l(x)), for l(x) > or = l(y). Here, l(parallel) (l(perpendicular)) is the correlation length along (perpendicular to) the average field B(0)=B(0)ê(z). We have anomalous, non-Gaussian transport for R less, similar 0.1, in which case the mean square deviation scales nonlinearly with time. For R greater, similar 1 we have several Gaussian regimes: an almost quasilinear regime for 0.1 less, similar R less, similar 1, an intermediate, transition regime for 1 less, similar R less, similar 10, and a percolative regime for R greater, similar 10. An analytical form of the diffusion coefficient is proposed, D(i)=D(deltaBl(z)/B(0)l(x))(mu)(l(i)/l(x))(nu)l(2)(x)/l(z), which well describes the numerical simulation results in the quasilinear, intermediate, and percolative regimes.

  10. Computing the blood brain barrier (BBB) diffusion coefficient: A molecular dynamics approach

    NASA Astrophysics Data System (ADS)

    Shamloo, Amir; Pedram, Maysam Z.; Heidari, Hossein; Alasty, Aria

    2016-07-01

    Various physical and biological aspects of the Blood Brain Barrier (BBB) structure still remain unfolded. Therefore, among the several mechanisms of drug delivery, only a few have succeeded in breaching this barrier, one of which is the use of Magnetic Nanoparticles (MNPs). However, a quantitative characterization of the BBB permeability is desirable to find an optimal magnetic force-field. In the present study, a molecular model of the BBB is introduced that precisely represents the interactions between MNPs and the membranes of Endothelial Cells (ECs) that form the BBB. Steered Molecular Dynamics (SMD) simulations of the BBB crossing phenomenon have been carried out. Mathematical modeling of the BBB as an input-output system has been considered from a system dynamics modeling viewpoint, enabling us to analyze the BBB behavior based on a robust model. From this model, the force profile required to overcome the barrier has been extracted for a single NP from the SMD simulations at a range of velocities. Using this data a transfer function model has been obtained and the diffusion coefficient is evaluated. This study is a novel approach to bridge the gap between nanoscale models and microscale models of the BBB. The characteristic diffusion coefficient has the nano-scale molecular effects inherent, furthermore reducing the computational costs of a nano-scale simulation model and enabling much more complex studies to be conducted.

  11. The apparent diffusion coefficient does not reflect cytotoxic edema on the uninjured side after traumatic brain injury.

    PubMed

    Lu, Hong; Lei, Xiaoyan

    2014-05-01

    After traumatic brain injury, vasogenic and cytotoxic edema appear sequentially on the involved side. Neuroimaging investigations of edema on the injured side have employed apparent diffusion coefficient measurements in diffusion tensor imaging. We investigated the changes occurring on the injured and uninjured sides using diffusion tensor imaging/apparent diffusion coefficient and histological samples in rats. We found that, on the injured side, that vasogenic edema appeared at 1 hour and intracellular edema appeared at 3 hours. Mixed edema was observed at 6 hours, worsening until 12-24 hours post-injury. Simultaneously, microglial cells proliferated at the trauma site. Apparent diffusion coefficient values increased at 1 hour, decreased at 6 hours, and increased at 12 hours. The uninjured side showed no significant pathological change at 1 hour after injury. Cytotoxic edema appeared at 3 hours, and vasogenic edema was visible at 6 hours. Cytotoxic edema persisted, but vasogenic edema tended to decrease after 12-24 hours. Despite this complex edema pattern on the uninjured side with associated pathologic changes, no significant change in apparent diffusion coefficient values was detected over the first 24 hours. Apparent diffusion coefficient values accurately detected the changes on the injured side, but did not detect the changes on the uninjured side, giving a false-negative result.

  12. A novel random void model and its application in predicting void content of composites based on ultrasonic attenuation coefficient

    NASA Astrophysics Data System (ADS)

    Lin, Li; Zhang, Xiang; Chen, Jun; Mu, Yunfei; Li, Ximeng

    2011-06-01

    A novel two-dimensional random void model (RVM) based on random medium theory and a statistical method is proposed to describe random voids in composite materials. The spatial autocorrelation function and statistical parameters are used to describe the large-scale heterogeneity from the composite matrix and the small-scale heterogeneities of elastic fluctuations from random voids, the values of which are determined by statistical data from microscopic observations of void morphology. A RVM for CFRP (carbon fiber reinforced polymer) composite specimens with void content of 0.03-4.62% is presented. It is found that the geometric morphology of voids from the RVM presents good matches to the microscopic images. Calculations of ultrasonic attenuation coefficients from the RVM at 5 MHz are much closer to the experiments than those from the previous deterministic model. Furthermore, the RVM can also cover abnormal coefficients from unusually large voids, which unpredictably occur during the composite preparation and have a detrimental effect on the strength and mechanical properties of the components. The significant enhancements in description of void morphology and quantitative correlation between void content and ultrasonic attenuation coefficient make this method a good candidate for predicting void content of composite materials non-destructively.

  13. Extracting seismic attenuation coefficients from cross-correlations of ambient noise at linear triplets of stations

    NASA Astrophysics Data System (ADS)

    Liu, Xin; Ben-Zion, Yehuda; Zigone, Dimitri

    2015-11-01

    We develop and apply an algorithm for deriving interstation seismic attenuation from cross-correlations of ambient noise recorded by linear arrays. Theoretical results on amplitude decay due to attenuation are used to form a linear least-square inversion for interstation QR values of Rayleigh surface waves propagating along linear arrays having three or more stations. The noise wave field is assumed stationary within each day and the interstation distances should be greater than the employed wavelength. The inversion uses differences of logarithmic amplitude decay curves measured at different stations from cross-correlation functions within a given frequency band. The background attenuation between noise sources and receivers is effectively cancelled with this method. The site amplification factors are assumed constant (or following similar patterns) in the frequency band of interest. The inversion scheme is validated with synthetic tests using ambient noise generated by ray-theory-based calculations with heterogeneous attenuation and homogenous velocity structure. The interstation attenuation and phase velocity dispersion curves are inverted from cross-correlations of the synthetic data. The method is then applied to triplets of stations from the regional southern California seismic network crossing the Mojave section of the San Andreas fault, and a dense linear array crossing the southern San Jacinto Fault zone. Bootstrap technique is used to derive empirical mean and confidence interval for the obtained inverse Q values. The results for the regional stations yield QR values around 25 for a frequency band 0.2-0.36 Hz. The results for the San Jacinto fault zone array give QR values of about 6-30 for frequencies in the range 15-25 Hz.

  14. Photon attenuation coefficients of Heavy-Metal Oxide glasses by MCNP code, XCOM program and experimental data: A comparison study

    NASA Astrophysics Data System (ADS)

    El-Khayatt, A. M.; Ali, A. M.; Singh, Vishwanath P.

    2014-01-01

    The mass attenuation coefficients, μ/ρ, total interaction cross-section, σt, and mean free path (MFP) of some Heavy Metal Oxides (HMO) glasses, with potential applications as gamma ray shielding materials, have been investigated using the MCNP-4C code. Appreciable variations are noted for all parameters by changing the photon energy and the chemical composition of HMO glasses. The numerical simulations parameters are compared with experimental data wherever possible. Comparisons are also made with predictions from the XCOM program in the energy region from 1 keV to 100 MeV. Good agreement noticed indicates that the chosen Monte Carlo method may be employed to make additional calculations on the photon attenuation characteristics of different glass systems, a capability particularly useful in cases where no analogous experimental data exist.

  15. Diffusion coefficients of organic molecules in sucrose-water solutions and comparison with Stokes-Einstein predictions

    NASA Astrophysics Data System (ADS)

    Chenyakin, Yuri; Ullmann, Dagny A.; Evoy, Erin; Renbaum-Wolff, Lindsay; Kamal, Saeid; Bertram, Allan K.

    2017-02-01

    The diffusion coefficients of organic species in secondary organic aerosol (SOA) particles are needed to predict the growth and reactivity of these particles in the atmosphere. Previously, viscosity measurements, along with the Stokes-Einstein relation, have been used to estimate the diffusion rates of organics within SOA particles or proxies of SOA particles. To test the Stokes-Einstein relation, we have measured the diffusion coefficients of three fluorescent organic dyes (fluorescein, rhodamine 6G and calcein) within sucrose-water solutions with varying water activity. Sucrose-water solutions were used as a proxy for SOA material found in the atmosphere. Diffusion coefficients were measured using fluorescence recovery after photobleaching. For the three dyes studied, the diffusion coefficients vary by 4-5 orders of magnitude as the water activity varied from 0.38 to 0.80, illustrating the sensitivity of the diffusion coefficients to the water content in the matrix. At the lowest water activity studied (0.38), the average diffusion coefficients were 1.9 × 10-13, 1.5 × 10-14 and 7.7 × 10-14 cm2 s-1 for fluorescein, rhodamine 6G and calcein, respectively. The measured diffusion coefficients were compared with predictions made using literature viscosities and the Stokes-Einstein relation. We found that at water activity ≥ 0.6 (which corresponds to a viscosity of ≤ 360 Pa s and Tg/T ≤ 0.81), predicted diffusion rates agreed with measured diffusion rates within the experimental uncertainty (Tg represents the glass transition temperature and T is the temperature of the measurements). When the water activity was 0.38 (which corresponds to a viscosity of 3.3 × 106 Pa s and a Tg/T of 0.94), the Stokes-Einstein relation underpredicted the diffusion coefficients of fluorescein, rhodamine 6G and calcein by a factor of 118 (minimum of 10 and maximum of 977), a factor of 17 (minimum of 3 and maximum of 104) and a factor of 70 (minimum of 8 and maximum of 494

  16. Neurite beading is sufficient to decrease the apparent diffusion coefficient after ischemic stroke.

    PubMed

    Budde, Matthew D; Frank, Joseph A

    2010-08-10

    Diffusion-weighted MRI (DWI) is a sensitive and reliable marker of cerebral ischemia. Within minutes of an ischemic event in the brain, the microscopic motion of water molecules measured with DWI, termed the apparent diffusion coefficient (ADC), decreases within the infarcted region. However, although the change is related to cell swelling, the precise pathological mechanism remains elusive. We show that focal enlargement and constriction, or beading, in axons and dendrites are sufficient to substantially decrease ADC. We first derived a biophysical model of neurite beading, and we show that the beaded morphology allows a larger volume to be encompassed within an equivalent surface area and is, therefore, a consequence of osmotic imbalance after ischemia. The DWI experiment simulated within the model revealed that intracellular ADC decreased by 79% in beaded neurites compared with the unbeaded form. To validate the model experimentally, excised rat sciatic nerves were subjected to stretching, which induced beading but did not cause a bulk shift of water into the axon (i.e., swelling). Beading-induced changes in cell-membrane morphology were sufficient to significantly hinder water mobility and thereby decrease ADC, and the experimental measurements were in excellent agreement with the simulated values. This is a demonstration that neurite beading accurately captures the diffusion changes measured in vivo. The results significantly advance the specificity of DWI in ischemia and other acute neurological injuries and will greatly aid the development of treatment strategies to monitor and repair damaged brain in both clinical and experimental settings.

  17. Diffusion Coefficients of Endogenous Cytosolic Proteins from Rabbit Skinned Muscle Fibers

    PubMed Central

    Carlson, Brian E.; Vigoreaux, Jim O.; Maughan, David W.

    2014-01-01

    Efflux time courses of endogenous cytosolic proteins were obtained from rabbit psoas muscle fibers skinned in oil and transferred to physiological salt solution. Proteins were separated by gel electrophoresis and compared to load-matched standards for quantitative analysis. A radial diffusion model incorporating the dissociation and dissipation of supramolecular complexes accounts for an initial lag and subsequent efflux of glycolytic and glycogenolytic enzymes. The model includes terms representing protein crowding, myofilament lattice hindrance, and binding to the cytomatrix. Optimization algorithms returned estimates of the apparent diffusion coefficients, D(r,t), that were very low at the onset of diffusion (∼10−10 cm2 s−1) but increased with time as cytosolic protein density, which was initially high, decreased. D(r,t) at later times ranged from 2.11 × 10−7 cm2 s−1 (parvalbumin) to 0.20 × 10−7 cm2 s−1 (phosphofructose kinase), values that are 3.6- to 12.3-fold lower than those predicted in bulk water. The low initial values are consistent with the presence of complexes in situ; the higher later values are consistent with molecular sieving and transient binding of dissociated proteins. Channeling of metabolic intermediates via enzyme complexes may enhance production of adenosine triphosphate at rates beyond that possible with randomly and/or sparsely distributed enzymes, thereby matching supply with demand. PMID:24559981

  18. Determinations of equilibrium segregation, effective segregation and diffusion coefficients for Nd+3 doped in molten YAG

    NASA Astrophysics Data System (ADS)

    Asadian, M.; Saeedi, H.; Yadegari, M.; Shojaee, M.

    2014-06-01

    In this paper, a new mathematical model has been presented to determine the equilibrium segregation (k0) and effective segregation (keff) coefficients for neodymium (Nd) in YAG crystal grown by Czochralski (CZ) method. Determination of diffusion coefficient (DL) of Nd impurity in molten YAG is also investigated. In this model, utilizing Lambert W-function is a new idea to solve the Scheil equation for calculation of effective segregation coefficient. The Nd concentration in the crystal has been measured by optical absorption method to calculate keff. The analyses show that the keff is related to the growth parameters such as crystal growth rate (ug) and crystal rotation rate (ω), ( ug/√{ω}) but it is independent of the Nd concentration in the initial melt (C0). Based on obtained keff and experimental growth data, k0 and DL of Nd in molten YAG have been calculated. For all experiments, the average value of k0=0.216 and DL=1.4×10-6 (cm2/s) are obtained. Our results are corroborated by the theoretical and experimental data from the literature.

  19. Method qualification and application of diffusion interaction parameter and virial coefficient.

    PubMed

    Shi, Shuai; Uchida, Makiko; Cheung, Jason; Antochshuk, Valentyn; Shameem, Mohammed

    2013-11-01

    This research focused on evaluation and application of two methods in studying weak protein-protein interactions, i.e. diffusion interaction parameter (KD) and second virial coefficient (B22), both of which are first-order coefficients of protein interactions. Although the plate-based KD method successfully distinguished KD values with relatively large difference in a pH ranging study, it failed to make a consistent statistical decision to determine close interactions as shown by the comprehensive ANOVA analysis. We also validated the DLS-based B22 method by using a model protein lysozyme. The dramatic change of solution appearance for lysozyme as a function of NaCl concentration highlighted the importance of B22 in understanding protein interactions. Moreover, B22 measurement for a MAb fragment suggested a more repulsive protein interaction in histidine buffer than in citrate buffer. The coefficient of variation was <10% when B22 was on an order of magnitude of 10(-4) L mmol/g(2) in contrast to >30% when it approached 10(-5) L mmol/g(2). In this research, we also made an attempt to study protein-protein interactions in concentrated MAb fragment solutions (e.g. >50 mg/mL). Our data suggested that such interactions could be empirically modeled by high-order virial expansions.

  20. Drag and diffusion coefficient of a spherical particle attached to a fluid interface

    NASA Astrophysics Data System (ADS)

    Hardt, Steffen; Doerr, Aaron; Masoud, Hassan; Stone, Howard

    2015-11-01

    We consider a spherical particle attached to the interface between two immiscible fluids of large viscosity contrast. The degree of immersion in the two fluids is determined by the contact angle. For small enough particles and significant contact-angle hysteresis, it can be assumed that the three-phase contact line is pinned at the particle surface. We study the movement of such particles along the fluid interface for the case of small Reynolds and capillary numbers. We solve the Stokes equation based on two geometric perturbation expansions around contact angles of 90 degrees and 180 degrees, the latter corresponding to a particle completely immersed in the less viscous phase. Based on the Lorentz Reciprocity Theorem we obtain expressions for the drag coefficient of an interfacial particle which are analogs of the well-known Stokes drag coefficient for a particle moving in an unbounded medium. Interpolation of the two results gives a relationship which approximates the drag coefficient quite accurately over the entire range of contact angles. A comparison with previously published numerical results for contact angles below 90 degrees shows good agreement. Using the fluctuation-dissipation theorem, we also obtain expressions for the diffusion constant of a small particle attached to a fluid interface.

  1. Measurements of attenuation coefficient for evaluating the hardness of a cataract lens by a high-frequency ultrasonic needle transducer

    NASA Astrophysics Data System (ADS)

    Huang, Chih-Chung; Chen, Ruimin; Tsui, Po-Hsiang; Zhou, Qifa; Humayun, Mark S.; Shung, K. Kirk

    2009-10-01

    A cataract is a clouding of the lens in the eye that affects vision. Phacoemulsification is the mostly common surgical method for treating cataracts, and determining that the optimal phacoemulsification energy is dependent on measuring the hardness of the lens. This study explored the use of an ultrasound needle transducer for invasive measurements of ultrasound attenuation coefficient to evaluate the hardness of the cataract lens. A 47 MHz high-frequency needle transducer with a diameter of 0.9 mm was fabricated by a polarized PMN-33%PT single crystal in the present study. The attenuation coefficients at different stages of an artificial porcine cataract lens were measured using the spectral shift approach. The hardness of the cataract lens was also evaluated by mechanical measurement of its elastic properties. The results demonstrated that the ultrasonic attenuation coefficient was increased from 0.048 ± 0.02 to 0.520 ± 0.06 dB mm-1 MHz-1 corresponding to an increase in Young's modulus from 6 ± 0.4 to 96 ± 6.2 kPa as the cataract further developed. In order to evaluate the feasibility of combining needle transducer and phacoemulsification probe for real-time measurement during cataract surgery, the needle transducer was mounted on the phacoemulsification probe for a vibration test. The results indicated that there was no apparent damage to the tip of the needle transducer and the pulse-echo test showed that a good performance in sensitivity was maintained after the vibration test.

  2. Study of mass attenuation coefficients and effective atomic numbers of bismuth-ground granulated blast furnace slag concretes

    NASA Astrophysics Data System (ADS)

    Kumar, Sandeep; Singh, Sukhpal

    2016-05-01

    Five samples of Bismuth-Ground granulated blast furnace slag (Bi-GGBFS) concretes were prepared using composition (0.6 cement + x Bi2O3 + (0.4-x) GGBFS, x = 0.05, 0.10, 0.15, 0.20 and 0.25) by keeping constant water (W) cement (C) ratio. Mass attenuation coefficients (μm) of these prepared samples were calculated using a computer program winXCOM at different gamma ray energies, whereas effective atomic numbers (Zeff) is calculated using mathematical formulas. The radiation shielding properties of Bi-GGBFS concrete has been compared with standard radiation shielding concretes.

  3. Mass transfer of SCWO processes: Molecular diffusion and mass transfer coefficients of inorganic nitrate species in sub- and supercritical water

    SciTech Connect

    Goemans, M.G.E.; Gloyna, E.F.; Buelow, S.J.

    1996-04-01

    Molecular diffusion coefficients of lithium-, sodium-, potassium-, cesium-, calcium-, and strontium nitrate in subcritical water were determined by analysis of Taylor dispersion profiles. Pressures ranged from 300 to 500 bar at temperatures ranging from 25{degrees}C to 300{degrees}C. The reported diffusion values were determined at infinite dilution. Molecular diffusion coefficients were 10 to 20 times faster in near-critical subcritical water than in water at ambient temperature and pressure (ATP). These findings implied that the diffusion rates were more liquid like than they were gas like, hence experimental results were correlated with diffusion models for liquids. The subcritical diffusion data presented in this work, and supercritical diffusion results published elsewhere were correlated with hydrodynamic diffusion equations. Both the Wilke-Chang correlation and the Stokes-Einstein equation yielded predictions within 10% of the experimental results if the structure of the diffusing species could be estimated. The effect of the increased diffusion rates on mass transfer rates in supercritical water oxidation applications was quantified, with emphasis on heterogeneous oxidation processes. This study and results published elsewhere showed that diffusion limited conditions are much more likely to be encountered in SCWO processes than commonly acknowledged.

  4. Liver Apparent Diffusion Coefficient Changes during Telaprevir-Based Therapy for Chronic Hepatitis C

    PubMed Central

    Gürcan, Nagihan İnan; Sakçı, Zakir; Akhan, Sıla; Altunok, Elif Sargın; Aynıoğlu, Aynur; Gürbüz, Yeşim; Sarisoy, Hasan Tahsin; Akansel, Gür

    2016-01-01

    Background Diffusion-weighted imaging (DWI) has become an established diagnostic modality for the evaluation of liver parenchymal changes in diseases such as diffuse liver fibrosis. Aims To evaluate the parenchymal apparent diffusion coefficient value (ADC) changes using diffusion-weighted imaging (DWI) during telaprevir-based triple therapy. Study Design Diagnostic accuracy study. Methods Seventeen patients with chronic hepatitis C virus (HCV) virus and twenty-five normal volunteers were included. All of the patients took 12-weeks of telaprevir-based triple therapy followed by 12-weeks of PEGylated interferon and ribavirin therapy. They were examined before treatment (BT), as well as 12-weeks (W12) and 24-weeks (W24) after treatment by 3 Tesla magnetic resonance imaging (MRI). DWI was obtained using a breath-hold single-shot echo-planar spin echo sequence. Histopathologically, liver fibrosis was classified in accordance with the modified Knodell score described by Ishak. Quantitatively, liver ADCs were compared between patients and normal volunteers to detect the contribution of DWI in the detection of fibrosis. In addition, liver ADCs were compared during the therapy to analyze the effect of antiviral medication on liver parenchyma. Results The liver ADC values of fibrotic liver parenchyma were significantly lower than those of the healthy liver parenchyma (p<0.001). However, we were not able to reach a sufficiently discriminative threshold value. The ADC values showed a declining trend with increasing fibrotic stage. No statistically significant correlation (p=0.204) was observed. Compared with those before treatment, the liver ADC values after telaprevir-based triple therapy were significantly decreased at W12. A significant increase in the liver ADC values was also observed after the cessation of telaprevir therapy at W24 with a return to initial values. Conclusion Liver ADC values appear to indicate the present but not the stage of liver fibrosis. DWI may be

  5. Short-term reproducibility of apparent diffusion coefficient estimated from diffusion-weighted MRI of the prostate

    PubMed Central

    Sadinski, Meredith; Medved, Milica; Karademir, Ibrahim; Wang, Shiyang; Peng, Yahui; Jiang, Yulei; Sammet, Steffen; Karczmar, Gregory; Oto, Aytekin

    2015-01-01

    Purpose The purpose of the study is to determine short-term reproducibility of apparent diffusion coefficient (ADC) estimated from diffusion-weighted magnetic resonance (DW-MR) imaging of the prostate. Methods Fourteen patients with biopsy-proven prostate cancer were studied under an Institutional Review Board-approved protocol. Each patient underwent two, consecutive and identical DW-MR scans on a 3T system. ADC values were calculated from each scan and a deformable registration was performed to align corresponding images. The prostate and cancerous regions of interest (ROIs) were independently analyzed by two radiologists. The prostate volume was analyzed by sextant. Per-voxel absolute and relative percentage variations in ADC were compared between sextants. Per-voxel and per-ROI variations in ADC were calculated for cancerous ROIs. Results Per-voxel absolute difference in ADC in the prostate ranged from 0 to 1.60 × 10−3 mm2/s (per-voxel relative difference 0% to 200%, mean 10.5%). Variation in ADC was largest in the posterior apex (0% to 200%, mean 11.6%). Difference in ADC variation between sextants was not statistically significant. Cancer ROIs’ per-voxel variation in ADC ranged from 0.001 × 10−3 to 0.841 × 10−3 mm2/s (0% to 67.4%, mean 11.2%) and per-ROI variation ranged from 0 to 0.463 × 10−3 mm2/s (mean 0.122 × 10−3 mm2/s). Conclusions Variation in ADC within the human prostate is reasonably small, and is on the order of 10%. PMID:25805558

  6. Ground-level spectral distribution of solar direct-normal irradiance and marine aerosol attenuation coefficients at Reunion Island

    SciTech Connect

    Vaxelaire, P.; Leveau, J.; Baldy, S. ); Menguy, G. )

    1991-01-01

    The ground-level spectral distribution of direct solar irradiance at Reunion Island was measured for six bands covering the spectrum of solar radiation. The measurements, distributed over one year, were made under clear sky conditions with a pyrheliometer (Eppley, NIP) and six large pass-band flat filters. Good stability of spectral irradiances as a function of solar height allows us to propose approximate relationships which significantly characterize the irradiance into each spectral band. Measurements at Reunion vary significantly from data obtained with the same apparatus in a northern hemisphere continental area (Lyon). The determination of aerosol attenuation coefficients, for different spectral bands, allows the establish of a mean curve, for these coefficients as a function of wavelength, characteristic for marine aerosols.

  7. Multi-frequency characterization of the speed of sound and attenuation coefficient for longitudinal transmission of freshly excised human skulls.

    PubMed

    Pichardo, Samuel; Sin, Vivian W; Hynynen, Kullervo

    2011-01-07

    For medical applications of ultrasound inside the brain, it is necessary to understand the relationship between the apparent density of skull bone and its corresponding speed of sound and attenuation coefficient. Although there have been previous studies exploring this phenomenon, there is still a need to extend the measurements to cover more of the clinically relevant frequency range. The results of measurements of the longitudinal speed of sound and attenuation coefficient are presented for specimens of human calvaria. The study was performed for the frequencies of 0.27, 0.836, 1.402, 1.965 and 2.525 MHz. Specimens were obtained from fresh cadavers through a protocol with the Division of Anatomy of the University of Toronto. The protocol was approved by the Research Ethics Board of Sunnybrook Health Sciences Centre. The specimens were mounted in polycarbonate supports that were marked for stereoscopic positioning. Computer tomography (CT) scans of the skulls mounted on their supports were performed, and a three-dimensional skull surface was reconstructed. This surface was used to guide a positioning system to ensure the normal sound incidence of an acoustic signal. This signal was produced by a focused device with a diameter of 5 cm and a focal length of 10 cm. Measurements of delay in time of flight were carried out using a needle hydrophone. Measurements of effective transmitted energy were carried out using a radiation force method with a 10 µg resolution scale. Preliminary functions of speed of sound and attenuation coefficient, both of which are related to apparent density, were established using a multi-layer propagation model that takes into account speed of sound, density and thickness of the layer. An optimization process was executed from a large set of random functions and the best functions were chosen for those ones that closest reproduced the experimental observations. The final functions were obtained after a second pass of the optimization

  8. Multi-frequency characterization of the speed of sound and attenuation coefficient for longitudinal transmission of freshly excised human skulls

    NASA Astrophysics Data System (ADS)

    Pichardo, Samuel; Sin, Vivian W.; Hynynen, Kullervo

    2011-01-01

    For medical applications of ultrasound inside the brain, it is necessary to understand the relationship between the apparent density of skull bone and its corresponding speed of sound and attenuation coefficient. Although there have been previous studies exploring this phenomenon, there is still a need to extend the measurements to cover more of the clinically relevant frequency range. The results of measurements of the longitudinal speed of sound and attenuation coefficient are presented for specimens of human calvaria. The study was performed for the frequencies of 0.27, 0.836, 1.402, 1.965 and 2.525 MHz. Specimens were obtained from fresh cadavers through a protocol with the Division of Anatomy of the University of Toronto. The protocol was approved by the Research Ethics Board of Sunnybrook Health Sciences Centre. The specimens were mounted in polycarbonate supports that were marked for stereoscopic positioning. Computer tomography (CT) scans of the skulls mounted on their supports were performed, and a three-dimensional skull surface was reconstructed. This surface was used to guide a positioning system to ensure the normal sound incidence of an acoustic signal. This signal was produced by a focused device with a diameter of 5 cm and a focal length of 10 cm. Measurements of delay in time of flight were carried out using a needle hydrophone. Measurements of effective transmitted energy were carried out using a radiation force method with a 10 µg resolution scale. Preliminary functions of speed of sound and attenuation coefficient, both of which are related to apparent density, were established using a multi-layer propagation model that takes into account speed of sound, density and thickness of the layer. An optimization process was executed from a large set of random functions and the best functions were chosen for those ones that closest reproduced the experimental observations. The final functions were obtained after a second pass of the optimization

  9. Effect of the computational domain size and shape on the self-diffusion coefficient in a Lennard-Jones liquid.

    PubMed

    Kikugawa, Gota; Ando, Shotaro; Suzuki, Jo; Naruke, Yoichi; Nakano, Takeo; Ohara, Taku

    2015-01-14

    In the present study, molecular dynamics (MD) simulations on the monatomic Lennard-Jones liquid in a periodic boundary system were performed in order to elucidate the effect of the computational domain size and shape on the self-diffusion coefficient measured by the system. So far, the system size dependence in cubic computational domains has been intensively investigated and these studies showed that the diffusion coefficient depends linearly on the inverse of the system size, which is theoretically predicted based on the hydrodynamic interaction. We examined the system size effect not only in the cubic cell systems but also in rectangular cell systems which were created by changing one side length of the cubic cell with the system density kept constant. As a result, the diffusion coefficient in the direction perpendicular to the long side of the rectangular cell significantly increases more or less linearly with the side length. On the other hand, the diffusion coefficient in the direction along the long side is almost constant or slightly decreases. Consequently, anisotropy of the diffusion coefficient emerges in a rectangular cell with periodic boundary conditions even in a bulk liquid simulation. This unexpected result is of critical importance because rectangular fluid systems confined in nanospace, which are present in realistic nanoscale technologies, have been widely studied in recent MD simulations. In order to elucidate the underlying mechanism for this serious system shape effect on the diffusion property, the correlation structures of particle velocities were examined.

  10. The Effect of a Fluorophore Photo-Physics on the Lipid Vesicle Diffusion Coefficient Studied by Fluorescence Correlation Spectroscopy.

    PubMed

    Drabik, Dominik; Przybyło, Magda; Sikorski, Aleksander; Langner, Marek

    2016-03-01

    Fluorescence Correlation Spectroscopy (FCS) is a technique, which allows determination of the diffusion coefficient and concentration of fluorescent objects suspended in the solution. The measured parameter is the fluctuation of the fluorescence signal emitted by diffusing molecules. When 100 nm DOPC vesicles labeled with various fluorescent dyes (Fluorescein-PE, NBD-PE, Atto488 DOPE or βBodipy FL) were measured, different values of diffusion coefficients have been obtained. These diffusion coefficients were different from the expected values measured using the dynamic light scattering method (DLS). The FCS was initially developed for solutions containing small fluorescent molecules therefore the observed inconsistency may result from the nature of vesicle suspension itself. The duration of the fluorescence signal may depend on the following factors: the exposure time of the labeled object to the excitation beam, the photo-physical properties (e.g., stability) of a fluorophore, the theoretical model used for the calculations of the diffusion coefficient and optical properties of the vesicle suspension. The diffusion coefficients determined for differently labeled liposomes show that its dependence on vesicle size and quantity of fluorescent probed used for labeling was significant demonstrating that the fluorescence properties of the fluorophore itself (bleaching and/or blinking) were critical factors for a correct outcome of FCS experiment. The new, based on combined FCS and DLS measurements, method for the determination of the focal volume prove itself to be useful for the evaluation of a fluorescence dye with respect to its applicability for FCS experiment.

  11. An assessment of the ability of the obstruction-scaling model to estimate solute diffusion coefficients in hydrogels.

    PubMed

    Hadjiev, Nicholas A; Amsden, Brian G

    2015-02-10

    The ability to estimate the diffusion coefficient of a solute within hydrogels has important application in the design and analysis of hydrogels used in drug delivery, tissue engineering, and regenerative medicine. A number of mathematical models have been derived for this purpose; however, they often rely on fitted parameters and so have limited predictive capability. Herein we assess the ability of the obstruction-scaling model to provide reasonable estimates of solute diffusion coefficients within hydrogels, as well as the assumption that a hydrogel can be represented as an entangled polymer solution of an equivalent concentration. Fluorescein isothiocyanate dextran solutes were loaded into sodium alginate solutions as well as hydrogels of different polymer volume fractions formed from photoinitiated cross-linking of methacrylate sodium alginate. The tracer diffusion coefficients of these solutes were measured using fluorescence recovery after photobleaching (FRAP). The measured diffusion coefficients were then compared to the values predicted by the obstruction-scaling model. The model predictions were within ±15% of the measured values, suggesting that the model can provide useful estimates of solute diffusion coefficients within hydrogels and solutions. Moreover, solutes diffusing in both sodium alginate solutions and hydrogels were demonstrated to experience the same degree of solute mobility restriction given the same effective polymer concentration, supporting the assumption that a hydrogel can be represented as an entangled polymer solution of equivalent concentration.

  12. The absorption of trapped particles by the inner satellites of Jupiter and the radial diffusion coefficient of particle transport

    NASA Technical Reports Server (NTRS)

    Mogro-Campero, A.; Fillius, W.

    1976-01-01

    The process of trapped particle absorption by the inner Jovian satellites is considered in detail taking into account both the particle and satellite motions in a magnetic dipole field which is displaced from the center of the planet and tilted with respect to the planetary rotation axis. An expression is derived for computing the sweeping time at a given satellite, defined as the time required for the satellite to sweep up a given fraction of the trapped particles within its sweeping region. By making use of the sweeping time and the radial diffusion equation of particle transport approximate expressions for the diffusion coefficient are derived. Measurements obtained by Pioneer 10 are then used to obtain estimates of the diffusion coefficient at the orbits of Io and Europa. We find that the diffusion coefficient is a function of energy and magnetic latitude for electrons in the energy range 0.7-14 MeV.

  13. Experimental investigation of benzoic acid diffusion coefficient in γ-Al2O3 nanofluids at different temperatures

    NASA Astrophysics Data System (ADS)

    Manouchehrian Fard, Manouchehr; Beiki, Hossein

    2016-10-01

    An experimental study was performed to measure benzoic acid diffusion coefficient in water-based γ-Al2O3 nanofluids at different temperatures. Measurements were carried out at 15, 20 and 25 °C. γ-Al2O3 nanoparticles with an average diameter of 10-20 nm were added into de-ionized water as the based fluid. Nanoparticles volume fractions used in the based fluid were 0.025, 0.05, 0.1, 0.2, 0.4 and 0.8 %. Measurements showed that the diffusion coefficients was not changed with nanoparticles concentration and no enhancement was found. Dependence of diffusion coefficients on nanoparticles concentration followed the same trend in all temperatures investigated in this work. Nano stirring and nano-obstacles could be regarded as two reasons for mass diffusivity changes in nanofluids.

  14. Effect of confining pressure on diffusion coefficients in clay-rich, low-permeability sedimentary rocks.

    PubMed

    Xiang, Y; Al, T; Mazurek, M

    2016-12-01

    The effect of confining pressure (CP) on the diffusion of tritiated-water (HTO) and iodide (I(-)) tracers through Ordovician rocks from the Michigan Basin, southwestern Ontario, Canada, and Opalinus Clay from Schlattingen, Switzerland was investigated in laboratory experiments. Four samples representing different formations and lithologies in the Michigan Basin were studied: Queenston Formation shale, Georgian Bay Formation shale, Cobourg Formation limestone and Cobourg Formation argillaceous limestone. Estimated in situ vertical stresses at the depths from which the samples were retrieved range from 12.0 to 17.4MPa (Michigan Basin) and from 21 to 23MPa (Opalinus Clay). Effective diffusion coefficients (De) were determined in through-diffusion experiments. With HTO tracer, applying CP resulted in decreases in De of 12.5% for the Queenston Formation shale (CPmax=12MPa), 30% for the Georgian Bay Formation shale (15MPa), 34% for the Cobourg Formation limestone (17.4MPa), 31% for the Cobourg Formation argillaceous limestone (17.4MPa) and 43-46% for the Opalinus Clay (15MPa). Decreases in De were larger for the I(-) tracer: 13.8% for the Queenston shale, 42% for the Georgian Bay shale, 50% for the Cobourg Formation limestone, 55% for the Cobourg Formation argillaceous limestone and 63-68% for the Opalinus Clay. The tracer-specific nature of the response is attributed to an increasing influence of anion exclusion as the pore size decreases at higher CP. Results from the shales (including Opalinus Clay) indicate that the pressure effect on De can be represented by a linear relationship between De and ln(CP), which provides valuable predictive capability. The nonlinearity results in a relatively small change in De at high CP, suggesting that it is not necessary to apply the exact in situ pressure conditions in order to obtain a good estimate of the in situ diffusion coefficient. Most importantly, the CP effect on shale is reversible (±12%) suggesting that, for

  15. Effect of confining pressure on diffusion coefficients in clay-rich, low-permeability sedimentary rocks

    NASA Astrophysics Data System (ADS)

    Xiang, Y.; Al, T.; Mazurek, M.

    2016-12-01

    The effect of confining pressure (CP) on the diffusion of tritiated-water (HTO) and iodide (I-) tracers through Ordovician rocks from the Michigan Basin, southwestern Ontario, Canada, and Opalinus Clay from Schlattingen, Switzerland was investigated in laboratory experiments. Four samples representing different formations and lithologies in the Michigan Basin were studied: Queenston Formation shale, Georgian Bay Formation shale, Cobourg Formation limestone and Cobourg Formation argillaceous limestone. Estimated in situ vertical stresses at the depths from which the samples were retrieved range from 12.0 to 17.4 MPa (Michigan Basin) and from 21 to 23 MPa (Opalinus Clay). Effective diffusion coefficients (De) were determined in through-diffusion experiments. With HTO tracer, applying CP resulted in decreases in De of 12.5% for the Queenston Formation shale (CPmax = 12 MPa), 30% for the Georgian Bay Formation shale (15 MPa), 34% for the Cobourg Formation limestone (17.4 MPa), 31% for the Cobourg Formation argillaceous limestone (17.4 MPa) and 43-46% for the Opalinus Clay (15 MPa). Decreases in De were larger for the I- tracer: 13.8% for the Queenston shale, 42% for the Georgian Bay shale, 50% for the Cobourg Formation limestone, 55% for the Cobourg Formation argillaceous limestone and 63-68% for the Opalinus Clay. The tracer-specific nature of the response is attributed to an increasing influence of anion exclusion as the pore size decreases at higher CP. Results from the shales (including Opalinus Clay) indicate that the pressure effect on De can be represented by a linear relationship between De and ln(CP), which provides valuable predictive capability. The nonlinearity results in a relatively small change in De at high CP, suggesting that it is not necessary to apply the exact in situ pressure conditions in order to obtain a good estimate of the in situ diffusion coefficient. Most importantly, the CP effect on shale is reversible (± 12%) suggesting that, for

  16. Apparent diffusion coefficient evaluation for secondary changes in the cerebellum of rats after middle cerebral artery occlusion.

    PubMed

    Yang, Yunjun; Gao, Lingyun; Fu, Jun; Zhang, Jun; Li, Yuxin; Yin, Bo; Chen, Weijian; Geng, Daoying

    2013-11-05

    Supratentorial cerebral infarction can cause functional inhibition of remote regions such as the cerebellum, which may be relevant to diaschisis. This phenomenon is often analyzed using positron emission tomography and single photon emission CT. However, these methods are expensive and radioactive. Thus, the present study quantified the changes of infarction core and remote regions after unilateral middle cerebral artery occlusion using apparent diffusion coefficient values. Diffusion-weighted imaging showed that the area of infarction core gradually increased to involve the cerebral cortex with increasing infarction time. Diffusion weighted imaging signals were initially increased and then stabilized by 24 hours. With increasing infarction time, the apparent diffusion coefficient value in the infarction core and remote bilateral cerebellum both gradually decreased, and then slightly increased 3-24 hours after infarction. Apparent diffusion coefficient values at remote regions (cerebellum) varied along with the change of supratentorial infarction core, suggesting that the phenomenon of diaschisis existed at the remote regions. Thus, apparent diffusion coefficient values and diffusion weighted imaging can be used to detect early diaschisis.

  17. Optimal Experiment Design for Monoexponential Model Fitting: Application to Apparent Diffusion Coefficient Imaging.

    PubMed

    Alipoor, Mohammad; Maier, Stephan E; Gu, Irene Yu-Hua; Mehnert, Andrew; Kahl, Fredrik

    2015-01-01

    The monoexponential model is widely used in quantitative biomedical imaging. Notable applications include apparent diffusion coefficient (ADC) imaging and pharmacokinetics. The application of ADC imaging to the detection of malignant tissue has in turn prompted several studies concerning optimal experiment design for monoexponential model fitting. In this paper, we propose a new experiment design method that is based on minimizing the determinant of the covariance matrix of the estimated parameters (D-optimal design). In contrast to previous methods, D-optimal design is independent of the imaged quantities. Applying this method to ADC imaging, we demonstrate its steady performance for the whole range of input variables (imaged parameters, number of measurements, and range of b-values). Using Monte Carlo simulations we show that the D-optimal design outperforms existing experiment design methods in terms of accuracy and precision of the estimated parameters.

  18. Assessment of natural radiation exposure levels and mass attenuation coefficients of lime and gypsum samples used in Turkey.

    PubMed

    Damla, Nevzat; Cevik, Uğur; Kobya, Ali Ihsan; Celik, Ahmet; Celik, Necati

    2010-11-01

    The activity concentrations of 226Ra, 232Th, and 40K in lime and gypsum samples used as building materials in Turkey were measured using gamma spectrometry. The mean activity concentrations of 226Ra, 232Th, and 40K were found to be 38±16, 20±9, and 156±54 Bq kg(-1) for lime and found to be 17±6, 13±5, and 429±24 Bq kg(-1) for gypsum, respectively. The radiological hazards due to the natural radioactivity in the samples were inferred from calculations of radium equivalent activities (Raeq), indoor absorbed dose rate in the air, the annual effective dose, and gamma and alpha indices. These radiological parameters were evaluated and compared with the internationally recommended limits. The experimental mass attenuation coefficients (μ/ρ) of the samples were determined in the energy range 81-1,332 keV. The experimental mass attenuation coefficients were compared with theoretical values obtained using XCOM. It is found that the calculated values and the experimental results are in good agreement.

  19. Prediction of broadband attenuation computed using band-averaged mass extinction coefficients and band-averaged transmittance

    NASA Astrophysics Data System (ADS)

    Farmer, W. M.

    1991-09-01

    A common method of estimating the attenuation capabilities of military smokes/obscurants is to use a band-averaged mass-extinction coefficient with concentration-length values in the Beer-Bouguer transmission law. This approach ignores the effects of source spectra, sensor response, and normal atmospheric attenuation on broadband transmittance characteristics, which can significantly affect broadband transmittance. The differences that can occur in predicting relative transmittance as a function of concentration length by using band-averaged mass-extinction coefficients as opposed to more properly computing the band-averaged transmittance are discussed in this paper. Two examples are provided to illustrate the differences in results. The first example considers 3- to 5-micron and 8- to 14-micron band transmission through natural fogs. The second example considers 3- to 5-micron and 8- to 12-micron transmission through phosphorus-derived smoke (a common military obscurant) produced at 17 percent and at 90 percent relative humidity. Major differences are found in the values of concentration lengths predicted by the two methods when the transmittance relative to an unobscured atmosphere falls below about 20 percent. These results can affect conclusions concerning the detection of targets in smokes screens, smoke concentration lengths required to obscure a target, and radiative transport through polluted atmospheres.

  20. Survival analysis for apparent diffusion coefficient measures in children with embryonal brain tumours.

    PubMed

    Grech-Sollars, Matthew; Saunders, Dawn E; Phipps, Kim P; Clayden, Jonathan D; Clark, Chris A

    2012-10-01

    Embryonal brain tumors constitute a large and important subgroup of pediatric brain tumors. Apparent diffusion coefficient (ADC) measures have been previously used in the analysis of these tumors. We investigated a newly described ADC-derived parameter, the apparent transient coefficient in tumor (ATCT), a measure of the gradient change of ADC from the peri-tumoral edema into the tumor core, to study whether ATCT correlates with survival outcome. Sixty-one patients with histologically proven embryonal brain tumors and who had diffusion-weighted imaging (DWI) as part of their clinical imaging were enrolled in a retrospective study correlating ADC measures with survival. Kaplan-Meier survival curves were constructed for extent of surgical resection, age <3 years at diagnosis, tumor type, and metastasis at presentation. A multivariate survival analysis was performed that took into consideration ATCT and variables found to be significant in the Kaplan-Meier analysis as covariates. Results from the multivariate analysis showed that ATCT was the only significant covariate (P < .001). Survival analysis using Kaplan-Meier curves, dividing the patients into 4 groups of increasing values of ATCT, showed that more negative values of ATCT were significantly associated with a poorer prognosis (P < .001). A statistically significant difference was observed for survival data with respect to the change in ADC from edema into the tumor volume. Results show that more negative ATCT values are significantly associated with a poorer survival among children with embryonal brain tumors, irrespective of tumor type, extent of resection, age <3 years at diagnosis, and metastasis at presentation.

  1. Iterative methods for solving coefficient inverse problems of wave tomography in models with attenuation

    NASA Astrophysics Data System (ADS)

    Goncharsky, Alexander V.; Romanov, Sergey Y.

    2017-02-01

    We develop efficient iterative methods for solving inverse problems of wave tomography in models incorporating both diffraction effects and attenuation. In the inverse problem the aim is to reconstruct the velocity structure and the function that characterizes the distribution of attenuation properties in the object studied. We prove mathematically and rigorously the differentiability of the residual functional in normed spaces, and derive the corresponding formula for the Fréchet derivative. The computation of the Fréchet derivative includes solving both the direct problem with the Neumann boundary condition and the reversed-time conjugate problem. We develop efficient methods for numerical computations where the approximate solution is found using the detector measurements of the wave field and its normal derivative. The wave field derivative values at detector locations are found by solving the exterior boundary value problem with the Dirichlet boundary conditions. We illustrate the efficiency of this approach by applying it to model problems. The algorithms developed are highly parallelizable and designed to be run on supercomputers. Among the most promising medical applications of our results is the development of ultrasonic tomographs for differential diagnosis of breast cancer.

  2. Region specific optimization of continuous linear attenuation coefficients based on UTE (RESOLUTE): application to PET/MR brain imaging.

    PubMed

    Ladefoged, Claes N; Benoit, Didier; Law, Ian; Holm, Søren; Kjær, Andreas; Højgaard, Liselotte; Hansen, Adam E; Andersen, Flemming L

    2015-10-21

    The reconstruction of PET brain data in a PET/MR hybrid scanner is challenging in the absence of transmission sources, where MR images are used for MR-based attenuation correction (MR-AC). The main challenge of MR-AC is to separate bone and air, as neither have a signal in traditional MR images, and to assign the correct linear attenuation coefficient to bone. The ultra-short echo time (UTE) MR sequence was proposed as a basis for MR-AC as this sequence shows a small signal in bone. The purpose of this study was to develop a new clinically feasible MR-AC method with patient specific continuous-valued linear attenuation coefficients in bone that provides accurate reconstructed PET image data. A total of 164 [(18)F]FDG PET/MR patients were included in this study, of which 10 were used for training. MR-AC was based on either standard CT (reference), UTE or our method (RESOLUTE). The reconstructed PET images were evaluated in the whole brain, as well as regionally in the brain using a ROI-based analysis. Our method segments air, brain, cerebral spinal fluid, and soft tissue voxels on the unprocessed UTE TE images, and uses a mapping of R(*)2 values to CT Hounsfield Units (HU) to measure the density in bone voxels. The average error of our method in the brain was 0.1% and less than 1.2% in any region of the brain. On average 95% of the brain was within  ±10% of PETCT, compared to 72% when using UTE. The proposed method is clinically feasible, reducing both the global and local errors on the reconstructed PET images, as well as limiting the number and extent of the outliers.

  3. Region specific optimization of continuous linear attenuation coefficients based on UTE (RESOLUTE): application to PET/MR brain imaging

    NASA Astrophysics Data System (ADS)

    Ladefoged, Claes N.; Benoit, Didier; Law, Ian; Holm, Søren; Kjær, Andreas; Højgaard, Liselotte; Hansen, Adam E.; Andersen, Flemming L.

    2015-10-01

    The reconstruction of PET brain data in a PET/MR hybrid scanner is challenging in the absence of transmission sources, where MR images are used for MR-based attenuation correction (MR-AC). The main challenge of MR-AC is to separate bone and air, as neither have a signal in traditional MR images, and to assign the correct linear attenuation coefficient to bone. The ultra-short echo time (UTE) MR sequence was proposed as a basis for MR-AC as this sequence shows a small signal in bone. The purpose of this study was to develop a new clinically feasible MR-AC method with patient specific continuous-valued linear attenuation coefficients in bone that provides accurate reconstructed PET image data. A total of 164 [18F]FDG PET/MR patients were included in this study, of which 10 were used for training. MR-AC was based on either standard CT (reference), UTE or our method (RESOLUTE). The reconstructed PET images were evaluated in the whole brain, as well as regionally in the brain using a ROI-based analysis. Our method segments air, brain, cerebral spinal fluid, and soft tissue voxels on the unprocessed UTE TE images, and uses a mapping of R2* values to CT Hounsfield Units (HU) to measure the density in bone voxels. The average error of our method in the brain was 0.1% and less than 1.2% in any region of the brain. On average 95% of the brain was within  ±10% of PETCT, compared to 72% when using UTE. The proposed method is clinically feasible, reducing both the global and local errors on the reconstructed PET images, as well as limiting the number and extent of the outliers.

  4. Apparent Diffusion Coefficient Measurement in Mediastinal Lymphadenopathies: Differentiation between Benign and Malignant Lesions

    PubMed Central

    Ustabasioglu, Fethi Emre; Samanci, Cesur; Alis, Deniz; Samanci, Nilay Sengul; Kula, Osman; Olgun, Deniz Cebi

    2017-01-01

    Objectives: We aimed to prospectively assess the diagnostic value of apparent diffusion coefficient (ADC) measurement in the differentiation of benign and malignant mediastinal lymphadenopathies. Materials and Methods: The study included 63 consecutive patients (28 women, 35 men; mean age 59.3 years) with 125 mediastinal lymphadenopathies. Echoplanar diffusion-weighted magnetic resonance imaging of the mediastinum was performed with b-factors of 0 and 600 mm2/s before mediastinoscopy and mediastinotomy, and ADC values were measured. The ADC values were compared with the histological results, and statistical analysis was done. P < 0.05 was considered statistically significant. Results: The mean ADC value of malignant mediastinal lymphadenopathy (1.030 ± 0.245 × 10−3 mm2/s) was significantly lower (P < 0.05) when compared to benign lymphadenopathies (1.571 ± 0.559 × 10−3 mm2/s). For differentiating malignant from benign mediastinal lymphadenopathy, the best result was obtained when an ADC value of 1.334 × 10−3 mm2/s was used as a threshold value; area under the curve 0.848, accuracy 78.4%, sensitivity 66%, specificity of 86%, positive predictive value 76.7%, and negative predictive value of 79.2%. Interobserver agreement was excellent for ADC measurements. Conclusions: ADC measurements could be considered an important supportive method in differentiating benign from malignant mediastinal lymphadenopathies.

  5. Mesure des coefficients de la matrice de diffusion d'une jonction mécanique

    NASA Astrophysics Data System (ADS)

    Moulet, M.-H.; Gautier, F.; Pascal, J.-C.

    2002-12-01

    La caractérisation expérimentale des jonctions mécaniques souvent complexes rencontrées dans nombre d'applications industrielles est un élément essentiel intervenant dans l'élaboration de modèles vibratoires. Les jonctions permettant de relier des structures simples de type plaque ou poutre peuvent être représentées à l'aide de matrice de diffusion. L'objet de cette communication est de présenter un dispositif expéri mental permettant la mesure des caractéristiques d'une jonction constituée d'une masse symétrique raccordant deux poutres soumises à des vibrations de flexion. La méthode de mesure et ses conditions optimales de mise en oeuvre sont présentées et permettent d'obtenir les coefficients de transmission et de réflexion. Un modèle, tenant compte de l'élasticité des liaisons poutre/masse permet de rendre compte des coefficients mesurés et d'interpréter leur variation fréquentielle à l'aide du phénomène de masse bloquante.

  6. Singular 1-soliton solution of the nonlinear variable-coefficient diffusion reaction and mKdV equations

    NASA Astrophysics Data System (ADS)

    Guner, Ozkan; Bekir, Ahmet; Unsal, Omer; Cevikel, Adem C.

    2017-01-01

    In this paper, we pay attention to the analytical method named, ansatz method for finding the exact solutions of the variable-coefficient modified KdV equation and variable coefficient diffusion-reaction equation. As a result the singular 1-soliton solution is obtained. These solutions are important for the explanation of some practical physical problems. The obtained results show that these methods provides a powerful mathematical tool for solving nonlinear equations with variable coefficients. This method can be extended to solve other variable coefficient nonlinear partial differential equations.

  7. Apparent diffusion coefficient values of normal testis and variations with age

    PubMed Central

    Tsili, Athina C; Giannakis, Dimitrios; Sylakos, Anastasios; Ntorkou, Alexandra; Astrakas, Loukas G; Sofikitis, Nikolaos; Argyropoulou, Maria I

    2014-01-01

    The usefulness of diffusion-weighted magnetic resonance imaging (DWI) in the evaluation of scrotal pathology has recently been reported. A standard reference of normal testicular apparent diffusion coefficient (ADC) values and their variations with age is necessary when interpreting normal testicular anatomy and pathology. We evaluated 147 normal testes using DWI, including 71 testes from 53 men aged 20–39 years (group 1), 67 testes from 42 men aged 40–69 years (group 2) and nine testes from six men older than 70 years (group 3). DWI was performed along the axial plane, using a single shot, multislice spin-echo planar diffusion pulse sequence and b-values of 0 and 900 s mm−2. The mean and standard deviation of the ADC values of normal testicular parenchyma were calculated for each age group separately. Analysis of variance (ANOVA) followed by post hoc analysis (Dunnett T3) was used for statistical purposes. The ADC values (× 10−3 mm2 s−1) of normal testicular tissue were different among age groups (group 1: 1.08 ± 0.13; group 2: 1.15 ± 0.15 and group 3: 1.31 ± 0.22). ANOVA revealed differences in mean ADC among age groups (F = 11.391, P < 0.001). Post hoc analysis showed differences between groups 1 and 2 (P = 0.008) and between groups 1 and 3 (P = 0.043), but not between groups 2 and 3 (P = 0.197). Our findings suggest that ADC values of normal testicular tissue increase with advancing age. PMID:24556745

  8. Assimilation of remotely-sensed diffuse attenuation data to improve the simulation of a marine ecosystem model

    NASA Astrophysics Data System (ADS)

    Ciavatta, Stefano; Torres, Ricardo; Martinez-Vicente, Victor; Smyth, Timothy; Dall'Olmo, Giorgio; Polimene, Luca; Allen, Icarus

    2014-05-01

    Biogeochemical processes in shelf seas and coastal areas can determine the health and productivity of local systems and are important terms of the global carbon budget. The quantitative characterization of the spatial-temporal evolution of biogeochemical variables in shelf-seas is thus relevant in the framework of marine system management and climate change studies In this work we evaluate, for the first time, whether the assimilation of remotely-sensed diffuse attenuation coefficient data into a marine ecosystem model can improve the simulation of key biogeochemical variables and processes in a shelf sea. A localized Ensemble Kalman filter was used to assimilate weekly SeaWiFS data of diffuse light attenuation coefficient, i.e. Kd(443), into an ecosystem model of the western English Channel, for the simulation of year 2006. The spatial distributions of (unassimilated) surface chlorophyll from SeaWiFS, and eighteen time series of biogeochemical and optical data measured weekly at the monitoring station L4 were used to evaluate the system performance. A comparative assimilation experiment was run by using SeaWiFS chlorophyll data. We found that Kd(443) assimilation reduced the root mean square error and improved the correlation with the assimilated satellite observations in the largest part area of the WEC. The error for the (unassimilated) chlorophyll tended to decrease as well, but the estimates deteriorated in some parts of the study area. Assimilation of Kd(443) provided better estimates of the (unassimilated) in situ data when compared with both the reference simulation and chlorophyll assimilation. Indeed, model RMSE and bias of the estimates decreased for more than a half of the variables, and the skill metrics resulted in general better for the assimilation of the optical data. Importantly, assimilation of Kd(443) impacted the simulation of biogeochemical fluxes and ecosystem processes (e.g. shifted the simulated food web towards the microbial loop), and in

  9. Universality of Viscosity Dependence of Translational Diffusion Coefficients of Carbon Monoxide, Diphenylacetylene, and Diphenylcyclopropenone in Ionic Liquids under Various Conditions.

    PubMed

    Kimura, Y; Kida, Y; Matsushita, Y; Yasaka, Y; Ueno, M; Takahashi, K

    2015-06-25

    Translational diffusion coefficients of diphenylcyclopropenone (DPCP), diphenylacetylene (DPA), and carbon monoxide (CO) in 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([BMIm][NTf2]) and 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([EMIm][NTf2]) were determined by the transient grating (TG) spectroscopy under pressure from 0.1 to 200 MPa at 298 K and from 298 to 373 K under 0.1 MPa. Diffusion coefficients of these molecules at high temperatures in tributylmethylphosphonium bis(trifluoromethanesulfonyl)imide ([P4441][NTf2]), and tetraoctylphosphonium bis(trifluoromethanesulfonyl)imide ([P8888][NTf2]), and also in the mixtures of [BMIm][NTf2], N-methyl-N-propylpiperidinium bis(trifluoromethanesulfonyl)imide ([Pp13][NTf2]), and trihexyltetradecylphosphonium bis(trifluoromethanesulfonyl)imide ([P66614][NTf2]) with ethanol or chloroform have been determined. Diffusion coefficients except in ILs of phosphonium cations were well scaled by the power law of T/η, i.e., (T/η)(P), where T and η are the absolute temperature and the viscosity, irrespective of the solvent species, pressure and temperature, and the compositions of mixtures. The values of the exponent P were smaller for the smaller size of the molecules. On the other hand, the diffusion coefficients in ILs of phosphonium cations with longer alkyl chains were larger than the values expected from the correlation obtained by other ILs and conventional liquids. The deviation becomes larger with increasing the number of carbon atoms of alkyl-chain of cation, and with decreasing the molecular size of diffusing molecules. The molecular size dependence of the diffusion coefficient was correlated by the ratio of the volume of the solute to that of the solvent as demonstrated by the preceding work (Kaintz et al., J. Phys. Chem. B 2013 , 117 , 11697 ). Diffusion coefficients have been well correlated with the power laws of both T/η and the relative volume of the solute to the solvent.

  10. First-principles binary diffusion coefficients for H, H₂, and four normal alkanes + N₂.

    PubMed

    Jasper, Ahren W; Kamarchik, Eugene; Miller, James A; Klippenstein, Stephen J

    2014-09-28

    Collision integrals related to binary (dilute gas) diffusion are calculated classically for six species colliding with N2. The most detailed calculations make no assumptions regarding the complexity of the potential energy surface, and the resulting classical collision integrals are in excellent agreement with previous semiclassical results for H + N2 and H2 + N2 and with recent experimental results for CnH(2n+2) + N2, n = 2-4. The detailed classical results are used to test the accuracy of three simplifying assumptions typically made when calculating collision integrals: (1) approximating the intermolecular potential as isotropic, (2) neglecting the internal structure of the colliders (i.e., neglecting inelasticity), and (3) employing unphysical R(-12) repulsive interactions. The effect of anisotropy is found to be negligible for H + N2 and H2 + N2 (in agreement with previous quantum mechanical and semiclassical results for systems involving atomic and diatomic species) but is more significant for larger species at low temperatures. For example, the neglect of anisotropy decreases the diffusion coefficient for butane + N2 by 15% at 300 K. The neglect of inelasticity, in contrast, introduces only very small errors. Approximating the repulsive wall as an unphysical R(-12) interaction is a significant source of error at all temperatures for the weakly interacting systems H + N2 and H2 + N2, with errors as large as 40%. For the normal alkanes in N2, which feature stronger interactions, the 12/6 Lennard-Jones approximation is found to be accurate, particularly at temperatures above ∼700 K where it predicts the full-dimensional result to within 5% (although with somewhat different temperature dependence). Overall, the typical practical approach of assuming isotropic 12/6 Lennard-Jones interactions is confirmed to be suitable for combustion applications except for weakly interacting systems, such as H + N2. For these systems, anisotropy and inelasticity can safely be

  11. First-principles binary diffusion coefficients for H, H2 and four normal alkanes + N2

    DOE PAGES

    Jasper, Ahren W.; Kamarchik, Eugene; Miller, James A.; ...

    2014-09-30

    Collision integrals related to binary (dilute gas) diffusion are calculated classically for six species colliding with N2. The most detailed calculations make no assumptions regarding the complexity of the potential energy surface, and the resulting classical collision integrals are in excellent agreement with previous semiclassical results for H + N2 and H2 + N2 and with recent experimental results for C n H2n+2 + N2, n = 2–4. The detailed classical results are used to test the accuracy of three simplifying assumptions typically made when calculating collision integrals: (1) approximating the intermolecular potential as isotropic, (2) neglecting the internal structuremore » of the colliders (i.e., neglecting inelasticity), and (3) employing unphysical R–12 repulsive interactions. The effect of anisotropy is found to be negligible for H + N2 and H2 + N2 (in agreement with previous quantum mechanical and semiclassical results for systems involving atomic and diatomic species) but is more significant for larger species at low temperatures. For example, the neglect of anisotropy decreases the diffusion coefficient for butane + N2 by 15% at 300 K. The neglect of inelasticity, in contrast, introduces only very small errors. Approximating the repulsive wall as an unphysical R–12 interaction is a significant source of error at all temperatures for the weakly interacting systems H + N2 and H2 + N2, with errors as large as 40%. For the normal alkanes in N2, which feature stronger interactions, the 12/6 Lennard–Jones approximation is found to be accurate, particularly at temperatures above –700 K where it predicts the full-dimensional result to within 5% (although with somewhat different temperature dependence). Overall, the typical practical approach of assuming isotropic 12/6 Lennard–Jones interactions is confirmed to be suitable for combustion applications except for weakly interacting systems, such as H + N2. For these systems, anisotropy and inelasticity

  12. Assessment of satellite derived diffuse attenuation coefficients and euphotic depths in south Florida coastal waters

    EPA Science Inventory

    Optical data collected in coastal waters off South Florida and in the Caribbean Sea between January 2009 and December 2010 were used to evaluate products derived with three bio-optical inversion algorithms applied to MOIDS/Aqua, MODIS/Terra, and SeaWiFS satellite observations. Th...

  13. A New Coarse-Grained Model for E. coli Cytoplasm: Accurate Calculation of the Diffusion Coefficient of Proteins and Observation of Anomalous Diffusion

    PubMed Central

    Hasnain, Sabeeha; McClendon, Christopher L.; Hsu, Monica T.; Jacobson, Matthew P.; Bandyopadhyay, Pradipta

    2014-01-01

    A new coarse-grained model of the E. coli cytoplasm is developed by describing the proteins of the cytoplasm as flexible units consisting of one or more spheres that follow Brownian dynamics (BD), with hydrodynamic interactions (HI) accounted for by a mean-field approach. Extensive BD simulations were performed to calculate the diffusion coefficients of three different proteins in the cellular environment. The results are in close agreement with experimental or previously simulated values, where available. Control simulations without HI showed that use of HI is essential to obtain accurate diffusion coefficients. Anomalous diffusion inside the crowded cellular medium was investigated with Fractional Brownian motion analysis, and found to be present in this model. By running a series of control simulations in which various forces were removed systematically, it was found that repulsive interactions (volume exclusion) are the main cause for anomalous diffusion, with a secondary contribution from HI. PMID:25180859

  14. Diffusion-weighted magnetic resonance imaging in cancer: Reported apparent diffusion coefficients, in-vitro and in-vivo reproducibility

    PubMed Central

    Jafar, Maysam M; Parsai, Arman; Miquel, Marc E

    2016-01-01

    There is considerable disparity in the published apparent diffusion coefficient (ADC) values across different anatomies. Institutions are increasingly assessing repeatability and reproducibility of the derived ADC to determine its variation, which could potentially be used as an indicator in determining tumour aggressiveness or assessing tumour response. In this manuscript, a review of selected articles published to date in healthy extra-cranial body diffusion-weighted magnetic resonance imaging is presented, detailing reported ADC values and discussing their variation across different studies. In total 115 studies were selected including 28 for liver parenchyma, 15 for kidney (renal parenchyma), 14 for spleen, 13 for pancreatic body, 6 for gallbladder, 13 for prostate, 13 for uterus (endometrium, myometrium, cervix) and 13 for fibroglandular breast tissue. Median ADC values in selected studies were found to be 1.28 × 10-3 mm2/s in liver, 1.94 × 10-3 mm2/s in kidney, 1.60 × 10-3 mm2/s in pancreatic body, 0.85 × 10-3 mm2/s in spleen, 2.73 × 10-3 mm2/s in gallbladder, 1.64 × 10-3 mm2/s and 1.31 × 10-3 mm2/s in prostate peripheral zone and central gland respectively (combined median value of 1.54×10-3 mm2/s), 1.44 × 10-3 mm2/s in endometrium, 1.53 × 10-3 mm2/s in myometrium, 1.71 × 10-3 mm2/s in cervix and 1.92 × 10-3 mm2/s in breast. In addition, six phantom studies and thirteen in vivo studies were summarized to compare repeatability and reproducibility of the measured ADC. All selected phantom studies demonstrated lower intra-scanner and inter-scanner variation compared to in vivo studies. Based on the findings of this manuscript, it is recommended that protocols need to be optimised for the body part studied and that system-induced variability must be established using a standardized phantom in any clinical study. Reproducibility of the measured ADC must also be assessed in a volunteer population, as variations are far more significant in vivo compared

  15. Early Changes in Apparent Diffusion Coefficient From Diffusion-Weighted MR Imaging During Radiotherapy for Prostate Cancer

    SciTech Connect

    Park, Sung Yoon; Kim, Chan Kyo; Park, Byung Kwan; Park, Won; Park, Hee Chul; Han, Deok Hyun; Kim, Bohyun

    2012-06-01

    Purpose: To investigate the feasibility of diffusion-weighted MRI (DWI) as an early and reproducible change indicator in patients receiving radiotherapy for prostate cancer (PC). Methods and Materials: Eight consecutive patients with biopsy-proven PC underwent DWI at 3T. All patients who received external-beam radiotherapy had four serial MR scans, as follows: before therapy (PreTx); after 1 week of therapy (PostT1); after 3 weeks of therapy (PostT2); and 1 month after the completion of therapy (PostT3). At each time, the apparent diffusion coefficient (ADC) was measured in tumors and normal tissues. For reproducibility of the ADC measurement, five patients also had two separate pretreatment DWI scans at an interval of <2 weeks. Serum prostate-specific antigen (PSA) levels were evaluated at the same time as MR scans. Results: Thirteen tumors (peripheral zone = 10; transition zone = 3) were found. The mean ADC values for the tumors from PreTx to PostT3 were 0.86, 1.03, 1.15, and 1.26 Multiplication-Sign 10{sup -3} mm{sup 2}/s in sequence, respectively. Compared with PreTx, PostT1 (p = 0.005), PostT2 (p = 0.003), and PostT3 (p < 0.001) showed a significant increase in ADC values. The mean ADC values of the benign tissues from PreTx to PostT3 were 1.60, 1.58, 1.47, and 1.46 Multiplication-Sign 10{sup -3} mm{sup 2}/s in sequence, respectively. Reproducibility of ADC measurements was confirmed with a mean difference in ADC of -0.04 in peripheral zone and -0.017 in transition zone between two separate pretreatment MR scans. The mean PSA levels from PreTx to PostT3 were 9.05, 9.18, 9.25, and 4.11 ng/mL in sequence, respectively. Conclusions: DWI, as a reproducible biomarker, has the potential to evaluate the early therapeutic changes of PC to radiotherapy.

  16. Small effect of water on upper mantle rheology based on silicon self-diffusion coefficients

    NASA Astrophysics Data System (ADS)

    Fei, H.; Wiedenbeck, M.; Yamazaki, D.; Katsura, T.

    2012-12-01

    Water has been considered to significantly affect the mantle dynamics. In particular, experimental deformation studies [1-4] claimed that even small amount of water enhanced the creep in olivine by orders of magnitude. However, we note that their results are experimental artifact due to a number of limitations: e.g., unavoidable grain boundary sliding when polycrystalline samples were used; limited ranges of water contents due to the limited pressures; several orders higher stress and strain rate than those in nature. High temperature creep of silicate minerals is controlled by silicon self-diffusion. Therefore, measurement of silicon self-diffusion coefficients (DSi) in minerals, which can be performed without these limitations, is an independent way to study the mantle rheology. In this study, we measured DSi in Mg end-member of olivine, namely, forsterite, as a function of water content (CH2O) across a wide range, and concluded that effect of water on upper mantle rheology is very small. Forsterite single crystals were doped with <1 to ~800 μg/g of water at 1600 K, 8 GPa using talc+brucite water sources and graphite buffer. The CH2O in the samples were controlled by the ratio of water sources to graphite. The water doped samples were polished, deposited with 500 nm 29Si enriched Mg2SiO4 thin films, and annealed at 8 GPa, 1600 or 1800 K for diffusion with the same proportion of water sources, which successfully made constant values of CH2O during diffusion annealing. The diffusion profiles were obtained by SIMS. CH2O in the samples were determined by FT-IR before and after diffusion, and also examined by SIMS. Our results yield a relationship: DSi ∝ (CH2O)1/3. This is explained by defect chemistry, where DSi∝[VSi‧‧‧‧]×[VO●●]∝(CH2O)2/3×(CH2O)-1/3=(CH2O)1/3 under the charge neutrality condition of [(OH)O●]=2[VMg‧‧] because both Si and O vacancies are needed for Si ions to diffuse. The water contents exponent (1/3) determined in this study

  17. Measurements of the thermal coefficient of optical attenuation at different depth regions of in vivo human skins using optical coherence tomography: a pilot study.

    PubMed

    Su, Ya; Yao, X Steve; Li, Zhihong; Meng, Zhuo; Liu, Tiegen; Wang, Longzhi

    2015-02-01

    We present detailed measurement results of optical attenuation's thermal coefficients (referenced to the temperature of the skin surface) in different depth regions of in vivo human forearm skins using optical coherence tomography (OCT). We first design a temperature control module with an integrated optical probe to precisely control the surface temperature of a section of human skin. We propose a method of using the correlation map to identify regions in the skin having strong correlations with the surface temperature of the skin and find that the attenuation coefficient in these regions closely follows the variation of the surface temperature without any hysteresis. We observe a negative thermal coefficient of attenuation in the epidermis. While in dermis, the slope signs of the thermal coefficient of attenuation are different at different depth regions for a particular subject, however, the depth regions with a positive (or negative) slope are different in different subjects. We further find that the magnitude of the thermal coefficient of attenuation coefficient is greater in epidermis than in dermis. We believe the knowledge of such thermal properties of skins is important for several noninvasive diagnostic applications, such as OCT glucose monitoring, and the method demonstrated in this paper is effective in studying the optical and biological properties in different regions of skin.

  18. Relationship between Gleason score and apparent diffusion coefficients of diffusion-weighted magnetic resonance imaging in prostate cancer patients

    PubMed Central

    Kim, Tae Heon; Kim, Chan Kyo; Park, Byung Kwan; Jeon, Hwang Gyun; Jeong, Byung Chang; Seo, Seong Il; Lee, Hyun Moo; Choi, Han Yong; Jeon, Seong Soo

    2016-01-01

    Introduction We assessed the correlation between the apparent diffusion coefficient (ADC) and pathological Gleason score (GS) of prostate cancer patients. Methods A total of 125 patients who underwent multiparametric magnetic resonance imaging before radical prostatectomy for prostate cancer were included in this study. ADC values were compared with different GS. We used receiver operating characteristic analysis and determined the ADC cutoff value to differentiate tumours with a GS of 6 from those with a GS ≥7. Results We identified 34 patients (27.2%) with a GS of 6; 33 patients (26.4%) with a GS of 7; 22 patients (17.6%) with a GS of 8; and 36 patients (28.8%) with a GS of ≥9. The mean ADC value for disease with a GS of 6 was 0.914 ± 0.161 ×10−3 mm2/s; GS of 7: 0.741 ± 0.164 ×10−3 mm2/s; GS of 8: 0.679 ± 0.130 ×10−3 mm2/s; and GS of ≥9: 0.593 ± 0.089 ×10−3 mm2/s. An ADC value of 0.830 ×10−3mm2/s was the best cutoff value to identify prostate cancer with a GS of 6. Conclusions We observed an inverse relationship between GS and ADC value. Moreover, a cutoff ADC value may help differentiate disease with a GS of 6 from disease with a GS ≥7. PMID:28096922

  19. Diffusion of responsibility attenuates altruistic punishment: A functional magnetic resonance imaging effective connectivity study.

    PubMed

    Feng, Chunliang; Deshpande, Gopikrishna; Liu, Chao; Gu, Ruolei; Luo, Yue-Jia; Krueger, Frank

    2016-02-01

    Humans altruistically punish violators of social norms to enforce cooperation and pro-social behaviors. However, such altruistic behaviors diminish when others are present, due to a diffusion of responsibility. We investigated the neural signatures underlying the modulations of diffusion of responsibility on altruistic punishment, conjoining a third-party punishment task with event-related functional magnetic resonance imaging and multivariate Granger causality mapping. In our study, participants acted as impartial third-party decision-makers and decided how to punish norm violations under two different social contexts: alone (i.e., full responsibility) or in the presence of putative other third-party decision makers (i.e., diffused responsibility). Our behavioral results demonstrated that the diffusion of responsibility served as a mediator of context-dependent punishment. In the presence of putative others, participants who felt less responsible also punished less severely in response to norm violations. Our neural results revealed that underlying this behavioral effect was a network of interconnected brain regions. For unfair relative to fair splits, the presence of others led to attenuated responses in brain regions implicated in signaling norm violations (e.g., AI) and to increased responses in brain regions implicated in calculating values of norm violations (e.g., vmPFC, precuneus) and mentalizing about others (dmPFC). The dmPFC acted as the driver of the punishment network, modulating target regions, such as AI, vmPFC, and precuneus, to adjust altruistic punishment behavior. Our results uncovered the neural basis of the influence of diffusion of responsibility on altruistic punishment and highlighted the role of the mentalizing network in this important phenomenon. Hum Brain Mapp 37:663-677, 2016. © 2015 Wiley Periodicals, Inc.

  20. Fe Mg diffusion in olivine II: point defect chemistry, change of diffusion mechanisms and a model for calculation of diffusion coefficients in natural olivine

    NASA Astrophysics Data System (ADS)

    Dohmen, Ralf; Chakraborty, Sumit

    2007-08-01

    Analysis of existing data and models on point defects in pure (Fe,Mg)-olivine (Phys Chem Miner 10:27 37,1983; Phys Chem Miner 29:680 694, 2002) shows that it is necessary to consider thermodynamic non-ideality of mixing to adequately describe the concentration of point defects over the range of measurement. In spite of different sources of uncertainties, the concentrations of vacancies in octahedral sites in (Fe,Mg)-olivine are on the order of 10-4 per atomic formula unit at 1,000 1,200 °C according to both the studies. We provide the first explicit plots of vacancy concentrations in olivine as a function of temperature and oxygen fugacity according to the two models. It is found that in contrast to absolute concentrations at ˜1,100 °C and dependence on fO2, there is considerable uncertainty in our knowledge of temperature dependence of vacancy concentrations. This needs to be considered in discussing the transport properties such as diffusion coefficients. Moreover, these defect models in pure (Fe,Mg)-olivine need to be extended by considering aliovalent impurities such as Al, Cr to describe the behavior of natural olivine. We have developed such a formulation, and used it to analyze the considerable database of diffusion coefficients in olivine from Dohmen et al. (Phys Chem Miner this volume, 2007) (Part - I) and older data in the literature. The analysis documents unequivocally for the first time a change of diffusion mechanism in a silicate mineral—from the transition metal extrinsic (TaMED) to the purely extrinsic (PED) domain, at fO2 below 10-10 Pa, and consequently, temperatures below 900 °C. The change of diffusion mechanism manifests itself in a change in fO2 dependence of diffusivity and a slight change in activation energy of diffusion—the activation energy increases at lower temperatures. These are consistent with the predictions of Chakraborty (J Geophys Res 102(B6):12317 12331, 1997). Defect formation enthalpies in the TaMED regime (distinct

  1. A new approach to evaluating the effects of pharmacologic vitreolysis on vitreous diffusion coefficients using dynamic light scattering

    NASA Astrophysics Data System (ADS)

    Ansari, Rafat R.; Suh, Kwang I.; Sebag, J.

    2006-02-01

    PURPOSE: Pharmacologic vitreolysis is a new approach to improve vitreo-retinal surgery. Ultimately, the development of drugs to liquefy and detach vitreous from retina should prevent disease by mitigating the contribution of vitreous to retinopathy and eliminate the need for surgery. However, the mechanism of action of pharmacologic vitreolysis remains unclear. The technique of Dynamic light scattering (DLS) was used to evaluate the effects of microplasmin by following the diffusion coefficients of spherical polystyrene nano-particles injected with microplasmin into the vitreous. METHODS: Diffusion coefficients in dissected (n=9) porcine eyes were measured in vitro. DLS was performed on all specimens at 37°C as often as every 10 minutes for up to 6 hours following injections of human recombinant microplasmin at doses ranging from 0.125 mg to 0.8 mg, with 20 nm diameter tracer nanospheres. RESULTS: DLS findings in untreated porcine vitreous were similar to the previously described findings in bovine and human vitreous, demonstrating a fast (early) component, resulting from the flexible hyaluronan molecules, and a slow (late) component, resulting form the stiff collagen molecules. Microplasmin increased porcine vitreous diffusion coefficients. A new approach was developed to use DLS measurements of vitreous diffusion coefficients to evaluate the effects of microplasmin in intact eyes. CONCLUSIONS: Pharmacologic vitreolysis with human recombinant microplasmin increases vitreous diffusion coefficients in vitro. The results of these studies indicate that this new approach using DLS to measure vitreous diffusion coefficients can be used to study the effects of pharmacologic vitreolysis using microplasmin and other agents in intact eyes and ultimately in vivo.

  2. Chronoamperometry at micropipet electrodes for determination of diffusion coefficients and transferred charges at liquid/liquid interfaces.

    PubMed

    Yuan, Yi; Wang, Lei; Amemiya, Shigeru

    2004-09-15

    Chronoamperometry was carried out at liquid/liquid interfaces supported at the tip of micropipet electrodes for direct determination of the diffusion coefficient of a species in the outer solution. The diffusion coefficient was used for subsequent determination of the transferred charges per species from the diffusion-limited steady-state current. A large tip resistance of the micropipets causes prolonged charging current so that the faradic current can be measured accurately only at a long-time regime (typically t > 5 ms). At the same time, the long-time current response at the interfaces surrounded by a thin glass wall of the pipets is enhanced by diffusion of the species from behind the pipet tip. Therefore, numerical simulations of the long-time chronoamperometric response were carried out using the finite element method for accurate determination of diffusion coefficients. Validity of the simulation results was confirmed by studying simple transfer of tetraethylammonium ion. The technique was applied for transfer/adsorption reactions of the natural polypeptide protamine and also for Ca2+ and Mg2+ transfers facilitated by ionophore ETH 129. With the diffusion coefficient of protamine determined to be (1.2 +/- 0.1) x 10(-6) cm(2)/s, the ionic charge transferred by each protamine molecule was obtained as +20 +/- 1, which is close to the excess positive charge of protamine. Also, the diffusion coefficient of ETH 129 was determined to demonstrate that each ionophore molecule transfers +0.67 and +1 charge per Ca2+ and Mg2+ transfer, respectively, which corresponds to formation of 1:3 and 1:2 complexes with the respective ions.

  3. Precise measurement of the self-diffusion coefficient for poly(ethylene glycol) in aqueous solution using uniform oligomers

    NASA Astrophysics Data System (ADS)

    Shimada, Kayori; Kato, Haruhisa; Saito, Takeshi; Matsuyama, Shigetomo; Kinugasa, Shinichi

    2005-06-01

    Uniform poly(ethylene glycol) (PEG) oligomers, with a degree of polymerization n =1-40, were separated by preparative supercritical fluid chromatography from commercial monodispersed samples. Diffusion coefficients, D, for separated uniform PEG oligomers were measured in dilute solutions of deuterium oxide (D2O) at 30 ° C, using pulsed-field gradient nuclear magnetic resonance. The measured D for each molecular weight was extrapolated to infinite dilution. Diffusion coefficients obtained at infinite dilution follow the scaling behavior of Zimm-type diffusion, even in the lower molecular weight range. Molecular-dynamics simulations for PEG in H2O also showed this scaling behavior, and reproduced close hydrodynamic interactions between PEG and water. These findings suggest that diffusion of PEG in water is dominated by hydrodynamic interaction over a wide molecular weight range, including at low molecular weights around 1000.

  4. Assessment of non-Gaussian diffusion with singly and doubly stretched biexponential models of diffusion-weighted MRI (DWI) signal attenuation in prostate tissue.

    PubMed

    Hall, Matt G; Bongers, Andre; Sved, Paul; Watson, Geoffrey; Bourne, Roger M

    2015-04-01

    Non-Gaussian diffusion dynamics was investigated in the two distinct water populations identified by a biexponential model of diffusion in prostate tissue. Diffusion-weighted MRI (DWI) signal attenuation was measured ex vivo in two formalin-fixed prostates at 9.4 T with diffusion times Δ = 10, 20 and 40 ms, and b values in the range 0.017-8.2 ms/µm(2) . A conventional biexponential model was compared with models in which either the lower diffusivity component or both of the components of the biexponential were stretched. Models were compared using Akaike's Information Criterion (AIC) and a leave-one-out (LOO) test of model prediction accuracy. The doubly stretched (SS) model had the highest LOO prediction accuracy and lowest AIC (highest information content) in the majority of voxels at Δ = 10 and 20 ms. The lower diffusivity stretching factor (α2 ) of the SS model was consistently lower (range ~0.3-0.9) than the higher diffusivity stretching factor (α1 , range ~0.7-1.1), indicating a high degree of diffusion heterogeneity in the lower diffusivity environment, and nearly Gaussian diffusion in the higher diffusivity environment. Stretched biexponential models demonstrate that, in prostate tissue, the two distinct water populations identified by the simple biexponential model individually exhibit non-Gaussian diffusion dynamics.

  5. Modeling exposure close to air pollution sources in naturally ventilated residences: association of turbulent diffusion coefficient with air change rate.

    PubMed

    Cheng, Kai-Chung; Acevedo-Bolton, Viviana; Jiang, Ruo-Ting; Klepeis, Neil E; Ott, Wayne R; Fringer, Oliver B; Hildemann, Lynn M

    2011-05-01

    For modeling exposure close to an indoor air pollution source, an isotropic turbulent diffusion coefficient is used to represent the average spread of emissions. However, its magnitude indoors has been difficult to assess experimentally due to limitations in the number of monitors available. We used 30-37 real-time monitors to simultaneously measure CO at different angles and distances from a continuous indoor point source. For 11 experiments involving two houses, with natural ventilation conditions ranging from <0.2 to >5 air changes per h, an eddy diffusion model was used to estimate the turbulent diffusion coefficients, which ranged from 0.001 to 0.013 m² s⁻¹. The model reproduced observed concentrations with reasonable accuracy over radial distances of 0.25-5.0 m. The air change rate, as measured using a SF₆ tracer gas release, showed a significant positive linear correlation with the air mixing rate, defined as the turbulent diffusion coefficient divided by a squared length scale representing the room size. The ability to estimate the indoor turbulent diffusion coefficient using two readily measurable parameters (air change rate and room dimensions) is useful for accurately modeling exposures in close proximity to an indoor pollution source.

  6. Value of Apparent Diffusion Coefficient Values in Differentiating Malignant and Benign Breast Lesions

    PubMed Central

    Bozkurt Bostan, Tuğba; Koç, Gonca; Sezgin, Gülten; Altay, Canan; Fazıl Gelal, M.; Oyar, Orhan

    2016-01-01

    Background: Magnetic resonance imaging (MRI) has become a diagnostic and problem solving method for the breast examinations in addition to conventional breast examination methods. Diffusion-weighted imaging (DWI) adds valuable information to conventional MRI. Aims: Our aim was to show the impact of apparent diffusion coefficient (ADC) values acquired with DWI to differentiate benign and malignant breast lesions. Study Design: Diagnostic accuracy study. Methods: Forty-six women with 58 breast masses (35 malignant, 23 benign) were examined on a 1.5 T clinical MRI scanner. The morphologic characteristics of the lesions on conventional MRI sequences and contrast uptake pattern were assessed. ADC values of both lesions and normal breast parenchyma were measured. The ADC values obtained were statistically compared with the histopathologic results using Paired Samples t-Test. Results: Multiple lesions were detected in 12 (26%) of the patients, while only one lesion was detected in 34 (74%). Overall, 35 lesions out of 58 were histopathologically proven to be malignant. In the dynamic contrast-enhanced series, 5 of the malignant lesions were type 1, while 8 benign lesions revealed either type 2 or 3 time signal intensity curves (85% sensitivity, 56% spesifity). Mean ADC values were significantly different in malignant vs. benign lesions. (1.04±0.29×10−3 cm2/sec vs. 1.61±0.50×10−3 cm2/sec for the malignant and benign lesions, respectively, p=0.03). A cut-off value of 1.30×10−3 mm2/sec for ADC detected with receiver operating characteristic analysis yielded 89.1% sensitivity and 100% specificity for the differentiation between benign and malignant lesions. Conclusion: ADC values improve the diagnostic accuracy of solid breast lesions when evaluated with the conventional MRI sequences. Therefore, DWI should be incorporated to routine breast MRI protocol. PMID:27308073

  7. Diffusion length damage coefficient and annealing studies in proton-irradiated InP

    NASA Technical Reports Server (NTRS)

    Hakimzadeh, Roshanak; Vargas-Aburto, Carlos; Bailey, Sheila G.; Williams, Wendell

    1993-01-01

    We report on the measurement of the diffusion length damage coefficient (K(sub L)) and the annealing characteristics of the minority carrier diffusion length (L(sub n)) in Czochralski-grown zinc-doped indium phosphide (InP), with a carrier concentration of 1 x 10(exp l8) cm(exp -3). In measuring K(sub L) irradiations were made with 0.5 MeV protons with fluences ranging from 1 x 10(exp 11) to 3 x 10(exp 13) cm(exp -2). Pre- and post-irradiation electron-beam induced current (EBIC) measurements allowed for the extraction of L(sub n) from which K(sub L) was determined. In studying the annealing characteristics of L(sub n) irradiations were made with 2 MeV protons with fluence of 5 x 10(exp 13) cm(exp -2). Post-irradiation studies of L(sub n) with time at room temperature, and with minority carrier photoinjection and forward-bias injection were carried out. The results showed that recovery under Air Mass Zero (AMO) photoinjection was complete. L(sub n) was also found to recover under forward-bias injection, where recovery was found to depend on the value of the injection current. However, no recovery of L(sub n) after proton irradiation was observed with time at room temperature, in contrast to the behavior of 1 MeV electron-irradiated InP solar cells reported previously.

  8. Association between apparent diffusion coefficient and intervertebral disc degeneration in patients with ankylosing spondylitis

    PubMed Central

    Resorlu, Mustafa; Gokmen, Ferhat; Resorlu, Hatice; Adam, Gurhan; Akbal, Ayla; Cevizci, Sibel; Sariyildirim, Abdullah; Savas, Yilmaz; Guven, Mustafa; Aras, Adem Bozkurt

    2015-01-01

    Purpose: To assess the relation between ankylosing spondylitis (AS) and degenerative disc disease emerging in association with various intrinsic and extrinsic factors and to evaluate the correlation between degree of degeneration in intervertebral discs and apparent diffusion coefficient (ADC) values. Methods: Thirty-five patients with AS and a control group of 35 patients were included in the study. Three hundred fifty intervertebral discs were assessed in terms of degeneration by analyzing signal intensities and morphologies on T2 weighted series of a 1.5 Tesla magnetic resonance scanner. ADC values were determined in diffusion weighted images (DWI) using a “b value of 500 s/mm2”. Patients in the AS and control groups were compared in terms of intervertebral disc degeneration, and association between degree of degeneration and ADC values was analyzed. Results: The mean of total degeneration degrees for five lumbar intervertebral discs was significantly higher in the patients with AS compared to the control group (16.77±4.67 vs 13.00±4.08, respectively; P=0.001). When intervertebral discs were analyzed separately, disc degeneration was again significantly higher in patients with AS compared to the control group, with the exception of L5-S1. Age, cholesterol level, triglyceride level, duration of disease and BASFI index were significantly associated with degree of degeneration in patients with AS. A negative correlation was determined between disc degeneration and ADC value. Conclusion: AS is a risk factor for degenerative disc disease due to its systemic effects, the fact it leads to posture impairment and its inflammatory effects on the vertebrae. A decrease in ADC values is observed as degeneration worsens in degenerative disc disease. PMID:25785119

  9. Value of apparent diffusion coefficient measurement for discrimination of focal benign and malignant hepatic masses.

    PubMed

    Kilickesmez, O; Bayramoglu, S; Inci, E; Cimilli, T

    2009-02-01

    The purpose of our study was to investigate the value of diffusion-weighted magnetic resonance imaging (DW-MRI) to discriminate benign and malignant focal lesions of the liver using parallel imaging technique. A total of 77 patients and 65 healthy controls were enrolled in the study. DW-MRI was performed with b-factors of 0, 500 and 1000 s/mm(2), and the apparent diffusion coefficients (ADC) values of the normal liver and the lesions were calculated. The mean ADC value of the focal liver lesions were as follows: simple cysts (3.16 +/- 0.18 x 10(-3) mm(2)/s), hydatid cysts (2.58 +/- 0.53 x 10(-3) mm(2)/s), hemangiomas (1.97 +/- 0.49 x 10(-3) mm(2)/s), metastases (1.14 +/- 0.41 x 10(-3) mm(2)/s) and hepatocellular carcinomas (HCC) (1.15 +/- 0.36 x 10(-3) mm(2)/s). The mean ADC values of all the disease groups were statistically significant when compared with the mean ADC value of the normal liver (1.56 +/- 0.14 x 10(-3) mm(2)/s), (P < 0.01). There were also statistically significant differences among the ADC values of hemangiomas and HCC metastases (P < 0.01), and simple and hydatid cysts (P < 0.008). However, there was no statistically significant difference between HCC and metastases. The present study showed that ADC measurement has the potential to differentiate benign and malignant focal hepatic lesions. We propose to add DW sequence in the MR protocol for the detection and quantitative discrimination of hepatic pathologies.

  10. Images of soft materials: a 3D visualization of interior of the sample in terms of attenuation coefficient

    NASA Astrophysics Data System (ADS)

    Golosio, B.; Brunetti, A.; Cesareo, R.; Amendolia, S. R.; Rao, D. V.; Seltzer, S. M.

    2001-06-01

    Images of soft materials are obtained using image intensifier based X-ray system (Rao et al., Nucl. Instr. and Meth. A 437 (1999) 141). The interior of the soft material is visualized using the novel software in order to know the distribution of attenuation coefficient in terms of density. The novel software is based mainly on graphical library and applicable to several operating systems without any change. It can be applied to several applications starting from biomedical to industries, for example, quality control. The results for walnut and brew tooth are presented as a set of images from the internal parts of the sample. A description of the principal parameters required for tomographic visualization is given and some results based on this technique are reported and discussed.

  11. Spatially resolved absolute diffuse reflectance measurements for noninvasive determination of the optical scattering and absorption coefficients of biological tissue

    NASA Astrophysics Data System (ADS)

    Kienle, Alwin; Lilge, Lothar; Patterson, Michael S.; Hibst, Raimund; Steiner, Rudolf; Wilson, Brian C.

    1996-05-01

    The absorption and transport scattering coefficients of biological tissues determine the radial dependence of the diffuse reflectance that is due to a point source. A system is described for making remote measurements of spatially resolved absolute diffuse reflectance and hence noninvasive, noncontact estimates of the tissue optical properties. The system incorporated a laser source and a CCD camera. Deflection of the incident beam into the camera allowed characterization of the source for absolute reflectance measurements. It is shown that an often used solution of the diffusion equation cannot be applied for these measurements. Instead, a neural network, trained on the results of Monte Carlo simulations, was used to estimate the absorption and scattering coefficients from the reflectance data. Tests on tissue-simulating phantoms with transport scattering coefficients between 0.5 and 2.0 mm-1 and absorption coefficients between 0.002 and 0.1 mm -1 showed the rms errors of this technique to be 2.6% for the transport scattering coefficient and 14% for the absorption coefficients. The optical properties of bovine muscle, adipose, and liver tissue, as well as chicken muscle (breast), were also measured ex vivo at 633 and 751 nm. For muscle tissue it was found that the Monte Carlo simulation did not agree with experimental measurements of reflectance at distances less than 2 mm from the incident beam. Carlo, neural network.

  12. Nanoparticle shapes of LiMnPO4, Li+ diffusion orientation and diffusion coefficients for high volumetric energy Li+ ion cathodes

    NASA Astrophysics Data System (ADS)

    Kwon, Nam Hee; Yin, Hui; Vavrova, Tatiana; Lim, Jonathan H.-W.; Steiner, Ullrich; Grobéty, Bernard; Fromm, Katharina M.

    2017-02-01

    Nanoparticles of LiMnPO4 were fabricated in rod, elongated as well as cubic shapes. The 1D Li+ preferred diffusion direction for each shape was determined via electron diffraction spot patterns. The shape of nano-LiMnPO4 varied the diffusion coefficient of Li+ because the Li+ diffusion direction and the path length were different. The particles with the shortest dimension along the b-axis provided the highest diffusion coefficient, resulting in the highest gravimetric capacity of 135, 100 and 60 mAh g-1 at 0.05C, 1C and 10C, respectively. Using ball-milling, a higher loading of nano-LiMnPO4 in the electrode was achieved, increasing the volumetric capacity to 263 mAh cm-3, which is ca. 3.5 times higher than the one obtained by hand-mixing of electrode materials. Thus, the electrochemical performance is governed by both the diffusion coefficient of Li+, which is dependent on the shape of LiMnPO4 nanoparticles and the secondary composite structure.

  13. Evaluation of Particle Pinch and Diffusion Coefficients in the Edge Pedestal of DIII-D H-mode Discharges

    NASA Astrophysics Data System (ADS)

    Stacey, W. M.; Groebner, R. J.

    2009-11-01

    Momentum balance requires that the radial particle flux satisfy a pinch-diffusion relationship. The pinch can be evaluated in terms of measurable quantities (rotation velocities, Er, etc.) by the use of momentum and particle balance [1,2], the radial particle flux can be determined by momentum balance, and then the diffusion coefficient can be evaluated from the pinch diffusion relation using the measured density gradient. Applications to several DIII-D H-mode plasmas are presented. 6pt [1] W.M. Stacey, Contr. Plasma Phys. 48, 94 (2008). [2] W.M. Stacey and R.J. Groebner, Phys. Plasmas 15, 012503 (2008).

  14. Effects of molecular size and structure on self-diffusion coefficient and viscosity for saturated hydrocarbons having six carbon atoms.

    PubMed

    Iwahashi, Makio; Kasahara, Yasutoshi

    2007-01-01

    Self-diffusion coefficients and viscosities for the saturated hydrocarbons having six carbon atoms such as hexane, 2-methylpentane (2MP), 3-methylpentane (3MP), 2,2-dimethylbutane (22DMB), 2,3-dimethylbutane (23DMB), methylcyclopentane (McP) and cyclohexane (cH) were measured at various constant temperatures; obtained results were discussed in connection with their molar volumes, molecular structures and thermodynamic properties. The values of self-diffusion coefficients as the microscopic property were inversely proportional to those of viscosities as the macroscopic property. The order of their viscosities was almost same to those of their melting temperatures and enthalpies of fusion, which reflect the attractive interactions among their molecules. On the other hand, the order of the self-diffusion coefficients inversely related to the order of the melting temperatures and the enthalpies of the fusion. Namely, the compound having the larger attractive interaction mostly shows the less mobility in its liquid state, e.g., cyclohexane (cH), having the largest attractive interaction and the smallest molar volume exhibits an extremely large viscosity and small self-diffusion coefficient comparing with other hydrocarbons. However, a significant exception was 22DMB, being most close to a sphere: In spite of the smallest attractive interaction and the largest molar volume of 22DMB in the all samples, it has the thirdly larger viscosity and the thirdly smaller self-diffusion coefficient. Consequently, the dynamical properties such as self-diffusion and viscosity for the saturated hydrocarbons are determined not only by their attractive interactions but also by their molecular structures.

  15. Isotopic mass-dependence of metal cation diffusion coefficients in liquid water

    SciTech Connect

    Bourg, I.C.; Richter, F.M.; Christensen, J.N.; Sposito, G.

    2009-01-11

    Isotope distributions in natural systems can be highly sensitive to the mass (m) dependence of solute diffusion coefficients (D) in liquid water. Isotope geochemistry studies routinely have assumed that this mass dependence either is negligible (as predicted by hydrodynamic theories) or follows a kinetic-theory-like inverse square root relationship (D {proportional_to} m{sup -0.5}). However, our recent experimental results and molecular dynamics (MD) simulations showed that the mass dependence of D is intermediate between hydrodynamic and kinetic theory predictions (D {proportional_to} m{sup -{beta}} with 0 {<=} {beta} < 0.2 for Li{sup +}, Cl{sup -}, Mg{sup 2+}, and the noble gases). In this paper, we present new MD simulations and experimental results for Na{sup +}, K{sup +}, Cs{sup +}, and Ca{sup 2+} that confirm the generality of the inverse power-law relation D {proportional_to} m{sup -{beta}}. Our new findings allow us to develop a general description of the influence of solute valence and radius on the mass dependence of D for monatomic solutes in liquid water. This mass dependence decreases with solute radius and with the magnitude of solute valence. Molecular-scale analysis of our MD simulation results reveals that these trends derive from the exponent {beta} being smallest for those solutes whose motions are most strongly coupled to solvent hydrodynamic modes.

  16. Probability distribution of financial returns in a model of multiplicative Brownian motion with stochastic diffusion coefficient

    NASA Astrophysics Data System (ADS)

    Silva, Antonio

    2005-03-01

    It is well-known that the mathematical theory of Brownian motion was first developed in the Ph. D. thesis of Louis Bachelier for the French stock market before Einstein [1]. In Ref. [2] we studied the so-called Heston model, where the stock-price dynamics is governed by multiplicative Brownian motion with stochastic diffusion coefficient. We solved the corresponding Fokker-Planck equation exactly and found an analytic formula for the time-dependent probability distribution of stock price changes (returns). The formula interpolates between the exponential (tent-shaped) distribution for short time lags and the Gaussian (parabolic) distribution for long time lags. The theoretical formula agrees very well with the actual stock-market data ranging from the Dow-Jones index [2] to individual companies [3], such as Microsoft, Intel, etc. [] [1] Louis Bachelier, ``Th'eorie de la sp'eculation,'' Annales Scientifiques de l''Ecole Normale Sup'erieure, III-17:21-86 (1900).[] [2] A. A. Dragulescu and V. M. Yakovenko, ``Probability distribution of returns in the Heston model with stochastic volatility,'' Quantitative Finance 2, 443--453 (2002); Erratum 3, C15 (2003). [cond-mat/0203046] [] [3] A. C. Silva, R. E. Prange, and V. M. Yakovenko, ``Exponential distribution of financial returns at mesoscopic time lags: a new stylized fact,'' Physica A 344, 227--235 (2004). [cond-mat/0401225

  17. Dependence of ion drift velocity and diffusion coefficient in parent gas on its temperature

    NASA Astrophysics Data System (ADS)

    Maiorov, Sergey; Golyatina, Rusudan

    2016-09-01

    The results of Monte Carlo calculations of the ion drift characteristics are presented: ions of noble gases and Ti, Fe, Co, Cs, Rb, W and mercury ions in case of constant and uniform electric field are considered. The dependences of the ion mobility on the field strength and gas temperature are analyzed. The parameters of the drift velocity approximation by the Frost formula for gas temperatures of 4.2, 77, 300, 1000, and 2000 K are presented. A universal drift velocity approximation depending on the reduced electric field strength and gas temperature is obtained. In the case of strong electric fields or low gas temperatures, the deviation of the ion distribution function from the Maxwellian one (including the shifted Maxwellian one) can be very significant. The average energies of chaotic motion of ions along and across the electric field can also differ significantly. It is analyzed the kinetic characteristics of ion drift in own gas: ion diffusion coefficient along the field and across the field; thermal spread of velocities (temperature) along the field and across the field. The unexpected and nontrivial fact takes place: collision with backscattering represent only 10-50% of the total number of collisions. This calculation can be used when analyzing experiments with dusty plasma under cryogenic discharge, ultracold plasma. The work was supported by the Russian Science Foundation (grant RNF 14-19-01492).

  18. Apparent diffusion coefficient in normal and abnormal pattern of intervertebral lumbar discs: initial experience☆

    PubMed Central

    Niu, Gang; Yu, Xuewen; Yang, Jian; Wang, Rong; Zhang, Shaojuan; Guo, Youmin

    2011-01-01

    The aim of the present study was to compare the relationship of morphologically defined non-bulging/herniated, bulging and herniated intervertebral lumbar discs with quantitative apparent diffusion coefficient (ADC). Thirty-two healthy volunteers and 28 patients with back pain or sciatica were examined by MRI. All intervertebral lumbar discs from L1 to S1 were classified according to morphological abnormality and degenerated grades. The ADC values of nucleus pulposus (NP) were measured and recorded. The significant differences about mean ADC values of NP were found between non-bulging/herniated discs and bulging discs as well as herniated discs (P < 0.05), whereas there were no significant differences in ADC values between bulging and herniated discs (P > 0.05). Moreover, statistically significant relationship was found in the mean ADC values of NP between “non-bulging/herniated and non-degenerated discs” and “non-bulging/herniated degenerated discs” as well as herniated discs (P < 0.05). Linear regression analysis between ADC value and disc level revealed an inverse correlation (r = -0.18). The ADC map of the NP is a potentially useful tool for the quantitative assessment of componential and molecular alterations accompanied with lumbar disc abnormalities. PMID:23554690

  19. Sensitivity Analysis of Semi-Analytical Models of Diffuse Attenuation of Downwelling Irradiance in Lake Balaton

    NASA Astrophysics Data System (ADS)

    Van der Zande, D.; Blaas, M.; Nechad, B.

    2015-12-01

    A quantification of the available light in the water column is key to evaluate the water quality in lakes as it is one of the major factors determining primary production. The light environment in water is generally described in terms of the vertical attenuation coefficient (Kd) and euphotic depth (Ze) where the light is reduced to 1% of its (just below) surface value. Reliable models to estimate KdPAR (and Ze) from remote sensing measurements have been successfully demonstrated in marine applications using typical ocean colour missions such as MERIS-envisat (300m) and MODIS-AQUA (250-1000m). In this study, we present the adaptation of a semi-analytical model for Kd and Ze, developed for MERIS/MODIS, to the new and upcoming sensors bands for inland water cases.

  20. Response of radiation belt simulations to different radial diffusion coefficients for relativistic and ultra-relativistic electrons

    NASA Astrophysics Data System (ADS)

    Drozdov, Alexander; Mann, Ian; Baker, Daniel N.; Subbotin, Dmitriy; Ozeke, Louis; Shprits, Yuri; Kellerman, Adam

    Two parameterizations of the resonant wave-particle interactions of electrons with ULF waves in the magnetosphere by Brautigam and Albert [2000] and Ozeke et al. [2012] are evaluated using the Versatile Electron Radiation Belt (VERB) diffusion code to estimate the effect of changing a diffusion coefficient on the radiation belt simulation. The period of investigation includes geomagnetically quiet and active time. The simulations take into account wave-particle interactions represented by radial diffusion transport, local acceleration, losses due to pitch-angle diffusion, and mixed diffusion. 1. Brautigam, D. H., and J. M. Albert (2000), Radial diffusion analysis of outer radiation belt electrons during the October 9, 1990, magnetic storm, J. Geophys. Res., 105(A1), 291-309, doi:10.1029/1999JA900344 2. Ozeke, L. G., I. R. Mann, K. R. Murphy, I. J. Rae, D. K. Milling, S. R. Elkington, A. A. Chan, and H. J. Singer (2012), ULF wave derived radiation belt radial diffusion coefficients, J. Geophys. Res., 117, A04222, doi:10.1029/2011JA017463.

  1. A novel visualization technique for measuring liquid diffusion coefficient based on asymmetric liquid-core cylindrical lens

    NASA Astrophysics Data System (ADS)

    Sun, Licun; Pu, Xiaoyun

    2016-06-01

    A visualization and quantification optical method for measuring binary liquid diffusion coefficient (D) based on an asymmetric liquid-core cylindrical lens (ALCL) is introduced in this paper. Four groups of control experiments were performed to verify the influences of diffusing substance category, concentration and temperature on diffusion process, and the measured D values were well consistent with data measured by Holographic interferometry and Taylor dispersion methods. The drifting of the diffusion image recorded by CCD reflects the diffusion rate visually in an easily understandable way. This optical method for measuring D values based on the ALCL is characterized by visual measurement, simplified device, and easy operation, which provides a new way for measuring liquid D value visually.

  2. A novel visualization technique for measuring liquid diffusion coefficient based on asymmetric liquid-core cylindrical lens

    PubMed Central

    Sun, Licun; Pu, Xiaoyun

    2016-01-01

    A visualization and quantification optical method for measuring binary liquid diffusion coefficient (D) based on an asymmetric liquid-core cylindrical lens (ALCL) is introduced in this paper. Four groups of control experiments were performed to verify the influences of diffusing substance category, concentration and temperature on diffusion process, and the measured D values were well consistent with data measured by Holographic interferometry and Taylor dispersion methods. The drifting of the diffusion image recorded by CCD reflects the diffusion rate visually in an easily understandable way. This optical method for measuring D values based on the ALCL is characterized by visual measurement, simplified device, and easy operation, which provides a new way for measuring liquid D value visually. PMID:27325006

  3. Determination of power-law attenuation coefficient and dispersion spectra in multi-wall carbon nanotube composites using Kramers-Kronig relations.

    PubMed

    Mobley, Joel; Mack, Richard A; Gladden, Joseph R; Mantena, P Raju

    2009-07-01

    Using a broadband through-transmission technique, the attenuation coefficient and phase velocity spectra have been measured for a set of multi-wall carbon nanotube (MWCNT)-nylon composites (from pure nylon to 20% MWCNT by weight) in the ultrasonic frequency band from 4 to 14 MHz. The samples were found to be effectively homogeneous on spatial scales from the low end of ultrasonic wavelengths investigated and up (>0.2 mm). Using Kramers-Kronig relations, the attenuation and dispersion data were found to be consistent with a power-law attenuation model with a range of exponents from y=1.12 to y=1.19 over the measurement bandwidth. The attenuation coefficients of the respective samples are found to decrease with increasing MWCNT content and a similar trend holds also for the dispersion. In contrast, the mean phase velocities for the samples rise with increasing MWCNT content indicating an increase in the mechanical moduli.

  4. New consistency tests for high-accuracy measurements of X-ray mass attenuation coefficients by the X-ray extended-range technique

    SciTech Connect

    Chantler, C.T.; Islam, M.T.; Rae, N.A.; Tran, C.Q.; Glover, J.L.; Barnea, Z.

    2012-09-25

    An extension of the X-ray extended-range technique is described for measuring X-ray mass attenuation coefficients by introducing absolute measurement of a number of foils - the multiple independent foil technique. Illustrating the technique with the results of measurements for gold in the 38-50 keV energy range, it is shown that its use enables selection of the most uniform and well defined of available foils, leading to more accurate measurements; it allows one to test the consistency of independently measured absolute values of the mass attenuation coefficient with those obtained by the thickness transfer method; and it tests the linearity of the response of the counter and counting chain throughout the range of X-ray intensities encountered in a given experiment. In light of the results for gold, the strategy to be ideally employed in measuring absolute X-ray mass attenuation coefficients, X-ray absorption fine structure and related quantities is discussed.

  5. Diffusion coefficients of the uranium(III) and (IV) ions in the LiCl-KCl-CsCl eutectic melt

    NASA Astrophysics Data System (ADS)

    Maltsev, D. S.; Volkovich, V. A.; Vasin, B. D.

    2016-08-01

    Diffusion coefficients of the uranium(III) and (IV) ions in the eutectic melt of the lithium, potassium, and cesium chlorides in the temperature range of 573-1073 K have been determined using two independent methods: cyclic voltammetry and chronopotentiometry.

  6. Estimation of CO2 diffusion coefficient at 0-10 cm depth in undisturbed and tilled soils

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Diffusion coefficients (D) of CO2 at 0 – 10 cm layers in undisturbed and tilled soil conditions were estimated using Penman, Millington-Quirk, Ridgwell et al. (1999), Troeh et al., and Moldrup et al. models. Soil bulk density and volumetric soil water content ('v) at 0 – 10 cm were measured on April...

  7. Electrochemical measurement of lateral diffusion coefficients of ubiquinones and plastoquinones of various isoprenoid chain lengths incorporated in model bilayers.

    PubMed Central

    Marchal, D; Boireau, W; Laval, J M; Moiroux, J; Bourdillon, C

    1998-01-01

    The long-range diffusion coefficients of isoprenoid quinones in a model of lipid bilayer were determined by a method avoiding fluorescent probe labeling of the molecules. The quinone electron carriers were incorporated in supported dimyristoylphosphatidylcholine layers at physiological molar fractions (<3 mol%). The elaborate bilayer template contained a built-in gold electrode at which the redox molecules solubilized in the bilayer were reduced or oxidized. The lateral diffusion coefficient of a natural quinone like UQ10 or PQ9 was 2.0 +/- 0.4 x 10(-8) cm2 s(-1) at 30 degrees C, two to three times smaller than the diffusion coefficient of a lipid analog in the same artificial bilayer. The lateral mobilities of the oxidized or reduced forms could be determined separately and were found to be identical in the 4-13 pH range. For a series of isoprenoid quinones, UQ2 or PQ2 to UQ10, the diffusion coefficient exhibited a marked dependence on the length of the isoprenoid chain. The data fit very well the quantitative behavior predicted by a continuum fluid model in which the isoprenoid chains are taken as rigid particles moving in the less viscous part of the bilayer and rubbing against the more viscous layers of lipid heads. The present study supports the concept of a homogeneous pool of quinone located in the less viscous region of the bilayer. PMID:9545054

  8. Evaluation of depth profiling using laser resonant desorption as a method to measure diffusion coefficients in ice.

    PubMed

    Dominé, F; Xueref, I

    2001-09-01

    Diffusion of gases in ice is involved in cloud, snow, and ice core chemistry, but few data exist on the relevant diffusion coefficients. A novel method to measure diffusion coefficients in ice has recently been proposed by Livingston et al. (Anal. Chem., 2000, 72, 5590-5599). It is based on depth profiling of doped ice crystals epitaxially grown on Ru(001) by laser resonant desorption (LRD). Using this method, Livingston et al. obtained a value of the diffusion coefficient of the HCl hydrate in ice at 190 K of about 5 x 10(-11) cm2/s. We argue here that this value is many orders of magnitude higher than what could be expected from literature values, which are not reported in sufficient detail by Livingston et al. We investigate the possibilities that their high value could be due to (1) diffusion in defects in the ice, which would be present in very high concentrations because of the ice growth method; and (2) the fact that diffusion of high concentrations of HCl in ice at 190 K forms an amorphous HCl:H2O solid mixture, where HCl diffusion is fast. We present new infrared spectroscopic data on solid HCl:H2O mixtures that confirm that such mixtures can indeed be formed in an amorphous state at 190 K. Our proposed interpretation is that by depositing large amounts of HCl on epitaxially grown ice, Livingston et al. created a superficial amorphous binary mixture and that fast diffusion of HCl in the ice, possibly accelerated by a high defect density, produced an amorphous HCl:H2O mixture. We conclude that the processes studied by Livingston et al. are different from those involved in the atmospheric and cryospheric sciences, and that their data, obtained by depth profiling using LRD, probably cannot be applied to those fields.

  9. Diffusion-weighted 19F-MRI of lung periphery: Influence of pressure and air-SF6 composition on apparent diffusion coefficients.

    PubMed

    Ruiz-Cabello, Jesús; Pérez-Sánchez, José Manuel; Pérez de Alejo, Rigoberto; Rodríguez, Ignacio; González-Mangado, Nicolás; Peces-Barba, Germán; Cortijo, Manuel

    2005-08-25

    Lung functional magnetic resonance imaging (MRI) has become a reality using different inert hyperpolarized gases, such as 3He and 129Xe, which have provided an extraordinary boost in lung imaging and has also attracted interest to other chemically inert gaseous contrast agents. In this context, we have recently demonstrated the first diffusion-weighted images using thermally polarized inhaled sulfur hexafluoride (SF6) in small animals. The aim of this study was to evaluate whether or not the diffusion coefficient of this fluorinated gas is sensitive to pulmonary structure, gas concentration and air pressure in the airways. Diffusion coefficients of SF6 (both pure and in air mixtures) measured in vitro at different pressures and 20 degrees C showed an excellent agreement with theoretical values. Measurements of diffusion coefficients were also performed in vivo and post-mortem on healthy rats, achieving satisfactory signal-to-noise ratios (SNRs), and SF6 gas was found to be in an almost completely restricted diffusion regime in the lung, i.e., the transport by molecular diffusion is delayed by collisions with barriers such as the alveolar septa. This observed low diffusivity means that this gas will be less sensitive to structural changes in the lungs than other magnetic resonance sensitive gas such as 3He, particularly at human scale. However, it is still possible that SF6 plays a role since it opens a new structural window. Thus, the interest of researchers in delimiting the important limiting technical factors that makes this process very challenging is obvious. Among them, T2 relaxation is very fast, so gradient systems with very fast switching rate and probably large radiofrequency (RF) power and high field systems will be needed for hexafluoride to be used in human studies.

  10. In situ estimation of the effective chemical diffusion coefficient of a rock matrix in a fractured aquifer

    USGS Publications Warehouse

    Gebrekristos, R.A.; Shapiro, A.M.; Usher, B.H.

    2008-01-01

    An in situ method of estimating the effective diffusion coefficient for a chemical constituent that diffuses into the primary porosity of a rock is developed by abruptly changing the concentration of the dissolved constituent in a borehole in contact with the rock matrix and monitoring the time-varying concentration. The experiment was conducted in a borehole completed in mudstone on the campus of the University of the Free State in Bloemfontein, South Africa. Numerous tracer tests were conducted at this site, which left a residual concentration of sodium chloride in boreholes that diffused into the rock matrix over a period of years. Fresh water was introduced into a borehole in contact with the mudstone, and the time-varying increase of chloride was observed by monitoring the electrical conductivity (EC) at various depths in the borehole. Estimates of the effective diffusion coefficient were obtained by interpreting measurements of EC over 34 d. The effective diffusion coefficient at a depth of 36 m was approximately 7.8??10-6 m2/d, but was sensitive to the assumed matrix porosity. The formation factor and mass flux for the mudstone were also estimated from the experiment. ?? Springer-Verlag 2007.

  11. Determination of hydrogen diffusion coefficients in F82H by hydrogen depth profiling with a tritium imaging plate technique

    SciTech Connect

    Higaki, M.; Otsuka, T.; Hashizume, K.; Tokunaga, K.; Ezato, K.; Suzuki, S.; Enoeda, M.; Akiba, M.

    2015-03-15

    Hydrogen diffusion coefficients in a reduced activation ferritic/martensitic steel (F82H) and an oxide dispersion strengthened F82H (ODS-F82H) have been determined from depth profiles of plasma-loaded hydrogen with a tritium imaging plate technique (TIPT) in the temperature range from 298 K to 523 K. Data on hydrogen diffusion coefficients, D, in F82H, are summarized as D [m{sup 2}*s{sup -1}] =1.1*10{sup -7}exp(-16[kJ mol{sup -1}]/RT). The present data indicate almost no trapping effect on hydrogen diffusion due to an excess entry of energetic hydrogen by the plasma loading, which results in saturation of the trapping sites at the surface and even in the bulk. In the case of ODS-F82H, data of hydrogen diffusion coefficients are summarized as D [m{sup 2}*s{sup -1}] =2.2*10{sup -7}exp(-30[kJ mol{sup -1}]/RT) indicating a remarkable trapping effect on hydrogen diffusion caused by tiny oxide particles (Y{sub 2}O{sub 3}) in the bulk of F82H. Such oxide particles introduced in the bulk may play an effective role not only on enhancement of mechanical strength but also on suppression of hydrogen penetration by plasma loading.

  12. Spatial dependence of the local diffusion coefficient measured upstream of the November 12, 1978 interplanetary traveling shock

    NASA Technical Reports Server (NTRS)

    Gloeckler, G.; Ipavich, F. M.; Klecker, B.; Hovestadt, D.; Scholer, M.

    1985-01-01

    Characteristics of wuprathermal particles accelerated by quasi-parallel interplanetary traveling shocks have been generally explained in terms of a first order Fermi mechanism. Such models require diffusive scattering of particles upstream of the shock. This scattering is characterized by a local diffusion coefficient, kappa, which is determined by the local power density of waves in the upstream region. The dependence of the diffusion coefficient of suprathermal upstream protons on distance from the November 12, 1978 interplanetary traveling shock using a different approach is studied. Unlike previous studies this method, which is based on measurements of particle streaming and intensity gradients, does not rely on predictions. The local spatial variations of Kappa upstream of the November 12, 1978 shock have been chosen for study because the characteristics of this quasi-parallel shock have been extensively studied, and also because of its favorable geometry (i.e. B field nearly radial).

  13. Analysis of ligand-protein exchange by Clustering of Ligand Diffusion Coefficient Pairs (CoLD-CoP).

    PubMed

    Snyder, David A; Chantova, Mihaela; Chaudhry, Saadia

    2015-06-01

    NMR spectroscopy is a powerful tool in describing protein structures and protein activity for pharmaceutical and biochemical development. This study describes a method to determine weak binding ligands in biological systems by using hierarchic diffusion coefficient clustering of multidimensional data obtained with a 400 MHz Bruker NMR. Comparison of DOSY spectrums of ligands of the chemical library in the presence and absence of target proteins show translational diffusion rates for small molecules upon interaction with macromolecules. For weak binders such as compounds found in fragment libraries, changes in diffusion rates upon macromolecular binding are on the order of the precision of DOSY diffusion measurements, and identifying such subtle shifts in diffusion requires careful statistical analysis. The "CoLD-CoP" (Clustering of Ligand Diffusion Coefficient Pairs) method presented here uses SAHN clustering to identify protein-binders in a chemical library or even a not fully characterized metabolite mixture. We will show how DOSY NMR and the "CoLD-CoP" method complement each other in identifying the most suitable candidates for lysozyme and wheat germ acid phosphatase.

  14. Analysis of ligand-protein exchange by Clustering of Ligand Diffusion Coefficient Pairs (CoLD-CoP)

    NASA Astrophysics Data System (ADS)

    Snyder, David A.; Chantova, Mihaela; Chaudhry, Saadia

    2015-06-01

    NMR spectroscopy is a powerful tool in describing protein structures and protein activity for pharmaceutical and biochemical development. This study describes a method to determine weak binding ligands in biological systems by using hierarchic diffusion coefficient clustering of multidimensional data obtained with a 400 MHz Bruker NMR. Comparison of DOSY spectrums of ligands of the chemical library in the presence and absence of target proteins show translational diffusion rates for small molecules upon interaction with macromolecules. For weak binders such as compounds found in fragment libraries, changes in diffusion rates upon macromolecular binding are on the order of the precision of DOSY diffusion measurements, and identifying such subtle shifts in diffusion requires careful statistical analysis. The "CoLD-CoP" (Clustering of Ligand Diffusion Coefficient Pairs) method presented here uses SAHN clustering to identify protein-binders in a chemical library or even a not fully characterized metabolite mixture. We will show how DOSY NMR and the "CoLD-CoP" method complement each other in identifying the most suitable candidates for lysozyme and wheat germ acid phosphatase.

  15. Towards a quantitative, measurement-based estimate of the uncertainty in photon mass attenuation coefficients at radiation therapy energies

    NASA Astrophysics Data System (ADS)

    Ali, E. S. M.; Spencer, B.; McEwen, M. R.; Rogers, D. W. O.

    2015-02-01

    In this study, a quantitative estimate is derived for the uncertainty in the XCOM photon mass attenuation coefficients in the energy range of interest to external beam radiation therapy—i.e. 100 keV (orthovoltage) to 25 MeV—using direct comparisons of experimental data against Monte Carlo models and theoretical XCOM data. Two independent datasets are used. The first dataset is from our recent transmission measurements and the corresponding EGSnrc calculations (Ali et al 2012 Med. Phys. 39 5990-6003) for 10-30 MV photon beams from the research linac at the National Research Council Canada. The attenuators are graphite and lead, with a total of 140 data points and an experimental uncertainty of ˜0.5% (k = 1). An optimum energy-independent cross section scaling factor that minimizes the discrepancies between measurements and calculations is used to deduce cross section uncertainty. The second dataset is from the aggregate of cross section measurements in the literature for graphite and lead (49 experiments, 288 data points). The dataset is compared to the sum of the XCOM data plus the IAEA photonuclear data. Again, an optimum energy-independent cross section scaling factor is used to deduce the cross section uncertainty. Using the average result from the two datasets, the energy-independent cross section uncertainty estimate is 0.5% (68% confidence) and 0.7% (95% confidence). The potential for energy-dependent errors is discussed. Photon cross section uncertainty is shown to be smaller than the current qualitative ‘envelope of uncertainty’ of the order of 1-2%, as given by Hubbell (1999 Phys. Med. Biol 44 R1-22).

  16. Simultaneous Rapid Determination of the Solubility and Diffusion Coefficients of a Poorly Water-Soluble Drug Based on a Novel UV Imaging System.

    PubMed

    Lu, Yan; Li, Mingzhong

    2016-01-01

    The solubility and diffusion coefficient are two of the most important physicochemical properties of a drug compound. In practice, both have been measured separately, which is time consuming. This work utilizes a novel technique of UV imaging to determine the solubility and diffusion coefficients of poorly water-soluble drugs simultaneously. A 2-step optimal method is proposed to determine the solubility and diffusion coefficients of a poorly water-soluble pharmaceutical substance based on the Fick's second law of diffusion and UV imaging measurements. Experimental results demonstrate that the proposed method can be used to determine the solubility and diffusion coefficients of a drug with reasonable accuracy, indicating that UV imaging may provide a new opportunity to accurately measure the solubility and diffusion coefficients of a poorly water-soluble drug simultaneously and rapidly.

  17. Measurements of the Fe³⁺ diffusion coefficient in Fricke xylenol gel using optical density measurements.

    PubMed

    de Oliveira, Lucas Nonato; Sampaio, Francisco Glaildo Almeida; Moreira, Marcos Vasques; de Almeida, Adelaide

    2014-08-01

    In Fricke dosimetry, optical density measurements are performed some time after dosimeter irradiation. Values of the diffusion coefficient of Fe(3+) in Fricke Xylenol gel (FXG) are necessary for determining the spatial distribution of the absorbed dose from measurements of the optical density. Five sets of FXG dosimeters, kept at different constant temperatures, were exposed to collimated 6 MV photons. The optical density profile, proportional to the Fe(3+) concentration, at the boundary between irradiated and non-irradiated parts of each dosimeter was measured periodically over a period of 60 h. By comparing the experimental data with a function that accounts for the unobserved initial concentration profile of Fe(3+) in the FXG, we obtained diffusion coefficients 0.30±0.05, 0.40±0.05, 0.50±0.05, 0.60±0.05 and 0.80±0.05 mm(2)/h for the temperatures 283.0±0.5, 286.0±0.5, 289.0±0.5, 292.0±0.5, and 296.0±0.5 K, respectively. The activation energy of Fe(3+) diffusion in the gel, 0.54±0.06 eV, was determined from the temperature dependence of the diffusion coefficients.

  18. Low temperature diffusion coefficients in the Fe-Ni and FeNiP systems: Application to meteorite cooling rates

    NASA Technical Reports Server (NTRS)

    Dean, D. C.; Goldstein, J. I.

    1984-01-01

    The interdiffusion coefficient of FeNi in fcc taenite (gamma) of Fe-Ni and Fe-Ni-0.2 P alloys was measured as a function of temperature between 600 and 900 C. This temperature range is directly applicable to the nucleation and growth of the Widmanstatten pattern in iron meteorites and metal regions of stony and stony-iron meteorites. Diffusion couples were made from FeNi or FeNiP alloys which ensured that the couples were in the taenite phase at the diffusion temperature. The presence or absence of grain boundary diffusion was determined by measuring the Ni profile normal to the existing grain boundaries with the AEM. Ignoring any variation of interdiffusion coefficient with composition, the measured data was plotted versus the reciprocal of the diffusion temperature. The FeNi data generally follow the extrapolated Goldstein, et al. (1965) data from high temperatures. The FeNiP data indicates that small additions of P (0.2 wt%) cause a 3 to 10 fold increase in the FeNi interdifussion coefficient increasing with decreasing temperature. This increase is about the same as that predicted by Narayan and Goldstein (1983) at the Widmanstatten growth temperature.

  19. Validation of quantitative attenuation and backscattering coefficient measurements by optical coherence tomography in the concentration-dependent and multiple scattering regime.

    PubMed

    Almasian, Mitra; Bosschaart, Nienke; van Leeuwen, Ton G; Faber, Dirk J

    2015-01-01

    Optical coherence tomography (OCT) has the potential to quantitatively measure optical properties of tissue such as the attenuation coefficient and backscattering coefficient. However, to obtain reliable values for strong scattering tissues, accurate consideration of the effects of multiple scattering and the nonlinear relation between the scattering coefficient and scatterer concentration (concentration-dependent scattering) is required. We present a comprehensive model for the OCT signal in which we quantitatively account for both effects, as well as our system parameters (confocal point spread function and sensitivity roll-off). We verify our model with experimental data from controlled phantoms of monodisperse silica beads (scattering coefficients between 1 and 30  mm(−1) and scattering anisotropy between 0.4 and 0.9). The optical properties of the phantoms are calculated using Mie theory combined with the Percus–Yevick structure factor to account for concentration-dependent scattering. We demonstrate excellent agreement between the OCT attenuation and backscattering coefficient predicted by our model and experimentally derived values. We conclude that this model enables us to accurately model OCT-derived parameters (i.e., attenuation and backscattering coefficients) in the concentration-dependent and multiple scattering regime for spherical monodisperse samples.

  20. Determination of spatially-resolved porosity, tracer distributions and diffusion coefficients in porous media using MRI measurements and numerical simulations.

    PubMed

    Marica, Florea; Jofré, Sergio Andrés Bea; Mayer, K Ulrich; Balcom, Bruce J; Al, Tom A

    2011-07-01

    This work is focused on measuring the concentration distribution of a conservative tracer in a homogeneous synthetic porous material and in heterogeneous natural sandstone using MRI techniques, and on the use of spatially resolved porosity data to define spatially variable diffusion coefficients in heterogeneous media. The measurements are made by employing SPRITE, a fast MRI method that yields quantitative, spatially-resolved tracer concentrations in porous media. Diffusion experiments involving the migration of H(2)O into D(2)O-saturated porous media are conducted. One-dimensional spatial distributions of H(2)O-tracer concentrations acquired from experiments with the homogeneous synthetic calcium silicate are fitted with the one-dimensional analytical solution of Fick's second law to confirm that the experimental method provides results that are consistent with expectations for Fickian diffusion in porous media. The MRI-measured concentration profiles match well with the solution for Fick's second law and provide a pore-water diffusion coefficient of 1.75×10(-9)m(2)s(-1). The experimental approach was then extended to evaluate diffusion in a heterogeneous natural sandstone in three dimensions. The relatively high hydraulic conductivity of the sandstone, and the contrast in fluid density between the H(2)O tracer and the D(2)O pore fluid, lead to solute transport by a combination of diffusion and density-driven advection. The MRI measurements of spatially distributed tracer concentration, combined with numerical simulations allow for the identification of the respective influences of advection and diffusion. The experimental data are interpreted with the aid of MIN3P-D - a multicomponent reactive transport code that includes the coupled processes of diffusion and density-driven advection. The model defines local diffusion coefficients as a function of spatially resolved porosity measurements. The D(e) values calculated for the heterogeneous sandstone and used to

  1. Attenuation of second sound in superfluid 3He-A1

    PubMed

    Sato; Coleman; de Vegvar PG; Kojima; Okuda

    2000-02-14

    The attenuation of second sound (spin-entropy) wave in the superfluid A1 phase has been measured in magnetic fields up to 11 T and to sufficiently high frequency to observe the bulk attenuation proportional to the square of frequency. The measured attenuation coefficient is compared with the existing theories of hydrodynamics and dissipative coefficients. The resulting "excess" attenuation is discussed in terms of the temperature dependent spin diffusion coefficient in the superfluid.

  2. Gas exchange dependency on diffusion coefficient: direct /sup 222/Rn and /sup 3/He comparisons in a small lake

    SciTech Connect

    Torgersen, T.; Mathieu, G.; Hesslein, R.H.; Broecker, W.S.

    1982-01-20

    A direct field comparison was conducted to determine the dependency of gas exchange coefficient (k/sub x/) on the diffusion coefficient (D/sub x/). The study also sought to confirm the enhanced vertical exchange properties of limnocorrals and similar enclosures. Gas exchange coefficients for /sup 222/Rn and /sup 3/He were determined in a small northern Ontario lake, using a /sup 226/Ra and /sup 3/H spike to gain the necessary precision. The results indicate that the gas exchange coefficient is functionally dependent on the diffusion coefficient raised to the 1.22/sub -35//sup + > 12/ power (k/sub x/ = f(D/sub x//sup 1.22)), clearly supporting the stagnant film model of gas exchange. Limnocorrals were found to have gas exchange rates up to 1.7 times higher than the whole lake in spite of the observation of more calm surface conditions in the corral than in the open lake. 33 references, 6 figures, 8 tables.

  3. Estimating the runaway diffusion coefficient in the TEXT tokamak from shift and externally applied resonant magnetic-field experiments

    SciTech Connect

    Catto, P.J.; Myra, J.R. ); Wang, P.W.; Wootton, A.J.; Bengtson, R.D. )

    1991-08-01

    Two techniques are employed on the TEXT tokamak (Nucl. Fusion {bold 29}, 547 (1989); {bold 30}, 167 (1990)) to measure the runaway diffusion coefficient {ital D}: (i) displacing the plasma column, and (ii) externally applying resonant magnetic fields. Model diffusion equations for the experiments are solved to obtain analytic predictions which then can be used to interpret the measurements. The initial transient response of the x-ray flux to the perturbing shift or applied magnetic field is used to measure a {ital D} of order 1 m{sup 2} sec{sup {minus}1} near the edge that decreases inward.

  4. Tomographic imaging of absolute optical absorption coefficient in turbid media using combined photoacoustic and diffusing light measurements.

    PubMed

    Yin, Lu; Wang, Qiang; Zhang, Qizhi; Jiang, Huabei

    2007-09-01

    We present a new method that can provide high resolution images of absolute optical absorption coefficient in heterogeneous turbid media. In this method, acoustic measurements in conventional photoacoustic tomography are combined with diffusing light measurements to separate the product of absorption coefficient and optical fluence or photon density. We validate this method using a series of tissuelike phantom experiments. The experimental results show that targets as small as 0.5 mm in diameter with optical absorption contrasts as low as 1.5 relative to a 50 mm diameter scattering background medium can be clearly detected.

  5. Measurement of the x-ray mass attenuation coefficients of gold in the 38-50-keV energy range

    SciTech Connect

    Islam, M T; Rae, N A; Glover, J L; Barnea, Z; de Jonge, M D; Tran, C Q; Wang, J; Chantler, C T

    2010-11-12

    We used synchrotron x rays to measure the x-ray mass attenuation coefficients of gold at nine energies from 38 to 50 keV with accuracies of 0.1%. Our results are much more accurate than previous measurements in this energy range. A comparison of our measurements with calculated mass attenuation coefficients shows that our measurements fall almost exactly midway between the XCOM and FFAST calculated theoretical values, which differ from one another in this energy region by about 4%, even though the range includes no absorption edge. The consistency and accuracy of these measurements open the way to investigations of the x-ray attenuation in the region of the L absorption edge of gold.

  6. Evaluation of Fourier transform coefficients for the diagnosis of rheumatoid arthritis from diffuse optical tomography images

    NASA Astrophysics Data System (ADS)

    Montejo, Ludguier D.; Jia, Jingfei; Kim, Hyun K.; Hielscher, Andreas H.

    2013-03-01

    We apply the Fourier Transform to absorption and scattering coefficient images of proximal interphalangeal (PIP) joints and evaluate the performance of these coefficients as classifiers using receiver operator characteristic (ROC) curve analysis. We find 25 features that yield a Youden index over 0.7, 3 features that yield a Youden index over 0.8, and 1 feature that yields a Youden index over 0.9 (90.0% sensitivity and 100% specificity). In general, scattering coefficient images yield better one-dimensional classifiers compared to absorption coefficient images. Using features derived from scattering coefficient images we obtain an average Youden index of 0.58 +/- 0.16, and an average Youden index of 0.45 +/- 0.15 when using features from absorption coefficient images.

  7. Validity of the Ruff-MKW boiling point method: Vapor pressures, diffusion coefficients in argon and helium, and viscosity coefficients for gaseous cadmium and zinc

    NASA Astrophysics Data System (ADS)

    Wahlbeck, P. G.; Myers, D. L.; Truong, V. V.

    1985-09-01

    The Ruff-MKW boiling point method is used to determine equilibrium vapor pressures greater than 660 Pa (5 Torr). Samples are vaporized from a Ruff cell, which has a capillary exit, in the presence of an inert gas. Viscosity coefficients and gaseous interdiffusion coefficients may be determined also. This is a second study of the method using Cd(l) and Zn(l) as samples. For the first study with CsCl(l), see J. Chem. Phys. 81, 915 (1984). Vapor pressure data are in good agreement with previous data and gave a third-law ΔsubH0(298) for Cd(s) of 111.95±0.42 kJ/mol and for Zn(s) of 130.65±0.48 kJ/mol. Analyses of the diffusion coefficients gave atomic diameters of 4.06×10-10 m for Cd and 3.46×10-10 m for Zn; these values are somewhat larger than previously measured values. In these experiments when the equilibrium vapor pressures were greater than 13 000 Pa (100 Torr), the need to consider heat transfer from the furnace to the vaporizing sample was noted, i.e., sample cooling occured due to rapid vaporization. Validity of the MKW analysis was found.

  8. A QSPR model for prediction of diffusion coefficient of non-electrolyte organic compounds in air at ambient condition.

    PubMed

    Mirkhani, Seyyed Alireza; Gharagheizi, Farhad; Sattari, Mehdi

    2012-03-01

    Evaluation of diffusion coefficients of pure compounds in air is of great interest for many diverse industrial and air quality control applications. In this communication, a QSPR method is applied to predict the molecular diffusivity of chemical compounds in air at 298.15K and atmospheric pressure. Four thousand five hundred and seventy nine organic compounds from broad spectrum of chemical families have been investigated to propose a comprehensive and predictive model. The final model is derived by Genetic Function Approximation (GFA) and contains five descriptors. Using this dedicated model, we obtain satisfactory results quantified by the following statistical results: Squared Correlation Coefficient=0.9723, Standard Deviation Error=0.003 and Average Absolute Relative Deviation=0.3% for the predicted properties from existing experimental values.

  9. A new refinement indicator for adaptive parameterization: Application to the estimation of the diffusion coefficient in an elliptic problem

    NASA Astrophysics Data System (ADS)

    Hayek, Mohamed; Ackerer, Philippe; Sonnendrücker, Éric

    2009-02-01

    We propose a new refinement indicator (NRI) for adaptive parameterization to determine the diffusion coefficient in an elliptic equation in two-dimensional space. The diffusion coefficient is assumed to be a piecewise constant space function. The unknowns are both the parameter values and the zonation. Refinement indicators are used to localize parameter discontinuities in order to construct iteratively the zonation (parameterization). The refinement indicator is obtained usually by using the first-order effect on the objective function of removing degrees of freedom for a current set of parameters. In this work, in order to reduce the computation costs, we propose a new refinement indicator based on the second-order effect on the objective function. This new refinement indicator depends on the objective function, and its first and second derivatives with respect to the parameter constraints. Numerical experiments show the high efficiency of the new refinement indicator compared to the standard one.

  10. Extensive database of liquid phase diffusion coefficients of some frequently used test molecules in reversed-phase liquid chromatography and hydrophilic interaction liquid chromatography.

    PubMed

    Song, Huiying; Vanderheyden, Yoachim; Adams, Erwin; Desmet, Gert; Cabooter, Deirdre

    2016-07-15

    Diffusion plays an important role in all aspects of band broadening in chromatography. An accurate knowledge of molecular diffusion coefficients in different mobile phases is therefore crucial in fundamental column performance studies. Correlations available in literature, such as the Wilke-Chang equation, can provide good approximations of molecular diffusion under reversed-phase conditions. However, these correlations have been demonstrated to be less accurate for mobile phases containing a large percentage of acetonitrile, as is the case in hydrophilic interaction liquid chromatography. A database of experimentally measured molecular diffusion coefficients of some 45 polar and apolar compounds that are frequently used as test molecules under hydrophilic interaction liquid chromatography and reversed-phase conditions is therefore presented. Special attention is given to diffusion coefficients of polar compounds obtained in large percentages of acetonitrile (>90%). The effect of the buffer concentration (5-10mM ammonium acetate) on the obtained diffusion coefficients is investigated and is demonstrated to mainly influence the molecular diffusion of charged molecules. Diffusion coefficients are measured using the Taylor-Aris method and hence deduced from the peak broadening of a solute when flowing through a long open tube. The validity of the set-up employed for the measurement of the diffusion coefficients is demonstrated by ruling out the occurrence of longitudinal diffusion, secondary flow interactions and extra-column effects, while it is also shown that radial equilibration in the 15m long capillary is effective.

  11. Use of NMR Imaging to Determine the Diffusion Coefficient of Water in Bio-based Hydrogels

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The diffusion of liquid in a hydrogel material is a fundamental property which must be controlled in order to create effective delivery systems for the agricultural and pharmaceutical industries. NMR spectroscopy has been used to determine the diffusion of water and deuterium oxide in a bio-based h...

  12. Relationships of radon diffusion coefficient with saturated hydraulic conductivity, fines content and moisture saturation of radon/infiltration barriers for the UMTRA Project

    SciTech Connect

    Li, P.Y.; Chen, P.K.

    1994-01-24

    The release of {sup 222}Radon to the atmosphere is controlled by the rate of its gas transport through earthen materials. Of the many soil-related parameters, radon diffusion coefficient is the key parameter that characterizes this transport. We compared the radon diffusion coefficients measured at the laboratories for the UMTRA Project with simple empirical correlations developed by others. The empirical correlations predict the radon diffusion coefficient based on the fraction of moisture saturation and porosity. One of the more recent correlations agrees reasonably well with the measurements. In addition, by using a series of correlation curves, we studied the empirical relationships of the. radon diffusion coefficient with the saturated hydraulic conductivity, the fines content, and the moisture saturation in soil. The results reveal that a reliable determination of the long-term moisture and porosity is essential in the design of an adequate radon barrier with respect to the radon diffusion coefficient.

  13. Toward Universal Half-Saturation Coefficients: Describing Extant K(s) as a Function of Diffusion.

    PubMed

    Shaw, Andrew; Takacs, Imre; Pagilla, Krishna; Riffat, Rumana; DeClippeleir, Haydee; Wilson, Christopher; Murthy, Sudhir

    2015-05-01

    Observed (extant) K(s) is not a constant and it is strongly influenced by diffusion. This paper argues that diffusion can be used to describe bacterial kinetic effects that are sometimes attributed to "K-strategists" and, in fact, the physics of the system is the dominant mechanism affecting the apparent (extant) Ks--not intrinsic biological characteristics--in real water resource recovery facility systems. Four different biological processes have been modeled using the "porter-diffusion" model that was originally developed by Pasciak and Gavis (1974) for aquatic systems. The results demonstrate that diffusion is the dominant mechanism affecting K(s) in all four biological processes. Therefore, the authors argue that for treatment processes in which substrate concentrations are low, it is important to consider shifting to variable extant K(s) values or explicitly modeling the effects of diffusion.

  14. Divergence of the Long Wavelength Collective Diffusion Coefficient in Quasi-one and Quasi-two Dimensional Colloid Suspensions

    NASA Astrophysics Data System (ADS)

    Lin, Binhua; Cui, Bianxiao; Xu, Xinliang; Zangi, Ronen; Diamant, Haim; Rice, Stuart A.

    2015-03-01

    We report the results of experimental studies of the short time-long wavelength behavior of collective particle displacements in q1D and q2D colloid suspensions. Our results are reported via the q->0 behavior of the hydrodynamic function H (q) that relates the effective collective diffusion coefficient, De (q) , with the static structure factor S (q) and the self-diffusion coefficient of isolated particles Do: H (q) De (q) S (q) /Do. We find an apparent divergence of H (q) as q->0 with the form H(q)q-(1.7 < γ<1.9), for both q1D and q2D colloid suspensions. Given that S (q) does not diverge as we infer that De (q) does. This behavior is qualitatively different from that of the three-dimensional H (q) and De (q) as q->0, and the divergence is of a different functional form from that predicted for the diffusion coefficient in one component 1D and 2D fluids not subject to boundary conditions that define the dimensionality of the system. The research was supported by the NSF MRSEC at the U of Chicago (NSF/DMR-MRSEC 0820054), NSF/CHE 0822838 (ChemMatCARS), and Israel Science Foundation (Grant No. 8/10).

  15. The determination of SO 42-, NaSO 4-, and MgSO 40 tracer diffusion coefficients and their application to diagenetic flux calculations

    NASA Astrophysics Data System (ADS)

    Applin, Kenneth R.; Lasaga, Antonio C.

    1984-10-01

    Sulfur-35 was used to monitor the non-steady-state tracer diffusion of the free sulfate ion and sulfate ion-pairs in aqueous solutions of MgSO 4 and Na 2SO 4. Diffusion coefficients were derived from radiotracer flux measurements taken over ionic strengths ranging from 0.001 to 0.7. The experimental tracer diffusion coefficient is a function of the diffusion coefficients of the free sulfate ion and the sulfate ion-pairs as well as the ion pair equilibrium constant. The free sulfate ion tracer diffusion coefficient was determined independently from both the MgSO 4 and Na 2SO 4, experiments and found to be 1.11 and 1.08 (in units of 10 -5cm2sec-1, ± 10%, respectively. These values closely agree with that calculated from the Nernst expression, 1.07 sx 10 -5cm2sec-1. The tracer diffusion coefficients of MgSO 40 and NaSO 4- were determined to be 0.85 and 1.23 sx 10 -5cm2sec-1, respectively. These numbers are in reasonable agreement with the earlier work on mutual diffusion coefficients by RARD and MILLER (1979b) ( DMgSO4o = 0.65, Dnaso4- = 1.19) and Harned and Hudson (1951) DMgSO40 = (0.70). A modified version of the theoretical equation developed by Pikal (1971) is proposed for predicting the tracer diffusion coefficients of many ion-pairs relevant to seawater. Many of these predicted values are found to be within 10-20% of the empirical values extracted from mutual diffusion data. The experimental and theoretical diffusion coefficient data are used to calculate revised coupled diffusion coefficients, D g, according to the model of Lasaga (1979).

  16. The temperature-dependent diffusion coefficient of helium in zirconium carbide studied with first-principles calculations

    SciTech Connect

    Yang, Xiao-Yong; Lu, Yong; Zhang, Ping

    2015-04-28

    The temperature-dependent diffusion coefficient of interstitial helium in zirconium carbide (ZrC) matrix is calculated based on the transition state theory. The microscopic parameters in the activation energy and prefactor are obtained from first-principles total energy and phonon frequency calculations including the all atoms. The obtained activation energy is 0.78 eV, consistent with experimental value. Besides, we evaluated the influence of C and Zr vacancies as the perturbation on helium diffusion, and found the C vacancy seems to confine the mobility of helium and the Zr vacancy promotes helium diffusion in some extent. These results provide a good reference to understand the behavior of helium in ZrC matrix.

  17. Permeability and kinetic coefficients for mesoscale BCF surface step dynamics: Discrete two-dimensional deposition-diffusion equation analysis

    SciTech Connect

    Zhao, Renjie; Evans, James W.; Oliveira, Tiago J.

    2016-04-08

    Here, a discrete version of deposition-diffusion equations appropriate for description of step flow on a vicinal surface is analyzed for a two-dimensional grid of adsorption sites representing the stepped surface and explicitly incorporating kinks along the step edges. Model energetics and kinetics appropriately account for binding of adatoms at steps and kinks, distinct terrace and edge diffusion rates, and possible additional barriers for attachment to steps. Analysis of adatom attachment fluxes as well as limiting values of adatom densities at step edges for nonuniform deposition scenarios allows determination of both permeability and kinetic coefficients. Behavior of these quantities is assessed as a function of key system parameters including kink density, step attachment barriers, and the step edge diffusion rate.

  18. Permeability and kinetic coefficients for mesoscale BCF surface step dynamics: Discrete two-dimensional deposition-diffusion equation analysis

    DOE PAGES

    Zhao, Renjie; Evans, James W.; Oliveira, Tiago J.

    2016-04-08

    Here, a discrete version of deposition-diffusion equations appropriate for description of step flow on a vicinal surface is analyzed for a two-dimensional grid of adsorption sites representing the stepped surface and explicitly incorporating kinks along the step edges. Model energetics and kinetics appropriately account for binding of adatoms at steps and kinks, distinct terrace and edge diffusion rates, and possible additional barriers for attachment to steps. Analysis of adatom attachment fluxes as well as limiting values of adatom densities at step edges for nonuniform deposition scenarios allows determination of both permeability and kinetic coefficients. Behavior of these quantities is assessedmore » as a function of key system parameters including kink density, step attachment barriers, and the step edge diffusion rate.« less

  19. Remarks concerning the validity of the measured diffusion coefficients in liquid metal systems on the Russian MIR space station

    NASA Astrophysics Data System (ADS)

    Shirkhanzadeh, M.

    2008-02-01

    Acta Astronautica, Vol. 48 (2001), contains in pp. 59-70 an article discussing the benefits of conducting liquid metal diffusion experiments in space using the Canadian Microgravity Vibration Isolation Mount (MIM) [B.V. Tryggvason, R.F. Redden, R.A. Herring, W.M.B. Duval, R.W. Smith, K.S. Rezkallah, S.Varma, The vibration environment on the International Space Station: its significance to fluid-based experiments, Acta Astronautica 48 (2001) 59-70]. Two main problems have been identified with this published article: (1) On the basis of experimental results, the authors claim that the diffusion coefficients of gold in lead measured on the ground are much higher than those obtained under microgravity conditions. Close examination of the problems encountered during processing of the capillary diffusion couples on the MIR space station reveals that this claim cannot be justified. (2) The authors further conclude that there is a linear relationship between diffusion coefficient (D) and temperature (T) when g-jitter is suppressed. This conclusion is questionable because the methodology used to determine the processing time and temperatures on the MIR space station does not seem to be scientific.

  20. Theoretical examination of effective oxygen diffusion coefficient and electrical conductivity of polymer electrolyte fuel cell porous components

    NASA Astrophysics Data System (ADS)

    Inoue, Gen; Yokoyama, Kouji; Ooyama, Junpei; Terao, Takeshi; Tokunaga, Tomomi; Kubo, Norio; Kawase, Motoaki

    2016-09-01

    The reduction of oxygen transfer resistance through porous components consisting of a gas diffusion layer (GDL), microporous layer (MPL), and catalyst layer (CL) is very important to reduce the cost and improve the performance of a PEFC system. This study involves a systematic examination of the relationship between the oxygen transfer resistance of the actual porous components and their three-dimensional structure by direct measurement with FIB-SEM and X-ray CT. Numerical simulations were carried out to model the properties of oxygen transport. Moreover, based on the model structure and theoretical equations, an approach to the design of new structures is proposed. In the case of the GDL, the binder was found to obstruct gas diffusion with a negative effect on performance. The relative diffusion coefficient of the MPL is almost equal to that of the model structure of particle packing. However, that of CL is an order of magnitude less than those of the other two components. Furthermore, an equation expressing the relative diffusion coefficient of each component can be obtained with the function of porosity. The electrical conductivity of MPL, which is lower than that of the carbon black packing, is considered to depend on the contact resistance.

  1. A new optimization method for a class of time fractional convection-diffusion-wave equations with variable coefficients

    NASA Astrophysics Data System (ADS)

    Dahaghin, M. Sh.; Hassani, H.

    2017-03-01

    In this paper, we consider a class of time fractional convection-diffusion-wave equations (TFCDWE) with variable coefficients involving fractional derivatives in the Caputo sense. We also propose an optimization method based on the generalized polynomials (GPs) for solving TFCDWE. Our objective in the proposed method is to expand the solution of the problem under consideration in terms of GPs with unknown free coefficients and control parameters. Furthermore, we derive some operational matrices of the ordinary and fractional derivatives for these basis functions. Finally, we obtain the free coefficients and control parameters optimally by minimizing the error of the approximate solution. Some numerical examples are provided to demonstrate the validity and accuracy of the proposed method. The obtained results show that the proposed method is very efficient and accurate.

  2. Diffusion-weighted imaging in the prostate: an apparent diffusion coefficient comparison of half-Fourier acquisition single-shot turbo spin-echo and echo planar imaging.

    PubMed

    Babourina-Brooks, Ben; Cowin, Gary J; Wang, Deming

    2012-02-01

    Prostate cancer detection using diffusion-weighted imaging is highly affected by the accuracy of the apparent diffusion coefficient (ADC) values in an image. Echo planar imaging (EPI) is a fast sequence commonly used for diffusion imaging but has inherent magnetic susceptibility and chemical shift artefacts associated. A diffusion sequence that is less affected by these artefacts is therefore advantageous. The half-Fourier acquisition single-shot turbo spin-echo (HASTE) sequence was chosen. The diffusion sequences were compared in image quality, repeatability of the ADC value and the effect on the ADC value with varied b values. Eight volunteers underwent three scans of each sequence, on a 1.5-T Siemens system, using b values of 0, 150, 300, 450, 600, 750, 900 and 1000 s/mm(2). ADC maps were created to address the reproducibility of the ADC value when using two b values compared to eight b values. The ADC value using all b values with the HASTE sequence gave the best performance in all tested categories. Both sequences gave significantly different ADC mean values for two b values compared to when using eight b values (P<.05) suggesting larger error is present when using two b values. HASTE was shown to be an improvement over EPI in terms of repeatability, signal variation within a region of interest and standard deviation over the volunteer set. The improved accuracy of the ADC value in the HASTE sequence makes it potentially a more sensitive tumor detection technique.

  3. Wave intensity amplification and attenuation in non-linear flow: implications for the calculation of local reflection coefficients.

    PubMed

    Mynard, Jonathan; Penny, Daniel J; Smolich, Joseph J

    2008-12-05

    Local reflection coefficients (R) provide important insights into the influence of wave reflection on vascular haemodynamics. Using the relatively new time-domain method of wave intensity analysis, R has been calculated as the ratio of the peak intensities (R(PI)) or areas (R(CI)) of incident and reflected waves, or as the ratio of the changes in pressure caused by these waves (R(DeltaP)). While these methods have not yet been compared, it is likely that elastic non-linearities present in large arteries will lead to changes in the size of waves as they propagate and thus errors in the calculation of R(PI) and R(CI). To test this proposition, R(PI), R(CI) and R(DeltaP) were calculated in a non-linear computer model of a single vessel with various degrees of elastic non-linearity, determined by wave speed and pulse amplitude (DeltaP(+)), and a terminal admittance to produce reflections. Results obtained from this model demonstrated that under linear flow conditions (i.e. as DeltaP(+)-->0), R(DeltaP) is equivalent to the square-root of R(PI) and R(CI) (denoted by R(PI)(p) and R(CI)(p)). However for non-linear flow, pressure-increasing (compression) waves undergo amplification while pressure-reducing (expansion) waves undergo attenuation as they propagate. Consequently, significant errors related to the degree of elastic non-linearity arise in R(PI) and R(CI), and also R(PI)(p) and R(CI)(p), with greater errors associated with larger reflections. Conversely, R(Delta)(P) is unaffected by the degree of non-linearity and is thus more accurate than R(PI) and R(CI).

  4. Quantitative measurement of attenuation coefficients of bladder biopsies using optical coherence tomography for grading urothelial carcinoma of the bladder

    NASA Astrophysics Data System (ADS)

    Cauberg, Evelyne C. C.; de Bruin, Daniël M.; Faber, Dirk J.; de Reijke, Theo M.; Visser, Mike; de La Rosette, Jean J. M. C. H.; van Leeuwen, Ton G.

    2010-11-01

    Real-time grading of bladder urothelial carcinoma (UC) is clinically important, but the current standard for grading (histopathology) cannot provide this information. Based on optical coherence tomography (OCT)-measured optical attenuation (μt), the grade of bladder UC could potentially be assessed in real time. We evaluate ex vivo whether μt differs between different grades of UC and benign bladder tissue. Human bladder tissue specimens are examined ex vivo by 850-nm OCT using dynamic focusing. Three observers independently determine the μt from the OCT images, and three pathologists independently review the corresponding histology slides. For both methods, a consensus diagnosis is made. We include 76 OCT scans from 54 bladder samples obtained in 20 procedures on 18 patients. The median (interquartile range) μt of benign tissue is 5.75 mm-1 (4.77 to 6.14) versus 5.52 mm-1 (3.47 to 5.90), 4.85 mm-1 (4.25 to 6.50), and 5.62 mm-1 (5.01 to 6.29) for grade 1, 2, and 3 UC, respectively (p = 0.732). Interobserver agreement of histopathology is ``substantial'' [Kappa 0.62, 95% confidence interval (IC) 0.54 to 0.70] compared to ``almost perfect'' [interclass correlation coefficient (ICC) 0.87, 95% CI 0.80 to 0.92] for OCT. Quantitative OCT analysis (by μt) does not detect morphological UC changes. This may be due to factors typical for an ex-vivo experimental setting.

  5. Anomalous attenuation of the positive temperature coefficient of resistivity in a carbon-black-filled polymer composite with electrically conductive in situ microfibrils

    NASA Astrophysics Data System (ADS)

    Xu, Xiang-Bin; Li, Zhong-Ming; Dai, Kun; Yang, Ming-Bo

    2006-07-01

    The positive temperature coefficient of resistivity (PTCR) of in situ microfibrillar carbon black/poly (ethylene terephthalate)/polyethylene composite attenuates dramatically after a sufficient time of isothermal treatment without oxygen above the melting region of polyethylene. The inhomogeneous surface microstructure and the large size of the microfibrils are the key factors controlling PTCR attenuation, through which a model is proposed to explain this anomalous phenomenon. An effective approach is accordingly developed to prepare recyclable semicrystalline thermoplastic based electrically conductive polymer composite with steady conductivity in wide temperature range.

  6. Simultaneous tracer diffusion and interdiffusion in a sandwich-type configuration to provide the composition dependence of the tracer diffusion coefficients

    NASA Astrophysics Data System (ADS)

    Belova, I. V.; Kulkarni, N. S.; Sohn, Y. H.; Murch, G. E.

    2014-11-01

    In this paper, a new formalism of a combined tracer and interdiffusion experiment for a binary interdiffusion couple is developed. The analysis requires an interdiffusion couple that initially contains a thin layer of tracers of one or both of the constituent elements at the original interface of the couple (sandwich interdiffusion experiment). This type of interdiffusion experiment was first performed in 1958 by J.R. Manning. The theoretical analysis presented in this paper is based on a newly developed phenomenological theory of isotopic interdiffusion combined with the Boltzmann-Matano formalism. This new analysis now provides the means to obtain the composition dependent interdiffusion coefficient and tracer diffusion coefficients simultaneously from analysis of the interdiffusion and tracer profiles in a single sandwich interdiffusion experiment. The new analysis is successfully applied to the results of Manning's original 'sandwich interdiffusion' experiment in the Ag-Cd system (six couples in total) and is validated with an independent determination of the Ag and Cd tracer diffusion coefficients by Schoen using the conventional thin film technique. Suggestions for further development of the sandwich interdiffusion experiment and analysis to the case of multicomponent alloys are provided.

  7. Effect of porous structure of catalyst layer on effective oxygen diffusion coefficient in polymer electrolyte fuel cell

    NASA Astrophysics Data System (ADS)

    Inoue, Gen; Kawase, Motoaki

    2016-09-01

    It is important to reduce the oxygen diffusion resistance through PEFC porous electrode, because it is the key to reduce the PEFC cost. However, the gas diffusion coefficient of CL is lower than MPL in spite of framework consisted of same carbon blacks. In this study, in order to understand the reasons of the lower gas diffusion performance of CL, the relationship between a carbon black agglomerate structure and ionomer adhesion condition is evaluated by a numerical analysis with an actual reconstructed structure and a simulated structure. As a result, the gas diffusion property of CL strongly depends on the ionomer adhesion shape. In the case of adhesion shape with the same curvature of ionomer interface, each pore can not be connected enough. So the pore tortuosity increases. Moreover, in the case of existence of inefficient large pores formed by carbon black agglomerate and ununiformly coated ionomer, the gas diffusion performance decrease rapidly. As the measurement values in actual CL are almost equal to that with model structure with inefficient large pores. These characteristics can be confirmed by actual cross-section image obtained by FIB-SEM.

  8. Measurement of Soret and Fickian diffusion coefficients by orthogonal phase-shifting interferometry and its application to protein aqueous solutions

    NASA Astrophysics Data System (ADS)

    Torres, Juan F.; Komiya, Atsuki; Henry, Daniel; Maruyama, Shigenao

    2013-08-01

    We have developed a method to measure thermodiffusion and Fickian diffusion in transparent binary solutions. The measuring instrument consists of two orthogonally aligned phase-shifting interferometers coupled with a single rotating polarizer. This high-resolution interferometer, initially developed to measure isothermal diffusion coefficients in liquid systems [J. F. Torres, A. Komiya, E. Shoji, J. Okajima, and S. Maruyama, Opt. Lasers Eng. 50, 1287 (2012)], was modified to measure transient concentration profiles in binary solutions subject to a linear temperature gradient. A convectionless thermodiffusion field was created in a binary solution sample that is placed inside a Soret cell. This cell consists of a parallelepiped cavity with a horizontal cross-section area of 10 × 20 mm2, a variable height of 1-2 mm, and transparent lateral walls. The small height of the cell reduces the volume of the sample, shortens the measurement time, and increases the hydrodynamic stability of the system. An additional free diffusion experiment with the same optical apparatus provides the so-called contrast factors that relate the unwrapped phase and concentration gradients, i.e., the measurement technique is independent and robust. The Soret coefficient is determined from the concentration and temperature differences between the upper and lower boundaries measured by the interferometer and thermocouples, respectively. The Fickian diffusion coefficient is obtained by fitting a numerical solution to the experimental concentration profile. The method is validated through the measurement of thermodiffusion in the well-known liquid pairs of ethanol-water (ethanol 39.12 wt.%) and isobutylbenzene-dodecane (50.0 wt.%). The obtained coefficients agree with the literature values within 5.0%. Finally, the developed technique is applied to visualize biomolecular thermophoresis. Two protein aqueous solutions at 3 mg/ml were used as samples: aprotinin (6.5 kDa)-water and lysozyme (14.3 k

  9. Determination of Kubelka-Munk scattering and absorption coefficients by diffuse illumination.

    PubMed

    Molenaar, R; ten Bosch, J J; Zijp, J R

    1999-04-01

    The Kubelka-Munk theory, although it provides an equation that relates the reflection of a sample under diffuse illumination to certain of its properties, does not take boundary reflectance into account. Boundary reflection is always present because there is always a difference between the refractive indices of the sample and of the surrounding medium. We describe how a half-sphere is used to achieve diffuse illumination, and we present and exemplify equations that correct for boundary reflection with measurements of four composite restorative dental materials. The refractive index of the sample is measured with a matching technique that employs a glycerol-water mixture. Edge loss errors are estimated.

  10. The influence of gravity on the precise measurement of solute diffusion coefficients in dilute liquid metals and metalloids.

    PubMed

    Smith, Reginald W; Zhu, Xiaohe; Tunnicliffe, Mark C; Smith, Timothy J N; Misener, Lowell; Adamson, Josee

    2002-10-01

    It is now well known that the diffusion coefficient (D) measured in a laboratory in low earth orbit (LEO) is less than the corresponding value measured in a terrestrial laboratory. However, all LEO laboratories are subject to transient accelerations (g-jitter) superimposed on the steady reduced gravity environment of the space platform. In measurements of the diffusion coefficients for dilute binary alloys of Pb-(Ag, Au,Sb), Sb-(Ga,In), Bi-(Ag,Au,Sb), Sn-(Au,Sb), Al-(Fe, Ni,Si), and In-Sb in which g-jitter was suppressed, it was found that D proportional to T (temperature) if g-jitter was suppressed, rather than D proportional to T(2) as observed by earlier workers with g-jitter present. Furthermore, when a forced g-jitter was applied to a diffusion couple, the value measured for D increased. The significance of these results is reviewed in the light of recent work in which ab initio molecular dynamics simulations predicted a D proportional to T relationship.

  11. Effects of dielectric saturation and ionic screening on the proton self-diffusion coefficients in perfluorosulfonic acid membranes.

    PubMed

    Paul, Reginald; Paddison, Stephen J

    2005-12-08

    Proton transport in perfluorosulfonic acid (PFSA) membranes is investigated through a statistical mechanical model that includes the effects of the interaction of the tethered sulfonate groups with both the water and solvated protons. We first derive a potential that describes the electrostatic field due to the dissociated sulfonic acid groups by extending the work of Gronbech-Jensen et al. [ Mol. Phys. 92, 941 (1997)] to a finite array of point charges. A highly convergent series is obtained which includes the effects of screening due to the protons. We then investigate the effects of both dielectric saturation and two distinct formulations of ionic screening on the proton self-diffusion coefficient in Nafion membranes over a range of water contents. Our computations show that the two phenomena (i.e., dielectric saturation and ionic screening) under constant temperature conditions result in canceling affects. Our calculations provide a radial dependence of the proton mobility suggesting that the dominant self-diffusion occurs in the central region of the pores, well separated from the sulfonate groups. Through comparison of our calculated diffusion coefficients with the experimental values we derived a slightly smaller average separation distance of the hydronium ion from the sulfonate ions than suggested by either electronic structure calculations or multistate empirical valence bond molecular-dynamics simulations.

  12. On the air-filled effective porosity parameter of Rogers and Nielson's (1991) bulk radon diffusion coefficient in unsaturated soils.

    PubMed

    Saâdi, Zakaria

    2014-05-01

    The radon exhalation rate at the earth's surface from soil or rock with radium as its source is the main mechanism behind the radon activity concentrations observed in both indoor and outdoor environments. During the last two decades, many subsurface radon transport models have used Rogers and Nielson's formula for modeling the unsaturated soil bulk radon diffusion coefficient. This formula uses an "air-filled effective porosity" to account for radon adsorption and radon dissolution in the groundwater. This formula is reviewed here, and its hypotheses are examined for accuracy in dealing with subsurface radon transport problems. The author shows its limitations by comparing one dimensional steady-state analytical solutions of the two-phase (air/water) transport equation (Fick's law) with Rogers and Nielson's formula. For radon diffusion-dominated transport, the calculated Rogers and Nielson's radon exhalation rate is shown to be unrealistic as it is independent of the values of the radon adsorption and groundwater dissolution coefficients. For convective and diffusive transport, radon exhalation rates calculated using Fick's law and this formula agree only for high values of gas-phase velocity and groundwater saturation. However, these conditions are not usually met in most shallow subsurface environments where radon migration takes place under low gas phase velocities and low water saturation.

  13. Measuring the ratio of aqueous diffusion coefficients between [sup 6]Li[sup +]Cl[sup [minus

    SciTech Connect

    Fritz, S.J. )

    1992-10-01

    Osmotic equilibrium is a singular occurrence in the evolution of an osmotic cell because at this event the net solution flux is zero such that [minus]J[sub w] [center dot] [bar V][sub w] = J[sub s] [center dot] [bar V][sub s]. At this juncture, the diffusion coefficient of the solute through the membrane ([omega]) equals the solute flux (J[sub s]) divided by the osmotic pressure ([delta]II). Because the solute permeability coefficient ([omega]) is related to the Fickian diffusion coefficient (D) through the gas constant, temperature, and the membrane's thickness and tortuosity, the ratio of [omega] values for individual isotopic species equals the ratio of D values for the same isotopic components. A 0.9450 molal LiCl solution was placed within sealed dialysis tubing and osmoted against a kilogram of deionized water at 22C. Osmotic equilibrium occurred at 164 [plus minus] 10 min. The ratio of [omega][sub [sup 6]Li[sup +]Cl[sup [minus

  14. Calculation of the second self-diffusion and viscosity virial coefficients of Lennard-Jones fluid by equilibrium molecular dynamics simulations.

    PubMed

    Oderji, Hassan Yousefi; Ding, Hongbin; Behnejad, Hassan

    2011-06-01

    The second self-diffusion and viscosity virial coefficients of the Lennard-Jones (LJ) fluid were calculated by a detailed evaluation of the velocity and shear-stress autocorrelation functions using equilibrium molecular dynamics simulations at low and moderate densities. Accurate calculation of these coefficients requires corresponding transport coefficient values with low degrees of uncertainty. These were obtained via very long simulations by increasing the number of particles and by using the knowledge of correlation functions in the Green-Kubo method in conjunction with their corresponding generalized Einstein relations. The values of the self-diffusion and shear viscosity coefficients have been evaluated for systems with reduced densities between 0.0005 and 0.05 and reduced temperatures from 0.7 to 30.0. This provides a new insight into the transport coefficients beyond what can be offered by the Rainwater-Friend theory, which has not been developed for the self-diffusion coefficient.

  15. Mass attenuation coefficient of binderless, pre-treated and tannin-based Rhizophora spp. particleboards using 16.59 - 25.26 keV photon energy range

    NASA Astrophysics Data System (ADS)

    Mohd Yusof, Mohd Fahmi; Hamid, Puteri Nor Khatijah Abdul; Bauk, Sabar; Hashim, Rokiah; Tajuddin, Abdul Aziz

    2015-04-01

    The Rhizophora spp. particleboards were fabricated using ≤ 104 µm particle size at three different fabrication methods; binderless, steam pre-treated and tannin-added. The mass attenuation coefficient of Rhizophora spp. particleboards were measured using x-ray fluorescent (XRF) photon from niobium, molybdenum, palladium, silver and tin metal plates that provided photon energy between 16.59 to 25.26 keV. The results were compared to theoretical values for water calculated using photon cross-section database (XCOM).The results showed that all Rhizophora spp. particleboards having mass attenuation coefficient close to calculated XCOM for water. Tannin-added Rizophora spp. particleboard was nearest to calculated XCOM for water with χ2 value of 13.008 followed by binderless Rizophora spp. (25.859) and pre-treated Rizophora spp. (91.941).

  16. Experimental Study of Diffusion Coefficients of Water through the Collagen: Apatite Porosity in Human Trabecular Bone Tissue

    PubMed Central

    Bini, Fabiano; Marinozzi, Andrea

    2014-01-01

    We firstly measured the swelling of single trabeculae from human femur heads during water imbibition. Since the swelling is caused by water diffusing from external surfaces to the core of the sample, by measuring the sample swelling over time, we obtained direct information about the transport of fluids through the intimate constituents of bone, where the mineralization process takes place. We developed an apparatus to measure the free expansion of the tissue during the imbibition. In particular, we measured the swelling along three natural axes (length L, width W, and thickness T) of plate-like trabeculae. For this aim, we developed a 3D analytical model of the water uptake by the sample that was performed according to Fickian transport mechanism. The results were then utilized to predict the swelling over time along the three sample directions (L, W, T) and the apparent diffusion coefficients DT, DW, and DL. PMID:24967405

  17. Force-Clamp Experiments Reveal the Free-Energy Profile and Diffusion Coefficient of the Collapse of Protein Molecules

    NASA Astrophysics Data System (ADS)

    Lannon, H.; Haghpanah, J. S.; Montclare, J. K.; Vanden-Eijnden, E.; Brujic, J.

    2013-03-01

    We present force-clamp data on the collapse of ubiquitin polyproteins from a highly extended state to the folded length, in response to a quench in the force from 110 pN to 5 or 10 pN. Using a recent method for free-energy reconstruction from the observed nonequilibrium trajectories, we find that their statistics is captured by simple diffusion along the end-to-end length. The estimated diffusion coefficient of ˜100nm2s-1 is significantly slower than expected from viscous effects alone, possibly because of the internal degrees of freedom of the protein. The free-energy profiles give validity to a physical model in which the multiple protein domains collapse all at once and the role of the force is approximately captured by the Bell model.

  18. Study on anisotropy of effective diffusion coefficient and activation energy for deuterated water in compacted sodium bentonite.

    PubMed

    Suzuki, Satoru; Sato, Haruo; Ishidera, Takamitsu; Fujii, Naoki

    2004-01-01

    To quantify the effects of temperature on the diffusivity of deuterated water (HDO) in compacted sodium bentonite, through-diffusion experiments were conducted at elevated temperatures ranging from 298 to 333 K. Kunipia F (Na-montmorillonite content>98 wt.%; Kunimine Industries) was compacted to a dry density of 0.9 or 1.35 Mg/m(3). As montmorillonite particles were oriented perpendicular to the direction of compaction, the anisotropy of diffusivity was investigated both parallel and normal to the preferred orientation of the montmorillonite. The effective diffusion coefficient D(e) of HDO was larger when the diffusional direction was parallel as opposed to normal to the preferred orientation for both dry densities. The magnitude of D(e) and the anisotropy for HDO were in good accordance with previously reported results for tritiated water at room temperature. Activation energies of D(e) were isotropic and increased with increasing dry density over the range of 19-25 kJ/mol. This relationship was considered to be due to both pore structure development and the high activation energy of water near the montmorillonite surface.

  19. Direct evaluation of the position dependent diffusion coefficient and persistence time from the equilibrium density profile in anisotropic fluids.

    PubMed

    Olivares-Rivas, Wilmer; Colmenares, Pedro J; López, Floralba

    2013-08-21

    We derive expressions for the transverse diffusion coefficient D(z) and the average persistence time τ(z; L) within a layer of width L, for particles of a non-homogeneous fluid enclosed in a planar nanopore. The method allows the direct evaluation of these position-dependent dynamical quantities from the equilibrium local particle density profile. We use results for the density and persistence time profiles from the virtual layer molecular dynamics method to numerically assess the significance of the Smoluchowski approximation.

  20. Oxygen potentials, oxygen diffusion coefficients and defect equilibria of nonstoichiometric (U,Pu)O2±x

    NASA Astrophysics Data System (ADS)

    Kato, Masato; Watanabe, Masashi; Matsumoto, Taku; Hirooka, Shun; Akashi, Masatoshi

    2017-04-01

    Oxygen potential of (U,Pu)O2±x was evaluated based on defect chemistry using an updated experimental data set. The relationship between oxygen partial pressure and deviation x in (U,Pu)O2±x was analyzed, and equilibrium constants of defect formation were determined as functions of Pu content and temperature. Brouwer's diagrams were constructed using the determined equilibrium constants, and a relational equation to determine O/M ratio was derived as functions of O/M ratio, Pu content and temperature. In addition, relationship between oxygen potential and oxygen diffusion coefficients were described.

  1. Gene interference regulates aquaporin-4 expression in swollen tissue of rats with cerebral ischemic edema: Correlation with variation in apparent diffusion coefficient.

    PubMed

    Hu, Hui; Lu, Hong; He, Zhanping; Han, Xiangjun; Chen, Jing; Tu, Rong

    2012-07-25

    To investigate the effects of mRNA interference on aquaporin-4 expression in swollen tissue of rats with ischemic cerebral edema, and diagnose the significance of diffusion-weighted MRI, we injected 5 μL shRNA- aquaporin-4 (control group) or siRNA- aquaporin-4 solution (1:800) (RNA interference group) into the rat right basal ganglia immediately before occlusion of the middle cerebral artery. At 0.25 hours after occlusion of the middle cerebral artery, diffusion-weighted MRI displayed a high signal; within 2 hours, the relative apparent diffusion coefficient decreased markedly, aquaporin-4 expression increased rapidly, and intracellular edema was obviously aggravated; at 4 and 6 hours, the relative apparent diffusion coefficient slowly returned to control levels, aquaporin-4 expression slightly increased, and angioedema was observed. In the RNA interference group, during 0.25-6 hours after injection of siRNA- aquaporin-4 solution, the relative apparent diffusion coefficient slightly fluctuated and aquaporin-4 expression was upregulated; during 0.5-4 hours, the relative apparent diffusion coefficient was significantly higher, while aquaporin-4 expression was significantly lower when compared with the control group, and intracellular edema was markedly reduced; at 0.25 and 6 hours, the relative apparent diffusion coefficient and aquaporin-4 expression were similar when compared with the control group; obvious angioedema remained at 6 hours. Pearson's correlation test results showed that aquaporin-4 expression was negatively correlated with the apparent diffusion coefficient (r = -0.806, P < 0.01). These findings suggest that upregulated aquaporin-4 expression is likely to be the main molecular mechanism of intracellular edema and may be the molecular basis for decreased relative apparent diffusion coefficient. Aquaporin-4 gene interference can effectively inhibit the upregulation of aquaporin-4 expression during the stage of intracellular edema with time

  2. Generalized Cahn-Hilliard equation for solutions with drastically different diffusion coefficients. Application to exsolution in ternary feldspar

    NASA Astrophysics Data System (ADS)

    Petrishcheva, E.; Abart, R.

    2012-04-01

    We address mathematical modeling and computer simulations of phase decomposition in a multicomponent system. As opposed to binary alloys with one common diffusion parameter, our main concern is phase decomposition in real geological systems under influence of strongly different interdiffusion coefficients, as it is frequently encountered in mineral solid solutions with coupled diffusion on different sub-lattices. Our goal is to explain deviations from equilibrium element partitioning which are often observed in nature, e.g., in a cooled ternary feldspar. To this end we first adopt the standard Cahn-Hilliard model to the multicomponent diffusion problem and account for arbitrary diffusion coefficients. This is done by using Onsager's approach such that flux of each component results from the combined action of chemical potentials of all components. In a second step the generalized Cahn-Hilliard equation is solved numerically using finite-elements approach. We introduce and investigate several decomposition scenarios that may produce systematic deviations from the equilibrium element partitioning. Both ideal solutions and ternary feldspar are considered. Typically, the slowest component is initially "frozen" and the decomposition effectively takes place only for two "fast" components. At this stage the deviations from the equilibrium element partitioning are indeed observed. These deviations may became "frozen" under conditions of cooling. The final equilibration of the system occurs on a considerably slower time scale. Therefore the system may indeed remain unaccomplished at the observation point. Our approach reveals the intrinsic reasons for the specific phase separation path and rigorously describes it by direct numerical solution of the generalized Cahn-Hilliard equation.

  3. Albedo and flux extinction coefficient of impure snow for diffuse shortwave radiation

    NASA Technical Reports Server (NTRS)

    Choudhury, B. J.; Mo, T.; Wang, J. R.; Chang, A. T. C.

    1981-01-01

    Impurities enter a snowpack as a result of fallout of scavenging by falling snow crystals. Albedo and flux extinction coefficient of soot contaminated snowcovers were studied using a two stream approximation of the radiative transfer equation. The effect of soot was calculated by two methods: independent scattering by ice grains and impurities and average refractive index for ice grains. Both methods predict a qualitatively similar effect of soot; the albedo is decreased and the extinction coefficient is increased compared to that for pure snow in the visible region; the infrared properties are largely unaffected. Quantitatively, however, the effect of soot is more pronounced in the average refractive index method. Soot contamination provides a qualitative explanation for several snow observations.

  4. Dynamics of supercooled water in nanotubes: Cage correlation function and diffusion coefficient

    NASA Astrophysics Data System (ADS)

    Khademi, Mahdi; Kalia, Rajiv K.; Sahimi, Muhammad

    2015-09-01

    Dynamics of low-temperature water in nanostructured materials is important to a variety of phenomena, ranging from transport in cement and asphaltene, to conformational dynamics of proteins in "crowded" cellular environments, survival of microorganisms at very low temperatures, and diffusion in nanogeoscience. Using silicon-carbide nanotubes as a prototype of nanostructured materials, extensive molecular dynamics simulations were carried out to study the cage correlation function C (t ) and self-diffusivity D of supercooled water in the nanotubes. C (t ) , which measures changes in the atomic surroundings inside the nanotube, follows the Kohlrausch-Williams-Watts law, C (t ) ˜exp[-(t/τ ) β] , where τ is a relaxation time and β is a topological exponent. For the temperature range 220 Kdiffusivity manifests a transition around 230 K, very close to 228 K, the temperature at which a fragile-to-strong dynamic crossover is supposed to happen. Thus the results indicate that water does not freeze in the nanotube over the studied temperature range, and that the Stokes-Einstein relation breaks down.

  5. A novel multiple headspace extraction gas chromatographic method for measuring the diffusion coefficient of methanol in water and in olive oil.

    PubMed

    Zhang, Chun-Yun; Chai, Xin-Sheng

    2015-03-13

    A novel method for the determination of the diffusion coefficient (D) of methanol in water and olive oil has been developed. Based on multiple headspace extraction gas chromatography (MHE-GC), the methanol released from the liquid sample of interest in a closed sample vial was determined in a stepwise fashion. A theoretical model was derived to establish the relationship between the diffusion coefficient and the GC signals from MHE-GC measurements. The results showed that the present method has an excellent precision (RSD<1%) in the linear fitting procedure and good accuracy for the diffusion coefficients of methanol in both water and olive oil, when compared with data reported in the literature. The present method is simple and practical and can be a valuable tool for the determination of the diffusion coefficient of volatile analyte(s) into food simulants from food and beverage packaging material, both in research studies and in actual applications.

  6. Influence of diffuse reflectance measurement accuracy on the scattering coefficient in determination of optical properties with integrating sphere optics (a secondary publication).

    PubMed

    Horibe, Takuro; Ishii, Katsunori; Fukutomi, Daichi; Awazu, Kunio

    2015-12-30

    An estimation error of the scattering coefficient of hemoglobin in the high absorption wavelength range has been observed in optical property calculations of blood-rich tissues. In this study, the relationship between the accuracy of diffuse reflectance measurement in the integrating sphere and calculated scattering coefficient was evaluated with a system to calculate optical properties combined with an integrating sphere setup and the inverse Monte Carlo simulation. Diffuse reflectance was measured with the integrating sphere using a small incident port diameter and optical properties were calculated. As a result, the estimation error of the scattering coefficient was improved by accurate measurement of diffuse reflectance. In the high absorption wavelength range, the accuracy of diffuse reflectance measurement has an effect on the calculated scattering coefficient.

  7. Influence of diffuse reflectance measurement accuracy on the scattering coefficient in determination of optical properties with integrating sphere optics (a secondary publication)

    PubMed Central

    Horibe, Takuro; Ishii, Katsunori; Fukutomi, Daichi

    2015-01-01

    An estimation error of the scattering coefficient of hemoglobin in the high absorption wavelength range has been observed in optical property calculations of blood-rich tissues. In this study, the relationship between the accuracy of diffuse reflectance measurement in the integrating sphere and calculated scattering coefficient was evaluated with a system to calculate optical properties combined with an integrating sphere setup and the inverse Monte Carlo simulation. Diffuse reflectance was measured with the integrating sphere using a small incident port diameter and optical properties were calculated. As a result, the estimation error of the scattering coefficient was improved by accurate measurement of diffuse reflectance. In the high absorption wavelength range, the accuracy of diffuse reflectance measurement has an effect on the calculated scattering coefficient. PMID:26877594

  8. Quantitative full-colour transmitted light microscopy and dyes for concentration mapping and measurement of diffusion coefficients in microfluidic architectures.

    PubMed

    Werts, Martinus H V; Raimbault, Vincent; Texier-Picard, Rozenn; Poizat, Rémi; Français, Olivier; Griscom, Laurent; Navarro, Julien R G

    2012-02-21

    A simple and versatile methodology has been developed for the simultaneous measurement of multiple concentration profiles of colourants in transparent microfluidic systems, using a conventional transmitted light microscope, a digital colour (RGB) camera and numerical image processing combined with multicomponent analysis. Rigorous application of the Beer-Lambert law would require monochromatic probe conditions, but in spite of the broad spectral bandwidths of the three colour channels of the camera, a linear relation between the measured optical density and dye concentration is established under certain conditions. An optimised collection of dye solutions for the quantitative optical microscopic characterisation of microfluidic devices is proposed. Using the methodology for optical concentration measurement we then implement and validate a simplified and robust method for the microfluidic measurement of diffusion coefficients using an H-filter architecture. It consists of measuring the ratio of the concentrations of the two output channels of the H-filter. It enables facile determination of the diffusion coefficient, even for non-fluorescent molecules and nanoparticles, and is compatible with non-optical detection of the analyte.

  9. Describing Temperature-Dependent Self-Diffusion Coefficients and Fluidity of 1- and 3-Alcohols with the Compensated Arrhenius Formalism.

    PubMed

    Fleshman, Allison M; Forsythe, Grant E; Petrowsky, Matt; Frech, Roger

    2016-09-22

    The location of the hydroxyl group in monohydroxy alcohols greatly affects the temperature dependence of the liquid structure due to hydrogen bonding. Temperature-dependent self-diffusion coefficients, fluidity (the inverse of viscosity), dielectric constant, and density have been measured for several 1-alcohols and 3-alcohols with varying alkyl chain lengths. The data are modeled using the compensated Arrhenius formalism (CAF). The CAF follows a modified transition state theory using an Arrhenius-like expression to describe the transport property, which consists of a Boltzmann factor containing an energy of activation, Ea, and an exponential prefactor containing the temperature-dependent solution dielectric constant, εs(T). Both 1- and 3-alcohols show the Ea of diffusion coefficients (approximately 43 kJ mol(-1)) is higher than the Ea of fluidity (approximately 35 kJ mol(-1)). The temperature dependence of the exponential prefactor in these associated liquids is explained using the dielectric constant and the Kirkwood-Frölich correlation factor, gk. It is argued that the dielectric constant must be used to account for the additional temperature dependence due to variations in the liquid structure (e.g., hydrogen bonding) for the CAF to accurately model the transport property.

  10. Measurement of mass attenuation coefficients of Eremurus-Rhizophora spp. particleboards for X-ray in the 16.63-25.30 keV energy range

    NASA Astrophysics Data System (ADS)

    Tousi, E. T.; Bauk, S.; Hashim, R.; Jaafar, M. S.; Abuarra, A.; Aldroobi, K. S. A.; Al-Jarrah, A. M.

    2014-10-01

    The roots of Eremurus spp. were used as a bio-adhesive in the fabrication of Rhizophora spp. particleboards. The mass attenuation coefficients of Eremurus-Rhizophora spp. particleboard of six samples with two different weight percentages of the Eremurus spp. root (6% and 12%) and three various Rhizophora spp. particle sizes (≤149 μm, 149-500 μm and 500-1000 μm) were determined by using X-ray fluorescence (XRF) photons in 16.63 keV and 25.30 keV of the photon energy range. The results were compared with theoretically calculated mass attenuations using the XCOM computer program for younger-age (breast 1: 75% muscle+25% fat), middle-age (breast 2: 50% muscle+50% fat), and old-age (breast 3: 25% muscle+75% fat) breasts. The results indicated that Eremurus-Rhizophora spp. particleboard is the appropriate suitable phantom in the diagnostic energy region. The mass attenuation coefficient in the low weight percentage of the bio-adhesive and the large Rhizophora spp. particle size were found very close to breast 1. Moreover the mass attenuation coefficient of the sample with high weight percentage of the bio-adhesive and small Rhizophora spp. particle size was found very close to water as a standard material phantom. In addition, the viscosity of dissolved Eremurus spp. root in water could be considerably higher than that of formaldehyde-based adhesives, which affects on some properties such as high strength and high binding.

  11. Strategies for Diagnosing and Alleviating Artifactual Attenuation Associated with Large Gradient Pulses in PGSE NMR Diffusion Measurements

    NASA Astrophysics Data System (ADS)

    Price, William S.; Hayamizu, Kikuko; Ide, Hiroyuki; Arata, Yoji

    1999-08-01

    The generation of phase-based artifacts resulting from mismatch in the effective areas (i.e., the time integrals) of sequential gradient pulses is discussed in the context of large gradient pulsed-gradient spin-echo (PGSE) NMR diffusion measurements. Such effects result in artifactual attenuation and distortion in the spectra which, in the first instance, are similar to (and commonly mistaken for) the effects of eddy currents. Small degrees of mismatch cause "unphysical" concave downward curvature in PGSE attenuation plots of freely diffusing species. However, larger mismatches can result in artifactual diffraction peaks in the plots which could easily be confused for true restricted diffusion effects. Although "rectangular" gradient pulses are preferable from a theoretical viewpoint, we found that shaped gradient (e.g., half-sine) pulses, which due to their slower rise and fall times were more tractable for the current amplifier, were more sequentially reproducible. As well as generating fewer phase-based artifacts such shaped pulses also decrease the likelihood of vibration problems.

  12. Self-intermediate scattering function of strongly interacting three-dimensional lattice gases: time- and wave-vector-dependent tracer diffusion coefficient.

    PubMed

    Skarpalezos, Loukas; Argyrakis, Panos; Vikhrenko, Vyacheslav S

    2014-05-01

    We investigate the self-intermediate scattering function (SISF) in a three-dimensional (3D) cubic lattice fluid (interacting lattice gas) with attractive nearest-neighbor interparticle interactions at a temperature slightly above the critical one by means of Monte Carlo simulations. A special representation of SISF as an exponent of the mean tracer diffusion coefficient multiplied by the geometrical factor and time is considered to highlight memory effects that are included in time and wave-vector dependence of the diffusion coefficient. An analytical expression for the diffusion coefficient is suggested to reproduce the simulation data. It is shown that the particles' mean-square displacement is equal to the time integral of the diffusion coefficient. We make a comparison with the previously considered 2D system on a square lattice. The main difference with the two-dimensional case is that the time dependence of particular characteristics of the tracer diffusion coefficient in the 3D case cannot be described by exponentially decreasing functions, but requires using stretched exponentials with rather small values of exponents, of the order of 0.2. The hydrodynamic values of the tracer diffusion coefficient (in the limit of large times and small wave vectors) defined through SIFS simulation results agree well with the results of its direct determination by the mean-square displacement of the particles in the entire range of concentrations and temperatures.

  13. Effects of Barrier-Induced Nuclear Spin Magnetization Inhomogeneities on Diffusion-Attenuated MR Signal

    PubMed Central

    Sukstanskii, A.L.; Ackerman, J.J.H.; Yablonskiy, D.A.

    2007-01-01

    The spatial distribution of the transverse nuclear spin magnetization, appearing in a single compartment with impermeable boundaries in a Stejskal-Tanner gradient pulse MR experiment, is analyzed in detail. At short diffusion times the presence of diffusion-restrictive barriers (membranes) reduces effective diffusivity near the membranes and leads to an inhomogeneous spin magnetization distribution (the edge-enhancement effect). In this case, the signal reveals a quasi-two-compartment behavior and can be empirically modeled remarkably well by a biexponential function. The current results provide a framework for interpreting experimental MR data on various phenoma, including water diffusion in giant axons, metabolite diffusion in the brain, and hyperpolarized gas diffusion in lung airways. PMID:14523959

  14. Molecular dynamics simulation of diffusion coefficients and structural properties of some alkylbenzenes in supercritical carbon dioxide at infinite dilution

    SciTech Connect

    Wang, Jinyang; Zhong, Haimin; Qiu, Wenda; Chen, Liuping; Feng, Huajie

    2014-03-14

    The binary infinite dilute diffusion coefficients, D{sub 12}{sup ∞}, of some alkylbenzenes (Ph-C{sub n}, from Ph-H to Ph-C{sub 12}) from 313 K to 333 K at 15 MPa in supercritical carbon dioxide (scCO{sub 2}) have been studied by molecular dynamics (MD) simulation. The MD values agree well with the experimental ones, which indicate MD simulation technique is a powerful way to predict and obtain diffusion coefficients of solutes in supercritical fluids. Besides, the local structures of Ph-C{sub n}/CO{sub 2} fluids are further investigated by calculating radial distribution functions and coordination numbers. It qualitatively convinces that the first solvation shell of Ph-C{sub n} in scCO{sub 2} is significantly influenced by the structure of Ph-C{sub n} solute. Meanwhile, the mean end-to-end distance, the mean radius of gyration and dihedral angle distribution are calculated to gain an insight into the structural properties of Ph-C{sub n} in scCO{sub 2}. The abnormal trends of radial distribution functions and coordination numbers can be reasonably explained in term of molecular flexibility. Moreover, the computed results of dihedral angle clarify that flexibility of long-chain Ph-C{sub n} is the result of internal rotation of C-C single bond (σ{sub c-c}) in alkyl chain. It is interesting that compared with n-alkane, because of the existence of benzene ring, the flexibility of alkyl chain in Ph-C{sub n} with same carbon atom number is significantly reduced, as a result, the carbon chain dependence of diffusion behaviors for long-chain n-alkane (n ≥ 5) and long-chain Ph-C{sub n} (n ≥ 4) in scCO{sub 2} are different.

  15. Molecular dynamics simulation of diffusion coefficients and structural properties of some alkylbenzenes in supercritical carbon dioxide at infinite dilution.

    PubMed

    Wang, Jinyang; Zhong, Haimin; Feng, Huajie; Qiu, Wenda; Chen, Liuping

    2014-03-14

    The binary infinite dilute diffusion coefficients, D₁₂(∞), of some alkylbenzenes (Ph-C(n), from Ph-H to Ph-C12) from 313 K to 333 K at 15 MPa in supercritical carbon dioxide (scCO2) have been studied by molecular dynamics (MD) simulation. The MD values agree well with the experimental ones, which indicate MD simulation technique is a powerful way to predict and obtain diffusion coefficients of solutes in supercritical fluids. Besides, the local structures of Ph-C(n)/CO2 fluids are further investigated by calculating radial distribution functions and coordination numbers. It qualitatively convinces that the first solvation shell of Ph-C(n) in scCO2 is significantly influenced by the structure of Ph-C(n) solute. Meanwhile, the mean end-to-end distance, the mean radius of gyration and dihedral angle distribution are calculated to gain an insight into the structural properties of Ph-C(n) in scCO2. The abnormal trends of radial distribution functions and coordination numbers can be reasonably explained in term of molecular flexibility. Moreover, the computed results of dihedral angle clarify that flexibility of long-chain Ph-C(n) is the result of internal rotation of C-C single bond (σ(c-c)) in alkyl chain. It is interesting that compared with n-alkane, because of the existence of benzene ring, the flexibility of alkyl chain in Ph-C(n) with same carbon atom number is significantly reduced, as a result, the carbon chain dependence of diffusion behaviors for long-chain n-alkane (n ≥ 5) and long-chain Ph-C(n) (n ≥ 4) in scCO2 are different.

  16. Statistics of velocity fluctuations arising from a random distribution of point vortices: the speed of fluctuations and the diffusion coefficient

    PubMed

    Chavanis; Sire

    2000-07-01

    This paper is devoted to a statistical analysis of the fluctuations of velocity and acceleration produced by a random distribution of point vortices in two-dimensional turbulence. We show that the velocity probability density function PDF behaves in a manner which is intermediate between Gaussian and Levy laws, while the distribution of accelerations is governed by a Cauchy law. Our study accounts properly for a spectrum of circulations among the vortices. In the case of real vortices (with a finite core), we show analytically that the distribution of accelerations makes a smooth transition from Cauchy (for small fluctuations) to Gaussian (for large fluctuations), probably passing through an exponential tail. We introduce a function T(V) which gives the typical duration of a velocity fluctuation V; we show that T(V) behaves like V and V-1 for weak and large velocities, respectively. These results have a simple physical interpretation in the nearest neighbor approximation, and in Smoluchowski theory concerning the persistence of fluctuations. We discuss the analogies with respect to the fluctuations of the gravitational field in stellar systems. As an application of these results, we determine an approximate expression for the diffusion coefficient of point vortices. When applied to the context of freely decaying two-dimensional turbulence, the diffusion becomes anomalous and we establish a relationship nu=1+(xi/2) between the exponent of anomalous diffusion nu and the exponent xi which characterizes the decay of the vortex density.

  17. A novel (ex situ) method to quantify oxygen diffusion coefficient of polymer fuel cells backing and catalyst layers

    NASA Astrophysics Data System (ADS)

    Baricci, Andrea; Casalegno, Andrea

    2016-09-01

    Limiting current density of oxygen reduction reaction in polymer electrolyte fuel cells is determined by several mass transport resistances that lower the concentration of oxygen on the catalyst active site. Among them, diffusion across porous media plays a significant role. Despite the extensive experimental activity documented in PEMFC literature, only few efforts have been dedicated to the measurement of the effective transport properties in porous layers. In the present work, a methodology for ex situ measurement of the effective diffusion coefficient and Knudsen radius of porous layers for polymer electrolyte fuel cells (gas diffusion layer, micro porous layer and catalyst layer) is described and applied to high temperature polymer fuel cells State of Art materials. Regression of the measured quantities by means of a quasi 2D physical model is performed to quantify the Knudsen effect, which is reported to account, respectively, for 30% and 50% of the mass transport resistance in micro porous layer and catalyst layer. On the other side, the model reveals that pressure gradient consequent to permeation in porous layers of high temperature polymer fuel cells has a negligible effect on oxygen concentration in relevant operating conditions.

  18. Comparison of hyperspectral measurements of the attenuation and scattering coefficients spectra with modeling results in the north-eastern Baltic Sea

    NASA Astrophysics Data System (ADS)

    Sipelgas, Liis; Raudsepp, Urmas

    2015-11-01

    The spectral variations in the attenuation and scattering coefficients measured with a hyperspectral ac-spectra (Wetlabs) instrument were analyzed from a dataset collected in the vicinity of commercial harbors on the Estonian coast of the Gulf of Finland, Baltic Sea. In total, the measured TSM concentration varied from 0.4 to 30 mg L-1 and the concentration of Chl a varied from values below the detection limit (0.05) to 23 mg m-3. The reliability of the power law describing the particle attenuation cp (λ) and scattering bp(λ) coefficients was evaluated by means of a determination coefficient (R2). The power law described the particle attenuation spectra with high accuracy (R2 > 0.67), giving the dataset an average cp (λ) slope of 1.3. In the case of particle scattering coefficients, the power law did not represent the whole dataset. Depending on a particular spectrum, the R2 varied from 0 to 1.0 and the slope varied from 1.15 to -0.56. Decomposition of bp(λ) into dominant modes using principal component analyses resulted in the first principal mode accounting for the power law dependence of bp(λ), i.e. the "mineral-type" spectrum, and the second and third mode representing the characteristic bp(λ) of dominant algal particles, i.e. the "algae-type" spectrum. From our dataset we estimated that if Chl a concentration is above 10 mg m-3 or below 5 mg m-3 then most likely the "algae-type" or the "mineral-type" spectrum is dominant, respectively. There was strong linear relationship (R2 > 0.92) between TSM concentration and cp(555) and bp(555),irrespective of the dominant shape of the particle scattering spectra. The estimated TSM-specific attenuation and scattering coefficients at 555 nm were 0.8 m2 g-1 and 0.68 m2 g-1, respectively. Corresponding values for water samples with a dominant "mineral-type" spectrum were 0.85 m2 g-1 and 0.73 m2 g-1, respectively and for water samples with a dominant "algae-type" spectrum were 0.64 m2 g-1 and 0.52 m2 g-1, respectively.

  19. Determining the mass attenuation coefficient, effective atomic number, and electron density of raw wood and binderless particleboards of Rhizophora spp. by using Monte Carlo simulation

    NASA Astrophysics Data System (ADS)

    Marashdeh, Mohammad W.; Al-Hamarneh, Ibrahim F.; Abdel Munem, Eid M.; Tajuddin, A. A.; Ariffin, Alawiah; Al-Omari, Saleh

    Rhizophora spp. wood has the potential to serve as a solid water or tissue equivalent phantom for photon and electron beam dosimetry. In this study, the effective atomic number (Zeff) and effective electron density (Neff) of raw wood and binderless Rhizophora spp. particleboards in four different particle sizes were determined in the 10-60 keV energy region. The mass attenuation coefficients used in the calculations were obtained using the Monte Carlo N-Particle (MCNP5) simulation code. The MCNP5 calculations of the attenuation parameters for the Rhizophora spp. samples were plotted graphically against photon energy and discussed in terms of their relative differences compared with those of water and breast tissue. Moreover, the validity of the MCNP5 code was examined by comparing the calculated attenuation parameters with the theoretical values obtained by the XCOM program based on the mixture rule. The results indicated that the MCNP5 process can be followed to determine the attenuation of gamma rays with several photon energies in other materials.

  20. Determination of diffusion coefficients of carbon dioxide in water between 268 and 473 K in a high-pressure capillary optical cell with in situ Raman spectroscopic measurements

    USGS Publications Warehouse

    Lu, Wanjun; Guo, Huirong; Chou, I.-Ming; Burruss, R.C.; Li, Lanlan

    2013-01-01

    Accurate values of diffusion coefficients for carbon dioxide in water and brine at reservoir conditions are essential to our understanding of transport behavior of carbon dioxide in subsurface pore space. However, the experimental data are limited to conditions at low temperatures and pressures. In this study, diffusive transfer of carbon dioxide in water at pressures up to 45 MPa and temperatures from 268 to 473 K was observed within an optical capillary cell via time-dependent Raman spectroscopy. Diffusion coefficients were estimated by the least-squares method for the measured variations in carbon dioxide concentration in the cell at various sample positions and time. At the constant pressure of 20 MPa, the measured diffusion coefficients of carbon dioxide in water increase with increasing temperature from 268 to 473 K. The relationship between diffusion coefficient of carbon dioxide in water [D(CO2) in m2/s] and temperature (T in K) was derived with Speedy–Angell power-law approach as: D(CO2)=D0[T/Ts-1]m where D0 = 13.942 × 10−9 m2/s, Ts = 227.0 K, and m = 1.7094. At constant temperature, diffusion coefficients of carbon dioxide in water decrease with pressure increase. However, this pressure effect is rather small (within a few percent).

  1. A least-squares error minimization approach in the determination of ferric ion diffusion coefficient of Fricke-infused dosimeter gels

    SciTech Connect

    Tseng, Y.J.; Huang, S.-C.; Chu, W.C.

    2005-04-01

    A least-squares error minimization approach was adopted to assess ferric ion diffusion coefficient of Fricke-agarose gels. Ferric ion diffusion process was modeled as a Gaussian-shaped degradation kernel operating on an initial concentration distribution. Diffusion coefficient was iteratively determined by minimizing the error function defined as the difference between the theoretically calculated and the experimentally measured dose distributions. A rapid MR image-based differential gel dosimetry technique that time resolves the evolution of the ferric ion diffusion process minimizes smearing of the dose distribution. Our results showed that for a Fricke-agarose gel contained 1 mM ammonium ferrous sulfate, 1% agarose, 1 mM sodium chloride, and 50 mM sulfuric acid, its ferric ion diffusion coefficient is (1.59{+-}0.28)x10{sup -2} cm{sup 2} h{sup -1} at room temperature. This value falls within the 1.00-2.00x10{sup -2} cm{sup 2} h{sup -1} range previously reported under varying gelling ingredients and concentrations. This method allows a quick, nondestructive evaluation of the ferric ion diffusion coefficient that can be used in conjunction with the in situ gel dosimetry experiment to provide a practical diffusion characterization of the dosimeter gel.

  2. Evaluation of Free Breathing Versus Breath Hold Diffusion Weighted Imaging in Terms Apparent Diffusion Coefficient (ADC) and Signal-to-Noise Ratio (SNR) Values for Solid Abdominal Organs

    PubMed Central

    Herek, Duygu; Karabulut, Nevzat; Kocyıgıt, Ali; Yagcı, Ahmet Baki

    2016-01-01

    Summary Background Our aim was to compare the apparent diffusion coefficient (ADC) values of normal abdominal parenchymal organs and signal-to-noise ratio (SNR) measurements in the same patients with breath hold (BH) and free breathing (FB) diffusion weighted imaging (DWI). Material/Methods Forty-eight patients underwent both BH and FB DWI. Spherical region of interest (ROI) was placed on the right hepatic lobe, spleen, pancreas, and renal cortices. ADC values were calculated for each organ on each sequence using an automated software. Image noise, defined as the standard deviation (SD) of the signal intensities in the most artifact-free area of the image background was measured by placing the largest possible ROI on either the left or the right side of the body outside the object in the recorded field of view. SNR was calculated using the formula: SNR=signal intensity (SI)(organ)/standard deviation (SD)(noise). Results There were no statistically significant differences in ADC values of the abdominal organs between BH and FB DWI sequences (p>0.05). There were statistically significant differences between SNR values of organs on BH and FB DWIs. SNRs were found to be better on FB DWI than BH DWI (p<0.001). Conclusions Free breathing DWI technique reduces image noise and increases SNR for abdominal examinations. Free breathing technique is therefore preferable to BH DWI in the evaluation of abdominal organs by DWI. PMID:27822326

  3. Empirical relationship between Kubelka-Munk and radiative transfer coefficients for extracting optical parameters of tissues in diffusive and nondiffusive regimes

    NASA Astrophysics Data System (ADS)

    Roy, Arindam; Ramasubramaniam, Rajagopal; Gaonkar, Harshavardhan A.

    2012-11-01

    Kubelka-Munk (K-M) theory is a phenomenological light transport theory that provides analytical expressions for reflectance and transmittance of diffusive substrates such as tissues. Many authors have derived relations between coefficients of K-M theory and that of the more fundamental radiative transfer equations. These relations are valid only in diffusive light transport regime where scattering dominates over absorption. They also fail near boundaries where incident beams are not diffusive. By measuring total transmittance and total reflectance of tissue phantoms with varying optical parameters, we have obtained empirical relations between K-M coefficients and the radiative transport coefficients for integrating sphere-based spectrophotometers that use uniform, nondiffusive incident beams. Our empirical relations show that the K-M scattering coefficients depend only on reduced scattering coefficient (μs‧), whereas the K-M absorption coefficient depends on both absorption (μa) and reduced scattering (μs‧) coefficients of radiative transfer theory. We have shown that these empirical relations are valid in both the diffusive and nondiffusive regimes and can predict total reflectance within an error of 10%. They also can be used to solve the inverse problem of obtaining multiple optical parameters such as chromophore concentration and tissue thickness from the measured reflectance spectra with a maximum accuracy of 90% to 95%.

  4. Empirical relationship between Kubelka-Munk and radiative transfer coefficients for extracting optical parameters of tissues in diffusive and nondiffusive regimes.

    PubMed

    Roy, Arindam; Ramasubramaniam, Rajagopal; Gaonkar, Harshavardhan A

    2012-11-01

    Kubelka–Munk (K-M) theory is a phenomenological light transport theory that provides analytical expressions for reflectance and transmittance of diffusive substrates such as tissues. Many authors have derived relations between coefficients of K-M theory and that of the more fundamental radiative transfer equations. These relations are valid only in diffusive light transport regime where scattering dominates over absorption. They also fail near boundaries where incident beams are not diffusive. By measuring total transmittance and total reflectance of tissue phantoms with varying optical parameters, we have obtained empirical relations between K-M coefficients and the radiative transport coefficients for integrating sphere-based spectrophotometers that use uniform, nondiffusive incident beams. Our empirical relations show that the K-M scattering coefficients depend only on reduced scattering coefficient (μ's), whereas the K-M absorption coefficient depends on both absorption (μa ) and reduced scattering (μs' ) coefficients of radiative transfer theory. We have shown that these empirical relations are valid in both the diffusive and nondiffusive regimes and can predict total reflectance within an error of 10%. They also can be used to solve the inverse problem of obtaining multiple optical parameters such as chromophore concentration and tissue thickness from the measured reflectance spectra with a maximum accuracy of 90% to 95%.

  5. Numerical solutions and error estimations for the space fractional diffusion equation with variable coefficients via Fibonacci collocation method.

    PubMed

    Bahşı, Ayşe Kurt; Yalçınbaş, Salih

    2016-01-01

    In this study, the Fibonacci collocation method based on the Fibonacci polynomials are presented to solve for the fractional diffusion equations with variable coefficients. The fractional derivatives are described in the Caputo sense. This method is derived by expanding the approximate solution with Fibonacci polynomials. Using this method of the fractional derivative this equation can be reduced to a set of linear algebraic equations. Also, an error estimation algorithm which is based on the residual functions is presented for this method. The approximate solutions are improved by using this error estimation algorithm. If the exact solution of the problem is not known, the absolute error function of the problems can be approximately computed by using the Fibonacci polynomial solution. By using this error estimation function, we can find improved solutions which are more efficient than direct numerical solutions. Numerical examples, figures, tables are comparisons have been presented to show efficiency and usable of proposed method.

  6. A CUMULATIVE MIGRATION METHOD FOR COMPUTING RIGOROUS TRANSPORT CROSS SECTIONS AND DIFFUSION COEFFICIENTS FOR LWR LATTICES WITH MONTE CARLO

    SciTech Connect

    Zhaoyuan Liu; Kord Smith; Benoit Forget; Javier Ortensi

    2016-05-01

    A new method for computing homogenized assembly neutron transport cross sections and dif- fusion coefficients that is both rigorous and computationally efficient is proposed in this paper. In the limit of a homogeneous hydrogen slab, the new method is equivalent to the long-used, and only-recently-published CASMO transport method. The rigorous method is used to demonstrate the sources of inaccuracy in the commonly applied “out-scatter” transport correction. It is also demonstrated that the newly developed method is directly applicable to lattice calculations per- formed by Monte Carlo and is capable of computing rigorous homogenized transport cross sections for arbitrarily heterogeneous lattices. Comparisons of several common transport cross section ap- proximations are presented for a simple problem of infinite medium hydrogen. The new method has also been applied in computing 2-group diffusion data for an actual PWR lattice from BEAVRS benchmark.

  7. A practical method of determining water current velocities and diffusion coefficients in coastal waters by remote sensing techniques

    NASA Technical Reports Server (NTRS)

    James, W. P.

    1971-01-01

    A simplified procedure is presented for determining water current velocities and diffusion coefficients. Dye drops which form dye patches in the receiving water are made from an aircraft. The changes in position and size of the patches are recorded from two flights over the area. The simplified data processing procedure requires only that the ground coordinates about the dye patches be determined at the time of each flight. With an automatic recording coordinatograph for measuring coordinates and a computer for processing the data, this technique provides a practical method of determining circulation patterns and mixing characteristics of large aquatic systems. This information is useful in assessing the environmental impact of waste water discharges and for industrial plant siting.

  8. Measurement of the mass attenuation coefficient from 81 keV to 1333 keV for elemental materials Al, Cu and Pb

    NASA Astrophysics Data System (ADS)

    Gjorgieva, Slavica; Barandovski, Lambe

    2016-03-01

    The mass attenuation coefficients (μ/ρ) for 3 high purity elemental materials Al, Cu and Pb were measured in the γ-ray energy range from 81 keV up to 1333 keV using 22Na, 60Co 133Ba and 133Cs as sources of gamma radiation. Well shielded detector (NaI (Tl) semiconductor detector) was used to measure the intensity of the transmitted beam. The measurements were made under condition of good geometry, assuring that any photon absorbed or deflected appreciably does not reach the detector. The measured values are compared with the theoretical ones obtained by Seltzer (1993).

  9. Mass attenuation coefficient of the Earth, Moon and Mars samples over 1keV-100GeV energy range.

    PubMed

    Camargo Moreira, Anderson; Roberto Appoloni, Carlos

    2006-09-01

    This work presents the calculation of the mass attenuation coefficient (micro) of lunar, Martian and terrestrial samples in function of the energy. WinXCOM software was employed to determine the micro values for the samples in the range from 1 keV to 100 GeV. The obtained values were practically the same for energies larger than 100 keV, but marked differences among the samples were observed for energies below 25 keV, which is the energy range of interest for the XRF system used in space probes.

  10. Relationships between Water Attenuation Coefficients Derived from Active and Passive Remote Sensing: A Case Study from Two Coastal Environments

    DTIC Science & Technology

    2011-06-14

    surface (p0 ) (Table 1). Far from the sea surface, the Kd distribution is mainly driven by variations on the absorption co- efficient [8]. Attenuation...directions) and variations associated with the transmitter beam width. In this case, a __... Kd, and the lidar volume backscattering can be modeled...551)) that are sensitive to variations on particle size distribution. Unlike Rl, R2 is based on a particle size distribution proxy developed with

  11. Interaction of ring current and radiation belt protons with ducted plasmaspheric hiss. 1: Diffusion coefficients and timescales

    NASA Technical Reports Server (NTRS)

    Kozyra, J. U.; Rasmussen, C. E.; Miller, R. H.; Lyons, L. R.

    1994-01-01

    Protons that are convected into the inner magnetosphere in response to enhanced magnetic activity can resonate with ducted plasmaspheric hiss in the outer plasmasphere via an anomalous Doppler-shifted cyclotron resonance. Plasmaspheric hiss is a right-hand-polarized electromagnetic emission that is observed to fill the plasmasphere on a routine basis. When plasmaspheric hiss is confined within field-aligned ducts or guided along density gradients, wave normal angles remain largely below 45 deg. This allows resonant interactions with ions at typical ring current and radiation belt energies to take place. Such field-aligned ducts have been observed both within the plasmasphere and in regions outside of the plasmasphere. Wave intensities are estimated using statistical information from studies of detached plasma regions. Diffusion coefficients are presented for a range of L shells and proton energies for a fixed wave distribution. Harmonic resonances in the range N = +/-100 are considered in order to include interactions between hiss at 100 Hz to 2 kHz frequencies, and protons in the energy range between approximately 10 keV and 1000 keV. Diffusion timescales are estimated to be of the order of tens of days and comparable to or shorter than lifetimes for Coulomb decay and charge exchange losses over most of the energy and spatial ranges of interest.

  12. Calculation of the convective heat transfer coefficient and thermal diffusivity of cucumbers using numerical simulation and the inverse method.

    PubMed

    da Silva, Wilton Pereira; E Silva, Cleide M D P S

    2014-09-01

    Cooling of fruits and vegetables, immediately after the harvest, has been a widely used method for maximizing post-harvest life. In this paper, an optimization algorithm and a numerical solution are used to determine simultaneously the convective heat transfer coefficient, hH, and the thermal diffusivity, α, for an individual solid with cylindrical shape, using experimental data obtained during its cooling. To this end, the one-dimensional diffusion equation in cylindrical coordinates is discretized and numerically solved through the finite volume method, with a fully implicit formulation. This solution is coupled to an optimizer based on the inverse method, in which the chi-square referring to the fit of the numerical simulation to the experimental data is used as objective function. The optimizer coupled to the numerical solution was applied to experimental data relative to the cooling of a cucumber. The obtained results for α and hH were coherent with the values available in the literature. With the results obtained in the optimization process, the cooling kinetics of cucumbers was described in details.

  13. Consequences of using nonlinear particle trajectories to compute spatial diffusion coefficients. [for charged particles in interplanetary space

    NASA Technical Reports Server (NTRS)

    Goldstein, M. L.

    1976-01-01

    The propagation of charged particles through interstellar and interplanetary space has often been described as a random process in which the particles are scattered by ambient electromagnetic turbulence. In general, this changes both the magnitude and direction of the particles' momentum. Some situations for which scattering in direction (pitch angle) is of primary interest were studied. A perturbed orbit, resonant scattering theory for pitch-angle diffusion in magnetostatic turbulence was slightly generalized and then utilized to compute the diffusion coefficient for spatial propagation parallel to the mean magnetic field, Kappa. All divergences inherent in the quasilinear formalism when the power spectrum of the fluctuation field falls off as K to the minus Q power (Q less than 2) were removed. Various methods of computing Kappa were compared and limits on the validity of the theory discussed. For Q less than 1 or 2, the various methods give roughly comparable values of Kappa, but use of perturbed orbits systematically results in a somewhat smaller Kappa than can be obtained from quasilinear theory.

  14. Effects of hypotonic stress and ouabain on the apparent diffusion coefficient of water at cellular and tissue levels in Aplysia.

    PubMed

    Jelescu, Ileana Ozana; Ciobanu, Luisa; Geffroy, Françoise; Marquet, Pierre; Le Bihan, Denis

    2014-03-01

    There is evidence that physiological or pathological cell swelling is associated with a decrease of the apparent diffusion coefficient (ADC) of water in tissues, as measured with MRI. However the mechanism remains unclear. Magnetic resonance microscopy, performed on small tissue samples, has the potential to distinguish effects occurring at cellular and tissue levels. A three-dimensional diffusion prepared fast imaging with steady-state free precession sequence for MR microscopy was implemented on a 17.2 T imaging system and used to investigate the effect of two biological challenges known to cause cell swelling, exposure to a hypotonic solution or to ouabain, on Aplysia nervous tissue. The ADC was measured inside isolated neuronal soma and in the region of cell bodies of the buccal ganglia. Both challenges resulted in an ADC increase inside isolated neuronal soma (+31 ± 24% and +30 ± 11%, respectively) and an ADC decrease at tissue level in the buccal ganglia (-12 ± 5% and -18 ± 8%, respectively). A scenario involving a layer of water molecules bound to the inflating cell membrane surface is proposed to reconcile this apparent discrepancy.

  15. Prognostic value of the primary lesion apparent diffusion coefficient (ADC) in nasopharyngeal carcinoma: a retrospective study of 541 cases

    PubMed Central

    Zhang, Yuan; Liu, Xu; Zhang, Yun; Li, Wen-Fei; Chen, Lei; Mao, Yan-Ping; Shen, Jing-Xian; Zhang, Fan; Peng, Hao; Liu, Qing; Sun, Ying; Ma, Jun

    2015-01-01

    The prognostic value of the primary lesion pretreatment apparent diffusion coefficient (ADC), which is obtained by diffusion-weighted magnetic resonance imaging (MR-DWI), remains unknown in nasopharyngeal carcinoma (NPC). Thus, to investigate whether the pretreatment ADC value as measured from the primary site on MR-DWI is an independent prognostic factor in NPC, we retrospectively reviewed a cohort of 541 patients with histologically-proven stage I-IVB NPC. All patients underwent MRI using a 3-Tesla system (Trio Tim; Siemens, Erlangen Germany). To calculate ADC, the primary lesion was designated on the ADC map at the level of the largest tumor diameter to cover most of the lesion, avoiding cystic or necrotic components. Median and mean (±SD) pretreatment ADC were 0.713 and 0.716 ± 0.079 × 10−3 mm2/s, respectively. Univariate and multivariate analysis confirmed high pretreatment ADC was a good prognostic factor for poor local relapse-free survival and disease-free survival. Furthermore, the area under the ROC curve for prediction of local failure significantly increased when pretreatment ADC was combined with T classification (P = 0.004). Thus, pretreatment ADC might provide useful information for predicting outcome and selecting high-risk patients appropriate for more aggressive therapy. Further studies are warranted to investigate the biological basis of this observation. PMID:26184509

  16. Diffusion and sedimentation interaction parameters for measuring the second virial coefficient and their utility as predictors of protein aggregation.

    PubMed

    Saluja, Atul; Fesinmeyer, R Matthew; Hogan, Sabine; Brems, David N; Gokarn, Yatin R

    2010-10-20

    The concentration-dependence of the diffusion and sedimentation coefficients (k(D) and k(s), respectively) of a protein can be used to determine the second virial coefficient (B₂), a parameter valuable in predicting protein-protein interactions. Accurate measurement of B₂ under physiologically and pharmaceutically relevant conditions, however, requires independent measurement of k(D) and k(s) via orthogonal techniques. We demonstrate this by utilizing sedimentation velocity (SV) and dynamic light scattering (DLS) to analyze solutions of hen-egg white lysozyme (HEWL) and a monoclonal antibody (mAb1) in different salt solutions. The accuracy of the SV-DLS method was established by comparing measured and literature B₂ values for HEWL. In contrast to the assumptions necessary for determining k(D) and k(s) via SV alone, k(D) and ks were of comparable magnitudes, and solution conditions were noted for both HEWL and mAb1 under which 1), k(D) and k(s) assumed opposite signs; and 2), k(D) ≥k(s). Further, we demonstrate the utility of k(D) and k(s) as qualitative predictors of protein aggregation through agitation and accelerated stability studies. Aggregation of mAb1 correlated well with B₂, k(D), and k(s), thus establishing the potential for k(D) to serve as a high-throughput predictor of protein aggregation.

  17. Self-diffusion coefficients and shear viscosity of inverse power fluids: from hard- to soft-spheres.

    PubMed

    Heyes, D M; Brańka, A C

    2008-07-21

    Molecular dynamics computer simulation has been used to compute the self-diffusion coefficient, D, and shear viscosity, eta(s), of soft-sphere fluids, in which the particles interact through the soft-sphere or inverse power pair potential, phi(r) = epsilon(sigma/r)(n), where n measures the steepness or stiffness of the potential, and epsilon and sigma are a characteristic energy and distance, respectively. The simulations were carried out on monodisperse systems for a range of n values from the hard-sphere (n --> infinity) limit down to n = 4, and up to densities in excess of the fluid-solid co-existence value. A new analytical procedure is proposed which reproduces the transport coefficients at high densities, and can be used to extrapolate the data to densities higher than accurately accessible by simulation or experiment, and tending to the glass transition. This formula, DX(c-1) proportional, variant A/X + B, where c is an adjustable parameter, and X is either the packing fraction or the pressure, is a development of one proposed by Dymond. In the expression, -A/B is the value of X at the ideal glass transition (i.e., where D and eta(s)(-1) --> 0). Estimated values are presented for the packing fraction and the pressure at the glass transition for n values between the hard and soft particle limits. The above expression is also shown to reproduce the high density viscosity data of supercritical argon, krypton and nitrogen. Fits to the soft-sphere simulation transport coefficients close to solid-fluid co-existence are also made using the analytic form, ln(D) = alpha(X)X, and n-dependence of the alpha(X) is presented (X is either the packing fraction or the pressure).

  18. Determination of silicone rubber and low-density polyethylene diffusion and polymer/water partition coefficients for emerging contaminants.

    PubMed

    Pintado-Herrera, Marina G; Lara-Martín, Pablo A; González-Mazo, Eduardo; Allan, Ian J

    2016-09-01

    There is a growing interest in assessing the concentration and distribution of new nonregulated organic compounds (emerging contaminants) in the environment. The measurement of freely dissolved concentrations using conventional approaches is challenging because of the low concentrations that may be encountered and their temporally variable emissions. Absorption-based passive sampling enables the estimation of freely dissolved concentrations of hydrophobic contaminants of emerging concern in water. In the present study, calibration was undertaken for 2 polymers, low-density polyethylene (LDPE) and silicone rubber for 11 fragrances, 5 endocrine-disrupting compounds, 7 ultraviolet (UV) filters, and 8 organophosphate flame retardant compounds. Batch experiments were performed to estimate contaminant diffusion coefficients in the polymers (Dp ), which in general decreased with increasing molecular weight. The values for fragrances, endocrine-disrupting compounds, and UV filters were in ranges similar to those previously reported for polycyclic aromatic hydrocarbons, but were 1 order of magnitude lower for organophosphate flame retardant compounds. Silicone rubber had higher Dp values than LDPE and was therefore selected for further experiments to calculate polymer/water partition coefficients (KPW ). The authors observed a positive correlation between log KPW and log octanol/water partition coefficient values. Field testing of silicone rubber passive samplers was undertaken though exposure in the River Alna (Norway) for an exposure time of 21 d to estimate freely dissolved concentration. Some fragrances and UV filters were predominant over other emerging and regulated contaminants, at levels up to 1600 ng L(-1) for galaxolide and 448 ng L(-1) for octocrylene. Environ Toxicol Chem 2016;35:2162-2172. © 2016 SETAC.

  19. First-principles binary diffusion coefficients for H, H{sub 2}, and four normal alkanes + N{sub 2}

    SciTech Connect

    Jasper, Ahren W. Kamarchik, Eugene; Miller, James A.; Klippenstein, Stephen J.

    2014-09-28

    Collision integrals related to binary (dilute gas) diffusion are calculated classically for six species colliding with N{sub 2}. The most detailed calculations make no assumptions regarding the complexity of the potential energy surface, and the resulting classical collision integrals are in excellent agreement with previous semiclassical results for H + N{sub 2} and H{sub 2} + N{sub 2} and with recent experimental results for C{sub n}H{sub 2n+2} + N{sub 2}, n = 2–4. The detailed classical results are used to test the accuracy of three simplifying assumptions typically made when calculating collision integrals: (1) approximating the intermolecular potential as isotropic, (2) neglecting the internal structure of the colliders (i.e., neglecting inelasticity), and (3) employing unphysical R{sup −12} repulsive interactions. The effect of anisotropy is found to be negligible for H + N{sub 2} and H{sub 2} + N{sub 2} (in agreement with previous quantum mechanical and semiclassical results for systems involving atomic and diatomic species) but is more significant for larger species at low temperatures. For example, the neglect of anisotropy decreases the diffusion coefficient for butane + N{sub 2} by 15% at 300 K. The neglect of inelasticity, in contrast, introduces only very small errors. Approximating the repulsive wall as an unphysical R{sup −12} interaction is a significant source of error at all temperatures for the weakly interacting systems H + N{sub 2} and H{sub 2} + N{sub 2}, with errors as large as 40%. For the normal alkanes in N{sub 2}, which feature stronger interactions, the 12/6 Lennard–Jones approximation is found to be accurate, particularly at temperatures above ∼700 K where it predicts the full-dimensional result to within 5% (although with somewhat different temperature dependence). Overall, the typical practical approach of assuming isotropic 12/6 Lennard–Jones interactions is confirmed to be suitable for combustion applications except for

  20. Correlation of (18)F-FDG PET and MR Apparent Diffusion Coefficient (ADC) Histogram Metrics with Survival in Diffuse Intrinsic Pontine Glioma: A Report from the Pediatric Brain Tumor Consortium.

    PubMed

    Zukotynski, Katherine; Vajapeyam, Sridhar; Fahey, Frederic H; Kocak, Mehmet; Brown, Douglas; Ricci, Kelsey; Onar-Thomas, Arzu; Fouladi, Maryam; Poussaint, Tina Young

    2017-03-30

    Rationale: To describe baseline (18)F-labeled 2-fluoro-2-deoxy-D-glucose positron emission tomography (FDG-PET) voxel characteristics in pediatric diffuse intrinsic pontine glioma (DIPG) and to correlate these metrics with baseline magnetic resonance (MR) apparent diffusion coefficient (ADC) histogram metrics, progression-free survival (PFS) and overall survival (OS). Methods: Baseline brain FDG-PET and MR scans were obtained in 33 children from Pediatric Brain Tumor Consortium (PBTC) clinical DIPG trials. FDG-PET, post-gadolinium (PG) and ADC images were registered to baseline fluid attenuation inversion recovery (FLAIR) images. Three-dimensional regions of interest on FLAIR and PG images and FDG-PET and ADC histograms were generated. Metrics evaluated included peak number, skewness and kurtosis. Correlation between PET and ADC histogram metrics was evaluated. PET pixel values within the ROI for each tumor were plotted against ADC values. Association of these imaging markers with survival was described. Results: PET histograms were almost always unimodal (94% vs. 6% bimodal). None of the PET histogram parameters (skewness or kurtosis) had a significant association with PFS, although a higher PET PG skewness tended towards less favorable PFS (Hazard Ratio (95% CI)=3.48 (0.75, 16.28); P = 0.11). There was a significant association of higher ADC PG skewness with shorter PFS (Hazard Ratio (95% CI)=2.56 (1.11, 5.91); P = 0.028) and the suggestion that this also led to shorter OS (Hazard Ratio (95% CI)=2.18 (0.95, 5.04); P = 0.067). Higher ADC PG kurtosis tended towards shorter PFS (Hazard Ratio (95% CI)=1.30 (0.98, 1.74); P = 0.073). In a number of cases, PET and ADC pixel values were negatively correlated using the Pearson correlation coefficient. Further, the level of PET and ADC correlation was significantly positively associated with PFS; tumors with higher values of ADC-PET correlation had more favorable PFS (Hazard Ratio (95% CI)=0.17 (0.03, 0.89), P = 0

  1. Estimating Attenuation Coefficients and P-Wave Velocities of the Shallow San Jacinto Fault Zone from Betsy Gunshots Data Recorded by a Spatially Dense Array with 1108 Sensors

    NASA Astrophysics Data System (ADS)

    Ozakin, Yaman; Ben-Zion, Yehuda

    2016-04-01

    We estimate values of P wave velocity and P attenuation coefficients (QP) for the subsurface material at the Sage Brush Flat site along the Clark branch of the San Jacinto Fault Zone. The data are generated by 33 Betsy gunshots and recorded by a spatially dense array of 1108 vertical component geophones deployed in a rectangular grid that is approximately 600 m x 600 m. We automatically pick the arrival times of the seismic body waves from each explosion arriving at stations within 200 m. These measurements are used to derive an average velocity map with velocity values ranging from 500 m/s to 1250 m/s. We estimate the energy of the early P waves by squaring the amplitudes in a short window relative to the automatic picks. These energies are fitted to a decay function representing the geometrical spreading and intrinsic attenuation. By separating the stations into spatial bins and calculating attenuation values for each by linear regression, we construct a QP values map. Most of the QP values are in 5-20 range, which is consistent with other studies of shallow fault zone regions.

  2. Prognostic Value of Diffusion-Weighted Imaging (DWI) Apparent Diffusion Coefficient (ADC) in Patients with Hyperacute Cerebral Infarction Receiving rt-PA Intravenous Thrombolytic Therapy

    PubMed Central

    Sui, Hai-Jing; Yan, Cheng-Gong; Zhao, Zhen-Guo; Bai, Qing-Ke

    2016-01-01

    Background The aim of this study was to investigate the potential value of apparent diffusion coefficient (ADC) of diffusion-weighted imaging (DWI) in the prognosis of patients with hyperacute cerebral infarction (HCI) receiving intravenous thrombolytic therapy with recombinant tissue plasminogen activator (rt-PA). Material/Methods From June 2012 to June 2015, 58 cases of HCI (<6 h) undergoing rt-PA intravenous thrombolytic therapy (thrombolysis group) and 70 cases of HCI (<6 h) undergoing conventional antiplatelet and anticoagulant therapy (control group) in the same period were collected. DWI was conducted on all the subjects, and ADC maps were generated with Functool software to quantify ADC value. The clinical outcomes of HCI patients were observed for 3 months, and prognostic factors were analyzed. Results Before thrombolysis treatment, the lesion area presented high signal intensity on DWI map and low signal intensity on ADC map, and gradually weakened signal intensity on DWI map and gradually enhanced signal intensity on ADC map were observed after thrombolysis. The ADC values of the thrombolysis group were significantly higher than those of the control group after treatment (24 h, 7 d, 30 d, and 90 d) (all P<0.05), and the ADC and rADC values in the thrombolysis group gradually increased over time (all P<0.05). Multiple logistic regression analysis showed that baseline National Institutes of Health Stroke Scale (NIHSS) score, baseline rADC value, and stroke history were the independent factors for the prognosis of HIC patients with thrombolysis (all P<0.05). Conclusions The values of ADC and rADC may provide guidance in the prognosis of HCI patients receiving rt-PA, and the baseline rADC value is the protective factor for the prognosis of HCI patients receiving rt-PA. PMID:27864581

  3. Diffuse dispersive delay and the time convolution/attenuation of transients

    NASA Technical Reports Server (NTRS)

    Bittner, Burt J.

    1991-01-01

    Test data and analytic evaluations are presented to show that relatively poor 100 KHz shielding of 12 Db can effectively provide an electromagnetic pulse transient reduction of 100 Db. More importantly, several techniques are shown for lightning surge attenuation as an alternative to crowbar, spark gap, or power zener type clipping which simply reflects the surge. A time delay test method is shown which allows CW testing, along with a convolution program to define transient shielding effectivity where the Fourier phase characteristics of the transient are known or can be broadly estimated.

  4. Calculation of the fractional interstitial component of boron diffusion and segregation coefficient of boron in Si0.8Ge0.2

    NASA Astrophysics Data System (ADS)

    Fang, Tilden T.; Fang, Wingra T. C.; Griffin, Peter B.; Plummer, James D.

    1996-02-01

    Investigation of boron diffusion in strained silicon germanium buried layers reveals a fractional interstitial component of boron diffusion (fBI) in Se0.8Ge0.2 approximately equal to the fBI value in silicon. In conjunction with computer-simulated boron profiles, the results yield an absolute lower-bound of fBI in Si0.8Ge0.2 of ˜0.8. In addition, the experimental methodology provides a unique vehicle for measuring the segregation coefficient; oxidation-enhanced diffusion is used instead of an extended, inert anneal to rapidly diffuse the dopant to equilibrium levels across the interface, allowing the segregation coefficient to be measured more quickly.

  5. The distribution of the apparent diffusion coefficient as an indicator of the response to chemotherapeutics in ovarian tumour xenografts.

    PubMed

    Tourell, Monique C; Shokoohmand, Ali; Landgraf, Marietta; Holzapfel, Nina P; Poh, Patrina S P; Loessner, Daniela; Momot, Konstantin I

    2017-02-21

    Diffusion-weighted magnetic resonance imaging (DW-MRI) was used to evaluate the effects of single-agent and combination treatment regimens in a spheroid-based animal model of ovarian cancer. Ovarian tumour xenografts grown in non-obese diabetic/severe-combined-immunodeficiency (NOD/SCID) mice were treated with carboplatin or paclitaxel, or combination carboplatin/paclitaxel chemotherapy regimens. After 4 weeks of treatment, tumours were extracted and underwent DW-MRI, mechanical testing, immunohistochemical and gene expression analyses. The distribution of the apparent diffusion coefficient (ADC) exhibited an upward shift as a result of each treatment regimen. The 99-th percentile of the ADC distribution ("maximum ADC") exhibited a strong correlation with the tumour size (r(2) = 0.90) and with the inverse of the elastic modulus (r(2) = 0.96). Single-agent paclitaxel (n = 5) and combination carboplatin/paclitaxel (n = 2) treatment regimens were more effective in inducing changes in regions of higher cell density than single-agent carboplatin (n = 3) or the no-treatment control (n = 5). The maximum ADC was a good indicator of treatment-induced cell death and changes in the extracellular matrix (ECM). Comparative analysis of the tumours' ADC distribution, mechanical properties and ECM constituents provides insights into the molecular and cellular response of the ovarian tumour xenografts to chemotherapy. Increased sample sizes are recommended for future studies. We propose experimental approaches to evaluation of the timeline of the tumour's response to treatment.

  6. Peritumoral apparent diffusion coefficient as a metric of response in patients with recurrent glioblastoma multiforme treated with bevacizumab and irinotecan.

    PubMed

    Andre, J B; Lu, S; Spearman, K; Raval, S N

    2008-06-03

    Bevacizumab and irinotecan have shown promising results in patients with recurrent glioblastoma multiforme (GBM), which traditionally carries a poor prognosis after first-line therapies have been exhausted. Retrospectively documenting the short-term effects of this chemotherapeutic regimen on recurrent GBM, as evidenced by comparative magnetic resonance images obtained two weeks prior to, and one-month following initiation of treatment, we hypothesize that peritumoral apparent diffusion coefficient (ADC) values will decrease on post-treatment scans. Brain MR data were collected from August 2005 to December 2006, in which post-contrast T1-weighted images demonstrated measurable enhancement or GBM tumor mass. Pre- and post-treatment MR images for ten consecutive patients were collected, each having failed temozolomide and radiation therapy. Pre- and post-treatment recurrent GBM bulk tumor and peritumoral T2 signal abnormality were measured in three dimensions. Diffusion of peritumoral T2 signal abnormality was evaluated on pre- and post-treatment ADC. All patients witnessed a significant decrease in tumor bulk ranging from 15.3% to 96.7% with a mean reduction of 48.2%, having received an average of two cycles of chemotherapy. FLAIR images demonstrated a mean volumetric reduction in peritumoral T2 signal abnormality of 44.3%. ADC measurements demonstrated an average reduction in peritumoral ADC of 20.6%, which was statistically significant (p-value < .005). Recurrent GBM tumor bulk demonstrated a 48.2% mean reduction, with corresponding decrease in peritumoral ADC values of 20.6%, suggesting that ADC may represent a valuable metric in the evaluation of the chemotherapeutic response of recurrent GBM, when treated with bevacizumab and irinotecan.

  7. Predicting biochemical recurrence in patients with high-risk prostate cancer using the apparent diffusion coefficient of magnetic resonance imaging

    PubMed Central

    Yoon, Min Young; Park, Juhyun; Cho, Jeong Yeon; Jeong, Chang Wook; Ku, Ja Hyeon; Kim, Hyeon Hoe

    2017-01-01

    Purpose We aimed to investigate whether the apparent diffusion coefficient (ADC) value in diffusion-weighted magnetic resonance imaging predicts the prognoses of patients with high-risk prostate cancer. Materials and Methods A total of 157 patients with high-risk prostate cancer (based on D'Amico's criteria) were included in the analysis. Patients underwent preoperative 3.0 Tesla magnetic resonance imaging within 2 months before radical prostatectomy. Those who received neoadjuvant hormone therapy (33 persons) or radiation therapy (18 persons) were excluded. The ADC of the tumor calculated from 2 b-values (0 and 1,000 s/mm2) was measured. Areas under receiver operating characteristics curves were calculated to maximize the accuracy of the ADC value. Based on the obtained cutoff value, the patients were stratified into 2 groups: Group A consisted of patients with ADC values <746×10−6 mm2/s and group B comprised those with ADC values ≥746×10−6 mm2/s. Results Group A showed higher rate of lymph positive and biochemical recurrence (BCR) rates than group B. Kaplan-Meier analysis showed that the BCR-free survival rate of group A was much lower than that of group B (p<0.001). On Cox proportional regression analyses, ADC group A (hazard ratio [HR], 3.238, p=0.002) and pathologic lymph node positive (HR, 2.242; p=0.009) were independent predictors of BCR. Conclusions In patients with high-risk prostate cancer, ADC value is significantly associated with BCR-free survival. Therefore, the ADC value is a useful tool for predicting the prognoses of these high-risk patients. PMID:28097263

  8. The distribution of the apparent diffusion coefficient as an indicator of the response to chemotherapeutics in ovarian tumour xenografts

    PubMed Central

    Tourell, Monique C.; Shokoohmand, Ali; Landgraf, Marietta; Holzapfel, Nina P.; Poh, Patrina S. P.; Loessner, Daniela; Momot, Konstantin I.

    2017-01-01

    Diffusion-weighted magnetic resonance imaging (DW-MRI) was used to evaluate the effects of single-agent and combination treatment regimens in a spheroid-based animal model of ovarian cancer. Ovarian tumour xenografts grown in non-obese diabetic/severe-combined-immunodeficiency (NOD/SCID) mice were treated with carboplatin or paclitaxel, or combination carboplatin/paclitaxel chemotherapy regimens. After 4 weeks of treatment, tumours were extracted and underwent DW-MRI, mechanical testing, immunohistochemical and gene expression analyses. The distribution of the apparent diffusion coefficient (ADC) exhibited an upward shift as a result of each treatment regimen. The 99-th percentile of the ADC distribution (“maximum ADC”) exhibited a strong correlation with the tumour size (r2 = 0.90) and with the inverse of the elastic modulus (r2 = 0.96). Single-agent paclitaxel (n = 5) and combination carboplatin/paclitaxel (n = 2) treatment regimens were more effective in inducing changes in regions of higher cell density than single-agent carboplatin (n = 3) or the no-treatment control (n = 5). The maximum ADC was a good indicator of treatment-induced cell death and changes in the extracellular matrix (ECM). Comparative analysis of the tumours’ ADC distribution, mechanical properties and ECM constituents provides insights into the molecular and cellular response of the ovarian tumour xenografts to chemotherapy. Increased sample sizes are recommended for future studies. We propose experimental approaches to evaluation of the timeline of the tumour’s response to treatment. PMID:28220831

  9. The distribution of the apparent diffusion coefficient as an indicator of the response to chemotherapeutics in ovarian tumour xenografts

    NASA Astrophysics Data System (ADS)

    Tourell, Monique C.; Shokoohmand, Ali; Landgraf, Marietta; Holzapfel, Nina P.; Poh, Patrina S. P.; Loessner, Daniela; Momot, Konstantin I.

    2017-02-01

    Diffusion-weighted magnetic resonance imaging (DW-MRI) was used to evaluate the effects of single-agent and combination treatment regimens in a spheroid-based animal model of ovarian cancer. Ovarian tumour xenografts grown in non-obese diabetic/severe-combined-immunodeficiency (NOD/SCID) mice were treated with carboplatin or paclitaxel, or combination carboplatin/paclitaxel chemotherapy regimens. After 4 weeks of treatment, tumours were extracted and underwent DW-MRI, mechanical testing, immunohistochemical and gene expression analyses. The distribution of the apparent diffusion coefficient (ADC) exhibited an upward shift as a result of each treatment regimen. The 99-th percentile of the ADC distribution (“maximum ADC”) exhibited a strong correlation with the tumour size (r2 = 0.90) and with the inverse of the elastic modulus (r2 = 0.96). Single-agent paclitaxel (n = 5) and combination carboplatin/paclitaxel (n = 2) treatment regimens were more effective in inducing changes in regions of higher cell density than single-agent carboplatin (n = 3) or the no-treatment control (n = 5). The maximum ADC was a good indicator of treatment-induced cell death and changes in the extracellular matrix (ECM). Comparative analysis of the tumours’ ADC distribution, mechanical properties and ECM constituents provides insights into the molecular and cellular response of the ovarian tumour xenografts to chemotherapy. Increased sample sizes are recommended for future studies. We propose experimental approaches to evaluation of the timeline of the tumour’s response to treatment.

  10. Using the apparent diffusion coefficient to identifying MGMT promoter methylation status early in glioblastoma: importance of analytical method

    SciTech Connect

    Rundle-Thiele, Dayle; Day, Bryan; Stringer, Brett; Fay, Michael; Martin, Jennifer; Jeffree, Rosalind L; Thomas, Paul; Bell, Christopher; Salvado, Olivier; Gal, Yaniv; Coulthard, Alan; Crozier, Stuart; Rose, Stephen

    2015-06-15

    Accurate knowledge of O{sup 6}-methylguanine methyltransferase (MGMT) gene promoter subtype in patients with glioblastoma (GBM) is important for treatment. However, this test is not always available. Pre-operative diffusion MRI (dMRI) can be used to probe tumour biology using the apparent diffusion coefficient (ADC); however, its ability to act as a surrogate to predict MGMT status has shown mixed results. We investigated whether this was due to variations in the method used to analyse ADC. We undertook a retrospective study of 32 patients with GBM who had MGMT status measured. Matching pre-operative MRI data were used to calculate the ADC within contrast enhancing regions of tumour. The relationship between ADC and MGMT was examined using two published ADC methods. A strong trend between a measure of ‘minimum ADC’ and methylation status was seen. An elevated minimum ADC was more likely in the methylated compared to the unmethylated MGMT group (U = 56, P = 0.0561). In contrast, utilising a two-mixture model histogram approach, a significant reduction in mean measure of the ‘low ADC’ component within the histogram was associated with an MGMT promoter methylation subtype (P < 0.0246). This study shows that within the same patient cohort, the method selected to analyse ADC measures has a significant bearing on the use of that metric as a surrogate marker of MGMT status. Thus for dMRI data to be clinically useful, consistent methods of data analysis need to be established prior to establishing any relationship w