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Sample records for acid diffusion length

  1. How fatty acids of different chain length enter and leave cells by free diffusion.

    PubMed

    Kamp, Frits; Hamilton, James A

    2006-09-01

    Opposing views exist as to how unesterified fatty acids (FA) enter and leave cells. It is commonly believed that for short- and medium-chain FA free diffusion suffices whereas it is questioned whether proteins are required to facilitate transport of long-chain fatty acid (LCFA). Furthermore, it is unclear whether these proteins facilitate binding to the plasma membrane, trans-membrane movement, dissociation into the cytosol and/or transport in the cytosol. In this mini-review we approach the controversy from a different point of view by focusing on the membrane permeability constant (P) of FA with different chain length. We compare experimentally derived values of the P of short and medium-chain FA with values of apparent permeability coefficients for LCFA calculated from their dissociation rate constant (k(off)), flip-flop rate constant (k(flip)) and partition coefficient (Kp) in phospholipid bilayers. It was found that Overton's rule is valid as long as k(flip)length, the permeability increases according to increasing Kp and reaches a maximum for LCFA with chain length of 18 carbons or longer. For fast flip-flop (e.g. k(flip)=15s(-1)), the apparent permeability constant for palmitic acid is very high (P(app)=1.61 cm/s). Even for a slow flip-flop rate constant (e.g. k(flip)=0.3s(-1)), the permeability constant of LCFA is still several orders of magnitude larger than the P of water and other small non-electrolytes. Since polyunsaturated FA have basically the same physico-chemical properties as LCFA, they have similar membrane permeabilities. The implications for theories involving proteins to facilitate uptake of FA are discussed. PMID:16829065

  2. Diffusion length and solar cell efficiency

    NASA Astrophysics Data System (ADS)

    Huber, D.; Wahlich, R.; Bachmaier, A.

    The diffusion length of the minority carriers of a solar cell defines the appropriate technology which should be applied for the solar cell fabrication. Back surface techniques only pay off if the diffusion length is long enough. Monocrystalline material with different lifetime killing defects was investigated and an experimental correlation between the diffusion length measured on the unprocessed wafer and the efficiency of the finished cell could be established.

  3. Connecting molecular structure and exciton diffusion length in rubrene derivatives.

    PubMed

    Mullenbach, Tyler K; McGarry, Kathryn A; Luhman, Wade A; Douglas, Christopher J; Holmes, Russell J

    2013-07-19

    Connecting molecular structure and exciton diffusion length in rubrene derivatives demonstrates how the diffusion length of rubrene can be enhanced through targeted functionalization aiming to enhance self-Förster energy transfer. Functionalization adds steric bulk, forcing the molecules farther apart on average, and leading to increased photoluminescence efficiency. A diffusion length enhancement greater than 50% is realized over unsubstituted rubrene. PMID:23754475

  4. A novel method to evaluate spin diffusion length of Pt

    NASA Astrophysics Data System (ADS)

    Zhang, Yan-qing; Sun, Niu-yi; Che, Wen-ru; Shan, Rong; Zhu, Zhen-gang

    2016-05-01

    Spin diffusion length of Pt is evaluated via proximity effect of spin orbit coupling (SOC) and anomalous Hall effect (AHE) in Pt/Co2FeAl bilayers. By varying the thicknesses of Pt and Co2FeAl layer, the thickness dependences of AHE parameters can be obtained, which are theoretically predicted to be proportional to the square of the SOC strength. According to the physical image of the SOC proximity effect, the spin diffusion length of Pt can easily be identified from these thickness dependences. This work provides a novel method to evaluate spin diffusion length in a material with a small value.

  5. Long Minority Carrier Diffusion Lengths in Bridged Silicon Nanowires

    NASA Astrophysics Data System (ADS)

    Yu, Dong; Triplett, Mark; Yang, Yiming; Leonard, Francois; Talin, Alec; Islam, Saif

    2015-03-01

    Nanowires have large surface areas which create new challenges for their optoelectronic applications. Lithographic processes involved in device fabrication and substrate interfaces can lead to surface defects and substantially reduce charge carrier lifetimes and diffusion lengths. Here, we show that using a bridging method to suspend pristine nanowires allows for circumventing detrimental fabrication steps and interfacial effects associated with planar device architectures. We report electron diffusion lengths up to 2.7 μm in bridged silicon nanowire devices, much longer than previously reported values for silicon nanowires with a diameter of 100 nm. Strikingly, electron diffusion lengths are reduced to only 45 nm in planar devices incorporating nanowires grown under the same conditions. The highly scalable and low-cost silicon nano-bridge devices with the demonstrated long diffusion lengths may find exciting applications in photovoltaics, image sensing and photodetectors. DMR-1310678, CMMI-1235592, DEAC01-94-AL85000.

  6. Long minority carrier diffusion lengths in bridged silicon nanowires.

    PubMed

    Triplett, M; Yang, Y; Léonard, F; Talin, A Alec; Islam, M Saif; Yu, D

    2015-01-14

    Nanowires have large surface areas that create new challenges for their optoelectronic applications. Lithographic processes involved in device fabrication and substrate interfaces can lead to surface defects and substantially reduce charge carrier lifetimes and diffusion lengths. Here, we show that using a bridging method to suspend pristine nanowires allows for circumventing detrimental fabrication steps and interfacial effects associated with planar device architectures. We report electron diffusion lengths up to 2.7 μm in bridged silicon nanowire devices, much longer than previously reported values for silicon nanowires with a diameter of 100 nm. Strikingly, electron diffusion lengths are reduced to only 45 nm in planar devices incorporating nanowires grown under the same conditions. The highly scalable silicon nanobridge devices with the demonstrated long diffusion lengths may find exciting applications in photovoltaics, sensing, and photodetectors.

  7. Acid diffusion through polyaniline membranes

    SciTech Connect

    Su, T.M.; Huang, S.C.; Conklin, J.A.

    1995-12-01

    Polyaniline membranes in the undoped (base) and doped (acid) forms are studied for their utility as pervaporation membranes. The separation of water from mixtures of propionic acid, acetic acid and formic acid have been demonstrated from various feed compositions. Doped polyaniline displays an enhanced selectivity of water over these organic acids as compared with undoped polyaniline. For as-cast polyaniline membranes a diffusion coefficient (D) on the order of 10{sup -9} cm{sup 2}/sec has been determined for the flux of protons through the membranes using hydrochloric acid.

  8. Measurement of radon diffusion length in thin membranes.

    PubMed

    Malki, A; Lavi, N; Moinester, M; Nassar, H; Neeman, E; Piasetzky, E; Steiner, V

    2012-07-01

    Building regulations in Israel require the insulating of buildings against radon (222)Rn penetration from soil. In radon-prone areas membranes stretched between the soil and the building foundation are used, together with sealing other possible penetration routes. Designing the radon mitigation procedure requires checking that all sealing materials are practically, radon tight, having a thickness of at least three times the radon diffusion length. In this work, a very simple technique to evaluate the radon diffusion length in thin membranes, using a radon source of known activity and an activated charcoal canister as radon detector is presented. The theoretical formalism and measurement results for polyethylene membranes of different densities obtained in a recent comparison exercise are presented. PMID:22232779

  9. The Reactive-Diffusive Length of OH Radical in Squalane

    NASA Astrophysics Data System (ADS)

    Lee, L.; Wilson, K. R.

    2015-12-01

    With the technique of core-shell particle configuration, we have measured the radical penetration length in a reactive matrix by observing the transmission efficiency of OH radical through squalane shell of various thickness ranging from 0 nm (without coating) to 16 nm. The result indicates a penetration depth of 2.2 nm. Our data suggest that the OH concentration profile in squalane as a function of the distance from the squalane/air interface can be satisfactorily described by the analytical solution to diffusion equation with an added chemical loss term experienced by the OH radical. This allowed an almost unambiguous determination of either OH diffusivity or OH reactivity given that one of the value is known in systems where radical chain propagation is not a significant factor and can shed new lights on the lifetime alteration of particulate matters in the atmosphere where possible coating processes are abundant.

  10. Long Spin Diffusion Length in Few-Layer Graphene Flakes

    NASA Astrophysics Data System (ADS)

    Yan, W.; Phillips, L. C.; Barbone, M.; Hämäläinen, S. J.; Lombardo, A.; Ghidini, M.; Moya, X.; Maccherozzi, F.; van Dijken, S.; Dhesi, S. S.; Ferrari, A. C.; Mathur, N. D.

    2016-09-01

    We report a spin valve with a few-layer graphene flake bridging highly spin-polarized La0.67Sr0.33MnO3 electrodes, whose surfaces are kept clean during lithographic definition. Sharp magnetic switching is verified using photoemission electron microscopy with x-ray magnetic circular dichroism contrast. A naturally occurring high interfacial resistance ˜12 M Ω facilitates spin injection, and a large resistive switching (0.8 M Ω at 10 K) implies a 70 - 130 μ m spin diffusion length that exceeds previous values obtained with sharp-switching electrodes.

  11. Exciton diffusion lengths of organic semiconductor thin films measured by spectrally resolved photoluminescence quenching

    NASA Astrophysics Data System (ADS)

    Lunt, Richard R.; Giebink, Noel C.; Belak, Anna A.; Benziger, Jay B.; Forrest, Stephen R.

    2009-03-01

    We demonstrate spectrally resolved photoluminescence quenching as a means to determine the exciton diffusion length of several archetype organic semiconductors used in thin film devices. We show that aggregation and crystal orientation influence the anisotropy of the diffusion length for vacuum-deposited polycrystalline films. The measurement of the singlet diffusion lengths is found to be in agreement with diffusion by Förster transfer, whereas triplet diffusion occurs primarily via Dexter transfer.

  12. Diffusion length in nanoporous TiO{sub 2} films under above-band-gap illumination

    SciTech Connect

    Park, J. D.; Son, B. H.; Park, J. K.; Kim, Sang Yong; Park, Ji-Yong; Lee, Soonil; Ahn, Y. H.

    2014-06-15

    We determined the carrier diffusion lengths in TiO{sub 2} nanoporous layers of dye-sensitized solar cells by using scanning photocurrent microscopy using an ultraviolet laser. Here, we excited the carrier directly in the nanoporous layers where the diffusion lengths were found to 140 μm as compared to that of visible illumination measured at 90 μm. The diffusion length decreased with increasing laser modulation frequency, in which we determined the electron lifetimes and the diffusion coefficients for both visible and UV illuminations. The diffusion lengths have been studied in terms of the sintering temperatures for both cells with and without binding molecules. We found a strong correlation between the diffusion length and the overall light-to-current conversion efficiency, proving that improving the diffusion length and hence the interparticle connections, is key to improving cell efficiency.

  13. Influence of Alkyl Chain Length and Structure on the Extraction of Copper(II) from Aqueous Acid by 5-Alkyl-2-hydroxybenzaldoximes in Hydrocarbon Solvents: Diffusion Coefficients of Extractants and Their Complexes.

    PubMed

    Ainscow; Aldalur; Beezer; Connor; Garbett; Mitchell; Page; Tindale; Turner; Willson

    1999-05-01

    Measurement of the kinetics of extraction of copper(II) by 19 different 5-alkyl-2-hydroxybenzaldoximes (alkyl is C7H15 and C9H19) from acidic (hydrogen sulfate buffer) aqueous solution in the range pH 3.4-2.0, into 20% v/v toluene in n-hexane is reported. The lowering of the interfacial tension has been measured in some cases. The solubility of the extractants in water has been measured spectrophotometrically. A modified Taylor-Aris dispersion technique has been used to measure the diffusion coefficients in n-hexane and Orfom SX7 of some of the extractants and of the copper(II) complexes which they form. At low initial bulk concentrations (<10 mol m-3) of the extractants, the rate of extraction is controlled by the rate of diffusion of the extractant from the bulk to the organic-aqueous interface. The diffusion coefficient is related to the steric bulk of the alkyl substituent. At higher initial bulk concentrations (200 mol m-3) of the extractants, when the interface is saturated, the rate of extraction is inversely related to the apparent steric bulk of the alkyl substituent. Copyright 1999 Academic Press.

  14. Scale Length of Mantle Heterogeneities: Helium Diffusion Constraints

    NASA Astrophysics Data System (ADS)

    Hart, S.; Kurz, M.; Wang, Z.

    2007-12-01

    will be >20 Ra. In essence, slabs may lose their He signature by diffusion, but it will remain recorded in the surrounding mantle; i.e. veins may run but they can't hide! For both enriched and depleted upper mantle slabs, sampled along a spreading ridge, the 3/4He variability on 10-20 km scale lengths would be easily observed; even massive along-axis melt mixing (50-100 km) would not hide these signatures. We have evaluated 3 extant ridge-crest data sets in this context (MAR 0-47S; EPR 19-23S; SWIR 16- 24E), with a view to defining scale-lengths of He isotope variability. The average 3/4He variability for these 3 areas is 0.47, 0.19 and 0.21 Ra (±1 sigma); a well-sampled sub-area on the MAR (25.7-26.5S) is 0.13 Ra. There is a monotonic variation along the SWIR, from 6.6 to 7.3 Ra; variability about a best fit line is 0.09 Ra (maximum deviation is only 0.20 Ra). At the smallest scale, a single 20 km EPR flow field shows similar variability (0.29 Ra) to the above examples. Since these ridges range from slow to very fast-spreading, the variability in size of along- axis magma chambers will lead inevitably to various scales of melt averaging. We conclude that these ridge areas are not sampling mantle that contains enriched veins or recycled oceanic crust slabs of any significant size. This is especially clear for the 500 km domain on the SWIR, where very small He variability is observed, superimposed on a large scale He gradient. In particular, the view of the upper mantle as a ubiquitous mixture of veins and depleted matrix, with MORB always representing an averaging of this mixture, appears untenable.

  15. Waste acid recycling via diffusion dialysis

    SciTech Connect

    Steffani, C.

    1995-05-26

    Inorganic acids are commonly used for surface cleaning and finishing of metals. The acids become unuseable due to contamination with metals or diluted and weakened. Diffusion dialysis has become a way to recover the useable acid and allow separation of the metals for recovery and sale to refineries. This technique is made possible by the use of membranes that are strong enough to withstand low ph and have long service life.

  16. Studies of minority carrier diffusion length increase in p-type ZnO:Sb

    SciTech Connect

    Lopatiuk-Tirpak, O.; Chernyak, L.; Xiu, F. X.; Liu, J. L.; Jang, S.; Ren, F.; Pearton, S. J.; Gartsman, K.; Feldman, Y.; Osinsky, A.; Chow, P.

    2006-10-15

    Minority electron diffusion length was measured in p-type, Sb-doped ZnO as a function of temperature using the electron beam induced current technique. A thermally induced increase of electron diffusion length was determined to have an activation energy of 184{+-}10 meV. Irradiation with a low energy (5 kV) electron beam also resulted in an increase of diffusion length with a similar activation energy (219{+-}8 meV). Both phenomena are suggested to involve a Sb{sub Zn}-2V{sub Zn} acceptor complex. Saturation and relaxation dynamics of minority carrier diffusion length are explored. Details of a possible mechanism for diffusion length increase are presented.

  17. Fossil rocks of slow earthquake detected by thermal diffusion length

    NASA Astrophysics Data System (ADS)

    Hashimoto, Yoshitaka; Morita, Kiyohiko; Okubo, Makoto; Hamada, Yohei; Lin, Weiren; Hirose, Takehiro; Kitamura, Manami

    2016-04-01

    Fault motion has been estimated by diffusion pattern of frictional heating recorded in geology (e.g., Fulton et al., 2012). The same record in deeper subduction plate interface can be observed from micro-faults in an exhumed accretionary complex. In this study, we focused on a micro-fault within the Cretaceous Shimanto Belt, SW Japan to estimate fault motion from the frictional heating diffusion pattern. A carbonaceous material concentrated layer (CMCL) with ~2m of thickness is observed in study area. Some micro-faults cut the CMCL. Thickness of a fault is about 3.7mm. Injection veins and dilatant fractures were observed in thin sections, suggesting that the high fluid pressure was existed. Samples with 10cm long were collected to measure distribution of vitrinite reflectance (Ro) as a function of distance from the center of micro-fault. Ro of host rock was ~1.0%. Diffusion pattern was detected decreasing in Ro from ~1.2%-~1.1%. Characteristic diffusion distance is ~4-~9cm. We conducted grid search to find the optimal frictional heat generation per unit area per second (Q (J/m^2/s), the product of friction coefficient, normal stress and slip velocity) and slip duration (t(s)) to fit the diffusion pattern. Thermal diffusivity (0.98*10^8m^2/s) and thermal conductivity (2.0 w/mK) were measured. In the result, 2000-2500J/m^2/s of Q and 63000-126000s of t were estimated. Moment magnitudes (M0) of slow earthquakes (slow EQs) follow a scaling law with slip duration and its dimension is different from that for normal earthquakes (normal EQ) (Ide et al., 2007). The slip duration estimated in this study (~10^4-~10^5s) consistent with 4-5 of M0, never fit to the scaling law for normal EQ. Heat generation can be inverted from 4-5 of M0, corresponding with ~10^8-~10^11J, which is consistent with rupture area of 10^5-10^8m2 in this study. The comparisons in heat generation and slip duration between geological measurements and geophysical remote observations give us the

  18. Measurement of minority carrier diffusion lengths in GaAs nanowires by a nanoprobe technique

    NASA Astrophysics Data System (ADS)

    Darbandi, A.; Watkins, S. P.

    2016-07-01

    Minority carrier diffusion lengths in both p-type and n-type GaAs nanowires were studied using electron beam induced current by means of a nanoprobe technique without lithographic processing. The diffusion lengths were determined for Au/GaAs rectifying junctions as well as axial p-n junctions. By incorporating a thin lattice-matched InGaP passivating shell, a 2-fold enhancement in the minority carrier diffusion lengths and one order of magnitude reduction in the surface recombination velocity were achieved.

  19. First working group meeting on the minority carrier diffusion length/lifetime measurement: Results of the round robin lifetime/diffusion length tests

    SciTech Connect

    Cudzinovic, M; Sopori, B

    1995-11-01

    As was noted in the cover letter that accompanied the samples, the eleven bare silicon samples were from various manufacturers. Table I lists the codes for the samples and the manufacturer of each sample. It also notes if the sample was single or poly-crystalline. The samples had been polished on one side before being sent out for measurements, but no further processing was done. The participants of the study were asked to measure either the lifetime or diffusion length of each of the samples using their standard procedure. Table II shows the experimental conditions used by the groups who measured diffusion length. All the diffusion length measurements were performed using the Surface Photovoltage method (SPV). Table M shows the experimental conditions for the lifetime measurements. All the lifetime measurements were made using the Photoconductance Decay method (PCD) under low level injection. These tables show the diameter of the spot size used during the measurement (the effective sampling area), the locations where measurements were taken, and the number of measurements taken at each location. Table N shows the results of the measurements. The table is divided into diffusion length and lifetime measurements for each sample. The values listed are the average values reported by each group. One of the immediate artifacts seen in the data is the large variation in the lifetime measurements. The values from MIT and Mobil are generally close. However, the measurements from NCSU are typically an order of magnitude lower.

  20. Estimation and calibration of the water isotope differential diffusion length in ice core records

    NASA Astrophysics Data System (ADS)

    van der Wel, G.; Fischer, H.; Oerter, H.; Meyer, H.; Meijer, H. A. J.

    2015-08-01

    Palaeoclimatic information can be retrieved from the diffusion of the stable water isotope signal during firnification of snow. The diffusion length, a measure for the amount of diffusion a layer has experienced, depends on the firn temperature and the accumulation rate. We show that the estimation of the diffusion length using power spectral densities (PSDs) of the record of a single isotope species can be biased by uncertainties in spectral properties of the isotope signal prior to diffusion. By using a second water isotope and calculating the difference in diffusion lengths between the two isotopes, this problem is circumvented. We study the PSD method applied to two isotopes in detail and additionally present a new forward diffusion method for retrieving the differential diffusion length based on the Pearson correlation between the two isotope signals. The two methods are discussed and extensively tested on synthetic data which are generated in a Monte Carlo manner. We show that calibration of the PSD method with this synthetic data is necessary to be able to objectively determine the differential diffusion length. The correlation-based method proves to be a good alternative for the PSD method as it yields precision equal to or somewhat higher than the PSD method. The use of synthetic data also allows us to estimate the accuracy and precision of the two methods and to choose the best sampling strategy to obtain past temperatures with the required precision. In addition to application to synthetic data the two methods are tested on stable-isotope records from the EPICA (European Project for Ice Coring in Antarctica) ice core drilled in Dronning Maud Land, Antarctica, showing that reliable firn temperatures can be reconstructed with a typical uncertainty of 1.5 and 2 °C for the Holocene period and 2 and 2.5 °C for the last glacial period for the correlation and PSD method, respectively.

  1. The Reactive-Diffusive Length of OH and Ozone in Model Organic Aerosols.

    PubMed

    Lee, Lance; Wilson, Kevin

    2016-09-01

    A key step in the heterogeneous oxidation of atmospheric aerosols is the reaction of ozone (O3) and hydroxyl radicals (OH) at the gas-particle interface. The formation of reaction products and free radical intermediates and their spatial distribution inside the particle is a sensitive function of the length over which these oxidants diffuse prior to reaction. The reactive-diffusive length of OH and ozone at organic aerosol interfaces is determined by observing the change in the effective uptake coefficient for size-selected model aerosols comprising a reactive core and a thin nanometer-sized (0-12 nm) organic shell. The core and shell materials are selected so that they are immiscible and adopt an assumed core-shell configuration. The results indicate a reactive-diffusive length of 1.4 nm for hydroxyl (OH) radicals in squalane and 1.0 nm for ozone in squalene. Measurements for a purely diffusive system allow for an estimate for diffusion constant (1.6 × 10(-6) cm(2)/s) of ozone in squalane to be determined. The reactive-diffusive length offers a simple first order estimate of how shielding of aerosols by immiscible layers can alter estimates of oxidative lifetimes of aerosols in the atmosphere. PMID:27509443

  2. The Reactive-Diffusive Length of OH and Ozone in Model Organic Aerosols.

    PubMed

    Lee, Lance; Wilson, Kevin

    2016-09-01

    A key step in the heterogeneous oxidation of atmospheric aerosols is the reaction of ozone (O3) and hydroxyl radicals (OH) at the gas-particle interface. The formation of reaction products and free radical intermediates and their spatial distribution inside the particle is a sensitive function of the length over which these oxidants diffuse prior to reaction. The reactive-diffusive length of OH and ozone at organic aerosol interfaces is determined by observing the change in the effective uptake coefficient for size-selected model aerosols comprising a reactive core and a thin nanometer-sized (0-12 nm) organic shell. The core and shell materials are selected so that they are immiscible and adopt an assumed core-shell configuration. The results indicate a reactive-diffusive length of 1.4 nm for hydroxyl (OH) radicals in squalane and 1.0 nm for ozone in squalene. Measurements for a purely diffusive system allow for an estimate for diffusion constant (1.6 × 10(-6) cm(2)/s) of ozone in squalane to be determined. The reactive-diffusive length offers a simple first order estimate of how shielding of aerosols by immiscible layers can alter estimates of oxidative lifetimes of aerosols in the atmosphere.

  3. Study of acid diffusion behaves form PAG by using top coat method

    NASA Astrophysics Data System (ADS)

    Sekiguchi, Atsushi; Matsumoto, Yoko

    2014-03-01

    Our past research on measurements of simulation parameters for ArF resists focused on establishing methods for measuring the following parameters:[1]-[4] • Development parameters[1] • PEB parameters[2] • Dill's ABC parameters[3] • Quencher parameter[4] We entered these parameters into a lithography simulator and performed ArF resist simulations.We then explored ways to optimize the ArF resist material and process. This paper reports on our study of methods for measuring the diffusion length of acid generated from PAG during exposures. In our experiment, we applied a PAG-containing top coat (TC) material (second layer) to a PAG-free ArF resist (first layer), then performed the exposure and PEB processes. The acid generated in the TC during the exposure diffused into the ArF resist in the lower layer (first layer) when PEB was performed. The process of developing this sample removed the TC in the second layer and the parts of the first layer into which the acid had diffused.We obtained the acid diffusion length based on the quantity of film removed by the development. We calculated the acid diffusion coefficient after varying the exposure value and repeating the measurement. For this report, we also performed measurements to determine how differences in PAG anion size, amount of quencher additive, and PEB temperature affected the acid diffusion coefficient.We entered the measurements obtained into the PROLITH simulator and explored the effects of acid diffusion on pattern profile.

  4. Diffusion length and resistivity distribution characteristics of silicon wafer by photoluminescence

    SciTech Connect

    Baek, Dohyun; Lee, Jaehyeong; Choi, Byoungdeog

    2014-10-15

    Highlights: • Analytical photoluminescence efficiency calculation and PL intensity ratio method are developed. • Wafer resistivity and diffusion length characteristics are investigated by PL intensity ratio. • PL intensity is well correlated with resistivity, diffusion length or defect density on wafer measurement. - Abstract: Photoluminescence is a convenient, contactless method to characterize semiconductors. Its use for room-temperature silicon characterization has only recently been implemented. We have developed the PL efficiency theory as a function of substrate doping densities, bulk trap density, photon flux density, and reflectance and compared it with experimental data initially for bulk Si wafers. New developed PL intensity ratio method is able to predict the silicon wafer properties, such as doping densities, minority carrier diffusion length and bulk trap density.

  5. Lifetime and diffusion length measurements on silicon material and solar cells

    NASA Technical Reports Server (NTRS)

    Othmer, S.; Chen, S. C.

    1978-01-01

    Experimental methods were evaluated for the determination of lifetime and diffusion length in silicon intentionally doped with potentially lifetime-degrading impurities found in metallurgical grade silicon, impurities which may be residual in low-cost silicon intended for use in terrestrial flat-plate arrays. Lifetime measurements were made using a steady-state photoconductivity method. Diffusion length determinations were made using short-circuit current measurements under penetrating illumination. Mutual consistency among all experimental methods was verified, but steady-state photoconductivity was found preferable to photoconductivity decay at short lifetimes and in the presence of traps. The effects of a number of impurities on lifetime in bulk material, and on diffusion length in cells fabricated from this material, were determined. Results are compared with those obtained using different techniques. General agreement was found in terms of the hierarchy of impurities which degrade the lifetime.

  6. Laser interferometric method for determining the carrier diffusion length in semiconductors

    SciTech Connect

    Manukhov, V. V.; Fedortsov, A. B.; Ivanov, A. S.

    2015-09-15

    A new laser interferometric method for measuring the carrier diffusion length in semiconductors is proposed. The method is based on the interference–absorption interaction of two laser radiations in a semiconductor. Injected radiation generates additional carriers in a semiconductor, which causes a change in the material’s optical constants and modulation of the probing radiation passed through the sample. When changing the distance between carrier generation and probing points, a decrease in the carrier concentration, which depends on the diffusion length, is recorded. The diffusion length is determined by comparing the experimental and theoretical dependences of the probe signal on the divergence of the injector and probe beams. The method is successfully tested on semiconductor samples with different thicknesses and surface states and can be used in scientific research and the electronics industry.

  7. Probing sub-alveolar length scales with hyperpolarized-gas diffusion NMR

    NASA Astrophysics Data System (ADS)

    Miller, Wilson; Carl, Michael; Mooney, Karen; Mugler, John; Cates, Gordon

    2009-05-01

    Diffusion MRI of the lung is a promising technique for detecting alterations of normal lung microstructure in diseases such as emphysema. The length scale being probed using this technique is related to the time scale over which the helium-3 or xenon-129 diffusion is observed. We have developed new MR pulse sequence methods for making diffusivity measurements at sub-millisecond diffusion times, allowing one to probe smaller length scales than previously possible in-vivo, and opening the possibility of making quantitative measurements of the ratio of surface area to volume (S/V) in the lung airspaces. The quantitative accuracy of simulated and experimental measurements in microstructure phantoms will be discussed, and preliminary in-vivo results will be presented.

  8. Determination of the spin diffusion length in germanium by spin optical orientation and electrical spin injection

    NASA Astrophysics Data System (ADS)

    Rinaldi, C.; Bertoli, S.; Asa, M.; Baldrati, L.; Manzoni, C.; Marangoni, M.; Cerullo, G.; Bianchi, M.; Sordan, R.; Bertacco, R.; Cantoni, M.

    2016-10-01

    The measurement of the spin diffusion length and/or lifetime in semiconductors is a key issue for the realisation of spintronic devices, exploiting the spin degree of freedom of carriers for storing and manipulating information. In this paper, we address such parameters in germanium (0 0 1) at room temperature (RT) by three different measurement methods. Exploiting optical spin orientation in the semiconductor and spin filtering across an insulating MgO barrier, the dependence of the resistivity on the spin of photo-excited carriers in Fe/MgO/Ge spin photodiodes (spin-PDs) was electrically detected. A spin diffusion length of 0.9  ±  0.2 µm was obtained by fitting the photon energy dependence of the spin signal by a mathematical model. Electrical techniques, comprising non-local four-terminal and Hanle measurements performed on CoFeB/MgO/Ge lateral devices, led to spin diffusion lengths of 1.3  ±  0.2 µm and 1.3  ±  0.08 µm, respectively. Despite minor differences due to experimental details, the order of magnitude of the spin diffusion length is the same for the three techniques. Although standard electrical methods are the most employed in semiconductor spintronics for spin diffusion length measurements, here we demonstrate optical spin orientation as a viable alternative for the determination of the spin diffusion length in semiconductors allowing for optical spin orientation.

  9. Amplified quenching of conjugated polymer nanoparticle photoluminescence for robust measurement of exciton diffusion length

    NASA Astrophysics Data System (ADS)

    Bjorgaard, Josiah A.; Köse, Muhammet E.

    2013-05-01

    A new method for measuring exciton diffusion length in nanoparticles (NPs) of conjugated materials is presented. Cationic acceptor dyes are used to quench the photoluminescence in NPs of the prototypical conjugated polymer poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV). Amplified quenching of MEH-PPV emission is observed with an initial Stern-Volmer constant in excess of 105 M-1. Stern-Volmer plots are nonlinear with two distinct quenching regimes, hinting saturation of NP surfaces with acceptor molecules at some point during titration experiments. Using an assumption that highly efficient quenching of excitons occurs after saturation with acceptors at the NP surfaces, the amount of maximum emission quenching can be compared with a model of exciton diffusion to determine exciton diffusion length. By assuming quenching efficiency above 80%, the measured three dimensional exciton diffusion length is estimated to be 12 ± 1 nm. This result is in the lower region of reported values ranging from 10 to 25 nm in MEH-PPV thin films. Both the derived model and the experimental methodology allow robust measurement of exciton diffusion length for any luminescent conjugated material from which NPs can be prepared.

  10. Quantification of the effects of generation volume, surface recombination velocity, and diffusion length on the electron-beam-induced current and its derivative Determination of diffusion lengths in the low micron and submicron ranges

    NASA Technical Reports Server (NTRS)

    Luke, K. L.; Von Roos, O.; Cheng, L.-J.

    1985-01-01

    A systematic and quantitative analysis is carried out to investigate the effects of the shape (point, cube, Gaussian) and size of the generation volume, the surface recombination velocity, and the diffusion length on the electron-beam-induced current (EBIC) and its derivative (DEIC). Thick homogeneously doped samples exhibiting diffusion lengths in the low micron and submicron range are considered. The results are presented in computed EBIC curves as a function of scanning distance and of the ratio true diffusion length/effective diffusion length. Shown using these curves are: (1) a simple and yet rigorous method for the determination of the true diffusion length, taking into consideration all of the factors cited above, (2) a method for the rapid determination of the surface recombination velocity, (3) the condition under which the source shape becomes insignificant, and (4) a new value for the lower limit of the diffusion length which can be determined by the EBOC technique.

  11. Diffusion length measurements in solar cells: An analysis and comparison of techniques

    NASA Technical Reports Server (NTRS)

    Woollam, J. A.; Khan, A. A.; Soukup, R. J.; Hermann, A. M.

    1982-01-01

    A brief review of the major techniques for measuring minority carrier diffusion lengths in solar cells is given. Emphasis is placed on comparing limits of applicability for each method, especially as applied to silicon cells or to gallium arsenide cells, including the effects of radiation damage.

  12. Two Birds with One Stone: Tailoring Singlet Fission for Both Triplet Yield and Exciton Diffusion Length.

    PubMed

    Zhu, Tong; Wan, Yan; Guo, Zhi; Johnson, Justin; Huang, Libai

    2016-09-01

    By direct imaging of singlet and triplet populations with ultrafast microscopy, it is shown that the triplet diffusion length and singlet fission yield can be simultaneously optimized for tetracene and its derivatives, making them ideal structures for application in bilayer solar cells. PMID:27348847

  13. Effective defect diffusion lengths in Ar-ion bombarded 3C-SiC

    DOE PAGES

    Bayu Aji, L. B.; Wallace, J. B.; Shao, L.; Kucheyev, S. O.

    2016-04-14

    Above room temperature, SiC exhibits pronounced processes of diffusion and interaction of radiation-generated point defects. Here, we use the recently developed pulsed ion beam method to measure effective defect diffusion lengths in 3C-SiC bombarded in the temperature range of 25–200 °C with 500 keV Ar ions. Results reveal a diffusion length of ~10 nm, which exhibits a weak temperature dependence, changing from 9 to 13 nm with increasing temperature. Lastly, these results have important implications for understanding and predicting radiation damage in SiC and for the development of radiation-resistant materials via interface-mediated defect reactions.

  14. Effective defect diffusion lengths in Ar-ion bombarded 3C-SiC

    NASA Astrophysics Data System (ADS)

    Bayu Aji, L. B.; Wallace, J. B.; Shao, L.; Kucheyev, S. O.

    2016-05-01

    Above room temperature, SiC exhibits pronounced processes of diffusion and interaction of radiation-generated point defects. Here, we use the recently developed pulsed ion beam method to measure effective defect diffusion lengths in 3C-SiC bombarded in the temperature range of 25–200 °C with 500 keV Ar ions. Results reveal a diffusion length of  ∼10 nm, which exhibits a weak temperature dependence, changing from 9 to 13 nm with increasing temperature. These results have important implications for understanding and predicting radiation damage in SiC and for the development of radiation-resistant materials via interface-mediated defect reactions.

  15. Length of intact plasma membrane determines the diffusion properties of cellular water

    PubMed Central

    Eida, Sato; Van Cauteren, Marc; Hotokezaka, Yuka; Katayama, Ikuo; Sasaki, Miho; Obara, Makoto; Okuaki, Tomoyuki; Sumi, Misa; Nakamura, Takashi

    2016-01-01

    Molecular diffusion in a boundary-free medium depends only on the molecular size, the temperature, and medium viscosity. However, the critical determinant of the molecular diffusion property in inhomogeneous biological tissues has not been identified. Here, using an in vitro system and a high-resolution MR imaging technique, we show that the length of the intact plasma membrane is a major determinant of water diffusion in a controlled cellular environment and that the cell perimeter length (CPL) is sufficient to estimate the apparent diffusion coefficient (ADC) of water in any cellular environment in our experimental system (ADC = −0.21 × CPL + 1.10). We used this finding to further explain the different diffusion kinetics of cells that are dying via apoptotic or non-apoptotic cell death pathways exhibiting characteristic changes in size, nuclear and cytoplasmic architectures, and membrane integrity. These results suggest that the ADC value can be used as a potential biomarker for cell death. PMID:26750342

  16. Length Scale Dependence of the Dynamic Properties of Hyaluronic Acid Solutions in the Presence of Salt

    SciTech Connect

    Horkay, Ferenc; Falus, Peter; Hecht, Anne-Marie; Geissler, Erik

    2010-12-07

    In solutions of the charged semirigid biopolymer hyaluronic acid in salt-free conditions, the diffusion coefficient D{sub NSE} measured at high transfer momentum q by neutron spin echo is more than an order of magnitude smaller than that determined by dynamic light scattering, D{sub DLS}. This behavior contrasts with neutral polymer solutions. With increasing salt content, D{sub DLS} approaches D{sub NSE}, which is independent of ionic strength. Contrary to theoretical expectation, the ion-polymer coupling, which dominates the low q dynamics of polyelectrolyte solutions, already breaks down at distance scales greater than the Debye-Hueckel length.

  17. Diffusion of benzoic acid (1); carbon dioxide (2); methanol (3)

    NASA Astrophysics Data System (ADS)

    Winkelmann, J.

    This document is part of Subvolume A `Gases in Gases, Liquids and their Mixtures' of Volume 15 `Diffusion in Gases, Liquids and Electrolytes' of Landolt-Börnstein Group IV `Physical chemistry'. It is part of the chapter of the chapter `Diffusion in Pure Gases' and contains data on diffusion of (1) benzoic acid; (2) carbon dioxide; (3) methanol

  18. Diffusion of benzoic acid (1); sulfur hexafluoride (2)

    NASA Astrophysics Data System (ADS)

    Winkelmann, J.

    This document is part of Subvolume A `Gases in Gases, Liquids and their Mixtures' of Volume 15 `Diffusion in Gases, Liquids and Electrolytes' of Landolt-Börnstein Group IV `Physical Chemistry'. It is part of the chapter of the chapter `Diffusion in Pure Gases' and contains data on diffusion of (1) benzoic acid; (2) sulfur hexafluoride

  19. Diffusion of benzoic acid (1); carbon dioxide (2)

    NASA Astrophysics Data System (ADS)

    Winkelmann, J.

    This document is part of Subvolume A `Gases in Gases, Liquids and their Mixtures' of Volume 15 `Diffusion in Gases, Liquids and Electrolytes' of Landolt-Börnstein Group IV `Physical Chemistry'. It is part of the chapter of the chapter `Diffusion in Pure Gases' and contains data on diffusion of (1) benzoic acid; (2) carbon dioxide

  20. Controlled ambipolar doping and gate voltage dependent carrier diffusion length in lead sulfide nanowires.

    PubMed

    Yang, Yiming; Li, Jiao; Wu, Hengkui; Oh, Eunsoon; Yu, Dong

    2012-11-14

    We report a simple, controlled doping method for achieving n-type, intrinsic, and p-type lead sulfide (PbS) nanowires (NWs) grown by chemical vapor deposition without introducing any impurities. A wide range of carrier concentrations is realized by adjusting the ratio between the Pb and S precursors. The field effect electron mobility of n-type PbS NWs is up to 660 cm(2)/(V s) at room temperature, in agreement with a long minority carrier diffusion length measured by scanning photocurrent microscopy (SPCM). Interestingly, we have observed a strong dependence of minority carrier diffusion length on gate voltage, which can be understood by considering a carrier concentration dependent recombination lifetime. The demonstrated ambipolar doping of high quality PbS NWs opens up exciting avenues for their applications in photodetectors and photovoltaics.

  1. Diffusion length and Langevin recombination of singlet and triplet excitons in organic heterojunction solar cells.

    PubMed

    Ompong, David; Singh, Jai

    2015-04-27

    We derived new expressions for the diffusion length of singlet and triplet excitons by using the Föster and Dexter transfer mechanisms, respectively, and have found that the diffusion lengths of singlet and triplet excitons are comparable. By using the Langevin recombination theory, we derived the rate of recombination of dissociated free charges into their excitonic states. We found that in some organic polymers the probabilities of recombination of free charge carriers back into the singlet and triplet states are approximately 65.6 and 34.4 %, respectively, indicating that Langevin-type recombination into triplet excitons in organic semiconductors is less likely. This implies that the creation of triplet excitons may be advantageous in organic solar cells, because this may lead to dissociated free charge carriers that can be collected at their respective electrodes, which should result in better conversion efficiency.

  2. Minority carrier diffusion length and edge surface-recombination velocity in InP

    NASA Technical Reports Server (NTRS)

    Hakimzadeh, Roshanak; Bailey, Sheila G.

    1993-01-01

    A scanning electron microscope was used to obtain the electron-beam-induced current (EBIC) profiles in InP specimens containing a Schottky barrier perpendicular to the scanned (edge) surface. An independent technique was used to measure the edge surface-recombination velocity. These values were used in a fit of the experimental EBIC data with a theoretical expression for normalized EBIC (Donolato, 1982) to obtain the electron (minority carrier) diffusion length.

  3. Effects of Coaxial Air on Nitrogen-Diluted Hydrogen Jet Diffusion Flame Length and NOx Emission

    SciTech Connect

    Weiland, N.T.; Chen, R.-H.; Strakey, P.A.

    2007-10-01

    Turbulent nitrogen-diluted hydrogen jet diffusion flames with high velocity coaxial air flows are investigated for their NOx emission levels. This study is motivated by the DOE turbine program’s goal of achieving 2 ppm dry low NOx from turbine combustors running on nitrogen-diluted high-hydrogen fuels. In this study, effects of coaxial air velocity and momentum are varied while maintaining low overall equivalence ratios to eliminate the effects of recirculation of combustion products on flame lengths, flame temperatures, and resulting NOx emission levels. The nature of flame length and NOx emission scaling relationships are found to vary, depending on whether the combined fuel and coaxial air jet is fuel-rich or fuel-lean. In the absence of differential diffusion effects, flame lengths agree well with predicted trends, and NOx emissions levels are shown to decrease with increasing coaxial air velocity, as expected. Normalizing the NOx emission index with a flame residence time reveals some interesting trends, and indicates that a global flame strain based on the difference between the fuel and coaxial air velocities, as is traditionally used, is not a viable parameter for scaling the normalized NOx emissions of coaxial air jet diffusion flames.

  4. Method and apparatus for determining minority carrier diffusion length in semiconductors

    DOEpatents

    Goldstein, Bernard; Dresner, Joseph; Szostak, Daniel J.

    1983-07-12

    Method and apparatus are provided for determining the diffusion length of minority carriers in semiconductor material, particularly amorphous silicon which has a significantly small minority carrier diffusion length using the constant-magnitude surface-photovoltage (SPV) method. An unmodulated illumination provides the light excitation on the surface of the material to generate the SPV. A manually controlled or automatic servo system maintains a constant predetermined value of the SPV. A vibrating Kelvin method-type probe electrode couples the SPV to a measurement system. The operating optical wavelength of an adjustable monochromator to compensate for the wavelength dependent sensitivity of a photodetector is selected to measure the illumination intensity (photon flux) on the silicon. Measurements of the relative photon flux for a plurality of wavelengths are plotted against the reciprocal of the optical absorption coefficient of the material. A linear plot of the data points is extrapolated to zero intensity. The negative intercept value on the reciprocal optical coefficient axis of the extrapolated linear plot is the diffusion length of the minority carriers.

  5. Improvement of carrier diffusion length in silicon nanowire arrays using atomic layer deposition.

    PubMed

    Kato, Shinya; Kurokawa, Yasuyoshi; Miyajima, Shinsuke; Watanabe, Yuya; Yamada, Akira; Ohta, Yoshimi; Niwa, Yusuke; Hirota, Masaki

    2013-01-01

    To achieve a high-efficiency silicon nanowire (SiNW) solar cell, surface passivation technique is very important because a SiNW array has a large surface area. We successfully prepared by atomic layer deposition (ALD) high-quality aluminum oxide (Al2O3) film for passivation on the whole surface of the SiNW arrays. The minority carrier lifetime of the Al2O3-depositedSiNW arrays with bulk silicon substrate was improved to 27 μs at the optimum annealing condition. To remove the effect of bulk silicon, the effective diffusion length of minority carriers in the SiNW array was estimated by simple equations and a device simulator. As a result, it was revealed that the effective diffusion length in the SiNW arrays increased from 3.25 to 13.5 μm by depositing Al2O3 and post-annealing at 400°C. This improvement of the diffusion length is very important for application to solar cells, and Al2O3 deposited by ALD is a promising passivation material for a structure with high aspect ratio such as SiNW arrays. PMID:23968156

  6. Taylor-Couette Flow with Hourglass Geometry of Varying Lengths Simulated by Reaction-Diffusion

    NASA Astrophysics Data System (ADS)

    Zhao, Yunjie; Halmstad, Andrew; Olsen, Thomas; Wiener, Richard

    2008-11-01

    Previously, we have observed chaotic formation of Taylor-Vortex pairs in Modified Taylor- Couette Flow with Hourglass Geometry. In the experiment, the chaotic formation in a shorter system has been restricted to a narrow band about the waist of the hourglass. Such behavior has been modeled by The Reaction-Diffusion equation, which has been previously studied, by Riecke and Paap. Their calculation suggested that quadrupling length of the system would lead to spatial chaos in the vortex formation. We present a careful recreation of this result and consider an intermediate length. We demonstrate that doubling the length should be sufficient to observe spatially chaotic behavior. Richard J. Wiener et al, Phys. Rev. E 55, 5489 (1997). H. Riecke and H.-G. Paap, Europhys. Lett. 14, 1235 (1991).

  7. Charge Transfer Fluorescence and 34 nm Exciton Diffusion Length in Polymers with Electron Acceptor End Traps.

    PubMed

    Zaikowski, Lori; Mauro, Gina; Bird, Matthew; Karten, Brianne; Asaoka, Sadayuki; Wu, Qin; Cook, Andrew R; Miller, John R

    2015-06-18

    Photoexcitation of conjugated poly-2,7-(9,9-dihexylfluorene) polyfluorenes with naphthylimide (NI) and anthraquinone (AQ) electron-acceptor end traps produces excitons that form charge transfer states at the end traps. Intramolecular singlet exciton transport to end traps was examined by steady state fluorescence for polyfluorenes of 17-127 repeat units in chloroform, dimethylformamide (DMF), tetrahydrofuran (THF), and p-xylene. End traps capture excitons and form charge transfer (CT) states at all polymer lengths and in all solvents. The CT nature of the end-trapped states is confirmed by their fluorescence spectra, solvent and trap group dependence, and DFT descriptions. Quantum yields of CT fluorescence are as large as 46%. This strong CT emission is understood in terms of intensity borrowing. Energies of the CT states from onsets of the fluorescence spectra give the depths of the traps which vary with solvent polarity. For NI end traps, the trap depths are 0.06 (p-xylene), 0.13 (THF), and 0.19 eV (CHCl3). For AQ, CT fluorescence could be observed only in p-xylene where the trap depth is 0.27 eV. Quantum yields, emission energies, charge transfer energies, solvent reorganization, and vibrational energies were calculated. Fluorescence measurements on chains >100 repeat units indicate that end traps capture ∼50% of the excitons, and that the exciton diffusion length is LD = 34 nm, which is much larger than diffusion lengths reported in polymer films or than previously known for diffusion along isolated chains. The efficiency of exciton capture depends on chain length but not on trap depth, solvent polarity, or which trap group is present.

  8. Charge transfer fluorescence and 34 nm exciton diffusion length in polymers with electron acceptor end traps

    SciTech Connect

    Zaikowski, Lori; Mauro, Gina; Bird, Matthew; Karten, Brianne; Asaoka, Sadayuki; Wu, Qin; Cook, Andrew R.; Miller, John R.

    2014-12-22

    Photoexcitation of conjugated poly-2,7-(9,9-dihexylfluorene) polyfluorenes with naphthylimide (NI) and anthraquinone (AQ) electron-acceptor end traps produces excitons that form charge transfer states at the end traps. Intramolecular singlet exciton transport to end traps was examined by steady state fluorescence for polyfluorenes of 17 to 127 repeat units in chloroform, dimethylformamide (DMF), tetrahydrofuran (THF), and p-xylene. End traps capture excitons and form charge transfer (CT) states at all polymer lengths and in all solvents. The CT nature of the end-trapped states is confirmed by their fluorescence spectra, solvent and trap group dependence and DFT descriptions. Quantum yields of CT fluorescence are as large as 46%. This strong CT emission is understood in terms of intensity borrowing. Energies of the CT states from onsets of the fluorescence spectra give the depths of the traps which vary with solvent polarity. For NI end traps the trap depths are 0.06 (p-xylene), 0.13 (THF) and 0.19 eV (CHCl3). For AQ, CT fluorescence could be observed only in p-xylene where the trap depth is 0.27 eV. Quantum yields, emission energies, charge transfer energies, solvent reorganization and vibrational energies were calculated. Fluorescence measurements on chains >100 repeat units indicate that end traps capture ~50% of the excitons, and that the exciton diffusion length LD =34 nm, which is much larger than diffusion lengths reported in polymer films or than previously known for diffusion along isolated chains. As a result, the efficiency of exciton capture depends on chain length, but not on trap depth, solvent polarity or which trap group is present.

  9. Charge transfer fluorescence and 34 nm exciton diffusion length in polymers with electron acceptor end traps

    DOE PAGES

    Zaikowski, Lori; Mauro, Gina; Bird, Matthew; Karten, Brianne; Asaoka, Sadayuki; Wu, Qin; Cook, Andrew R.; Miller, John R.

    2014-12-22

    Photoexcitation of conjugated poly-2,7-(9,9-dihexylfluorene) polyfluorenes with naphthylimide (NI) and anthraquinone (AQ) electron-acceptor end traps produces excitons that form charge transfer states at the end traps. Intramolecular singlet exciton transport to end traps was examined by steady state fluorescence for polyfluorenes of 17 to 127 repeat units in chloroform, dimethylformamide (DMF), tetrahydrofuran (THF), and p-xylene. End traps capture excitons and form charge transfer (CT) states at all polymer lengths and in all solvents. The CT nature of the end-trapped states is confirmed by their fluorescence spectra, solvent and trap group dependence and DFT descriptions. Quantum yields of CT fluorescence are asmore » large as 46%. This strong CT emission is understood in terms of intensity borrowing. Energies of the CT states from onsets of the fluorescence spectra give the depths of the traps which vary with solvent polarity. For NI end traps the trap depths are 0.06 (p-xylene), 0.13 (THF) and 0.19 eV (CHCl3). For AQ, CT fluorescence could be observed only in p-xylene where the trap depth is 0.27 eV. Quantum yields, emission energies, charge transfer energies, solvent reorganization and vibrational energies were calculated. Fluorescence measurements on chains >100 repeat units indicate that end traps capture ~50% of the excitons, and that the exciton diffusion length LD =34 nm, which is much larger than diffusion lengths reported in polymer films or than previously known for diffusion along isolated chains. As a result, the efficiency of exciton capture depends on chain length, but not on trap depth, solvent polarity or which trap group is present.« less

  10. Butyric acid esterification kinetics over Amberlyst solid acid catalysts: the effect of alcohol carbon chain length.

    PubMed

    Pappu, Venkata K S; Kanyi, Victor; Santhanakrishnan, Arati; Lira, Carl T; Miller, Dennis J

    2013-02-01

    The liquid phase esterification of butyric acid with a series of linear and branched alcohols is examined. Four strong cation exchange resins, Amberlyst™ 15, Amberlyst™ 36, Amberlyst™ BD 20, and Amberlyst™ 70, were used along with para-toluenesulfonic acid as a homogeneous catalyst. The effect of increasing alcohol carbon chain length and branching on esterification rate at 60°C is presented. For all catalysts, the decrease in turnover frequency (TOF) with increasing carbon chain length of the alcohol is described in terms of steric hindrance, alcohol polarity, and hydroxyl group concentration. The kinetics of butyric acid esterification with 2-ethylhexanol using Amberlyst™ 70 catalyst is described with an activity-based, pseudo-homogeneous kinetic model that includes autocatalysis by butyric acid.

  11. Diffusion length measurement in bulk and epitaxially grown III-V semiconductors using charge collection microscopy

    NASA Technical Reports Server (NTRS)

    Leon, R. P.

    1987-01-01

    Diffusion lengths and surface recombination velocities were measured in GaAs diodes and InP finished solar cells. The basic technique used was charge collection microscopy, also known as electron beam induced current (EBIC). The normalized currents and distances from the pn junction were read directly from the calibrated curves obtained while using the line-scan mode in an SEM. These values were then equated to integral and infinite series expressions resulting from the solution of the diffusion equation with both extended-generation and point-generation functions. This expands previous work by examining both thin and thick samples. The surface recombination velocity was either treated as an unknown in a system of two equations or measured directly using low e(-) beam accelerating voltages. These techniques give accurate results by accounting for the effects of surface recombination and the finite size of the generation volume.

  12. Diffusion length measurements in bulk and epitaxially grown 3-5 semiconductors using charge collection microscopy

    NASA Technical Reports Server (NTRS)

    Leon, R. P.

    1987-01-01

    Diffusion lengths and surface recombination velocities were measured in GaAs diodes and InP finished solar cells. The basic techniques used was charge collection microscopy also known as electron beam induced current (EBIC). The normalized currents and distances from the pn junction were read directly from the calibrated curves obtained while using the line scan mode in an SEM. These values were then equated to integral and infinite series expressions resulting from the solution of the diffusion equation with both extended generation and point generation functions. This expands previous work by examining both thin and thick samples. The surface recombination velocity was either treated as an unknown in a system of two equations, or measured directly using low e(-) beam accelerating voltages. These techniques give accurate results by accounting for the effects of surface recombination and the finite size of the generation volume.

  13. Surface recombination velocity and diffusion length of minority carriers in heavily doped silicon layers

    NASA Technical Reports Server (NTRS)

    Gatos, H. C.; Watanabe, M.; Actor, G.

    1977-01-01

    Quantitative analysis of the electron beam-induced current and the dependence of the effective diffusion length of the minority carriers on the penetration depth of the electron beam were employed for the analysis of the carrier recombination characteristics in heavily doped silicon layers. The analysis is based on the concept of the effective excitation strength of the carriers which takes into consideration all possible recombination sources. Two dimensional mapping of the surface recombination velocity of P-diffused Si layers will be presented together with a three dimensional mapping of minority carrier lifetime in ion implanted Si. Layers heavily doped with As exhibit improved recombination characteristics as compared to those of the layers doped with P.

  14. Defect density dependent photoluminescence yield and triplet diffusion length in rubrene

    NASA Astrophysics Data System (ADS)

    Irkhin, Pavel; Biaggio, Ivan; Zimmerling, Tino; Döbeli, Max; Batlogg, Bertram

    2016-02-01

    We investigate how excitonic processes in rubrene single crystals are affected by a deliberately implanted defect gradient induced by proton irradiation. Spatially resolved measurements show a gradually reduced photoluminescence quantum yield and triplet exciton diffusion length along the defect gradient. Both effects are caused by a decrease in the average triplet lifetime due to interaction with the implanted defects. The triplet lifetime was reduced by almost two orders of magnitude at the highest implanted defect density of 1017 cm-3. The strong sensitivity of the photoluminescence quantum yield to the defect density that is observed already at moderate excitation densities is caused by the combination of two effects: the dominant contribution of triplet-fusion to the observed photoluminescence and the long-range diffusion of triplet excitons.

  15. Diffusion length variation in 0.5- and 3-MeV-proton-irradiated, heteroepitaxial indium phosphide solar cells

    NASA Technical Reports Server (NTRS)

    Jain, Raj K.; Weinberg, Irving; Flood, Dennis J.

    1993-01-01

    Indium phosphide (InP) solar cells are more radiation resistant than gallium arsenide (GaAs) and silicon (Si) solar cells, and their growth by heteroepitaxy offers additional advantages leading to the development of light weight, mechanically strong, and cost-effective cells. Changes in heteroepitaxial InP cell efficiency under 0.5- and 3-MeV proton irradiations have been explained by the variation in the minority-carrier diffusion length. The base diffusion length versus proton fluence was calculated by simulating the cell performance. The diffusion length damage coefficient, K(sub L), was also plotted as a function of proton fluence.

  16. On the determination of diffusion lengths by means of angle-lapped p-n junctions

    NASA Technical Reports Server (NTRS)

    Von Roos, O.

    1979-01-01

    A standard procedure for determining the minority carrier diffusion length by means of SEM consists of scanning an angle-lapped surface of a p-n junction and measuring the resulting short circuit current as a function of beam position. The present paper points out that the usual expression linking the short circuit current induced by the electron beam to the angle between the semiconductor surface and the junction plane is incorrect. The correct expression is discussed and it is noted that, for angles less than 10 deg, the new and the old expression are practically indistinguishable.

  17. Lab on a chip Canada--rapid diffusion over large length scales.

    PubMed

    Juncker, David; Wheeler, Aaron R; Sinton, David

    2013-07-01

    The roots of lab on a chip in Canada are deep, comprising of some of the earliest contributions and first demonstrations of the potential of microfluidic chips. In an editorial leading off this special issue, Jed Harrison of University of Alberta reflects on these early days and Canada's role in the field's development (DOI: 10.1039/c3lc50522g). Over the last decade, microfluidics and lab-on-a-chip research efforts grew exponentially - rapidly diffusing across the vast Canadian length scales.

  18. The diffusion coefficient of vacancies and jump length of electrons in zinc doped manganese ferrite

    NASA Astrophysics Data System (ADS)

    Tawfik, A.; Olofa, S. A.

    1997-10-01

    Samples of mixed ferrite Mn 1- xZn xFe 2O 4 ( x = 0.0, 0.1, 0.3, 0.5 and 0.7) have been prepared by the usual ceramic technique. X-ray diffraction patterns confirmed the spinel cubic structure for the samples. The jump length of electrons in the octahedral sites and electrical conductivity were studied as a function of zinc concentration. The increase of the jump length with Zn concentration is attributed to the substitution of Fe 3+ for Zn 2+ at the A sites which increase the B-B interaction. The increase of the diffusion coefficient and jump rate of vacancies with increasing Zn concentration expedite densification of the samples during sintering.

  19. Aluminum gettering of crystalline silicon for improvement of minority carrier diffusion length and for studies of fundamental diffusion mechanisms

    NASA Astrophysics Data System (ADS)

    Joshi, Subhash Mukund

    Large-grained, multi crystalline silicon for solar cell applications is a very inhomogeneous material with localized regions of high dislocation density and large impurity and precipitate concentrations which limit solar cell efficiency by acting as carrier recombination sites. Due to slow dissolution of precipitates in multi crystalline silicon, these regions cannot be improved by conventional gettering treatments for removal of metal impurities which give good results for single crystal silicon. Extended, high-temperature aluminum gettering is shown to successfully improve the minority carrier diffusion lengths in these localized, poor quality regions and to homogenize the electrical properties of multicrystalline silicon wafers. Cold is a substitutional-interstitial impurity in silicon, whereby its diffusion creates non-equilibrium concentrations of the native point defects in silicon, self-interstitials and vacancies. The diffusion. of gold is therefore controlled by the relaxation of these non-equilibrium point defect concentrations by dislocations or surfaces. Deliberate gold contamination of single-crystal, dislocation-free silicon wafers has been performed followed by aluminum gettering of the gold in silicon. It is shown that the aluminum gettering process can successfully getter gold in silicon, and that the outdiffusion of gold from the silicon is controlled by the proximity to the wafer surfaces rather than by proximity to the aluminum gettering layer. The indiffusion of gold in silicon has been widely demonstrated by experiments and modeling to be dominated by the Kick-Out mechanism, whereby the indiffusion of gold causes supersaturation of self-interstitials, with a minimal contribution from the Frank-Turnbull mechanism, whereby the indiffusion of gold causes undersaturation of vacancies. Fitting of the above-mentioned experimental results on aluminum gettering of gold has been done to show that the opposite holds true for outdiffusion of gold, i

  20. Acid diffusion, standing waves, and information theory: a molecular-scale model of chemically amplified resist

    NASA Astrophysics Data System (ADS)

    Trefonas, Peter, III; Allen, Mary T.

    1992-06-01

    Shannon's information theory is adapted to analyze the photolithographic process, defining the mask pattern as the prior state. Definitions and constraints to the general theory are developed so that the information content at various stages of the lithographic process can be described. Its application is illustrated by exploring the information content within projected aerial images and resultant latent images. Next, a 3-dimensional molecular scale model of exposure, acid diffusion, and catalytic crosslinking in acid-hardened resists (AHR) is presented. In this model, initial positions of photogenerated acids are determined by probability functions generated from the aerial images and the local light intensity in the film. In order to simulate post-exposure baking processes, acids are diffused in a random walk manner, for which the catalytic chain length and the average distance between crosslinks can be set. Crosslink locations are defined in terms of the topologically minimized number required to link different chains. The size and location of polymer chains involved in a larger scale crosslinked network is established and related to polymer solubility. In this manner, the nature of the crosslinked latent image can be established. Good correlation with experimental data is found for the calculated percent insolubilization as a function of dose when the rms acid diffusion length is about 500 angstroms. Information analysis is applied in detail to the specific example of AHR chemistry. The information contained within the 3-D crosslinked latent image is explored as a function of exposure dose, catalytic chain length, average distance between crosslinks. Eopt (the exposure dose which optimizes the information contained within the latent image) was found to vary with catalytic chain length in a manner similar to that observed experimentally in a plot of E90 versus post-exposure bake time. Surprisingly, the information content of the crosslinked latent image remains

  1. Method and apparatus for determining minority carrier diffusion length in semiconductors

    DOEpatents

    Moore, Arnold R.

    1984-02-21

    Method and apparatus are provided for determining the diffusion length of minority carriers in semiconductor material, particularly amorphous silicon, which has a significantly small minority carrier diffusion length using the constant magnitude surface-photovoltage (SPV) method. Steady or modulated illumination at several wavelengths provides the light excitation on the surface of the material to generate the SPV. A manually controlled or automatic servo system maintains a constant predetermined value of the SPV for each wavelength. A probe electrode immersed in an electrolyte solution containing redox couples (preferably quinhydrone) having an oxidation-reduction potential (E) in the order of +0.6 to -1.65 volts couples the SPV to a measurement system. The redox couple solution functions to create a liquid Schottky barrier at the surface of the material. The Schottky barrier is contacted by merely placing the probe in the solution. The redox solution is placed over and in contact with the material to be tested and light is passed through the solution to generate the SPV. To compensate for colored redox solutions a portion of the redox solution not over the material is also illuminated for determining the color compensated light intensity. Steady red light is also used as an optical bias to reduce deleterious space-charge effects that occur in amorphous silicon.

  2. Method and apparatus for determining minority carrier diffusion length in semiconductors

    DOEpatents

    Moore, Arnold R.

    1984-01-01

    Method and apparatus are provided for determining the diffusion length of minority carriers in semiconductor material, particularly amorphous silicon which has a significantly small minority carrier diffusion length using the constant magnitude surface-photovoltage (SPV) method. Steady or modulated illumination at several wavelengths provides the light excitation on the surface of the material to generate the SPV. A manually controlled or automatic servo system maintains a constant predetermined value of the SPV for each wavelength. A drop of a transparent electrolyte solution containing redox couples (preferably quinhydrone) having an oxidation-reduction potential (E) in the order of +0.6 to -1.65 volts couples the SPV to a measurement system. The drop of redox couple solution functions to create a liquid Schottky barrier at the surface of the material. Illumination light is passed through a transparent rod supported over the surface and through the drop of transparent electrolyte. The drop is held in the gap between the rod and the surface. Steady red light is also used as an optical bias to reduce deleterious space-charge effects that occur in amorphous silicon.

  3. Effect of grain boundaries in silicon on minority-carrier diffusion length and solar-cell efficiency

    NASA Technical Reports Server (NTRS)

    Daud, T.; Koliwad, K. M.; Allen, F. G.

    1978-01-01

    The spatial variation of minority-carrier diffusion length in the vicinity of a grain boundary for a polycrystalline silicon sheet has been measured by the use of the EBIC technique. The effect of such a variation on solar-cell output has then been computed as a function of grain size. Calculations show that the cell output drops considerably for grain size smaller than three times the bulk diffusion length.

  4. Magnetic braking, ambipolar diffusion, cloud cores, and star formation - Natural length scales and protostellar masses

    NASA Astrophysics Data System (ADS)

    Mouschovias, Telemachos Ch.

    1991-05-01

    Magnetic braking is essential for cloud contraction and star formation. Ambipolar diffusion is unavoidable in self-gravitating, magnetic clouds and leads to single-stage (as opposed to hierarchical) fragmentation (or core formation) and protostar formation. Magnetic forces dominate thermal-pressure and centrifugal forces over scales comparable to molecular cloud radii. Magnetic support of molecular clouds and the imperfect collisional coupling between charged and neutral particles introduce a critical magnetic length scale (λM,cr = 0.62υAτff) and an Alfvén length scale ((λA = πυAτni), respectively, in the problem which together with a critical thermal length scale (λT,cr = 1.09Caτff) explain naturally the formation of fragments (or cores) in otherwise quiescent clouds and determine the sizes and masses of these fragments during the subsequent stages of contraction. (The quantity υA is the Alfvén speed, τni the mean neutral-ion collision time, Ca the adiabatic speed of sound, and τff the free4all time scale.) Numerical calculations based on new adaptive-grid techniques follow the formation of fragments by ambipolar diffusion and their subsequent collapse up to an enhancement in central density above its initial equilibrium value by a factor ≃106 with excellent spatial resolution. The results confirm the existence and relevance of the three length scales and extend the analytical understanding of fragmentation and star formation derived from them. The ultimately bimodal opposition to gravity (by magnetic forces in the envelope and by thermal-pressure forces in the core) introduces a break in the slope of the log pn -log r profile. The relation Bc ∞ pkc between the magnetic field strength and the gas density in cloud cores holds with K = 0.4 - 0.5 even in the presence of ambipolar diffusion up to densities ˜109 cm-3 for a wide variety of clouds. The value K ≃ ½ is fairly typical. At the late stages of evolution, for example, at a central density

  5. Anomalous stress diffusion in earthquake triggering: Correlation length, time dependence, and directionality

    NASA Astrophysics Data System (ADS)

    Huc, Mireille; Main, Ian G.

    2003-07-01

    It has been recently suggested that moderate and large earthquakes can be triggered by similarly sized events at very long range. Here we study the main characteristics of earthquake triggering by determining its correlation length, time dependence, and directionality. The problem is examined at a global level, by using the Harvard centroid moment tensor catalogue. Our results show that the correlation lengths depend only weakly on the magnitude thresholds involved. No significant systematic triggering is observed for distances greater than the lithospheric thickness (100-150 km), and the correlation length magnitude is similar to the seismogenic thickness (10-20 km). The mean triggering distance and correlation length both increase with time very slowly compared with what would be expected from a normal diffusion process. This is consistent with a clock advance on the failure time based on the constitutive rules for subcritical crack growth following a transient change in the loading stress. The power law scaling disappears after a few months. A functional form for the probability of triggering as a function of time and distance is proposed on the basis of the properties of near critical point systems. The model fits the data well and could be used to calculate conditional probabilities for time-dependent seismic hazard due to earthquake triggering. An apparent directionality effect that was observed in the data set can be attributed to an artefact of poor depth determination. These results do not preclude individual long-range triggering with a potential directionality effect, but they do rule out a statistical correlation at distances much greater than the thickness of the lithosphere.

  6. Coupled diffusion in aqueous weak acid + alkanolamine absorbents

    SciTech Connect

    Leaist, D.G.; Li, Y.; Poissant, R.

    1998-11-01

    Taylor dispersion and differential refractometry are used to measure ternary interdiffusion coefficients (D{sub ik}) for aqueous solutions of acetic acid + triethanolamine (TEA) and aqueous solutions of oxalic acid + TEA at 25 C. The D{sub ik} coefficients give the coupled fluxes of acid and TEA driven by the gradient in the concentration of each solute. Ternary Fick equations with variable D{sub ik} coefficients are integrated numerically to calculate accurate concentration profiles and the moving reaction front produced by the interdiffusion of TEA and acetic or oxalic acid. Ternary diffusion coefficients are also used to predict the rate of dissolution of oxalic acid in 1.00 mol/dm{sup 3} aqueous TEA, a process analogous to the absorption of a diprotic acid gas by an alkanolamine absorbent. The diffusion of oxalic acid drives a significant counterflow of TEA. The resulting buildup of TEA at the surface of the dissolving acid increases the interfacial concentration of TEA from 1.00 to 1.20 mol/dm{sup 3}, which in turn increases the solubility of the acid by 0.20 mol/dm{sup 3}. Nernst-Planck equations are used to predict D{sub ik} coefficients for aqueous weak acid + alkanolamine solutions. The fluxes of these solutes are shown to be strongly coupled by the electric field that is generated by the diffusing ions.

  7. Transition to Spatio-Temporal Chaos with Increasing Length in the Reaction-Diffusion System

    NASA Astrophysics Data System (ADS)

    Trail, Collin; Tomlin, Brett; Olsen, Thomas; Wiener, Richard J.

    2003-11-01

    Calculations based up the Reaction-Diffusion model (H. Riecke and H.-G. Paap, Europhys. Lett. 14), 1235 (1991).have proven to be suggestive for a wide variety of pattern forming systems, including Taylor-Couette flow with hourglass geometry(Richard J. Wiener et al), Phys. Rev. E 55, 5489 (1997).. Seeking insight to guide experimental investigations, we extend these calculations. Previous calculations indicated that in smaller systems, only temporal chaos, located in a small region, would be observed, while in longer systems instabilities would form over a wide region. Our simulations explore this transition from purely temporal chaos to spatio-temporal chaos as the length of the system is increased.

  8. 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.

  9. Effect of heat treatment on the bulk diffusion length of EFG ribbon silicon

    NASA Astrophysics Data System (ADS)

    Ho, C. T.; Moeller, G.; Mathias, J. D.

    1983-03-01

    The effect of thermal anneal on the bulk minority carrier diffusion length L(n) of Edge-defined Film-fed Growth ribbon silicon has been investigated. Statistical distributions of L(n) were gathered after the thermally treated ribbons were fabricated into solor cells by a cold junction formation method (ion implant and pulsed electron beam anneal). The measurements were made by using a bifurcated optical guide arrangement which was specifically designed for ribbon samples with variable surface reflectance. The experimental results indicated that, after a medium temperature (800 C) thermal anneal in a neutral ambient, the form of the L(n) distribution changed in an overall degradation in the average value. With the same thermal anneal in a gettering ambient, the distribution also altered, but with an overall improvement. The observations are discussed in terms of the interaction of metallic impurities with the local structural and chemical defects contained in the ribbons.

  10. 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.

  11. Role of impurities in determining the exciton diffusion length in organic semiconductors

    NASA Astrophysics Data System (ADS)

    Curtin, Ian J.; Blaylock, D. Wayne; Holmes, Russell J.

    2016-04-01

    The design and performance of organic photovoltaic cells is dictated, in part, by the magnitude of the exciton diffusion length (LD). Despite the importance of this parameter, there have been few investigations connecting LD and materials purity. Here, we investigate LD for the organic small molecule N,N'-bis(naphthalen-1-yl)-N,N'-bis(phenyl)-benzidine as native impurities are systematically removed from the material. Thin films deposited from the as-synthesized material yield a value for LD, as measured by photoluminescence quenching, of (3.9 ± 0.5) nm with a corresponding photoluminescence efficiency (ηPL) of (25 ± 1)% and thin film purity of (97.1 ± 1.2)%, measured by high performance liquid chromatography. After purification by thermal gradient sublimation, the value of LD is increased to (4.7 ± 0.5) nm with a corresponding ηPL of (33 ± 1)% and purity of (98.3 ± 0.8)%. Interestingly, a similar behavior is also observed as a function of the deposition boat temperature. Films deposited from the purified material at a high temperature give LD = (5.3 ± 0.8) nm with ηPL = (37 ± 1)% for films with a purity of (99.0 ± 0.3)% purity. Using a model of diffusion by Förster energy transfer, the variation of LD with purity is predicted as a function of ηPL and is in good agreement with measurements. The removal of impurities acts to decrease the non-radiative exciton decay rate and increase the radiative decay rate, leading to increases in both the diffusivity and exciton lifetime. The results of this work highlight the role of impurities in determining LD, while also providing insight into the degree of materials purification necessary to achieve optimized exciton transport.

  12. Gate-dependent carrier diffusion length in lead selenide quantum dot field-effect transistors.

    PubMed

    Otto, Tyler; Miller, Chris; Tolentino, Jason; Liu, Yao; Law, Matt; Yu, Dong

    2013-08-14

    We report a scanning photocurrent microscopy (SPCM) study of colloidal lead selenide (PbSe) quantum dot (QD) thin film field-effect transistors (FETs). PbSe QDs are chemically treated with sodium sulfide (Na2S) and coated with amorphous alumina (a-Al2O3) by atomic layer deposition (ALD) to obtain high mobility, air-stable FETs with a strongly gate-dependent conductivity. SPCM reveals a long photocurrent decay length of 1.7 μm at moderately positive gate bias that decreases to below 0.5 μm at large positive gate voltage and all negative gate voltages. After excluding other possible mechanisms including thermoelectric effects, a thick depletion width, and fringing electric fields, we conclude from photocurrent lifetime measurements that the diffusion of a small fraction of long-lived carriers accounts for the long photocurrent decay length. The long minority carrier lifetime is attributed to charge traps for majority carriers. PMID:23802707

  13. Disk diffusion susceptibility testing of ticarcillin plus clavulanic acid.

    PubMed Central

    Fuchs, P C; Jones, R N; Barry, A L; Thornsberry, C

    1984-01-01

    Disk diffusion susceptibility testing of ticarcillin plus the beta-lactamase inhibitor clavulanic acid was performed on 489 clinical isolates, and the results were compared with reference broth microdilution susceptibilities. Four different disks containing 75 micrograms of ticarcillin plus 2.5, 5, 10, and 15 micrograms of clavulanic acid were evaluated. Based on test performance and clavulanic acid stability, the 75-10-micrograms disk is recommended. Interpretive criteria for ticarcillin as published by the National Committee for Clinical Laboratory Standards appear to be satisfactory for the combination drug, but because the number of ticarcillin-clavulanic acid-resistant isolates was small, this proposal must be considered only tentative. PMID:6715524

  14. The narrow pulse approximation and long length scale determination in xenon gas diffusion NMR studies of model porous media.

    PubMed

    Mair, R W; Sen, P N; Hürlimann, M D; Patz, S; Cory, D G; Walsworth, R L

    2002-06-01

    We report a systematic study of xenon gas diffusion NMR in simple model porous media, random packs of mono-sized glass beads, and focus on three specific areas peculiar to gas-phase diffusion. These topics are: (i) diffusion of spins on the order of the pore dimensions during the application of the diffusion encoding gradient pulses in a PGSE experiment (breakdown of the narrow pulse approximation and imperfect background gradient cancellation), (ii) the ability to derive long length scale structural information, and (iii) effects of finite sample size. We find that the time-dependent diffusion coefficient, D(t), of the imbibed xenon gas at short diffusion times in small beads is significantly affected by the gas pressure. In particular, as expected, we find smaller deviations between measured D(t) and theoretical predictions as the gas pressure is increased, resulting from reduced diffusion during the application of the gradient pulse. The deviations are then completely removed when water D(t) is observed in the same samples. The use of gas also allows us to probe D(t) over a wide range of length scales and observe the long time asymptotic limit which is proportional to the inverse tortuosity of the sample, as well as the diffusion distance where this limit takes effect (approximately 1-1.5 bead diameters). The Padé approximation can be used as a reference for expected xenon D(t) data between the short and the long time limits, allowing us to explore deviations from the expected behavior at intermediate times as a result of finite sample size effects. Finally, the application of the Padé interpolation between the long and the short time asymptotic limits yields a fitted length scale (the Padé length), which is found to be approximately 0.13b for all bead packs, where b is the bead diameter. PMID:12165255

  15. The narrow pulse approximation and long length scale determination in xenon gas diffusion NMR studies of model porous media

    NASA Technical Reports Server (NTRS)

    Mair, R. W.; Sen, P. N.; Hurlimann, M. D.; Patz, S.; Cory, D. G.; Walsworth, R. L.

    2002-01-01

    We report a systematic study of xenon gas diffusion NMR in simple model porous media, random packs of mono-sized glass beads, and focus on three specific areas peculiar to gas-phase diffusion. These topics are: (i) diffusion of spins on the order of the pore dimensions during the application of the diffusion encoding gradient pulses in a PGSE experiment (breakdown of the narrow pulse approximation and imperfect background gradient cancellation), (ii) the ability to derive long length scale structural information, and (iii) effects of finite sample size. We find that the time-dependent diffusion coefficient, D(t), of the imbibed xenon gas at short diffusion times in small beads is significantly affected by the gas pressure. In particular, as expected, we find smaller deviations between measured D(t) and theoretical predictions as the gas pressure is increased, resulting from reduced diffusion during the application of the gradient pulse. The deviations are then completely removed when water D(t) is observed in the same samples. The use of gas also allows us to probe D(t) over a wide range of length scales and observe the long time asymptotic limit which is proportional to the inverse tortuosity of the sample, as well as the diffusion distance where this limit takes effect (approximately 1-1.5 bead diameters). The Pade approximation can be used as a reference for expected xenon D(t) data between the short and the long time limits, allowing us to explore deviations from the expected behavior at intermediate times as a result of finite sample size effects. Finally, the application of the Pade interpolation between the long and the short time asymptotic limits yields a fitted length scale (the Pade length), which is found to be approximately 0.13b for all bead packs, where b is the bead diameter. c. 2002 Elsevier Sciences (USA).

  16. Roughness distribution of multiple hit and long surface diffusion length noise reduced discrete growth models

    NASA Astrophysics Data System (ADS)

    Disrattakit, P.; Chanphana, R.; Chatraphorn, P.

    2016-11-01

    Conventionally, the universality class of a discrete growth model is identified via the scaling of interface width. This method requires large-scale simulations to minimize finite-size effects on the results. The multiple hit noise reduction techniques (m > 1 NRT) and the long surface diffusion length noise reduction techniques (ℓ > 1 NRT) have been used to promote the asymptotic behaviors of the growth models. Lately, an alternative method involving comparison of roughness distribution in the steady state has been proposed. In this work, the roughness distribution of the (2 +1)-dimensional Das Sarma-Tamborenea (DT), Wolf-Villain (WV), and Larger Curvature (LC) models, with and without NRTs, are calculated in order to investigate effects of the NRTs on the roughness distribution. Additionally, effective growth exponents of the noise reduced (2 +1)-dimensional DT, WV and LC models are also calculated. Our results indicate that the NRTs affect the interface width both in the growth and the saturation regimes. In the steady state, the NRTs do not seem to have any impact on the roughness distribution of the DT model, but it significantly changes the roughness distribution of the WV and LC models to the normal distribution curves.

  17. Diffusion length in CdTe by measurement of photovoltage spectra in CdS/CdTe solar cells

    NASA Astrophysics Data System (ADS)

    Toušek, J.; Kindl, D.; Toušková, J.; Dolhov, S.; Poruba, A.

    2001-01-01

    Modified method of surface photovoltage (SPV), spectral response measurement, and constant photocurrent method (CPM) were applied to thin film CdS/CdTe solar cells with the aim of finding diffusion length of minority carriers (L) in the CdTe material. The SPV signal was theoretically calculated without constraints of absorption coefficients for the incident radiation and thickness of the sample assuming one space charge region (SCR) located on the CdS/CdTe interface. In addition to the diffusion length, the SPV is a function of the surface recombination velocity and the parameters of the SCR, which complicates the evaluation. Illuminating the back side of the solar cell (without ohmic contact) we obtain a photovoltage spectrum predominantly influenced by the diffusion length. On the other hand, the standard measurement using light penetrating from the CdS side strongly depends on the thickness of the SCR. The small signal approximation model presented here successfully explains both measured spectra and permits extraction of the diffusion length of minority carriers and thickness of the SCR in CdTe absorber. The CPM is used for determination of absorption coefficients in the CdTe layer. The absorption of this material depends on its preparation and must be known for correct evaluation of experimental data.

  18. The use of multiple EBIC curves and low voltage electron microscopy in the measurement of small diffusion lengths

    NASA Technical Reports Server (NTRS)

    Leon, R. P.

    1987-01-01

    Accurate evaluations of diffusion lengths for heavily to moderately doped III-V semiconductors and/or radiation damaged solar cells have been made possible by using experimental and numerical techniques. The techniques employed were electron beam induced current and low voltage electron microscopy.

  19. Method and apparatus for measuring minority carrier lifetimes and bulk diffusion length in P-N junction solar cells

    NASA Technical Reports Server (NTRS)

    Vonroos, O. H. (Inventor)

    1978-01-01

    Carrier lifetimes and bulk diffusion length are qualitatively measured as a means for qualification of a P-N junction photovoltaic solar cell. High frequency (blue) monochromatic light pulses and low-frequency (red) monochromatic light pulses were alternately applied to the cell while it was irradiated by light from a solar simulator, and synchronously displaying the derivative of the output voltage of the cell on an oscilloscope. The output voltage is a measure of the lifetimes of the minority carriers (holes) in the diffused N layer and majority carriers (electrons) in the bulk P material, and of the diffusion length of the bulk silicon. By connecting a reference cell in this manner with a test cell to be tested in reverse parallel, the display of a test cell that matches the reference cell will be a substantially zero output.

  20. Proton diffusion in the hexafluorophosphoric acid clathrate hydrate.

    PubMed

    Bedouret, Laura; Judeinstein, Patrick; Ollivier, Jacques; Combet, Jérôme; Desmedt, Arnaud

    2014-11-26

    The hexafluorophosphoric acid clathrate hydrate is known as a "super-protonic" conductor: its proton conductivity is of the order of 0.1 S/cm at ca. room temperature. The long-range proton diffusion and the associated mechanism have been analyzed with the help of incoherent quasi-elastic neutron scattering (QENS) and proton pulsed-field-gradient nuclear magnetic resonance ((1)H PFG-NMR). The system crystallizes into the so-called type I clathrate structure (SI) at low temperature and into the type VII structure (SVII) above ca. 230 K with a melting point close to room temperature. While, in the SI phase, no long-range proton diffusion is observed (at least faster than the present measurement capabilities, i.e., 10(-7) cm(2)·s(-1)) with respect to the probed time scale, both techniques evidence a long-range proton diffusion process in the SVII phase (3.85 × 10(-6) cm(2)·s(-1) at 275 K with an activation energy of 0.19 ± 0.04 eV). QENS experiments lead to modeling the microscopic mechanism of the long-range proton diffusion by means of a Chudley-Elliot jump diffusion model with a characteristic jump distance of 2.79 ± 0.17 Å. In other words, the long-range diffusion occurs through a Grotthus mechanism with proton jumping from one water-oxygen site to another. Moreover, the analysis of the proton diffusion for hydration numbers greater than 6 (i.e., in the SVII structure) reveals that the additional water molecules coexisting with the SVII structure act as a "structural defect" barrier for the proton diffusivity, responsible for the conductivity. PMID:24941122

  1. Characterization of tissue structure at varying length scales using temporal diffusion spectroscopy.

    PubMed

    Gore, John C; Xu, Junzhong; Colvin, Daniel C; Yankeelov, Thomas E; Parsons, Edward C; Does, Mark D

    2010-08-01

    The concepts, theoretical behavior and experimental applications of temporal diffusion spectroscopy are reviewed and illustrated. Temporal diffusion spectra are obtained using oscillating-gradient waveforms in diffusion-weighted measurements, and represent the manner in which various spectral components of molecular velocity correlations vary in different geometrical structures that restrict or hinder free movements. Measurements made at different gradient frequencies reveal information on the scale of restrictions or hindrances to free diffusion, and the shape of a spectrum reveals the relative contributions of spatial restrictions at different distance scales. Such spectra differ from other so-called diffusion spectra which depict spatial frequencies and are defined at a fixed diffusion time. Experimentally, oscillating gradients at moderate frequency are more feasible for exploring restrictions at very short distances which, in tissues, correspond to structures smaller than cells. We describe the underlying concepts of temporal diffusion spectra and provide analytical expressions for the behavior of the diffusion coefficient as a function of gradient frequency in simple geometries with different dimensions. Diffusion in more complex model media that mimic tissues has been simulated using numerical methods. Experimental measurements of diffusion spectra have been obtained in suspensions of particles and cells, as well as in vivo in intact animals. An observation of particular interest is the increased contrast and heterogeneity observed in tumors using oscillating gradients at moderate frequency compared with conventional pulse gradient methods, and the potential for detecting changes in tumors early in their response to treatment. Computer simulations suggest that diffusion spectral measurements may be sensitive to intracellular structures, such as nuclear size, and that changes in tissue diffusion properties may be measured before there are changes in cell

  2. Characterization of Tissue Structure at Varying Length Scales Using Temporal Diffusion Spectroscopy

    PubMed Central

    Gore, John C.; Xu, Junzhong; Colvin, Daniel C.; Yankeelov, Thomas E.; Parsons, Edward C.; Does, Mark D.

    2011-01-01

    The concepts, theoretical behavior and experimental applications of temporal diffusion spectroscopy are reviewed and illustrated. Temporal diffusion spectra are obtained by using oscillating gradient waveforms in diffusion-weighted measurements, and represent the manner in which various spectral components of molecular velocity correlations vary in different geometrical structures that restrict or hinder free movements. Measurements made at different gradient frequencies reveal information on the scale of restrictions or hindrances to free diffusion, and the shape of a spectrum reveals the relative contributions of spatial restrictions at different distance scales. Such spectra differ from other so-called diffusion spectra which depict spatial frequencies and are defined at a fixed diffusion time. Experimentally, oscillating gradients at moderate frequency are more feasible for exploring restrictions at very short distances, which in tissues correspond to structures smaller than cells. We describe the underlying concepts of temporal diffusion spectra and provide analytical expressions for the behavior of the diffusion coefficient as a function of gradient frequency in simple geometries with different dimensions. Diffusion in more complex model media that mimic tissues has been simulated using numerical methods. Experimental measurements of diffusion spectra have been obtained in suspensions of particles and cells, as well as in vivo in intact animals. An observation of particular interest is the increased contrast and heterogeneity observed in tumors using oscillating gradients at moderate frequency compared to conventional pulse gradient methods, and the potential for detecting changes in tumors early in their response to treatment. Computer simulations suggest that diffusion spectral measurements may be sensitive to intracellular structures such as nuclear size, and that changes in tissue diffusion properties may be measured before there are changes in cell

  3. Increasing polymer diffusivity by increasing the contour length: The surprising effect of YOYO-1 on DNA dynamics

    NASA Astrophysics Data System (ADS)

    Shin, Seunghwan; Dorfman, Kevin; Cheng, Xiang

    2015-03-01

    Double-stranded DNA (dsDNA) labeled with cyanine dyes such as YOYO-1 has been extensively used as a model to study equilibrium and dynamic properties of semiflexible polyelectrolytes. The ability to directly visualize the polymer dynamics is an attractive feature of these experiments, but positively charged cyanine dyes affect the physical properties of dsDNA, distorting the double helix and counterbalancing the intrinsic negative charge of the backbone. A variety of studies have been conducted to reveal the effect of the dye on the contour length and the persistence length of dsDNA. However, fewer efforts have been made to directly quantify the effect of dye on the diffusion behavior of dsDNA. In order to resolve this issue, we measured the in-plane diffusion coefficient of unconfined dsDNA using confocal microscopy. Although there is widespread consensus that intercalation increases the contour length of dsDNA, we find that increasing the dye:base pair ratio for YOYO-1 actually enhances the diffusion of dsDNA. This enhancement is more significant at lower ionic strengths, which implies that the increase in the diffusion coefficient by dye-DNA intercalation is mainly due to a reduction of excluded volume effect resulting from charge neutralization on the backbone.

  4. The spin Hall angle and spin diffusion length of Pd measured by spin pumping and microwave photoresistance

    SciTech Connect

    Tao, X. D.; Feng, Z.; Miao, B. F.; Sun, L.; You, B.; Wu, D.; Du, J.; Zhang, W.; Ding, H. F.

    2014-05-07

    We present the experimental study of the spin Hall angle (SHA) and spin diffusion length of Pd with the spin pumping and microwave photoresistance effects. The Py/Pd bilayer stripes are excited with an out-of-plane microwave magnetic field. The pure spin current is thus pumped and transforms into charge current via the inverse spin Hall effect (ISHE) in Pd layer, yielding an ISHE voltage. The ISHE voltage can be distinguished from the unwanted signal caused by the anisotropic magnetoresistance according to their different symmetries. Together with Pd thickness dependent measurements of in and out-of-plane precessing angles and effective spin mixing conductance, the SHA and spin-diffusion length of Pd are quantified as 0.0056 ± 0.0007 and 7.3 ± 0.7 nm, respectively.

  5. Amide Proton Transfer Imaging of Diffuse Gliomas: Effect of Saturation Pulse Length in Parallel Transmission-Based Technique

    PubMed Central

    Hiwatashi, Akio; Keupp, Jochen; Yamashita, Koji; Kikuchi, Kazufumi; Yoshiura, Takashi; Yoneyama, Masami; Kruiskamp, Marijn J.; Sagiyama, Koji; Takahashi, Masaya; Honda, Hiroshi

    2016-01-01

    In this study, we evaluated the dependence of saturation pulse length on APT imaging of diffuse gliomas using a parallel transmission-based technique. Twenty-two patients with diffuse gliomas (9 low-grade gliomas, LGGs, and 13 high-grade gliomas, HGGs) were included in the study. APT imaging was conducted at 3T with a 2-channel parallel transmission scheme using three different saturation pulse lengths (0.5 s, 1.0 s, 2.0 s). The 2D fast spin-echo sequence was used for imaging. Z-spectrum was obtained at 25 frequency offsets from -6 to +6 ppm (step 0.5 ppm). A point-by-point B0 correction was performed with a B0 map. Magnetization transfer ratio (MTRasym) and ΔMTRasym (contrast between tumor and normal white matter) at 3.5 ppm were compared among different saturation lengths. A significant increase in MTRasym (3.5 ppm) of HGG was found when the length of saturation pulse became longer (3.09 ± 0.54% at 0.5 s, 3.83 ± 0.67% at 1 s, 4.12 ± 0.97% at 2 s), but MTRasym (3.5 ppm) was not different among the saturation lengths in LGG. ΔMTRasym (3.5 ppm) increased with the length of saturation pulse in both LGG (0.48 ± 0.56% at 0.5 s, 1.28 ± 0.56% at 1 s, 1.88 ± 0.56% at 2 s and HGG (1.72 ± 0.54% at 0.5 s, 2.90 ± 0.49% at 1 s, 3.83 ± 0.88% at 2 s). In both LGG and HGG, APT-weighted contrast was enhanced with the use of longer saturation pulses. PMID:27227746

  6. Derivation of effective fission gas diffusivities in UO2 from lower length scale simulations and implementation of fission gas diffusion models in BISON

    SciTech Connect

    Andersson, Anders David Ragnar; Pastore, Giovanni; Liu, Xiang-Yang; Perriot, Romain Thibault; Tonks, Michael; Stanek, Christopher Richard

    2014-11-07

    This report summarizes the development of new fission gas diffusion models from lower length scale simulations and assessment of these models in terms of annealing experiments and fission gas release simulations using the BISON fuel performance code. Based on the mechanisms established from density functional theory (DFT) and empirical potential calculations, continuum models for diffusion of xenon (Xe) in UO2 were derived for both intrinsic conditions and under irradiation. The importance of the large XeU3O cluster (a Xe atom in a uranium + oxygen vacancy trap site with two bound uranium vacancies) is emphasized, which is a consequence of its high mobility and stability. These models were implemented in the MARMOT phase field code, which is used to calculate effective Xe diffusivities for various irradiation conditions. The effective diffusivities were used in BISON to calculate fission gas release for a number of test cases. The results are assessed against experimental data and future directions for research are outlined based on the conclusions.

  7. The effect of the cation alkyl chain length on density and diffusion in dialkylpyrrolidinium bis(mandelato)borate ionic liquids.

    PubMed

    Filippov, Andrei; Taher, Mamoun; Shah, Faiz Ullah; Glavatskih, Sergei; Antzutkin, Oleg N

    2014-12-28

    The physicochemical properties of ionic liquids are strongly affected by the selective combination of the cations and anions comprising the ionic liquid. In particular, the length of the alkyl chains of ions has a clear influence on the ionic liquid's performance. In this paper, we study the self-diffusion of ions in a series of halogen-free boron-based ionic liquids (hf-BILs) containing bis(mandelato)borate anions and dialkylpyrrolidinium cations with long alkyl chains CnH2n+1 with n from 4 to 14 within a temperature range of 293-373 K. It was found that the hf-BILs with n = 4-7 have very similar diffusion coefficients, while hf-BILs with n = 10-14 exhibit two liquid sub-phases in almost the entire temperature range studied (293-353 K). Both liquid sub-phases differ in their diffusion coefficients, while values of the slower diffusion coefficients are close to those of hf-BILs with shorter alkyl chains. To explain the particular dependence of diffusion on the alkyl chain length, we examined the densities of the hf-BILs studied here. It was shown that the dependence of the density on the number of CH2 groups in long alkyl chains of cations can be accurately described using a "mosaic type" model, where regions of long alkyl chains of cations (named 'aliphatic' regions) and the residual chemical moieties in both cations and anions (named 'ionic' regions) give additive contributions. Changes in density due to an increase in temperature and the number of CH2 groups in the long alkyl chains of cations are determined predominantly by changes in the free volume of the 'ionic' regions, while 'aliphatic' regions are already highly compressed by van der Waals forces, which results in only infinitesimal changes in their free volumes with temperature.

  8. Biosynthesis and Elongation of Short- and Medium-Chain-Length Fatty Acids

    PubMed Central

    van der Hoeven, Rutger S.; Steffens, John C.

    2000-01-01

    Short- and medium-chain-length fatty acids (FAs) are important constituents of a wide array of natural products. Branched and straight short-chain-length FAs originate from branched chain amino acid metabolism, and serve as primers for elongation in FA synthase-like reactions. However, a recent model proposes that the one-carbon extension reactions that utilize 2-oxo-3-methylbutyric acid in leucine biosynthesis also catalyze a repetitive one-carbon elongation of short-chain primers to medium-chain-length FAs. The existence of such a mechanism would require a novel form of regulation to control carbon flux between amino acid and FA biosynthesis. A critical re-analysis of the data used to support this pathway fails to support the hypothesis for FA elongation by one-carbon extension cycles of α-ketoacids. Therefore, we tested the hypothesis experimentally using criteria that distinguish between one- and two-carbon elongation mechanisms: (a) isotopomer patterns in terminal carbon atom pairs of branched and straight FAs resulting from differential labeling with [13C]acetate; (b) [13C]threonine labeling patterns in odd- and even chain length FAs; and (c) differential sensitivity of elongation reactions to inhibition by cerulenin. All three criteria indicated that biosynthesis of medium-chain length FAs is mediated primarily by FA synthase-like reactions. PMID:10631271

  9. Effect of Crystal Defects on Minority Carrier Diffusion Length in 6H SiC Measured Using the Electron Beam Induced Current Method

    NASA Technical Reports Server (NTRS)

    Tabib-Azar, Massood

    1997-01-01

    We report values of minority carrier diffusion length in n-type 6H SiC measured using a planar Electron Beam Induced Current (EBIC) method. Values of hole diffusion length in defect free regions of n-type 6H SiC, with a doping concentration of 1.7El7 1/cu cm, ranged from 1.46 microns to 0.68 microns. We next introduce a novel variation of the planar method used above. This 'planar mapping' technique measured diffusion length along a linescan creating a map of diffusion length versus position. This map is then overlaid onto the EBIC image of the corresponding linescan, allowing direct visualization of the effect of defects on minority carrier diffusion length. Measurements of the above n-type 6H SiC resulted in values of hole diffusion length ranging from 1.2 micron in defect free regions to below 0.1 gm at the center of large defects. In addition, measurements on p-type 6H SiC resulted in electron diffusion lengths ranging from 1.42 micron to 0.8 micron.

  10. Diffusion length of photo-generated charge carriers in layers and powders of CH3NH3PbI3 perovskite

    NASA Astrophysics Data System (ADS)

    Dittrich, Th.; Lang, F.; Shargaieva, O.; Rappich, J.; Nickel, N. H.; Unger, E.; Rech, B.

    2016-08-01

    The diffusion or transport lengths of photo-generated charge carriers in CH3NH3PbI3 layers (thickness up to 1 μm) and powders have been directly measured with high accuracy by modulated surface photovoltage after Goodman. The values of the diffusion lengths of photo-generated charge carriers ranged from 200 nm to tenths of μm. In thin CH3NH3PbI3 layers, the transport lengths corresponded to the layer thickness whereas in thicker layers and in crystallites of CH3NH3PbI3 powders the grain size limited the diffusion length. For grains, the diffusion length of photo-generated charge carriers depended on the measurement conditions.

  11. Effects of acid diffusibility and affinity to cellulose on strength loss of polycarboxylic acid crosslinked fabrics.

    PubMed

    Ji, Bolin; Zhao, Cunyi; Yan, Kelu; Sun, Gang

    2016-06-25

    1,2,3,4-Butanetetracarboxylic acid (BTCA) imparts good anti-wrinkle property to cotton fabrics and results in significant strength loss due to cross-linking and acid degradation of cellulose simultaneously. However, benzophenone-3,3',4,4'- tetracarboxylic acid (BPTCA), an aromatic acid, crosslinks cellulose effectively but causes less strength loss to the products under similar conditions. The difference in damages to cellulose fibers was analyzed by using diffusibility and corresponding affinity of the acids to cellulose fibers, which were estimated by their molecular sizes and Hansen solubility parameters (HSP). Both experimental results and theoretical speculations revealed consistent agreement, indicating that smaller acid molecules could diffuse into cellulose fiber more rapidly and deeply, resulting in more acid degradation. Besides, the aliphatic acid such as BTCA has higher molecular affinity than BPTCA to cellulose, causing additional more degradation of cellulose. Both factors are potential reasons of the observed more severe tensile strength loss of the BTCA treated cotton fabrics. PMID:27083819

  12. 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

  13. Electron beam energy and Ge nanocrystal size effects on the minority carrier diffusion length measured by the nano-electron beam induced current technique

    NASA Astrophysics Data System (ADS)

    Doan, Quang-Tri; El Hdiy, Abdelillah; Troyon, Michel

    2011-07-01

    The near-field electron beam induced current technique is used to study the minority carrier effective diffusion length versus electron beam energy on structures containing spherical Ge nanocrystals (NCs) with diameters of 50 nm and 70 nm formed by a two step dewetting/nucleation process. For both nanocrystal sizes, the effective diffusion length increases with the electron beam energy and then decreases from a threshold energy, which depends on the nanocrystal size. The effective diffusion length is smaller at low energy for NCs of larger size because of their larger surface recombination velocity, due to a better charge trapping efficiency.

  14. Measurement of N-Type 6H SiC Minority-Carrier Diffusion Lengths by Electron Bombardment of Schottky Barriers

    NASA Technical Reports Server (NTRS)

    Hubbard, S. M.; Tabib-Azar, M.; Balley, S.; Rybickid, G.; Neudeck, P.; Raffaelle, R.

    2004-01-01

    Minority-Carrier diffusion lengths of n-type 6H-SiC were measured using the electron-beam induced current (EBIC) technique. Experimental values of primary beam current, EBIC, and beam voltage were obtained for a variety of SIC samples. This data was used to calculate experimental diode efficiency vs. beam voltage curves. These curves were fit to theoretically calculated efficiency curves, and the diffusion length and metal layer thickness were extracted. The hole diffusion length in n-6H SiC ranged from 0.93 +/- 0.15 microns.

  15. Diffusion length variation and proton damage coefficients for InP/In(x)Ga(1-x)As/GaAs solar cells

    NASA Technical Reports Server (NTRS)

    Jain, R. K.; Weinberg, I.; Flood, D. J.

    1993-01-01

    Indium phosphide solar cells are more radiation resistant than gallium arsenide and silicon solar cells, and their growth by heteroepitaxy offers additional advantages leading to the development of lighter, mechanically strong and cost-effective cells. Changes in heteroepitaxial InP cell efficiency under 0.5 and 3 MeV proton irradiations are explained by the variation in the minority-carrier diffusion length. The base diffusion length versus proton fluence is calculated by simulating the cell performance. The diffusion length damage coefficient K(L) is plotted as a function of proton fluence.

  16. Measurement of the minority carrier diffusion length and edge surface-recombination velocity in InP

    NASA Technical Reports Server (NTRS)

    Bailey, Sheila G.; Hakimzadeh, Roshanak

    1993-01-01

    A scanning electron microscope (SEM) was used to measure the electron (minority carrier) diffusion length (L(sub n)) and the edge surface-recombination velocity (V(sub s)) in zinc-doped Czochralski-grown InP wafers. Electron-beam-induced current (EBIC) profiles were obtained in specimens containing a Schottky barrier perpendicular to the scanned (edge) surface. An independent technique was used to measure V(sub s), and these values were used in a theoretical expression for normalized EBIC. A fit of the experimental data with this expression enabled us to determine L(sub n).

  17. Cathodoluminescence of stacking fault bound excitons for local probing of the exciton diffusion length in single GaN nanowires

    SciTech Connect

    Nogues, Gilles Den Hertog, Martien; Auzelle, Thomas; Gayral, Bruno; Daudin, Bruno

    2014-03-10

    We perform correlated studies of individual GaN nanowires in scanning electron microscopy combined to low temperature cathodoluminescence, microphotoluminescence, and scanning transmission electron microscopy. We show that some nanowires exhibit well localized regions emitting light at the energy of a stacking fault bound exciton (3.42 eV) and are able to observe the presence of a single stacking fault in these regions. Precise measurements of the cathodoluminescence signal in the vicinity of the stacking fault give access to the exciton diffusion length near this location.

  18. Reaction-Diffusion Model Simulations relevant to Modified Taylor-Couette Flow in Systems of Varying Length

    NASA Astrophysics Data System (ADS)

    Halmstad, Andrew; Olsen, Thomas; Wiener, Richard

    2006-11-01

    Previously, we have observed a period-doubling cascade to chaos in Modified Taylor-Couette Flow with Hourglass Geometry. Such behavior had been predicted by The Reaction-Diffusion model simulations. The chaotic formation of Taylor-Vortex pair formation was restricted to a very narrow band about the waist of the hourglass. It was suggested that with increasing lengths of systems, the chaotic region would expand. We present a battery of simulations to determine the variation of the size of the chaotic region with length, seeking the transition to spatio- temporal chaos. Richard J. Wiener et al, Phys. Rev. E 55, 5489 (1997). H. Riecke and H.-G. Paap, Europhys. Lett. 14, 1235 (1991).

  19. Terahertz Conductivity within Colloidal CsPbBr3 Perovskite Nanocrystals: Remarkably High Carrier Mobilities and Large Diffusion Lengths.

    PubMed

    Yettapu, Gurivi Reddy; Talukdar, Debnath; Sarkar, Sohini; Swarnkar, Abhishek; Nag, Angshuman; Ghosh, Prasenjit; Mandal, Pankaj

    2016-08-10

    Colloidal CsPbBr3 perovskite nanocrystals (NCs) have emerged as an excellent light emitting material in last one year. Using time domain and time-resolved THz spectroscopy and density functional theory based calculations, we establish 3-fold free carrier recombination mechanism, namely, nonradiative Auger, bimolecular electron-hole recombination, and inefficient trap-assisted recombination in 11 nm sized colloidal CsPbBr3 NCs. Our results confirm a negligible influence of surface defects in trapping charge carriers, which in turn results into desirable intrinsic transport properties, from the perspective of device applications, such as remarkably high carrier mobility (∼4500 cm(2) V(-1) s(-1)), large diffusion length (>9.2 μm), and high luminescence quantum yield (80%). Despite being solution processed and possessing a large surface to volume ratio, this combination of high carrier mobility and diffusion length, along with nearly ideal photoluminescence quantum yield, is unique compared to any other colloidal quantum dot system. PMID:27367476

  20. Manipulating surface diffusion and elastic interactions to obtain quantum dot multilayer arrangements over different length scales

    SciTech Connect

    Placidi, E. Arciprete, F.; Latini, V.; Latini, S.; Patella, F.; Magri, R.

    2014-09-15

    An innovative multilayer growth of InAs quantum dots on GaAs(100) is demonstrated to lead to self-aggregation of correlated quantum dot chains over mesoscopic distances. The fundamental idea is that at critical growth conditions is possible to drive the dot nucleation only at precise locations corresponding to the local minima of the Indium chemical potential. Differently from the known dot multilayers, where nucleation of new dots on top of the buried ones is driven by the surface strain originating from the dots below, here the spatial correlations and nucleation of additional dots are mostly dictated by a self-engineering of the surface occurring during the growth, close to the critical conditions for dot formation under the fixed oblique direction of the incoming As flux, that drives the In surface diffusion.

  1. Characterization of light transport in scattering media at sub-diffusion length scales with Low-coherence Enhanced Backscattering.

    PubMed

    Turzhitsky, Vladimir; Rogers, Jeremy D; Mutyal, Nikhil N; Roy, Hemant K; Backman, Vadim

    2010-01-01

    Low-coherence enhanced backscattering (LEBS) is a technique that has recently shown promise for tissue characterization and the detection of early pre-cancer. Although several Monte Carlo models of LEBS have been described, these models have not been accurate enough to predict all of the experimentally observed LEBS features. We present an appropriate Monte Carlo model to simulate LEBS peak properties from polystyrene microsphere suspensions in water. Results show that the choice of the phase function greatly impacts the accuracy of the simulation when the transport mean free path (ls*) is much greater than the spatial coherence length (L(SC)). When ls* < L(SC), a diffusion approximation based model of LEBS is sufficiently accurate. We also use the Monte Carlo model to validate that LEBS can be used to measure the radial scattering probability distribution (radial point spread function), p(r), at small length scales and demonstrate LEBS measurements of p(r) from biological tissue. In particular, we show that pre-cancerous and benign mucosal tissues have different small length scale light transport properties.

  2. Characterization of light transport in scattering media at sub-diffusion length scales with Low-coherence Enhanced Backscattering

    PubMed Central

    Turzhitsky, Vladimir; Rogers, Jeremy D.; Mutyal, Nikhil N.; Roy, Hemant K.; Backman, Vadim

    2009-01-01

    Low-coherence enhanced backscattering (LEBS) is a technique that has recently shown promise for tissue characterization and the detection of early pre-cancer. Although several Monte Carlo models of LEBS have been described, these models have not been accurate enough to predict all of the experimentally observed LEBS features. We present an appropriate Monte Carlo model to simulate LEBS peak properties from polystyrene microsphere suspensions in water. Results show that the choice of the phase function greatly impacts the accuracy of the simulation when the transport mean free path (ls*) is much greater than the spatial coherence length (LSC). When ls* < LSC, a diffusion approximation based model of LEBS is sufficiently accurate. We also use the Monte Carlo model to validate that LEBS can be used to measure the radial scattering probability distribution (radial point spread function), p(r), at small length scales and demonstrate LEBS measurements of p(r) from biological tissue. In particular, we show that pre-cancerous and benign mucosal tissues have different small length scale light transport properties. PMID:21037980

  3. NEXAFS Chemical State and Bond Lengths of p-Aminobenzoic Acid in Solution and Solid State

    NASA Astrophysics Data System (ADS)

    Stevens, J. S.; Gainar, A.; Suljoti, E.; Xiao, J.; Golnak, R.; Aziz, E. F.; Schroeder, S. L. M.

    2016-05-01

    Solid-state and solution pH-dependent NEXAFS studies allow direct observation of the electronic state of para-aminobenzoic acid (PABA) as a function of its chemical environment, revealing the chemical state and bonding of the chemical species. Variations in the ionization potential (IP) and 1s→π* resonances unequivocally identify the chemical species (neutral, cationic, or anionic) present and the varying local environment. Shifts in σ* shape resonances relative to the IP in the NEXAFS spectra vary with C-N bond length, and the important effect of minor alterations in bond length is confirmed with nitrogen FEFF calculations, leading to the possibility of bond length determination in solution.

  4. Diffusion of cis-5,8,11,14,17-eicosapentaenoic acid (1); carbon dioxide (2)

    NASA Astrophysics Data System (ADS)

    Winkelmann, J.

    This document is part of Subvolume A `Gases in Gases, Liquids and their Mixtures' of Volume 15 `Diffusion in Gases, Liquids and Electrolytes' of Landolt-Börnstein Group IV `Physical Chemistry'. It is part of the chapter of the chapter `Diffusion in Pure Gases' and contains data on diffusion of (1) cis-5,8,11,14,17-eicosapentaenoic acid; (2) carbon dioxide

  5. Evaluating pedestal gradients and scale lengths without functional fits in order to test for non-diffusive transport processes

    NASA Astrophysics Data System (ADS)

    Eldon, D. P.; Tynan, G. R.; Groebner, R. J.; Osborne, T. H.; Bray, B. D.; Boivin, R. L.; Nazikian, R.

    2012-10-01

    The advent of the recent spatial resolution upgrade to the edge Thomson scattering diagnostic at DIII-D allows re-examination of methods for measuring electron density and temperature scale lengths. The modified hyperbolic tangent fit is widely used, however, this function is clearly inappropriate in some situations such as when density profiles are distorted by applied resonant magnetic perturbations (RMPs). In these cases, a flattening of the density profile is observed at or near the separatrix while the RMP is applied. However, no similar structure is observed in the temperature profile so far. Furthermore, the tanh fit is based on a diffusive model and recently observed differences between the tanh fit and measured profiles using newly available high spatial resolution data are revealing more subtle transport processes at the mm scale.

  6. Fatty Acid Chain Length Dependence of Phase Separation Kinetics in Stratum Corneum Models by IR Spectroscopy.

    PubMed

    Mendelsohn, Richard; Rabie, Emann; Walters, Russel M; Flach, Carol R

    2015-07-30

    The main barrier to permeability in human skin resides in the stratum corneum (SC), a layered structure consisting of anucleated, flattened cells (corneocytes) embedded in a heterogeneous lamellar lipid matrix. While lipid structures and packing propensities in the SC and in SC models have been extensively investigated, only limited data are available concerning the kinetics and mechanism of formation of lamellar phases and particular lipid packing motifs. In our prior investigation, kinetic IR spectroscopy measurements probed the temporal sequence of phase separation leading to ordered structures in a three component SC model of equimolar structurally heterogeneous ceramide[NS], chain perdeuterated stearic acid, and cholesterol. In the current work, the phase separation kinetic effects of specific fatty acid chain lengths with a synthetic structurally homogeneous ceramide[NS] in similar ternary mixtures are examined. These are compared with a mixture containing ceramide[NS] with an unsaturated acid chain. The kinetic events are sensitive to the difference in chain lengths between the ceramide acid chain and the fatty acid as well as to the presence of unsaturation in the former. The observed kinetic behaviors span a wide range of phase separation times, ranging from the formation of a solid solution stable for at least 200 h, to a system in which an orthorhombic fatty acid structure is essentially completely formed within the time resolution of the experiment (15 min). The data seem to offer some features of a spinodal phase separation at relatively short times. Overall the approach offers a possible means for addressing several unanswered questions pertinent to skin pharmacology, such as the roles of a wide variety of ceramide and fatty acid species and the design of therapeutic interventions for repair of pathological conditions of the SC.

  7. Reacto-Diffusive Length of N2O5 in Aqueous Sulfate- and Chloride-Containing Aerosol Particles.

    PubMed

    Gaston, Cassandra J; Thornton, Joel A

    2016-02-25

    Heterogeneous reactions of dinitrogen pentoxide (N2O5) on aerosol particles impact air quality and climate, yet aspects of the relevant physical chemistry remain unresolved. One important consideration is the competing effects of diffusion and the rate of chemical reaction within the particle, which determines the length that N2O5 travels within a particle before reacting, referred to as the reacto-diffusive length (l). Large values of l imply a dependence of the reactive uptake efficiency of N2O5, i.e., γ(N2O5), on particle size. We present measurements of the size dependence of γ(N2O5) on aqueous sodium chloride, ammonium sulfate, and ammonium bisulfate particles. γ(N2O5) on ammonium sulfate and ammonium bisulfate particles ranged from 0.016 ± 0.005 to 0.036 ± 0.001 as the surface-area-weighted particle radius increased from 39 to 127 nm, resulting in an estimated l of 32 ± 6 nm. In contrast, γ(N2O5) on sodium chloride particles was independent of particle size, suggesting a near-surface reaction dominated the uptake of N2O5. Differences in the reactivity of the N2O5 intermediate, NO2(+), with water and chloride can explain the observed dependencies. These results allow for parameterizations in atmospheric models to determine a more robust population mean value of γ(N2O5) that accounts for the distribution of particle sizes.

  8. Palladium Catalysts for Fatty Acid Deoxygenation: Influence of the Support and Fatty Acid Chain Length on Decarboxylation Kinetics

    SciTech Connect

    Ford, JP; Immer, JG; Lamb, HH

    2012-03-29

    Supported metal catalysts containing 5 wt% Pd on silica, alumina, and activated carbon were evaluated for liquid-phase deoxygenation of stearic (octadecanoic), lauric (dodecanoic), and capric (decanoic) acids under 5 % H-2 at 300 A degrees C and 15 atm. On-line quadrupole mass spectrometry (QMS) was used to measure CO + CO2 yield, CO2 selectivity, H-2 consumption, and initial decarboxylation rate. Post-reaction analysis of liquid products by gas chromatography was used to determine n-alkane yields. The Pd/C catalyst was highly active and selective for stearic acid (SA) decarboxylation under these conditions. In contrast, SA deoxygenation over Pd/SiO2 occurred primarily via decarbonylation and at a much slower rate. Pd/Al2O3 exhibited high initial SA decarboxylation activity but deactivated under the test conditions. Similar CO2 selectivity patterns among the catalysts were observed for deoxygenation of lauric and capric acids; however, the initial decarboxylation rates tended to be lower for these substrates. The influence of alkyl chain length on deoxygenation kinetics was investigated for a homologous series of C-10-C-18 fatty acids using the Pd/C catalyst. As fatty acid carbon number decreases, reaction time and H-2 consumption increase, and CO2 selectivity and initial decarboxylation rate decrease. The increase in initial decarboxylation rates for longer chain fatty acids is attributed to their greater propensity for adsorption on the activated carbon support.

  9. Length-Dependent Formation of Transmembrane Pores by 310-Helical α-Aminoisobutyric Acid Foldamers.

    PubMed

    Jones, Jennifer E; Diemer, Vincent; Adam, Catherine; Raftery, James; Ruscoe, Rebecca E; Sengel, Jason T; Wallace, Mark I; Bader, Antoine; Cockroft, Scott L; Clayden, Jonathan; Webb, Simon J

    2016-01-20

    The synthetic biology toolbox lacks extendable and conformationally controllable yet easy-to-synthesize building blocks that are long enough to span membranes. To meet this need, an iterative synthesis of α-aminoisobutyric acid (Aib) oligomers was used to create a library of homologous rigid-rod 310-helical foldamers, which have incrementally increasing lengths and functionalizable N- and C-termini. This library was used to probe the inter-relationship of foldamer length, self-association strength, and ionophoric ability, which is poorly understood. Although foldamer self-association in nonpolar chloroform increased with length, with a ∼ 14-fold increase in dimerization constant from Aib6 to Aib11, ionophoric activity in bilayers showed a stronger length dependence, with the observed rate constant for Aib11 ∼ 70-fold greater than that of Aib6. The strongest ionophoric activity was observed for foldamers with >10 Aib residues, which have end-to-end distances greater than the hydrophobic width of the bilayers used (∼ 2.8 nm); X-ray crystallography showed that Aib11 is 2.93 nm long. These studies suggest that being long enough to span the membrane is more important for good ionophoric activity than strong self-association in the bilayer. Planar bilayer conductance measurements showed that Aib11 and Aib13, but not Aib7, could form pores. This pore-forming behavior is strong evidence that Aibm (m ≥ 10) building blocks can span bilayers. PMID:26699898

  10. Length-Dependent Formation of Transmembrane Pores by 310-Helical α-Aminoisobutyric Acid Foldamers

    PubMed Central

    2015-01-01

    The synthetic biology toolbox lacks extendable and conformationally controllable yet easy-to-synthesize building blocks that are long enough to span membranes. To meet this need, an iterative synthesis of α-aminoisobutyric acid (Aib) oligomers was used to create a library of homologous rigid-rod 310-helical foldamers, which have incrementally increasing lengths and functionalizable N- and C-termini. This library was used to probe the inter-relationship of foldamer length, self-association strength, and ionophoric ability, which is poorly understood. Although foldamer self-association in nonpolar chloroform increased with length, with a ∼14-fold increase in dimerization constant from Aib6 to Aib11, ionophoric activity in bilayers showed a stronger length dependence, with the observed rate constant for Aib11 ∼70-fold greater than that of Aib6. The strongest ionophoric activity was observed for foldamers with >10 Aib residues, which have end-to-end distances greater than the hydrophobic width of the bilayers used (∼2.8 nm); X-ray crystallography showed that Aib11 is 2.93 nm long. These studies suggest that being long enough to span the membrane is more important for good ionophoric activity than strong self-association in the bilayer. Planar bilayer conductance measurements showed that Aib11 and Aib13, but not Aib7, could form pores. This pore-forming behavior is strong evidence that Aibm (m ≥ 10) building blocks can span bilayers. PMID:26699898

  11. Chain length, temperature and solvent effects on the structural properties of α-aminoisobutyric acid homooligopeptides.

    PubMed

    Grubišić, Sonja; Chandramouli, Balasubramanian; Barone, Vincenzo; Brancato, Giuseppe

    2016-07-27

    Non-coded α-amino acids, originally exploited by nature, have been successfully reproduced by recent synthetic strategies to confer special structural and functional properties to small peptides. The most known and well-studied atypical residue is α-aminoisobutyric acid (Aib), which is contained in a fairly large number of peptides with known antibiotic effects. Here, we report on a molecular dynamics (MD) study of a series of homooligopeptides based on α-aminoisobutyric acid (Aib) with increasing length (Ac-(Aib)n-NMe, n = 5, 6, 7 and 10) and at various temperatures, employing a recent extension of the AMBER force field tailored for the Aib residue. Solvent effects have been analyzed by comparative MD simulations of a heptapeptide in water and dimethylsulfoxide at different temperatures. Our results show that the preference for the 310- and/or α-helix structures, which typically characterize Aib based peptides, is finely tuned by several factors including the chain length, temperature and solvent nature. While the transitions between intra-molecular i → i + 3 and i → i + 4 hydrogen bonds characterizing 310 and α-helices, respectively, are rather fast in small peptides (in the picosecond timescale), our analysis shows that the above physical and chemical factors modulate the relative equilibrium populations of the two helical structures. The obtained results nicely agree with available experimental data and support the use of the new force field for modeling Aib containing peptides. PMID:27402118

  12. Interactions of /sup 14/N:/sup 15/N stearic acid spin-label pairs: effects of host lipid alkyl chain length and unsaturation

    SciTech Connect

    Feix, J.B.; Yin, J.J.; Hyde, J.S.

    1987-06-30

    Electron-electron double resonance (ELDOR) and saturation recovery electron paramagnetic resonance (EPR) spectroscopy have been employed to examine the interactions of /sup 14/N:/sup 15/N stearic acid spin-label pairs in fluid-phase model membrane bilayers composed of a variety of phospholipids. The (/sup 14/N)-16-doxylstearate:(/sup 15/N)-16-doxylstearate (16:16) pair was utilized to measure lateral diffusion of the spin-labels, while the (/sup 14/N)-16-doxylstearate:(/sup 15/N)-5-doxylstearate (16:5) pair provided information on vertical fluctuations of the 16-doxylstearate nitroxide moiety toward the membrane surface. Three saturated host lipids of varying alkyl chain length (dimyristoylphosphatidylcholine (DMPC), dipalmitoylphosphatidylcholine (DPPC), and distearoylphosphatidylcholine (DSPC)), an ..cap alpha..-saturated, ..beta..-unsaturated lipid (1-palmitoyl-2-oleoylphosphatidylcholine (POPC)), and phosphatidylcholine from a natural source (egg yolk phosphatidylcholine (egg PC)) were utilized as host lipids. Lateral diffusion of the stearic acid spin-labels was only slightly affected by alkyl chain length at a given reduced temperature (T/sub r/) in the saturated host lipids but was significantly decreased in POPC at the same T/sub r/. Lateral diffusion in DMPC, POPC, and egg PC was quite similar at 37/sup 0/C. A strong correlation was noted between lateral diffusion constants and rotational mobility of (/sup 14/N)-16-doxylstearate. Vertical fluctuations were likewise only slightly influenced by alklyl chain length but were strongly diminished in POPC and egg PC relative to the saturated systems. This diminution of the 16:5 interaction was observed even under conditions where no differences were discernible by conventional EPR.

  13. Omega-3 Fatty Acids, Oxidative Stress, and Leukocyte Telomere Length: A Randomized Controlled Trial

    PubMed Central

    Kiecolt-Glaser, Janice K.; Epel, Elissa S.; Belury, Martha A.; Andridge, Rebecca; Lin, Jue; Glaser, Ronald; Malarkey, William B.; Hwang, Beom Seuk; Blackburn, Elizabeth

    2012-01-01

    Shorter telomeres have been associated with poor health behaviors, age-related diseases, and early mortality. Telomere length is regulated by the enzyme telomerase, and is linked to exposure to proinflammatory cytokines and oxidative stress. In our recent randomized controlled trial, omega-3 (n-3) polyunsaturated fatty acid (PUFA) supplementation lowered the concentration of serum proinflammatory cytokines. This study assessed whether n-3 PUFA supplementation also affected leukocyte telomere length, telomerase, and oxidative stress. In addition to testing for group differences, changes in the continuous n-6:n-3 PUFA ratio were assessed to account for individual differences in adherence, absorption, and metabolism. The double-blind 4-month trial included 106 healthy sedentary overweight middle-aged and older adults who received (1) 2.5 g/day n-3 PUFAs, (2) l.25 g/day n-3 PUFAs, or (3) placebo capsules that mirrored the proportions of fatty acids in the typical American diet. Supplementation significantly lowered oxidative stress as measured by F2-isoprostanes (p=0.02). The estimated geometric mean log-F2-isoprostanes values were 15% lower in the two supplemented groups compared to placebo. Although group differences for telomerase and telomere length were nonsignificant, changes in the n-6:n-3 PUFA plasma ratios helped clarify the intervention’s impact: telomere length increased with decreasing n-6:n-3 ratios, p=0.02. The data suggest that lower n-6:n-3 PUFA ratios can impact cell aging. The triad of inflammation, oxidative stress, and immune cell aging represents important pre-disease mechanisms that may be ameliorated through nutritional interventions. This translational research broadens our understanding of the potential impact of the n-6:n-3 PUFA balance. ClinicalTrials.gov identifier: NCT00385723 PMID:23010452

  14. Effects of spacer chain length of amino acid-based gemini surfactants on wormlike micelle formation.

    PubMed

    Sakai, Kenichi; Nomura, Kazuyuki; Shrestha, Rekha Goswami; Endo, Takeshi; Sakamoto, Kazutami; Sakai, Hideki; Abe, Masahiko

    2014-01-01

    We studied the effects of the spacer chain length of amino acid-based gemini surfactants on the formation of wormlike micelles in aqueous solutions. The surfactants used were synthesized by reacting dodecanoylglutamic acid anhydride with diamine compounds (ethylenediamine, pentanediamine, and octanediamine), and were abbreviated as 12-GsG-12 (s: the spacer chain length of 2, 5, and 8 methylene units). These surfactants yielded viscoelastic wormlike micellar solutions at pH 9 upon mixing with a cationic monomeric surfactant, hexadecyltrimethylammonium bromide (HTAB). We found that the rheological behavior was strongly dependent on the spacer chain length and HTAB concentration. When the shortest spacer chain analogue (12-G2G-12) was used, an increased HTAB concentration resulted in the following structural transformations of the micelles: (i) spherical or rodlike micelles; (ii) anionic wormlike micelles exhibiting a transient network structure; (iii) anionic wormlike micelles with a micellar branching or interconnected structure; and (iv) cationic wormlike micelles. Similarly, when the middle spacer chain analogue (12-G5G-12) was used, a structural transformation from anionic to cationic wormlike micelles occurs; however, molecular aggregates with a lower positive curvature were also formed in this transition region. When the longest spacer analogue (12-G8G-12) was used, the formation of cation-rich molecular aggregates was not observed. These transition behaviors were attributed to the packing geometry of the gemini surfactants with HTAB. Additionally, as the spacer chain length increased, the zero-shear viscosity in the anionic wormlike micellar region decreased, suggesting limited one-dimensional micellar growth of spherical, rodlike, or anionic wormlike micelles.

  15. The Effect of Limited Diffusion and Wet-Dry Cycling on Reversible Polymerization Reactions: Implications for Prebiotic Synthesis of Nucleic Acids.

    PubMed

    Higgs, Paul G

    2016-06-08

    A long-standing problem for the origins of life is that polymerization of many biopolymers, including nucleic acids and peptides, is thermodynamically unfavourable in aqueous solution. If bond making and breaking is reversible, monomers and very short oligomers predominate. Recent experiments have shown that wetting and drying cycles can overcome this problem and drive the formation of longer polymers. In the dry phase, bond formation is favourable, but diffusion is restricted, and bonds only form between monomers that are initially close together. In the wet phase, some of the bonds are hydrolyzed. However, repositioning of the molecules allows new bonds to form in the next dry phase, leading to an increase in mean polymer length. Here, we consider a simple theoretical model that explains the effect of cycling. There is an equilibrium length distribution with a high mean length that could be achieved if diffusion occurred freely in the dry phase. This equilibrium is inaccessible without diffusion. A single dry cycle without diffusion leads to mean lengths much shorter than this. Repeated cycling leads to a significant increase in polymerization relative to a single cycle. In the most favourable case, cycling leads to the same equilibrium length distribution as would be achieved if free diffusion were possible in the dry phase. These results support the RNA World scenario by explaining a potential route to synthesis of long RNAs; however, they also imply that cycling would be beneficial to the synthesis of other kinds of polymers, including peptides, where bond formation involves a condensation reaction.

  16. Determination of charge-carrier diffusion length in the photosensing layer of HgCdTe n-on-p photovoltaic infrared focal plane array detectors

    SciTech Connect

    Vishnyakov, A. V.; Stuchinsky, V. A. Brunev, D. V.; Zverev, A. V.; Dvoretsky, S. A.

    2014-03-03

    In the present paper, we propose a method for evaluating the bulk diffusion length of minority charge carriers in the photosensing layer of photovoltaic focal plane array (FPA) photodetectors. The method is based on scanning a strip-shaped illumination spot with one of the detector diodes at a low level of photocurrents j{sub ph} being registered; such scanning provides data for subsequent analysis of measured spot-scan profiles within a simple diffusion model. The asymptotic behavior of the effective (at j{sub ph} ≠ 0) charge-carrier diffusion length l{sub d} {sub eff} as a function of j{sub ph} for j{sub ph} → 0 inferred from our experimental data proved to be consistent with the behavior of l{sub d} {sub eff} vs j{sub ph} as predicted by the model, while the obtained values of the bulk diffusion length of minority carriers (electrons) in the p-HgCdTe film of investigated HgCdTe n-on-p FPA photodetectors were found to be in a good agreement with the previously reported carrier diffusion-length values for HgCdTe.

  17. Diversion of phagosome trafficking by pathogenic Rhodococcus equi depends on mycolic acid chain length.

    PubMed

    Sydor, Tobias; von Bargen, Kristine; Hsu, Fong-Fu; Huth, Gitta; Holst, Otto; Wohlmann, Jens; Becken, Ulrike; Dykstra, Tobias; Söhl, Kristina; Lindner, Buko; Prescott, John F; Schaible, Ulrich E; Utermöhlen, Olaf; Haas, Albert

    2013-03-01

    Rhodococcus equi is a close relative of Mycobacterium spp. and a facultative intracellular pathogen which arrests phagosome maturation in macrophages before the late endocytic stage. We have screened a transposon mutant library of R. equi for mutants with decreased capability to prevent phagolysosome formation. This screen yielded a mutant in the gene for β-ketoacyl-(acyl carrier protein)-synthase A (KasA), a key enzyme of the long-chain mycolic acid synthesizing FAS-II system. The longest kasA mutant mycolic acid chains were 10 carbon units shorter than those of wild-type bacteria. Coating of non-pathogenic E. coli with purified wild-type trehalose dimycolate reduced phagolysosome formation substantially which was not the case with shorter kasA mutant-derived trehalose dimycolate. The mutant was moderately attenuated in macrophages and in a mouse infection model, but was fully cytotoxic.Whereas loss of KasA is lethal in mycobacteria, R. equi kasA mutant multiplication in broth was normal proving that long-chain mycolic acid compounds are not necessarily required for cellular integrity and viability of the bacteria that typically produce them. This study demonstrates a central role of mycolic acid chain length in diversion of trafficking by R. equi. PMID:23078612

  18. Chain-length heterogeneity allows for the assembly of fatty acid vesicles in dilute solutions.

    PubMed

    Budin, Itay; Prwyes, Noam; Zhang, Na; Szostak, Jack W

    2014-10-01

    A requirement for concentrated and chemically homogeneous pools of molecular building blocks would severely restrict plausible scenarios for the origin of life. In the case of membrane self-assembly, models of prebiotic lipid synthesis yield primarily short, single-chain amphiphiles that can form bilayer vesicles only at very high concentrations. These high critical aggregation concentrations (cacs) pose significant obstacles for the self-assembly of single-chain lipid membranes. Here, we examine membrane self-assembly in mixtures of fatty acids with varying chain lengths, an expected feature of any abiotic lipid synthesis. We derive theoretical predictions for the cac of mixtures by adapting thermodynamic models developed for the analogous phenomenon of mixed micelle self-assembly. We then use several complementary methods to characterize aggregation experimentally, and find cac values in close agreement with our theoretical predictions. These measurements establish that the cac of fatty acid mixtures is dramatically lowered by minor fractions of long-chain species, thereby providing a plausible route for protocell membrane assembly. Using an NMR-based approach to monitor aggregation of isotopically labeled samples, we demonstrate the incorporation of individual components into mixed vesicles. These experiments suggest that vesicles assembled in dilute, mixed solutions are depleted of the shorter-chain-length lipid species, a finding that carries implications for the composition of primitive cell membranes. PMID:25296310

  19. Chain-Length Heterogeneity Allows for the Assembly of Fatty Acid Vesicles in Dilute Solutions

    PubMed Central

    Budin, Itay; Prwyes, Noam; Zhang, Na; Szostak, Jack W.

    2014-01-01

    A requirement for concentrated and chemically homogeneous pools of molecular building blocks would severely restrict plausible scenarios for the origin of life. In the case of membrane self-assembly, models of prebiotic lipid synthesis yield primarily short, single-chain amphiphiles that can form bilayer vesicles only at very high concentrations. These high critical aggregation concentrations (cacs) pose significant obstacles for the self-assembly of single-chain lipid membranes. Here, we examine membrane self-assembly in mixtures of fatty acids with varying chain lengths, an expected feature of any abiotic lipid synthesis. We derive theoretical predictions for the cac of mixtures by adapting thermodynamic models developed for the analogous phenomenon of mixed micelle self-assembly. We then use several complementary methods to characterize aggregation experimentally, and find cac values in close agreement with our theoretical predictions. These measurements establish that the cac of fatty acid mixtures is dramatically lowered by minor fractions of long-chain species, thereby providing a plausible route for protocell membrane assembly. Using an NMR-based approach to monitor aggregation of isotopically labeled samples, we demonstrate the incorporation of individual components into mixed vesicles. These experiments suggest that vesicles assembled in dilute, mixed solutions are depleted of the shorter-chain-length lipid species, a finding that carries implications for the composition of primitive cell membranes. PMID:25296310

  20. Chain-length heterogeneity allows for the assembly of fatty acid vesicles in dilute solutions.

    PubMed

    Budin, Itay; Prwyes, Noam; Zhang, Na; Szostak, Jack W

    2014-10-01

    A requirement for concentrated and chemically homogeneous pools of molecular building blocks would severely restrict plausible scenarios for the origin of life. In the case of membrane self-assembly, models of prebiotic lipid synthesis yield primarily short, single-chain amphiphiles that can form bilayer vesicles only at very high concentrations. These high critical aggregation concentrations (cacs) pose significant obstacles for the self-assembly of single-chain lipid membranes. Here, we examine membrane self-assembly in mixtures of fatty acids with varying chain lengths, an expected feature of any abiotic lipid synthesis. We derive theoretical predictions for the cac of mixtures by adapting thermodynamic models developed for the analogous phenomenon of mixed micelle self-assembly. We then use several complementary methods to characterize aggregation experimentally, and find cac values in close agreement with our theoretical predictions. These measurements establish that the cac of fatty acid mixtures is dramatically lowered by minor fractions of long-chain species, thereby providing a plausible route for protocell membrane assembly. Using an NMR-based approach to monitor aggregation of isotopically labeled samples, we demonstrate the incorporation of individual components into mixed vesicles. These experiments suggest that vesicles assembled in dilute, mixed solutions are depleted of the shorter-chain-length lipid species, a finding that carries implications for the composition of primitive cell membranes.

  1. Free fatty acids chain length distribution affects the permeability of skin lipid model membranes.

    PubMed

    Uchiyama, Masayuki; Oguri, Masashi; Mojumdar, Enamul H; Gooris, Gert S; Bouwstra, Joke A

    2016-09-01

    The lipid matrix in the stratum corneum (SC) plays an important role in the barrier function of the skin. The main lipid classes in this lipid matrix are ceramides (CERs), cholesterol (CHOL) and free fatty acids (FFAs). The aim of this study was to determine whether a variation in CER subclass composition and chain length distribution of FFAs affect the permeability of this matrix. To examine this, we make use of lipid model membranes, referred to as stratum corneum substitute (SCS). We prepared SCS containing i) single CER subclass with either a single FFA or a mixture of FFAs and CHOL, or ii) a mixture of various CER subclasses with either a single FFA or a mixture of FFAs and CHOL. In vitro permeation studies were performed using ethyl-p-aminobenzoic acid (E-PABA) as a model drug. The flux of E-PABA across the SCS containing the mixture of FFAs was higher than that across the SCS containing a single FA with a chain length of 24 C atoms (FA C24), while the E-PABA flux was not effected by the CER composition. To select the underlying factors for the changes in permeability, the SCSs were examined by Fourier transform infrared spectroscopy (FTIR) and Small angle X-ray scattering (SAXS). All lipid models demonstrated a similar phase behavior. However, when focusing on the conformational ordering of the individual FFA chains, the shorter chain FFA (with a chain length of 16, 18 or 20 C atoms forming only 11m/m% of the total FFA level) had a higher conformational disordering, while the conformational ordering of the chains of the CER and FA C24 and FA C22 hardly did not change irrespective of the composition of the SCS. In conclusion, the conformational mobility of the short chain FFAs present only at low levels in the model SC lipid membranes has a great impact on the permeability of E-PABA. PMID:27287726

  2. Temperature dependence of the non-local resistance and spin diffusion length in metallic lateral spin valves

    NASA Astrophysics Data System (ADS)

    Erickson, Michael J.; Leighton, Chris; Crowell, Paul A.

    2010-03-01

    We report measurements of the T dependence of the non-local spin signal in lateral metallic spin valves with transparent ferromagnet (FM) / normal metal (N) interfaces. We have employed complementary spin valve and Hanle effect measurements to systematically study spin injection and relaxation. Devices were deposited in UHV from high purity sources of all four combinations of Ni0.8Fe0.2 or Co FM's and Cu or Al N channels. Devices of width 250 nm, thicknesses 200 - 400 nm, and FM contact separations (d = 250 to 2000 nm) were fabricated on a single substrate using an in-situ shadow masking technique. δRNL measurements show a very different T dependence for NiFe and Co devices while showing similar behavior for both Al and Cu. This is generally consistent with the measured resistivities and modeling based on the assumption of transparent interfaces. Fitting δRNL vs. d yields a spin diffusion length with weak T dependence for both Al and Cu and is independent of FM. Hanle effect measurements confirm a consistent picture of spin relaxation. Work supported by the University of Minnesota NSF MRSEC.

  3. Determination of bulk diffusion lengths for angle-lapped semiconductor material via the scanning electron microscope: A theoretical analysis

    NASA Technical Reports Server (NTRS)

    Vonroos, O.

    1978-01-01

    A standard procedure for the determination of the minority carrier diffusion length by means of a scanning electron microscope (SEM) consists in scanning across an angle-lapped surface of a P-N junction and measuring the resultant short circuit current I sub sc as a function of beam position. A detailed analysis of the I sub sc originating from this configuration is presented. It is found that, for a point source excitation, the I sub sc depends very simply on x, the variable distance between the surface and the junction edge. The expression for the I sub sc of a planar junction device is well known. If d, the constant distance between the plane of the surface of the semiconductor and the junction edge in the expression for the I of a planar junction is merely replaced by x, the variable distance of the corresponding angle-lapped junction, an expression results which is correct to within a small fraction of a percent as long as the angle between the surfaces, 2 theta sub 1, is smaller than 10 deg.

  4. Effect of side chain length on intrahelical interactions between carboxylate- and guanidinium-containing amino acids.

    PubMed

    Kuo, Hsiou-Ting; Yang, Po-An; Wang, Wei-Ren; Hsu, Hao-Chun; Wu, Cheng-Hsun; Ting, Yu-Te; Weng, Ming-Huei; Kuo, Li-Hung; Cheng, Richard P

    2014-08-01

    The charge-containing hydrophilic functionalities of encoded charged amino acids are linked to the backbone via different numbers of hydrophobic methylenes, despite the apparent electrostatic nature of protein ion pairing interactions. To investigate the effect of side chain length of guanidinium- and carboxylate-containing residues on ion pairing interactions, α-helical peptides containing Zbb-Xaa (i, i + 3), (i, i + 4) and (i, i + 5) (Zbb = carboxylate-containing residues Aad, Glu, Asp in decreasing length; Xaa = guanidinium residues Agh, Arg, Agb, Agp in decreasing length) sequence patterns were studied by circular dichroism spectroscopy (CD). The helicity of Aad- and Glu-containing peptides was similar and mostly pH independent, whereas the helicity of Asp-containing peptides was mostly pH dependent. Furthermore, the Arg-containing peptides consistently exhibited higher helicity compared to the corresponding Agp-, Agb-, and Agh-containing peptides. Side chain conformational analysis by molecular mechanics calculations showed that the Zbb-Xaa (i, i + 3) and (i, i + 4) interactions mainly involved the χ 1 dihedral combinations (g+, g+) and (g-, g+), respectively. These low energy conformations were also observed in intrahelical Asp-Arg and Glu-Arg salt bridges of natural proteins. Accordingly, Asp and Glu provides variation in helix characteristics associated with Arg, but Aad does not provide features beyond those already delivered by Glu. Importantly, nature may have chosen the side chain length of Arg to support helical conformations through inherent high helix propensity coupled with stabilizing intrahelical ion pairing interactions with the carboxylate-containing residues.

  5. Electron-hole diffusion lengths >175 μm in solution-grown CH3NH3PbI3 single crystals

    DOE PAGES

    Dong, Qingfeng; Fang, Yanjun; Shao, Yuchuan; Mulligan, Padhraic; Qiu, Jie; Cao, Lei; Huang, Jinsong

    2015-02-27

    Long, balanced electron and hole diffusion lengths greater than 100 nanometers in the polycrystalline organolead trihalide compound CH3NH3PbI3 are critical for highly efficient perovskite solar cells. We found that the diffusion lengths in CH3NH3PbI3 single crystals grown by a solution-growth method can exceed 175 micrometers under 1 sun (100 mW cm–2) illumination and exceed 3 millimeters under weak light for both electrons and holes. The internal quantum efficiencies approach 100% in 3-millimeter-thick single-crystal perovskite solar cells under weak light. These long diffusion lengths result from greater carrier mobility, longer lifetime, and much smaller trap densities in the single crystals thanmore » in polycrystalline thin films. As a result, the long carrier diffusion lengths enabled the use of CH3NH3PbI3 in radiation sensing and energy harvesting through the gammavoltaic effect, with an efficiency of 3.9% measured with an intense cesium-137 source.« less

  6. Solar cells. Electron-hole diffusion lengths > 175 μm in solution-grown CH3NH3PbI3 single crystals.

    PubMed

    Dong, Qingfeng; Fang, Yanjun; Shao, Yuchuan; Mulligan, Padhraic; Qiu, Jie; Cao, Lei; Huang, Jinsong

    2015-02-27

    Long, balanced electron and hole diffusion lengths greater than 100 nanometers in the polycrystalline organolead trihalide compound CH3NH3PbI3 are critical for highly efficient perovskite solar cells. We found that the diffusion lengths in CH3NH3PbI3 single crystals grown by a solution-growth method can exceed 175 micrometers under 1 sun (100 mW cm(-2)) illumination and exceed 3 millimeters under weak light for both electrons and holes. The internal quantum efficiencies approach 100% in 3-millimeter-thick single-crystal perovskite solar cells under weak light. These long diffusion lengths result from greater carrier mobility, longer lifetime, and much smaller trap densities in the single crystals than in polycrystalline thin films. The long carrier diffusion lengths enabled the use of CH3NH3PbI3 in radiation sensing and energy harvesting through the gammavoltaic effect, with an efficiency of 3.9% measured with an intense cesium-137 source.

  7. Macromolecular Crowding Studies of Amino Acids Using NMR Diffusion Measurements and Molecular Dynamics Simulations

    NASA Astrophysics Data System (ADS)

    Virk, Amninder; Stait-Gardner, Timothy; Willis, Scott; Torres, Allan; Price, William

    2015-02-01

    Molecular crowding occurs when the total concentration of macromolecular species in a solution is so high that a considerable proportion of the volume is physically occupied and therefore not accessible to other molecules. This results in significant changes in the solution properties of the molecules in such systems. Macromolecular crowding is ubiquitous in biological systems due to the generally high intracellular protein concentrations. The major hindrance to understanding crowding is the lack of direct comparison of experimental data with theoretical or simulated data. Self-diffusion is sensitive to changes in the molecular weight and shape of the diffusing species, and the available diffusion space (i.e., diffusive obstruction). Consequently, diffusion measurements are a direct means for probing crowded systems including the self-association of molecules. In this work, nuclear magnetic resonance measurements of the self-diffusion of four amino acids (glycine, alanine, valine and phenylalanine) up to their solubility limit in water were compared directly with molecular dynamics simulations. The experimental data were then analyzed using various models of aggregation and obstruction. Both experimental and simulated data revealed that the diffusion of both water and the amino acids were sensitive to the amino acid concentration. The direct comparison of the simulated and experimental data afforded greater insights into the aggregation and obstruction properties of each amino acid.

  8. Contributions of Cell Metabolism and H+ Diffusion to the Acidic pH of Tumors1

    PubMed Central

    Schornack, Paul A; Gillies, Robert J

    2003-01-01

    Abstract The tumor microenvironment is hypoxic and acidic. These conditions have a significant impact on tumor progression and response to therapies. There is strong evidence that tumor hypoxia results from inefficient perfusion due to a chaotic vasculature. Consequently, some tumor regions are well oxygenated and others are hypoxic. It is commonly believed that hypoxic regions are acidic due to a stimulation of glycolysis through hypoxia, yet this is not yet demonstrated. The current study investigates the causes of tumor acidity by determining acid production rates and the mechanism of diffusion for H+ equivalents through model systems. Two breast cancer cell lines were investigated with divergent metabolic profiles: nonmetastatic MCF-7/s and highly metastatic MDA-mb-435 cells. Glycolysis and acid production are inhibited by oxygen in MCF-7/s cells, but not in MDA-mb-435 cells. Tumors of MDAmb-435 cells are significantly more acidic than are tumors of MCF-7/s cells, suggesting that tumor acidity is primarily caused by endogenous metabolism, and not the lack of oxygen. Metabolically produced protons are shown to diffuse in association with mobile buffers, in concordance with previous studies. The metabolic and diffusion data were analyzed using a reaction-diffusion model to demonstrate that the consequent pH profiles conform well to measured pH values for tumors of these two cell lines. PMID:12659686

  9. On the possibility of using short chain length mono-carboxylic acids for stabilization of magnetic fluids

    NASA Astrophysics Data System (ADS)

    Avdeev, Mikhail V.; Bica, Doina; Vékás, Ladislau; Marinica, Oana; Balasoiu, Maria; Aksenov, Victor L.; Rosta, László; Garamus, Vasil M.; Schreyer, Andreas

    2007-04-01

    Short chain length mono-carboxylic acids (lauric and myristic acids) are used to coat magnetite nanoparticles in non-polar organic liquids, which results in highly stable magnetic fluids. The new fluids are compared with classical organic fluids stabilized by oleic acid (OA). Magnetic granulometry and small-angle neutron scattering (polarized mode) reveal a great difference in the particle size distribution function for the studied magnetic fluids, particularly a decrease in the characteristic particle radius of magnetite when lauric and myristic acids are used instead of OA.

  10. Dissolution of acidic and basic compounds from the rotating disk: influence of convective diffusion and reaction.

    PubMed

    McNamara, D P; Amidon, G L

    1986-09-01

    A mass transfer model was developed to describe the dissolution and reaction of acidic and basic compounds from a rotating disk in unbuffered water. Dissolution of two carboxylic acids, 2-naphthoic acid (1) and naproxen [(+)-6-methoxy-alpha-methyl-2-naphthaleneacetic acid, 2], and the free base, papaverine (6,7-dimethoxy-1-veratrylisoquinoline, 3), in aqueous solutions (mu = 0.1 with KCI) at 25 degrees C were investigated. An automated dissolution apparatus, which consisted of microcomputer-controlled autoburets, was constructed to monitor and adjust the pH of the aqueous solutions during the experiments. Unique features of the mass transfer model include treatment of mass transfer as a convective diffusion process rather than a stagnant film diffusion only process; treatment of ionization and acid-base reactions as heterogeneous reactions; use of experimental diffusion coefficients for all species, particularly H+ and OH-; and application of boundary conditions that specify flux for surface ionization produced species. The model accurately predicted the dissolution rate assuming the solubility, pKa, and diffusion coefficient of the compound were independently known. The model also predicted pH at the solid-liquid surface, the flux of H+ from the surface, and the contribution of A- to the total acid flux as a function of bulk pH of the aqueous solution. PMID:3783452

  11. Determination of critical diameters for intrinsic carrier diffusion-length of GaN nanorods with cryo-scanning near-field optical microscopy

    PubMed Central

    Chen, Y. T.; Karlsson, K. F.; Birch, J.; Holtz, P. O.

    2016-01-01

    Direct measurements of carrier diffusion in GaN nanorods with a designed InGaN/GaN layer-in-a-wire structure by scanning near-field optical microscopy (SNOM) were performed at liquid-helium temperatures of 10 K. Without an applied voltage, intrinsic diffusion lengths of photo-excited carriers were measured as the diameters of the nanorods differ from 50 to 800 nm. The critical diameter of nanorods for carrier diffusion is concluded as 170 nm with a statistical approach. Photoluminescence spectra were acquired for different positions of the SNOM tip on the nanorod, corresponding to the origins of the well-defined luminescence peaks, each being related to recombination-centers. The phenomenon originated from surface oxide by direct comparison of two nanorods with similar diameters in a single map has been observed and investigated. PMID:26876009

  12. Parallel transport of an organic acid by solid-phase and macropore diffusion in a weakly basic ion exchanger

    SciTech Connect

    Yoshida, Hiroyuki; Takatsuji; Wataru

    2000-04-01

    The parallel transport of an organic acid by solid-phase and macropore diffusion within a porous ion exchanger was studied by measuring equilibrium isotherms and uptake curves for adsorption of acetic acid and lactic acid on a weakly basic ion exchanger, DIAION WA30. Experimental adsorption isotherms were correlated by the Langmuir equation. The Langmuir equilibrium constant of acetic acid was close to that of lactic acid, and the saturation capacity of acetic acid was about 84% that of lactic acid. Intraparticle effective diffusivity D{sub eff} was determined using the homogeneous Fickian diffusion model. The value of D{sub eff} for acetic acid was about 1.5 times lactic acid. Because D{sub eff} increased with linearly increasing bulk phase concentration C{sub 0}, D{sub eff} was separated to the solid-phase diffusivity D{sub s} and the macropore diffusivity D{sub P} by applying the parallel diffusion model. The model agreed well with the experimental curves. The values of D{sub S} and D{sub P} for acetic acid were about 2 and 1.5 times those of lactic acid, respectively. The acetic acid and the lactic acid may be separated by the difference of the diffusion rates.

  13. Diffusion dialysis. Effect of membrane composition on acid/salt separation

    SciTech Connect

    Narebska, A.; Warszawski, A. )

    1992-05-01

    Diffusion dialysis is an energy-saving separation technique. In order to highlight the relationship between membrane composition and ability to separate acid/salt mixtures by diffusion dialysis, a few anion-exchange membranes were examined. Experiments on solubility/diffusivity phenomena were carried out in contact with hydrochloric acid and sodium chloride solutions (single- and two-solute experiments). Computations using Glueckauf and Tye models have indicated high nonuniformity in the distribution of fixed charged within the membranes and different accessibilities of the internal membrane volumes for the acid and salt. The Neosepta AFN-7 membrane (Tokuymam Soda Co.) has proved effective in differentiating the permeants by sorption (k{sub HCl}/k{sub NaCl} {approx} 2) and diffusivity ({bar D}{sub HCl}/{bar D}{sub NaCl} up to 10). This membrane is also the only one which, when in contact with two-solutes solutions, absorbs the acid preferentially to the salt. For this membrane the preferential sorption and transport of the acid depends not only on the physical structure of the membrane but also on the chemical nature of the polymer which contains pyridine moieties.

  14. The Effect of Limited Diffusion and Wet-Dry Cycling on Reversible Polymerization Reactions: Implications for Prebiotic Synthesis of Nucleic Acids.

    PubMed

    Higgs, Paul G

    2016-01-01

    A long-standing problem for the origins of life is that polymerization of many biopolymers, including nucleic acids and peptides, is thermodynamically unfavourable in aqueous solution. If bond making and breaking is reversible, monomers and very short oligomers predominate. Recent experiments have shown that wetting and drying cycles can overcome this problem and drive the formation of longer polymers. In the dry phase, bond formation is favourable, but diffusion is restricted, and bonds only form between monomers that are initially close together. In the wet phase, some of the bonds are hydrolyzed. However, repositioning of the molecules allows new bonds to form in the next dry phase, leading to an increase in mean polymer length. Here, we consider a simple theoretical model that explains the effect of cycling. There is an equilibrium length distribution with a high mean length that could be achieved if diffusion occurred freely in the dry phase. This equilibrium is inaccessible without diffusion. A single dry cycle without diffusion leads to mean lengths much shorter than this. Repeated cycling leads to a significant increase in polymerization relative to a single cycle. In the most favourable case, cycling leads to the same equilibrium length distribution as would be achieved if free diffusion were possible in the dry phase. These results support the RNA World scenario by explaining a potential route to synthesis of long RNAs; however, they also imply that cycling would be beneficial to the synthesis of other kinds of polymers, including peptides, where bond formation involves a condensation reaction. PMID:27338479

  15. The Effect of Limited Diffusion and Wet–Dry Cycling on Reversible Polymerization Reactions: Implications for Prebiotic Synthesis of Nucleic Acids

    PubMed Central

    Higgs, Paul G.

    2016-01-01

    A long-standing problem for the origins of life is that polymerization of many biopolymers, including nucleic acids and peptides, is thermodynamically unfavourable in aqueous solution. If bond making and breaking is reversible, monomers and very short oligomers predominate. Recent experiments have shown that wetting and drying cycles can overcome this problem and drive the formation of longer polymers. In the dry phase, bond formation is favourable, but diffusion is restricted, and bonds only form between monomers that are initially close together. In the wet phase, some of the bonds are hydrolyzed. However, repositioning of the molecules allows new bonds to form in the next dry phase, leading to an increase in mean polymer length. Here, we consider a simple theoretical model that explains the effect of cycling. There is an equilibrium length distribution with a high mean length that could be achieved if diffusion occurred freely in the dry phase. This equilibrium is inaccessible without diffusion. A single dry cycle without diffusion leads to mean lengths much shorter than this. Repeated cycling leads to a significant increase in polymerization relative to a single cycle. In the most favourable case, cycling leads to the same equilibrium length distribution as would be achieved if free diffusion were possible in the dry phase. These results support the RNA World scenario by explaining a potential route to synthesis of long RNAs; however, they also imply that cycling would be beneficial to the synthesis of other kinds of polymers, including peptides, where bond formation involves a condensation reaction. PMID:27338479

  16. Detailed atomistic simulation of the nano-sorption and nano-diffusivity of water, tyrosol, vanillic acid, and p-coumaric acid in single wall carbon nanotubes.

    PubMed

    Anastassiou, Alexandros; Karahaliou, Elena K; Alexiadis, Orestis; Mavrantzas, Vlasis G

    2013-10-28

    We report results from a detailed computer simulation study for the nano-sorption and mobility of four different small molecules (water, tyrosol, vanillic acid, and p-coumaric acid) inside smooth single-wall carbon nanotubes (SWCNTs). Most of the results have been obtained with the molecular dynamics (MD) method, but especially for the most narrow of the CNTs considered, the results for one of the molecules addressed here (water) were further confirmed through an additional Grand Canonical (μVT) Monte Carlo (GCMC) simulation using a value for the water chemical potential μ pre-computed with the particle deletion method. Issues addressed include molecular packing and ordering inside the nanotube for the four molecules, average number of sorbed molecules per unit length of the tube, and mean residence time and effective axial diffusivities, all as a function of tube diameter and tube length. In all cases, a strong dependence of the results on tube diameter was observed, especially in the way the different molecules are packed and organized inside the CNT. For water for which predictions of properties such as local structure and packing were computed with both methods (MD and GCMC), the two sets of results were found to be fully self-consistent for all types of SWCNTs considered. Water diffusivity inside the CNT (although, strongly dependent on the CNT diameter) was computed with two different methods, both of which gave identical results. For large enough CNT diameters (larger than about 13 Å), this was found to be higher than the corresponding experimental value in the bulk by about 55%. Surprisingly enough, for the rest of the molecules simulated (phenolic), the simulations revealed no signs of mobility inside nanotubes with a diameter smaller than the (20, 20) tube. This is attributed to strong phenyl-phenyl attractive interactions, also to favorable interactions of these molecules with the CNT walls, which cause them to form highly ordered, very stable

  17. Detailed atomistic simulation of the nano-sorption and nano-diffusivity of water, tyrosol, vanillic acid, and p-coumaric acid in single wall carbon nanotubes

    NASA Astrophysics Data System (ADS)

    Anastassiou, Alexandros; Karahaliou, Elena K.; Alexiadis, Orestis; Mavrantzas, Vlasis G.

    2013-10-01

    We report results from a detailed computer simulation study for the nano-sorption and mobility of four different small molecules (water, tyrosol, vanillic acid, and p-coumaric acid) inside smooth single-wall carbon nanotubes (SWCNTs). Most of the results have been obtained with the molecular dynamics (MD) method, but especially for the most narrow of the CNTs considered, the results for one of the molecules addressed here (water) were further confirmed through an additional Grand Canonical (μVT) Monte Carlo (GCMC) simulation using a value for the water chemical potential μ pre-computed with the particle deletion method. Issues addressed include molecular packing and ordering inside the nanotube for the four molecules, average number of sorbed molecules per unit length of the tube, and mean residence time and effective axial diffusivities, all as a function of tube diameter and tube length. In all cases, a strong dependence of the results on tube diameter was observed, especially in the way the different molecules are packed and organized inside the CNT. For water for which predictions of properties such as local structure and packing were computed with both methods (MD and GCMC), the two sets of results were found to be fully self-consistent for all types of SWCNTs considered. Water diffusivity inside the CNT (although, strongly dependent on the CNT diameter) was computed with two different methods, both of which gave identical results. For large enough CNT diameters (larger than about 13 Å), this was found to be higher than the corresponding experimental value in the bulk by about 55%. Surprisingly enough, for the rest of the molecules simulated (phenolic), the simulations revealed no signs of mobility inside nanotubes with a diameter smaller than the (20, 20) tube. This is attributed to strong phenyl-phenyl attractive interactions, also to favorable interactions of these molecules with the CNT walls, which cause them to form highly ordered, very stable

  18. Acid back-diffusion and mucosal H+ handling in the rat stomach under normal and stress-induced conditions.

    PubMed

    Takeuchi, K; Okabe, S

    1983-02-01

    We determined acid back-diffusion and pepsin output simultaneously in vagotomized rats after instillation of HCl into the stomach under normal and stress-induced conditions. With exposure to 6 ml of 100 mM HCl, spontaneous acid back-diffusion increased with the duration of the experiment under both conditions, and the magnitude of the acid back-diffusion was decreased significantly by stress. There was no change in the output of pepsin. While disappearance of luminal acid caused by aspirin or taurocholic acid was not altered by stress, the pepsin output in response to H+ increased significantly in the stressed rats. With exposure to various concentrations of HCl for 3 hr, disappearance of the luminal acid increased linearly with the grade of HCl under both conditions. Except for the concentration of 300 mM, the magnitude of the acid back-diffusion was triple in the normal condition, and the ratio of pepsin output/net flux of H+ was significantly increased by stress. Thus, (1) spontaneous acid back-diffusion decreased with stress, while diffusion induced by chemical barrier breakers remained the same; (2) the action of H+ diffused back into the mucosa did not always parallel the amount of diffusion determined from the loss of H+ in the lumen; (3) intramucosal H+ may be largely dissipated in normal mucosa; and (4) the initiation or aggravation of drug-induced mucosal damages by stress may be related to insufficiency of the H+ dissipating mechanisms. PMID:6410110

  19. The importance of free fatty acid chain length for the skin barrier function in atopic eczema patients.

    PubMed

    van Smeden, Jeroen; Janssens, Michelle; Kaye, Edward C J; Caspers, Peter J; Lavrijsen, Adriana P; Vreeken, Rob J; Bouwstra, Joke A

    2014-01-01

    An important feature of atopic eczema (AE) is a decreased skin barrier function. The stratum corneum (SC) lipids - comprised of ceramides (CERs), free fatty acids (FFAs) and cholesterol - fulfil a predominant role in the skin barrier function. In this clinical study, the carbon chain length distribution of SC lipids (FFAs and CERs) and their importance for the lipid organization and skin barrier function were examined in AE patients and compared with control subjects. A reduction in FFA chain length and an increase in unsaturated FFAs are observed in non-lesional and lesional SC of AE patients. The reduction in FFA chain length associates with a reduced CER chain length, suggesting a common synthetic pathway. The lipid chain length reduction correlates with a less dense lipid organization and a decreased skin barrier function. All changes are more pronounced in lesional SC compared with non-lesional skin. No association was observed between lipid properties and filaggrin mutations, an important predisposing factor for developing AE. The results of this study demonstrate an altered SC lipid composition and signify the importance of these changes (specifically regarding the CER and FFA chain lengths) for the impaired skin barrier function in AE. This provides insights into epidermal lipid metabolism as well as new opportunities for skin barrier repair.

  20. Evaluation of the minority carrier diffusion length and surface-recombination velocity in GaAs p/n solar cells

    NASA Technical Reports Server (NTRS)

    Hakimzadeh, Roshanak; Moeller, Hans J.; Bailey, Sheila

    1991-01-01

    The minority carrier diffusion length (Lp) and the surface recombination velocity (Vs) were measured as a function of distance (x) from the p-n junction in GaAs p/n concentrator solar cells. The measured Vs values were used in a theoretical expression for the normalized electron-beam-induced current. A fitting procedure was then used to fit this expression with experimental values to obtain Lp. The results show that both Vs and Lp vary with x. Lp measured in irradiated cells showed a marked reduction. These values were compared to those measured previously which did not account for Vs.

  1. Penicillium chrysogenum Takes up the Penicillin G Precursor Phenylacetic Acid by Passive Diffusion

    PubMed Central

    Hillenga, D. J.; Versantvoort, H.; van der Molen, S.; Driessen, A.; Konings, W. N.

    1995-01-01

    Penicillium chrysogenum utilizes phenylacetic acid as a side chain precursor in penicillin G biosynthesis. During industrial production of penicillin G, phenylacetic acid is fed in small amounts to the medium to avoid toxic side effects. Phenylacetic acid is taken up from the medium and intracellularly coupled to 6-aminopenicillanic acid. To enter the fungal cell, phenylacetic acid has to pass the plasma membrane. The process via which phenylacetic acid crosses the plasma membrane was studied in mycelia and liposomes. Uptake of phenylacetic acid by mycelium was nonsaturable, and the initial velocity increased logarithmically with decreasing external pH. Studies with liposomes demonstrated a rapid passive flux of the protonated species through liposomal membranes. These results indicate that phenylacetic acid passes the plasma membrane via passive diffusion of the protonated species. The rate of phenylacetic acid uptake at an external concentration of 3 mM is at least 200-fold higher than the penicillin production rate in the Panlabs P2 strain. In this strain, uptake of phenylacetic acid is not the rate-limiting step in penicillin G biosynthesis. PMID:16535072

  2. A case of diffuse alveolar hemorrhage associated with hyaluronic acid dermal fillers

    PubMed Central

    Basora, Jose F.; Fernandez, Ricardo; Gonzalez, Modesto; Adorno, Jose

    2014-01-01

    Patient: Male, 25 Final Diagnosis: Diffuse alveolar hemorrhage Symptoms: Cough dry • short of breath Medication: — Clinical Procedure: — Specialty: — Objective: Unusual clinical course Background: Hyaluronic acid is a substance that is naturally present in the human body, especially in joints and eyes. Hyaluronic acid injectable gels have been available for the general market since 2003 as cosmetic dermal fillers and skin boosters. Diffuse alveolar hemorrhage is an acute event that threatens the life of the patient and can lead to pulmonary fibrosis. Alveolar hemorrhage associated with hyaluronic acid dermal fillers is an entity that to the best of our knowledge has never been described in the medical literature. Case Report: We describe a patient who presented with dyspnea and cough after a subcutaneous injection of hyaluronic acid, with radiographic abnormalities including ground glass opacities and consolidation. The patient underwent flexible bronchoscopy and was diagnosed with diffuse alveolar hemorrhage. Conclusions: This case emphasizes that this life threatening condition may occur with the use of this medication and physicians must be aware of this disorder, as early recognition and management can reduce morbidity. PMID:24826208

  3. Light-Induced Increase of Electron Diffusion Length in a p-n Junction Type CH3NH3PbBr3 Perovskite Solar Cell.

    PubMed

    Kedem, Nir; Brenner, Thomas M; Kulbak, Michael; Schaefer, Norbert; Levcenko, Sergiu; Levine, Igal; Abou-Ras, Daniel; Hodes, Gary; Cahen, David

    2015-07-01

    High band gap, high open-circuit voltage solar cells with methylammonium lead tribromide (MAPbBr3) perovskite absorbers are of interest for spectral splitting and photoelectrochemical applications, because of their good performance and ease of processing. The physical origin of high performance in these and similar perovskite-based devices remains only partially understood. Using cross-sectional electron-beam-induced current (EBIC) measurements, we find an increase in carrier diffusion length in MAPbBr3(Cl)-based solar cells upon low intensity (a few percent of 1 sun intensity) blue laser illumination. Comparing dark and illuminated conditions, the minority carrier (electron) diffusion length increases about 3.5 times from Ln = 100 ± 50 nm to 360 ± 22 nm. The EBIC cross section profile indicates a p-n structure between the n-FTO/TiO2 and p-perovskite, rather than the p-i-n structure, reported for the iodide derivative. On the basis of the variation in space-charge region width with varying bias, measured by EBIC and capacitance-voltage measurements, we estimate the net-doping concentration in MAPbBr3(Cl) to be 3-6 × 10(17) cm(-3).

  4. The chain length of biologically produced (R)-3-hydroxyalkanoic acid affects biological activity and structure of anti-cancer peptides.

    PubMed

    Szwej, Emilia; Devocelle, Marc; Kenny, Shane; Guzik, Maciej; O'Connor, Stephen; Nikodinovic-Runic, Jasmina; Radivojevic, Jelena; Maslak, Veselin; Byrne, Annete T; Gallagher, William M; Zulian, Qun Ren; Zinn, Manfred; O'Connor, Kevin E

    2015-06-20

    Conjugation of DP18L peptide with (R)-3-hydroxydecanoic acid, derived from the biopolymer polyhydroxyalkanoate, enhances its anti-cancer activity (O'Connor et al., 2013. Biomaterials 34, 2710-2718). However, it is unknown if other (R)-3-hydroxyalkanoic acids (R3HAs) can enhance peptide activity, if chain length affects enhancement, and what effect R3HAs have on peptide structure. Here we show that the degree of enhancement of peptide (DP18L) anti-cancer activity by R3HAs is carbon chain length dependent. In all but one example the R3HA conjugated peptides were more active against cancer cells than the unconjugated peptides. However, R3HAs with 9 and 10 carbons were most effective at improving DP18L activity. DP18L peptide variant DP17L, missing a hydrophobic amino acid (leucine residue 4) exhibited lower efficacy against MiaPaCa cells. Circular dichroism analysis showed DP17L had a lower alpha helix content and the conjugation of any R3HA ((R)-3-hydroxyhexanoic acid to (R)-3-hydroxydodecanoic acid) to DP17L returned the helix content back to levels of DP18L. However (R)-3-hydroxyhexanoic did not enhance the anti-cancer activity of DP17L and at least 7 carbons were needed in the R3HA to enhance activity of D17L. DP17L needs a longer chain R3HA to achieve the same activity as DP18L conjugated to an R3HA. As a first step to assess the synthetic potential of polyhydroxyalkanoate derived R3HAs, (R)-3-hydroxydecanoic acid was synthetically converted to (±)3-chlorodecanoic acid, which when conjugated to DP18L improved its antiproliferative activity against MiaPaCa cells.

  5. [Detection of erucic acid and glucosinolate in intact rapeseed by near-infrared diffuse reflectance spectroscopy].

    PubMed

    Riu, Yu-kui; Huang, Kun-lun; Wang, Wei-min; Guo, Jing; Jin, Yin-hua; Luo, Yun-bo

    2006-12-01

    With the rapid development of transgenic food, more and more transgenic food has been pouring into the market, raising great concern about transgenic food' s edible safety. To analyze the content of erucic acid and glucosinolate in transgenic rapeseed and its parents, all the seeds were scanned intact by continuous wave of near infrared diffuse reflectance spectrometry ranging from 12 000 to 4 000 cm(-1) with a resolution of 4 cm(-1) and 64 times of scanning. Bruker OPUS software package was applied for quantification, while the results were compared with the standard methods. The results showed that the method of NIRS was very precise, which proved that infrared diffuse reflectance spectroscopy can be applied to detect the toxins in transgenic food. On the other hand, the results also showed that the content of erucic acid in transgenic rapeseeds is 0. 5-1. 0 times

  6. A relation between the chain length of fatty acids and the slowing of gastric emptying

    PubMed Central

    Hunt, J. N.; Knox, M. T.

    1968-01-01

    1. Test meals of solutions and suspensions of potassium and sodium salts of a series of saturated fatty acids, from C2 to C18, were given to healthy subjects. 2. From the volume of these meals recovered after a fixed interval the relative effectiveness of the salts of the acids in slowing gastric emptying was assessed. 3. On a molar basis the salts of fatty acids from acetic up to decanoic were relatively ineffective in slowing gastric emptying. 4. The salts of fatty acids with 12-18 carbon atoms were much more effective than those with up to 10 carbon atoms. Myristate was the most effective of the salts. 5. Buffering the test meals with 33 mM sodium citrate increased the effectiveness of the salts in slowing gastric emptying. PMID:5639357

  7. Thermal effects on the diffusive layer convection instability of an exothermic acid-base reaction front.

    PubMed

    Almarcha, C; Trevelyan, P M J; Grosfils, P; De Wit, A

    2013-09-01

    A buoyancy-driven hydrodynamic instability appearing when an aqueous acid solution of HCl overlies a denser alkaline aqueous solution of NaOH in a vertically oriented Hele-Shaw cell is studied both experimentally and theoretically. The peculiarity of this reactive convection pattern is its asymmetry with regard to the initial contact line between the two solutions as convective plumes develop in the acidic solution only. We investigate here by a linear stability analysis (LSA) of a reaction-diffusion-convection model of a simple A+B→C reaction the relative role of solutal versus thermal effects in the origin and location of this instability. We show that heat effects are much weaker than concentration-related ones such that the heat of reaction only plays a minor role on the dynamics. Computation of density profiles and of the stability analysis eigenfunctions confirm that the convective motions result from a diffusive layer convection mechanism whereby a locally unstable density stratification develops in the upper acidic layer because of the difference in the diffusion coefficients of the chemical species. The growth rate and wavelength of the pattern are determined experimentally as a function of the Brinkman parameter of the problem and compare favorably with the theoretical predictions of both LSA and nonlinear simulations.

  8. Thermal effects on the diffusive layer convection instability of an exothermic acid-base reaction front

    NASA Astrophysics Data System (ADS)

    Almarcha, C.; Trevelyan, P. M. J.; Grosfils, P.; De Wit, A.

    2013-09-01

    A buoyancy-driven hydrodynamic instability appearing when an aqueous acid solution of HCl overlies a denser alkaline aqueous solution of NaOH in a vertically oriented Hele-Shaw cell is studied both experimentally and theoretically. The peculiarity of this reactive convection pattern is its asymmetry with regard to the initial contact line between the two solutions as convective plumes develop in the acidic solution only. We investigate here by a linear stability analysis (LSA) of a reaction-diffusion-convection model of a simple A+B→C reaction the relative role of solutal versus thermal effects in the origin and location of this instability. We show that heat effects are much weaker than concentration-related ones such that the heat of reaction only plays a minor role on the dynamics. Computation of density profiles and of the stability analysis eigenfunctions confirm that the convective motions result from a diffusive layer convection mechanism whereby a locally unstable density stratification develops in the upper acidic layer because of the difference in the diffusion coefficients of the chemical species. The growth rate and wavelength of the pattern are determined experimentally as a function of the Brinkman parameter of the problem and compare favorably with the theoretical predictions of both LSA and nonlinear simulations.

  9. Enhancing the catalytic repertoire of nucleic acids: a systematic study of linker length and rigidity

    PubMed Central

    Lee, Sarah E.; Sidorov, Alexander; Gourlain, Thierry; Mignet, Nathalie; Thorpe, Simon J.; Brazier, John A.; Dickman, Mark J.; Hornby, David P.; Grasby, Jane A.; Williams, David M.

    2001-01-01

    The incorporation of potentially catalytic groups in DNA is of interest for the in vitro selection of novel deoxyribozymes. A series of 10 C5-modified analogues of 2′-deoxyuridine triphosphate have been synthesised that possess side chains of differing flexibility and bearing a primary amino or imidazole functionality. For each series of nucleotide analogues differing degrees of flexibility of the C5 side chain was achieved through the use of alkynyl, alkenyl and alkyl moieties. The imidazole function was conjugated to these C5-amino-modified nucleotides using either imidazole 4-acetic acid or imidazole 4-acrylic acid (urocanic acid). The substrate properties of the nucleotides (fully replacing dTTP) with Taq polymerase during PCR have been investigated in order to evaluate their potential applications for in vitro selection experiments. 5-(3-Aminopropynyl)dUTP and 5-(E-3-aminopropenyl)dUTP and their imidazole 4-acetic acid- and urocanic acid-modified conjugates were found to be substrates. In contrast, C5-amino-modified dUTPs with alkane or Z-alkene linkers and their corresponding conjugates were not substrates. The incorporation of these analogues during PCR has been confirmed by inhibition of restriction enzyme digestion using XbaI and by mass spectrometry of the PCR products. PMID:11266559

  10. Effect of diffusion layer pH and solubility on the dissolution rate of pharmaceutical acids and their sodium salts. II: Salicylic acid, theophylline, and benzoic acid.

    PubMed

    Serajuddin, A T; Jarowski, C I

    1985-02-01

    The pH-solubility profiles of salicylic acid and theophylline, as determined by the addition of HCl or NaOH to their aqueous suspensions, were identical with those of their sodium salts except during phase transitions from acid to salt or vice versa. Supersaturated solutions were formed during phase transitions. Unlike the solubility profiles, the pH-intrinsic dissolution rate profiles of an acid and its salt differed greatly. Good conformity with the Noyes-Whitney equation was demonstrated when the solubility values under pH conditions as the diffusion layer thickness, h, approaches zero (Cs,h = 0) were used rather than solubilities under pH conditions of the bulk media (Cs). The pH when h approaches zero (pHh = 0) was estimated by equilibration of a dissolution medium with an excess of material. Good correlation was shown between the pHh = 0 values of benzoic acid estimated according to this method and the pHh = 0 values reported in the literature. The intrinsic dissolution rate constant, the ratio of the diffusion coefficient to the diffusion layer thickness (D/h), may be assumed constant when comparing the dissolution rates of salicylic acid, theophylline and sodium theophylline. On the other hand, D/h decreased significantly during dissolution of sodium salicylate due to a large increase in Cs,h = 0 and the consequent increase in viscosity in the diffusion layer. A simple method of predicting the dissolution rate of an acid or a salt at different pH values has been developed.

  11. Relation between acid back-diffusion and luminal surface hydrophobicity in canine gastric mucosa: Effects of salicylate and prostaglandin

    SciTech Connect

    Goddard, P.J.

    1989-01-01

    The stomach is thought to be protected from luminal acid by a gastric mucosal barrier that restricts the diffusion of acid into tissue. This study tested the hypothesis that the hydrophobic luminal surface of canine gastric mucosa incubated in Ussing chambers, impedes the back-diffusion of luminal acid into the tissue. Isolated sheets of mucosa were treated with cimetidine to inhibit spontaneous acid secretion, and incubated under conditions that prevented significant secretion of luminal bicarbonate. By measuring acid loss from the luminal compartment using the pH-stat technique, acid back-diffusion was continuously monitored; potential difference (PD) was measured as an index of tissue viability. Tissue luminal surface hydrophobicity was estimated by contact angle analysis at the end of each experiment. Addition of 16,16-dimethyl prostaglandin E{sub 2} to the nutrient compartment enhanced luminal surface hydrophobicity, but did not reduce acid back-diffusion in tissues that maintained a constant PD. 10 mM salicylate at pH 4.00 in the luminal compartment reduced surface hydrophobicity, but this decrease did not occur if 1 ug/ml prostaglandin was present in the nutrient solution. Despite possessing relatively hydrophilic and relatively hydrophobic surface properties, respectively, acid back-diffusion in the absence of salicylate was not significantly different between these two groups. Neither group maintained a PD after incubation with salicylate. Lastly, radiolabeled salicylate was used to calculate the free (non-salicylate associated) acid loss in tissues incubated with salicylate and/or prostaglandin. No significant correlation was found between free acid back-diffusion and luminal surface hydrophobicity. These data do not support the hypothesis that acid back-diffusion in impeded by the hydrophobic surface presented by isolated canine gastric mucosa.

  12. Nuclemeter: A Reaction-Diffusion Based Method for Quantifying Nucleic Acids Undergoing Enzymatic Amplification

    PubMed Central

    Liu, Changchun; Sadik, Mohamed M.; Mauk, Michael G.; Edelstein, Paul H.; Bushman, Frederic D.; Gross, Robert; Bau, Haim H.

    2014-01-01

    Real-time amplification and quantification of specific nucleic acid sequences plays a major role in medical and biotechnological applications. In the case of infectious diseases, such as HIV, quantification of the pathogen-load in patient specimens is critical to assess disease progression and effectiveness of drug therapy. Typically, nucleic acid quantification requires expensive instruments, such as real-time PCR machines, which are not appropriate for on-site use and for low-resource settings. This paper describes a simple, low-cost, reaction-diffusion based method for end-point quantification of target nucleic acids undergoing enzymatic amplification. The number of target molecules is inferred from the position of the reaction-diffusion front, analogous to reading temperature in a mercury thermometer. The method was tested for HIV viral load monitoring and performed on par with conventional benchtop methods. The proposed method is suitable for nucleic acid quantification at point of care, compatible with multiplexing and high-throughput processing, and can function instrument-free. PMID:25477046

  13. Direct measurement of the electronic spin diffusion length in a fully functional organic spin valve by low-energy muon spin rotation.

    PubMed

    Drew, A J; Hoppler, J; Schulz, L; Pratt, F L; Desai, P; Shakya, P; Kreouzis, T; Gillin, W P; Suter, A; Morley, N A; Malik, V K; Dubroka, A; Kim, K W; Bouyanfif, H; Bourqui, F; Bernhard, C; Scheuermann, R; Nieuwenhuys, G J; Prokscha, T; Morenzoni, E

    2009-02-01

    Electronic devices that use the spin degree of freedom hold unique prospects for future technology. The performance of these 'spintronic' devices relies heavily on the efficient transfer of spin polarization across different layers and interfaces. This complex transfer process depends on individual material properties and also, most importantly, on the structural and electronic properties of the interfaces between the different materials and defects that are common to real devices. Knowledge of these factors is especially important for the relatively new field of organic spintronics, where there is a severe lack of suitable experimental techniques that can yield depth-resolved information about the spin polarization of charge carriers within buried layers of real devices. Here, we present a new depth-resolved technique for measuring the spin polarization of current-injected electrons in an organic spin valve and find the temperature dependence of the measured spin diffusion length is correlated with the device magnetoresistance. PMID:19029892

  14. Adipose tissue fatty acid chain length and mono-unsaturation increases with obesity and insulin resistance

    PubMed Central

    Yew Tan, Chong; Virtue, Samuel; Murfitt, Steven; Robert, Lee D.; Phua, Yi Hui; Dale, Martin; Griffin, Julian L.; Tinahones, Francisco; Scherer, Philipp E.; Vidal-Puig, Antonio

    2015-01-01

    The non-essential fatty acids, C18:1n9, C16:0, C16:1n7, C18:0 and C18:1n7 account for over 75% of fatty acids in white adipose (WAT) triacylglycerol (TAG). The relative composition of these fatty acids (FA) is influenced by the desaturases, SCD1-4 and the elongase, ELOVL6. In knock-out models, loss of SCD1 or ELOVL6 results in reduced Δ9 desaturated and reduced 18-carbon non-essential FA respectively. Both Elovl6 KO and SCD1 KO mice exhibit improved insulin sensitivity. Here we describe the relationship between WAT TAG composition in obese mouse models and obese humans stratified for insulin resistance. In mouse models with increasing obesity and insulin resistance, there was an increase in scWAT Δ9 desaturated FAs (SCD ratio) and FAs with 18-carbons (Elovl6 ratio) in mice. Data from mouse models discordant for obesity and insulin resistance (AKT2 KO, Adiponectin aP2-transgenic), suggested that scWAT TAG Elovl6 ratio was associated with insulin sensitivity, whereas SCD1 ratio was associated with fat mass. In humans, a greater SCD1 and Elovl6 ratio was found in metabolically more harmful visceral adipose tissue when compared to subcutaneous adipose tissue. PMID:26679101

  15. Hexavalent uranium diffusion into soils from concentrated acidic and alkaline solutions

    SciTech Connect

    Tokunaga, Tetsu K.; Wan, Jiamin; Pena, Jasquelin; Sutton, Stephen R.; Newville, Matthew

    2004-03-29

    Uranium contamination of soils and sediments often originates from acidic or alkaline waste sources, with diffusion being a major transport mechanism. Measurements of U(VI) diffusion from initially pH 2 and pH 11 solutions into a slightly alkaline Altamont soil and a neutral Oak Ridge soil were obtained through monitoring uptake from boundary reservoirs and from U concentration profiles within soil columns. The soils provided pH buffering, resulting in diffusion at nearly constant pH. Micro x-ray absorption near edge structure spectra confirmed that U remained in U(VI) forms in all soils. Time trends of U(VI) depletion from reservoirs, and U(VI) concentration profiles within soil columns yielded K{sub d} values consistent with those determined in batch tests at similar concentrations ({approx} 1 mM), and much lower than values for sorption at much lower concentrations (nM to {mu}M). These results show that U(VI) transport at high concentrations can be relatively fast at non-neutral pH, with negligible surface diffusion, because of weak sorption.

  16. Sorption and diffusion of organic acids through clayrock: Comparison with inorganic anions

    NASA Astrophysics Data System (ADS)

    Dagnelie, R. V. H.; Descostes, M.; Pointeau, I.; Klein, J.; Grenut, B.; Radwan, J.; Lebeau, D.; Georgin, D.; Giffaut, E.

    2014-04-01

    Organic complexing species are known to affect radionuclide mobility in the environment. The migration behaviour of several organic ligands was evaluated in the context of a proposed French radioactive waste repository in the Callovo-Oxfordian clayrock formation (COx). This study focuses on four anthropogenic acids (ethylenediaminetetraacetate, isosaccharinate, phthalate, oxalate) that are used in the nuclear fuel cycle or that occur as hydrosoluble degradation products of waste materials. Batch sorption and diffusion experiments were performed with COx clayrock samples using 14C-labelled radiotracers. The observed effective diffusion coefficients were low (De ∼ 1-6 × 10-12 m2 s-1), an order of magnitude lower than that of tritiated water in the same material, and roughly the same as values for inorganic anions such as I-, Cl- and SO42-. The observed correlation of De with molecular mass, M-1/3, differs significantly from that observed for cations. The organic ligands displayed significant affinity for the COx clayrock, with distribution ratios measured in batch experiments, Rd = 1-30 L kg-1, which are much higher than usually observed for anionic species. While this result was confirmed by through-diffusion experiments, the Kd values obtained by fitting diffusion modelling were significantly lower than those measured in the batch experiments.

  17. Solute transport through fractured rock: Radial diffusion into the rock matrix with several geological layers for an arbitrary length decay chain

    NASA Astrophysics Data System (ADS)

    Mahmoudzadeh, Batoul; Liu, Longcheng; Moreno, Luis; Neretnieks, Ivars

    2016-05-01

    The paper presents a model development to derive a semi-analytical solution to describe reactive solute transport through a single channel in a fracture with cylindrical geometry. The model accounts for advection through the channel, radial diffusion into the adjacent heterogeneous rock matrix comprising different geological layers, adsorption on both the channel surface, and the geological layers of the rock matrix and radioactive decay chain. Not only an arbitrary-length decay chain, but also as many number of the rock matrix layers with different properties as observed in the field can be handled. The solution, which is analytical in the Laplace domain, is transformed back to the time domain numerically e.g. by use of de Hoog algorithm. The solution is verified against experimental data and analytical solutions of limiting cases of solute transport through porous media. More importantly, the relative importance and contribution of different processes on solute transport retardation in fractured rocks are investigated by simulating several cases of varying complexity. The simulation results are compared with those obtained from rectangular model with linear matrix diffusion. It is found that the impact of channel geometry on breakthrough curves increases markedly as the transport distance along the flow channel and away into the rock matrix increase. The effect of geometry is more pronounced for transport of a decay chain when the rock matrix consists of a porous altered layer.

  18. Differentiation of mixed lactic acid bacteria communities in beverage fermentations using targeted terminal restriction fragment length polymorphism.

    PubMed

    Bokulich, Nicholas A; Mills, David A

    2012-08-01

    Lactic acid bacteria (LAB) are an important group of bacteria in beer and wine fermentations both as beneficial organisms and as spoilage agents. However, sensitive, rapid, culture-independent methods for identification and community analyses of LAB in mixed-culture fermentations are limited. We developed a terminal restriction fragment length polymorphism (TRFLP)-based assay for the detection and identification of lactic acid bacteria and Bacilli during wine, beer, and food fermentations. This technique can sensitively discriminate most species of Lactobacillales, and most genera of Bacillales, in mixed culture, as indicated by both bioinformatic predictions and empirical observations. This method was tested on a range of beer and wine fermentations containing mixed LAB communities, demonstrating the efficacy of this technique for discriminating LAB in mixed culture. PMID:22475950

  19. Influence of alkyl chain length on calcium phosphate deposition onto titanium surfaces modified with alkylphosphonic acid monolayers.

    PubMed

    Wu, Jiang; Hirata, Isao; Zhao, Xianghui; Gao, Bo; Okazaki, Masayuki; Kato, Koichi

    2013-08-01

    Much attention has been paid to the modification of a titanium surface with an alkylphosphonic acid (PA)-based self-assembled monolayer (SAM) to accelerate hydroxyapatite (HA) deposition on the surface. In order to further accelerate the rate of HA deposition, we examined here the effect of alkyl chain length of SAMs on the formation of a HA layer. PAs with three different alkyl chain lengths (3, 6, and 16 methylene units) were used for the preparation of a SAM on titanium. The titanium specimens with monolayers were soaked in a simulated body fluid under physiological conditions for 4 weeks. The deposited substances were analyzed by scanning electron microscopy, X-ray photoelectron spectroscopy, and X-ray diffraction. These analyses revealed that the formation of PA SAMs accelerate the deposition of poorly crystallized HA, in an alkyl chain length-dependent manner. Among PAs studied here, PA containing a 16-carbon alkyl chain gave rise to the titanium surface most effective for the deposition of HA.

  20. Intake of small-to-medium-chain saturated fatty acids is associated with peripheral leukocyte telomere length in postmenopausal women.

    PubMed

    Song, Yan; You, Nai-Chieh Y; Song, Yiqing; Kang, Mo K; Hou, Lifang; Wallace, Robert; Eaton, Charles B; Tinker, Lesley F; Liu, Simin

    2013-06-01

    Dietary factors, including dietary fat, may affect the biological aging process, as reflected by the shortening of telomere length (TL), by affecting levels of oxidative stress and inflammatory responses. We examined the direct relations of total and types of dietary fats and fat-rich foods to peripheral leukocyte TL. In 4029 apparently healthy postmenopausal women who participated in the Women's Health Initiative, intakes of total fat, individual fatty acids, and fat-rich foods were assessed by a questionnaire. TL was measured by quantitative polymerase chain reaction. Intake of short-to-medium-chain saturated fatty acids (SMSFAs; aliphatic tails of ≤ 12 carbons) was inversely associated with TL. Compared with participants in other quartiles of SMSFA intake, women who were in the highest quartile (median: 1.29% of energy) had shorter TLs [mean: 4.00 kb (95% CI: 3.89, 4.11 kb)], whereas women in the lowest quartile of intake (median: 0.29% of energy) had longer TLs [mean: 4.13 kb (95% CI: 4.03, 4.24 kb); P-trend = 0.046]. Except for lauric acid, all other individual SMSFAs were inversely associated with TL (P < 0.05). In isoenergetic substitution models, the substitution of 1% of energy from SMSFAs with any other energy source was associated with 119 bp longer TLs (95% CI: 21, 216 bp). Intakes of nonskim milk, butter, and whole-milk cheese (major sources of SMSFAs) were all inversely associated with TL. No significant associations were found with long-chain saturated fatty acids, monounsaturated fatty acids, and polyunsaturated fatty acids. In conclusion, we found that higher intakes of SMSFAs and SMSFA-rich foods were associated with shorter peripheral leukocyte TL among postmenopausal women. These findings suggest the potential roles of SMSFAs in the rate of biological aging.

  1. Extending the Diffuse Layer Model of Surface Acidity Constant Behavior: IV. Diffuse Layer Charge/Potential Relationships

    EPA Science Inventory

    Most current electrostatic surface complexation models describing ionic binding at the particle/water interface rely on the use of Poisson - Boltzmann (PB) theory for relating diffuse layer charge densities to diffuse layer electrostatic potentials. PB theory is known to contain ...

  2. Imbalance in fatty-acid-chain length of gangliosides triggers Alzheimer amyloid deposition in the precuneus.

    PubMed

    Oikawa, Naoto; Matsubara, Teruhiko; Fukuda, Ryoto; Yasumori, Hanaki; Hatsuta, Hiroyuki; Murayama, Shigeo; Sato, Toshinori; Suzuki, Akemi; Yanagisawa, Katsuhiko

    2015-01-01

    Amyloid deposition, a crucial event of Alzheimer's disease (AD), emerges in distinct brain regions. A key question is what triggers the assembly of the monomeric amyloid ß-protein (Aß) into fibrils in the regions. On the basis of our previous findings that gangliosides facilitate the initiation of Aß assembly at presynaptic neuritic terminals, we investigated how lipids, including gangliosides, cholesterol and sphingomyelin, extracted from synaptic plasma membranes (SPMs) isolated from autopsy brains were involved in the Aß assembly. We focused on two regions of the cerebral cortex; precuneus and calcarine cortex, one of the most vulnerable and one of the most resistant regions to amyloid deposition, respectively. Here, we show that lipids extracted from SPMs isolated from the amyloid-bearing precuneus, but neither the amyloid-free precuneus nor the calcarine cortex, markedly accelerate the Aß assembly in vitro. Through liquid chromatography-mass spectrometry of the lipids, we identified an increase in the ratio of the level of GD1b-ganglioside containing C20:0 fatty acid to that containing C18:0 as a cause of the enhanced Aß assembly in the precuneus. Our results suggest that the local glycolipid environment play a critical role in the initiation of Alzheimer amyloid deposition.

  3. Imbalance in Fatty-Acid-Chain Length of Gangliosides Triggers Alzheimer Amyloid Deposition in the Precuneus

    PubMed Central

    Oikawa, Naoto; Matsubara, Teruhiko; Fukuda, Ryoto; Yasumori, Hanaki; Hatsuta, Hiroyuki; Murayama, Shigeo; Sato, Toshinori; Suzuki, Akemi; Yanagisawa, Katsuhiko

    2015-01-01

    Amyloid deposition, a crucial event of Alzheimer’s disease (AD), emerges in distinct brain regions. A key question is what triggers the assembly of the monomeric amyloid ß-protein (Aß) into fibrils in the regions. On the basis of our previous findings that gangliosides facilitate the initiation of Aß assembly at presynaptic neuritic terminals, we investigated how lipids, including gangliosides, cholesterol and sphingomyelin, extracted from synaptic plasma membranes (SPMs) isolated from autopsy brains were involved in the Aß assembly. We focused on two regions of the cerebral cortex; precuneus and calcarine cortex, one of the most vulnerable and one of the most resistant regions to amyloid deposition, respectively. Here, we show that lipids extracted from SPMs isolated from the amyloid-bearing precuneus, but neither the amyloid-free precuneus nor the calcarine cortex, markedly accelerate the Aß assembly in vitro. Through liquid chromatography-mass spectrometry of the lipids, we identified an increase in the ratio of the level of GD1b-ganglioside containing C20:0 fatty acid to that containing C18:0 as a cause of the enhanced Aß assembly in the precuneus. Our results suggest that the local glycolipid environment play a critical role in the initiation of Alzheimer amyloid deposition. PMID:25798597

  4. Pectin functionalised by fatty acids: Diffuse reflectance infrared Fourier transform (DRIFT) spectroscopic characterisation

    NASA Astrophysics Data System (ADS)

    Kamnev, Alexander A.; Calce, Enrica; Tarantilis, Petros A.; Tugarova, Anna V.; De Luca, Stefania

    2015-01-01

    Chemically modified pectin derivatives obtained by partial esterification of its hydroxyl moieties with fatty acids (FA; oleic, linoleic and palmitic acids), as well as the initial apple peel pectin were comparatively characterised using diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy. Characteristic changes observed in DRIFT spectra in going from pectin to its FA esters are related to the corresponding chemical modifications. Comparing the DRIFT spectra with some reported data on FTIR spectra of the same materials measured in KBr or NaCl matrices has revealed noticeable shifts of several polar functional groups both in pectin and in its FA-esterified products induced by the halide salts. The results obtained have implications for careful structural analyses of biopolymers with hydrophilic functional groups by means of different FTIR spectroscopic methodologies.

  5. Effects of L-glutamine on acetylsalycylic acid induced gastric lesions and acid back diffusion in dogs.

    PubMed

    Hung, C R; Takeuchi, K; Okabe, S; Murata, T; Takagi, K

    1976-12-01

    Effects of L-glutamine on acetylsalicylic acid (ASA)-induced gastric mucosal lesions were studied in mongrel dogs. It was confirmed that when oral ASA at 1.0 or 2.0 g per dog is given in two divided doses, there is severe and consistent dose-dependent mucosal damage in the glandular portion of the stomach in fasted dogs. However, when L-glutamine 2.0 or 4.0 g per dog in two divided doses is given concomitantly with ASA 2.0 g per dog orally, the gastric irritation is significantly inhibited. Instillation of 20 mM of ASA in 100 mM HCl solution into the Heidenhain pouch of Beagle dogs produced a significant loss of H+ from the pouch and a gain of Na+ in the lumen compared with ASA-free controls. When L-glutamine (100 mM) was given concomitantly with ASA (20 mM) into the pouch, changes of electrolyte fluxes in response to ASA alone were significantly suppressed. However, 50 mM of L-glutamine had no appreciable effect on acid back diffusion caused by ASA 20 mM. The amino acid itself had little effect on the ionic movement in the pouch. Gross bleeding from the pouch treated with ASA was never observed with the concomitant dosing of ASA and L-glutamine 50 or 100 mM. PMID:15154

  6. Quantifying diffuse and point inputs of perfluoroalkyl acids in a nonindustrial river catchment.

    PubMed

    Müller, Claudia E; Spiess, Nora; Gerecke, Andreas C; Scheringer, Martin; Hungerbühler, Konrad

    2011-12-01

    Recently, the role of diffuse inputs of perfluoroalkyl acids (PFAAs) into surface waters has been investigated. It has been observed that river loads increased during rain and that street runoff contained considerable loads of PFAAs. This study aims at quantifying these diffuse inputs and identifying the initial sources in a small nonindustrial river catchment. The river was sampled in three distinct subcatchments (rural, urban, and wastewater treatment plant) at high temporal resolution during two rain events and samples were analyzed for perfluorocarboxylates and perfluorosulfonates. Additionally, rain, stormwater runoff, wastewater effluent, and drinking water were sampled. PFAA concentrations in river water were all low (e.g., < 10 ng/L for perfluorooctanoate, PFOA), but increased during rainfall. PFAA concentrations and water discharge data were integrated into a mass balance assessment that shows that 30-60% of PFAA loads can be attributed to diffuse inputs. Rain contributed 10-50% of the overall loads, mobilization of dry deposition and outdoor release of PFAA from products with 20-60%. We estimated that within a year 2.5-5 g of PFOA originating from rain and surface runoff are emitted into this small catchment (6 km(2), 12,500 persons).

  7. Quantifying diffuse and point inputs of perfluoroalkyl acids in a nonindustrial river catchment.

    PubMed

    Müller, Claudia E; Spiess, Nora; Gerecke, Andreas C; Scheringer, Martin; Hungerbühler, Konrad

    2011-12-01

    Recently, the role of diffuse inputs of perfluoroalkyl acids (PFAAs) into surface waters has been investigated. It has been observed that river loads increased during rain and that street runoff contained considerable loads of PFAAs. This study aims at quantifying these diffuse inputs and identifying the initial sources in a small nonindustrial river catchment. The river was sampled in three distinct subcatchments (rural, urban, and wastewater treatment plant) at high temporal resolution during two rain events and samples were analyzed for perfluorocarboxylates and perfluorosulfonates. Additionally, rain, stormwater runoff, wastewater effluent, and drinking water were sampled. PFAA concentrations in river water were all low (e.g., < 10 ng/L for perfluorooctanoate, PFOA), but increased during rainfall. PFAA concentrations and water discharge data were integrated into a mass balance assessment that shows that 30-60% of PFAA loads can be attributed to diffuse inputs. Rain contributed 10-50% of the overall loads, mobilization of dry deposition and outdoor release of PFAA from products with 20-60%. We estimated that within a year 2.5-5 g of PFOA originating from rain and surface runoff are emitted into this small catchment (6 km(2), 12,500 persons). PMID:22035097

  8. Increase in the diffusion length of minority carriers in Al{sub x}Ga{sub 1–x}N alloys ({sub x} = 0–0.1) fabricated by ammonia molecular beam epitaxy

    SciTech Connect

    Malin, T. V. Gilinsky, A. M.; Mansurov, V. G.; Protasov, D. Yu.; Kozhuhov, A. S.; Yakimov, E. B.; Zhuravlev, K. S.

    2015-10-15

    The room-temperature diffusion length of minority carriers in n-Al{sub 0.1}Ga{sub 0.9}N layers grown by ammonia molecular beam epitaxy on sapphire (0001) substrates used in structures for ultraviolet photodetectors is studied. Measurements were performed using the spectral dependence of the photocurrent recorded in a built-in p–n junction for thin samples and using the induced electron-current procedure for films up to 2 µm thick. The results show that the hole diffusion length in n-AlGaN films is 120–150 nm, which is larger than in GaN films grown under similar growth conditions by a factor of 3–4. This result can be associated with the larger lateral sizes characteristic of hexagonal columns in AlGaN layers grown by molecular beam epitaxy. No increase in the hole diffusion length is observed for thicker films.

  9. Nuclemeter: A Reaction-Diffusion Column for Quantifying Nucleic Acids Undergoing Enzymatic Amplification

    NASA Astrophysics Data System (ADS)

    Bau, Haim; Liu, Changchun; Killawala, Chitvan; Sadik, Mohamed; Mauk, Michael

    2014-11-01

    Real-time amplification and quantification of specific nucleic acid sequences plays a major role in many medical and biotechnological applications. In the case of infectious diseases, quantification of the pathogen-load in patient specimens is critical to assessing disease progression, effectiveness of drug therapy, and emergence of drug-resistance. Typically, nucleic acid quantification requires sophisticated and expensive instruments, such as real-time PCR machines, which are not appropriate for on-site use and for low resource settings. We describe a simple, low-cost, reactiondiffusion based method for end-point quantification of target nucleic acids undergoing enzymatic amplification. The number of target molecules is inferred from the position of the reaction-diffusion front, analogous to reading temperature in a mercury thermometer. We model the process with the Fisher Kolmogoroff Petrovskii Piscounoff (FKPP) Equation and compare theoretical predictions with experimental observations. The proposed method is suitable for nucleic acid quantification at the point of care, compatible with multiplexing and high-throughput processing, and can function instrument-free. C.L. was supported by NIH/NIAID K25AI099160; M.S. was supported by the Pennsylvania Ben Franklin Technology Development Authority; C.K. and H.B. were funded, in part, by NIH/NIAID 1R41AI104418-01A1.

  10. A novel diffusion-biphasic hydrolysis coupled kinetic model for dilute sulfuric acid pretreatment of corn stover.

    PubMed

    Chen, Longjian; Zhang, Haiyan; Li, Junbao; Lu, Minsheng; Guo, Xiaomiao; Han, Lujia

    2015-02-01

    Kinetic experiments on the dilute sulfuric acid pretreatment of corn stover were performed. A high xylan removal and a low inhibitor concentration were achieved by acid pretreatment. A novel diffusion-hydrolysis coupled kinetic model was proposed. The contribution to the xylose yield was analyzed by the kinetic model. Compared with the inhibitor furfural negatively affecting xylose yield, the fast and slow-hydrolyzing xylan significantly contributed to the xylose yield, however, their dominant roles were dependent on reaction temperature and time. The impact of particle size and acid concentration on the xylose yield were also investigated. The diffusion process may significantly influence the hydrolysis of large particles. Increasing the acid concentration from 0.15 M to 0.30 M significantly improved the xylose yield, whereas the extent of improvement decreased to near-quantitative when further increasing acid loading. These findings shed some light on the mechanism for dilute sulfuric acid hydrolysis of corn stover.

  11. Effect of alkyl chain length on the rotational diffusion of nonpolar and ionic solutes in 1-alkyl-3-methylimidazolium-bis(trifluoromethylsulfonyl)imides.

    PubMed

    Gangamallaiah, V; Dutt, G B

    2013-10-10

    Rotational diffusion of a nonpolar solute 9-phenylanthracene (9-PA) and a cationic solute rhodamine 110 (R110) has been examined in a series of 1-alkyl-3-methylimidazolium (alkyl = octyl, decyl, dodecyl, tetradecyl, hexadecyl, and octadecyl) bis(trifluoromethylsulfonyl)imides to understand the influence of alkyl chain length on solute rotation. In this study, reorientation times (τr) have been measured as a function of viscosity (η) by varying the temperature (T) of the solvents. These results have been analyzed using the Stokes-Einstein-Debye (SED) hydrodynamic theory along with the ones obtained for the same solutes in 1-alkyl-3-methylimidazolium (alkyl = methyl, ethyl, propyl, butyl, and hexyl) bis(trifluoromethylsulfonyl)imides (Gangamallaiah and Dutt, J. Phys. Chem. B 2012, 116, 12819-12825). It has been noticed that the data for 9-PA and R110 follows the relation τr = A(η/T)(n) with A being the ratio of hydrodynamic volume of the solute to the Boltzmann constant and n = 1 as envisaged by the SED theory. However, upon increasing the alkyl chain length from methyl to octadecyl significant deviations from the SED theory have been observed especially from the octyl derivative onward. From methyl to octadecyl derivatives, the value of A decreases by a factor of 3 for both the solutes and n by a factor of 1.4 and 1.6 for 9-PA and R110, respectively. These observations have been rationalized by taking into consideration the organized structure of the ionic liquids, whose influence appears to be pronounced when the number of carbon atoms in the alkyl chain attached to the imidazolium cation exceeds eight.

  12. Formulation of oil-in-water β-carotene microemulsions: effect of oil type and fatty acid chain length.

    PubMed

    Roohinejad, Shahin; Oey, Indrawati; Wen, Jingyuan; Lee, Sung Je; Everett, David W; Burritt, David J

    2015-05-01

    The impact of oil type and fatty acid chain length on the development of food-grade microemulsions for the entrapment of β-carotene was investigated. The microemulsion region of a ternary phase diagram containing short chain monoglycerides was larger than for di- and triglycerides when Tween 80 was used as surfactant. The cytotoxicity of microemulsions composed of a 30% monoglyceride oil, 20% Tween 80 and 50% aqueous buffer were evaluated using an in vitro cell culture model (human epithelial colorectal adenocarcinoma, Caco-2). The cytotoxicity test showed that the viability of Caco-2 cells against β-carotene microemulsions at concentrations of 0.03125% (v/v) was higher than 90%. This study suggests that short chain monoglycerides could be used with Tween 80 to prepare transparent β-carotene-encapsulated O/W microemulsions in the particle size range of 12-100 nm. PMID:25529680

  13. Translational and rotational diffusion of flexible PEG and rigid dendrimer probes in sodium caseinate dispersions and acid gels.

    PubMed

    Salami, Souad; Rondeau-Mouro, Corinne; Barhoum, Myriam; van Duynhoven, John; Mariette, François

    2014-09-01

    The dynamics of rigid dendrimer and flexible PEG probes in sodium caseinate dispersions and acid gels, including both translational diffusion and rotational diffusion, were studied by NMR. Above the onset of the close-packing limit (C ∼ 10 g/100 g H2 O), translational diffusion of the probe depended on its flexibility and on the fluctuations of the matrix chains. The PEG probe diffused more rapidly than the spherical dendrimer probe of corresponding hydrodynamic radius. The greater conformational flexibility of PEG facilitated its motion through the crowded casein matrix. Rotational diffusion was, however, substantially less hindered than the translational diffusion and depended on the local protein-probe friction which became high when the casein concentration increased. The coagulation of the matrix led to the formation of large voids, which resulted in an increase in the translational diffusion of the probes, whereas the rotational diffusion of the probes was retarded in the gel, which could be attributed to the immobilized environment surrounding the probe. Quantitative information from PFG-NMR and SEM micrographs have been combined for characterizing microstructural details in SC acid gels.

  14. Dependence of buffer acidity and surfactant chain-length on electro-osmotic mobility in thermoplastic microchannels.

    PubMed

    Wang, Shau-Chun; Lee, Chia-Yu; Chen, Hsiao-Ping

    2005-04-15

    In this paper, we report the dependence of buffer pH and coating surfactant chain-length on electro-osmotic (EO) mobility in co-polyester microchannels. Thermoplastics co-polyester hydrolyzes to anionic functionality to create electrical double layer on the micro-channel walls. These negatively charged sites are partially or completely screened when long-chain surfactants are added into the buffer. This ancillary technique to modify surface charge polarity to avoid analyte adsorption is known as dynamic coating. We develop a theory to predict the EO mobility tendency on buffer acidity considering the combination of pH-dependent surfactant aggregation and surface dissociation. Our findings of pH-dependent EO mobility in coated channels, using three types of quaternary ammonium surfactants, lauryltrimethyammonium bromide (LTAB), trimethyl (tetradecyl) ammonium bromide (TTAB), and cetyltrimethyammonium bromide (CTAB), agree with our theoretical prediction. We also explain the chain-length dependence of mobility with a collaborative adsorption mechanism of surfactant aggregates.

  15. Minority-carrier diffusion length, minority-carrier lifetime, and photoresponsivity of β-FeSi2 layers grown by molecular-beam epitaxy

    NASA Astrophysics Data System (ADS)

    Akutsu, Keiichi; Kawakami, Hideki; Suzuno, Mitsushi; Yaguchi, Takashi; Jiptner, Karolin; Chen, Jun; Sekiguchi, Takashi; Ootsuka, Teruhisa; Suemasu, Takashi

    2011-06-01

    We have epitaxially grown undoped β-FeSi2 films on Si(111) substrates via atomic-hydrogen-assisted molecular-beam epitaxy. β-FeSi2 films grown without atomic hydrogen exhibited p-type conduction with a hole density of over 1019 cm-3 at room temperature (RT). In contrast, those prepared with atomic hydrogen showed n-type conduction and had a residual electron density that was more than two orders of magnitude lower than the hole density of films grown without atomic hydrogen (of the order of 1016 cm-3 at RT). The minority-carrier diffusion length was estimated to be approximately 16 μm using an electron-beam-induced current technique; this value is twice as large as that for β-FeSi2 prepared without atomic hydrogen. This result could be well explained in terms of the minority-carrier lifetimes measured by a microwave photoconductance decay technique. The 1/e decay time using a 904 nm laser pulse was approximately 17 μs, which is much longer than that for β-FeSi2 prepared without atomic hydrogen (3 μs). The photoresponsivity reached 13 mA/W at 1.31 μm, which is the highest value ever reported for β-FeSi2 films.

  16. Minority-carrier diffusion length, minority-carrier lifetime, and photoresponsivity of {beta}-FeSi{sub 2} layers grown by molecular-beam epitaxy

    SciTech Connect

    Akutsu, Keiichi; Kawakami, Hideki; Suzuno, Mitsushi; Yaguchi, Takashi; Jiptner, Karolin; Chen, Jun; Sekiguchi, Takashi; Ootsuka, Teruhisa; Suemasu, Takashi

    2011-06-15

    We have epitaxially grown undoped {beta}-FeSi{sub 2} films on Si(111) substrates via atomic-hydrogen-assisted molecular-beam epitaxy. {beta}-FeSi{sub 2} films grown without atomic hydrogen exhibited p-type conduction with a hole density of over 10{sup 19} cm{sup -3} at room temperature (RT). In contrast, those prepared with atomic hydrogen showed n-type conduction and had a residual electron density that was more than two orders of magnitude lower than the hole density of films grown without atomic hydrogen (of the order of 10{sup 16} cm{sup -3} at RT). The minority-carrier diffusion length was estimated to be approximately 16 {mu}m using an electron-beam-induced current technique; this value is twice as large as that for {beta}-FeSi{sub 2} prepared without atomic hydrogen. This result could be well explained in terms of the minority-carrier lifetimes measured by a microwave photoconductance decay technique. The 1/e decay time using a 904 nm laser pulse was approximately 17 {mu}s, which is much longer than that for {beta}-FeSi{sub 2} prepared without atomic hydrogen (3 {mu}s). The photoresponsivity reached 13 mA/W at 1.31 {mu}m, which is the highest value ever reported for {beta}-FeSi{sub 2} films.

  17. Lactic acid bacterial population dynamics during fermentation and storage of Thai fermented sausage according to restriction fragment length polymorphism analysis.

    PubMed

    Wanangkarn, Amornrat; Liu, Deng-Cheng; Swetwiwathana, Adisorn; Jindaprasert, Aphacha; Phraephaisarn, Chirapiphat; Chumnqoen, Wanwisa; Tan, Fa-Jui

    2014-09-01

    This study applied restriction fragment length polymorphism (RFLP) analysis to identify the lactic acid bacteria (LAB) isolated from "mum" Thai fermented sausages during fermentation and storage. A total of 630 lactic acid bacteria were isolated from the sausages prepared using 2 methods. In Method 1, after stuffing, the sausages were stored at 30 °C for 14 days. In Method 2, after stuffing and storage at 30 °C for 3 days, the sausages were vacuum-packed and stored at 4 °C until Day 28. The sausages were sampled on Days 0, 3, 14, and 28 for analyses. The 16S rDNA was amplified and digested using restriction enzymes. Of the restriction enzymes evaluated, Dde I displayed the highest discrimination capacity. The LAB were classified and 7 species were identified For Methods 1 and 2, during fermentation, the Lactobacillus sakei and Lactobacillus plantarum species were dominant. For Method 2, the proportion of Leuconostoc mesenteroides markedly increased during storage, until L. sakei and Ln. mesenteroides represented the dominant species. The identification of LAB in the sausage samples could facilitate the selection of appropriate microorganisms for candidate starter cultures for future controlled mum production.

  18. Diffuse alveolar hemorrhage: retrospective review of clinical outcome in allogeneic transplant recipients treated with aminocaproic acid.

    PubMed

    Wanko, Sam O; Broadwater, Gloria; Folz, Rodney J; Chao, Nelson J

    2006-09-01

    Diffuse alveolar hemorrhage (DAH) after allogeneic hematopoietic stem cell transplantation (HSCT) is often fatal. Standard therapy with high-dose corticosteroid is not always effective. There is paucity of data in the literature about other potentially useful agents, such as aminocaproic acid (Amicar) in the post-transplantation setting. We retrospectively reviewed our data on 115 consecutive patients who underwent HSCT and had pulmonary complications, with the aim of determining the overall clinical outcome in recipients of allogeneic transplants and in the subgroup of these patients who were treated with concomitant Solu-Medrol and aminocaproic acid. Aminocaproic acid was added at the discretion of the attending physician. We identified 14 allogeneic transplant recipients (median age, 41 years) with 15 episodes of DAH who were treated with Solu-Medrol (250 mg to 1 g intravenously per day). Of these, 8 patients also received concomitant aminocaproic acid at 1000 mg intravenously every 6 hours. Failure to improve was the most common reason for adding aminocaproic acid. The incidence of DAH was 12.2% (10.3% in myeloablative versus 1.9% in nonmyeloablative recipients). The overall 100-day DAH mortality and median transplantation survival were 60% and 99 days, respectively. Among the subset of patients treated with the combination of Solu-Medrol and aminocaproic acid, we observed a 100-day DAH mortality and median transplantation survival of 44% and 167 days, respectively, compared with 83% and 96.5 days in those treated with Solu-Medrol alone. The median time to DAH was 40.5 days, and the median time to death was 53 days in the combined treatment group compared with 29.5 days in those treated with steroid alone. There were no significant differences in coagulation parameters between subsets. Infections (yeast, respiratory syncytial virus, herpes simplex virus, and parainfluenza) were isolated and treated from 6 diagnostic bronchial alveolar lavage samples and were

  19. Electron-hole diffusion lengths >175 μm in solution-grown CH3NH3PbI3 single crystals

    SciTech Connect

    Dong, Qingfeng; Fang, Yanjun; Shao, Yuchuan; Mulligan, Padhraic; Qiu, Jie; Cao, Lei; Huang, Jinsong

    2015-02-27

    Long, balanced electron and hole diffusion lengths greater than 100 nanometers in the polycrystalline organolead trihalide compound CH3NH3PbI3 are critical for highly efficient perovskite solar cells. We found that the diffusion lengths in CH3NH3PbI3 single crystals grown by a solution-growth method can exceed 175 micrometers under 1 sun (100 mW cm–2) illumination and exceed 3 millimeters under weak light for both electrons and holes. The internal quantum efficiencies approach 100% in 3-millimeter-thick single-crystal perovskite solar cells under weak light. These long diffusion lengths result from greater carrier mobility, longer lifetime, and much smaller trap densities in the single crystals than in polycrystalline thin films. As a result, the long carrier diffusion lengths enabled the use of CH3NH3PbI3 in radiation sensing and energy harvesting through the gammavoltaic effect, with an efficiency of 3.9% measured with an intense cesium-137 source.

  20. Gas diffusion electrode setup for catalyst testing in concentrated phosphoric acid at elevated temperatures

    SciTech Connect

    Wiberg, Gustav K. H. E-mail: m.arenz@chem.ku.dk; Fleige, Michael; Arenz, Matthias E-mail: m.arenz@chem.ku.dk

    2015-02-15

    We present a detailed description of the construction and testing of an electrochemical cell setup allowing the investigation of a gas diffusion electrode containing carbon supported high surface area catalysts. The setup is designed for measurements in concentrated phosphoric acid at elevated temperature, i.e., very close to the actual conditions in high temperature proton exchange membrane fuel cells (HT-PEMFCs). The cell consists of a stainless steel flow field and a PEEK plastic cell body comprising the electrochemical cell, which exhibits a three electrode configuration. The cell body and flow field are braced using a KF-25 vacuum flange clamp, which allows an easy assembly of the setup. As demonstrated, the setup can be used to investigate temperature dependent electrochemical processes on high surface area type electrocatalysts, but it also enables quick screening tests of HT-PEMFC catalysts under realistic conditions.

  1. Gambogic acid induces apoptosis in diffuse large B-cell lymphoma cells via inducing proteasome inhibition

    PubMed Central

    Shi, Xianping; Lan, Xiaoying; Chen, Xin; Zhao, Chong; Li, Xiaofen; Liu, Shouting; Huang, Hongbiao; Liu, Ningning; Zang, Dan; Liao, Yuning; Zhang, Peiquan; Wang, Xuejun; Liu, Jinbao

    2015-01-01

    Resistance to chemotherapy is a great challenge to improving the survival of patients with diffuse large B-cell lymphoma (DLBCL), especially those with activated B-cell-like DLBCL (ABC-DLBCL). Therefore it is urgent to search for novel agents for the treatment of DLBCL. Gambogic acid (GA), a small molecule derived from Chinese herb gamboges, has been approved for Phase II clinical trial for cancer therapy by Chinese FDA. In the present study, we investigated the effect of GA on cell survival and apoptosis in DLBCL cells including both GCB- and ABC-DLBCL cells. We found that GA induced growth inhibition and apoptosis of both GCB- and ABC-DLBCL cells in vitro and in vivo, which is associated with proteasome malfunction. These findings provide significant pre-clinical evidence for potential usage of GA in DLBCL therapy particularly in ABC-DLBCL treatment. PMID:25853502

  2. Use of weak acids to determine the bulk diffusion limitation of H+ ion conductance through the gramicidin channel.

    PubMed Central

    Decker, E R; Levitt, D G

    1988-01-01

    The addition of 2 M formic acid at pH 3.75 increased the single channel H+ ion conductance of gramicidin channels 12-fold at 200 mV. Other weak acids (acetic, lactic, oxalic) produce a similar, but smaller increase. Formic acid (and other weak acids) also blocks the K+ conductance at pH 3.75, but not at pH 6.0 when the anion form predominates. This increased H+ conductance and K+ block can be explained by formic acid (HF) binding to the mouth of the gramicidin channel (Km = 1 M) and providing a source of H+ ions. A kinetic model is derived, based on the equilibrium binding of formic acid to the channel mouth, that quantitatively predicts the conductance for different mixtures of H+, K+, and formic acid. The binding of the neutral formic acid to the mouth of the gramicidin channel is directly supported by the observation that a neutral molecule with a similar structure, formamide (and malonamide and acrylamide), blocks the K+ conductance at pH 6.0. The H+ conductance in the presence of formic acid provides a lower bound for the intrinsic conductance of the gramicidin channel when there is no diffusion limitation at the channel mouth. The 12-fold increase in conductance produced by formic acid suggests that greater than 90% of the total resistance to H+ results from diffusion limitation in the bulk solution. PMID:2449253

  3. Effect of perfluoroalkyl chain length on monolayer behavior of partially fluorinated oleic acid molecules at the air-water interface.

    PubMed

    Baba, Teruhiko; Takai, Katsuki; Takagi, Toshiyuki; Kanamori, Toshiyuki

    2013-01-01

    A series of oleic acid (OA) analogs containing terminal perfluoroalkyl groups (CF3, C2F5, n-C3F7, n-C4F9 or n-C8F17) was synthesized to clarify how the fluorinated chain length affects the stability and molecular packing of liquid-expanded OA monolayers at the air-water interface. Although the substitution of terminal CF3 group for CH3 in OA had no effect on monolayer stability, further fluorination led to a gradual increase in monolayer stability at 25 °C. Surface pressure-area isotherm revealed that partially fluorinated OA analogs form more expanded monolayers than OA at low surface pressures, and that the monolayer behavior of OA analogs with the even-carbon numbered fluorinated chain is almost the same as that of OA upon monolayer compression, whereas the behavior of OA analogs with the odd-carbon numbered fluorinated chain significantly differs from that of OA. These results indicate: (i) the terminal short part (at least C2 residue) in OA predominantly determines the liquid-expanded monolayer stability; (ii) the molecular packing state of OA may be perturbed by the substitution of a short odd-carbon numbered fluorinated chain; (iii) hence, OA analogs with even-carbon numbered chain are considered to be preferable as hydrophobic building blocks for the synthesis of fluorinated phospholipids.

  4. A correlation between the proton stretching vibration red shift and the hydrogen bond length in polycrystalline amino acids and peptides.

    PubMed

    Rozenberg, Mark; Shoham, Gil; Reva, Igor; Fausto, Rui

    2005-06-01

    The FTIR spectra of pure and isotopically diluted (H/D and D/H) polycrystalline L-glutamine, L-hystidine, L-tyrosine, DL-serine, L-threonine, di-, tri-glycine and di-glycine x HCl x H2O salt were measured in the range 4000-2000 cm(-1) at temperatures from 300 to 10 K. The frequencies of decoupled proton stretching mode bands upsilon1, which can be observed only at low temperature, were used for estimation of the of upsilon1-bands red shift, which occurs upon formation of H-bonds involving ionized NH3+ and/or peptide HN-CO groups. The empirical correlation between the red shift and H-bond length, which was found previously for binary gas phase H-bonded complexes, carbohydrates and nucleosides [M. Rozenberg, A. Loewenschuss and Y. Marcus, Phys. Chem. Chem. Phys., 2000, 2, 2699-2702; M. Rozenberg, C. Jung and G. Shoham, Phys. Chem. Chem. Phys., 2003, 5, 1533-1535], was now extended to H-bonded networks in polycrystalline amino acids and peptides. The energies of the different H-bonds present in the crystalline structures could also be successfully estimated from the well-established empirical correlation [A. V. Iogansen, Spectrochim. Acta, 1999, A55, 1585-1612] between this property and the red shifts of the corresponding upsilon1 mode bands.

  5. Effect of modification of the length and flexibility of the acyl carrier protein-thioesterase interdomain linker on functionality of the animal fatty acid synthase.

    PubMed

    Joshi, Anil K; Witkowski, Andrzej; Berman, Harvey A; Zhang, Lei; Smith, Stuart

    2005-03-15

    A natural linker of approximately 20 residues connects the acyl carrier protein with the carboxy-terminal thioesterase domain of the animal fatty acid synthase. This study examines the effects of changes in the length and amino acid composition of this linker on catalytic activity, product composition, and segmental motion of the thioesterase domain. Deletion of 10 residues, almost half of the interdomain linker, had no effect on either mobility of the thioesterase domain, estimated from fluorescence polarization of a pyrenebutyl methylphosphono moiety bound covalently to the active site serine residue, or functionality of the fatty acid synthase; further shortening of the linker limited mobility of the thioesterase domain and resulted in reduced fatty acid synthase activity and an increase in product chain length from 16 to 18 and 20 carbon atoms. Surprisingly, however, even when the entire linker region was deleted, the fatty acid synthase retained 28% activity. Lengthening of the linker, by insertion of an unusually long acyl carrier protein-thioesterase linker from a modular polyketide synthase, increased mobility of the thioesterase domain without having any significant effect on catalytic properties of the complex. Interdomain linkers could also be used to tether, to the acyl carrier protein domain of the fatty acid synthase, a thioesterase active toward shorter chain length acyl thioesters generating novel short-chain fatty acid synthases. These studies reveal that although truncation of the interdomain linker partially impacts the ability of the thioesterase domain to terminate growth of the acyl chain, the overall integrity of the fatty acid synthase is quite tolerant to moderate changes in linker length and flexibility. The retention of fatty acid synthesizing activity on deletion of the entire linker region implies that the inherent flexibility of the phosphopantetheine "swinging arm" also contributes significantly to the successful docking of the long

  6. 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.

  7. Diffusion-reaction modelling of early diagenesis of sediments affected by acid mine drainage.

    NASA Astrophysics Data System (ADS)

    Torres, E.; Ayora, C.; Arias, J. L.; Garcia Robledo, E.; Papaspyrou, S.; Corzo, A.

    2012-04-01

    The Sancho Reservoir (SW Spain) is a monomictic water reservoir affected by acid mine drainage. It has a pH of ~4, with high sulfate (200 ppm) and heavy metal concentrations in the water column. The reservoir develops reducing conditions at the bottom during the stratification period. A laboratory experiment was carried out to study the effect of this oxygen variation on the early diagenesis processes and the cycling of metals. Sediment cores and bottom water were collected during the stratification period and brought to the laboratory. The cores were maintained in an aquarium bubbled with nitrogen gas to maintain hypoxic conditions (~10 µmol O2 L-1) for 1 day. Then, oxic conditions were induced by bubbling with air and maintained for 50 days. Finally, hypoxia was re-established for 10 days. Triplicate cores were sliced in a anaerobic glove box at each stage. Pore water was extracted by centrifugation and: Eh, pH, DO, DOC, sulfate, Fe and trace metals were analyzed. The sediment was freeze-dried and a sequential extraction protocol was applied to determine the exchangeable, AVS, Fe-(oxy)hydroxides, Fe-oxides, organic matter, pyrite sulfur and residual phase iron fractions. Organic carbon and total C, N, H and S were also analyzed in the sediment. A reactive diffusion model has been used to obtain the rates of biogeochemical reactions by fitting to the experimental data. During hypoxic conditions sulfate and Fe-(oxy)hydroxides are reduced, due to the anaerobic oxidation of organic matter, at the very first few cm, releasing sulfide and Fe(II) which precipitate as iron sulfide. When oxygen diffuses in the sediment, sulfate-reduction and the sulfide peaks are displaced deeper into the sediment. Oxygen penetration depth and its consumption rates in the sediment increase quickly, resulting in the reoxidation of the iron sulfides that had precipitated during hypoxic conditions. Sulfide and Fe(II) are released and are again oxidized to Fe(III) and sulfate respectively

  8. Urinary loss of glucose, phosphate, and protein by diffusion into proximal straight tubules injured by D-serine and maleic acid

    SciTech Connect

    Carone, F.A.; Nakamura, S.; Goldman, B.

    1985-06-01

    In several models of acute renal failure leakage of glomerular filtrate out of the tubule is an important pathogenetic mechanism; however, bidirectional diffusion of solute to account for certain pathophysiologic features of acute renal failure has received meager attention. Using micropuncture and clearance methods, the authors assessed sequentially leakage of solutes and inulin across proximal straight tubules (PST) injured by two nephrotoxins. In d-serine-treated rats with extensive necrosis of PST, the basis for glucosuria and tubular leakage of inulin was studied. Glucose absorption by the proximal convoluted tubule and glucose delivery to the PST were normal, but glucose delivery to the distal tubule was increased nearly 8-fold, indicating diffusion of glucose from interstitial to tubular luminal fluid across the necrotic PST. Total kidney inulin clearance was greatly reduced, but single nephron glomerular filtration rate, based on proximal convoluted tubule samples, was normal, indicating tubular loss of inulin. Urinary recovery of (/sup 14/C)inulin infused into tubular lumina revealed that proximal convoluted tubule and distal tubule were impermeable to inulin and that inulin diffused out of the necrotic PST. The progressive return over 6 days of tubular impermeability for inulin correlated with relining of PST with new cells. In maleic acid-treated rats the site and extent of tubular necrosis and the nature of urinary loss of solutes were studied. Microdissection revealed that maleic acid caused limited necrosis of PST which averaged 7.4% of total proximal tubular length. Increased urinary excretion of protein, phosphate, and glucose and increased tubular permeability to microinfused (/sup 14/C)inulin occurred with the onset of PST necrosis, and return of these abnormalities to normal correlated with the degree of cellular repair of the PST.

  9. Simultaneous diffuse reflectance infrared determination of clavulanic acid and amoxicillin using multivariate calibration techniques.

    PubMed

    Müller, Aline Lima Hermes; Picoloto, Rochele Sogari; Ferrão, Marco Flores; da Silva, Fabiana Ernestina Barcellos; Müller, Edson Irineu; Flores, Erico Marlon de Moraes

    2012-06-01

    A method for simultaneous determination of clavulanic acid (CA) and amoxicillin (AMO) in commercial tablets was developed using diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and multivariate calibration. Twenty-five samples (10 commercial and 15 synthetic) were used as a calibration set and 15 samples (10 commercial and 5 synthetic) were used for a prediction set. Calibration models were developed using partial least squares (PLS), interval PLS (iPLS), and synergy interval PLS (siPLS) algorithms. The best algorithm for CA determination was siPLS model with spectra divided in 30 intervals and combinations of 2 intervals. This model showed a root mean square error of prediction (RMSEP) of 5.1 mg g(-1). For AMO determination, the best siPLS model was obtained with spectra divided in 10 intervals and combinations of 4 intervals. This model showed a RMSEP of 22.3 mg g(-1). The proposed method was considered as a suitable for the simultaneous determination of CA and AMO in commercial pharmaceuticals products.

  10. Effect of dicarboxylic acid chain length on the self-cleaning property of Nano-TiO2-coated cotton fabrics.

    PubMed

    Khajavi, Ramin; Berendjchi, Amirhosein

    2014-11-12

    In this study, the effect of dicarboxylic acid chain length on the amount of TiO2 nanoparticles (TiO2NPs) adsorption-produced self-cleaning property and washing durability on cotton fabrics were investigated. First, cotton fabric samples were treated with three kinds of dicarboxylic acids--oxalic, succinic, and adipic acids--and then dipped in TiO2NP solution with a certain concentration. Attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) was used to investigate bonds formation between dicarboxylic acid groups and hydroxyl groups of cellulose, and a scanning electron microscope (SEM) was applied for the analysis of surface morphology in specimens. Drop absorbency time was determined for samples using the AATCC TM 79:2000. Washing stability and the amount absorption of TiO2NPs were determined by weighing and absorption spectrophotometry procedures, and the stain removal evaluation was conducted to assess the self-cleaning property. Results showed that all of the dicarboxylic acids used in this experiment improved the amount of TiO2NPs absorbed onto cotton samples and their durability to washing. In addition, color variation of samples treated with oxalic acid after 180 min of UV irradiation and drop absorbency time for samples treated with succinic acid were significantly increased by about 126 and 600%, respectively. The best durability was obtained from adipic acid, while a better self-cleaning property was obtained from oxalic acid.

  11. Effect of dicarboxylic acid chain length on the self-cleaning property of Nano-TiO2-coated cotton fabrics.

    PubMed

    Khajavi, Ramin; Berendjchi, Amirhosein

    2014-11-12

    In this study, the effect of dicarboxylic acid chain length on the amount of TiO2 nanoparticles (TiO2NPs) adsorption-produced self-cleaning property and washing durability on cotton fabrics were investigated. First, cotton fabric samples were treated with three kinds of dicarboxylic acids--oxalic, succinic, and adipic acids--and then dipped in TiO2NP solution with a certain concentration. Attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) was used to investigate bonds formation between dicarboxylic acid groups and hydroxyl groups of cellulose, and a scanning electron microscope (SEM) was applied for the analysis of surface morphology in specimens. Drop absorbency time was determined for samples using the AATCC TM 79:2000. Washing stability and the amount absorption of TiO2NPs were determined by weighing and absorption spectrophotometry procedures, and the stain removal evaluation was conducted to assess the self-cleaning property. Results showed that all of the dicarboxylic acids used in this experiment improved the amount of TiO2NPs absorbed onto cotton samples and their durability to washing. In addition, color variation of samples treated with oxalic acid after 180 min of UV irradiation and drop absorbency time for samples treated with succinic acid were significantly increased by about 126 and 600%, respectively. The best durability was obtained from adipic acid, while a better self-cleaning property was obtained from oxalic acid. PMID:25275802

  12. Cysteamine-induced inhibition of acid neutralization and the increase in hydrogen ion back-diffusion in duodenal mucosa

    SciTech Connect

    Ohe, K.; Okada, Y.; Fujiwara, T.; Inoue, M.; Miyoshi, A.

    1982-03-01

    To investigate the possible impairment of defensive mechanisms in cysteamine-induced duodenal ulceration, the effect of cysteamine on the neutralization of acid by the duodenum and the back-diffusion of hydrogen ions into the duodenal mucosa has been studied. The results obtained were as follows. (1) The intraduodenal pH started to decrease between 3 and 4 hr after cysteamine injection. (2) By perfusion of the duodenal loop excluding the opening of bile and pancreatic ducts, the amount of hydrogen ions (H+) neutralized was found to be significantly lower in cysteamine-treated animals than in the controls. (3) the back-diffusion of luminal H+ into the duodenal mucosa, estimated by measuring the H+ disappearance from the test solution including 100 mM HCl, was significantly increased by cysteamine. From these findings, it has been concluded that cysteamine reduces the resistance of duodenal mucosa to acid coming from the stomach.

  13. The synthesis of short- and medium-chain-length poly(hydroxyalkanoate) mixtures from glucose- or alkanoic acid-grown Pseudomonas oleovorans.

    PubMed

    Ashby, R D; Solaiman, D K Y; Foglia, T A

    2002-03-01

    Pseudomonas oleovorans NRRL B-778 accumulated mixtures of poly-3-hydroxybutyrate (PHB) and medium-chain-length poly(hydroxyalkanoates) (mcl-PHAs) when grown on glucose, octanoic acid or oleic acid, whereas growth on nonanoic acid or undecanoic acid resulted in copolymers of poly-3-hydroxybutyrate-co-3-hydroxyvalerate (PHB-co-HV). Acetone fractionation verified the presence of PHB/mcl-PHA mixtures. The acetone-insoluble (AIS) fractions of the polymers derived from glucose (PHA-glucose), octanoic acid (PHA-octanoic) and oleic acid (PHA-oleic) were exclusively PHB while the acetone-soluble (AS) fractions contained mcl-PHA composed of differing ratios of 3-hydroxy-acid monomer units, which ranged in chain length from 6 to 14 carbon atoms. In contrast, both the AIS and AS fractions from the polymers derived from nonanoic acid (PHA-nonanoic) and undecanoic acid (PHA-undecanoic) were composed of comparable ratios of 3-hydroxybutyrate (3HB) and 3-hydroxyvalerate (3HV). The unfractionated PHA-glucose, PHA-octanoic and PHA-oleic polymers had melting temperatures (Tm) between 177 and 179 degrees C, enthalpies of fusion (AHf) of 20 cal/g and glasstransition temperatures (Tg) of 3-4 degrees C. This was due to the large PHB content in the polymer mixtures. On the other hand, the PHA-nonanoic and PHA-undecanoic polymers had thermal properties that supported their copolymer nature. In both cases, the Tm values were 161 degrees C, deltaHf values were 7 cal/g and Tg values were - 3 degrees C. PMID:12074088

  14. The thermostability of two kinds of recombinant ∆6-fatty acid desaturase with different N-terminal sequence lengths in low temperature.

    PubMed

    Lu, He; Zhu, Yu

    2013-09-01

    Two recombinant Rhizopus stolonifer ∆6-fatty acid desaturase enzymes with different-length N-termini were cloned and expressed in Saccharomyces cerevisiae strain INVScl: LRsD6D begins with the sequence of the N-terminal of the R. stolonifer ∆6-fatty acid desaturase native, encoding a deduced polypeptide of 459 amino acids (M-S-T-L-D-R-Q-S-I-F-T-I-K-E-L-E-S-I-S-Q-R-I-H-D-G-D-E-E-A-M-K-F), whereas SRsD6D begins with the amino acid sequence of the predicted ORF, encoding a deduced polypeptide of 430 amino acids (M-K-F) and LRsD6D is longer than SRsD6D by 29 amino acids (M-S-T-L-D-R-Q-S-I-F-T-I-K-E-L-E-S-I-S-Q-R-I-H-D-G-D-E-E-A). Bioinformatic analysis characterized the two recombinant ∆6-fatty acid desaturase enzymes with different-length N-termini, including three conserved histidine-rich motifs, hydropathy profile, and a cytochrome b5-like domain in the N-terminus. When the coding sequence was expressed in S. cerevisiae strain INVScl, the coding produced ∆6-fatty acid desaturase activity exhibited by RsD6D, leading to a novel peak corresponding to γ-linolenic acid methyl ester standards, which was detected with the same retention time. The residual activity of LRsD6D was 74 % at 15 °C for 4 h and that of SRsD6D was 43 %. Purified recombinant LRsD6D was more stable than SRsD6D, indicating that the N-terminal extension, containing mostly hydrophobic residues, affected the overall stability of recombinant LRsD6D.

  15. Molecular surface area based predictive models for the adsorption and diffusion of disperse dyes in polylactic acid matrix.

    PubMed

    Xu, Suxin; Chen, Jiangang; Wang, Bijia; Yang, Yiqi

    2015-11-15

    Two predictive models were presented for the adsorption affinities and diffusion coefficients of disperse dyes in polylactic acid matrix. Quantitative structure-sorption behavior relationship would not only provide insights into sorption process, but also enable rational engineering for desired properties. The thermodynamic and kinetic parameters for three disperse dyes were measured. The predictive model for adsorption affinity was based on two linear relationships derived by interpreting the experimental measurements with molecular structural parameters and compensation effect: ΔH° vs. dye size and ΔS° vs. ΔH°. Similarly, the predictive model for diffusion coefficient was based on two derived linear relationships: activation energy of diffusion vs. dye size and logarithm of pre-exponential factor vs. activation energy of diffusion. The only required parameters for both models are temperature and solvent accessible surface area of the dye molecule. These two predictive models were validated by testing the adsorption and diffusion properties of new disperse dyes. The models offer fairly good predictive ability. The linkage between structural parameter of disperse dyes and sorption behaviors might be generalized and extended to other similar polymer-penetrant systems.

  16. Electrochemical Reduction of CO2 to Organic Acids by a Pd-MWNTs Gas-Diffusion Electrode in Aqueous Medium

    PubMed Central

    Lu, Guang; Bian, Zhaoyong; Liu, Xin

    2013-01-01

    Pd-multiwalled carbon nanotubes (Pd-MWNTs) catalysts for the conversion of CO2 to organic acids were prepared by the ethylene glycol reduction and fully characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS), and cyclic voltammetry (CV) technologies. The amorphous Pd particles with an average size of 5.7 nm were highly dispersed on the surface of carbon nanotubes. Functional groups of the MWNTs played a key role in the palladium deposition. The results indicated that Pd-MWNTs could transform CO2 into organic acid with high catalytic activity and CO2 could take part in the reduction reaction directly. Additionally, the electrochemical reduction of CO2 was investigated by a diaphragm electrolysis device, using a Pd-MWNTs gas-diffusion electrode as a cathode and a Ti/RuO2 net as an anode. The main products in present system were formic acid and acetic acid identified by ion chromatograph. The selectivity of the products could be achieved by reaction conditions changing. The optimum faraday efficiencies of formic and acetic acids formed on the Pd-MWNTs gas-diffusion electrode at 4 V electrode voltages under 1 atm CO2 were 34.5% and 52.3%, respectively. PMID:24453849

  17. Compositional effects on Si–OH bond length in hydrous silicates with implications for trends in the SiOH acidity

    SciTech Connect

    Zarubin, Dmitri P.

    2014-04-01

    Theoretical calculations of the structure and Brønsted acidity of SiOH groups in silica clusters have never addressed the question if these vary with the degree of SiOH deprotonation. In this connection, a statistical analysis is presented of Si–OH bond lengths in crystalline hydrogen silicates with well-determined structures with a special emphasis placed on effects of the silicate composition. It is found that among hydrogen silicates of large cations with low charges the Si–OH bonds are always longer than terminal Si–O bonds in the same anion and correlate in length with the anionic charge per tetrahedron. The findings are explained by steric limitations on charge balancing at oxygen atoms by hydrogen bonds and/or cations. It is suggested that similar limitations and imbalances may underlie the well-known trends in the Brønsted acidity of silicic acids and silicas in aqueous media: decreased acidity with increased SiOH deprotonation and increased acidity with increased tetrahedra connectivity. - Graphical abstract: Si–OH bonds in crystalline silicates lengthen with the anionic charge per tetrahedron, which is in parallel with the well-known trend of decreased acidity of silicic acids and silicas in solution with increased degree of deprotonation. - Highlights: • Si–OH bonds in alkali hydrogen silicates are always longer than terminal Si–O bonds. • Si–OH bonds in silicates lengthen with the anionic charge per tetrahedron. • The Si–OH bond elongation results from inherent underbonding of terminal O atoms. • The longer the Si–OH bond, the less acidic the OH group is.

  18. Use of agar diffusion assay to measure bactericidal activity of alkaline salts of fatty acids against bacteria associated with poultry processing

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The agar diffusion assay was used to examine antibacterial activity of alkaline salts of caproic, caprylic, capric, lauric, and myristic acids. A 0.5M concentration of each fatty acid was dissolved in 1.0 M potassium hydroxide (KOH), and pH of the mixtures was adjusted to 10.5 with citric acid. Solu...

  19. Identification of Amino Acids Conferring Chain Length Substrate Specificities on Fatty Alcohol-forming Reductases FAR5 and FAR8 from Arabidopsis thaliana*

    PubMed Central

    Chacón, Micaëla G.; Fournier, Ashley E.; Tran, Frances; Dittrich-Domergue, Franziska; Pulsifer, Ian P.; Domergue, Frédéric; Rowland, Owen

    2013-01-01

    Fatty alcohols play a variety of biological roles in all kingdoms of life. Fatty acyl reductase (FAR) enzymes catalyze the reduction of fatty acyl-coenzyme A (CoA) or fatty acyl-acyl carrier protein substrates to primary fatty alcohols. FAR enzymes have distinct substrate specificities with regard to chain length and degree of saturation. FAR5 (At3g44550) and FAR8 (At3g44560) from Arabidopsis thaliana are 85% identical at the amino acid level and are of equal length, but they possess distinct specificities for 18:0 or 16:0 acyl chain length, respectively. We used Saccharomyces cerevisiae as a heterologous expression system to assess FAR substrate specificity determinants. We identified individual amino acids that affect protein levels or 16:0-CoA versus 18:0-CoA specificity by expressing in yeast FAR5 and FAR8 domain-swap chimeras and site-specific mutants. We found that a threonine at position 347 and a serine at position 363 were important for high FAR5 and FAR8 protein accumulation in yeast and thus are likely important for protein folding and stability. Amino acids at positions 355 and 377 were important for dictating 16:0-CoA versus 18:0-CoA chain length specificity. Simultaneously converting alanine 355 and valine 377 of FAR5 to the corresponding FAR8 residues, leucine and methionine, respectively, almost fully converted FAR5 specificity from 18:0-CoA to 16:0-CoA. The reciprocal amino acid conversions, L355A and M377V, made in the active FAR8-S363P mutant background converted its specificity from 16:0-CoA to 18:0-CoA. This study is an important advancement in the engineering of highly active FAR proteins with desired specificities for the production of fatty alcohols with industrial value. PMID:24005667

  20. Effect of side chain length on bile acid conjugation: glucuronidation, sulfation and coenzyme A formation of nor-bile acids and their natural C24 homologs by human and rat liver fractions.

    PubMed

    Kirkpatrick, R B; Green, M D; Hagey, L R; Hofmann, A F; Tephly, T R

    1988-01-01

    The effect of side chain length on bile acid conjugation by human and rat liver fractions was examined. The rate of conjugation with glucuronic acid, sulfate and coenzyme A of several natural (C24) bile acids was compared with that of their corresponding nor-bile acids. The rate of coenzyme A ester formation by nor-bile acids was much lower than that of the natural bile acids. In human liver microsomes, the rate of coenzyme A formation was less than 8% of the rate for the corresponding C24 bile acid. Rat liver microsomes formed the coenzyme A ester of nor-bile acids less than 20% of the rate of their corresponding C24 homologs. Glucuronidation rates were greater than sulfation rates in both species. With human liver microsomes, nor-bile acids were glucuronidated more rapidly than their corresponding C24 homologs, whereas with rat liver microsomes the reverse was true. Purified 3 alpha-OH androgen UDP-glucuronyltransferase catalyzed the glucuronidation of both nor-bile acids and bile acids. Human liver cytosol sulfated nor-bile acids more slowly than the corresponding bile acids. Rat liver cytosol, however, sulfated nor-bile acids more rapidly than the corresponding bile acids. The highest rate was seen with lithocholylglycine. The results indicate that the novel biotransformation of nor-bile acids seen in vivo--sulfation and glucuronidation rather than amidation--is most likely explained as a consequent of defective amidation, to which the rate of coenzyme A formation contributes. Thus, side chain and nuclear structures as well as species differences in conjugating enzyme activity are determinants of the pattern of bile acid biotransformation by the mammalian liver.

  1. Genetic replacement of tesB with PTE1 affects chain-length proportions of 3-hydroxyalkanoic acids produced through β-oxidation of oleic acid in Escherichia coli.

    PubMed

    Seto, Yoshiaki; Kang, Junkyu; Ming, Li; Habu, Naoto; Nihei, Ken-ichi; Ueda, Shunsaku; Maeda, Isamu

    2010-10-01

    Acyl-CoA thioesterase II (TesB), which catalyzes hydrolysis of acyl-CoAs to free fatty acids and CoA, is involved in 3-hydroxyalkanoic acid production in Escherichia coli. Effects of genetic replacement of tesB with Saccharomyces cerevisiae acyl-CoA thioesterase gene PTE1 on 3-hydroxyalkanoic acid production from oleic acid through β-oxidation were examined. Kinetic analyses using β-oxidation intermediates showed that hydrolyses of C4-acyl substrates are more efficient by PTE1 than by TesB. Deletion of tesB in E. coli decreased 3-hydroxybutyric acid, 3-hydroxyhexanoic acid, 3-hydroxyoctanoic acid, and hexanoic acid in medium after cultivation with oleic acid as a sole carbon source. Hexanoic acid concentration was much lower than those of 3-hydroxyacids. In genetic complementation of tesB deletion, use of PTE1, instead of tesB, affected proportions of the 3-hydroxyalkanoic acids. Proportion of 3-hydroxybutyric acid was higher in a PTE1-complemented strain than in a tesB-complemented strain, while proportions of 3-hydroxyhexanoic acid and 3-hydroxyoctanoic acid markedly increased in the tesB-complemented strain. Proportion of 3-hydroxyoctanoic acid did not significantly increase in the PTE1-complemented strain. These data indicate possibilities of 3-hydroxyalkanoic acid production from oleic acid through β-oxidation and customization of their chain-length proportions by genetic replacement of tesB with a gene encoding acyl-CoA thioesterase with a different kinetic property.

  2. H-bond length dependence of the distortion in acid tetrahedron groups H nAsO 4 ( n=1-3)

    NASA Astrophysics Data System (ADS)

    Ichikawa, Mizuhiko

    1988-07-01

    The H-bond length O⋯O dependence of the distortions of the AsO 4 tetrahedra of acid arsenate groups H nAsO 4 ( n=1-3) have been studied by examining the correlations of the As sbnd O bond lengths, OAsO angles, O sbnd O lengths and Baur's distortion indices (DI) with O⋯O and comparing them with those of the corresponding H nPO 4 groups previously reported. The behavior of the O⋯O dependence of the AsO 4 distortion is analogous to that of PO 4 distortion as a whole, that is (a) all DI increase with increasing O⋯O, and correspondingly some of the individual or average As sbnd O lengths, OAsO angles and O sbnd O lengths correlate with O⋯O consistently; (b) the overall mean values of As sbnd O, OAsO and O sbnd O are reasonably constant in each H nAsO 4 type, most notably in the case of OAsO. The dependence of the PO 4 distortion on O⋯O can be described approximately by a model in which the P atom shifts away from the centroid of the regular tetrahedral framework, but the O⋯O dependence of the AsO 4 distortion is more complicated.

  3. The relative diffusive transport rate of SrI2 in water changes over the nanometer length scale as measured by coherent quasielastic neutron scattering.

    PubMed

    Rubinson, Kenneth A; Faraone, Antonio

    2016-05-14

    X-ray and neutron scattering have been used to provide insight into the structures of ionic solutions for over a century, but the probes have covered distances shorter than 8 Å. For the non-hydrolyzing salt SrI2 in aqueous solution, a locally ordered lattice of ions exists that scatters slow neutrons coherently down to at least 0.1 mol L(-1) concentration, where the measured average distance between scatterers is over 18 Å. To investigate the motions of these scatterers, coherent quasielastic neutron scattering (CQENS) data on D2O solutions with SrI2 at 1, 0.8, 0.6, and 0.4 mol L(-1) concentrations was obtained to provide an experimental measure of the diffusive transport rate for the motion between pairs of ions relative to each other. Because CQENS measures the motion of one ion relative to another, the frame of reference is centered on an ion, which is unique among all diffusion measurement methods. We call the measured quantity the pairwise diffusive transport rate Dp. In addition to this ion centered frame of reference, the diffusive transport rate can be measured as a function of the momentum transfer q, where q = (4π/λ)sin θ with a scattering angle of 2θ. Since q is related to the interion distance (d = 2π/q), for the experimental range 0.2 Å(-1)≤q≤ 1.0 Å(-1), Dp is, then, measured over interion distances from 40 Å to ≈6 Å. We find the measured diffusional transport rates increase with increasing distance between scatterers over the entire range covered and interpret this behavior to be caused by dynamic coupling among the ions. Within the model of Fickian diffusion, at the longer interionic distances Dp is greater than the Nernst-Hartley value for an infinitely dilute solution. For these nm-distance diffusional transport rates to conform with the lower, macroscopically measured diffusion coefficients, we propose that local, coordinated counter motion of at least pairs of ions is part of the transport process. PMID:27096293

  4. The evolution of proteins from random amino acid sequences: II. Evidence from the statistical distributions of the lengths of modern protein sequences.

    PubMed

    White, S H

    1994-04-01

    This paper continues an examination of the hypothesis that modern proteins evolved from random heteropeptide sequences. In support of the hypothesis, White and Jacobs (1993, J Mol Evol 36:79-95) have shown that any sequence chosen randomly from a large collection of nonhomologous proteins has a 90% or better chance of having a lengthwise distribution of amino acids that is indistinguishable from the random expectation regardless of amino acid type. The goal of the present study was to investigate the possibility that the random-origin hypothesis could explain the lengths of modern protein sequences without invoking specific mechanisms such as gene duplication or exon splicing. The sets of sequences examined were taken from the 1989 PIR database and consisted of 1,792 "super-family" proteins selected to have little sequence identity, 623 E. coli sequences, and 398 human sequences. The length distributions of the proteins could be described with high significance by either of two closely related probability density functions: The gamma distribution with parameter 2 or the distribution for the sum of two exponential random independent variables. A simple theory for the distributions was developed which assumes that (1) protoprotein sequences had exponentially distributed random independent lengths, (2) the length dependence of protein stability determined which of these protoproteins could fold into compact primitive proteins and thereby attain the potential for biochemical activity, (3) the useful protein sequences were preserved by the primitive genome, and (4) the resulting distribution of sequence lengths is reflected by modern proteins. The theory successfully predicts the two observed distributions which can be distinguished by the functional form of the dependence of protein stability on length. The theory leads to three interesting conclusions. First, it predicts that a tetra-nucleotide was the signal for primitive translation termination. This prediction is

  5. The diffusive transport of gibberellins and abscisic acid through the aleurone layer of germinating barley grain: a mathematical model.

    PubMed

    Bruggeman, F J; Libbenga, K R; Van Duijn, B

    2001-11-01

    A mathematical model of the diffusive transport of abscisic acid (ABA) and gibberellins (GAs) through the aleurone layer of barley (Hordeum vulgare L.) grain is presented. The model consists of two partial differential equations describing the accumulation of phytohormone in the apoplastic and symplasmic compartments of the aleurone layer, both spatially and temporally. The mathematical model contains the morphology of the barley grain and the physicochemical properties of the two phytohormones. A mathematical derivation of the accumulation ratios for the two phytohormones between the symplast and apoplast under equilibrium conditions resulted in different distribution mechanisms for GAs and ABA. A sensitivity analysis of the accumulation ratio for GAs indicated high sensitivity to the apoplastic pH and the membrane potential, whereas the accumulation ratio for ABA proved to be most sensitive to the pH difference between the apoplast and symplast. The diffusive transport time for GAs to the basal site of the aleurone layer as calculated with the mathematical model is within a physiologically plausible timescale according to experimental data from the literature. Abscisic acid cannot be transported by diffusion to the end of the aleurone layer as quickly as GAs, according to model simulations. Therefore, the functional role of ABA in germination is likely to be in the vicinity of the embryo.

  6. Effects of dielectric saturation and ionic screening on the proton self-diffusion coefficients in perfluorosulfonic acid membranes

    NASA Astrophysics Data System (ADS)

    Paul, Reginald; Paddison, Stephen J.

    2005-12-01

    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 Grønbech-Jensen et al. [Grønbech-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.

  7. Discrepancies between disk diffusion and broth susceptibility studies of the activity of ticarcillin plus clavulanic acid against ticarcillin-resistant Pseudomonas aeruginosa.

    PubMed Central

    Manian, F A; Alford, R H

    1986-01-01

    Ticarcillin and clavulanic acid in combination were tested against 40 Pseudomonas aeruginosa isolates resistant to ticarcillin by disk diffusion. A total of 21 isolates (53%) were susceptible to ticarcillin-clavulanate by disk diffusion, under currently recommended criteria for ticarcillin susceptibility. Macro-broth dilution tests (ticarcillin plus clavulanic acid, 2 micrograms/ml) confirmed susceptibility (MIC less than or equal to 64 micrograms/ml) of only 8 (38%) of 21 isolates. Time-kill studies of disk diffusion susceptible isolates indicated 2 log10 or greater killing of most isolates at 6 h in broth containing ticarcillin (64 micrograms/ml) combined with clavulanic acid (1, 2, 5, or 10 micrograms/ml). After 6 h, regrowth was common in all concentrations of clavulanic acid except 10 micrograms/ml. Regrowth populations were resistant to ticarcillin-clavulanate by MIC determination. Poor bactericidal activity of ticarcillin-clavulanate against ticarcillin-resistant P. aeruginosa was confirmed, as most isolates did not undergo 99.9% or greater killing at 24 h in all concentrations of clavulanic acid. Serotype O-11 was our most common serotype and was associated with disk diffusion "pseudosusceptibility." Concomitant disk diffusion testing of ticarcillin-clavulanate and ticarcillin is recommended for testing the susceptibility of P. aeruginosa to ticarcillin-clavulanate by disk diffusion. P. aeruginosa isolates resistant to ticarcillin should as a rule be considered also resistant to ticarcillin-clavulanate, despite apparent susceptibility by disk diffusion. PMID:3092732

  8. Multifold Increases in Turing Pattern Wavelength in the Chlorine Dioxide-Iodine-Malonic Acid Reaction-Diffusion System

    NASA Astrophysics Data System (ADS)

    Gaskins, Delora K.; Pruc, Emily E.; Epstein, Irving R.; Dolnik, Milos

    2016-07-01

    Turing patterns in the chlorine dioxide-iodine-malonic acid reaction were modified through additions of sodium halide salt solutions. The range of wavelengths obtained is several times larger than in the previously reported literature. Pattern wavelength was observed to significantly increase with sodium bromide or sodium chloride. A transition to a uniform state was found at high halide concentrations. The observed experimental results are qualitatively well reproduced in numerical simulations with the Lengyel-Epstein model with an additional chemically realistic kinetic term to account for the added halide and an adjustment of the activator diffusion rate to allow for interhalogen formation.

  9. Multifold Increases in Turing Pattern Wavelength in the Chlorine Dioxide-Iodine-Malonic Acid Reaction-Diffusion System.

    PubMed

    Gaskins, Delora K; Pruc, Emily E; Epstein, Irving R; Dolnik, Milos

    2016-07-29

    Turing patterns in the chlorine dioxide-iodine-malonic acid reaction were modified through additions of sodium halide salt solutions. The range of wavelengths obtained is several times larger than in the previously reported literature. Pattern wavelength was observed to significantly increase with sodium bromide or sodium chloride. A transition to a uniform state was found at high halide concentrations. The observed experimental results are qualitatively well reproduced in numerical simulations with the Lengyel-Epstein model with an additional chemically realistic kinetic term to account for the added halide and an adjustment of the activator diffusion rate to allow for interhalogen formation. PMID:27517779

  10. 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...

  11. Sodium Chloride Diffusion in Low-Acid Foods during Thermal Processing and Storage.

    PubMed

    Bornhorst, Ellen R; Tang, Juming; Sablani, Shyam S

    2016-05-01

    This study aimed at modeling sodium chloride (NaCl) diffusion in foods during thermal processing using analytical and numerical solutions and at investigating the changes in NaCl concentrations during storage after processing. Potato, radish, and salmon samples in 1% or 3% NaCl solutions were heated at 90, 105, or 121 °C for 5 to 240 min to simulate pasteurization and sterilization. Selected samples were stored at 4 or 22 °C for up to 28 d. Radish had the largest equilibrium NaCl concentrations and equilibrium distribution coefficients, but smallest effective diffusion coefficients, indicating that a greater amount of NaCl diffused into the radish at a slower rate. Effective diffusion coefficients determined using the analytical solution ranged from 0.2 × 10(-8) to 2.6 × 10(-8) m²/s. Numerical and analytical solutions showed good agreement with experimental data, with average coefficients of determination for samples in 1% NaCl at 121 °C of 0.98 and 0.95, respectively. During storage, food samples equilibrated to a similar NaCl concentration regardless of the thermal processing severity. The results suggest that sensory evaluation of multiphase (solid and liquid) products should occur at least 14 d after processing to allow enough time for the salt to equilibrate within the product. PMID:27060992

  12. Sodium Chloride Diffusion in Low-Acid Foods during Thermal Processing and Storage.

    PubMed

    Bornhorst, Ellen R; Tang, Juming; Sablani, Shyam S

    2016-05-01

    This study aimed at modeling sodium chloride (NaCl) diffusion in foods during thermal processing using analytical and numerical solutions and at investigating the changes in NaCl concentrations during storage after processing. Potato, radish, and salmon samples in 1% or 3% NaCl solutions were heated at 90, 105, or 121 °C for 5 to 240 min to simulate pasteurization and sterilization. Selected samples were stored at 4 or 22 °C for up to 28 d. Radish had the largest equilibrium NaCl concentrations and equilibrium distribution coefficients, but smallest effective diffusion coefficients, indicating that a greater amount of NaCl diffused into the radish at a slower rate. Effective diffusion coefficients determined using the analytical solution ranged from 0.2 × 10(-8) to 2.6 × 10(-8) m²/s. Numerical and analytical solutions showed good agreement with experimental data, with average coefficients of determination for samples in 1% NaCl at 121 °C of 0.98 and 0.95, respectively. During storage, food samples equilibrated to a similar NaCl concentration regardless of the thermal processing severity. The results suggest that sensory evaluation of multiphase (solid and liquid) products should occur at least 14 d after processing to allow enough time for the salt to equilibrate within the product.

  13. Analysis of the electron-beam-induced current of a polycrystalline p-n junction when the diffusion lengths of the material on either side of a grain boundary differ

    NASA Technical Reports Server (NTRS)

    Von Roos, O.; Luke, K. L.

    1984-01-01

    The short circuit current generated by the electron beam of a scanning electron microscope in p-n junctions is reduced by enhanced recombination at grain boundaries in polycrystalline material. Frequently, grain boundaries separate the semiconductor into regions possessing different minority carrier life times. This markedly affects the short circuit current I(sc) as a function of scanning distance from the grain boundary. It will be shown theoretically that (1) the minimum of the I(sc) in crossing the grain boundary with the scanning electron beam is shifted away from the grain boundary toward the region with smaller life time (shorter diffusion length), (2) the magnitude of the minimum differs markedly from those calculated under the assumption of equal diffusion lengths on either side of the grain boundary, and (3) the minimum disappears altogether for small surface recombination velocities (s less than 10,000 cm/s). These effects become negligible, however, for large recombination velocities s at grain boundaries. For p-type silicon this happens for s not less than 100,000 cm/s.

  14. Development of a bioprocess to convert PET derived terephthalic acid and biodiesel derived glycerol to medium chain length polyhydroxyalkanoate.

    PubMed

    Kenny, Shane T; Runic, Jasmina Nikodinovic; Kaminsky, Walter; Woods, Trevor; Babu, Ramesh P; O'Connor, Kevin E

    2012-08-01

    Sodium terephthalate (TA) produced from a PET pyrolysis product and waste glycerol (WG) from biodiesel manufacture were supplied to Pseudomonas putida GO16 in a fed-batch bioreactor. Six feeding strategies were employed by altering the sequence of TA and WG feeding. P. putida GO16 reached 8.70 g/l cell dry weight (CDW) and 2.61 g/l PHA in 48 h when grown on TA alone. When TA and WG were supplied in combination, biomass productivity (g/l/h) was increased between 1.3- and 1.7-fold and PHA productivity (g/l/h) was increased 1.8- to 2.2-fold compared to TA supplied alone. The monomer composition of the PHA accumulated from TA or WG was predominantly composed of 3-hydroxydecanoic acid. PHA monomers 3-hydroxytetradeeanoic acid and 3-hydroxytetradecenoic acid were not present in PHA accumulated from TA alone but were present when WG was supplied to the fermentation. When WG was either the sole carbon source or the predominant carbon source supplied to the fermentation the molecular weight of PHA accumulated was lower compared to PHA accumulated when TA was supplied as the sole substrate. Despite similarities in data for the properties of the polymers, PHAs produced with WG present in the PHA accumulation phase were tacky while PHA produced where TA was the sole carbon substrate in the polymer accumulation phase exhibited little or no tackiness at room temperature. The co-feeding of WG to fermentations allows for increased utilisation of TA. The order of feeding of WG and TA has an effect on TA utilisation and polymer properties. PMID:22581066

  15. Development of a bioprocess to convert PET derived terephthalic acid and biodiesel derived glycerol to medium chain length polyhydroxyalkanoate.

    PubMed

    Kenny, Shane T; Runic, Jasmina Nikodinovic; Kaminsky, Walter; Woods, Trevor; Babu, Ramesh P; O'Connor, Kevin E

    2012-08-01

    Sodium terephthalate (TA) produced from a PET pyrolysis product and waste glycerol (WG) from biodiesel manufacture were supplied to Pseudomonas putida GO16 in a fed-batch bioreactor. Six feeding strategies were employed by altering the sequence of TA and WG feeding. P. putida GO16 reached 8.70 g/l cell dry weight (CDW) and 2.61 g/l PHA in 48 h when grown on TA alone. When TA and WG were supplied in combination, biomass productivity (g/l/h) was increased between 1.3- and 1.7-fold and PHA productivity (g/l/h) was increased 1.8- to 2.2-fold compared to TA supplied alone. The monomer composition of the PHA accumulated from TA or WG was predominantly composed of 3-hydroxydecanoic acid. PHA monomers 3-hydroxytetradeeanoic acid and 3-hydroxytetradecenoic acid were not present in PHA accumulated from TA alone but were present when WG was supplied to the fermentation. When WG was either the sole carbon source or the predominant carbon source supplied to the fermentation the molecular weight of PHA accumulated was lower compared to PHA accumulated when TA was supplied as the sole substrate. Despite similarities in data for the properties of the polymers, PHAs produced with WG present in the PHA accumulation phase were tacky while PHA produced where TA was the sole carbon substrate in the polymer accumulation phase exhibited little or no tackiness at room temperature. The co-feeding of WG to fermentations allows for increased utilisation of TA. The order of feeding of WG and TA has an effect on TA utilisation and polymer properties.

  16. Molecular design of boronic acid-functionalized squarylium cyanine dyes for multiple discriminant analysis of sialic acid in biological samples: selectivity toward monosaccharides controlled by different alkyl side chain lengths.

    PubMed

    Ouchi, Kazuki; Colyer, Christa L; Sebaiy, Mahmoud; Zhou, Jin; Maeda, Takeshi; Nakazumi, Hiroyuki; Shibukawa, Masami; Saito, Shingo

    2015-02-01

    We designed a new series of boronic acid-functionalized squarylium cyanine dyes (SQ-BA) with different lengths of alkyl chain residues, suitable for multiple discriminant analysis (MDA) of sialic acid (Neu5Ac) in biological samples. The SQ-BA dyes form aggregates based on hydrophobic interactions, which result in quenched fluorescence in aqueous solutions. When the boronic acid binds with saccharides, the fluorescence intensity increases as a result of dissociation to the emissive monomeric complex. We inferred that different dye aggregate structures (H-aggregates and J-aggregates) were induced depending on the alkyl chain length, so that monosaccharides would be recognized in different ways (especially, multipoint interaction with J-aggregates). A distinctive emission enhancement of SQ-BA dyes with shorter-alkyl-chains in the presence of Neu5Ac was observed (2.4-fold fluorescence enhancement; with formation constant 10(1.7) M(-1)), with no such enhancement for SQ-BA dyes with longer-alkyl-chain. In addition, various enhancement factors for other monosaccharides were observed depending on the alkyl chain length. Detailed thermodynamic and NMR studies of the SQ-BA complexes revealed the unique recognition mechanism: the dye aggregate with a shorter-alkyl-chain causes the slipped parallel structure and forms a stable 2:1 complex with Neu5Ac, as distinct from longer-alkyl-chain dyes, which form a 1:1 monomeric complex. MDA using the four SQ-BA dyes was performed for human urine samples, resulting in the successful discrimination between normal and abnormal Neu5Ac levels characteristic of disease. Thus, we successfully controlled various responses to similar monosaccharides with a novel approach that chemically modified not the boronic acid moiety itself but the length of the alkyl chain residue attached to the dye in order to generate specificity.

  17. YfcX Enables Medium-Chain-Length Poly(3-Hydroxyalkanoate) Formation from Fatty Acids in Recombinant Escherichia coli fadB Strains

    PubMed Central

    Snell, Kristi D.; Feng, Feng; Zhong, Luhua; Martin, David; Madison, Lara L.

    2002-01-01

    Expression of Escherichia coli open reading frame yfcX is shown to be required for medium-chain-length polyhydroxyalkanoate (PHAMCL) formation from fatty acids in an E. coli fadB mutant. The open reading frame encodes a protein, YfcX, with significant similarity to the large subunit of multifunctional β-oxidation enzymes. E. coli fadB strains modified to contain an inactivated copy of yfcX and to express a medium-chain-length synthase are unable to form PHAMCLs when grown in the presence of fatty acids. Plasmid-based expression of yfcX in the FadB− YfcX− PhaC+ strain restores polymer formation. YfcX is shown to be a multifunctional enzyme that minimally encodes hydratase and dehydrogenase activities. The gene encoding YfcX is located downstream from yfcY, a gene encoding thiolase activity. Results of insertional inactivation studies and enzyme activity analyses suggest a role for yfcX in PHA monomer unit formation in recombinant E. coli fadB mutant strains. Further studies are required to determine the natural role of YfcX in the metabolism of E. coli. PMID:12270828

  18. Synthesis of polyhydroxyalkanoates from glucose that contain medium-chain-length monomers via the reversed fatty acid β-oxidation cycle in Escherichia coli.

    PubMed

    Zhuang, Qianqian; Wang, Qian; Liang, Quanfeng; Qi, Qingsheng

    2014-07-01

    Polyhydroxyalkanoates that contain the medium-chain-length monomers (mcl-PHAs) have a wide range of applications owing to their superior physical and mechanical properties. A challenge to synthesize such mcl-PHAs from unrelated and renewable sources is exploiting the efficient metabolic pathways that lead to the formation of precursor (R)-3-hydroxyacyl-CoA. Here, by engineering the reversed fatty acid β-oxidation cycle, we were able to synthesize mcl-PHAs in Escherichia coli directly from glucose. After deletion of the major thioesterases, the engineered E. coli produced 6.62wt% of cell dry weight mcl-PHA heteropolymers. Furthermore, when a low-substrate-specificity PHA synthase from Pseudomonas stutzeri 1317 was employed, recombinant E. coli synthesized 12.10wt% of cell dry weight scl-mcl PHA copolymers, of which 21.18mol% was 3-hydroxybutyrate and 78.82mol% was medium-chain-length monomers. The reversed fatty acid β-oxidation cycle offered an efficient metabolic pathway for mcl-PHA biosynthesis in E. coli and can be further optimized.

  19. A supramolecular strategy to leverage the liquid-phase exfoliation of graphene in the presence of surfactants: unraveling the role of the length of fatty acids.

    PubMed

    Haar, Sébastien; Ciesielski, Artur; Clough, Joseph; Yang, Huafeng; Mazzaro, Raffaello; Richard, Fanny; Conti, Simone; Merstorf, Nicolas; Cecchini, Marco; Morandi, Vittorio; Casiraghi, Cinzia; Samorì, Paolo

    2015-04-01

    Achieving the full control over the production as well as processability of high-quality graphene represents a major challenge with potential interest in the field of fabrication of multifunctional devices. The outstanding effort dedicated to tackle this challenge in the last decade revealed that certain organic molecules are capable of leveraging the exfoliation of graphite with different efficiencies. Here, a fundamental understanding on a straightforward supramolecular approach for producing homogenous dispersions of unfunctionalized and non-oxidized graphene nanosheets in four different solvents is attained, namely N-methyl-2-pyrrolidinone, N,N-dimethylformamide, ortho-dichlorobenzene, and 1,2,4-trichlorobenzene. In particular, a comparative study on the liquid-phase exfoliation of graphene in the presence of linear alkanes of different lengths terminated by a carboxylic-acid head group is performed. These molecules act as graphene dispersion-stabilizing agents during the exfoliation process. The efficiency of the exfoliation in terms of concentration of exfoliated graphene is found to be proportional to the length of the employed fatty acid. Importantly, a high percentage of single-layer graphene flakes is revealed by high-resolution transmission electron microscopy and Raman spectroscopy analyses. A simple yet effective thermodynamic model is developed to interpret the chain-length dependence of the exfoliation yield. This approach relying on the synergistic effect of a ad-hoc solvent and molecules to promote the exfoliation of graphene in liquid media represents a promising and modular strategy towards the rational design of improved dispersion-stabilizing agents.

  20. Valorization of fatty acids-containing wastes and byproducts into short- and medium-chain length polyhydroxyalkanoates.

    PubMed

    Cruz, Madalena V; Freitas, Filomena; Paiva, Alexandre; Mano, Francisca; Dionísio, Madalena; Ramos, Ana Maria; Reis, Maria A M

    2016-01-25

    Olive oil distillate (OOD), biodiesel fatty acids-byproduct (FAB) and used cooking oil (UCO) were tested as inexpensive carbon sources for the production of polyhydroxyalkanoates (PHA) with different composition using twelve bacterial strains. OOD and FAB were exploited for the first time as alternative substrates for PHA production. UCO, OOD and FAB were used by Cupriavidus necator and Pseudomonas oleovorans to synthesize the homopolymer poly-3-hydroxybutyrate, while Pseudomonas resinovorans and Pseudomonas citronellolis produced mcl-PHA polymers mainly composed of hydroxyoctanoate and hydroxydecanoate monomers. The highest polymer content in the biomass was obtained for C. necator (62 wt.%) cultivated on OOD. Relatively high mcl-PHA content (28-31 wt.%) was reached by P. resinovorans cultivated in OOD. This study shows, for the first time, that OOD is a promising substrate for PHA production since it gives high polymer yields and allows for the synthesis of different polymers (scl- or mcl-PHA) by selection of the adequate strains.

  1. Increased in vitro glial fibrillary acidic protein expression, telomerase activity, and telomere length after productive human immunodeficiency virus-1 infection in murine astrocytes.

    PubMed

    Ojeda, Diego; López-Costa, Juan José; Sede, Mariano; López, Ester María; Berria, María Isabel; Quarleri, Jorge

    2014-02-01

    Although HIV-associated neurocognitive disorders (HAND) result from injury and loss of neurons, productive infection routinely takes place in cells of macrophage lineage. In such a complex context, astrocytosis induced by local chemokines/cytokines is one of the hallmarks of HIV neuropathology. Whether this sustained astrocyte activation is able to alter telomere-aging process is unknown. We hypothesized that interaction of HIV with astrocytes may impact astrocyte telomerase activity (TA) and telomere length in a scenario of astrocytic activation measured by expression of glial fibrillary acidic protein (GFAP). To test this hypothesis, cultured murine astrocytes were challenged with pseudotyped HIV/vesicular stomatitis virus (HIV/VSV) to circumvent the absence of viral receptors; and GFAP, telomerase activity, and telomere length were quantified. As an early and transient event after HIV infection, both TA activity and telomere length were significantly augmented (P < 0.001). Later, a strong negative correlation (-0.8616, P < 0.0001) between virus production and telomerase activity was demonstrated. Once HIV production had reached a peak (7 dpi), the TA decreased, showing levels similar to those of noninfected cells. In contrast, the astrocyte became activated, exhibiting significantly increased levels of GFAP expression directly related to the level of HIV/VSV replication (P < 0.0001). Our results suggest that HIV-infected astrocytes exhibit early disturbance in their cellular functions, such as telomerase activity and telomere length, that may attenuate cell proliferation and enhance the astrocyte dysregulation, contributing to HIV neuropathogenesis. Understanding the mechanisms involved in HIV-mediated persistence by altering the telomere-related aging processes could aid in the development of therapeutic modalities for neurological complications of HIV infection.

  2. Effect of pH, urea, peptide length, and neighboring amino acids on alanine alpha-proton random coil chemical shifts.

    PubMed

    Carlisle, Elizabeth A; Holder, Jessica L; Maranda, Abby M; de Alwis, Adamberage R; Selkie, Ellen L; McKay, Sonya L

    2007-01-01

    Accurate random coil alpha-proton chemical shift values are essential for precise protein structure analysis using chemical shift index (CSI) calculations. The current study determines the chemical shift effects of pH, urea, peptide length and neighboring amino acids on the alpha-proton of Ala using model peptides of the general sequence GnXaaAYaaGn, where Xaa and Yaa are Leu, Val, Phe, Tyr, His, Trp or Pro, and n = 1-3. Changes in pH (2-6), urea (0-1M), and peptide length (n = 1-3) had no effect on Ala alpha-proton chemical shifts. Denaturing concentrations of urea (8M) caused significant downfield shifts (0.10 +/- 0.01 ppm) relative to an external DSS reference. Neighboring aliphatic residues (Leu, Val) had no effect, whereas aromatic amino acids (Phe, Tyr, His and Trp) and Pro caused significant shifts in the alanine alpha-proton, with the extent of the shifts dependent on the nature and position of the amino acid. Smaller aromatic residues (Phe, Tyr, His) caused larger shift effects when present in the C-terminal position (approximately 0.10 vs. 0.05 ppm N-terminal), and the larger aromatic tryptophan caused greater effects in the N-terminal position (0.15 ppm vs. 0.10 C-terminal). Proline affected both significant upfield (0.06 ppm, N-terminal) and downfield (0.25 ppm, C-terminal) chemical shifts. These new Ala correction factors detail the magnitude and range of variation in environmental chemical shift effects, in addition to providing insight into the molecular level interactions that govern protein folding.

  3. Assessing the Impact of Backbone Length and Capping Agent on the Conformational Preferences of a Model Peptide: Conformation Specific IR and UV Spectroscopy of 2-AMINOISOBUTYRIC Acid

    NASA Astrophysics Data System (ADS)

    Gord, Joseph R.; Hewett, Daniel M.; Kubasik, Matthew A.; Zwier, Timothy S.

    2015-06-01

    2-Aminoisobutyric acid (Aib) is an achiral, α-amino acid having two equivalent methyl groups attached to C_α. Extended Aib oligomers are known to have a strong preference for the adoption of a 310-helical structure in the condensed phase. Here, we have taken a simplifying step and focused on the intrinsic folding propensities of Aib by looking at a series of capped Aib oligomers in the gas phase, free from the influence of solvent molecules and cooled in a supersonic expansion. Resonant two-photon ionization and IR-UV holeburning have been used to record single-conformation UV spectra using the Z-cap as the UV chromophore. Resonant ion-dip infrared (RIDIR) spectroscopy provides single-conformation IR spectra in the OH stretch and NH stretch regions. Data have been collected on a set of Z-(Aib)n-X oligomers with n = 1, 2, 4, 6 and X = -OH and -OMethyl. The impacts of these capping groups and differences in backbone length have been found to dramatically influence the conformational space accessed by the molecules studied here. Oligomers of n=4 have sufficient backbone length for a full turn of the 310-helix to be formed. Early interpretation of the data collected shows clear spectroscopic markers signaling the onset of 310-helix formation as well as evidence of structures incorporating C7 and C14 hydrogen bonded rings. Toniolo, C.; Bonora, G. M.; Barone, V.; Bavoso, A.; Benedetti, E.; Di Blasio, B.; Grimaldi, P.; Lelj, F.; Pavone, V.; Pedone, C., Conformation of Pleionomers of α-Aminoisobutyric Acid. Macromolecules 1985, 18, 895-902.

  4. Valorization of fatty acids-containing wastes and byproducts into short- and medium-chain length polyhydroxyalkanoates.

    PubMed

    Cruz, Madalena V; Freitas, Filomena; Paiva, Alexandre; Mano, Francisca; Dionísio, Madalena; Ramos, Ana Maria; Reis, Maria A M

    2016-01-25

    Olive oil distillate (OOD), biodiesel fatty acids-byproduct (FAB) and used cooking oil (UCO) were tested as inexpensive carbon sources for the production of polyhydroxyalkanoates (PHA) with different composition using twelve bacterial strains. OOD and FAB were exploited for the first time as alternative substrates for PHA production. UCO, OOD and FAB were used by Cupriavidus necator and Pseudomonas oleovorans to synthesize the homopolymer poly-3-hydroxybutyrate, while Pseudomonas resinovorans and Pseudomonas citronellolis produced mcl-PHA polymers mainly composed of hydroxyoctanoate and hydroxydecanoate monomers. The highest polymer content in the biomass was obtained for C. necator (62 wt.%) cultivated on OOD. Relatively high mcl-PHA content (28-31 wt.%) was reached by P. resinovorans cultivated in OOD. This study shows, for the first time, that OOD is a promising substrate for PHA production since it gives high polymer yields and allows for the synthesis of different polymers (scl- or mcl-PHA) by selection of the adequate strains. PMID:26047553

  5. Fast Diffusion of Very Long Chain Saturated Fatty Acids across a Bilayer Membrane and Their Rapid Extraction by Cyclodextrins

    PubMed Central

    Pillai, Biju K.; Jasuja, Ravi; Simard, Jeffrey R.; Hamilton, James A.

    2009-01-01

    Abnormalities in the transport of saturated very long chain fatty acids (VLCFA; >C18:0) contribute to their toxic levels in peroxisomal disorders of fatty acid metabolism, such as adrenoleukodystrophy and adrenomyeloneuropathy. We previously showed that VLCFA desorb much slower than normal dietary fatty acids from both albumin and protein-free lipid bilayers. The important step of transbilayer movement (flip-flop) was not measured directly as a consequence of this very slow desorption from donors, and the extremely low aqueous solubility of VLCFA precludes addition of unbound VLCFA to lipid membranes. We have overcome these limitations using methyl-β-cyclodextrin to solubilize VLCFA for rapid delivery to “acceptor” phosphatidylcholine vesicles (small and large unilamellar) and to cells. VLCFA binding was monitored in real time with the fluorescent probe fluorescein-labeled phosphatidylethanolamine in the outer membrane leaflet, and entrapped pyranine was used to detect flip-flop across the membrane. The upper limit of the rate of flip-flop across the membrane was independent of temperature and media viscosity and was similar for model raft and non-raft membranes as well as living cells. We further showed that cyclodextrins can extract VLCFA rapidly (within seconds) from vesicles and cells, which have implications for the mechanism and potential alternative approaches to treat adrenoleukodystrophy. Because VLCFA diffuse through the lipid bilayer, proteins may not be required for their transport across the peroxisomal membrane. PMID:19801636

  6. Difference in Hepatic Metabolism of Long- and Medium-Chain Fatty Acids: the Role of Fatty Acid Chain Length in the Production of the Alcoholic Fatty Liver*

    PubMed Central

    Lieber, Charles S.; Lefèvre, André; Spritz, Norton; Feinman, Lawrence; DeCarli, Leonore M.

    1967-01-01

    Replacement of dietary triglycerides containing long-chain fatty acids (LCFA) by triglycerides containing medium-chain fatty acids (MCFA) markedly reduced the capacity of alcohol to produce fatty liver in rats. After 24 days of ethanol and MCFA, the increase in hepatic triglycerides was only 3 times that of controls, whereas an 8-fold rise was observed after ethanol and LCFA. The triglyceride fatty acids that accumulated in the liver after feeding of ethanol with MCFA contained only a small percentage of the MCFA; their composition also differed strikingly from that of adipose lipids. To study the mechanism of the reduction in steatosis, we compared oxidation to CO2 and incorporation into esterified lipids of 14C-labeled chylomicrons or palmitate-14C (representing LCFA), and of octanoate-14C (as MCFA) in liver slices and isolated perfused livers, in the presence or absence of ethanol. Ethanol depressed the oxidation of all substrates to CO2; MCFA, however, was much more oxidized and reciprocally much less esterified than LCFA, with a 100-fold difference in the ratio of esterified lipid-14C to 14CO2. Furthermore, in hepatic microsomal fractions incubated with α-glycerophosphate, octanoate was much less esterified than palmitate. This propensity of MCFA to oxidation rather than esterification represents a likely explanation for the reduction in alcoholic steatosis upon replacement of dietary LCFA by MCFA. PMID:6036539

  7. Effect of Structure on Transport Properties (Viscosity, Ionic Conductivity, and Self-Diffusion Coefficient) of Aprotic Heterocyclic Anion (AHA) Room Temperature Ionic Liquids. 2. Variation of Alkyl Chain Length in the Phosphonium Cation.

    PubMed

    Sun, Liyuan; Morales-Collazo, Oscar; Xia, Han; Brennecke, Joan F

    2016-06-30

    A series of room-temperature ionic liquids (ILs) composed of triethyl(alkyl)phosphonium cations paired with three different aprotic heterocyclic anions (AHAs) (alkyl = butyl ([P2224](+)) and octyl ([P2228](+))) were prepared to investigate the effect of cationic alkyl chain length on transport properties. The transport properties and density of these ILs were measured from 283.15 to 343.15 K at ambient pressure. The dependence of the transport properties (viscosity, ionic conductivity, diffusivity, and molar conductivity) on temperature can be described by the Vogel-Fulcher-Tamman (VFT) equation. The ratio of the molar conductivity obtained from the molar concentration and ionic conductivity measurements to that calculated from self-diffusion coefficients (measured by pulsed gradient spin-echo nuclear magnetic resonance spectroscopy) using the Nernst-Einstein equation was used to quantify the ionicity of these ILs. The molar conductivity ratio decreases with increasing number of carbon atoms in the alkyl chain, indicating that the reduced Coulombic interactions resulting from lower density are more than balanced by the increased van der Waals interactions between the alkyl chains. The results of this study may provide insight into the design of ILs with enhanced dynamics that may be suitable as electrolytes in lithium ion batteries and other electrochemical applications.

  8. Visualization of diffusion of the drug solution during aluminum potassium tannic acid injection therapy: a pilot study.

    PubMed

    Yamamoto, Yutaka; Miwa, Mitsuharu

    2013-06-01

    Sclerotherapy with aluminum potassium tannic acid (ALTA), which was approved in Japan for the treatment of internal hemorrhoids in July 2004 (Takano et al., Int J Colorectal Dis 21:44-51, 2006), has been widely accepted because of its effectiveness and low invasiveness. More than 200,000 patients have received ALTA injection therapy. ALTA is injected directly into 4 points of an internal hemorrhoid (4-step injection) to induce sclerosis and remission of the hemorrhoids, and consequently, resolution of symptoms such as prolapse and bleeding. The precision of the 4-step injection is considered to be a crucial determinant of the success of this therapy and the risk of complications. However, sufficient evidence has not yet been obtained concerning the diffusion and distribution of the injected drug. A pilot study visualized the real-time diffusion/distribution of the drug solution following the 4-step injection, using the ICG (indocyanine green) fluorescence technique, and an infrared camera (Photodynamic EYE; PDE, Hamamatsu Photonics K.K.).

  9. The effect of vehicle on the diffusion of salicylic acid through hairless mouse skin.

    PubMed

    Sloan, K B; Siver, K G; Koch, S A

    1986-08-01

    The solubilities of salicylic acid in, and the fluxes through, hairless mouse skin from isopropyl myristate, 1-octanol, 1-propanol, propylene glycol, and formamide have been determined experimentally. Values for permeability coefficients (Kp) corresponding to the respective fluxes were determined from: flux/solubility = Kp. These values were then compared with values for the respective partition coefficients (P) which were calculated from the known solubility parameters for the vehicles (delta v), salicylic acid (delta i), and skin (delta s). Two different delta i values were used to calculate theoretical P values, one based on the peak solubility method and the other based on calculation from group contributions (11 and 14.4 (cal/cm3)1/2, respectively). There was good correlation between the values for theoretical log P - 1.42 and experimental log Kp for the delivery of salicylic acid from vehicles exhibiting solubility parameters in the range of delta v = 10-18 (cal/cm3)1/2, when delta i was assumed to be 14.4 (cal/cm3)1/2. There was also a good correlation between the values for theoretical log P - 2.09 and experimental log Kp for vehicles exhibiting solubility parameters in the range of delta v = 7.6-10 (cal/cm3)1/2, when delta i was assumed to be 11 (cal/cm3)1/2. Two different delta i values were used because salicylic acid apparently behaves like a polar molecule in polar vehicles and a nonpolar molecule in nonpolar vehicles. Qualitatively, fluxes and permeability coefficients were found to be inversely dependent on drug solubility in the vehicles, with a minimum that corresponded approximately to the point where delta v = delta i, and the minimum within the theoretical P curve.(ABSTRACT TRUNCATED AT 250 WORDS)

  10. Hindered Diffusion of Oligosaccharides in High Strength Poly(ethylene glycol)/Poly(acrylic acid) Interpenetrating Network Hydrogels: Hydrodynamic Versus Obstruction Models

    PubMed Central

    Waters, Dale J.; Frank, Curtis W.

    2010-01-01

    Diffusion coefficients of small oligosaccharides within high strength poly(ethylene glycol)/poly(acrylic acid) interpenetrating network (PEG/PAA IPN) hydrogels were measured by diffusion through hydrogel slabs. The ability of hindered diffusion models previously presented in the literature to fit the experimental data is examined. A model based solely on effects due to hydrodynamics is compared to a model based solely on solute obstruction. To examine the effect of polymer volume fraction on the observed diffusion coefficients, the equilibrium volume fraction of polymer in PEG/PAA IPNs was systematically varied by changing the initial PEG polymer concentration in hydrogel precursor solutions from 20 to 50 wt./wt.%. To examine the effect of solute radius on the observed diffusion coefficients, solute radii were varied from 3.3 to 5.1 Å by measuring diffusion coefficients of glucose, a monosaccharide; maltose, a disaccharide; and maltotriose, a trisaccharide. Both the hydrodynamic and obstruction models rely on scaling relationships to predict diffusion coefficients. The proper scaling relationship for each of the hindered diffusion models is evaluated based on fits to experimental data. The scaling relationship employed is found to have a greater significance for the hydrodynamic model than the obstruction model. Regardless of the scaling relationship employed, the obstruction model provides a better fit to our experimental data than the hydrodynamic model. PMID:20514136

  11. Highlighting the role of polymer length, carbohydrate size, and nucleic acid type in potency of glycopolycation agents for pDNA and siRNA delivery.

    PubMed

    Xue, Lian; Ingle, Nilesh P; Reineke, Theresa M

    2013-11-11

    While nucleic acids such as small interfering RNA (siRNA) and plasmid DNA (pDNA) are promising research tools and therapeutic modalities, their potential in medical applications is limited by a fundamental mechanistic understanding and inadequate efficiency. Herein, two series of carbohydrate-based polycations were synthesized and examined that varied in the degree of polymerization (n), one containing trehalose [Tr4(n) series: Tr4(23), Tr4(55), Tr4(77)] and the other containing β-cyclodextrin [CD4(n) series: CD4(10), CD4(26), CD4(39), CD4(143), CD4(239)]. In addition, two monosaccharide models were examined for comparison that contain tartaramidoamine (T4) and galactaramidoamine (G4 or Glycofect) repeats. Delivery profiles for pDNA were compared with those obtained for siRNA delivery and reveal that efficacy differs significantly as a function of carbohydrate type, nucleic acid type and dose, polymer length, and presence of excess polymer in the formulation. The Tr4 polymers yielded higher efficacy for pDNA delivery, yet the CD4 polymers achieved higher siRNA delivery and gene down-regulation. The T4 and Glycofect derivatives, while efficient for pDNA delivery, were completely ineffective for siRNA delivery. A strong polymer length and dose dependence on target gene knockdown was observed for all polymers tested. Also, free polymer in solution (uncomplexed) was demonstrated to be a key factor in promoting siRNA uptake and gene down-regulation. PMID:24028685

  12. Highlighting the Role of Polymer Length, Carbohydrate Size, and Nucleic Acid Type in Potency of Glycopolycation Agents for pDNA and siRNA Delivery

    PubMed Central

    Xue, Lian; Ingle, Nilesh P.; Reineke, Theresa M.

    2013-01-01

    While nucleic acids such as small interfering RNA (siRNA) and plasmid DNA (pDNA) are promising research tools and therapeutic modalities, their potential in medical applications is limited by a fundamental mechanistic understanding and inadequate efficiency. Herein, two series of carbohydrate-based polycations were synthesized and examined that varied in the degree of polymerization (n)—one containing trehalose [Tr4(n) series: Tr4(23), Tr4(55), Tr4(77)] and the other containing beta-cyclodextrin [CD4(n) series: CD4(10), CD4(26), CD4(39), CD4(143), CD4(239)]. In addition, two monosaccharide models were examined for comparison that contain tartaramidoamine (T4) and galactaramidoamine (G4 or Glycofect) repeats. Delivery profiles for pDNA were compared with those obtained for siRNA delivery and reveal that efficacy differs significantly as a function of carbohydrate type, nucleic acid type and dose, polymer length, and presence of excess polymer in the formulation. The Tr4 polymers yielded higher efficacy for pDNA delivery, yet, the CD4 polymers achieved higher siRNA delivery and gene down regulation. The T4 and Glycofect derivatives, while efficient for pDNA delivery, were completely ineffective for siRNA delivery. A strong polymer length and dose dependence on target gene knockdown was observed for all polymers tested. Also, free polymer in solution (uncomplexed) was demonstrated to be a key factor in promoting siRNA uptake and gene down regulation. PMID:24028685

  13. Impact of fatty acid chain length of rosmarinate esters on their antimicrobial activity against Staphylococcus carnosus LTH1502 and Escherichia coli K-12 LTH4263.

    PubMed

    Suriyarak, Sarisa; Bayrasy, Christelle; Schmidt, Herbert; Villeneuve, Pierre; Weiss, Jochen

    2013-09-01

    The effect of the addition of a newly synthesized series of rosmarinic acid (RA) estes (REs) and alcohols with chain lengths of 1, 4, 8, 10, 12, 16, and 18 carbons (RE1 to 18) on the growth behavior of Staphylococcus carnosus LTH1502 and Escherichia coli K-12 LTH4263 was investigated. An initial microtiter dilution assay indicated activity of compounds against S. carnosus LTH1502, whereas esters with chain lengths, RA, n-methyl rosmarinate (RE1), n-dodecyl rosmarinate (RE12), and n-octadecyl rosmarinate (RE18) were used in a time-kill assay S. carnosus LTH1502. Compounds were added at 0.75 mM in the log phase, 5 mM in the exponential phase, 10 mM in the stationary phase. RA had no effect in the lag and exponential phase but decreased cell counts during the stationary phase. In contrast, RE1 and RE12 decreased cell number in all three phase, will RE12 reducing counts most rapidly. Addition of RE18 did not affect regardless of the growth phase. Appearance and physiological state of S. carnosus LTH1502 cells indicated difference in the way the compounds interacted with and damaged cells. Results were attributed to the different physicochemical properties of RA and its esters.

  14. Long chain polyunsaturated fatty acid supplementation in infancy increases length- and weight-for-age but not BMI to 6 years when controlling for effects of maternal smoking.

    PubMed

    Currie, L M; Tolley, E A; Thodosoff, J M; Kerling, E H; Sullivan, D K; Colombo, J; Carlson, S E

    2015-07-01

    Long chain polyunsaturated fatty acids (LCPUFA) are added to infant formula but their effect on long-term growth of children is under studied. We evaluated the effects of feeding LCPUFA-supplemented formula (n = 54) compared to control formula (n = 15) throughout infancy on growth from birth-6 years. Growth was described using separate models developed with the MIXED procedure of SAS(®) that included maternal smoking history and gender. Compared to children fed control formula, children who consumed LCPUFA supplemented formula had higher length-/stature-/and weight-for-age percentiles but not body mass index (BMI) percentile from birth to 6 years. Maternal smoking predicted lower stature (2-6 years), higher weight-for-length (birth-18 months) and BMI percentile (2-6 years) independent of LCPUFA effects. Gender interacted with the effect of LCPUFA on stature, and the relationship between smoking and BMI, with a larger effect for boys. Energy intake did not explain growth differences. A relatively small control sample is a limitation. PMID:25936840

  15. Long chain polyunsaturated fatty acid supplementation in infancy increases length- and weight-for-age but not BMI to 6 years when controlling for effects of maternal smoking.

    PubMed

    Currie, L M; Tolley, E A; Thodosoff, J M; Kerling, E H; Sullivan, D K; Colombo, J; Carlson, S E

    2015-07-01

    Long chain polyunsaturated fatty acids (LCPUFA) are added to infant formula but their effect on long-term growth of children is under studied. We evaluated the effects of feeding LCPUFA-supplemented formula (n = 54) compared to control formula (n = 15) throughout infancy on growth from birth-6 years. Growth was described using separate models developed with the MIXED procedure of SAS(®) that included maternal smoking history and gender. Compared to children fed control formula, children who consumed LCPUFA supplemented formula had higher length-/stature-/and weight-for-age percentiles but not body mass index (BMI) percentile from birth to 6 years. Maternal smoking predicted lower stature (2-6 years), higher weight-for-length (birth-18 months) and BMI percentile (2-6 years) independent of LCPUFA effects. Gender interacted with the effect of LCPUFA on stature, and the relationship between smoking and BMI, with a larger effect for boys. Energy intake did not explain growth differences. A relatively small control sample is a limitation.

  16. Δ6-fatty acid desaturase and fatty acid elongase mRNA expression, phagocytic activity and weight-to-length relationships in channel catfish (Ictalurus punctatus) fed alternative diets with soy oil and a probiotic.

    PubMed

    Santerre, A; Téllez-Bañuelos, M C; Casas-Solís, J; Castro-Félix, P; Huízar-López, M R; Zaitseva, G P; Horta-Fernández, J L; Trujillo-García, E A; de la Mora-Sherer, D; Palafox-Luna, J A; Juárez-Carrillo, E

    2015-09-22

    A time-course feeding trial was conducted for 120 days on juvenile channel catfish (Ictalurus punctatus) to study the effects of diets differing in oil source (fish oil or soy oil) and supplementation with a commercial probiotic. Relative levels of Δ6-fatty acid desaturase (Δ6-FAD) and fatty acid elongase (FAE) expression were assessed in brain and liver tissues. Both genes showed similar expression levels in all groups studied. Fish weight-to-length relationships were evaluated using polynomial regression analyses, which identified a burst in weight and length in the channel catfish on day 105 of treatment; this increase was related to an increase in gene expression. Mid-intestinal lactic acid bacterium (LAB) count was determined according to morphological and biochemical criteria using API strips. There was no indication that intestinal LAB count was affected by the modified diets. The Cunningham glass adherence method was applied to evaluate phagocytic cell activity in peripheral blood. Reactive oxygen species (ROS) generation was assessed through the respiratory burst activity of spleen macrophages by the NBT reduction test. Probiotic-supplemented diets provided a good substrate for innate immune system function; the phagocytic index was significantly enhanced in fish fed soy oil and the probiotic, and at the end of the experimental period, ROS production increased in fish fed soy oil. The substitution of fish oil by soy oil is recommended for food formulation and will contribute to promoting sustainable aquaculture. Probiotics are also recommended for channel catfish farming as they may act as immunonutrients.

  17. The seed's protein and oil content, fatty acid composition, and growing cycle length of a single genotype of chia (Salvia hispanica L.) as affected by environmental factors.

    PubMed

    Ayerza, Ricardo

    2009-01-01

    As a botanical source, variability in chia seed composition could be expected between growing locations, and between years within a location, due to genotype and environment effects as well genetic x environment's interactions. The objective of the present study was to determine the location effect on the growing cycle length, and seed's protein content, lipid content, and fatty acid profiles, of a single chia genotype. Seeds of chia genotype Tzotzol grown on eight sites in five different ecosystems were tested. One site was in Argentina, in the Semi-Arid Chaco ecosystem (T(5)); one was in Bolivia, in the Sub-Humid Chaco ecosystem (T(4)); and six in Ecuador, one in the Coastal Desert (T(3)), two on the Tropical Rain Forest (T(2)), and three in the Inter-Andean Dry Valley ecosystem (T(1)). Seeds from plants grown in T(4) and in T(3) contained significantly (P <0.05) more protein percentage than did seeds from the other three ecosystems. No significant (P <0.05) differences in protein content were found between T(3) and T(4), and between T(1), T(2), and T(5). Seeds from T(1) and T(5) ecosystems, with 33.5 and 32.2%, respectively, were the numerically highest oil content producers, but their results were only significantly (P <0.05) higher when compared with the T(2) seeds. Significant (P <0.05) differences in palmitic, stearic, oleic, linoleic and alpha-linolenic fatty acids between oils from seeds grown in different ecosystems were detected, however. Oil of seeds grown in the T(3) ecosystem had the palmitic, stearic and oleic fatty acids' highest contents. Palmitic and oleic fatty acid levels were significantly (P <0.05) higher when were compared to that of seeds grown in the T(1) ecosystem, and stearic when was compared to that of seeds grown in the T(5) ecosystem; omega-6 linoleic fatty acid content was significantly (P <0.05) lower in oils of seeds produced in T(1), and T(2) than in those produced in T(3), T(4), and T(5) ecosystems; omega-3 alpha-linolenic fatty

  18. Complex coacervation of hyaluronic acid and chitosan: effects of pH, ionic strength, charge density, chain length and the charge ratio.

    PubMed

    Kayitmazer, A B; Koksal, A F; Kilic Iyilik, E

    2015-11-28

    Hyaluronic acid (HA) and chitosan (CH) can form nanoparticles, hydrogels, microspheres, sponges, and films, all with a wide range of biomedical applications. This variety of phases reflects the multiple pathways available to HA/CH complexes. Here, we use turbidimetry, dynamic light scattering, light microscopy and zeta potential measurements to show that the state of the dense phase depends on the molar ratio of HA carboxyl to CH amines, and is strongly dependent on their respective degrees of ionization, α and β. Due to the strong charge complementarity between HA and CH, electrostatic self-assembly takes place at very acidic pH, but is almost unobservable at ionic strength (I) ≥ 1.5 M NaCl. All systems display discontinuity in the I-dependence of the turbidity, corresponding to a transition from coacervates to flocculates. An increase in either polymer chain length or charge density enhances phase separation. Remarkably, non-stoichiometric coacervate suspensions form at zeta potentials far away from zero. This result is attributed to the entropic effects of chain semi-flexibility as well as to the charge mismatch between the two biopolymers. PMID:26406548

  19. Quantitative 'Omics Analyses of Medium Chain Length Polyhydroxyalkanaote Metabolism in Pseudomonas putida LS46 Cultured with Waste Glycerol and Waste Fatty Acids.

    PubMed

    Fu, Jilagamazhi; Sharma, Parveen; Spicer, Vic; Krokhin, Oleg V; Zhang, Xiangli; Fristensky, Brian; Cicek, Nazim; Sparling, Richard; Levin, David B

    2015-01-01

    Transcriptomes and proteomes of Pseudomonas putida LS46 cultured with biodiesel-derived waste glycerol or waste free fatty acids, as sole carbon sources, were compared under conditions that were either permissive or non-permissive for synthesis of medium chain length polyhydroxyalkanoates (mcl-PHA). The objectives of this study were to elucidate mechanisms that influence activation of biopolymer synthesis, intra-cellular accumulation, and monomer composition, and determine if these were physiologically specific to the carbon sources used for growth of P. putida LS46. Active mcl-PHA synthesis by P. putida LS46 was associated with high expression levels of key mcl-PHA biosynthesis genes and/or gene products including monomer-supplying proteins, PHA synthases, and granule-associated proteins. 'Omics data suggested that expression of these genes were regulated by different genetic mechanisms in P. putida LS46 cells in different physiological states, when cultured on the two waste carbon sources. Optimal polymer production by P. putida LS46 was primarily limited by less efficient glycerol metabolism during mcl-PHA synthesis on waste glycerol. Mapping the 'Omics data to the mcl-PHA biosynthetic pathway revealed significant variations in gene expression, primarily involved in: 1) glycerol transportation; 2) enzymatic reactions that recycle reducing equivalents and produce key mcl-PHA biosynthesis pathway intermediates (e.g. NADH/NADPH, acetyl-CoA). Active synthesis of mcl-PHAs was observed during exponential phase in cultures with waste free fatty acids, and was associated with the fatty acid beta-oxidation pathway. A putative Thioesterase in the beta-oxidation pathway that may regulate the level of fatty acid beta-oxidation intermediates, and thus carbon flux to mcl-PHA biosynthesis, was highly up-regulated. Finally, the data suggested that differences in expression of selected fatty acid metabolism and mcl-PHA monomer-supplying enzymes may play a role in determining the

  20. Quantitative ‘Omics Analyses of Medium Chain Length Polyhydroxyalkanaote Metabolism in Pseudomonas putida LS46 Cultured with Waste Glycerol and Waste Fatty Acids

    PubMed Central

    Fu, Jilagamazhi; Sharma, Parveen; Spicer, Vic; Krokhin, Oleg V.; Zhang, Xiangli; Fristensky, Brian; Cicek, Nazim; Sparling, Richard; Levin, David. B.

    2015-01-01

    Transcriptomes and proteomes of Pseudomonas putida LS46 cultured with biodiesel-derived waste glycerol or waste free fatty acids, as sole carbon sources, were compared under conditions that were either permissive or non-permissive for synthesis of medium chain length polyhydroxyalkanoates (mcl-PHA). The objectives of this study were to elucidate mechanisms that influence activation of biopolymer synthesis, intra-cellular accumulation, and monomer composition, and determine if these were physiologically specific to the carbon sources used for growth of P. putida LS46. Active mcl-PHA synthesis by P. putida LS46 was associated with high expression levels of key mcl-PHA biosynthesis genes and/or gene products including monomer-supplying proteins, PHA synthases, and granule-associated proteins. ‘Omics data suggested that expression of these genes were regulated by different genetic mechanisms in P. putida LS46 cells in different physiological states, when cultured on the two waste carbon sources. Optimal polymer production by P. putida LS46 was primarily limited by less efficient glycerol metabolism during mcl-PHA synthesis on waste glycerol. Mapping the ‘Omics data to the mcl-PHA biosynthetic pathway revealed significant variations in gene expression, primarily involved in: 1) glycerol transportation; 2) enzymatic reactions that recycle reducing equivalents and produce key mcl-PHA biosynthesis pathway intermediates (e.g. NADH/NADPH, acetyl-CoA). Active synthesis of mcl-PHAs was observed during exponential phase in cultures with waste free fatty acids, and was associated with the fatty acid beta-oxidation pathway. A putative Thioesterase in the beta-oxidation pathway that may regulate the level of fatty acid beta-oxidation intermediates, and thus carbon flux to mcl-PHA biosynthesis, was highly up-regulated. Finally, the data suggested that differences in expression of selected fatty acid metabolism and mcl-PHA monomer-supplying enzymes may play a role in determining

  1. Dissociation of a strong acid in neat solvents: diffusion is observed after reversible proton ejection inside the solvent shell.

    PubMed

    Veiga-Gutiérrez, Manoel; Brenlla, Alfonso; Carreira Blanco, Carlos; Fernández, Berta; Kovalenko, Sergey A; Rodríguez-Prieto, Flor; Mosquera, Manuel; Lustres, J Luis Pérez

    2013-11-14

    Strong-acid dissociation was studied in alcohols. Optical excitation of the cationic photoacid N-methyl-6-hydroxyquinolinium triggers proton transfer to the solvent, which was probed by spectral reconstruction of picosecond fluorescence traces. The process fulfills the classical Eigen-Weller mechanism in two stages: (a) solvent-controlled reversible dissociation inside the solvent shell and (b) barrierless splitting of the encounter complex. This can be appreciated only when fluorescence band integrals are used to monitor the time evolution of the reactant and product concentrations. Band integrals are insensitive to solvent dynamics and report relative concentrations directly. This was demonstrated by first measuring the fluorescence decay of the conjugate base across the full emission band, independently of the proton-transfer reaction. Multiexponential decay curves at single wavelengths result from a dynamic red shift of fluorescence in the course of solvent relaxation, whereas clean single exponential decays are obtained if the band integral is monitored instead. The extent of the shift is consistent with previously reported femtosecond transient absorption measurements, continuum theory of solvatochromism, and molecular properties derived from quantum chemical calculations. In turn, band integrals show clean biexponential decay of the photoacid and triexponential evolution of the conjugate base in the course of the proton transfer to solvent reaction. The dissociation step follows the slowest stage of solvation, which was measured here independently by picosecond fluorescence spectroscopy in five aliphatic alcohols. Also, the rate constant of the encounter-complex splitting stage is compatible with proton diffusion. Thus, for this photoacid, both stages reach the highest possible rates: solvation and diffusion control. Under these conditions, the concentration of the encounter complex is substantial during the earliest nanosecond.

  2. Δ6-fatty acid desaturase and fatty acid elongase mRNA expression, phagocytic activity and weight-to-length relationships in channel catfish (Ictalurus punctatus) fed alternative diets with soy oil and a probiotic.

    PubMed

    Santerre, A; Téllez-Bañuelos, M C; Casas-Solís, J; Castro-Félix, P; Huízar-López, M R; Zaitseva, G P; Horta-Fernández, J L; Trujillo-García, E A; de la Mora-Sherer, D; Palafox-Luna, J A; Juárez-Carrillo, E

    2015-01-01

    A time-course feeding trial was conducted for 120 days on juvenile channel catfish (Ictalurus punctatus) to study the effects of diets differing in oil source (fish oil or soy oil) and supplementation with a commercial probiotic. Relative levels of Δ6-fatty acid desaturase (Δ6-FAD) and fatty acid elongase (FAE) expression were assessed in brain and liver tissues. Both genes showed similar expression levels in all groups studied. Fish weight-to-length relationships were evaluated using polynomial regression analyses, which identified a burst in weight and length in the channel catfish on day 105 of treatment; this increase was related to an increase in gene expression. Mid-intestinal lactic acid bacterium (LAB) count was determined according to morphological and biochemical criteria using API strips. There was no indication that intestinal LAB count was affected by the modified diets. The Cunningham glass adherence method was applied to evaluate phagocytic cell activity in peripheral blood. Reactive oxygen species (ROS) generation was assessed through the respiratory burst activity of spleen macrophages by the NBT reduction test. Probiotic-supplemented diets provided a good substrate for innate immune system function; the phagocytic index was significantly enhanced in fish fed soy oil and the probiotic, and at the end of the experimental period, ROS production increased in fish fed soy oil. The substitution of fish oil by soy oil is recommended for food formulation and will contribute to promoting sustainable aquaculture. Probiotics are also recommended for channel catfish farming as they may act as immunonutrients. PMID:26400353

  3. Direct determination of rosmarinic acid in Lamiaceae herbs using diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and chemometrics.

    PubMed

    Saltas, Dimitrios; Pappas, Christos S; Daferera, Dimitra; Tarantilis, Petros A; Polissiou, Moschos G

    2013-04-01

    For the determination of rosmarinic acid (RA) directly in pulverized plant material, a method is developed using diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) without any physicochemical pretreatment of samples. The RA content of 11 samples of eight different Lamiaceae herbs, as determined by high performance liquid chromatography (HPLC), varied between 86 ± 1 mg/g (in lemon balm) and 12.0 ± 0.8 mg/g (in hyssop) of dried plant material. The 11 samples and 50 other additional samples, which were prepared by mixing initial samples with KBr, were measured using DRIFTS. The second derivative of the spectral region 1344-806 cm(-1) was used and the corresponding data were analyzed using partial least squares (PLS) regression. The correlation between infrared spectral analysis and HPLC measurements shows that the DRIFTS method is sufficiently accurate, simple, and rapid. The RA content of the 11 Lamiaceae samples determined by DRIFTS ranged from 81 ± 4 mg/g (in lemon balm) to 12 ± 3 mg/g (in hyssop) of dried plant material. PMID:23496773

  4. [Acid phosphatase of leukocytes in patients with diffuse toxic goiter in evaluating the stage of the disease].

    PubMed

    Vaiuta, N P; Livshits, A Kh; Mendeleev, I M

    1987-01-01

    Acid phosphatase (AP) of lymphocytes and neutrophils was examined cytochemically in 23 patients with associated diffuse toxic goiter (DTG) and thyrotoxicosis during thiamazol treatment, in 20 persons with a DTG remission, and in 5 patients with postradiation and postoperative hypothyroses. AP activity with multiple-granule distribution of the enzyme was high in the majority of the patients with thyrotoxicosis, decreasing with thiamazol treatment. Thyrotoxicosis recurred in 4 out of 11 patients whose lymphocytes had an increased amount of AP during a DTG remission. In 9 patients with normal AP content, no relapses were noted during a DTG remission. Two patients with iatrogenic hypothyroses associated with high lymphocytic AP activity manifested elevated titres of antithyroglobulin immunoglobulins (ATI). In 3 patients with normal content of cellular AP, the ATI titre was low. Cellular AP, a non-specific marker of immunogenesis activity, makes it possible to presumably differentiate the stages of DTG and to evaluate to a definite degree the character of a remission. The preserved high activity of lymphocytic AP in patients with a DTG remission is a prognostically unfavourable factor as regards thyrotoxicosis relapses. The high titre of ATI and activity of lymphocytic AP attest to the predominant autoimmune component of such hypothyroses in part of DTG patients. The authors stress that such patients should receive combined thyroid and glucocorticoid therapy.

  5. Direct determination of rosmarinic acid in Lamiaceae herbs using diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and chemometrics.

    PubMed

    Saltas, Dimitrios; Pappas, Christos S; Daferera, Dimitra; Tarantilis, Petros A; Polissiou, Moschos G

    2013-04-01

    For the determination of rosmarinic acid (RA) directly in pulverized plant material, a method is developed using diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) without any physicochemical pretreatment of samples. The RA content of 11 samples of eight different Lamiaceae herbs, as determined by high performance liquid chromatography (HPLC), varied between 86 ± 1 mg/g (in lemon balm) and 12.0 ± 0.8 mg/g (in hyssop) of dried plant material. The 11 samples and 50 other additional samples, which were prepared by mixing initial samples with KBr, were measured using DRIFTS. The second derivative of the spectral region 1344-806 cm(-1) was used and the corresponding data were analyzed using partial least squares (PLS) regression. The correlation between infrared spectral analysis and HPLC measurements shows that the DRIFTS method is sufficiently accurate, simple, and rapid. The RA content of the 11 Lamiaceae samples determined by DRIFTS ranged from 81 ± 4 mg/g (in lemon balm) to 12 ± 3 mg/g (in hyssop) of dried plant material.

  6. Synergistic efficacy of salicylic acid with a penetration enhancer on human skin monitored by OCT and diffuse reflectance spectroscopy

    PubMed Central

    Zhao, Qingliang; Dai, Cuixia; Fan, Shanhui; Lv, Jing; Nie, Liming

    2016-01-01

    Salicylic acid (SA) has been frequently used as a facial chemical peeling agent (FCPA) in various cosmetics for facial rejuvenation and dermatological treatments in the clinic. However, there is a tradeoff between therapeutic effectiveness and possible adverse effects caused by this agent for cosmetologists. To optimize the cosmetic efficacy with minimal concentration, we proposed a chemical permeation enhancer (CPE) azone to synergistically work with SA on human skin in vivo. The optical properties of human skin after being treated with SA alone and SA combined with azone (SA@azone) were successively investigated by diffuse reflectance spectroscopy (DRS) and optical coherence tomography (OCT). Our results revealed that as the SA concentration increased, the light reflectance decreased and the absorption increased. We also found that SA@azone exhibited a synergistic effect on enhancing light penetration and OCT imaging depth. We demonstrated that the combination of DRS and OCT techniques could be used as a noninvasive, rapid and accurate measurement method to monitor the subtle changes of skin tissue after treatment with FCPA and CPE. The approach will greatly benefit the development of clinical cosmetic surgery, dermatosis diagnosis and therapeutic effect inspection in related biomedical studies. PMID:27721398

  7. Synergistic efficacy of salicylic acid with a penetration enhancer on human skin monitored by OCT and diffuse reflectance spectroscopy

    NASA Astrophysics Data System (ADS)

    Zhao, Qingliang; Dai, Cuixia; Fan, Shanhui; Lv, Jing; Nie, Liming

    2016-10-01

    Salicylic acid (SA) has been frequently used as a facial chemical peeling agent (FCPA) in various cosmetics for facial rejuvenation and dermatological treatments in the clinic. However, there is a tradeoff between therapeutic effectiveness and possible adverse effects caused by this agent for cosmetologists. To optimize the cosmetic efficacy with minimal concentration, we proposed a chemical permeation enhancer (CPE) azone to synergistically work with SA on human skin in vivo. The optical properties of human skin after being treated with SA alone and SA combined with azone (SA@azone) were successively investigated by diffuse reflectance spectroscopy (DRS) and optical coherence tomography (OCT). Our results revealed that as the SA concentration increased, the light reflectance decreased and the absorption increased. We also found that SA@azone exhibited a synergistic effect on enhancing light penetration and OCT imaging depth. We demonstrated that the combination of DRS and OCT techniques could be used as a noninvasive, rapid and accurate measurement method to monitor the subtle changes of skin tissue after treatment with FCPA and CPE. The approach will greatly benefit the development of clinical cosmetic surgery, dermatosis diagnosis and therapeutic effect inspection in related biomedical studies.

  8. In situ measurements of labile Al and Mn in acid mine drainage using diffusive gradients in thin films.

    PubMed

    Søndergaard, Jens

    2007-08-15

    The technique of diffusive gradients in thin films (DGT) can be used for in situ measurements of labile metal species in water, but the application for this method on acid mine drainage (AMD) is complicated due to reduced sampler adsorption of metals at low pH. This study evaluates the use of DGT on labile Al and Mn in AMD (pH 3.1-4.2). DGT measurements were performed both in standard solutions in the laboratory and in situ in the field. Laboratory results show that DGT can be used in water with pH as low as 3.0 for Al and 4.0 for Mn without correcting for reduced adsorption. Below pH 4.0, the adsorption of Mn showed a linearly decrease with pH to approximately 55% at pH 3.0. Taking this correction into account revealed that 84-100% of the total dissolved Al and Mn measured in the field was DGT-labile. Measurements using DGT agreed well with predictions using the speciation program WHAM VI. This study shows that the use of DGT can be extended below the previously reported pH working range for Al, and for Mn using a simple linear correction with respect to pH, and demonstrates that the technique can be applied for monitoring time-integrated labile metal concentrations at AMD sites. PMID:17620010

  9. Impact of a mixed chain length omega-3 fatty acid diet on production variables in commercial free-range laying hens.

    PubMed

    Toscano, M J; Wilkins, L J; Tarlton, J F

    2012-01-01

    1. Previous studies found beneficial effects on the prevalence of keel fractures and bone health in laying hens receiving a short chain ω3 fatty acid diet. However, subsequent work using a mixed short and long chain ω3 diet (MCD) found little benefit to bone health and substantial production losses. 2. The current study examined commercial use of a mixed chain length ration in multiple farms and flocks and identified a detrimental effect on productivity including: mortality, number of poor quality eggs, hen daily average, feed consumption, and increased egg weight. 3. Production data were acquired from 11 flocks housed on 5 farms and modelled using MlwiN, a statistical package developed for analysis of hierarchical data. Production responses were individually modelled with duration of exposure to the diet, age of introduction, flock size and farm, included as prediction variables. 4. Analysis indicated birds receiving the MCD manifested dramatic increases in mortality, poor quality eggs, mean egg weight, feed consumption and decreased production in comparison to control flocks receiving a standard ration. Increased exposure time appeared to increase the magnitude of the diet effect. 5. Although no data were collected to explain the potential mechanisms of this diet, the authors discuss several possible scenarios including excessive long chain ω3 content overwhelming eicosanoid regulatory capacity and changes in behaviour patterns.

  10. Length and Amino Acid Sequence of Peptides Substituted for the 5-HT3A Receptor M3M4 Loop May Affect Channel Expression and Desensitization

    PubMed Central

    McKinnon, Nicole K.; Bali, Moez; Akabas, Myles H.

    2012-01-01

    5-HT3A receptors are pentameric neurotransmitter-gated ion channels in the Cys-loop receptor family. Each subunit contains an extracellular domain, four transmembrane segments (M1, M2, M3, M4) and a 115 residue intracellular loop between M3 and M4. In contrast, the M3M4 loop in prokaryotic homologues is <15 residues. To investigate the limits of M3M4 loop length and composition on channel function we replaced the 5-HT3A M3M4 loop with two to seven alanine residues (5-HT3A-An = 2–7). Mutants were expressed in Xenopus laevis oocytes and characterized using two electrode voltage clamp recording. All mutants were functional. The 5-HT EC50's were at most 5-fold greater than wild-type (WT). The desensitization rate differed significantly among the mutants. Desensitization rates for 5-HT3A-A2, 5-HT3A-A4, 5-HT3A-A6, and 5-HT3A-A7 were similar to WT. In contrast, 5-HT3A-A3 and 5-HT3A-A5 had desensitization rates at least an order of magnitude faster than WT. The one Ala loop construct, 5-HT3A-A1, entered a non-functional state from which it did not recover after the first 5-HT application. These results suggest that the large M3M4 loop of eukaryotic Cys-loop channels is not required for receptor assembly or function. However, loop length and amino acid composition can effect channel expression and desensitization. We infer that the cytoplasmic ends of the M3 and M4 segments may undergo conformational changes during channel gating and desensitization and/or the loop may influence the position and mobility of these segments as they undergo gating-induced conformational changes. Altering structure or conformational mobility of the cytoplasmic ends of M3 and M4 may be the basis by which phosphorylation or protein binding to the cytoplasmic loop alters channel function. PMID:22539982

  11. A mechanistic model of wormhole growth in carbonate matrix acidizing and acid fracturing

    SciTech Connect

    Hung, K.M.; Hill, A.D.; Sepehrnoorl, K.

    1989-01-01

    A mathematical model that describes the growth and competition of wormholes during ann acidizing treatment in a carbonate formation was developed. The model is initialized with the distribution of largest pores. Wormhole characteristics (size, length, and distribution) were found too be controlled by acid-injection, diffusion, and fluid-loss rates.

  12. Nonideal mixing and phase separation in phosphatidylcholine-phosphatidic acid mixtures as a function of acyl chain length and pH.

    PubMed Central

    Garidel, P; Johann, C; Blume, A

    1997-01-01

    The miscibilities of phosphatidic acids (PAs) and phosphatidylcholines (PCs) with different chain lengths (n = 14, 16) at pH 4, pH 7, and pH 12 were examined by differential scanning calorimetry. Simulation of heat capacity curves was performed using a new approach that incorporates changes of cooperativity of the transition in addition to nonideal mixing in the gel and the liquid-crystalline phase as a function of composition. From the simulations of the heat capacity curves, first estimates for the nonideality parameters for nonideal mixing as a function of composition were obtained, and phase diagrams were constructed using temperatures for onset and end of melting, which were corrected for the broadening effect caused by a decrease in cooperativity. In all cases the composition dependence of the nonideality parameters indicated nonsymmetrical mixing behavior. The phase diagrams were therefore further refined by simulations of the coexistence curves using a four-parameter approximation to account for nonideal and nonsymmetrical mixing in the gel and the liquid-crystalline phase. The mixing behavior was studied at three different pH values to investigate how changes in headgroup charge of the PA influences the miscibility. The experiments showed that at pH 7, where the PA component is negatively charged, the nonideality parameters are in most cases negative, indicating that electrostatic effects favor a mixing of the two components. Partial protonation of the PA component at pH 4 leads to strong changes in miscibility; the nonideality parameters for the liquid-crystalline phase are now in most cases positive, indicating clustering of like molecules. The phase diagram for 1,2-dimyristoyl-sn-glycero-3-phosphatidic acid:1,2-dipalmitoyl-sn-glycero-3-phosphorylcholine mixtures at pH 4 indicates that a fluid-fluid immiscibility is likely. The results show that a decrease in ionization of PAs can induce large changes in mixing behavior. This occurs because of a

  13. Flocculation of hematite with polyacrylic acid: Fractal structures in the reaction- and diffusion-limited aggregation regimes

    SciTech Connect

    Ferretti, R.; Zhang, J.; Buffle, J.

    1998-12-15

    The structure of hematite aggregates in the presence of fairly monodisperse polyacrylic acid (PAA) with two different molecular weights (M{sub w} = 1.36 {times} 10{sup 6}, M{sub w}/M{sub n} = 1.53; M{sub w} = 3.69 {times} 10{sup 4}, M{sub w}/M{sub n} = 1.60) was studied using static light scattering (SLS). The fractal dimensions were calculated from the scattering exponents, after taking into account the finite size of aggregates, using exponential and Gaussian cutoff functions. Three flocculation regimes, namely, pre-DLA, DLA (diffusion-limited aggregation), and post-DLA, were defined based on the polymer concentration. In the DLA regime, fractal dimension values, D{sub f} = 1.84 {+-} 0.02 and 1.73 {+-} 0.02, were obtained using exponential and Gaussian cutoff functions, respectively. A fractal dimension of approximately 2.0 was found, as expected, in the pre-DLA regime (at PAA concentrations lower than the optimal dosage for a DLA regime) where the flocculation rate was reaction limited. In contrast, in the post-DLA regime, the flocculation was slow but the structure of aggregates was as tenuous as in the DLA regime with a fractal dimension D{sub f} {approx} 1.8. Moreover, for all three regimes, the D{sub f} values were independent of the molecular weights of PAA. The lower fractal dimension in post-DLA was probably due to the increased concentration of polymer chains between adjacent particles in aggregates. The steric hindrance favored tip-to-tip aggregation, leading to a more tenuous structure.

  14. Determination of uronic acids in isolated hemicelluloses from kenaf using diffuse reflectance infrared fourier transform spectroscopy (DRIFTS) and the curve-fitting deconvolution method.

    PubMed

    Batsoulis, A N; Nacos, M K; Pappas, C S; Tarantilis, P A; Mavromoustakos, T; Polissiou, M G

    2004-02-01

    Hemicellulose samples were isolated from kenaf (Hibiscus cannabinus L.). Hemicellulosic fractions usually contain a variable percentage of uronic acids. The uronic acid content (expressed in polygalacturonic acid) of the isolated hemicelluloses was determined by diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and the curve-fitting deconvolution method. A linear relationship between uronic acids content and the sum of the peak areas at 1745, 1715, and 1600 cm(-1) was established with a high correlation coefficient (0.98). The deconvolution analysis using the curve-fitting method allowed the elimination of spectral interferences from other cell wall components. The above method was compared with an established spectrophotometric method and was found equivalent for accuracy and repeatability (t-test, F-test). This method is applicable in analysis of natural or synthetic mixtures and/or crude substances. The proposed method is simple, rapid, and nondestructive for the samples.

  15. Negligible penetration of incidental amounts of alpha-hydroxy acid from rinse-off personal care products in human skin using an in vitro static diffusion cell model.

    PubMed

    Okuda, M; Donahue, D A; Kaufman, L E; Avalos, J; Simion, F A; Story, D C; Sakaguchi, H; Fautz, R; Fuchs, A

    2011-12-01

    Alpha-hydroxy acids (AHAs), primarily glycolic and lactic acids, are widely used in cosmetics to alleviate dyspigmentation, photodamage, and other aging skin conditions and as pH adjusters. Glycolic acid reportedly enhances skin damage after repeated ultraviolet light exposure, e.g., increased sunburn cell formation. This study assessed potential in vitro skin penetration of lactic acid and malic acid incorporated into rinse-off personal care products, compared with rinse-off and leave-on exposures to glycolic acid (10%, pH 3.5) in a reference lotion. Radiolabeled AHA-fortified shampoo, conditioner, and lotion were evenly applied as single doses to human epidermal membranes mounted in static diffusion cells (not occluded). Exposures were 1-3 min (rinse-off) or 24 h (leave-on). Epidermal penetration of malic acid and lactic acid from the rinse-off shampoo and conditioner, respectively, was negligible, with >99% removed by rinsing, a negligible portion remaining in the stratum corneum (≤0.15%), and even less penetrating into the viable epidermis (≤0.04%). Glycolic acid penetration from the leave-on reference lotion was 1.42 μg equiv./cm2/h, with total absorbable dose recovery (receptor fluid plus epidermis) of 2.51%, compared to 0.009%, 0.003%, and 0.04% for the rinse-off reference lotion, shampoo (malic acid), and conditioner (lactic acid) exposures, respectively. Dermal penetration of AHAs into human skin is pH-, concentration-, and time-dependent. Alpha-hydroxy acids in rinse-off shampoos and conditioners are almost entirely removed from the skin within minutes by rinsing (resulting in negligible epidermal penetration). This suggests that ultraviolet radiation-induced skin effects of AHA-containing rinse-off products are negligible. PMID:21871557

  16. Negligible penetration of incidental amounts of alpha-hydroxy acid from rinse-off personal care products in human skin using an in vitro static diffusion cell model.

    PubMed

    Okuda, M; Donahue, D A; Kaufman, L E; Avalos, J; Simion, F A; Story, D C; Sakaguchi, H; Fautz, R; Fuchs, A

    2011-12-01

    Alpha-hydroxy acids (AHAs), primarily glycolic and lactic acids, are widely used in cosmetics to alleviate dyspigmentation, photodamage, and other aging skin conditions and as pH adjusters. Glycolic acid reportedly enhances skin damage after repeated ultraviolet light exposure, e.g., increased sunburn cell formation. This study assessed potential in vitro skin penetration of lactic acid and malic acid incorporated into rinse-off personal care products, compared with rinse-off and leave-on exposures to glycolic acid (10%, pH 3.5) in a reference lotion. Radiolabeled AHA-fortified shampoo, conditioner, and lotion were evenly applied as single doses to human epidermal membranes mounted in static diffusion cells (not occluded). Exposures were 1-3 min (rinse-off) or 24 h (leave-on). Epidermal penetration of malic acid and lactic acid from the rinse-off shampoo and conditioner, respectively, was negligible, with >99% removed by rinsing, a negligible portion remaining in the stratum corneum (≤0.15%), and even less penetrating into the viable epidermis (≤0.04%). Glycolic acid penetration from the leave-on reference lotion was 1.42 μg equiv./cm2/h, with total absorbable dose recovery (receptor fluid plus epidermis) of 2.51%, compared to 0.009%, 0.003%, and 0.04% for the rinse-off reference lotion, shampoo (malic acid), and conditioner (lactic acid) exposures, respectively. Dermal penetration of AHAs into human skin is pH-, concentration-, and time-dependent. Alpha-hydroxy acids in rinse-off shampoos and conditioners are almost entirely removed from the skin within minutes by rinsing (resulting in negligible epidermal penetration). This suggests that ultraviolet radiation-induced skin effects of AHA-containing rinse-off products are negligible.

  17. Estimation of Free, Conjugated, and Diffusible Indole-3-acetic Acid in Etiolated Maize Shoots by the Indolo-α-pyrone Fluorescence Method

    PubMed Central

    Iino, Moritoshi; Carr, Denis J.

    1982-01-01

    Procedures for estimating free indoleacetic acid (IAA extracted from tissue homogenates by aqueous acetone), conjugated IAA (extracted by aqueous acetone and hydrolyzed by 1 n KOH), and diffusible IAA (diffused from the excised tissue into water), in shoots of etiolated 3-day-old maize (Zea mays L. cv. GH 390) seedlings are described, the indolo-α-pyrone fluorescence method being used to assay IAA. The reliability of the procedure is shown by comparative IAA determinations of the extracts using the gas chromatography-mass spectrometry method in which the methyl ester, heptafluorobutyryl derivative of IAA is assayed using the selected-ion-monitoring technique with deuterated IAA as an internal standard. A 3-millimeter-long coleoptile tip, a coleoptile with its included leaves and nodal region (whole coleoptile), and a mesocotyl each contains 0.2, 1.7, and 1.5 nanograms of free IAA, respectively. The whole coleoptile and the mesocotyl contain slightly less conjugated IAA than their content of free IAA. IAA diffuses from the coleoptile tip at the rate of 1.0 nanograms per tip per hour; from the base of the whole coleoptile and a set of leaves excised from a coleoptile, IAA diffuses at the rate of 0.62 and 0.17 nanogram per plant part per hour, respectively. The data obtained support the classical assumption that the coleoptile tip produces IAA. It is also suggested that some IAA is decomposed during its downward transport in the coleoptile. PMID:16662325

  18. The Effect of Omega-3 Docosahexaenoic Acid Supplementation on Gestational Length: Randomized Trial of Supplementation Compared to Nutrition Education for Increasing n-3 Intake from Foods

    PubMed Central

    Harris, Mary A.; Reece, Melanie S.; McGregor, James A.; Wilson, John W.; Burke, Shannon M.; Wheeler, Marsha; Anderson, Jennifer E.; Auld, Garry W.; French, Janice I.; Allen, Kenneth G. D.

    2015-01-01

    Objective. DHA supplementation was compared to nutrition education to increase DHA consumption from fish and DHA fortified foods. Design. This two-part intervention included a randomized double-blind placebo controlled DHA supplementation arm and a nutrition education arm designed to increase intake of DHA from dietary sources by 300 mg per day. Setting. Denver Health Hospitals and Clinics, Denver, Colorado, USA. Population. 871 pregnant women aged 18–40 were recruited between16 and 20 weeks of gestation of whom 564 completed the study and complete delivery data was available in 505 women and infants. Methods. Subjects received either 300 or 600 mg DHA or olive oil placebo or nutrition education. Main Outcome Variable. Gestational length. Results. Gestational length was significantly increased by 4.0–4.5 days in women supplemented with 600 mg DHA per day or provided with nutrition education. Each 1% increase in RBC DHA at delivery was associated with a 1.6-day increase in gestational length. No significant effects on birth weight, birth length, or head circumference were demonstrated. The rate of early preterm birth (1.7%) in those supplemented with DHA (combined 300 and 600 mg/day) was significantly lower than in controls. Conclusion. Nutrition education or supplementation with DHA can be effective in increasing gestational length. PMID:26413500

  19. Polyketide chain length control by chain length factor.

    PubMed

    Tang, Yi; Tsai, Shiou-Chuan; Khosla, Chaitan

    2003-10-22

    Bacterial aromatic polyketides are pharmacologically important natural products. A critical parameter that dictates product structure is the carbon chain length of the polyketide backbone. Systematic manipulation of polyketide chain length represents a major unmet challenge in natural product biosynthesis. Polyketide chain elongation is catalyzed by a heterodimeric ketosynthase. In contrast to homodimeric ketosynthases found in fatty acid synthases, the active site cysteine is absent from the one subunit of this heterodimer. The precise role of this catalytically silent subunit has been debated over the past decade. We demonstrate here that this subunit is the primary determinant of polyketide chain length, thereby validating its designation as chain length factor. Using structure-based mutagenesis, we identified key residues in the chain length factor that could be manipulated to convert an octaketide synthase into a decaketide synthase and vice versa. These results should lead to novel strategies for the engineered biosynthesis of hitherto unidentified polyketide scaffolds.

  20. Electro-fenton and photoelectro-fenton degradation of sulfanilic acid using a boron-doped diamond anode and an air diffusion cathode.

    PubMed

    El-Ghenymy, Abdellatif; Garrido, José Antonio; Centellas, Francesc; Arias, Conchita; Cabot, Pere Lluís; Rodríguez, Rosa María; Brillas, Enric

    2012-04-01

    The mineralization of sulfanilic acid has been studied by electro-Fenton (EF) and photoelectro-Fenton (PEF) reaction with UVA light using an undivided electrochemical cell with a boron-doped diamond (BDD) anode and an air diffusion cathode able to generate H(2)O(2). Organics were then oxidized by hydroxyl radicals formed at the anode surface from water oxidation and in the bulk from Fenton's reaction between generated H(2)O(2) and added Fe(2+). The UVA irradiation in PEF enhanced the production of hydroxyl radicals in the bulk, accelerating the removal of organics and photodecomposed intermediates like Fe(III)-carboxylate complexes. Partial decontamination of 1.39 mM sulfanilic acid solutions was achieved by EF until 100 mA cm(-2) at optimum conditions of 0.4 mM Fe(2+) and pH 3.0. The increase in current density and substrate content led to an almost total mineralization. In contrast, the PEF process was more powerful, yielding almost complete mineralization in less electrolysis time under comparable conditions. The kinetics for sulfanilic acid decay always followed a pseudo-first-order reaction. Hydroquinone and p-benzoquinone were detected as aromatic intermediates, whereas acetic, maleic, formic, oxalic, and oxamic acids were identified as generated carboxylic acids. NH(4)(+) ion was preferentially released in both treatments, along with NO(3)(-) ion in smaller proportion.

  1. Tuning the diffusion dialysis performance by surface cross-linking of PPO anion exchange membranes--simultaneous recovery of sulfuric acid and nickel from electrolysis spent liquor of relatively low acid concentration.

    PubMed

    Tongwen, Xu; Weihua, Yang

    2004-06-18

    The results of the development of the industrial diffusion dialysis technology and the unit based on it for sulfate acid recovery from nickel electrolysis waste have been considered. Unlike most acid recovery systems, this system has a relatively low acid concentration and the main aim is to recover both nickel and acid sulfate by recycling the waste and the recovered acid to the respective steps of electrolysis process. So the waste volume control seems to be the most important thing. To satisfy with this new request, the membrane is surface-cross-linked with aqueous ammonium to decrease waste volume expansion caused by the water osmosis. The results showed that the best membrane for such operation is the one that cross-linked at least 8 h with a volumetric expansion factor (volumetric ratio of waste to feed) less than 1.1. Pilot diffusional runs were conducted with this membrane at various feed flow rate and flow ratio of stripping water and feed. After comprehensively considering all factors, the range of feed flow and the flow ratio has been recommended to be 1.2-1.8 l/h and 1.05-1.1, respectively. Under these conditions, nickel leakage can be controlled within 4% and the acid recover ratio can attain as high as 66-72%. The recovered acid can be recycled to the back-extraction step by mixing it with high concentration acid and the waste recycled to the initial leaching stage by adjusting the acid concentration to recover valuable metal nickel and the residual acid. Therefore, the new technology discards nothing and shows many advantages whether in environmental aspect or economical aspect and thus should be deserved attention. PMID:15177755

  2. Structural and Biochemical Analysis of a Single Amino-Acid Mutant of WzzBSF That Alters Lipopolysaccharide O-Antigen Chain Length in Shigella flexneri

    PubMed Central

    Casey, Lachlan W.; Lonhienne, Thierry; Benning, Friederike; Morona, Renato; Kobe, Bostjan

    2015-01-01

    Lipopolysaccharide (LPS), a surface polymer of Gram-negative bacteria, helps bacteria survive in different environments and acts as a virulence determinant of host infection. The O-antigen (Oag) component of LPS exhibits a modal chain-length distribution that is controlled by polysaccharide co-polymerases (PCPs). The molecular basis of the regulation of Oag chain-lengths remains unclear, despite extensive mutagenesis and structural studies of PCPs from Escherichia coli and Shigella. Here, we identified a single mutation (A107P) of the Shigella flexneri WzzBSF, by a random mutagenesis approach, that causes a shortened Oag chain-length distribution in bacteria. We determined the crystal structures of the periplasmic domains of wild-type WzzBSF and the A107P mutant. Both structures form a highly similar open trimeric assembly in the crystals, and show a similar tendency to self-associate in solution. Binding studies by bio-layer interferometry reveal cooperative binding of very short (VS)-core-plus-O-antigen polysaccharide (COPS) to the periplasmic domains of both proteins, but with decreased affinity for the A107P mutant. Our studies reveal that subtle and localized structural differences in PCPs can have dramatic effects on LPS chain-length distribution in bacteria, for example by altering the affinity for the substrate, which supports the role of the structure of the growing Oag polymer in this process. PMID:26378781

  3. A mass transfer model for the fixed-bed adsorption of ferulic acid onto a polymeric resin: axial dispersion and intraparticle diffusion.

    PubMed

    Davila-Guzman, Nancy E; Cerino-Córdova, Felipe J; Soto-Regalado, Eduardo; Loredo-Cancino, Margarita; Loredo-Medrano, José A; García-Reyes, Refugio B

    2016-08-01

    In this study, amberlite XAD-16 (XAD-16) bed column system was used to remove ferulic acid (FA) from aqueous solutions. Laboratory-scale column experiments were conducted in downflow fixed bed at initial FA concentration of 1 g/L, initial pH 3, and 25°C. The performance of the adsorbent bed under different flow rates (1.3-7.7 mL/min) was studied. The bed utilization efficiency was in the range of 64.64-72.21% at the studied flow rates. A mass transfer model considering both axial dispersion and intraparticle diffusion was developed to predict the breakthrough curves of FA adsorption on XAD-16. This model predicted the experimental data better than Bohart-Adams model and Thomas model, based on the low deviation between predicted and experimental data. The axial dispersion coefficient value varied from 6.45 × 10(-6) to 1.10 × 10(-6) m(2)/s at flow rate from 1.3 to 7.7 mL/min, whereas the intraparticle diffusion coefficient was 1.04 × 10(-10) m(2)/s, being this last resistance the rate-limiting step. In conclusion, axial dispersion and intraparticle diffusion phenomena play the major role in predicting the adsorption of FA onto XAD-16 in fixed-bed columns.

  4. Probe diffusion in phase-separated bicontinuous biopolymer gels.

    PubMed

    Wassén, Sophia; Bordes, Romain; Gebäck, Tobias; Bernin, Diana; Schuster, Erich; Lorén, Niklas; Hermansson, Anne-Marie

    2014-11-01

    Probe diffusion was determined in phase separated bicontinuous gels prepared by acid-induced gelation of the whey protein isolate-gellan gum system. The topological characterization of the phase-separated gel systems is achieved by confocal microscopy and the diffusion measurements are performed using pulsed field gradient (PFG) NMR and fluorescence recovery after photo-bleaching (FRAP). These two techniques gave complementary information about the mass transport at different time- and length scales, PFG NMR provided global diffusion rates in the gel systems, while FRAP enabled the measurements of diffusion in different phases of the phase-separated gels. The results revealed that the phase-separated gel with the largest characteristic wavelength had the fastest diffusion coefficient, while the gel with smaller microstructures had a slower probe diffusion rate. By using the diffusion data obtained by FRAP and the structural data from confocal microscopy, modelling through the lattice-Boltzmann framework was carried out to simulate the global diffusion and verify the validity of the experimental measurements. With this approach it was found that discrepancies between the two experimental techniques can be rationalized in terms of probe distribution between the different phases of the system. The combination of different techniques allowed the determination of diffusion in a phase-separated biopolymer gel and gave a clearer picture of this complex system. We also illustrate the difficulties that can arise if precautions are not taken to understand the system-probe interactions.

  5. Intramolecular general acid catalysis of the hydrolysis of 2-(2'-imidazolium)phenyl phosphate, and bond length-reactivity correlations for reactions of phosphate monoester monoanions.

    PubMed

    Brandão, Tiago A S; Orth, Elisa S; Rocha, Willian R; Bortoluzzi, Adailton J; Bunton, Clifford A; Nome, Faruk

    2007-05-11

    Rate constants for the hydrolysis of 2-(2'-imidazolium)phenyl hydrogen phosphate (IMPP) in water at pH<6 indicate that activation by the imidazolium moiety disappears with the deprotonation of the phosphate group, and the reaction involves the hydrogen-bonding of the imidazolium NH with the aryl oxygen leaving group. The reaction should involve a near-planar conformation of the imidazolium and the phenyl groups in the activated complex, which favors proton-transfer. The crystal structure of IMPP was solved, and a bond length-reactivity correlation for reactions of phosphate monoester monoanions is described.

  6. A study of hydrogen-bond dynamics in carboxylic acids by NMR T1 measurements: isotope effects and hydrogen-bond length dependence

    NASA Astrophysics Data System (ADS)

    Agaki, T.; Imashiro, F.; Terao, T.; Hirota, N.; Hayashi, S.

    1987-08-01

    Proton (deuteron) transfer of hydrogen bonds in benzoic, glutaric and p-formylbenzoic acids was studied by proton (deuteron) T1 measurements. Deuteration of carboxylic protons was found to increase the barriers to classical proton jumping as well as quantum-mechanical tunneling. The former barriers increase as the hydrogen-bond distance increases.

  7. Internode length in Pisum. Gene na may block gibberellin synthesis between ent-7. cap alpha. -hydroxykaurenoic acid and biggerellin A/sub 12/-aldehyde. [Pisum sativum

    SciTech Connect

    Ingram, T.J.; Reid, J.B.

    1987-04-01

    The elongation response of the gibberellin (GA) deficient genotypes na, ls, and lh of peas (Pisum sativum L.) to a range of GA-precursors was examined. Plants possessing gene na did not respond to precursors in the GA biosynthetic pathway prior to GA/sub 12/-aldehyde. In contrast, plants possessing lh and ls responded as well as wild-type plants (dwarfed with AMO-1618) to these compounds. The results suggest that GA biosynthesis is blocked prior to ent-kaurene in the lh and ls mutants and between ent-7..cap alpha..-hydroxykaurenoic acid and GA/sub 12/-aldehyde in the na mutant. Feeds of ent(/sup 3/H)kaurenoic acid and (/sup 2/H)GA/sub 12/-aldehyde to a range of genotypes supported the above conclusions. The na line WL1766 was shown by gas chromatography-mass spectrometry (GC-MS) to metabolize(/sup 2/H)GA/sub 12/-aldehyde to a number of (/sup 2/H)C/sub 19/-GAs including GA/sub 1/. However, there was no indication in na genotypes for the metabolism of ent-(/sup 3/H)kaurenoic acid to these GAs. In contrast, the expanding shoot tissue of all Na genotypes examined metabolized ent-(/sup 3/H)kaurenoic acid to radioactive compounds that co-chromatographed with GA/sub 1/, GA/sub 8/, GA/sub 20/, and GA/sub 29/. However, insufficient material was present for unequivocal identification of the metabolites. The radioactive profiles from HPLC of extracts of the node treated with ent-(/sup 3/H)kaurenoic acid were similar for both Na and na plants and contained ent-16..cap alpha..,17-dihydroxykaurenoic acid and ent-6..cap alpha..,7..cap alpha..,16..beta..,17-tetrahydroxykaurenoic acid (both characterized by GC-MS), suggesting that the metabolites arose from side branches of the main GA-biosynthetic pathway. Thus, both Na and na plants appear capable of ent-7..cap alpha..-hydroxylation.

  8. Saturated fatty acid chain length and positional distribution in infant formula: effects on growth and plasma lipids and ketones in piglets.

    PubMed

    Innis, S M; Quinlan, P; Diersen-Schade, D

    1993-03-01

    Human milk contains a large proportion of palmitic acid (16:0) with > 70% esterified to the center sn-2 position of the milk triglyceride. Infant formulas often use 8:0 + 10:0 [medium-chain triglyceride (MCT)] or 12:0 + 14:0 (coconut oil) as the saturated fat. The effect of formula saturated fatty acid composition; 8:0 + 10:0, 12:0 + 14:0, or 16:0 from palm oil or synthesized triglyceride containing predominantly sn-2 16:0 on plasma lipids and fatty acids was studied in piglets. Although the formulas contained similar 18:1 and 18:2n-6, plasma lipid percentages of 18:1 and 18:2n-6 were higher in piglets fed the formula with MCT or coconut oil rather than the formulas with 16:0, or sow milk. The sn-2 16:0 of the synthesized triglyceride had unique properties. Specifically, piglets fed synthesized triglyceride had significantly higher cholesteryl ester 16:0 identical to that in piglets fed sow milk and higher plasma total and high-density-lipoprotein cholesterol than piglets fed the other formulas. PMID:8438772

  9. Photoconductivity of PbSe quantum-dot solids: dependence on ligand anchor group and length.

    PubMed

    Gao, Yunan; Aerts, Michiel; Sandeep, C S Suchand; Talgorn, Elise; Savenije, Tom J; Kinge, Sachin; Siebbeles, Laurens D A; Houtepen, Arjan J

    2012-11-27

    The assembly of quantum dots is an essential step toward many of their potential applications. To form conductive solids from colloidal quantum dots, ligand exchange is required. Here we study the influence of ligand replacement on the photoconductivity of PbSe quantum-dot solids, using the time-resolved microwave conductivity technique. Bifunctional replacing ligands with amine, thiol, or carboxylic acid anchor groups of various lengths are used to assemble quantum solids via a layer-by-layer dip-coating method. We find that when the ligand lengths are the same, the charge carrier mobility is higher in quantum-dot solids with amine ligands, while in quantum-dot solids with thiol ligands the charge carrier lifetime is longer. If the anchor group is the same, the charge carrier mobility is ligand length dependent. The results show that the diffusion length of charge carriers can reach several hundred nanometers.

  10. Effects of micronutrient antioxidants (alpha-tocopherol and ascorbic acid) on skin thickening and lung function in patients with early diffuse systemic sclerosis.

    PubMed

    Ostojic, Predrag; Damjanov, Nemanja

    2011-08-01

    To assess the effects of alpha-tocopherol and ascorbic acid on skin thickening and lung function in patients with early diffuse systemic sclerosis (SSc), thirteen patients with early diffuse SSc, with positive anti-topoisomerase-I antibody, high skin thickening progression rate (STPR ≥ 12/year) and decreased lung diffusing capacity (DLCO ≤ 75%) were included in this study. Patients were randomized into two subgroups: Subgroup A-six patients, treated with intravenous cyclophosphamide (CyP) (500 mg/m(2) of body surface monthly) and antioxidants (alpha-tocopherol 400 IU/day and ascorbic acid 1,000 mg/day), and Subgroup B-seven patients, who received CyP without antioxidants. In both subgroups, effects of treatment on skin thickening and lung function were evaluated by comparison of the modified Rodnan skin score (MRSS), STPR, forced vital capacity (FVC), transfer-factor (DLCO) and diffusing coefficient for carbon monoxide (DLCO/VA) at baseline and 1 month after the sixth pulse of CyP. The mean MRSS did not change from baseline to the end of the follow-up in subgroup A (15.7 vs. 16.4, P = 0.50), but it increased significantly in subgroup B (17.9 vs. 23.6, P = 0.03). Although the mean STPR decreased notably in both subgroups of patients (in subgroup A-from 18.9/year to 2.2/year, P = 0.03, and in subgroup B-from 17.5/year to 8.6/year, P = 0.03), the mean STPR at the end of the treatment period was significantly lower in subgroup A (2.2/year vs. 8.6/year, P = 0.04). The mean value of FVC did not change either in subgroup A (91.0-87%, P = 0.2) or in subgroup B (from 101.2 to 99.7%, P = 0.7). Parameters of lung diffusing capacity improved somewhat in subgroup A (DLCO from 55.7 to 62.0% and DLCO/VA from 68.7 to 74.2%) and decreased in subgroup B (DLCO from 66.2 to 60.6% and DLCO/VA from 76.9 to 71.6%), but differences were not statistically significant. After 6 months of therapy, patients treated with CyP and antioxidants had a significantly lower STPR, compared to

  11. Rapid nuclear import of short nucleic acids.

    PubMed

    Kitagawa, Mai; Okamoto, Akimitsu

    2016-10-01

    Exogenous short-chain nucleic acids undergo rapid import into the nucleus. Fluorescence-labeled dT1-13 DNA microinjected into the cytoplasm domain of a HeLa cell was rapidly imported into the nucleus domain within 1min. This is much more rapid than what has been observed for intracellular diffusion of small molecules. In contrast, import of longer nucleic acids with a length of over 30nt into the nucleus was suppressed.

  12. Rapid nuclear import of short nucleic acids.

    PubMed

    Kitagawa, Mai; Okamoto, Akimitsu

    2016-10-01

    Exogenous short-chain nucleic acids undergo rapid import into the nucleus. Fluorescence-labeled dT1-13 DNA microinjected into the cytoplasm domain of a HeLa cell was rapidly imported into the nucleus domain within 1min. This is much more rapid than what has been observed for intracellular diffusion of small molecules. In contrast, import of longer nucleic acids with a length of over 30nt into the nucleus was suppressed. PMID:27597250

  13. Combustor diffuser interaction program

    NASA Technical Reports Server (NTRS)

    Srinivasan, Ram; Thorp, Daniel

    1986-01-01

    Advances in gas turbine engine performance are achieved by using compressor systems with high stage loading and low part count, which result in high exit Mach numbers. The diffuser and combustor systems in such engines should be optimized to reduce system pressure loss and to maximize the engine thrust-to-weight ratio and minimize length. The state-of-the-art combustor-diffuser systems do not meet these requirements. Detailed understanding of the combustor-diffuser flow field interaction is required for designing advanced gas turbine engines. An experimental study of the combustor-diffuser interaction (CDI) is being conducted to obtain data for the evaluation and improvement of analytical models applicable to a wide variety of diffuser designs. The CDI program consists of four technical phases: Literature Search; Baseline Configuration; Parametric Configurations; and Performance Configurations. Phase 2 of the program is in progress.

  14. Li diffusion in zircon

    NASA Astrophysics Data System (ADS)

    Cherniak, D. J.; Watson, E. B.

    2010-09-01

    Diffusion of Li under anhydrous conditions at 1 atm and under fluid-present elevated pressure (1.0-1.2 GPa) conditions has been measured in natural zircon. The source of diffusant for 1-atm experiments was ground natural spodumene, which was sealed under vacuum in silica glass capsules with polished slabs of zircon. An experiment using a Dy-bearing source was also conducted to evaluate possible rate-limiting effects on Li diffusion of slow-diffusing REE+3 that might provide charge balance. Diffusion experiments performed in the presence of H2O-CO2 fluid were run in a piston-cylinder apparatus, using a source consisting of a powdered mixture of spodumene, quartz and zircon with oxalic acid added to produce H2O-CO2 fluid. Nuclear reaction analysis (NRA) with the resonant nuclear reaction 7Li(p,γ)8Be was used to measure diffusion profiles for the experiments. The following Arrhenius parameters were obtained for Li diffusion normal to the c-axis over the temperature range 703-1.151°C at 1 atm for experiments run with the spodumene source: D_{text{Li}} = 7.17 × 10^{ - 7} { exp }( - 275 ± 11 {text{kJmol}}^{ - 1} /{text{RT}}){text{m}}2 {text{s}}^{ - 1}. Diffusivities are similar for transport parallel to the c-axis, indicating little anisotropy for Li diffusion in zircon. Similar Li diffusivities were also found for experiments run under fluid-present conditions and for the experiment run with the Dy-bearing source. Li diffusion is considerably faster than diffusion of other cations in zircon, with a smaller activation energy for diffusion. Although Li diffusion in zircon is comparatively rapid, zircons will be moderately retentive of Li signatures at mid-crustal metamorphic temperatures, but they are unlikely to retain this information for geologically significant times under high-grade metamorphism.

  15. A NOTE ON PERPENDICULAR SCATTERING LENGTHS

    SciTech Connect

    Tautz, R. C.

    2009-10-01

    The problem of cosmic ray diffusion in magnetostatic slab turbulence is revisited. It is known that, for large timescales, the perpendicular diffusion coefficient is subdiffusive. Although, for small timescales, the field line random walk limit should apply, it is shown that the perpendicular motion is dominated by the Larmor orbit, and that no constant scattering length can be seen. It is therefore concluded that, in magnetostatic slab turbulence, perpendicular transport is completely suppressed.

  16. Repeat length variation in the 5'UTR of myo-inositol monophosphatase gene is related to phytic acid content and contributes to drought tolerance in chickpea (Cicer arietinum L.).

    PubMed

    Joshi-Saha, Archana; Reddy, Kandali S

    2015-09-01

    Myo-inositol metabolism plays a significant role in plant growth and development, and is also used as a precursor for many important metabolites, such as ascorbate, pinitol, and phytate. Phytate (inositol hexakisphosphate) is the major storage pool for phosphate in the seeds. It is utilized during seed germination and growth of the developing embryo. In addition, it is implicated in protection against oxidative stress. In the present study, a panel of chickpea accessions was used for an association analysis. Association analysis accounting for population structure and relative kinship identified alleles of a simple sequence repeat marker, NCPGR90, that are associated with both phytic acid content and drought tolerance. These alleles varied with respect to the dinucleotide CT repeats present within the marker. NCPGR90 located to the 5'UTR of chickpea myo-inositol monophosphatase gene (CaIMP) and showed transcript length variation in drought-tolerant and drought-susceptible accessions. CaIMP from a drought-tolerant accession with a smaller repeat was almost 2-fold upregulated as compared to a susceptible accession having a longer repeat, even under control non-stressed conditions. This study suggests an evolution of simple sequence repeat length variation in CaIMP, which might be regulating phytic acid levels to confer drought tolerance in natural populations of chickpea.

  17. The 35-amino acid C2 protein of Cotton leaf curl Kokhran virus, Burewala, implicated in resistance breaking in cotton, retains some activities of the full-length protein.

    PubMed

    Akbar, Fazal; Iqbal, Zafar; Briddon, Rob W; Vazquez, Franck; Saeed, Muhammad

    2016-10-01

    With one exception, all the begomoviruses characterized so far encode an ~134-amino acid (aa) (A)C2 protein. The exception is the "Burewala" strain of Cotton leaf curl Kokhran virus (CLCuKoV-Bu), associated with resistance breaking in cotton across Pakistan and northwestern India, that encodes a truncated 35-aa C2. The C2 protein encoded by begomoviruses performs multiple functions including suppression of post-transcriptional gene silencing (PTGS), modulating microRNA (miRNA) expression and may be a pathogenicity determinant. The study described here was designed to investigate whether the CLCuKoV-Bu 35-aa C2 retains the activities of the full-length C2 protein. The results showed the 35-aa C2 of CLCuKoV-Bu acts as a pathogenicity determinant, suppresses PTGS and upregulates miRNA expression when expressed from a Potato virus X vector in Nicotiana benthamiana. The symptoms induced by expression of full-length C2 were more severe than those induced by the 35-aa C2. The accumulation of most developmental miRNAs decreases with the full-length C2 protein and increases with the 35-aa peptide of CLCuKoV-Bu. The study also revealed that 35-aa peptide of CLCuKoV-Bu maintains suppressor of silencing activity at a level equal to that of full-length C2. The significance of the results with respect to virus fitness and resistance breaking is discussed.

  18. Structure-related aspects on water diffusivity in fatty acid-soap and skin lipid model systems.

    PubMed

    Norlén, L; Engblom, J

    2000-01-01

    Simplified skin barrier models are necessary to get a first hand understanding of the very complex morphology and physical properties of the human skin barrier. In addition, it is of great importance to construct relevant models that will allow for rational testing of barrier perturbing/occlusive effects of a large variety of substances. The primary objective of this work was to study the effect of lipid morphology on water permeation through various lipid mixtures (i.e., partly neutralised free fatty acids, as well as a skin lipid model mixture). In addition, the effects of incorporating Azone((R)) (1-dodecyl-azacycloheptan-2-one) into the skin lipid model mixture was studied. Small- and wide-angle X-ray diffraction was used for structure determinations. It is concluded that: (a) the water flux through a crystalline fatty acid-sodium soap-water mixture (s) is statistically significantly higher than the water flux through the corresponding lamellar (L(alpha)) and reversed hexagonal (H(II)) liquid crystalline phases, which do not differ between themselves; (b) the water flux through mixtures of L(alpha)/s decreases statistically significantly with increasing relative amounts of lamellar (L(alpha)) liquid crystalline phase; (c) the addition of Azone((R)) to a skin lipid model system induces a reduction in water flux. However, further studies are needed to more closely characterise the structural basis for the occlusive effects of Azone((R)) on water flux. PMID:10640594

  19. Optimizing the models for rapid determination of chlorogenic acid, scopoletin and rutin in plant samples by near-infrared diffuse reflectance spectroscopy

    NASA Astrophysics Data System (ADS)

    Mao, Zhiyi; Shan, Ruifeng; Wang, Jiajun; Cai, Wensheng; Shao, Xueguang

    2014-07-01

    Polyphenols in plant samples have been extensively studied because phenolic compounds are ubiquitous in plants and can be used as antioxidants in promoting human health. A method for rapid determination of three phenolic compounds (chlorogenic acid, scopoletin and rutin) in plant samples using near-infrared diffuse reflectance spectroscopy (NIRDRS) is studied in this work. Partial least squares (PLS) regression was used for building the calibration models, and the effects of spectral preprocessing and variable selection on the models are investigated for optimization of the models. The results show that individual spectral preprocessing and variable selection has no or slight influence on the models, but the combination of the techniques can significantly improve the models. The combination of continuous wavelet transform (CWT) for removing the variant background, multiplicative scatter correction (MSC) for correcting the scattering effect and randomization test (RT) for selecting the informative variables was found to be the best way for building the optimal models. For validation of the models, the polyphenol contents in an independent sample set were predicted. The correlation coefficients between the predicted values and the contents determined by high performance liquid chromatography (HPLC) analysis are as high as 0.964, 0.948 and 0.934 for chlorogenic acid, scopoletin and rutin, respectively.

  20. Sorbitol dehydrogenase. Full-length cDNA sequencing reveals a mRNA coding for a protein containing an additional 42 amino acids at the N-terminal end.

    PubMed

    Wen, Y; Bekhor, I

    1993-10-01

    A cDNA clone encoding rat sorbitol dehydrogenase (SDH) was isolated from a rat testis lambda ZAP II cDNA library. The full-length cDNA insert contained 2277 base pairs (bp), starting 182 bp upstream from an ATG codon where translation to the active enzyme SDH is presumed to be initiated. A second ATG codon, however, was found 126 bp upstream, aligned in the same reading frame as that of the active enzyme. Therefore, the coding sequence for SDH can be translated into an additional 42-amino-acid polypeptide linked to the N-terminal amino acid of the enzyme, generating a pre-sorbitol dehydrogenase. The sequence data indicate that the nucleotide environment around this ATG codon is more favorable towards it being the actual open reading frame (ORF) for a pre-SDH than the ATG codon preceding the nucleotide sequence for SDH. Since no known SDH starts with the additional 42 amino acids, it may be that post-translational removal of this polypeptide accompanies the release of the active enzyme. Next, the 3' untranslated region of the cDNA contained a non-coding 1021 bp downstream from the TAA stop codon. The latter sequence included three putative poly(A) signals: one at nucleotides 1362-1367, the second at nucleotides 1465-1470, and the third at nucleotides 2212-2217 [17 bp away from the poly(A) tail]. In addition to the above findings we also report a variance in one of the amino acids in the SDH cDNA sequence. This variance occurs at position 957-960, where threonine is coded for instead of aspartic acid; in the rat testis SDH cDNA, we find the sequence is ACG instead of GAC, as was reported for the rat liver SDH cDNA. Northern-blot hybridization analysis showed that SDH mRNA is a doublet, one band of 4 kb and the other of 2.3-2.4 kb, in both the rat liver and the rat lens, further confirming that the isolated SDH cDNA constituted a full-length cDNA.

  1. Formation of polyesters consisting of medium-chain-length 3-hydroxyalkanoic acids from gluconate by Pseudomonas aeruginosa and other fluorescent pseudomonads.

    PubMed Central

    Timm, A; Steinbüchel, A

    1990-01-01

    Pseudomonas aeruginosa PAO and 15 other strains of this species synthesized a polyester with 3-hydroxydecanoate as the main constituent (55 to 76 mol%) if the cells were cultivated in the presence of gluconate and if the nitrogen source was exhausted; 3-hydroxyhexanoate, 3-hydroxyoctanoate, and 3-hydroxydodecanoate were minor constituents of the polymer. The polymer was deposited in granules within the cell and amounted to 70% of the cell dry matter in some strains. Among 55 different strains of 41 Pseudomonas species tested, P. aureofaciens (21.6% of cellular dry matter), P. citronellolis (78.0%), P. chlororaphis (8.5%), P. marginalis (11.4%), P. mendocina (50.7%), P. putida (33.5%), and Pseudomonas sp. strain DSM 1650 (54.6%) accumulated this type of polymer at significant levels (greater than 5%) during cultivation on gluconate. In two strains of P. facilis and P. fluorescens, as well as in one strain of P. syringae, this polymer was detected as a minor constituent (much less than 5%). All other strains accumulated either poly(3-hydroxybutyrate) or a polymer consisting mainly of 3-hydroxyoctanoate with octanoate but no polyester with gluconate as the carbon source. Only a few species (e.g., P. stutzeri) were unable to accumulate poly(hydroxyalkanoic acids) (PHA) at all. These results indicated that the formation of PHA depends on a pathway which is distinct from all other known PHA-biosynthetic pathways. The polyesters accumulated by gluconate- or octanoate-grown cells of recombinant strains of P. aeruginosa and P. putida, which harbored the Alcaligenes eutrophus poly(3-hydroxybutyrate)biosynthetic genes, contained 3-hydroxybutyrate as an additional constituent. Images PMID:2125185

  2. Co-drug strategy for promoting skin targeting and minimizing the transdermal diffusion of hydroquinone and tranexamic acid.

    PubMed

    Hsieh, Pei-Wen; Chen, Wei-Yu; Aljuffali, Ibrahim A; Chen, Chun-Che; Fang, Jia-You

    2013-01-01

    Hydroquinone and tranexamic acids (TXA) are skin-lightening agents with a hydrophilic nature and low skin absorption. A high dose is needed for clinical use, resulting in a high incidence of skin irritation. Co-drugs formed by conjugating hydroquinone and TXA were synthesized and their in vitro and in vivo skin absorption characteristics were evaluated. The two synthesized co-drugs were 4-hydroxyphenyl 4-(aminomethyl)cyclohexanecarboxylate (HAC) and 1,4- phenylene bis(aminomethyl)cyclohexanecarboxylate (BAC). The co-drugs were chemically stable in aqueous solution, but rapidly degraded to the respective parent drug in esterases and skin homogenates. Compared to hydroquinone application, 7.2- and 2.4-fold increments in the hydroquinone skin deposition were obtained with the in vitro application of HAC and BAC. HAC and BAC led to 3- and 2-fold enhancements of equivalent TXA deposition compared to TXA administration. The in vivo experiment showed a further enhancement of co-drugs compared to the in vitro setup. The transdermal penetration of co-drugs, especially BAC, was much lower than that of hydroquinone and TXA. This indicated high-level skin targeting by the co-drugs. HAC and BAC revealed strong affinities for the viable epidermis/dermis. Hair follicles are important reservoirs for co-drug delivery. Daily administration of co-drugs to the skin did not generate irritation for up to 7 days. Both co-drugs are superior candidates for treating skin hyperpigmentation. PMID:23931279

  3. Co-drug strategy for promoting skin targeting and minimizing the transdermal diffusion of hydroquinone and tranexamic acid.

    PubMed

    Hsieh, Pei-Wen; Chen, Wei-Yu; Aljuffali, Ibrahim A; Chen, Chun-Che; Fang, Jia-You

    2013-01-01

    Hydroquinone and tranexamic acids (TXA) are skin-lightening agents with a hydrophilic nature and low skin absorption. A high dose is needed for clinical use, resulting in a high incidence of skin irritation. Co-drugs formed by conjugating hydroquinone and TXA were synthesized and their in vitro and in vivo skin absorption characteristics were evaluated. The two synthesized co-drugs were 4-hydroxyphenyl 4-(aminomethyl)cyclohexanecarboxylate (HAC) and 1,4- phenylene bis(aminomethyl)cyclohexanecarboxylate (BAC). The co-drugs were chemically stable in aqueous solution, but rapidly degraded to the respective parent drug in esterases and skin homogenates. Compared to hydroquinone application, 7.2- and 2.4-fold increments in the hydroquinone skin deposition were obtained with the in vitro application of HAC and BAC. HAC and BAC led to 3- and 2-fold enhancements of equivalent TXA deposition compared to TXA administration. The in vivo experiment showed a further enhancement of co-drugs compared to the in vitro setup. The transdermal penetration of co-drugs, especially BAC, was much lower than that of hydroquinone and TXA. This indicated high-level skin targeting by the co-drugs. HAC and BAC revealed strong affinities for the viable epidermis/dermis. Hair follicles are important reservoirs for co-drug delivery. Daily administration of co-drugs to the skin did not generate irritation for up to 7 days. Both co-drugs are superior candidates for treating skin hyperpigmentation.

  4. Measuring Thermodynamic Length

    SciTech Connect

    Crooks, Gavin E

    2007-09-07

    Thermodynamic length is a metric distance between equilibrium thermodynamic states. Among other interesting properties, this metric asymptotically bounds the dissipation induced by a finite time transformation of a thermodynamic system. It is also connected to the Jensen-Shannon divergence, Fisher information, and Rao's entropy differential metric. Therefore, thermodynamic length is of central interestin understanding matter out of equilibrium. In this Letter, we will consider how to denethermodynamic length for a small system described by equilibrium statistical mechanics and how to measure thermodynamic length within a computer simulation. Surprisingly, Bennett's classic acceptance ratio method for measuring free energy differences also measures thermodynamic length.

  5. Diffusive gradients in thin films sampler predicts stress in brown trout (Salmo trutta L.) exposed to aluminum in acid fresh waters.

    PubMed

    Røyset, Oddvar; Rosseland, Bjørn Olav; Kristensen, Torstein; Kroglund, Frode; Garmo, Oyvind Aaberg; Steinnes, Eiliv

    2005-02-15

    Increased levels of aluminum ions released from nutrient-poor soils affected by acid rain have been the primary cause of fish deaths in the acidified watersheds of southern Norway. The complex aluminum chemistry in water requires speciation methods to measure the gill-reactive species imposing toxic effects toward fish. Previously, aluminum speciation has mainly followed the fractionation principles outlined by Barnes/Driscoll, and several analogues of these fractionation principles have been used both in situ and in the laboratory. Due to rapid transformation processes, aluminum speciation in water samples may change even during short storage times. Thus, results obtained by laboratory fractionation methods might be misleading for the assessment of potentially toxic aluminum species in the water. Until now, all in situ field fractionation methods have been time and labor consuming. The DGT technique (diffusive gradients in thin films) is a new in situ sampler collecting a fraction of dissolved metal weighted according to the rate of diffusion and dissociation kinetics. In a field experiment with acid surface water we studied the DGT sampler as a new prediction tool for the gill accumulation of aluminum in trout (Salmo trutta L.) and the induced physiological stress responses measured as changes in blood glucose and plasma chloride. Aluminum determined with DGT (DGT-AI) was higher than labile monomeric aluminum (Ali) determined with a laboratory aluminum fractionation procedure (PCV--a pyrocatechol violet analogue of Barnes/Driscoll), a difference due to collection of a fraction of organically complexed aluminum by DGT and a reduction of the Ali fraction during sample storage. DGT-AI predicted the gill uptake and the aluminum-induced physiological stress responses (increased blood glucose and decreased plasma chloride, r2 from 0.6 to 0.9). The results indicate that DGT-AI is a better predictor for the stress response than laboratory-determined Ali, because the DGT

  6. Diffusion MRI

    NASA Astrophysics Data System (ADS)

    Fukuyama, Hidenao

    Recent advances of magnetic resonance imaging have been described, especially stressed on the diffusion sequences. We have recently applied the diffusion sequence to functional brain imaging, and found the appropriate results. In addition to the neurosciences fields, diffusion weighted images have improved the accuracies of clinical diagnosis depending upon magnetic resonance images in stroke as well as inflammations.

  7. Low-, medium- and high-dose steroids with or without aminocaproic acid in adult hematopoietic SCT patients with diffuse alveolar hemorrhage.

    PubMed

    Rathi, N K; Tanner, A R; Dinh, A; Dong, W; Feng, L; Ensor, J; Wallace, S K; Haque, S A; Rondon, G; Price, K J; Popat, U; Nates, J L

    2015-03-01

    Diffuse alveolar hemorrhage (DAH) is a poorly understood complication of transplantation carrying a high mortality. Patients commonly deteriorate and require intensive care unit (ICU) admission. Treatment with high-dose steroids and aminocaproic acid (ACA) has been suggested. The current study examined 119 critically ill adult hematopoietic transplant patients treated for DAH. Patients were subdivided into low-, medium- and high-dose steroid groups with or without ACA. All groups had similar baseline characteristics and severity of illness scores. Primary objectives were 30, 60, 100 day, ICU and hospital mortality. Overall mortality (n=119) on day 100 was high at 85%. In the steroids and ACA cohort (n=82), there were no significant differences in 30, 60, 100, day, ICU and hospital mortality between the dosing groups. In the steroids only cohort (n=37), the low-dose steroid group had a lower ICU and hospital mortality (P=0.02). Adjunctive treatment with ACA did not produce differences in outcomes. In the multivariate analysis, medium- and high-dose steroids were associated with a higher ICU mortality (P=0.01) as compared with the low-dose group. Our data suggest that treatment strategies may need to be reanalyzed to avoid potentially unnecessary and potentially harmful therapies.

  8. Effect of pectins on the mass transfer kinetics of monosaccharides, amino acids, and a corn oil-in-water emulsion in a Franz diffusion cell.

    PubMed

    Espinal-Ruiz, Mauricio; Restrepo-Sánchez, Luz-Patricia; Narváez-Cuenca, Carlos-Eduardo

    2016-10-15

    The effect of high (HMP) and low (LMP) methoxylated pectins (2%w/w) on the rate and extent of the mass transfer of monosaccharides, amino acids, and a corn oil-in-water emulsion across a cellulose membrane was evaluated. A sigmoidal response kinetic analysis was used to calculate both the diffusion coefficients (rate) and the amount of nutrients transferred through the membrane (extent). In all cases, except for lysine, HMP was more effective than LMP in inhibiting both the rate and extent of the mass transfer of nutrients through the membrane. LMP and HMP, e.g., reduced 1.3 and 3.0times, respectively, the mass transfer rate of glucose, as compared to control (containing no pectin), and 1.3 and 1.5times, respectively, the amount of glucose transferred through the membrane. Viscosity, molecular interactions, and flocculation were the most important parameters controlling the mass transfer of electrically neutral nutrients, electrically charged nutrients, and emulsified lipids, respectively. PMID:27173546

  9. Effect of pectins on the mass transfer kinetics of monosaccharides, amino acids, and a corn oil-in-water emulsion in a Franz diffusion cell.

    PubMed

    Espinal-Ruiz, Mauricio; Restrepo-Sánchez, Luz-Patricia; Narváez-Cuenca, Carlos-Eduardo

    2016-10-15

    The effect of high (HMP) and low (LMP) methoxylated pectins (2%w/w) on the rate and extent of the mass transfer of monosaccharides, amino acids, and a corn oil-in-water emulsion across a cellulose membrane was evaluated. A sigmoidal response kinetic analysis was used to calculate both the diffusion coefficients (rate) and the amount of nutrients transferred through the membrane (extent). In all cases, except for lysine, HMP was more effective than LMP in inhibiting both the rate and extent of the mass transfer of nutrients through the membrane. LMP and HMP, e.g., reduced 1.3 and 3.0times, respectively, the mass transfer rate of glucose, as compared to control (containing no pectin), and 1.3 and 1.5times, respectively, the amount of glucose transferred through the membrane. Viscosity, molecular interactions, and flocculation were the most important parameters controlling the mass transfer of electrically neutral nutrients, electrically charged nutrients, and emulsified lipids, respectively.

  10. Neandertal clavicle length

    PubMed Central

    Trinkaus, Erik; Holliday, Trenton W.; Auerbach, Benjamin M.

    2014-01-01

    The Late Pleistocene archaic humans from western Eurasia (the Neandertals) have been described for a century as exhibiting absolutely and relatively long clavicles. This aspect of their body proportions has been used to distinguish them from modern humans, invoked to account for other aspects of their anatomy and genetics, used in assessments of their phylogenetic polarities, and used as evidence for Late Pleistocene population relationships. However, it has been unclear whether the usual scaling of Neandertal clavicular lengths to their associated humeral lengths reflects long clavicles, short humeri, or both. Neandertal clavicle lengths, along with those of early modern humans and latitudinally diverse recent humans, were compared with both humeral lengths and estimated body masses (based on femoral head diameters). The Neandertal do have long clavicles relative their humeri, even though they fall within the ranges of variation of early and recent humans. However, when scaled to body masses, their humeral lengths are relatively short, and their clavicular lengths are indistinguishable from those of Late Pleistocene and recent modern humans. The few sufficiently complete Early Pleistocene Homo clavicles seem to have relative lengths also well within recent human variation. Therefore, appropriately scaled clavicular length seems to have varied little through the genus Homo, and it should not be used to account for other aspects of Neandertal biology or their phylogenetic status. PMID:24616525

  11. GEMAS: prediction of solid-solution phase partitioning coefficients (Kd) for oxoanions and boric acid in soils using mid-infrared diffuse reflectance spectroscopy.

    PubMed

    Janik, Leslie J; Forrester, Sean T; Soriano-Disla, José M; Kirby, Jason K; McLaughlin, Michael J; Reimann, Clemens

    2015-02-01

    The authors' aim was to develop rapid and inexpensive regression models for the prediction of partitioning coefficients (Kd), defined as the ratio of the total or surface-bound metal/metalloid concentration of the solid phase to the total concentration in the solution phase. Values of Kd were measured for boric acid (B[OH]3(0)) and selected added soluble oxoanions: molybdate (MoO4(2-)), antimonate (Sb[OH](6-)), selenate (SeO4(2-)), tellurate (TeO4(2-)) and vanadate (VO4(3-)). Models were developed using approximately 500 spectrally representative soils of the Geochemical Mapping of Agricultural Soils of Europe (GEMAS) program. These calibration soils represented the major properties of the entire 4813 soils of the GEMAS project. Multiple linear regression (MLR) from soil properties, partial least-squares regression (PLSR) using mid-infrared diffuse reflectance Fourier-transformed (DRIFT) spectra, and models using DRIFT spectra plus analytical pH values (DRIFT + pH), were compared with predicted log K(d + 1) values. Apart from selenate (R(2)  = 0.43), the DRIFT + pH calibrations resulted in marginally better models to predict log K(d + 1) values (R(2)  = 0.62-0.79), compared with those from PSLR-DRIFT (R(2)  = 0.61-0.72) and MLR (R(2)  = 0.54-0.79). The DRIFT + pH calibrations were applied to the prediction of log K(d + 1) values in the remaining 4313 soils. An example map of predicted log K(d + 1) values for added soluble MoO4(2-) in soils across Europe is presented. The DRIFT + pH PLSR models provided a rapid and inexpensive tool to assess the risk of mobility and potential availability of boric acid and selected oxoanions in European soils. For these models to be used in the prediction of log K(d + 1) values in soils globally, additional research will be needed to determine if soil variability is accounted on the calibration.

  12. Hydroxycarboxylic acids and salts

    DOEpatents

    Kiely, Donald E; Hash, Kirk R; Kramer-Presta, Kylie; Smith, Tyler N

    2015-02-24

    Compositions which inhibit corrosion and alter the physical properties of concrete (admixtures) are prepared from salt mixtures of hydroxycarboxylic acids, carboxylic acids, and nitric acid. The salt mixtures are prepared by neutralizing acid product mixtures from the oxidation of polyols using nitric acid and oxygen as the oxidizing agents. Nitric acid is removed from the hydroxycarboxylic acids by evaporation and diffusion dialysis.

  13. Myofilament length dependent activation

    SciTech Connect

    de Tombe, Pieter P.; Mateja, Ryan D.; Tachampa, Kittipong; Mou, Younss Ait; Farman, Gerrie P.; Irving, Thomas C.

    2010-05-25

    The Frank-Starling law of the heart describes the interrelationship between end-diastolic volume and cardiac ejection volume, a regulatory system that operates on a beat-to-beat basis. The main cellular mechanism that underlies this phenomenon is an increase in the responsiveness of cardiac myofilaments to activating Ca{sup 2+} ions at a longer sarcomere length, commonly referred to as myofilament length-dependent activation. This review focuses on what molecular mechanisms may underlie myofilament length dependency. Specifically, the roles of inter-filament spacing, thick and thin filament based regulation, as well as sarcomeric regulatory proteins are discussed. Although the 'Frank-Starling law of the heart' constitutes a fundamental cardiac property that has been appreciated for well over a century, it is still not known in muscle how the contractile apparatus transduces the information concerning sarcomere length to modulate ventricular pressure development.

  14. Length Paradox in Relativity

    ERIC Educational Resources Information Center

    Martins, Roberto de A.

    1978-01-01

    Describes a thought experiment using a general analysis approach with Lorentz transformations to show that the apparent self-contradictions of special relativity concerning the length-paradox are really non-existant. (GA)

  15. Editorial: Redefining Length

    SciTech Connect

    Sprouse, Gene D.

    2011-07-15

    Technological changes have moved publishing to electronic-first publication where the print version has been relegated to simply another display mode. Distribution in HTML and EPUB formats, for example, changes the reading environment and reduces the need for strict pagination. Therefore, in an effort to streamline the calculation of length, the APS journals will no longer use the printed page as the determining factor for length. Instead the journals will now use word counts (or word equivalents for tables, figures, and equations) to establish length; for details please see http://publish.aps.org/authors/length-guide. The title, byline, abstract, acknowledgment, and references will not be included in these counts allowing authors the freedom to appropriately credit coworkers, funding sources, and the previous literature, bringing all relevant references to the attention of readers. This new method for determining length will be easier for authors to calculate in advance, and lead to fewer length-associated revisions in proof, yet still retain the quality of concise communication that is a virtue of short papers.

  16. Equilibrium CO bond lengths

    NASA Astrophysics Data System (ADS)

    Demaison, Jean; Császár, Attila G.

    2012-09-01

    Based on a sample of 38 molecules, 47 accurate equilibrium CO bond lengths have been collected and analyzed. These ultimate experimental (reEX), semiexperimental (reSE), and Born-Oppenheimer (reBO) equilibrium structures are compared to reBO estimates from two lower-level techniques of electronic structure theory, MP2(FC)/cc-pVQZ and B3LYP/6-311+G(3df,2pd). A linear relationship is found between the best equilibrium bond lengths and their MP2 or B3LYP estimates. These (and similar) linear relationships permit to estimate the CO bond length with an accuracy of 0.002 Å within the full range of 1.10-1.43 Å, corresponding to single, double, and triple CO bonds, for a large number of molecules. The variation of the CO bond length is qualitatively explained using the Atoms in Molecules method. In particular, a nice correlation is found between the CO bond length and the bond critical point density and it appears that the CO bond is at the same time covalent and ionic. Conditions which permit the computation of an accurate ab initio Born-Oppenheimer equilibrium structure are discussed. In particular, the core-core and core-valence correlation is investigated and it is shown to roughly increase with the bond length.

  17. The length distribution function of semiconductor filamentary nanocrystals

    NASA Astrophysics Data System (ADS)

    Dubrovskii, V. G.

    2016-07-01

    The length distribution function of semiconductor filamentary nanocrystals is analyzed based on the adsorption-diffusion growth model. It is demonstrated that the asymptotic distribution has a Gaussian shape. If the diffusion flux to the apex comes from the entire lateral surface, the average length increases exponentially with time, and the mean-square deviation is proportional to the average length (exponential growth regime). If the diffusion collection of adatoms is limited to the top of the crystal, the average length increases linearly and the mean-square deviation equals the square root of average length (linear Poisson growth regime). In real-world systems, transition from exponential to Poisson growth occurs at lengths of the order of the diffusion length of adatoms. The dispersion of the distribution is actually defined at the exponential stage. The general classification of length distributions of various crystals is given. It is demonstrated that self-induced GaN- and Ga-catalytic III-V filamentary nanocrystals should be more homogeneous than Au-catalytic ones.

  18. Vaneless diffusers

    NASA Astrophysics Data System (ADS)

    Senoo, Y.

    The influence of vaneless diffusers on flow in centrifugal compressors, particularly on surge, is discussed. A vaneless diffuser can demonstrate stable operation in a wide flow range only if it is installed with a backward leaning blade impeller. The circumferential distortion of flow in the impeller disappears quickly in the vaneless diffuser. The axial distortion of flow at the diffuser inlet does not decay easily. In large specific speed compressors, flow out of the impeller is distorted axially. Pressure recovery of diffusers at distorted inlet flow is considerably improved by half guide vanes. The best height of the vanes is a little 1/2 diffuser width. In small specific speed compressors, flow out of the impeller is not much distorted and pressure recovery can be predicted with one-dimensional flow analysis. Wall friction loss is significant in narrow diffusers. The large pressure drop at a small flow rate can cause the positive gradient of the pressure-flow rate characteristic curve, which may cause surging.

  19. Degradation of bulk diffusion length in CZ silicon solar cells

    SciTech Connect

    Reiss, J.H.; King, R.R.; Mitchell, K.W.

    1995-08-01

    Commercially-produced, unencapsulated, CZ silicon solar cells can lose 3 to 4% of their initial efficiency after exposure to light. After this initial, rapid ( < 30 min.) decrease, the cell power output remains stable. The cell performance recovers in a matter of hours in the dark at room temperature, and degrades again under light exposure. The different conditions under which CZ silicon cells degrade, and the reverse process, annealing, are characterized with the methods of spectral response and current-voltage (I-V) measurements. Iron impurities are a possible cause of this effect.

  20. Diffuse radiation

    NASA Technical Reports Server (NTRS)

    1981-01-01

    A diffuse celestial radiation which is isotropic at least on a course scale were measured from the soft X-ray region to about 150 MeV, at which energy the intensity falls below that of the galactic emission for most galactic latitudes. The spectral shape, the intensity, and the established degree of isotropy of this diffuse radiation already place severe constraints on the possible explanations for this radiation. Among the extragalactic theories, the more promising explanations of the isotropic diffuse emission appear to be radiation from exceptional galaxies from matter antimatter annihilation at the boundaries of superclusters of galaxies of matter and antimatter in baryon symmetric big bang models. Other possible sources for extragalactic diffuse gamma radiation are discussed and include normal galaxies, clusters of galaxies, primordial cosmic rays interacting with intergalactic matter, primordial black holes, and cosmic ray leakage from galaxies.

  1. Diffusion barriers

    NASA Technical Reports Server (NTRS)

    Nicolet, M. A.

    1983-01-01

    The choice of the metallic film for the contact to a semiconductor device is discussed. One way to try to stabilize a contact is by interposing a thin film of a material that has low diffusivity for the atoms in question. This thin film application is known as a diffusion barrier. Three types of barriers can be distinguished. The stuffed barrier derives its low atomic diffusivity to impurities that concentrate along the extended defects of a polycrystalline layer. Sacrificial barriers exploit the fact that some (elemental) thin films react in a laterally uniform and reproducible fashion. Sacrificial barriers have the advantage that the point of their failure is predictable. Passive barriers are those most closely approximating an ideal barrier. The most-studied case is that of sputtered TiN films. Stuffed barriers may be viewed as passive barriers whose low diffusivity material extends along the defects of the polycrystalline host.

  2. Mappability and read length

    PubMed Central

    Li, Wentian; Freudenberg, Jan

    2014-01-01

    Power-law distributions are the main functional form for the distribution of repeat size and repeat copy number in the human genome. When the genome is broken into fragments for sequencing, the limited size of fragments and reads may prevent an unique alignment of repeat sequences to the reference sequence. Repeats in the human genome can be as long as 104 bases, or 105 − 106 bases when allowing for mismatches between repeat units. Sequence reads from these regions are therefore unmappable when the read length is in the range of 103 bases. With a read length of 1000 bases, slightly more than 1% of the assembled genome, and slightly less than 1% of the 1 kb reads, are unmappable, excluding the unassembled portion of the human genome (8% in GRCh37/hg19). The slow decay (long tail) of the power-law function implies a diminishing return in converting unmappable regions/reads to become mappable with the increase of the read length, with the understanding that increasing read length will always move toward the direction of 100% mappability. PMID:25426137

  3. 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

  4. Tracer diffusion in silica inverse opals.

    PubMed

    Cherdhirankorn, Thipphaya; Retsch, Markus; Jonas, Ulrich; Butt, Hans-Juergen; Koynov, Kaloian

    2010-06-15

    We employed fluorescence correlation spectroscopy (FCS) to study the diffusion of small fluorescence tracers in liquid filled silica inverse opals. The inverse opals consisted of a nanoporous silica scaffold spanning a hexagonal crystal of spherical voids of 360 nm diameter connected by circular pores of 70 nm diameter. The diffusion of Alexa Fluor 488 in water and of perylene-3,4,9,10-tetracarboxylic diimide (PDI) in toluene was studied. Three diffusion modes could be distinguished: (1) Free diffusion limited by the geometric constraints given by the inverse opal, where, as compared to the free solution, this diffusion is slowed down by a factor of 3-4, (2) slow diffusion inside the nanoporous matrix of the silica scaffold, and (3) diffusion limited by adsorption. On the length scale of the focus of a confocal microscope of roughly 400 nm diffusion was non-Fickian in all cases.

  5. Spin diffusion in disordered organic semiconductors

    NASA Astrophysics Data System (ADS)

    Li, Ling; Gao, Nan; Lu, Nianduan; Liu, Ming; Bässler, Heinz

    2015-12-01

    An analytical theory for spin diffusion in disordered organic semiconductors is derived. It is based on percolation theory and variable range hopping in a disordered energy landscape with a Gaussian density of states. It describes universally the dependence of the spin diffusion on temperature, carrier density, material disorder, magnetic field, and electric field at the arbitrary magnitude of the Hubbard energy of charge pairs. It is found that, compared to the spin transport carried by carriers hopping, the spin exchange will hinder the spin diffusion process at low carrier density, even under the condition of a weak electric field. Importantly, under the influence of a bias voltage, anomalous spreading of the spin packet will lead to an abnormal temperature dependence of the spin diffusion coefficient and diffusion length. This explains the recent experimental data for spin diffusion length observed in Alq3.

  6. Vowel length in Farsi

    NASA Astrophysics Data System (ADS)

    Shademan, Shabnam

    2001-05-01

    This study tests whether Farsi vowels are contrastive with respective to length. Farsi has a six-vowel system with three lax vowels and three tense vowels. Both traditional grammarians and modern linguists believe that Farsi tense vowels are longer than lax vowels, and that there are no vowel pairs that contrast only in length. However, it has been suggested that Farsi exhibits compensatory lengthening, which is triggered by the deletion of glottal consonants in coda position in informal speech (Darzi, 1991). As a result, minimal pairs such as [tar] and [tarh] should contrast only with respect to vowel length. A corpus of 90 words of the form CVC, CVCG, CVGC, and CVCC (where V=a vowel and G=a glottal consonant) was recorded, and durations of vowels in different contexts were measured and compared. Preliminary results show that lax vowel durations fall into three groups with CVCC longer than CVCG/CVGC, and the latter longer than CVC. It remains to be seen whether CVCG/CVGC words show compensatory lengthening when the glottal consonant is deleted.

  7. Delayed Feedback Model of Axonal Length Sensing

    PubMed Central

    Karamched, Bhargav R.; Bressloff, Paul C.

    2015-01-01

    A fundamental question in cell biology is how the sizes of cells and organelles are regulated at various stages of development. Size homeostasis is particularly challenging for neurons, whose axons can extend from hundreds of microns to meters (in humans). Recently, a molecular-motor-based mechanism for axonal length sensing has been proposed, in which axonal length is encoded by the frequency of an oscillating retrograde signal. In this article, we develop a mathematical model of this length-sensing mechanism in which advection-diffusion equations for bidirectional motor transport are coupled to a chemical signaling network. We show that chemical oscillations emerge due to delayed negative feedback via a Hopf bifurcation, resulting in a frequency that is a monotonically decreasing function of axonal length. Knockdown of either kinesin or dynein causes an increase in the oscillation frequency, suggesting that the length-sensing mechanism would produce longer axons, which is consistent with experimental findings. One major prediction of the model is that fluctuations in the transport of molecular motors lead to a reduction in the reliability of the frequency-encoding mechanism for long axons. PMID:25954897

  8. Demonstrating Diffusion

    ERIC Educational Resources Information Center

    Foy, Barry G.

    1977-01-01

    Two demonstrations are described. Materials and instructions for demonstrating movement of molecules into cytoplasm using agar blocks, phenolphthalein, and sodium hydroxide are given. A simple method for demonstrating that the rate of diffusion of a gas is inversely proportional to its molecular weight is also presented. (AJ)

  9. Relativistic diffusion

    NASA Astrophysics Data System (ADS)

    Haba, Z.

    2009-02-01

    We discuss relativistic diffusion in proper time in the approach of Schay (Ph.D. thesis, Princeton University, Princeton, NJ, 1961) and Dudley [Ark. Mat. 6, 241 (1965)]. We derive (Langevin) stochastic differential equations in various coordinates. We show that in some coordinates the stochastic differential equations become linear. We obtain momentum probability distribution in an explicit form. We discuss a relativistic particle diffusing in an external electromagnetic field. We solve the Langevin equations in the case of parallel electric and magnetic fields. We derive a kinetic equation for the evolution of the probability distribution. We discuss drag terms leading to an equilibrium distribution. The relativistic analog of the Ornstein-Uhlenbeck process is not unique. We show that if the drag comes from a diffusion approximation to the master equation then its form is strongly restricted. The drag leading to the Tsallis equilibrium distribution satisfies this restriction whereas the one of the Jüttner distribution does not. We show that any function of the relativistic energy can be the equilibrium distribution for a particle in a static electric field. A preliminary study of the time evolution with friction is presented. It is shown that the problem is equivalent to quantum mechanics of a particle moving on a hyperboloid with a potential determined by the drag. A relation to diffusions appearing in heavy ion collisions is briefly discussed.

  10. Defusing Diffusion

    ERIC Educational Resources Information Center

    Dou, Remy; Hogan, DaNel; Kossover, Mark; Spuck, Timothy; Young, Sarah

    2013-01-01

    Diffusion has often been taught in science courses as one of the primary ways by which molecules travel, particularly within organisms. For years, classroom teachers have used the same common demonstrations to illustrate this concept (e.g., placing drops of food coloring in a beaker of water). Most of the time, the main contributor to the motion…

  11. Relativistic diffusion.

    PubMed

    Haba, Z

    2009-02-01

    We discuss relativistic diffusion in proper time in the approach of Schay (Ph.D. thesis, Princeton University, Princeton, NJ, 1961) and Dudley [Ark. Mat. 6, 241 (1965)]. We derive (Langevin) stochastic differential equations in various coordinates. We show that in some coordinates the stochastic differential equations become linear. We obtain momentum probability distribution in an explicit form. We discuss a relativistic particle diffusing in an external electromagnetic field. We solve the Langevin equations in the case of parallel electric and magnetic fields. We derive a kinetic equation for the evolution of the probability distribution. We discuss drag terms leading to an equilibrium distribution. The relativistic analog of the Ornstein-Uhlenbeck process is not unique. We show that if the drag comes from a diffusion approximation to the master equation then its form is strongly restricted. The drag leading to the Tsallis equilibrium distribution satisfies this restriction whereas the one of the Jüttner distribution does not. We show that any function of the relativistic energy can be the equilibrium distribution for a particle in a static electric field. A preliminary study of the time evolution with friction is presented. It is shown that the problem is equivalent to quantum mechanics of a particle moving on a hyperboloid with a potential determined by the drag. A relation to diffusions appearing in heavy ion collisions is briefly discussed.

  12. Length of stain dosimeter

    NASA Technical Reports Server (NTRS)

    Lueck, Dale E. (Inventor)

    1994-01-01

    Payload customers for the Space Shuttle have recently expressed concerns about the possibility of their payloads at an adjacent pad being contaminated by plume effluents from a shuttle at an active pad as they await launch on an inactive pad. As part of a study to satisfy such concerns a ring of inexpensive dosimeters was deployed around the active pad at the inter-pad distance. However, following a launch, dosimeters cannot be read for several hours after the exposure. As a consequence factors such as different substrates, solvent systems, and possible volatilization of HCl from the badges were studied. This observation led to the length of stain (LOS) dosimeters of this invention. Commercial passive LOS dosimeters are sensitive only to the extent of being capable of sensing 2 ppm to 20 ppm if the exposure is 8 hours. To map and quantitate the HCl generated by Shuttle launches, and in the atmosphere within a radius of 1.5 miles from the active pad, a sensitivity of 2 ppm HCl in the atmospheric gases on an exposure of 5 minutes is required. A passive length of stain dosimeter has been developed having a sensitivity rendering it capable of detecting a gas in a concentration as low as 2 ppm on an exposure of five minutes.

  13. Skin permeation enhancement of diclofenac by fatty acids.

    PubMed

    Kim, Min-Jung; Doh, Hea-Jeong; Choi, Min-Koo; Chung, Suk-Jae; Shim, Chang-Koo; Kim, Dae-Duk; Kim, Jung Sun; Yong, Chul-Soon; Choi, Han-Gon

    2008-08-01

    This study systematically investigated the enhancing effect of fatty acids on the skin permeation of diclofenac. The fatty acids were evaluated in terms of their carbon-chain length, the degree of unsaturation, and their functional groups. The rat-skin permeation rates of diclofenac, saturated in propylene glycol (PG) containing 1% (w/v) fatty acid, were determined using the Keshary-Chien diffusion cells at 37 degrees C. The effect of fatty acids on the saturated solubility of diclofenac in PG was also determined at 37 degrees C using high-performance liquid chromatography. Among the saturated fatty acids tested, palmitic acid (C16:0) showed the most potent skin permeation-enhancing effect. A parabolic correlation was observed between the enhancement effect and the fatty acid carbon-chain length among these saturated fatty acids of C12-C20 units. For the monounsaturated fatty acid series, an increase in permeation was observed as the carbon-chain length increased, and oleic acid (C18:1) showed the highest permeation-enhancing effect. Increasing the number of double bonds in the octadecanoic acids resulted in a parabolic effect in the permeation of diclofenac, revealing oleic acid as the most effective enhancer used in this study. When the carboxylic acid moiety of oleic acid was changed to an amide (oleamide) or hydroxyl (oleyl alcohol) group, a decrease in permeation activity was observed. These results, therefore, suggest that the cis-monounsaturated configuration and the carboxylic acid moiety of an 18-carbon unit fatty acid in PG are the optimum requirements for the effective skin permeation of diclofenac.

  14. Modelling charge transport lengths in heterojunction solar cells

    NASA Astrophysics Data System (ADS)

    Musselman, K. P.; Ievskaya, Y.; MacManus-Driscoll, J. L.

    2012-12-01

    A drift-diffusion model is used to estimate the minority carrier transport length and depletion width in heterojunction solar cells from measured external quantum efficiency (EQE) data. The model is applied to Cu2O-ZnO heterojunctions synthesized by electrodeposition and thermal oxidation, and the electron drift and diffusion lengths are estimated: Ldrift ≈ 110 nm for electrodeposited Cu2O and Ldrift ≈ 2790 nm and Ldiff ≈ 310 nm for thermally oxidized Cu2O. Better fitting of EQE data is obtained than with traditional models that neglect recombination in the depletion region.

  15. Diffusion bonding

    DOEpatents

    Anderson, Robert C.

    1976-06-22

    1. A method for joining beryllium to beryllium by diffusion bonding, comprising the steps of coating at least one surface portion of at least two beryllium pieces with nickel, positioning a coated surface portion in a contiguous relationship with an other surface portion, subjecting the contiguously disposed surface portions to an environment having an atmosphere at a pressure lower than ambient pressure, applying a force upon the beryllium pieces for causing the contiguous surface portions to abut against each other, heating the contiguous surface portions to a maximum temperature less than the melting temperature of the beryllium, substantially uniformly decreasing the applied force while increasing the temperature after attaining a temperature substantially above room temperature, and maintaining a portion of the applied force at a temperature corresponding to about maximum temperature for a duration sufficient to effect the diffusion bond between the contiguous surface portions.

  16. Revealing mesoscopic structural universality with diffusion.

    PubMed

    Novikov, Dmitry S; Jensen, Jens H; Helpern, Joseph A; Fieremans, Els

    2014-04-01

    Measuring molecular diffusion is widely used for characterizing materials and living organisms noninvasively. This characterization relies on relations between macroscopic diffusion metrics and structure at the mesoscopic scale commensurate with the diffusion length. Establishing such relations remains a fundamental challenge, hindering progress in materials science, porous media, and biomedical imaging. Here we show that the dynamical exponent in the time dependence of the diffusion coefficient distinguishes between the universality classes of the mesoscopic structural complexity. Our approach enables the interpretation of diffusion measurements by objectively selecting and modeling the most relevant structural features. As an example, the specific values of the dynamical exponent allow us to identify the relevant mesoscopic structure affecting MRI-measured water diffusion in muscles and in brain, and to elucidate the structural changes behind the decrease of diffusion coefficient in ischemic stroke.

  17. Random diffusion model.

    PubMed

    Mazenko, Gene F

    2008-09-01

    We study the random diffusion model. This is a continuum model for a conserved scalar density field varphi driven by diffusive dynamics. The interesting feature of the dynamics is that the bare diffusion coefficient D is density dependent. In the simplest case, D=D[over ]+D_{1}deltavarphi , where D[over ] is the constant average diffusion constant. In the case where the driving effective Hamiltonian is quadratic, the model can be treated using perturbation theory in terms of the single nonlinear coupling D1 . We develop perturbation theory to fourth order in D1 . The are two ways of analyzing this perturbation theory. In one approach, developed by Kawasaki, at one-loop order one finds mode-coupling theory with an ergodic-nonergodic transition. An alternative more direct interpretation at one-loop order leads to a slowing down as the nonlinear coupling increases. Eventually one hits a critical coupling where the time decay becomes algebraic. Near this critical coupling a weak peak develops at a wave number well above the peak at q=0 associated with the conservation law. The width of this peak in Fourier space decreases with time and can be identified with a characteristic kinetic length which grows with a power law in time. For stronger coupling the system becomes metastable and then unstable. At two-loop order it is shown that the ergodic-nonergodic transition is not supported. It is demonstrated that the critical properties of the direct approach survive, going to higher order in perturbation theory.

  18. DIFFUSION PUMP

    DOEpatents

    Levenson, L.

    1963-09-01

    A high-vacuum diffusion pump is described, featuring a novel housing geometry for enhancing pumping speed. An upright, cylindrical lower housing portion is surmounted by a concentric, upright, cylindrical upper housing portion of substantially larger diameter; an uppermost nozzle, disposed concentrically within the upper portion, is adapted to eject downwardly a conical sheet of liquid outwardly to impinge upon the uppermost extremity of the interior wall of the lower portion. Preferably this nozzle is mounted upon a pedestal rising coaxially from within the lower portion and projecting up into said upper portion. (AEC)

  19. Crystallization and preliminary X-ray diffraction analysis of full-length and proteolytically activated pyruvate oxidase from Escherichia coli

    SciTech Connect

    Weidner, Annett; Neumann, Piotr; Wille, Georg; Stubbs, Milton T.; Tittmann, Kai

    2008-03-01

    The peripheral membrane flavoprotein pyruvate oxidase from E. coli has been crystallized in the full-length form and as a proteolytically activated truncation variant lacking the last 23 amino acids at the C-terminus. The thiamine diphosphate- and flavin-dependent peripheral membrane enzyme pyruvate oxidase from Escherichia coli (EcPOX) has been crystallized in the full-length form and as a proteolytically activated C-terminal truncation variant which lacks the last 23 amino acids (Δ23 EcPOX). Crystals were grown by the hanging-drop vapour-diffusion method using either protamine sulfate (full-length EcPOX) or 2-methyl-2,4-pentanediol (Δ23 EcPOX) as precipitants. Native data sets were collected at a X-ray home source to a resolution of 2.9 Å. The two forms of EcPOX crystallize in different space groups. Whereas full-length EcPOX crystallizes in the tetragonal space group P4{sub 3}2{sub 1}2 with two monomers per asymmetric unit, the crystals of Δ23 EcPOX belong to the orthorhombic space group P2{sub 1}2{sub 1}2{sub 1} and contain 12 monomers per asymmetric unit.

  20. Codes with Monotonic Codeword Lengths.

    ERIC Educational Resources Information Center

    Abrahams, Julia

    1994-01-01

    Discusses the minimum average codeword length coding under the constraint that the codewords are monotonically nondecreasing in length. Bounds on the average length of an optimal monotonic code are derived, and sufficient conditions are given such that algorithms for optimal alphabetic codes can be used to find the optimal monotonic code. (six…

  1. Ti Diffusion in Zircon

    NASA Astrophysics Data System (ADS)

    Cherniak, D. J.; Watson, E. B.

    2006-12-01

    Diffusion of Ti under anhydrous conditions at 1 atmosphere and under fluid-present conditions at 1.1-1.2 GPa has been measured in natural zircon. The source of diffusant for 1-atm experiments was a ZrO2- TiO2-ZrSiO4 mixture, with experiments run in Pt capsules. Diffusion experiments conducted in the presence of H2O-CO2 fluid were run in a piston-cylinder apparatus, using a source of ground TiO2, ZrSiO4 and SiO2, with oxalic acid added to produce H2O-CO2 vapor and partially melt the solid source material, yielding an assemblage of rutile + zircon + melt + vapor. Resonant nuclear reaction analysis (NRA) with the nuclear reaction ^{48}Ti(p,Γ)^{49}V was used to measure diffusion profiles for both sets of experiments. The following Arrhenius relation was obtained for Ti diffusion normal to c over the temperature range 1350-1550C at one atmosphere: DTi = 3.3x102 exp(-754 ± 56 kJ mol-1 /RT) m2sec-1 Ti diffusivities were found to be similar for experiments run under fluid-present conditions. A fit to all of the data yields the Arrhenius relation D = 1.3x103 exp(-741 ± 46 kJ mol-1 /RT) m2sec-1. These data suggest that zircon should be extremely retentive of Ti chemical signatures, indicating that the recently developed Ti-in-zircon crystallization geothermometer (Watson and Harrison, 2005; Watson et al., 2006) will be quite robust in preserving temperatures of zircon crystallization. Titanium diffuses somewhat faster in zircon than larger tetravalent cations U, Th, and Hf, but considerably more slowly than Pb, the REE, and oxygen; hence Ti crystallization temperatures may be retained under circumstances when radiometric ages or other types of geochemical information are lost. Watson EB, Harrison TM (2005) Science 308, 841-844. Watson EB, Wark DA, Thomas JB (2006) CMP(in press).

  2. Anomalous diffusion due to obstacles: a Monte Carlo study.

    PubMed Central

    Saxton, M J

    1994-01-01

    In normal lateral diffusion, the mean-square displacement of the diffusing species is proportional to time. But in disordered systems anomalous diffusion may occur, in which the mean-square displacement is proportional to some other power of time. In the presence of moderate concentrations of obstacles, diffusion is anomalous over short distances and normal over long distances. Monte Carlo calculations are used to characterize anomalous diffusion for obstacle concentrations between zero and the percolation threshold. As the obstacle concentration approaches the percolation threshold, diffusion becomes more anomalous over longer distances; the anomalous diffusion exponent and the crossover length both increase. The crossover length and time show whether anomalous diffusion can be observed in a given experiment. PMID:8161693

  3. Water vapor diffusion membranes, 2

    NASA Technical Reports Server (NTRS)

    Holland, F. F.; Klein, E.; Smith, J. K.; Eyer, C.

    1976-01-01

    Transport mechanisms were investigated for the three different types of water vapor diffusion membranes. Membranes representing porous wetting and porous nonwetting structures as well as dense diffusive membrane structures were investigated for water permeation rate as a function of: (1) temperature, (2) solids composition in solution, and (3) such hydrodynamic parameters as sweep gas flow rate, solution flow rate and cell geometry. These properties were measured using nitrogen sweep gas to collect the effluent. In addition, the chemical stability to chromic acid-stabilized urine was measured for several of each type of membrane. A technology based on the mechanism of vapor transport was developed, whereby the vapor diffusion rates and relative susceptibility of membranes to fouling and failure could be projected for long-term vapor recovery trials using natural chromic acid-stabilized urine.

  4. Pore-water distribution and quantification of diffusive benthic fluxes of silicic acid, nitrate and phosphate in surface sediments of the deep Arabian Sea

    NASA Astrophysics Data System (ADS)

    Grandel, Sibylle; Rickert, Dirk; Schlüter, Michael; Wallmann, Klaus

    Benthic fluxes and pore-water compositions of silicic acid, nitrate and phosphate were investigated for surface sediments of the abyssal Arabian Sea during four cruises (1995-1998). Five sites located in the northern (NAST), western (WAST), central (CAST), eastern (EAST), and southern (SAST) Arabian Sea were revisited during intermonsoonal periods after the NE- and SW-Monsoon. At these sites, benthic fluxes of remineralized nutrients from the sediment to the bottom water of 36-106, 102-350 and 4-16 mmol m -2 yr -1 were measured for nitrate, silicic acid and phosphate, respectively. The benthic fluxes and pore-water compositions showed a distinct regional pattern. Highest fluxes were observed in the western and northern region of the Arabian Sea, whereas decreasing fluxes were derived towards the southeast. At WAST, the general temporal pattern of primary production, related to the NE- and SW-Monsoon, is reflected by benthic fluxes. In contrast, at sites NAST, SAST, CAST, and EAST a temporal pattern of fluxes in response to the monsoon is not obvious. Our results reveal a clear coupling between the general regional pattern of production in surface waters and the response of the benthic environment, as indicated by the flux of remineralized nutrients, though a spatially differing degree of decoupling during transport and remineralization of particulate organic matter and biogenic opal was observed. This has to be taken into account regarding budget calculations and paleoceanographic topics.

  5. Diffusion of intracerebrally injected (1-/sup 14/C)arachidonic acid and (2-/sup 3/H)glycerol in the mouse brain. Effects of ischemia and electroconvulsive shock

    SciTech Connect

    Pediconi, M.F.; Rodriguez de Turco, E.B.; Bazan, N.G.

    1982-12-01

    (2-/sup 3/H)Glycerol and (1-/sup 14/C)arachidonic acid were injected into the region of the frontal horn of the left ventricle of mice and were distributed rapidly throughout the brain. After 10 sec, most of the radioactive fatty acid was found in the hemisphere near the injection site; after 10 min, it was recovered in similar proportions in the cerebellum and brain stem. (2-/sup 3/H)Glycerol showed a heterogeneous distribution, with most of the label remaining in the left hemisphere even after 10 min. On a fresh weight basis, cerebrum, cerebellum, and brain stem were found to contain similar amounts of labeled glycerol. However, the amount of (1-/sup 14/C)arachidonate in cerebrum was only 50% of that recovered from cerebellum or brain stem. Brain ischemia or a single electroconvulsive shock reduced the spread of the label, producing an accumulation of radioactivity in the injected hemisphere, except for an increase in (2-/sup 3/H)glycerol in the brain stem during ischemia. Despite the significant decrease in available precursor in the cerebellum and brain stem after electroshock, the amount of label incorporated into lipids was not altered in these areas and only slightly diminished in the cerebrum.

  6. IMPEDANCE OF FINITE LENGTH RESISTOR

    SciTech Connect

    KRINSKY, S.; PODOBEDOV, B.; GLUCKSTERN, R.L.

    2005-05-15

    We determine the impedance of a cylindrical metal tube (resistor) of radius a, length g, and conductivity {sigma}, attached at each end to perfect conductors of semi-infinite length. Our main interest is in the asymptotic behavior of the impedance at high frequency, k >> 1/a. In the equilibrium regime, , the impedance per unit length is accurately described by the well-known result for an infinite length tube with conductivity {sigma}. In the transient regime, ka{sup 2} >> g, we derive analytic expressions for the impedance and wakefield.

  7. Resolving and measuring diffusion in complex interfaces: Exploring new capabilities

    SciTech Connect

    Alam, Todd M.

    2015-09-01

    This exploratory LDRD targeted the use of a new high resolution spectroscopic diffusion capabilities developed at Sandia to resolve transport processes at interfaces in heterogeneous polymer materials. In particular, the combination of high resolution magic angle spinning (HRMAS) nuclear magnetic resonance (NMR) spectroscopy with pulsed field gradient (PFG) diffusion experiments were used to directly explore interface diffusion within heterogeneous polymer composites, including measuring diffusion for individual chemical species in multi-component mixtures. Several different types of heterogeneous polymer systems were studied using these HRMAS NMR diffusion capabilities to probe the resolution limitations, determine the spatial length scales involved, and explore the general applicability to specific heterogeneous systems. The investigations pursued included a) the direct measurement of the diffusion for poly(dimethyl siloxane) polymer (PDMS) on nano-porous materials, b) measurement of penetrant diffusion in additive manufactures (3D printed) processed PDMS composites, and c) the measurement of diffusion in swollen polymers/penetrant mixtures within nano-confined aluminum oxide membranes. The NMR diffusion results obtained were encouraging and allowed for an improved understanding of diffusion and transport processes at the molecular level, while at the same time demonstrating that the spatial heterogeneity that can be resolved using HRMAS NMR PFG diffusion experiment must be larger than ~μm length scales, expect for polymer transport within nanoporous carbons where additional chemical resolution improves the resolvable heterogeneous length scale to hundreds of nm.

  8. Line Lengths and Starch Scores.

    ERIC Educational Resources Information Center

    Moriarty, Sandra E.

    1986-01-01

    Investigates readability of different line lengths in advertising body copy, hypothesizing a normal curve with lower scores for shorter and longer lines, and scores above the mean for lines in the middle of the distribution. Finds support for lower scores for short lines and some evidence of two optimum line lengths rather than one. (SKC)

  9. A Systematic Comparison of Mathematical Models for Inherent Measurement of Ciliary Length: How a Cell Can Measure Length and Volume

    PubMed Central

    Ludington, William B.; Ishikawa, Hiroaki; Serebrenik, Yevgeniy V.; Ritter, Alex; Hernandez-Lopez, Rogelio A.; Gunzenhauser, Julia; Kannegaard, Elisa; Marshall, Wallace F.

    2015-01-01

    Cells control organelle size with great precision and accuracy to maintain optimal physiology, but the mechanisms by which they do so are largely unknown. Cilia and flagella are simple organelles in which a single measurement, length, can represent size. Maintenance of flagellar length requires an active transport process known as intraflagellar transport, and previous measurements suggest that a length-dependent feedback regulates intraflagellar transport. But the question remains: how is a length-dependent signal produced to regulate intraflagellar transport appropriately? Several conceptual models have been suggested, but testing these models quantitatively requires that they be cast in mathematical form. Here, we derive a set of mathematical models that represent the main broad classes of hypothetical size-control mechanisms currently under consideration. We use these models to predict the relation between length and intraflagellar transport, and then compare the predicted relations for each model with experimental data. We find that three models—an initial bolus formation model, an ion current model, and a diffusion-based model—show particularly good agreement with available experimental data. The initial bolus and ion current models give mathematically equivalent predictions for length control, but fluorescence recovery after photobleaching experiments rule out the initial bolus model, suggesting that either the ion current model or a diffusion-based model is more likely correct. The general biophysical principles of the ion current and diffusion-based models presented here to measure cilia and flagellar length can be generalized to measure any membrane-bound organelle volume, such as the nucleus and endoplasmic reticulum. PMID:25809250

  10. A systematic comparison of mathematical models for inherent measurement of ciliary length: how a cell can measure length and volume.

    PubMed

    Ludington, William B; Ishikawa, Hiroaki; Serebrenik, Yevgeniy V; Ritter, Alex; Hernandez-Lopez, Rogelio A; Gunzenhauser, Julia; Kannegaard, Elisa; Marshall, Wallace F

    2015-03-24

    Cells control organelle size with great precision and accuracy to maintain optimal physiology, but the mechanisms by which they do so are largely unknown. Cilia and flagella are simple organelles in which a single measurement, length, can represent size. Maintenance of flagellar length requires an active transport process known as intraflagellar transport, and previous measurements suggest that a length-dependent feedback regulates intraflagellar transport. But the question remains: how is a length-dependent signal produced to regulate intraflagellar transport appropriately? Several conceptual models have been suggested, but testing these models quantitatively requires that they be cast in mathematical form. Here, we derive a set of mathematical models that represent the main broad classes of hypothetical size-control mechanisms currently under consideration. We use these models to predict the relation between length and intraflagellar transport, and then compare the predicted relations for each model with experimental data. We find that three models-an initial bolus formation model, an ion current model, and a diffusion-based model-show particularly good agreement with available experimental data. The initial bolus and ion current models give mathematically equivalent predictions for length control, but fluorescence recovery after photobleaching experiments rule out the initial bolus model, suggesting that either the ion current model or a diffusion-based model is more likely correct. The general biophysical principles of the ion current and diffusion-based models presented here to measure cilia and flagellar length can be generalized to measure any membrane-bound organelle volume, such as the nucleus and endoplasmic reticulum.

  11. NIST Diffusion Data Center

    National Institute of Standards and Technology Data Gateway

    NIST Diffusion Data Center (Web, free access)   The NIST Diffusion Data Center is a collection of over 14,100 international papers, theses, and government reports on diffusion published before 1980.

  12. Parallel flow diffusion battery

    DOEpatents

    Yeh, H.C.; Cheng, Y.S.

    1984-01-01

    A parallel flow diffusion battery for determining the mass distribution of an aerosol has a plurality of diffusion cells mounted in parallel to an aerosol stream, each diffusion cell including a stack of mesh wire screens of different density.

  13. Parallel flow diffusion battery

    DOEpatents

    Yeh, Hsu-Chi; Cheng, Yung-Sung

    1984-08-07

    A parallel flow diffusion battery for determining the mass distribution of an aerosol has a plurality of diffusion cells mounted in parallel to an aerosol stream, each diffusion cell including a stack of mesh wire screens of different density.

  14. Numerical analysis of a vortex controlled diffuser

    NASA Technical Reports Server (NTRS)

    Spall, Robert E.

    1993-01-01

    A numerical study of a prototypical vortex controlled diffuser is performed. The basic diffuser geometry consists of a step expansion in a pipe of area ratio 2.25:1. The incompressible Reynolds averaged Navier-Stokes equations, employing the K-epsilon turbulence model, are solved. Results are presented for bleed rates ranging from 1 to 7 percent. Diffuser efficiencies in excess of 80 percent are obtained. Reattachment lengths are reduced by a factor of up to 3. These results are in qualitative agreement with previous experimental work. However, differences in some basic details of experimentally observed and the present numerically generated flowfields exist. The effect of swirl is also investigated.

  15. Anomalous diffusion in neutral evolution of model proteins

    NASA Astrophysics Data System (ADS)

    Nelson, Erik D.; Grishin, Nick V.

    2015-06-01

    Protein evolution is frequently explored using minimalist polymer models, however, little attention has been given to the problem of structural drift, or diffusion. Here, we study neutral evolution of small protein motifs using an off-lattice heteropolymer model in which individual monomers interact as low-resolution amino acids. In contrast to most earlier models, both the length and folded structure of the polymers are permitted to change. To describe structural change, we compute the mean-square distance (MSD) between monomers in homologous folds separated by n neutral mutations. We find that structural change is episodic, and, averaged over lineages (for example, those extending from a single sequence), exhibits a power-law dependence on n . We show that this exponent depends on the alignment method used, and we analyze the distribution of waiting times between neutral mutations. The latter are more disperse than for models required to maintain a specific fold, but exhibit a similar power-law tail.

  16. Quantification in an Introductory Diffusion Experiment.

    ERIC Educational Resources Information Center

    Snow, George E.

    1991-01-01

    Describes a take-home experiment in which students measure the diffusion of acid through acid-filled capillary tubes immersed into base solutions and vice versa. Students represent and analyze the effects of ambient temperature, molecular weight, and concentrations of the solutions on that movement. (MDH)

  17. Diffusing Diffusivity: A Model for Anomalous, yet Brownian, Diffusion

    NASA Astrophysics Data System (ADS)

    Chubynsky, Mykyta V.; Slater, Gary W.

    2014-08-01

    Wang et al. [Proc. Natl. Acad. Sci. U.S.A. 106, 15160 (2009)] have found that in several systems the linear time dependence of the mean-square displacement (MSD) of diffusing colloidal particles, typical of normal diffusion, is accompanied by a non-Gaussian displacement distribution G(x ,t), with roughly exponential tails at short times, a situation they termed "anomalous yet Brownian" diffusion. The diversity of systems in which this is observed calls for a generic model. We present such a model where there is diffusivity memory but no direction memory in the particle trajectory, and we show that it leads to both a linear MSD and a non-Gaussian G(x ,t) at short times. In our model, the diffusivity is undergoing a (perhaps biased) random walk, hence the expression "diffusing diffusivity". G(x ,t) is predicted to be exactly exponential at short times if the distribution of diffusivities is itself exponential, but an exponential remains a good fit for a variety of diffusivity distributions. Moreover, our generic model can be modified to produce subdiffusion.

  18. Review of HxPyOz-Catalyzed H + OH Recombination in Scramjet Nozzle Expansions; and Possible Phosphoric Acid Enhancement of Scramjet Flameholding, from Extinction of H3PO4 + H2 - Air Counterflow Diffusion Flames

    NASA Technical Reports Server (NTRS)

    Pellett, Gerald

    2005-01-01

    Recent detailed articles by Twarowski indicate that small quantities of phosphorus oxides and acids in the fuel-rich combustion products of H2 + phosphine (PH3) + air should significantly catalyze H, OH and O recombination kinetics during high-speed nozzle expansions -- to reform H2O, release heat, and approach equilibrium more rapidly and closely than uncatalyzed kinetics. This paper is an initial feasibility study to determine (a) if addition of phosphoric acid vapor (H3PO4) to a H2 fuel jet -- which is much safer than using PH3 -- will allow combustion in a high-speed scramjet engine test without adverse effects on localized flameholding, and (b) if phosphorus-containing exhaust emissions are environmentally acceptable. A well-characterized axisymmetric straight-tube opposed jet burner (OJB) tool is used to evaluate H3PO4 addition effects on the air velocity extinction limit (flame strength) of a H2 versus air counterflow diffusion flame. Addition of nitric oxide (NO), also believed to promote catalytic H-atom recombination, was evaluated for comparison. Two to five mass percent H3PO4 in the H2 jet increased flame strength 4.2%, whereas airside addition decreased it 1%. Adding 5% NO to the H2 caused a 2% decrease. Products of H-atom attack on H3PO4 produced an intense green chemiluminescence near the stagnation point. The resultant exothermic production of phosphorus oxides and acids, with accelerated H-atom recombination, released sufficient heat near the stagnation point to increase flame strength. In conclusion, the addition of H3PO4 vapor (or more reactive P sources) to hydrogen in scramjet engine tests may positively affect flameholding stability in the combustor and thrust production during supersonic expansion -- a possible dual benefit with system design / performance implications. Finally, a preliminary assessment of possible environmental effects indicates that scramjet exhaust emissions should consist of phosphoric acid aerosol, with gradual

  19. Definition of Magnetic Exchange Length

    SciTech Connect

    Abo, GS; Hong, YK; Park, J; Lee, J; Lee, W; Choi, BC

    2013-08-01

    The magnetostatic exchange length is an important parameter in magnetics as it measures the relative strength of exchange and self-magnetostatic energies. Its use can be found in areas of magnetics including micromagnetics, soft and hard magnetic materials, and information storage. The exchange length is of primary importance because it governs the width of the transition between magnetic domains. Unfortunately, there is some confusion in the literature between the magnetostatic exchange length and a similar distance concerning magnetization reversal mechanisms in particles known as the characteristic length. This confusion is aggravated by the common usage of two different systems of units, SI and cgs. This paper attempts to clarify the situation and recommends equations in both systems of units.

  20. Diffusion in solid-Earth systems

    NASA Astrophysics Data System (ADS)

    Watson, E. Bruce; Baxter, Ethan F.

    2007-01-01

    Recent years have seen a rapid expansion in the acquisition and use of information on diffusive transport in phases relevant to the solid Earth (crystals, melts and fluids). Although far from complete, the data base on diffusion coefficients is now sufficiently large that broad constraints can be placed upon the length- and time scales of many natural transport phenomena in which diffusion plays a role. Conversely, observations of diffusion progress in specific natural samples can be used to extract time-temperature information for a variety of geologic and geochemical processes, ranging from sediment burial and crustal erosion to fluid-mediated reactions and biosignature retention. Despite this undeniable progress, several major challenges remain that largely define the frontiers of research in solid-Earth diffusion. Perhaps foremost among these is the need to address and understand the multi-scale, multi-path aspects of diffusion in many systems—a complication that is not limited to polyphase materials (individual mineral grains can exhibit clear indications of multi-path behavior even when visible evidence of such paths is lacking). Many other diffusion frontiers are linked in one way or another to this multi-scale issue; they include: diffusion of molecular H 2O and the effect of H species on diffusion in minerals and rocks; diffusive fractionation of multiple isotopes of a single element; diffusion at the extreme conditions of the deep Earth; reconciliation of observations from natural samples and laboratory studies; and development of theoretical approaches to 'predict' diffusion behavior in regions inaccessible to observation.

  1. Proton conduction in exchange membranes across multiple length scales.

    PubMed

    Jorn, Ryan; Savage, John; Voth, Gregory A

    2012-11-20

    Concerns over global climate change associated with fossil-fuel consumption continue to drive the development of electrochemical alternatives for energy technology. Proton exchange fuel cells are a particularly promising technology for stationary power generation, mobile electronics, and hybrid engines in automobiles. For these devices to work efficiently, direct electrical contacts between the anode and cathode must be avoided; hence, the separator material must be electronically insulating but highly proton conductive. As a result, researchers have examined a variety of polymer electrolyte materials for use as membranes in these systems. In the optimization of the membrane, researchers are seeking high proton conductivity, low electronic conduction, and mechanical stability with the inclusion of water in the polymer matrix. A considerable number of potential polymer backbone and side chain combinations have been synthesized to meet these requirements, and computational studies can assist in the challenge of designing the next generation of technologically relevant membranes. Such studies can also be integrated in a feedback loop with experiment to improve fuel cell performance. However, to accurately simulate the currently favored class of membranes, perfluorosulfonic acid containing moieties, several difficulties must be addressed including a proper treatment of the proton-hopping mechanism through the membrane and the formation of nanophase-separated water networks. We discuss our recent efforts to address these difficulties using methods that push the limits of computer simulation and expand on previous theoretical developments. We describe recent advances in the multistate empirical valence bond (MS-EVB) method that can probe proton diffusion at the nanometer-length scale and accurately model the so-called Grotthuss shuttling mechanism for proton diffusion in water. Using both classical molecular dynamics and coarse-grained descriptions that replace atomistic

  2. Proton conduction in exchange membranes across multiple length scales.

    PubMed

    Jorn, Ryan; Savage, John; Voth, Gregory A

    2012-11-20

    Concerns over global climate change associated with fossil-fuel consumption continue to drive the development of electrochemical alternatives for energy technology. Proton exchange fuel cells are a particularly promising technology for stationary power generation, mobile electronics, and hybrid engines in automobiles. For these devices to work efficiently, direct electrical contacts between the anode and cathode must be avoided; hence, the separator material must be electronically insulating but highly proton conductive. As a result, researchers have examined a variety of polymer electrolyte materials for use as membranes in these systems. In the optimization of the membrane, researchers are seeking high proton conductivity, low electronic conduction, and mechanical stability with the inclusion of water in the polymer matrix. A considerable number of potential polymer backbone and side chain combinations have been synthesized to meet these requirements, and computational studies can assist in the challenge of designing the next generation of technologically relevant membranes. Such studies can also be integrated in a feedback loop with experiment to improve fuel cell performance. However, to accurately simulate the currently favored class of membranes, perfluorosulfonic acid containing moieties, several difficulties must be addressed including a proper treatment of the proton-hopping mechanism through the membrane and the formation of nanophase-separated water networks. We discuss our recent efforts to address these difficulties using methods that push the limits of computer simulation and expand on previous theoretical developments. We describe recent advances in the multistate empirical valence bond (MS-EVB) method that can probe proton diffusion at the nanometer-length scale and accurately model the so-called Grotthuss shuttling mechanism for proton diffusion in water. Using both classical molecular dynamics and coarse-grained descriptions that replace atomistic

  3. Fiberoptic Microneedles: Novel Optical Diffusers for Interstitial Delivery of Therapeutic Light

    PubMed Central

    Kosoglu, Mehmet A.; Hood, Robert L.; Rossmeisl, John H.; Grant, David C.; Xu, Yong; Robertson, John L.; Rylander, M. Nichole; Rylander, Christopher G.

    2012-01-01

    Background and Objectives Photothermal therapies have limited efficacy and application due to the poor penetration depth of light inside tissue. In earlier work, we described the development of novel fiberoptic microneedles to provide a means to mechanically penetrate dermal tissue and deliver light directly into a localized target area. This paper presents an alternate fiberoptic microneedle design with the capability of delivering more diffuse, but therapeutically useful photothermal energy. Laser lipolysis is envisioned as a future clinical application for this design. Materials and Methods A novel fiberoptic microneedle was developed using hydrofluoric acid etching of optical fiber to permit diffuse optical delivery. Microneedles etched for 10, 30, and 50 minutes, and an optical fiber control were compared with three techniques. First, red light delivery from the microneedles was evaluated by imaging the reflectance of the light from a white paper. Second, spatial temperature distribution of the paper in response to near-IR light (1064 nm, 1 W CW) was recorded using infrared thermography. Third, ex vivo adipose tissue response during 1064 nm, (5 W CW) irradiation was recorded with bright field microscopy. Results The acid etching exposed a 3 mm length of the fiber core, allowing circumferential delivery of light along this length. Increasing etching time decreased microneedle diameter, resulting in increased uniformity of red and 1064 nm light delivery along the microneedle axis. For equivalent total energy delivery, thinner microneedles reduced carbonization in the adipose tissue experiments. Conclusions We developed novel microscale optical diffusers that provided a more homogeneous light distribution from their surfaces, and compared performance to a flat-cleaved fiber, a device currently utilized in clinical practice. These fiberoptic microneedles can potentially enhance clinical laser procedures by providing direct delivery of diffuse light to target

  4. Promiscuous Diffusible Signal Factor Production and Responsiveness of the Xylella fastidiosa Rpf System

    PubMed Central

    Ionescu, Michael; Yokota, Kenji; Antonova, Elena; Garcia, Angelica; Beaulieu, Ellen; Hayes, Terry; Iavarone, Anthony T.

    2016-01-01

    ABSTRACT Cell density-dependent regulation of gene expression in Xylella fastidiosa that is crucial to its switching between plant hosts and insect vectors is dependent on RpfF and its production of 2-enoic acids known as diffusible signal factor (DSF). We show that X. fastidiosa produces a particularly large variety of similar, relatively long-chain-length 2-enoic acids that are active in modulating gene expression. Both X. fastidiosa itself and a Pantoea agglomerans surrogate host harboring X. fastidiosa RpfF (XfRpfF) is capable of producing a variety of both saturated and unsaturated free fatty acids. However, only 2-cis unsaturated acids were found to be biologically active in X. fastidiosa. X. fastidiosa produces, and is particularly responsive to, a novel DSF species, 2-cis-hexadecanoic acid that we term XfDSF2. It is also responsive to other, even longer 2-enoic acids to which other taxa such as Xanthomonas campestris are unresponsive. The 2-enoic acids that are produced by X. fastidiosa are strongly affected by the cellular growth environment, with XfDSF2 not detected in culture media in which 2-tetradecenoic acid (XfDSF1) had previously been found. X. fastidiosa is responsive to much lower concentrations of XfDSF2 than XfDSF1. Apparently competitive interactions can occur between various saturated and unsaturated fatty acids that block the function of those agonistic 2-enoic fatty acids. By altering the particular 2-enoic acids produced and the relative balance of free enoic and saturated fatty acids, X. fastidiosa might modulate the extent of DSF-mediated quorum sensing. PMID:27435463

  5. Persistence Length of Stable Microtubules

    NASA Astrophysics Data System (ADS)

    Hawkins, Taviare; Mirigian, Matthew; Yasar, M. Selcuk; Ross, Jennifer

    2011-03-01

    Microtubules are a vital component of the cytoskeleton. As the most rigid of the cytoskeleton filaments, they give shape and support to the cell. They are also essential for intracellular traffic by providing the roadways onto which organelles are transported, and they are required to reorganize during cellular division. To perform its function in the cell, the microtubule must be rigid yet dynamic. We are interested in how the mechanical properties of stable microtubules change over time. Some ``stable'' microtubules of the cell are recycled after days, such as in the axons of neurons or the cilia and flagella. We measured the persistence length of freely fluctuating taxol-stabilized microtubules over the span of a week and analyzed them via Fourier decomposition. As measured on a daily basis, the persistence length is independent of the contour length. Although measured over the span of the week, the accuracy of the measurement and the persistence length varies. We also studied how fluorescently-labeling the microtubule affects the persistence length and observed that a higher labeling ratio corresponded to greater flexibility. National Science Foundation Grant No: 0928540 to JLR.

  6. Statistical length measurement method by direct imaging of carbon nanotubes.

    PubMed

    Bengio, E Amram; Tsentalovich, Dmitri E; Behabtu, Natnael; Kleinerman, Olga; Kesselman, Ellina; Schmidt, Judith; Talmon, Yeshayahu; Pasquali, Matteo

    2014-05-14

    The influence of carbon nanotube (CNT) length on their macroscopic properties requires an accurate methodology for CNT length measurement. So far, existing techniques are limited to short (less than a few micrometers) CNTs and sample preparation methods that bias the measured values. Here, we show that the average length of carbon nanotubes (CNTs) can be measured by cryogenic transmission electron microscopy (cryo-TEM) of CNTs in chlorosulfonic acid. The method consists of dissolving at low concentration CNTs in chlorosulfonic acid (a true solvent), imaging the individual CNTs by cryo-TEM, and processing and analyzing the images to determine CNT length. By measuring the total CNT contour length and number of CNT ends in each image, and by applying statistical analysis, we extend the method to cases where each CNT is long enough to span many cryo-TEM images, making the direct length measurement of an entire CNT impractical. Hence, this new technique can be used effectively to estimate samples in a wide range of CNT lengths, although we find that cryo-TEM imaging may bias the measurement towards longer CNTs, which are easier to detect. Our statistical method is also applied to AFM images of CNTs to show that, by using only a few AFM images, it yields estimates that are consistent with literature techniques, based on individually measuring a higher number of CNTs. PMID:24773046

  7. When Does Length Cause the Word Length Effect?

    ERIC Educational Resources Information Center

    Jalbert, Annie; Neath, Ian; Bireta, Tamra J.; Surprenant, Aimee M.

    2011-01-01

    The word length effect, the finding that lists of short words are better recalled than lists of long words, has been termed one of the benchmark findings that any theory of immediate memory must account for. Indeed, the effect led directly to the development of working memory and the phonological loop, and it is viewed as the best remaining…

  8. Length-Scale Dependent Viscosity in Semidilute Polyelectrolyte Solutions

    NASA Astrophysics Data System (ADS)

    Poling-Skutvik, Ryan; Krishnamoorti, Ramanan; Conrad, Jacinta

    2015-03-01

    Using optical microscopy and particle tracking algorithms, we measured the mean-squared displacements (MSDs) of fluorescent polystyrene particles with diameters ranging from 300 nm to 2 μm suspended in semidilute solutions of high molecular weight partially hydrolyzed polyacrylamide. The solutions had polymer concentrations ranging from 0.67 to 67c*, where c* is the overlap concentration, and estimated correlation lengths of ~ 100 to 900 nm. At short times, the particles exhibited subdiffusive behavior characterized by MSD ~tα with α < 1 . On long time scales, the particles transitioned to Fickian diffusion (α = 1) and their diffusivity was calculated from the slope of the MSD. Whereas the large particles agreed with predictions using the Stokes-Einstein equation and bulk zero-shear viscosity, the smaller particles diffused much faster than predicted. The relative diffusivities do not collapse onto a single curve, but rather form a continuum that varies with particle size. This indicates that the particles experience a size-dependent effective viscosity mediated by the ratio of particle diameter to characteristic length scales in the polymer solution.

  9. Continuously variable focal length lens

    DOEpatents

    Adams, Bernhard W; Chollet, Matthieu C

    2013-12-17

    A material preferably in crystal form having a low atomic number such as beryllium (Z=4) provides for the focusing of x-rays in a continuously variable manner. The material is provided with plural spaced curvilinear, optically matched slots and/or recesses through which an x-ray beam is directed. The focal length of the material may be decreased or increased by increasing or decreasing, respectively, the number of slots (or recesses) through which the x-ray beam is directed, while fine tuning of the focal length is accomplished by rotation of the material so as to change the path length of the x-ray beam through the aligned cylindrical slows. X-ray analysis of a fixed point in a solid material may be performed by scanning the energy of the x-ray beam while rotating the material to maintain the beam's focal point at a fixed point in the specimen undergoing analysis.

  10. Structural and diffusion characterizations of steam-stable mesostructured zeolitic UL-ZSM-5 materials.

    PubMed

    Vinh-Thang, Hoang; Huang, Qinglin; Ungureanu, Adrian; Eić, Mladen; Trong-On, Do; Kaliaguine, Serge

    2006-05-01

    A series of mesoporous UL-ZSM-5 materials (Si/Al = 50) with different micro- and mesoporosity as well as crystallinity was prepared following the procedure proposed in one of our recent studies (Trong-On, D.; Kaliaguine, S. Angew. Chem. Int. Ed. 2001, 40, 3248-3251. Trong-On, D.; Kaliaguine, S. U.S. Patent 6,669,924, B1, 2003). These materials have zeolitic structure in the form of nanoparticles intergrown in the walls of the amorphous wormhole-like aluminosilicate mesopores of Al-Meso-50, which was used as a precursor in the synthesis. The structure, crystallinity, and textural properties of the synthesized materials, as well as a reference ZSM-5 zeolite sample, were determined by X-ray diffraction (XRD), transmission electron microscopy (TEM)/scanning electron microscoy (SEM) analyses, Fourier transform infrared spectroscopy (FTIR), 27Al magic angle spinning (MAS) nuclear magnetic resonance (NMR), and nitrogen adsorption/desorption techniques. The acid properties were examined by FTIR of adsorbed pyridine. UL-ZSM-5 materials were shown to be highly hydrothermally stable. The diffusion of two C7 hydrocarbons, i.e., n-heptane and toluene, in four UL-ZSM-5 materials with different microporosities, related acidities, and crystallinities were investigated using the zero-length column (ZLC) method. Furthermore, the wormhole-like mesostructured aluminosilicate precursor (Al-Meso-50) and a reference MFI zeolite sample were also investigated using the same technique. A theoretical model considering a combination of mesopore diffusion (with surface slip in the main channels) with an activated, mainly surface diffusion mechanism in the intrawall biporous structure, was proposed and employed to interpret the experimental ZLC results. A classical Knudsen type of diffusion was replaced by an activated surface slip type of diffusion mechanism in the mesopores. The transport of n-heptane in UL-ZSM-5 materials was found to be mainly controlled by mesopore diffusion in the main

  11. Continuous lengths of oxide superconductors

    DOEpatents

    Kroeger, Donald M.; List, III, Frederick A.

    2000-01-01

    A layered oxide superconductor prepared by depositing a superconductor precursor powder on a continuous length of a first substrate ribbon. A continuous length of a second substrate ribbon is overlaid on the first substrate ribbon. Sufficient pressure is applied to form a bound layered superconductor precursor powder between the first substrate ribbon and the second substrate ribbon. The layered superconductor precursor is then heat treated to establish the oxide superconducting phase. The layered oxide superconductor has a smooth interface between the substrate and the oxide superconductor.

  12. Overview of bunch length measurements.

    SciTech Connect

    Lumpkin, A. H.

    1999-02-19

    An overview of particle and photon beam bunch length measurements is presented in the context of free-electron laser (FEL) challenges. Particle-beam peak current is a critical factor in obtaining adequate FEL gain for both oscillators and self-amplified spontaneous emission (SASE) devices. Since measurement of charge is a standard measurement, the bunch length becomes the key issue for ultrashort bunches. Both time-domain and frequency-domain techniques are presented in the context of using electromagnetic radiation over eight orders of magnitude in wavelength. In addition, the measurement of microbunching in a micropulse is addressed.

  13. Search for selective ion diffusion through membranes

    NASA Technical Reports Server (NTRS)

    May, C. E.; Philipp, W. H.

    1983-01-01

    The diffusion rates of several ions through some membranes developed as battery separators were measured. The ions investigated were Li(+), Rb(+), Cl(-), and So4. The members were crosslinked polyvinyl alcohol, crosslinked polyacrylic acid, a copolymer of the two, crosslinked calcium polyacrylate, cellulose, and several microporous polyphenylene oxide based films. No true specificity for diffusion of any of these ions was found for any of the membranes. But the calcium polyacrylate membrane was found to exhibit ion exchange with the diffusing ions giving rise to the leaching of the calcium ion and low reproducibility. These findings contrast earlier work where the calcium polyacrylate membrane did show specificity to the diffusion of the copper ion. In general, Fick's law appeared to be obeyed. Except for the microporous membranes, the coefficients for ion diffusion through the membranes were comparable with their values in water. For the microporous membranes, the values found for the coefficients were much less, due to the tortuosity of the micropores.

  14. Diffusion of oxygen in cork.

    PubMed

    Lequin, Sonia; Chassagne, David; Karbowiak, Thomas; Simon, Jean-Marc; Paulin, Christian; Bellat, Jean-Pierre

    2012-04-01

    This work reports measurements of effective oxygen diffusion coefficient in raw cork. Kinetics of oxygen transfer through cork is studied at 298 K thanks to a homemade manometric device composed of two gas compartments separated by a cork wafer sample. The first compartment contains oxygen, whereas the second one is kept under dynamic vacuum. The pressure decrease in the first compartment is recorded as a function of time. The effective diffusion coefficient D(eff) is obtained by applying Fick's law to transient state using a numerical method based on finite differences. An analytical model derived from Fick's law applied to steady state is also proposed. Results given by these two methods are in close agreement with each other. The harmonic average of the effective diffusion coefficients obtained from the distribution of 15 cork wafers of 3 mm thickness is 1.1 × 10(-9) m(2) s(-1) with a large distribution over four decades. The statistical analysis of the Gaussian distribution obtained on a 3 mm cork wafer is extrapolated to a 48 mm cork wafer, which length corresponds to a full cork stopper. In this case, the probability density distribution gives a mean value of D(eff) equal to 1.6 × 10(-9) m(2) s(-1). This result shows that it is possible to obtain the effective diffusion coefficient of oxygen through cork from short time (few days) measurements performed on a thin cork wafer, whereas months are required to obtain the diffusion coefficient for a full cork stopper. Permeability and oxygen transfer rate are also calculated for comparison with data from other studies.

  15. Internode length in pisum: do the internode length genes effect growth in dark-grown plants?

    PubMed

    Reid, J B

    1983-07-01

    Internode length in light-grown peas (Pisum sativum L.) is controlled by the interaction of genes occupying at least five major loci, Le, La, Cry, Na, and Lm. The present work shows that the genes at all of the loci examined (Le, Cry, and Na) also exert an effect on internode length in plants grown in complete darkness. Preliminary results using pure lines were verified using either segregating progenies or near isogenic lines. The major cause of the differences was due to a change in the number of cells per internode rather than to an alteration of the cell length. Since the genes occupying at least two of these loci, Le and Na, have been shown to be directly involved with gibberellin metabolism, it appears that gibberellins are not only essential for elongation in the dark but are limiting for elongation in the nana (extremely short, na), dwarf (Na le), and tall (Na Le) phenotypes. These results are supported by the large inhibitory effects of AMO 1618 treatments on stem elongation in dwarf and tall lines grown in the dark and the fact that applied gibberellic acid could overcome this inhibition and greatly promote elongation in a gibberellin-deficient na line. It is clear that the internode length genes, and in particular the alleles at the Le locus, are not acting by simply controlling the sensitivity of the plant to light. PMID:16663081

  16. A theoretical study of rotational diffusion models for rod-shaped viruses. The influence of motion on 31P nuclear magnetic resonance lineshapes and transversal relaxation.

    PubMed Central

    Magusin, P C; Hemminga, M A

    1993-01-01

    Information about the interaction between nucleic acids and coat proteins in intact virus particles may be obtained by studying the restricted backbone dynamics of the incapsulated nucleic acids using 31P nuclear magnetic resonance (NMR) spectroscopy. In this article, simulations are carried out to investigate how reorientation of a rod-shaped virus particle as a whole and isolated nucleic acid motions within the virion influence the 31P NMR lineshape and transversal relaxation dominated by the phosphorus chemical shift anisotropy. Two opposite cases are considered on a theoretical level. First, isotropic rotational diffusion is used as a model for mobile nucleic acids that are loosely or partially bound to the protein coat. The effect of this type of diffusion on lineshape and transversal relaxation is calculated by solving the stochastic Liouville equation by an expansion in spherical functions. Next, uniaxial rotational diffusion is assumed to represent the mobility of phosphorus in a virion that rotates as a rigid rod about its length axis. This type of diffusion is approximated by an exchange process among discrete sites. As turns out from these simulations, the amplitude and the frequency of the motion can only be unequivocally determined from experimental data by a combined analysis of the lineshape and the transversal relaxation. In the fast motional region both the isotropic and the uniaxial diffusion model predict the same transversal relaxation as the Redfield theory. For very slow motion, transversal relaxation resembles the nonexponential relaxation as observed for water molecules undergoing translational diffusion in a magnetic field gradient. In this frequency region T2e is inversely proportional to the cube root of the diffusion coefficient. In addition to the isotropic and uniaxial diffusion models, a third model is presented, in which fast restricted nucleic acid backbone motions dominating the lineshape are superimposed on a slow rotation of the

  17. Microfabricated diffusion source

    DOEpatents

    Oborny, Michael C.; Frye-Mason, Gregory C.; Manginell, Ronald P.

    2008-07-15

    A microfabricated diffusion source to provide for a controlled diffusion rate of a vapor comprises a porous reservoir formed in a substrate that can be filled with a liquid, a headspace cavity for evaporation of the vapor therein, a diffusion channel to provide a controlled diffusion of the vapor, and an outlet to release the vapor into a gas stream. The microfabricated diffusion source can provide a calibration standard for a microanalytical system. The microanalytical system with an integral diffusion source can be fabricated with microelectromechanical systems technologies.

  18. Finite length Taylor Couette flow

    NASA Technical Reports Server (NTRS)

    Streett, C. L.; Hussaini, M. Y.

    1987-01-01

    Axisymmetric numerical solutions of the unsteady Navier-Stokes equations for flow between concentric rotating cylinders of finite length are obtained by a spectral collocation method. These representative results pertain to two-cell/one-cell exchange process, and are compared with recent experiments.

  19. Incubation length of dabbling ducks

    USGS Publications Warehouse

    Wells-Berlin, A. M.; Prince, H.H.; Arnold, T.W.

    2005-01-01

    We collected unincubated eggs from wild Mallard (Anas platyrhynchos), Gadwall (A. strepera), Blue-winged Teal (A. discors), and Northern Shoveler (A. clypeata) nests and artificially incubated them at 37.5??C. Average incubation lengths of Mallard, Gadwall, and Northern Shoveler eggs did not differ from their wild-nesting counterparts, but artificially incubated Blue-winged Teal eggs required an additional 1.7 days to hatch, suggesting that wild-nesting teal incubated more effectively. A small sample of Mallard, Gadwall, and Northern Shoveler eggs artificially incubated at 38.3??C hatched 1 day sooner, indicating that incubation temperature affected incubation length. Mean incubation length of Blue-winged Teal declined by 1 day for each 11-day delay in nesting, but we found no such seasonal decline among Mallards, Gadwalls, or Northern Shovelers. There is no obvious explanation for the seasonal reduction in incubation length for Blue-winged Teal eggs incubated in a constant environment, and the phenomenon deserves further study. ?? The Cooper Ornithological Society 2005.

  20. Critical waves and the length problem of biology

    PubMed Central

    Laughlin, Robert B.

    2015-01-01

    It is pointed out that the mystery of how biological systems measure their lengths vanishes away if one premises that they have discovered a way to generate linear waves analogous to compressional sound. These can be used to detect length at either large or small scales using echo timing and fringe counting. It is shown that suitable linear chemical potential waves can, in fact, be manufactured by tuning to criticality conventional reaction–diffusion with a small number substance. Min oscillations in Escherichia coli are cited as precedent resonant length measurement using chemical potential waves analogous to laser detection. Mitotic structures in eukaryotes are identified as candidates for such an effect at higher frequency. The engineering principle is shown to be very general and functionally the same as that used by hearing organs. PMID:26240329

  1. Hydrodynamic length-scale selection in microswimmer suspensions

    NASA Astrophysics Data System (ADS)

    Heidenreich, Sebastian; Dunkel, Jörn; Klapp, Sabine H. L.; Bär, Markus

    2016-08-01

    A universal characteristic of mesoscale turbulence in active suspensions is the emergence of a typical vortex length scale, distinctly different from the scale invariance of turbulent high-Reynolds number flows. Collective length-scale selection has been observed in bacterial fluids, endothelial tissue, and active colloids, yet the physical origins of this phenomenon remain elusive. Here, we systematically derive an effective fourth-order field theory from a generic microscopic model that allows us to predict the typical vortex size in microswimmer suspensions. Building on a self-consistent closure condition, the derivation shows that the vortex length scale is determined by the competition between local alignment forces, rotational diffusion, and intermediate-range hydrodynamic interactions. Vortex structures found in simulations of the theory agree with recent measurements in Bacillus subtilis suspensions. Moreover, our approach yields an effective viscosity enhancement (reduction), as reported experimentally for puller (pusher) microorganisms.

  2. Hydrodynamic length-scale selection in microswimmer suspensions.

    PubMed

    Heidenreich, Sebastian; Dunkel, Jörn; Klapp, Sabine H L; Bär, Markus

    2016-08-01

    A universal characteristic of mesoscale turbulence in active suspensions is the emergence of a typical vortex length scale, distinctly different from the scale invariance of turbulent high-Reynolds number flows. Collective length-scale selection has been observed in bacterial fluids, endothelial tissue, and active colloids, yet the physical origins of this phenomenon remain elusive. Here, we systematically derive an effective fourth-order field theory from a generic microscopic model that allows us to predict the typical vortex size in microswimmer suspensions. Building on a self-consistent closure condition, the derivation shows that the vortex length scale is determined by the competition between local alignment forces, rotational diffusion, and intermediate-range hydrodynamic interactions. Vortex structures found in simulations of the theory agree with recent measurements in Bacillus subtilis suspensions. Moreover, our approach yields an effective viscosity enhancement (reduction), as reported experimentally for puller (pusher) microorganisms. PMID:27627229

  3. Seismic Hazard and Fault Length

    NASA Astrophysics Data System (ADS)

    Black, N. M.; Jackson, D. D.; Mualchin, L.

    2005-12-01

    If mx is the largest earthquake magnitude that can occur on a fault, then what is mp, the largest magnitude that should be expected during the planned lifetime of a particular structure? Most approaches to these questions rely on an estimate of the Maximum Credible Earthquake, obtained by regression (e.g. Wells and Coppersmith, 1994) of fault length (or area) and magnitude. Our work differs in two ways. First, we modify the traditional approach to measuring fault length, to allow for hidden fault complexity and multi-fault rupture. Second, we use a magnitude-frequency relationship to calculate the largest magnitude expected to occur within a given time interval. Often fault length is poorly defined and multiple faults rupture together in a single event. Therefore, we need to expand the definition of a mapped fault length to obtain a more accurate estimate of the maximum magnitude. In previous work, we compared fault length vs. rupture length for post-1975 earthquakes in Southern California. In this study, we found that mapped fault length and rupture length are often unequal, and in several cases rupture broke beyond the previously mapped fault traces. To expand the geologic definition of fault length we outlined several guidelines: 1) if a fault truncates at young Quaternary alluvium, the fault line should be inferred underneath the younger sediments 2) faults striking within 45° of one another should be treated as a continuous fault line and 3) a step-over can link together faults at least 5 km apart. These definitions were applied to fault lines in Southern California. For example, many of the along-strike faults lines in the Mojave Desert are treated as a single fault trending from the Pinto Mountain to the Garlock fault. In addition, the Rose Canyon and Newport-Inglewood faults are treated as a single fault line. We used these more generous fault lengths, and the Wells and Coppersmith regression, to estimate the maximum magnitude (mx) for the major faults in

  4. How Acidic Is Carbonic Acid?

    PubMed

    Pines, Dina; Ditkovich, Julia; Mukra, Tzach; Miller, Yifat; Kiefer, Philip M; Daschakraborty, Snehasis; Hynes, James T; Pines, Ehud

    2016-03-10

    Carbonic, lactic, and pyruvic acids have been generated in aqueous solution by the transient protonation of their corresponding conjugate bases by a tailor-made photoacid, the 6-hydroxy-1-sulfonate pyrene sodium salt molecule. A particular goal is to establish the pK(a) of carbonic acid H2CO3. The on-contact proton transfer (PT) reaction rate from the optically excited photoacid to the carboxylic bases was derived, with unprecedented precision, from time-correlated single-photon-counting measurements of the fluorescence lifetime of the photoacid in the presence of the proton acceptors. The time-dependent diffusion-assisted PT rate was analyzed using the Szabo-Collins-Kimball equation with a radiation boundary condition. The on-contact PT rates were found to follow the acidity order of the carboxylic acids: the stronger was the acid, the slower was the PT reaction to its conjugate base. The pK(a) of carbonic acid was found to be 3.49 ± 0.05 using both the Marcus and Kiefer-Hynes free energy correlations. This establishes H2CO3 as being 0.37 pK(a) units stronger and about 1 pK(a) unit weaker, respectively, than the physiologically important lactic and pyruvic acids. The considerable acid strength of intact carbonic acid indicates that it is an important protonation agent under physiological conditions. PMID:26862781

  5. Cyclodextrin and its complexation for resolution of isomers using diffusion ordered spectroscopy

    NASA Astrophysics Data System (ADS)

    Chaudhari, Sachin R.; Srinivasa; Suryaprakash, N.

    2013-02-01

    Diffusion ordered spectroscopy (DOSY) generally fails to separate the peaks pertaining to isomeric species possessing identical molecular weights and similar hydrodynamic radii. The present study demonstrates the resolution of isomers using α/β-cyclodextrin as a co-solute by Matrix Assisted Diffusion Ordered Spectroscopy. The resolution of isomers has been achieved by measuring the significant differences in the diffusion rates between the positional isomers of aminobenzoic acids, benzenedicarboxylic acids and between the cis, trans isomers, fumaric acid and maleic acid.

  6. Hybrid Diffusion Imaging

    PubMed Central

    Wu, Yu-Chien; Alexander, Andrew L.

    2007-01-01

    Diffusion measurements in the human central nervous system are complex to characterize and a broad spectrum of methods have been proposed. In this study, a comprehensive diffusion encoding and analysis approach, Hybrid Diffusion Imaging (HYDI), is described. The HYDI encoding scheme is composed of multiple concentric “shells” of constant diffusion-weighting, which may be used to characterize the signal behavior with low, moderate and high diffusion-weighting. HYDI facilitates the application of multiple data-analyses strategies including diffusion tensor imaging (DTI), multi-exponential diffusion measurements, diffusion spectrum imaging (DSI) and q-ball imaging (QBI). These different analysis strategies may provide complementary information. DTI measures (mean diffusivity and fractional anisotropy) may be estimated from either data in the inner shells or the entire HYDI data. Fast and slow diffusivities were estimated using a nonlinear least-squares bi-exponential fit on geometric means of the HYDI shells. DSI measurements from the entire HYDI data yield empirical model-independent diffusion information and are well-suited for characterizing tissue regions with complex diffusion behavior. DSI measurements were characterized using the zero displacement probability and the mean squared displacement. The outermost HYDI shell was analyzed using QBI analysis to estimate the orientation distribution function (ODF), which is useful for characterizing the directions of multiple fiber groups within a voxel. In this study, a HYDI encoding scheme with 102 diffusion-weighted measurements was obtained over most of the human cerebrum in under 30 minutes. PMID:17481920

  7. Characteristic lengths affecting evaporative drying of porous media.

    PubMed

    Lehmann, Peter; Assouline, Shmuel; Or, Dani

    2008-05-01

    Evaporation from porous media involves mass and energy transport including phase change, vapor diffusion, and liquid flow, resulting in complex displacement patterns affecting drying rates. Force balance considering media properties yields characteristic lengths affecting the transition in the evaporation rate from a liquid-flow-based first stage limited only by vapor exchange with air to a second stage controlled by vapor diffusion through the medium. The characteristic lengths determine the extent of the hydraulically connected region between the receding drying front and evaporating surface (film region) and the onset of flow rate limitations through this film region. Water is displaced from large pores at the receding drying front to supply evaporation from hydraulically connected finer pores at the surface. Liquid flow is driven by a capillary pressure gradient spanned by the width of the pore size distribution and is sustained as long as the capillary gradient remains larger than gravitational forces and viscous dissipation. The maximum extent of the film region sustaining liquid flow is determined by a characteristic length L_{C} combining the gravity characteristic length L_{G} and viscous dissipation characteristic length L_{V} . We used two sands with particle sizes 0.1-0.5 mm ("fine") and 0.3-0.9 mm ("coarse") to measure the evaporation from columns of different lengths under various atmospheric evaporative demands. The value of L_{G} determined from capillary pressure-saturation relationships was 90 mm for the coarse sand and 140 mm for the fine sand. A significant decrease in drying rate occurred when the drying front reached the predicted L_{G} value (viscous dissipation was negligibly small in sand and L_{C} approximately L_{G} ). The approach enables a prediction of the duration of first-stage evaporation with the highest water losses from soil to the atmosphere. PMID:18643163

  8. Diffusion of photoacid generators by laser scanning confocal microscopy

    NASA Astrophysics Data System (ADS)

    Zhang, Ping L.; Webber, Stephen E.; Mendenhall, J.; Byers, Jeffrey D.; Chao, Keith K.

    1998-06-01

    Diffusion of the photogenerated acid during the period of time between exposure and development can cause contrast loss and ultimately loss of the latent image. This is especially relevant for chemically amplified photoresists that require a post-exposure baking step, which in turn facilitates acid diffusion due to the high temperature normally employed. It is thus important to develop techniques with good spatial resolution to monitor the photogeneration of acid. More precisely, we need techniques that provide two distinct types of information: spatial resolution on various length scales within the surface layer and also sufficient depth resolution so that one can observe the transition from very surface layer to bulk structure in the polymer blend coated on silicon substrate. Herein laser scanning confocal microscopy is used to evaluate the resist for the first time. We report the use of the confocal microscopy to map the pag/dye distribution in PHS matrices, with both reflectance images and fluorescence images. A laser beam is focused onto a small 3D volume element, termed a voxel. It is typically 200 nm X 200 nm laterally and 800 nm axially. The illuminated voxel is viewed such that only signals emanating from this voxel are detected, i.e., signal from outside the probed voxel is not detected. By adjusting the vertical position of the laser focal point, the voxel can be moved to the designated lateral plane to produce an image. Contrast caused by topology difference between the exposed and unexposed area can be eliminated. Bis-p-butylphenyl iodonium triflat (7% of polyhydroxystyrene) is used as photoacid generators. 5% - 18% (by weight, PHS Mn equals 13 k) resist in PGMEA solution is spin cast onto the treated quartz disk with thickness of 1.4 micrometers , 5 micrometers space/10 micrometers pitch chrome mask is used to generate the pattern with mercury DUV illumination. Fluoresceinamine, the pH-sensitive dye, is also used to enhance the contrast of

  9. Diffusion bonding aeroengine components

    NASA Astrophysics Data System (ADS)

    Fitzpatrick, G. A.; Broughton, T.

    1988-10-01

    The use of diffusion bonding processes at Rolls-Royce for the manufacture of titanium-alloy aircraft engine components and structures is described. A liquid-phase diffusion bonding process called activated diffusion bonding has been developed for the manufacture of the hollow titanium wide chord fan blade. In addition, solid-state diffusion bonding is being used in the manufacture of hollow vane/blade airfoil constructions mainly in conjunction with superplastic forming and hot forming techniques.

  10. Updating applied diffusion models

    SciTech Connect

    Weil, J.C.

    1985-11-01

    Most diffusion models currently used in air quality applications are substantially out of date with understanding of turbulence and diffusion in the planetary boundary layer. Under a Cooperative Agreement with the Environmental Protection Agency, the American Meteorological Society organized a workshop to help improve the basis of such models, their physics and hopefuly their performance. Reviews and recommendations were made on models in three areas: diffusion in the convective boundary layer (CBL), diffusion in the stabe boundary layer (SBL), and model uncertainty.

  11. Diffusion Strategy Guide.

    ERIC Educational Resources Information Center

    McCutcheon, James R.; Sanders, John R.

    A methodology is presented for planning and managing the spread of educational innovations. The first portion of the guide develops a theoretical framework for diffusion which summarizes and capitalizes on the latest marketing and on the latest marketing and diffusion research findings. Major stages in the diffusion paradigm discussed include…

  12. Reduce Confusion about Diffusion.

    ERIC Educational Resources Information Center

    Hebrank, Mary R.

    1997-01-01

    Presents activities that allow students to explore the fundamental but poorly understood concept of diffusion by appealing to their kinesthetic senses first, then challenging their analytical skills as they try to deduce the mathematical principle involved. Presents a computer simulation of diffusion and discusses diffusion's limitations and…

  13. Handbook on atmospheric diffusion

    SciTech Connect

    Hanna, S.R.; Briggs, G.A.; Hosker, R.P. Jr.

    1982-01-01

    Basic meteorological concepts are covered as well as plume rise, source effects, and diffusion models. Chapters are included on cooling tower plumes and urban diffusion. Suggestions are given for calculating diffusion in special situations, such as for instantaneous releases over complex terrain, over long distances, and during times when chemical reactions or dry or wet deposition are important. (PSB)

  14. Welding arc length control system

    NASA Technical Reports Server (NTRS)

    Iceland, William F. (Inventor)

    1993-01-01

    The present invention is a welding arc length control system. The system includes, in its broadest aspects, a power source for providing welding current, a power amplification system, a motorized welding torch assembly connected to the power amplification system, a computer, and current pick up means. The computer is connected to the power amplification system for storing and processing arc weld current parameters and non-linear voltage-ampere characteristics. The current pick up means is connected to the power source and to the welding torch assembly for providing weld current data to the computer. Thus, the desired arc length is maintained as the welding current is varied during operation, maintaining consistent weld penetration.

  15. Variable focal length deformable mirror

    DOEpatents

    Headley, Daniel; Ramsey, Marc; Schwarz, Jens

    2007-06-12

    A variable focal length deformable mirror has an inner ring and an outer ring that simply support and push axially on opposite sides of a mirror plate. The resulting variable clamping force deforms the mirror plate to provide a parabolic mirror shape. The rings are parallel planar sections of a single paraboloid and can provide an on-axis focus, if the rings are circular, or an off-axis focus, if the rings are elliptical. The focal length of the deformable mirror can be varied by changing the variable clamping force. The deformable mirror can generally be used in any application requiring the focusing or defocusing of light, including with both coherent and incoherent light sources.

  16. Softness Correlations Across Length Scales

    NASA Astrophysics Data System (ADS)

    Ivancic, Robert; Shavit, Amit; Rieser, Jennifer; Schoenholz, Samuel; Cubuk, Ekin; Durian, Douglas; Liu, Andrea; Riggleman, Robert

    In disordered systems, it is believed that mechanical failure begins with localized particle rearrangements. Recently, a machine learning method has been introduced to identify how likely a particle is to rearrange given its local structural environment, quantified by softness. We calculate the softness of particles in simulations of atomic Lennard-Jones mixtures, molecular Lennard-Jones oligomers, colloidal systems and granular systems. In each case, we find that the length scale characterizing spatial correlations of softness is approximately a particle diameter. These results provide a rationale for why localized rearrangements--whose size is presumably set by the scale of softness correlations--might occur in disordered systems across many length scales. Supported by DOE DE-FG02-05ER46199.

  17. Hospitalization length of insanity acquittees.

    PubMed

    Steadman, H J; Pasewark, R A; Hawkins, M; Kiser, M; Bieber, S

    1983-07-01

    Used step-wise multiple regression procedures to predict length of hospitalization of 225 defendants acquitted by reason of insanity in New York state. Of the 21 variables considered, only 9 (severity of offense, sex, marital status, days prior imprisonment, homicide offense, days previous civil hospitalization, educational level, race, number of victims) contributed to the significance of the regression equation. However, these accounted for but 11% of the observed variance.

  18. Effects of anisosmotic stress on cardiac muscle cell length, diameter, area, and sarcomere length

    NASA Technical Reports Server (NTRS)

    Tanaka, R.; Barnes, M. A.; Cooper, G. 4th; Zile, M. R.

    1996-01-01

    The purpose of this study was to examine the effects of anisosmotic stress on adult mammalian cardiac muscle cell (cardiocyte) size. Cardiocyte size and sarcomere length were measured in cardiocytes isolated from 10 normal rats and 10 normal cats. Superfusate osmolarity was decreased from 300 +/- 6 to 130 +/- 5 mosM and increased to 630 +/- 8 mosM. Cardiocyte size and sarcomere length increased progressively when osmolarity was decreased, and there were no significant differences between cat and rat cardiocytes with respect to percent change in cardiocyte area or diameter; however, there were significant differences in cardiocyte length (2.8 +/- 0.3% in cat vs. 6.1 +/- 0.3% in rat, P < 0.05) and sarcomere length (3.3 +/- 0.3% in cat vs. 6.1 +/- 0.3% in rat, P < 0.05). To determine whether these species-dependent differences in length were related to diastolic interaction of the contractile elements or differences in relative passive stiffness, cardiocytes were subjected to the osmolarity gradient 1) during treatment with 7 mM 2,3-butanedione monoxime (BDM), which inhibits cross-bridge interaction, or 2) after pretreatment with 1 mM ethylene glycol-bis(beta-aminoethyl ether)-N, N,N',N'-tetraacetic acid (EGTA), a bivalent Ca2+ chelator. Treatment with EGTA or BDM abolished the differences between cat and rat cardiocytes. Species-dependent differences therefore appeared to be related to the degree of diastolic cross-bridge association and not differences in relative passive stiffness. In conclusion, the osmolarity vs. cell size relation is useful in assessing the cardiocyte response to anisosmotic stress and may in future studies be useful in assessing changes in relative passive cardiocyte stiffness produced by pathological processes.

  19. Single-file diffusion near channel boundaries.

    PubMed

    Vasenkov, Sergey; Schüring, Andreas; Fritzsche, Siegfried

    2006-06-20

    Molecular transport under the conditions of single-file diffusion was investigated near the channel boundaries by using dynamic Monte Carlo and molecular dynamics simulations of tracer exchange between single-file channels and their surroundings. The boundary effect reported in our recent papers (Vasenkov S.; Kärger, J. Phys. Rev. E 2002, 66, 052601. Schüring, A.; Vasenkov S.; Fritzsche, S. J. Phys. Chem. B 2005, 109, 16711) was studied in detail. This boundary effect is characterized by deviations of the intrachannel concentration profiles of tracer molecules observed in the case of single-file diffusion near the channel boundaries from the corresponding profiles typical for normal diffusion. It has been shown in our previous studies that these deviations occur under the conditions when the potential-energy difference inside and outside of single-file channels was both comparable and much larger than the activation energy of intrachannel diffusion. Here, we report a quantitative model describing the boundary effect. According to this model, an occurrence of the boundary effect is related to a complex character of diffusion in finite single-file systems. Such diffusion can be described by the following two types of movements occurring in parallel: (i) correlated displacements of all molecules in any particular channel and (ii) fast displacements of single molecules, which are uncorrelated with the displacements of all other molecules in the same channel. The latter displacements are restricted to a certain length interval that depends on the channel length and the channel occupancy. This length interval is shown to determine the extensions of the channel margins where the boundary effect is observed.

  20. Universality of modulation length exponents

    NASA Astrophysics Data System (ADS)

    Chakrabarty, Saurish; Seidel, Alexander; Nussinov, Zohar

    2012-02-01

    We study systems (classical or quantum) with general pairwise interactions. Our prime interest is in frustrated spin systems. First, we focus on systems with a crossover temperature T^* across which the correlation function changes from exhibiting commensurate to incommensurate modulations. We report on a new exponent, νL, characterizing the universal nature of this crossover. Near the crossover, the characteristic wave-vector k on the incommensurate side differs from that on the commensurate side, q by |k-q||T-T^*|^νL. We find, in general, that νL=1/2, or in some special cases, other rational numbers. We discuss applications to the axial next nearest neighbor Ising model, Fermi systems (with application to the metal to band insulator transition) and Bose systems. Second, we obtain a universal form of the high temperature correlation function in general systems. From this, we show the existence of a diverging correlation length in the presence of long range interactions. Such a correlation length tends to the screening length in the presence of screening. We also find a way of obtaining the pairwise interaction potentials in the high temperature phase from the correlation functions.

  1. Heterogeneity of Alkane Chain Length in Freshwater and Marine Cyanobacteria

    PubMed Central

    Shakeel, Tabinda; Fatma, Zia; Fatma, Tasneem; Yazdani, Syed Shams

    2015-01-01

    The potential utilization of cyanobacteria for the biological production of alkanes represents an exceptional system for the next generation of biofuels. Here, we analyzed a diverse group of freshwater and marine cyanobacterial isolates from Indian culture collections for their ability to produce both alkanes and alkenes. Among the 50 cyanobacterial isolates screened, 32 isolates; 14 freshwater and 18 marine isolates; produced predominantly alkanes. The GC-MS/MS profiles revealed a higher percentage of pentadecane and heptadecane production for marine and freshwater strains, respectively. Oscillatoria species were found to be the highest producers of alkanes. Among the freshwater isolates, Oscillatoria CCC305 produced the maximum alkane level with 0.43 μg/mg dry cell weight, while Oscillatoria formosa BDU30603 was the highest producer among the marine isolates with 0.13 μg/mg dry cell weight. Culturing these strains under different media compositions showed that the alkane chain length was not influenced by the growth medium but was rather an inherent property of the strains. Analysis of the cellular fatty acid content indicated the presence of predominantly C16 chain length fatty acids in marine strains, while the proportion of C18 chain length fatty acids increased in the majority of freshwater strains. These results correlated with alkane chain length specificity of marine and freshwater isolates indicating that alkane chain lengths may be primarily determined by the fatty acid synthesis pathway. Moreover, the phylogenetic analysis showed clustering of pentadecane-producing marine strains that was distinct from heptadecane-producing freshwater strains strongly suggesting a close association between alkane chain length and the cyanobacteria habitat. PMID:25853127

  2. Acid distribution in phosphoric acid fuel cells

    SciTech Connect

    Okae, I.; Seya, A.; Umemoto, M.

    1996-12-31

    Electrolyte acid distribution among each component of a cell is determined by capillary force when the cell is not in operation, but the distribution under the current load conditions had not been clear so far. Since the loss of electrolyte acid during operation is inevitable, it is necessary to store enough amount of acid in every cell. But it must be under the level of which the acid disturbs the diffusion of reactive gases. Accordingly to know the actual acid distribution during operation in a cell is very important. In this report, we carried out experiments to clarify the distribution using small single cells.

  3. Generalized Drift-Diffusion Model In Semiconductors

    SciTech Connect

    Mesbah, S.; Bendib-Kalache, K.; Bendib, A.

    2008-09-23

    A new drift-diffusion model is proposed based on the computation of the stationary nonlocal current density. The semi classical Boltzmann equation is solved keeping all the anisotropies of the distribution function with the use of the continued fractions. The conductivity is calculated in the linear approximation and for arbitrary collision frequency with respect to Kv{sub t} where K{sup -1} is the characteristic length scale of the system and V{sub t} is the thermal velocity. The nonlocal conductivity can be used to close the generalized drift-diffusion equations valid for arbitrary collisionality.

  4. Varying nanoparticle pseudostationary phase plug length during capillary electrophoresis†

    PubMed Central

    Subramaniam, Varuni; Griffith, Lindsay; Haes, Amanda J.

    2016-01-01

    Capillary electrophoresis based separations of the hypothesized Parkinson’s disease biomarkers dopamine, epinephrine, pyrocatechol, L-3,4-dihydroxyphenylalanine (L-DOPA), glutathione, and uric acid are performed in the presence of a 1 nM 11-mercaptoundecanoic acid functionalized gold (Au@MUA) nanoparticle pseudostationary phase plug. Au@MUA nanoparticles are monitored in the capillary and remain stable in the presence of electrically-driven flow. Migration times, peak areas, and relative velocity changes (vs. no pseudostationary) are monitored upon varying (1) the Au@MUA nanoparticle pseudostationary phase plug length at a fixed separation voltage and (2) the separation voltage for a fixed Au@MUA nanoparticle pseudostationary phase plug length. For instance, the migration times of positively charged dopamine and epinephrine increase slightly as the nanoparticle pseudostationary phase plug length increases with concomitant decreases in peak areas and relative velocities as a result of attractive forces between the positively charged analytes and the negatively charged nanoparticles. Migration times for neutral pyrocatechol and slightly negative L-DOPA did not exhibit significant changes with increasing nanoparticle pseudostationary plug length; however, reduction in peak areas for these two molecules were evident and attributed to non-specific interactions (i.e. hydrogen bonding and van der Waals interactions) between the biomarkers and nanoparticles. Moreover, negatively charged uric acid and glutathione displayed progressively decreasing migration times and peak areas and as a result, increased relative velocities with increasing nanoparticle pseudostationary phase plug length. These trends are attributed to partitioning and exchanging with 11-mercaptoundecanoic acid on nanoparticle surfaces for uric acid and glutathione, respectively. Similar trends are observed when the separation voltage decreased thereby suggesting that nanoparticle-biomarker interaction

  5. Fibreoptic diffuse-light irradiators of biological tissues

    SciTech Connect

    Volkov, Vladimir V; Loshchenov, V B; Konov, Vitalii I; Kononenko, Vitalii V

    2010-10-15

    We report techniques for the fabrication of laser radiation diffusers for interstitial photodynamic therapy. Using chemical etching of the distal end of silica fibre with a core diameter of 200 - 600 {mu}m, we have obtained long (up to 40 mm) diffusers with good scattering uniformity. Laser ablation has been used to produce cylindrical diffusers with high emission contrast and a scattering uniformity no worse than {approx}10 % in their middle part. The maximum length of the diffusers produced by this method is 20 - 25 mm. (laser applications and other topics in quantum electronics)

  6. Simulations of singlet exciton diffusion in organic semiconductors: a review

    SciTech Connect

    Bjorgaard, Josiah A.; Kose, Muhammet Erkan

    2014-12-22

    Our review describes the various aspects of simulation strategies for exciton diffusion in condensed phase thin films of organic semiconductors. Several methods for calculating energy transfer rate constants are discussed along with procedures for how to account for energetic disorder. Exciton diffusion can be modelled by using kinetic Monte-Carlo methods or master equations. Recent literature on simulation efforts for estimating exciton diffusion lengths of various conjugated polymers and small molecules are introduced. Moreover, these studies are discussed in the context of the effects of morphology on exciton diffusion and the necessity of accurate treatment of disorder for comparison of simulation results with those of experiment.

  7. Radon Diffusion Measurement in Polyethylene based on Alpha Detection

    SciTech Connect

    Rau, Wolfgang

    2011-04-27

    We present a method to measure the diffusion of Radon in solid materials based on the alpha decay of the radon daughter products. In contrast to usual diffusion measurements which detect the radon that penetrates a thin barrier, we let the radon diffuse into the material and then measure the alpha decays of the radon daughter products in the material. We applied this method to regular and ultra high molecular weight poly ethylene and find diffusion lengths of order of mm as expected. However, the preliminary analysis shows significant differences between two different approaches we have chosen. These differences may be explained by the different experimental conditions.

  8. Length dependence of carbon nanotube thermal conductivity and the "problem of long waves"

    NASA Technical Reports Server (NTRS)

    Mingo, N.; Broido, D. A.

    2005-01-01

    We present the first calculations of finite length carbon nanotube thermal conductivity that extend from the ballistic to the diffusive regime, throughout a very wide range of lengths and temperatures. The long standing problem of vanishing scattering of the "long wavelength phonf dramatically here, making the thermal conductivity diverge as the nanotube length increases. We show that the divergence disappears if 3-phonon scattering processes are considered to second or higher order. Nevertheless, for defect free nanotubes, the thermal conductivity keeps increasing up to very large lengths (10 gm at 300 K). Defects in the nanotube are also able to remove the long wavelength divergence.

  9. Perfluorooctanoic acid and environmental risks

    EPA Science Inventory

    Perfluorooctanoic acid (PFOA) is a member of the perfluoroalkyl acids (PFAA) family of chemicals, which consist of a carbon backbone typically four to fourteen carbons in length and a charged functional moiety.

  10. Path length enhancement in disordered media for increased absorption.

    PubMed

    Mupparapu, Rajeshkumar; Vynck, Kevin; Svensson, Tomas; Burresi, Matteo; Wiersma, Diederik S

    2015-11-30

    We theoretically and numerically investigate the capability of disordered media to enhance the optical path length in dielectric slabs and augment their light absorption efficiency due to scattering. We first perform a series of Monte Carlo simulations of random walks to determine the path length distribution in weakly to strongly (single to multiple) scattering, non-absorbing dielectric slabs under normally incident light and derive analytical expressions for the path length enhancement in these two limits. Quite interestingly, while multiple scattering is expected to produce long optical paths, we find that media containing a vanishingly small amount of scatterers can still provide high path length enhancements due to the very long trajectories sustained by total internal reflection at the slab interfaces. The path length distributions are then used to calculate the light absorption efficiency of media with varying absorption coefficients. We find that maximum absorption enhancement is obtained at an optimal scattering strength, in-between the single-scattering and the diffusive (strong multiple-scattering) regimes. This study can guide experimentalists towards more efficient and potentially low-cost solutions in photovoltaic technologies.

  11. Telomere length in Hepatitis C.

    PubMed

    Kitay-Cohen, Y; Goldberg-Bittman, L; Hadary, R; Fejgin, M D; Amiel, A

    2008-11-01

    Telomeres are nucleoprotein structures located at the termini of chromosomes that protect the chromosomes from fusion and degradation. Hepatocyte cell-cycle turnover may be a primary mechanism of telomere shortening in hepatitis C virus (HCV) infection, inducing fibrosis and cellular senescence. HCV infection has been recognized as potential cause of B-cell lymphoma and hepatocellular carcinoma. The present study sought to assess relative telomere length in leukocytes from patients with chronic HCV infection, patients after eradication of HCV infection (in remission), and healthy controls. A novel method of manual evaluation was applied. Leukocytes derived from 22 patients with chronic HCV infection and age- and sex-matched patients in remission and healthy control subjects were subjected to a fluorescence-in-situ protocol (DAKO) to determine telomere fluorescence intensity and number. The relative, manual, analysis of telomere length was validated against findings on applied spectral imaging (ASI) in a random sample of study and control subjects. Leukocytes from patients with chronic HCV infection had shorter telomeres than leukocytes from patients in remission and healthy controls. On statistical analysis, more cells with low signal intensity on telomere FISH had shorter telomeres whereas more cells with high signal intensity had longer telomeres. The findings were corroborated by the ASI telomere software. Telomere shortening in leukocytes from patients with active HCV infection is probably due to the lower overall telomere level rather than higher cell cycle turnover. Manual evaluation is an accurate and valid method of assessing relative telomere length between patients with chronic HCV infection and healthy subjects. PMID:18992639

  12. The NIST Length Scale Interferometer

    PubMed Central

    Beers, John S.; Penzes, William B.

    1999-01-01

    The National Institute of Standards and Technology (NIST) interferometer for measuring graduated length scales has been in use since 1965. It was developed in response to the redefinition of the meter in 1960 from the prototype platinum-iridium bar to the wavelength of light. The history of the interferometer is recalled, and its design and operation described. A continuous program of modernization by making physical modifications, measurement procedure changes and computational revisions is described, and the effects of these changes are evaluated. Results of a long-term measurement assurance program, the primary control on the measurement process, are presented, and improvements in measurement uncertainty are documented.

  13. The Length of Time's Arrow

    SciTech Connect

    Feng, Edward H.; Crooks, Gavin E.

    2008-08-21

    An unresolved problem in physics is how the thermodynamic arrow of time arises from an underlying time reversible dynamics. We contribute to this issue by developing a measure of time-symmetry breaking, and by using the work fluctuation relations, we determine the time asymmetry of recent single molecule RNA unfolding experiments. We define time asymmetry as the Jensen-Shannon divergencebetween trajectory probability distributions of an experiment and its time-reversed conjugate. Among other interesting properties, the length of time's arrow bounds the average dissipation and determines the difficulty of accurately estimating free energy differences in nonequilibrium experiments.

  14. Applicability of Mixing Length Theory to a Turbulent Vortex System

    NASA Technical Reports Server (NTRS)

    Ragsdale, Robert G.

    1961-01-01

    The ability of mixing length theory to correlate vortex data is evaluated. Expressions are derived for eddy diffusivity by applying the techniques of von Karman and Prandtl which have been established for pipe flow. Total and static pressures were measured from the outer radius to the exhaust-nozzle radius of a vortex generator for a range of mass flows. These data are combined with Navier-Stokes solutions for this region of a compressible vortex to determine turbulent Reynolds numbers. The Reynolds number is related to Prandtl and Karman functions for various assumed boundary conditions, and the experimental data are used to determine the usefulness of these expressions. The following conclusions were reached: (1) Mixing length functions developed by applying von Karman's similarity hypothesis to vortex motion correlate the data better than do Prandtl functions obtained with the assumption that mixing length is proportional to radius. (2) Some of the expressions developed do not adequately represent the experimental data. (3) The data are correlated with acceptable scatter by evaluating the fluid radial inertia at the outer boundary and the shear stress at the inner boundary. The universal constant K was found to be 0.04 to 0.08, rather than the value of 0.4 which is accepted for rectilinear flow. (4) The data are best correlated by a modified Karman expression which includes an effect of radial inertia, as well as shear stress, on eddy diffusivity.

  15. Dependence on chain length of NMR relaxation times in mixtures of alkanes

    NASA Astrophysics Data System (ADS)

    Freed, Denise E.

    2007-05-01

    Many naturally occurring fluids, such as crude oils, consist of a very large number of components. It is often of interest to determine the composition of the fluids in situ. Diffusion coefficients and nuclear magnetic resonance (NMR) relaxation times can be measured in situ and depend on the size of the molecules. It has been shown [D. E. Freed et al., Phys. Rev. Lett. 94, 067602 (2005)] that the diffusion coefficient of each component in a mixture of alkanes follows a scaling law in the chain length of that molecule and in the mean chain length of the mixture, and these relations were used to determine the chain length distribution of crude oils from NMR diffusion measurements. In this paper, the behavior of NMR relaxation times in mixtures of chain molecules is addressed. The author explains why one would expect scaling laws for the transverse and longitudinal relaxation times of mixtures of short chain molecules and mixtures of alkanes, in particular. It is shown how the power law dependence on the chain length can be calculated from the scaling laws for the translational diffusion coefficients. The author fits the literature data for NMR relaxation in binary mixtures of alkanes and finds that its dependence on chain length agrees with the theory. Lastly, it is shown how the scaling laws in the chain length and the mean chain length can be used to determine the chain length distribution in crude oils that are high in saturates. A good fit is obtained between the NMR-derived chain length distributions and the ones from gas chromatography.

  16. Thermal diffusivity of some crystalline rocks

    SciTech Connect

    Drury, M.J.

    1987-01-01

    Thermal diffusivity data at room temperature and uniaxial pressure of 1 MPa are reported for five sets of crystalline rocks - granite, granodiorite, gabbro, basalt and gneiss. Diffusivity ranges between approximately 0.6 and 1.9 mm/sup 2//s, the lower end of the range being appropriate for basic rocks and the upper end for quartz-bearing acidic rocks. The scatter in diffusivity for each data set is significantly more than that of thermal conductivity, because the diffusivity of water is typically less than 10% of the diffusivity of most common minerals, whereas water conductivity is 25 - 30% of the conductivity of the minerals. For a sample set of uniform mineralogy in which porosity varies, a greater variation of diffusivity than of conductivity is therefore expected. For three of the sets sufficient mineralogical data were available to permit the assessment of methods of estimating thermal diffusivity from mineral content. All models tested yielded higher mean values of diffusivity than the means of the measured values. No model was found to be able to predict diffusivity to better than approximately 20%, but if that accuracy is sufficient, a simple geometrical model, for which only quartz content must be known, is adequate. The diffusivity data have been combined with measurements of thermal conductivity and density to provide estimates of specific heat. These all tend to be higher than those reported in the literature. For some rocks, such as the basalts, this can be explained in terms of relatively high water content and the very high specific heat of water compared with that of most common minerals. For the granites and granodiorites, the new specific heat data redefine the previously published means and ranges, by increasing the data base by approximately an order of magnitude.

  17. TPR repeats and ELTR pattern: length variation as a function evolution mechanism.

    PubMed

    Yang, Ke-Qian

    2007-12-01

    TPR repeat was originally defined as a 34 amino acid structural repeat (TPR-34). Equal length tandem repeats (ELTR) was proposed to represent the ancestral repeat pattern. Length polymorphism of TPR repeats was analyzed using PATTINPROT, two new versions of TPR repeat of 40 and 42 amino acids were identified. These 'long' TPRs endow new functional capacities to the resulting proteins. A strong correlation between varied lengths and new functions supports the hypothesis that length variation is an underlying mechanism for the function evolution of repeat containing proteins.

  18. NMR Measures of Heterogeneity Length

    NASA Astrophysics Data System (ADS)

    Spiess, Hans W.

    2002-03-01

    Advanced solid state NMR spectroscopy provides a wealth of information about structure and dynamics of complex systems. On a local scale, multidimensional solid state NMR has elucidated the geometry and the time scale of segmental motions at the glass transition. The higher order correlation functions which are provided by this technique led to the notion of dynamic heterogeneities, which have been characterized in detail with respect to their rate memory and length scale. In polymeric and low molar mass glass formers of different fragility, length scales in the range 2 to 4 nm are observed. In polymeric systems, incompatibility of backbone and side groups as in polyalkylmethacrylates leads to heteogeneities on the nm scale, which manifest themselves in unusual chain dynamics at the glass transition involving extended chain conformations. References: K. Schmidt-Rohr and H.W. Spiess, Multidimensional Solid-State NMR and Polymers,Academic Press, London (1994). U. Tracht, M. Wilhelm, A. Heuer, H. Feng, K. Schmidt-Rohr, H.W. Spiess, Phys. Rev. Lett. 81, 2727 (1998). S.A. Reinsberg, X.H. Qiu, M. Wilhelm, M.D. Ediger, H.W. Spiess, J.Chem.Phys. 114, 7299 (2001). S.A. Reinsberg, A. Heuer, B. Doliwa, H. Zimmermann, H.W. Spiess, J. Non-Crystal. Solids, in press (2002)

  19. Updating applied diffusion models

    SciTech Connect

    Weil, J.C.

    1985-01-01

    Most diffusion models currently used in air-quality applications are substantially out of date with understanding of turbulence and diffusion in the planetary boundary layer. Under a Cooperative Agreement with the Environmental Protection Agency, the American Meteorological Society organized a workshop to help improve the basis of such models, their physics and hopefully their performance. Reviews and recommendations were made on models in three areas: diffusion in the convective boundary layer (CBL), diffusion in the stable boundary layer (SBL), and model uncertainty. Progress has been made in all areas, but it is most significant and ready for application to practical models in the case of the CBL. This has resulted from a clear understanding of the vertical structure and diffusion in the CBL, as demonstrated by laboratory experiments, numerical simulations, and field observations. Understanding of turbulence structure and diffusion in the SBL is less complete and not yet ready for general use in applications.

  20. Narrow groove welding gas diffuser assembly and welding torch

    SciTech Connect

    Rooney, Stephen J.

    2000-02-04

    A diffuser assembly is provided for narrow groove welding using an automatic gas tungsten arc welding torch. The diffuser assembly includes manifold adapted for adjustable mounting on the welding torch which is received in a central opening in the manifold. Laterally extending manifold sections communicate with a shield gas inlet such that shield gas supplied to the inlet passes to gas passages of the manifold sections. First and second tapered diffusers are respectively connected to the manifold sections in fluid communication with the gas passages thereof. The diffusers extend downwardly along the torch electrode on opposite sides thereof so as to release shield gas along the length of the electrode and at the distal tip of the electrode. The diffusers are of a transverse width which is on the order of the thickness of the electrode so that the diffusers can, in use, be inserted into a narrow welding groove before and after the electrode in the direction of the weld operation.

  1. Narrow groove welding gas diffuser assembly and welding torch

    DOEpatents

    Rooney, Stephen J.

    2001-01-01

    A diffuser assembly is provided for narrow groove welding using an automatic gas tungsten arc welding torch. The diffuser assembly includes a manifold adapted for adjustable mounting on the welding torch which is received in a central opening in the manifold. Laterally extending manifold sections communicate with a shield gas inlet such that shield gas supplied to the inlet passes to gas passages of the manifold sections. First and second tapered diffusers are respectively connected to the manifold sections in fluid communication with the gas passages thereof. The diffusers extend downwardly along the torch electrode on opposite sides thereof so as to release shield gas along the length of the electrode and at the distal tip of the electrode. The diffusers are of a transverse width which is on the order of the thickness of the electrode so that the diffusers can, in use, be inserted into a narrow welding groove before and after the electrode in the direction of the weld operation.

  2. Gaseous diffusion system

    DOEpatents

    Garrett, George A.; Shacter, John

    1978-01-01

    1. A gaseous diffusion system comprising a plurality of diffusers connected in cascade to form a series of stages, each of said diffusers having a porous partition dividing it into a high pressure chamber and a low pressure chamber, and means for combining a portion of the enriched gas from a succeeding stage with a portion of the enriched gas from the low pressure chamber of each stage and feeding it into one extremity of the high pressure chamber thereof.

  3. Favorite Demonstrations: Gaseous Diffusion: A Demonstration of Graham's Law.

    ERIC Educational Resources Information Center

    Kauffman, George B.; Ebner, Ronald D.

    1985-01-01

    Describes a demonstration in which gaseous ammonia and hydrochloric acid are used to illustrate rates of diffusion (Graham's Law). Simple equipment needed for the demonstration include a long tube, rubber stoppes, and cotton. Two related demonstrations are also explained. (DH)

  4. Inpainting using airy diffusion

    NASA Astrophysics Data System (ADS)

    Lorduy Hernandez, Sara

    2015-09-01

    One inpainting procedure based on Airy diffusion is proposed, implemented via Maple and applied to some digital images. Airy diffusion is a partial differential equation with spatial derivatives of third order in contrast with the usual diffusion with spatial derivatives of second order. Airy diffusion generates the Airy semigroup in terms of the Airy functions which can be rewritten in terms of Bessel functions. The Airy diffusion can be used to smooth an image with the corresponding noise elimination via convolution. Also the Airy diffusion can be used to erase objects from an image. We build an algorithm using the Maple package ImageTools and such algorithm is tested using some images. Our results using Airy diffusion are compared with the similar results using standard diffusion. We observe that Airy diffusion generates powerful filters for image processing which could be incorporated in the usual packages for image processing such as ImageJ and Photoshop. Also is interesting to consider the possibility to incorporate the Airy filters as applications for smartphones and smart-glasses.

  5. Multicomponent diffusion revisited

    NASA Astrophysics Data System (ADS)

    Lam, S. H.

    2006-07-01

    The derivation of the multicomponent diffusion law is revisited. Following Furry [Am. J. Phys. 16, 63 (1948)], Williams [Am. J. Phys. 26, 467 (1958); Combustion Theory, 2nd ed. (Benjamin/Cummings , Menlo Park, CA,1985)] heuristically rederived the classical kinetic theory results using macroscopic equations, and pointed out that the dynamics of the mixture fluid had been assumed inviscid. This paper generalizes the derivation, shows that the inviscid assumption can easily be relaxed to add a new term to the classical diffusion law, and the thermal diffusion term can also be easily recovered. The nonuniqueness of the multicomponent diffusion coefficient matrix is emphasized and discussed.

  6. Diffusing-Wave Spectroscopy of Gelling Dairy Systems

    NASA Astrophysics Data System (ADS)

    Hemar, Y.; Hebraud, P.; Sarcia, R.; Pinder, D. N.

    2004-04-01

    Conventional diffusing-wave spectroscopy (DWS) was combined with a CCD-camera based diffusing-wave spectroscopy (MSDWS) to study acid induced skim milk gels. This allowed the measurement of intensity autocorrelation functions from 10-6 to 3×103 s, giving access to both fast and slow dynamic modes of these gels.

  7. Geometry of area without length

    NASA Astrophysics Data System (ADS)

    Ho, Pei-Ming; Inami, Takeo

    2016-01-01

    To define a free string by the Nambu-Goto action, all we need is the notion of area, and mathematically the area can be defined directly in the absence of a metric. Motivated by the possibility that string theory admits backgrounds where the notion of length is not well defined but a definition of area is given, we study space-time geometries based on the generalization of a metric to an area metric. In analogy with Riemannian geometry, we define the analogues of connections, curvatures, and Einstein tensor. We propose a formulation generalizing Einstein's theory that will be useful if at a certain stage or a certain scale the metric is ill defined and the space-time is better characterized by the notion of area. Static spherical solutions are found for the generalized Einstein equation in vacuum, including the Schwarzschild solution as a special case.

  8. Proton friction and diffusion coefficients in hydrated polymer electrolyte membranes: Computations with a non-equilibrium statistical mechanical model

    NASA Astrophysics Data System (ADS)

    Paddison, Stephen J.; Paul, Reginald; Zawodzinski, Thomas A.

    2001-10-01

    A recently derived mathematical model to compute the effective friction and diffusion coefficients of hydronium ions in hydrated polymer electrolyte membranes is described and tested for dependence on membrane-specific parameters. Contributions to the friction coefficient due to water-polymer, water-hydronium, and hydronium-polymer interactions are determined through computation of force-force correlation functions. The conventional Stokes law friction coefficient of the hydronium ion in bulk water is then "corrected" with these statistically derived contributions and the corresponding diffusion coefficient calculated. For a Nafion® membrane pore with an hydration level of six water molecules per sulfonic acid functional, the model was used to compute friction coefficients for various distributions of the fixed sites, and for different side chain lengths. The model showed substantial sensitivity to these parameters and predicted that for pores of fixed volume and a constant total number of sulfonate groups, the friction on the hydrated proton is the greatest for distributions with high local anionic charge density. In a second series of computations where the radius and length of the pore were varied, the model demonstrated that the proton diffusion increases with increasing channel diameter. These calculations, therefore, demonstrate the important predictive capability of this molecular-based, nonequilibrium statistical mechanical model.

  9. Experimental study of vortex diffusers

    SciTech Connect

    Shakerin, S.; Miller, P.L.

    1995-11-01

    This report documents experimental research performed on vortex diffusers used in ventilation and air-conditioning systems. The main objectives of the research were (1) to study the flow characteristics of isothermal jets issuing from vortex diffusers, (2) to compare the vortex diffuser`s performance with that of a conventional diffuser, and (3) to prepare a report that disseminates the results to the designers of ventilation and air-conditioning systems. The researchers considered three diffusers: a conventional round ceiling diffuser and two different styles of vortex diffusers. Overall, the vortex diffusers create slightly more induction of ambient air in comparison to the conventional diffuser.

  10. Back diffusion from thin low permeability zones.

    PubMed

    Yang, Minjune; Annable, Michael D; Jawitz, James W

    2015-01-01

    Aquitards can serve as long-term contaminant sources to aquifers when contaminant mass diffuses from the aquitard following aquifer source mass depletion. This study describes analytical and experimental approaches to understand reactive and nonreactive solute transport in a thin aquitard bounded by an adjacent aquifer. A series of well-controlled laboratory experiments were conducted in a two-dimensional flow chamber to quantify solute diffusion from a high-permeability sand into and subsequently out of kaolinite clay layers of vertical thickness 15 mm, 20 mm, and 60 mm. One-dimensional analytical solutions were developed for diffusion in a finite aquitard with mass exchange with an adjacent aquifer using the method of images. The analytical solutions showed very good agreement with measured breakthrough curves and aquitard concentration distributions measured in situ by light reflection visualization. Solutes with low retardation accumulated more stored mass with greater penetration distance in the aquitard compared to high-retardation solutes. However, because the duration of aquitard mass release was much longer, high-retardation solutes have a greater long-term back diffusion risk. The error associated with applying a semi-infinite domain analytical solution to a finite diffusion domain increases as a function of the system relative diffusion length scale, suggesting that the solutions using image sources should be applied in cases with rapid solute diffusion and/or thin clay layers. The solutions presented here can be extended to multilayer aquifer/low-permeability systems to assess the significance of back diffusion from thin layers.

  11. Back diffusion from thin low permeability zones.

    PubMed

    Yang, Minjune; Annable, Michael D; Jawitz, James W

    2015-01-01

    Aquitards can serve as long-term contaminant sources to aquifers when contaminant mass diffuses from the aquitard following aquifer source mass depletion. This study describes analytical and experimental approaches to understand reactive and nonreactive solute transport in a thin aquitard bounded by an adjacent aquifer. A series of well-controlled laboratory experiments were conducted in a two-dimensional flow chamber to quantify solute diffusion from a high-permeability sand into and subsequently out of kaolinite clay layers of vertical thickness 15 mm, 20 mm, and 60 mm. One-dimensional analytical solutions were developed for diffusion in a finite aquitard with mass exchange with an adjacent aquifer using the method of images. The analytical solutions showed very good agreement with measured breakthrough curves and aquitard concentration distributions measured in situ by light reflection visualization. Solutes with low retardation accumulated more stored mass with greater penetration distance in the aquitard compared to high-retardation solutes. However, because the duration of aquitard mass release was much longer, high-retardation solutes have a greater long-term back diffusion risk. The error associated with applying a semi-infinite domain analytical solution to a finite diffusion domain increases as a function of the system relative diffusion length scale, suggesting that the solutions using image sources should be applied in cases with rapid solute diffusion and/or thin clay layers. The solutions presented here can be extended to multilayer aquifer/low-permeability systems to assess the significance of back diffusion from thin layers. PMID:25478850

  12. Macromolecular Diffusion in Dynamic Polymer Nanocomposite

    NASA Astrophysics Data System (ADS)

    Lin, Chia-Chun; Cargnello, Matteo; Clarke, Nigel; Winey, Karen; Composto, Russell

    2015-03-01

    We consider diffusion of tracer polymers in the presence of mobile nanoparticles in polymer nanocomposites (PNCs). These nanoparticles are mobile on the time scale of polymer diffusion and have dimensions less than the entanglement mesh size (i.e., tube diameter). The PNC consists of titanium dioxide nanorods (NR, diameter=4.5nm; length=30.1nm) grafted with phenyl groups uniformly dispersed in a polystyrene (P=650kg/mol; tube diameter=8nm) matrix up to 10 volume percent. Three deuterated polystyrenes (dPS; M=800, 1800 and 3200 kg/mol) are chosen because their diffusion relative to NR allows for investigating fixed and mobile NR by simply changing M. For all M, the reduced tracer diffusivities are observed to decrease monotonically as NR loading increases. However, the reduced diffusivity of dPS (3200 kg/mol) is faster than expected compared to the fixed NR case. These findings suggest that mobile NR do not effectively slow down tracer diffusion relative to fixed particles. To test this hypothesis, dPS diffusion is investigated in a high molecular weight matrix PS (2000 kg/mol) in order to slow down NR diffusion relative to dPS (3200 kg/mol). New models are needed to incorporate these mobility dependent entanglements into a comprehensive understanding of dynamics in PNCs. Primary fundings: NSF/EPSRC Materials World Network DMR-1210379 (KIW, RJC) and EP/5065373/1 (NC). Support also by the NSF/MRSEC-DMR 11-20901, and Polymer Programs DMR 09-07493.

  13. Numerical study of a cylinder model of the diffusion MRI signal for neuronal dendrite trees.

    PubMed

    Van Nguyen, Dang; Grebenkov, Denis; Le Bihan, Denis; Li, Jing-Rebecca

    2015-03-01

    We study numerically how the neuronal dendrite tree structure can affect the diffusion magnetic resonance imaging (dMRI) signal in brain tissue. For a large set of randomly generated dendrite trees, synthetic dMRI signals are computed and fitted to a cylinder model to estimate the effective longitudinal diffusivity D(L) in the direction of neurites. When the dendrite branches are short compared to the diffusion length, D(L) depends significantly on the ratio between the average branch length and the diffusion length. In turn, D(L) has very weak dependence on the distribution of branch lengths and orientations of a dendrite tree, and the number of branches per node. We conclude that the cylinder model which ignores the connectivity of the dendrite tree, can still be adapted to describe the apparent diffusion coefficient in brain tissue. PMID:25681802

  14. Effect of hourglass-shaped nanopore length on osmotic water transport

    NASA Astrophysics Data System (ADS)

    Shahbabaei, Majid; Kim, Daejoong

    2016-09-01

    In the present research, molecular dynamic (MD) simulations are utilized in order to examine the water transport properties through hourglass-shaped pore structures with various lengths. The length elongates in a range of 100-200 Å, while the size of the narrowest diameter remains constant at 3 Å. The results show that the defect effect can be substantially diminished as the length increases, so that the fluctuations of the energy barrier reaches zero inside 200 Å pore structure, which is an indication of rapid increase of water transport rate. The flux increases with length, suggesting a reduction in hydrodynamic resistance, that water molecules are able to easily enter the pore. The axial diffusivity and permeability are increased once the length increments, which indicate a fast water transport. It is concluded that the thermal fluctuations of water molecules inside reservoir affect the motion of water molecules inside the pore as length decreases.

  15. Synthetic hydraphile channels of appropriate length kill Escherichia coli.

    PubMed

    Leevy, W Matthew; Donato, Gina M; Ferdani, Riccardo; Goldman, William E; Schlesinger, Paul H; Gokel, George W

    2002-08-01

    Crown ether-based synthetic cation conducting channels called hydraphiles show clear ionophoretic activity in phospholipid vesicles. These compounds are shown to be active against the bacterium E. coli. Disk diffusion assays were performed to assess the toxicity of different hydraphile derivatives. Liquid culture tests were conducted to quantitate the dependence of bacterical activity on channel length. It is proposed that hydraphiles are toxic to bacteria as a result of channel formation in the membrane. The bactericidal activity is found to depend at least on the presence of a functional central relay and proper channel length. It is speculated that hydraphiles insert into the bilayer and disrupt the cell's osmotic balance, leading to cell death.

  16. Control of exit velocity profile of an asymmetric annular diffuser using wall suction

    NASA Technical Reports Server (NTRS)

    Juhasz, A. J.

    1973-01-01

    An asymmetric annular diffuser equipped with wall bleed (suction) capability was tested for controllability of exit velocity profile. The diffuser area ratio was 3.2, and the length to inlet height ratio was 1.6. Results show that the diffuser radial exit velocity profile could be controlled from a hub peaked to a tip peaked form by selective use of bleed on the outer wall or on both diffuser walls. Based on these results, application of the diffuser bleed technique to gas turbine combustors may be possible. Diffuser bleed could be used to tailor the airflow distribution for optimizing combustor performance at a variety of operating conditions.

  17. A Simple Single Step diffusion and Emitter Etching Process for High Efficiency Gallium Antimonide Thermophotovoltaic Devices

    SciTech Connect

    G. Rajagopalan; N.S. Reddy; E. Ehsani; I.B. Bhat; P.S. Dutta; R.J. Gutmann; G. Nichols; G.W. Charache; O. Sulima

    2003-08-29

    A single step diffusion followed by precise etching of the diffused layer has been developed to obtain a diffusion profile appropriate for high efficiency GaSb thermophotovoltaic cells. The junction depth was controlled through monitoring of light current-voltage (I-V) curves (photovoltaic response) during the post diffusion emitter etching process. The measured photoresponses (prior to device fabrication) have been correlated with the quantum efficiencies and the open circuit voltages in the fabricated devices. An optimum junction depth for obtaining highest quantum efficiency and open circuit voltage is presented based on diffusion lengths (or monitoring carrier lifetimes), carrier mobility and typical diffused impurity profile in GaSb.

  18. Natural convection within a vertical finite-length channel in free space

    SciTech Connect

    Lin, S.C.; Chang, K.P.; Hung, Y.H. )

    1994-04-01

    Natural convection within a vertical finite length channel in free space is studied in this article to remove assumptions that need to be made on velocity and temperature profiles at the channel entrance. For small channel aspect ratios and low Rayleigh numbers, significant deviations of the Nusselt number and temperature distributions exist due to the effects of vertical thermal diffusion and free space stratification in the channel. A new correlation was proposed on induced Reynolds number for vertical finite length channel. 8 refs.

  19. Adhesive ligand tether length affects the size and length of focal adhesions and influences cell spreading and attachment

    PubMed Central

    Attwood, Simon J.; Cortes, Ernesto; Haining, Alexander William M.; Robinson, Benjamin; Li, Danyang; Gautrot, Julien; del Río Hernández, Armando

    2016-01-01

    Cells are known to respond to physical cues from their microenvironment such as matrix rigidity. Discrete adhesive ligands within flexible strands of fibronectin connect cell surface integrins to the broader extracellular matrix and are thought to mediate mechanosensing through the cytoskeleton-integrin-ECM linkage. We set out to determine if adhesive ligand tether length is another physical cue that cells can sense. Substrates were covalently modified with adhesive arginylglycylaspartic acid (RGD) ligands coupled with short (9.5 nm), medium (38.2 nm) and long (318 nm) length inert polyethylene glycol tethers. The size and length of focal adhesions of human foreskin fibroblasts gradually decreased from short to long tethers. Furthermore, we found cell adhesion varies in a linker length dependent manner with a remarkable 75% reduction in the density of cells on the surface and a 50% reduction in cell area between the shortest and longest linkers. We also report the interplay between RGD ligand concentration and tether length in determining cellular spread area. Our findings show that without varying substrate rigidity or ligand density, tether length alone can modulate cellular behaviour. PMID:27686622

  20. Adhesive ligand tether length affects the size and length of focal adhesions and influences cell spreading and attachment

    NASA Astrophysics Data System (ADS)

    Attwood, Simon J.; Cortes, Ernesto; Haining, Alexander William M.; Robinson, Benjamin; Li, Danyang; Gautrot, Julien; Del Río Hernández, Armando

    2016-09-01

    Cells are known to respond to physical cues from their microenvironment such as matrix rigidity. Discrete adhesive ligands within flexible strands of fibronectin connect cell surface integrins to the broader extracellular matrix and are thought to mediate mechanosensing through the cytoskeleton-integrin-ECM linkage. We set out to determine if adhesive ligand tether length is another physical cue that cells can sense. Substrates were covalently modified with adhesive arginylglycylaspartic acid (RGD) ligands coupled with short (9.5 nm), medium (38.2 nm) and long (318 nm) length inert polyethylene glycol tethers. The size and length of focal adhesions of human foreskin fibroblasts gradually decreased from short to long tethers. Furthermore, we found cell adhesion varies in a linker length dependent manner with a remarkable 75% reduction in the density of cells on the surface and a 50% reduction in cell area between the shortest and longest linkers. We also report the interplay between RGD ligand concentration and tether length in determining cellular spread area. Our findings show that without varying substrate rigidity or ligand density, tether length alone can modulate cellular behaviour.

  1. Novel light diffusing fiber for use in medical applications

    NASA Astrophysics Data System (ADS)

    Klubben, W. Spencer; Logunov, Stephan L.; Fewkes, Edward J.; Mooney, Jeff; Then, Paul M.; Wigley, Peter G.; Schreiber, Horst; Matias, Kaitlyn; Wilson, Cynthia J.; Ocampo, Manuela

    2016-03-01

    Fiber-based cylindrical light diffusers are often used in photodynamic therapy to illuminate a luminal organ, such as the esophagus. The diffusers are often made of plastic and suffer from short diffusion lengths and low transmission efficiencies over a broad spectrum. We have developed FibranceTM, a glass-based fiber optic cylindrical diffuser which can illuminate a fiber from 0.5 cm to 10 meters over a broad wavelength range. With these longer illumination lengths, a variety of other medical applications are possible beyond photodynamic therapy. We present a number of applications for Fibrance ranging from in situ controllable illumination for Photodynamic Therapy to light guided anatomy highlighting for minimally invasive surgery to mitigating hospital acquired infections and more.

  2. High-power diffusing-tip fibers for interstitial photocoagulation

    NASA Astrophysics Data System (ADS)

    Sinofsky, Edward L.; Farr, Norman; Baxter, Lincoln; Weiler, William

    1997-05-01

    A line of optical fiber based diffusing tips has been designed, developed, and tested that are capable of distributing tens of watts of cw laser power over lengths ranging from two millimeters to over 10 cm. The result is a flexible non-stick diffuser capable of coagulating large volumes of tissue in reasonably short exposures of 3 - 5 minutes. Sub-millimeter diameter devices have a distinct effect on reducing the force needed to insert the applicator interstitially into tissue. Utilizing our design approach, we have produced diffusers based on 200 micrometer core fiber that has delivered over 35 watts of Nd:YAG energy over diffusion lengths as short as 4 mm. These applicators are being tested for applications in oncology, cardiology, electrophysiology, urology and gynecology.

  3. Cosmology with matter diffusion

    SciTech Connect

    Calogero, Simone; Velten, Hermano E-mail: velten@cce.ufes.br

    2013-11-01

    We construct a viable cosmological model based on velocity diffusion of matter particles. In order to ensure the conservation of the total energy-momentum tensor in the presence of diffusion, we include a cosmological scalar field φ which we identify with the dark energy component of the universe. The model is characterized by only one new degree of freedom, the diffusion parameter σ. The standard ΛCDM model can be recovered by setting σ = 0. If diffusion takes place (σ > 0) the dynamics of the matter and of the dark energy fields are coupled. We argue that the existence of a diffusion mechanism in the universe may serve as a theoretical motivation for interacting models. We constrain the background dynamics of the diffusion model with Supernovae, H(z) and BAO data. We also perform a perturbative analysis of this model in order to understand structure formation in the universe. We calculate the impact of diffusion both on the CMB spectrum, with particular attention to the integrated Sachs-Wolfe signal, and on the matter power spectrum P(k). The latter analysis places strong constraints on the magnitude of the diffusion mechanism but does not rule out the model.

  4. Speckle reducing anisotropic diffusion.

    PubMed

    Yu, Yongjian; Acton, Scott T

    2002-01-01

    This paper provides the derivation of speckle reducing anisotropic diffusion (SRAD), a diffusion method tailored to ultrasonic and radar imaging applications. SRAD is the edge-sensitive diffusion for speckled images, in the same way that conventional anisotropic diffusion is the edge-sensitive diffusion for images corrupted with additive noise. We first show that the Lee and Frost filters can be cast as partial differential equations, and then we derive SRAD by allowing edge-sensitive anisotropic diffusion within this context. Just as the Lee and Frost filters utilize the coefficient of variation in adaptive filtering, SRAD exploits the instantaneous coefficient of variation, which is shown to be a function of the local gradient magnitude and Laplacian operators. We validate the new algorithm using both synthetic and real linear scan ultrasonic imagery of the carotid artery. We also demonstrate the algorithm performance with real SAR data. The performance measures obtained by means of computer simulation of carotid artery images are compared with three existing speckle reduction schemes. In the presence of speckle noise, speckle reducing anisotropic diffusion excels over the traditional speckle removal filters and over the conventional anisotropic diffusion method in terms of mean preservation, variance reduction, and edge localization.

  5. Galactic Diffuse Emissions

    SciTech Connect

    Digel, Seth W.; /SLAC

    2007-10-25

    Interactions of cosmic rays with interstellar nucleons and photons make the Milky Way a bright, diffuse source of high-energy {gamma}-rays. Observationally, the results from EGRET, COMPTEL, and OSSE have now been extended to higher energies by ground-based experiments, with detections of diffuse emission in the Galactic center reported by H.E.S.S. in the range above 100 GeV and of diffuse emission in Cygnus by MILAGRO in the TeV range. In the range above 100 keV, INTEGRAL SPI has found that diffuse emission remains after point sources are accounted for. I will summarize current knowledge of diffuse {gamma}-ray emission from the Milky Way and review some open issues related to the diffuse emission -- some old, like the distribution of cosmic-ray sources and the origin of the 'excess' of GeV emission observed by EGRET, and some recently recognized, like the amount and distribution of molecular hydrogen not traced by CO emission -- and anticipate some of the advances that will be possible with the Large Area Telescope on GLAST. We plan to develop an accurate physical model for the diffuse emission, which will be useful for detecting and accurately characterizing emission from Galactic point sources as well as any Galactic diffuse emission from exotic processes, and for studying the unresolved extragalactic emission.

  6. Investigating Diffusion with Technology

    ERIC Educational Resources Information Center

    Miller, Jon S.; Windelborn, Augden F.

    2013-01-01

    The activities described here allow students to explore the concept of diffusion with the use of common equipment such as computers, webcams and analysis software. The procedure includes taking a series of digital pictures of a container of water with a webcam as a dye slowly diffuses. At known time points, measurements of the pixel densities…

  7. Anatomy of Particle Diffusion

    ERIC Educational Resources Information Center

    Bringuier, E.

    2009-01-01

    The paper analyses particle diffusion from a thermodynamic standpoint. The main goal of the paper is to highlight the conceptual connection between particle diffusion, which belongs to non-equilibrium statistical physics, and mechanics, which deals with particle motion, at the level of third-year university courses. We start out from the fact…

  8. Diffusion in Coulomb crystals.

    PubMed

    Hughto, J; Schneider, A S; Horowitz, C J; Berry, D K

    2011-07-01

    Diffusion in Coulomb crystals can be important for the structure of neutron star crusts. We determine diffusion constants D from molecular dynamics simulations. We find that D for Coulomb crystals with relatively soft-core 1/r interactions may be larger than D for Lennard-Jones or other solids with harder-core interactions. Diffusion, for simulations of nearly perfect body-centered-cubic lattices, involves the exchange of ions in ringlike configurations. Here ions "hop" in unison without the formation of long lived vacancies. Diffusion, for imperfect crystals, involves the motion of defects. Finally, we find that diffusion, for an amorphous system rapidly quenched from Coulomb parameter Γ=175 to Coulomb parameters up to Γ=1750, is fast enough that the system starts to crystalize during long simulation runs. These results strongly suggest that Coulomb solids in cold white dwarf stars, and the crust of neutron stars, will be crystalline and not amorphous. PMID:21867316

  9. Diffusion in Coulomb crystals.

    PubMed

    Hughto, J; Schneider, A S; Horowitz, C J; Berry, D K

    2011-07-01

    Diffusion in Coulomb crystals can be important for the structure of neutron star crusts. We determine diffusion constants D from molecular dynamics simulations. We find that D for Coulomb crystals with relatively soft-core 1/r interactions may be larger than D for Lennard-Jones or other solids with harder-core interactions. Diffusion, for simulations of nearly perfect body-centered-cubic lattices, involves the exchange of ions in ringlike configurations. Here ions "hop" in unison without the formation of long lived vacancies. Diffusion, for imperfect crystals, involves the motion of defects. Finally, we find that diffusion, for an amorphous system rapidly quenched from Coulomb parameter Γ=175 to Coulomb parameters up to Γ=1750, is fast enough that the system starts to crystalize during long simulation runs. These results strongly suggest that Coulomb solids in cold white dwarf stars, and the crust of neutron stars, will be crystalline and not amorphous.

  10. Helium Diffusion in Olivine

    NASA Astrophysics Data System (ADS)

    Cherniak, D. J.; Watson, E. B.

    2011-12-01

    Diffusion of helium has been characterized in natural Fe-bearing olivine (~Fo90) and synthetic forsterite. Polished, oriented slabs of olivine were implanted with 3He, at 100 keV at a dose of 5x1015/cm2 or at 3.0 MeV at a dose of 1x1016/cm2. A set of experiments on the implanted olivine were run in 1-atm furnaces. In addition to the one-atm experiments, experiments on implanted samples were also run at higher pressures (2.6 and 2.7 GPa) to assess the potential effects of pressure on He diffusion and the applicability of the measured diffusivities in describing He transport in the mantle. The high-pressure experiments were conducted in a piston-cylinder apparatus using an "ultra-soft" pressure cell, with the diffusion sample directly surrounded by AgCl. 3He distributions following experiments were measured with Nuclear Reaction Analysis using the reaction 3He(d,p)4He. This direct profiling method permits us to evaluate anisotropy of diffusion, which cannot be easily assessed using bulk-release methods. For diffusion in forsterite parallel to c we obtain the following Arrhenius relation over the temperatures 250-950°C: D = 3.91x10-6exp(-159 ± 4 kJ mol-1/RT) m2/sec. The data define a single Arrhenius line spanning more than 7 orders of magnitude in D and 700°C in temperature. Diffusion parallel to a appears slightly slower, yielding an activation energy for diffusion of 135 kJ/mol and a pre-exponential factor of 3.73x10-8 m2/sec. Diffusion parallel to b is slower than diffusion parallel to a (by about two-thirds of a log unit); for this orientation an activation energy of 138 kJ/mol and a pre-exponential factor of 1.34x10-8 m2/sec are obtained. This anisotropy is broadly consistent with observations for diffusion of Ni and Fe-Mg in olivine. Diffusion in Fe-bearing olivine (transport parallel to b) agrees within uncertainty with findings for He diffusion in forsterite. The higher-pressure experiments yield diffusivities in agreement with those from the 1-atm

  11. Investigation of Perforated Convergent-divergent Diffusers with Initial Boundary Layer

    NASA Technical Reports Server (NTRS)

    Weinstein, Maynard I

    1950-01-01

    An experimental investigation was made at Mach number 1.90 of the performance of a series of perforated convergent-divergent supersonic diffusers operating with initial boundary layer, which was induced and controlled by lengths of cylindrical inlets affixed to the diffusers. Supercritical mass-flow and peak total-pressure recoveries were decreased slightly by use of the longest inlets (4 inlet diameters in length). Combinations of cylindrical inlets, perforated diffusers, and subsonic diffuser were evaluated as simulated wind tunnels having second throats. Comparisons with noncontracted configurations of similar scale indicated conservatively computed power reductions of 25 percent.

  12. Toxicology of Perfluoroalkyl acids

    EPA Science Inventory

    The Perfluoroalkyl acids(PFAAs) area a family of organic chemicals consisting of a perflurinated carbon backbone (4-12in length) and a acidic functional moiety (Carboxylate or sulfonate). These compounds have excellent surface-tension reducing properties and have numerous industr...

  13. Toxicology of Perfluoroalkyl Acids*

    EPA Science Inventory

    The perfluoroalkyl acids (PFAAs) are a family of organic chemicals consisting of a perfluorinated carbon backbone (4-12 in length) and an acidic functional moiety (carboxylate or sulfonate). These compounds are chemically stable, have excellent surface-tension reducing properties...

  14. Size of diffusion pore of Alcaligenes faecalis.

    PubMed Central

    Ishii, J; Nakae, T

    1988-01-01

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

  15. 28 CFR 551.4 - Hair length.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... 28 Judicial Administration 2 2012-07-01 2012-07-01 false Hair length. 551.4 Section 551.4 Judicial... Hair length. (a) The Warden may not restrict hair length if the inmate keeps it neat and clean. (b) The Warden shall require an inmate with long hair to wear a cap or hair net when working in food service...

  16. 28 CFR 551.4 - Hair length.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... 28 Judicial Administration 2 2014-07-01 2014-07-01 false Hair length. 551.4 Section 551.4 Judicial... Hair length. (a) The Warden may not restrict hair length if the inmate keeps it neat and clean. (b) The Warden shall require an inmate with long hair to wear a cap or hair net when working in food service...

  17. 28 CFR 551.4 - Hair length.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 28 Judicial Administration 2 2013-07-01 2013-07-01 false Hair length. 551.4 Section 551.4 Judicial... Hair length. (a) The Warden may not restrict hair length if the inmate keeps it neat and clean. (b) The Warden shall require an inmate with long hair to wear a cap or hair net when working in food service...

  18. 28 CFR 551.4 - Hair length.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 28 Judicial Administration 2 2011-07-01 2011-07-01 false Hair length. 551.4 Section 551.4 Judicial... Hair length. (a) The Warden may not restrict hair length if the inmate keeps it neat and clean. (b) The Warden shall require an inmate with long hair to wear a cap or hair net when working in food service...

  19. 7 CFR 51.610 - Midrib length.

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    ... 7 Agriculture 2 2011-01-01 2011-01-01 false Midrib length. 51.610 Section 51.610 Agriculture... Consumer Standards for Celery Stalks Definitions § 51.610 Midrib length. Midrib length of a branch means the distance between the point of attachment to the root and the first node....

  20. 7 CFR 51.610 - Midrib length.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... 7 Agriculture 2 2010-01-01 2010-01-01 false Midrib length. 51.610 Section 51.610 Agriculture... Consumer Standards for Celery Stalks Definitions § 51.610 Midrib length. Midrib length of a branch means the distance between the point of attachment to the root and the first node....

  1. 28 CFR 551.4 - Hair length.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 28 Judicial Administration 2 2010-07-01 2010-07-01 false Hair length. 551.4 Section 551.4 Judicial Administration BUREAU OF PRISONS, DEPARTMENT OF JUSTICE INSTITUTIONAL MANAGEMENT MISCELLANEOUS Grooming § 551.4 Hair length. (a) The Warden may not restrict hair length if the inmate keeps it neat and clean. (b)...

  2. Biochemical rationale for the use of fatty acid analogs as agents for studying myocardial metabolism

    SciTech Connect

    Elmaleh D.R.; Livni E.; Brownell, G.L.; Strauss, H.W.

    1987-01-01

    Since fatty acids are the major energy source for myocardial contractile work, the rate of utilization of these substrates/unit work performed, should be an indicator of the health of the muscle. (1-C-11) palmitic acid has been shown to be useful as a myocardial imaging agent for positron tomography. The main limitations for the use of this substrate are the fast washout and translocation of the activity from the normal myocardium and the back diffusion in ischemia. Since alpha and omega oxidation are only present to a limited degree, branched chain fatty acids should have a prolonged residence time in the myocardium. The similarity in structure, chain length, solubility, and charge of the branched to the non-branched fatty acids should make these compounds behave in similar fashion in terms of their blood clearance and entry into tissues. 15 refs., 3 tabs.

  3. Scale length study in TFTR (Tokamak Fusion Test Reactor)

    SciTech Connect

    Hiroe, S.; Goldston, R.J.; Bitter, M.; Bush, C.E.; Efthimion, P.C.; Grek, B.; Johnson, D.W.; Murakami, M.; Schivell, J.; Towner, H.H.

    1988-12-01

    The scale lengths of the electron density (L/sub n//sub e/), temperature (L/sub T//sub e/), and pressure (L/sub p//sub e/) gradients were investigated during the 1985 operating period of the Tokamak Fusion Test Reactor (TFTR) for gas-fueled plasmas with neutral beam injection and movable limiter. Although the global energy confinement time degrades as the heating power increases or the plasma current decreases, the radial profiles of the scale lengths (L/sub T//sub e/ and L/sup p//sub e/) remain unchanged. Especially, the electron pressure profile is constrained not to change. This trend appears to hold over a fairly wide range of TFTR operational regimes. The radial profiles of L/sub n//sub e/ and /eta//sub e/ (= L/sub n//sub e//L/sub T//sub e/) also appear to remain unchanged, although the uncertainties of the experimental data for these quantities are greater than those for L/sub T//sub e/ and L/sub p//sub e/. The experimental parameters are used to evaluate theoretical predictions of the electron thermal diffusivity, and the results are compared with the empirical thermal diffusivity. 34 refs., 18 figs., 2 tabs.

  4. Tungsten diffusion in silicon

    SciTech Connect

    De Luca, A.; Texier, M.; Burle, N.; Oison, V.; Pichaud, B.; Portavoce, A.; Grosjean, C.

    2014-01-07

    Two doses (10{sup 13} and 10{sup 15} cm{sup −2}) of tungsten (W) atoms were implanted in different Si(001) wafers in order to study W diffusion in Si. The samples were annealed or oxidized at temperatures between 776 and 960 °C. The diffusion profiles were measured by secondary ion mass spectrometry, and defect formation was studied by transmission electron microscopy and atom probe tomography. W is shown to reduce Si recrystallization after implantation and to exhibit, in the temperature range investigated, a solubility limit close to 0.15%–0.2%, which is higher than the solubility limit of usual metallic impurities in Si. W diffusion exhibits unusual linear diffusion profiles with a maximum concentration always located at the Si surface, slower kinetics than other metals in Si, and promotes vacancy accumulation close to the Si surface, with the formation of hollow cavities in the case of the higher W dose. In addition, Si self-interstitial injection during oxidation is shown to promote W-Si clustering. Taking into account these observations, a diffusion model based on the simultaneous diffusion of interstitial W atoms and W-Si atomic pairs is proposed since usual models used to model diffusion of metallic impurities and dopants in Si cannot reproduce experimental observations.

  5. Tungsten diffusion in olivine

    NASA Astrophysics Data System (ADS)

    Cherniak, D. J.; Van Orman, J. A.

    2014-03-01

    Diffusion of tungsten has been characterized in synthetic forsterite and natural olivine (Fo90) under dry conditions. The source of diffusant was a mixture of magnesium tungstate and olivine powders. Experiments were prepared by sealing the source material and polished olivine under vacuum in silica glass ampoules with solid buffers to buffer at NNO or IW. Prepared capsules were annealed in 1 atm furnaces for times ranging from 45 min to several weeks, at temperatures from 1050 to 1450 °C. Tungsten distributions in the olivine were profiled by Rutherford Backscattering Spectrometry (RBS). The following Arrhenius relation is obtained for W diffusion in forsterite: D=1.0×10-8exp(-365±28 kJ mol/RT) m s Diffusivities for the synthetic forsterite and natural Fe-bearing olivine are similar, and tungsten diffusion in olivine shows little dependence on crystallographic orientation or oxygen fugacity. The slow diffusivities measured for W in olivine indicate that Hf-W ages in olivine-metal systems will close to diffusive exchange at higher temperatures than other chronometers commonly used in cosmochronology, and that tungsten isotopic signatures will be less likely to be reset by subsequent thermal events.

  6. Microrheology and characteristic lengths in wormlike micelles made of a zwitterionic surfactant and SDS in brine.

    PubMed

    Sarmiento-Gomez, Erick; Lopez-Diaz, David; Castillo, Rolando

    2010-09-30

    We study the Brownian motion of probe particles embedded in a wormlike micellar fluid made of a zwitterionic surfactant N-tetradecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate (TDPS), sodium dodecyl sulfate (SDS), and salty water to get structural and dynamical information of the micellar network. The motion of the probe particles was tracked with diffusing wave spectroscopy, and the mean square displacement as a function of time for the particles was obtained. This allowed us to obtain the long-time diffusion coefficient for microspheres moving in the micellar network and the cage size where each particle is harmonically bound at short times in that network. The bulk mechanical susceptibility of the fluid determines the response of the probe particles excited by the thermal stochastic forces. As a consequence, the mean square displacement curves allowed us to calculate the elastic (storage) and the viscous (loss) moduli as a function of the frequency. From these curves, spanning a wide frequency range, we estimated the characteristic lengths as the mesh size, the entanglement length, the persistence length, and the contour length for micellar solutions of different zwitterionic surfactant concentration, surfactant ratio ([SDS]/[TDPS]), salt concentration, and temperature. Mesh size, entanglement length, and persistence length are almost insensitive to the change of these variables. In contrast, the contour length changes in an important way. The contour length becomes shorter as the temperature increases, and it presents a peak at a surfactant ratio of ∼0.50-0.55. When salt is added to the solution, the contour length presents a peak at a salt concentration of ∼0.225 M, and in some solutions, this length can reach values of ∼12 μm. Scission energies help us to understand why the contour length first increases and then decreases when salt is added. PMID:20825212

  7. Diffusion Flame Stabilization

    NASA Technical Reports Server (NTRS)

    Takahashi, Fumiaki; Katta, V. R.

    2006-01-01

    Diffusion flames are commonly used for industrial burners in furnaces and flares. Oxygen/fuel burners are usually diffusion burners, primarily for safety reasons, to prevent flashback and explosion in a potentially dangerous system. Furthermore, in most fires, condensed materials pyrolyze, vaporize, and burn in air as diffusion flames. As a result of the interaction of a diffusion flame with burner or condensed-fuel surfaces, a quenched space is formed, thus leaving a diffusion flame edge, which plays an important role in flame holding in combustion systems and fire spread through condensed fuels. Despite a long history of jet diffusion flame studies, lifting/blowoff mechanisms have not yet been fully understood, compared to those of premixed flames. In this study, the structure and stability of diffusion flames of gaseous hydrocarbon fuels in coflowing air at normal earth gravity have been investigated experimentally and computationally. Measurements of the critical mean jet velocity (U(sub jc)) of methane, ethane, or propane at lifting or blowoff were made as a function of the coflowing air velocity (U(sub a)) using a tube burner (i.d.: 2.87 mm). By using a computational fluid dynamics code with 33 species and 112 elementary reaction steps, the internal chemical-kinetic structures of the stabilizing region of methane and propane flames were investigated. A peak reactivity spot, i.e., reaction kernel, is formed in the flame stabilizing region due to back-diffusion of heat and radical species against an oxygen-rich incoming flow, thus holding the trailing diffusion flame. The simulated flame base moved downstream under flow conditions close to the measured stability limit.

  8. Diffusion Flame Stabilization

    NASA Technical Reports Server (NTRS)

    Takahashi, Fumiaki; Katta, Viswanath R.

    2007-01-01

    Diffusion flames are commonly used for industrial burners in furnaces and flares. Oxygen/fuel burners are usually diffusion burners, primarily for safety reasons, to prevent flashback and explosion in a potentially dangerous system. Furthermore, in most fires, condensed materials pyrolyze, vaporize, and burn in air as diffusion flames. As a result of the interaction of a diffusion flame with burner or condensed-fuel surfaces, a quenched space is formed, thus leaving a diffusion flame edge, which plays an important role in flame holding in combustion systems and fire spread through condensed fuels. Despite a long history of jet diffusion flame studies, lifting/blowoff mechanisms have not yet been fully understood, compared to those of premixed flames. In this study, the structure and stability of diffusion flames of gaseous hydrocarbon fuels in coflowing air at normal earth gravity have been investigated experimentally and computationally. Measurements of the critical mean jet velocity (U(sub jc)) of methane, ethane, or propane at lifting or blowoff were made as a function of the coflowing air velocity (U(sub a)) using a tube burner (i.d.: 2.87 mm) (Fig. 1, left). By using a computational fluid dynamics code with 33 species and 112 elementary reaction steps, the internal chemical-kinetic structures of the stabilizing region of methane and propane flames were investigated (Fig. 1, right). A peak reactivity spot, i.e., reaction kernel, is formed in the flame stabilizing region due to back-diffusion of heat and radical species against an oxygen-rich incoming flow, thus holding the trailing diffusion flame. The simulated flame base moved downstream under flow conditions close to the measured stability limit.

  9. Germanium nanowire growth controlled by surface diffusion effects

    SciTech Connect

    Schmidtbauer, Jan; Bansen, Roman; Heimburger, Robert; Teubner, Thomas; Boeck, Torsten; Fornari, Roberto

    2012-07-23

    Germanium nanowires (NWs) were grown onto Ge(111) substrates by the vapor-liquid-solid process using gold droplets. The growth was carried out in a molecular beam epitaxy chamber at substrate temperatures between 370 Degree-Sign C and 510 Degree-Sign C. The resulting nanowire growth rate turns out to be highly dependent on the substrate temperature exhibiting the maximum at T = 430 Degree-Sign C. The temperature dependence of growth rate can be attributed to surface diffusion both along the substrate and nanowire sidewalls. Analyzing the diffusive material transport yields a diffusion length of 126 nm at a substrate temperature of 430 Degree-Sign C.

  10. Going up in time and length scales in modeling polymers

    NASA Astrophysics Data System (ADS)

    Grest, Gary S.

    Polymer properties depend on a wide range of coupled length and time scales, with unique macroscopic viscoelastic behavior stemming from interactions at the atomistic level. The need to probe polymers across time and length scales and particularly computational modeling is inherently challenging. Here new paths to probing long time and length scales including introducing interactions into traditional bead-spring models and coarse graining of atomistic simulations will be compared and discussed. Using linear polyethylene as a model system, the degree of coarse graining with two to six methylene groups per coarse-grained bead derived from a fully atomistic melt simulation were probed. We show that the degree of coarse graining affects the measured dynamic. Using these models we were successful in probing highly entangled melts and were able reach the long-time diffusive regime which is computationally inaccessible using atomistic simulations. We simulated the relaxation modulus and shear viscosity of well-entangled polyethylene melts for scaled times of 500 µs. Results for plateau modulus are in good agreement with experiment. The long time and length scale is coupled to the macroscopic viscoelasticity where the degree of coarse graining sets the minimum length scale instrumental in defining polymer properties and dynamics. Results will be compared to those obtained from simple bead-spring models to demonstrate the additional insight that can be gained from atomistically inspired coarse grained models. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.

  11. Normal and anomalous diffusion of Brownian particles on disordered potentials

    NASA Astrophysics Data System (ADS)

    Salgado-García, R.

    2016-07-01

    In this work we study the transition from normal to anomalous diffusion of Brownian particles on disordered potentials. The potential model consists of a series of "potential hills" (defined on a unit cell of constant length) whose heights are chosen randomly from a given distribution. We calculate the exact expression for the diffusion coefficient in the case of uncorrelated potentials for arbitrary distributions. We show that when the potential heights have a Gaussian distribution (with zero mean and a finite variance) the diffusion of the particles is always normal. In contrast, when the distribution of the potential heights is exponentially distributed the diffusion coefficient vanishes when the system is placed below a critical temperature. We calculate analytically the diffusion exponent for the anomalous (subdiffusive) phase by using the so-called "random trap model". Our predictions are tested by means of Langevin simulations obtaining good agreement within the accuracy of our numerical calculations.

  12. Coiled to diffuse: Brownian motion of a helical bacterium.

    PubMed

    Butenko, Alexander V; Mogilko, Emma; Amitai, Lee; Pokroy, Boaz; Sloutskin, Eli

    2012-09-11

    We employ real-time three-dimensional confocal microscopy to follow the Brownian motion of a fixed helically shaped Leptospira interrogans (LI) bacterium. We extract from our measurements the translational and the rotational diffusion coefficients of this bacterium. A simple theoretical model is suggested, perfectly reproducing the experimental diffusion coefficients, with no tunable parameters. An older theoretical model, where edge effects are neglected, dramatically underestimates the observed rates of translation. Interestingly, the coiling of LI increases its rotational diffusion coefficient by a factor of 5, compared to a (hypothetical) rectified bacterium of the same contour length. Moreover, the translational diffusion coefficients would have decreased by a factor of ~1.5, if LI were rectified. This suggests that the spiral shape of the spirochaete bacteria, in addition to being employed for their active twisting motion, may also increase the ability of these bacteria to explore the surrounding fluid by passive Brownian diffusion.

  13. Hereditary Diffuse Gastric Cancer

    MedlinePlus

    ... with the syndrome is recommended. What are the estimated cancer risks associated with HDGC? Not everyone who ... the lifetime risk for diffuse gastric cancer is estimated to be 70% to 80% for men and ...

  14. Multinomial Diffusion Equation

    SciTech Connect

    Balter, Ariel I.; Tartakovsky, Alexandre M.

    2011-06-01

    We have developed a novel stochastic, space/time discrete representation of particle diffusion (e.g. Brownian motion) based on discrete probability distributions. We show that in the limit of both very small time step and large concentration, our description is equivalent to the space/time continuous stochastic diffusion equation. Being discrete in both time and space, our model can be used as an extremely accurate, efficient, and stable stochastic finite-difference diffusion algorithm when concentrations are so small that computationally expensive particle-based methods are usually needed. Through numerical simulations, we show that our method can generate realizations that capture the statistical properties of particle simulations. While our method converges converges to both the correct ensemble mean and ensemble variance very quickly with decreasing time step, but for small concentration, the stochastic diffusion PDE does not, even for very small time steps.

  15. Lung diffusion testing

    MedlinePlus

    Lung diffusion testing measures how well the lungs exchange gases. This is an important part of lung testing , because ... gases do not move normally across the lung tissues into the blood vessels of the lung. This ...

  16. Investigating diffusion with technology

    NASA Astrophysics Data System (ADS)

    Miller, Jon S.; Windelborn, Augden F.

    2013-07-01

    The activities described here allow students to explore the concept of diffusion with the use of common equipment such as computers, webcams and analysis software. The procedure includes taking a series of digital pictures of a container of water with a webcam as a dye slowly diffuses. At known time points, measurements of the pixel densities (darkness) of the digital pictures are recorded and then plotted on a graph. The resulting graph of darkness versus time allows students to see the results of diffusion of the dye over time. Through modification of the basic lesson plan, students are able to investigate the influence of a variety of variables on diffusion. Furthermore, students are able to expand the boundaries of their thinking by formulating hypotheses and testing their hypotheses through experimentation. As a result, students acquire a relevant science experience through taking measurements, organizing data into tables, analysing data and drawing conclusions.

  17. Hydrogen Diffusion in Forsterite

    NASA Astrophysics Data System (ADS)

    Demouchy, S.; Mackwell, S.

    2002-12-01

    Physical and chemical properties of Earth's mantle are readily modified by interaction with volatiles, such as water. Thus, characterization of solubility and kinetics of incorporation for water in nominally anhydrous minerals is important in order to understand the behavior of Earth's interior under hydrous conditions. Experimental studies on the olivine-water system indicate that significant amounts of OH can dissolve within olivine as point defects (Bell and Rossman, 1992; Kohlstedt et al. 1996). Extending Kohlstedt and Mackwell's (1998) work, our study concerns the kinetics of hydrogen transport in the iron-free olivine-water system. This study is based on hydrogenation of forsterite samples during piston-cylinder and TZM cold-seal vessel experiments. We use infrared analyses in order to constrain the speciation of the mobile water-derived defects in forsterite single-crystal sample, and the rates of diffusion of such species under uppermost mantle conditions (0.2 to 1.5 GPa, 900 to 1100° C). Hydrogen defect transport in single crystals of forsterite is investigated for diffusion parallel to each crystallographic axis. Defect diffusivities are obtained by fitting a diffusion law to the OH content as a function of position in the sample. Our current results indicate that incorporation of hydroxyl species into iron-free olivine is a one-stage process with hydrogen diffusion linked to magnesium vacancy self-diffusion DV, such that DV = D~/3 = 10-12 m2/s at 1000° C parallel to [001], where D~ represents the chemical diffusivity. Those diffusion rates are slightly lower than in iron-bearing olivine for the same incorporation mechanism. The different concentration profiles show a clear anisotropy of diffusion, with fastest diffusion parallel to [001] as in iron-bearing olivine. Thus, while hydrogen solubilities are dependent on iron content, the rate of incorporation of water-derived species in olivine is not strongly coupled to the concentration of iron. This

  18. A statistical model for the length distribution of meshes in a polymer network

    NASA Astrophysics Data System (ADS)

    Lang, M.; Michalke, W.; Kreitmeier, S.

    2001-05-01

    A statistical model is introduced which allows estimation of the length distribution of meshes in a unimodal polymer network. The length distribution is responsible for the type and number of entanglements in a network and can thus provide information about the deformation behavior of polymers. The model can also predict the influence of certain simulation parameters such as the degree of cross linkage, the chain length, or the density of the melt from which the network is built. Both a reaction- and a diffusion-controlled cross-linking process can be mapped. We found that a shorter chain length implies a smaller number of chains per mesh. An increase of the degree of cross linkage as well as a lowering of the density of the melt also leads to a smaller average length of the meshes.

  19. Nodal Diffusion & Transport Theory

    1992-02-19

    DIF3D solves multigroup diffusion theory eigenvalue, adjoint, fixed source, and criticality (concentration, buckling, and dimension search) problems in 1, 2, and 3-space dimensions for orthogonal (rectangular or cylindrical), triangular, and hexagonal geometries. Anisotropic diffusion theory coefficients are permitted. Flux and power density maps by mesh cell and regionwise balance integrals are provided. Although primarily designed for fast reactor problems, upscattering and internal black boundary conditions are also treated.

  20. Analysis of reaction-diffusion systems with anomalous subdiffusion.

    PubMed

    Haugh, Jason M

    2009-07-22

    Reaction-diffusion equations are the cornerstone of modeling biochemical systems with spatial gradients, which are relevant to biological processes such as signal transduction. Implicit in the formulation of these equations is the assumption of Fick's law, which states that the local diffusive flux of species i is proportional to its concentration gradient; however, in the context of complex fluids such as cytoplasm and cell membranes, the use of Fick's law is based on empiricism, whereas evidence has been mounting that such media foster anomalous subdiffusion (with mean-squared displacement increasing less than linearly with time) over certain length scales. Particularly when modeling diffusion-controlled reactions and other systems where the spatial domain is considered semi-infinite, assuming Fickian diffusion might not be appropriate. In this article, two simple, conceptually extreme models of anomalous subdiffusion are used in the framework of Green's functions to demonstrate the solution of four reaction-diffusion problems that are well known in the biophysical context of signal transduction: fluorescence recovery after photobleaching, the Smolochowski limit for diffusion-controlled reactions in solution, the spatial range of a diffusing molecule with finite lifetime, and the collision coupling mechanism of diffusion-controlled reactions in two dimensions. In each case, there are only subtle differences between the two subdiffusion models, suggesting how measurements of mean-squared displacement versus time might generally inform models of reactive systems with partial diffusion control.

  1. Advanced manufacturing: Technology diffusion

    SciTech Connect

    Tesar, A.

    1995-12-01

    In this paper we examine how manufacturing technology diffuses rom the developers of technology across national borders to those who do not have the capability or resources to develop advanced technology on their own. None of the wide variety of technology diffusion mechanisms discussed in this paper are new, yet the opportunities to apply these mechanisms are growing. A dramatic increase in technology diffusion occurred over the last decade. The two major trends which probably drive this increase are a worldwide inclination towards ``freer`` markets and diminishing isolation. Technology is most rapidly diffusing from the US In fact, the US is supplying technology for the rest of the world. The value of the technology supplied by the US more than doubled from 1985 to 1992 (see the Introduction for details). History shows us that technology diffusion is inevitable. It is the rates at which technologies diffuse to other countries which can vary considerably. Manufacturers in these countries are increasingly able to absorb technology. Their manufacturing efficiency is expected to progress as technology becomes increasingly available and utilized.

  2. Flow Control in a Transonic Diffuser

    NASA Astrophysics Data System (ADS)

    Gartner, Jeremy; Amitay, Michael

    2014-11-01

    In some airplanes such as fighter jets and UAV, short inlet ducts replace the more conventional ducts due to their shorter length. However, these ducts are associated with low length-to-diameter ratio and low aspect ratio and, thus, experience massive separation and the presence of secondary flow structures. These flow phenomena are undesirable as they lead to pressure losses and distortion at the Aerodynamic Interface Plane (AIP), where the engine face is located. It causes the engine to perform with a lower efficiency as it would with a straight duct diffuser. Different flow control techniques were studied on the short inlet duct, with the goal to reattach the flow and minimize the distortions at the AIP. Due to the complex interaction between the separation and the secondary flow structures, the necessity to understand the flow mechanisms, and how to control them at a more fundamental level, a new transonic diffuser with an upper ramp and a straight floor was designed and built. The objective of this project is to explore the effectiveness of different flow control techniques in a high subsonic (up to Mach 0.8) diffuser, so that the quasi two-dimensional separation and the formation of secondary flow structure can be isolated using a canonical flow field. Supported by Northrop Grumman.

  3. Viscous diffusion of vorticity in unsteady wall layers using the diffusion velocity concept

    SciTech Connect

    Strickland, J.H.; Kempka, S.N.; Wolfe, W.P.

    1995-03-01

    The primary purpose of this paper is to provide a careful evaluation of the diffusion velocity concept with regard to its ability to predict the diffusion of vorticity near a moving wall. A computer code BDIF has been written which simulates the evolution of the vorticity field near a wall of infinite length which is moving in an arbitrary fashion. The simulations generated by this code are found to give excellent results when compared to several exact solutions. We also outline a two-dimensional unsteady viscous boundary layer model which utilizes the diffusion velocity concept and is compatible with vortex methods. A primary goal of this boundary layer model is to minimize the number of vortices generated on the surface at each time step while achieving good resolution of the vorticity field near the wall. Preliminary results have been obtained for simulating a simple two-dimensional laminar boundary layer.

  4. Viscous diffusion of vorticity in unsteady wall layers using the diffusion velocity concept

    NASA Astrophysics Data System (ADS)

    Strickland, J. H.; Kempka, S. N.; Wolfe, W. P.

    The primary purpose of this paper is to provide a careful evaluation of the diffusion velocity concept with regard to its ability to predict the diffusion of vorticity near a moving wall. A computer code BDIF has been written which simulates the evolution of the vorticity field near a wall of infinite length which is moving in an arbitrary fashion. The simulations generated by this code are found to give excellent results when compared to several exact solutions. We also outline a two-dimensional unsteady viscous boundary layer model which utilizes the diffusion velocity concept and is compatible with vortex methods. A primary goal of this boundary layer model is to minimize the number of vortices generated on the surface at each time step while achieving good resolution of the vorticity field near the wall. Preliminary results have been obtained for simulating a simple two-dimensional laminar boundary layer.

  5. Chain length dependence of {alpha}-olefin readsorption in Fischer-Tropsch synthesis

    SciTech Connect

    Kuipers, E.W.; Vinkenburg, I.H.; Oosterbeek, H.

    1995-03-01

    The total product concentration and the paraffin/olefin ratio have been measured up to C{sub 14} for Fischer-Tropsch synthesis on polycrystalline Co foils. The influences due to surface area, a wax coating, the H{sub 2}/CO ratio and flow velocity on concentration and selectivity have been determined. The paraffin/olefin ratio increases exponentially with chain length which is attributed to a chain-length-dependent olefin readsorption mechanism. The probability of readsorption depends on the heat of physisorption of the olefins on the catalyst as well as on their heat of dissolution in and their diffusivity through the product wax. All three factors predict an increase of the paraffin/olefin ratio with carbon number. Physisorption and dissolution are shown to cause a much stronger chain-length dependence than diffusion and will usually dominate. 36 refs., 9 figs.

  6. Multispecies diffusion models: A study of uranyl species diffusion

    SciTech Connect

    Liu, Chongxuan; Shang, Jianying; Zachara, John M.

    2011-12-14

    Rigorous numerical description of multi-species diffusion requires coupling of species, charge, and aqueous and surface complexation reactions that collectively affect diffusive fluxes. The applicability of a fully coupled diffusion model is, however, often constrained by the availability of species self-diffusion coefficients, as well as by computational complication for imposing charge conservation. In this study, several diffusion models with variable complexity in charge and species coupling were formulated and compared to describe reactive multi-species diffusion in groundwater. Diffusion of uranyl [U(VI)] species was used as an example in demonstrating the effectiveness of the models in describing multi-species diffusion. Numerical simulations found that a diffusion model with a single, common diffusion coefficient for all species was sufficient to describe multi-species U(VI) diffusion under steady-state condition of major chemical composition, but not under transient chemical conditions. Simulations revealed that a fully coupled diffusion model can be well approximated by a component-based diffusion model, which considers difference in diffusion coefficients between chemical components, but not between the species within each chemical component. This treatment significantly enhanced computational efficiency at the expense of minor charge conservation. The charge balance in the component-based diffusion model can be rigorously enforced, if necessary, by adding an artificial kinetic reaction term induced by the charge separation. The diffusion models were applied to describe U(VI) diffusive mass transfer in intragranular domains in two sediments collected from US Department of Energy's Hanford 300A where intragrain diffusion is a rate-limiting process controlling U(VI) adsorption and desorption. The grain-scale reactive diffusion model was able to describe U(VI) adsorption/desorption kinetics that has been described using a semi-empirical, multi-rate model

  7. Measurement of Solute Diffusion Behavior in Fractured Waste Glass Media

    SciTech Connect

    Saripalli, Kanaka P.; Lindberg, Michael J.; Meyer, Philip D.

    2008-10-01

    Determination of aqueous phase diffusion coefficients of solutes through fractured media is essential for understanding and modeling contaminants transport at many hazardous waste disposal sites. No methods for earlier measurements are available for the characterization of diffusion in fractured glass blocks. We report here the use of time-lag diffusion experimental method to assess the diffusion behavior of three different solutes (Cs, Sr and Pentafluoro Benzoic Acid or PFBA) in fractured, immobilized low activity waste (ILAW) glass forms. A fractured media time-lag diffusion experimental apparatus that allows the measurement of diffusion coefficients has been designed and built for this purpose. Use of time-lag diffusion method, a considerably easier experimental method than the other available methods, was not previously demonstrated for measuring diffusion in any fractured media. Hydraulic conductivity, porosity and diffusion coefficients of a solute were experimentally measured in fractured glass blocks using this method for the first time. Results agree with the range of properties reported for similar rock media earlier, indicating that the time-lag experimental method can effectively characterize the diffusion coefficients of fractured ILAW glass media.

  8. Anomalous diffusion in neutral evolution of model proteins.

    PubMed

    Nelson, Erik D; Grishin, Nick V

    2015-06-01

    Protein evolution is frequently explored using minimalist polymer models, however, little attention has been given to the problem of structural drift, or diffusion. Here, we study neutral evolution of small protein motifs using an off-lattice heteropolymer model in which individual monomers interact as low-resolution amino acids. In contrast to most earlier models, both the length and folded structure of the polymers are permitted to change. To describe structural change, we compute the mean-square distance (MSD) between monomers in homologous folds separated by n neutral mutations. We find that structural change is episodic, and, averaged over lineages (for example, those extending from a single sequence), exhibits a power-law dependence on n. We show that this exponent depends on the alignment method used, and we analyze the distribution of waiting times between neutral mutations. The latter are more disperse than for models required to maintain a specific fold, but exhibit a similar power-law tail. PMID:26172648

  9. Measurement of molecular length of self-assembled monolayer probed by localized surface plasmon resonance

    NASA Astrophysics Data System (ADS)

    Ito, Juri; Kajikawa, Kotaro

    2016-02-01

    We propose a method to measure the variation of the molecular length of self-assembled monolayers (SAMs) when it is exposed to solutions at different pH conditions. The surface immobilized gold nanospheres (SIGNs) shows strong absorption peak at the wavelengths of 600-800 nm when p-polarized light is illuminated. The peak wavelength depends on the length of the gap distance between the SIGNs and the substrate. The gap is supported by the SAM molecules. According to the analytical calculation based on multiple expansion, the relation between the peak wavelength of the SIGN structures and the gap distance is calculated, to evaluate the molecular length of the SAM through the optical absorption spectroscopy for the SIGN structures. The molecular length of the SIGN structure was measured in air, water, acidic, and basic solutions. It was found that the molecular lengths are longer in acidic solutions.

  10. Dimensional crossover of free exciton diffusion in etched GaAs wire structures

    NASA Astrophysics Data System (ADS)

    Bieker, S.; Stühler, R.; Kiessling, T.; Ossau, W.; Molenkamp, L. W.

    2015-09-01

    We report on low-temperature spatially resolved photoluminescence spectroscopy to study the diffusion of free excitons in etched wire structures of high-purity GaAs. We assess the stationary diffusion profiles by the free exciton second LO-phonon replica to circumvent the inherent interpretation ambiguities of the previously investigated free exciton zero-phonon line. Moreover, strictly resonant optical excitation prevents the distortion of the diffusion profiles due to local heating in the carrier system. We observe a dimensional crossover from 2D to 1D exciton diffusion when the lateral wire width falls below the diffusion length.

  11. Controlling Arc Length in Plasma Welding

    NASA Technical Reports Server (NTRS)

    Iceland, W. F.

    1986-01-01

    Circuit maintains arc length on irregularly shaped workpieces. Length of plasma arc continuously adjusted by control circuit to maintain commanded value. After pilot arc is established, contactor closed and transfers arc to workpiece. Control circuit then half-wave rectifies ac arc voltage to produce dc control signal proportional to arc length. Circuit added to plasma arc welding machines with few wiring changes. Welds made with circuit cleaner and require less rework than welds made without it. Beads smooth and free of inclusions.

  12. Measuring Crack Length in Coarse Grain Ceramics

    NASA Technical Reports Server (NTRS)

    Salem, Jonathan A.; Ghosn, Louis J.

    2010-01-01

    Due to a coarse grain structure, crack lengths in precracked spinel specimens could not be measured optically, so the crack lengths and fracture toughness were estimated by strain gage measurements. An expression was developed via finite element analysis to correlate the measured strain with crack length in four-point flexure. The fracture toughness estimated by the strain gaged samples and another standardized method were in agreement.

  13. A diffuse soft X-ray spectrometer

    NASA Technical Reports Server (NTRS)

    Mccammon, D.

    1981-01-01

    A design for a diffuse X-ray spectrometer utilizing Bragg reflection is described. The geometry has a very high throughput for a given physical size and allows simultaneous observation at all wavelengths within its range. Spectral resolving power is about 35 to 50. A similar unit equipped with thallium acid pthallate crystals will cover the 11 - 24 A-range with about half this throughput and twice the resolving power.

  14. The vector effective length of slot antennas

    NASA Astrophysics Data System (ADS)

    Wunsch, A. D.

    1991-05-01

    A suitable definition for the vector effective length of an arbitrary slot receiving antenna placed in a large conducting plane is presented, and a general formula is obtained for its derivation. To derive the definition and formula is, the effective length of a general wire antenna is derived, and then an analogous method is applied to the slot problem. The relationship of the slot's effective length to that for a flat strip wire antenna driven by a specified current is obtained. Formulas for the lengths of some specific common slot antennas are derived from the general expression. The current sampling property of a small straight slot is discussed.

  15. Generalizations of Brandl's theorem on Engel length

    NASA Astrophysics Data System (ADS)

    Quek, S. G.; Wong, K. B.; Wong, P. C.

    2013-04-01

    Let n < m be positive integers such that [g,nh] = [g,mh] and assume that n and m are chosen minimal with respect to this property. Let gi = [g,n+ih] where i = 1,2,…,m-n. Then π(g,h) = (g1,…,gm-n) is called the Engel cycle generated by g and h. The length of the Engel cycle is m-n. A group G is said to have Engel length r, if all the length of the Engel cycles in G divides r. In this paper we discuss the Brandl's theorem on Engel length and give some of its generalizations.

  16. Pi Bond Orders and Bond Lengths

    ERIC Educational Resources Information Center

    Herndon, William C.; Parkanyi, Cyril

    1976-01-01

    Discusses three methods of correlating bond orders and bond lengths in unsaturated hydrocarbons: the Pauling theory, the Huckel molecular orbital technique, and self-consistent-field techniques. (MLH)

  17. Multiple path length dual polarization interferometry.

    PubMed

    Coffey, Paul D; Swann, Marcus J; Waigh, Thomas A; Schedin, Fred; Lu, Jian R

    2009-06-22

    An optical sensor for quantitative analysis of ultrathin films and adsorbed layers is described. Quantification of both layer thickness and refractive index (density) can be made for in situ and ex-situ coated films. With the use of two polarizations, in situ measurements are made via one path length in a young's interferometer arrangement while ex-situ measurements use multiple path lengths. The multiple path length young's interferometer arrangement is embodied in a solid state waveguide configuration called the multiple path length dual polarization interferometer (MPL-DPI). The technique is demonstrated with ultrathin layers of poly(methylmethacrylate) and human serum albumin.

  18. Counterion self-diffusion in polyelectrolyte solutions

    NASA Astrophysics Data System (ADS)

    Schipper, F. J. M.; Hollander, J. G.; Leyte, J. C.

    1997-12-01

    The self-diffusion coefficient of 0953-8984/9/50/019/img1, tetra-methylammonium 0953-8984/9/50/019/img2, tetra-ethylammonium 0953-8984/9/50/019/img3, tetra-propylammonium 0953-8984/9/50/019/img4 and tetra-butylammonium 0953-8984/9/50/019/img5 in solutions of the weak polymethacrylic acid (PMA) were measured with PFG NMR. No additional salt was present in any of the experiments. The polyion concentration and degree of neutralization were varied. The maximum relative counterion self-diffusion coefficient against polyion concentration, that was reported earlier, was observed for both alkali and tetra-alkylammonium 0953-8984/9/50/019/img6 counterions. We propose that the maximum is due to the combination of the obstruction by the polyion and the changing counterion distribution at increasing polyion concentration. An explanation of this proposal is offered in terms of the Poisson - Boltzmann - Smoluchowski (PBS) model for polyelectrolytes. Qualitative agreement of this model with experiment was found for the dependence of the counterion self-diffusion coefficient on the degree of neutralization of the polyion, on counterion radius and on polyion concentration, over a concentration range from 0.01 to 1 0953-8984/9/50/019/img7. Adaption of the theoretical obstruction, to fit the self-diffusion data of the solvent, also greatly improves the model predictions on the counterion self-diffusion.

  19. Precise bacterial polyprenol length control fails in Saccharomyces cerevisiae.

    PubMed

    Poznański, Jarosław; Szkopinska, Anna

    2007-06-01

    A comparison of amino acid sequences of yeast Rer2p and Srt1p Z-prenyltransferases shows that the spatial organization of their substrate tunnels agrees with that determined by X-ray for the E. coli undecaprenyl diphosphate synthase (UPPs). The observed trend in the maxima of product length distribution shifted from C(55) in UPPs to C(80) in Rer2p and to C(110) in Srt1p. This suggests a significant increase in the size of the enzyme hydrophobic tunnel from approximately 1000 A(3) of E. coli UPPs to approximately 1300 A(3) required to accommodate C(80) in Rer2p and to 1700 A(3) for C(110) in Srt1p. Moreover, Srt1p products reaching C(290) indicate the failure of a strict bacterial-like chain length control. On the basis of E. coli UPPs crystallographic structure the yeast Rer2p model was constructed. In the model three amino acid residues inserted into the sequence corresponding to the "floor" region of the tunnel extends the bottom loop what results in the required increase of the tunnel volume. Moreover, thermal fluctuations of this loop occasionally create a hole in the tunnel floor, making escape of polyprenol omega end out of the tunnel possible what switches off the control mechanism of product length thereby allowing a practically unlimited elongation process leading to an exponential distribution of longer chain polyprenols.

  20. Amber mutation affecting the length of Escherichia coli cells.

    PubMed Central

    Martínez-Salas, E; Vicente, M

    1980-01-01

    An amber mutation in a newly found gene (wee) of Escherichia coli has been isolated from strain OV-2, which harbors a temperature-sensitive suppressor. At 42 degrees C cells of the mutant, OV-25, increased in mass and deoxyribonucleic acid content and divided at normal rates, compared with the wild type under the same growth conditions. Total cell length increased under the restrictive conditions, although at a slightly lower rate. Values of mean cell length and cell volume, contrary to what would be expected from the increment in the rate of increase in particles, mass, and deoxyribonucleic acid, became at 42 degrees C smaller than those found in the wild type. A parallel increase in protein content per length and cell density and a loss of viability were found to occur after four generations at the restrictive temperature. The behavior of strain OV-25 in the absence of the wee gene product could be interpreted in terms of either a faulty regulation of the elongation processes or their abnormal coordination with the cell cycle. The genetic location of the wee gene has been found to be at 83.5 min on the E. coli genetic map. PMID:7000749

  1. Extension and Diffusion of DNA in Nanochannels

    NASA Astrophysics Data System (ADS)

    Tree, Douglas; Wang, Yanwei; Dorfman, Kevin

    2012-02-01

    Nanochannels are an ideal platform for studying the basic physics of confined polymers, using DNA as the model polymer. While the scaling laws for strong (Odijk) and weak (de Gennes) confinement were established decades ago, recent experiments have illuminated the complex physics arising between these limiting cases. We will first present Monte Carlo simulation data on the extension of DNA in nanochannels. Our results provide clear evidence for the existence of two transition regimes between the Odijk and de Gennes regimes, thereby resolving the apparent contradiction between these scaling theories and the corresponding experiments by Austin and coworkers. We will then present results for the diffusivity of DNA in nanochannels and explain their connection to the different regimes of extension. By using Monte Carlo sampling of the Kirkwood diffusivity and a numerical solution for the confined Green's function, we have calculated the diffusivity for DNA contour lengths ranging over three orders of magnitude and nanochannel sizes over two orders of magnitude. By using a DNA model that accurately reproduces the free solution radius of gyration and diffusivity over a range of molecular weights, we can directly connect the simulation data and experiments.

  2. Multigroup Complex Geometry Neutron Diffusion Code System.

    2002-12-18

    Version 01 SNAP-3D is based on SNAP2 and is a one- two- or three-dimensional multigroup diffusion code system. It is primarily intended for neutron diffusion calculations, but it can also carry out gamma-ray calculations if the diffusion approximation is accurate enough. It is suitable for fast and thermal reactor core calculations and for shield calculations. SNAP-3D can solve the multi-group neutron diffusion equations using finite difference methods in (x,y,z), (r,theta,z), (TRI,z), (HEX,z) or (spherical) coordinates.more » The one-dimensional slab and cylindrical geometries and the two-dimensional (x,y), (r,z), (r,theta), (HEX) and (TRI) are all treated as simple special cases of three-dimensional geometries. Numerous reflective and periodic symmetry options are available and may be used to reduce the number of mesh points necessary to represent the system. Extrapolation lengths can be specified at internal and external boundaries. The problem classes are: 1) eigenvalue search for critical k-effective, 2) eigenvalue search for critical buckling, 3) eigenvalue search for critical time-constant, 4) fixed source problems in which the sources are functions of regions, 5) fixed source problems in which the sources are provided, on disc, for every mesh point and group.« less

  3. Multigroup Complex Geometry Neutron Diffusion Code System.

    SciTech Connect

    MCCALLIEN, C. W.J.

    2002-12-18

    Version 01 SNAP-3D is based on SNAP2 and is a one- two- or three-dimensional multigroup diffusion code system. It is primarily intended for neutron diffusion calculations, but it can also carry out gamma-ray calculations if the diffusion approximation is accurate enough. It is suitable for fast and thermal reactor core calculations and for shield calculations. SNAP-3D can solve the multi-group neutron diffusion equations using finite difference methods in (x,y,z), (r,theta,z), (TRI,z), (HEX,z) or (spherical) coordinates. The one-dimensional slab and cylindrical geometries and the two-dimensional (x,y), (r,z), (r,theta), (HEX) and (TRI) are all treated as simple special cases of three-dimensional geometries. Numerous reflective and periodic symmetry options are available and may be used to reduce the number of mesh points necessary to represent the system. Extrapolation lengths can be specified at internal and external boundaries. The problem classes are: 1) eigenvalue search for critical k-effective, 2) eigenvalue search for critical buckling, 3) eigenvalue search for critical time-constant, 4) fixed source problems in which the sources are functions of regions, 5) fixed source problems in which the sources are provided, on disc, for every mesh point and group.

  4. Anomalous Diffusion Near Resonances

    SciTech Connect

    Sen, Tanaji; /Fermilab

    2010-05-01

    Synchro-betatron resonances can lead to emittance growth and the loss of luminosity. We consider the detailed dynamics of a bunch near such a low order resonance driven by crossing angles at the collision points. We characterize the nature of diffusion and find that it is anomalous and sub-diffusive. This affects both the shape of the beam distribution and the time scales for growth. Predictions of a simplified anomalous diffusion model are compared with direct simulations. Transport of particles near resonances is still not a well understood phenomenon. Often, without justification, phase space motion is assumed to be a normal diffusion process although at least one case of anomalous diffusion in beam dynamics has been reported [1]. Here we will focus on the motion near synchro-betatron resonances which can be excited by several means, including beams crossing at an angle at the collision points as in the LHC. We will consider low order resonances which couple the horizontal and longitudinal planes, both for simplicity and to observe large effects over short time scales. While the tunes we consider are not practical for a collider, nonetheless the transport mechanisms we uncover are also likely to operate at higher order resonances.

  5. Diffusive behavior of a greedy traveling salesman

    NASA Astrophysics Data System (ADS)

    Lipowski, Adam; Lipowska, Dorota

    2011-06-01

    Using Monte Carlo simulations we examine the diffusive properties of the greedy algorithm in the d-dimensional traveling salesman problem. Our results show that for d=3 and 4 the average squared distance from the origin is proportional to the number of steps t. In the d=2 case such a scaling is modified with some logarithmic corrections, which might suggest that d=2 is the critical dimension of the problem. The distribution of lengths also shows marked differences between d=2 and d>2 versions. A simple strategy adopted by the salesman might resemble strategies chosen by some foraging and hunting animals, for which anomalous diffusive behavior has recently been reported and interpreted in terms of Lévy flights. Our results suggest that broad and Lévy-like distributions in such systems might appear due to dimension-dependent properties of a search space.

  6. Mutant fatty acid desaturase

    DOEpatents

    Shanklin, John; Cahoon, Edgar B.

    2004-02-03

    The present invention relates to a method for producing mutants of a fatty acid desaturase having a substantially increased activity towards fatty acid substrates with chains containing fewer than 18 carbons relative to an unmutagenized precursor desaturase having an 18 carbon atom chain length substrate specificity. The method involves inducing one or more mutations in the nucleic acid sequence encoding the precursor desaturase, transforming the mutated sequence into an unsaturated fatty acid auxotroph cell such as MH13 E. coli, culturing the cells in the absence of supplemental unsaturated fatty acids, thereby selecting for recipient cells which have received and which express a mutant fatty acid desaturase with an elevated specificity for fatty acid substrates having chain lengths of less than 18 carbon atoms. A variety of mutants having 16 or fewer carbon atom chain length substrate specificities are produced by this method. Mutant desaturases produced by this method can be introduced via expression vectors into prokaryotic and eukaryotic cells and can also be used in the production of transgenic plants which may be used to produce specific fatty acid products.

  7. Intermediate temperature proton conductors for PEM fuel cells based on phosphonic acid as protogenic group: a progress report.

    PubMed

    Steininger, H; Schuster, M; Kreuer, K D; Kaltbeitzel, A; Bingöl, B; Meyer, W H; Schauff, S; Brunklaus, G; Maier, J; Spiess, H W

    2007-04-21

    The melting behaviour and transport properties of straight chain alkanes mono- and difunctionalized with phosphonic acid groups have been investigated as a function of their length. The increase of melting temperature and decrease of proton conductivity with increasing chain length is suggested to be the consequence of an increasing ordering of the alkane segments which constrains the free aggregation of the phosphonic acid groups. However, the proton mobility is reduced to a greater extent than the proton diffusion coefficient indicating an increasing cooperativity of proton transport with increasing length of the alkane segment. The results clearly indicate that the "spacer concept", which had been proven successful in the optimization of the proton conductivity of heterocycle based systems, fails in the case of phosphonic acid functionalized polymers. Instead, a very high concentration of phosphonic acid functional groups forming "bulky" hydrogen bonded aggregates is suggested to be essential for obtaining very high proton conductivity. Aggregation is also suggested to reduce condensation reactions generally observed in phosphonic acid containing systems. On the basis of this understanding, the proton conductivities of poly(vinyl phosphonic acid) and poly(meta-phenylene phosphonic acid) are discussed. Though both polymers exhibit a substantial concentration of phosphonic acid groups, aggregation seems to be constrained to such an extent that intrinsic proton conductivity is limited to values below sigma = 10(-3) S cm(-1) at T = 150 degrees C. The results suggest that different immobilization concepts have to be developed in order to minimize the conductivity reduction compared to the very high intrinsic proton conductivity of neat phosphonic acid under quasi dry conditions. In the presence of high water activities, however, (as usually present in PEM fuel cells) the very high ion exchange capacities (IEC) possible for phosphonic acid functionalized ionomers (IEC

  8. Apparatus for diffusion separation

    DOEpatents

    Nierenberg, William A.; Pontius, Rex B.

    1976-08-10

    1. The method of testing the separation efficiency of porous permeable membranes which comprises causing a stream of a gaseous mixture to flow into contact with one face of a finely porous permeable membrane under such conditions that a major fraction of the mixture diffuses through the membrane, maintaining a rectangular cross section of the gaseous stream so flowing past said membrane, continuously recirculating the gas that diffuses through said membrane and continuously withdrawing the gas that does not diffuse through said membrane and maintaining the volume of said recirculating gas constant by continuously introducing into said continuously recirculating gas stream a mass of gas equivalent to that which is continuously withdrawn from said gas stream and comparing the concentrations of the light component in the entering gas, the withdrawn gas and the recirculated gas in order to determine the efficiency of said membrane.

  9. Cesium diffusion in graphite

    SciTech Connect

    Evans, R.B. III; Davis, W. Jr.; Sutton, A.L. Jr.

    1980-05-01

    Experiments on diffusion of /sup 137/Cs in five types of graphite were performed. The document provides a completion of the report that was started and includes a presentation of all of the diffusion data, previously unpublished. Except for data on mass transfer of /sup 137/Cs in the Hawker-Siddeley graphite, analyses of experimental results were initiated but not completed. The mass transfer process of cesium in HS-1-1 graphite at 600 to 1000/sup 0/C in a helium atmosphere is essentially pure diffusion wherein values of (E/epsilon) and ..delta..E of the equation D/epsilon = (D/epsilon)/sub 0/ exp (-..delta..E/RT) are about 4 x 10/sup -2/ cm/sup 2//s and 30 kcal/mole, respectively.

  10. A simple differential diffusion model to account for the discrepancy between 223Ra- and 224Ra-based eddy diffusivities

    NASA Astrophysics Data System (ADS)

    Stachelhaus, Scott L.; Moran, S. Bradley

    2012-03-01

    A series of 223Ra (t1/2 = 11.4 d) and 224Ra (t1/2 = 3.66 d) measurements made in the Mid-Atlantic Bight yield eddy diffusivity (K) estimates of 1.2 ± 0.3 × 102 m2 s-1 and 1.4 ± 0.2 × 102 m2 s-1, respectively. These results fall in line with previous studies from multiple locations throughout the ocean, in which 224Ra-based eddy diffusivities invariably exceed those determined using 223Ra. Such a pattern conflicts with the Fickian model for eddy diffusivity, in which K is constant. Moreover, this trend runs counter to the length scale-dependent view of eddy diffusion, which suggests that K values estimated using 223Ra should exceed those of 224Ra, because the length scale of the former is greater than that of the latter. A finite mixing-length model based on the concept of differential diffusion is used to provide an explanation for this discrepancy.

  11. A computational kinetic model of diffusion for molecular systems.

    PubMed

    Teo, Ivan; Schulten, Klaus

    2013-09-28

    Regulation of biomolecular transport in cells involves intra-protein steps like gating and passage through channels, but these steps are preceded by extra-protein steps, namely, diffusive approach and admittance of solutes. The extra-protein steps develop over a 10-100 nm length scale typically in a highly particular environment, characterized through the protein's geometry, surrounding electrostatic field, and location. In order to account for solute energetics and mobility of solutes in this environment at a relevant resolution, we propose a particle-based kinetic model of diffusion based on a Markov State Model framework. Prerequisite input data consist of diffusion coefficient and potential of mean force maps generated from extensive molecular dynamics simulations of proteins and their environment that sample multi-nanosecond durations. The suggested diffusion model can describe transport processes beyond microsecond duration, relevant for biological function and beyond the realm of molecular dynamics simulation. For this purpose the systems are represented by a discrete set of states specified by the positions, volumes, and surface elements of Voronoi grid cells distributed according to a density function resolving the often intricate relevant diffusion space. Validation tests carried out for generic diffusion spaces show that the model and the associated Brownian motion algorithm are viable over a large range of parameter values such as time step, diffusion coefficient, and grid density. A concrete application of the method is demonstrated for ion diffusion around and through the Eschericia coli mechanosensitive channel of small conductance ecMscS.

  12. Hydrogen diffusion in Zircon

    NASA Astrophysics Data System (ADS)

    Ingrin, Jannick; Zhang, Peipei

    2016-04-01

    Hydrogen mobility in gem quality zircon single crystals from Madagascar was investigated through H-D exchange experiments. Thin slices were annealed in a horizontal furnace flushed with a gas mixture of Ar/D2(10%) under ambient pressure between 900 ° C to 1150 ° C. FTIR analyses were performed on oriented slices before and after each annealing run. H diffusion along [100] and [010] follow the same diffusion law D = D0exp[-E /RT], with log D0 = 2.24 ± 1.57 (in m2/s) and E = 374 ± 39 kJ/mol. H diffusion along [001] follows a slightly more rapid diffusion law, with log D0 = 1.11 ± 0.22 (in m2/s) and E = 334 ± 49 kJ/mol. H diffusion in zircon has much higher activation energy and slower diffusivity than other NAMs below 1150 ° C even iron-poor garnets which are known to be among the slowest (Blanchard and Ingrin, 2004; Kurka et al. 2005). During H-D exchange zircon incorporates also deuterium. This hydration reaction involves uranium reduction as it is shown from the exchange of U5+ and U4+ characteristic bands in the near infrared region during annealing. It is the first time that a hydration reaction U5+ + OH‑ = U4+ + O2‑ + 1/2H2, is experimentally reported. The kinetics of deuterium incorporation is slightly slower than hydrogen diffusion, suggesting that the reaction is limited by hydrogen mobility. Hydrogen isotopic memory of zircon is higher than other NAMs. Zircons will be moderately retentive of H signatures at mid-crustal metamorphic temperatures. At 500 ° C, a zircon with a radius of 300 μm would retain its H isotopic signature over more than a million years. However, a zircon is unable to retain this information for geologically significant times under high-grade metamorphism unless the grain size is large enough. Refrences Blanchard, M. and Ingrin, J. (2004) Hydrogen diffusion in Dora Maira pyrope. Physics and Chemistry of Minerals, 31, 593-605. Kurka, A., Blanchard, M. and Ingrin, J. (2005) Kinetics of hydrogen extraction and deuteration in

  13. Hydrogen diffusion in Zircon

    NASA Astrophysics Data System (ADS)

    Ingrin, Jannick; Zhang, Peipei

    2016-04-01

    Hydrogen mobility in gem quality zircon single crystals from Madagascar was investigated through H-D exchange experiments. Thin slices were annealed in a horizontal furnace flushed with a gas mixture of Ar/D2(10%) under ambient pressure between 900 ° C to 1150 ° C. FTIR analyses were performed on oriented slices before and after each annealing run. H diffusion along [100] and [010] follow the same diffusion law D = D0exp[-E /RT], with log D0 = 2.24 ± 1.57 (in m2/s) and E = 374 ± 39 kJ/mol. H diffusion along [001] follows a slightly more rapid diffusion law, with log D0 = 1.11 ± 0.22 (in m2/s) and E = 334 ± 49 kJ/mol. H diffusion in zircon has much higher activation energy and slower diffusivity than other NAMs below 1150 ° C even iron-poor garnets which are known to be among the slowest (Blanchard and Ingrin, 2004; Kurka et al. 2005). During H-D exchange zircon incorporates also deuterium. This hydration reaction involves uranium reduction as it is shown from the exchange of U5+ and U4+ characteristic bands in the near infrared region during annealing. It is the first time that a hydration reaction U5+ + OH- = U4+ + O2- + 1/2H2, is experimentally reported. The kinetics of deuterium incorporation is slightly slower than hydrogen diffusion, suggesting that the reaction is limited by hydrogen mobility. Hydrogen isotopic memory of zircon is higher than other NAMs. Zircons will be moderately retentive of H signatures at mid-crustal metamorphic temperatures. At 500 ° C, a zircon with a radius of 300 μm would retain its H isotopic signature over more than a million years. However, a zircon is unable to retain this information for geologically significant times under high-grade metamorphism unless the grain size is large enough. Refrences Blanchard, M. and Ingrin, J. (2004) Hydrogen diffusion in Dora Maira pyrope. Physics and Chemistry of Minerals, 31, 593-605. Kurka, A., Blanchard, M. and Ingrin, J. (2005) Kinetics of hydrogen extraction and deuteration in

  14. 7 CFR 29.6024 - Length.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... 7 Agriculture 2 2010-01-01 2010-01-01 false Length. 29.6024 Section 29.6024 Agriculture Regulations of the Department of Agriculture AGRICULTURAL MARKETING SERVICE (Standards, Inspections, Marketing... INSPECTION Standards Definitions § 29.6024 Length. The linear measurement of cured tobacco leaves from...

  15. Food-chain length and adaptive foraging.

    PubMed

    Kondoh, Michio; Ninomiya, Kunihiko

    2009-09-01

    Food-chain length, the number of feeding links from the basal species to the top predator, is a key characteristic of biological communities. However, the determinants of food-chain length still remain controversial. While classical theory predicts that food-chain length should increase with increasing resource availability, empirical supports of this prediction are limited to those from simple, artificial microcosms. A positive resource availability-chain length relationship has seldom been observed in natural ecosystems. Here, using a theoretical model, we show that those correlations, or no relationships, may be explained by considering the dynamic food-web reconstruction induced by predator's adaptive foraging. More specifically, with foraging adaptation, the food-chain length becomes relatively invariant, or even decreases with increasing resource availability, in contrast to a non-adaptive counterpart where chain length increases with increasing resource availability; and that maximum chain length more sharply decreases with resource availability either when species richness is higher or potential link number is larger. The interactive effects of resource availability, adaptability and community complexity may explain the contradictory effects of resource availability in simple microcosms and larger ecosystems. The model also explains the recently reported positive effect of habitat size on food-chain length as a result of increased species richness and/or decreased connectance owing to interspecific spatial segregation.

  16. Multispecies diffusion models: A study of uranyl species diffusion

    NASA Astrophysics Data System (ADS)

    Liu, Chongxuan; Shang, Jianying; Zachara, John M.

    2011-12-01

    Rigorous numerical description of multispecies diffusion requires coupling of species, charge, and aqueous and surface complexation reactions that collectively affect diffusive fluxes. The applicability of a fully coupled diffusion model is, however, often constrained by the availability of species self-diffusion coefficients, as well as by computational complication in imposing charge conservation. In this study, several diffusion models with variable complexity in charge and species coupling were formulated and compared to describe reactive multispecies diffusion in groundwater. Diffusion of uranyl [U(VI)] species was used as an example in demonstrating the effectiveness of the models in describing multispecies diffusion. Numerical simulations found that a diffusion model with a single, common diffusion coefficient for all species was sufficient to describe multispecies U(VI) diffusion under a steady state condition of major chemical composition, but not under transient chemical conditions. Simulations revealed that for multispecies U(VI) diffusion under transient chemical conditions, a fully coupled diffusion model could be well approximated by a component-based diffusion model when the diffusion coefficient for each chemical component was properly selected. The component-based diffusion model considers the difference in diffusion coefficients between chemical components, but not between the species within each chemical component. This treatment significantly enhanced computational efficiency at the expense of minor charge conservation. The charge balance in the component-based diffusion model can be enforced, if necessary, by adding a secondary migration term resulting from model simplification. The effect of ion activity coefficient gradients on multispecies diffusion is also discussed. The diffusion models were applied to describe U(VI) diffusive mass transfer in intragranular domains in two sediments collected from U.S. Department of Energy's Hanford 300A

  17. Scaling laws in the diffusion limited aggregation of persistent random walkers

    NASA Astrophysics Data System (ADS)

    Nogueira, Isadora R.; Alves, Sidiney G.; Ferreira, Silvio C.

    2011-11-01

    We investigate the diffusion limited aggregation of particles executing persistent random walks. The scaling properties of both random walks and large aggregates are presented. The aggregates exhibit a crossover between ballistic and diffusion limited aggregation models. A non-trivial scaling relation ξ∼ℓ1.25 between the characteristic size ξ, in which the cluster undergoes a morphological transition, and the persistence length ℓ, between ballistic and diffusive regimes of the random walk, is observed.

  18. Lateral Diffusion Length Changes in HgCdTe Detectors in a Proton Environment

    NASA Technical Reports Server (NTRS)

    Hubbs, John E.; Marshall, Paul W.; Marshall, Cheryl J.; Gramer, Mark E.; Maestas, Diana; Garcia, John P.; Dole, Gary A.; Anderson, Amber A.

    2007-01-01

    This paper presents a study of the performance degradation in a proton environment of very long wavelength infrared (VLWIR) HgCdTe detectors. The energy dependence of the Non-Ionizing Energy Loss (NIEL) in HgCdTe provides a framework for estimating the responsivity degradation in VLWIR HgCdTe due to on orbit exposure from protons. Banded detector arrays that have different detector designs were irradiated at proton energies of 7, 12, and 63 MeV. These banded detector arrays allovedin sight into how the fundamental detector parameters degraded in a proton environment at the three different proton energies. Measured data demonstrated that the detector responsivity degradation at 7 MeV is 5 times larger than the degradation at 63 MeV. The comparison of the responsivity degradation at the different proton energies suggests that the atomic Columbic interaction of the protons with the HgCdTe detector is likely the primary mechanism responsible for the degradation in responsivity at proton energies below 30 MeV.

  19. Biased diffusion in three-dimensional comb-like structures

    PubMed Central

    Berezhkovskii, Alexander M.; Dagdug, Leonardo; Bezrukov, Sergey M.

    2015-01-01

    In this paper, we study biased diffusion of point Brownian particles in a three-dimensional comb-like structure formed by a main cylindrical tube with identical periodic cylindrical dead ends. It is assumed that the dead ends are thin cylinders whose radius is much smaller than both the radius of the main tube and the distance between neighboring dead ends. It is also assumed that in the main tube, the particle, in addition to its regular diffusion, moves with a uniform constant drift velocity. For such a system, we develop a formalism that allows us to derive analytical expressions for the Laplace transforms of the first two moments of the particle displacement along the main tube axis. Inverting these Laplace transforms numerically, one can find the time dependences of the two moments for arbitrary values of both the drift velocity and the dead-end length, including the limiting case of infinitely long dead ends, where the unbiased diffusion becomes anomalous at sufficiently long times. The expressions for the Laplace transforms are used to find the effective drift velocity and diffusivity of the particle as functions of its drift velocity in the main tube and the tube geometric parameters. As might be expected from common-sense arguments, the effective drift velocity monotonically decreases from the initial drift velocity to zero as the dead-end length increases from zero to infinity. The effective diffusivity is a more complex, non-monotonic function of the dead-end length. As this length increases from zero to infinity, the effective diffusivity first decreases, reaches a minimum, and then increases approaching a plateau value which is proportional to the square of the particle drift velocity in the main tube. PMID:25854222

  20. Reduction of ethylenediaminetetraacetic acid iron(III) by Klebsiella sp. FD-3 immobilized on iron(II, III) oxide poly (styrene-glycidyl methacrylate) magnetic porous microspheres: effects of inorganic compounds and kinetic study of effective diffusion in porous media.

    PubMed

    Zhou, Zuo-Ming; Wang, Xiao-Yan; Lin, Tian-Ming; Jing, Guo-Hua

    2014-11-01

    Fe3O4 poly (styrene-glycidyl methacrylate) magnetic porous microspheres (MPPMs) were introduced to immobilize Klebsiella sp. FD-3, an iron-reducing bacterium applied to reduce Fe(III)EDTA. The effects of potential inhibitors (S(2-), SO3(2-), NO3(-), NO2(-) and Fe(II)EDTA-NO) on Fe(III)EDTA reduction were investigated. S(2-) reacted with Fe(III)EDTA as an electron-shuttling compound and enhanced the reduction. But Fe(III)EDTA reduction was inhibited by SO3(2-) and Fe(II)EDTA-NO due to their toxic to microorganisms. Low concentrations of NO3(-) and NO2(-) accelerated Fe(III)EDTA reduction, but high concentrations inhibited the reduction, whether by free or immobilized FD-3. The immobilized FD-3 performed better than freely-suspended style. The substrate mass transfer and diffusion kinetics in the porous microspheres were calculated. The value of Thiele modulus and effectiveness factors showed that the intraparticle diffusion was fairly small and neglected in this carrier. Fe(III)EDTA reduction fitted first-order model at low Fe(III)EDTA concentration, and changed to zero-order model at high concentrations.